THE THERMAL AND CEMENTATION HISTORIES OF A SANDSTONE PETROLEUM RESERVOIR, ELK HILLS, CALIFORNIA - PART 1 - AR-40 AR-39 THERMAL HISTORY RESULTS/

Recent developments in K-feldspar Ar-40/Ar-39 thermochronometry have p rovided new tools to deal with interpretive impediments that previousl y limited its application to investigating sedimentary basin thermal h istories. These new methodologies were applied to detrital K-feldspars recovered at various depths from a deep well drilled through a carbon ate-cemented sandstone petroleum reservoir in the southern San Joaquin Valley, California. Thermal histories obtained from both thermochrono logical analysis and burial history constraints were used to constrain a conductive heat flow model of basin evolution. The basin appears to have experienced a broadly linear heating history due to burial throu ghout the early and middle Miocene followed by a significant increase in heating rate between 9 and 6 Ma. In a companion paper [Mahon, K.I., Harrison, T.M., McKeegan, K.D., 1998. The thermal and cementation his tories of a sandstone petroleum reservoir, Elk Hills, California. Part 2: In situ oxygen and carbon isotopic results. Chem. Geol. 152, 257-2 71], we apply the thermal model to predict the temperature evolution o f the much shallower late Miocene Stevens sands, a prolific petroleum producer. Ratios of excess Ar-40 to chlorine calculated from the diffe rential release of radiogenic and nucleogenic argon during isothermal heating steps indicate a uniform value of 5.4 +/- 0.9 x 10(-5) over th e 2.5 km vertical distance separating the samples from well 934-29R su ggesting that the basin receives a high basal flux of radiogenic argon . (C) 1998 Elsevier Science B.V. All rights reserved.