TRIASSIC RADIOLARIAN ASSEMBLAGES FROM THE CHERTS ASSOCIATED WITH PILLOW LAVAS IN ARGOLIS PENINSULA (GREECE)

Abstract

In this work we consider the radiolarian assemblages of the cherts associated with the pillow basalts in the northern part of the Argolis Peninsula. The Argolis Peninsula is the southern portion of the internal zone of the Hellenides, in which ophiolitic successions belonging to the “Subpelagonian isopic zone” crop out. This zone consists of several imbricate thrust units, made of deep sea basin successions deposited on both oceanic and continental margin domains. The ophiolites of Northern Argolis, in which three main tectonic units have been recognised (Photiades 1986, 1987), lie on the Trapezonian platform (Subpelagonian isopic zone), and are often included in, or in relation with melange levels (Photiades 1986; 1987; Dostal et al., 1991). The basalts topped by the cherts we deal with, were considered up to now as the upper portion of the Jurassic ophiolite complexes, but the new age determinations call this attribution into question. 15 samples of cherts have been collected at the top of the basalts in six sections near Dimena, Palea Epidavros and Vothiki villages. Most of these samples contain radiolarian assemblages referable to Late Triassic age (Carnian-Norian), for the occurrence of Capnodoce anapetes De Wever, Capnodoce sarisa De Wever and Capnucosphaera triassica De Wever. Basalts topped by Jurassic cherts were already know in the same Argolis Peninsula (Baumgartner 1984) and our non-published data. Radiolarian assemblages of both Triassic and Jurassic ages, whose study is in progress, are also present in the cherts associated with the basalts of the Othris area. These data can suggest the following hypotheses: i The presence of a melange in which the chert-basalt successions are included as exotic blocks: they would be fragments of the Triassic volcano-sedimentary succession, widespread on the continental margins of Dinarides and Hellenides. According to this hypothesis, the basic lavas outpoured in an aborted rift alignment. ii The local existence of a minor oceanic basin during the Triassic. iii The western prolongation, till the Argolis Peninsula, of the Paleotethys.