Stratigraphic Dipmeter Interpretation of Turbidite Sequences, Gulf of Mexico

Henry S. Pettingill

High-resolution dipmeter logs have been compared to conventional and sidewall cores from Gulf of Mexico turbidite depositional sequences. These calibrations, in conjunction with seismic and conventional log data, allow numerous stratigraphic interpretations from dipmeter data. Bedding styles and lithological information can be interpreted from resistivity character and vertical dip progressions.

Examples in sand-rich deposits demonstrate (1) thin-bedded vs. thick-bedded or massive lithologies, (2) subtle layering in sands which are visually massive, (3) parallel-bedded strata vs. pinch and swell bedding, and (4) massive, shaly nonreservoir sands (interpreted to be debris flow deposits). The amount of dip scatter in sands is directly or indirectly related to depositional energy level.

Deep-water shales exhibit a range of dip patterns which may be used to differentiate them and thus better understand their significance to fan-related processes. The amount of dip scatter is apparently inversely related to the presence of silty and/or calcareous layers. Shales without substantial layering characteristically have random dip patterns. Turbiditic shales have constant dip, reflecting intercalated clay-rich and silt-rich beds; hemipelagic shales of varying CaCO₃ composition likewise have patterns of constant dip.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.