Abstract
The study focuses on authigenic carbonates that are widespread in different deposition environments and are a component part of the terrestrial biogeochemical cycle of carbon. Samples from the Kolyma Yedoma Ice Complex that formed during the Sartan Cryochrone (MIS 2), the coldest period of the Late Pleistocene, in the northeastern Siberian lowlands, have been studied utilizing scanning electron microscopy and energy-dispersive spectroscopy with replica technique. The samples bear signatures of irreversible multistage cryogenic changes in structure and composition, with the formation of authigenic minerals. Authigenic carbonates as secondary phases in the Ice Complex deposits are remarkable by local changes in chemical, physical, and other properties, which induce gradual changes in the lattice and conversion of one mineral species to another. As a result, the sediments may contain stable and metastable minerals. Crystalline species like calcite or aragonite precipitate from aqueous solutions and their presence are restricted to free pore space in segregation ice. Metastable phases may be produced as an initial reaction product between the CO2 and the aqueous phase, while mineral surfaces and small pores act as possible nucleation sites. Organic matter is also an important agent in the cryometamorphism of sediments, including precipitation of authigenic phases due to the freezing of colloids and high-molecular compounds.
Highlights
Authigenic minerals in sediments are formed by physicochemical and biochemical reactions during and after deposition in various environmental settings
One of the last summary publications concerning the Yedoma Ice Complex from the Kolyma Lowland to test the processes and environmental conditions of silt deposition has been given by Murton et al, 2015
The sediment particles within a seasonal freezing and thawing layer acquire a particular morphology during diagenesis due to the exposition to cryogenic deformation
Summary
Authigenic minerals in sediments are formed by physicochemical and biochemical reactions during and after deposition in various environmental settings. The mineralogical alteration of sediments soon after the deposition (early diagenesis) is controlled primarily by their original compositions and relative percentages of four main components: chemically passive and active minerals, organic matter, and pore fluids. Passive phases are commonly predominant and mostly include primary minerals (quartz, feldspar, garnet, and ilmenite) except for a few relatively reactive Fe- and Ca-bearing silicates. Active minerals encompass such inorganic phases as Fe, Al, and Mn hydroxides, mix gels, amorphous silica, carbonates, and water-soluble salts, which are in equilibrium with pore fluids only at the time of precipitation (Curtis, 1990; Buggle et al, 2011). The decay of organic matter produces SP2 and O2S, NH3, CH4, and other reactive components, which become involved in the alteration of sediments and control the chemical environment, though are as low as a few percents or less (Davidson and Janssens, 2006). As for pore fluids, they commonly acquire higher pH during early diagenesis (Tranter, 2003)
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