Mercury Anomaly in Oligocene–Miocene Maykop Group Sediments (Caucasus Continental Collision Zone): Mercury Hosts, Distribution, and Sources

The Oligocene–Miocene Maykop Group sediments, mainly composed of illite–smectite, store mercury in strongly variable concentrations from 10 to 920 μg/kg. Extremely high Hg levels (98–920 μg/kg) coupled with abnormal mercury-to-total organic carbon (TOC) ratios (Hg/TOC = 109 3000 μg/kg/wt%; TOC 0.2 wt% 1.2 wt%) were measured the Middle marine shales that deposited deepwater Indol–Kuban Basin under anoxic conditions. contain up 70% total sulfide form. In heavy mineral fractions, abundant Hg-bearing pyrite (with 4810 µg/kg hand-picked concentrates) is accompanied by sporadic cinnabar. Relative Upper have much lower and Hg/TOC ratios: 63 μg/kg (34 on average) 7.7 137 μg/kg/wt% (39 average), respectively. Mercury sequestration inferred occur mostly binding hosts deep-sea sediments matter, Fe3+-(oxy)hydroxides, clay particles which a more oxygenated environment. inputs during Maykopian sedimentation possibly associated local Oligocene–Lower Miocene volcanic activity Caucasus Continental Collision Zone. At same time, mode was controlled redox conditions changed disoxic suboxic at Middle-to-Upper transition.