Concentrations of silicified cephalopods within upper Frasnian carbonate concretions from the Holy Cross Mountains, Poland

• Concentrations of Frasnian cephalopods within carbonate concretions were found.
• Cephalopods suffered mass mortality during storm events shortly after mass spawning.
• The excellent preservation of the fossils resulted from rapid silicification.
• The age of the concentration has been determined as the linguiformis conodont Zone.

Concentrations of silicified juvenile cephalopods from upper Frasnian carbonate nodules from the Jaźwica quarry in the Holy Cross Mountains are described here for the first time. Using conodonts, the age of the investigated cephalopod-rich nodules has been determined as the linguiformis conodont Zone, and may correspond to the Upper Kellwasser Event. The concentrations of silicified juvenile ammonoids described here resulted from a combination of biological and physical factors related to environmentally-driven mass mortality (induced by storms and perhaps additionally by anoxia) following mass spawning and post-mortem transport with the aid of bottom currents, which enabled them to drift to small depressions on the sea floor. Rapid silification led to excellent preservation of the fossil assemblage.