Geologic, geomorphic, tectonic, and paleoclimatic controls on the distribution and preservation of Chicxulub distal ejecta: A global perspective

Abstract

The Cretaceous-Paleogene Boundary (KPB), the only known global impact ejecta layer, resulted from the Chicxulub Impact Event (66 Ma). KPB is well-documented across the different distal locations (paleodistances >5000 km), yet an understanding on the preservation of KPB remains evasive. Identification of the different preservation controls is thus quintessential, especially when the distal KPB maintains a constant thickness of 2–5 mm globally. We evaluate 84 distal KPB sites (as exposed on land today) through review and assessment of different parameters. The parameters include current geological provinces, nearest active tectonic boundary, geomorphic setting, lithological associations, paleoposition (at 66 Ma), paleodistance from impact point (at 66 Ma), paleoclimate and paleobathymetry. The most common geological province, closest plate boundary type and geomorphic setting are accretionary complex (43 sites), collisional boundary (53 sites) and bedrock mountain (35 sites), respectively. KPB layer manifests in different lithologies, but most commonly in clay, marl, clay-limestone, and clay-marl dominant litho-units. At 66 Ma, 68 KPB deposited in marine settings, meanwhile only 16 in terrestrial conditions. Cenozoic paleobathymetry depicts the increased exposure of KPB sites to non-marine settings as time progresses (Paleocene-Holocene). During Cenozoic, the warm temperate climate remains the dominant climate across majority of the distal KPB sites. Evaluation of the different parameters leads to the conclusion that the preservation of KPB is aided by deposition within sedimentary basins in marine conditions during early Paleocene, presence of thick sedimentary units overlying KPB and dominance of low-denudational climates (warm temperate/subtropical arid) during Cenozoic. Furthermore, the study weighs the Chicxulub ejecta transport mechanisms by assessing the different chemical (Ir-anomaly, boundary clay) and physical attributes (impact spherules, shocked minerals, Ni-rich spinels) at KPB. The observations support the dust cloud (non-ballistic) model of ejecta transportation and emplacement over the ballistic ejecta plume model.