The Muleros 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 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 ...

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

El Paso, Texas El Paso (; ; or ) is a city in and the county seat of El Paso County, Texas, United States. The 2020 United States census, 2020 population of the city from the United States Census Bureau, U.S. Census Bureau was 678,815, making it the List of ...

. 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 (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

Description

The formation consists of highly fossiliferous nodular

argillaceous Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay mineral ...

(

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

-rich)

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

at its base and in its upper portion, with

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

dominating the middle section and

interbedding In geology, interbedding occurs when beds (layers of rock) of a particular lithology lie between or alternate with beds of a different lithology. For example, sedimentary rocks may be interbedded if there were sea level variations in their sedimen ...

with the limestone towards the top of the formation. Total thickness is . The formation conformably overlies the Smeltertown Formation and grades into the overlying Mesilla Valley Formation. The formation is interpreted as an outer shelf formation that later experienced shallowing and deposition of limestone in an inner shelf environment subject to storm influence, then deepened again to deposit shale with some storm layers.

Fossils

The formation contains at least 20 genera and 23 species of fossils. These include the molluscs ''

Lima Lima ( ; ), founded in 1535 as the Ciudad de los Reyes (, Spanish for "City of Biblical Magi, Kings"), is the capital and largest city of Peru. It is located in the valleys of the Chillón River, Chillón, Rímac River, Rímac and Lurín Rive ...

wacoensis'' Roemer, ''Lima mexicana'' Bose, '' Pecten texanus'' var. ''elongatus'' Bose, ''Pecten subalpinus'' Bose, '' Plicatula incongrua'' Conrad, ''

Ostrea ''Ostrea'' is a genus of edible oysters, marine bivalve mollusks in the family Ostreidae, the oysters. Fossil records Although molecular studies suggest that ''Ostrea'' first appeared around the Eocene and originated no earlier than the Cre ...

quadriplicata'' (Shumard), ''

Texigryphaea ''Texigryphaea'' is an extinct genus of oyster belonging to the order Ostreida and family Gryphaeidae. It dates to the Albian to Cenomanian Age (geology), Ages of the Cretaceous Period (geology), period and is primarily found in Texas and the ...

washitaensis''. '' Trigonia emery'' Conrad, '' Helicocryptus mexicanus'' Bose, and ''

Turritella ''Turritella'' is a genus of medium-sized sea snails with an operculum, marine gastropod mollusks in the family Turritellidae.Vos, C.; Gofas, S. (2013). Turritella Lamarck, 1799. Accessed through: World Register of Marine Species at http://www. ...

granulata'' Sowerby var. ''cenomanensis'' d'Orbigny and the echinoderm '' Heteraster bravoensis'' (Bose). These are characteristic of the

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

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 ...

. The formation is highly fossiliferous, with some beds consisting almost entirely of fossils of the oyster ''Texigryphaea washitaensis''.

History of investigation

The beds making up the formation were first described by E. Bose in 1906 as subdivision 5 of his

stratigraphic section A stratigraphic section is a sequence of layers of rocks in the order they were deposited. It is based on the principle of original horizontality, which states that layers of sediment are originally deposited horizontally under the action of ...

. W.S. Strain assigned the name Muleros Formation to this subdivision in 1976.

Footnotes

References

* * * {{cite journal , last1=Strain , first1=W.S. , year=1976 , title=New formation names in the Cretaceous at Cerro de Cristo Rey, Dona Ana County, New Mexico; Appendix 2 , journal=New Mexico Bureau of Mines and Mineral Resources Memoir , volume=31 , pages=77–82 , url=https://geoinfo.nmt.edu/publications/monographs/memoirs/downloads/31/Memoir-31.pdf , accessdate=5 August 2020 Cretaceous formations of New Mexico Limestone formations of the United States Shale formations of the United States

Description

Fossils

History of investigation

See also

Footnotes

References