Permineralización en restos de dinosaurios preservados en depósitos de desbordamiento de la Formación Bajo Barreal (Cretácico Superior), Patagonia central, Argentina.

Abstract

The fossil deposit Cañadón Las Horquetas, placed in the centre-south of the Chubut Province, includes the Bajo Barreal Formation of early Cenomanian – late Turonian age. This site presents the greater abundance and diversity of fossil vertebrates in the San Jorge Gulf Basin. The diagenetic processes reported herein represent a little addressed subject in taphonomic studies involving dinosaurs. We present for the first time information on the permineralization processes that affected the dinosaur remains preserved in overflow deposits from the Bajo Barreal Formation, as well as new sedimentological data of the studied unit.Samples from three specimens were studied by chemical analysis, polarization petrographic microscope, X-ray diffraction and scanning electron microscopy (SEM). These studies show that all the dinosaurs have had a similar diagenetic history, with the same pattern of mineral replacement. Besides, the similar chemical composition found in the fossils and in the bearing rocks suggest that the enrichment with new elements found in the studied dinosaur remains was due to the direct exchange with the sediments in which they were buried. The now reported diagenetic conditions can be preliminarily extended to the whole lower member of the Bajo Barreal Formation.