Abstract Garden Banks 191 is about 160 miles (257 km) from Lafayette, Louisiana, in 700 feet (214 m) of water. Block 191 has produced over 230 BCF dry gas from Pleistocene reservoirs since 1993. We will address the production characteristics of turbidite sheet (4500’ Sand) and channel (8500’ Sand) sand reservoirs. Understanding the distribution of shale breaks within both reservoir types is critical because the shales compartmentalize gas production and control water encroachment through the reservoirs. The 4500’ Sand reservoir is about 1000 ft (305 m) thick and is composed of interbedded sands and shales typical of amalgamated and layered sheet sands. The sand is subdivided into four production members (designated 1-4) by shale breaks that extend across the reservoir interval. The reservoir has exhibited a good water drive. Water encroachment occurs individually within each member. The 8500’ Sand is an approximately 900 ft (274 m) thick “fining-upward” channel succession that was deposited in a slope mini-basin formed by salt withdrawal. Shale breaks in this stacked channel succession do not extend across the reservoir, but they do control water encroachment in individual wells. The sand is informally divided into five members based on shale breaks and perched water contacts. Members 3, 4 and 5 are connected, based on RFT pressures. The 8500’ Sand has produced from a combination pressure depletion/limited water drive mechanism resulting in excellent recoveries.

Abstract Medium- to high-sinuosity, aggradational submarine channels have frequently been considered analogous to subaerial channels. However, planform evolution and resulting architecture in these submarine channels are characterized by absence of downstream migration, eventual cessation of movement, and ribbon geometries. In contrast, alluvial rivers undergo continuous downstream and lateral movement to form tabular, sheetlike bodies. A simple process model of flow structure and evolution is described for these submarine channels. Flows are predicted to be highly stratified, have significant supra-levee thicknesses, and form broad over-bank wedges of low-concentration fluid. The model, for the first time, provides a coherent set of process explanations for the primary observations of submarine channels.

Abstract A 1400-ft continuous core from the Inglewood Field in the Los Angeles Basin consists of poorly consolidated sandstones and mudstones that represent deposition in the middle to outer parts of a deep-sea fan. Biostratigraphy indicates that the basin floor remained at lower bathyal depths (>2000 m or 6500 ft) throughout deposition of the cored interval. Both shallow and deep-water microfossils are present in all samples, implying downslope transport of shallow-water fauna to deeper depths as is typical for turbidites. The core contains several hundred alternating sandstone and mudstone beds that range from less than 0.1 to over 16 ft thick. The sandstones are arkosic arenites, lithic arenites, and arkosic wackes. The thinner sandstones are well sorted and cross-bedded, whereas the thicker sandstones are poorly sorted and massive. Variations in bed thickness, internal character, and sandstone percentage were used to define five lithofacies; these range from massive mudstone to massive sandstone with three intermediate, interbedded sandstone and mudstone facies. The five lithofacies represent laterally continuous subenvironments across depositional lobes of a deep-sea fan system. Vertical sequences show alternating thickening- and thinning-upward cycles that suggest gradual lateral shifting of the depositional lobes across the basin floor.

Abstract The Zambales Ophiolite in western Luzon is a large fragment of oceanic crust that was uplifted several kilometers without being obducted onto a continental margin. Deposition of pelagic limestone on the ophiolite during the late Eocene through Oligocene gave way to deposition of ophiolite-derived clastics during the early Miocene. The uplift of the western edge of the ophiolite probably was related to the initiation of subduction along the Manila Trench in the late Oligocene, but the Zambales crust predates the oldest crust in the adjacent South China Basin by about 8 million years. A new sandstone petrology method traces the uplift and erosional history of the ophiolite through the changing compositions of the ophiolite-derived clastics.

A comprehensive data set of more than 200 profiles across the Peru-Chile Trench between 4° and 45°S is used to describe the morphology and shallow structure of the trench axis and the downbending oceanic plate just prior to subduction. Five morphotectonic provinces (4°–12°, 12°–17°, 17°–28°, 28°–45°S) show distinct changes in trench depth, axial sediment thickness, oceanic plate fault structures, and dip of the seaward trench slope. In general, the northern and southern regions are characterized by relatively shallow axial depths, moderate to thick trench axis turbidites, and a gently dipping seaward trench slope that exhibits minor normal faults. The deeper central area is almost barren of axial sediments and bends downward more steeply prior to subduction; bending has developed an extensive network of major faults with up to 1,000 m vertical offset on the seaward slope. Two systems of faulting occur in conjunction with subduction. Bending of the oceanic plate causes extensional stress and brittle failure of the upper oceanic crust, resulting in step faults, grabens, and tilted fault blocks on the seaward trench slope. Extensional faulting begins near the outer edge of the trench and develops progressively toward the trench axis. Basaltic ridges and tilted, uplifted trench fill at several locales along the trench can both be explained by thrust faulting. Compressional stress due to plate convergence occasionally can be transmitted seaward from beneath the continental margin through the oceanic plate, emerging as thrust faults within the oceanic crust near the trench axis. Axial turbidites are commonly tilted landward as they are uplifted, probably as a result of downward curving of the underlying thrust fault. Faulting of the oceanic crust prior to and during subduction may have important implications for evolution of convergent continental margins.