Saskatchewan Geological Society Special Publication Number 5: LLOYDMINSTER AND BEYOND: GEOLOGY OF MANNVILLE HYDROCARBON, A Conference and Core Seminar, Regina, October 15, 16, 17, 1980. Editors: L. S Beck, J. E. Christopher, and D. M. Kent.
Pages 1-2.

EARLY CRETACEOUS PALEOGEOGRAPHY IN THE ALBERTA FOOTHILLS AND ADJACENT PLAINS - ABSTRACT

J.R. McLean¹ and J.H. Wall^2
1Shell Canada Resources Limited, 400 - 4th Avenue S.W., Calgary, Alberta.
²Geological Survey of Canada, 3303 - 33rd Street N.W., Calgary, Alberta T2L 2A7

The Early Cretaceous paleogeography of the Alberta Foot­hills region developed in two principal stages. The first was a period of predominantly erosion, with an extensive drainage system carved into the underlying Mesozoic and Paleozoic sediments. Local topographic relief exceeded 100 m in some areas. Rivers flowed generally in a northerly direction towards a boreal sea.

The second stage was predominantly depositional and accompanied the gradual southward transgression of the Moosebar-Clearwater sea. River valleys were flooded, forming extensive estuaries and, with stream gradients lowered, aggradation took place in alluvial valleys, eventually filling them.

The Cadomin Formation represents deposition during the erosional and earliest depositional phases. The overlying Glad­stone Formation represents deposition during the marine trans­gression when the drainage system was infilled, and the Moosebar Member of the Malcolm Creek Formation represents the phase of maximum transgression of the sea.

The Gladstone Formation in the Alberta Foothills between the Crowsnest Pass and Smoky River can be divided into two infor­mal units: a lower unit characterized by fluvial deposits and an upper part (Calcareous member) characterized by generally fine grained sediments containing diagnostic microfossil suites.

The lower unit represents aggradational deposits in alluvial valleys during transgression of the sea, and is generally more prevalent in the western Foothills and southern Plains. The upper unit, south of the North Saskatchewan River, contains an entirely nonmarine faunal suite, but between the North Saskatchewan and Berland Rivers, a mixed fresh and brackish water faunal suite is present. The southern sequence is interpreted as deposition in a lacustrine or inner estuarine environment and the northern sequ­ence as outer estuarine to marginal marine. Equivalent beds in the upper part of the Gething Formation between the Smoky and Wolverine Rivers do not contain a marine fauna and were deposited in an alluvial-deltaic complex which extended eastward beyond the limits of the Foothills.

The Moosebar Member abruptly overlies the Gladstone Formation and is present in the Foothills at least as far south as the Clearwater River, considerably beyond the recognized limit of marine influence in the Gladstone Formation. A thin glauconite and pebble bed occurs at the base of the Moosebar Member in the central Foothills, but was not observed in more southerly sections. The pebbles are a lag deposit of the transgressing sea and the glauconite formed under slow sedimentation conditions during, and immediately following, the transgression. The upper part of the Moosebar Member, as well as the overlying Torrens and Grande Cache Members of the Malcolm Creek Formation represent deposition during regression of the Moosebar-Clearwater sea.

Events in the development of the Lower Cretaceous sequence in the Alberta Foothills can be extrapolated to the adjacent plains of Alberta and Saskatchewan where similar sedimen­tary sequences have been reported.

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