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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


Modern and Ancient Examples of Clastic Tidal Deposits: A Core and Peel Workshop, 1989
Pages 50-59

Estuarine Channel Deposition Within the Lower Cretaceous Waseca Formation, Upper Mannville Group, Lloydminster Area, Saskatchewan

James A. MacEachern

Abstract

Within the Waseca Formation of the Lloydminster area, an anomalously thick (up to 35 m), laterally shale-bound, NNE-SSW trending linear sand body, 0.8 to 2.7 km wide and at least 50 km long, has been delineated. The sand body consists of four main sequences reflecting: 1) in-channel deposition of high angle, planar cross-stratified sand and shale-pebble conglomerates; 2) tidally influenced, point bar accretion of inclined heterolithic stratification, showing at least two scales of unsteady flow; 3) progressive landward shift of an estuarine turbidity maximum zone, draping the pre-existing channel deposits with burrowed mudstone containing abundant interstitial silt; and 4) laterally flanking levee accumulation, characterized by shales containing abundant interstitial silt and sand, and possessing penecontemporaneous gravity faults and steeply tilted beds.

Tidally generated features and brackish to marine conditions were more pronounced in the northern portion of the study area, diminishing to south. The southern portion of the anomalous sand body reflects deposition under dominantly fluvial conditions, within a laterally migrating channel. The above conditions demonstrate an estuarine channel depositional system for the anomalous sand body. The presence of flanking levee deposits and the coeval relationship of the channel with interchannel sands of possible delta front origin suggests the estuary may be more accurately described as a tidally influenced estuarine distributary.


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