Tectonic and eustatic controls on the origin of shelf sands, offshore northern Trinidad and Tobago,
northeastern South America
By:
Stefan Punnette
Graduate Student
University of Texas at Austin
When: |
Friday, 7, 2010, 10:30 a.m. to 11:30 a.m. |
Where: |
Seminar Conference Room, 10100 Burnet Road, Bldg 196-ROC, Austin, Texas 78758 |
Host: |
Gail Christeson, UTIG |
Abstract
The northern continental shelf of Trinidad preserves an immense thickness of Tertiary stratigraphy over a highly structured accommodation zone impacted by the present day tectonics of the Caribbean plate margin. The study area is located 40 km north of the island of Trinidad and 60 km west of the island of Tobago. The study area straddles the east-northeast-trending continental shelf and slope of northern offshore Trinidad and is affected by the right-lateral oblique transtensive fault system on the shelf. The basins along the northern shelf of Trinidad and Tobago received large volumes of coarse-grained Tertiary sediments shed from the South American continent.
These sediments are deposited within actively deforming basins in shallow marine settings along the northern margin of Trinidad and are subject to significant reworking by the northwestward-moving Atlantic Equatorial Current. Similar current-influenced sand deposits worldwide are host to significant hydrocarbon accumulations and such is the case for basins along the offshore North Coast regions of Trinidad and Tobago which host giant biogenic gas fields in sandstone of Miocene and younger age.
Seismic geomorphic analysis and architecture of shelfal sands found in the offshore northern shelf of Trinidad and Tobago have been examined using 1350 km2 of high quality 3D seismic and numerous well penetrations, as well as high-resolution 2D lines. We characterize two, ~400 ms (~275 meters) thick Late Pleistocene-age (~ 600 kya and younger) sequences and assess the varying influences of sea-level, continental climate and syn-depositional tectonics on their formation and morphology. Sequence thicknesses vary across the shelf in response to syn-depositional tectonic accommodation development, and post-depositional uplift and erosion by both subaerial and submarine processes. "Channeled" bodies form a near braided network of complex meandering to straight incisions over the older clinoform packages. These channels range in width from 100 to 1400 m. Clinoform geometries dip from south-southwest to north-northeast with angles ranging from 0.10° - 0.26°, and heights ranging from 19m - 46m.
Key observations from this data set include the 3D hierarchical nature of key surfaces bounding facies packages in these units, the relationship between the paleo-shelf edge and the lowstand shelf wedges, and the influence of shallow fault deformation on delta top thicknesses. A review and comparison of modern and ancient analogs to the north coast deposits support the interpretation of a subaqueously deposited shelf edge delta system with muddy clinoform development being attributed to progradational deposition as opposed to longshore advection. The muddy nature of these deposits is under ongoing study.
