LATE SANTONIAN−CAMPANIAN PALEOSOLS FROM SOUTHWEST UTAH: IMPLICATIONS FOR WEATHERING AND PALEOCLIMATE

The greenhouse climate of the Late Cretaceous is generally considered to be consistently warm and wet, with abundant carbon burial in both terrestrial and marine environments. Significant research has been devoted to understanding the Cretaceous environment in the marine realm, while relatively less work has focused on understanding the heterogeneity of presumably warm and wet terrestrial environments at this time. These terrestrial environments are intimately linked to proximal marine environments as they provide a source of nutrients that can potentially enhance primary productivity and subsequently organic carbon burial and freshwater runoff that can stratify.

This study will focus on rocks deposited in SW Utah dating to the Late Santonian−Campanian, when the Sevier Mountains were being uplifted to the west and the Western Interior Seaway (WIS) was sustaining elevated organic carbon burial to the east. Here we present bulk whole-rock geochemistry data from paleosols found within the late Santonian John Henry Member of the Straight Cliffs Formation and the early Campanian Wahweap and Iron Springs Formations. This data will be used to evaluate the hypotheses that (a) terrestrial environments in Utah were consistently warm and wet during the Late Cretaceous and (b) chemical weathering remained sufficiently high to provide a sustained source of nutrients to the highly productive WIS. Initial geochemical results indicate that paleosols from the Wahweap and Iron Springs Formation (avg. CIA = 77) are more weathered than those of the Straight Cliffs Formation (avg. CIA = 71), even though all three Formations likely had a similar provenance. Comparing paleosols from the Wahweap Formation to those of the Iron Springs Formation will also allow us to examine whether paleosols of a roughly similar age and geographic setting preserve similar geochemical weathering profiles across different depositional environments. The Iron Springs paleosols were deposited on a sandy braidplain, while the Wahweap represents a more distal alluvial floodplain. The sandier paleosols of the Iron Springs are slightly less developed and produce lower climofunction derived precipitation estimates, suggesting a potential depositional setting bias for higher versus lower energy environments.