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LAUGHLAND, MATTHEW M., Mobil Research and Development Corporation, Dallas, TX

ABSTRACT: Evaluating Basin Thermal Histories: A Comparative Study of Models for Vitrinite Previous HitMaturationNext Hit

Different models of vitrinite Previous HitmaturationNext Hit yield markedly different values of vitrinite reflectance (%R) under identical conditions of thermal exposure. Therefore, these models still require evaluation by empirical data. Because the thermal history of a sedimentary basin never is known exactly, few studies compare %R to maximum temperature. In this study, detailed temperature histories were calculated for computer-simulated basins based on published reconstructions of heating associated with specific tectonic environments. Values of %R from published models of vitrinite Previous HitmaturationNext Hit are compared directly to paleotemperature to identify models that yield viable predictions of %R for each of these basins.

Five %R models incorporate chemical kinetics and follow the traditional contention that vitrinite Previous HitmaturationNext Hit is a function of temperature and time. Two of these "time-dependent" models essentially treat vitrinite Previous HitmaturationTop as a single activation-energy reaction, but these models calculate unreasonably high values of %R for basins with high rates of heating or protracted episodes of burial. Alternatively, models that incorporate multiple activation energies yield reasonable predictions of %R for diverse geologic conditions, despite that these models allow %R to increase during burial at constant or decreasing temperature.

Four models are based on empirical correlations between %R and temperature and treat %R as an absolute paleogeothermometer for burial times in excess of about 10{4} to 10{6} yrs. Use of three of these "time-independent" models may be restricted to geologic settings similar to where the correlations were calibrated. One model yields realistic predictions of %R for all of the synthetic basin histories.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.