55. Kent, BAP; Dashtgard, SE; Huang, CQ; MacEachern, JA; Gibson, HD; Cathyl-Huhn, G.Initiation and early evolution of a forearc basin: Georgia Basin, Canada.Basin Res., 2020, 32: 163-185 Initiation and early evolution of a forearc basin: Georgia Basin, Canada
coal; forearc basins; Late Cretaceous; sequence stratigraphy; stratigraphy; T-R sequences; transgression
The lower Nanaimo Group was deposited in the (forearc) Georgia Basin, Canada and records the basin's initiation and early depositional evolution. Nanaimo Group strata are subdivided into 11 lithostratigraphic units, which are identified based on lithology, paleontology, texture and position relative to both the basal nonconformity and to each other. Significant topography on the basal nonconformity, however, has resulted in assignment of lithostratigraphic units that are not time correlative, and hence, cannot reliably be used to accurately reconstruct basin evolution. Herein, we present a sequence stratigraphic framework for lower Nanaimo Group strata in the Comox Sub-Basin (northern Georgia Basin) that integrates both facies analysis and maximum depositional ages (MDAs) derived from detrital zircon. This stratigraphic framework is used to define significant sub-basin-wide surfaces that bound depositional units and record the evolution of the basin during its early stages of development. Seven distinct depositional phases are identified in the lower 700 m of the lower Nanaimo Group. Depositional phases are separated by marine flooding surfaces, regressive surfaces, or disconformities. The overall stratigraphy reflects net transgression manifested as an upwards transition from braided fluvial conglomerates to marine mudstones. Transgression was interrupted by periods of shoreline progradation, and both facies analysis and MDAs reveal a disconformity in the lowermost part of the Nanaimo Group in the Comox Sub-Basin. Stratigraphic reconstruction of the Comox Sub-Basin reveals two dominant depocenters (along depositional strike) for coarse clastics (sandstones and conglomerates) during early development of the Georgia Basin. The development and position of these depocenters is attributed to subduction/tectonism driving both subsidence in the north-northwest and uplift in the central Comox Sub-Basin. Our work confirms that in its earliest stages of development, the Georgia Basin evolved from an underfilled, ridged forearc basin that experienced slow and stepwise drowning to a shoal-water ridged forearc basin that experienced rapid subsidence. We also propose that the Georgia Basin is a reasonable analogue for ridged forearc basins globally, as many ridged forearcs record similar depositional histories during their early evolution. DOI
52. Chateau, CCF; Dashtgard, SE; MacEachern, JA; Hauck, TE.Parasequence architecture in a low-accommodation setting, impact of syndepositional carbonate epikarstification, McMurray Formation, Alberta, Canada.Mar. Pet. Geol., 2019, 104: 168-179 Parasequence architecture in a low-accommodation setting, impact of syndepositional carbonate epikarstification, McMurray Formation, Alberta, Canada
Parasequences; Depositional units; Accommodation space; Syndepositional epikarst associated subsidence
The Sparrow Paleovalley (SPV) is situated in the southwest corner of the McMurray Sub-Basin, Alberta, Canada, and drained a portion of the Grosmont Highlands on a sub-Cretaceous paleotopographic surface. The regional stratigraphic architecture of the Lower Cretaceous McMurray Formation in SPV comprises a series of regressive parasequences (PS) organized into depositional units (DU), the latter of which are separated by regionally mappable flooding surfaces. Isopach maps of individual DUs show that in general they have a consistent thickness, although stratal thickening of DUs occurs in the landward part of the SPV and extends over an area of 400 km(2). This stratal thickening ranges from +21% to +45% and is accompanied by increases in both the abundance of soft-sediment deformation structures (SSD) and normal micro-faults in PSs, and an increase in the number and thickness of PSs. The thickness disparity between the over-thickened zone compared to the rest of the SPV is statistically significant and points to an external control on the accumulation of DUs. The McMurray Formation unconformably overlies a complex distribution of Devonian strata that subcrop at the sub-Cretaceous unconformity below the SPV. Devonian strata include, from east to west (oldest to youngest), the Beaverhill Lake, Woodbend, and Winterburn groups. In the western reaches of the SPV, McMurray Fm deposits overlie and are flanked by strata of the Woodbend and Winterburn groups, the latter of which experienced erosion and carbonate epikarstification when subaerially exposed. Subsidence through epikarstification of Devonian carbonates generated localized deepening in the McMurray Sub-Basin, which was infilled during deposition of DUs and resulted in over-thickening of McMurray strata. The correspondence of topographic lows on the sub-Cretaceous unconformity and over-thickening of DUs overlying these topographic lows indicates that active carbonate epikarstification of Devonian strata was contemporaneous with deposition of the McMurray Formation. DOI
51. La Croix, AD; Dashtgard, SE; MacEachern, JA.Using a modern analogue to interpret depositional position in ancient fluvial-tidal channels: Example from the McMurray Formation, Canada.Geosci. Front., 2019, 10: 2219-2238 Using a modern analogue to interpret depositional position in ancient fluvial-tidal channels: Example from the McMurray Formation, Canada
Fluvial-tidal transition; McMurray Formation; Fraser river; Inclined heterolithic stratification; Modern analogue; Quantitative sedimentology and ichnology
The fluvial-tidal transition (FTT) is a complex depositional zone, where fluvial flow is modified by tides as rivers approach a receiving marine basin. Variations in the relative importance of tidal versus fluvial processes lead to a distinctive distribution of sediments that accumulate on channel bars. The FIT generally consists of three broad zones: (1) a freshwater-tidal zone; (2) a tidally influenced freshwater to brackish-water transition; and (3) a zone of relatively sustained brackish-water conditions with stronger tides. A very common type of deposit through the fluvial-tidal transition, especially on the margins of migrating channels, is inclined heterolithic stratification (IHS). At present, a detailed account of changes in the character of IHS across the FIT of a paleo-channel system has not been reported, although a number of modern examples have been documented. To fill this gap, we quantitatively assess the sedimentology and ichnology of IHS from seven cored intervals in three geographic areas situated within the youngest paleovalley ("A" Valley) in the Lower Cretaceous McMurray Formation of Alberta, Canada. We compare the data to trends defined along the FIT in the present-day Fraser River in British Columbia, Canada to interpret paleo-depositional position in the ancient fluvial-tidal channels. Analysis determined that the mean mudstone thickness is 8.2 cm in the southern study area (SA). Mean thickness increases to 11 cm in the central study area (CA), and decreases again to 4.4 cm in the northern study area (NA). The proportion of mudstone is 31% in SA, 44% in CA, and 27% in NA. Thickness-weighted mean bioturbation intensity in sands varied from 0.29 in SA and CA, to 0.28 in NA. On the other hand, thickness-weighted mean bioturbation intensity (BI) in mudstone increases from 1.46 in SA, to 1.77 in CA, and is 1.94 in NA. The ichnological diversity also increased from south to north. Sedimentological results show similar trends to those of the Fraser River, enabling the identification of a freshwater to brackish-water transition zone with tidal influence. The interpreted position of the transition is underpinned by the bioturbation intensity and trace-fossil diversity trends, indicating periodic brackish-water conditions throughout SA in the McMurray Formation during low river flow conditions. Together, these data suggest that a broad FTT existed in the "A" Valley, with fluvial-dominated channels to the south that experienced seasonal brackish-water inundation during base flow, and channels experiencing increasing brackish-water influence lying further north towards a turbidity maximum zone. The FIT zone appears to have extended for several hundred kilometers from south to north. Based on the sedimentological and ichnological data, as well as estimations of lateral accretion rates, we refute the commonly applied Mississippi River depositional analogue for McMurray Formation channels. Rather, we show that while not a perfect fit, the tidally influenced Fraser River shows much greater agreement with the depositional character recorded in McMurray Formation IHS. Future work on the McMurray system should focus on characterizing tide-dominated deltaic and estuarine systems, such as the Ganges-Brahmaputra, and on forward-modeling the evolution of tide-dominated and tide-influenced river systems. (C) 2019. China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. DOI
50. Morshedian, A; MacEachern, JA; Dashtgard, SE; Bann, KL; Pemberton, SG.Systems tracts and their bounding surfaces in the low- accommodation Upper Mannville group, Saskatchewan, Canada.Mar. Pet. Geol., 2019, 110: 35-54 Systems tracts and their bounding surfaces in the low- accommodation Upper Mannville group, Saskatchewan, Canada
Mannville group; Sparky formation; Waseca formation; McLaren formation; Sequence stratigraphy; Facies analysis; Ichnology; Systems tract; Autogenic surfaces; Allogenic surfaces
Sequence stratigraphic interpretations of paralic successions can be challenging, because such settings are commonly controlled by a combination of allogenic controls and autogenic processes, leading to complex depositional architectures. In low-accommodation systems where parasequences are less than 15 m thick, the challenges in recognizing discrete stratigraphic surfaces are exacerbated by limited vertical separation between surfaces or their outright erosional amalgamation, requiring high-resolution facies analysis to resolve their geometries. Herein, we present criteria derived from core data and well logs to differentiate between allogenic and autogenic surfaces in a low-accommodation paralic setting, using the Lower Cretaceous Mannville Group of west-central Saskatchewan, Canada as a case study. The upper part of the Mannville Group (Sparky, Waseca and McLaren formations) displays complex stratigraphic relationships related to base-level changes. Marine flooding surfaces (MFS) and transgressive surfaces of erosion (TSE) of 3rd and 4th order record allogenic changes (e.g., basin subsidence and/or eustatic changes in sea level), and are used to define parasequence boundaries of strandplain-shoreface successions. Deltaic deposits not only possess these allogenic transgressive surfaces, but autogenic 5th-order flooding surfaces, which are broadly similar in appearance, as well. These autogenic surfaces record responses to channel avulsion or lobe abandonment, separate discrete delta lobes, and display limited lateral extents. Shoreface-related flooding surfaces, by contrast, bound true allogenic parasequences and, therefore, have regional correlatability. The Waseca Formation also possesses surfaces related to base-level fall. To the north, a subtle regressive surface of marine erosion (RSME) marks the base of the falling stage systems tract. Elsewhere, a widespread subaerial unconformity (SU) separates the Waseca into lower and upper members. In most areas, the SU is amalgamated with surfaces generated by later base-level rise. Upper Mannville strata in the study area, therefore, can be separated into parts of two depositional sequences. The main deposits of the lower sequence comprise a highstand systems tracts (HST) in the Sparky Formation. The base of the Lower Waseca Member marks the onset of a transgressive systems tract (TST), associated with widespread shoreline retreat. A 3rd-order maximum flooding surface (MxFS) marks the end of transgression and resumption of normal progradational regression in a highstand systems tract associated with the Lower Waseca Member. Following highstand normal regression, a major base-level fall initiated a subaerial unconformity that marks the base of the upper sequence. Fluvial valley incision led to sediment bypass and deposition of forced regressive and lowstand shoreface and delta complexes of the falling stage systems tract (FSST) and lowstand systems tract (LST), respectively, in the northern part of the study area. Pedogenic modification of subaerially exposed sediment occurred in interfluve areas. Ensuing TST accumulation was initially confined to the tidal-fluvial estuarine infill of the incised valleys and transgressive bay deposits of the Upper Waseca Member. The Upper Waseca is capped by a 3rd-order maximum flooding surface (MxFS), which separates it from the overlying McLaren Formation. This marks the return to regional shoreline progradational regression and corresponds to the highstand systems tract (HST) of the upper sequence. DOI
49. Rinke-Hardekopf, L; Dashtgard, SE; MacEachern, JA.Earliest Cretaceous Transgression of North America Recorded in Thick Coals: McMurray Sub-Basin, Canada.Int. J. Coal Geol., 2019, 204: 18-33 Earliest Cretaceous Transgression of North America Recorded in Thick Coals: McMurray Sub-Basin, Canada
Coal; Terrestrial stratigraphy; Petrography; Coastal plain; Relative sea-level; CA-TIMS
Strata of the Lower Cretaceous McMurray Formation in the McMurray Sub-Basin (MSB) of Alberta and Saskatchewan, Canada, comprise marginal marine, tidal-fluvial, fluvial and interfluve deposits. In the Firebag Tributary located in the northeastern portion of the sub-basin, a thick coal seam (up to > 20 m) forms a semi continuous bed at the top of the lowermost McMurray Fm deposits (herein referred to as Lower McMurray). In coastal plain settings, peat-forming mires are highly sensitive archives of base-level. We investigate the stratigraphic significance of coals in the Firebag Tributary by analyzing coal petrography (4 cores), coal geochemistry (2 cores), and coal distribution in similar to 4500 wells. Additionally, we record the first absolute age for the McMurray Fm through the dating of an ash layer within the coal seam. The petrographic character and distribution of coals in the northeastern part of the MSB suggest a complex history of base-level rise at the end of Lower McMurray deposition. Wetting-upward character coal seams record initial transgression of the Boreal Sea during a 4th order sea level rise (Milankovitch-scale) within lowstand to early transgressive systems tract conditions. Sea-level rise during Lower McMurray times was estimated based on temperate climate peat formation rates, as well as peat-to-coal compaction factors, and probably occurred on a scale of 0.5-3 mm a(-1). Seam-internal wetting-upward cycles suggest that base-level rise was punctuated. Locally, compound and drying-upward character coals represent zones of high accommodation, wherein peat accumulation in mires was influenced by phases of syn-depositional subsidence and karst collapse. The thickest coals in the study area form an arc on a coastal plain as the Boreal Sea inundated east- to southeastward into the Firebag Tributary. Within the arc of thick coals, a north-south decrease in coal thickness is interpreted to reflect the general southward inundation of the Boreal Sea across the MSB. Exceptionally thick coals (> 10 m) likely formed where basement processes (e.g., karsting in Devonian carbonates) provided preferential groundwater pathways. Chemical abrasion thermal ionization mass spectrometry dating of 5 sharply faceted zircons recovered from an ash bed within the coal provides the first absolute age (121.39 +/- 0.2 Ma - Aptian) to the southward transgression of the Boreal Sea. We hypothesize that initial inundation of the MSB was related to tectonic activity in the Canadian Cordillera and the onset of magmatic flow in the western Coast Plutonic Complex. DOI
48. Schultz, SK; MacEachern, JA; Gibson, HD.Late Mesozoic reactivation of Precambrian basement structures and their resulting effects on the sequence stratigraphic architecture of the Viking Formation of east-central Alberta, Canada.Lithosphere, 2019, 11: 308-321 Late Mesozoic reactivation of Precambrian basement structures and their resulting effects on the sequence stratigraphic architecture of the Viking Formation of east-central Alberta, Canada
The Lower Cretaceous Viking Formation is a siliciclastic unit that occurs in the subsurface of Alberta in the Western Canadian sedimentary basin. This study focuses on a lowstand paleoshoreline trend extending along strike between two hydrocarbon-producing fields, Joarcam and Judy Creek (250 km NW). The Viking Formation in these fields records depositional thicknesses ranging from 20 to 30 m. Between these two fields, however, the formation is anomalously thick (45-60 m), complicating the recognition and correlation of key stratigraphic surfaces. Marine flooding surfaces above and below the Viking Formation are routinely employed as stratigraphic datums in order to remove postdepositional deformation and facilitate the development of a sequence stratigraphic framework. However, as each successive surface is employed as the datum, the other flooding surfaces within the formation become distorted, resulting in unrealistic depositional geometries. These geometries are best explained to be the result of structural readjustments during Viking deposition. The Precambrian lithosphere of the Canadian Shield forms the Western Canadian sedimentary basin basement, with major structures previously mapped using gravity and magnetic anomaly studies. Locally, the increased accommodation observed within the Viking Formation of central Alberta is attributed to differential reactivation of the Paleoproterozoic Snowbird tectonic zone basement structures, which flank the areas of anomalously thick deposits and trend approximately normal to the regional strike of the Western Canadian sedimentary basin. The Snowbird tectonic zone faults are interpreted to have been reactivated during renewed tectonic loading in the southern Canadian Cordillera during Aptian-Albian time, causing subtle readjustments along basement faults that caused variable syndepositional subsidence. By selecting successive datums, the gross Viking interval can be recognized to have accumulated prior to, during, and following structural reactivation. DOI
47. Jones, MT; Dashtgard, SE; MacEachern, JA.A conceptual model for preservation of thick, transgressive shoreline successions with examples from a forearc basin: Nanaimo Basin, British Columbia, Canada.J. Sediment. Res., 2018, 88: 811-826 A conceptual model for preservation of thick, transgressive shoreline successions with examples from a forearc basin: Nanaimo Basin, British Columbia, Canada
Sequence stratigraphic models derived from passive margins and foreland basins characterize transgressive shorelines (excluding incised valleys) as recording periods of sediment starvation, and are commonly represented as thin (< 1 m) coarse-grained lags overlain by offshore mudstones. Preservation of thick, transgressive successions is relatively uncommon, but is possible in settings characterized by high sedimentation rates coupled with rapid base-level rise. Examples of such settings are found in deposits of the Upper Cretaceous Nanaimo Group, exposed on Vancouver Island and the Gulf Islands of British Columbia, Canada. The Nanaimo Basin is interpreted as a rapidly subsiding forearc basin that formed as a result of accretion of Wrangellia Terrane during subduction of the Farallon Plate beneath North America. The transgressive units of the Comox and Protection formations in the Nanaimo Basin display thick shoreline successions ranging from 3 m to 66 m, wherein base-level changes were dominantly controlled by tectonics. By comparing our results to previously studied transgressive successions and to mechanisms leading to transgression, a conceptual model for predicting transgressive architectures is proposed. Thick transgressive shoreline successions (> 10 m) are more likely to be developed in active tectonic settings (e.g., forearc and rift basins), which generally experience high sedimentation rates and relatively rapid changes in base level. Settings with high sedimentation rates and moderate base-level rise lead to progradational trends despite overall transgression of the shoreline. In settings where changes in eustatic sea level mainly control the resulting stratigraphic architecture (e.g., passive margins), thin transgressive successions (1-10 m) are more likely to be produced. Finally, in settings defined by relatively slow base-level change (e.g., foreland basins), the resultant transgressive succession typically comprises a lag (< 1 m) overlain by offshore mudstones. This conceptual model highlights the importance of the interplay between sedimentation rates and base-level rise, and is intended as a guide for the predictive modeling of sedimentary basins. DOI
46. Pemberton, SG; MacEachern, JA; Gingras, MK; Pemberton, EAL; Davis, RA.History of Ichnology Tradition and Passing the Torch: The Cincinnati School of Ichnology.Ichnos, 2018, 25: 299-322 History of Ichnology Tradition and Passing the Torch: The Cincinnati School of Ichnology
History of Ichnology; Cincinnati; J. F. James; U. P. James; S. A. Miller; C. B. Dyer; E. O. Ulrich; K. E. Caster; R. G. Osgood; W. A. Pryor
The Cincinnati school of ichnology derives from a lineage of researchers whose work spans more than a century of excellent ichnological research. In the latter part of the 1800sstudying the trace-fossil-rich Paleozoic strata of the Cincinnati areaUriah James, Joseph James, Samuel Miller and Charles Dyer built the foundations of Cincinnati ichnology by collecting, cataloging and naming many fucoids that Joseph James later recognized to represent trace fossils and in some cases inorganic markings. Many of the ichnotaxa that these workers established are still valid.In the Twentieth Century, the Cincinnati school evolved through the work of Kenneth Caster, Richard Osgood and Wayne Pryor. These men contributed significantly to our modern view of ichnological principles. Using actualistic principles, Caster ably reinterpreted a range of trace fossils to represent limulid trackways, and revealed some stratigraphic aspects of trace fossil occurrence. Osgood conducted detailed analyses, provided superb descriptions and aptly engaged in ichnotaxonomy. Osgood understood that trace fossils represented the ethological activities of animals and even proposed that ethology should provide a basis for taxonomy. Most importantly, Osgood recognized the significance of Ediacaran trace-fossil diversification and prophetically postulated that key aspects of evolutionary history are preserved therein. Pryor employed actualistic studies of the sedimentary record, and integrated ichnological studies with sedimentology and stratigraphy in a profoundly modern manner, comparable to that undertaken by specialists today.The Cincinnati school research work was of such a quality that ensuing Cincinnati workers could rely heavily on this preceding work and so the efforts incrementally enlightened the field of ichnology. Importantly, all of these scientist were pedagogs: Uriah to his son Joseph and through his collaboration with Miller; Joseph James, a prodigious publisher and vocal critic of the classification of trace fossils as various seaweeds; Miller and Dyer, primarily as enthusiastic collection builders with high-quality published descriptions and who were avid fossil society participants; and Caster, Osgood and Pryor as academic teachers of the highest order, engaged in undergraduate and graduate student training, all of whom were recognized in various ways for their masterful teaching and training.The Cincinnati school is a fine example of the enduring influence that excellent collecting, describing, interpreting, documenting and especially teaching have in science. Even giants, it appears, can stand on the shoulders of giants and thus see even further. DOI
45. Ainsworth, RB; Vakarelov, BK; MacEachern, JA; Rarity, F; Lane, TI; Nanson, RA.ANATOMY OF A SHORELINE REGRESSION: IMPLICATIONS FOR THE HIGH-RESOLUTION STRATIGRAPHIC ARCHITECTURE OF DELTAS.J. Sediment. Res., 2017, 87: 425-459 ANATOMY OF A SHORELINE REGRESSION: IMPLICATIONS FOR THE HIGH-RESOLUTION STRATIGRAPHIC ARCHITECTURE OF DELTAS
The regressive and subsequent transgressive transit of a shoreline across a clastic shelf generates the standard reservoir flow unit in most marginal to shallow marine hydrocarbon reservoirs. The stratigraphic unit produced by the shoreline transits is commonly referred to as the high-frequency (10(4) to 10(5) years), regressivetransgressive sequence (RT sequence). The unit is usually bounded top and base by marine shales marking flooding surfaces, which can act as barriers to fluid flow. Stratigraphic architecture in the RT-sequence is also known to control the internal flow behavior of many reservoirs. Hence, an ability to consistently characterize reservoirs at a sub RTsequence scale is critical to enabling prediction of reservoir performance and optimization of resource extraction strategies. This study describes the internal architecture of one shallow-water (< 10 m), low-accommodation regressive shoreline succession from the Campanian of the Alberta Basin, Canada, based on an extensive outcrop and subsurface dataset that has been convolved into a 3D geocellular computer model. The architecture and evolution of the ancient mixed-process (waves, tides, and fluvial processes) regressive deltaic shoreline system is compared and contrasted with a partial Holocene analog from northeastern Australia. The same stratigraphic surfaces and units are identified in both the modern and the ancient regressive systems. The key architectural unit is the element complex set (ECS), which is a multi-kilometer-scale, discontinuity-bounded unit that is the product of the reorganization of the coastline, often caused by autogenic backwater-driven avulsions. Multiple avulsions during a regressive shelf transit episode lead to lateral offsets of ECS units in low-accommodation systems. These systems are termed "avulsion-driven systems.'' An increasing component of vertical stacking of ECS units is observed in higher-accommodation regressive systems. The mechanisms for generating accommodation on a regressive-shoreline shelf-transit time frame may be allogenic (tectonic subsidence or eustatic sea-level change), autogenic, or a combination of the two mechanisms. A key, localized, autogenic mechanism is related to the distance of progradation during the transit of a deposystem across the shelf. In proximal shelf positions, ECS units tend to offset laterally due to limited available accommodation, whilst in more distal positions, early differential, load-induced, compactional subsidence of underlying prodelta and shelf muds can promote vertical stacking of ECS units. The critical down depositional-dip distance from the transgressive turnaround point at which ECS units become preferentially vertically stacked is a function of shelf gradient, shoreline trajectory, sandstone fraction, and prodelta and shelf mud rheology and is termed the "critical autogenic ECS stacking distance.'' Vertical stacking of ECS units may also occur when ECS units overstep underlying shelf topography, such as the distal termination of an older RT sequence. Recognition criteria and nomenclature for intra-regressive-shoreline surfaces and stratigraphic units, as well as predictive models for the ancient record are detailed across a spectrum of types of deltaic systems. DOI
44. Brekke, H; MacEachern, JA; Roenitz, T; Dastgard, SE.The use of microresistivity image logs for facies interpretations: An example in point-bar deposits of the McMurray Formation, Alberta, Canada.AAPG Bull., 2017, 101: 655-682 The use of microresistivity image logs for facies interpretations: An example in point-bar deposits of the McMurray Formation, Alberta, Canada
Well logs such as spontaneous potential and gamma ray historically have been the only tools available for facies evaluation of noncored wells in the McMurray Formation. The addition of microresistivity image logs has greatly improved facies identifications and interpretations, particularly when integrated with core data sets. In the case of McMurray channel complexes, core descriptions provide detail about bedding contacts, sedimentary texture, stratification, bioturbation intensity, and trace fossil diversity. Image logs provide texture, fabric, bedding contact style, dip directions and angles, and bedding architecture information, yielding paleoflow and lateral accretion directions. This study characterizes facies by integrating interpretations from 414 image logs with core-based descriptions from 138 of these wells. The reservoir targets, and most prolific depositional facies in this study, are associated with channel systems and their associated point-bar deposits. Facies identifications are based on several image log criteria. Mud clast breccias display variable dip angles and dip directions. Cross-stratified sands comprise vertical successions of stacked, internally consistent bedsets with high dip angles (>15 degrees) that indicate paleoflow direction. Lateral accretion beds show consistent dip directions with a progressive change from shallow-to-steep-to-shallow dip angles (e.g., <4 to 15 degrees to <4 degrees) from the base to the top of the succession, as well as beds that dip toward the thalweg of the paleochannel. Flat-lying (<4 degrees) mud records vertical accretion associated with point-bar tops or channel abandonment. Although this facies classification is specific to the McMurray Formation in the study area, the principles provided here are applicable to other subsurface studies and demonstrate the enhanced reliability of integrated core-image log data sets. DOI
43. Dashtgard, SE; Ainsworth, RB; MacEachern, JA.Preferential orientation of arthropod-generated Diplocraterion parallelum and their statistical reliability as paleocurrent indicators.Palaios, 2017, 32: 429-438 Preferential orientation of arthropod-generated Diplocraterion parallelum and their statistical reliability as paleocurrent indicators
Arthropods from the late Campanian (Late Cretaceous) of the Western Interior Seaway produced U-shaped Diplocraterion parallelum in mudstones along two closely spaced surfaces (10 cm apart), one of which corresponds to a maximum transgressive surface. Diplocraterion parallelum are widely distributed across both surfaces, with substantial variations in burrow orientations. Based on a comparison of paleocurrent indicators to burrow orientations, we demonstrate that D. parallelum are preferentially oriented parallel to the prevailing fair-weather wave propagation direction (wave-forced currents) that acted upon the colonized surfaces. There is an apparent maximum (34% above uniformity) preferential orientation of the burrows, attributed to the fact that wave-forced currents represent only one of several factors controlling shrimp burrowing behaviors. Based on this study, we propose that in the absence of paleocurrent data, Diplocraterion and other U-shaped burrows can be used to resolve flow directions, and that preferential burrow orientations >= 2% above uniformity are significant. However, it is noted that it is only possible to resolve 2-way flow directions (trend) from U-shaped burrows, as there is no way to determine vector directions. DOI
42. Hsieh, AI; Allen, DM; MacEachern, JA.Upscaling permeability for reservoir-scale modeling in bioturbated, heterogeneous tight siliciclastic reservoirs: Lower Cretaceous Viking Formation, Provost Field, Alberta, Canada.Mar. Pet. Geol., 2017, 88: 1032-1046 Upscaling permeability for reservoir-scale modeling in bioturbated, heterogeneous tight siliciclastic reservoirs: Lower Cretaceous Viking Formation, Provost Field, Alberta, Canada
Bioturbation; Permeability; Upscaling; Numerical flow modeling; Siliciclastic
Variations in bed-and bedset-scale permeability in bioturbated siliciclastic rocks result in heterogeneity that is difficult to model at a reservoir scale. This paper presents a technique to upscale permeability, such that the permeabilities of the bioturbated zones are explicitly included in the upscaled values. Study of 28 cored wells of the Lower Cretaceous Viking Formation in the Provost Field, Alberta, Canada integrated sedimentologic and ichnologic features to define recurring bed-/bedset-scale hydrofacies (HFs) characterized by a geometric mean permeability derived from plug samples. Permeability was upscaled by calculating equivalent vertical and horizontal permeabilities for composite hydrofacies (CHFs) using expressions for layered media. The equivalency of the vertical and horizontal permeability values assigned to the CHFs against those of the HFs was evaluated using a simple numerical flow model. Reservoir-scale flow was then simulated along a hydrogeological cross-section that was constructed using the CHFs. The resulting flow regime was consistent with flows simulated using published permeability estimates from tight reservoir units of the Viking Formation. This approach has the potential, therefore, for upscaling permeability for reservoir-scale modeling in tight oil and gas reservoirs, and more broadly in reservoirs where permeability is highly variable at the bed bedset scale. (C) 2017 Elsevier Ltd. All rights reserved. DOI
41. La Croix, AD; MacEachern, JA; Ayranci, K; Hsieh, A; Dashtgard, SE.An ichnological-assemblage approach to reservoir heterogeneity assessment in bioturbated strata: Insights from the Lower Cretaceous Viking Formation, Alberta, Canada.Mar. Pet. Geol., 2017, 86: 636-654 An ichnological-assemblage approach to reservoir heterogeneity assessment in bioturbated strata: Insights from the Lower Cretaceous Viking Formation, Alberta, Canada
Viking Formation; Ichnofacies; Ichnological assemblage; Facies analysis; Shoreface; Porosity; Permeability
Facies-scale trends in porosity and permeability are commonly mapped for reservoir models and flow simulation; however, these trends are too broad to capture bed and bed-set heterogeneity, and there is a need to up-scale detailed, bed-scale observations, especially in low-permeability reservoir intervals. Here we utilize sedimentology and ichnology at the bed- and bedset-scale to constrain the range of porosity and permeability that can be expected within facies of the Lower Cretaceous Viking Formation of south-central, Alberta, Canada. Three main fades were recognized, representing deposition from the middle shoreface to the upper offshore. Amalgamated, hummocky cross-stratified sandstone fades (Facies SHcs) consist of alternations between intensely bioturbated beds and sparsely bioturbated/laminated beds. Trace fossil assemblages in bioturbated beds of Facies SHcs are attributable to the archetypal Skolithos Ichnofacies, and are morphologically characterized by vertical, sand-filled shafts (VSS). Bioturbated beds show poor reservoir properties (max: 10% porosity, mean: 85.1 mD) compared to laminated beds (max 20% porosity, mean: 186 mD). Bioturbated muddy sandstone fades (Facies S-B) represent trace fossil assemblages primarily attributable to the proximal expression of the Cruziana Ichnofacies. Four ichnological assemblages occur in varying proportions, namely sediment-churning assemblages (SC), horizontal sand-filled tube assemblages (HSF), VSS assemblages, and mud-filled, lined, or with spreiten (MLS) assemblages. Ichnological assemblages containing horizontal (max: 30% porosity, mean: 1.28 mD) or vertical sand-filled burrows (max: 10% porosity, mean: 2.2 mD) generally have better reservoir properties than laminated beds (max: 20% porosity, mean: 0.98 mD). Conversely, ichnological assemblages that consist of muddy trace fossils have lower porosity and permeability (max 10% porosity, mean: 0.89 mD). Highly bioturbated, sediment churned fabrics have only slightly higher porosity and permeability overall (max: 15% porosity, mean: 1.29 mD). Bioturbated sandy mudstone facies (Facies M-B) contain ichnofossils representing an archetypal expression of the Cruziana Ichnofacies. Four ichnological assemblages occur throughout Facies MB that are similar to Facies SB; SC, HSF, VSS, and MLS assemblages. The SC (max: 15% porosity, mean: 21.67 mD), HSF (max: 20% porosity, mean: 3.79 mD), and VSS (max: 25% porosity, mean: 7.35 mD) ichnological assemblages have similar or slightly lower values than the laminated beds (max: 20% porosity, mean: 10.7 mD). However, MLS assemblages have substantially lower reservoir quality (max: 10% porosity, mean: 0.66 mD). Our results indicate that the most likely occurrence of good reservoir characteristics in bioturbated strata exists in sand-filled ichnological assemblages. This is especially true within the muddy upper offshore to lower shoreface, where vertically-oriented trace fossils can interconnect otherwise hydraulically isolated laminated sandstone beds; this improves vertical fluid transmission. The results of this work largely corroborate previous findings about ichnological impacts on reservoir properties. Unlike previous studies, however, we demonstrate that the characteristics of the ichnological assemblage, such as burrow form and the nature of burrow fill, also play an important role in determining reservoir characteristics. It follows that not all bioturbated intervals (attributed to the same facies) should be treated equally. When upscaling bed-scale observations to the reservoir, a range of possible permeability porosity values can be tested for model sensitivity and to help determine an appropriate representative elementary volume. (C) 2017 Elsevier Ltd. All rights reserved. DOI
40. Martinius, AW; Fustic, M; Garner, DL; Jablonski, BVJ; Strobl, RS; MacEachern, JA; Dashtgard, SE.Reservoir characterization and multiscale heterogeneity modeling of inclined heterolithic strata for bitumen-production forecasting, McMurray Formation, Corner, Alberta, Canada.Mar. Pet. Geol., 2017, 82: 336-361 Reservoir characterization and multiscale heterogeneity modeling of inclined heterolithic strata for bitumen-production forecasting, McMurray Formation, Corner, Alberta, Canada
Bitumen pool; Reservoir characterization; Inclined heterolithic stratification; Point bar geomodel; McMurray Formation
Bitumen reservoirs dominated by inclined heterolithic stratification (IHS) formed in large point bars of the Aptian (Lower Cretaceous) McMurray Formation in the northwestern part of the Corner oil sand lease (Alberta, Canada) were investigated to establish their value. Hybrid production technologies were applied to thin pay, typified by homogeneous reservoir sand units thicker than 5 m at the base overlain by IHS (so-called 'thin pay'), as well as IHS-dominated reservoirs in which the IHS extends down to the base of the reservoir. High-resolution seismic data and well data (core, dipmeter, HMI) were used to map four facies associations, comprising a total of 16 sedimentary facies, as well as various fluid contacts to assist in reservoir characterization and risk assessment. The conceptual depositional model was based on the analysis of the migration and re-orientation history of the IHS-dominated point bars reflecting lateral accretion, downstream migration, rotation and relocation of the bars. Multiple reactivation events, which control the heterolithic nature and reservoir quality of the deposits, create developable "pools". Seven electrofacies (with generally increasing mud content) were defined and used as input to construct vertical proportion curves that relate the electrofacies distribution to geomodel statistics in the main reservoir zone. At the electrofacies scale, numerical effective porosity-permeability models were created using micromodeling and minimodeling concepts. The geometrical shape of the electrofacies in the geomodel was investigated using non-stationary Truncated Gaussian (TG) facies simulation to enforce the stacking patterns. Each geomodel area was characterized using one variogram to efficiently compute the horizontal and vertical variogram ranges and average azimuths. Sequential Gaussian simulation (SGS) was used to map the distribution of key petrophysical parameters such as effective porosity, effective water saturation and V-shale Empirically derived saturation versus elevation profiles for each electrofacies were included in the modeling. The distributions from the micro- and mini-modeling were introduced using probability field (P-field) simulation. To investigate the amount of connected resources (the degree of connectivity of good sand as well as IHS) were extractable flow simulation studies were performed at the pad scale. In preparation for reservoir simulation, connectivity calculations within the local pool geomodel realizations were tailored for the reservoir heterogeneities (i.e., IHS) that are expected to have a major impact on the specific thermal and gravity drainage extraction processes. The geomodel realizations were ranked by expected pseudo-dynamic behaviour with connected exploitable pay as a critical parameter. (C) 2017 Elsevier Ltd. All rights reserved. DOI
39. Abdel-Fattah, ZA; Gingras, MK; Caldwell, MW; Pemberton, SG; MacEachern, JA.The Glossifungites Ichnofacies and Sequence Stratigraphic Analysis: A Case Study from Middle to Upper Eocene Successions in Fayum, Egypt.Ichnos, 2016, 23: 157-179 The Glossifungites Ichnofacies and Sequence Stratigraphic Analysis: A Case Study from Middle to Upper Eocene Successions in Fayum, Egypt
Glossifungites; Sequence stratigraphy; Middle-Upper Eocene; Fayum; Egypt
The Glossifungites Ichnofacies was erected by Dolf Seilacher (the father of modern ichnology) in the mid-nineteen sixties to encompass burrows excavated into firm or compacted substrates. Correspondingly, this firmground ichnofacies has been used extensively in the identification of omission surfaces and the identification and interpretation of sequence stratigraphic discontinuities. A case study from Eocene strata in the Fayum depression of Egypt presents an opportunity to showcase a genetic approach for classifying occurrences of the Glossifungites Ichnofacies. More than twenty-five Glossifungites Ichnofacies-demarcated surfaces are documented and examined in this study. Based on the origin and character of these discontinuities, the examined surfaces are grouped into two main types: those of autogenic origin and those of allogenic derivation. The allogenically generated expressions of the Glossifungites Ichnofacies are associated with key-stratigraphic discontinuities of sequence stratigraphic significance and are the most common in the Eocene succession. Such surfaces are attributed, herein, to transgressively modified sequence-bounding discontinuities (FS/SU), systems tract-bounding surfaces (maximum flooding surfaces, MFS, and transgressive surfaces, TS), and finally parasequence-bounding surfaces (flooding surfaces, FS). These Glossifungites Ichnofacies-demarcated surfaces have proven to be crucial in the sequence stratigraphic interpretation of the middle to upper Eocene succession in the Fayum depression. DOI
38. Ainsworth, RB; Vakarelov, BK; MacEachern, JA; Nanson, RA; Lane, TI; Rarity, F; Dashtgard, SE.Process-driven architectural variability in mouth-bar deposits: A case study from a mixed-process mouth-bar complex, Drumheller, Alberta, Canada.J. Sediment. Res., 2016, 86: 512-541 Process-driven architectural variability in mouth-bar deposits: A case study from a mixed-process mouth-bar complex, Drumheller, Alberta, Canada
Mouth bars can develop in locations where fluvial distributary channels deliver coarse sediment to the shoreline. As a consequence, they are typically considered, by default, to be fluvially dominated. However, depending upon the relative balance of fluvial, wave, and tidal energies at any given shoreline location, the preserved sedimentary structures, geometry, and internal architecture of the mouth bar will reflect the relative balance of these energies. Hence, mouth bars can be fluvial-, wave-, or tide-dominated and can also exhibit sedimentary structures formed by more than one of these processes. The ability to recognize, and to predict the architecture of these mixed-process systems is important for accurately interpreting the ancient record and has implications for hydrocarbon exploration and exploitation strategies. A detailed description and interpretation is given herein of a mixed-process mouth-bar complex which forms part of an asymmetrical delta system from the Campanian of Alberta, Canada. This mouth-bar complex is interpreted as a mixed-influence, wave-dominated system that transitions laterally into a mixed-influence, fluvially dominated system. The mouth-bar complex represents a single progradational phase of deposition, is up to 8 m thick, and can be traced over an area of approximately 60 km(2) in both outcrop and the subsurface. It comprises multiple, kilometer-scale lobe geometries (elements, element sets, and element complexes) with internal dipping, mudstone- and carbonaceous-draped clinoform surfaces at two scales (intra-element and inter-element set). The lobe geometries are oriented subparallel to the coastline. The influence of tides on the system is illustrated by tidal bundle sequences in intra-element mouth-bar clinoform bedsets, networks of tidally overdeepened, mudstone-filled distributary channels, and the development of significant thicknesses (up to 3.5 m) of swash-zone deposits at the tops of the wave-dominated mouth-bar successions. Depositional architectural units of the mouth-bar complex are estimated to have been generated by autogenic events from daily (tidal couplets), through decadal (elements) to centennial (element sets) and millennial (element complex and element complex set) time frames. A Holocene partial analog for these types of depositional systems is suggested from the Gulf of Carpentaria, Australia. Geometries, aspect ratios, and facies relationships of these mixed-process mouth-bar complexes vary significantly from the archetypal fluvial-dominated mouth bars described in the published literature. DOI
37. Campbell, SG; Botterill, SE; Gingras, MK; MacEachern, JA.EVENT SEDIMENTATION, DEPOSITION RATE, AND PALEOENVIRONMENT USING CROWDED ROSSELIA ASSEMBLAGES OF THE BLUESKY FORMATION, ALBERTA, CANADA.J. Sediment. Res., 2016, 86: 380-393 EVENT SEDIMENTATION, DEPOSITION RATE, AND PALEOENVIRONMENT USING CROWDED ROSSELIA ASSEMBLAGES OF THE BLUESKY FORMATION, ALBERTA, CANADA
Spectacular examples of well-preserved, stacked Rosselia occur in cores of the Lower Cretaceous Bluesky Formation from Alberta's Peace River oil-sands deposit. Stacked Rosselia segments reflect burrow readjustments of single tracemakers following erosion and sedimentation events. Where present, these traces help to refine paleoenvironmental interpretations and can be used as proxies for assessing the magnitude and frequency of depositional events. In this study, six cores were logged in detail. Two representative cores containing densely packed (crowded), stacked Rosselia were described sedimentologically and ichnologically and burrow lengths and numbers were measured. The Bluesky sections are interpreted to represent storm-influenced, wave-dominated delta-front deposits on the basis of modal sedimentation measurements and the presence of storm- and wave-generated sedimentary structures. The stacked Rosselia burrows record up to four post-depositional re-establishments per tracemaker, with each readjustment representing a response to abrupt sediment accumulation. Decimeter-length burrows occurring in the core datasets suggest multiple decimeter-scale depositional events in a relatively short time frame, i.e., months to perhaps a few years, depending on the lifespan and growth rate of the organism. The use of Rosselia in this study illustrates a method of evaluating sedimentation events within a brief temporal window, one lying beyond the resolution of more traditional dating methods. Furthermore, the assemblages of crowded, stacked Rosselia are presented as the first documented occurrence from the Mesozoic and the first recognized in a cored succession. DOI
36. Dashtgard, SE; MacEachern, JA.Unburrowed mudstones may record only slightly lowered oxygen conditions in warm, shallow basins.Geology, 2016, 44: 371-374 Unburrowed mudstones may record only slightly lowered oxygen conditions in warm, shallow basins
Unbioturbated mudstones and highly bioturbated silty and sandy mudstones from the late Albian of Alberta, Canada, are characterized by their ichnological, foraminiferal, and geochemical signatures. A comparison of these data sets is undertaken to isolate the dissolved oxygen (DO) conditions that led to the preservation of unbioturbated mudstones versus highly bioturbated silty and sandy mudstones. Highly diverse and abundant benthic foraminiferal assemblages, coupled with conclusive geochemical signatures, indicate that unbioturbated mudstones were deposited under oxic bottom waters. The paucity of bioturbation in these rocks is attributed to the persistence of low-oxic conditions (5 > DO > 2 mg L-1) at the seafloor, comparable to the present-day Gulf of Mexico. We assert that unbioturbated mudstone should not automatically be attributed to oxygen deficiency (< 2 mg L-1). Instead, it may reflect oxygenation sufficient to support benthic microfauna (foraminifera) but insufficient to sustain a diverse ecosystem of macrofauna (burrowing fauna). Moreover, we propose that the distribution of unburrowed mudstones deposited below low-oxic waters is predictable. A paucity of bioturbation is normal in shallow marine (below fair-weather wave base to similar to 200 m water depth) deposits of subtropical to tropical ocean basins and/or semienclosed seaways. DOI
35. Pemberton, SG; Bhattacharya, JP; MacEachern, JA; Pemberton, EAL.Unsung Pioneers of Sequence Stratigraphy: Eliot Blackwelder, Joseph Barrell, Amadeus Grabau, John Rich and Harry Wheeler.Stratigraphy, 2016, 13: 223-243 Unsung Pioneers of Sequence Stratigraphy: Eliot Blackwelder, Joseph Barrell, Amadeus Grabau, John Rich and Harry Wheeler
Few facies analysts or stratigraphers would argue against the contention that the transition to facies-driven sequence stratigraphic correlations represents one of the most important paradigm shifts in modern stratigraphy. What is less commonly appreciated is that most of the fundamental underpinnings of sequence stratigraphy were derived from a relatively small number of pioneers in the early to mid-1900s; most of them largely unknown or underappreciated by the current generation of sequence stratigraphers. Chief among these are Eliot Blackwelder, Amadeus Grabau, Joseph Barrell, John Rich, and Harry Wheeler. Blackwelder was perhaps the first to point out the presence and significance of regional unconformities in the packaging of strata in North America, which would later come to form the basis of the well-known cratonic megasequences of Larry Sloss. However, Blackwelder is best appreciated as the mentor and colleague of not only these other pioneers, but also of keyworkers who themselves ultimately mentored some of themost renowned sequence stratigraphers of the 1970s and 1980s. Amadeus Grabau focused his attention on expounding the law of the correlation of facies of Johannes Walther and bringing facies-driven correlations into stratigraphy; an approach at odds with the then prevailing view of lithostratigraphy as the principal physical stratigraphic framework. Grabau recognized that the rock record contains numerous temporal gaps that partition facies successions, for which he defined the term "hiatus". His Pulsation theory was used to explain the cycles of deposition and hiatal erosion/bypass, and although the mechanism is different, the net outcome of such "oscillations" is broadly similar to the effects of eustacy and tectonism thatwe assign to such changes today. Joseph Barrell developed the concept of base level and explored its role in controlling erosion versus deposition. Like Grabau, Barrell insisted that sedimentation was not continuous, leading to a stratigraphy that is replete with breaks of varying durations. For these he coined the term "diastems" for the small but more numerous breaks, which could be contrasted with those reflecting longer breaks which he referred to as "discontinuities". John Rich evaluated depositional topography, for which he coined the terms clinoform, undaform and fondoform. He recognized that such depositional bodies necessarily link genetically related associations of sediment deposited from the shoreline to the basin center; what today we regard as the depositional system. The resulting architectures bounded by these surfaces form the underpinning of all systems tracts in modern sequence stratigraphy. Harry Wheeler formalized the concept of time-stratigraphy, demonstrating that temporal gaps in stratigraphy are as important in understanding the rock record as the rocks themselves. His novel approach of developing stratigraphic cross-sections with time on the vertical axis pioneered the concept of chronostratigraphy through the development of what are now referred to asWheeler Diagrams. His resurrection of the base-level concept expounded by earlier workers was instrumental in defining sequences as unconformity-bounded units, re-establishing the concepts pioneered by Blackwelder himself. In concert, these stratigraphic visionaries erected a stratigraphic framework focused on the understanding of the stratigraphic record as opposed to its simple lithostratigraphic mapping or biostratigraphic dating. These unsung pioneers put into place virtually all components of modern sequence stratigraphy more than two decades before its popularization in the scientific community.
34. Pemberton, SG; Bhattacharya, JP; MacEachern, JA; Pemberton, EAL.Harry Eugene Wheeler (1907-1987): A Pioneer of Sequence Stratigraphy.Stratigraphy, 2016, 13: 95-110 Harry Eugene Wheeler (1907-1987): A Pioneer of Sequence Stratigraphy
Harry Eugene Wheeler (1907-1987) of the University of Washington was a pioneer of genetic stratigraphic principles that form the basis of our modern concept of sequence stratigraphy. Wheeler's papers on what he liked to refer to as "stratology" included the classification of stratigraphic units into lithostratigraphic and biostratigraphic entities, as well as cyclothems, unconformity-bounded units, and the analysis of base-level and its role in forming stratigraphic discontinuities. His work on unconformity-bounded "sequences" ultimately led the International Subcommission on Stratigraphic Classification to define them formally in 1987. The plots used to clarify the time-relationships of rock units are now referred to as "Wheeler diagrams". It is not uncommon that, in any scientific paradigm shift, many of the key pioneers are not fully recognized for their contributions at the time, being significantly ahead of prevailing concepts. It is also not uncommon that, by the time their points of view come into vogue, their contributions may have been largely forgotten with greater recognition given to those who synthesized or "popularized" their concepts. This is certainly true in the fields of seismic and sequence stratigraphy, where, despite the theoretical framework for sequence analysis formulated by Wheeler (1958a), little reference was made to Wheeler's work in the early formulation of these concepts in the 1970s and 1980s. Wheeler, schooled by Blackwelder, Mueller, and Schenck at Stanford and armed with the base-level concept of Joseph Barrell, was one of the first to recognize the concept of time stratigraphy. Due to his unorthodox view of stratigraphy, Wheeler was involved in one controversy after another and his views were deemed to be provocative. While the valuable contributions of latter practitioners and synthesizers are justifiably lauded, the works of original pioneers such as Harry Eugene Wheeler are largely underappreciated.
32. Ainsworth, RB; Vakarelov, BK; Lee, C; MacEachern, JA; Montgomery, AE; Ricci, LP; Dashtgard, SE.Architecture and evolution of a regressive, tide-influenced marginal-marine succession, Drumheller, Alberta, Canada.J. Sediment. Res., 2015, 85: 596-625 Architecture and evolution of a regressive, tide-influenced marginal-marine succession, Drumheller, Alberta, Canada
Tide-dominated and tide-influenced clastic depositional environments are typically interpreted to be associated with landward-stepping or transgressive systems. Here, we present an example of an overall regressive succession dominated by high-frequency sequences that exhibit abundant sedimentary and ichnological evidence of tidal processes. These strata comprise the Campanian Bearpaw-Horseshoe Canyon Formation transition exposed near Drumheller, Alberta, Canada. The clastic marine to marginal-marine sediments were deposited in mixed-process (wave-, tide-, and fluvial-influenced) depositional environments along the western margin of a foreland basin. The deposits are subdivided into six relatively thin (10 m on average), high-frequency (similar to 140,000 years), transgressive-regressive (T-R) sequences (A to F). Outcrop sedimentary logs and hand-held gamma-ray profiles were correlated to subsurface data (4 cored wells and 75 wells with wireline logs) within an area of 22 km x 16 km in order to generate a 3D geocellular computer model. This model along with paleocurrent data from outcrop were used to analyze the stratigraphic architecture and evolution of the succession. The evolution of the successive T-R sequences was mapped on a subregional scale using the 3D geocellular model. The orientations of the paleoshorelines rotate in a predictable manner during transgression and regression. Transgressive shorelines are oriented approximately S-N and rotate clockwise during regression to approximately SW-NE. The rotations are attributed to the paleogeography of the region, with the study area interpreted to sit on the western flank of a large structurally controlled embayment. The progradational high-frequency sequence set is dominated by tide-influenced strata and clearly demonstrates that tidal deposits can be preserved in both regressive as well as transgressive successions. Tidal influence in this regressive setting is attributed to shallow water depths on a wide shelf, which resulted in amplification of the tidal wave as it moved across the shelf. The embayed character of the coastline may also have augmented this effect. Tidal range is estimated to have been mesotidal to macrotidal. A modern partial analogue for the Horseshoe Canyon systems is identified from the tropical Mitchell River Delta in the Gulf of Carpentaria, Queensland, Australia. This delta system is analogous in terms of its tide-influenced facies, mesotidal range, low-gradient shelf with accompanying shallow water depths, the mixed-process character of its shoreline systems, and its horizontal to falling shoreline trajectory. DOI
31. Dashtgard, SE; Snedden, JW; MacEachern, JA.Unbioturbated sediments on a muddy shelf: Hypoxia or simply reduced oxygen saturation?Paleogeogr. Paleoclimatol. Paleoecol., 2015, 425: 128-138 Unbioturbated sediments on a muddy shelf: Hypoxia or simply reduced oxygen saturation?
Hypoxia; Anoxia; Shale; Bioturbation; Ichnology; Shelf
X-radiographs of sediment box cores acquired from the western Gulf of Mexico reveal limited bioturbation in sediment deposited in bathymetries greater than 35 m. Between 15 and 35 m, sediments are thoroughly bioturbated with averaged bioturbation indices (for all beds in a core) between 2.1 and 5.6, and trace diversities between 2 and 9 distinct burrow forms. Below 35 m water depth, box cores exhibit trace diversities of 1-3, and core-averaged bioturbation indices range between 0.3 and 3.6. There is an overall decrease in trace diversity and bioturbation indices in the offshore direction. Cross-shore ichnological trends are compared to dissolved oxygen contents of bottom waters. Above 35 m, dissolved oxygen (DO) contents show pronounced variability, ranging from 100% DO saturation through to hypoxia (<2.0 mg l(-1)), and reflect the periodic introduction of oxygen-depleted waters into otherwise fully oxygensaturated seawater. Below 35 m, DO content of bottom waters is consistently at 60-75% saturation. DO decreases by an average of 0.117 mg l(-1) per one-meter increase in water depth, such that bottom waters in 100 m water depth contain an average of 4.55 mg l(-1) DO. The data reveal a direct correlation between: a) the density of infauna and the diversity and density of burrows, and b) DO of bottom water. The degree of bioturbation is significantly reduced in waters that are oxic, but below 80% DO saturation. Based on these observations, we suggest that it is inappropriate to link low bioturbation intensities and diversities to hypoxia (<2.0 mg l(-1)), and by extension, anoxia (0 mg l(-1)). Instead, reduced oxygen contents (4.3-5.3 mg l(-1)) that lie well above hypoxic levels have a dramatic impact on the health of infaunal communities, and this is reflected by severe reductions in the ichnological character of sediments. (C) 2015 Elsevier B.V. All rights reserved. DOI
30. Hsieh, AI; Allen, DM; MacEachern, JA.Statistical modeling of biogenically enhanced permeability in tight reservoir rock.Mar. Pet. Geol., 2015, 65: 114-125 Statistical modeling of biogenically enhanced permeability in tight reservoir rock
Bioturbation; Hydrofacies; Statistical modeling; Markov chain; Permeability
Bioturbation is generally perceived to be detrimental to bulk permeability by reducing primary grain sorting, homogenizing sediment, and introducing mud as burrow linings and feces. Recent studies show, however, that some ichnogenera and biogenic fabrics serves to increase porosity and permeability. In tight hydrocarbon reservoirs, subtle changes in sand and silt distributions, such as may be generated by bioturbation, can greatly affect the resulting porosity and permeability distribution. Despite this, permeability across unfractured sedimentary reservoirs is commonly assessed solely on the basis of average grain size. This study of the Lower Cretaceous Viking Fm integrates sedimentary and ichnologic features to define recurring "hydrofacies" that possess distinct permeability grades. Grain size, lithology, bioturbation index, and trace fossil suites were described from a cored section of well 14-30-22-16W4. The k(max) values from small plugs and full-diameter core samples were used to represent each hydrofacies. Hydrofacies were qualitatively defined at the bed/bedset scale, based on sedimentary, ichnological and permeability attributes, all of which affect flow pathways in heterolithic facies. The Markov chain method was employed to compare the vertical transitions of permeability (k(max)) within a borehole against grain size and hydrofacies at the bed to bedset scale. This provided an intuitive framework for interpreting facies relationships such as coarsening-upwards successions. The results show that in the studied core, grain size only correlates to permeability in homogeneous rock units. The transiograms show that the volumetric proportions of different kmax classes show a 15% correlation with grain size, compared to a 97% correlation with the hydrofacies, indicating that variations in permeability down the well are strongly related to variations in the hydrofacies. The hydrofacies approach potentially can be used as a conceptual framework for the spatial modeling of permeability in tight hydrocarbon reservoirs, where grain size may not be the primary factor on permeability distributions. (C) 2015 Elsevier Ltd. All rights reserved. DOI
29. La Croix, AD; Dashtgard, SE; Gingras, MK; Hauck, TE; MacEachern, JA.Bioturbation trends across the freshwater to brackish-water transition in rivers.Paleogeogr. Paleoclimatol. Paleoecol., 2015, 440: 66-77 Bioturbation trends across the freshwater to brackish-water transition in rivers
Brackish-water ichnological model; Neoichnology; Trace fossils; Freshwater; Brackish water; Deltas; Estuaries
Most existing ichnological models predict an increase in burrow density and diversity from the zone of persistent brackish-water into the realm of persistent freshwater. Herein we compare the neoichnology of five tidal-fluvial channels with varying tidal magnitudes, saltwater incursion distances, and river discharge. The results indicate that there is a noticeable diminution in the sizes of marine traces and a corresponding decrease in their distribution (reduced abundance of burrowed versus unburrowed beds) with decreasing salinity. From the landward limit of saltwater incursion into the wholly freshwater tidal backwater, there is no concurrent increase in terrestrial or freshwater burrow forms; rather, burrow diversities remain low (range: 10 to 35% of the "open marine" signature) and burrow densities decrease from BI 0-3 to BI 0-1 in both sand and mud units. The five modern systems described in this study do not support the hypothesis that there is an increase in bioturbation from the brackish-water reaches of channels into freshwater reaches. In fact, freshwater channels, including those in the tidal backwater zone, are characterized by very low trace-fossil diversities (1 to 2 forms) as well as low and sporadically distributed bioturbation intensities (BI 0-1). (C) 2015 Elsevier B.V. All rights reserved. DOI
28. Ayranci, K; Dashtgard, SE; MacEachern, JA.A quantitative assessment of the neoichnology and biology of a delta front and prodelta, and implications for delta ichnology.Paleogeogr. Paleoclimatol. Paleoecol., 2014, 409: 114-134 A quantitative assessment of the neoichnology and biology of a delta front and prodelta, and implications for delta ichnology
echinoderm Deltas; Ichnology; Fraser River delta; Asymmetric deltas
The Fraser River delta front exhibits asymmetry with respect to its neoichnological, biological, and sedimentological characteristics on opposing sides of the main distributary channel, as well as the submarine canyon seaward of the channel. This phenomenon is attributed to asymmetric tidal flow, wherein there is a net northward tidal flow along the delta front. The southern delta front lying updrift of the Main Channel, is primarily composed of sandy beds and bedsets that exhibit low bioturbation intensities (BI 0-3) and limited biodiversity (H 0.9-1.4). Tracemakers in the updrift delta front predominantly consist of polychaetes and bivalves that produce suites dominated by simple vertical and horizontal traces attributable to the Skolithos Ichnofacies. The suites consist of traces comparable to Thalassinoides, Planolites, Skolithos, rare Conichnus, and Cylindrichnus. The northern delta front lying downdrift of the Main Channel, and the prodelta consist of muddy beds and bedsets that display high bioturbation intensities (BI 3-6) and diverse infaunal populations (H 1.4-23). Polychaetes, bivalves, and echinoderms comprise the main tracemakers, and these infauna produce complex and robust ichnological suites typical of the Cruziana Ichnofacies. The downdrift delta front and prodelta trace assemblage includes traces comparable to Skolithos, Planolites, Thalassinoides, Artichnus, Palaeophycus, Conichnus, Asterosoma, Rosselia, Cylindrichnus, Gyrolithes, Teichichnus, Phycosiphon, Arenicolites, Polykladichnus, and Scolicia. The spatial distribution (area and volume) of biogenically induced sediment disruption indicates that the updrift delta front is significantly less bioturbated than its downdrift counterpart. Additionally, the prodelta does not exhibit evidence of asymmetry with respect to its neoichnological character; all spatial variability is recorded in delta front positions. (C) 2014 Elsevier B.V. All rights reserved. DOI
27. Czarnecki, JM; Dashtgard, SE; Pospelova, V; Mathewes, RW; MacEachern, JA.Palynology and geochemistry of channel-margin sediments across the tidal-fluvial transition, lower Fraser River, Canada: Implications for the rock record.Marine and Petroleum Geology, 2014, 51: 152-166 Palynology and geochemistry of channel-margin sediments across the tidal-fluvial transition, lower Fraser River, Canada: Implications for the rock record
Dinoflagellate cyst; Pollen; Carbon isotopes; Estuary; Delta; Marginal-marine; McMurray Formation
In the tidally influenced Fraser River, Canada, palynological and carbon isotope (delta C-13(org)) signatures of channel-margin sediments are compared to environmental parameters (e.g., grain size, water salinity) to establish how the signatures vary across the tidal-fluvial transition. Palynological assemblages in the Fraser River are dominated by tree pollen, which constitutes between 85% and 95% of all assemblages. Dinocyst abundances do not exceed 2% of the total palynological assemblage, and the number and diversity of dinocysts gradually decreases landward. The calculated landward limit for dinocysts is at approximately 83 river km, which is relatively close to the upstream limit of the tidal backwater (at similar to 100 km). delta C-13(org) values show minimal variability across the tidal fluvial transition, and the average value is approximately -26 parts per thousand. The delta C-13(org) signature of river sediments indicates a dominance of terrestrially sourced organic matter regardless of brackish-water and tidal influence on sediment deposition. Six palynological and geochemical trends are identified as relevant to the rock record. 1) In deltaic environments, palynological and geochemical characteristics are less useful than sedimentological and ichnological characteristics for establishing depositional conditions. 2) In marginal-marine settings, low abundances and low species diversities of dinocysts, coupled with a "terrestrial" geochemical signature (delta C-13(org) < -25 parts per thousand.) do not necessarily indicate deposition in a terrestrial environment. 3) Dinocyst abundances above 1% of the total palynomorph population can indicate a significant marine influence on sediment deposition. 4) Mud beds, preferably bioturbated, should be preferentially sampled in order to maximize palynomorph recovery. 5) Marine palynomorphs can occur, albeit in very low concentrations, to the landward limit of the tidal-backwater zone. 6) Palynological and geochemical data should be compared across the paleo-depositional environment in order to establish general trends and remove local variations caused by biases such as grain size. (C) 2013 Elsevier Ltd. All rights reserved. DOI
26. Ravnas, R; Cook, A; Engenes, K; Germs, H; Grecula, M; Haga, J; Harvey, C; Maceachern, JA.The Ormen Lange turbidite systems: sedimentary architectures and sequence structure of sandy slope fans in a sediment-starved basin., 2014, 46: 609-645 The Ormen Lange turbidite systems: sedimentary architectures and sequence structure of sandy slope fans in a sediment-starved basin
Slope topography; turbidite systems; megasequences; turbidite architectures; controlling factors
The reservoirs of the giant Ormen Lange field, located off the More coast, consist of deep-marine turbidites within the Upper Maastrichtian Springar Formation and the Danian Egga sandstone unit. The two sandstone units are interpreted in terms of inner to middle and outer parts of two, stacked lower slope sandy fan systems, respectively. The two fan systems were sourced from an uplifted hinterland; the tectonic rejuvenation of this is related to rift-margin uplift in response to phased late Campanian to Danian rifting within the western More Basin. Rift-margin uplift was accompanied by basinward tilting and draped folding over deep-seated basement highs along the More Margin, which produced a stepped slope margin with local slope minibasins and terraces. Each phase of repeated hinterland uplift, basin-margin tilting and sandy fan development represents a time span of a few million years. The Springar and Egga turbidite systems evolved through fill-spill processes on the slope terraces or minibasin(s). Within an individual minibasin or slope terrace, an early phase of 'infilling' or smoothing of inherited topography appears to have been followed by a more organised backfilling or upslope onlapping combined with forestepping or outbuilding of the sandy fan across the individual terraces or minibasins. Compensationally stacked channel storeys and lobe storeys form the fundamental architectural elements and probably reflect major flooding events in the hinterland or drainage basin. Multistorey channel belts represent further outbuilding of the local terrace or minibasin-filling fan, with sediment bypass and delivery to further downslope minibasins and terraces. The uppermost parts of the fan systems appear less organised and contain disorganised, slumped and gravitationally re-sedimented units alternating with multistorey channel-fills. These less-organised facies associations formed in response to an early stage or initial tilting of the basin margin slope. Final backstepping and return to predominantly hemipelagic to pelagic slope deposition is attributed to renewed upslope or hinterland structuring, which resulted in capture of sand in proximal subbasins.
25. La Croix, AD; Gingras, MK; Pemberton, SG; Mendoza, CA; MacEachern, JA; Lemiski, RT.Biogenically enhanced reservoir properties in the Medicine Hat gas field, Alberta, Canada.Mar. Pet. Geol., 2013, 43: 464-477 Biogenically enhanced reservoir properties in the Medicine Hat gas field, Alberta, Canada
Bioturbation; Porosity; Permeability; Reservoir quality; Micro-CT; Spot-minipermeametry; Medicine Hat gas field; Ichnology
Spot-minipermeametry and micro-CT analytical techniques were employed to evaluate the effect(s) of bioturbation on porosity and permeability distributions in reservoir facies of the highly prolific Medicine Hat gas field of Alberta, Canada. This study focuses on five cm-scale samples that occur at different stratigraphic positions and intersect discrete bioturbated horizons within the Medicine Hat Member. Spot-minipermeability results demonstrate that permeability in bioturbated sandstones is up to two orders of magnitude greater than those of the muddy matrix, thus corresponding to a dual-porosity fluid flow system. Graphing bioturbation intensity versus measured permeability indicates that burrows are well connected horizontally and provide flow conduits. Micro-CT models reveal that burrowed sandstones are isolated and planiform in character; rare interpenetrations from vertically oriented trace fossils serve to interconnect these hydraulically isolated strata. Results show that bioturbated sandstones possess reservoir properties comparable to those associated with laminated sandstones, yielding an anisotropic porous medium. Understanding the impact of trace fossils on porosity permeability distributions in the Medicine Hat gas field can be used to identify potential reservoir from previously interpreted non-reservoir rock, and, ultimately, improve reserve estimations. (C) 2012 Elsevier Ltd. All rights reserved. DOI
24. MacEachern, JA; Roberts, MC.Ichnological evidence of jokulhlaup deposit recolonization from the Touchet Beds, Mabton, WA, USA.Quat. Res., 2013, 79: 37-48 Ichnological evidence of jokulhlaup deposit recolonization from the Touchet Beds, Mabton, WA, USA
Ichnology; Jokulhlaup; Recolonization; Touchet Beds; Mabton Washington; Natal dispersal; Rodent burrows; Paleosurfaces
The late Wisconsinan Touchet Beds section at Mabton, Washington reveals at least seven stacked jokulhlaup deposits, five showing evidence of post-flood recolonization by vertebrates. Tracemakers are attributed to voles or pocket mice (1-3 cm diameter burrows) and pocket gophers or ground squirrels (3-6 cm diameter burrows). The Mount St. Helens S tephra deposited between flood beds contains the invertebrate-generated burrows Naktodemasis and Macanopsis. Estimates of times between floods are based on natal dispersal distances of the likely vertebrate tracemakers (30-50 m median distances; 127-525 m maximum distances) from upland areas containing surviving populations to the Mabton area, a distance of about 7.9 km. Tetrapods would have required at least two to three decades to recolonize these flood beds, based on maximum dispersal distances. Invertebrate recolonization was limited by secondary succession and estimated at only a few years to a decade. These ichnological data support multiple floods from failure of the ice dam at glacial Lake Missoula, separated by hiatal surfaces on the order of decades in duration. Ichnological recolonization times are consistent with published estimates of refill times for glacial Lake Missoula, and complement the other field evidence that points to repeated, autogenically induced flood discharge. Crown Copyright (C), 2012 Published by Elsevier Inc. on behalf of University of Washington. All rights reserved. DOI
23. Pemberton, SG; MacEachern, JA.History of Ichnology: The Origins of Trace Fossil Taxonomy and the Contributions of Joseph F. James and Walter H. Hantzschel.Ichnos, 2013, 20: 181-194 History of Ichnology: The Origins of Trace Fossil Taxonomy and the Contributions of Joseph F. James and Walter H. Hantzschel
J. F. James; Taxonomy; W. H. Hantzschel
The taxonomy of trace fossils has had a somewhat controversial history because they do not represent the actual animal remains but rather their work on and in the substrate. As such, traditional palaeontologists and zoologists have viewed them with some skepticism. Ichnologists owe a great debt to two geologists: Joseph F. James of Cincinnati and Walter H. Hantzschel of Hamburg, who took it upon themselves to impose some order on the chaos that constituted trace fossil taxonomy at the time. James, working independently and in ignorance of Alfred Nathorst, arrived at and utilized many of the same criteria his Swedish counterpart employed to criticize the fucoid origins of many trace fossils in the late 19th century. With his restudy of the systematics of Fucoides, Skolithos, and Arthrophycus, James brought to light many of the taxonomical nightmares that faced-and are still facing-the fledging science and can be rightfully considered the first trace fossil taxonomist. During the 1940s and 1950s, Hantzschel collected the widely scattered pertinent data from the literature, an immense task that, when published in 1962 (and later revised and expanded in 1975), made trace fossils accessible to further research and started a worldwide boom in trace fossil research. DOI
22. Dashtgard, SE; MacEachern, JA; Frey, SE; Gingras, MK.Tidal effects on the shoreface: Towards a conceptual framework.Sediment. Geol., 2012, 279: 42-61 Tidal effects on the shoreface: Towards a conceptual framework
Tides; Beach; Facies models; Sedimentology; Ichnology; Storm-dominated
Tidal processes can have a significant impact on the sedimentological and ichnological character of wave-dominated shoreface deposits. As the influence of tides increases, the resulting shoreface successions begin to depart markedly from those postulated by the conventional, wave-dominated shoreface model, which was built upon essentially non-tidal shoreline settings. In shoreface settings subject to stronger tidal flux, tides can be manifest either directly or indirectly. Direct tidal effects refer to those characteristics imparted by tidal energy (e.g., tidal currents) per se, and are best expressed in offshore and lower shoreface positions. Key evidence of direct tidal control includes uniform sediment calibres from the upper shoreface to the offshore, and little or no mud preserved in the lower shoreface. Additionally, sands in the lower shoreface and offshore tend to be intensely bioturbated. Where primary stratification is preserved, it largely comprises current-generated structures. Such shoreface deposits are referred to herein as "tide-influenced shorefaces", and are expected in settings with low storm-wave input coupled with strong tidal currents (e.g., straits). Indirect tidal influences are manifest by the lateral translation of wave zones across the shoreface profile owing to changes in water depth during the tidal cycle. This is best developed in macrotidal to megatidal settings. Indirect tidal influences are more pronounced in the upper and lower shoreface, and are recorded through the interbedding of sedimentary structures produced by shoaling waves, breakers and surf, swash-backwash, and surface runoff. The boundaries between shoreface subenvironments are correspondingly poorly defined. The foreshore in settings of elevated tidal range is also generally much thicker (typically 4 to 5 m). Bioturbation tends to be patchy in distribution across the shoreface, and dominated by vertical structures. Such systems are defined as "tidally modulated shorefaces". Using well-established sedimentological and ichnological criteria for recognizing wave-dominated (nontidal) shorefaces - wherein sediment deposition is nearly wholly controlled by fair-weather wave and storm-wave processes - a conceptual model is developed for discriminating fair-weather (non-tidal) shorefaces, storm-influenced (non-tidal) shorefaces, and tidally influenced shorefaces. Five shoreface archetypes are defined: storm-affected, storm-influenced, storm-dominated, tide-influenced, and tidally modulated. (C) 2010 Elsevier B.V. All rights reserved. DOI
21. Gingras, MK; MacEachern, JA; Dashtgard, SE.The potential of trace fossils as tidal indicators in bays and estuaries.Sediment. Geol., 2012, 279: 97-106 The potential of trace fossils as tidal indicators in bays and estuaries
Ichnology; Trace fossil; Tubular tidalite; Intertidal flat; Tidal sedimentary structures
identification of trace-fossil assemblages characteristic of brackish-water settings. However, this limited means of (ichnologically) identifying tidal settings is unsatisfying and the establishment of ichnological-tidal relationships for the purpose of discerning tidal depositional processes is desirable. We suggest that several types of ichnological data can be used to identify tidal influence: (1) ichnological response to rhythmic sedimentation; (2) the presence of tubular tidalites (i.e. biogenic structures infilled by tidally derived sediments); (3) the identification of anisotropic resource exploitation associated with food-rich slack-tide laminations; (4) the identification of tidal-flat deposits through bioturbation intensity and ichnological composition; (5) the recognition of brackish-water trace fossils; and potentially (6) system-scale ichnological distributions (which are presently poorly understood). As with tidal sedimentary structures, the inference of tidal processes from biogenic sedimentary structures should depend on identifying as many of the above characteristics as possible. (C) 2011 Elsevier B.V. All rights reserved. DOI
20. Gingras, MK; MacEachern, JA; Dashtgard, SE; Zonneveld, J-P; Schoengut, J; Ranger, MJ; Pemberton, SG.Chapter 16: Estuaries.Trace Fossils as Indicators of Sedimentary Environments (Knaust, D; Bromley, RG (eds.)), 2012, Developments in Sedimentology 64: 471-514 Chapter 16: Estuaries
DOI
19. MacEachern, JA; Bann, KL; Gingras, MK; Zonneveld, J-P; Dashtgard, SE; Pemberton, SG.Chapter 4: The Ichnofacies Paradigm.Trace Fossils as Indicators of Sedimentary Environments (Knaust, D; Bromley, RG (eds.)), 2012, Developments in Sedimentology 64: 101-136 Chapter 4: The Ichnofacies Paradigm
DOI
18. MacEachern, JA; Dashtgard, SE; Knaust, D; Catuneanu, O; Pemberton, SG.Chapter 6: Sequence stratigraphy.Trace Fossils as Indicators of Sedimentary Environments (Knaust, D; Bromley, RG (eds.)), 2012, Developments in Sedimentology 64: 155-192 Chapter 6: Sequence stratigraphy
DOI
17. Pemberton, SG; MacEachern, JA; Dashtgard, SE; Bann, KL; Gingras, MK; Zonneveld, J-P.Chapter 19: Shorefaces.Trace Fossils as Indicators of Sedimentary Environments (Knaust, D; Bromley, RG (eds.)), 2012, Developments in Sedimentology 64: 585-625 Chapter 19: Shorefaces
DOI
16. Gingras, MK; MacEachern, JA; Dashtgard, SE.Process ichnology and the elucidation of physico-chemical stress.Sediment. Geol., 2011, 237: 115-134 Process ichnology and the elucidation of physico-chemical stress
Ichnology; Ichnofacies; Ichnofabrics; Process ichnology; Trace fossil
This paper sets out a philosophical approach to ichnological (trace fossil) analysis, which focuses on the interpretation of trace fossils as sedimentary structures rather than as paleontological entities per se. Using wide-ranging datasets and a large number of observations and interpretations, a "Process Ichnology" framework is proposed. This interpretive framework provides an improved means of estimating the presence and magnitude of various physical and chemical (i.e., physico-chemical) depositional stresses (e.g., water turbidity, sedimentation rates, substrate consistency, salinity, and oxygenation) in ancient sedimentary environments. Ichnological datasets that are considered include: 1) trace-fossil distributions; 2) ethological diversity and the range of diversity; 3) the significance of burrow linings; 4) trace-fossil size; and, 5) post-depositional compaction of trace fossils. From these data, higher-resolution estimates can be made for the determination of sedimentation rates, temporal variation in sedimentation rate, sediment consistency, and aspects of the bottom- and interstitial-water chemistries. Additionally, the character of depositional bypassing of sediment grains can be determined. The methodologies and interpretations herein are intended for use by non-ichnologists in a manner akin to the interpretation of physical sedimentary structures. However, the outlined framework is complementary to other methods of ichnological analysis, such as ichnofacies- or ichnofabric-analysis, and can be applied as such. Indeed, this method is a derivative of these and other earlier techniques, and should be employed where a systematic approach to obtaining high-resolution sedimentological interpretations is a required aspect of the study. (C) 2011 Published by Elsevier B.V. DOI
14. Bhattacharya, JP; MacEachern, JA.HYPERPYCNAL RIVERS AND PRODELTAIC SHELVES IN THE CRETACEOUS SEAWAY OF NORTH AMERICA.J. Sediment. Res., 2009, 79: 184-209 HYPERPYCNAL RIVERS AND PRODELTAIC SHELVES IN THE CRETACEOUS SEAWAY OF NORTH AMERICA
Despite the historical assumption that the bulk of marine "shelf" mud is deposited by gradual fallout from suspension in quiet water, recent studies of modern muddy shelves and their associated rivers show that they are dominated by hyperpycnal fluid mud. This has not been widely applied to the interpretation of ancient sedimentary fluvio-deltaic systems, such as dominate the mud-rich Cretaceous Western Interior Seaway of North America. We analyze two such systems, the Turonian Ferron Sandstone Member of the Mancos Shale Formation, in Utah, and the Cenomanian Dunvegan Formation in Alberta. Paleodischarge estimates of trunk rivers show that they fall within the predicted limits of rivers that are capable of generating hyperpycnal plumes. The associated prodeltaic mudstones match modern hyperpycnite facies models, and suggest a correspondingly hyperpycnal character. Physical sedimentary structures include diffusely stratified beds that show both normal and inverse grading, indicating sustained flows that waxed and waned. They also display low intensities of bioturbation, which reflect the high physical and chemical stresses of hyperpycnal environments. Distinct "mantle and swirl" biogenic structures indicate soupground conditions, typical of the fluid muds that represent the earliest stages of deposition in a hyperpycnal plume. Hyperpycnal conditions are ameliorated by the fact that these rivers were relatively small, dirty systems that drained an active orogenic belt during humid temperate (Dunvegan Formation) to subtropical (Ferron Sandstone Member) "greenhouse" conditions. During sustained periods of flooding, such as during monsoons, the initial river flood may lower salinities within the inshore area, effectively "prepping" the area and allowing subsequent floods to become hyperpycnal much more easily. Although shelf slopes were too low to allow long-run-out hyperpycnal flows, the storm-dominated nature of the seaway likely allowed fluid mud to be transported for significant distances across and along the paleo-shelf. Rapidly deposited prodeltaic hyperpycnites are thus considered to form a significant component of the muddy shelf successions that comprise the thick shale formations of the Cretaceous Western Interior Seaway. DOI
13. Dashtgard, SE; Gingras, MK; MacEachern, JA.Tidally modulated shorefaces.J. Sediment. Res., 2009, 79: 793-807 Tidally modulated shorefaces
Tidally modulated shorefaces (TMS) are wave-dominated, but differ from conventional shorefaces in that sediments deposited in water depths equivalent to the upper, middle, and lower shoreface (depending upon the tidal range) are regularly subjected to variable wave processes, including swash-backwash, breaking-wave and surf processes, and shoaling waves; during the tidal cycle. In upper macrotidal and megatidal settings, it is also possible that these shoreface deposits are subaerially exposed during low tide. TMS exhibit the morphology, seaward decrease in sediment caliber, and dominance of wave-generated sedimentary structures consistent with beach-shoreface settings. However, the sedimentological and ichnological structures of deposits exposed in the laterally extensive intertidal zone are more akin to those of the upper and lower shoreface, and not the beach. Four major differences permit the ready differentiation of tidally modulated shoreface successions from conventional shorefaces. (1) Sedimentary structures generated by swash-backwash (plane beds), surf and breaking waves (current ripples and trough cross-beds), shoaling waves (oscillation ripples), and storm waves (hummocky and swaly cross-stratification) are interbedded with one another across the shoreface. (2) Ebb-oriented tidal currents and surface runoff during the failing tide and at low tide deposit offshore-directed current ripples and combined-flow ripples in sandy sediments, or trough cross beds in gravel-dominated sediments. (3) Ichnologically, TMS exhibit a reduction in both the diversity of ichnogenera and density of burrowing across the entire shoreface profile. However, the incipient-trace associations are most similar to the Skolithos Ichnofacies in the upper shoreface-equiva lent zone, and to the Cruziana Ichnofacies in the lower shoreface-equiva lent zone. (4) The sedimentological and ichnological criteria commonly employed to identify the middle shoreface are spread out across the upper and lower shoreface, making this subenvironment difficult to differentiate. DOI
12. Bann, KL; Tye, SC; MaEachern, JA; Fielding, CR; Jones, BG.ICHNOLOGICAL AND SEDIMENTOLOGIC SIGNATURES OF MIXED WAVE- AND STORM-DOMINATED DELTAIC DEPOSITS: EXAMPLES FROM THE EARLY PERMIAN SYDNEY BASIN, AUSTRALIA., 2008, 90: 293-+ ICHNOLOGICAL AND SEDIMENTOLOGIC SIGNATURES OF MIXED WAVE- AND STORM-DOMINATED DELTAIC DEPOSITS: EXAMPLES FROM THE EARLY PERMIAN SYDNEY BASIN, AUSTRALIA
wave-dominated delta; ichnology; ichnofacies; Australia; Permian; Sydney Basin
The lithological characteristics of wave- and/or storm-dominated delta-front deposits are fundamentally similar to those of facies deposited on the wave-formed shorefaces of strandplain settings. Differentiating ancient shoreface deposits from those that record deposition in proximity to contemporaneous wave-dominated deltas, therefore, is challenging, especially where the facies represent deposits that are intermediate between end-member strandplains and delta fronts. To date, archetypal facies models are inadequate to describe and distinguish between such deposits. The challenge is further accentuated where studies are limited entirely to core and other subsurface data. Depositional processes typical of deltaic settings influence infaunal organisms in subtle but significant ways. The resulting ichnological signatures clearly reflect the innate differences in physicochemical conditions and paleoenvironmental stresses operating in these settings, such as variations in sedimentation rates, substrate consistencies, oxygenation, salinities, energy conditions, increased turbidity levels, and episodic deposition associated with river floods. Lower Permian successions of the Wasp I-lead, Pebbley Beach, and Snapper Point Formations of the south ern Sydney Basin in southeastern Australia are spectacularly exposed in extensive coastal Outcrops. The preserved lithologies and many of the primary sedimentary structures are virtually identical to those characteristic of offshore and strandplain shoreface deposits. Integration of the lithological, sedimentological, and subtle ichnological differences, however, demonstrate that these units were deposited under the influence of paleoenvironmental stresses. There is also considerable evidence of very cold climatic conditions and concomitant effects oil the depositional environment from ice rafting, which imposed additional paleoenvironmental stresses. For the most part, fair-weather beds closely resemble strandplain shoreface deposits, with trace-fossil Suites that are very diverse and contain a mixture of structures that reflect a variety of feeding strategies characteristic of the Cruziana and Skolithos Ichnofacies. Variations in the ichnological signatures, and departures from the archetypal ichnofacies expressions, in the form of sporadic bioturbation levels, reduced assemblage diversities, and reductions in ichnogenera sizes compared to their unstressed counterparts, suggest intermittent physicochemical stresses. Associated storm deposits display many of the sedimentological and ichnological characteristics associated with river influx and deltaic conditions, including: soft-sediment deformation structures and sediment-gravity-flow deposits, recording rapid sediment emplacement; mudstone drapes that are characteristic of hyperpycnally emplaced fluid muds and rapidly flocculated muds that are produced along the zone of mixing at the base of a hypopycnal (buoyant) mud Plume; unbioturbated, carbonaceous mudstone interbeds with synaeresis cracks consistent with freshet-induced salinity fluctuations; an abundance of phytodetrital material, and allochthonous wood and large logs; and sandstone beds with "stressed" trace-fossil suites attributable to the Cruziana Ichnofacies, where ordinarily suites representative of the Skolithos Ichnofacies would be expected. These characteristics suggest that fair-weather beds reflect ambient wave shoaling, but during and immediately following storms, increased river discharge strongly influenced the depositional environment and thus the characteristics of the resultant event beds. Overall, the successions are therefore interpreted as wave- and storm-dominated prodelta to proximal delta-front deposits. Variations in storm signature throughout the successions reflect temporal and spatial variations in the preservation and, therefore, abundance of fair-weather beds. Such variations may represent changing storm climates, climatic seasonality, fluctuations in river discharge, increased amalgamation of beds by persistent storm activity, subtle changes in storm tracks with respect to delta-front orientation, and subtle shallowing or deepening along the delta front.
11. Gingras, MK; Dashtgard, SE; MacEachern, JA; Pemberton, SG.Biology of shallow marine ichnology: a modern perspective.Aquat. Biol., 2008, 2: 255-268 Biology of shallow marine ichnology: a modern perspective
ichnology; neoichnology; traces; crustacea; vermiforms; bivalves; echinoderms; anemones
This study considers the construction and functionality of biogenic structures made by marine, vermiform nemerteans, polychaetes and hemichordates; marine crustaceans; motile bivalves; motile echinoderms; and sponges and sea anemones. We report on a range of modern biogenic structures similar to several known ichnogenera. Vermiform animals dominantly occupy vertical burrows that range from simple through helical shafts to Y- and U-shapes. Horizontal traces made by worms range in form, but are dominated by branching and variably sinuous to meandering burrows. Crustaceans primarily excavate open burrow systems that possess a range of architectures that are similar to either Thalassinoides or Psilonichnus. Smaller crustaceans, such as amphipods, mix the sediment. Bivalve traces vary in form, but generally preserve evidence of vertically oriented filter or interface-deposit feeding from a stationary location, rapid vertical escape, or horizontal grazing. Echinoderms dominantly preserve body impressions and motility traces, such as Asteriacites. An important class of biogenic structure, Scolicia and Bichordites, are made by urchins. Finally, sea anemones can generate large, penetrative, conical biogenic structures. Large, open horizontal networks serve as domiciles and deposit-feeding structures for crustaceans, but with worms similar burrow types are used more for passive carnivory and establishing an interface-feeding network. We report that the trace fossil Gyrolithes potentially represents mechanical ramps for shrimp, but is used as a sediment holdfast when made by worms. Finally, Y-shaped burrows are used for filter feeding in shrimp, and interface-deposit feeding in worms. These examples emphasize that inferences of behavior in the rock record are interpretive. DOI
10. Hovikoski, J; Lemiski, R; Gingras, M; Pemberton, G; MacEachern, JA.ICHNOLOGY AND SEDIMENTOLOGY OF A MUD-DOMINATED DELTAIC COAST: UPPER CRETACEOUS ALDERSON MEMBER (LEA PARK FM), WESTERN CANADA.J. Sediment. Res., 2008, 78: 803-824 ICHNOLOGY AND SEDIMENTOLOGY OF A MUD-DOMINATED DELTAIC COAST: UPPER CRETACEOUS ALDERSON MEMBER (LEA PARK FM), WESTERN CANADA
Current depositional models largely promote the perception that all open-coastal distal (sea)-proximal (land) gradients are reflected by upward-coarsening grain-size trends, and that shoreline deposits are represented by prominent sand bodies. Although commonly the case, significant departures from this model may occur when the availability of coarser sediment calibers (sand-sized and larger) is limited. This is especially true where alongshore sediment-transport-influenced depositional systems are associated with rivers that supply abundant suspended sediments. Underestimating the role of grain-size segregation may lead to misinterpretations of energy levels and water depths, especially in some shale-dominated sedimentary units. The Upper Cretaceous Alderson Member (Lea Park Fm) is an up to 180-m-thick, gas-charged shale unit that we interpret as an ancient analogue for modern offshore and mud-dominated deltaic coasts. Sedimentological and ichnological data collected from 27 cores indicate that much of the sediment volume of the Alderson Member was deposited in relatively shallow water under the influence of tidal and wave processes in a deltaic coastal setting. Characteristic features reflecting these depositional affinities include: (1) increased proportions of terrestrially derived organic matter; (2) indications of thixotropic to soupy substrates (e.g., fluid mud) coupled with rapid depositional rates; (3) an impoverished ichnological signal (Planolites-dominated suites); (4) micro-laminated shale; (5) shale-on-shale erosional contacts; (6) scour-and-fill structures; and (7) intervals of low-angle cross-stratification. The interpretation of relatively shallow-water settings is also supported by recurring root-bearing horizons, Glossifungites Ichnofacies-demarcated transgressive surfaces of erosion, and conglomeratic surfaces at particular stratigraphic levels. The deposits are interpreted to include offshore, "subaqueous deltas," muddy shoreface and/or tidal flat, and aggradational muddy coastal plain (chenier plain) sub-environments. The results of this study improve our knowledge of ichnological and sedimentological characteristics of shallow-marine shale units, and are potentially useful for recognition of similar nearshore mud-prone deposits elsewhere. DOI
9. Pemberton, SG; MacEachern, JA; Gingras, MK; Saunders, TDA.Biogenic chaos: Cryptobioturbation and the work of sedimentologically friendly organisms.Paleogeogr. Paleoclimatol. Paleoecol., 2008, 270: 273-279 Biogenic chaos: Cryptobioturbation and the work of sedimentologically friendly organisms
Ichnology; Cryptobioturbation; Physical sedimentary structures; Biogenic sedimentary structures; Reservoir properties
Biogenic chaos, from an ichnological point of view, can be defined as total bioturbation of sediment by infaunal organisms, such that the original sedimentary fabric and associated sedimentary structures are entirely destroyed. The truth, however, is that not all forms of thorough bioturbation are purely destructive. As improbable as it initially sounds, sediment can be pervasively (potentially 100%) bioturbated, and yet have suffered remarkably little distortion of the original bedding. In nature there exist many different levels of organism communities. Historically, the study of any natural system begins with the most obvious, attention-grabbing elements. Only later do the more innocuous aspects come to be discovered and appreciated. lchnology shows a similar historical pattern. The most obvious aspects of the science, the discrete burrow or track forms, have been well studied for many years. Only recently have more subtle biogenic disturbances, such as micro borings, bacterial trails, meiofaunal burrows, infaunal tiering. etc., gained attention. Likewise, another level of bioturbation - cryptobioturbation - exists and is becoming more evident in the rock record. Owing to its diminutive and obscure nature, cryptobioturbation has not received widespread attention. As the name implies, cryptobioturbation is characteristically small in scale and exceedingly subtle in expression. What sets it apart from other forms of bioturbation, however is its tendency to preserve rather than to destroy the sediment's primary physical structure. The fabric that results from cryptobioturbation can have significant influence on resulting permeability and porosity trends. In some systems where both cryptically bioturbated sandstone and generally unburrowed sandstone are present, mini-permeameter measurements show that numerous heterogeneities are retained in the unburrowed sandstone, resulting in a wide range of permeabilities. In contrast, cryptically bioturbated sandstone intervals show that these heterogeneities are less pronounced, and the resulting permeability curve is more uniform. The effect of cryptobioturbation does not result in enhanced permeabilities, but rather diminishes internal heterogeneities, leading to a more uniform permeability distribution. (C) 2008 Elsevier B.V. All rights reserved. DOI
8. Pemberton, SG; McCrea, R; Gingras, MK; Sarjeant, WAS; MacEachern, JA.History of ichnology: The correspondence between the reverend Henry Duncan and the reverend William Buckland and the discovery of the first vertebrate footprints.Ichnos, 2008, 15: 5-18 History of ichnology: The correspondence between the reverend Henry Duncan and the reverend William Buckland and the discovery of the first vertebrate footprints
history of ichnology; Henry Duncan; William Buckland; vertebrate ichnology
The Reverend Henry Duncan (1774-1846), clergyman, philosopher, writer, politician, archeologist, poet, educator, social reformer, and the founder of savings banks, was indeed a Man for All Seasons. In 1824, while Minister of the Church of Scotland at Ruthwell, Dumfriesshire, he was presented with a slab of red sandstone from the Corneockle Muir quarry in Annandale, exhibiting a set of footprints on it. Although Duncan felt from the start that he was dealing with the tracks of an animal, he wrote to the Reverend William Buckland, Reader in Mineralogy and Geology at the University of Oxford, to solicit his opinion on the origin of these curious markings. Buckland was at first skeptical, but after receiving casts of the markings from Duncan, he became convinced that they did in fact represent footprints. Duncan and Buckland maintained a correspondence about the footprints, and on January 7, 1828, Duncan described the Corncockle Muir footprints to the Royal Society of Edinburgh and quoted Buckland's findings. Duncan's paper was not published by the Society until 1831, but it aroused considerable interest-"Footsteps before the Flood"!-and was reported in several newspapers. This was the first scientific report of a fossil track; although a schoolboy, Pliny Moody, had found fossil footprints in Connecticut in 1802, they were not scientifically described until 1836. The Scottish tracks are now considered to be not reptilian but of synapsid origin and the rocks containing them are now known to be of Permian age. DOI
7. MacEachern, JA; Gingras, MK.RECOGNITION OF BRACKISH-WATER TRACE-FOSSIL SUITES IN THE CRETACEOUS WESTERN INTERIOR SEAWAY OF ALBERTA, CANADA., 2007, 88: 149+ RECOGNITION OF BRACKISH-WATER TRACE-FOSSIL SUITES IN THE CRETACEOUS WESTERN INTERIOR SEAWAY OF ALBERTA, CANADA
The concept of "brackish water" encompasses a wide range of salinities that occupy a continuum between fresh water (< 2 parts per thousand salinity) and fully marine waters (35 parts per thousand salinity). Ichnological assemblages in brackish-water settings are inherently variable, as a consequence of temporal and geographic variations in such factors as average salinity, magnitude of salinity fluctuations, nature of the colonized substrate, presence and/or duration of subaerial exposure, and fluctuations in hydrodynamic energy. Trace-fossil suites attributable to brackish-water conditions are recognizable as departures from archetypal, fully marine expressions of recurring ichnofacies. These departures are characterized principally by impoverishment of assemblage diversities. Facies-crossing forms, Such as Planolites, Teichichnus, "Terebellina", Cylindrichnus, Skolithos, Palaeophycus, and Ophiomorpha, are persistent, particularly with decreasing salinities and/or increasing environmental stresses. Ichnogenera that are largely "confined" to the open-marine realm versus those "diagnostic" of brackish-water environments are variable, and depend in part upon the nature of the adjoining open system and the age of the study interval. Nevertheless, with increasingly stenohaline conditions, ichnogenera such as Helminthopsis, Helminthorhaphe, Cosmorhaphe, Phycosiphon, Zoophycos, Chondrites, Asterosoma, Rosselia, Rhizocorallium, Bergaueria, Schaubcylindrichnus, Scolicia, and Conichnus tend to be more recurrent. Additional aspects of brackish-water suites include size reduction of ichnogenera, introduction of monogeneric and monospecific suites, and repeated juxtaposition of facies-crossing elements of both the Skolithos Ichnofacies and the Cruziana Ichnofacies. This paper summarizes the ichnological characteristics of a large number of well-studied Cretaceous intervals that reflect brackish-water deposition. These units define four broad settings: (1) restricted or barrier-barred bays (e.g., Ostracode Zone, Paddy Member, and the Grand Rapids Fm); (2) open, non-barred bays (e.g., McMurray Fm, Basal Colorado Sandstone, Viking Fm, and Ben Nevis Fm); (3) riverine estuaries (e.g., McMurray Fm, Grand Rapids Fm, Waseca Fm, Glauconite Fm, and Ostracode Zone); and (4) barred, wave-dominated estuaries (e.g., Viking Fm, Bluesky Fm, and Bow Island Fm). Subenvironments within these broad groupings can be further delineated, using a combination of ichnological characteristics and primary sedimentological features. Although general ichnological trends from fully marine conditions into brackish-water settings can be determined, the aforementioned complexities serve to inhibit the development of a universally applicable, recurring brackish-water "ichnofacies". As such, brackish-water deposits are best characterized by comparison with their genetically related open-marine counterparts.
6. Fielding, CR; Bann, KL; Maceachern, JA; Tye, SC; Jones, BG.Cyclicity in the nearshore marine to coastal, Lower Permian, Pebbley Beach Formation, southern Sydney Basin, Australia: a record of relative sea-level fluctuations at the close of the Late Palaeozoic Gondwanan ice age.Sedimentology, 2006, 53: 435-463 Cyclicity in the nearshore marine to coastal, Lower Permian, Pebbley Beach Formation, southern Sydney Basin, Australia: a record of relative sea-level fluctuations at the close of the Late Palaeozoic Gondwanan ice age
estuarine facies; icehouse; Lower Permian; sequence stratigraphy; shallow marine facies
The Lower Permian (Artinskian to Sakmarian) Pebbley Beach Formation (PBF) of the southernmost Sydney Basin in New South Wales, Australia, records sediment accumulation in shallow marine to coastal environments at the close of the Late Palaeozoic Gondwanan ice age. This paper presents a sequence stratigraphic re-evaluation of the upper half of the unit based on the integration of sedimentology and ichnology. Ten facies are recognized, separated into two facies associations. Facies Association A (seven facies) comprises variably bioturbated siltstones and sandstones with marine body fossils, interpreted as recording sediment accumulation in open marine environments ranging from lower offshore to middle shoreface water depths. Evidence of deltaic influence is seen in several Association A facies. Facies Association B (three facies) comprises mainly heterolithic, interlaminated and thinly interbedded sandstone and siltstone with some thicker intervals of dark grey, organic-rich mudstone, some units clearly filling incised channel forms. These facies are interpreted as the deposits of estuarine channels and basins. Throughout the upper half of the formation, erosion surfaces with several metres relief abruptly separate open marine facies of Association A (below) from estuarine facies of Association B (above). Vertical facies changes imply significant basinward shift of environment across these surfaces, and lowering of relative sea level in the order of 50 m. These surfaces can be traced over several kilometres along depositional strike, and are defined as sequence boundaries. On this basis, at least nine sequences have been recognized in the upper half of the formation, each of which is < 10 m thick, condensed, incomplete and top-truncated. Sequences contain little if any record of the lowstand systems tract, a more substantial transgressive systems tract and a highstand systems tract that is erosionally truncated (or in some cases, missing). This distinctive stacking pattern (which suggests a dominance of retrogradation and progradation over aggradation) and the implied relative sea-level drop across sequence boundaries of tens of metres are remarkably similar to some other studies of continental margin successions formed under the Neogene icehouse climatic regime. Accordingly, it is suggested that the stratigraphic architecture of the PBF was a result of an Icehouse climate regime characterized by repeated, high-amplitude cycles of relative sea-level change. DOI
5. Johnstone, PD; Mustard, PS; MacEachern, JA.The basal unconformity of the Nanaimo Group, southwestern British Columbia: A late Cretaceous storm-swept rocky shoreline.Can. J. Earth Sci., 2006, 43: 1165-1181 The basal unconformity of the Nanaimo Group, southwestern British Columbia: A late Cretaceous storm-swept rocky shoreline
The Turonian to Santonian Comox Formation forms the basal unit of the Nanaimo Group. In the southern Gulf Islands of British Columbia, the Comox Formation nonconformably overlies Devonian metavolcanic and Jurassic intrusive rocks and is interpreted to reflect a rocky foreshore reworked by waves and ultimately drowned during transgression. The nonconformity displays a relief of metres to tens of metres. Basal deposits vary in thickness, as does the facies character along the several kilometres of paleoshoreline studied. In the study area, three distinct but related environments are expressed, typical of a complex rocky shoreline with headlands and protected coves. Crudely stratified conglomerates represent gravel-dominated fans characterized by debris-flow processes, building out from local coastal cliffs and gullies directly onto the rocky shoreline. Fine-grained basal units represent shoreline environments protected from higher energy shoreline processes, presumably in small embayments. Sandstone facies associations reflect storm-dominated shoreface environments. The unusual thickness and coarseness of these shoreface intervals suggest a combination of increasing accommodation space, proximal and high sediment supply, and high frequency and energy of storm activity. This, in turn, suggests that the majority of the shoreline was exposed to the full effects of large, open-ocean storms. This interpretation differs from most previous models for the lower Nanaimo Group, which suggest that deposition occurred in more sheltered strait or bay environments. DOI
4. Gingras, MK; Maceachern, JA; Pickerill, RK.Modem perspectives on the Teredolites ichnofacies: Observations from Willapa Bay, Washington.Palaios, 2004, 19: 79-88 Modem perspectives on the Teredolites ichnofacies: Observations from Willapa Bay, Washington
This study details occurrences of Teredolites ichnocoenoses from modern bay-margin settings in Willapa Bay, Washington. In particular, the paper scrutinizes in situ log-grounds from two intertidal zones situated immediately seaward of low-lying, supratidal, forested marshlands that are fed by small streams. Vestiges of remnant marshes and streams are preserved on intertidal flats as in-situ roots, broken stumps, strewn logs, abundant organic detritus, and organic sandy mud. Xylic material and organic sediment were deposited in the supratidal marshes: tide and wave processes truncated the swamps, exposing in situ tree-root networks and the lowermost supratidal sediments. Stream and swamp deposits overlie and incise older Pleistocene strata. Both units are overlain by discontinuous, modern intertidal deposits. The intertidally exposed stumps and logs support a diverse community of animal and plant life. Boring organisms, encrusters, and refugium seekers are found on and within the xylic substrates. Some encrusting animals and all of the boring fauna produce traces that are comparable to ichnofossils reported by palichnologists. Wood-boring traces reported in this study are similar morphologically to the ichnogenera Caulostrepsis, Entobia, Meandropolydora, Psilonichnus, Rogerella, Teredolites, Thalassinoides, and Trypanites. Most of these ichnogenera have not been reported from rock-record examples of the Teredolites ichno-facies. The stratigraphic and environmental significance of the reported (modern) locales is consistent with previous studies that associate Teredolites ichnofacies with base-level rise in marginal-marine environments. At Willapa Bay, bored xylic media form a coeval surface with adjacent, burrowed firmgrounds as well as softgrounds. DOI
3. MacEachern, JA; Hobbs, TW.The ichnological expression of marine and marginal marine conglomerates and conglomeratic intervals, Cretaceous Western Interior Seaway, Alberta and northeastern British Columbia.Bull. Can. Pet. Geol., 2004, 52: 77-104 The ichnological expression of marine and marginal marine conglomerates and conglomeratic intervals, Cretaceous Western Interior Seaway, Alberta and northeastern British Columbia
Although uncommon, conglomeratic successions and their associated interbeds do contain trace fossils that attest to their marine or marginal marine origins. Intervals within the Cretaceous of the Western Interior Seaway of Alberta and northeastern British Columbia contain ichnological assemblages consistent with open bay, estuarine incised valley, shoreface, and transgressive ravinement settings. Conglomerates and conglomeratic sandstones of open bays are largely confined to bay margins, and are markedly heterolithic, commonly trough cross-stratified, and moderately bioturbated with Diplocraterion, Skolithos, Palaeophycus, Conichnus and Ophiomorpha. Interbedded sandstones and mudstones contain Teichichnus, Planolites, Terebellina, Arenicolites, Bergaueria, Rosselia, Asterosoma, Cylindrichnus, Thalassinoides, and fagichnia. Burrowed incised valley conglomerates and pebbly sandstones mainly record channel fills of tidal inlets or flood-tidal deltas at wave-dominated estuary mouths. Trace fossil suites comprise Teichichnus, Ophiomorpha, Skolithos, Diplocraterion, Arenicolites, Rosselia, Cylindrichnus, and fugichnia. Intercalated sandstone and mudstone beds are moderately burrowed with Planolites, Teichichnus, Terebellina (sensu lato), Ophiomorpha, Palaeophycus, Asterosoma, Chondrites, Conichnus and fugichnia. Upper shoreface and foreshore conglomerates are well sorted, clast supported, and display good clast segregation. Bioturbation is uncommon, comprising Palaeophycus, Ophiomorpha, Cylindrichnus, Rosselia and fugichnia. Interbedded sandstones and pebbly sandstones may contain Macaronichnus and Palaeophycus. The Cardium Formation locally contains conglomeratic intervals interpreted to reflect the entire shoreface succession. These conglomeratic inter-vats are unburrowed, though they overlie Glossifungites ichnofacies-demarcated discontinuities, and grade upward into burrowed shelf mudstones. Conglomeratic transgressive lags and pebbly sandstones mantle wave or tidal scour ravinement surfaces, and commonly infill palimpsest Diplocraterion, Skolithos, Arenicolites, Thalassinoides, and Rhizocorallium of the Glossifungites ichnofacies, which demarcate these discontinuities. Transgressive lags may be variably burrowed with virtually any softground suite, depending on the depositional setting. Tidal scour ravinement lags at incised valley mouths, for example, may be weakly burrowed with an impoverished Skolithos ichnofacies, whereas wave ravinement lags produced during regional transgression can contain open marine, diverse mixed Skolithos-Cruziana ichnofacies assemblages. DOI
2. Groenewald, GH; Welman, J; MacEachern, JA.Vertebrate burrow complexes from, the Early Triassic Cynognathus Zone (Driekoppen Formation, Beaufort Group) of the Karoo Basin, South Africa.Palaios, 2001, 16: 148-160 Vertebrate burrow complexes from, the Early Triassic Cynognathus Zone (Driekoppen Formation, Beaufort Group) of the Karoo Basin, South Africa
A scratch-marked burrow complex with multiple branching tunnels and terminal chambers was excavated from the Lower Triassic Driekoppen Formation, northeastern Free State, South Africa. The burrow complex is attributed to the therapsid Trirachodon, based on disarticulated but fairly complete skulls and skeletons of at least 20 individuals recovered from a nearby less well-preserved system. The entrance shaft slopes gently downward and is characterized by a bilobate floor and vaulted roof: The bilobate floor has a central flat-topped scratch-marked ridge flanked by two smooth grooves, each approximately the width of the occupant. At deeper levels, tunnels display tighter lateral curvatures, progressively decreasing burrow diameters, variable orientations, and some right angle branches. Burrow floors at these levels are vaguely bilobate. Distally, burrows flatten dorso-ventrally, becoming wedge-shaped before they terminate. These complexes are interpreted as colonial dwelling structures. Numerous branching tunnels and terminal chambers, as well as an enlarged entrance constitute an unrealistically high expenditure of energy for a single occupant. Furthermore, the bilobate floor is atypical of a single occupant system. Absence of scratch marks in the depressions reflects the regular locomotory activity of Trirachodon. In single-occupant burrows, the center of the structure is worn. The bilobate floor with preferential wear along the flanks suggests routine travel on one side of the tunnel or the other, as multiple occupants moved past one another during daily activity. The presence of numerous fossilized Trirachodon individuals in terminal chambers at the second locality supports multiple cohabitation There, the uniform sedimentary fill and vertebrate taphonomy suggest that the occupants were drowned in a flash flood. Vertebrate remains are absent at the first locality where sediment influx was incremental, permitting the escape of burrow occupants. This constitutes the earliest record of multiple cohabitation of a burrow complex by tetrapods. The Trirachodon (Cynodontia) of the Early Triassic Cynognathus Zone probably displayed complex social behaviors previously regarded to be restricted to the mammals of the Cenozoic. This fossorial behavior may have been for thermoregulation, protection from predators, sites of reproduction, and the rearing of young. DOI
1. Gingras, MK; MacEachern, JA; Pemberton, SG.A comparative analysis of the ichnology of wave- and river-dominated allomembers of the Upper Cretaceous Dunvegan Formation.Bull. Can. Pet. Geol., 1998, 46: 51-73 A comparative analysis of the ichnology of wave- and river-dominated allomembers of the Upper Cretaceous Dunvegan Formation
The Upper Cretaceous (Cenomanian) Dunvegan Formation is a siliciclastic unit, which lies in the subsurface of western Alberta and crops out in the west-central portion of the province. The Dunvegan is deltaic in origin. Previous workers have subdivided the Dunvegan into 7 allocyclic members (A through G) in the subsurface, based on detailed sedimentological and stratigraphic analyses. Each allomember corresponds to a deltaic lobe and exhibits varying degrees of wave and river dominance, Allomembers D and E were chosen to test ichnological variations in deltaic systems because D is strongly wave-dominated and E is strongly river-dominated. Tidally influenced end members were not included in the scope of this study. The study area comprises Townships 59 to 67, and Range 20 W5M to 8 W6M. Fifteen cores, totaling 269 m in length, were analysed sedimentologically and ichnologically in order to compare the ichnological characteristics of river-and wave-dominated deltas. Allomember E is characterized by an overall lower intensity of bioturbation, a lower diversity of ichnogenera within proximal facies, and a general suppression of the Skolithos ichnofacies. In contrast, Allomember D shows a greater intensity of burrowing, a generally higher ichnogeneric diversity, and a diverse Skolithos ichnofacies. The contrasting ichnology provides insights into the ethology exhibited by infauna in the different depositional settings. More importantly, the differences observed are independent of bathymetry and emphasize the influences that environmental parameters such as variability in salinity, temperature, sedimentation rates, water turbidity, and substrate consistency play in an organism's selection of an ethological survival strategy. As such, ichnological data can be successfully integrated with physical sedimentological data in order to form predictive models that may be used to better comprehend and ultimately differentiate between these two depositional systems.
