DEEP MARINE TRACE FOSSIL ASSEMBLAGES FROM THE LOWER CARBONIFEROUS OF MENORCA, BALEARIC-ISLANDS, WESTERN MEDITERRANEAN

Sediments of Lower Carboniferous age in eastern Menorca, Balearic Isla nds contain a diverse and exceptionally well preserved ichnofauna, inc luding Neonereites biserialis, Nereites isp., Arthrophycus isp., Dicty odora liebeana, two ichnospecies of Chondrites, several ichnospecies o f Lophoctenium, two ichnospecies of Phycosiphon, Syncoprulus pharmaceu s, annulated burrows and a vertical burrow. The host lithologies are c onglomerates, sandstones, siltstones and mudstones; most are the produ ct of debris flows, and of high concentration [Ta(bc) intervals] to re latively dilute (Tcd/Tde intervals) turbidity currents. The rocks are interpreted as deposits of an inner- to mid-fan palaeoenvironment. Cha nnelized deposits, sequences of overbank deposition and interchannel d eposits interspersed with the deposits of unconfined debris flows and high concentration turbidity currents are present. The ichnofauna is m ost frequently, and best, preserved within the Td interval of turbidit ies, which are interpreted as interchannel deposits, produced by low c oncentration turbidity flows. The distribution of the ichnofauna is pa rtly controlled by the lithologies in which they are preserved. The ra rity and poor preservation of trace fossils in the coarser grained fac ies contrasts with the detailed preservation of very delicate traces i n the finer grained lithologies. However, the ichnofauna is also parti tioned between different subenvironments of the mid-fan to produce a s eries of palaeoichnocoenoses. Thin intervals of interchannel deposits, separated by deposits of high concentration turbidity currents, repea tedly contain only Phycosiphon incertum and small (?juvenile) Dictyodo ra liebeana. These traces are interpreted as the products of opportuni stic colonization of near-channel environments during episodes of quie scent deposition. Thicker intervals of interchannel deposits contain d iverse assemblages of trace fossils characteristic of more stable envi ronments, in which widespread colonization occurred. Overbank deposits at Cabo de Favaritz are medium- to thick-bedded, fine-grained beds. I n these, the ichnofauna occurs in a simple, two-tier profile. The uppe r tier is dominated by Nereites isp.; this is underlain by a partially bioturbated layer characterized by large Dictyodora liebeana and Arth rophycus isp.