MUCUCHACHI Group

CAMBRIAN?-DEVONIAM

State of Mérida, Venezuela

Author of name: P. Christ, 1927.

Original reference: P. Christ, 1927, p. 397.

Original description: ibid.

The name Mucuchachí series was first used by Christ (1927, p. 397) to designate the metamorphosed sediments exposed near the town of Mucuchachí on the southeast flank of the Mérida Andes in the southern part of the State of Mérida. Christ described black, argillaceous schists, which in places are calcareous or siliceous.

Kündig (1938, p. 23) used also the name Mucuchachí series in the English text but in the Spanish text he refers to it as "Grupo de Mucuchachí". The use of the name Mucuchachí group is considered preferable. He gives the following description of the rocks of the Mucuchachí group:

Phyllites, dark grey to black, mostly with a slight silky lustre. Quartz, sericitic and graphitic matter as major constituents; chlorite, epidote, feldspar, pyrite and calcite as minor constituents. Epizonal metamorphism with all the transitions into semi-metamorphic types. Diminutive crumbling into thin sections; new minerals in the very beginning of crystallization; porphyroblasts are absent. Honeystone, a semi-metamorphic siltstone-claystone as thin seams and local intercalations within the phyllites. Sandstones, locally even, fine, conglomeratic sandstones slightly metamorphosed, finegrained, dark-greenish, as thin beds within the phyllite series.Quartz veins and stringers.

The thickness, according to Sutton (1946, p. 1631), is unknown but probably exceeds 300 meters, according to Kündig (1938, p. 23) it may be estimated to be more than 1000 meters and according to González de Juana (1951, p. 131) even more than 2000 meters. Fossils sufficiently well preserved for an accurate age determination have not yet been found, though Kehrer (1938, p. 53) mentions a private report in which Woodring writes that incomplete fossil material suggests an ammonite and Halobia. According to Sutton (1946, p. 1634) these fossils may have come from the Upper Triassic beds of the La Quinta formation, which rest unconformably on the Mucuchachí group in the type area.

The age according to Sutton (1946, p. 1634) is upper Cambrian to upper Ordovician; according to González de Juana (1951, p. 130) Silurian? to Devonian.

The Mucuchachí group is widespread in the Venezuelan Andes south of the Sierra Nevada.

W. A. Mohler

MUCUCHAHI "Serie"

See MUCUCHACHI Group