Citation:

odp.proc.sr.119.166.1991

Name: Element stratigraphy across the Cretaceous-Tertiary boundary in ODP Hole 119-738C
Published: 1991
License: https://creativecommons.org/licenses/by/3.0/

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Abstract:

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.

Project(s):

Ocean Drilling Program (ODP)

Coverage:

Latitude: -62.709000 * Longitude: 82.787800

Date/Time Start: 1988-01-11T18:45:00 * Date/Time End: 1988-01-17T05:00:00

Event(s):

119-738C * Latitude: -62.709000 * Longitude: 82.787800 * Date/Time Start: 1988-01-11T18:45:00 * Date/Time End: 1988-01-17T05:00:00 * Elevation: -2263.0 m * Penetration: 533.8 m * Recovery: 146.03 m * Location: Indian Ocean * Campaign: * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 35 cores; 337.2 m cored; 0 m drilled; 43.3 % recovery

License:

Creative Commons Attribution 3.0 Unported (CC-BY-3.0)

Size:

4 datasets

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Datasets listed in this publication series

Schmitz, B; Asaro, F; Michel, HV et al. (1991): (Table 1) Element analyses across the Cretaceous-Tertiary boundary in ODP Hole 119-738C. https://doi.org/10.1594/PANGAEA.758197
Schmitz, B; Asaro, F; Michel, HV et al. (1991): (Table 3) Average element concentrations in upper and lower laminated Cretaceous-Tertiary boundary intervals in OP Hole 119-738C. https://doi.org/10.1594/PANGAEA.758200
Schmitz, B; Asaro, F; Michel, HV et al. (1991): (Table 4) Possible abundance of extraneous component in the clay fraction of ODP Hole 119-738C. https://doi.org/10.1594/PANGAEA.758201
Schmitz, B; Asaro, F; Michel, HV et al. (1991): (Table 2) Rare earth element analyses across the Cretaceous-Tertiary boundary in ODP Hole 119-738C. https://doi.org/10.1594/PANGAEA.758199