Exploring the archive data of low grade - high pressure metamorphic sedimentary successions

• Applicants: Professor Dr. Adrian Immenhauser; Professor Dr. Roland Oberhänsli
• Subject Area: Palaeontology ; Mineralogy, Petrology and Geochemistry
• Term: from 2015 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 270096603

• Final Report Year: 2020

Final Report Abstract

Low T/high P meta-sedimentary successions represent under favorable conditions, an important - albeit underexplored - archive of their past depositional environment. This main hypothesis of the present DFG project was verified by a multidisciplinary approach with the aim to extract palaeoenvironmental/diagenetic/metamorphic data/pathways of high-pressure metagypsum pseudomorphs. Anatolian gypsum-pseudomorph-successions of Mid-Late Cretaceous age served as natural laboratories. A first relevant step was to document the former mineralogy (here selenites) of these mainly calcitic marbles. Metaselenite successions (regionally referred to as “Rosetta Marbles“) are widely distributed along Anatolia’s high pressure metamorphic belts and were studied in detail by means of combined field observations, geochemical and petrographic data. The field observations included a careful characterization of fabrics, the compilation of stratigraphic sections and the assessment of the regional tectonic and metamorphic pathways. The geochemical analyses include main and trace element concentrations and isotope geochemistry. By means of field observations comparing crystal morphology and geochemical data with modern semi-equivalent evaporitic analogues, the following conclusions were drawn: i) The primary mineralogy of the Rosetta marbles was undoubtedly gypsum (selenite, in a variety of typical and unique morphologies). ii) The environmental information of these meta-sediments can be reconstructed to a remarkable degree. Meta-gypsum morphologies, growth modes, host sediments and remnants of siliceous planktonic organisms were used to reconstruct seawater (brine) salinity, hydrodynamic level, water depth, i.e., distance from shoreline etc.). The isotope and trace elemental geochemistry is undoubtedly highly complex and support several possible interpretations. Generally, a seawater signal characterizes these rocks but it remains unclear if this signature reflects the large volumes of marine fluids incorporated in the subduction zone or if these meta-selenite successions are conservative with regard to their primary geochemical signatures. Remarkably, the gypsum-radiolarite alternations, that were documented from the most proximal of these outcrops have no analogue in the Modern world. (iii) In terms of their depositional age, these eastern Tethys meta-evaporites correlate with the marginal evaporites of the middle Cretaceous proto-Atlantic domain. In terms of thickness (>2km), lateral extension (~600km) and rock forming character of the meta-evaporites, the Rosetta marbles are comparable to the Messinian saline giants. As such these metasediments document a lost evaporitic basin in the present day eastern Mediterranean realm and probably represent the volumetrically most important and best preserved meta-sedimentary units worldwide. A reasonable step forward is to apply lessons learnt here to Archean and Proterozoic meta-evaporites.

Publications

• (2015) - Pseudomorphs of Neotethyan Evaporites in Anatolia’s HP/LT belts - Aptian basin-wide pelagic gypsum deposits. European Geosciences Union, General Assembly 2015, Vienna, Austria
  Franziska Scheffler, Roland Oberhänsli, Amaury Pourteau, Adrian Immenhauser, Osman Candan
  
• (2015) - Selenite Pseudomorphs in Mid-Cretaceous Neotethyan Metasediments of Anatolia’s HP/LT belts. IAS 31st Meeting of Sedimentology, Krakow, Poland
  Franziska Scheffler, Roland Oberhänsli, Amaury Pourteau, Adrian Immenhauser, Osman Candan
  
• (2015) Sedimentologic to metamorphic processes recorded in the high-pressure/lowtemperature Mesozoic Rosetta Marble of Anatolia. International Journal of Earth Sciences, 105(1), 225-246
  Franziska Scheffler, Roland Oberhänsli, Amaury Pourteau, Adrian Immenhauser, Osman Candan
  
• (September 2016) - Metamorphosed hemi-pelagic evaporites in Anatolia: a Mid- Cretaceous salinity crisis in the Neotethys? 35th International Geological Congress, Cape Town, South Africa
  Franziska Scheffler, Roland Oberhänsli, Adrian Immenhauser, Amaury Pourteau, Osman Candan
  
• (2017) - Vanished Evaporites in the Paleoproterozoic Koegas Fromation, South Africa. Second Generall SPP meeting (Building a habitable Earth), Jena, Germany
  Franziska Scheffler, Christoph Heubeck, Wladyslaw Alterman
  
• (2018) - Cretaceous gypsum pseudomorphs in Anatolia—Deciphering textures and isotopic signatures (C, O) from formation to metamorphism. Goldschmidt, Boston, USA
  Franziska Scheffler, Adrian Immenhauser, Amaury Pourteau, Osman Candan, Roland Oberhänsli
  
• (2018) - Metamorphosed Meta-Selenites and their bearing on a lost Cretaceous Evaporitic Basin of the Eastern Mediterranean, 17th Symposium on Tectonics, Structural Geology and Geology of Crystalline Rocks (TSK), Jena, Germany
  Franziska Scheffler, Adrian Immenhauser, Amaury Pourteau, Osman Candan, Roland Oberhänsli
  
• (2019) A lost Tethyan evaporitic basin — Evidence from a Cretaceous meta-selenite – red chert association in the Eastern Mediterranean realm, Sedimentology
  Franziska Scheffler, Adrian Immenhauser, Amaury Pourteau, Osman Candan, Roland Oberhänsli