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BOARDMAN, DARWIN R., II
Oklahoma State University, 105 Noble Research Center, Stillwater, OK 74078

Abstract: Changes in Patterns of Cyclicity in Upper Carboniferous through Lower Permian (Virgilian-Sakmarian) Depositional Sequences in the North American Midcontinent

Analysis of outcropping Virgilian-Sakmarian depositional sequences from the North American Midcontinent reveals major changes in the nature of the cyclothernic-scale depositional sequences and patterns of cyclicity that is considered to result from allocyclic as well as autocyclic mechanisms.

Lower-Middle Virgilian (Douglas, Shawnee, and basal Wabaunsee) strata are grouped into mixed composite carbonate-siliciclastic sequences with a regular pattern of minor to major depositional sequences that have the thickest sequence containing well-developed marine condensed sections represented by non-skeletal phosphatic black shales. Incised valley fills and laterally extensive paleosols are well developed during, lowstands.

Upper Virgilian (Wabaunsee, and Admire) strata are grouped into mixed composite carbonate sequences-siliciclastic sequences with a regular pattern of between two to three minor to intermediate sequences With no marine condensed sections but with updip maximum marine flooding surfaces that are either fossiliferous gray shales or phosphatic and glauconitic wackestones. Also, an upward trend towards more rninor cycles is noted. Incised valley fills and laterally extensive paleosols are well developed during lowstands.

Lower Council Grove strata are grouped into mixed composite carbonate-siliciclastic sequences with a pattern of minor to major, depositional sequences that have the thickest sequence containing well-developed marine condensed sections represented by black shales or laterally equivalent black shaly, phosphatic, and glauconitic wackestones. No non-skeletal phosphate is denoted in these sequences. Lowstands are denoted by well developed paleosols are represented in the majority of the outcrop belt with incised valley fills restricted to the Oklahoma part of the outcrop belt.

Upper Council Grove strata are grouped into mixed composite sequences with a pattern of minor to intermediate depositional sequences that have the thickest sequence containing no marine condensed sections but only minor condensation at the level that corresponds to maximum marine flooding.

AAPG Search and Discovery Article #90921©1999 AAPG Mid-Continent Section Meeting, Wichita, Kansas