Cretaceous radiolarians from the Siquisique Ophiolite (northern Venezuela)

Abstract

The Siquisique Ophiolite is one of the few remnants of the proto-Caribbean Seaway. Located in northern Venezuela, in the border between Lara and Falcón states. At Los Algodones, the type locality, the ophiolite is composed of cumulate gabbros, basalts, and stratigraphically overlying dark cherts. Mafic complexes identical to Siquisique have been identified in three other localities of northern Venezuela: the extended outcrop of Chorrerones-Macure, and the reduced outcrops of Llanaditas and Limon. A previous study reported Bajocian–Bathonian ammonites in inter-pillow sediment of basalt blocks from Las Petacas Creek in Los Algodones area. These ammonites were associated with the Siquisique Ophiolite, hence considered as a remnant of the Jurassic proto-Caribbean seaway. However, recent detailed geological mapping has shown that these ammonites are associated with basaltic blocks of unknown origin embedded in a Paleogene-Eocene turbidites (Matatere Formation). Radiolarians recovered in a black chert sample obtained from the Middle Jurassic ammonite locality yields a Bajocian-Bathonian age. Thus, the Middle Jurassic age given by ammonites and radiolarians could reflect the presence of older deposits that are not part of the Siquisique Ophiolite.Aditionally, poorly preserved radiolarians were recovered in a green to black laminated ribbon bedded cherts of the Guaparo creek area (Chorrerones-Macuere), in stratigraphic contact with basaltic breccias. The determined assemblage includes Parvimitrella communis (Squinabol), Dictyomitra sp. cf. D. multicostata, Dictyomitra sp. cf. D. communis, Dictyomitra sp., Diacanthocapsa sp., Praeconocaryomma sp., Archaeodictyomitra sp., Rhopalosyringium sp. aff. R. fossile, indicating a Cretaceous (Albian–Coniacian) deposit.