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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 64 (1980)

Issue: 5. (May)

First Page: 802

Last Page: 803

Title: "Middle" Cretaceous (Albian-Turonian) Depositional Environments Along a Part of Eastern Margin of North American Epicontinental Seaway: ABSTRACT

Author(s): Donald L. Whitley, Greg A. Ludvigson, Bill J. Bunker

Article Type: Meeting abstract

Abstract:

In Iowa and bordering states the Dakota Formation, Graneros Shale, Greenhorn Limestone, and Carlile Shale were deposited along the eastern margin of the North American epicontinental seaway during the middle part of the Creteceous (Albian to Turonian). The pre-Cretaceous physiographic surface of northwestern Iowa consisted of ridges and valleys developed upon tilted Paleozoic rock. This surface profoundly affected the deposition of sediment. Detailed studies of surface outcrops, subsurface cores and cuttings, and gamma-ray well logs reveal that this part of the seaway was the scene of fluvial-deltaic deposition followed by an extensive marine transgression. The Dakota Formation commonly consists of a quartzarenite sequence which has a sharp basal contact and grades upward and laterally into clay shales. This sequence is commonly capped with organic-rich mudrocks, or lignite beds. Analyses of textures, sedimentary structures, and lateral relations indicate that these lithologies represent southwestward-flowing fluvial systems which floored topographic valleys. The Dakota Formation grades upward into fluvially

End_Page 802------------------------------

dominated deltaic and shallow-marine sands and muds of the Graneros Shale. These deposits completed the filling of pre-Cretaceous valleys and buried the predepositional topography. By early Turonian time, the eastern edge of the seaway had transgressed far to the east, leaving western Iowa far from siliciclastic source areas. The result was the deposition of the carbonate muds of the Greenhorn Limestone. Renewed introduction of siliciclastic muds, probably from the northeast, resulted in deposition of the Carlile Shale.

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