Unravelling hidden glacial effects in the Cryogenian marine depositional settings of the Tandilia Basin, Argentina

The Cryogenian Period (720-635 Ma) is wide known by the occurrence of two global glaciations, Sturtian and Marinoan, responsible of dramatic climate and sea level changes as well as seawater oxygenation events. Constrained Sr-87/Sr-86 ratios from 0.7064 to 0.7071 and delta C-13 excursion are consistent with Cryogenian cap carbonates as documented in the upper Villa Monica Formation. This unit constitutes the basal sedimentary cover of the Rio de La Plata Craton in Central Argentina which begins its deposition in a shallow marine siliciclastic shelf, turning to a carbonate succession with exceptionally well-preserved stromatolites. The detailed facies analysis added to stromatolite morphologies included in paleoenvironmental models of deposition remain unknown. The later are considered necessary to establish the stratigraphic framework and the regional correlation of the unit across the basin as a piece for the Cryogenian assembly. The entire Villa Monica Formation in the Tandilia Basin was deposited on a shelf with sedimentary facies variations observed from the shallow margins to the offshore transition zone. The transition from the lower to the upper sections implies the conquer of microbial communities to paleogeographically controlled chemocline fluctuations where the stromatolites evidence the development from a post-glaciation phosphorus-rich ocean. This drastic shift in paleoenvironments represented on the two distinctive marker sections was influenced by changes in climatic and oxygenation conditions. In this context, presumed glacial influence is predictable in a partially ice-covered Cryogenian Earth surface.

Automated summary

The Cryogenian Period is characterized by two global glaciations, Sturtian and Marinoan, which led to significant climate and sea level changes. The study of the Villa Monica Formation in Central Argentina provides insights into sedimentary facies variations and stromatolite development in a post-glaciation, phosphorus-rich ocean. Further research is needed to understand the paleoenvironmental models and regional correlation of this unit.