The Murca Formation ( es, Formación Murca, Kim) is a

geological 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 expo ...

of the

Altiplano Cundiboyacense The Altiplano Cundiboyacense () is a high plateau located in the Eastern Cordillera of the Colombian Andes covering parts of the departments of Cundinamarca and Boyacá. The altiplano corresponds to the ancient territory of the Muisca. The Alt ...

Eastern Ranges The Eastern Ranges is an Australian rules football team in the NAB League, the Victorian statewide under-18s competition. The club is a founding member of the competition (1992) and has produced several players for the Australian Football Le ...

of the Colombian

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

. The predominantly subarkose

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 ...

with

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 ...

s 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, ...

s formation dates 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;

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretac ...

epoch and has a maximum thickness of .

Etymology

The formation was defined and named in 1990 by Moreno after the Murca River, Cundinamarca.Acosta & Ulloa, 2002, p.37Moreno, 1990, p.66

Description

Lithologies

The Murca Formation has a maximum thickness of , and is characterised by a sequence of subarkose coarse-grained, locally cross-bedded

s with intercalating

s and

s. The basal part of the black and grey

feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feld ...

bearing sandstone beds contains large

pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue giv ...

crystals. The matrix is formed by cements of calcite, iron oxide,

sericite Sericite is the name given to very fine, ragged grains and aggregates of white (colourless) micas, typically made of muscovite, illite, or paragonite. Sericite is produced by the alteration of orthoclase or plagioclase feldspars in areas th ...

and

chlorite The chlorite ion, or chlorine dioxide anion, is the halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as salts of chl ...

. Fossils of '' Berriasella colombiana'' and '' Pseudoosterella ubalaensis'' have been found in the Murca Formation.Acosta & Ulloa, 2002, p.38Dorado Galindo, 1990, p.23Moreno, 1990, p.76Piraquive et al., 2011, p.207''Pseudoosterella ubalaensis''
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Stratigraphy and depositional environment

The Murca Formation, belonging to the

Cáqueza Group Cáqueza () is a municipality and town of Colombia in the department of Cundinamarca. The town, located on the Altiplano Cundiboyacense, is from the capital Bogotá. The municipality borders Fosca in the south, Ubaque in the north, Une and Chi ...

, underlies the

Trincheras Formation The Trincheras Formation ( es, Formación Trincheras, Kitr) is a geological formation of the Altiplano Cundiboyacense, Eastern Ranges of the Colombian Andes. The formation consisting of a lower unit of calcareous shales and an upper sequence of sh ...

, lowermost unit of the

Villeta Group The Villeta Group ( es, Grupo Villeta) is a geological group of the Eastern Ranges of the Colombian Andes, to the west of the Altiplano Cundiboyacense. The group, a sequence of shales, limestones and sandstones, is subdivided into various formatio ...

. The contact with the underlying unit has not been observed.Moreno, 1990, p.72 The age has been estimated to be

. Stratigraphically, the formation is time equivalent with the

Cumbre ''Cumbre'' is a genus of skippers in the family Hesperiidae Skippers are a family of the Lepidoptera (moths and butterflies) named the Hesperiidae. Being diurnal, they are generally called butterflies. They were previously placed in a separ ...

, Rosablanca and Útica Formations. The formation has been deposited in a marine

environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...

characterised by

turbidite A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites w ...

s. A mid submarine fan and outer fan setting have been observed in the Murca Formation.Acosta & Ulloa, 2001, p.19 A possible source for the sandstones were Precambrian sandstones,

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures a ...

es and

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies und ...

s, belonging to the

Guiana Shield The Guiana Shield (french: Plateau des Guyanes, Bouclier guyanais; nl, Hoogland van Guyana, Guianaschild; pt, Planalto das Guianas, Escudo das Guianas; es, Escudo guayanés) is one of the three cratons of the South American Plate. It is a ...

.Villamil, 2012, p.165

Outcrops

The Murca Formation is apart from its

type locality Type locality may refer to: * Type locality (biology) * Type locality (geology) See also * Local (disambiguation) * Locality (disambiguation) {{disambiguation ...

, found near Nimaima and Guayabal in the western flank and

Ubalá Ubalá is a municipality and town of Colombia in the department of Cundinamarca. It is located in the Eastern Ranges of the Colombian Andes. It is the only municipality of Cundinamarca that is split in two parts. Climate Etymology In the ...

and

Labranzagrande Labranzagrande is a town and municipality in the Colombian Department Department may refer to: * Departmentalization, division of a larger organization into parts with specific responsibility Government and military *Department (administrativ ...

in the eastern flank of the Eastern Ranges.

Regional correlations

References

Bibliography

* * * * * *

Maps

External links

* {{cite LSA , last=Gómez , first=J. , last2=Montes , first2=N.E. , last3=Nivia , first3=Á. , last4=Diederix , first4=H. , year=2015 , title=Plancha 5-09 del Atlas Geológico de Colombia 2015 – escala 1:500,000 , url=https://www.researchgate.net/publication/309533589_Plancha_5-09_del_Atlas_Geologico_de_Colombia_2015 , publisher=

Servicio Geológico Colombiano The Colombian Geological Survey (CGS) ( es, Servicio Geológico Colombiano; formerly known as INGEOMINAS) is a scientific agency of the Colombian government in charge of contributing to the socioeconomic development of the nation through research ...

, pages=1 , accessdate=2017-03-16 Geologic formations of Colombia Cretaceous Colombia Lower Cretaceous Series of South America Valanginian Stage Sandstone formations Shale formations Open marine deposits Turbidite deposits Formations Geography of Cundinamarca Department Geography of Boyacá Department