The Lower Congo Basin lies offshore of the west coast of Africa and covers 115,000 square kilometers from the Republic of Congo to central Angola, in water depths extending to over 3500 meters. A large number of oil and gas fields occur in the basin (14 MMMBOEG produced and proven). Two main producing trends have been discovered. The first, discovered in Block 0 in Cabinda, Angola over 30 years ago, produces from Cretaceous reservoirs in water depths less than 200 meters. In the past four years, approximately 50 exploratory and appraisal wells have been drilled in the Lower Congo Basin Tertiary deepwater turbidite trend, which is associated with ancient deepwater channel deposition of the Congo River fan. At least 21 new oil fields have been discovered in the deepwater trend, in water depths between 200 and 1500 meters. Three-dimensional seismic data is the key to mapping these complex turbidite channel prospects. Significant areas of this new province remain undrilled, with numerous channels and trap features. Structural traps (fault truncations, channel drape over structural highs, and salt domes) dominate. Reservoirs are complex high quality turbidite sand systems. Source rocks occur in three separate intervals (Cretaceous Bucomazi and Iabe, and Tertiary Malembo formations).
The Precambrian Farmington Canyon complex crops out in the Wasatch Mountains between Ogden and Bountiful, Utah. Additional exposures are present at Durst Mountain and at Antelope Island. East of Ogden, between Ogden Canyon and Strongs Canyon, the Farmington Canyon complex has been thrust eastward over Lower Cambrian Tintic Quartzite and Middle Cambrian shales and limestones of the Ophir Formation and Maxfield Limestone. This thrust is named the Ogden thrust. Similarly, at Durst Mountain, east of Morgan Valley, the Farmington Canyon complex has been thrust over Lower Cambrian Tintic Quartzite and Middle Cambrian shales and limestones. This thrust fault is the Durst Mountain thrust. If subsequent vertical offset of 2,000-4,000 ft (610-1,220 m) down to the west on the Morgan Valley normal fault is restored, it appears that the two similar thrusts involving the Farmington Canyon complex could once have been continuous. Such a reconstruction requires a minimum of 12 mi (19 3 km) of thrust displacement of the complex eastward over the sequence of basal Cambrian rocks. This evidence is significant for two reasons: (1) the Farmington Canyon complex of the Wasatch Mountains may not be in place, but may be allochthonous above a decollement at depth; and (2) the Paleozoic-Mesozoic sequence east of Morgan may also overlie the same decollement, which would increase the potential for petroleum plays in the area north of Croyden. Thus, the northern Utah uplift, proposed for this area by A. J. Eardley and discussed by M. D. Crittenden, may result from a sequence of Farmington Canyon complex thrust upsection eastward, rather than a vertical uplift of basement. End_of_Article - Last_Page 948------------
Abstract The Precambrian Farmington Canyon Complex crops out in the Wasatch Mountains between Ogden and Bountiful, Utah. Additional exposures are present at Durst Mountain and at Antelope Island. These exposures form the northern Utah highland, a large basement uplift in north-central Utah. Recent mapping in and around the highland, cast of the Wasatch Fault was combined with well data from the Henefer-Coalville area to provide a basis for interpretation of the basement uplift using a thin-skinned, piggy-back thrusting model. Three cross sections illustrate the inferred subsurface geometry of the northern Utah highland. Correlation of the Ogden and Durst thrusts established a long, thin basement thrust sheet at a high structural position with 8 to 12 miles of eastward transport. The East Canyon thrust is interpreted as a westward-dipping thrust fault and correlated with the Ogden-Durst thrusts. The high structural position of these folded thrusts, compared to deeper thrusts encountered by drilling in the Henefer Anticline, indicates piggy-back motion on deeper basement-cored thrusts. The basement thrusting is theorized as occurring late in the Willard-Paris thrust movement. The rise in basement temperature, due to thrust loading, weakened a steep Precambrian rift margin in the footwall that collapsed, producing basement-cored thrust sheets. The resulting culmination in the thrust belt is illustrated by the westward re-entrant in the Willard thrust trace west of Antelope Island and the parallel trend of structures and bedding around the margins of the highland. The overall geometry of the northern Utah highland consists of a series of stacked basement thrust sheets. These basement-cored thrusts ramp eastward and connect with regional detachments in the overlying sedimentary pile.
Detailed mapping and cross-section traverses provide the control for structural analysis and geometric modeling of the Ogden duplex, a complex thrust system exposed in the Wasatch Mountains, east of Ogden, Utah. The structures consist of east-dipping folded thrust faults, basement-cored horses, lateral ramps and folds, and tear faults. The sequence of thrusting determined by means of lateral overlap of horses, thrust-splay relationships, and a top-to-bottom piggyback development is Willard thrust, Ogden thrust, Weber thrust, and Taylor thrust. Major decollement zones occur in the Cambrian shales and limestones. The Tintic Quartzite is the marker for determining gross geometries of horses. This exposed duplex serves as a good model to illustrate the method of constructing hanging-wall sequence diagram--a series of longitudinal cross sections that move forward in time and space, and show how a thrust system formed as it moved updip over various footwall ramps. A hanging-wall sequence diagram also shows the complex lateral variations in a thrust system and helps to locate lateral ramps, lateral folds, tear faults, and other features not shown on dip-oriented cross sections.
'%3e%3ccircle r='20' fill='%23008'/%3e%3ccircle r='17.5' fill='%23fff'/%3e%3ccircle r='3.5' fill='%23008'/%3e%3cg id='d'%3e%3cg id='c'%3e%3cg id='b'%3e%3cg id='a' fill='%23008'%3e%3ccircle r='.875' transform='rotate(7.5 -8.75 133.5)'/%3e%3cpath d='M0 17.5.6 7 0 2l-.6 5L0 17.5z'/%3e%3c/g%3e%3cuse xlink:href='%23a' transform='rotate(15)'/%3e%3c/g%3e%3cuse xlink:href='%23b' transform='rotate(30)'/%3e%3c/g%3e%3cuse xlink:href='%23c' transform='rotate(60)'/%3e%3c/g%3e%3cuse xlink:href='%23d' transform='rotate(120)'/%3e%3cuse xlink:href='%23d' transform='rotate(-120)'/%3e%3c/g%3e%3c/svg%3e)