MOMBOY, "Series"

See RIO MOMBOY, "Series".

RIO MOMBOY, "Series"

PALEOZOIC

State of Trujillo, Venezuela

Author of name: R. A. Liddle, 1928.

Original reference: R. A. Liddle, 1928, p. 99-101.

Original description: ibid.

The Río Momboy "series" as used by Liddle (1928, p. 99; 1946, p. 114) denotes an assemblage of Paleozoic rocks occuring in the valley of Río Momboy near Mendoza in the State of Trujillo. These rocks form many of the high peaks of the Venezuelan Andes and are said to ovèrlie the granitic eve of these mountains and to underlie unconformably various formations of pre-Cretaceous age.

The Río Momboy "series" is composed in large part of gray schistose shales and slaty shales containing powdery limonite nodules. In places there are dark gray and black phyllites and slates and, southwest of the Río Momboy, there are reddish garnet schists, lead-colored gneissoid and mica schists intruded by quartz and pegmatite dikes, and dark gray to black schistose slates and phyllites. Apparently interbedded in the upper part of these schists and phyllites are less metamorphosed slaty shales, thin sandstones and quartzites, and indurated sandy limestones. Liddle states that the thickness of these partially altered rocks cannot be less than 4 000 to 5,000 feet (1,219 to 1,524 meters) although it is not certain that all of them pertain to the Rio Momboy "series".

In the upper course of the Rio Momboy, Liddle reports the presence of crinoids, bryozoa and the brachiopod Spirifer arenosus (Conrad) and suggests that the deposition of these particular beds of the Río Momboy series took place at about the same time as those of the lower subdivision of the Río Cachirí group or in Lower-Middle Devonian time. Liddle acknowledges however, that his Río Momboy "series" has not been adequately delimited and may include the lower part of the Mucuchachí and Caparo-Bellavista series of Christ (1927, p. 404), and the Imataca "series" of Liddle (1928, p. 6468). This uncertainty is emphasized by Kündig (1938, p. 53) who considers the Mucuchachí series as equivalent to the Momboy on the basis of similar physical appearance. The Caparo formation, on the other hand, is Middle Ordovician in age according to Schuchert (1935, p. 692-694) and Leith (1938), whereas Christ's Bellavista series is believed by Kündig (1938, p. 24) to be a facies variant of the Mucuchachí series and should not be combined with the Caparo formation. The age of Liddle's Imataca "series" is not known with certainty although Zuloaga and Tello (1939, p. 416) state that it is strikingly similar in Ethology and geologic relations to the Itabira formation of Brazil which is believed to be Lower Paleozoic.

From the foregoing it is apparent that the Río Momboy "series" is not clearly enough defined to be accepted as a stratigraphic entity. Even the Lower-Middle Devonian age of a part of the "series" is based on a few fossils found in float (Sutton, 1946, p. 1635-1636) and although the correlation of the fossil-bearing beds with the Río Cachirí group of northwest Zulia is suggestive, it is by no means conclusive, as the forms thus far identified are not diagnostic. Therefore, about all that can be said at present concerning the age of the Río Momboy "series" is that it is Paleozoic.

Norman E. Weisbord