Rock magnetism of a loess-palaeosol sequence from the western Black Sea shore (Romania)

• Published in: Geophysical journal international 2015-09, Vol.202 (3), p.1733-1748
• Main Authors: Necula, Cristian, Dimofte, Daniela, Panaiotu, Cristian
• Format: Article
• Language: English
• ISSN: 0956-540X; 1365-246X
• DOI: 10.1093/gji/ggv250

The Lower Danube Basin is one of the most important loess regions from Europe, which have provided excellent archives for long-term high-resolution palaeoclimate studies. The aim of this paper is to derive new information on the Middle–Late Pleistocene palaeoenvironment from a high resolution multiproxy assessment of the iron mineralogical composition at the Costineşti loess-palaeosol sequence located on the western Black Sea shore. It is the easternmost loess section in the Romanian loess region studied and its distinct pattern of the proxy records can be used to correlate the lower Danube loess to other key sites of the Moldavia and Ukraine loess regions. To investigate the climatic control on soft and hard ferromagnetic minerals we used several types of rock magnetic properties: magnetic susceptibility and its frequency dependence, anhysteretic remanent magnetization, isothermal remanent magnetization, hysteresis properties and FORC distributions, an unmixing model for isothermal remanent magnetization curves and high field (up to 8 T) isothermal remanence measurements. Our results show that the palaeosol horizons, formed during interglacials and climatically more favored periods of the Pleistocene, experienced pedogenic alteration, resulting in high amounts of superparamagnetic, single domain and pseudosingle domain magnetite/maghemite grains and hematite. The loess layers, formed during glacial periods, are mainly dominated by multidomain and/or pseudosingle domain oxidized magnetite and some hematite, all probably of aeolian origin. Goethite contribution is probably minor and constant both in loess and palaeosol horizons. We review the correlation of the loess sections from the lower Danube basin concluding that the new results can be interpreted as a support for the transition of a Mediterranean type climate to a steppe type climate in the last two interglacial periods in the western Black Sea. Because the pattern of magnetic susceptibility data from the lower Danube basin is changing relative fast with distance from the Black Sea shore, it probably reflects the local influence of the Black Sea on continental scale climatic oscillations during the last 600 ka. The values of background magnetic susceptibility of the Romanian loess-palaeosol sections indicate that the main source area of the dust changed during this climatic transition. Our analysis also shows that the age of the loess-palaeosol sections from the Eastern European low lands (Moldavia a