The regional distribution of salt in the northwestern Gulf of Mexico : styles of emplacement and implications for early tectonic history

Abstract

The regional distribution of salt in the northwestern Gulf of Mexico reflects a complex interplay between tectonic basin architecture and subsequent salt kinematics. Persistent northwest-southeast structural trends across the Texas-Louisiana margin are attributed to a structural fabric of the transitional crust upon which the Louann Salt was deposited, and which formed during the Late Triassic to Middle Jurassic as the Yucatan block moved southeast out of the northwestern Gulf. Major transfer faults divide the Gulf Coast into segments characterized by markedly different salt abundances and structural styles. Complimentary asymmetry in salt volumes between the Louann and Campeche provinces is consistent with a reversal in the dip direction of crystal detachment faulting over a narrow corridor characterized by an abundance of northwest-southeast oriented salt structures and greater than 100 km of right-lateral offset between the Perdido and Mississippi Fan foldbelts. Separation of the Louann and Campeche provinces suggests a possible counterclockwise rotation of the Yucatan block during Late Jurassic seafloor spreading. Major depocenters developed above susidiary basins containing thicker accumulations of Louann Salt. Expansion of stratigraphic intervals was accommodated by the mobilization of salt into a variety of structural styles. The Perdido and Mississippi Fan foldbelts formed in response to compressional forces transmitted via shelf margin growth faults to the basinward limit of Louann Salt. Associated salt wedges are overthrust on the order of one to 10 km. Salt wedges of the Sigsbee Bulge are overthrust up to 60 km or more, and possibly away from an abrupt limit of Louann Salt against right-lateral offsets of the continent/ocean boundary. The Sigsbee Escarpment represents the basinward limit of allochthonous salt deformed away from the Pleistocene depocenter. Isolated supralobal basins are subsiding into a nearly continuous substrate of overthrusting salt wedges across the lower slope. Across the upper to middle slope numerous lateral intrusions of allochthonous salt are spreading from the crests of isolated domes and massifs forming distinct interlobal basin margins. As the lateral intrusions converge interlobal areas are reduced. Eventually source layers are almost completely evacuated and the salt redistributed in the shallow subsurface as allochthonous canopies.