NEWLY DISCOVERED PALEOSOLS FROM THE PALEOCENE GOLER FORMATION OF SOUTHERN CALIFORNIA

The Goler Formation of California is the western-most non-marine Paleocene Formation in the U.S. that has been well constrained temporally (Albright et al, 2010), allowing for regional comparison of paleoclimatic data. Although sub-tropical to tropical forests extended into high latitudes during the Paleogene (Frakes, 1979), terrestrial sections in the U.S. show evidence of seasonality with respect to rainfall (Koch et al, 2003;Retallack, 2005). Newly identified paleosols from the Goler Formation were described and sampled in the field and analyzed for clay mineralogy (XRD), whole-rock geochemistry (ICPMS), and microfabrics associated with calcite nodules in order to interpret the paleoclimate under which they formed.

Two paleosol types, which developed on overbank deposits within the fluvial succession of the Goler Formation, were identified and suggest that pedogenesis occurred under seasonal precipitation. Within well-developed gleyed vertisols, ineffective leaching is shown by the enrichment of Mg and retention of Ca within the profile relative to the parent material. Fluctuations of the Fe and Mn concentrations within single horizons suggests changing redox conditions as a result of alternating dry and waterlogged conditions. Pedogenic smectite-illite mixed layer clays and abundant slickensides within profiles are consistent with seasonal precipitation (Retallack, 2001).

Within incipient paleosols, abundant calcite nodules are present and occur scattered throughout the profile, which is indicative of formation under a monsoonal climate (Retallack, 1991). Petrographic analysis of the nodules reveals dissolution textures between nodule cores and the surrounding matrix, complex patterns of cracking, and multiple generations of cement, which are all likely related to alternating dry and waterlogged conditions.

Strong evidence for seasonality with respect to rainfall in the Goler Formation suggests similarities with other Paleogene formations in the western U.S. Previous research has attributed the seasonality of precipitation evident in the Paleogene formations of Wyoming and Utah to Laramide uplift (Norris et al, 2003;Retallack, 2005). Similarly, regional paleotopography surrounding the Goler Formation was likely an important control on precipitation.