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Title:Stratigraphy, Depositional History, and Brachiopod Paleontology of Virgilian Strata of East-Central Illinois
Author(s):Weibel, Carl Pius
Doctoral Committee Chair(s):Langenheim, Ralph L., Jr.
Department / Program:Geology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Abstract:The Virgilian outlier, upper Mattoon Formation, in east-central Illinois consists of alternating marine and nonmarine strata divided into eight modified cyclothems: Omega, Shumway, Bogota, Newton, Mint Creek, Greenup, Toledo, and Woodbury. The modified cyclothems are recognized with lower boundaries at top of coal or base of the lowest marine stratum. The perceived stratigraphic succession is revised, incorporating cyclotherms and formal members, and utilizes outcrop and newly acquired subsurface data.
Cyclothems containing black, fissile shale were deposited in successive environments of (1) local, shallow, tidal lagoon, (2) shallow, nearshore, open marine, (3) offshore, marine, (4) shallow, nearshore, open marine, (5) subaqueous deltaic progadation, and (6) coastal plain progradation. Marine units in cyclothems lacking the shale were deposited in either shallow, nearshore, open marine or in shallow, offshore, open marine environments. Analysis of the Bogota cyclothem indicates slow transgression consisting of a series of progressively more widespread advances with minor retreats.
Limestone petrography indicates diagenesis in successive environments of marine phreatic, saturated meteoric phreatic, and burial environment. Some limestones included diagenesis in mixed marine-freshwater, unsaturated meteoric phreatic, or meteoric vadose environments. Diagenetic sequences are compatible with the inferred depositional environments.
Shumway, Bogota, Newton, and Mint Creek cyclothems correlate with equivalent cyclic sequences in the midcontinent and north-central Texas. Biostratigraphic correlation of 21 brachiopod species, indicates strata above the Omega Limestone Member are middle to upper Virgilian, supporting the extrabasinal, lithostratigraphic correlation. Inability to correlate with cyclic strata in New Mexico and Nevada suggests correlable Virgilian cyclothems are restricted to the craton, or that eustatic fluctuations are not yet discernable in the these platform carbonates. This study supports, in part, the validity of widespread, glacial-eustatic, cyclothemic deposition.
Issue Date:1988
Description:257 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.
Other Identifier(s):(UMI)AAI8823283
Date Available in IDEALS:2015-05-14
Date Deposited:1988

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