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 within 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 coincides with 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 and forming the focus of Chapter 2 of this thesis.
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 subvertical,
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; during
the mid-Pliocene to present the source area changed to the southeast through the Gulf of
Paria. The shallow seismic stratigraphic study of Chapter 3 analysed two Pleistocene
fourth-order shelf and shelf-edge stratigraphic sequences deposited over the past ~500 k.y
in the western part of the NCMA. New micropaleontologic data tied to a well through the
two sequences B and C constrain the initial deposition of each sequence ~450 k.y
(Sequence B) and ~260 k.y. (Sequence C). The lithologic well log shows that the
sequences are sand, shale, and thin limestone. Seismic interpretation allows division of
sequences B and C into eight system tracts which include: 1) lowstand system tracts, 2)
transgressive system tracts, 3) highstand system tracts and 4) falling stage system tracts.
Two lowstand systems tracts in sequences B and C are characterized by delta plain
deposition of the Orinoco Delta with a north-eastward terrigenous source direction
coming from the western side of Trinidad, through the Gulf of Paria. The falling stage
systems tract of sequence C consists of a suite of ~20 – 45-m-high, 0.1° – 0.25°-inclined,
and north-eastward-prograding muddy, shelf deltaic clinoforms marking the paleo-shelf
edge. Fault controls penetrate into Sequence B and may have produced accommodation
space but do not penetrate into overlying Sequence C which therefore must have been
eustatically controlled. These Pleistocene sequences may provide a more recent analog
for Miocene and Pliocene age sequences and reservoirs that form the highly productive
horizons of the NCMA gas field. / text
| Identifer | oai:union.ndltd.org:UTEXAS/oai:repositories.lib.utexas.edu:2152/ETD-UT-2010-08-1862 |
| Date | 23 December 2010 |
| Creators | Punnette, Stefan Wayne |
| Source Sets | University of Texas |
| Language | English |
| Detected Language | English |
| Type | thesis |
| Format | application/pdf |
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