The Palm Park Formation is a geologic formation in southern New Mexico. It preserves

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

dating back to the Eocene epoch.

Description

The formation consists of reddish

clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...

sediments, including some beds of boulder

conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geology) * Conglomerate (mathematics) In popular culture: * The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes ** Co ...

with individual boulders up to in diameter. The red color is attributed to a source in the Abo Formation. The upper beds contains considerable latite to andesite breccia interbedded with tuffaceous

claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone, slate, and shale. Most of the particles of which the stone is composed are less than and are too sm ...

and

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

. The Palm Park Formation rests gradationally on the

Love Ranch Formation The Love Ranch Formation is a geologic formation in southern New Mexico. It was likely deposited during the late Paleocene and early Eocene epochs. Description The formation consists of boulder conglomerate interbedded with calcareous red ...

, is unconformably overlain by the Bell Top Formation, Rincon Valley Formation, or

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, and has a thickness of about . The original age estimate, based on radiometric ages of intrusions and interbedded flows, ranged from 42 to 51 million years. More recent high-precision U-Pb dating gives an age of 45.0±0.7 Ma for an ash fall tuff in the lower part of the formation in the Robledo Mountains and an age of 39.6±0.5 Ma for an ash fall tuff in the upper part of the formation in the

Sierra de las Uvas The Sierra de las Uvas or Grape Mountains are a mountain range in Doña Ana County, New Mexico. The John D. Dingell, Jr. Conservation, Management, and Recreation Act The John D. Dingell Jr. Conservation, Management, and Recreation Act of 2019 i ...

. The interbedded ash fall tuffs and volcaniclastic beds of the formation are interpreted as volcanic activity after the end of Laramide mountain building but before the opening of the Rio Grande Rift. At this time, the remnants of the Farallon Plate began to sink into the deep

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

and hot mantle rock rose to take their place, triggering the Mid-Tertiary ignimbrite flare-up.

Fossils

The Palm Park Formation contains hot-water stromatolites. Stable oxygen isotope measurements show that the fine layers (laminae) making up the stromatolites were deposited seasonally, with the sparry (coarsely crystalline) layers deposited in the spring and summer, and the micritic (fine-grained) layers deposited in the fall and winter. This suggests that laminae in more ancient stromatolites are also seasonal in nature. The formation also contains Eocene fossil vertebrates of Chadronian age. These are found in deeply weathered volcaniclastic beds of the middle and upper part of the formation that are interbedded with plant- and

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

-bearing travertines, and most are also badly weathered. However, they include shell fragments of the tortoise ''

Stylemys ''Stylemys'' (meaning "pillar turtle") is the first fossil genus of dry land tortoise belonging to the order Testudines discovered in the United States. The genus lived in temperate to subtropical areas of North America, Europe, and Asia, based ...

'', jaw fragments of '' Hyaenodon horriblis'', tooth fragments likely of ''

Hyracodon ''Hyracodon'' ('hyrax tooth') is an extinct genus of perissodactyl mammal. It was a lightly built, pony-like mammal of about 1.5 m (5 ft) long. ''Hyracodons skull was large in comparison to the rest of the body. ''Hyracodon's'' dentiti ...

'', and a partial skeleton of a protoceratid.

Economic geology

Barite Baryte, barite or barytes ( or ) is a mineral consisting of barium sulfate ( Ba S O4). Baryte is generally white or colorless, and is the main source of the element barium. The ''baryte group'' consists of baryte, celestine (strontium sulfate), ...

galena Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver. Galena is one of the most abundant and widely distributed sulfide minerals. It cryst ...

- manganese deposits are present in the Palm Park Formation in the Rincon basin. These had produced 10,520 tons of barite and 1529 tons of 27%-40% manganese ore by 1998. The formation also contains gypsum and travertine, but not in economic amounts for the 1998 market.

History of investigation

The formation was first named by V.C. Kelley and

Caswell Silver Caswell Silver (June 25, 1916 – October 18, 1988) was an American geologist and entrepreneur who was President of Sundance Oil Company from 1960 to 1984. In addition to the business of oil and gas exploration, he was active in the American Ass ...

in 1952 for exposures in Palm Park, southeast of

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. Because no complete section exists, a type locality was designated instead of a type section. Steven M. Cather and his coinvestigators assigned the Palm Park Formation to the

Spears Group The Spears Group is a group of geologic formations exposed in and around the northeast Mogollon-Datil volcanic field of southwestern New Mexico. It has a radiometric age of 33 to 39 million years, corresponding to the Eocene to Oligocene epochs ...

in 1994.

Footnotes

References