Polyphase Faulting and Raft Tectonics in Sureste Basin Offshore Mexico

Abstract

Summary The eastern edge of Campeche salt basin (aka Sureste basin in the shallow water) consists of a NW-SE trending Reforma-Akal fold and thrust belt along the flank of the Yucatan platform. This fold belt represents the eastern limit of the Chiapaneca orogenic belt. An area of the fold belt was studied which experienced three tectonic events: (1) NW-directed extension during the Middle-Late Mesozoic associated with rifting and later gravity tectonics during drifting of the Gulf of Mexico, (2) Tertiary NE-directed contraction which led to the development of a series of NW-SE trending folds, and (3) Middle Miocene to present NW-directed extensional and transtension associated with gravity sliding. Interpretation of sub-regional seismic data in the eastern Sureste basin along with well data suggest that the Late Jurassic – Middle Cretaceous extension event happened in two phases. Two sets of extensional faults with different initiation ages both trend northwest-southeast with predominately opposite dip. The faults sole into the autochthonous salt layer or its equivalent weld and their footwalls typically have triangular shape salt roller that merge with the mother salt detachment layer. The first phase of faulting is Late Jurassic and is characterized by faults which principally dip basinward and have slightly curved fault surfaces. Kimmerdgian and Tithonian sections thickness growth are observed on the hanging walls of these faults. The second phase of faulting is Middle-Late Cretaceous. Phase two faults characteristically have landward dips, pronounced listric shapes, and offset the older phase of extensional faults. The second phase of faulting shows growth in the Middle-Upper Cretaceous sedimentary section on their hanging walls. The extreme extension of the second phase of faulting in the northern part of the eastern Sureste basin led to the development of Mesozoic rafts, where the adjacent footwall and hanging wall blocks are separated and are no longer in contact. The first phase of extension is interpreted to be associated extensional faulting associated with rifting, but the second phase is thought to be have been occurred during and after the rift to drift transition of the Gulf of Mexico opening. Thermal subsidence related to the formation of oceanic crust to the west is considered the principal drivers of the Middle-Late Mesozoic extension. A westerly dipping base of salt developed during the Mesozoic which triggered gravity sliding causing supra-salt strata to slide basin-ward on autochthonous salt. The rugosity along base salt probably increased friction along the salt detachment hindering movement along the basin-ward faults which caused landward dipping faults to form. Raft development associated with the landward-dipping faults is mainly observed in the northern part of the study area. The absence of raft tectonics, and characteristic overlap of hanging wall cut-offs against their footwalls is typical in the south of the study area. This relationship might have been caused by variable original salt thicknesses. Thick salt in the north probably facilitated more extreme extension. The observed structural relationships provide additional insights in understanding the geometry and development of the extensional system and helps in describing the risk associated with hydrocarbon exploration in this part of the basin.