Beach Sands: Recorder of Varying Geologic Processes at Periodicities from 10⁸ to 10⁰ Years

Rhodes W. Fairbridge, Allen Lowrie

Beach sands are the residual of climatic and sea level processes interacting in an oscillating geologic continuum. The location of a shoreface is the result of tectonic, sedimentary, oceanographic, and climatic processes, all interweaving to create a single location. The combining processes include passive continental margin subsidence, lithospheric flexuring and epirogenic uplift, depositional processes, fluvial transportation traits, sediment compaction and lithostatic pressure, global wind and ocean currents, global average temperature, and insolation rate. These mechanisms are either synergistic or algebraically additive positive or negative, and act with periodicities ranging from 10⁸ to 10⁰ years.

Sea level oscillations have maximal impact, with climate-weather characteristics and associated oscillation ranges occurring at different periods: plate margin rifted-basin tectonics at 10⁸ years, characterized by periods of major glacial activity lasting 10⁷ years and sea level oscillation ranges of up to 0.5 km; regional basin evolution at 10⁷ years and oscillation ranges of several hundreds of meters; local basin tectonics and sedimentation patterns and long-term sets of climate and sea level oscillation patterns at 10⁶ years, with oscillation ranges of up to 125 m and averaging 50 m; individual glacial and sea level cycles (controlled by planetary orbital motions and insolation) at 10⁵ and 10⁴ years, and oscillation ranges of up to 125 m and averaging 50 m; medium-term climate cycles at 10³ years, characterized by peaks of storminess and oscillation ranges of meters to decameters; short-term climate-weather cycles at 10², 10¹, and 10⁰ years, and oscillation ranges of meters to centimeters. All of these processes impact on sea level oscillations, thus, on the shoreface, leaving a residuum of beach sands.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.