Abstract

The postglacial Beacon sequence in the Beardmore Glacier area comprises 2000 m of nonmarine clastic sediments. Approximately 3000 paleocurrent measurements were taken in sets of about six from stratigraphic intervals less than 30 m thick from the Mackellar, Fairchild, and Buckley Formations of Permian age and the Fremouw and Falla Formations of Triassic age. These data yielded 432 current directions, 168 from small-scale cross-bedding, 162 from medium-scale cross-bedding, 69 from parting lineation, and 33 from logs, ripple marks, and slump folds. Analysis of variance, using vector rather than arithmetic means, was used to indicate the likelihood that differences in current direction for different areas, formations, or types of sedimentary structures are due to variations in a normally distributed population. Four formations have essentially a unimodal current pattern, while the Buckley Formation has a centripetal pattern. There is no significant difference (F (sub .10) ) between mean directions to the southeast for the three Permian formations, or to the northwest for the two Triassic formations. This reversal implies a laterally constraint of both Permian and Triassic paleocurrent systems. Mean current directions for small- and medium-scale cross-bedding and parting lineation within each formation are not significantly different, and for the Fairchild and Buckley Formations, values for standard deviation are also similar. For these two units, each structure is an equally reliable indicator of paleocurrent direction, and a hierarchy of bedforms like that proposed by Allen (1966) is not indicated. However, such a hierarchy might exist for the Fremouw Formation, where parting lineation is significantly less variable than medium-scale cross-bedding, and medium-scale cross-bedding is significantly less variable than small-scale cross-bedding.

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