georefid:2003-052755SEDIS Publication Catalogue

ana.macario@awi.de

http://sedis.iodp.org/pub-catalogue/informationpointOfContact2011-06-23T00:00:00Zhttp://sedis.iodp.org/pub-catalogue/index.php?id=2003-0527552000-01-01publicationgeorefid:2003-052755Kelly, Daniel C.Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA, United StatesauthorZachos, James C.University of California at Santa Cruz, United StatesauthorNorris, Richard D.authorGeological Society of America (GSA), Boulder, CO, United StatespublisherdocumentHardcopyIn: Anonymous, Geological Society of America, 2000 annual meeting32 (7)299One of the more fascinating conundrums of the Oligocene epoch is its Braarudosphaera chalks and oozes. These unusual pelagic deposits have nannofloral diversities that are nearly monospecific, with braarudosphaerid nannofossils composing >90% of the sediment. Oxygen isotope analyses of bulk sediment from various braarudosphaerid layers in the southeastern Atlantic (DSDP Sites 363, 522, and 526) show increases ranging from 0.6 to 1.1 per mil over background values. Multi-species planktic foraminiferal isotope records spanning selected braarudosphaerid layers (DSDP Sites 363 and 526) indicate that sea surface temperatures decreased during braarudosphaerid blooms. This apparent cooling is seen in the oxygen isotopic values of both shallow, mixed layer- and deep, thermocline-dwelling species, although it is best expressed in the former group. We infer that the braarudosphaerid blooms are related to intervals of enhanced upwelling and overturning of surface waters. We note that braarudosphaerid "vital effects" and/or diagenesis have amplified the magnitude of the oxygen isotope increase seen in the bulk-isotope record. The Oligocene section recovered at DSDP Site 362 (southeastern Atlantic) exhibits a pronounced cyclicity with white braarudosphaerid chalk intercalated between layers of olive-gray, marly chalk. Spectral analysis of color records from selected cores yields a robust spectrum which resembles various components of Milankovitch cycles (e.g., obliquity and precession). This 100 meter thick section of "braarudosphaerid cycles" lies directly beneath the modern Benguela Current. We therefore postulate that the DSDP 362 deposits reflect orbitally-modulated variations in upwelling associated with the Benguela Current. Similar cyclic successions of braarudosphaerid layers have been found in the subtropics of the southwestern Atlantic. Hence, we speculate that braarudosphaerid blooms in the South Atlantic were triggered by orbitally-driven changes to surface water hydrography.completedStratigraphyIsotope geochemistryalgaeAtlantic OceanBenguela CurrentBraarudosphaeracarbonate rocksCenozoicchalkclastic sedimentscoolingcyclesDeep Sea Drilling ProjectdiagenesisDSDP Site 363DSDP Site 522DSDP Site 526ForaminiferaInvertebrataIPODisotope ratiosisotopesLeg 40Leg 73Leg 74microfossilsMilankovitch theorynannofossilsO-18/O-16OligoceneoozeoxygenPaleogenepaleotemperaturepelagic environmentPlantaeProtistasedimentary rockssedimentsSouth AtlanticSoutheast Atlanticspecies diversitystable isotopessubtropical environmentTertiarythermoclineupwellingvariationsurn:org.iodp:exp:40urnlargerWorkCitationcampaignurn:org.iodp:exp:73urnlargerWorkCitationcampaignurn:org.iodp:exp:74urnlargerWorkCitationcampaignurn:org.iodp:exp:40:site:363urnlargerWorkCitationstudyurn:org.iodp:exp:40urnlargerWorkCitationcampaignurn:org.iodp:exp:73:site:522urnlargerWorkCitationstudyurn:org.iodp:exp:73urnlargerWorkCitationcampaignurn:org.iodp:exp:74:site:526urnlargerWorkCitationstudyurn:org.iodp:exp:74urnlargerWorkCitationcampaignEnglishgeoscientificInformation-5.06479.0248-30.0724-19.3845