Current Rift-Related Wrenching of the Gulf Coast Margin: Implications for the Human Habitat
The northern Gulf of Mexico is believed to have formed between north and south Americas during the Triassic-Jurassic time. Its rifted northern margin appears to have been right laterally segmented by a series of northwest-southeast trending transfer faults that date back to Triassic-Jurassic rifting Pilger, 1981, Salvador, 1987, Buffler, 1991; Huh et al., 1996) (Fig. 1).
In general, the post-rift tectonics of the Gulf of Mexico are described in terms of thin-skinned growth faulting, salt movements, and gravity tectonics, none of which are supposed to affect basement below the Louann Salt. However, a cursory look at the tectonics of the continental interior and historic seismicity of the Gulf of Mexico reveal that this entire region is active and, along with the surrounding areas, has been episodically active since the Mesozoic. Also, some of the more recent deep hypocenters on the Gulf Coast and the Gulf of Mexico apparently represent basement deformation below the Louann Salt (Figs. 2–3).
Aeromagnetic and gravity anomalies on the Gulf Coast and the Gulf of Mexico shelf show northwest-southeast lineaments that parallel the transfer faults. In southern Louisiana, these northwest-southeast lineaments laterally offset (wrench) east-northeast trending gravity highs and lows that follow the half graben and horsts of the buried rift margin (Fig. 4), which control the general east-west strike of Tertiary growth faults.
Based on such observations, this writer is of the opinion that basement involved wrenching of the Gulf Coast (as evidenced by deep hypocenters) is real and constitutes a hitherto ignored factor contributing to coastal subsidence and land loss along the Gulf Coast (Sarwar, 2002, 2003; Sarwar and Bohlinger, 2005; Dokka, 2006; Gagliano, 2008; Stephens, 2010).
Further, given the above neo-tectonic framework and seismicity patterns, we should also study the risk of a sudden and more catastrophic collapse somewhere along the Louisiana-Texas coast than has so far been considered (see, for example, Edwards, 2000; Gagliano, 2008). The eastern tectonic province, as defined by Peel et al. (1995), involves active growth faults like the Baton Rouge Fault, and the overloaded Mississippi River slope fan. Since this province also overlies active northwest-southeast transfer faults, (like the Pearl River; Sarwar, unpublished), it seems to be highly vulnerable to seismic jolts even if they travel from far away.
AAPG Datapages/Search and Discovery Article #90196 © 2014 GCAGS, Lafayette, Louisiana, October 5-7, 2014