RADIOLARIAN BIOSTRATIGRAPHY OF THE NORTHERN ALBANIA OPHIOLITES: NEW DATA FROM THE SUB-OPHIOLITIC MÉLANGE AND EASTERN MIRDITA OPHIOLITES

In this paper we present new data on the Jurassic radiolarian assemblages collected in seven sections of the sedimentary cover of the Mirdita ophiolites in Albania. These ophiolites form an outstanding NNW-SSE trending ophiolitic belt representing the remnants of the Mesozoic Neo-Tethyan oceanic lithosphere in the Mediterranean area. The studied sections were sampled in the sub-ophiolitic mélange of the Western Mirdita ophiolites (Rubik Complex) and in the Eastern Mirdita ophiolitic sequences. In the sub-ophiolitic mélange the oldest ages of radiolarians associated with the basalts are referable to the UAZ 4-5 (late Bajocian to latest Bajocian-early Bathonian) and UAZ 5 (latest Bajocian-early Bathonian). In the radiolarian cherts belonging to the Eastern Mirdita ophiolites similar ages were found: from UAZ 5 (latest Bajocian-early Bathonian) to UAZ 5-7 (latest Bajocian-early Bathonian to late Bathonian-early Callovian). These new biostratigraphic ages are consistent with the tectono-magmatic evolution of the Jurassic Neo-Tethys. In fact, the UAZ 4-5 and UAZ 5 correspond to the very early stages of subduction initiation, whereas the slightly younger UAZ 5 and UAZ 5-7 ages found in the Eastern Mirdita ophiolites could correspond to the subsequent mature stage of the subduction.