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Taxonomy and paleoecology of late Neogene benthic foraminifera from the Caribbean Sea and eastern equatorial Pacific Ocean.

Journal article
Authors Lennart Bornmalm
Published in Fossils and Strata
Volume 41
Pages 1-96
ISSN 0300-9491
Publication year 1997
Published at Department of Earth Sciences
Pages 1-96
Language en
Links https://foreninger.uio.no/ngf/FOS/p...
Keywords Benthic Foraminifera, Pliocene, Caribbean Sea, Eastern equatorial Pacific Ocean, DSDP sites 502 and 503
Subject categories History of geology and palaeontology

Abstract

Benthic foraminifera ( l47 taxa) were investigated from the Caribbean Sea (Deep Sea Drilling Project; DSDP Hole 502A, depth 3,05 1 m) and eastern equatorial Pacific Ocean (DSDP Hole 503B, 3,672 m) over an interval between the terminal Miocene and the basal Pleistocene (5.5- 1.7 Ma). To determine the influence over time of the Central American Isthmus (closure of the Isthmus of Panama occurring some time between 3.5 and 3.0 Ma) on the benthic fauna, the composition and diversity of the fauna as well as many physico-chemical variables were considered. The latter include changes in coarse-fraction (>63 �m), calcite dissolution (estimated from the degree of fragmentation of planktic foraminifera), accumulation rates of benthic foraminifera (BFAR, used as an index of the flux of organic matter to the sea floor) , CaC03 content, and stable isotopes in planktic and benthic foraminifera. In the Caribbean Hole 502A, the 0180 of planktic foraminifera increased at about 4.2 Ma relative to the benthic values and also relative to the planktic and benthic values in the Pacific Hole 503. This change may reflect increasing surface-water salinity in the Caribbean Sea as a result of restricted surface-water exchange between the Atlantic and Pacific caused by the emergent Panama Isthmus. Most of the physico-chemical va ria bles in Hole 502A have similar trends to those in the Pacific Hole 503 between late Miocene and 3.85 Ma. After that, Hole 503 continued to show a typical equatorial Pacific character, whereas Hole 502A was affected by local tectonics and bottom-water exchange between Caribbean Sea and the Atlantic. The increased BFAR at 3.85 Ma in Hole 502A may indicate increased productivity of the sur face water in the Caribbean Sea, but it could als o be a result of a decrease in dissolution and intensified ventilation of the bottom water. The increased 0180 and ol3C values in the benthic foraminifer record, increased coarse-fraction CaC03 content, as well as decreased fragmentation of planktic foraminifera are probably related to greater inflow ofUpper North Atlantic Deep Water (UNADW) to the Caribbean Sea since 3.85 Ma, most likely initiated by increased northward transport of warm, high-salinity waters to high latitudes via the Gulf Stream, which in turn was caused by progressive uplift of the Central American land bridge. The fluctuations in the physico-chemical parameters in Hole 503 are overall iarger than in Hole 502A, which probably is a result of dissolution signals caused by vertical oscillations of the Iysocline in Hole 503 because of the deeper location of this site. The increased planktic and benthic foraminifer oxygen isotope values from 3.2 Ma in Hole 503 probably reflect oceanographic and c1imatic changes in the Antarctic area from this time. Qmode principal component analysis on benthic foraminifer abundances (accumulation rates of selected species) distinguished two major faunal groups in both Hole 502A and Hole 503. Nuttallides umbonifera is the most abundant species and makes up one group, while the other group is made up of both Cibicidoides wuellerstorfi and Oridorsalis umbonatus in Hole 502A, and only o. umbonatus in Hole 503. In Hole 502A C. wuellerstorfi and o. umbonatus are abundant in the interval between 4.2 and 3.7 Ma. From about 3.7 Ma N. umbonifera increased and became the most abundant benthic species. In Hole 503 N. umbonifera was the most abundant species between 4.8 and 2.1 Ma, except for a few intervals where O. umbonifera was more frequent. These changes in the abundance of N. umbonifera may be due to (I) changes in volurne of different water masses, (2) changes in productivity, and/or (3) a transitory shift in an environmental preference of N. umbonifera. However, in both Hoies 502A and 503 there is no significant correlation among dissolution, CaC03 content, BFAR, and the variation in the abundance of N. umbonifera. DBenthic foraminifera, biostratigraphy, paleoecology, paleoceanography, late Neogene, Isthmus of Panama, Deep Sea Drilling Project, DSDP Sites 502 and 503, Caribbean Sea, Colombia Basin, eastern equatorial Pacific Ocean, Guatemala Basin.

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