Lithology and palaeomagnetic record of Late Weichselian varved clays from NW Russia

Abstract

A lithological and palaeomagnetic analysis of Late Weichselian glaciolacustrine deposits from two ancient periglacial lakes was carried out in the valley of the Shuja (S Karelia) and Ust-Pjalka (S-E Kola Peninsula) rivers, NW Russia. The rhythmic structure of the varved clays is interpreted as turbiditic with systematic differences between the proximal and distal areas of accumulation. In the proximal area the textural and structural properties of the deposits towards both distal and (partly) lateral directions are described. It is shown that the proximal varve successions are incomplete while distally they are continuous. The accumulation of one varve (DE rhythm, second order cycle) during one year is consistent with palaeomagnetic data. Significant differences in magnetic parameters and in the palaeomagnetic "records" of declination-inclination between proximal and distal varves are established. Analysis of palaeomagnetic properties was combined with lithological analysis in all sections. Locally, the varved clays in the proximal area could be used for palaeomagnetic research. Taking into account the erosion of underlying deposits by turbidity currents and inclination shallowing, these sediments could not precisely record palaeosecular variation (PSV). The distal varved clays (represented by the DE rhythms) are clearly most useful both for varve-clay chronology and PSV recovery. The palaeomagnetic declination and inclination records are correlated with chrono- and magnetostratigraphy scheme of NW Russia. This paper also examines lithology-dependent "inclination error" and anisotropy of magnetic susceptibility in glaciolacustrine sediments.