Exceptionally favourable life conditions for macrobenthos during the Late Cenomanian OAE-2 event: Ichnological record from the Bonarelli Level in the Grajcarek Unit, Polish Carpathians

Pelagic and hemipelagic sediments of the Bonarelli Level (uppermost Cenomanian) in the Sztolnia section(Grajcarek Unit, Polish Carpathians) contain trace fossils of the Zoophycos ichnofacies, including (indescending order of abundance):Chondrites (smaller and larger forms), Planolites, Thalassinoides, Palaeophycus, Taenidium, Teichichnus, and Zoophycos. They occur in thick bioturbated layers, which are inter-bedded with rare, thin layers of unbioturbated black shales. The black shale layers mark the Bonarelli Level and are interpreted as a record of anoxia or dysoxia. Coeval sections in the Western Tethys containsimilar trace fossils but they are less abundant and these sections are characterized by thicker unbio-turbated black shale layers and thinner bioturbated layers. This confirms the exceptionally favourable lifeconditions in sediments of the Sztolnia section, which do not record strong global anoxia during the OAE-2 event. Such favourable conditions were probably caused by effective oxygenation of pore waters anddeep burial of organic matter, which are a consequence of high rates of accumulation and the palae-ogeographical location of the section on aflank of a submarine high, under strong circulation.