Aptian anoxia in the Pacific Basin

Abstract

Marine strata of Aptian age in the Pacific Basin include two distinct levels that represent episodes during which sediments rich in organic carbon were deposited. Both episodes lasted less than 1 m.y., as revealed in strata deposited atop submerged topographic highs. One unusually widespread episode of early Aptian age (∼117.5 Ma) correlates with coeval units in Europe and thus is analogous to the Cenomanian-Turonian oceanic anoxic event in its short duration and wide geographic extent. The second episode of late Aptian age (∼116.5 Ma) is restricted to allochthonous pelagic deposits in the Franciscan Complex of California. These results support the concept of widespread and narrowly synchronous anoxic events. Further, they show that organic carbon deposition in the Pacific Basin took place in intermediate water oxygen-minimum zones and thus differed in the mode of deposition, and hence paleoceanography, from that in other middle Cretaceous ocean basins.