Río Cachirí Group

Río Cachirí Group
Stratigraphic range: Devonian
419–360 Ma
Type Geological group
Unit of Cesar-Ranchería Basin, Serranía del Perijá
Sub-units Caño Grande Fm., Caño del Oeste Fm., Campo Chico Fm., Los Guineos Fm.
Underlies Carboniferous sequence
Overlies Perijá Formation
Thickness ~1,100 m (3,600 ft) (Colombia)
2,438 m (7,999 ft) (Venezuela)
Lithology
Primary Shale, sandstone
Other Limestone
Location
Coordinates 10°50′03″N 72°14′23″W / 10.83417°N 72.23972°W / 10.83417; -72.23972Coordinates: 10°50′03″N 72°14′23″W / 10.83417°N 72.23972°W / 10.83417; -72.23972
Region Cesar, La Guajira
Zulia
Country  Colombia
 Venezuela
Extent ~110 km (68 mi) (Venezuela)
Type section
Named for Río Cachirí
Named by Liddle
Location Mara
Year defined 1928
Coordinates 10°50′03″N 72°14′23″W / 10.83417°N 72.23972°W / 10.83417; -72.23972
Region Zulia
Country  Venezuela
Thickness at type section 2,438 m (7,999 ft)

Paleogeography of the Middle Devonian
380 Ma, by Stampfli & Borel

The Río Cachirí Group (Spanish: Grupo Río Cachirí, PZc) is a geological group of the Cesar-Ranchería Basin, Colombia and the Serranía del Perijá of the northernmost Colombian and Venezuelan Andes. The group of shales, sandstones and limestones is of Devonian age and has a maximum thickness in the Venezuelan section of 2,438 metres (7,999 ft). The group contains abundant fauna; crinoids, bryozoa, brachiopods and molluscs have been found in the group.

Etymology and definition

The formation was defined by Liddle in 1928 in Río Cachirí, part of Mara, Zulia, 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.[1]

Description

Lithologies

The group contains black, grey and red shales, grey micaceous sandstones, quartzitic sandstones and red and bluish grey limestones.[1]

Stratigraphy and correlation

The Río Cachirí Group, dated to span the Devonian, is subdivided into the Caño Grande, Caño del Oeste, Campo Chico and Los Guineos Formations. The maximum thickness has been recorded in Venezuela, with 2,438 metres (7,999 ft), while the thickness on the Colombian side of the range does not exceed 1,100 metres (3,600 ft).[1] The group is recognised along a section of approximately 110 kilometres (68 mi) in the Venezuelan terrain.[2] The group unconformably overlies the Perijá Formation and is overlain by an unnamed Carboniferous sequence. The Río Cachirí Group is time-equivalent with the Floresta and Cuche Formations of the Floresta Massif, Altiplano Cundiboyacense and the Quetame Group of the Eastern Ranges.[3] The sediments of the Río Cachirí Group were deposited in an epicontinental sea at the edge of the Paleo-Tethys Ocean.[1]

Fossil content

The group contains abundant fossils of crinoids, bryozoa, brachiopods and molluscs as Acrospirifer olssoni, Spirifer kingi, Leptaena boyaca, Fenestella venezuelansis, Neospirifer latus, Composita subtilita, Phricodrotis planoconvexa and Pecten sp.[4]

Outcrops

Type locality of the Río Cachirí Group in Venezuela

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 and Curumaní, Cesar.[5][6]

See also

Geology of the Eastern Hills
Geology of the Ocetá Páramo
Geology of the Altiplano Cundiboyacense

References

  1. 1 2 3 4 Ayala, 2009, p.20
  2. ↑ Hernández Ferrer, 2011, p.47
  3. ↑ Ayala, 2009, p.21
  4. ↑ García González et al., 2007, p.68
  5. ↑ Plancha 34, 2007
  6. ↑ Plancha 48, 2008

Bibliography

Maps

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