Three-Dimensional Fluvial Architecture of the Gypsy Sandstone (Pennsylvanian), Central Oklahoma

DOYLE, JIM D., MICHAEL L. SWEET,* and KIMBERLY K. THOMAS, BP Exploration, Houston, TX

Exposures of the Virgilian-age Gypsy Sandstone west of Tulsa, Oklahoma, were used with shallow cores to determine the three-dimensional geometry of bounding surfaces and channel-fill complexes within a multistoried fluvial sand body.

Individual fourth- and fifth-order bonding surfaces were initially mapped on two parallel 300-m-long road cuts using photomosaics. Fifth-order surfaces bound three large and three smaller channel-fill complexes. Vertical sequences within the larger channel-fill complexes typically consist, from the base up, of a 0.3-1 m thick lag of trough cross-bedded, granule- to cobble-sized mudstone intraclasts that grade up into 0.1-1.5 m thick trough sets of medium- to fine-grained sublithic arenite. This part of the sequence is often carbonate cemented. Planar and ripple-laminated fine sandstones occur near the top of the sequence. Some sequences are capped by red, root-mottled siltstone. Laterally, channel-fill complexes are either truncated by fifth-order bounding surfaces or thin into the ad acent red siltstone unit.

Twenty-two shallow cores, spaced 30-60 m apart, were cut 5 to 245 m from the northern road cut. Fifth-order bounding surfaces associated with the three large channel-fill complexes could be recognized and correlated between cores and the road cuts. Third- and fourth-order bounding surfaces, while recognizable on the outcrop facies and in individual cores, could not be traced throughout the study area. Individual channel-fill complexes are up to 10 m thick and 100-250 m wide. They have a high degree of longitudinal continuity.

Paleocurrent and other sedimentologic data suggest that, where they can be identified, macroforms, while lacking well-defined sigmoidal bedding, are lateral accretion deposits modified by chute channels.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)