GUACURIPIA, Formation

PALEOZOIC or older

Distrito Piar, State of Bolívar, Venezuela

Author of name: R. P. Morrison.

Original reference: R. P. Morrison, 1954, p. 55.

Original description: ibid, p. 51.

The formation consists of dolomite marble which is very uniform in color, texture and composition throughout its known distribution. The rock is completely recrystallized, and is composed predominantly of dolomite crystals averaging about three millimeters in diameter. Under the microscope it is seen to have a well defined, coarse granoblastic texture. In color it is light to medium bluish-gray, and has a pearly lustre. Accessory minerals, which represent about three percent of the rock, are forsterite, tremoliteactinolite, phlogopite and muscovite. The accessory minerals are much more strongly developed in the uppermost two or three meters of the formation.

The rock is exposed along an east-west trending range of hills from the río Curipiaima, near the village of El Palmar, westward to within three kilometers of Cerro Peluca, which is situated about twenty kilometers east of the town of Upata. The exposure of the formation throughout the fifteen-kilometer length of known occurrence is fairly continuous although it is folded or faulted down beneath the surface at three localities. It has not been found elsewhere; however, the region has only been partially explored.

The dolomite is overlain by a unit of hornblende schist which, in turn, is overlain conformably by the Imataca ferruginous quartzites. The contact between the dolomite and the schist is abrupt, and the surface of the dolomite is very irregular. As there is no apparent angular discordance between the two rocks the contact is considered to be a disconformity. The lower contact of the formation has not been seen, but in the vicinity of cerro Hacha and Guacuripia, structural relations indicate that it lies unconformably on an orthogneiss. At this locality its thickness is calculated to be 85 meters.

The best section of the formation that has yet been seen occurs in a cliff at the east end of cerro Hacha, where the upper sixty meters of it are exposed. This is considered to be the type section of the formation. It is located across a narrow valley from cerro Guacuripia. As Guacuripia is an indigenous name, and the one applied by the local people to the general area, it is considered to be an appropiate name for the formation.

As the Guacuripia formation has had, almost undoubtedly, a sedimentary origin and is only separated from the overlying metasediments of the Imataca group by a minor disconformity, it is included in this group as a formational unit.

R. P. Morrison