The Santa Rosa Formation is a geologic formation exposed in

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

that was deposited in the

Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227.3 ...

Age Age or AGE may refer to: Time and its effects * Age, the amount of time someone has been alive or something has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

of the

late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

Period.

Description

The formation consists mostly of white to brown

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

and

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

with some interbedded conglomerate. The formation lies on the Anton Chico Formation and is overlain by the Garita Creek Formation. The total thickness of the formation is . The formation is divided into (in ascending stratigraphic order) the ''Tecolotito

Member Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...

'', which is primarily sandstone; the ''Los Esteros Member'', which is primarily mudstone; and the ''Tres Lagunas Member'', which is primarily sandstone. The sandstone members are interpreted as

alluvial Alluvium (, ) is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluvium is also sometimes called alluvial deposit. Alluvium is ...

sheets deposited by

braided stream A braided river (also called braided channel or braided stream) consists of a network of river channels separated by small, often temporary, islands called '' braid bars'' or, in British English usage, '' aits'' or ''eyots''. Braided streams t ...

s. The Los Esteros Member is interpreted as a

lacustrine A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...

deposit in lakes that formed due to local subsidence from dissolution of underlying

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

salt beds.

Paleocurrent A paleocurrent or paleocurrent indicator is a geological feature (typically a sedimentary structure) that helps one determine the direction of flowing water in the geologic past. This is an invaluable tool in the reconstruction of ancient deposi ...

s were primarily to the south in the Tecolotito Member and northeast in the Tres Lagunas Member but are indeterminate in the Los Esteros Member.

Fossils

The Los Esteros Member has yielded fossils of the

fern The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...

'' Cynepteria lasiophora'', the

cycad Cycads are seed plants that typically have a stout and woody (ligneous) trunk (botany), trunk with a crown (botany), crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants o ...

'' Zamites powelli'', the

conifer Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...

'' Pelourdea pleoensis'', the

gymnosperm The gymnosperms ( ; ) are a group of woody, perennial Seed plant, seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, conifers, cycads, Ginkgo, and gnetoph ...

'' Dinophyton spinusos'', and seeds ('' Samaropsis''). This member also includes a microvertebrate site in

Santa Fe County, New Mexico Santa Fe County (; meaning "County of the Holy faith" in Spanish) is a county located in the U.S. state of New Mexico. As of the 2020 census, its population was 154,823, making it New Mexico's third-most populous county, after Bernalillo Count ...

that has yielded a diverse fossil assemblage. Fish fossils include lungfish toothplates of ''

Arganodus ''Arganodus'' is an extinct genus of freshwater lungfish that had a wide global distribution throughout much of the Triassic period, with a single species surviving across Gondwana into the Cretaceous. It is the only member of the family Argano ...

dorothea'', a redfieldiid dermopteric, and scales from '' Turseodus'', including from

coprolite A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name ...

s. Amphibian fossil fragments are probably from '' Buttneria perfecta'' and ''

Apachesaurus ''Apachesaurus'' is an extinct genus of metoposaurid temnospondyls from western North America. Description and taxonomy ''Apachesaurus'' was described from the Late Triassic (late Norian-Rhaetian The Rhaetian is the latest age (geology), ...

gregorii''. Reptiles include '' Trilophosaurus'', indeterminate

phytosaur Phytosaurs (Φυτόσαυροι in Greek, meaning 'plant lizard') are an extinct group of large, mostly semiaquatic Late Triassic archosauriform or basal archosaurian reptiles. Phytosaurs belong to the order Phytosauria and are sometimes ref ...

s, ''

Desmatosuchus ''Desmatosuchus'' (, from Greek language, Greek δεσμός ''desmos'' 'link' + σοῦχος ''soûkhos'' 'crocodile') is an extinct genus of archosaur belonging to the Order Aetosauria. It lived during the Late Triassic. Description ''Desma ...

haplocerus'', '' Stagonolepis wellesii'', several new

aetosaur Aetosaurs () are heavily armored reptiles belonging to the extinct order (biology), order Aetosauria (; from Ancient Greek, Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized Omnivore, omnivorous or Herbivore, herbivor ...

s, '' Chatterjeea elegans'', '' Hesperosuchus'', and '' Parrishia mcreai''. Synapsids are represented by an indeterminate

kannemeyeriiform Kannemeyeriiformes is a group of large-bodied Triassic dicynodonts. As a clade, Kannemeyeriiformes has been defined to include the species ''Kannemeyeria simocephalus'' and all dicynodonts more closely related to it than to the species ''Lystrosa ...

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, t ...

and an unnamed

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

. In east-central New Mexico, the Los Esteros Member has also yielded a Otischalkian dinosauromorph assemblage that includes specimens of

Silesauridae Silesauridae is an extinct family of Triassic dinosauriforms. It is most commonly considered to be a clade of non-dinosaur dinosauriforms, and the sister group of dinosaurs. Some studies have instead suggested that most or all silesaurids compr ...

and

Lagerpetidae Lagerpetidae (; originally Lagerpetonidae) is a family of basal avemetatarsalians (early-diverging members of the reptile lineage leading to birds and other dinosaurs). Though traditionally considered the earliest-diverging dinosauromorphs (ar ...

, including ''

Dromomeron ''Dromomeron'' (meaning "running femur") is a genus of Lagerpetidae, lagerpetid Avemetatarsalia, avemetatarsalian which lived around 220 to 211.9 ± 0.7 million years ago. The genus contains species known from Late Triassic-age rocks of the South ...

'', the latter of unusually large size.

History of investigation

The formation was first named as the Santa Rosa Sandstone by N.H. Darton in July 1919 but the report was not published until 1922. By then the name had already appeared in other publications. A type locality was not formally designated until 1972. In 1987, Spencer G. Lucas and Adrian Hunt removed the lower sandstone beds into the Anton Chico Formation and divided the remaining beds into members. W.I. Finch and coinvestigators redesignated the unit as the Santa Rosa Formation in 1988.

References

Bibliography

* * * * * * * * * * * * {{cite journal , last1=Rich , first1=J.L. , year=1921 , title=The stratigraphy of eastern New Mexico; a correction , journal=American Journal of Science , series=5th Series , volume=2 , issue=11 , pages=295–298, doi=10.2475/ajs.s5-2.11.295 , bibcode=1921AmJS....2..295R Sandstone formations of the United States Triassic geology of Texas Triassic formations of New Mexico Mudstone formations of the United States Conglomerate formations