The Tinajitas and Peñas Blancas Limestones are thin bioclastic carbonate units of Eocene age in the foreland fold and thrust belt of eastern Venezuela. They represent the only limestone deposits in the otherwise siliciclastic Cenozoic succession of the eastern Venezuelan shelf. The geometry of the carbonate units suggests a coast-parallel, bar-like form; the particle population (larger benthic forams, glauconite, and algal balls) indicates shallowmarine provenance; and there is a regional unconformity with major lacuna landward from the location of the limestone units. We interpret these carbonates as the capping deposit of a coast-parallel ridge on the continental shelf that rose and sank in the Eocene. We propose that this transient ridge was an elastic forebulge that migrated landward across the shelf and craton hinge of the South American continent because of a brief episode of Eocene subduction of northern South American lithosphere. Such subduction may have been caused by closure between the North and South American plates. The bulge had an amplitude of at least 800 m and migrated landward at least 50-100 km. This distance suggests the minimum closure between the plates at the subduction zone. Supporting evidence comes from facies suites of the passive-margin wedge, now juxtaposed in the thrust and fold belt. The most seaward facies suite contains no evident Eocene lacuna or limestone; these facies were at too great a depth for the passing bulge to affect sedimentation. In the shallower intermediate facies, which contains the Tinajitas-Peñas Blancas Limestones, the passing ridge brought the seabed to depths of carbonate production, but not to shoal. In the most landward facies of the passive-margin wedge and on the platform, the ridge caused emergence and erosion, producing the Eocene unconformity of large coast-parallel extent. The resubsidence of the margin in the Oligocene is attributed to passage of a foreland basin, which trailed the forebulge.
|Original language||English (US)|
|Number of pages||3|
|State||Published - Dec 1 2005|
ASJC Scopus subject areas
- Economic Geology