All DSDP pelagic sediment cores penetrating the Cretaceous-Tertiary boundary exhibit a major unconformity between the Cretaceous and Tertiary. The hiatuses in these cores are greater than in most marine shelf sections, although all are paleontologically unconformable. Furthermore, calcareous nannofossil biostratigraphy indicates that the magnitude of the Cretaceous-Tertiary unconformity is nearly identical in many shelf sections. The lack of a paleontologically continuous section across the boundary prohibits direct measurement of the span of this missing interval. However, indirect measurements based on inferred sedimentation rates suggest a hiatus of 10<sup>5</sup>—10<sup>6</sup> years for shelf sections, and more for pelagic ones.
It appears likely that high carbonate production in the Maastrichtian, coupled with near base-levelling of the continents produced a nutrient-and-carbonate poor ocean, having a shallow CCD along with an oxygen-rich, cloud-free atmosphere characterized by sub-arid conditions and strongly differentiated climatic belts. The mass extinctions ending Cretaceous time would have occurred during the inferred 105-10<sup>6</sup> year interval when severe nutrient and carbonate depletion would have caused the CCD to approach the photic zone, thereby leaving only a thin layer of non-calareous deposits to record this spectacular event in the earth's history. The observed magnitude of the unconformity, as indicated by calcareous fossils would seem to be a function of paleobathymetry with pelagic sections having been below compensation depth longer than shelf sections and consequently exhibiting greater hiatuses.
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.