Depositional environments and paleogeography in the Albian Moosebar Formation and adjacent fluvial Gladstone and Beaver Mines formations, Alberta

Abstract

The marine Moosebar Formation (Albian) has a currently accepted southerly limit at Fall Creek (Ram River area). It consists of marine mudstones with some hummocky and swaley cross-stratified sandstones indicating a storm-dominated Moosebar (Clearwater) sea. We have traced a tongue of the Moosebar southward to the Elbow River area (150 km southeast of Fall Creek), where there is a brackish-water ostracod fauna. Paleoflow directions are essentially northwestward (vector mean 318°), roughly agreeing with turbidite sole marks (329°) in the Moosebar of northeastern British Columbia.The Moosebar sea transgressed southward over fluvial deposits of the Gladstone Formation. In the Gladstone, thick channel sands (4–8 m) are commonly multistorey (up to about 15 m), with well developed lateral accretion surfaces. The strike of the lateral accretion surfaces and the orientation of the walls of channels and scours indicate northwestward flow (various vector means in the range 307–339°). The Moosebar transgression was terminated by construction of the Beaver Mines floodplain, with thick, multistorey sand bodies up to about 35 m thick. Flow directions are variable, but various vector means roughly cluster in the north to northeast segment. This indicates a major change in dispersal direction from the Gladstone and Moosebar formations.A review of many Late Jurassic and Cretaceous units shows a dominant dispersal of sand parallel to regional strike. This flow is mostly north-northwestward (Passage beds, Cadomin, Gladstone, Moosebar, Gates, Chungo), with the southeasterly dispersal of the Cardium being the major exception. Only at times of maximum thickness of clastic input (Belly River and higher units, and possibly Kootenay but there are no published paleocurrent data) does the sediment disperse directly eastward or northeastward from the Cordillera toward the Plains.