LAS PIEDRAS, Formation

TERTIARY (upper Miocene to Pliocene)

State of Monagas, Venezuela

Author of name: H. D. Hedberg, 1933 (private report).

Original reference: H. D. Hedberg, L. C. Sass and H. J. Funkhouser, 1947, p. 2104-2105.

Original description: ibid.

Hedberg described the Las Piedras formation in a private report in 1933. This formation name has been in common use by stratigraphers in Eastern Venezuela since that time.

Hedberg et al. (1947, p. 2104-2105) described the Las Piedras formation as developed in well sections in the Greater Oficina area.

Hedberg (1950, p. 1206-1207) designated and described the type section of the Las Piedras formation placing it within the Sacacual group. The formation is named from the Las Piedras n° 1 well of the California Petroleum Corporation of Venezuela, which was drilled in 1931. It is located in the northern part of the State of Monagas at a point about 21 kilometers southwest of the city of Maturín. The interval from about 1600 to about 4500 feet in the above wells is the type section of the Las Piedras formation. The sediments consist typically of light gray and greenishgray interlaminated fine-grained more or less carbonaceous sandstone and clay-shale, light gray fine-grained friable sandstones, and lignites and lignitic shale. As to geographic distribution, the formation is present in well sections throughout Monagas, Delta Amacuro, and central and southern Anzoátegui. The principal outcrop area is in central and southern Anzoátegui just west of the mesa front where it has been called Campo Santo formation. Thicknesses from about 1,500 feet in the outcrop sections to as much as 5000 feet in well sections in the eastern axial portion of the basin are recorded. The Las Piedras formation underlies in part the Quiriquire formation and in part is its lateral equivalent, with the contact between the two being usually gradational. In south-central Anzoátegui, the Algarrobo formation overlies the Las Piedras. In the area east of the Leona oil field the Pando formation overlies the Las Piedras. Within the median portion of the basin, the Las Piedras formation overlies the Santa Inés group or the La Pica formation. In the Greater Oficina area, the lowermost sand of the Las Piedras formation, directly overlying the Freites formation, has been named Tau (t) sand.

It appears that Hedberg's Las Piedras formation of the well sections in the Greater Oficina area is the equivalent of the outcropping Campo Santo and Prespuntal formations.

The Las Piedras formation is a dominantly brackish-water deposit with fossils largely limited to plant remains, fish remains and occasional fresh to brackish-water mollusks and foraminifera. The age can be considered to be upper Miocene and Pliocene.

Wade N. Hadley Jr.