6533b820fe1ef96bd127a502

RESEARCH PRODUCT

Genesis of the Lower Triassic bonebeds from Gogolin (S Poland): The impact of microbial mats on trapping of vertebrate remains

subject

description

Three bone-bearing horizons, consis ting of seven bone-bearing beds with fi sh and reptile remains, were recently discovered in the Uppermost Röt (Buntsandstein, Lower Tri assic) peritidal and shallow marine carbonates in the vi- cinity of Gogolin (S Poland). The aim of this study is to reco gnize the genesis and deposi tional environments of the bonebeds. Detailed fi eldwork, microfacies analysis, and SEM-EDS anal ysis reveal that the vertebrate remains occur to a great extent alongside evidence for former microbial activity. The reptile remains represent at least Dactylosaurus and Nothosaurus (Sauropterygia) genera, while the fi sh remains belong to the Chondrichthyes and Actinopterygii. The vertebrate remains were deposited in a transitional zone between the costal sabkha and the epi- continental sea. The fi rst bone-bearing horizon originated in the most landward setting, in the uppermost intertidal zone, likely at the margins of a pond or coastal lagoon. T he second bone-bearing horizon was formed in the upper intertidal zone. The vertebrate remains of the third bon e-bearing horizon were accumulated in two different set- tings: in the lower intertidal zone (in a small palaeopon d) and in the subtidal zone (in a protected back-shoal la- goon). Three bone accumulations occur within planar stromatolites, while the other bone-bearing beds reveal more indirect evidence for former microbial activity. In our opinion, the presence of the sticky microbial mats in the intertidal settings was the crucial factor that allowe d the establishment of and controlled these accumulations of vertebrate remains. The soft gluey substrates trapped vertebrate remains that were transported across them. Once trapped, the vertebrate bioclasts were ef fi ciently immobilized and thus protected against damage due to sed- imentological agents. The lack of any orderly arrangemen t of the vertebrate bioclast s suggests that they may have been delivered to the individual mat surfaces by diverse media, from various directions, and also at different times.