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Anatomy of a Prograding Wave and Storm Dominated Delta Shoreline Complex, the Chungo Sandstone (Milk River - Eagle Equivalent) in the Southern Alberta Foothills: Abstract
The Chungo Member of the Upper Cretaceous Wapiabi Formation is the product of a major regressive pulse which introduced large volumes of clastic detritus into southern and western Alberta and central Montana.
South of the Highwood River, the Chungo consists of a coarsening and thickening upward sandstone/mudstone sequence which is capped by a thick clean sandstone which is, in turn, overlain by approximately 60 metres of nonmarine strata. Shallow marine turbidite structures and hummocky cross stratification are well developed in the lower Chungo whereas load structures, swaley cross stratification, angle of repose foresets and low angle to planar stratification are common in the ‘main’ Chungo sand. North of the High wood River, the uppermost non-marine strata is absent and the Chungo is represented by at least two distinct coarsening upward sequences, each of which is overlain by bioturbated mudstones which have a thin pebbly unit at their bases. Along the Bow River the bioturbated sandstone which comprises the Chungo Member is less than 5 metres thick.
The Chungo Member was laid down by a wave and storm dominated delta-shoreline complex which prograded NNE into the Cretaceous seaway. The advance of the shoreline was halted just north of the Highwood River, presumably due to a change in the rate of subsidence and/or sediment supply.
Acknowledgments and Associated Footnotes
1 Murphy Oil, 1700 - 800 - 6th Avenue S.W., Calgary, Alberta
2 Dept. of Geology, McMaster University, Hamilton, Ontario L8S 4M1
Copyright © 2009 by the Canadian Society of Petroleum Geologists