Glaucony authigenesis, maturity and alteration in the Weddell Sea: An indicator of paleoenvironmental conditions before the onset of Antarctic glaciation

• Published in: Scientific Reports
• Main Authors: López-Quirós, Adrián, Escutia, Carlota, Sánchez-Navas, Antonio, Nieto, Fernando, Garcia-Casco, Antonio, Martín-Algarra, Agustín, Evangelinos, Dimitris, Salabarnada, Ariadna
• Other Authors: Ministry of Economy and Competitiveness | Consejo Superior de Investigaciones Científicas, Ministry of Economy and Competitiveness | Agencia Estatal de Investigación
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer Science and Business Media LLC 2019
• Subjects: Multidisciplinary; Antarctic; Weddell; Weddell Sea; Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1038/s41598-019-50107-1; http://www.nature.com/articles/s41598-019-50107-1.pdf; http://www.nature.com/articles/s41598-019-50107-1

Abstract Three types of glaucony grains were identified in the late Eocene (~35.5–34.1 Ma) sediments from Ocean Drilling Program (ODP) Hole 696B in the northwestern Weddell Sea (Antarctica). The grains are K 2 O-rich (~7 wt%) and formed by smectite-poor interstratified ~10 Å glauconite-smectite with flaky/rosette-shaped surface nanostructures. Two glaucony types reflect an evolved (types 1 and 2 glaucony; less mature to mature) stage and long term glauconitization, attesting to the glaucony grains being formed in situ , whereas the third type (type 3 glaucony) shows evidences of alteration and reworking from nearby areas. Conditions for the glaucony authigenesis occurred in an open-shelf environment deeper than 50 m, under sub-oxic conditions near the sediment-water interface. These environmental conditions were triggered by low sedimentation rates and recurrent winnowing action by bottom-currents, leading to stratigraphic condensation. The condensed glaucony-bearing section provides an overview of continuous sea-level rise conditions pre-dating the onset of Antarctic glaciation during the Eocene-Oligocene transition. Sediment burial, drop of O 2 levels, and ongoing reducing (postoxic to sulphidic) conditions at Hole 696B, resulting in iron-sulphide precipitation, were a key limiting factor for the glauconitization by sequestration of Fe 2+ .