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, F., García-Casco, Antonio, Martín Algarra, A., Evangelinos, Dimitris
• Other Authors: Ministerio de Ciencia e Innovación (España), European Commission, Junta de Andalucía
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Nature Publishing Group 2019
• Subjects: Antarctic; Salas; Weddell; Weddell Sea; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/10261/205258; https://doi.org/10.1038/s41598-019-50107-1; https://doi.org/10.13039/501100000780; https://doi.org/10.13039/501100004837; https://doi.org/10.13039/501100011011

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 K2O-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 O2 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 Fe2+. This research used samples from the ODP. We thank the staff at the Gulf Coast core repository for assistance in ODP Leg 113 core handling and shipping. Funding for this research is provided by the Spanish Ministry of Science and Innovation (grants CTM2014-60451-C2-1-P and CTM2017-89711-C2-1-P, CGL2016-75679P) co-funded by the European Union through FEDER funds and RNM-208 group (Discontinuidades estratigráficas, Junta de Andalucía, Spain). We acknowledge the help of Dr. María del Mar Abad, Dr. Isabel Sánchez Almazo, Dr. Miguel Angel Hidalgo, Dr. Miguel Angel Salas, and Isabel Nieto (Scientific Instrumentation Center of the University of Granada, CIC) for their help along different ...