The Smeltertown Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...

, which is particularly well exposed at Cerro de Cristo Rey near

El Paso, Texas El Paso (; "the pass") is a city in and the seat of El Paso County in the western corner of the U.S. state of Texas. The 2020 population of the city from the U.S. Census Bureau was 678,815, making it the 23rd-largest city in the U.S., the ...

. 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 ...

dating back to the

early Cretaceous The Early Cretaceous (geochronological name) or the Lower Cretaceous ( chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pr ...

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

Description

The formation consists of gray

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...

with some interbedded

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, ...

and silty

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms wh ...

, with some fine grained

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

towards the top of the formation. The total thickness is . It rests conformably on the Del Norte Formation and is conformably overlain by the

Muleros Formation The Muleros Formation is a geologic formation in New Mexico, which is particularly well exposed at Cerro de Cristo Rey near El Paso, Texas. It preserves fossils dating back to the early Cretaceous period. Descriptiom The formation consists of hi ...

Fossils

Fossils are uncommon in the formation. However, the rare

nautiloid Nautiloids are a group of marine cephalopods ( Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and '' Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded speci ...

Cymatoceras ''Cymatoceras'' is a wide-ranging extinct genus from the nautilitacean cephalopod family, Cymatoceratidae. They lived from the Late Jurassic to Late Oligocene, roughly from 155 to 23 Ma.Sepkoski, JacSepkoski's Online Genus Database – Cephalopo ...

'' cf. ''C. Loeblichi'' Miller and Harris has been recovered from the formation, as have fossil

ophiuroid Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomo ...

s (brittle stars). The formation is also the type location for the bryozoan '' Reptomulticava texana''. The distribution of

foram Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly a ...

fossils in the formation (

planktonic Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruc ...

species more common towards the bottom and

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

species more common towards the top) suggests that the sea in the area was shallowing during deposition of the formation.

Footnotes

{{Reflist Cretaceous formations of New Mexico

Description

Fossils

See also

Footnotes