All-Russia Research Institute of Geology and Mineral Resources of the World Ocean (VNIIOkeangeologiya) (Saint Petersburg, Russia):

Ivanova V. V., Leading Researcher, Candidate of Geological and Mineralogical Sciences, e-mail: v_ivanova@rambler.ru

This paper presents the results of geological and geochemical studies, carried out at the pockmark area in the eastern part of the Gulf of Finland. According to the side-scan sonar and profilograph data, for the first time, the pockmark-type structures were discovered in the eastern part of the Gulf of Finland. The bottom sediments were sampled at two stations. Samples were collected with measurement of temperature and pH. Concentrations of macro- and microcomponents in the bottom sediment samples were defined by ICP-MS method (SUE «Vodokanal of St. Petersburg»). Pockmark bottom sediments are significantly different from the background aleuropelites with higher contents of all components. The analysis of lanthanides content in the sediments reveals certain patterns in distribution of rare earths. The high contents of europium in the sediments show the following peculiarities of sedimentation environment:
-position of sedimentary complexes within high permeable zones;
-change of redox conditions of sedimentation.
Pockmark areas in the eastern part of the Gulf of Finland are the indicators of geochemical barriers in the zones of saline solution discharge, which is confirmed by peculiarities of rare earth elements distribution in sediments. Geochemical anomalies, associated with pockmark area, make an influence on environment. Despite the evidence of saline solution filtration within pockmark area, their genesis remains unclear and requires further investigation. For this purpose, first of all, it is necessary to study the deeper levels of bottom sediments.

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