The Sierra Madre 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 ...

Chiapas Chiapas, officially the Free and Sovereign State of Chiapas, is one of the states that make up the Political divisions of Mexico, 32 federal entities of Mexico. It comprises Municipalities of Chiapas, 124 municipalities and its capital and large ...

state, southern

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

. It consists of marine dolomites and

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) ...

s. The formation dates to the Middle Cretaceous, spanning from the

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

of the

Early Early may refer to: Places in the United States * Early, Iowa, a city * Early, Texas, a city * Early Branch, a stream in Missouri * Early County, Georgia * Fort Early, Georgia, an early 19th century fort Music * Early B, stage name of Jamaican d ...

to the

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

of the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

. The dolomites, dolomitic breccias and limestones of the formation have been deposited in a

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...

al to

estuarine An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

environment and contain many fossil fish, flora and

rudist Rudists are a group of extinct box-, tube- or ring-shaped marine heterodont bivalves belonging to the order Hippuritida that arose during the Late Jurassic and became so diverse during the Cretaceous that they were major reef-building organis ...

s, typical reef-building organisms of the Cretaceous. The formation rests on top of the

Santiago Santiago (, ; ), also known as Santiago de Chile (), is the capital and largest city of Chile and one of the largest cities in the Americas. It is located in the country's central valley and is the center of the Santiago Metropolitan Regi ...

and San Ricardo Formations, and is overlain by the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

Ocozocoautla Formation. The thickness of a composite section of the formation amounts to .

Description

The Sierra Madre Formation was first formally described by Gutiérrez Gil in 1956, but previously reported by other authors (Böse, 1905; Ver Wiebe, 1925; Müllerried, 1936; Imlay, 1944). The formation was studied in more detail and subdivided in several members (Chubb, 1959; Sánchez-Montes de Oca, 1969; Zavala-Moreno, 1971; Castro-Mora et al., 1975; Michaud, 1987; Quezada-Muñetón, 1987). A composed thickness of was suggested by Steele and Waite (1986) for the Sierra Madre Formation, subdivided into 21 lithofacies. The lowermost lithofacies corresponds to the stratigraphic level of El Espinal quarry, defined by Steele and Waite (1986) as dolomite and

dolomitic Dolomite () is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite (see Dolomite (rock)). An alternative name sometimes ...

breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...

, located between from the base of the formation, which rests conformably on top of the

Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

to Early Cretaceous San Ricardo Formation. The top is covered

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

by the

Ocozocoautla Formation. The

depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will b ...

is described as an environment with high oxygen concentration and high primary productivity with sporadic influence of strong waves and/or currents in a

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

marginal marine environment; shallow lagoon or estuary.

Fossil content

The formation preserves

fossil 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 preserve ...

fish, flora and marine invertebrates dating back to the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

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 ...

, ranging from the

of 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 ...

to the

of the

.Sierra Madre Formation, Chiapas
at

Fossilworks Fossilworks was a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cr ...

.orgEl Espinal Quarry
at

.org The fossils in El Espinal quarry were found in finely laminated orange clay layers interbedded with dolomitic limestone and interbedded with relatively thick layers of cream limestone that range from , with some layers showing ripples, desiccation cracks,

algal mat Algal mats are one of many types of microbial mat that forms on the surface of water or rocks. They are typically composed of blue-green cyanobacteria and sediments. Formation occurs when alternating layers of blue-green bacteria and sediments a ...

s, and flat-pebble conglomerates. Similar fossils have been found in the

Tlayúa Formation The Tlayúa Formation is an Cretaceous Konservat-Lagerstätte near Tepexi de Rodríguez, Puebla, Central Mexico. It consists of three members (Lower, Middle and Upper), spanning the lower Albian of the Early Cretaceous to the lower Cenomanian of ...

, of Albian age in

Puebla Puebla, officially the Free and Sovereign State of Puebla, is one of the 31 states that, along with Mexico City, comprise the Federal Entities of Mexico. It is divided into 217 municipalities and its capital is Puebla City. Part of east-centr ...

, southern Mexico, as fishes, one odonate nymph and

isopods Isopoda is an Order (biology), order of crustaceans. Members of this group are called isopods and include both Aquatic animal, aquatic species and Terrestrial animal, terrestrial species such as woodlice. All have rigid, segmented exoskeletons ...

.Vega et al., 2006, p.324

Fish

Fossils of '' Archaeochiapasa mardoqueoi'' and '' Pepemkay'', a Cenomanian prehistoric ray-finned fish, were found in the formation. Other prehistoric fish fossils, found in quarries near the Municipality of Ocozocoautla de Espinosa, include Macrosemiids ('' Macrosemiocotzus'' species), Clupeomorphs ('' Triplomystus applegatei'' and '' Paraclupea''-like species), and

Alepisauriformes Aulopiformes is a diverse order of marine ray-finned fish consisting of some 15 extant and several prehistoric families with about 45 genera and over 230 species. The common names grinners, lizardfishes and allies, or aulopiforms are sometimes ...

('' Saurorhamphus'' and ''

Enchodus ''Enchodus'' (from , 'spear' and 'tooth') is an extinct genus of aulopiformes, aulopiform Actinopterygii, ray-finned fish related to alepisaurus, lancetfish and lizardfish. Species of ''Enchodus'' flourished during the Late Cretaceous, where t ...

'' species).Alvarado Ortega et al., 2009

Rudists

These

s are reported from the formation: * '' Caprinuloidea sp.'' * '' Coalcomana sp.'' * '' Kimbleia sp.'' * '' Radiolites sp.'' * '' Requienia sp.'' * '' Sauvagesia sp.'' * '' Texicaprina sp.'' * '' Toucasia sp.''

Flora

The following flora were found in the formation: * '' Ephedra'' * '' Arecipites sp.'' * '' Osmunda sp.'' * '' Selaginella sp.'' * '' Sphagnum sp.'' * Bombacaceae indet. * Lauraceae indet. * Moraceae indet.

References

Bibliography

* * {{citation , first1=F.J. , last1=Vega , first2=P. , last2=García Barrera , first3=M. Carmen , last3=Perrilliat , first4=M.A. , last4=Coutiño , first5=R. , last5=Mariño Pérez , year=2006 , title=El Espinal, a new plattenkalk facies locality from the Lower Cretaceous Sierra Madre Formation, Chiapas, southeastern Mexico , url=https://www.researchgate.net/publication/28131471 , journal=

Revista Mexicana de Ciencias Geológicas The ''Revista Mexicana de Ciencias Geológicas'' is a triannual peer-reviewed open-access scientific journal published by the National Autonomous University of Mexico, Sociedad Geológica Mexicana, Instituto Nacional de Geoquímica, and Socieda ...

, volume=23 , pages=323–333 , accessdate=2020-03-16

Description

Fossil content

Fish

Rudists

Flora

See also

References

Bibliography

Further reading