ABSTRACT

Several types of primary sedimentary structures have been used in determining the source and direction of transport of sediments. In the last fifteen years, much attention has been given to the description and measurement of the azimuthal directions of paleocurrent features and to the preparation of paleocurrent maps to illustrate ancient current patterns. Aside from the purely academic interests in paleocurrent patterns, the establishment of paleo current trends can be of economic significance.

The paleocurrent trends are indicative of the orientation of elongate sand bodies in which they commonly occur because their orientations typically parallel those of the sand bodies. Paleocurrent patterns may therefore be of assistance in more accurately depicting sand trends on isopach maps. Current trends may be determined by, or reflect, grain orientation and thus yield information regarding the fabric and preferential permeability directions of sands. A marked departure in the paleocurrent pattern of one fault block relative to the pattern in adjacent blocks can be indicative of the relative amount and direction and movement of the block.

Measurements of the orientation of paleocurrent features are readily obtained from outcrops. In the subsurface of the Gulf Coast, the recognition and measurement of current trends must be made through the use of oriented conventional cores and/or the high resolution dipmeter. From oriented cores, paleocurrent directions may be determined from cross-bedding or from the orientation of elongate particles.

Advancements in the instrumentation of dipmeters and improvements in the computation of dipmeter data have made possible the recognition of dip directions of cross-bedding in the subsurface. It is recommended that attention be given to paleocurrent features in the subsurface as an aid in the determination of sand, permeability, and structural trends.

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