Browsing by Subject "Structural framework"
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Item Structural framework and its influence on the Quaternary-age sequence architecture of the northern shelf of Trinidad and Tobago(2010-08) Punnette, Stefan Wayne; Wood, Lesli J.; Mann, Paul, 1956-; Tatham, Robert; Steel, Ronald J.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.Item Structural framework and seismic geomorphology of the Cretaceous beneath the Mad Dog Area, deep to ultradeep waters Gulf of Mexico(2013-05) Markez, Damian; Wood, Lesli J.Recent drilling of deep stratigraphy in subsalt offshore Gulf of Mexico has revealed the presence of thick, amalgamated, Cretaceous siliciclastic reservoirs with the potential to become valid exploration targets. Similar to the Lower Tertiary deepwater play, the significant down-dip distance (> 400 km) from the source deltaics, the data gap across the modern structurally complex salt-tectonics-dominated slope and the difficulties of imaging subsalt stratigraphy pose challenges for the construction of meaningful deepwater system models to aid in exploration and appraisal efforts. A 3D seismic dataset in the Mad Dog field at the basinward end of the modern allochthonous salt canopy and outboard of the Sigsbee Escarpment offers the opportunity to study the nature of the deep stratigraphy at central positions in the basin. The nature of the Cretaceous sedimentary system has been investigated through detailed structural and seismic geomorphologic mapping. An early syndepositional contractional event has been identified and temporally associated with Mesozoic emplacement of a deep salt sheet. These events are masked by the major Neogene-age phase of fold amplification that dominates the present-day subsalt structural framework. Ponded-basin deepwater sedimentation processes control early phases of deposition in the Cretaceous Mad Dog area and sediment-gravity flows are deposited as complexes of low sinuosity amalgamated channelized deposits in roughly-confined sediment pathways. Ponded fills show internal lateral accretion architectures that grow sigmoid in nature as the migrating systems interact with the approaching minibasin margins making evident the structural control on sediment architecture. Later phases of deposition are characterized by slightly sinuous feeder channels with multiple lobe development at their terminus. Variable directions of sediment source pathways indicate a linear-sourced slope apron depositional model for these systems. In addition to the more structured morphologic elements, there were also pervasive mass-transport processes active, presumably triggered by Mesozoic halokinesis. Data in sparse deep wells in the GoM that penetrate the Cretaceous suggest that the Late Cretaceous deepwater depositional system was composed of coarse-grained high density gravity flows. The geometries seen in seismic beneath the Mad Dog area support the existence of such a basinwardly extensive deepwater fan systems developed during the Cretaceous, and the low sinuosity channel geometries and small length:width ratio and amalgamated nature of fan lobes suggest that these systems may have indeed been high-density in nature.Item Structural framework of the Clemente-Tomas and Corsair growth fault systems in the Texas continental shelf margin of the Gulf of Mexico basin(2011-08) Ajiboye, Olabisi A.; Nagihara, Seiichi; Holterhoff, Peter; Gurrola, HaroldIn the Texas continental shelf margin, there exist the Clemente-Tomas and the neighboring Corsair growth fault systems, both of which run roughly parallel to the shoreline. The structural and stratigraphic development histories of some parts of these fault systems have not been investigated in detail, even though such knowledge would be crucial in understanding the hydrocarbon migration and trapping mechanisms associated with them. The present study attempts to characterize the structure and stratigraphy of these growth fault systems in the Mustang Island federal lease areas, off Corpus Christi, Texas. It utilizes a time-migrated three-dimensional seismic volume that covers an area of 867mi2 (2245km2), digital well data from 36 wells, wireline logs from 30 boreholes, paleontological reports from 15 boreholes, and velocity survey data from 33 boreholes. In characterizing the stratigraphy five biostratigraphic markers within the Miocene were determined from the paleontological data; Bigenerina ascensionensis (8 Ma), Discorbis 12 (9.11 Ma), Bigenerina humblei (13.4 Ma), Robulus L (16.3Ma) and Marginulina ascensionensis (18Ma). Seismic horizons corresponding to these biostratigraphic markers are tied to the well data, and mapped throughout the study area. Their depths are obtained from the seismic velocity structures at the well tie points. Lithologies of the strata are estimated from the well logs. Fault surfaces are mapped in three dimensions. The detailed mapping enables clear distinction of the two neighboring fault systems. Most of the work is performed on a computer workstation and yields a digital, quantitative model of the regional structure and stratigraphy. The present Study shows that the Clemente-Tomas growth fault detaches into a shaley mobile substrate. Basinward evacuation of the mobile substrate probably initiated the fault movement in the Oligocene. The evacuated shale body developed into a linear, diapiric ridge. By the early Miocene (between 23 to 18 Ma), the shale diapirism was causing the basinward sliding of the overlying sediments, and that initiated the primary Corsair growth fault. This early Corsair faulting process was relatively instantaneous and it led to temporary formation of a semi-starved mini-basin on the downthrown side of this fault. Subsequent depositions on the downthrown side kept the primary Corsair growth fault active though the late Miocene (18 to 8 Ma). By the late Miocene, (Discorbis 12 and Bigenerina ascensionensis) faulting of the Clemente-Tomas slowed down considerably while the Corsair remained active.