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OUTCROP-BASED HIGH RESOLUTION GAMMA-RAY CHARACTERIZATION OF ARSENIC-BEARING LITHOFACIES IN THE PERMIAN GARBER SANDSTONE AND WELLINGTON FORMATION, CENTRAL OKLAHOMA AQUIFER (COA). CLEVELAND COUNTY, OKLAHOMA
Citation:
Gromadzki, G. A., S. T. Paxton, S. J. Smith, S. Christenson, AND R W. Puls*. OUTCROP-BASED HIGH RESOLUTION GAMMA-RAY CHARACTERIZATION OF ARSENIC-BEARING LITHOFACIES IN THE PERMIAN GARBER SANDSTONE AND WELLINGTON FORMATION, CENTRAL OKLAHOMA AQUIFER (COA). CLEVELAND COUNTY, OKLAHOMA. Presented at American Assn. of Petroleum Geologists Annual Mtg, Dallas, TX, April 18 - 21, 2003.
Impact/Purpose:
To inform the public.
Description:
The COA supplies drinking water to a number of municipalities in central Oklahoma. Two major stratigraphic units in the COA, the Garber Sandstone and Wellington Formation, contain naturally occurring arsenic that exceeds government mandated drinking-water standards (EPA, 2001). Previous work in the COA (Schlottman et al., 1998) has shown that arsenic concentrations in the aquifer vary with subsurface water chemistry and proximity to finer-grained lithofacies. In order to better describe the aquifer quality and constrain the distribution of arsenic with lithofacies, we have constructed numerous high-resolution spectral gamma-ray profiles of the Garber-Wellington outcrops using a portable gamma-ray scintillometer. In addition, rock samples associated with each gamma ray reading taken from outcrops were returned to the laboratory for textural analysis and statistical evaluation. We find that many of the arsenic-bearing lithofacies are characterized by high total gamma-ray counts (associated with K, U and Th respectively). This result is because arsenic in the rocks is associated with iron oxide that appears to be enriched in the finer-grained, clay-rich lithofacies. Calculated permeability profiles mimic fining-upward grain-size profiles characteristic of fluvial depositional settings. Data from previous USGS studies (cores, geochemistry, petrography, and x-ray diffraction) are being incorporated into the evaluation of the gamma-ray responses as well. Results of this work are being integrated with other on-going companion studies to constrain subsurface well log correlation and the reconstruction of paleodepositional environments in the Garber-Wellington interval of the COA.