Abstract

Recently developed dipmeter techniques provide improved stratigraphic control for isopach projection of Paleozoic sands. These techniques, involving short-interval dip computation and a statistical approach to interpretation of the data, are extensions to the stratigraphic interpretation methods now widely used in Tertiary formations along the Gulf Coast.

Paleozoic sands, such as in the Pennsylvanian section of the Anadarko basin, have often been deposited over wide areas on underlying surfaces of low dip and low topographic relief. Lithologic unit boundaries are almost parallel, providing little information with which to predict the direction of improved sand development. Here, cross-stratification causes most of the anomalies from which dips are computed.

Because cross-bedded sedimentary units are relatively thin, correlation intervals used must be short, leading to computed dips for every few feet of formation.

These dips are the result of many factors, including the attitude of the underlying surface at the time of deposition and any post-depositional tilting. However, dips due to cross-stratification, comprising the large majority of those computed, primarily reflect the direction of sediment transport, although random variations in sedimentation confuse a superficial study of the computed data.

To emphasize trends and minimize random events, statistical methods are used.

Dip-direction frequency diagrams and modified Schmidt plots indicate the direction of sediment transport, show the direction of interval thickening, identify present structural dip, and enable greater accuracy and confidence in predicting sand development.