Abstract

The writer interprets the diastrophic history of Northeastern Venezuela, incorporating some hitherto unpublished data, especially from Margarita and Cubagua.

The first dated orogenesis is post-Tithonian, pre-Cretaceous, although there are indications that this may not be the earliest. Absence of Hato Viejo-Carrizal sediments from southeastern Anzoategui and southern Monagas suggests a Jurassic land there, uplifted in early Mesozoic or pre-Mesozoic time. In Margarita island, pre-Laramide granites may represent a post-Tithonian, or even earlier, orogenesis.

Barranquin to Chimana time represents an epeirogenetic cycle, ended by the Guayuta transgression. Guayuta to Santa Anita time is another epeirogenetic cycle, during which the basin was gradually filled.

In Margarita, a thick conglomeratic Lower Eocene section contains pebbles of ultrabasic rocks exposed on the island; these conglomerates, as well as the ultrabasics, are presumably related to a pre-Lower Eocene (Laramide) orogenesis. It is still uncertain to what extent these movements affected the center of the Maturin basin.

Late Eocene or post-Eocene orogenesis is demonstrated in the Cubagua basin by angular unconformity between the Eocene and Oligo-Miocene or Miocene. In the Maturin basin, post-Cretaceous, pre-Merecure movements produced: in the north, emergence of lowlands with coastal swamps (Naricual coals); in the south, uplift of the northern edge of the Guiana shield with northward offlap of the Merecure.

Oligo-Miocene (Carapita-Santa Inés) sedimentation was essentially epeirogenetic, interrupted by synepeirogenetic uplifts of the northern lands, which produced the Santa Inés flysch facies appearing at successively younger horizons from west to east. In the south of the Maturin basin, the sea was transgressive southward.

In early Pliocene or pre-Pliocene time, the Maturin basin suffered a short but violent orogeny, which folded and faulted older beds and led to a general transgression of Pliocene brackish-water sediments.

Medial or Late Pliocene (Antillean) orogenesis produced folding and faulting, generally along pre-existing structural lines. There has been some post-Pliocene uplift but no true orogenesis. Frequent earthquakes indicate that the region is still unstable.

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