Interdisciplinary investigations of the first reported laminated lacustrine sediments in Romania

摘要

An interdisciplinary study (cartographic and historical records, geomorphological, geological and bathymetric survey, water analysis, sediment coring and analysis and AMS radiocarbon dating) of two small and previously unreported lakes (Iezer and Bolatau) in Obcina Feredeului Mountains, northeastern Romania, provides new data into the environmental history and possible human impacts over the last millennium in this region. The first recorded historical reference to Iezer Lake dates to 1594 AD, and to Bolatau Lake to 1806 AD. Two sediment cores (420 cm for Iezer and 540 cm for Bolatau) of finely banded lake sediments and a radiocarbon age estimate at Iezer Lake suggest that this lake may represent the oldest landslide lake in Romania. The geomorphological, geological, and morphometric surveys indicate that these lakes' origins relate to landslide activity. Coarse grained, lighter sediment bands are generally characterized by higher values in magnetic susceptibility, Saturation Isothermal Remanent Magnetisation (SIRM), as well in geochemical indicators such as Ti and Zr, and low organic content, possibly indicating periods of increased runoff. Conversely, finer-grained, dark sediment bands show lower values in magnetic susceptibility, SIRM, Ti and Zr and higher organic content, and are likely to suggest quieter deposition periods. However, there are two significant episodes of markedly increased surface erosion. The oldest occurs between 100 and 110 cm, and might be coincident with the terminal part of Little Ice Age (LIA), whereas the youngest in the top 30 cm coincides with recent land use. These lakes hold significant potential in providing an important perspective on the environmental conditions over the last millennium and, more specifically, to supply new information about the Medieval Warm Period (MWP) and LIA signals in the NE Romanian Carpathians. These two landslide-dammed lakes should be defined as scientific reserves to ensure their protection and to enhance their use as a scientific and educational resource.