NEW DATA FROM GRAPTOLITES AND QUARTZ ARENITES FOR THE ORDOVICIAN-SILURIAN BOUNDARY IN THE MURZUQ BASIN, LIBYA

The graptolite-bearing interval in well A1-NC101, Libya indicates a Hirnantian age (persculptus graptolite Zone) for the lowermost Tanezzuft Fm based on the presence and stratigraphical distribution of N.? pseudovenustus. In the C1-NC101 core, the presence of N. inazaouae (recognised for the first time outside Algeria) and M. parvulus indicates either the uppermost Ordovician or the lowermost Silurian, but the revised total stratigraphical range of N. targuii (ascensus-acuminatus graptolite Zone) suggests an earliest Rhuddanian age. Several specimens of N. targuii are longer than those previously recorded. Pure quartz arenites of the uppermost Mamuniyat Fm (well A1-NC101) were deposited during the end-Hirnantian deglaciation probably in a nearshore marine environment. Their provenance was associated with sedimentary recycling of mature sands that were formed across North Gondwana in Cambrian and pre-glacial Ordovician times.