TECTONIC CYCLES AND THE HISTORY OF THE EARTH'S BIOGEOCHEMICAL AND PALEOCEANOGRAPHIC RECORD

An integrated approach to earth history for the last 2.5 b.y. reveals the strong interdependence of all geologic variables. Three earth history components are identified and interrelated: secular trends as the earth ages, recurring events of a previously proposed supercontinent megacycle (Worsley et al., 1984, 1985), and nonrecurring environmental shifts. Declining secular trends are endogenic heat production, atmospheric carbon dioxide levels, and surface temperatures. Continental differentiation, enzyme efficiency, atmospheric oxygen levels, and solar luminosity are increasing secular trends. Four phases of a supercontinent cycle (supercontinent fragmentation, maximum continent dispersal, continental assembly, and supercontinental stasis) recur with a similar to 0.5-b.y. period and are correlated with tectonism, cratonic sediment preservation, atmospheric and hydrospheric evolution, and the distribution of marine platform stable isotopes. These correlations reflect coupling among the various oceanic and continental constituents during consecutive supercontinent assemblies and fragmentations. Nonrecurring shifts are unique and irreversible events in earth history (e. g., development of photosynthesis, occurrence of banded iron formations, and deposition of detrital uraninite) that represent periods of rapid geochemical adjustment to biospheric evolution. Earth's tectonobiogeochemical history is then synthesized by integrating secular trends and nonrecurring events with the supercontinent cycle, emphasizing the preferentially preserved periods of fragmentation and continental dispersal. Paleoceanographic consequences of the megacycle are considered to reflect the stepwise coupling of secular trends and nonrecurring events to a biotically controlled, phosphorus-organic carbon-climate linkage required to maintain earth's post-Archean surface temperature.