CONICET | Buscador de Institutos y Recursos Humanos

Los Colorados Formation is a worldwide recognized continental unit deposited in the Ischigualasto-Villa Unión Basin in the San Juan and La RiojaProvinces, Northwestern Argentina. It is mainly composed of lenticular sandstone beds and laterally extensive laminated to massive mudstone units,recording sedimentation in different fluvial settings. These rocks represent a case study for the abundance and diversification events that affectedUpper Triassic tetrapods. Although the tetrapod fauna recovered from this unit is relatively well-known, their taphonomic modes are scarcelyunderstood. In this sense, we present a preliminary petrographic and X-ray diffraction analyses of both epiphyses and diaphyses of bone remainscollected in Los Colorados Fm., which allowed us to interpret the damaging processes that acted on the bone tissue. The most destructivetaphonomical process that affected the bones was the chemical interaction with circulating fluids during fossil-diagenesis. Thin section of the epiphysesshows preserved trabecular bone with cracks perpendicular to the bone fibers, obtured cavities filled with calcite set in two cycles: microgranular onthe periphery and polycristaline euhedral on the centre. Sub-periosteal bone, however, is relatively well-preserved. Diaphyses present a highly alteredtrabecular bone and obtured cavities with calcite in three cycles: two microgranular peripherical rows and large euhedral crystals in the internal lumen.Sub-periosteal bone is mostly altered. X-ray diffraction shows predominance of calcite in the epiphysis, whereas gypsum is mostly present in thediaphysis. Summing up, diagenetic cracks allowed the circulation solutions (rich in calcite and gypsum) in the bone, expanding and destroying it.