Stratigraphy and depositional trends in the Santa Fe Group near Espanola, north-central New Mexico: tectonic and climatic implications

Abstract

— Exposures of the Miocene Tesuque and Chamita Formations and interbedded tephra zones provide a record of extensional basin evolution in the northern Española basin of the northern Rio Grande rift. Geologic studies of these strata resulted in the definition of the Cuarteles Member (new name) in both the Tesuque and Chamita Formations. The Cuarteles Member is a 180 m-thick succession of light brown to reddish yellow to pink arkosic sandstone together with graniteand quartzite-bearing conglomerate derived from the Sangre de Cristo Mountains. It was deposited in an alluvial slope environment on the eastern basin margin. Six laterally extensive tephra-bearing intervals have been mapped in the study area and correlated between measured stratigraphic sections. The age of these tephra-bearing intervals are generally well-constrained and are used to estimate rates of stratal tilting and stratal accumulation during middle and late Miocene time. Additional geochronologic controls come from middle Miocene (late Barstovian) mammal fossils in these deposits. There is a noteworthy decrease in stratal tilt rates and sediment accumulation rates after about 13-14 Ma. This decrease is generally coincident with an overall coarsening of the stratigraphic succession and basinward progradation of deposits represented by the Cuarteles Member. The rate change in both stratal tilt and stratal accumulation rate data indicates a decrease in tectonic subsidence of the Española basin after about 13-14 Ma. The overall increase in the proportion of coarse channel deposits and clast sizes, in addition to the progradation of basin-margin detritus, after 13-14 Ma does not agree with previous half-graben models that relate tectonic subsidence with deposition. These sedimentologic changes could be the result of the Española basin transitioning from an underfilled to overfilled condition as the rate of tectonic subsidence decreased. Other factors besides tectonic changes that could have influenced this coarsening and progadation include: 1) a change in climate as inferred from the emplacement of a major dune field and marine proxy records, and 2) geomorphic changes in streams draining the Sangre de Cristo Mountains. that the basin here is a west-tilted half-graben. The Pajarito and Santa Clara faults, in addition to possible faults to the west buried by younger volcanic rocks, probably act as master faults for the half-graben (Golombek, 1983; Harrington and Aldrich, 1984; Baldridge et al., 1994; Koning et al., 2004b). A structurally shallower FIGURE 1. Location map of the northern Española and southern San Luis basins. The area of the geologic map of Figure 2 (the study area) is shown by the rectangle near the city of Española. Major geologic structures are shown by white lines, with the small perpendicular bars indicating throw direction of normal and normal-oblique faults. Important faults are abbreviated as: PFZ = Pajarito fault zone, SCF = Santa Clara fault, OCF = Ojo Caliente fault, BMF = Black Mesa fault, LMF = La Mesita fault, EF = Embudo fault, SDCF = Sangre de Cristo fault, and PPF = Pecos-Picuris fault. EF LM F BM San Luis Basin Tusas Mts