Palaeoenvironment of the Upper Cretaceous (Coniacian) concretion-bearing Lagerstätten from Poland

Abstract

Abundantly fossiliferous Upper Cretaceous sediments including decapod remains in the region of Stary Waliszów (Southern Poland) have been known for many years. To date, however, no study has dealt specifically with detailed palaeoenvironmental and palaeoecological reconstruction. The origin of these sediments is still uncertain and has been the source of considerable confusion and controversy, mainly due to the strong bioturbation and decalcification of these sediments. By using the fossil record, comparative taphonomy and geochemical analyses of concretions, we provide new insights into the paleoenvironment and the paleoecology of this unique Coniacian ecosystem.On the basis of ichno- and body fossil assemblages composed almost exclusively of benthic organisms such as decapods, molluscs and echinoderms, which are commonly disarticulated but rarely abraded, we suggest that the fossiliferous sediments in Stary Waliszów were formed in shallow, normal saline and well-oxygenated waters of the upper sublittoral zone with moderate sedimentation rate and low turbulence of waters. The presence of angular terrigenous clasts, well-preserved delicate land flora and the near absence of planktonic and nektonic fossils strongly imply proximity to the land. Recorded taxa inhabited a soft-bottom environment. Some organisms were fossilized inside siderite concretions. These concretions were formed within the sediment below the zone of active bioturbation during the early stage of diagenesis. Remarkable preservation of decapod remains is due to phosphatization, which replaced the cuticle.