The ophiolite-flysch range (accretionary prism) of the Sistan suture zone from eastern Iran includes several intensely deformed tectonic units, some of which consist of volcaniclastic rocks, volcanic rocks, siliceous pelagic sediments (cherts and radiolarites) and calcareous rocks (deep marine, platform), whereas others are represented by terrigenous turbidites. The Soulabest radiolarites are located in the Ratuk complex of the Tirrul’s subdivision [Tirrul et al. , 1983], or in the ophiolite suite of the Gazik province.
The local biostratigraphy of this region is based on two faunal assemblages. Faunal assemblage I is dated early Aptian, faunal assemblage II is attributed to middle-late Albian. The most abundant fauna is found in the middle-late Albian. The timing of the oceanic opening in eastern Iran remained questionable until now. The study of the radiolarites of the Soulabest area provides new data for dating the primary opening between two microcontinents : the Lut and Afghan blocks. It is proposed that the oceanic opening of the two blocks occurred prior to the early Aptian. In previous reports, the age of opening was attributed to Upper Cretaceous.
All reported Radiolaria are found in red radiolarites and green-red argillaceous cherts. This formation is unconformably overlain by Maastrichtian conglomerates. It indicates that the closure of the basin occurred in Maastrichtian age.