Paleogeographic Conditions and Age of a Strong Earthquake According to Data from Studying of the Holocene Deposits from Lake Sevan, Armenia

摘要

A field study of sections of loose deposits in the western part of the Lake Sevan basin (Armenia) is conducted to investigate geoecological and paleogeographic features of existence and development of high-mountain lakes. The typical lithological patterns of significant lake transgressions are revealed and stratigraphic layers with numerous remnants of human activity, as well as the traces of ancient earthquakes, such as horizons of seismogenic convolutions in lacustrine deposits (seismites), are found. To determine the absolute age of the stratigraphic units, four radiocarbon dates of the samples from the section near the village of Norashen are used. They estimate the age of limnologic deposits in the interval of 2020 +/- 120-6270 +/- 110 yr BP for a 4.5-m-thick section. Using these data, the average sedimentation rate in the studied region equal to 0.34mm/yr is calculated. It is established that there were two significant lake transgressions: in the Middle and Late Holocene. During the field study, special attention was paid to the section of lacustrine deposits near the village of Norashen because it had layers with significant traces of human activity: ceramics and bone remnants. The results of archeological investigations and radiocarbon dates of the samples from the Norashen section have shown that humans settled in this region twice: in the 3rd and the middle of the 2nd millenium BC. The analysis of the materials of studying the seismogenic convolutions in the lacustrine deposits and archaeological data has given us an idea about the possible connection of the transgression regime and a 500-year pause in human settlement of the study region with a strong earthquake that occurred approximately 4400 years ago in the Lake Sevan basin. These data can be used for determining the long-term trend of oscillations for the high-mountain lake in the Holocene and for revealing its causes, as well as for a more precise assessment of the seismic hazard in the western part of the Lake Sevan basin.