| Abstract: | For a long time the early Albian OAE 1b was among those Oceanic Anoxic Events we had comparably little knowledge of. Recent high resolution studies of multiple proxies from sections in France and DSDP/ODP sites from the Atlantic resulted in a new and comprehensive picture of this interval. OAE 1b was described from various Tethyan sections including well-known regional marker beds in the Vocontian Basin (Niveau Paquier) and the Umbria-Marche Basin (Livello Urbino). So far, no well-dated occurrences of OAE 1b are known from successions outside the Tethyan realm.
Based on various studies from the Vocontian Basin, the Blake Nose and Mazagan Plateau, we will present a review of these multiple proxy investigations which included planktic and benthic foraminifera, calcareous nannoplankton, palynology, and stable carbon and oxygen isotopes.
Time series analyses from the Vocontian Basin and the Blake Nose Plateau demonstrate that orbital forcing mechanisms probably controlled anoxia and suggest a ~45 kyr duration for OAE 1b. Moreover, they indicate orbital forcing of palaeoproductivity and -temperature, with a dominant precessional signal for surface-water productivity and a dominance of the eccentricity signal for changes in surface-water temperature.
Stable oxygen isotope gradients between benthic and planktic foraminifera, calcareous nannoplankton and palynology suggest a temperature increase at the base of OAE 1b, followed by an increased continental runoff and an pronounced thermohaline stratification during the anoxic interval. Such a scenario implies warm and humid climates prevailing during the OAE 1b.
Whether or not our observations support the Quaternary sapropel model suggested by Erbacher et al. (2001) or a model that favorites monsoonal activity and eccentricity-driven temperature changes as the driving mechanisms for OAE 1b (Herrle et al., in press) remains to be discussed. However, our results clearly demonstrate the great variability of causes for Cretaceous Oceanic Anoxic Events and the need for more, globally distributed high resolution multiple proxy studies of hopefully diagenetically uncompromised sections.
Erbacher, J., Huber, B.T., Norris, R., Markey, M. (2001): Intensified thermohaline stratification - a possible cause for Cretaceous oceanic anoxic events. Nature, 409, 325-327.
Herrle, J.O, Pross, J., Friedrich, O., Hemleben, Ch. (in press): Short-term environmental changes in the Cretaceous Tethyan Ocean: Micropalaeontological evidence from the Early Albian Oceanic Anoxic Event 1b. Terra Nova. |