Thomas A. Davies

Estimates of Cenozoic Oceanic Sedimentation Rates

Estimation of average Cenozoic sedimentation rates for the Atlantic, Indian, and Pacific oceans indicates global synchronous fluctuations. Paleocene-early Eocene and late Eocene-early Miocene rates are only a fraction of middle Eocene and middle Miocene-Recent rates. These changes must reflect significantly different modes of continental weathering, which may be due to alternate states of atmospheric circulation marked by reduction of global precipitation.

Sea-Level Fluctuations and Deep-Sea Sedimentation Rates

Sediment accumulation rate curves from 95 drilled cores from the Pacific basin and sea-level curves derived from continental margin seismic stratigraphy show that high biogenous sediment accumulation rates correspond to low eustatic sea levels for at least the last 48 million years. This relationship fits a simple model of high sea levels producing lower land/sea ratios and hence slower chemical erosion of the continents, and vice versa.

Indian Ocean sediment distribution since the Late Jurassic

Abstract Cores obtained by deep sea drilling in the Indian Ocean provide a sedimentary record from which are deduced changing patterns of sedimentation through the Late Mesozoic and Cenozoic. Comparisons between: (1) empirical subsidence curves and sediment sequences at individual sites; and (2) paleobathymetric reconstruction maps and past sediment distributions, convincingly demonstrate the interrelationship of sedimentary and tectonic development within this the most recently formed of the major oceans.

Oceanic Sediments and their Diagenesis: Some Examples from Deep-sea Drilling

Carbonate sediments dominant except during Eocene (siliceous sediments); progressive breakdown of coccoliths, common occurrence of dolomite rhombs, nodular chert biogenic, bedded chert source unknown; enrichment of basal sediments in iron attributed to sea-floor spreading

Cenozoic oceanic sedimentation rates: How good are the data?

Abstract The distribution of core material gathered by the Deep Sea Drilling Project (DSDP) is compared with known data concerning the distribution of the floors of the oceans with respect to latitude, water depth, physiographic province and age. Also patterns of sedimentation in Middle Miocene, Early Oligocene and Middle Eocene times, plotted on paleogeographic reconstructions, are shown to be readily interpretable in terms of our present understanding of the factors controlling oceanic sedimentation. The general conclusion is the DSDP core material is representative of the geologic record of the ocean floor but that considerable care must be exercised in any quantitative interpretation of the drilling results.

Cenozoic Sedimentation in the Pacific Ocean: Steps Toward a Quantitative Evaluation

ABSTRACT Computerized procedures have been developed for calculating ocean sediment accumulation rates in terms of mass per unit area. Using these procedures and a simplified plate tectonic model, palinspastic maps of sedimentation in the Pacific Ocean over the past 48 million years (m.y.) have been prepared. These maps show a relatively simple and persistent sedimentation pattern with maximum accumulation occurring around the perimeter of the ocean and along the equator. Sediment seems to be more uniformly distributed at times of low overall accumulation rates. The maps further show that the history of sedimentation in the Pacific over the past 48 m.y. can be divided into five broad time periods: 0-6 m.y., 6-15 m.y., 15-27 m.y., 27-42 m.y., and prior to 42 m.y. Detailed differences between the sediment accumulation patterns of these time periods are related to major reorganizations of Pacific Ocean circulation and climate.

Indian Ocean Sediment Distribution since the Late Jurassic

Abstract Cores obtained by deep sea drilling in the Indian Ocean provide a sedimentary record from which are deduced changing patterns of sedimentation through the Late Mesozoic and Cenozoic. Comparisons between: (1) empirical subsidence curves and sediment sequences at individual sites; and (2) paleobathymetric reconstruction maps and past sediment distributions, convincingly demonstrate the interrelationship of sedimentary and tectonic development within this the most recently formed of the major oceans.

Ocean Margin Drilling Program: ABSTRACT

End_Page 1660------------------------------Plate tectonics provides a valuable descriptive framework for understanding the evolution of the earth over the past 200 m.y. However, many important questions remain unanswered as to processes occurring at plate boundaries, the evolution of the ocean environment, and the relation between continental and oceanic crust. The Ocean Margin Drilling Program (OMDP) represents a cooperative effort by industry, academic, and government scientists to investigate these topics. The scientific objectives of OMDP may be conveniently grouped under the headings of passive and active ocean margins, ocean crust, and ocean paleoenvironment. They will be addressed by a comprehensive program involving regional marine geologic and geophysical studies, drilling and coring, and subsequent downhole experiments. The program will place particular emphasis on the ocean margins. As the basis for future planning, several regions have been selected to form a model drilling program. This model program will be refined as the program evolves. Although OMDP is a basic research effort, it will begin to build the geologic framework against which to assess the resource potential of the region beyond the continental shelves. End_of_Article - Last_Page 1661------------