{{Short description|Geologic formation in the Gallup-Zuni basin of New Mexico}} {{Infobox rockunit | name = Gallup Sandstone | image =Gallup sandstone.jpg | caption = Gallup Sandstone in the Nutria hogback east of Gallup, New Mexico, US, near its principal reference section | type = Formation | age = {{Geological range| Turonian | Coniacian}} | period = late Cretaceous | prilithology = Sandstone | otherlithology = Shale, siltstone | namedfor = Gallup, New Mexico | namedby = J.D. Sears | year_ts = 1925 | region = New Mexico | country = United States | coordinates = {{coord|35.532170|N|108.691030|W|display=inline}} | unitof = Mesaverde Group | subunits = | underlies = Crevasse Canyon Formation | overlies = Mancos Shale | thickness = {{convert|71|meters|feet}} | extent = | area = | map = {{Location map+ | United States#New Mexico | relief = 1 | width = 250 | float = center | places = {{Location map~ | United States#New Mexico | lat_deg = 35.532 | lon_deg = -108.691 | mark = Lightgreen pog.svg | marksize = 12 }} }} | map_caption = }}
The '''Gallup Sandstone''' is a geologic formation in the Gallup-Zuni basin of New Mexico. It preserves fossils dating back to the late Cretaceous period.{{sfn|Sears|1925}}{{sfn|Molenaar|1983}}{{sfn|Nummedal | Molenaar |1995}}
==Description== The formation consists of uniform, very well sorted, fine-grained pink to buff sandstone with lesser amounts of shale and siltstone. It has a total thickness of {{convert|71|meters|feet}}. The sandstone is highly bioturbated and in some place shows ripple marks and low-angle crossbedding. It overlies and intertongues with the Mancos Shale and is overlain and intertongues with the Crevasse Canyon Formation. The formation has few faunal fossils, but the age is likely late Turonian to early Coniacian.{{sfn|Molenaar|1983}}{{sfn|Nummedal|Molenaar|1995}}
The formation is interpreted as an offshore marine transgression-regression sequence.{{sfn|Molenaar|1983}}
==History of investigation== The unit was first defined by J.D. Sears in 1925 as the Gallup Sandstone Member of the Mesaverde Formation and named after Gallup, New Mexico, which is built partially on its uppermost bed. Sears originally defined the Gallup Sandstone as the three sandstone beds, separated by shale and coal beds, forming cliffs and hogbacks in the Gallup area{{sfn|Sears|1925}} Pike first observed in 1947 that the member intertongues with the Mancos Shale (Pescado Tongue).{{sfn|Pike|1947}} Allen and Balk raised the Mesaverde Formation to group rank in 1954, which also raised the Gallup Sandstone to formation rank.{{sfn|Allen|Balk|1954}} The unit has since undergone repeated revisions,<ref name="geolex">History of significant publications: GEOLEX (https://ngmdb.usgs.gov/Geolex/UnitRefs/GallupRefs_8228.html)</ref> with the most recent revision by Nummedal and Molenaar in 1995 removing the fluvial Torrivio Member and restricting the formation to the basal {{convert|71|meters|feet}} of marine sandstone of the Mesaverde Group.{{sfn|Nummedal|Molenaar|1995}}
==See also== {{Portal|Earth sciences|Paleontology}} * List of fossiliferous stratigraphic units in New Mexico * Paleontology in New Mexico
==Footnotes== {{Reflist}}
==References== * {{cite journal |last1=Allen |first1=J.E. |last2=Balk |first2=Robert |year=1954 |title=Mineral Resources of Fort Defiance and Tohatchi quadrangles, Arizona and New Mexico |journal=New Mexico Bureau of Mines and Mineral Resources Bulletin |volume=36 |url=https://geoinfo.nmt.edu/publications/monographs/bulletins/36/ |access-date=4 August 2020}} * {{cite journal |last1=Molenaar |first1=C.M. |year=1983 |title=A principal reference section and correlation of the Gallup Sandstone, northwestern New Mexico |journal=New Mexico Bureau of Mines and Mineral Resources Circular |volume=185 |pages=29–40 |url=https://geoinfo.nmt.edu/publications/monographs/circulars/downloads/185/Circular-185.pdf |access-date=11 September 2020}} * {{cite journal |last1=Nummedal |first1=Dag |last2=Molenaar |first2=C.M. |year=1995 |title=Sequence stratigraphy of ramp-setting strand plain successions; the Gallup Sandstone, New Mexico |journal=American Association of Petroleum Geologists Memoir |volume=64 |pages=277–310 |url=http://archives.datapages.com/data/specpubs/memoir64/ch09/0277.htm |access-date=11 September 2020}} * {{cite journal |last1=Pike |first1=W.S. Jr. |year=1947 |title=Intertonguing marine and nonmarine Upper Cretaceous deposits of New Mexico, Arizona, and southwestern Colorado |journal=Geological Society of America Memoir |series=Geological Society of America Memoirs |volume=24 |pages=1–115 |doi=10.1130/MEM24-p1 |isbn=9780813710242 |url=https://books.google.com/books?id=BBdiPPfzwQIC&q=Intertonguing+marine+and+nonmarine+Upper+Cretaceous+deposits+of+New+Mexico%2C+Arizona%2C+and+southwestern+Colorado&pg=PP1 |access-date=4 August 2020|url-access=subscription }} * {{cite journal |last1=Sears |first1=J.D. |year=1925 |title=Geology and coal resources of the Gallup-Zuni basin, New Mexico |journal=U.S. Geological Survey Bulletin |number=767 |url=https://books.google.com/books?id=KqkPAAAAIAAJ&q=Geology+and+coal+resources+of+the+Gallup+Zuni+basin%2C+New+Mexico&pg=PA1 |access-date=11 September 2020}}
Category:Cretaceous formations of New Mexico Category:Sandstone formations of the United States Category:Siltstone formations of the United States Category:Shale formations of the United States