Shallow water facies during the Cenomanian-Turonian anoxic event: bio-events, isotopes, and sea level in southern Germany

Abstract

The sediments, palynofacies, macrofossils, planktic and benthic foraminifera, radiolaria, ostracoda, stable carbon and oxygen isotopes (whole rock and inoceramid prisms) of the hemipelagic Eibrunn Marls at the northern Tethys margin were studied in the Mühlberg section of the Regensburg area, southern Germany. The biotas reveal extinction and origination events that are known elsewhere, although other species may be involved. The palaeontological evidence suggests a control of global changes on the biotas (macroevolutionary impact of the Oceanic Anoxic Event), rather than changes in the local environmental conditions. Carbon isotopes of inoceramid prisms do not reflect the standard isotope stratigraphy; differences in vital effects between Inoceramusand Mytiloidesprobably dominate the isotopic composition. Ridge facies (conglomerates, cliffs, erosional platforms) in Saxony (southeastern Germany) provide evidence of the timing of sea-level changes. The ∂ 1 3C values increase through the section representing a late Cenomanian, long-term sea-level rise, and have a maximum when widespread flooding occurs. Marine erosion (nutrient mobilization) during a long-term sea-level highstand that exceeded previous highstands may have supported higher productivity during the Cenomanian-Turonian Oceanic Anoxic Event, and potentially during other widespread anoxic events in the Mesozoic. Organic matter remineralization may have lead to more acidic bottom waters that reduced carbonate preservation, and amplified the ∂ 1 3C excursion through carbonate dissolution.