Mineralogical composition, isotopic and geochemical characteristics of Pleistocene glendonites from the outcrops of Bol’shaya Balakhnya River, eastern Taimyr, Russia

Abstract

ABSTRACT We present a complex study on mineralogical, U/Th dating, isotopic and geochemical characteristics of Pleistocene glendonites (calcite pseupomorphs after ikaite) from the outcrops of Bol’shaya Bakakhnya valley, eastern Taimyr, Russia. Based on the U/Th dating of the glendonites (37 ± 7 ka) we propose that the glendonites and host sediments were formed during the Karginsky interstadial (22–50 ka)—this data corresponds well with published ages of foraminifers and wood fragments from Karginsky deposits of eastern Taimyr. The main factors leading to ikaite crystallization was presence of organic matter (δ13C varies from –5 to –40‰ V-PDB) in the host clayey sediments and low temperatures (< 7°C) of bottom water. Isotope (δ18O ratios vary from –8 to –33.9‰ V-PDB) and geochemical (PAAS-normalized patterns of rare earth elements) characteristics of the studied glendonites confirm that ikaite crystallization and transformation was influenced by seawater. Carbon was derived from dissolved inorganic carbon, decomposed organic matter, and probably methane. Some glendonites are surrounded by concretions (host rock cemented by calcite). The isotopic characteristics of the host concretions and glendonites are similar, so we assume that glendonites and host nodules were formed by the same processes—sulfate reduction coupled with anaerobic decomposition of organic matter. Nevertheless, geochemical characteristics of the host concretions and glendonites differ: Mg/Ca ratio and values of Fe, Mn, Zn, Cd, and U are higher in host concretion than in glendonite. This may reflect differences in crystalline structure of ikaite and high magnesium calcite.