SANTA RITA, Conglomerate

TERTIARY (upper Eocene)

State of Lara, Venezuela

Author of name: A. Senn, 1932 (private report).

Original reference: A. Senn, 1935, p. 60.

Original description: ibid.

The name Santa Rita conglomerate was published by A. Senn (1935, p. 60) who described it as the basal member of his Agua Negra formation (now group) which he described in the same publication. The other two members (in ascending order) were called Jarillal shales and Churuguara beds. Senn's description reads (translated):

"Santa Rita conglomerate (400-450 meters), coarse-grained conglomerates, sandstones and sandy marls with intercalated orbitoidal limestones. The conglomerate consists principally of cobbles up to 10 cms in diameter, of white quartz, black Cretaceous cherts, and coarse quartzites of the Misoa-Trujillo and other sandstones." (Senn, 1935, p. 60.)

According to geologists who have worked in the region, pebbles of green jasper are especially characteristic of these conglomerates.

The name was doubtless given in allusion to the hamlet of Santa Rita, about 12 kms. NE of Baragua, in the state of Lara, on the old road between Baragua and Piedra Grande. Since Senn designates the type section of the Agua Negra "formation" as a whole as being located on the flanks of the Buena Vista anticline, in the Agua Negra range, along the old Spanish highway, the type section of the Santa Rita is included in this designation.

Senn interprets the basal contact of his Agua Negra "formation" (hence that of the Santa Rita conglomerate) as an angular unconformity above the underlying middle or upper Eocene formations. To the north (Seen states), the beds lie on the Paraiso formation or on the Paují shales; to the south on the lower Misoa-Trujillo beds. Senn states that it is difficult, however, to observe this lower contact, since it is generally hidden by later foldings. From geologists who have worked in the region we may add the following data: in the type locality of the Santa Rita, the conglomerate is overturned and the base is not visible: but N of Carora, a good section of Santa Rita is exposed, Iying on Paují shales. The Paraiso formation which Senn considered Eocene, is now believed to correspond to a higher horizon (Oligocene), so that the Santa Rita conglomerate could not overlie it in a normal sequence, as Senn believed. The upper contact of the Santa Rita conglomerate with the Jarillal shales, is transitional, as Senn states. He also observes that south of the town of Churuguara, the Jarillal shales thin out due to facies changes, so that the Santa Rita conglomerate comes to lie directly below the Churuguara beds.

Senn cites species of foraminifera and mollusks which determine the upper Eocene age of the Santa Rita. These same molluscan species are also characteristic of the lower 50 meters of the overlying Jarillal shales, which Senn distinguished as the "Raetomya shales"; hence Senn proposes to recognize a "Santa Rita stage", comprising the Santa Rita conglomerate plus the Raetomya shales, which would correspond in age to youngest upper Eocene. (The lower part of the upper Eocene, Senn would call the "San Pedro stage".) These proposed stages of Senn have not been recognized by later workers however.

Senn correlated the Santa Rita conglomerate with the Cerro Venado limestone (see article).

The Santa Rita conglomerate has been mentioned in various publications, without any additional details or modifications. As noted in the article on the Agua Negra, it seems convenient to treat that unit as a group, and hence raise the Santa Rita to the rank of formation.

Paleontology.- Senn recapitulates the identifications of foraminiferal species effected by Gorter and Van Der Vlerk (1932) and by Gravell (1933). (In the first named-paper, the species cited from the localities numbered 1142, 1149, 1152, and 1162, which were described as "Guayaval series, Cerro Campaha (sic) limestone", also belong to the Santa Rita beds) - Senn's list includes the following species: Discocyclina flintensis Cushman, D. (Asterocyclina) georgiana Cushman, Lepidocyclina trinitatis H. Douvillé, Nummulites cf. parvulus Cushman, Operculina cf. cookei Cushman, and Bulimina jacksonensis Cushman. Rutsch (1930, 1937) had identified the characteristic Eocene gastropod Rimella (Ectinochilus) gaudichaudi alauda Olsson, and Seitz and Rutsch (1930) identified a pelecypod, Mya (Raetomya) schweinfurthi falconensis Rutsch. In addition, Senn mentions several genera of mollusks. A. K. Miller (1947, p. 105) has identified the nautiloid Aturia peruviana Olsson from two localities near Santa Rita, which provides still further confirmation of the upper Eocene age.

Frances De Rivero