&amp;quot;OAE 3&amp;quot; – regional Atlantic organic carbon burial during the Coniacian–Santonian

M Wagreich

doi:10.5194/cp-8-1447-2012

Abstract

Abstract. The Coniacian–Santonian time interval is the inferred time of oceanic anoxic event 3 (OAE 3), the last of the Cretaceous OAEs. A detailed look on the temporal and spatial distribution of organic-rich deposits attributed to OAE 3 suggests that black shale occurrences are restricted to the equatorial to mid-latitudinal Atlantic and adjacent basins, shelves and epicontinental seas like parts of the Caribbean, the Maracaibo Basin and the Western Interior Basin, and are largely absent in the Tethys, the North Atlantic, the southern South Atlantic, and the Pacific. Here, oxic bottom waters prevailed as indicated by the widespread occurrence of red deep-marine CORBs (Cretaceous Oceanic Red Beds). Widespread CORB sedimentation started during the Turonian after Oceanic Anoxic Event 2 (OAE 2) except in the Atlantic realm where organic-rich strata continue up to the Santonian. The temporal distribution of black shales attributed to OAE 3 indicates that organic-rich strata do not define a single and distinct short-time event, but are distributed over a longer time span and occur in different basins during different times. This suggests intermittent and regional anoxic conditions from the Coniacian to the Santonian. A comparison of time-correlated high-resolution δ13C curves for this interval indicates several minor positive excursions of up to 0.5‰, probably as a result of massive organic carbon burial cycles in the Atlantic. Regional wind-induced upwelling and restricted deep basins may have contributed to the development of anoxia during a time interval of widespread oxic conditions, thus highlighting the regional character of inferred OAE 3 as regional Atlantic event(s).

Highlights

Oceanic anoxic events (OAEs; Schlanger and Jenkyns, 1976) have been recognized in the geological record, especially in Cretaceous marine sections, as climatically influenced major perturbations of the Earth system, especially concerning Earth’s carbon cycle. These events were characterized by the widespread deposition of pelagic sediments rich in organic matter such as black shales, and are considered as key mechanisms for organic carbon burial and, in such, buffering Cretaceous runaway super-greenhouse gas (e.g. Arthur et al, 1990)
During the last three decades of intensive investigations in Cretaceous OAEs, it became clear that not all OAEs (OAE 1a, 1b, 1c, 1d, Oceanic Anoxic Event 2 (OAE 2), oceanic anoxic event 3 (OAE 3); see Arthur and Schlanger, 1979; Jenkyns, 1980, 2003) record similar scenarios, and more regional controls and several models have been suggested
Looking for published case studies on typical Coniacian– Santonian OAE 3 strata indicates the fact that such studies are relatively rare, especially if compared to numerous works dedicated to the slightly older Cenomanian–Turonian boundary interval OAE 2

Summary

Introduction

Oceanic anoxic events (OAEs; Schlanger and Jenkyns, 1976) have been recognized in the geological record, especially in Cretaceous marine sections, as climatically influenced major perturbations of the Earth system, especially concerning Earth’s carbon cycle. These events were characterized by the widespread deposition of pelagic sediments rich in organic matter such as black shales, and are considered as key mechanisms for organic carbon burial and, in such, buffering Cretaceous runaway super-greenhouse gas Significant positive δ13C excursions are mainly controlled by enhanced burial of organic carbon-rich deposits and characterize and define OAEs, especially in the absence of significant black shales During the last three decades of intensive investigations in Cretaceous OAEs, it became clear that not all OAEs (OAE 1a, 1b, 1c, 1d, OAE 2, OAE 3; see Arthur and Schlanger, 1979; Jenkyns, 1980, 2003) record similar scenarios, and more regional controls and several models have been suggested

Results

Discussion

Conclusion