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Stratigraphic Statistical Curvature Analysis Techniques

C. A. Bengtson, John P. Ziagos

SCAT applies statistical techniques to dipmeter data to identify patterns of bulk curvature, determine transverse and longitudinal structural directions, and reconstruct cross sections and contour maps. STRAT-SCAT applies the same concepts to geometric interpretation of multistoried unimodal, bimodal, or trough-type cross-bedding and also to seismic stratigraphy-scale stratigraphic structures. "Structural dip," which comprises the bulk of dipmeter data, is related to beds that (statistically) were deposited with horizontal attitudes; "stratigraphic dip" is related to beds that were deposited with preferentially oriented nonhorizontal attitudes or to beds that assumed such attitudes because of differential compaction. Stratigraphic dip generates local zones of departure fr m structural dip on special SCAT plots. The RMS (root-mean-square) of apparent structural dip is greatest in the (structural) T-direction and least in the perpendicular L-direction; the RMS of stratigraphic dip (measured with respect to structural dip) is greatest in the stratigraphic T*-direction and least in the stratigraphic L*-direction. Multistoried cross-bedding appears on T*-plots as local zones of either greater scatter or statistically significant departure of stratigraphic median dip from structural dip. In contrast, the L*-plot (except for trough-type cross-bedding) is sensitive to cross-bedding.

Seismic stratigraphy-scale depositional sequences are identified on Mercator dip versus azimuth plots and polar tangent plots as secondary cylindrical-fold patterns imposed on global structural patterns. Progradational sequences generate local cycloid-type patterns on T*-plots, and compactional sequences generate local half-cusp patterns. Both features, however, show only structural dip on L*-plots.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.