Upside down: Resilience and recolonization of overturned stromatolite from the Maastrichtian-Danian Yacoraite formation (northwestern Argentina)

Stromatolites are organo-sedimentary structures, internally laminated, which grow attached to the substrate. This lamination mirrors the dynamic interaction of environmental and biological factors where its formation takes place. However, some stromatolites from the Yacoraite Formation, from Amblayo locality, in northwestern Argentina, present an unconventional internal structure characterized by bilateral symmetry, where the development of lamination extends towards both sides of an imaginary plane. This contribution reports a multi-scale analysis of these particular stromatolites, with the aim of determining the extent to which environmental factors have influenced their internal structure. In addition to this, a sequence of stages that gave rise to these organo-sedimentary structures will be proposed. Results suggest a microbialitic growth by in-situ biologically induced, carbonate precipitation, which was carried out in a shallow intertidal environment with good luminosity and significant sedimentary input. However, the stromatolitic growth occurred over two stages, interrupted by a stochastic event that generated a overturning of the structure, providing a new colonizing surface for growth of microorganisms and resulting in a bilateral internal structure. The characterization of these stages, including the overturning of the structure, not only provides a highly accurate proxy for reconstructing punctual environmental conditions of the Yacoraite Formation, but also opens up a field of discussion focused on the resilience and recolonization capacity of stromatolite-producing microorganisms after stochastic events.