186-11 A calibrated model of total organic carbon accumulation across the southern Denver – Julesburg Basin during the Cenomanian – Turonian boundary interval

Abstract:

Studies of carbon burial and the global carbon cycle during times of extreme climate events in the geologic past have recognized carbon sinks that are unaccounted for in scales ranging from basinal to global throughout the geologic record.  This lack of accounting for carbon sinks is driven by the reliance on core and outcrop data to provide the primary source inputs for regional and global models.  Oceanic Anoxic Event 2 occurs at the Cenomanian – Turonian boundary and represents a time in the geologic past that is globally recognized for extensive accumulations of organic-rich strata and a notable positive carbon isotope excursion reflected in the δ¹³C signatures of organic matter and carbonate.    Cenomanian – Turonian strata of the southern Denver – Julesburg Basin represent a prime example of the need to expand carbon burial models beyond intensively studied core and outcrop locations.  These strata have been evaluated at the Global Stratotype Point and Section in Pueblo, CO and extensively studied in the U.S. Geological Survey #1 Portland Core in Freemont County, CO.  While data from these locales provide key insights into the drivers of carbon burial at the cm – dm scale, models derived from these studies are limited in scope to their specific location.  In this study we utilize a detailed facies classification based upon high resolution geochemical data and sedimentologic and petrographic observations of the Cenomanian – Turonian interval in the U.S. Geological Survey #1 Portland core to develop a calibrated and geophysical log-based DeltaLogR model estimates of total organic carbon (TOC) concentrations.  From this calibrated model, we mapped TOC concentrations for the Cenomanian – Turonian interval (averaging 125 ft in thickness) on over 30 geophysical logs in the southern Denver – Julesburg Basin (spanning an area over 1000 km².  This method and map provide a means of addressing missing TOC concentrations at the regional scale during extreme climate events and perturbations to the global carbon cycle throughout geologic history.  

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