Abstract

Lower Permian strata in the Sierra Diablo of West Texas consist of carbonate platform, platform margin and slope facies tracts that range from middle Wolfcampian to late Leonardian in age. The Wolfcampian Hueco Group overlies a widespread angular unconformity and second order sequence boundary, which truncates Precambrian through Pennsylvanian (Desmoinesian) formations of the Diablo Platform. The Hueco Group consists of a basal siliciclastic unit (Powwow Formation; 0-246 ft (0-75 m) thick) and an upper platform carbonate unit (main body of the Hueco Group; ≤1380 ft (≤420 m) thick). The Powwow Formation is a time-transgressive, non-marine to marginal-marine facies tract of the main body of the Hueco Group. The Hueco Group consists of two middle Wolfcampian high-frequency sequences (W1-HFS and W2-HFS), which together constitute a composite sequence, and one late Wolfcampian high-frequency sequence (W3-HFS), which represents all or part(?) of a second composite sequence. Wolfcampian high-frequency sequences in the Sierra Diablo are cross-cut by a subaerial-to-submarine unconformity that truncates 886 ft (270 m) of slope, platform margin and outer platform strata. The erosional products of this truncation consist of carbonate breccias that onlap the toe-of-slope and basinal profile of the unconformity. The submarine erosion along this unconformity is attributed to platform margin slumping, which may have been initiated in the early late Wolfcampian following a major platform margin backstepping event. Paleokarst development associated with this unconformity is represented by collapse breccias that occur up to 141 ft (43 m) below the unconformity surface, suggesting a minimum relative sea-level fall of this magnitude.

The Leonardian Victorio Peak and Bone Spring Formations represent largely time-equivalent platform and slope/basin facies tracts that can be subdivided into six high-frequency sequences, L1-HFS through L6-HFS, which constitute two larger-scale composite sequences. The lower composite sequence consists of lowstand (L1-HFS), transgressive (L2-HFS and L3-HFS) and highstand (L4-HFS) sequences; the upper composite sequence is subdivided into transgressive (L5-HFS) and highstand (L6-HFS) sequences. Proposed correlations to the subsurface are:

• L1-HFS=Abo, upper Wichita, and lower member of the Bone Spring formations;

• L2-HFS=lower Yeso, lower Clear Fork, Drinkard, and lower middle member of Bone Spring formations;

• L3-HFS=Tubb, middle Yeso, middle Clear Fork, lower Blinebry, third Bone Spring sand, and third Bone Spring carbonate formations;

• L4-HFS=lower Upper Yeso, lower upper Clear Fork, upper Blinebry, second Bone Spring sand, and second Bone Spring carbonate formations;

• L5-HFS=middle Upper Yeso, middle upper Clear Fork, lower Paddock, first Bone Spring sand, lower first Bone Spring carbonate formations;

• L6-HFS=Glorieta, upper upper Yeso, upper upper Clear Fork, upper Paddock, upper first Bone Spring carbonate formations.

Stacking patterns of meter-scale cycles and noncyclic bedsets within high-frequency sequences are described with respect to facies distributions, stratal architecture, key subaerial and submarine unconformities, and marine-flooding surfaces. These stacking patterns reflect the position of meter-scale cyclic strata within the larger framework of high-frequency sequences and composite sequences. Lowstand and highstand high-frequency sequences exhibit high positive progradation:aggradation ratios, seaward-stepping meter-scale cycle stacking patterns, low facies diversity, a shift in the position of maximum accommodation to the slope, stratal toplap below sequence boundaries, seaward-dipping sequence boundaries (resulting from differential compaction), and greater potential for karst development along unconformities. Transgressive sequences exhibit low positive to low negative progradation:aggradation ratios, landward-stepping to vertically-stacked meter-scale cycle stacking patterns, high facies diversity, a shift in the position of maximum accommodation to the platform top, relatively conformable, flat-lying strata across sequence boundaries, and greater potential for outer platform and platform margin reef development. Along-strike variability in meter-scale stacking patterns is best developed in transgressive sequences, and is attributed to spatial variations in antecedent topography, depositional energy (perhaps related to wind direction, headland-bight shoreline trends, and shelf paleobathymetry), and sediment accumulation rates.