Burrows and body fossil of decapod crustaceans in the Calcari Grigi, lowerJurassic, Trento platform (Italy)

Crustacean burrows are largely known and well described in the literature b ut a concurrence of abundant burrows and fossil remains of decapods represe nts an exceptional circumstance in the geological record. Well-preserved bu rrows of decapod crustaceans in the Pliensbachian of the Trento carbonate p latform, northern Italy, reveal several ichnoassemblages of Thalassinoides and Ophiomorpha from 2 to 16 cm in diameter forming complex burrow systems in the lagoonal facies of the Rotzo Member. These burrows have been found b oth in the lower surface of beds and within shallowing-upwards cycles of fo ssiliferous limestones (Lithiotis facies), which reveal peculiar taphonomic characteristics. The abundant concentration of decapod crustacean burrows suggests intense burrowing activity of such organisms during the Early Jura ssic as indicated also by an exuvia of Phlyctisoma (Erymidae), although we do not know if it was an active tracemaker. Many shallowing-upward parasequ ences occur and burrow systems were concentrated mainly in their lower part suggesting intense biological activity in deeper and quiet subtidal condit ions; conversely, biologic activity was interactive with physical agents in the middle part of cycles and progressively replaced by wave or tidal-indu ced physical agents in the upper part where intertidal/supratidal condition s were formed. (C) 2001 Editions scientifiques et medicales Elsevier SAS.