20. Hong, I; Pilarczyk, JE; Horton, BP; Fritz, HM; Kosciuch, TJ; Wallace, DJ; Dike, C; Rarai, A; Harrison, MJ; Jockley, FR.Sedimentological characteristics of the 2015 Tropical Cyclone Pam overwash sediments from Vanuatu, South Pacific.Mar. Geol., 2018, 396: 205-214 Sedimentological characteristics of the 2015 Tropical Cyclone Pam overwash sediments from Vanuatu, South Pacific
Overwash sediment; Tropical cyclone; Coastal hazards; Sediment transport; Inverse sediment transport model
The interpretation of sediments deposited by prehistoric tropical cyclones (TC's) is limited by a lack of modernanalogues, particularly in the South Pacific. On 13 March 2015, TC Pam made landfall on Vanuatu, reaching Category 5 intensity with 10-minute sustained wind speeds as high as 270 km/h. Three months after landfall, we measured flow height (terrain elevation plus storm flow depth) and inland extent of TC Pam's maximum coastalinundation (composed of astronomical tides, storm surge, and superimposed storm waves), and described the sedimentological characteristics of the TC Pam overwash sediments from trenches and transects at two sites(Manuro and Port Resolution Bay). At Manuro (a mixed-carbonate embayment), the maximum flow height was 5.29 m mean sea level (MSL),with an inland extent of 106 m. The TC Pam sediments transition from a coarse to medium grained (mean: 1.07F) carbonate sand (<= 10 cm thick) to pumice (<= 18 cm thick) that extends 400 m inland into Lake Otas. The TC Pam overwash sediments are characterized by a coarsening upward sequence (1.45 to 0.23 Phi) followed by a finer grained eolian cap. At Port Resolution Bay (a volcaniclastic beach, PRB), the maximum flow height was 3.30 m MSL (1.51 m flow depth), with an inland extent of 117 m. The TC Pam overwash sediments transition from a medium grained (mean: 1.76 Phi) volcanic sand (<= 44 cm thick) to pumice (<= 5 cm thick) that extends 320 m from the shoreline. A subtle fining upward sequence was present in trench PRB2, whereas PRB1, PRB3,and PRB4 contained TC Pam sediments that were laminated and showed little to no vertical gradation in grainsize. At PRB, we applied an inverse sediment transport model to reconstruct maximum flow depths using laboratory derived settling velocities and the distance from the berm. The reconstructed flow depths at PRB2(1.43 m), PRB3 (1.36 m), and PRB4 (1.34 m) compare favorably with the observed estimate (1.51 m), illustrating the applicability of the inverse sediment transport model to reconstruct flow depths of prehistoric landfalling TC's. DOI
19. Kosciuch, TJ; Pilarczyk, JE; Hong, I; Fritz, HM; Horton, BP; Rarai, A; Harrison, MJ; Jockley, FR.Foraminifera reveal a shallow nearshore origin for overwash sediments deposited by Tropical Cyclone Pam in Vanuatu (South Pacific).Mar. Geol., 2018, 396: 171-185 Foraminifera reveal a shallow nearshore origin for overwash sediments deposited by Tropical Cyclone Pam in Vanuatu (South Pacific)
Storm deposits; Coastal hazards; Taphonomy; Sediment provenance
Tropical cyclone inundation is a major threat to the highly exposed islands of the South Pacific. This vulnerability was highlighted in March 2015 when Tropical Cyclone (TC) Pam made landfall on Vanuatu as a Category 5 storm, impacting coastlines with storm surges that produced high water marks up to 7 m above mean sea level (MSL) and deposited overwash sediments up to 400 m inland. We examined the foraminiferal assemblages contained within TC Pam sediments at two locations in Vanuatu: a mixed-carbonate embayment at Manuro on Efate Island and a volcaniclastic beach at Port Resolution Bay on Tanna Island. At Manuro, the TC Pam sediments were up to 10 cm thick and composed of coarse to medium sand that contained abundant foraminifera (955 to 2015 individuals per 5 cm(3)) and fragments of corals and mollusks. At Port Resolution Bay, TC Pam sediments were up to 44 cm thick and composed of medium sand-sized volcaniclastics with low to moderate abundances of foraminifera (27 to 206 individuals per 5 cm(3)). TC Pam sediments could be discriminated from underlying units by a sharp basal contact, an abrupt decrease in organic matter, and an increase in the concentration of foraminifera. Foraminiferal assemblages between the two sites varied in terms of taxonomy and taphonomy. At both sites, the TC Pam assemblage was generally dominated by intertidal (e.g., Amphistegina spp., Baculogypsina sphaerulata, Calcarina mayori, Elphidium spp., Pararotalia spp.) and subtidal (e.g., Peneroplis pertusus, Quinqueloculina spp.) foraminifera that are characteristic of beach, reef flat, and reef crest environments. The TC Pam assemblage at Manuro was characterized by individuals that were dominantly unaltered (i.e., pristine), but also those that showed signs of abrasion (including edge rounded fragments). By contrast, TC Pam sediments at Port Resolution Bay contained fewer unaltered and more corraded (i.e., combined influence of corrosion and abrasion) foraminifera. We compared modern surface foraminiferal distributions with those from TC Pam sediments to assess provenance. Partitioning Around a Medoid (PAM) cluster analysis discriminated six sub environments within the modern coastal zone: open bay, forereef, reef crest, reef flat, mangrove, and beach. Discrete intervals sampled from TC Pam sediments at Manuro were individually clustered with the surface samples and revealed a shallow nearshore to supratidal (reef crest to beach; -4.9 to 1.3 m above MSL) source for the sand. DOI
18. Soria, JLA; Switzer, AD; Pilarczyk, JE; Tang, H; Weiss, R; Siringan, F; Manglicmot, M; Gallentes, A; Lau, AYA; Cheong, AYL; Koh, TWL.Surf beat-induced overwash during Typhoon Haiyan deposited two distinct sediment assemblages on the carbonate coast of Hernani, Samar, central Philippines.Mar. Geol., 2018, 396: 215-230 Surf beat-induced overwash during Typhoon Haiyan deposited two distinct sediment assemblages on the carbonate coast of Hernani, Samar, central Philippines
Storm wave; Sand; Reef boulders; TSUFLIND; Foraminifera; Natural defenses
Wave set-up steepened and accentuated the storm surge during Typhoon Haiyan in November 2013 resulting in bore-like flooding with surge heights of 7 m and flow velocities reaching 5 m s(-1) on the open-sea coastal plain near Hernani. This study investigates two distinct sediment assemblages left behind by the coastal flooding associated with this surge. The first assemblage consists of numerous coastal boulders that now occupy the reef flat, and the second pertains to a laterally extensive sand sheet that blanketed the coastal plain up to similar to 300 m inland. The majority of the boulders has b axes between 1 and 2 m, weigh no >10 t, and were originally submerged on the reef edge. The boulders found more landwards of the reef edge were potentially lying loosely on the reef flat prior to Haiyan. In contrast, the coarse carbonate sand sheet starts at similar to 10 m inland of the current shoreline and has a maximum thickness of 10 cm and gradually thins to 3 mm at similar to 300 m inland. The Haiyan sand contains moderate concentrations of foraminifera (Amphistegina spp., Baculogypsina sphaerulata, and Peneroplis spp.) that were both abraded and unaltered, pointing to a reef flat and beach source for the sand. Sediment transport inverse modeling complements previous flow velocity estimates using numerical modeling, which altogether indicate sustained high-velocity overland flow despite the presence of coral reefs and mangroves as natural defenses to extreme waves. DOI
17. Dura, T; Horton, BP; Cisternas, M; Ely, LL; Hong, I; Nelson, AR; Wesson, RL; Pilarczyk, JE; Parnell, AC; Nikitina, D.Subduction zone slip variability during the last millennium, south-central Chile.Quat. Sci. Rev., 2017, 175: 112-137 Subduction zone slip variability during the last millennium, south-central Chile
Prehistoric earthquakes; Subduction zone segmentation; Tsunami deposits; Diatom paleoecology; Coastal paleoseismology; Coastal hazards
The Arauco Peninsula (37 degrees-38 degrees S) in south-central Chile has been proposed as a possible barrier to the along-strike propagation of megathrust ruptures, separating historical earthquakes to the south (1960 AD 1837, 1737, and 1575) and north (2010 AD, 1835, 1751, 1657, and 1570) of the peninsula. However, the 2010 (Mw 8.8) earthquake propagated into the Arauco Peninsula, re-rupturing part of the megathrust that had ruptured only 50 years earlier during the largest subduction zone earthquake in the instrumental record (M-w 9.5). To better understand long-term slip variability in the Arauco Peninsula region, we analyzed four coastal sedimentary sections from two sites (Tirua, 38.3 degrees S and Quidico, 38.1 degrees S) located within the overlap of the 2010 and 1960 ruptures to reconstruct a similar to 600-year record of coseismic land-level change and tsunami inundation. Stratigraphic, lithologic, and diatom results show variable coseismic land-level change coincident with tsunami inundation of the Tirua and Quidico marshes that is consistent with regional historical accounts of coseismic subsidence during earthquakes along the Valdivia portion of the subduction zone (1960 AD and 1575) and coseismic uplift during earthquakes along the Maule portion of the subduction zone (2010 AD, 1835, 1751). In addition, we document variable coseismic land-level change associated with three new prehistoric earthquakes and accompanying tsunamis in 1470-1570 AD, 1425-1455, and 270-410. The mixed record of coseismic subsidence and uplift that we document illustrates the variability of down-dip and lateral slip distribution at the overlap of the 2010 and 1960 ruptures, showing that ruptures have repeatedly propagated into, but not through the Arauco Peninsula and suggesting the area has persisted as a long-term impediment to slip through at least seven of the last megathrust earthquakes (similar to 600 years). (C) 2017 Elsevier Ltd. All rights reserved. DOI
16. Rubin, CM; Horton, BP; Sieh, K; Pilarczyk, JE; Daly, P; Ismail, N; Parnell, AC.Highly variable recurrence of tsunamis in the 7,400 years before the 2004 Indian Ocean tsunami.Nat. Commun., 2017, 8 Highly variable recurrence of tsunamis in the 7,400 years before the 2004 Indian Ocean tsunami
The devastating 2004 Indian Ocean tsunami caught millions of coastal residents and the scientific community off-guard. Subsequent research in the Indian Ocean basin has identified prehistoric tsunamis, but the timing and recurrence intervals of such events are uncertain. Here we present an extraordinary 7,400 year stratigraphic sequence of prehistoric tsunami deposits from a coastal cave in Aceh, Indonesia. This record demonstrates that at least 11 prehistoric tsunamis struck the Aceh coast between 7,400 and 2,900 years ago. The average time period between tsunamis is about 450 years with intervals ranging from a long, dormant period of over 2,000 years, to multiple tsunamis within the span of a century. Although there is evidence that the likelihood of another tsunamigenic earthquake in Aceh province is high, these variable recurrence intervals suggest that long dormant periods may follow Sunda megathrust ruptures as large as that of the 2004 Indian Ocean tsunami. DOI PubMed
15. Soria, JLA; Switzer, AD; Pilarczyk, JE; Siringan, FP; Khan, NS; Fritz, HM.Typhoon Haiyan overwash sediments from Leyte Gulf coastlines show local spatial variations with hybrid storm and tsunami signatures.Sediment. Geol., 2017, 358: 121-138 Typhoon Haiyan overwash sediments from Leyte Gulf coastlines show local spatial variations with hybrid storm and tsunami signatures
Storm deposit; Tsunami deposit; Siliciclastic; Carbonate; Topography; Vegetation
Marine inundation associated with the 5 to 8 m storm surge of Typhoon Haiyan in 2013 left overwash sediments inland on the coastal plains of the northwestern shores of Leyte Gulf, Philippines. The Haiyan overwash deposit provides a modern sedimentary record of storm surge deposition from a Category 5 landfalling typhoon. We studied overwash sediments at two locations that experienced similar storm surge conditions but represent contrasting sedimentological regimes, namely a siliciclastic coast and a mixed siliciclastic-carbonate coast. The contrasting local geology is significantly reflected in the differences in sediment grain size, composition and sorting at the two sites. The Haiyan overwash sediments are predominantly sand and silt and can be traced up to similar to 1.6 km inland, extending farther beyond the previously reported <300 m inland limit of sedimentation. Sites with similar geology, topographic relief, and overland flow conditions show significant spatial variability of sediment thickness and inland extent. We infer that other local factors such as small-scale variations in topography and the type of vegetation cover might influence the spatial distribution of overwash sediments. The Haiyan overwash deposits exhibit planar stratification, a coarsening upward sequence, a non-systematic landward fining trend, and a sharp depositional (rarely erosional) basal contact with the underlying substrate. Overall, the Haiyan deposits have sedimentologic and stratigraphic characteristics that show a hybrid signature common to both storm and tsunami deposits. (C) 2017 The Authors. Published by Elsevier B.V. DOI
14. Matsumoto, D; Sawai, Y; Yamada, M; Namegaya, Y; Shinozaki, T; Takeda, D; Fujino, S; Tanigawa, K; Nakamura, A; Pilarczyk, JE.Erosion and sedimentation during the September 2015 flooding of the Kinu River, central Japan.Sci Rep, 2016, 6 Erosion and sedimentation during the September 2015 flooding of the Kinu River, central Japan
Erosional and sedimentary features associated with flooding have been documented in both modern and past cases. However, only a few studies have demonstrated the relationship between these features and the corresponding hydraulic conditions that produced them, making it difficult to evaluate the magnitude of paleo-flooding. This study describes the characteristics associated with inundation depth and flow direction, as well as the erosional and sedimentary features resulting from the disastrous flooding of the Kinu River, central Japan, in September 2015. Water levels rose rapidly due to heavy rainfall that eventually overtopped, and subsequently breached, a levee in Joso City, causing destructive flooding on the surrounding floodplain. Distinctive erosional features are found next to the breached levee, while depositional features, such as a sandy crevasse-splay deposit are found further away from the breach. The deposit can be divided into three units based on sedimentary facies. The vertical and lateral changes of these sedimentary facies may be the result of temporal and spatial changes associated with flow during the single flooding event. These observations and quantitative data provide information that can be used to reveal the paleohydrology of flood deposits in the stratigraphic record, leading to improved mitigation of future flooding disasters. DOI PubMed
13.Pilarczyk, JE; Horton, BP; Soria, JLA; Switzer, AD; Siringan, F; Fritz, HM; Khan, NS; Ildefonso, S; Doctor, AA; Garcia, ML.Micropaleontology of the 2013 Typhoon Haiyan overwash sediments from the Leyte Gulf, Philippines.Sediment. Geol., 2016, 339: 104-114 Micropaleontology of the 2013 Typhoon Haiyan overwash sediments from the Leyte Gulf, Philippines
Tropical cyclone; Overwash; Foraminifera; Testate amoebae; Sediments; Paleotempestology
Coastal geologic records allow for the assessment of long-term patterns of tropical cyclone variability. However, the accuracy of geologic reconstructions of tropical cyclones is limited by the lack of modern analogues. We describe the microfossil (foraminifera and testate amoebae) assemblages contained within overwash sediments deposited by Typhoon Haiyan when it made landfall on the islands of Leyte and Samar in the Philippines on 7 November 2013 as a Category 5 super typhoon. The overwash sediments were transported up to 1.7 km inland at four study sites. The sediments consisted of light brown medium sand in a layer <1 to 8 cm thick. We used Partitioning Around a Medoid (PAM) cluster analysis to identify lateral and vertical changes in the foraminiferal and testate amoebae data. The presence of intertidal and subtidal benthic, and planktic foraminifera that were variably unaltered and abraded identify the microfossil signature of the overwash sediments. Agglutinated mangrove foraminifera and testate amoebae were present within the overwash sediments at many locations and indicate terrestrial scouring by Haiyan's storm surge. PAM cluster analysis subdivided the Haiyan microfossil dataset into two assemblages based on depositional environment: (1) a low-energy mixed-carbonate tidal flat located on Samar Island (Basey transect); and (2) a higher-energy clastic coastline near Tanauan on Leyte Island (Santa Cruz, Solano, and Magay transects). The assemblages and the taphonomy suggest a mixed provenance, including intertidal and subtidal sources, as well as a contribution of sediment sourced from deeper water and terrestrial environments. (C) 2016 Elsevier B.V. All rights reserved. DOI
12. Dura, T; Cisternas, M; Horton, BP; Ely, LL; Nelson, AR; Wesson, RL; Pilarczyk, JE.Coastal evidence for Holocene subduction-zone earthquakes and tsunamis in central Chile.Quat. Sci. Rev., 2015, 113: 93-111 Coastal evidence for Holocene subduction-zone earthquakes and tsunamis in central Chile
Prehistoric earthquakes; Tsunami deposits; Diatom paleoecology; Coastal paleoseismology; Coastal hazards
The similar to 500-year historical record of seismicity along the central Chile coast (30-34 degrees S) is characterized by a series of similar to M 8.0-8.5 earthquakes followed by low tsunamis (<4 m) occurring on the megathrust about every 80 years. One exception is the AD 1730 great earthquake (M 9.0-9.5) and high tsunami (>10 m), but the frequency of such large events is unknown. We extend the seismic history of central Chile through a study of a lowland stratigraphic sequence along the metropolitan coast north of Valparaiso (33 degrees S). At this site, higher relative sea level during the mid Holocene created a tidal marsh and the accommodation space necessary for sediment that preserves earthquake and tsunami evidence. Within this 2600-yr-long sequence, we traced six laterally continuous sand beds probably deposited by high tsunamis. Plant remains that underlie the sand beds were radiocarbon dated to 6200, 5600, 5000, 4400, 3800, and 3700 cal yr BP. Sediment properties and diatom assemblages of the sand beds for example, anomalous marine planktonic diatoms and upward fining of silt-sized diatom valves point to a marine sediment source and high-energy deposition. Grain-size analysis shows a strong similarity between inferred tsunami deposits and modern coastal sediment. Upward fining sequences characteristic of suspension deposition are present in five of the six sand beds. Despite the lack of significant lithologic changes between the sedimentary units under- and overlying tsunami deposits, we infer that the increase in freshwater siliceous microfossils in overlying units records coseismic uplift concurrent with the deposition of five of the sand beds. During our mid-Holocene window of evidence preservation, the mean recurrence interval of earthquakes and tsunamis is similar to 500 years. Our findings imply that the frequency of historical earthquakes in central Chile is not representative of the greatest earthquakes and tsunamis that the central Chilean subduction zone has produced. (C) 2014 Elsevier Ltd. All rights reserved. DOI
11. Kelsey, HM; Engelhart, SE; Pilarczyk, JE; Horton, BP; Rubin, CM; Daryono, MR; Ismail, N; Hawkes, AD; Bernhardt, CE; Cahill, N.Accommodation space, relative sea level, and the archiving of paleo-earthquakes along subduction zones.Geology, 2015, 43: 675-678 Accommodation space, relative sea level, and the archiving of paleo-earthquakes along subduction zones
The spatial variability of Holocene relative sea-level (RSL) change influences the capacities of coastal environments to accommodate a sedimentary record of paleoenvironmental change. In this study we couch a specific investigation in more general terms in order to demonstrate the applicability of the relative sea-level history approach to paleoseismic investigations. Using subsidence stratigraphy, we trace the different modes of coastal sedimentation over the course of time in the eastern Indian Ocean where RSL change evolved from rapidly rising to static from 8000 yr ago to present. Initially, the coastal sites from the Aceh, Sumatra, coastal plain, which are subject to repeated great earthquakes and tsunamis, built up a sedimentary sequence in response to a RSL rise of 1.4 mm/yr. The sequence found at 2 sites 8 km apart contained 3 soils of a mangrove origin (Rhizophora, Bruguiera/Ceriops, Avicennia pollen, and/or intertidal foraminifera) buried by sudden submergence related to coseismic subsidence and 6 tsunami sands that contain pristine subtidal and planktic foraminifera. After 3800 cal yr B.P. (years before A.D. 1950), sea level stabilized and remained such to the present. The stable relative sea level reduced accommodation space in the late Holocene, suggesting that the continued aggradation of the coastal plain was a consequence of periodic coastal inundation by tsunamis. DOI
10. Sieh, K; Daly, P; McKinnon, EE; Pilarczyk, JE; Chiang, HW; Horton, B; Rubin, CM; Shen, CC; Ismail, N; Vane, CH; Feener, RM.Penultimate predecessors of the 2004 Indian Ocean tsunami in Aceh, Sumatra: Stratigraphic, archeological, and historical evidence.J. Geophys. Res.-Solid Earth, 2015, 120: 308-325 Penultimate predecessors of the 2004 Indian Ocean tsunami in Aceh, Sumatra: Stratigraphic, archeological, and historical evidence
tsunami; Sumatra; Aceh; paleotsunami; Archeology; megathrust
We present stratigraphic, archeological and historical evidence for two closely timed predecessors of the giant 2004 tsunami on the northern coast of Aceh, northern Sumatra. This is the first direct evidence that a tsunami played a role in a fifteenth century cultural hiatus along the northern Sumatran portion of the maritime silk route. One seacliff exposure on the eastern side of the Lambaro headlands reveals two beds of tsunamigenic coral rubble within a small alluvial fan. Radiocarbon and Uranium-Thorium disequilibrium dates indicate emplacement of the coral rubble after 13443 C.E. Another seacliff exposure, on the western side of the peninsula, contains evidence of nearly continuous settlement from similar to 1240 C.E. to soon after 13663 C.E., terminated by tsunami destruction. At both sites, the tsunamis are likely coincident with sudden uplift of coral reefs above the Sunda megathrust 13942 C.E., evidence for which has been published previously. The tsunami (or tsunami pair) appears to have destroyed a vibrant port community and led to the temporary recentering of marine trade dominance to more protected locations farther east. The reestablishment of vibrant communities along the devastated coast by about 1500 CE set the stage for the 2004 disaster. DOI
9. Brown, AL; Reinhardt, EG; van Hengstum, PJ; Pilarczyk, JE.A Coastal Yucatan Sinkhole Records Intense Hurricane Events.J. Coast. Res., 2014, 30: 418-428 A Coastal Yucatan Sinkhole Records Intense Hurricane Events
Sediment; depositional model; particle size analysis; sinkhole; hurricanes
The potential of tropical sinkholes as archives for historical hurricane events has yet to be fully explored. This study uses high-resolution (1-cm interval) particle-size analysis to examine two sediment push cores from Laguna Chumkopo, located on the Yucatan Peninsula, Mexico. Core CKC1 (62 cm) was collected from the base of a deep sinkhole located in Laguna Churokopo at -79.9 m (nisi), while the second core, CKC2 (93 cm), was collected from the shallow peripheral margin at -6.4 m (msl). Two coarse fining upward sequences (12 to 35 cm, 46 to 62 cm) in CKC1 had mean particle sizes of approximately 1.5 phi (medium sand) with intervening intervals of lime mud (<4 phi). Measured Cs-137 activity in the bulk sediment (n = 15) and radiocarbon dating (n = 3) using bomb-carbon calibration determined that the lower coarse unit was deposited in the 1960s (after September 1957 AD), and the upper unit between January 1985 and August 1991 AD. Hurricane Gilbert struck the Yucatan on 15 September 1988 as a category 5 storm, generating the upper fining upward sequence. Hurricane Beulah (category 2-3) likely generated the lower unit when it struck on 18 September 1967. CKC2 revealed small textural changes, alternating between silt and sand-sized particles and radiocarbon ages dated to similar to 6.7 to 7.1 ka. The rapid accumulation of sediment in the shallow lagoon likely occurred with rising sea level flooding the area at approximately 6.8 ka. Based on the sedimentary results, a depositional model is proposed for inland sinkholes, explaining the formation of hurricane deposits through density and debris flows along the shallow margin. DOI
8.Pilarczyk, JE; Dura, T; Horton, BP; Engelhart, SE; Kemp, AC; Sawai, Y.Microfossils from coastal environments as indicators of paleo-earthquakes, tsunamis and storms.Paleogeogr. Paleoclimatol. Paleoecol., 2014, 413: 144-157 Microfossils from coastal environments as indicators of paleo-earthquakes, tsunamis and storms
Overwash; Transfer functions; Land-level change; Foraminifera; Diatoms; Pollen
Coastal risk assessment and hazard mitigation require datasets on centennial and millennial temporal scales to capture natural variability and multiple occurrences of the largest, but least frequent, events. Coastal sediments from low-energy depositional environments archive geologic evidence of paleo-earthquakes, tsunamis, and storms. Many of the best reconstructions of these events are derived from changes in microfossil (diatoms, foraminifera, and pollen) assemblages. In this review we explain how microfossils are used to reconstruct records of paleoearthquakes by quantifying the amount of coseismic and interseismic vertical land movements along tectonically active coastlines. Examples from the United States (Alaska and the Pacific Northwest), Japan, and Chile show that microfossil-based transfer functions may provide continuous records of vertical land movement during earthquake deformation cycles. We discuss how microfossil habitat preferences and taphonomic character are used to constrain sediment provenance (e.g., beach, nearshore, or offshore sources) and identify overwash deposits, and how this information can be used to reconstruct the recurrence of tsunamis and storms. Analysis of overwash deposits from Thailand and Malaysia indicates the ability of microfossils to resolve individual waves within tsunami sediments, and an example from the Sendai coastal plain in Japan uses foraminifera to ascribe a beach to nearshore provenance for the 2011 Tohoku tsunami deposit. Finally, we present recent examples from the Gulf of Mexico on the use of foraminifera to estimate the volume and distance of transport of storm overwash from hurricanes. (C) 2014 Elsevier B.V. All rights reserved. DOI
7.Pilarczyk, JE; Goff, J; Mountjoy, J; Lamarche, G; Pelletier, B; Horton, BP.Sediment transport trends from a tropical Pacific lagoon as indicated by Homotrema rubra taphonomy: Wallis Island, Polynesia.Mar. Micropaleontol., 2014, 109: 21-29 Sediment transport trends from a tropical Pacific lagoon as indicated by Homotrema rubra taphonomy: Wallis Island, Polynesia
Homotrema; Taphonomy; Carbonate reef; Overwash; Storm; Tsunami; Wallis Island
The assessment of sediment transport pathways in carbonate settings is complicated by ecologically sourced sediment. Tracers such as foraminifera have previously been used in these settings to describe the movement of coastal sediments on spatial and temporal scales where traditional grain size methods have limited use. The present study builds on the foraminifera-based tracer method by using Homotrema rubra, a foraminifer with an attached life habit (i.e., defined provenance in the reef) to document modern sediment transport trends at Wallis Island, a tropical Pacific lagoon. At Wallis Island, Homotrema taphonomic results discriminated amongst modern reef, lagoon, and island (beach) samples. Reef samples contained high concentrations of fragments that were large (>250 mu m) and exceptionally- to well-preserved (e.g., intact chambers, red color, angularity). In general, concentrations and degree of taphonomic alteration decreased with distance landward from the reef; lagoon samples were characterized by lower concentrations of Homotrema that were smaller in size and less preserved (e.g., pink in color, no chamber structure, rounding of edges). At the greatest distance from the reef, island (beach) samples contained the lowest concentrations of Homotrema fragments that were small, well rounded and bleached. In this regard, Homotrema taphonomy is a useful indicator of the direction and forcing of sediment transport and will therefore be useful in detecting overwash deposits in tropical settings, where distinguishing event deposits from surrounding sediment is problematic. (C) 2014 Elsevier B.V. All rights reserved. DOI
6.Pilarczyk, JE; Horton, BP; Witter, RC; Vane, CH; Chague-Goff, C; Goff, J.Sedimentary and foraminiferal evidence of the 2011 Tohoku-oki tsunami on the Sendai coastal plain, Japan.Sediment. Geol., 2012, 282: 78-89 Sedimentary and foraminiferal evidence of the 2011 Tohoku-oki tsunami on the Sendai coastal plain, Japan
Sendai Plain; 2011 Tohoku-oki tsunami; Jogan tsunami; Foraminifera
The 2011 Tohoku-oki megathrust earthquake (Mw 9.0) generated a tsunami that reached the Sendai coastal plain with flow heights of similar to 2 to 11 m above TP (Tokyo Peil). We examined the tsunami deposit exposed in 14 shallow trenches along a similar to 4.5-km transect perpendicular to the coast. We primarily document the stratigraphical, sedimentological, foraminiferal and geochemical characteristics of the Tohoku-oki tsunami deposit and perform a preliminary comparison with sediments deposited by the Jogan tsunami of A.D. 869. In the coastal forest and rice fields inundated by the Tohoku-oki tsunami, a poorly sorted, dark brown soil is buried by a poorly sorted, brown, medium-grained sand deposit. In some trenches located more than 1.2 km inland, the sand is capped by a thin muddy-sand layer. The tsunami deposit, although highly variable in thickness, is generally thickest (25 cm) near the coastal dune and thins to less than 5 mm at similar to 4.5 km inland. The tsunami deposit was discriminated from the underlying soil by the appearance of recent and fossil foraminifera and a pronounced increase in grain size that fined upward and landward. The recent foraminifera preserved in the sandy facies of the deposit are rare and showed evidence of prolonged subaerial exposure (e.g. pitting, corrosion, fragmentation). Recent foraminifera likely originated from coastal dune and beach sediments that were breached by the tsunami. Calcified and sediment in-filled, fossil foraminifera are abundant and were eroded from sedimentary units and transported by fluvial or wave activity to Sendai Bay. Trends associated with test size (e.g. decreasing concentration of large test sizes with distance inland) are in agreement with grain size data. At two locations a decrease in total organic carbon and an increase in delta C-13 were found in the tsunami sand compared with the underlying soil, supporting a beach to intertidal origin for the upper unit. (c) 2012 Elsevier B.V. All rights reserved. DOI
5.Pilarczyk, JE; Reinhardt, EG.Homotrema rubrum (Lamarck) taphonomy as an overwash indicator in Marine Ponds on Anegada, British Virgin Islands.Nat. Hazards, 2012, 63: 85-100 Homotrema rubrum (Lamarck) taphonomy as an overwash indicator in Marine Ponds on Anegada, British Virgin Islands
Foraminifera; Taphonomy; Homotrema; Storm; Tsunami; Gulf of Mexico
Marine hypersaline ponds on Anegada, British Virgin Islands contain stratigraphic evidence (Shell and Sand Sheet) of a A.D. 1650-1800 overwash event that could have formed through a hurricane or tsunami. Candidates for the deposit include far-field (e.g. 1755 Lisbon tsunami) and local Puerto Rico Trench events (e.g. 1690), but hurricanes cannot be ignored. The goal of this study is to provide additional information to assess the origin of the deposit by examining the taphonomic characters of Homotrema rubrum, a common encrusting foraminifer in Caribbean reef settings. Surface samples (n = 12) from major sub-environments (reef-flat, beach, storm wrack, and dune) and pond sections (n = 6; 20-80 cm thick) are analyzed for their Homotrema concentration (specimens/cm(3)) and taphonomic character. Particle-size analysis was conducted on the same sections and samples. Highly Preserved (red colored, angular, intact chambers) Homotrema dominate the beach, storm wrack, and reef-flat deposits relative to the dune sand, but the beach and storm wrack contain the largest specimens. The Shell and Sand Sheet in the pond has Highly Preserved and abundant Homotrema (specimens/cm(3)) versus other sedimentary units in the ponds (e.g. Mud Cap and Shelly Mud). Its taphonomic character is most similar (test size and condition) to the storm wrack deposit on the beach indicating an outside provenance for the sand. Concentration of Homotrema in the Shell and Sand Sheet declined southward indicating a northerly reef-flat provenance for the overwash, although it does not preclude a southern inundation as well. It is unclear whether Homotrema individuals originated from the reef itself or were eroded from older beach ridge deposits during the overwash event. Conclusions from Homotrema taphonomic analysis were limited by the lack of comparative data from known hurricane and tsunami deposits in other Caribbean regions. DOI
4.Pilarczyk, JE; Reinhardt, EG.Testing foraminiferal taphonomy as a tsunami indicator in a shallow arid system lagoon: Sur, Sultanate of Oman.Mar. Geol., 2012, 295: 128-136 Testing foraminiferal taphonomy as a tsunami indicator in a shallow arid system lagoon: Sur, Sultanate of Oman
foraminifera; lagoon; overwash; taphonomy; tsunami; particle size distribution; Oman
The tsunami produced by the 1945 Makran Trench earthquake is considered to be the second deadliest in the Indian Ocean after the 26 December 2004 Indonesian event. The tsunami struck Iran, Pakistan, India and Oman: however, historical records outside of India and Pakistan are sparse due to limited populations in those regions and little communication with larger cities. Sur Lagoon, Oman, a small microtidal lagoon, contains stratigraphic evidence of the 1945 tsunami. The goal of this study is to test the utility of foraminiferal provenance and taphonomy as an indicator of the 1945 event and examine its potential in detecting older events in the geologic record. Foraminiferal (taxa and taphonomy) and high resolution particle size analysis show that high abundances of predominantly marine taxa (Amphistegina sop., Ammonia inflate, and planktics) associated with the tsunami bed indicate an outside marine origin for the sediment. Influxes of large test sizes and fossil specimens support a shallow marine provenance. Findings indicate that foraminiferal analysis, when combined with other proxies (e.g. mollusc taphonomy, particle size distribution), can be used to delineate tsunami units from normal background sedimentation in intertidal systems. This technique holds potential for detecting older events in Sur Lagoon which are documented in historical texts, but as of yet, have not been 'ground-truthed'. (C) 2011 Elsevier B.V. All rights reserved. DOI
3. Reinhardt, EG; Pilarczyk, J; Brown, A.Probable tsunami origin for a Shell and Sand Sheet from marine ponds on Anegada, British Virgin Islands.Nat. Hazards, 2012, 63: 101-117 Probable tsunami origin for a Shell and Sand Sheet from marine ponds on Anegada, British Virgin Islands
Mollusk taphonomy; Event stratigraphy; Hurricane; Tsunami; Caribbean
A distinctive Shell and Sand Sheet found beneath the marine ponds of Anegada, British Virgin Islands, was formed by a post-1650 AD overwash event, but its origin (tsunami or hurricane) was unclear. This study assesses the taphonomic characters of the shell and large clast material (> 2 mm) to determine its provenance and origin. Pond-wide stratigraphic units (Shelly Mud, Shell and Sand Sheet, Mud Cap) were analyzed (12 samples) at four sites in Bumber Well and Red Pond along with eight samples from the Shell and Sand Sheet in a 2-km transect of Bumber Well. Mollusks in the pond muds include Anomalocardia spp. and cerithids with no allochthonous shells from the offshore reef-flat. Results show that the shells and clasts (> 2 mm) are derived from the erosion and winnowing of the underlying Shelly Mud of the former marine pond, forming a distinctive sheet-like deposit with Homotrema sand. The Shell and Sand Sheet contains articulated Anomalocardia bivalves and moderate numbers of angular fragments (approximately 35%) that are likely from crab predation. Radiocarbon dates of articulated Anomalocardia specimens from the Shell and Sand Sheet range widely (approximately 4000 years), with shell condition (pristine to variably preserved) showing no correlation with age. The articulated condition of the bivalves with the wide-ranging dates suggests erosion and winnowing of the underlying Shelly Mud but minimal transport of the bivalves. The Shell and Sand Sheet has taphonomic characteristics indicative of a widespread tsunami overwash (sheet-like extent and articulated specimens) but lacks allochthonous reef-flat shells. Reef-flat shell material may not have penetrated the pond, as a tsunami would have to cross the reef-flat and overtop high dunes (2.2 m) hindering transport of larger shell material but allowing the Homotrema sand to penetrate. Processes including hurricane overwash, pond wave action, or tidal channel opening and closure are not favoured interpretations as they would not produce extensive sheet-like deposits. Taphonomic analysis is hampered by the limited (400-500 years BP) depositional history from Anegada's ponds and the lack of comparative data from other Caribbean locations. DOI
2.Pilarczyk, JE; Reinhardt, EG; Boyce, JI; Schwarcz, HP; Donato, SV.Assessing surficial foraminiferal distributions as an overwash indicator in Sur Lagoon, Sultanate of Oman.Mar. Micropaleontol., 2011, 80: 62-73 Assessing surficial foraminiferal distributions as an overwash indicator in Sur Lagoon, Sultanate of Oman
Foraminifera; Lagoon; Taphonomy; Stable isotopes; Particle-size distribution; Oman
The identification of tsunami and storm deposits in arid coastal environments can be problematic, as overwash sediments may not show significant contrasting lithologic characters with lagoonal sediments. In this study foraminifera were evaluated as an overwash indicator in a small (12 km(2)) intertidal lagoon located at Sur, in the Sultanate of Oman. The lagoon is shallow (<5 m depth), tidally-controlled and communicates with the open sea through a narrow subtidal entrance channel. The lagoon is largely composed of intertidal sand and mudflats with fringing mangroves. Previous work at Sur identified evidence for overwash deposits associated with the 28 November 1945 Makran Trench tsunami (M-w 8.1) which were identified based on the presence of a laterally extensive shelly bed with distinctive taphonomic characters. In this study, particle size, stable isotopic and foraminiferal (taxa and taphonomy) analyses were conducted on surface sediment samples from Sur lagoon to determine modem spatial trends in the lagoon for future comparison with overwash sediments deeper in the geologic record. Q-mode cluster analysis of the foraminiferal data (n = 54) found three main biofacies which follow lagoon sub-environments: Shallow Marine Area, Main Lagoon Basin, and Distal Lagoon Basin. The Shallow Marine Area is mainly subtidal with higher wave energy, the Main Lagoon Basin is predominantly intertidal with moderate wave energy, whereas the Distal Lagoon Basin is isolated and mainly intertidal with low wave energy. The most useful parameters for assessing overwash events in Sur lagoon are the foraminifera taxa rather than the taphonomic characters themselves. The most useful taxa for recognizing an overwash (e.g. tsunami or storm) will be the abundance of Amphistegina spp., Ammonia inflata, Elphidium advenum and planktics which are predominantly found in the Shallow Marine Area. The abundance trend of these species with distance into the lagoon has an inverse relationship with higher r(2) values than the other taxa. Taphonomically there is a predominance of larger specimens in the Shallow Marine Area along with a higher abundance of fossil specimens. (C) 2011 Elsevier B.V. All rights reserved. DOI
1. Donato, SV; Reinhardt, EG; Boyce, JI; Pilarczyk, JE; Jupp, BP.Particle-size distribution of inferred tsunami deposits in Sur Lagoon, Sultanate of Oman.Mar. Geol., 2009, 257: 54-64 Particle-size distribution of inferred tsunami deposits in Sur Lagoon, Sultanate of Oman
Sur Lagoon; Oman; tsunami deposits; particle size; cluster analysis
The sedimentary characteristics of shell beds within an interpreted tsunami deposit from Sur Lagoon, Oman were examined using shell taphonomy and high-resolution particle-size analysis. The tsunami bed was deposited by the 28 November, 1945 tsunami generated by the Makran subduction zone. Q-mode cluster analysis of particle-size data was evaluated as a means of discriminating individual tsunamite shell layers from lagoonal intertidal deposits. Results showed that the tsunami shell bed was more poorly sorted, and heterogeneous (in both the digested and undigested samples) than the background lagoonal sediments. The tsunami bed thickness correlated generally with the thickness of the shell-bed, however, cluster analysis extended the tsunami unit several centimeters above or below the shell bed in some cores. The particle-size analysis also showed subtle textural trends in the tsunami unit, suggesting that the tsunami bed was deposited in several distinctive phases during tsunami incursion into Sur Lagoon. The findings indicate that cluster analysis of particle-size data can be used to identify tsunami beds in intertidal environments and holds potential for identifying paleotsunami deposits in sediments from embayed intertidal-subtidal siliciclastic systems where obvious sedimentary structures may be absent. (C) 2008 Elsevier B.V. All rights reserved. DOI
