Quantitative conditions for the development of systems tracts

Abstract

Systems tracts are defined on the basis of stratal stacking patterns. This paper explores quantitatively the possible relationships between different systems tracts and the relative sea-level in siliciclastic depositional systems. The development of systems tracts depends on the manifestation of forced regressions, normal regressions (lowstand and highstand) and transgressions, irrespective of the magnitudes of relative sea-level rise preceding and succeeding a stage of relative fall. As such, the transgressive and highstand systems tracts of one sequence may form when the elevation of the relative sea level is lower than the highstand or even lowstand in relative sea level of the previous sequence. Similarly, the lowstand systems tract of one sequencemay formwhen the relative sea-level is higher than the highstand elevation of the previous sequence. Because subsidence/uplift and depositional ratemay change considerably along strike of the coastal zone, all the systems tracts may form synchronously along strike. The maximum diachroneity of a systems tract boundary along the coast is half the duration of the accommodation cycle.