The Pennsylvanian System in the Sacramento Mountains, New Mexico, USA: Stratigraphy, Petrography, Depositional Systems, Paleontology, Biostratigraphy and Geologic History

Pennsylvanian sedimentary rocks in the Sacramento Mountains, New Mexico, comprise an ~1 km thick stratigraphic section. The Morrowan-Desmoinesian Gobbler Formation was deposited by shallow marine processes in and near the Alamo clastic trough. In this trough, the Desmoinesian-Missourian Gray Mesa Formation (Bug Scuffle Member, Gobbler Formation) is a relatively thin unit (Space History Member) representing the glacioeustatic Amado event. The Missourian-Virgilian Beeman Formation includes the lower, siliciclastic Indian Wells Canyon Member and overlying, carbonate-rich Horse Ridge Member. The Virgilian Holder Formation consists of algal bioherms (Little Dry Canyon Member) overlain by the mixed carbonate-siliciclastic Mill Ridge Member. The Virgilian-Wolfcampian Bursum Formation is mixed siliciclastic-carbonate strata that represent shallow marine and nonmarine paleoenvironments. Animal and plant remains occur throughout the section. Unit age determinations are primarily based on conodont faunas recovered from the Gobbler, Gray Mesa, and Beeman Formations. Many conodont faunas correlate with Midcontinent cyclothems. Extensive algal and foraminiferal fossils also were identified in limestones from the section and contributed to age determinations. The Beeman Formation in particular contains an extensive Missourian macroflora. The macroflora is of “mixed” composition, containing typical wetland elements intimately intermixed with taxa indicative of seasonally dry habitats. A seasonally wet-dry background climate is indicated. It is unlikely that drought-tolerant plants were transported exclusively from “uplands.” Some plant remains have arthropod-feeding evidence. Previous analyses identified late Paleozoic ice-age glacioeustasy as the primary depositional driver of Pennsylvanian sedimentation in the Sacramento Mountains. We question this because of problems with those analyses and because of ample evidence of local tectonics and microclimate changes as important drivers of sedimentation in this area. Three Pennsylvanian Ancestral Rocky Mountain orogeny tectonic pulses can be identified in the Sacramento Mountains: Morrowan-Atokan, Missourian, and late Virgilian-Wolfcampian.

The Pennsylvanian System in the Sacramento Mountains, New Mexico, USA: Stratigraphy, Petrography, Depositional Systems, Paleontology, Biostratigraphy and Geologic History

Pennsylvanian sedimentary rocks in the Sacramento Mountains, New Mexico, comprise an ~1 km thick stratigraphic section. The Morrowan-Desmoinesian Gobbler Formation was deposited by shallow marine processes in and near the Alamo clastic trough. In this trough, the Desmoinesian-Missourian Gray Mesa Formation (Bug Scuffle Member, Gobbler Formation) is a relatively thin unit (Space History Member) representing the glacioeustatic Amado event. The Missourian-Virgilian Beeman Formation includes the lower, siliciclastic Indian Wells Canyon Member and overlying, carbonate-rich Horse Ridge Member. The Virgilian Holder Formation consists of algal bioherms (Little Dry Canyon Member) overlain by the mixed carbonate-siliciclastic Mill Ridge Member. The Virgilian-Wolfcampian Bursum Formation is mixed siliciclastic-carbonate strata that represent shallow marine and nonmarine paleoenvironments. Animal and plant remains occur throughout the section. Unit age determinations are primarily based on conodont faunas recovered from the Gobbler, Gray Mesa, and Beeman Formations. Many conodont faunas correlate with Midcontinent cyclothems. Extensive algal and foraminiferal fossils also were identified in limestones from the section and contributed to age determinations. The Beeman Formation in particular contains an extensive Missourian macroflora. The macroflora is of “mixed” composition, containing typical wetland elements intimately intermixed with taxa indicative of seasonally dry habitats. A seasonally wet-dry background climate is indicated. It is unlikely that drought-tolerant plants were transported exclusively from “uplands.” Some plant remains have arthropod-feeding evidence. Previous analyses identified late Paleozoic ice-age glacioeustasy as the primary depositional driver of Pennsylvanian sedimentation in the Sacramento Mountains. We question this because of problems with those analyses and because of ample evidence of local tectonics and microclimate changes as important drivers of sedimentation in this area. Three Pennsylvanian Ancestral Rocky Mountain orogeny tectonic pulses can be identified in the Sacramento Mountains: Morrowan-Atokan, Missourian, and late Virgilian-Wolfcampian.

Detrital zircon geochronology of quartzite clasts in the Permian Abo Formation, Sacramento Mountains, New Mexico, USA

More than 2500 m of Paleozoic strata, ranging in age from Cambrian to Permian occur in the Sacramento Mountains of New Mexico, making these rocks the largest and most complete exposures of Paleozoic strata in North America. The core of the Sacramento Mountains reveals compressional structures associated with the Pennsylvanian-Permian Ancestral Rocky Mountain orogeny. The Permian Abo Formation is 120–450 m in thickness, and consists of interbedded sandstone, conglomerate, limestone and shale and rests above the Ancestral Rocky Mountain unconformity. U-Pb analysis of detrital zircons extracted from quartzite clasts in basal conglomerates reveal a maximum depositional age of their protolith to be 1110 ± 15 Ma. Most (∼40%) of the detrital zircon age spectrum is Grenville (1000–1300 Ma) in age, with a peak age of 1209 Ma. Midcontinent Granite-Rhyolite (1300–1500 Ma) ages comprise about 33% of the data, and have a peak age of 1431 Ma. Smaller age populations of Yavapai-Mazatzal (1600–1800 Ma; age peak =1676 Ma), Trans-Hudson (1800–2000 Ma; peak age = 1820 Ma), and Archean (>2.5 Ga, age peak = 2819 Ma) also are present. U-Pb detrital zircon ages from these quartzite clasts indicate that they were likely derived from the Proterozoic Lanoria Formation, which is exposed now in the Franklin Mountains >150 km to the south. The Lanoria is identical to the Abo clasts in terms of maximum depositional age and detrital zircon age peaks. The protolith sandstone of these quartzite clasts and quartzites of the Lanoria were derived from the Grenville high-lands of the Llano region of central Texas, and then transported west to the Rodinian continental margin at ∼1110 Ma, where they were eventually buried and metamorphosed to quartzite. These quartzites were subsequently uplifted and eroded during the Ancestral Rocky Mountain orogeny and transported north and west along the Pedernal Uplift to the adjacent Orogrande Basin during the early Permian.