San Rafael Group

The San Rafael Group is a geologic group or collection of related rock formations that is spread across the U.S. states of New Mexico, Arizona, Utah and Colorado. As part of the Colorado Plateau, this group of formations was laid down in the Middle Jurassic during the Bajocian, Bathonian and Callovian Stages.[1]

San Rafael Group
Stratigraphic range:
San Rafael Group on the east side of the San Rafael Swell. Entrada at the base, overlain by the Curtis, then Summerville, and capped by the Morrison (Tidwell and Salt Wash Members).
TypeGroup
UnderliesMorrison Formation
OverliesGlen Canyon Group
Thickness490 meters (1,610 ft)
Lithology
PrimarySandstone
OtherMudstone, limestone
Location
Coordinates39.174°N 110.466°W / 39.174; -110.466
RegionFour Corners
CountryUnited States
Type section
Named forSan Rafael Reef
Named byGilluly and Reeside
Year defined1928
San Rafael Group is located in the United States
San Rafael Group
San Rafael Group (the United States)
San Rafael Group is located in Utah
San Rafael Group
San Rafael Group (Utah)
San Rafael Group strata exposed east of the San Rafael Swell, north of Hanksville. Sequence from orange cliff in foreground to cliff top in background Entrada Formation, Curtis Formation, Summerville Formation, capped by the (pink) Tidwell Member of the Morrison Formation.

Description

The group consists of Jurassic beds younger than the Navajo Sandstone and older than the Morrison Formation. These show marine influence in their formation in the northwestern exposures at San Rafael Swell, with formations composed of limestone, mudstone, gypsum, and silty sandstone. Further east, the group becomes more continental in character, with the Entrada Formation resembling the underlying clean sandstones of the Glen Canyon Group.[2][3] The group is up to 490 meters (1,610 ft) thick.[3]

Subunits

Subunits by basin:

Black Mesa Basin:[4]

Great Basin province:[5][6]

Peterson concluded that the Henrieville Sandstone was simply the bleached upper zone of the Entrada Sandstone and recommended abandoning the formation.[4]

Palo Duro Basin/Sierra Grande Uplift:[7]

Paradox Basin:[4]

Piceance Basin:[8][9]

  • Summerville Formation (youngest)
  • Entrada Sandstone (oldest)

Plateau Sedimentary Province:[4]

  • Romana Sandstone (youngest)
  • Entrada Sandstone
  • Carmel Formation
  • Page Sandstone

San Juan Basin:[10]

southern San Juan Basin:[11]

History of investigation

There is no designated type locality for the group. It was named for exposures in the San Rafael Swell in Emery County, Utah by James Gilluly and J.B. Reeside in 1928. They divided the group into (ascending): Carmel Formation, Entrada Sandstone (new), Curtis Formation (new), and Summerville Formation (new).[2] Areal extent limits were established by Herbert E. Gregory and Raymond Cecil Moore in 1931.[3] Smith in 1954 revised and divided the group into Entrada, Todilto, and Thoreau (new) formations in the San Juan Basin.[12]

In 1959 another revision, this time by Griggs and Read, divided it into Entrada and Bell Ranch (new) formations in the Palo Duro Basin and Sierra Grande Uplift.[7] The Carmel-Navajo contact was revised by Wright and others in 1962[8] and the Carmel-Entrada contact was revised by Phoenix in 1963.[13] Thompson and Stokes created an overview and named the Henrieville Sandstone in 1970.[5] The Temple Cap Sandstone was revised and the Page Sandstone added (new) by Peterson and Pipiringos in 1979.[6] A revision by O'Sullivan in 1980 divided the group into Carmel, Entrada, and Wanakah formations in Paradox Basin. O'Sullivan revised the upper contact in 1984.[9]

In 1988 Peterson revised earlier work and divided the group into Page, Carmel, and Entrada formations in the Black Mesa Basin; divided it into Page, Carmel, Entrada and Romana (new) formations in the Plateau Sedimentary Province; and divided it into Page, Carmel, Entrada, Curtis, and Summerville formations in Paradox Basin.[4] Condon in 1989 revised the group in San Juan Basin and divided it into Entrada and Wanakah formations in southeastern area; divided it into Entrada, Wanakah, and Cow Springs formations in south-central area; and divided it into Entrada and Cow Springs Sandstones in southwestern area.[10]

References
  1. Ejembi, John I.; Potter-McIntyre, Sally L.; Sharman, Glenn R.; Smith, Tyson M.; Saylor, Joel E.; Hatfield, Kendall; Ferré, Eric C. (1 October 2021). "Detrital zircon geochronology and provenance of the Middle to Late Jurassic Paradox Basin and Central Colorado trough: Paleogeographic implications for southwestern Laurentia". Geosphere. 17 (5): 1494–1516. doi:10.1130/GES02264.1. ISSN 1553-040X.
  2. Gilluly, James; Reeside, J.B. Jr. (1928). "Sedimentary rocks of the San Rafael Swell and some adjacent areas in eastern Utah". U.S. Geological Survey Professional Paper. 150-D. doi:10.3133/pp150D.
  3. Gregory, H.E.; Moore, R.C. (1931). "The Kaiparowits region, a geographic and geologic reconnaissance of parts of Utah and Arizona". U.S. Geological Survey Professional Paper. 164. doi:10.3133/pp164.
  4. Peterson, Fred (1988). "Stratigraphy and nomenclature of Middle and Upper Jurassic rocks, western Colorado Plateau, Utah and Arizona, IN Revisions to stratigraphic nomenclature of Jurassic and Cretaceous rocks of the Colorado Plateau". U.S. Geological Survey Bulletin. 1633-B: B13-56. doi:10.3133/b1633AC.
  5. Thompson, A.E.; Stokes, W.L. (1970). "Stratigraphy of the San Rafael Group, southwest and south central Utah". Utah Geological and Mineral Survey Bulletin (87).
  6. Peterson, Fred; Pipiringos, G.N. "Stratigraphic relations of the Navajo Sandstone to Middle Jurassic formations, southern Utah and northern Arizona". U.S. Geological Survey Professional Paper. 1035-B. doi:10.3133/pp1035B.
  7. Griggs, R.L.; Read, C.B. (1959). "Revisions in stratigraphic nomenclature in Tucumcari-Sabinoso area, northeastern New Mexico". American Association of Petroleum Geologists Bulletin. 43 (8): 2003–2007. Retrieved 21 March 2022.
  8. Wright, J.C.; Shawe, D.R.; Lohman, S.W. (1962). "Definition of members of Jurassic Entrada Sandstone in east-central Utah and west-central Colorado". American Association of Petroleum Geologists Bulletin. 46 (11): 2057–2070. Retrieved 21 March 2022.
  9. O'Sullivan, R.B. (1984). "The base of the Upper Jurassic Morrison Formation in east-central Utah". U.S. Geological Survey Bulletin. 1561. doi:10.3133/b1561.
  10. Condon, S.M. (1989). "Revisions of Middle Jurassic nomenclature in the southeastern San Juan Basin, New Mexico". U.S. Geological Survey Bulletin. 1808E: E1–E21. doi:10.3133/b1808EF.
  11. Cather, Steven M. (2020). "Jurassic stratigraphic nomenclature for northwestern New Mexico" (PDF). New Mexico Geological Society Special Publication. 14: 145–151. Retrieved 31 October 2020.
  12. Smith, C.T. (1954). "Geology of the Thoreau Quadrangle, McKinley and Valencia (now Cibola) Counties, New Mexico". New Mexico Bureau of Geology and Mineral Resources Bulletin. 31. Retrieved 21 March 2022.
  13. Phoenix, David A. (1963). "Geology of the Lees Ferry area, Coconino County, Arizona". U.S. Geological Survey Bulletin. 1137. doi:10.3133/b1137.
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