Stratigraphic signatures of translation of thrust-sheet top basins over low-angle detachment faults

摘要

Low-angle detachment faults and thrust-sheet top basins are common features in foreland basins. However, in stratigraphic analysis their influence on sequence architecture is commonly neglected. Usually, only eustatic sea level and changing flexural subsidence are accounted for, and when deformation is considered, the emphasis is on the generation of local thrust-flank unconformities. This study analyses the effects of detachment angle and repetitive detachment activation on stratigraphic stacking patterns in a large thrust-sheet top basin by applying a three-dimensional numerical model. Model experiments show that displacement over low-angle faults (2-6°) at moderate rates (～5.0 m kyr~(-1)) results in a vertical uplift component sufficient to counteract the background flexural subsidence rate. Consequently, the basin-wide accommodation space is reduced, fluvio-deltaic systems carried by the thrust-sheet prograde and part of the sediment supply is spilled over towards adjacent basins. The intensity of the forced regression and the interconnectedness of fluvial sheet sandstones increases with the dip angle of the detachment fault or rate of displacement. In addition, the delta plain is susceptible to the formation of incised valleys during eustatic falls because these events are less compensated by regional flexural subsidence, than they would be in the absence of fault displacement.