STRUCTURAL FRAMEWORK AND TERTIARY HISTORY OF THE SOUTHERN ESPAÑOLA BASIN, NEW MEXICO, USA, INTERPRETED FROM SEISMIC REFLECTION PROFILES

The Española Basin is a small, transitional segment of the Rio Grande Rift linking the larger Albuquerque Basin to the south and the San Luis Basin to the north. This transitional basin comprises a main active segment between "platforms" that became stable after the initial phases of rifting in the Miocene. We will focus on the Albuquerque Basin transition. The SAGE Geophysical Field Course has access to over 200 km of seismic reflection profiles and some borehole data in the southern Española Basin that were acquired for petroleum exploration in the 1970's. These data have been a valuable supplement to the geophysical data gathered by SAGE in its 25 years of operation in the area. The interpretation has been integrated with the recent geophysical and geologic investigations by the U. S. Geological Survey and NM Bureau of Geology in the area.

Several previously unappreciated results have been obtained from these data. The SW margin of the Laramide Sangre de Cristo/Brazos uplift has been mapped in the subsurface adjacent to a complete pre-Tertiary section. A fault zone, controlling deposition of Oligocene volcanic rocks, has been identified on the eastern side of the basin extending from the Tijeras-Cañoncito fault zone in the south, underneath western Santa Fe to where it connects to better exposed faults to the north. The western-most fault in this zone is the 35km long San Isidro Crossing fault. The fault zone is always associated with changes in dip of the basin floor, and may have pre-rift ancestry. The Eocene Galisteo Basin has been mapped from its northern and eastern margins, thickening to the south. Uplift associated with rift extension in the northern Albuquerque Basin to the west has folded all pre-rift units about a N-S axis in the platform area. The transfer of extension from the Albuquerque Basin to the Española Basin terminates the folding in a hinge zone and develops the Española rift basin to the north. The hinge zone roughly coincides with the thinning of the pre-Tertiary sediments on the Laramide uplift. We now view the Española Basin as a composite expression of both Laramide and rift elements.