ABSTRACT The Pliocene-Pleistocene sequence cored in the Ewing Bank 826 Field in the Gulf of Mexico provides an example of sand distribution and reservoir quality produced by reworking by deep-marine bottom currents. A distinctive attribute of reworked sands is their traction bedforms. Common sedimentary features of traction currents include small-scale cross-bedding, starved current ripples, horizontal lamination, sharp upper contacts, and inverse size grading. The sands also exhibit internal erosional surfaces and mud-offshoots indicating oscillating current conditions. Presumably, the Loop current, a strong wind-driven surface current in the Gulf of Mexico, impinged on the sea bottom, as it does today, and reworked sand. A depositional model based on the integration of core, wireline log, and 3-D seismic data suggests that the reworked sediment package may be thick and continuous, but individual sand layers within the package may be thin and discontinuous. This model, which depicts the distribution of bottom-current reworked sand in interchannel slope areas as a distinctly different facies from channel-levee facies, has the potential for general application to other deep-water plays outside the study area. In the Ewing Bank 826 Field, the Type 1 (L-l) reservoir with 80% sand exhibits higher permeability values (100-1800 mD) than the Type 2 (N-l) reservoir with 26% sand (50-800 mD). The increased permeability in the Type 1 sand has been attributed to high sand content, vigorous reworking, and microfractures. The clean, porous and well-sorted Type 1 sands with good communication between sand layers have produced at higher rates and recovery efficiencies than the Type 2 sands with numerous interbedded mud layers.

ABSTRACT The Pennsylvanian Jackfork Group in the Ouachita Mountains of Arkansas and Oklahoma has conventionally been considered a classic example of a turbidite sequence deposited in a submarine-fan setting. However, the apparent “Bouma turbidite sequences” in these strata, which were used as evidence for single-event turbidity current deposition, were in reality deposited by multiple events, including debris flows and slumps. These were commonly reworked by bottom currents. Normal size grading and Bouma Sequences are essentially absent in these sandstone beds, which appear “massive” (i.e., structureless) in outcrop, but when slabbed reveal diagnostic internal features. Beds exhibit sharp and irregular upper bedding contacts, inverse size grading, floating mudstone clasts, a planar clast fabric, lateral pinch out geometries, moderate to high matrix content (up to 25%) , contorted layers, and fluid escape structures. All these features are indicative of sand emplacement by debris flows (mass flows) and slumps. Mud matrix in these sandstones were sufficient to provide cohesive strength to the flow. The dominance of debris-flow and slump deposits (nearly 70% at DeGray Spillway section) and bottom-current reworked deposits (40% at Kiamichi Mountain section), and the lack of turbidites in the Jackfork Group have led us to propose a mass flow dominatewd slope setting. Conventional submarine fan models, designed for turbidite systems, are not applicable to the debris-flow emplaced and bottom-current reworked sandstone beds of the Jackfork Group. This unconventional model has direct implication for sand-body geometry and continuity because deposits of fluidal (suspension) turbidity currents are laterally more continuous than those of plastic ( en masse ) debris flows.