Abstract: A Sequence Stratigraphic Model for Midcontinent Pennsylvanian Foreland Basin

Allan P. Bennison

Modelling of Pennsylvanian foreland basinal deposits along their outcrop belt throughout southeastern Kansas and eastern Oklahoma revealed considerable differences in the geometry of their sequences and system tracts compared to those widely accepted for passive marginal basins. The former trapped much more regressive deposits, owing to bordering tectonic highlands complicated by interplay of sediments from opposing land masses.

The transgressive flood occurred commonly on eroded bedrock and/or

soil and achieved maximum advance within the duration of a parasequence, owing to relatively fast meltdown of distant Gondwanan ice sheets. Organic limestone, coal and gray to black shales dominated the cratonic shelf, whereas the tectonic shelf featured redbeds and sandstones.

During the ensuing highstand phase, a fluctuating equilibrium involving subsidence, eustacy and deposition, resulted in alternating retrogradational and progradational beds lasting two or more parasequences and involving carbonate banks and black shale on the cratonic shelf and thick clinoform siliciclastic deposits on the tectonic shelf and slope. A shoaling phase followed when deposition began to exceed accommodation and deposits became increasingly aggradational.

The final depositional phase of a complete sequence was forced regression, when deposits shifted basinward in a down-stepping progradational mode. Soil formation (pedogenesis) followed.

Many sequences are incomplete, owing to renewed subsidence at almost any phase within the sequence, and a moderate transgression may precede the next major overlapping sequence.

Foreland basins commonly shift their depocenters toward their cratonic shelves, owing to the greater load of sediments from adjacent orogenic highlands.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994