AAPG Bulletin, V. 82 (1998), No. 3 (March 1998), P. 484-496.

Radiogenic Heat Production in Sedimentary Rocks

of the Gulf of Mexico Basin, South Texas

Thomas E. McKenna² and John M. Sharp, Jr.³

©Copyright 1998.  The American Association of Petroleum Geologists.  All Rights Reserved

¹Manuscript received June 17, 1996; revised manuscript received February 24, 1997; final acceptance October 21, 1997.
²University of Texas at Austin, Department of Geological Sciences, Austin, Texas 78712. Current address: Delaware Geological Survey, University of Delaware, Newark, Delaware 19716-7501.
³University of Texas at Austin, Department of Geological Sciences, Austin, Texas 78712.

Funding for this project was provided by the office of Basic Energy Research of the U.S. Department of Energy and the Donors of The Petroleum Research Fund, which is administered by the American Chemical Society. We gratefully acknowledge Rich Ketcham and Mark Cloos for access to the a-scintillation counter; Lynton Land, Leo Lynch, and Kitty Milliken for access to their mudrock collection; Larry Mack for analyzing samples to determine the accuracy of our U and Th measurements; and Steve Ingebritsen, Larry Lawver, and the three Bulletin reviewers (Stefan Bachu, Dave Blackwell, and John Sclater) for their reviews of this manuscript. 

Data is offered under the AAPG Bulletin Datashare program (Data 10). Users can obtain the data set by downloading the file for free from the Internet (http://www.geobyte.com/download.html).

ABSTRACT

Radiogenic heat production within the sedimentary section of the Gulf of Mexico basin is a significant source of heat. Radiogenic heat should be included in thermal models of this basin (and perhaps other sedimentary basins). We calculate that radiogenic heat may contribute up to 26% of the overall surface heat-flow density for an area in south Texas. Based on measurements of the radioactive decay rate of a-particles, potassium concentration, and bulk density, we calculate radiogenic heat production for Stuart City (Lower Cretaceous) limestones, Wilcox (Eocene) sandstones and mudrocks, and Frio (Oligocene) sandstones and mudrocks from south Texas. Heat production rates range from a low of 0.07 ±0.01 µW/m³ in clean Stuart City limestones to 2.21 ±0.24 µW/m³ in Frio mudrocks. Mean heat production rates for Wilcox sandstones, Frio sandstones, Wilcox mudrocks, and Frio mudrocks are 0.88, 1.19, 1.50, and 1.72 µW/m3, respectively. In general, the mudrocks produce about 30-40% more heat than stratigraphically equivalent sandstones. Frio rocks produce about 15% more heat than Wilcox rocks per unit volume of clastic rock (sandstone/mudrock). A one-dimensional heat- conduction model indicates that this radiogenic heat source has a significant effect on subsurface temperatures. If a thermal model were calibrated to observed temperatures by optimizing basal heat-flow density and ignoring sediment heat production, the extrapolated present-day temperature of a deeply buried source rock would be overestimated.