Implications of Some Pre-Quaternary Sediment Cores and Dredgings
The Lamont-Doherty deep-sea sediment core library contains over 900 deep-sea sediment cores and dredgings containing pre-Quaternary microfossils.
The oldest outcropping or near-outcropping sediments in the collection are Early Cretaceous and are from the Northwestern Atlantic Ocean. Late Cretaceous sediments have been cored in widely scattered localities throughout the world's oceans but principally from the ocean margins. Paleocene and Oligocene sediment cores are rare but have been recovered from the three major oceans. More than 90 cores containing Eocene sediments have been recovered and are broadly distributed throughout the ocean. Three hundred and thirty Miocene cores have been obtained and several contain complete or nearly complete sequences back to the late Miocene. Pliocene is the most common pre-Quaternary sediment in the collection. The majority of these contain biogenic silica (Radiolaria and diatoms) and are commonly found in areas of low sedimentation rate where a complete Quaternary section is less than ten meters thick. Most pre-Quaternary cores have been recovered from submarine topographic highs such as plateaus marginal to continents, flanks of the mid-ocean ridge system, aseismic ridges and seamounts. Notable exceptions to this are two areas of broadly outcropping sediments, one of Middle and Late Cretaceous age northeast of the Bahama Islands and a second of Eocene to Pliocene age in the Eastern Equatorial Pacific.
Cores recovered from plateaus marginal to continents reflect varying geologic histories. For example, features such as the Blake Plateau, East Falkland Plateau, and Walvis Ridge show fossil evidence for having been considerably shallower than at present. Features such as the Agulhas Plateau and the Naturaliste Plateau, on the other hand, display little or no evidence of vertical movement. In general, cores from the flanks of the mid-ocean ridge system show increasing age with greater distance from the axis, reflecting the lateral movement of the sea floor away from the ridge axis as suggested by sea floor spreading theory.