Downbuilding salt stocks and sheets quantified in 3‐D analytical models

Abstract

AbstractThe 2‐D concept of diapiric downbuilding is expanded to the third dimension. Our advanced approach shows which range of salt fluxes and sedimentation rates (time dependency included) can explain the formation of upward narrowing diapirs (previously thought of as < 1), upward widening diapirs (~ > 1), and vertical cylindrical diapirs (~ = 1). In addition to being a nonrigorous measure, does not account for the effect of a regional slope on diapir shape during downbuilding. When a regional topographic slope is absent and lateral changes in sedimentation rate are negligible, our models confirm downbuilding diapirs always develop axisymmetric shapes. However, when the salt source lies on a regional slope, asymmetric diapirs will form. The rate of salt supply from the source and the superposed gravity flow downslope control the flow lines and shape of the advancing salt sheet. In the 2‐D gravity spreading plane, the ratio of source flow to gravity flow strengths can be characterized by a Rankine number. Obstruction of lateral spreading of salt issued from the feeder sources due to sedimentation lifts the salt from its 2‐D spreading plane, which our model simulates by superposing a velocity component normal to the sedimentation surface. We next apply the 3‐D analytical model to an offshore salt sheet in the Gulf of Mexico and analyze which conditions controlled its flow kinematics down the continental slope. Stratal cutoffs at the base of salt combined with the analytical gravity spreading model provide estimates for the dimensional flow rates and the effective viscosity of the Louann Salt.