--> ABSTRACT: Response of a Nonmarine Coastal Plain/Fluvial Depositional System to High Frequency Relative Sea Level Fluctuations: The Judith River Formation, Wyoming, USA, by Stephen Johnson; #91019 (1996)

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Response of a Nonmarine Coastal Plain/Fluvial Depositional System to High Frequency Relative Sea Level Fluctuations: The Judith River Formation, Wyoming, USA

Stephen Johnson

Detailed facies and architectural element analysis of the regionally well exposed Late Cretaceous Judith River Formation of the Big Horn Basin, Wyoming revealed a cyclicity in both coarse and fine members. Three man in sedimentary packages were observed:- Unit 1: Carbonaceous shales with common poorly drained soils and rare, well drained soils, coals, isolated small-scale meandering, tidally-influenced fluvial channels and rare crevasse splay sandstones. Deposition in a poorly drained coastal swamp environment. Unit 2: Grey shales, well drained soils, common crevasse splay and single storey channel sandstones. Deposition in a well drained alluvial plain. Unit 3: Stacked, fluvial and fluvial/tidal channel complexes of both low and high sinuosity. Deposition in incised sand-rich fluvial/estuarine systems. The most common arrangement in a vertical profile is 3-->1-->2-->3. This cyclicity was then traced into the coeval shallow marine succession where known flooding surfaces and sequence boundaries allowed the non-marine succession to be interpreted in terms of relative sea level cycles. Sequence boundaries, when traced via continuous outcrop up-dip into nonmarine strata, are defined by regional scale erosion surfaces overlain by vertically amalgamated fluvial-tidal systems, (unit 3). increase in accommodation space in up-dip areas during the transgressive systems tract is marked by high water table deposits (unit 2). Finally the well drained alluvial plain deposits of unit 1 correlate down-dip with rogradational shorefaces characteristic of the highstand systems tract.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California