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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 69 (1985)

Issue: 5. (May)

First Page: 856

Last Page: 856

Title: Carboniferous Tectonics, Stratigraphy, and Mississippian-Pennsylvanian Boundary, Western Interior United States: ABSTRACT

Author(s): Edwin K. Maughan

Article Type: Meeting abstract

Abstract:

Current proposals for the mid-Carboniferous boundary at the first occurrence of Declinognathodus noduliferus place this boundary within rocks previously considered Morrowan by many workers in the Western Interior. This placement is higher than that of the Mississippian-Pennsylvanian systemic boundary between the Big Snowy and Amsden Groups in Montana by E. K. Maughan and A. E. Roberts, which is approximately coincident with the transition from Foraminifera Zone 18 to 19 and the first occurrence of Adetognathus unicornis and Rhachistognathus muricatur, based on paleontologic identifications by B. R. Wardlaw. An episode of differential regional uplift in the west, which seems to have been coincident with a major mid-Carboniferous event during the Allegheny orogeny and conti ent-wide epeirogeny, interrupted the deposition of Mississippian dominantly carbonate sediments. It created a regional erosional unconformity, and it initiated the deposition of Pennsylvanian dominantly siliciclastic sediments. Uppermost Big Snowy strata indicate regression of the sea from the western continental shelf and weathering and erosion of rocks exposed there, coincident with the approximately 320 Ma global sea level decrease shown by P. R. Vail. Lowermost Amsden strata record alluviation in valleys on the subaerially exposed continental shelf, and subsequent transgression of the sea. Valleys in the shelf margin were inundated first, and the sea then transgressed onto the adjacent platforms and shelves. This lithostratigraphic placement of the boundary corresponds to the criteri originally indicated by T. C. Chamberlin and R. D. Salisbury in 1906 for dividing the Carboniferous in North America; this is the Mississippian-Pennsylvanian boundary indicated by M. G. Cheney in 1945 to correspond to the Namurian A-B boundary in western Europe. Also, this boundary is about coincident with the base of the Pennsylvanian System stratotype in Virginia and West Virginia proposed by K. J. Englund in 1979.

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