CUMACA, Formation

TERTIARY (middle Miocene)

State of Miranda, Venezuela

Author of name: P. P. Wolcott, 1940 (private report).

Original reference: W. H. Bucher, 1949, p. 167.

Original description: None published.

W. H. Bucher (1950, p. 167) mentioned a pre-Oligocene discordance between the Cumaca formation (upper Oligocene or lower Miocene) and the metamorphic rocks of the Tuy embayment.

E. Mencher et al. (1951, correlation chart) assigned the Cumaca formation to the uppermost part of the upper Oligocene plus the lower half of the lower Miocene. They showed it overlain with local unconformity by the lower Miocene Aramina formation and underlain conformably by the upper Oligocene Ocumare formation.

W. H. Bucher (1952, p. 58) provided the additional information that the Cumaca formation consists of fresh water deposits and that its author is Wolcott.

R. J. Smith (1951, p. 59) placed the Cumaca in the early Miocene together with the Aramina and stated that the Cumaca is nonmarine.

The following description of the Cumaca formation is mostly abstracted from a private report by P. P. Wolcott (1954). This formation is named aiter the Quebrada La Cumaca, which is a northern subtributary of the Río Tuy and crosses the Caucagua-Aragüita trail seven kilometers southwest of Caucagua. The base of the type section lies approximately 515 meters upstream from the trail crossing, and the highest exposure is 325 meters downstream from the crossing. The Cumaca formation consists principally of greenish gray, chocolate brown and black shales and clay shales with a relatively small percentage of greenish gray sandstones. The maximum thickness noted is about 100 meters in the Río Merecure section. The Cumaca is composed of fresh water deposits that are now considered to be the lateral equivalent of the middle Miocene shallow marine Aramina formation. Like the adjacent Aramina, the Cumana rests with angular unconformity upon Cretaceous metamorphics and lies unconformably beneath the Guatire formation (of upper Miocene and/or Pliocene age) in the outcrop area, the upper Miocene Tuy formation having apparently been completely overlapped. The fossils of the Cumaca formation are undescribed species of fresh water pelecypods and gastropods. The Cumaca formation is geographically restricted to the west end of the lower Río Tuy embayment in eastern Miranda.

A. N. Dusenbury, Jr.