Program > By author > Huber Brian T.

The response of biota and the paleoceanographic conditions at high latitudes are investigated across the Cenomanian/Turonian boundary interval characterized by the Oceanic Anoxic Event 2 (OAE 2), an episode of major perturbations in the global carbon cycle. We present data from Integrated Ocean Discovery Program (IODP) Sites U1513 and U1516 drilled in the Mentelle Basin (Indian Ocean, offshore SW Australia, paleolatitude 59°-60° S in the mid-Cretaceous).

The correlation between the stable isotopic data and the integrated calcareous plankton biostratigraphy with the reference section at Eastbourne (UK) indicates that a complete record of OAE 2 was recovered at southern high latitudes. The distribution and variations in abundance of planktonic and benthic foraminifera, radiolaria, and calcipheres and their paleoecological preferences permit interpretation of the dynamics of the water mass stratification, and provide support for the paleobathymetric reconstruction of the two sites, with Site U1513 located northwest of the Mentelle Basin depocenter and at a deeper depth than Site U1516.

The lower OAE 2 interval is characterized by reduced water mass stratification with alternating episodes of enhanced surface water productivity and variations of the thickness of the mixed layer. Lithologies in the middle OAE 2 interval are almost entirely composed of radiolaria reflecting extremely high marine productivity and the low CaCO3 content is consistent with marked shoaling of the CCD which resulted from the emission of volcanogenic CO2 from the Kerguelen Plateau Large Igneous Province making waters more corrosive.

Conditions moderate after this extreme perturbation as reflected by the microfossil changes indicating a likely stable water column that was apparently more stable at Site U1513 than at Site U1516 where episodes of enhanced eutrophy continue into the lower Turonian. At both sites the termination of OAE 2 does not correspond to modifications in the microfossils assemblages; rather, they maintain the same features observed in the underlying interval.

Overall, this study provides a complete record of the paleoceanographic changes registered by the microfossil biota for understanding the causes and consequences of the paleoenvironmental perturbations associated to the OAE 2 at southern high latitudes.