KAIETEURIAN, Conglomerate

See KAIETEURIAN, "Series"

KAIETEURIAN, "Series"

MIDDLE or UPPER MESOZOIC ?

Potaro River, English Guiana

Synonym of RORAIMA FORMATION

Author of name: C. W. Anderson and W. A. Dunn, 1895.

Original reference (in Venezuela): G. Zuloaga, 1930, p. 473.

Original description: C. B. Brown and J. G. Sawkins, 1875, p. 13-15.

The name Kaieteurian "conglomerate" must be assigned to C. W. Anderson and W. A. Dunn (1895) who on that date were prospecting the area comprehended between Amatuk and Ireng River, including the Kaieteur Falls and the upper Potaro River. Their report includes a brief description of the "conglomeratic" rocks.

Although not formally named, such rocks had been described in detail by C. B. Brown and J. G. Sawkins (1875, p. 13-15). These authors described greenstone sill intrusions up to 1000 ft. thick within a sandstone formation, as well as contact metamorphism in the sediments, producing locally "a green slaty rock with great feldspar crystals". The thickness of intrusive rocks comes up to 7.000 feet. The sandstones are separated from the Basal Complex by a greenstone sill, 740 feet thick. Brown and Sawkins indicate also that the sandstones extend along a line that goes through Wandaik, Arnick, Chenapowu and Potaro River, which is affluent of the Esequibo River, in particular at the Kaieteur Falls, previously unknown (p. 116-123, 278-297).

The Geological Survey of British Guiana published in 1913, a Geological Map of the Colony, in which the "Kaieteurian sandstones and conglomerates" are shown as outcropping from Amatuk to Ireng River.

G. Zuloaga was the first to mention the "Kaieteurian Series" in Venezuela. This author (1930, p. 473) uses indistinctly this name and the name "Roraima Series". Later on (1934, p. 1182) he chooses the name "Kaieteurian Series" to designate the same sediments. Due to a misinterpretation of Zuloaga's latter definition, Liddle (1946, p. 178) asserts that the author divides the Roraima Series into a "lower Pastora Series and an upper Kaieteurian Series".

In the following years, the name Kaieteurian was given up in Venezuela, and later on in British Guiana (P.H.A. Martin-Kaye, 1951 (1952) p. 2) in spite of its evident priority over the name Roraima.

H. G. Kugler et al., (1942 (1944), p. 21-24) intended to include under the name "Kaieteurian series", a "diabase formation" (upper Kaieteurian) which they tentatively associated with the Laramide orogenesis and therefore assigned to a probable Upper Cretaceous age, besides the sediments grouped under a Roraima formation (lower Kaieteurian), and referred to the Mesozoic (Triassic ?, Jurassic ?, Lower Cretaceous ?).

Martin-Kaye (1952, p. 3) objects about the meaning, given by Kugler et al. (loc. cit.), of the name Kaieteurian, considering that the gabbros included under such name "are not necessarily confined to the sandstones". He adds that it seems better to give up now the term "Kaieteurian", assigned erroneously by him, to H.J.C. Conolly, 1925; and therefore, Martin-Kaye asserts the supposed priority of the name Roraima.

The unit of intrusive and extrusive basic igneous rocks (sills, dikes and trap sheets) is represented by gabbros and dolerites up to 2.000 feet, associated with batholites and granitic apophysis (porhyres at Berbice Bay). Brown and Sawkins (1875, p. 15) had already described these trap sheets, up to 700 feet thick, associated with the continental sediments of the Pakaraima Sierra. Such rocks belong to the same intrusive cycle which is represented in Venezuela by the extensive gabbro intrusions of the Gran Sabana and surroundings, petrographically and petrogenetically studied by V. M. López (in Aguerrevere et al. (1939) p. 659-697). López relates the Cerro Roraima diabase laccolith and the gabbro of the Camarata Valley and surroundings which are forming semi-circular sills, dikes and laccoliths around the Gran Sabana, with the latter post-Roraima intrusive cycle. Such intrusions are locally responsible for the structural disturbances noticed in the sediments. López indicates that the gabbros were altered in its contact areas, into acid rocks (granite) by injections rich in silica. R. Ijzerman (1931) and B. Maguire (1945) observed also an intrusive diabase in the sedimentary mass, associated with granite, at the Tafelberg Plateau, Surinam.

The name of the unit, appears erroneously as "Kaiteurian Series" on Hedberg's (1938) list of names of the geological formations of Venezuela.

(See also RORAIMA, "MAGMATIC PROVINCE".)

J. M. Sellier de Civrieux