MAPPING THE STRUCTURAL EVOLUTION OF THE CHAMA-ESPANOLA BASIN FROM EOCENE LARAMIDE COMPRESSION TO MIOCENE RIO GRANDE RIFT EXTENSION IN NORTH-CENTRAL NEW MEXICO

The transition from Laramide compression to Rio Grande Rift extension is recorded in three distinct sedimentary units found in the Chama-Espanola Basin in north-central New Mexico. The Abiquiu embayment, within the Chama-Espanola Basin, comprises an area whose northeast to southwest distance spans 60 km. Here, it is possible to find outcrops of these units on the Colorado Plateau to the west, in the Tusas Mountains to the east and within the rift valley near the Chama River. The oldest unit, the El Rito formation, unconformably overlies Precambrian to Cretaceous units and was deposited in the Eocene during the waning stages of compressional tectonics. Unconformably above the El Rito formation lays the Ritito conglomerate, which was deposited in the Oligocene to early Miocene, followed by the Abiquiu Formation which is marked by rift related Miocene volcanism. To better understand the structural kinematics found during the transition from Laramide compression to Rio Grande Rift extension it has become important to analyze the unconformities and sedimentary units using digital mapping techniques. A database compiled using personal field measurements along with compilations of previous geologic map data have made it possible to measure and model the orientations and displacements found in the Eocene and Oligocene unconformities throughout the Abiquiu Embayment. Using digital two-dimensional and three-dimensional reconstructions of these key features it is possible to identify the amount of tilting in the basin during late stage Laramide compression and the magnitude of vertical displacement caused by Rio Grande rift extension. This project aims to illustrate any overlay or hiatus apparent in the timing of Laramide compression and Rio Grande rift extension.