Multiple sulfur isotopes and stratigraphic constraints for the ³⁴S enrichments in the late Ediacaran-Cambrian pyrite-sulfur record: A product of supercontinent assembly and restricted seas

Autor(es)

Caetano-Filho, Sergio ; Sansjofre, Pierre ; Paula-Santos, Gustavo M. ; Ader, Magali ; Cartigny, Pierre ; Guacaneme, Cristian ; Babinski, Marly ; Kuchenbecker, Matheus ; Reis, Humberto L. S. ; Trindade, Ricardo I. F.

• Tipo de documento: Artigo Científico
• Fonte: GONDWANA RESEARCH; v. 131, p. 16-pg., 2024-03-21.

Resumo

The late Ediacaran record encompasses frequent occurrences of 34S-enriched pyrites, which can surpass the coexisting sulfate isotope values. Deciphering what controls this marine isotope record is important to understand its biogeochemical implications, especially considering the early metazoan evolution. We present here multiple sulfur isotope compositions from pyrites of two distinct geotectonic settings within the late Ediacaran-early Cambrian West Gondwana, allowing to constraint spatial and temporal distribution of 34S-enrichments. The Tamengo Formation represents a carbonate-siliciclastic ramp at Gondwana's continental margin, whereas the Bambui Group records an epeiric sea within the core of this supercontinent. Both units display positive 834Spy excursions matching regressive trends (834Spy up to 51 parts per thousand), with a drop in 834Spy values associated with transgressions. A scenario of sulfate-distillation events throughout regressions is supported by the multiple sulfur isotope data, after transgressive events that episodically recharged sulfate in these environments. However, in the epicontinental Bambui sea, 834Spy, A33Spy and A36Spy values suggest almost quantitative conversion of the initial sulfate into sulfide at the end of regressive stage, forced by enhanced stratification and inefficient circulation within continental areas. In this case, widespread toxic euxinic conditions were developed in inland seas, accompanied by methanogenesis, which resulted in highly 13C-enriched DIC due to methanogenic CO2, as recorded in the Bambui Group. In the Tamengo ramp, on the other hand, sulfate levels would have not been completely consumed due to more frequent and efficient mixing with open waters, preventing perturbations in the carbon cycling and representing more favorable conditions to metazoan colonization, considering the abundant metazoan fossil record in this unit. The studied basins illustrate how 1st-order tectonic cycles may have been the major player over remarkable 34S-enrichments in pyrite for specific time intervals of the sedimentary record, through supercontinent assembly and expansion of restricted settings more prone to sulfate distillation. (c) 2024 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. (AU)

• Processo FAPESP: 16/06114-6 - O Sistema Terra e a evolução da vida durante o Neoproterozoico
• Beneficiário: Ricardo Ivan Ferreira da Trindade
• Modalidade de apoio: Auxílio à Pesquisa - Temático
• Processo FAPESP: 17/00399-1 - Intemperismo químico e fluxo de nutrientes para o oceano no Ediacarano superior e suas relações com a diversificação da vida
• Beneficiário: Gustavo Macedo de Paula Santos
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 16/11496-5 - Ciclos biogeoquímicos de enxofre e carbono no Ediacarano e seu registro em sucessões sedimentares brasileiras
• Beneficiário: Sergio Caetano Filho
• Modalidade de apoio: Bolsas no Brasil - Doutorado
• Processo FAPESP: 18/19302-0 - Análises isotópicas pareadas de enxofre e carbono em rochas carbonáticas ediacaranas brasileiras e inferências sobre os ciclos biogeoquímicos marinhos no Gondwana Ocidental
• Beneficiário: Sergio Caetano Filho
• Modalidade de apoio: Bolsas no Exterior - Estágio de Pesquisa - Doutorado