ABSTRACT

Several authors, Campbell (1968) and McDaniel (1968) for example, have demonstrated the dipmeter's ability to resolve internal cross-bed dips. Analysis of the dip patterns, which result from paleocurrent flow directions, are then interpreted to determine different sand body types.

The Purpose of this paper is to show the relationship between cross-bed variation in a fluvial sand bar and known channel patterns which existed during deposition. The sand bar studied is in the Arkansas River valley approximately 10 miles upstream from Tulsa. From aerial photo sequences plus discharge and river stage records, it can be shown that the entire sand bar (600,000 cubic yards) was deposited during two floods--May 19 to 22, 1957 (60 hours) and October 3 through 6, 1959 (96 hours).

The sand bar was studied in detail along a 500-foot long natural cutbank parallel to the valley and in a 700-foot long trench dug at right angles to the valley. Cross-bed types were studied and 210 cross-bed measurements (true dip direction and true dip angle) were recorded a 12 vertical sections.

Results show that the highly variable patterns of cross-bed dips do match the erratic and changing flow directions prevalent during flood stages. In some vertical sections cross-bed dip directions are at all angles to the overall east-west orientation of the Arkansas River valley. These results verify the expected cross-bed variability in fluvial sands and suggest that dipmeter patterns from wells in channel sandstone bodies should be interpreted and projected with caution.