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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 63 (1979)

Issue: 3. (March)

First Page: 504

Last Page: 504

Title: Eolian Sedimentology Interpreted from Dipmeter Results: ABSTRACT

Author(s): R. D. Nurmi, V. R. Hepp

Article Type: Meeting abstract


The dipmeter is an effective tool for subsurface analysis of sedimentary bedding as well as for interpretation of structure. Improved computer processing of dipmeter surveys allows efficient and reliable dip (arrow) plots for interpretation of structural and depositional dips. Structural tilt and borehole Previous HitdeviationNext Hit, which make precise analysis of sedimentary dips and transport direction impossible with Previous HitstandardNext Hit cores, are routinely removed in processing dipmeter surveys for depositional analysis. Statistical analysis of sedimentary dips is possible using polar-frequency plots.

Dipmeter surveys of eolian formations have been analyzed as part of a systematic study of depositional environments. Applying eolian sedimentologic principles to dipmeter data allows regional analysis of eolian formations in hydrocarbon exploration and detailed modeling of eolian reservoirs. Dipmeter surveys clearly reveal cyclic dune and interdune deposits and distinguish lateral and longitudinal dune types, which may have different reservoir characteristics. Lateral-type dunes--barchan, transverse, and parabolic--are elongate perpendicular to the wind direction and are characterized by cross-bedding with a unimodal distribution of dip azimuths about the wind direction. Longitudinal, or seif, dunes are elongate parallel with wind direction and are characterized by a bimodal distribut on of cross-bedding dip azimuths about the wind direction.

A polar-frequency plot of sedimentary dips from two dipmeter surveys of a thick North American eolian system revealed an association of the angle of dip with the relative azimuth position about the transport direction. The high-angle dips (10 to 40°) have the narrowest Previous HitdeviationNext Hit of dip azimuth and should be used to interpret the transport direction. The medium-angle dips (5 to 10°) have a bimodal azimuth distribution with a greater Previous HitdeviationNext Hit about the transport direction. The low-angle dips (< 5°) have a greater bimodal Previous HitdeviationTop of dip azimuth about the transport direction. These results tend to support an interpretation of foresets of barchanlike dunes.

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Copyright 1997 American Association of Petroleum Geologists