Abstract

A detailed study of the sedimentology and stratigraphy of the middle to late Albian Pense Formation was undertaken in southwestern Saskatchewan (Twp. 1-20, Rge. 10-22W3). Shallow-marine shelf sandstones and shales of the Pense Formation overlie either pre-existing interfluve deposits of the Success S2 Formation (fluvial), or valley-fill deposits of the Chokecherry Creek (subtidal, estuarine) or Atlas (non-marine, valley-fill) members of the Cantuar Formation all within the Mannville Group. The base of the Pense Formation represents a transgressive surface of erosion but may also be a sequence boundary. A transgressive systems tract is identified, culminating in deposition of a condensed section historically identified as the Index Horizon Above the Cantuar Marker (IHACM). The IHACM represents sediments deposited during maximum marine inundation of the Pense transgression. The IHACM is characterized by nonbioturbated shale having elevated total organic carbon content and hydrogen indices. Five coarsening-upward/fining-upward cycles are mapped within the Pense Formation above the IHACM. The lowermost of these sandstone/shale cycles is interpreted to be the result of a forced regression. Incised valley deposits occur in Cycles R3 and R5 in the northeast. The shelfal sandstone bodies of the Pense Formation are dominantly quartzose, storm-dominated, originated from sources outside and to the north and northeast of the study area, and were probably transported to this region by longshore shelf processes.

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