ABSTRACT The North Coast Marine Area (NCMA) extends across approximately 7000 km 2 (4300 mi 2 ) of the northern Trinidad and Tobago shelf in water depths between 50 and 200 m (165–655 ft). In 2009, the NCMA had two exploration blocks under active oil and gas exploration with gas production from the NCMA totaling approximately 1.1 tcf since 2002. The NCMA is located within a complex, tectonic environment characterized by oblique, right-lateral–strike-slip displacement between the Caribbean and South American plates moving at a rate of about 20 mm/yr. This study analyzes two Pleistocene, fourth-order, shelf, and shelf-edge stratigraphic sequences (sequences B and C) deposited over the past approximately 500 k.y. in the western part of the NCMA. Micropaleontologic well data through Sequences B and C constrain the basal deposition to have initiated at ~500 k.y. and ~125 k.y., respectively. The lithologic interpretation from well log analysis tied to the seismic data shows these sequences composed of sand, shale, and thin limestone. Seismic interpretation allows division of both Sequences B and C into eight system tracts, which include (1) lowstand, (2) transgressive, (3) highstand, and (4) falling stage. The Sequences B and C lowstand systems tracts are characterized by subaerial or subaqueous delta top deposition from the paleo-Orinoco River as it prograded northward through the narrow region known as the Dragon’s Mouth on the northwestern side of Trinidad. The falling stage systems tract of Sequence C consists of a package of approximately 20–45-m (65–150 ft)-high, 0.1°–0.25°-inclined, and northeastward-prograding muddy, shelf-deltaic clinoforms whose northward termination marks the paleoshelf edge. Normal and strike-slip faults deform Sequence B and produced accommodation space to thieve sediment, and inhibit the extent of progradation and subsequent gravity deposition off the delta front. Faults do not penetrate into overlying Sequence C whose deposition was more eustatically controlled. These Pleistocene sequences provide an analog for underlying Miocene and Pliocene age sequences and reservoirs that form the most productive, NCMA gas fields.

Abstract Landslides are common in aquatic settings worldwide, from lakes and coastal environments to the deep sea. Fast-moving, large-volume landslides can potentially trigger destructive tsunamis. Landslides damage and disrupt global communication links and other critical marine infrastructure. Landslide deposits act as foci for localized, but important, deep-seafloor biological communities. Under burial, landslide deposits play an important role in a successful petroleum system. While the broad importance of understanding subaqueous landslide processes is evident, a number of important scientific questions have yet to receive the needed attention. Collecting quantitative data is a critical step to addressing questions surrounding subaqueous landslides. Quantitative metrics of subaqueous landslides are routinely recorded, but which ones, and how they are defined, depends on the end-user focus. Differences in focus can inhibit communication of knowledge between communities, and complicate comparative analysis. This study outlines an approach specifically for consistent measurement of subaqueous landslide morphometrics to be used in the design of a broader, global open-source, peer-curated database. Examples from different settings illustrate how the approach can be applied, as well as the difficulties encountered when analysing different landslides and data types. Standardizing data collection for subaqueous landslides should result in more accurate geohazard predictions and resource estimation.

Abstract The study area is situated along the obliquely converging boundary of the Caribbean and South American plates in eastern offshore Trinidad. Major structural elements in the shelf break and deep-water slope regions include growth and counter-regional faults to the south and large transpressional faults to the north. Well logs and biostratigraphic data were analyzed for 24 wells in the study area to refine previous deposi-tional environment interpretations. Transgressive and regressive cycles were interpreted on the basis of well log patterns and depositional facies shifts. Six T/R cycles were interpreted within the Pliocene to Recent stratigraphic succession. Shelf-edge trajectories were also mapped for each of the six T/R cycles on the basis of earlier stratigraphic correlations. Net-to-gross (NTG) ratios were calculated for each component of the T/R cycles and plotted against total thicknesses and net-sand values. In addition, NTG trends were mapped for each interval and analyzed on the basis of their proximity to the corresponding shelf edge. Mapping of shelf-edge trajectories (SETs) revealed that (1) SETs migrate northeasterly across the Columbus basin through time and (2) shelf-edge orientations parallel the strike of growth faults in the south but deflect to the northeast near the Darien ridge, indicating strong, underlying structural control. NTG plots and maps also revealed that (1) for transgressive units, NTG values never exceed 60%, and they are inversely proportional to total thickness; (2) for regressive cycles, NTG values are highly variable, ranging from 35% to 90%; (3) NTG values increase as the shelf break is approached; and (4) distribution of NTG ratios is also controlled by accommodation space created by local structures.

Abstract The front of any salt margin is an important geomorphologic area for understanding the manner in which sediments move from the proximal mini-basin regions of sedimentation to the distal unconfined basin floor regions of sedimentation. The link between tectonics and the development of major geomorphologic features of sediment bypass is an important but poorly understood process across this boundary. The purpose of this study has been to map and quantify the morphology, sedimentology, and architecture of a large Plio-Pleistocene-age deep-water valley outboard of the Poseidon mini-basin, near the salt front along the south-western edge of the Atwater fold belt in the deep water Gulf of Mexico. Objectives were to not only better document the architecture of these large confined valley reservoir systems but also, due to their importance for moving sediments from the salt province to the basin floor province, to understand their timing and relationship to the salt movements. The data available for this study includes ~2200 km sq. of 3D seismic data, along with information from several wells. Wireline logs show that the Tertiary deposits outboard of the Sigsbee Salt Escarpment to be several hundred feet thick, sharp-based, dominantly coarse-grained (sandy) but fining up cycles interpreted to be sandy basin floor fans, mass transport complexes and leveed channels developed in a confined setting within deep water “valleys.” The largest valley in this deep-water system formed in five main stages: initiating from narrow channel incisions, widening through lateral incision and sidewall slumping, straightening, and finally flooding and infilling. This valley system is ~20,000 feet across and ~ 1,400 feet deep, and has what look like well-developed master levees ranging from 700 to 1300 feet at their thickest point extending ~19000 feet away from the channel. This system is underlain by a ~700 foot thick mass transport complex and overlain by younger, low sinuosity leveed channel systems. Both of these systems appear to have been sourced by large submarine drainages, originating from a shelf edge sediment source system to feed the rugose slope with deep-water channel pathways uninhibited by salt wall inflation at the time of valley deposition. Major phases of salt thrusting along the southern edge of the Atwater were contemporaneous with the formation of this large, through-going valley system. These valleys appear to be associated with a period of sheet thickening and development of monoclinal basin-ward dip related to rafted mini-basin docking. Internally, these fills are composed of multiple, medial, and lateral accretionary wedges, which only fill a portion of the valley at any one time. Well log signatures show evidence for armored clay drapes along the valley margins. Seismically, the armored lateral accretionary packages appear to “flattening” toward the distal end of the valley, which runs off the seismic volume to the south. This flattening accretionary dip might signal proximity to the fan terminus.