Abstract

Regional studies using lithology, oil well samples, and acid residues of both surface and subsurface samples give evidence for delineation of a miogeosynclinal belt and shelf area in the Midcontinent region. The geosynclinal belt was S-shaped, extended through central Arkansas and Oklahoma, thence southward around the Central Texas uplift and westward into West Texas. The geosynclinal belt was structurally responsible for the deep depositional basin into which the thick carbonates of the Arbuckle Group were deposited, and controlled the site for the deposition of the succeding Simpson Group. During Simpson time, hundreds of minor and several major oscillations occurred causing transgressions and regressions that resulted in the great verical and lateral variability of green shales, limestones, and major sandstones. During late Simpson time the sequence spread over the shelf area and the thick geosynclinal sediments merged into thinner equivalents. Sheet sands were spread over the shelf area by southwestward longshore drift from northern, intermediate, and local source areas, and some of the sands became important oil-producing beds.

The study led to the correlation of lower Simpson formations with pre-St. Peter formations which were deposited chiefly in the geosynclinal belt. The upper Simpson beds starting with the basal McLish sand merged northward with the Tulip Creek sand over the shelf area to become what is called the St. Peter Sandstone, with the associated other beds lensing out. North-ward and eastward the Bromide became the Platteville or its equivalents. Zones A to D of the Simpson Group in West Texas can be correlated with the Arbuckle Mountains section. The existence of the Ozark island had a significant influence on the deposition of both lower and upper Simpson beds.