Biostratigraphy of a Paleocene-Eocene Foreland Basin boundary in southern Tibet

来源 :Geoscience Frontiers | 被引量 : 0次 | 上传用户:yushu522216869
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This study of the Paleocene—Eocene boundary within a foreland basin of southern Tibet, which was dominated by a carbonate ramp depositional environment,documents more complex environmental conditions than can be derived from studies of the deep oceanic environment.Extinction rates for larger foraminiferal species in the Zongpu-1 Section apply to up to 46%of the larger foraminiferal taxa. The extinction rate in southern Tibet is similar to rates elsewhere in the world,but it shows that the Paleocene fauna disappeared stepwise through the Late Paleocene,with Eocene taxa appearing abruptly above the boundary.A foraminifera turnover was identified between Members 3 and 4 of the Zongpu Formation—from the Miscellanea—Daviesina assemblage to an Orbitolites—Alveolina assemblage.The Paleocene and Eocene boundary is between the SBZ 4 and SBZ 5,where it is marked by the extinction of Miscellanea miscella and the first appearance of Alveolina ellipsodalis and a large number of Orbitolites. Chemostratigraphically,theδ~(13)C values from both the Zongpu-1 and Zongpu-2 Sections show three negative excursions in the transitional strata,one in Late Paleocene,one at the boundary,and one in the early Eocene.The second negative excursion ofδ~(13),which is located at the P—E boundary,coincides with larger foraminifera overturn.These faunal changes and the observedδ~(13)C negative excursions provide new evidence on environmental changes across the Paleocene—Eocene boundary in Tibet. This study of the Paleocene-Eocene boundary within a foreland basin of southern Tibet, which was dominated by a carbonate ramp depositional environment, documents more complex environmental conditions than can be derived from studies of the deep oceanic environment. Exposure rate for larger foraminiferal species in the Zongpu-1 Section apply to up to 46% of the larger foraminiferal taxa. The extinction rate in southern Tibet is similar to rates elsewhere in the world, but it shows that the Paleocene fauna disappeared stepwise through the Late Paleocene, with Eocene taxa appearing abruptly above the boundary. A foraminifera turnover was identified between Members 3 and 4 of the Zongpu Formation-from the Miscellanea-Daviesina assemblage to an Orbitolites-Alveolina assemblage. The Paleocene and Eocene boundary is between the SBZ 4 and SBZ 5, where it is marked by the extinction of Miscellanea miscella and the first appearance of Alveolina ellipsodalis and a large number of Orbitolites. Chemostratigraphically, the δ ~ (13) C values ​​from both the Zongpu-1 and Zongpu-2 Sections show three negative excursions in the transitional strata, one in Late Paleocene, one at the boundary, and one in the early Eocene. Second negative excursion of δ ~ (13), which is located at the P-E boundary, coincides with larger foraminifera overturn. These faunal changes and the observed δ ~ (13) C negative excursions provide new evidence on environmental changes across the Paleocene-Eocene boundary in Tibet.
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