SAN LUIS, Formation

TERTIARY (middle Oligocene)

State of Falcón, Venezuela

Author of name: R. L. Marston, 1922 (prívate map).

Original reference: F. Hodson, 1926, p. 174.

Original description: ibid.

Hodson (1926, p. 174) describes the "San Luis series" as foraminiferal limestones interbedded with shales and sandstones; the limestones and sandstones at times conglomeratic, where the main trail from Coro to Cabure crosses the Serranía de San Luis.

Liddle (1928, p. 252) modifies the description saying "the San Luis formation consists of blue gray reef limestones, in a few places interbedded with greenish, coarse sandstones and with shales, with a thickness of about 460 meters".

Senn (1935, p. 70-74) gives further details and includes not only the cliff-forming reef limestones of the Serranía de San Luis but also underlying and laterally equivalent rocks. Including the Pedregoso, Pecaya and San Juan de la Vega formations the thickness is about 1,000 meters. Senn (1940, p. 1580) clearly used San Luis in three ways: as the middle Oligocene stage, as a formation in the European sense including most of the Mitare group, and as a lithologic unit for the reef limestone in the Serranía de San Luis. Mencher et al. (1951, correlation chart) show the last usage which is preferred.

The great regional extent of the San Luis formation postulated by Liddle (1928, p. 252) was due to the similarity of reef limestone faunas over all of central and western Falcón. But the microfauna from the associated shales show an age range from lower Oligocene to Miocene. Clearly many of the local reefs do not correlate directly with the San Luis. On the other hand, reef deposition in the Serranía de San Luis may have been continuous through and beyond the middle Oligocene.

G. D. Johnson