Parasequence architecture in a low-accommodation setting, impact of syndepositional carbonate epikarstification, McMurray Formation, Alberta, Canada
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| Authors: | Chateau, CCF; Dashtgard, SE; MacEachern, JA; Hauck, TE |
| Year: | 2019 |
| Journal: | Mar. Pet. Geol. 104: 168-179 Article Link (DOI) |
| Title: | Parasequence architecture in a low-accommodation setting, impact of syndepositional carbonate epikarstification, McMurray Formation, Alberta, Canada |
| Abstract: | 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. |
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