Abstract: Leonardian Carbonate Platform Sequences, Sierra Diablo, West Texas: Composite Relative Sea Level Control on Sequence Attributes

William M. Fitchen

Outcrops of the Leonardian (Lower Permian) Victorio Peak and Bone Spring formations in the northern Sierra Diablo region of west Texas expose a carbonate platform-to-basin transition along the eastern margin of the Diablo Platform. These formations are largely time-equivalent lithostratigraphic units that are composed of six intermediate-scale sequences (ca. 1.8-2.0 My duration, 20-150 m thick). Each of the intermediate-scale sequences (VPI-VP6) is composed of a number of small-scale (1-10 m thick) cycles. The six sequences stack into a single large-scale sequence. Intermediate-scale sequence attributes such as stratal architecture, systems tract proportions, facies tract composition and geometry, and sequence boundary character change systematically through the large-scale sequence, hich suggests modulation of the intermediate-scale accommodation cycle by the large-scale accommodation cycle. Scant fusulinid biostratigraphic data, platform sandstone marker beds, and sequence stacking pattern guide tentative correlations to equivalent units in the subsurface.

A basinward-sloping submarine unconformity at the base of the Leonard truncates over 300 m of upper Wolfcampian platform carbonates; an extensive karstic horizon is developed along the landward part of the unconformity. VP1 (Abo/Wichita equivalent) is a highstand-dominated, oblique progradational sequence that downlaps the unconformity and is capped by a widespread karstic horizon. VP2 (lower Clear Fork/lower Yeso equivalent) contains a laterally discontinuous lowstand fringing reef, an onlapping transgressive wedge of shore-zone grainstones, and an aggradational-to-retrogradational highstand platform capped by a karstic horizon. Locally, this sequence boundary is a basinward-sloping submarine unconformity that truncates up to 120 m of platform margin strata. VP3 (Tubb/middle Clear Fo k/middle Yeso equivalent) consists of an onlapping mixed siliciclastic-carbonate-transgressive wedge and an aggradational-to-retrogradational highstand platform. The sequence is capped by a marine-flooding surface that represents the maximum flooding of the large-scale sequence. VP4, VP5, and VP6 (upper Clear Fork/upper Yeso equivalent) are sigmoid to oblique progradational, highstand-dominated sequences with thin silt-rich transgressive wedges. VP6 is capped by siliciclastic-rich tidal flat cycles of the Glorieta member, which are overlain by subtidal cycles of the uppermost Leonardian lower San Andres Formation.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994