This review is the result of many years of research on stratigraphical correlation, sedimentology and mineralogy of one of the oldest sedimentaiy basins of Argentina that experimented numerous diagenetic changes along the evolution of its geological histoiy: Tandilia. Previous and new data are presented and supported with photographs that illustrate different aspects of microscale diagnostic features of diagenesis recorded in weathered crystalline basement rocks and the overlying sedimentaiy succession represented by the Neoproterozoic Villa Monica, Olavarria, Cerro Largo and Las Aguilas formations and the Late Ordovician Balcarce Formation. The study gathers optical and scanning electron microscopy data supported by X-ray diffraction analysis. The finding of Microbially Induced Sedimentaiy Structures (MISS) in siliciclastic and mixed facies helped to unveil hidden biosignatures, fundamental to understanding the origin of life on Earth. A? 2010 Asian Network for Scientific Information.