Lower Triassic strata in the Wellington Flat and Tully cores reflect a lateral transition from shallow water strata (Wellington Flats core) to strata that indicate deposition on a relatively more distal, storm-dominated ramp (Tully core). The Sinbad Member, along with the upper part of the underlying Black Dragon Member and the lower part of the overlying Torrey Member (Moenkopi Formation), are composed of ten carbonate, siliciclastic and mixed carbonate/siliciclastic facies deposited on a west-facing ramp/shelf that reached maximum flooding during Smithian time. Individual beds and facies display a large degree of lateral homogeneity and regional persistence in the study area. The Wellington Flats core contains the three units characteristic of outcropping Sinbad Limestone: a basal skeletal unit, a middle peloidal unit, and an upper, oolitic dolomite unit. The more offshore Tully core is composed of skeletal grainstone, with fewer shallow-water carbonate and siliciclastic deposits. Discontinuity surfaces (hardgrounds, firmgrounds, and change surfaces) are common and indicate that sedimentation was punctuated by short-lived hiatuses accompanied by cementation, scour, and/or encrustation of the sediment-water interface. The Black Dragon, Sinbad, and lower Torrey Members represent at least one 3rd-order depositional sequence bounded below by the Tr-1 unconformity and above by lowstand deposits in the middle Torrey Member. Amalgamated fluvial channels in the middle of the Black Dragon Member may represent an additional 3rd-order sequence boundary that separates a Greisbachian sequence (lower Black Dragon Member) from the Smithian sequence (upper Black Dragon through lower Torrey members), but this is unsubstantiated by biostratigraphic data at present. Diagenesis is strongly controlled by facies. Diagenetic elements include marine fibrous calcite cements, micritized grains, compaction, dissolution and neomorphism of aragonite grains, meteoric cements, pressure dissolution, and dolomitization. The paragenetic sequence progresses from marine to meteoric to burial. Marine and meteoric cements occlude much of the depositional porosity, which ranges from 0 to 10 % in the sample interval. The best reservoir qualities in core (1.0 md) occur in grainstones and quartz-siltstones. Although its relative thinness precludes it from being a major producer, the Sinbad Limestone Member of the Moenkopi Formation bears potential for modest future oil production.



College and Department

Physical and Mathematical Sciences; Geological Sciences



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Document Type





Moenkopi, Sinbad, Limestone, Reservoir Characterization, Facies, Petroleum, Stratigraphy, Sedimentology



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Geology Commons