Tectonics of passive margins: implications for the stratigraphic record

Abstract

Thermo-mechanical modelling demonstrates that tectonically induced vertical motions of the lithosphere can explain the major part of the short-term fluctuations in apparent sea level deduced from the seismostratigraphic record at passive margins. The interaction of intraplate stresses and the deflection of the lithosphere caused by sedimentary loading can produce apparent sea level changes of up to 100 metres at the flanks of passive margins. This mechanism is most effective for young passive margins subject to rapid sediment loading. Stress variations in the lithosphere of a few hundred bar are sufficient to explain most of the lowerings in sea level shown in the Vail et al. (1977) curves. To induce apparent sea level fluctuations with magnitudes greater than 50 metres, changes in stress level of more than 1 kbar are required, which must be related to major reorganizations at convergent plate boundaries, fragmentation of plates, or collision processes. By its nature, the tectonic model can explain contemporaneous fluctuations in apparent sea level in neighbouring depositional environments. In principle, it implies the possibility of regional correlations in different basin settings. Specific short-term fluctuations in the Vail et al. curves can be associated quantitatively with particular plate-tectonic reorganizations of lithospheric stress fields. The seismostratigraphic record may provide a new source of information on paleo-stress fields to be correlated with results of independent numerical modelling of intraplate stresses.