The Río Cachirí Group (, PZc) is a

geological group In geology, a group is a lithostratigraphy, lithostratigraphic Stratigraphic unit, unit consisting of a series of related Geological formation, formations that have been classified together to form a group. Formations are the fundamental unit of ...

of the

Cesar-Ranchería Basin The Cesar-Ranchería Basin () is a sedimentary basin in northeastern Colombia. It is located in the southern part of the departments of Colombia, department of La Guajira Department, La Guajira and northeastern portion of Cesar Department, Cesar. ...

, Colombia and the

Serranía del Perijá The Serranía del Perijá, Cordillera de Perijá or Sierra de Perijá is a mountain range, an extension of the eastern Andean branch ( Cordillera Oriental), in northern South America, between Colombia and Venezuela, ending further north in the ...

of the northernmost

Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...

n and

Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...

Andes The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...

. The group of

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 ...

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 ...

s 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 is of

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

age and has a maximum thickness in the Venezuelan section of . The group contains abundant fauna;

crinoid Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that remain attached to the sea floor by a stalk in their adult form are commonly called sea lilies, while the unstalked forms, called feather stars or comatulids, are ...

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...

s and

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

s have been found in the group.

Etymology and definition

The formation was defined by Liddle in 1928 in Río Cachirí, part of Mara,

Zulia Zulia State (, ; Wayuu: ''Mma’ipakat Suuria'') is one of the 23 states of Venezuela. The state capital is Maracaibo. As of the 2011 census, it has a population of 3,704,404, the largest population among Venezuela's states. It is also one of t ...

, in the Venezuelan part of the Serranía del Perijá, and the same author subdivided the group into three formations in 1943. In 1972, Bowen added a fourth formation to the group.Ayala, 2009, p.20

Description

Lithologies

The group contains black, grey and red

s, grey

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into fragile elastic plates. This characteristic is described as ''perfect basal cleavage''. Mica is co ...

ceous

quartzitic Quartzite is a hard, non-Foliation (geology), foliated metamorphic rock that was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usuall ...

sandstones and red and bluish grey

Stratigraphy and correlation

The Río Cachirí Group, dated to span the

, is subdivided into the Caño Grande, Caño del Oeste, Campo Chico and Los Guineos Formations. The maximum thickness has been recorded in Venezuela, with , while the thickness on the Colombian side of the range does not exceed . The group is recognised along a section of approximately in the Venezuelan terrain.Hernández Ferrer, 2011, p.47 The group

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 ...

overlies the Perijá Formation and is overlain by an unnamed

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

sequence. The Río Cachirí Group is time-equivalent with the Floresta and

Cuche Formation The Cuche Formation (, Cc) is a geological formation of the Floresta Massif, Altiplano Cundiboyacense in the Eastern Ranges of the Colombian Andes. The sequence of siltstones, shales, and sandstone beds dates to the Late Devonian and Early Carbon ...

s of the Floresta Massif,

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. (Do not confuse with The Altiplano or the Altiplano Nariñense, both fur ...

and the Quetame Group of the

Eastern Ranges The Eastern Ranges is an Australian rules football team that currently competes in the Talent League, the Victorian statewide under-18s competition. History Inaugural playing squad (1992) Honours *Premiers (2): 2002, 2013 *Runners-up (6): 199 ...

.Ayala, 2009, p.21 The sediments of the Río Cachirí Group were deposited in an epicontinental sea at the edge of the

Paleo-Tethys Ocean The Paleo-Tethys or Palaeo-Tethys Ocean was an ocean located along the northern margin of the paleocontinent Gondwana that started to open during the Middle Cambrian, grew throughout the Paleozoic, and finally closed during the Late Triassic; ex ...

Fossil content

The group contains abundant fossils of

s and

s as '' Acrospirifer olssoni'', '' Spirifer kingi'', ''

Leptaena boyaca ''Leptaena'' is an extinct genus of mid-sized brachiopod that existed from the Dariwilian epoch to the Emsian epoch, though some specimens have been found in strata as late in age as the Tournasian epoch. Like some other Strophomenids, ''Lept ...

'', '' Fenestella venezuelansis'', '' Neospirifer latus'', '' Composita subtilita'', '' Phricodrotis planoconvexa'' and '' Pecten sp.''García González et al., 2007, p.68

Outcrops

Apart from its type locality on the eastern flank of the Serranía del Perijá in Zulia, Venezuela, the formation is also found in other parts of the mountain range, on the Colombian western side in the east of

San Diego San Diego ( , ) is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. With a population of over 1.4 million, it is the List of United States cities by population, eighth-most populous city in t ...

and

Curumaní Curumaní is a town and municipality in the Colombian Department of Cesar Cesar or César may refer to: Arts and entertainment * ''César'' (film), a 1936 French romantic drama * ''César'' (play), a play by Marcel Pagnolt Places * Cesar ...

Cesar Cesar or César may refer to: Arts and entertainment * ''César'' (film), a 1936 French romantic drama * ''César'' (play), a play by Marcel Pagnolt Places * Cesar, Portugal * Cesar Department, Colombia * Cesar River, in Colombia * Cesar ...

.Plancha 34, 2007Plancha 48, 2008

Regional correlations

Notes

References

Bibliography

* * *

Maps

* * {{DEFAULTSORT:Rio Cachiri Group Geologic groups of South America Geologic formations of Colombia Geologic formations of Venezuela Formations Devonian System of South America Devonian Colombia Devonian Venezuela Shale groups Sandstone groups Limestone groups Shallow marine deposits Fossiliferous stratigraphic units of South America Paleontology in Colombia Paleontology in Venezuela Formations Formations Formations Colombia–Venezuela border

Etymology and definition

Description

Lithologies

Stratigraphy and correlation

Fossil content

Outcrops

Regional correlations

See also

Notes

References

Bibliography

Maps