The Early Aptian C-cycle perturbation leading to Oceanic Anoxic Event(OAE) 1a

Early Cretaceous marine sediments are important archives for studies of major climate perturbations and of response mechanisms of the biosphere to such events. This is evidenced by several high amplitude positive carbon isotope excursions, which are assumed to be the result of an increased burial of organic matter (OM) caused by a volcanically induced greenhouse climate. The Ontong-Java volcanism is thought to have indirectly caused the major C-isotope excursion of the Early Aptian. Its onset coincides with the OM-rich deposits of OAE1a (Menegatti et al., 1998) and is preceded by a prominent short-term negative “spike”. The latter has been attributed to marine volcanism (Arthur et al., 1985; Arthur, 2000) or dissociation of methane gas hydrates (Jahren et al., 2001; Dickens, 2003).