Polyphase Deformation of Salt Diapirs in the Shallow Water Campeche Basin of Mexico

Abstract

The Campeche basin of SE Mexico (shallow water area) has salt-involved structures with polyphase deformation. Tectonic deformation from plate convergence (Chiapaneca orogeny) and oblique gravity sliding reshaped the structures. The Chiapaneca orogeny involved a high-strain deformation pulse during the Middle Miocene. This orogenic event involved folding, thrusting, contracted mushroom-shaped salt diapirs and the formation of an erosional unconformity. Diapirs were partly dissolved along the seabed leading to the formation of cap rock. Subsequent tilting of the margin from regional orogenic uplift, initiated regional extension in a gravity slide which moved North into the Gulf perpendicular to the Chiapaneca contraction direction. This extension caused precursor contracted-diapirs to become “fallen diapirs”. Caprock which formed during peak contraction was broken during the fall of the diapirs. Extension probably outpaced the ability of autochthonous salt layer to resupply the diapirs from additional contraction. Diapirs widened and subsided between separating rafts made of the orogenic structures. The crests of precursor diapirs became the locus of brittle normal faults during regional extension. Syn-extension overburden began to deposit on salt as diapirs began to fall. Top salt and the distinctive Middle Miocene unconformity surface were displaced by extensional faults. Wide extensional gaps of the source rock unit formed over the site of the precursor salt diapirs and pillows where the overburden was the weakest. The Middle Miocene unconformity at the base of the syn-extension package was the key tectonostratigraphic surface utilized to establish the polyphase deformational history. The Middle Miocene surface corresponds to an erosional unconformity rather than a weld.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019