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