Diagenesis of spiculites and carbonates in a Permian temperate ramp succession - Tempelfjorden Group, Spitsbergen, Arctic Norway

作者：Matysik Michal; Stemmerik Lars^*; Olaussen Snorre; Brunstad Harald

来源：Sedimentology, 2018, 65(3): 745-774.

DOI：10.1111/sed.12404

• Burial diagenesis
• chert
• Permian
• quartz cement
• silicification
• spicule diagenesis

This paper explores little investigated diagenesis of spicule-dominated sediments, based on Permian spiculites and cool-water carbonates of the Tempelfjorden Group in central Spitsbergen. Field observations, petrography, stable isotope geochemistry, and mineralogical and chemical analyses reveal that the strata have been subjected to multistage diagenesis as the result of silica phase transitions at medium burial depths and deep-burial overprinting. The growth of silica concretions occurred during the opal-A/opal-CT conversion and was controlled by the content and distribution of clay and spicules in the sediment, resulting in a variety of megascopic silica fabrics. Opal-CT was subsequently dissolved, and all silica is now in a stable quartz stage. Petrographically, the rocks are characterized by a variety of chalcedony and quartz cements which perfectly preserve precursor textures. Most cements precipitated from silica-oversaturated fluids, and their shapes reflect the silica saturation state and geometry of the pore space. Some microquartz and cryptoquartz also formed by a solid-solid inversion (recrystallization) of chalcedony. The cements have O-18 values between +30 parts per thousand and +20 parts per thousand Standard Mean Ocean Water and display a systematic depletion in O-18 from the first to the last crystallized, interpreted to reflect a gradual increase in temperature during burial. The precipitation of quartz cements started in the Middle Triassic when the strata passed the 19 degrees C isotherm at burial depths of ca 600m, and was completed in the mid-Cretaceous, 23km beneath the sea floor at temperatures of 75 degrees C. Late diagenetic overprinting of the chert includes fracturing, brecciation and cementation with carbonate cements having O-18 values between +2 parts per thousand and -30 parts per thousand Pee Dee Belemnite and C-13 values between +4 parts per thousand and -14 parts per thousand Pee Dee Belemnite; they are linked to hot solutions introduced during Cretaceous volcanism or Palaeogene tectonism. This study illustrates the diagenetic pathway during burial of spicule-rich sediments in a closed system and thereby provides a baseline for studies of more complexly altered chert deposits.

• 出版日期2018-4