Geophysical Aspects of Shale Mobilization in the Deep Water Off the East Coast of Trinidad
The southeastern Caribbean is a geologically challenging region, and nowhere is this more evident than off the east coast of Trinidad. Rapid and prolific deposition in a deltaic setting and the effects of tectonic interaction between the Caribbean, North American, and South American plates serve to make this a unique area. The unpredictability that characterizes petroleum exploration in this region bears witness to this intricate geologic scenario. Similarities between this extended shelf and the Barbados accretionary prismto the north have been assumed mostly based on scant seismic coverage over this region. Analysis of newly acquired seismic data has revealed a subregion of intermittent shale mobilization, and vast sedimentary deposition exists eastward of the currently producing area. Although a great similarity to the shale belt in the region off the Darien Ridge is observed, this subregion exhibits its own distinct character. Shale flow features with associated bottom-simulating reflectors, syndepositional and postdepositional intrusives, which constrain subbasin development, and extrusive features are apparent. A distinguishing characteristic of this subregion is the association of mobilized shales with thrust faulting within the thick sequence of unconsolidated overburden, providing pathways for shale movement; this has the potential of initiating flow not only of shale but also of hydrocarbons from deeper source rocks. This may explain the presence of thermogenic hydrocarbons shown in this region and may have implications for petroleum exploration in this deep-water area.
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The phenomenon of rocks moving under their own means has always fascinated both scientists and nonscientists alike. The 2006 AAPG Hedberg Conference on Mobile Shale Basins was held in response to a need to gather industry and academic communities in a common forum to address the very existence of mobile shales. Stimulating and informative discussions at that Conference led to this special volume on shale tectonics. AAPG Memoir 93 documents shale tectonics from a variety of basins around the world, including the southern Beaufort Sea; the Krishna-Godavari Basin, India; eastern offshore Trinidad; offshore Brunei; and along the westernmost portion of the Mediterranean Sea. The book also provides information on the petrographic framework, behavior, geometries, and geodynamic models of shales. Publication of this Memoir coincides with a growing interest in shales as hydrocarbon reservoirs, and will add to the body of literature that significantly addresses both extrusive and intrusive shales.