Importance of Gravity-Driven Compressional Tectonics in Northern Offshore and Deep-Offshore Gulf of Mexico: New Observations and Implications for Subsalt Interpretation

Philippe, Yann, David Wittoesch, Gwenael Guerin, Total E&P USA, Inc, Houston, TX

The offshore and deep-offshore GoM is characterized by the massive allochthonous Sigsbee salt canopy that was sourced from autochthonous salt by vertical or oblique salt feeders. This canopy is now buried below Late Miocene or younger mini-basins. Salt feed­ers are generally considered as Mesozoic to Early Miocene passive diapirs squeezed by con­traction in the Middle-Late Miocene.

Our seismic interpretations suggest that salt feeders originated as salt-cored contrac­tional anticlines rather than passive diapirs. Seismic and well data also reveal the presence of condensed Mesozoic-Middle Miocene slabs above the Sigsbee canopy. These slabs rep­resent autochthonous Mesozoic-Paleogene anticlines or plateaus that were incorporated into the canopy in the form of allochthonous rafts. These initial anticlines and plateaus were part of a broad contractional domain which included the Louisiana and Texas shelf. During the Neogene, most of these folds were rejuvenated and breached to form salt feeders, allow­ing the autochthonous salt to supply the Sigsbee canopy above. Lower-Middle Miocene fair­ways were preferentially restricted to surrounding synclines. Due to the Late Miocene to Recent southward progradation of the passive margin, these contractional structures have often been overprinted by younger gravity-driven extension. Consequently, many anticlines have partially collapsed, causing primary synclines to evolve into apparent turtle-back struc­tures.

As it covers the whole deep-water GoM and parts of the Louisiana-Texas shelf, the Mesozoic to Miocene gravity-driven contractional domain is thus much wider than previous­ly believed. This alternate interpretation helps to clarify the tectono-sedimentary evolution in the subsalt interval prior to, during and after Sigsbee canopy development.