Actualistic Petrofacies: Applications in Paleotectonic Reconstructions

Raymond V. Ingersoll

Modal analysis of modern alluvial sand from known source areas provides fundamental data on source rock control on sand composition in active tectonic settings. These data may be used to statistically divide and group compositions according to their source areas, thus defining actualistic petrofacies. Ancient petrofacies may be compared to the actualistic petrofacies, in order to better constrain provenance and paleotectonic reconstructions. This approach may be applied at several scales of investigation. Plate-tectonic settings of sand and sandstone are consistently predicted using the first-order actualistic petrofacies of Dickinson and Suczek, and others. Second-order actualistic petrofacies may be used to identify specific source regions within a given tectonic settin , such as specific source terranes within the Rio Grande rift of New Mexico and the Transverse Ranges of California. Use of consistent methodology (e.g., Gazzi-Dickinson point-counting method) is essential for consistent results. Stepwise Discriminant Analysis provides the objective basis for comparison between actualistic petrofacies of known provenance and ancient petrofacies of inferred provenance. Application of this methodology provides needed objectivity in source rock and paleotectonic reconstructions.

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