Geology and water resources of the Santa Fe area, New Mexico
Abstract: largely restricted to the geologic units of fairly recent geologic age, but a great many features of these units could not be understood without detailed study of the geology of the entire area.
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Cited by 17 publications
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A model of the subsurface structure of the eastern part of the Española Basin in the northern Rio Grande rift of New Mexico was constructed from geophysical data obtained since 1983 by the Summer of Applied Geophysical Experience (SAGE) field course. Approximately 742 new gravity observations, 1276 ground magnetic stations, 30 km of seismic refraction lines, 19 km of seismic reflection lines, 22 magnetotelluric stations, and several Schlumberger and dipole‐dipole resistivity lines were established. Our studies provide new information on one boundary of a major continental rift and on the depositional and structural style of an extensional basin within the rift. Integration of these data sets into a single transect indicates that the Española Basin is asymmetrical with approximately 2 to 3 km of sediments and sedimentary rocks near the center, thinning eastward to the Precambrian outcrop of the flanking Sangre de Cristo uplift. Several minor faults with throws of less than 200 m were found, but no major eastern bounding fault was observed. Thus, the Española Basin could be an asymmetrical, west‐dipping half‐graben. However, major fault offset, down toward the basin axis, may occur within Precambrian rocks of the Sangre de Cristo uplift. In either case, the geometry of the basin does not agree well with current models for the structural evolution of continental rifts, which emphasize low‐angle detachment faults which create asymmetrical, hinged half‐grabens. These models predict that major shoulder uplift should occur adjacent to the side of the graben bounded by a listric master fault rather than adjacent to the hinged side. In contrast, for the Española Basin major uplift occurred adjacent to the eastern side, which could be the hinged side of the basin. A thick wedge of older sedimentary rocks with high P‐wave velocity (4.4 km/s) and low electrical resistivity (5 Ω⋅m) was discovered under the younger Tertiary sediments and sedimentary rocks near the center of the basin. This wedge has maximum thickness of 1.2 km at the western end of the profile and thins eastward. The physical properties suggest this layer could be older Tertiary, or possibly a Mesozoic‐Paleozoic, section of rocks. If the latter, it has potential economic importance because of the possible presence of a Cretaceous section which is known to produce oil and gas in the Albuquerque Basin to the south and the San Luis Basin to the north. However, based on data from the Yates La Mesa no. 2 well, 10 km south of the transect, this wedge is likely middle Tertiary lacustrine deposits (NMOCD, 1986). The great thickness of lake deposits may represent a major lacustrine facies of the Eocene Galisteo and El Rito formations, exposed around the southern, southwestern, and northwestern margins of the basin. Magnetotelluric data suggest the crystalline basement underlying the central Española Basin may be more conductive than near the eastern margin. The entire Española Basin is also underlain by a highly conductive layer of about 1 Ω⋅m at a depth of 15 km. Both the shallow and deep low‐resistivity zones may result from hot, saline fluids. Such fluids deep within the crust may reduce the shear strength of the crust significantly and concentrate crustal extension on the west side of the rift.
A model of the subsurface structure of the eastern part of the Española Basin in the northern Rio Grande rift of New Mexico was constructed from geophysical data obtained since 1983 by the Summer of Applied Geophysical Experience (SAGE) field course. Approximately 742 new gravity observations, 1276 ground magnetic stations, 30 km of seismic refraction lines, 19 km of seismic reflection lines, 22 magnetotelluric stations, and several Schlumberger and dipole‐dipole resistivity lines were established. Our studies provide new information on one boundary of a major continental rift and on the depositional and structural style of an extensional basin within the rift. Integration of these data sets into a single transect indicates that the Española Basin is asymmetrical with approximately 2 to 3 km of sediments and sedimentary rocks near the center, thinning eastward to the Precambrian outcrop of the flanking Sangre de Cristo uplift. Several minor faults with throws of less than 200 m were found, but no major eastern bounding fault was observed. Thus, the Española Basin could be an asymmetrical, west‐dipping half‐graben. However, major fault offset, down toward the basin axis, may occur within Precambrian rocks of the Sangre de Cristo uplift. In either case, the geometry of the basin does not agree well with current models for the structural evolution of continental rifts, which emphasize low‐angle detachment faults which create asymmetrical, hinged half‐grabens. These models predict that major shoulder uplift should occur adjacent to the side of the graben bounded by a listric master fault rather than adjacent to the hinged side. In contrast, for the Española Basin major uplift occurred adjacent to the eastern side, which could be the hinged side of the basin. A thick wedge of older sedimentary rocks with high P‐wave velocity (4.4 km/s) and low electrical resistivity (5 Ω⋅m) was discovered under the younger Tertiary sediments and sedimentary rocks near the center of the basin. This wedge has maximum thickness of 1.2 km at the western end of the profile and thins eastward. The physical properties suggest this layer could be older Tertiary, or possibly a Mesozoic‐Paleozoic, section of rocks. If the latter, it has potential economic importance because of the possible presence of a Cretaceous section which is known to produce oil and gas in the Albuquerque Basin to the south and the San Luis Basin to the north. However, based on data from the Yates La Mesa no. 2 well, 10 km south of the transect, this wedge is likely middle Tertiary lacustrine deposits (NMOCD, 1986). The great thickness of lake deposits may represent a major lacustrine facies of the Eocene Galisteo and El Rito formations, exposed around the southern, southwestern, and northwestern margins of the basin. Magnetotelluric data suggest the crystalline basement underlying the central Española Basin may be more conductive than near the eastern margin. The entire Española Basin is also underlain by a highly conductive layer of about 1 Ω⋅m at a depth of 15 km. Both the shallow and deep low‐resistivity zones may result from hot, saline fluids. Such fluids deep within the crust may reduce the shear strength of the crust significantly and concentrate crustal extension on the west side of the rift.
Raton Basin.-The Raton basin of northeastern New Mexico and southeastern Colorado is a Laramide structural basin bounded on the west by the Sangre de Cristo uplift, on the north by the Wet Mountains uplift and Apishapa arch, and on the east by the Sierra Grande arch. The basin is asymmetrical and the northerly trending axis generally is near the Sangre de Cristo uplift. The jntrabasinal Cimarron arch separates the structurally deeper northern part of the Raton basin from the shallower, southern, Las Vegas sub-basin. During most of Paleozoic time the Raton basin and its bounding uplifts were part of the relatively stable "continental backbone." The oldest known sedimentary rocks in the basin are marine beds of Devonian(?) and Mississippian age. In Early Pennsylvanian time the Rowe-Mora and Central Colorado geosynclinal basins were formed in the area of the present Sangre de Cristo uplift and the western half of the present Raton basin. The basins were bounded on the west by the intermittently rising San Luis uplift, and on the east and north by the ancestral Sierra Grande, Apishapa, and Wet Mountains uplifts. A mainly marine unstable shelf facies of the Magdalena CJroup of Pennsylvanian age in the Las Vegas sub-basin is 1,500-2,500 feet thick. These rocks •_-rade abruptly northward into a marine geosynclinal facies which is as much as 6,000 feet thick in the Las Vegas sub-basin. The Magdalena Group is absent from the Cimarron arch, but it probably is present in the western half of the northern Raton basin where it may be 4,000 feet thick. Orogenic debris of the Sangre de Cristo Formation of Pennsylvanian and Early Permian age was derived mainly from the San Luis uplift, filled the Rowe-Mora and Central Colorado basins, and lapped onto Precambrian rocks of the other bounding uplifts. The Sangre de Cristo Formation is 700-3,500 feet thick at the south, and 6,000-9,500 feet thick at the north. Higher Permian rocks, and Upper Triassic and Upper Jurassic rocks have average aggregate thicknesses ranging from 2,300 feet at the south to 1,100 feet at the north. These deposits blanketed the region of the present Raton basin and buried the late Paleozoic, Sierra Grande, and Apishapa uplifts. Cretaceous marine shale interbedded with some sandstone blanketed the entire region. The Cretaceous rocks are about 4,500 feet thick at the north, and remnants in the Las Vegas subbasin are 900-1,000 feet thick. The terrestrial latest Cretaceous and early Tertiary rocks, which are about 12,000 feet in aL'u'regate maximum thickness in the northern part of the Raton basin, were derived mainly from the rejuvenated San Luis uplift. During early and middle Tertiary time, the San Luis uplift and the western parts of the Paleozoic Rowe-Mora and Central Colorado basins were elevated to form the Sangre de Cristo uplift. The present Raton basin, Wet Mountains uplift, and the Apishapa, Las Animas, and Sierra Grande arches were formed in early Tertiary time. The Raton basin has been a basinal area for most of its history since Early Pennsylvanian t...
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