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Sedimentology and architecture of the Upper Cambrian Hickory Sandstone, central Texas, U.S.A.

Isaac Perez,

Texas A&M University Department of Geology and Geophysics,

College Station, TX.

[email protected]

Sedimentary environments may have been quite different before the development of land plants in the late Silurian. Rapid drainage of terrestrial surfaces, flashy rivers with poorly stabilized banks and coarse sediment loads supplied to coasts from landscapes dominated by physical weathering are expected to have altered depositional patterns and preserved facies. Quarries of the Hickory Sandstone located in central Texas provide an exceptional opportunity to examine facies variations and stratal architecture in deposits of this age in order to interpret depositional processes and sedimentary environments. The Hickory Sandstone is an Upper Cambrian transgressive siliciclastic succession in the Riley Formation, which has been interpreted as a transgressive succession from fluvial to shallow marine deposits.

Active quarrying of the Hickory Sandstone exposures highwalls, kilometers long and several tens of meters high, in both depositional dip and strike orientations. Locations of vertical highwalls, blasted back a few tens of meters at a time and then excavated during quarrying, were surveyed using a reflectorless total station. Orthorectified photomossaics have been constructed from high-resolution digital images using photogramity techniques to provide a base for the mapping of sedimentologic variations within successive quarry walls. Detailed stratal architecture and facies analysis of these deposits are being done in order to define the patterns of deposition that characterize different depositional environments and contrasts between these ancient deposits and those that comprise younger strata. Comparison of spatially-oriented bedding diagrams constructed from successive parallel highwalls exposures will allow strata and facies variations to be correlated in three dimensions.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid