GEOCHEMISTRY AND GENESIS OF UNDERGROUND BRINES IN THE NORTHEASTERN PART OF USSURI BAY (PRIMORSKI KRAI)
The article presents original data on chemical and isotope structure of underground brines and accompanying gases in the coastal zone of the southern Primorski Krai (the Sukhodol Bay). Proceeding from the ratios of oxygen and hydrogen isotopes in brines and surrounding water, as well as the data on chemical composition and the rare-earth element content, we managed to reveal the genesis of brines, to defi ne probable recharge areas and to estimate the circulation time. It is established that weak Ca-Na-Cl brines are highly metamorphosed and are not infl uenced by the modern sea water. The pattern of rare-earth elements distribution shows that water metamorphism is most likely related to diagenesis of marine and fresh-water sediments as well as to the interaction with continental carbonate deposits. 3H determinations proved that brines are formed in the zone of slow water exchange. The studied brines are typical for the earth-crust sites bearing oil and gas deposits; and brine occurrence in Cretaceous rocks most likely results from the overfl ow from parental Triassic sediments.