LATE CRETACEOUS AND EARLY PALEOCENE PALEOSOL MORPHOLOGY AND GEOCHEMISTRY OF THE SOUTHWESTERN US

Late Cretaceous paleoclimate was warmer and more humid relative to the modern. However, million-year scale global cooling is inferred from proxy records from the Campanian–Maastrichtian. The long-term paleoclimate change, and effects on terrestrial ecosystems, were incontrovertibly interrupted by the K-Pg impactor, resulting in rapid climate effects in the Paleogene. This study addresses how the processes that acted on pre-extinction paleolandscapes affected the climate response of these environments in the aftermath of the K-Pg impact. The experimental design includes three study areas over a northwest-southeast trending region that ranges from 1,000–2,500 km from the impact site. Sedimentary strata preserved in the study region include Campanian and Campanian–Maastrichtian/Danian paralic facies and in-channel facies with associated overbank facies. The overbank facies are preserved and exposed over 10’s of km in a given field location and include: alluvial paleosols, lacustrine/palustrine deposits, and wetland facies (peat accumulating and non-accumulating). Colluvial paleosols occur locally in Maastrichtian strata of the Love Ranch Basin (New Mexico). The interplay of erosion, deposition, and pedogenesis broadly varied from erosion-dominated compound paleosol profiles in Campanian and Lower Maastrichtian strata to aggradational to composite profiles in Upper Maastrichtian strata. Composite, pedoegenesis-driven, paleosol profiles are observed immediately above the K-Pg boundary in the Tornillo Basin (Texas), which gradually change to aggradational paleosol profiles. Neosynthesis of minerals is broadly divided into iron mobilization in the northern Love Ranch and San Juan basins, and predominantly calcic in the Tornillo Basin. Clay synthesis and illuviation was predominant in the southern Love Ranch and Tornillo basins, where vertic properties developed in clay-rich subsurface horizons. Paleosol morphology, when controlled for landscape variability, indicates that the most prominent effects of the K-Pg impact were: 1) a decrease in chemical weathering; and 2) the balance of erosion and depositional processes in the study area. These observations likely reflect the combined influence of ecosystem restructuring of soil formation and depositional processes.