The Vallejo Formation; new early Tertiary red-beds in southern Colorado

Upson, J. E.

doi:10.2475/ajs.239.8.577

Cited by 10 publications

(6 citation statements)

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“…Aplite dikes commonly intrude the stocks. Present in several areas as steep-sided stocks along north-trending belt in the San Luis Hills (Thompson and Machette, 1989 Wallace and Lindsey (1996), and Wallace and Soulliere (1996) as the Vallejo Formation of Upson (1941). Rounded clasts in the conglomerate were derived chiefly from Paleozoic and Proterozoic rocks, although some deposits are composed almost entirely of Proterozoic gneiss and quartzite clasts.…”

Section: Tiqmentioning

confidence: 99%

Geologic map of the Alamosa 30’ × 60’ quadrangle, south-central Colorado

Thompson¹,

Shroba²,

Machette³

et al. 2015

Scientific Investigations Map

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and reinterpretation. Mapped surficial deposits and descriptions reflect reinterpretation and reclassification of units and revisions to geographic extent, and lithologic character and map unit representation particularly with respect to mapping of tills in glaciated valleys on the east flanks of the Sangre de Cristo Mountains and Culebra Range by Shroba. Bedrock mapping represents a regional synthesis of geologic data compiled and published over the past quarter century and necessarily includes both simplification and expansion of previously published data with respect to the adopted stratigraphic nomenclature and aerial depiction of map units and faults. Regional and local unit nomenclature is constrained by reference to recently published and previously unpublished 40 Ar/ 39 Ar age determinations on Neogene volcanic deposits-the primary Cenozoic stratigraphic markers in the map area. Map unit descriptions rely heavily on previously published data and are simplified to embody the dominant characteristics of map units particularly where units depicted on larger-scale maps were combined for inclusion in this 1:100,000-scale map. Fault depictions are largely simplified and reflect our interpretation of the most regionally significant and better-exposed structures. Inferred faults that were previously mapped, particularly those buried beneath younger surficial deposits in the San Luis Valley, typically have large locational uncertainties and are poorly dated. Consequently, depiction of these buried faults on this map compilation is minimized (fig. 3; map sheet). Surficial deposits were mapped and compiled by Machette and Shroba (2005-2013). Bedrock deposits were mapped and compiled by Thompson and Fridrich (2005-2013). All authors contributed to the fault compilation. Brandt prepared the digital topographic base map, digital compilation, and GIS database of the geologic map.

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Section: Tiqmentioning

confidence: 99%

Geologic map of the Alamosa 30’ × 60’ quadrangle, south-central Colorado

Thompson¹,

Shroba²,

Machette³

et al. 2015

Scientific Investigations Map

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“…Red clays and conglomerates considered to be equivalent to the Vallejo Formation of Upson (1941) were deposited in local irregularities and depositional basins on the eroded surface. The Vallejo Formation appears to be overlain by unconsolidated gravels and sediments considered equivalent to the lower part of the Santa Fe Group.…”

Section: Geologic Settingmentioning

confidence: 99%

Extension and uplift of the northern Rio Grande Rift: Evidence from <sup>40</sup>Ar/<sup>39</sup>Ar geochronology from the Sangre de Cristo Mountains, south-central Colorado and northern New Mexico

Miggins¹,

Thompson²,

Pillmore³

et al. 2002

Volcanic Rifted Margins

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New 40 Ar/ 39 Ar dating and geologic mapping of middle to late Cenozoic volcanic rocks and basin-µll sedimentary rocks preserved in the San Luis Valley and adjacent Sangre de Cristo Mountains give new insights into the timing of rift volcanism and opening of the northern Rio Grande Rift. The age, orientation, and elevation of these preserved sections delimit the timing of early rift volcanism, establishment of protorift or paleorift basins, and the uplift rate of the Sangre De Cristo crustal block along the eastern rift margin. We use offset geomorphic surfaces along with newly dated volcanic rocks to determine the exhumation or uplift rate of the Culebra Range relative to the adjacent San Luis Valley. On a µrst-order scale, we determined an exhumation rate of 58 m/m.y. based on the preserved section of 25 Ma volcanic rocks in the Culebra Range and ageequivalent volcanic rocks preserved in the San Luis Hills. A second uplift rate based on a 400 m offset section of Servilleta basalt dated as 4.7 Ma yields an exhumation rate of 87 m/m.y. Previous age data, exhumation and uplift rates, and µeld observations from the San Luis Valley region indicate that a major period of uplift and subsequent block faulting occurred during the middle Miocene (15 Ma), ~10 m.y. after the initiation of rifting.

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“…The last-deposited sediments may have been as young as Oligocene. Redbeds of the Vallejo Formation of prob-able early Tertiary age (Upson, 1941) occur in the San Luis basin on the margin of the Sangre de Cristo uplift in Colorado. Redbeds in the lower part of the Tertiary Picuris Tuff of Cabot (1938) rest on Precambrian and Pennsylvanian rocks in the Sangre de Cristo uplift in New Mexico (Montgomery, 1953).…”

Section: Age and Correlationmentioning

confidence: 99%