McRae Group explained

McRae Group
Type:Geological formation
Age:Maastrichtian (Lancian)
~
Period:Maastrichtian
Prilithology:Sandstone, shale, conglomerate
Otherlithology:Tuff
Namedfor:Fort McRae
Namedby:Kelley & Silver
Year Ts:1952
Region:New Mexico
Coordinates:33.197°N -107.167°W
Paleocoordinates:40.4°N -85.7°W
Subunits:Hall Lake Formation,
Jose Creek Formation,
Double Canyon Formation
Underlies:Love Ranch Formation
Overlies:Mesaverde Group
Thickness:3000feet

The McRae Group is a geological group exposed in southern New Mexico whose strata, including layers of the Hall Lake Formation and Jose Creek Formation, date to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from this unit.[1] [2] [3]

Description

The group consists of a basal conglomerate interbedded with shale and siltstone and a sequence of alternating sandstone and shale. The lower conglomerates contain volcanic debris, while the upper beds contain sparse nonvolcanic rock fragments. The shales are reddish brown to purplish while the sandstones are light gray. The sandstones are medium bedded to massive and sometimes form hogbacks. The total thickness is in excess of 3000feet. The group is present around Elephant Butte Reservoir, in the Caballo Mountains, and under much of the Jornada del Muerto. It overlies the Mesaverde Group, from which it derives much of its sediments. It is overlain by the Love Ranch Formation.

The group is divided into the lower Jose Creek Formation, the middle Hall Lake Formation, and the upper Double Canyon Formation. The Jose Creek Formation is interpreted as mudflow or alluvial fan deposits emplaced in a humid tropical to semitropical environment. It includes distinctive breccia conglomerate beds.

Fossil evidence firmly establishes that most of the McRae Group is late Cretaceous in age. However, it is possible that some of the uppermost beds extend into the Paleocene.

Fossil content

The group contains a floral assemblage that includes Geinitzia cf. formosa, Canna magnifolia, Phyllites cf. ratonensis, Salix, Cinnamomum, Sabalites montana, Araucarites longifolia, Ficus planicostata, and Sequoia.[4] [5]

Vertebrate paleofauna

W.T. Lee found a ceratopsian skeleton in the area in 1905. Additional vertebrate fossil fragments have been found at twelve locations, generally along the contact between the Jose Creek and Hall Lake members, that include ceratopsian frill and jaw fragments, ankylosaur armor fragments, a sauropod femur, and the holotype specimen of Tyrannosaurus mcraeensis (found by a yachtsman in 1983.) Turtle fossils have also been unearthed here.[6]

History of investigation

The group was first named as the McRae Formation by V.C. Kelley and Caswell Silver in 1952 for Fort McRae. They designated the type location as the base of Elephant Butte and the eastern shore of Elephant Butte Reservoir. H.P. Bushnell divided the formation into members in 1955.

Kenneth Segerstrom and his coinvestigators argued in 1979 that the beds of the Cub Mountain Formation properly belong to the McRae Formation. Spencer G. Lucas and his coinvestigators disagreed on the basis of fossil evidence, placing the former formation in the Eocene.

In 2019, Lucas and his coinvestigators proposed promoting the McRae Formation to group rank and adding the Double Canyon Formation as its uppermost member. The Double Canyon Formation is over 425m (1,394feet) of mudstone with some sandstone and conglomerate found between Elaphant Butte Reservoir and the Fra Cristobal Mountains to the northeast.

See also

References

Bibliography

Notes and References

  1. Lozinsky . Richard . Hunt . Adrian . Wolberg . Donald . Lucas . Spencer . 1984. November 1984 . Late Cretaceous (Lancian) dinosaurs from the McRae Formation, Sierra County, New Mexico . New Mexico Geology . 6 . 4 . 72–77. 10.58799/NMG-v6n4.72 .
  2. Wolberg . Donald . Lozinsky . Richard . Hunt . Adrian . 1986 . Late Cretaceous (Maastrichtian-Lancian) vertebrate paleontology of the McRae Formation, Elephant Butte area, Sierra County, New Mexico . New Mexico Geological Society . 37 . 227–234.
  3. Buck . Brenda J. . Mack . Greg H. . October 1995 . Latest Cretaceous (Maastrichtian) aridity indicated by paleosols in the McRae Formation, south-central New Mexico . Cretaceous Research . 16 . 5 . 559–572 . 10.1006/cres.1995.1036 . 1995CrRes..16..559B . 0195-6671.
  4. Estrada-Ruiz . Emilio . Upchurch . Garland R. . Wheeler . Elisabeth A. . Mack . Greg H. . May 2012 . Late Cretaceous Angiosperm Woods from the Crevasse Canyon and McRae Formations, South-Central New Mexico, USA: Part 1 . International Journal of Plant Sciences . 173 . 4 . 412–428 . 10.1086/664714 . 83998771 . 1058-5893.
  5. Estrada-Ruiz . Emilio . Wheeler . Elisabeth A. . Upchurch . Garland R. . Mack . Greg H. . February 2018 . Late Cretaceous Angiosperm Woods from the McRae Formation, South-Central New Mexico, USA: Part 2 . International Journal of Plant Sciences . 179 . 2 . 136–150 . 10.1086/695503 . 90756137 . 1058-5893.
  6. Lichtig . Asher . Lucas . Spencer . 2015 . Cretaceous Turtles of New Mexico . Fossil Record . 4 . 67 . 129–138.
  7. Gillette . David . Wolberg . David . Hunt . Adrian . 1986 . Tyrannosaurus rex from the McRae Formation (Lancian, Upper Cretaceous), Elephant Butte reservoir, Sierra County, New Mexico . New Mexico Geological Society 37th Annual Fall Field Conference Guidebook . 235–238.
  8. Dalman, S. G; Loewen, M. A.; Pyron, R. A.; Jasinski, S. E.; Malinzak, D. E.; Lucas, S. G.; Fiorillo, A. R.; Currie, P. J.; Longrich, N. R. (2024). "A giant tyrannosaur from the Campanian–Maastrichtian of southern North America and the evolution of tyrannosaurid gigantism". Scientific Reports. 13. Article number 22124. doi:10.1038/s41598-023-47011-0.
  9. Hunt . Rebecca K. . Lehman . Thomas M. . November 2008 . Attributes of the ceratopsian dinosaur Torosaurus, and new material from the Javelina Formation (Maastrichtian) of Texas . Journal of Paleontology . 82 . 6 . 1127–1138 . 10.1017/s0022336000055335 . 0022-3360.
  10. Williamson . Thomas E. . Weil . Anne . 2008-12-12 . Stratigraphic distribution of sauropods in the Upper Cretaceous of the San Juan Basin, New Mexico, with comments on North America's Cretaceous 'sauropod hiatus' . Journal of Vertebrate Paleontology . 28 . 4 . 1218–1223 . 10.1671/0272-4634-28.4.1218 . 2008JVPal..28.1218W . 129950838 . 0272-4634.

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