Ichnological characteristics of Late Cretaceous hemipelagic and pelagic sediments in a submarine high around the OAE-2 event: a case from the Rybie section, Polish Carpathians

The trace fossils Alcyonidiopsis isp., Chondrites isp. (small and large), Palaeophycus isp., Planolites isp., Taenidium isp., Thalassinoides isp., Zoophycos isp., and unnamed small spreite burrow structures have been found in the Cenomanian–Turonian sediments in the Rybie section. They show significant stratigraphic variations in respect to the Bonarelli Level. In the Cenomanian, from the base of the section up to just below the Bonarelli Level (the “fucoid marl” in local lithostratigraphy), a decrease in diversity and abundance of trace fossils and benthic foraminifers is present and related mainly to decreasing benthic food levels. Oxygenation changes have comparatively minor incidence, but at least three thin anoxic layers occur about 2 m below the Bonarelli Level. The Bonarelli Level shows the at least episodically anoxic sedimentation. In the Turonian part, only small Chondrites isp. and Planolites isp. rarely occur. The burial of organic matter and probably benthic food content was extremely low as revealed by red marls. A gradual recovery of environmental conditions is marked by an increase in the diversity and abundance of trace fossils and benthic foraminifers by the Turonian, when grey marls (Żegocina Marl) accumulated above the red marls. The trends in ichnological record are confirmed by data on benthic foraminifers.