Fluctuations in the rate of solution of cnlcium carbonate, and in the calcium carbonate compensation depth have occurred since the Jurassic The alternating dissolution facies in calcareous sequences in oceanic basins show that fluctuations in the rate of solution can have a duration of 250,000 years or less. The oscillatory nature of the calcium carbonate compensation depth is attributed primarily to changes in plankton productivity, particularly in the high latitude fertile belts which result from global variations in temperature, through time. Warm periods, which are associated with high productivity and possibly with increased oceanic mixing, are characterized by an increase in the removal of carbonate by organisms, deposition of carbonates in high latitudes, and the enhanced solution of calcareous tests and an elevated compensation level in mid-latitudes. Cold periods correspond to intervals of low surface productivity which in high latitudes leads to a decrease in the diversity of calcareous species and a reduction in the rate of carbonate deposition; in the mid-latitudes these changes in surface productivity are reflected by a decrease in the rate of carbonate solution, depression of the compensation depth, and an increase in the distribution of carbonates.
The areal distribution of carbonates at any one time is attributed to a combination of surface topography and the position of the calcium carbonate compensation depth. Palaeobathymetric models of the Tertiary Atlantic indicate an approximately twofold increase in the areal extent of sediments of the hololytic facies (red clays and/or biogenic siliceous ooze) in this basin during periods of maximum elevation of the calcium carbonate compensation depth.
Changes in surface productivity and the associated fluctuations in the compensation depth may provide a unifying concept for pelagic sedimentation in the Mesozoic to Recent oceans. Apart from the carbonate cycles which are differentially developed in high and mid-latitudes, increases in the extent of organic siliceous ooze and the formation of cherts in Late Cretaceous and Eocene equatorial sequences correspond with intervals when the compensation depth was elevated. It is also possible that submarine lithification and the formation of hardgrounds in the oceanic environment may be related to the low rates of sedimentation which accompanied periods of enhanced carbonate solution.
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.