Macroborings, their tracemakers and nestlers in clasts of a fan delta: the Savignone Conglomerate (Lower Oligocene), Northern Apennines, Italy

The lower part of the Val Borbera Unit of the Savignone Conglomerate (south-eastern part of the Tertiary Piedmont Basin; Lower Oligocene) contains bored clasts of limestones and marly limestones. Their borings are dominated by the bivalve-produced Gastrochaenolites (G. lapidicus, G. orbicularis, G. torpedo, G. isp. indet.). The clionaid boring Entobia cf. resinensis, vermetid gastropod etching trace Renichnus isp., spionid polychaete borings Maeandropolydora isp. and Maeandropolydora cf. sulcans, and the "worm" boring Trypanites solitarius are also present. At least some of these borings were produced in the intertidal and shallow subtidal environment. The clasts show multiphase colonization, which suggests their relatively long exposition. Several shallow borings and encrusting organisms were likely eliminated by abrasion prior to redeposition. The clasts were redeposited and buried on the slope of the fan delta of the Savignone Conglomerate. Some of the bivalve borings contain well-preserved shells of their producers and nestlers.