MENECITO, Clay Member

TERTIARY (middle to upper Oligocene)

State of Falcón, Venezuela

Author of name: H. H. Renz, 1945 (private report).

Original reference: H. H. Suter, 1947, p. 2195.

See: SAN LORENZO, Formation.

SAN LORENZO, Formación

TERTIARY (middle to upper Oligocene)

State of Falcón, Venezuela.

Author of name: H. H. Renz, 1945 (private report).

Original reference: H. H. Suter, 1947, p. 2195.

Original description: H. H. Renz, 1948, p. 9-19.

H. H. Suter (1947, p. 2195) mentioned the name San Lorenzo formation for the first time in publication, but the unit was named by H. H. Renz in 1945 (private report) who described it (1948, p. 9-19) as the lower part of the Agua Salada group. The formation is named from the village of San Lorenzo, District of Acosta in Eastern Falcón, immediately north of the abandoned oil field of El Mene de Acosta. Since the basal section is not exposed at the surface, a combined well and surface section on the south flank of the El Mene anticline had to be chosen as type section. On lithologic grounds, the San Lorenzo formation can be subdivided into a lower El Salto sand member and an upper Menecito clay member. The type section for the former is represented in El Mene well n° 47, between the depths of 225 and 1140 feet. For the latter, the type section begins about 750 meters N 10° E of well n° 47 and runs almost due east (87° 30') for about 960 meters; at this point it turns southeast (126°) and continues for about 350 meters to end at the base of the Policarpio greensand member of the Pozón formation.

The total measured stratigraphic thickness of the San Lorenzo formation in the type section is about 400 meters, of which 261.5 belong to the El Salto sand member and 138.5 meters to the Menecito clay member. In the El Mene type section, the formation is in conformable and transitional contact with the underlying Guacharaca formation. The top of the formation is placed at the base of the Policarpio greensand member of the Pozón formation, which overlaps the San Lorenzo formation with a slight angular unconformity (up to 3-7° in dip and up to 2-5° in strike) but this unconformity becomes imperceptible toward the west and passes basinward (toward the north), into an accordant conformity. The San Lorenzo formation crops out over a distance of about 50 kilometers in the southern part of the Agua Salada basin from El Mene de Acosta to west of Pozón. The upper part of the formation is exposed over long stretches along the Aguide coast and at many places in the Agua Salada basin. Paleontologic evidence suggests that the age of the San Lorenzo formation extends from the middle Oligocene (Rupelian) to the upper Oligocene (Chattian-Aquitanian), covered by the "Uvigerinella" sparsicostata zone and the greater part of the Acostian stage.

The lower lithologic unit of the San Lorenzo formation is the El Salto sand member which has taken its name from El Mene del Salto, the old usage for El Mene de Acosta. Senn (1935, p. 77-78) referred to this unit as the "El Mene sand formation" but he included under this heading the underlying lithostratigraphic unit called Guacharaca formation. Although the type locality for this member is in El Mene well n° 47 (225 to 1140 feet), stratigraphic thickness 261.5 meters, the lithologic sequence can be observed along the road leading south from El Mene de Acosta (former camp of the Tocuyo Oilfields of Venezuela, Ltd.) to El Mene well n° 2, or in the Quebrada El Mene at El Mene de Acosta. Sand beds up to 10 meters thick are intercalated in blue-gray silty clays and silts. The sands are lenticular, friable, mostly medium-grained, but lenses of coarse and even gritty sands appear locally. Lateral changes in grade are rapid, and there is some false bedding. Some of the sands grade into sandy limestones, which occasionally contain larger foraminifera. Grains of glauconite are abundant, and several sands are laterally replaced by real greensands. Well-jointed dark blue-gray silts and clay increase toward the bottom. J. C. Griffiths (Renz, 1948, p. 15-18) described the petrography and petrology of the El Salto sands. The El Salto sand member has been referred to in literature by the now obsolete names: El Mene Acosta sands (Seen, 1940), El Mene de Acosta sands, El Mene Sands, El Mene de Acosta formation (Liddle, 1946) and Tocuyo horizon (Liddle, 1928).

The Menecito clay member, which is in conformable stratigraphic contact with the underlying El Salto sand member, is named from the area of Menecito, west of El Mene de Acosta and in the neighborhood of well n° 19. The member consists at the type locality of 138.5 meters of uniform, dull-gray to blue-gray clay with occasional layers of glauconitic and marly clay. The soils are mostly red, but change to sepiabrown in the marly layers.

H. H. Renz