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Recognition of Relative Sea-Level Change in Upper Cretaceous Coal-Bearing Strata: A Paleoecological Approach Using Agglutinated Foraminifera and Ostracodes to Detect Key Stratigraphic Surfaces

By
Neil E. Tibert
Neil E. Tibert
Department of Geosciences, University of Massachusetts, Amherst, Massachusetts 01003, U.S.A.
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R. Mark Leckie
R. Mark Leckie
Department of Geosciences, University of Massachusetts, Amherst, Massachusetts 01003, U.S.A.
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Jeffrey G. Eaton
Jeffrey G. Eaton
Department of Geosciences, Weber State University, Ogden, Utah 84408, U.S.A.
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James I. Kirkland
James I. Kirkland
Utah Geological Survey, Salt Lake City, Utah 84116, U.S.A.
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Jean-Paul Colin
Jean-Paul Colin
Global Ventures Consultants Inc., 3 Impasse des Biroulayres, 33610 Cestas, France
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Elana L. Leithold
Elana L. Leithold
Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina 27695, U.S.A.
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Michael E. Mccormic
Michael E. Mccormic
Neari School, Holyoke, Massachusetts 01040, U.S.A.
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Published:
January 01, 2003

Abstract

Microfossils from Cretaceous coal-bearing strata can be used to establish key stratigraphic surfaces that mark marine flooding events with intermediate-frequency (fourth-order) and high-frequency (fifth-order) periodicities. We document several examples of this cyclicity from the transgressive and regressive facies at the land–sea transition of the Greenhorn Marine Cycle on the Colorado Plateau. Estuarine strata from the upper Cenomanian Dakota and middle Turonian Straight Cliffs Formations yield four primary fossil assemblages: Assemblage A, the lagoonal assemblage, comprising a rich agglutinated foraminiferal population of Trochammina and Verneuilinoides and brackish ostracodes and molluscs in a skeletal shell accumulation; Assemblage B, the proximal estuarine assemblage, comprising the brackish ostracode Fossocytheridea, charophytes, and smooth admetopsid gastropods within bituminous coal zones giving rise to distal estuary with the addition of brackish gastropods and sparse agglutinated foraminifera in sandy marlstones; Assemblage C, the open-bay (distal estuarine) assemblage, comprising the ostracodes Fossocytheridea posterovata, Cytheromorpha, Looneyella, and Cytheropteron, the foraminifera Trochammina and Ammobaculites, and ornate brackish molluscs in calcareous shelly mudstones; and Assemblage D, the marsh, comprising an exclusive population of the foraminifera Trochammina, Miliammina, and Ammobaculites in rooted lignites. Intermediate flooding surfaces are marked by normal marine taxa that are superimposed on the background of a primary marginal marine assemblage. In general, intermediate flooding events approximate lithologic and biostratigraphic boundaries and record basin-wide paleoenvironmen-tal changes with the advancing Greenhorn Sea. We correlate coal zones from the coast to maxima in calcium carbonate and planktic foraminifera in the offshore. The intermediate cycles approximate ammonite biostratigraphic zones and therefore maintain periodicities within the 100–400 kyr bandwidth. The onshore–offshore correlations suggest that a regional and perhaps global sea-level mechanism controlled the stratigraphic position of the coal zones. Superimposed on the intermediate cycles are higher-frequency cycles that represent short-lived flooding events. As many as six high-frequency cycles constitute an intermediate cycle, and therefore periodicities fall within an approximate 10–25 kyr range. The general asymmetry of the packages suggests that a combination of oceanographic, climatic, and autogenic processes influenced the high-frequency stratal architecture. Overall, the primary mechanism controlling the stratigraphic position of the coals was tectono-eustasy. Compactional processes and/or climate modulations contributed to the observed internal coal-zone cyclicity that we interpret as a secondary coal-forming process.

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Contents

SEPM Special Publication

Micropaleontologic Proxies for Sea-Level Change and Stratigraphic Discontinuities

Hilary Clement Olson
Hilary Clement Olson
Institute for Geophysics, University of Texas, 4412 Spicewood Springs Rd., Bldg. 600, Austin, Texas 78759-8500, U.S.A.
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R. Mark Leckie
R. Mark Leckie
Department of Geosciences, University of Massachusetts, 611 N. Pleasant St., Amherst Massachusetts 01003, U.S.A.
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SEPM Society for Sedimentary Geology
Volume
75
ISBN electronic:
9781565762121
Publication date:
January 01, 2003

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