SHORT-TERM ENVIRONMENTAL CHANGES IN EPEIRIC SHALLOW MARINE STROMATOLITE FACIES (YACORAITE FORMATION, NORTHWESTERN ARGENTINA): INFLUENCE OF EXTRINSIC FACTORS IN ORGANO-SEDIMENTARY FABRIC

FRÍAS SABA, ROCIÓ DEL CIELO; VILLAFAÑE, PATRICIO GUILLERMO; DELLA VEDOVA, MICAELA; CÓNSOLE GONELLA CARLOS ALFREDO; CITTON, PAOLO; DIAZ MARTÍNEZ, IGNACIO; DE VALAIS, SILVINA

Parana, Argentina

Congreso; XVII RAS Reunión Argentina de sedimentología; 2021

Asociación Argentina de Sedimentología

The stromatolite facies reported from Yacoraite Formation (Maastrichtian - Danian) in Maimará locality (Jujuy, Argentina), developed in a subtidal/intertidal moderate to high-energy environment under wave and tides action. The 45 m thick integrated stratigraphic section exhibits 12 microbialite levels, all displaying different growth morphologies. Thus, there are many remaining gaps in understanding this morphological variability as a tool to the environmental context assessment at layer scale. The main goal of this contribution is to provide a detailed multiscale analysis of the stromatolite level M3, assessing the relationship between environmental factors and resulting fabrics. Stromatolites were studied following a traditional multiscale approach, using thin and polished sections. Level M3 displays a bioherm megastructure composed of domes up to 25 cm. At mesoscale, it exhibits two sectors with distinctive structure and composition. The Lower Sector (up to 18 cm), is characterized by three types of structures: i) Continuous laminated structures (LLH-C), composed of the alternation of micritemicrosparite; ii) Laminated columns with a constant basal radius (SH-C) composed of micrite, microsparite and radial-fibrous calcite with gypsum patches; and iii) Non-laminated zones characterized by intraclasts and bioclasts immersed in a micrite-microsparite matrix. Finally, the upper sector (up to 7 cm) that exhibits laminated columnar structures with a variable basal radius (SH-V). These columns display a composite repetitive lamination, made up of micrite and microsparite. The space between columns is filled by ooids, bioclasts and micritic intraclasts, immersed in a micrite matrix. Multiscale analysis allowed a high-resolution environmental reconstruction. LLH zones respond to episodes of relative low depth and calm hydrodynamic conditions. On the other hand, SH-Cstructures display an increase in hydrodynamic energy and a possible retreat of the water body with subsequent evaporation, which allowed evaporite supratidal development. Non-laminated zones suggest a key hydronomic influence, due to the development of an intraclastic-dominated fabric. In the Upper Sector, environmental conditions were likely more stable. Column morphologies, their composition and the filling of the channels are related to a shallow environment where hydrodynamic energy was gradually increasing. In overall sense, environmental variations controlling the development of level M3 can be related with a sudden and short-term change in the hydrodynamic regime, which might record a drastic withdrawal of the water body, and finally a recovery of the water level. Interestingly, microbialite-producer microorganisms seem to have recovered rapidly after these drastic environmental changes, which can provide suggestive approaches to further research.