2026-10-15T08:36:03Z https://oai.datacite.org/oai

doi:10.1594/pangaea.758202 2024-07-20T18:53:07Z PANGAEA PANGAEA.REPOSITORY

Element stratigraphy across the Cretaceous-Tertiary boundary in ODP Hole 119-738C Schmitz, Birger Asaro, Frank Michel, Helen V Thierstein, Hans R Huber, Brian T PANGAEA 1991 Issued: 1991 doi:10.2973/odp.proc.sr.119.166.1991 Drilling/drill rig Leg119 Joides Resolution Ocean Drilling Program (ODP) Neutron activation analyses of iridium and other chemical elements were performed across a 1-m-thick, partly nonbioturbated, clay-rich interval at the Cretaceous/Tertiary boundary in ODP Hole 738C. The results show that the boundary interval holds one of the highest Ir enrichments (320 ng Ir/cm2) of all known Cretaceous/Tertiary boundary layers. Iridium concentrations are highest (18 ppb Ir, whole-rock samples) a few centimeters above the base of the clayrich interval and gradually tail off upsection. Compared with background levels the most Ir-rich interval also shows strongly enhanced concentrations of Cr (215 ppm) and slightly elevated Co concentrations (13 ppm).The Ir-rich interval shows low As (< 15 ppm) and Sb (<0.8 ppm) concentrations, a fact that is congruent with absence of abundant authigenic sulfides in the sediment. Irregularly distributed Fe enrichments and a greenish gray color of the Fe-rich intervals may indicate the presence of glauconitic clay minerals and suboxic, slightly reducing conditions during deposition. Rare earth element (REE) abundance patterns change considerably across the Cretaceous/Tertiary boundary interval, reflecting either a change in Cretaceous/Tertiary boundary seawater REE composition or the occurrence of different REE fractionation processes due to changing depositional environment. Element-vs.-element ratios of Hf, Ta, Th, U, Cs, and Sc are similar between the most Ir-rich layers of the boundary section and other levels with lower Ir concentrations. This may imply that the clay fraction of the Ir-rich layers of the Cretaceous/Tertiary boundary interval is made up predominantly of locally derived material. Calculated calcite-free abundances of Hf, Ta, Th, U, Cs, and Sc, on the other hand, are reconcilable with an extraneous origin of the bulk of the clay in the most Ir-rich layers. The Ir in the Cretaceous/Tertiary boundary clay-rich zone in Hole 738C is most likely derived from an earth-impacting asteroid; however, the origin of the clay-rich zone remains enigmatic. Supplement to: Schmitz, Birger; Asaro, Frank; Michel, Helen V; Thierstein, Hans R; Huber, Brian T (1991): Element stratigraphy across the Cretaceous/Tertiary Boundary in Hole 738C. In: Barron, J; Larsen, B; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 119, 719-731 en Collection Supplementary Publication Series of Datasets application/zip Creative Commons Attribution 3.0 Unported https://creativecommons.org/licenses/by/3.0/legalcode