Facies Description and Interpretation of the Upper Lower Hickory Sandstone, Riley Formation, Central Texas

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Title: Facies Description and Interpretation of the Upper Lower Hickory Sandstone, Riley Formation, Central Texas
Author: Cook, Timothy D.
Abstract: 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 .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2009 -05 -459
Date: 2010-01-16

Citation

Facies Description and Interpretation of the Upper Lower Hickory Sandstone, Riley Formation, Central Texas. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2009 -05 -459 .

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