This review is the result of many years of research on stratigraphical correlation, sedimentology and mineralogy of one of the oldest sedimentary basins of Argentina that experimented numerous diagenetic changes along the evolution of its geological history: 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 sedimentary succession represented by the Neoproterozoic Villa Mónica, Olavarría, Cerro Largo and Las Aguilas formations and the Late Ordovician Balcarce Formation. The study gathers optical and scanningelectron microscopydata supported byX-ray diffractionanalysis. The finding of Microbially Induced Sedimentary Structures (MISS) in siliciclastic and mixed facies helped to unveil hidden biosignatures, fundamental to understanding the origin of life on Earth.