|Abstract - Recent advances
in 40Ar/39Ar thermochronology using K-feldspars overcome
interpretive and natural impediments which previously limited application
of this method to understanding sedimentary basin thermal histories.
We applied these new methodologies to detrital K-feldspars recovered from
a deep well drilled through a sandstone cemented petroleum reservoir in
the southern San Joaquin Valley, California. Coupled with a conductive
heat flow model, the thermochronological results suggest a broadly linear
heating due to burial throughout the early and Middle Miocene followed
by a significant increase in heating rate between 9 and 6 Ma. This
result is supported by stratigraphic constraints.
These results were extrapolated
using the thermal model to shallower levels to estimate the thermal evolution
of the strata, the Stevens sands, that is the focus of a companion study
(Mahon et al., 1997) focused on the cementation history of the unit.
We conclude that the Stevens sands experienced the enhanced rate of temperature
increase shortly after deposition. The thermal modeling of the thermochronometric
data yield results that are consistent with a depositional model for this
region of the basin, but generally predict bottomhole temperatures that
are ~20°C lower than that measured, consistent with previous findings.