Wolfcamp Facies and Stacking Patterns in the Delaware Basin, West Texas: Insights Into Mechanisms and Patterns of Sediment Delivery and Facies Architecture

Abstract

Although general patterns of facies distribution in Leonard basinal successions are reasonably well known in the Permian Basin, Wolfcamp rocks are much less known, especially in the Delaware Basin. The Wolfcamp succession is commonly subdivided into A, B, C, and D successions that have been correlated widely, in large part on wireline logs alone. Core-based facies studies suggest much less lateral continuity. We used legacy and modern cores to define facies and their vertical and lateral distribution within the upper Wolfcamp using integrated conventional and chemostratigraphic core description methods. Seven facies were defined, each containing varying amounts of detrital and biogenic quartz, calcite, dolomite, and clay minerals. Illite is the dominant clay mineral although chlorite is locally abundant suggesting multiple sediment input sources. Of particular note for understanding sediment transport mechanism and defining correlations are the calcitic and dolomitic facies. The former, which are largely restricted to the upper Wolfcamp (“A” and upper “B” units), comprise clay to gravel size carbonate detritus indicative of platform shedding during sea level highstands. Dolomitic mudrock facies, which probably formed during maximum platform flooding, are perhaps the most correlative. Three scales of cyclicity are apparent. The uppermost Wolfcamp (unit “A”) comprises thick (70-80 ft thick) cycles composed of basal detrital quartz siltstone facies indicative of lowstand shedding, overlying TOC-rich, argillaceous siliceous mudrocks suggestive of maximum flooding, and capping detrital carbonates related to highstand shedding. These highstand deposits consist of high frequency (3 to 6 ft thick) cycles of calcareous and argillaceous mudrocks. Intermediate scale cycles (20 to 50 ft thick), which characterize the lower part of Wolfcamp “B” but are also lateral equivalents of upper unit “B” carbonate dominated facies, comprise basal dolomitic mudrocks and overlying argillaceous siliceous mudrocks. Although uppermost Wolfcamp (unit “A”) deposits document probable sea level driven changes in sediment supply, underlying rocks suggest a dominance of eolian quartz sediment supply interrupted episodically by carbonate event deposits. The lateral discontinuity of platform-derived deposits suggests a dominance of point sourcing which makes lateral correlations difficult.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018