Abstract
We characterise the mineralogy and geochemistry of Oligo-Miocene Maykopian shales that are currently extruded by onshore mud volcanoes of the Kerch-Taman Province (the Northern Black Sea) from the depths of ~2.5–3 km. The ejected muds are remarkable by highly diverse authigenic mineralogy that comprises glauconite, apatite, siderite, mixed Fe–Mg–Mn–(Ca) and Mn–Ca–Fe-carbonates, pyrite, marcasite, sphalerite, cinnabar, chalcopyrite, nukundamite, akantite, native Cu, Au and Au–Ag alloys. Precise geochemical techniques and high-resolution methods are applied to study the composition of bulk rocks, sulphide and carbonate fractions, as well as individual mineral species, including trace element and isotopic compositions of carbonates (C, O) and pyrite (S). Mineralogy of clastic and heavy fractions is used as a provenance tracer. Oxygen-deficient to weakly sulphuric deposition conditions are inferred for the parent sediments proceeding from trace element partitioning between carbonate, sulphide, and metallic phases. The main conclusion of the study is that onshore mud volcanoes of the region only transport buried sedimentary material and authigenic minerals they store to the ground surface.
Highlights
Mud volcanoes (MVs), which are “tectonic windows” into the deeper subsurface, have attracted the attention of geoscientists for at least 150 years [1,2,3,4,5,6]
Mud masses consist of the liquefied Middle Maykop shale with a moderate amount of sand and low organic contents (≤0.5 wt %)
Abundant Fe(Mn)- and mix carbonates coexisting with relatively scare FeS2 in the samples we studied, as well as their concordantly changing trace element and isotopic patterns, suggest a syngenetic origin early during diagenesis of the Middle Maykop shales, by scenario (3)
Summary
Mud volcanoes (MVs), which are “tectonic windows” into the deeper subsurface, have attracted the attention of geoscientists for at least 150 years [1,2,3,4,5,6]. (2) ultra-high temperature alteration (combustion metamorphism) of mud masses triggered by MV flame eruptions and methane ignition [1,17,19,20,21,22,23,24]. In both cases, minerals owe their origin mainly. Minerals 2018, 8, 344 to fluids released through MV edifices Crystal growth under these conditions commonly occurs as a disequilibrium process at abruptly changing pressure and temperature, which leaves imprint on the habits, compositions, and zonation of the solids
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