DIATOM BIOSTRATIGRAPHIC AND PALEOCEANOGRAPHIC STUDIES OF NEOGENE MATERIAL RECOVERED FROM THE NORTH ATLANTIC AND EQUATORIAL PACIFIC OCEANS (ROCKALL PLATEAU, DIATOM TAXONOMY

Diatoms are useful for biostratigraphic correlation of Neogene through Quaternary sediments in the North Atlantic Ocean.;The Pliocene and Quaternary diatom datums are correlated directly with the paleomagnetic stratigraphy of DSDP Legs 81 and 94. This correlation allows the isochroneity of late Neogene and Quaternary events to be tested between the Atlantic and Pacific Oceans.;Quantitative procedures are used at DSDP Sites 572, 573, and 503 to refine the stratigraphic resolution for the upper Neogene sediment of the eastern equatorial Pacific Ocean. As a result, six additional secondary datums are defined for the stratigraphic interval 6.2 to 1.5 Ma.;Diatoms are also used to infer paleoceanographic conditions. The diatom assemblage indicates that surface waters were warm during the early Miocene in the Rockall Plateau region. A change in the quality of diatom preservation and the occurrence of numerous hiatuses at approximately the early/middle Miocene boundary suggests a major change in oceanic circulation. The lower middle Miocene interval typically contains common, moderate to well-preserved diatoms suggesting silica enriched surface waters within the Rockall region.;Siliceous sedimentation returned to the middle latitudes of the North Atlantic during the late Pliocene, possibly in response to increased intensity of the Gulf Stream current. The abundance and preservation of diatoms in Quaternary sediment at the high-latitude is partially controlled by climatic fluctuation. The occurrence of the Denticulopsis seminae group at several DSDP Leg 94 sites in the middle Quaternary suggests that open communication may have existed between the North Atlantic Ocean and the Bering Sea.;Within the equatorial Pacific Ocean, the greater abundance of Coscinodiscus nodulifer at Site 503 compared with Sites 572 and 573 suggests that this species is associated with equatorial upwelling in the easternmost equatorial Pacific Ocean. The greater abundance of Thalassionema nitzschioides at Site 572 suggests that this species is associated with the Equatorial Undercurrent. Furthermore, the gradual decline in the abundance of T. nitzschioides between 4.2 and 3.7 Ma at Sites 572 and 503 may have resulted from the restriction in surface water communication between the Atlantic and Pacific as a result of the emergence of the Isthmus of Panama. (Abstract shortened with permission of author.).