Environmental Magnetic Record of the Harletz (NW Bulgaria) Loess Sequence
Abstract
The Harletz loess sequence is located in NW Bulgaria on the western bank of the Ogosta River, a tributary of the Danube. The sequence is exposed on a cliff face carved by the meandering paleo-Ogosta River. A 20 m section, sitting on top of the river's alluvial plain was cleaned and sampled for a multi-disciplinary study. OSL age determinations and field observations suggest that the section spans the last two glacial-interglacial cycles equivalent to marine oxygen isotope stage (MOIS) 7 to the present. High-resolution continuous bulk sampling was carried out to characterise the composition, grain-size and concentration of the magnetic mineral assemblage. In addition to features observed in the field, environmental magnetism data reveal unobserved pedogenic alteration likely related to MOIS 3. Oscillations in, for example, coercivity of remanence, are also detected through MOIS 6 unaltered loess, which may be indicative of two different sources. Both low and high coercivity minerals are by-products of pedogenesis in all paleosols of the Harletz sequence supported by peaks in their respective concentration parameters and superparamagnetic behaviour is detected in most paleosols and the topsoil. Finally, evidence for tephra material is unambiguous at about 12 m depth and likely at about 1.5 m depth. Given the OSL age model for the Harletz sequence (Lomax et al., in preparation), the stratigraphic position of the lower tephra is similar to occurrences in other loess sequences of the region (ex. Mostistea in Romania) and the upper tephra, if confirmed, would correlate temporally with the Campanian tephra. Oriented samples were collected for anisotropy of magnetic susceptibility (AMS) analyses. Triaxial oblate AMS fabrics with horizontal foliation planes are obtained from 15 m depth through the top of MOIS 6 loess. A biaxial oblate AMS fabric with a horizontal foliation plane characterizes the soil complex of the last interglacial. Last glacial loess displays an isotropic AMS fabric reflecting the intense bioturbation observed in the field. The Harletz loess sequence provides a key climate and environmental record for SE Europe and is especially promising for furthering our understanding of climate oscillations persisting in this area through the MOIS 6 glacial period with respect to central and western Europe.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMGP51C1400L
- Keywords:
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- 1505 Biogenic magnetic minerals;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 1512 Environmental magnetism;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 1518 Magnetic fabrics and anisotropy;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 1540 Rock and mineral magnetism;
- GEOMAGNETISM AND PALEOMAGNETISM