Tremolada, Fabrizio; Erba, Elisabetta; Bralower, Timothy J. (2007): A review of calcareous nannofossil changes during the early Aptian oceanic anoxic event 1a and the Paleocene-Eocene thermal maximum; the influence of fertility, temperature, and pCO (sub 2). Geological Society of America (GSA), Boulder, CO, United States, In: Monechi, Simonetta (editor), Coccioni, Rodolfo (editor), Rampino, Michael R. (editor), Large ecosystem perturbations; causes and consequences, 424, 87-96, georefid:2007-111303

Abstract:

The comparison between calcareous nannofossils during the early Aptian Oceanic Anoxic Event 1a (OAE1a) and the Paleocene-Eocene Thermal Maximum (PETM) suggests different nannofloral reactions to extreme greenhouse conditions. Both events were likely characterized by major changes in nutrient concentrations, temperature, and pCO (sub 2) levels. OAE1a corresponds to an increase in opportunistic taxa associated with eutrophic surface-water conditions. Eutrophy also resulted in the demise of an oligotrophic group, the nannoconids. Nannofloral assemblages of the PETM interval suggest nutrient-depleted surface waters at open-ocean sites including those at high and low latitudes. However, the upper part of the PETM shows a return to mesotrophic conditions documented by the increase in abundance of mesotrophic taxa. PETM records from shelf sites are characterized by an increase in nannofossil taxa indicative of mesotrophic conditions, suggesting an increase in productivity. Fluctuations in primary productivity affected composition and abundance of calcareous nannofossil assemblages during both events. Whereas fertility increased in the global ocean during OAE1a, mesotrophic conditions mostly characterized proximal settings during the PETM. Nannofloral changes could have been partially triggered by the warming, but the influence of high pCO (sub 2) levels is not evident. Reductions in nannofossil calcification and paleofluxes are associated with the OAE1a, but the role of pCO (sub 2) variations in nannofloral calcification during the PETM is not obvious. In both events, variations in lysocline/CCD depth and enhanced dissolution and/or diagenesis strongly affected nannofossil assemblages in some locations, but the overall nannofloral changes reveal a primary paleoecological and paleoceanographic signal.

Coverage:

West: -179.3321 East: 158.1200 North: 36.0800 South: -65.0938

Relations:

Expedition: 113

Site: 113-690

Expedition: 143

Site: 143-865

Expedition: 165

Site: 165-1000

Site: 165-1001

Site: 165-999

Expedition: 171A