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.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-05-459 |
| Date | 16 January 2010 |
| Creators | Cook, Timothy D. |
| Contributors | Giardino, John R., Bouma, Arnold H. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis |
| Format | application/pdf |
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