Paleoclimatic signal of the Dobrogea loess-paleosol sections (Romania)

Abstract

The investigated area is located in Dobrogea (SE Romania). One site is near the village of Mircea Voda; the section is ~26 m thick; it comprises six well-developed palaeosols and intercalated loess layers. The second studied site is near Costinesti village, on the Black Sea coast; the section is 12.7 m thick; it comprises five well-developed palaeosols and intercalated loess layers. Samples were collected at 5-10 cm interval. For each sample granulometry was measured with a Horiba laser instrument (LA950) and magnetic susceptibility was measured on a MS2B Bartington susceptibility meter. Throughout the entire sections, the airborne dust (silt and fine sand above 16 µm) is present in large amount (generally over 50%). The pedogenic processes which involve hydrolysis of silicate minerals leading to formation of new clay-sized minerals (< 5 µm) can also be seen throughout the entire section with values always above 10% in the loess layers and values above 20% in the paleosol layers, suggesting that even during loess deposition, weak pedogenesis was present. Fine silt, coarse silt and fine sand material are present in substantial amount in the loess layers (above 10%, above 30% and above 10% respectively). This shows that the wind transportation competency was quite high at the time of loess deposition. Most of the grain-size distributions in the loess layers are bi-modal or even three-modal distribution, reflecting multiple sources of the clastic material. The studied loess sections are of Chinese loess type with a significant enhancement of magnetic susceptibility in paleosol horizons and low values in loess units. The new results from the Costisti section confirm change in the climate during the last two interglaciar stages (paleosols S1 and S2) with respect to the previous ones (paleosols S3, S4 and S5). This transition toward a dryer interglacial is reflected both in the amplitude of the magnetic susceptibility and the type of the paleosols.