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

Abstract

The 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 Ṙ = A˙< 1), upward widening diapirs (~Ṙ = Ȧ > 1), and vertical cylindrical diapirs (~Ṙ = A˙= 1). In addition to being a nonrigorous measure, Ṙ = A˙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.

The Impact of Pre‐Salt Rift Topography on Salt Tectonics: A Discrete‐Element Modeling Approach

“…While physical models provide invaluable insight into the 3D geometry, timing and planform sequential evolution of structures (Dooley et al, , ; Ferrer et al, , ; Vendeville and Jackson, ; ), they demand a significant amount of time, space and investment (Pichel et al, ). Numerical models based on continuum methods, such as finite‐element modeling (FEM), have proved very useful in understanding the dynamics of salt flow, allowing more numerical control and realistic stress–strain quantification (Albertz et al, ; Gemmer et al, ; Gradmann et al, ; Weijermars et al, ). They are not able, however, to reproduce spontaneous, realistic fault localization and propagation in the cover, which is critical to understand the kinematic and structural style of minibasins and diapirs in areas affected by regional stresses.…”

Numerical modelling study of mechanisms of mid‐basin salt canopy evolution and their potential applications to the Northwestern Gulf of Mexico

“…The mechanism leading to canopy formation is often described as a decreased ratio of sedimentation rate to salt-supply rate (McGuinness & Hossack 1993;Fletcher et al 1995;Weijermars et al 2015). In this paper, we investigate how the salt supply can be increased relative to the sedimentation rate.…”

“…; Weijermars et al . ). The salt viscosity is estimated to range from 10 18 ‐10 19 Pa s in extruding submarine salt, which is primarily halite (Fletcher et al .…”

“…; Weijermars et al . ). In this paper, we investigate how the salt supply can be increased relative to the sedimentation rate.…”

“…Significant developments have been made in understanding the mechanisms of salt-sheet advance through the wealth of data collected in the last decades (Hudec & Jackson 2006Hearon et al 2015). Salt-sheet advance, which follows the earlier 'extrusion' phase, is primarily controlled by the basal slope, the salt viscosity, and the ratio between salt-supply rate and sediment accumulation rate (Fletcher et al 1995;McBride et al 1998;Hudec & Jackson 2006Hearon et al 2015;Weijermars et al 2015). The salt viscosity is estimated to range from 10 18 -10 19 Pa s in extruding submarine salt, which is primarily halite (Fletcher et al 1995).…”