ESCORZONERA, Formation

CRETACEOUS (Maestrichtian )

State of Aragua, Venezuela

Author of name: P. Leuzinger, 1953 (private repórt).

Original reference: H. H. Renz, 1955, p. 52-54.

Original description: ibid.

P. Leuzinger named and originally described the Escorzonera formation in 1953 (private report) and H. H. Renz (1955, p. 52-54) first used the name in publication.

The formation derives its name from Cerro Escorzonera where the type locality is situated. It lies about four kilometers northwest of the town of San Sebastián, State of Aragua. Here the formation is 450 meters thick and transgresses, with an angular unconformity, on the early Cretaceous or preCretaceous metamorphic rocks. It is overlain, with a slight unconformity, by the Paleocene Guárico formation.

On lithological grounds, the formation can be divided into two members. The lower member, about 300 meters thick, consists of a sequence of shales, sandstones and limestones, interbedded with lava. At the base a bed of andesitic pillow lava frequently occurs, followed by a conglomeratic limestone with reworked pebbles of andesite and metamorphic rocks. The upper member, about 150 meters thick, is in transitional contact with the lower member. Locally, it overlaps the metamorphic series with the development of a conglomerate at the base. At Cerro Escorzonera, the upper member consists of well-bedded greenish-gray limestones with reworked green lava material and interbedded with greenish shales. The top of the Escorzonera formation consists of andesitic lava or is covered by the transgressive Guárico formation. The age of the upper part of the Escorzonera formation can be determined as Maestrichtian based on the occurrence of larger foraminifera (Renz, 1955, p. 52-71) but the lower part of the formation may be somewhat older. The Maestrichtian fauna described by M. de Cizancourt (1948, p. 670-671) from an unnamed formation of the San Sebastián area came most probably also from the Escorzonera formation.

It is suggested that the Escorzonera formation be included in the upper part of the Arrayanes group of Mencher et al. (1953, p. 701, 775). The name Arrayanes is applied to the Upper Cretaceous sedimentary volcanic sequence of north-central Venezuela. The lower part of the Arrayanes group consists of beds outcropping along the San Juan-San Sebastián road, at the foot of Cerro Garrapata where the Coniacian ammonite Peroniceras cf. moureti Degr. has been found (Bucher, 1952, p. 52). It is suggested that this lower part of the Arrayanes group be named the Garrapata formation.

See ARRAYANES, Group

H. H. Renz

ARRAYANES, Group

UPPER CRETACEOUS

State Aragua, Venezuela

Author of name: E. Mencher, 1942.

Original reference: E. Mencher et al., 1951, p. 13.

Original description: ibid.

E. Mencher et al. (1951, p. 13), suggested the use of the term Arrayanes formation in reference to a sedimentary-volcanic series of conglomerates, coarse to fine-grained graywacke sandstones and quartzites, and silty shales, all of a general dark-gray to black color, interbedded with flows of basaltic to andesitic composition, tuffs and agglomerates, in the correlation chart accompanying the report, the Arrayanes formation is listed as occurring in the piedemont zone of northcentral Venezuela. No other mention is made of the locality of outcrop. It is also mentioned that the total thickness of the formation is not known and that it is so broken by folding and faulting that more study is required before the details of deposition can be worked out.

Additional reference is made to the formation by Smith (1953, p. 61) who mentioned that G. Pardo, in 1942, while mapping in the vicinity of San Sebastián, State of Aragua, for the University of Caracas, discovered a Cretaceous ammonite in unmetamorphosed Arrayanes rocks. Careful study by Pardo and E. Mencher showed that it had not been reworked. This ammonite has been identified as Peroniceras cf. moureti De Grossouvre by A. A. Olsson, and given an early Senonian age. Other identifications confine its age to the Coniacian. H. H. Hess, in a heavy-mineral study of the matrix surrounding the fossil, noted the presence of an abundance of the same peculiar pyroxene, characteristic of the Tiara volcanic sequence, that has a pronounced, almost micaceous, parting. In addition, chromite was present, undoubtedly originating in the serpentine rocks intrusive into the Paracotos formation (Smith, 1953, p. 61).

E. Mencher et al., 1953, p.. 775 (Correlation chart) rise the Arrayanes to group, giving it an age from the Coniacian to the Danian included. H. H. Renz, 1955, p. 52, includes his Escorzonera formation in the upper part of the group. Renz proposes the name Garrapata formation for the lower part of the Arrayanes group.

H. Alberding