Coccoliths from the Cretaceous-Tertiary boundary of the Walvis Ridge, South Atlantic : biostratigraphic and paleoecological implications /
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| Other Authors: | , , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1989.
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| Subjects: | |
| Online Access: | ProQuest, Abstract Link to OAKTrust copy |
| Abstract: | Biostratigraphy, diversity, and oxygen and carbon isotopes are determined for calcareous nannoplankton from four sections of Cretaceous-Tertiary boundary interval sediments on Walvis Ridge in the South Atlantic (DSDP Sites 525A, 527, 528, and 529). Biostratigraphy and diversity determinations were made on 177 samples and stable isotope ratios for oxygen and carbon were measured on the coccolith fraction of 140 samples. The interval examined extends from the Maastrichtian Reinhardtites levis Zone (74.5 m.y.) to the Paleocene Discoaster mohleri Zone (60.6 m.y.). A drastic change in δ[^13]C ratios (1.4[ppt]) was recorded at Site 525A in a 1.62 m interval across the Cretaceous-Tertiary boundary that was not sampled. A more gradual decrease in signals occurs at Sites 527, 528, and 529, where more closely spaced samples were analyzed. The gradual decrease in δ[^13]C values above the Cretaceous-Tertiary boundary is related to the progressive decrease of the proportion of deposited Cretaceous species in the sample. The decrease in the δ[^13]C signal across the boundary is interpreted as a decrease in primary productivity. Evaluation of the shift of δ[^13]C values in relation to the proportion of redeposited species in early Tertiary samples at Sites 527 and 529 indicates that Cretaceous species did not survived into the Paleocene. Diversity calculated using the Shannon-Weaver equation decreased by 1.8 at Site 525A which is the shallowest location. The average decrease at Sites 527, 528, and 529 was 1.1. These decreases reflect the massive plankton extinctions at the Cretaceous-Tertiary boundary. The carbon isotope and diversity curves correlate across the Cretaceous-Tertiary transition. Diversity recovered in approximately 1.6 m.y.; however, the δ[^13]C signal recovered only some 5 m.y. after the boundary event and, thus lagged biotic recovery by a significant length of time. The paleontological record at the four Walvis Ridge sites indicates that the nannoflora does not record any significant stress or event preceding the massive extinction at the boundary, where the calcareous nannoplankton show an almost total and instant extinction... |
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| Item Description: | Typescript (photocopy). Part of illustrative matter folded in back pocket. Vita. "Major subject: Oceanography." |
| Physical Description: | xiv, 195 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |