Comparison of Paleotemperature Proxies from the Goler Formation, California

Abstract:

The Paleocene to Eocene Goler Formation in California preserves the oldest Cenozoic terrestrial deposition on the paleo-Pacific Coast, and is dominated by fluvial strata, including overbank and paleosol deposits, as well as rare lacustrine limestone. A wide variety of paleotemperature proxy materials are preserved, including paleosols, paleosol carbonate nodules, lacustrine micrites, carbonaceous shales, and lignites. Interbedded early Eocene marine strata suggest a near-sea-level elevation at the time of deposition. Thus, the Goler Formation is a valuable site from which to constrain both paleotemperatures in the early Cenozoic and pre-extensional paleotopography in the western U.S.
Mean annual temperature at the time of Goler Formation deposition was estimated from the whole-rock geochemistry of paleosols and yield paleo-MAAT estimates of 23°C. Clumped isotope measurements of paleosol carbonate nodules yield ∆47 temperatures of 33°C. Based on four recent studies, a new calibration of paleosol carbonate ∆47 temperatures to MAAT indicates that these temperatures equate to a Paleocene MAAT of ~22°C, which is in agreement with the paleosol geochemistry estimates. Preliminary δD_n-alkene. values of -166‰ are measured from carbonaceous shales of the Goler Formation; such values are consistent with low-elevation δD_n-alkene values from Eocene strata in the northern Sierra Nevada, where MAAT estimates are also estimated to lie between 20 and 25°C.
These results contrast with ∆47 temperatures of ~48°C from lacustrine micrites in the Goler Formation, as even with a warm season bias to lacustrine carbonate deposition, these values reflect MAAT >30°C. Vitrinite reflectance data indicate peak burial temperatures for the Goler Formation near 100°C. Thus, the micrite ∆47 temperatures do not appear to reflect re-equilibration to burial depth temperatures. The difference between the micrite ∆47 temperatures and the paleosol nodule ∆47 temperatures, however, suggest alteration of the micrite. This may be due to susceptibility to burial diagenesis or enhanced exposure to hydrothermal fluids during nearby Miocene volcanism. In either case, these results underscore the value of comparing multiple paleotemperature proxies both for paleoclimatic and paleoaltimetric reconstructions.