This study investigates the Middle Jurassic rocks of the Labino-Malkin zone(Caucasus),represented by ooidal ironstones,biogenic limestones,and nodular phosphorites.All rocks contain ooids/pisoids.Based on the mineral ...This study investigates the Middle Jurassic rocks of the Labino-Malkin zone(Caucasus),represented by ooidal ironstones,biogenic limestones,and nodular phosphorites.All rocks contain ooids/pisoids.Based on the mineral composition,nine types of ooids and three possible scenarios for their formation have been identified.The mineral composition of ooids indicates the variable conditions of their deposition and repeated changes in physical and chemical conditions of the environment,including fluctuations in theredox regime.The access of oxygen in the bottom environment as a factor of increasing oxic conditions was associated with the regression of the sea and/or the inflow of meteoric waters.The main sources of ooids are the drift of material from the continent and convecting metal-bearing meteoric and/or deep solutions.展开更多
This study investigates the process of formation of ooidal ironstones in the Upper Cretaceous-Paleogene succession in western Siberia.The formation of such carbonate-based ironstones is a continuing problem in sedimen...This study investigates the process of formation of ooidal ironstones in the Upper Cretaceous-Paleogene succession in western Siberia.The formation of such carbonate-based ironstones is a continuing problem in sedimentary geology,and in this study,we use a variety of data and proxies assembled from core samples to develop a model to explain how the ooidal ironstones formed.Research on pyrite framboids and geochemical redox proxies reveals three intervals of oceanic hypoxia during the deposition of marine ooidal ironstones in the Late Cretaceous to the Early Paleogene Bakchar ironstone deposit in western Siberia;the absence of pyrite indicates oxic conditions for the remaining sequence.While goethite formed in oxic depositional condition,chamosite,pyrite and siderite represented hypoxic seawater.Euhedral pyrite crystals form through a series of transition originating from massive aggregate followed by normal and polygonal framboid.Sediments associated with goethite-chamosite ironstones,encompassing hypoxic intervals exhibit positive cerium,negative europium,and negative yttrium anomalies.Mercury anomalies,associated with the initial stages of hypoxia,correlate with global volcanic events.Redox sensitive proxies and ore mineral assemblages of deposits reflect hydrothermal activation.Rifting and global volcanism possibly induced hydrothermal convection in the sedimentary cover of western Siberia,and released iron-rich fluid and methane in coastal and shallow marine environments.This investigation,therefore,reveals a potential geological connection between Large Igneous Provinces(LIPs),marine hypoxia,rifting and the formation of ooidal ironstones in ancient West Siberian Sea.展开更多
Portland Stone,a well known ooidal limestone of Jurassic age from the United Kingdom is here nominated as a suitable“Global Heritage Stone Resource”.Portland Stone is considered to ideally fit the newly proposed des...Portland Stone,a well known ooidal limestone of Jurassic age from the United Kingdom is here nominated as a suitable“Global Heritage Stone Resource”.Portland Stone is considered to ideally fit the newly proposed designation as it has been utilised since Roman times in England and since the Middle Ages in the construction of major historic buildings including St Pauls Cathedral,British Museum and Bank of England in London.It was also the preferred building stone of Sir Christopher Wren,England’s most famous architect.The international use of Portland Stone during the 20th century includes the United Nations building in New York City and the war graves of British and British Commonwealth soldiers.Portland Stone also continues to be quarried today in an environmentally sensitive manner whilst coastal outcrops of the material form a part of the“Dorset and East Devon Coast”World Heritage area(aka The Jurassic Heritage Coast).展开更多
文摘This study investigates the Middle Jurassic rocks of the Labino-Malkin zone(Caucasus),represented by ooidal ironstones,biogenic limestones,and nodular phosphorites.All rocks contain ooids/pisoids.Based on the mineral composition,nine types of ooids and three possible scenarios for their formation have been identified.The mineral composition of ooids indicates the variable conditions of their deposition and repeated changes in physical and chemical conditions of the environment,including fluctuations in theredox regime.The access of oxygen in the bottom environment as a factor of increasing oxic conditions was associated with the regression of the sea and/or the inflow of meteoric waters.The main sources of ooids are the drift of material from the continent and convecting metal-bearing meteoric and/or deep solutions.
基金Laboratory geochemical investigations were carried out at National Research Tomsk Polytechnic University within the framework of a Competitiveness Enhancement Program Grant(Project VIU-OG-61/2019)funded by Russian Foundation for Basic Research and Tomsk Region(19–45-703002).
文摘This study investigates the process of formation of ooidal ironstones in the Upper Cretaceous-Paleogene succession in western Siberia.The formation of such carbonate-based ironstones is a continuing problem in sedimentary geology,and in this study,we use a variety of data and proxies assembled from core samples to develop a model to explain how the ooidal ironstones formed.Research on pyrite framboids and geochemical redox proxies reveals three intervals of oceanic hypoxia during the deposition of marine ooidal ironstones in the Late Cretaceous to the Early Paleogene Bakchar ironstone deposit in western Siberia;the absence of pyrite indicates oxic conditions for the remaining sequence.While goethite formed in oxic depositional condition,chamosite,pyrite and siderite represented hypoxic seawater.Euhedral pyrite crystals form through a series of transition originating from massive aggregate followed by normal and polygonal framboid.Sediments associated with goethite-chamosite ironstones,encompassing hypoxic intervals exhibit positive cerium,negative europium,and negative yttrium anomalies.Mercury anomalies,associated with the initial stages of hypoxia,correlate with global volcanic events.Redox sensitive proxies and ore mineral assemblages of deposits reflect hydrothermal activation.Rifting and global volcanism possibly induced hydrothermal convection in the sedimentary cover of western Siberia,and released iron-rich fluid and methane in coastal and shallow marine environments.This investigation,therefore,reveals a potential geological connection between Large Igneous Provinces(LIPs),marine hypoxia,rifting and the formation of ooidal ironstones in ancient West Siberian Sea.
文摘Portland Stone,a well known ooidal limestone of Jurassic age from the United Kingdom is here nominated as a suitable“Global Heritage Stone Resource”.Portland Stone is considered to ideally fit the newly proposed designation as it has been utilised since Roman times in England and since the Middle Ages in the construction of major historic buildings including St Pauls Cathedral,British Museum and Bank of England in London.It was also the preferred building stone of Sir Christopher Wren,England’s most famous architect.The international use of Portland Stone during the 20th century includes the United Nations building in New York City and the war graves of British and British Commonwealth soldiers.Portland Stone also continues to be quarried today in an environmentally sensitive manner whilst coastal outcrops of the material form a part of the“Dorset and East Devon Coast”World Heritage area(aka The Jurassic Heritage Coast).
