Mesoproterozoic siliciclastic stromatolites of Chapada Diamantina (Brazil): Morphological types, genesis and environmental context

• Published in: Journal of South American earth sciences 2024-10, Vol.146, p.105052, Article 105052
• Main Authors: Formolo Ferronatto, João Pedro, Scherer, Claiton Marlon dos Santos, Angonese, Bruno Silverstone, Goulart Rodrigues, Amanda, de Souza, Ezequiel Galvão, Kifumbi, Carrel, dos Reis, Adriano Domingos, Guadagnin, Felipe, Cazarin, Caroline Lessio
• Format: Article
• Language: English
• Subjects: Agglutinated stromatolites; Espinhaço Supergroup; Microbial mat; Precambrian stromatolites; Proterozoic
• ISSN: 0895-9811
• DOI: 10.1016/j.jsames.2024.105052

Laminations of organosedimentary structures can be formed by three distinct processes: (i) bio-induced mineral precipitation, (ii) trapping and binding, and (iii) abiotic mineral precipitation and each of these processes predominates in a certain geological time interval. Agglutinated stromatolites are rare and seem to form in specific environmental conditions. Siliciclastic stromatolites are an even rarer class of agglutinated stromatolites, which are formed in response to the process of trapping and binding of siliciclastic grains by upright filaments or by extracellular polymeric substances (EPS). This study describes and interprets one of the oldest siliciclastic stromatolites of the geological record and discusses the microbial evidence and mechanisms that controlled their accumulation and preservation. Two compound sections were analyzed and ten thin sections were prepared to characterize the siliciclastic stromatolites from the Mesoproterozoic Caboclo Formation (Brazil). Stromatolites are present in two different lithofacies associations: (i) shoreface and (ii) offshore transition. The shoreface stromatolites are characterized by silty to sandy texture and poor lamination, and the distal ones by clay, silt grains, less sand, and distinct lamination. The volume of siliciclastic grains composing the stromatolite fabric is >85% in the shoreface and >30% in offshore transition. These stromatolites were deposited in a favorable environment for trapping and binding of siliciclastic sediments: a wave-dominated siliciclastic ramp with the availability of siliciclastic grains and frequent water column agitation. The marine environment is favorable for forming EPS with good adhesive properties. Besides, the Caboclo Formation age (1.3–1.0 Ga) coincides with an abrupt fall in the amount of atmospheric CO2 reflected in CaCO3 saturation in the oceans. This change in ocean chemistry may have led to a change in stromatolite fabric, from the sparry crust and fine-grained precipitated to agglutinated. •Siliciclastic stromatolites are linked to offshore transition and shoreface.•Macro and microscale features indicate biogenic signature.•Pyrite and carbonate precipitation influenced the stromatolite preservation.•Favorable conditions for the trapping and binding of sediments.