The Gilman Conglomerate is a geologic formation in northern New Mexico dating to the Oligocene epoch.
| Gilman Conglomerate | |
|---|---|
| Stratigraphic range: | |
 Gilman Conglomerate at Gilman, New Mexico | |
| Type | Formation |
| Underlies | Abiquiu Formation |
| Overlies | Abo Formation |
| Thickness | 59 m (194 ft) |
| Lithology | |
| Primary | Conglomerate |
| Location | |
| Coordinates | 35°43′03″N 106°46′01″W / 35.7175607°N 106.7669774°W |
| Region | New Mexico |
| Country | United States |
| Type section | |
| Named for | Gilman (settlement) |
| Named by | Kelley et al. |
| Year defined | 2009 |
  Gilman Conglomerate (the United States)  Gilman Conglomerate (New Mexico) | |
Description
editThe formation is composed of poorly sorted, weakly bedded, greenish-gray volcaniclastic conglomerate. Its lowermost and uppermost sections are a pinkish color from their content of Proterozoic pebbles, but the bulk of the formation is dominated by a mixture of crystal-rich porphyritic dacite and crystal-poor porphyritic andesite. Radiometric dating yields ages of 28.55 to 29.38 Ma for the clasts. Paleocurrents are to the north, suggesting a source in an Oligocene volcanic field now buried under the southern Jemez Mountains or in the northern Albuquerque Basin.[1]
The formation crops out in a limited area of the southwestern Jemez Mountains. Maximum thickness is 59 meters (194 feet).[1]
The formation rests unconformably on the Abo Formation and has a gradational contact with the overlying Abiquiu Formation. It occupies the same stratigraphic position as the Ritito Conglomerate, and was originally included in that formation,[2] but its composition and paleocurrent directions point to a quite different source provenance.[1]
History of investigation
editThe unit was originally included in the Ritito Conglomerate by H.R. DuChene in 1973.[3] It was broken out as a separate formation by Shari Kelley and her coinvestigators in 2009.[2][4]
Footnotes
editReferences
edit- DuChene, H.R. (1973). Structure and stratigraphy of Guadalupe Box and vicinity, Sandoval County, New Mexico [M.S. thesis]. Albuquerque: University of New Mexico.
- Kelley, S.A.; Kempter, K.A.; McIntosh, W.C.; Maldonado, F.; Smith, G.A.; Connell, S.D.; Koning, D.J. (2009). "Stratigraphy and paleogeography of Oligocene to early Miocene sedimentation in the Jemez Mountains region, north-central New Mexico". New Perspectives on the Rio Grande Rift: from Tectonics to Groundwater. Geological Society of America. ISBN 9780813724942.
- Maldonado, Florian; Kelley, Shari A. (February 2009). "Revisions to the stratigraphic nomenclature of the Abiquiu Formation, Abiquiu and contiguous areas, north-central New Mexico" (PDF). New Mexico Geology. 31 (1). Retrieved 9 June 2020.
- Osburn, G.R.; Kelley, Shari; Rampey, Michael; Ferguson, Charles; Frankel, Kurt; Pazzaglia, Frank (May 2002). "Preliminary geologic map of the Ponderosa 7.5-minute quarangle, Sandoval County, New Mexico" (PDF). New Mexico Bureau of Geology and Mineral Resources Open Map Series. DM-57b. Retrieved 9 June 2020.