Actualistic sandstone petrofacies: Discriminating modern and ancient source rocks

Abstract

Actualistic models relating plate-tectonic setting to sedimentary basins and provenance successfully predict modal compositions of sand and sandstone at the scale of continents and ocean basins (third-order models). Second-order models may be used to identify source regions within a given tectonic setting, such as source terranes within the Rio Grande rift of New Mexico. First-order models relate the composition of modern alluvial sand directly to specific source rocks (e.g., granite). Petrographic data from locally derived sand of known provenance may be used to statistically discriminate compositions according to their source rocks, 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 first-, second-, or third-order scales. At first- and second-order scales, stepwise discriminant analysis reveals the Tertiary provenance history of the Rio Grande rift of north-central New Mexico by comparing Tertiary petrofacies with modern petrofacies of known provenance. Application of this technique provides needed objectivity in source-rock and paleotectonic reconstructions.