Sequence-Stratigraphic and Depositional Framework of Wave-Influenced Deltaic Systems in the Lower and Middle Frio Formation, Redfish Bay, Corpus Christi, Texas
Zhang, Jinyu; Ambrose, William A.; Olariu, Mariana I.
Over 1,800 feet of continuous core, combined with log and 3-D seismic data, illustrate a stratigraphic succession of high-frequency progradational episodes composed of wave-modified deltaic and shoreface deposits within an overall second-order lowstand systems tract in the lower and middle Frio Formation in Redfish Bay, Texas.
This second-order succession is divided into 11 higher order (4th or 5th) sequences. Upward-coarsening parasequences display a transition of depositional environments from offshore to lower and middle shoreface. The typical facies succession within a parasequence consists of gray, massive mudstone interbedded with thin (0.1- to 0.2-ft), very fine grained, wavy rippled sandstone with Zoophycus at the base followed by alternating fair-weather and storm-dominated deposits. The fair-weather suite is characterized by highly bioturbated, very fine to fine grained sandstone, with Cruziana ichnofacies including Planolites, Thalassinoides, Asterosoma, Paleophycus, Chondrites and Rosselia. Remnant wavy laminations or ripples are also preserved. The coarser and cleaner sandstones of storm origin are massive and weakly bioturbated with Ophiomorpha. Parallel and low-angle laminations with possible hummocky cross-stratification and ripples are present. The lower part of the ARCO #470-4 core (10,335 to 11,460 ft), parasequences 1st - 7th is composed predominantly of low-energy deposits in a distal setting, indicated by the dominance of the deposit-feeding infauna over the suspension-feeding infauna. Soft-sediment deformation occurs below shoreface sandstones, implying an unstable substrate and rapid deposition in middle- to outer-shelf environments. The upper part of the cored interval (9,651 to 10,335 ft), parasequences 8th - 11th, has more opportunistic trace fossils with vertical to subvertical structures (mostly Ophiomorpha and possible Diplocraterion) and records proximal shoreface successions. The uppermost 285 feet core consists of fine- to medium-grained, sparsely bioturbated sandstone with Skolithos Ichnofacies including Ophiomorpha, Diplocraterion and Paleophycus. The coarser grain size, the sparsely bioturbation with Skolithos ichnofacies, integrated with the presence of shell layers and mud chips indicate a proximal-shoreline setting. In any single parasequence, cleaner storm beds with coarser grain size and less bioturbation have better reservoir quality (porosity and permeability) than highly bioturbated fair-weather beds.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013