Francois Thiébault

Paleogeographic and paleotectonic implications of clay mineral distribution in late Jurassic-early Cretaceous sediments of the Pindos-Olonos and Beotian Basins, Greece

Abstract A new method is proposed for solving the controversial problem of the location of oceanic areas from which the Pindos and Othrys ophiolites originated. Assuming that clay fractions, quickly disseminated over large areas, may be reliable markers of erosional processes, we studied these fractions in sediments from two “external” basins (Pindos-Olonos and Beotian) located between the main carbonate platforms of the Greek Hellenids. Chronologically, two different clay associations can be distinguished in the sedimentary sequences of the basins. The lower one is dominated by illite and subregular illite-smectite mixed-layers and poor in Mg, Ni and Cr; this association is consistent with common continental sources. The upper one, appearing in late Tithonian synchroneously in both basins, consists of trioctahedral smectite (saponite type) enriched in Fe, Mg, Ni and Cr; they are considered to be derived from weathered ophiolites. Thus, the beginning of the ophiolite detrital sedimentation, accepted as being middle to late Bathonian in the basinal sequences of the Maliac or Othrys zone from Hydra or lower-middle Oxfordian in all the internal units in the Argolis Peninsula, is much younger (late Tithonian) in the external basins. Such a diachronism is not consistent with a model postulating initial ophiolite displacements within the Pindos-Olonos basin by late Jurassic time. It suggests that a platform was acting as a barrier between the site of the ophiolite first intra-oceanic deformation and the “external” basins. This barrier cannot be the Parnassus platform that kept subsiding in neritic environments until late Cretaceous inside the “external” basins; it is likely to be the Pelagonian platform, positively known to have been submerged during the Tithonian. Consequently, we conclude that there was no genetic relationships between the “external” basins (Pindos-Olonos basin in a broad sense) and the “Pindos ophiolites” of which the zone of origin is to be located on the opposite eastern “internal” side of the Pelagonian platform.