|Title:||The thermal and cementation histories of a sandstone petroleum reservoir, Elk Hills, California ‐ Part 1: 40Ar/39Ar thermal history results|
|Authors:||K.I Mahon, T.M. Harrison, M.Grove|
|Publication:||Chem. Geol., v. 152, p. 227‐256.|
Recent developments in K‐feldspar 40Ar/39Ar thermochronometry have provided new tools to deal with interpretive impediments that previously limited its application to investigating sedimentary basin thermal histories. These new methodologies were applied to detrital K‐feldspars recovered at various depths from a deep well drilled through a carbonate‐cemented sandstone petroleum reservoir in the southern San Joaquin Valley, California. Thermal histories obtained from both thermochronological 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 throughout 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 histories of a sandstone petroleum reservoir, Elk Hills, California. Part 2: In situ oxygen and carbon isotopic results. Chem. Geol. 152, 257‐271], we apply the thermal model to predict the temperature evolution of the much shallower late Miocene Stevens sands, a prolific petroleum producer. Ratios of excess 40Ar to chlorine calculated from the differential release of radiogenic and nucleogenic argon during isothermal heating steps indicate a uniform value of 5.4 ± 0.9 x 10−5 over the 2.5 km vertical distance separating the samples from well 934‐29R suggesting that the basin receives a high basal flux of radiogenic argon.