Controls on Carbonate Tidal Grainstones – Examples From the Delaware Basin Outcrop and Midland Basin Reservoirs, Permian Basin

Abstract

Basin configuration and depositional profile are critical controls on tidal energy/velocity leading to formation of tide-dominated sands in Holocene and ancient platforms. Knowledge of dominant depositional process (wave, wind, tide) is important for predicting trends of shoal complexes as well as ooid geobody scale.

New data from outcropping tide-dominated skeletal-ooid bar complexes of the Guadalupe Mts., combined with data from Grayburg, Queen, Yates, and Tansill high-frequency sequences, highlights the importance of high-accommodation settings with sizable back-bar lagoons in the amplification of tidal currents. Lawyer Canyon Guadalupian San Andres G2-4 high-frequency sequences are re-examined using UAV-based outcrop models and 20 new measured sections Tide-dominated deposition in TST/MFS high-frequency cycles is now apparent. Grainstones previously modeled as barrier-inlet systems are reinterpreted as ebb-dominant tidal bar belts with 1-3m bar fronts and bi-modal/ebb-dominated decimeter-scale shield PT cross beds. A distinct shift to a foreshore-shoreface patterns with thin sheet-like sands occurs in seaward-stepping G3 HST. Upper Grayburg G12 TST grainstones are again distinctly ebb-dominated with 1-2m ooid tidal lobes developed during the high-accommodation TST. As for the G3 tidal complexes, a well-developed subtidal lagoon landward of the bar complexes during the Grayburg illustrates the importance of a high-accommodation TST setting for tidal processes to dominate. Remaining carbonate sands of the Capitan-equivalent and almost universally island-foreshore-shoreface wave-dominated systems.

Basin configuration is also a first-order controlling parameter for formation of carbonate tidal sands. Tidal resonance and increased tidal current velocity occurs in modern settings such as the Tongue of the Ocean and Schooner Cays, creating dip-elongate bars and intervening channels. Tidal focusing driven by basin configuration occurs in Midland Basin Grayburg reservoirs during G10 lowstand deposition. Tide-dominated ooid bar systems in this rapidly narrowing basin produce highly progradational channelized oolitic clinoforms building from north to south and east to west. A holistic approach combining understanding of core-scale sedimentology with seismic-scale sequence frameworks and basin configuration data is essential for accurate interpretation and prediction of carbonate tidal grainstone bodies within reservoirs.

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