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.
Figures & Tables
This volume represents some of the papers presented at the SEPM Research Symposium GeologicHistory of the Oceans at the Annual Meeting, March 1971, in Houston, Texas. Knowledge of oceanic sediments has been acquired in two ways: 1) directly by sampling and observation, and 2) indirectly through seismic investigations. Until the past decade, direct sampling and observation techniques could only provide information on the surficial materials of the ocean floor. The development of the piston corer has permitted oceanographic vessels to sample the upper 20 meters, and more recently the upper 30 meters, of the ocean floor, but such cores rarely penetrate the Pleistocene and enter older sediments. Until recently, most knowledge of the deeper sedimentary materials in the ocean basins was obtained through seismic reflection studies. The purpose of this volume is to present a number of observations, ideas, interpretations, and speculations which will be of value in considering the meaning of the increasing volume of data from older deep sea deposits.