Late Eocene to Holocene Diatom Biostratigraphy of the Equatorial Pacific Ocean, Deep Sea Drilling Project Leg 85

Excellent reference sections for lower Oligocene through Holocene diatoms were recovered at DSDP Sites 572 to 575 in the central equatorial Pacific. Diatoms are generally common and well preserved at all sites, except in the upper Oligocene. These sections are zoned and correlated on the basis of diatoms, including the identification and correlation of 89 additional secondary datum levels in the Miocene and Pliocene. Paleomagnetic stratigraphy was obtained for the entire Denticulopsis nicobarica Zone (17.8 to 16.4 Ma) at Site 575, and upper lower Miocene diatom datum levels are correlated directly to paleomagnetic stratigraphy for the first time. Quantitative diatom studies of upper lower Miocene to uppermost Miocene (18.0 to 6.2 Ma) of Sites 572, 574, and 575 are supplemented by quantitative diatom studies at Sites 77 and 158 to form transects across the central and eastern equatorial Pacific. Where the sampling interval is 100,000 yr. or less, quantitative trends in Cestodiscuspulchellus, Coscinodiscus radiatus, Denticulopsis hustedtii, D. nicobarica, and Thalassiothrix longissima are readily correctable, thereby greatly enhancing biostratigraphic resolution. Comparison of species abundance reveals minor differences between the eastern and central equatorial Pacific. Thalassionema nitzschioides, D. hustedtii, and D. nicobarica show preferences for the eastern equatorial Pacific, whereas C. pulchellus, Actinocyclus ellipticus, Coscinodiscus tuberculatus, and Nitzschia spp. seem to prefer the central equatorial Pacific. Five new diatom taxa are proposed: Actinocyclus ellipticus var. spiralis Barron, n. var., Coscinodiscus lewisianus van rhomboides Barron, n. var., C. loeblichii Barron, n. sp., C. yabei var. ellipticus Barron, n. var., and Thalassiosira tappanae Barron, n. sp.