ABSTRACT

An intrashelf basin located on the Upper Cambrian carbonate-rimmed shelf (miogeocline) of the Appalachian orogene, appears to have controlled facies distribution during deposition of the Nolichucky Formation (0 to 985 ft; 0 to 300 m thick). The intrashelf basin was bordered along strike and toward the regional shelf edge by a rim of peritidal carbonates and by nearshore clastics toward the craton. The peritidal carbonates passed into the intrashelf basin by way of a gently sloping carbonate ramp.

Peritidal facies are cyclic, upward-shallowing stromatolitic carbonates (Elbrook and/or Honaker Dolomite) that grade basinward into cross-bedded ooid and oncolitic intraclast grainstones. These pass downslope into subwave-base, deeper ramp, ribbon carbonates and thin limestone conglomerate (Maryville, Nolichucky lower limestone, and Maynardville limestone). Ribbon limestones are layers and lenses of trilobite packstone, parallel and wave-ripple-laminated quartzose calcisiltite, and lime mudstone arranged in storm-generated fining-upward sequences (0.39 to 2 in.; 1 to 5 cm thick) that may be burrowed. Intrashelf basin facies (Nolichucky lower and upper shale) are storm-generated sequences of green calcareous shale with open-marine biota; parallel with hummocky laminated calcareous siltstone; and intraformational flat-pebble conglomerate, and skeletal or ooid limestone with trace fossils, glauconite zones, and hardgrounds. A 49 ft (15 m) thick tongue of bioherm-bearing cyclic carbonates within the shale package (Nolichucky middle limestone) developed during a period of shoaling of the intrashelf basin.

Development of the Late Cambrian carbonate-rimmed shelf and its intrashelf ramp and basin may have been influenced by high carbonate production along the regional shelf edge, by tectonic subsidence associated with a major shelf depocenter, and by influx of terrigenous sediments which suppressed carbonate deposition in the basin. Understanding the Nolichucky facies within a ramp to intrashelf basin model provides a framework for understanding similar continental-shelf facies which are widely distributed in the lower Paleozoic and in the subsurface of the Mesozoic. Recognition of basins located on pericratonic shelves is important because such basins influence the distribution of potential petroleum source beds and reservoir facies whose trends may be unrelated to regional shelf-edge trends.

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