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Changes in Miocene deep-sea benthic foraminiferal distribution in the Pacific Ocean: Relationship to paleoceanography

Fay Woodruff
Fay Woodruff
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January 01, 1985

This paper reports the results of a detailed analysis of 25 Miocene Pacific Deep Sea Drilling Project (DSDP), sites at which 110 benthic foraminiferal species in 255 DSDP samples were quantified. The sites range in depth from 1.5 to 4.5 km between 45 degrees north and south latitudes. The faunal distributions were studied for many Pacific Ocean sites at different water depths through time; diagrams depicting both areal and water depth distributions are presented.

Miocene deep-sea benthic foraminifera form clear distribution patterns. Some species appear to have reacted to changes in water mass quality; others appear to reflect changes in food availability and sample preservation resulting from changes in surface productivity related to paleoceanographic change.

Many changes in faunal distribution, as well as evolutionary originations and extinctions, occurred between 13 and 16 Ma, concomitant with paleoclimatic and oceanographic changes presumably related to Antarctic glacier expansion and cooling of the deep Pacific Ocean. Late Miocene faunal changes between 8 and 10 Ma were primarily changes in species abundances and depth distribution which appear to be related to the effects of further Antarctic glaciation.

The oxygen isotopic record for most of the faunal samples is shown for different water depths through time. The data show clear isotopic changes 14.5 Ma and 8-10 Ma, concurrent with many changes in the foraminiferal distribution patterns.

A new species, Cibicidoides cenop n. sp. is named (Appendix I). It evolved in the early Miocene and is apparently an indicator of cold-water conditions in the Miocene Pacific Ocean.

The benthic foraminiferal data are compatible with the following paleoceanographic interpretations: (1) a warm early Miocene deep ocean with a less well-developed surface-to-bottom thermal-gradient that in mid-late Miocene time; 2) an increase in ocean margin surface productivity after 16 Ma related to intensification of atmospheric-oceanic circulation and upwelling; 3) a change in the deep ocean water mass after 15 Ma, including a cooling and a shallowing of deep-ocean conditions related to permanent establishment of the Antarctic ice sheet; 4) an increase in surface productivity along the equator after 15 Ma, related to intensification of the latitudinal thermal gradient, more vigorous deep-ocean circulation and perhaps establishment of the Equatorial Counter-current and Undercurrent systems; 5) an increase in sediment organic carbon and intensification of the low oxygen zone after 8-10 Ma as well as an increase in deep-ocean dissolution and Antarctic bottom water influence related to further Antarctic ice sheet expansion in latest Miocene time; and 6) a deep water corridor across the Indo-Pacific until at least 21 Ma.

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GSA Memoirs

The Miocene Ocean: Paleoceanography and Biogeography

James P. Kennett
James P. Kennett
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Geological Society of America
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Publication date:
January 01, 1985




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