Element stratigraphy across the Cretaceous-Tertiary boundary in ODP Hole 119-738C
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| Format: | Dataset Open Access |
| Sprache: | en |
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PANGAEA
1991
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| _version_ | 1867171361142603776 |
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| author | Schmitz, Birger Asaro, Frank Michel, Helen V Thierstein, Hans R Huber, Brian T |
| author_facet | Schmitz, Birger Asaro, Frank Michel, Helen V Thierstein, Hans R Huber, Brian T |
| collection | Datos científicos de ciencias marinas y ambientales |
| contents | 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. |
| format | Dataset Open Access |
| id | pangaea_https___doi_org_10_1594_PANGAEA_758202 |
| institution | PANGAEA |
| language | en |
| publishDate | 1991 |
| publisher | PANGAEA |
| record_format | pangaea |
| spellingShingle | 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 119-738C; DRILL; Drilling/drill rig; Indian Ocean; Joides Resolution; Leg119; 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. |
| title | Element stratigraphy across the Cretaceous-Tertiary boundary in ODP Hole 119-738C |
| topic | 119-738C; DRILL; Drilling/drill rig; Indian Ocean; Joides Resolution; Leg119; Ocean Drilling Program; ODP |
| url | https://doi.org/10.1594/PANGAEA.758202 |