GEOLOGIC SETTING AT OUTCROP The rocks of the Wilberns Formation have a very involved history. Today, the Wilberns outcrops are found in the Llano uplift region of central Texas, the most prolific Wilberns outcrops are to the west of the Llano uplift area (Bell and Barnes, 1972, p. 28). The Llano uplift area is a geologically complex region of central Texas (fig. 3). Precambrian metamorphic and plutonic igneous rocks mostly dominate the Llano region. The uplift brought Cambrian Wilberns rocks to the surface, which is where almost every study of the Wilberns is located (Barnes and Bell, 1977). The Llano uplift area contains a wide swath of central Texas, from Concho County in the west, to Travis County in the east. The western Llano Uplift area contains numerous outcrops of
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Each member of the Wilberns Formation boasts a different diagenetic history, due to this staggering complexity of the individual members that compose the Wilberns Formation; each member’s geologic history will be explored. The one common feature of the members of the Wilberns is that they were deposited from the middle Cambrian to the late Cambrian; however, depositional environments were varied throughout the depositional history of the Wilberns formation (Barnes and Bell, 1977). The Paleogeographic map of North America (fig. 5) from Blakely (2005) demonstrates that the Llano region of central Texas was submerged in a shallow sea, this map is an approximation, especially given that aeolian sedimentary phenomena, like calcrete (Read, in Walter, 1976, p. 56; Deso, 1998, p. 49), and desiccation cracks (Gann, 2000, p. 53) are foundsporadically at outcrop. These aeolian features are more than likely features of a subaerially exposed shoal or tidal flat during short-lived, local eustatic periods. The controlling factor during the deposition of the Wilberns formation, and for all of Texas and North America during the middle to late Cambrian is the Sauk Sequence
Each member of the Wilberns Formation boasts a different diagenetic history, due to this staggering complexity of the individual members that compose the Wilberns Formation; each member’s geologic history will be explored. The one common feature of the members of the Wilberns is that they were deposited from the middle Cambrian to the late Cambrian; however, depositional environments were varied throughout the depositional history of the Wilberns formation (Barnes and Bell, 1977). The Paleogeographic map of North America (fig. 5) from Blakely (2005) demonstrates that the Llano region of central Texas was submerged in a shallow sea, this map is an approximation, especially given that aeolian sedimentary phenomena, like calcrete (Read, in Walter, 1976, p. 56; Deso, 1998, p. 49), and desiccation cracks (Gann, 2000, p. 53) are foundsporadically at outcrop. These aeolian features are more than likely features of a subaerially exposed shoal or tidal flat during short-lived, local eustatic periods. The controlling factor during the deposition of the Wilberns formation, and for all of Texas and North America during the middle to late Cambrian is the Sauk Sequence