Present models suggest that fluvial and marine depositional patterns were distinct from modern patterns prior to the appearance of land plants. Although these models are likely correct, problems exist when one attempts to distinguish between fluvial and shallow marine deposits in pre-Silurian strata, making it difficult to accurately determine depositional patterns. The lack of land plants and scarcity of body and trace fossils, especially in Precambrian and early Cambrian strata, make identification difficult. Based on core data and limited outcrops, the Lower Hickory Sandstone, a late Cambrian sandstone, has been interpreted to progress from fluvial to shallow marine. These data have allowed the development of an overall depositional model, but minimal detail of facies changes is available. Based on the limited data, both deltaic and estuarine models have been suggested for the Lower Hickory. Mining of the Lower Hickory for frac sand has created highwalls in the CarmeuseNA Mine, which provides an opportunity to study facies changes at this site. The CarmeuseNA Mine, located in McCulloch County, Texas, has exposed the formation along ~500 m long and 20 m-high faces, respectively. Because of limited exposure, only the south and west walls, as well as part of the east wall, could be examined. Digital photographs of the faces were mosaiced using standard photogrammetrical practices to produce visual representation of the highwalls. Bedding geometry was then mapped on the digital images to facilitate a detailed interpretation of the depositional process. Core and well data were used to map Hickory thickness to produce an isopach map. Four primary facies were observed in the quarry, dominated by small-scale and large-scale cross-bedding. Paleocurrents are generally unidirectional to the southsoutheast indicating a braided fluvial origin, but rarely opposing directions are seen. Bioturbation is rare low in the section, but increases upwards. Together with the rare herringbone cross-bedding, clay drapes, and bioturbation, a tidal influence is strongly suggested. The model suggested is a braided stream setting influenced and reworked by tides. A braided-delta fed by braided streams guided by a ridge and swale-dominated setting, which served as the sediment supply for the delta, is proposed.

A magnetic study over a 95 m x 150 m area of the Hickory sandstone aquifer in central Texas was carried out as part of multitechnique geophysical investigation that included ground penetrating radar (GPR), electromagnetic (EM), seismic and seimoelectric. In geophysical exploration, the magnetic method can be utilized as an alternative to more expensive methods, such as seismic or it can be used to complement other methods. In this thesis, the magnetic method is applied to estimate the location of a previously mapped fault by Texas A&M geology students, and it is used to estimate the magnetic susceptibility contrast of the targeted fault. The main challenge of this study is imaging shallow faults using the geophysical magnetic method in a fractured aquifer with widely-scattered distribution of iron bearing rocks as in the case of the Hickory sandstone aquifer. A Geometric—G858 Cesium vapor magnetometer was used to collect magnetic data. The data consisted of 19 north-south and 1 east-west lines acquired in October and November of 2012. Elementary data processing such as diurnal correction, regional correction, reduction to pole (RTP) filter, Euler deconvolution, forward modeling and inversion were employed to characterize the faulted zone. This faulted zone separates granite basement rocks from the Hickory sandstone. As a result, this study emphasizes that Euler deconvolution applied to RTP-filtered data increases the interpretability of geological and structural contacts. The results of the magnetic method have been compared to results of GPR, EM and seismoelectric methods. Understanding the magnetic mineralogy of rocks and their properties can improve the geological interpretation of magnetic surveys.