Paleoenvironmental and paleoclimatic interpretations of the late paleocene goler formation, Southern California, U.S.A., based on paleosol geochemistry

摘要

The Paleocene was characterized by high global temperatures and elevated concentrations of atmospheric CO_2. Paleoclimate records of this epoch are of particular interest to understanding the effects of anthropogenic climate forcing as well as linkages between the Paleocene climate and major tectonic and evolutionary events. However, terrestrial paleoclimatic records of the Paleocene are limited in their spatial extent, and few such records are known from western North America. In this study, paleosols from two members in the late Paleocene Goler Formation of Southern California were used to investigate local paleoclimatic conditions. The paleosols were described in detail and analyzed for morphology, clay mineralogy, and bulk geochemistry. Carbonate nodules present in paleosols from the upper member (member 4a) were characterized using petrographic and cathodoluminescence microscopy and were analyzed for carbon and oxygen stable-isotope composition. Enrichment and retention of soluble elements (Ca, Mg, and Na) and the mobilization of Fe and Mn in the paleosol profiles suggest a climate with strongly seasonal precipitation. This interpretation is further supported by the presence of pedogenic slickensides and the clay minerals smectite and illite. The appearance of pedogenic carbonate nodules in paleosols from the upper member is suggestive of a shift to more arid or more seasonal conditions that is coincident with a prominent change in sediment provenance and an inferred increase in sedimentation rate. Uplift of the ancestral Sierra Nevada during the late Paleocene was likely an important control on regional paleoclimate due to the effects of elevated topography on mean annual precipitation and seasonal distribution of precipitation. The correlation of a shift in pedogenic processes with changes in provenance and sedimentation rate suggests that the evolution of regional tectonic activity was an important control on these processes during the deposition of the Goler Formation.