| Summary: | Comunicaciones del Congreso SEM 2023, XL Reunión Científica de la Sociedad Española de Mineralogía; Madrid, 16 de junio de 2023. [EN] The environmental changes leading up to the first continent-wide glaciation of Antarctica during the Eocene-Oligocene Transition (EOT) are still not fully understood. Declining atmospheric CO2 concentrations and associated feedbacks have been invoked as underlying mechanisms, but the role of the coeval opening/deepening of Southern Ocean gateways (Drake Passage and Tasman Gateway), and subsequent changes in paleoceanography remain poorly understood. Evidence suggests both a temperate late Eocene and cooling before the EOT, both broadly coetaneous with a wide, supra-regional diagenetic event that resulted in green-clay (glaucony) formation in the marine realm around Antarctica (Houben et al., 2019; López-Quirós et al., 2019). Glaucony formation and evolution are driven by the activity of bacteria thriving in the organic-rich environment, a bio-geochemical system now considered to play a key role in the control of global ocean chemistry. Investigation of the reaction mechanisms throughout the formation of glaucony provides reliable information about (i) macro-scale environmental conditions, such as ocean transgression-regression cycles and ocean circulation changes, and (ii) the micro-scale sedimentary environment, such us sediment permeability, ion mobility and organic matter content – all of which are registered in the fabric and crystal-chemical characteristics of glaucony (e.g., López-Quirós et al., 2019; 2020; 2023). In addition, K-Ar dating of glaucony has provided 40% of the absolute-age dates for the geological timescale of the past 250 Ma. Glaucony is thus an important tool to date depositional ages of sediments and to reconstruct paleoenvironmental conditions. In spite of all, the nature, depositional setting, paleoenvironmental implications and chronology of the late Eocene glaucony reported in diverse shallow-marine settings in the Southern Ocean are loosely ...
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