Development of Turtle-back Anticlines in Gravity-Driven Compressional Domains: Evidences from the Deepwater Gulf of Mexico

Yann Philippe¹ and Gwenael Guerin^2
1 TOTAL E&P, Pau, France
² Total E&P USA, Inc, Houston, TX

Mechanisms of development of turtle-back anticline in extensional gravity-driven domains were clearly described about fifteen years ago. It was established that turtle-back anticlines result from the inversion of primary extensional troughs flanked by salt diapirs that collapsed due to the depletion of the basal salt layer through time (Vendeville and Jackson, 1992). Consequently, extensional turtle-back anticlines strike perpendicular to the gravity-driven extensional axis.

However, seismic data from the deep-water Gulf of Mexico evidence that turtle-back anticlines are also widely present below the Sigsbee salt canopy in an area that basically corresponds to a wide Mesozoic to Present gravity-driven compressional domain. Contrary to extensional turtle-back structures, compressional turtle-back anticlines represent inverted synclines flanked by breached anticlines that acted as salt ascension points. These primary synclines and anticlines initiated in the Mesozoic in an area of converging displacements with folds showing diversified orientations. As the amount of shortening increased in response to the development of Neogene depocenters uphill, anticlines oriented perpendicular to the shortening axis tightened in the Miocene, allowing a relatively restricted volume of salt to extrude. On the contrary, pre-existing anticlines oriented parallel to the Neogene shortening axis acted as transfer zones allowing large volumes of salt to reach the surface. Preferential salt withdrawal along these transfer zones provoked the inversion of primary synclines, forming turtle-back anticlines oriented parallel to the shortening axis. This evolution helps to better understand the geometry and kinematics of subsalt deformations before, during and after the Sigsbee canopy development.

Reference: Vendeville, B. C., and Jackson, M. P. A., 1992.The fall of diapirs during thin-skinned extension: Marine and Petroleum Geology, v. 9, p. 354–371.