STRESS-INDUCED CHANGES IN PLATE DENSITY, VAIL SEQUENCES, EPEIROGENY, AND SHORT-LIVED GLOBAL SEA-LEVEL FLUCTUATIONS

The stratigraphic record contains clear evidence that broad regions have experienced rapid changes in sea level unrelated to changes in glacial ice volume (e.g., third- and higher-order Vail sea level variations, continental foundering). We propose that many of these changes can be caused by stress-induced changes in plate density. Stress changes produce significant changes in the density of the crust and lithosphere (a point missed in previous investigations) and propagate across even the largest plates in less than 30,000 years. Lithospheric plates interacting at existing boundaries can produce stress-related density changes sufficient to cause several meters change in plate elevation; these may account for many of the regressions and transgressions seen in the stratigraphic record. The creation of new rifts could increase plate compression enough to cause approximately 50 m of plate subsidence. Plate elevation changes of up to -200 m could result from increased plate compression during continental collisions. A particularly enigmatic kind of rapid nonglacial global (NGG) sea level change is a coupled approximately 50 m sea level fall (regression) and roughly equal rise (transgression) occurring in less than 10(6) years. These couplets, associated with black shales and marine extinctions, can be explained by the elastic snapback attending the rapid formation of a new rift. Isostatic disequilibria along the new rift depresses the seafloor sufficiently to cause a approximately 50 m fall in sea level. Mantle flow restores isostatic equilibrium along the rift axis and erases the fall in approximately 60,000 years. Unusually intense hydrothermal circulation along the new rift during the snapback promotes anoxic bottom water conditions and deposition of black shales. A rapid drop in global sea levels reduces the area of ocean bottom within the photic zone, causing overpopulation, food exhaustion, and extinctions. The connections between changes in plate stress and density have many implications. Perhaps the most far reaching is that tectonic events on the 3/4 of the globe that is covered by oceans, as well as the 1/4 that is subaerial, are recorded in sedimentary strata.