--> Abstract: Abundant Eastern Oklahoma Mid-Pennsylvanian Soil Zones as Proxies for Numerous Sea Level Changes, Roderick Tillman, #90097 (2009)

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Abundant Eastern Oklahoma Mid-Pennsylvanian Soil Zones as Proxies for Numerous Sea Level Changes

Roderick Tillman1

1Tillman & Associates

Evidence for abundant cyclicity in the Pennsylvanian section in eastern Oklahoma can be found in the numerous cores taken in the 1980s by LeRoy Hemish for the Oklahoma Geological Survey. Core-gamma logs add immeasurably to the value of these cores.

Underclays (soil zones) observable in the cores are particularly good evidence of relative sea level change when they occur in sequence with brackish and marine deposits. In northeast Oklahoma, between the Mississippian-Pennsylvanian unconformity and the Chelsea (Red Fork) Sandstone there are more than 15 underclays, averaging 2-feet in thickness. The interval containing the soil zones spans approximately 4 million years. This suggests that periods between sea level change average less, and possibly much less, than 300,000 years.

Commonly the soil zones are overlain by thin coals (0.5 ft average) and are in close proximity to thin limestones (1 ft average) and/or thin black shales (3 ft average). These lithologies individually, and/or collectively, can be correlated with responses on core-gamma logs of Hemish’s cores. Recognition of these associations allow subsurface correlation of “time lines” in otherwise monotonous shaly intervals punctuated only occasionally by sandstones.

A similar number of cycles (cyclothems?) have been recognized by Marshall in his unpublished Masters thesis on the Cherokee interval. His work is primarily outcrop work and his evidence is based primarily on Conodonts, which are extremely abundant in many of the outcrops he visited. He also suggests that by calculating relative percentage of species in individual samples that ”deep water” black shales and shallow water black shales can be differentiated.

 

 

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