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David S McCormick1, John B Thurmond2, John P Grotzinger2, Robert J Fleming2
(1) Schlumberger-Doll Research, Ridgefield, CT
(2) Massachusetts Institute of Technology, Cambridge, MA

Abstract: Creating a three-dimensional model of clinoforms in the upper San Andreas Formation, Last Chance Canyon, New Mexico

A fundamental problem of field studies is how to capture the inherent three-dimensionality of stratigraphic units. Sonnenfeld et al. documented spectacular exposures of clinoform geometries in the Permian mixed siliciclastic-carbonate system in the Last Chance Canyon area. However, cross-sections published in their work show geometrical relationships that are artifacts of the projection of 3D stratigraphic relationships into a plane of cross-section. These cross-sections rigorously represent relationships seen in the field, but they highlight how current field techniques do not deal well with the capture of 3D geometries.

To address this problem, we used realtime kinematic global positioning system (RTK GPS) receivers with a 20 cm accuracy, total station, and reflectorless laser rangefinder to survey key stratigraphic surfaces originally mapped by Sonnenfeld. We have also used photogrammetry to extract a digital elevation model (DEM) for the study area and draped aerial imagery on the DEM. This 3D model is the basis for studying the complex, 3D geometries of the upper San Andres units. This model documents that the clinoforms have a corrugated ramp geometry with wavelengths of 100's of meters with onlapping siliciclastic turbidites.

The collection of 3D digital data from outcrop enables the visualization of complex stratigraphic relationships that are not apparent from conventional 2D representations. Where such outcrop data sets have been collected with the intention of conditioning 3D reservoir models, the data must be collected in 3D so that the geometries are not misrepresented as a result of projections into 2D.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana