GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 223-2
Presentation Time: 1:45 PM


ERBA, Elisabetta and BOTTINI, Cinzia, Dept. Earth Sciences, Università degli Studi di Milano, Via Mangiagalli 34, Milan, 20133, Italy,

The Cretaceous was characterized by intervals of super-greenhouse climate and profound environmental perturbations, including Oceanic Anoxic Events (OAE)s being episodes of widespread organic matter burial in oxygen-depleted oceans. The early Aptian OAE 1a is thought to be related to the emplacement of the Ontong Java Plateau (OJP) which probably introduced in the atmosphere a large amount of CO2 with consequent impact on biota, global warming and ocean chemistry. The formation of the Kerguelen Plateau in the late Aptian is, conversely, associated to a prolonged cooling coeval with enhanced atmospheric CO2.

We quantified biogenic carbonate production of calcareous nannoplankton and reconstructed environmental stress influencing biocalcification. Laboratory experiments on coccolithophores indicate that coccolith type, abundance and degree of mineralization depend on chemical-physical-trophic conditions of seawater as well as on pCO2. Dwarf/malformed coccoliths were documented during OAE 1a and interpreted as the species-specific response to surface-water acidification under excess CO2. A remarkable crisis in nannofossil calcite production correlates with OAE 1a, when highest CO2 concentrations of the Aptian were reached under the most intense phase of OJP construction. During the late Aptian, nannofossil calcite fluxes were characterized by fluctuations, suggestive for variable paleoCO2. An interval of lower CO2 concentrations corresponds to the late Aptian N. truittii Acme that presumably testifies lowered enough values to promote a larger proliferation of nannoconids. In the latest Aptian, further injections of CO2 lead to the final collapse of nannoconids and suppressed nannofossil paleofluxes.

In the Aptian, nannoplankton biocalcification was ruled by complex ocean/atmosphere dynamics resulting from the balance between phases of volcanic emissions and CO2 uptake via ocean adsorption, weathering and organic matter burial.