Stable isotopes on foraminifera and ostracods for interpreting incidence of the Toarcian Oceanic Anoxic Event in Westernmost Tethys: Role of water stagnation and productivity

作者：Reolid Matias^*

来源：Palaeogeography, Palaeoclimatology, Palaeoecology, 2014, 395: 77-91.

DOI：10.1016/j.palaeo.2013.12.012

• Lagenina
• Vital effect
• Microhabitat effect
• Isotopic excursion
• Redox conditions
• Lower Jurassic

The analysis of delta C-13 and delta O-18 from whole rock and the shells of selected foraminifera (Lenticulina and Dentalina) and bairdioid ostracods from Lower Toarcian of the South Iberian Palaeomargin (Western Tethys) is presented with the aim of improving knowledge of the processes and the environmental effects of the Toarcian Oceanic Anoxic Event. In addition, isotopic data are compared with geochemical redox and palaeoproductivity proxies. The microhabitat affected delta C-13 values, delta C-13(Lenticulina) generally being lower than delta C-13(Dentalina) due to more depleted C-13 values for sediment pore-water in the deep infaunal microhabitat The lowest values of delta C-13 (lower part of Serpentinum Zone) happen during suboxic conditions, as indicated by redox proxies, low diversity and abundance of foraminifera and higher TOC values. The fine-grained, organic rich sediments allow for conditions favouring pore-water dissolved inorganic carbon that is depleted in C-13 with respect to that of the bottom sea-water, particularly during the suboxic conditions. The delta C-13 of potential deep infauna (Lenticulina) reflects the oxygen restricted conditions better than shallow infauna (Dentalina) and whole sediment. Regarding delta O-18, values from bulk rock present stronger fluctuations and lower values than delta O-18(Dentalina) and delta O-18(Lenticulina). The stratigraphic differences between delta O-18(Dentalina) and delta O-18(Lenticulina) correspond to vital effects, since no important fluctuations in temperature occurred in the bottom sea-water, as deduced from the absence of peaks and stratigraphic trends in the interval studied. The delta O-18 values do not allow us to infer temperature changes related to the Toarcian Oceanic Anoxic Event in this part of the palaeomargin.

• 出版日期2014-2-1