New Mexico Geological Society Annual Spring Meeting — Abstracts

Five major depositional environments preserved within the progradational sequence of the Point Lookout Saildstone are: Offshore Transition Zone, Shoreface/ Delta Front, Foreshore, Lower Coastal/Delta Plain, and Upper Coastal/Delta Plain. Reflecting the relative
influence of low wave energy, moderate tidal strength, and locally fluvial input, these environments are stacked vertically into two idealized sequences dominated by wave and deltaic processes, respectively.

Total distribution in sand size for the Poine Lookout falls within the narrow 2.0-to-4.0 phi range transported within the fluvial channels of the Menefee Formation. In spite of this narrow range in source material, subtle vertical differences in mode, standard deviation, and modal constancy serve to distinguish lower shoreface, upper shoreface, delta front/estuarine, and fluvial sandstones. Typically-applied bivariate plotting methods are unseccessful in distinguishing these facies. A distinct sediment textural progression characterizes of each of the two basic vertical sequences, and can be used to augment paleoenvironmental interpretations based upon independent field relationships. Results suggest that vertical textural progressions may be a useful diagnostic tool in ancient sandstones, including those for which the total range in grain size is narrow and which display diagenetic complications.