Origin of four Upper Pennsylvanian (Missourian) cyclothems in the subsurface of western Kansas: application to search for accumulation of petroleum

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1985

OSTI ID:5517116

Watney, W L

The four cyclothems are characterized by rapid transgression and relatively slow regression of the sea across a gently tilting shelf. A thin, basal transgressive carbonate is overlain by marine shale, representing maximum inundation by the sea. The marine shale completely covered the study area but for local areas over the more significant positive areas of the shelf and in one of the cyclothems, the I-Zone. The black organic-rich facies in the marine shale covers much of the southern two-thirds of the shelf excluding portions of the structurally positive areas and again in the I-Zone. The anoxic bottom conditions that brought on the deposition of the black shale resulted primarily from the combination of stagnant bottom waters due to a thermocline and scavenging of oxygen by large amount of terrestrial organic matter. Progressive, contemporaneous, epeirogenic deformation of the shelf significantly affected sedimentation and diagenesis in these cyclothems. These changes included varying but generally less subsidence over previously active structures such as the Central Kansas and Cambridge uplifts and increased subsidence along portions of the shelf closest to the Anadarko basin, most active during deposition of the earliest two cyclothems. These epeirogenic adjustments were however secondary in importance to a rapidly fluccuating sea level in controlling the formation of the cyclothems. Periodic changes in eustatic sea level due to continental Gondwana glaciation are deemed most plausible for producing the rhythmic flooding and subaerial exposure of the broad, gently-dipping shelf.

• Research Organization: Kansas Univ., Lawrence (USA)
• OSTI ID: 5517116
• Country of Publication: United States
• Language: English

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