Abstract

Sand(stone) petrofacies are an essential element in paleogeographic and paleotectonic reconstruction of nonmarine basins, such as those of the Rio Grande rift. The Miocene-Pliocene Santa Fe Group of the northern Albuquerque basin records development of the Rio Grande rift. The Santa Fe Group consists of alluvial, lacustrine, and eolian deposits. Three lithostratigraphic units (from oldest to youngest, the Zia, middle red, and Ceja) are petrologically indistinguishable, and therefore are all part of the Albuquerque petrofacies (QFL% 53-26-21). Also present is a locally derived volcanic-hypabyssal petrofacies. Sandstone composition and regional relations indicate that most of the Albuquerque petrofacies is the distal equivalent of Miocene petrofacies of the Espanola basin and southern Tusas Mountains. Equivalence of petrofacies in the two basins supports a hypothesis for two-stage development of the Rio Grande rift. During Middle to Late Miocene time, the two basins were connected to form one enlarged Espanola basin, an irregular west-tilted half graben formed by high-angle faulting on reactivated Laramide structures. In the latest Miocene, movement began on the Embudo-Pajarito-La Bajada-San Francisco-Rincon fault system, and the Sandia Mountains rose rapidly. In the process, the northern Albuquerque basin reversed its half-graben tilt from westward (as the southern part of the Miocene Espanola basin) to eastward (the modern Albuquerque basin). The modern Albuquerque basin bears little resemblance to its Miocene counterpart.

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