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Mesotidal Estuary Point Bar Deposits: A Comparative Sedimentology of Modern and Ancient Examples in Peels and Core: Abstract
Resin peels of vibracore taken from active mesotidally influenced estuary point bars in coastal Georgia State, U.S.A., are compared with drill core from the Athabasca Oil Sands, Lower Cretaceous, McMurray Formation, Alberta, Canada. In the vertical profiles the following ten sedimentological characteristics are similar in both peels and core: (1) inclined heterolithic stratification (IHS; same asepsilon cross-stratification) of sand and mud, (2) inclined strata and slope angles of point bar surfaces average 12 degrees, (3) bases of each sand unit are frequently in erosional contact with underlying mud, (4) tops of each sand are commonly gradational from sand to mud; gradation occurs as thin laminae, (5) sand beds normally contain ripple structures, (6) mud beds are usually thicker up-profile, (7) sand beds are usually thinner up-profile, (8) sand beds often contain mud balls, mud chips and mud blocks, interpreted as having been eroded from tidal marsh mud deposits, located at the top of the point bar deposits, (9) occurrence of bioturbation, organic litter beds and/or carbonaceous-rich (litter) mud increases up-profile, and (10) if preserved, a 2 to 4 m thick unit of marsh mud usually caps the point bar sequence ().
Other similar vertical sequences of modern estuary point bar deposits are present in the Willapa River estuary of southwest Washington State, U.S.A., and the Daule and Babahovo River estuaries of Ecuador, South America (Smith, 1988). Both sites have mesotidally influenced conditions. Analogous ancient deposits are present in the Upper Cretaceous Horseshoe Canyon Formation exposed in the Red Deer River Valley badlands at Willow Creek near Drumheller, Alberta, Canada (Rahmani, 1988).
Rahmani, R.A. 1988. Estuarine tidal channel and nearshore sedimentation of a Late Cretaceous epicontinental sea, Drumheller, Alberta, Canada. In: de Boer, P.L., Van Gelder, A. and Nio, S.D. (Eds.), Tide-Influenced Sedimentary Environments and Facies. Reidel Publishing Co., p. 433-471.
Smith, D.G. 1988. Modern point bar deposition analogous to the Athabasca Oil Sands, Alberta, Canada. In: de Boer, P.L., Van Gelder, A. and Nio, S.D. (Eds.), Tide-Influenced Sedimentary Environments and Facies. Reidel Publishing Co., p. 417-432.
Acknowledgments and Associated Footnotes
1 Department of Geography, University of Calgary, Calgary, Alberta T2N 1N4
Copyright © 2009 by the Canadian Society of Petroleum Geologists