EARLY PALEOCENE TEMPERATURE AND PRECIPITATION ESTIMATES FROM PALEOSOLS AT KIMBETO WASH, SAN JUAN BASIN, NEW MEXICO, U.S.A

The early Paleocene Nacimiento Formation at Kimbeto Wash, New Mexico (western San Juan Basin [SJB]), preserves laterally-continuous paleosols exhibiting vertic properties. We present estimates of Danian (Puercan/early Torrejonian NALMA; ~64 Ma) mean annual paleotemperature (MAT) and mean annual paleoprecipitation (MAP) garnered from these paleosols using XRF analysis and geochemical constitutive mass balance calculations on pedogenically altered horizons from the mudstone strata of the Nacimiento Formation. These estimates are the among the first gathered from Nacimiento Formation paleosols from throughout the San Juan Basin and will aid in a basin-scale understanding of Paleogene climate conditions and change. In addition, these estimates will supplement ongoing research on Paleocene climate change in the San Juan Basin and its effects on faunal and floral diversity. Our paleosol-derived climate estimates demonstrate a unique proxy for Paleocene San Juan Basin climate in that they likely result from 10²-10⁴ years of pedogenesis and therefore represent a long-term average of climate conditions and are less likely representative of seasonal variations or biases common in some proxies. This study also begins an investigation of the paleopedology of the SJB’s Paleogene units and the paradoxical presence of vertic paleosols in a paleoenvironment seemingly more conducive to the formation of more highly-weathered, horizonated, and base-poor soils (e.g. ultisols).