Controls from Organic Carbon Sequestration in the New Albany Shale: From Examination of the Relative Role of Organic Carbon Production, Preservation, and Dilution

Ovidiu R. Lazar¹ and Juergen Schieber^2
1ExxonMobil, Houston, TX
²Geological Sciences, Indiana University, Bloomington, IN

The New Albany Shale, an organic carbon-rich fine-grained Late Devonian succession, is a source and a reservoir of hydrocarbons in the Illinois Basin. Multiple sedimentologic, petrographic, and geochemical indicators were examined and integrated within a basin-wide, comprehensive sequence stratigraphic framework to evaluate the relative importance of organic matter preservation, surface production, and clastic dilution in the accumulation of organic carbon in the New Albany Shale.

This study reveals that organic production varied significantly during deposition of the New Albany Shale, and may have reached very high values intermittently. Complex non-linear relations among organic carbon production, preservation, and dilution resulted in multiple types of black shales and ultimately controlled carbon burial in the New Albany Shale. For example, shales with organic carbon contents < 2% resulted from low to moderate primary production, mostly oxygenated bottom waters, and relatively low to moderate bulk accumulation rates. Shales with organic carbon contents ~5% resulted from multiple combinations including (i) moderate primary production, moderate preservation, and relatively high bulk accumulation rate, as well as (ii) relatively high primary production, low preservation, and lower bulk accumulation rate. On the other hand, shales with organic carbon contents > ~9% resulted from moderate to high primary production rates, variably dysoxic conditions, and relatively low to moderate bulk accumulation rates.

Observations made in this study contribute to an improved understanding of the range and controls of carbon burial during the formation of other organic carbon-rich fine-grained successions, especially when comparable observational and analytical data sets are developed.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas