Unusual bedded manganese deposits occur within hemipelagic carbonates, dated as early Messinian (<6.82 Ma but >5.97 Ma) based on calcareous nannofossils. These sediments accumulated during a time of increased isolation of the Mediterranean Sea from the Atlantic Ocean but prior to major sea-level fall and evaporite precipitation during the Messinian salinity crisis. The manganese deposits form six main laterally continuous beds (up to 70 cm thick). Compositionally, they are dominated by poorly crystalline manganese oxide (birnessite), with associated mild enrichment in some trace elements (e.g., Ba, Ni, Cu, Mo, As, U). Background minerals include magnesian carbonate, kaolinite, chlorite, mixed-layer clays and talc (serpentinite-derived). A tectonically-controlled deep-water basin existed to the south of a topographic ridge (future Kyrenia Range) in which seawater alternated between oxidising and oxygen-depleted at depth. Orbital precession influenced the weathering of continental source areas that included basic igneous rocks and some pre-existing hydrothermal deposits. After entering the basin via land runoff, manganese was retained in solution below the chemocline during stagnant low-oxygen periods. Manganese oxide and associated trace elements (e.g., Mo, U) precipitated in response to cyclical seawater oxidation to form manganese-rich layers up to layers with up to with up to c. 30% MnO. To reach these very high concentrations, soluble manganese may have fluxed upwards from an anoxic environment represented by early Messinian sapropels. Manganese precipitation events diminished with time giving way to well-oxygenated hemipelagic marl accumulation with a shelly infauna. Gypsum appears abruptly upwards above the marls in adjacent sections. The Mn deposition mainly represents an interplay between tectonically-controlled basin formation, chemically favourable source climatic conditions, possible sea-level change effects and likely diagenetic manganese enrichment. The regional tectonic setting relates to early-stage collision of the African and Tauride (Eurasian) plates. (C) 2019 Elsevier B.V. All rights reserved.

Early Messinian manganese deposition in NE Cyprus related to cyclical redox changes in a silled hemipelagic basin prior to the Mediterranean salinity crisis

I. Raffi;
2019

Abstract

Unusual bedded manganese deposits occur within hemipelagic carbonates, dated as early Messinian (<6.82 Ma but >5.97 Ma) based on calcareous nannofossils. These sediments accumulated during a time of increased isolation of the Mediterranean Sea from the Atlantic Ocean but prior to major sea-level fall and evaporite precipitation during the Messinian salinity crisis. The manganese deposits form six main laterally continuous beds (up to 70 cm thick). Compositionally, they are dominated by poorly crystalline manganese oxide (birnessite), with associated mild enrichment in some trace elements (e.g., Ba, Ni, Cu, Mo, As, U). Background minerals include magnesian carbonate, kaolinite, chlorite, mixed-layer clays and talc (serpentinite-derived). A tectonically-controlled deep-water basin existed to the south of a topographic ridge (future Kyrenia Range) in which seawater alternated between oxidising and oxygen-depleted at depth. Orbital precession influenced the weathering of continental source areas that included basic igneous rocks and some pre-existing hydrothermal deposits. After entering the basin via land runoff, manganese was retained in solution below the chemocline during stagnant low-oxygen periods. Manganese oxide and associated trace elements (e.g., Mo, U) precipitated in response to cyclical seawater oxidation to form manganese-rich layers up to layers with up to with up to c. 30% MnO. To reach these very high concentrations, soluble manganese may have fluxed upwards from an anoxic environment represented by early Messinian sapropels. Manganese precipitation events diminished with time giving way to well-oxygenated hemipelagic marl accumulation with a shelly infauna. Gypsum appears abruptly upwards above the marls in adjacent sections. The Mn deposition mainly represents an interplay between tectonically-controlled basin formation, chemically favourable source climatic conditions, possible sea-level change effects and likely diagenetic manganese enrichment. The regional tectonic setting relates to early-stage collision of the African and Tauride (Eurasian) plates. (C) 2019 Elsevier B.V. All rights reserved.
File in questo prodotto:
File Dimensione Formato  
2019_Robertson_etal.pdf

Solo gestori archivio

Descrizione: Articolo principale
Tipologia: PDF editoriale
Dimensione 7.7 MB
Formato Adobe PDF
7.7 MB Adobe PDF   Visualizza/Apri   Richiedi una copia

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11564/710825
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 9
  • ???jsp.display-item.citation.isi??? 9
social impact