"SANDY SHALE HORIZON"

See "SANDY SHALE FORMATION"

SANDY SHALE FORMATION

TERTIARY (Eocene-Oligocene?)

State of Zulia, Venezuela

Author of name: Geologists working in the Colón district (private report).

Original reference: R. A. Liddle, 1928, p. 281.

Original description: ibid.

Liddle (1928, p. 411) was the first to have publish ed the name Sandy Shale horizon, which name he reports as being used previously by geologists working in the Colón district, state of Zulia. This name does not satisfy the requisites of nomenclature but its prevalent use warrants its being retained until a proper type locality is described. The staff of Caribbean Petroleum Co. (1948, p. 615) uses the name Sandy Shale formation (not horizon), which name is now generally used.

Liddle (1946, p. 411) gives the following decription: gray, sandy shales, thin fossiliferous limestone, thin sandstones and shaly sanstones. In places the thin sandstones are saturated with oil. Some geologists refer to the lower part of the Sandy Shale formation as the Second Coal horizon because it contains asphalt-bearing sands and sub-asphaltic coal. According to Liddle, the Sandy Shale formation rests with an unconformity on the Mirador formation. According to the Staff of Caribbean Petroleum Co. (1948, p. 615) the Sandy Shale formation overlies the Mirador formation with a transition and the contact with the Upper Shale formation is transitional as well.

The Sandy Shale formation is subdivided into several members: at the base a cannel coal occurs,overlain by the Cubo Sands, which are about 500 feet thick. Several shaly coal seams occur in the uppermost member.

Hedberg (1949, p. 150) correlates the Carbonera formation of the Notestein et al. with the Sandy Shale formation. According to Sutton (1946, p. 1672) the Sandy Shale formation seems to be limited to the upper Eocene, whereas the Carboneraformation apparently includes strata of upper Eocene and middle Oligocene age.

The best exposures of the Sandy Shale formation are on the Río de Oro and Río Tarra anticlines in the Colón district and on the Río Lora anticline in the southwestern part of the Perijá district. In the Colón district, the thickness of the Sabdy Shale formation, according to the Staff of Caribbean Petroleum Co. (1948, p.615) is approximately 1,500 feet.

The basal part of the Sandy Shale was described by Liddle (1928, p.282) as the Second Coal horizon. "Cienfuegos lignites" of Liddle (1928, p. 290) is an obsolete name foroutcrops of the First Coal horizon (uppermost part of the Sandy Shale formation) in the Cienfuegos area, Colón district.

The age of the Sandy Shale formation is considered to be Eocene to Oligocene. The fossils described of the Sandy Shale fromation (Carbonera formation) are mostly derived from localites in Colombia, close to the Venezuelan-Colombian border.

W. A. Mohler