New Mexico Geological Society Annual Spring Meeting — Abstracts

The Santa Fe embayment is a structural element of the Rio Grande rift-related Espanola basin. Until the advent of rifting in late Tertiary, the Espanola basin was essentially a synclinal sag bounded locally by remnants of the Laramide orogeny's Sangre de Cristo Mountains on the east and the Nacimiento Mountains on the west. During Eocene, up to 4700 ft of sediments of the Galisteo Formation were deposited between these uplifts. The region was modified in Oligocene time by the production and deposition of as much as 2000 ft of volcanic material of the Espinaso Formation, associated with emplacement of intrusives within older rock units and uplift of a range of hills from south of Cerillos to north of La Cinenga. Locally, the laccolithic Cerrillos Hills were responsible for deforming the pre-Oligocene Espanola basin upward in its center, forming synclines on both sides. The eastern depression became the Santa Fe embayment, and most of the western one foundered during Miocene rifting into a deep northern part of the Albuquerque basin.

Rifting on a regional scale through central New Mexico began in early Miocene time, 20-25 million years ago. This intense tectonic activity resulted in a flood of Tesuque Formation clastics that filled both deep and shallow depressions in and near the rift. The northern Santa Fe embayment received more than 4000 ft of these sediments, but the Tesuque Formation is missing or thin in much of the southern embayment. Distribution of the intrusives that constructed the Cerrillos Hills during Oligocene time extends into the southern Santa Fe embayment and, although there is no surface evidence of doming here, their presence is responsible for the absence of Tesuque sediments in the western part. A thin veneer of Ancha Formation overlies the Tesuque and older rocks in the southern embayment that masks subsurface relationships beneath it.

More than 7000 ft of Paleozoic and Mesozoic rocks were removed by pre-Galisteo erosion in less than 20 miles from Galisteo outcrops in the southern end of the Santa Fe embayment to its northern part, where an equally thick suite of Tertiary rocks is encountered overlying Precambrian. Included in this thick Tertiary suite are 1500 ft of lacustrine deposits, the La Mesa limestone, apparently of Eocene, upper Galisteo age that have been encountered nowhere else.

The Tesuque Formation is the primary aquifer in the region, so its presence or absence in the embayment has a profound effect on development in the Santa Fe region.