Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Structural and Stratigraphic Synthesis of the Gas Trend on the Northern Shelf of Trinidad and Tobago
(1) Jackson School of Geosciences, The University of Texas at Austin, Austin, TX.
The North Coast Marine Area (NCMA) extends across ~7000 km2 of the northern Trinidad and Tobago shelf in water depths between 50 to 200 meters. In 2009 the NCMA had two exploration blocks under active oil and gas exploration with gas production from the NCMA totaling ~ 1.1 tcf since 2002. All natural gas discovered to date in the NCMA has been interpreted as biogenic although one previous worker has speculated that a minor component of thermogenic gas is also present. The NCMA is located in a complex tectonic environment characterized by oblique strike-slip displacements between the Caribbean and South American plates at a rate of about 20 mm/yr. The main faults of the 200-km-wide plate boundary zone include: 1) the El Pilar right-lateral strike-slip fault zone to the south on the island of Trinidad and the Gulf of Paria which GPS results indicate to be largely inactive; 2) the North Coast fault zone (NCFZ) which marks the southern boundary of the Tobago basement terrane and appears to be slightly active with down-to-the-north, Miocene to recent oblique-slip movements on the NCFZ producing accommodation space for deposition of sediments along the northern shelf of Trinidad and Tobago; and 3) the Hinge Line fault zone (HLFZ) crossing through the NCMA. The ~120 km long Hinge Line fault zone has an average east-northeast strike approximately parallel to the GPS-derived plate motion direction (080°), and is a sub-vertical, thick-skinned right-lateral strike-slip fault. Localized zones of transpression and transtension form locally where the trace of the fault deviates from the 080° direction of pure, right-lateral shear and these localized areas of complex faulting and folding provide important structural traps for Pliocene and Miocene gas reservoirs in the NCMA north of the HLFZ. Growth sequences along the HLFZ indicate that the fault activated in Miocene time and continues to up to the late Pleistocene (~500 k.y.) and in some areas forms active scarps on the seafloor. Structural maps and isochron maps were made for four horizons underlying the northern shelf of Trinidad including top Mesozoic basement, top Miocene, top Pliocene and seafloor. These maps support a change in terrigenous source area for the northern shelf of Trinidad: during the Miocene and early Pliocene, terrigenous sources were coming from the southeast through the Atlantic Ocean; where as during the mid-Pliocene to present the source area changed to the southeast through the Gulf of Paria.