LOBATERITA, Formation

TERTIARY (Oligocene)

State of Táchira, Venezuela

Synonym of LEON FORMATION

Author of name: P. P. Wolcott, 1943 (private report).

Original reference: F. A. Sutton, 1946, p. 1677-1679.

Original description: ibid.

Sutton (1946, p. 1677-1679) referred the upper part of the "Sandy Shale horizon" of Táchira and southwestern Mérida (Liddle, 1928, p. 285; Kehrer, 1938, p. 47) to the Lobaterita formation. The type exposure of the formation is on Río Lobaterita in the west-central part of the State of Táchira. The base of the formation is at the top of the uppermost sandstone of the "Omuquena formation" at the river crossing of the Estación Táchira-Guavinas trail below Estación Táchira. The top is 1,030 meters downstream where the sandstone of the Bebedero formation first appears. In the type section, the formation is composed almost entirely of massive, dark greenish gray to dark gray, hard, platy shale. The shales are locally silty and sandy and commonly contain thin beds of hard, concretionary siltstones. In northern Mérida and western Trujillo, the formation consists almost entirely of massive, dark gray to black, conchoidally fracturing, rapidly weathering shales. There is a wide variation in thickness of the formation and its equivalents. Sutton cited a thickness of 500 meters for the type section of the formation. On the Río de Oro, in northern Táchira, the formation attains a thickness of 340 meters. The Lobaterita formation is everywhere gradational below into the "Omuquena formation" and the upper contact of the formation is unconformable with beds of the Oligocene Bebedero or younger formations. The Lobaterita formation is exposed in outcrops along the northwest flank of the Mérida Andes. Sutton pointed out that there is only a scant faunal evidence for an upper Eocene age of the formation.

Schaub (1948, p. 221) pointed out that the type section described by Sutton (1946, p. 1677) represents not the upper part of Kehrer's "Sandy Shale horizon", but his "Upper Shales" which are equivalent to the Le6n formation.

Dusenbury (1949, p. 148) stated that a Tropical Oil Company field party, with P. P. Wolcott as a member, was able to trace the Lobaterita formation of Táchira across the Venezuelan-Colombian border into the León formation of the Departament of Santander del Norte in Colombia. Notestein et al. (1944, p. 1201, 1203) considered the León formation to be "upper Oligocenelower Miocene" (p. 1201) or "late Oligocene" (p. 1203) in age. At present the name Lobaterita formation has fallen into disuse as a synonym of the León formation which most geologists consider to be Oligocene in age.

Leo Weiengeist