Abstract: Mid-Turonian Parasequence Correlations and Controls on Organic-matter Depositional Cyclicity in the Carlile Formation (Fm) and Non-Marine Time Equivalents

Timothy S. White, M. A. Arthur

Cores of marine sedimentary rocks from southern Colorado and western Kansas were sampled through the mid-Turonian Carlile Formation. These holes were drilled as a transect perpendicular to the paleoshoreline of the Cretaceous Western Interior Seaway. Carbonate (CaCO₃) and organic carbon (TOC), as well as pyrolysis and organic petrographic data were collected to determine the relative abundance(s) and the distribution of organic matter from sea-level highstand through marine regression and eventual seaway lowstand during the mid-Turonian (Mammites nodosoides through Prionocyclus hyatti biozones). CaCO₃ contents fluctuate between 9.5-38% during sea-level highstand (upper Bridge Creek Limestone to lower Fairport Shale), drop to very low values during regression (Fai port and Blue Hill Shales), but increase to pre-regression levels during lowstand (Codell Sandstone); values as high as 76% probably represent reinitiation of sea-level rise. TOC contents of 3-6% occur in highstand deposits, whereas values of O.5-1.5% were recorded in lowstand deposits. A gradual decrease in TOC characterized regressive portions of the sequence, in contrast to the rapid drop in CaCO₃. Both TOC and CaCO₃ contents exhibit potentially cyclic fluctuations during maximum sea-level highstand.

Ultimately the goal of this work is to tie depositional events and trends in organic-matter deposition between marine and nonmarine environments. Field stratigraphic and gamma-ray surveys of mid-Turonian units in Utah and Colorado provide a preliminary stratigraphic correlation between terrestrial and marine "paleorealms." Paleopalynological analyses and organic-petrographic/geochemical studies to assess stratigraphy and depositional cyclicity of mid-Turonian, coal-bearing units are in progress.

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