ABSTRACT

The Elgin Sandstone is a member of the Pennsylvanian Vamoosa Formation on outcrop in Oklahoma and a member of the Kanwaka Formation in southern Kansas. Surface exposures in the eastern part of the study area and electric well logs west of the outcrop belt permit a rather accurate description of the geometry and internal features of the sandstone.

Major sandstone development within the Elgin interval is represented by lenticular sandstones, which are multilateral and multistoried deltaic distributary and alluvial channel deposits. Thick sandstone belts are 1 to 3 mi wide and contain 100 to 150 ft of sand. Genetic units of lenticular sandstones which are characterized by sharp contacts, are 20 to 30 ft thick and as much as 600 ft wide. Characteristic sedimentary structures of this sandstone type include medium-scale cross-bedding, high-angle initial dip, cutouts, and parting lineation. Local trends are quite variable; the average paleocurrent direction in the study area is N 25°W. The alluvial sandstones are more extensively developed laterally and are coarser grained than the narrow distributary units, which are very fine to fine-grained. Both contain intraformational particles, wood fragments, and secondary concretions.

Thin-bedded sandstones are coastal and/or marine delta-fringe units. They are generally quite thin, with gradational lower and lateral contacts. The most common sedimentary structures are small-scale cross-bedding, ripple marks, low-angle initial dip, and interstratification. The primary paleocurrent direction is N 50°W; a secondary trend is N 40°E. The sandstones are very fine-grained and well sorted, and they contain carbonaceous matter, small wood fragments, and muscovite flakes. Paleocurrent data, regional distribution of sandstone, and southerly increase in chert content suggest the Ouachita and Arbuckle uplifts as principal source areas, with a possible contribution in the north from the Ozark province.

Maximum horizontal permeability corresponds to the direction of preferred grain orientation in the alluvial and distributary sandstones. However, a correlation does not appear to exist between grain orientation and permeability in delta-fringe sandstones. Water analyses show a rather wide variation in ion concentrations. Several of the samples have chloride and/or TDS concentrations in excess of the established limits for domestic use. The fresh-mineralized water boundary, which appears to be related to sandstone thickness and distribution, varies in depth from 150 to 600 ft. The Elgin Sandstone in the study area may contain as much as 3 10¹² gal of fresh water.