Testing the Concept of Diapiric Rise and Fall Using 3D Seismic Data from the U.K. Southern Gas Basin: ABSTRACT

Abstract

The U.K. Southern Gas Basin experienced a long and complicated developmental history-involving extension, salt tectonics, inversion, and subsidence-that began in the early Triassic and continued into the middle Tertiary. In our study areas, faulted Paleozoic rocks (Rotliegendes Fm. and older) are separated from a faulted overburden sequence (Bacton Grp. to Chalk) by the salt-dominated Zechstein Grp. Overburden structure is dominated by a series of broadly NW-SE trending graben and associated salt diapirs and walls. New insights into salt tectonics derived from scaled analog and numerical model studies, reveal that in areas with originally thick salt, regional extension of the overburden is important in triggering and controlling diapirism and graben growth. Diapiric piercement proceeds in a predictable series of modes-reactive, active, and passive. As extension continues, if for some reason the salt supply becomes restricted, the diapir can no longer grow and begins to fall. The diapir can then no longer support the graben floor and the graben collapses into the falling diapir. The change from diapiric rise to diapiric collapse is often marked by fundamental changes in sediment distribution patterns. We interpret graben and diapiric growth to be initiated by gravity-driven thin-skinned brittle extension of the overburden. The supply ofmore » salt to the developing diapirs eventually became restricted and continued extension lead to diapiric collapse. Collapse is marked by fundamental changes in sediment distribution patterns. While all graben continued to act as depocentres, many graben flanks, areas that were originally high, became syn-collapse depocentres; many integraben troughs, areas that had acted as depocentres during diapiric rise, became starved and received little sedimentation during diapiric collapse.« less