ABSTRACT

The Morrow Series in the area of the Postle Field, Township 5N, Range 13 ECM, Texas County, Oklahoma, is the subject of this paper. Numerous exploratory and development tests have been drilled in this area providing an abundance of subsurface data. These data were used to make a detailed study of the stratigraphy, geometry and petrography of the sediments which comprise the Morrow Series.

Maps and a cross section were prepared to illustrate structure, paleotopography and sandstone geometry within the investigated area. An interpretation of the environments in which the Morrowan sediment were deposited was made based on this work. Lower Morrowan sediments were deposited in a transitional to marine environment. The area was uplifted and eroded. A drainage system cut channels in Lower Morrowan sediments. These channels were filled later with sandstones deposited in a fluvial environment which persisted in the area until Atokan time.

Thin-sections were made from cores of the Upper Morrow sandstones and the long diameters of about 300 grains were measured from each thin-section. These data were grouped into 0.25 phi classes, corrected so that they would be equivalent to grain size data derived by conventional sieving and used to calculate statistical parameters. A plot of the Graphic Mean Diameter versus the Inclusive Graphic Standard Deviation is the most effective combination in differentiating between river and beach sands according to Moiola and Weiser. Samples from all Upper Morrow sandstones fall in the river field of the above plot supporting the environmental interpretation based on subsurface mapping.

It is concluded that thin-section derived grain size data produce statistical parameters that can be used effectively to prepare environmentally sensitive plots.