Loess deposits from the Tajik depression (Central Asia): Magnetic properties and paleoclimate

Abstract

Continuous accumulation of dust during the Quaternary has formed widespread loess deposits in southern Tajikistan. The magnetic susceptibility variations of these aeolian sediments have recorded the paleoclimatic fluctuations in a similar direct and complete way to the well-studied sediments from the central loess plateau in China [11]. Susceptibility measurements were carried out in situ at intervals of 10 cm along seven partly overlapping sections in the loess/paleosol sequence of Karamaidan (ca. 100 km east of Dushanbe). Nearly 250 oriented samples were taken for rock-magnetic investigations. Careful field observation revealed a total actual loess thickness of ca. 100 m for a composite profile with thirteen intervening pedocomplexes (PC). Standard demagnetization techniques yielded a characteristic component of natural remanent magnetization (NRM) which was used to obtain a well-defined magnetostratigraphy. The section covers a total timespan of approximately 1 m.y., including the Brunhes and the youngest part of the Matuyama polarity chron. The susceptibility variations correlate excellently with those of the Chinese loess record at Xifeng [22], although minor differences in the relative amplitude of the susceptibility signal occur. Close correlation with the astronomically tuned oxygen isotope record [26] enables refined dating of the loess sequence at Karamaidan and demonstrates the global significance of the recorded paleoclimatic variations, especially with respect to paleoprecipitation on land during the Quaternary.