Abstract The West African continental margin evolution is preserved in a small source-distant setting (20 × 30 km area) by changes in lobe-channel–levee seismic geomorphological elements within a threefold seismic stratigraphic hierarchy. The c. 32 Ma depositional record of rift, drift and depositional outbuilding of the margin by gravity-driven adjustment, deformation and deposition produced a hierarchy of second- through fourth-order stratigraphic cycles bounded by laterally continuous fine-grained drapes inferred to record prolonged periods of sediment starvation. The margin outbuilding phase, the focus of this contribution, consists of three second-order adjustment bounded cycles (ABCs) that record major adjustment and/or modification of the deep-marine depositional system. Seven third-order cycles also show changes in depositional trend and seismic facies architecture. Ten fourth-order cycles, best resolved within the upper part of the succession, consist of multiple, wedge-shaped and compensating, lobe–channel–levee complexes up to 20 km wide. These complexes show an upward increase in channel–levee and decrease in lobe proportion. They also show an upward change from lobes incised by sinuous channels to channels deflected to lobe flanks. Outcrop and shallow core-calibrated analogues from the Permian Brushy Canyon Formation, and modern Amazon and Zaire Fans help constrain these patterns. Changes in the sediment composition and volume of subaqueous flows at their point of origin, and subsequent gravitational deformation, syn-sedimentary mass-wasting and large-scale fan avulsion punctuating deep-marine sedimentation, adjust deep-marine depositional pattern during basin margin outbuilding. Lobe-channel-levee distributions in this sediment source-distant setting record a progressive increase in local topographic relief and gradient related to the basinward migration of deformation during depositional outbuilding of the continental margin. Two important conclusions derived from this record include (1) the importance of local seabed topography and gradient on producing changes in depositional pattern, and (2) that repeated and cyclic changes in these patterns reflect adjustment/deformation within, and probably restricted to, the deep-marine record. Integrated seismic stratigraphic and geomorphic analysis delineates multiple scales of these adjustment-bounded cycles. The evolving map patterns record adjustment by shifts in geomorphic pattern and orientation. These local geomorphic changes can be used to predict longer-term and larger-scale changes in the depositional record of the continental margin evolution. This analytical approach should have general utility along high shelf-to-basin relief margins with similar gravity-driven deformation.

Abstract Subsurface and outcrop data show the distribution of siliciclastics, carbonates, and evaporites across the inner, middle, and outer portions of the shelf for the Yates Formation (Permian, Late Guadalupian) of the Permian Basin. The evaporitic inner shelf consists of thick intervals of anhydrite and minor halite interbedded with anhydrite-cemented, Red Argillaceous Siltstone/Sandstone. The sheet-like geometry of the beds and lack of evidence for channels, as shown by log correlations, suggest that sheetflood and eolian processes may have been the dominant modes of sediment transport. The middle shelf was dominated by siliciclastic deposits and separated the evaporitic inner shelf from the carbonate-rich shelf margin. Siliciclastic facies in the middle shelf consist of alternating Light Brown Arkosic Sandstones (shoreline deposits), Dark Gray Argillaceous Siltstones (wet mud flats transitional to shallow lagoons), and Red Argillaceous Siltstones similar to that of the inner shelf. Carbonate lithologies consist predominantly of structureless to algal-laminated, peloidal dolomudstones that locally show signs of erosion (ripped-up clasts). Green-Gray Dolomitic Subarkosic Siltstones/Sandstones occur in the middle- to outer-shelf region and are associated with algal-laminated dolomudstones and minor, thin-bedded, pisolitic packstones (tidal flat to shallow lagoon deposits). The shelf margin consists of Red Anhydritic Siltstone/Sandstone that passes downdip to Gray Bioturbated, Kaolinitic Dolomitic Quartz Sandstone. These siliciclastics occur with dolomites of the shelf margin pisolite shoal complex, with the Gray Sandstones deposited in a more shallow marine environment than the subaerially deposited Red Siltstones. Vertical stacking of the various facies is interpreted to be the result of cyclic sea-level variation and is thus a shelf-wide phenomenon. Silts and sands were transported across the shelf and to the shelf margin during lowstands of sea level, and outer-shelf clastics were reworked during subsequent sea-level rises. Cyclostratigraphic analyses suggest that the siliciclastic deposition and stacking of facies occurred during three orders of relatively low-amplitude, sea-level fluctuations. A depositional model summarizes the effect of these sea-level fluctuations on facies distribution for shelf areas with different slopes and/or subsidence (i.e., Central Basin Platform vs Northwest Shelf). An understanding of the sea-level fluctuations and the variable shelf profiles enhances facies correlations in a mixed siliciclastic and carbonate system like the Yates Formation.

Abstract Four outcrops in the Guadalupe Mountains are investigated in order to evaluate two current models that describe the depositional setting of siltstones and sandstones in the Upper Guadalupian, Yates Formation. The outcrops are described and placed in their relative position along a dip-oriented cross section that is representative of the Yates Formation on the Northwest Shelf. Facies relations and cyclic stratigraphic sequences suggest that the siliciclastics were transported across a very shallow to subaerially exposed shelf during eustatic sea-level low stands and were trapped on the shelf during subsequent sea-level rises. Clastics near the shelf margin were reworked during the sea-level rises.