MAGNETIC SUSCEPTIBILITY CALIBRATION AND LITHOLOGICAL CHARACTERIZATION OF THE LAKE SEDIMENTS FROM THE BLACK SEA LITTORAL ZONE (ROMANIA): NATURAL AND ANTHROPOGENIC INFERENCES

Sorin - Corneliu Rădan, Geological Institute of Romania, Romania
Silviu Rădan, Camelia Vărzaru, GeoEcoMar, Romania

Abstract

The modern sediments from four lakes in the Black Sea Littoral Zone (Romania) were investigated with regard to the integrated magnetic susceptibility and lithological characterization. Located southward of the Razim – Sinoie Lagoonal Complex, the littoral lakes under attention are characterized as fluvio-marine limans, closed by littoral bars (i.e., Taşaul, Techirghiol and Mangalia) or as littoral lagoons (i.e., Siutghiol).
Based on the Magnetic Susceptibility (MS; k) measurements and on the lithological analyses (SIL – mineral-SILiciclastic fraction; CAR – CARbonates; TOM – Total Organic Matter content), a number of maps were drawn, showing the areal distribution of each parameter in the lakes.
Following the location of the littoral lakes from north to south, the Taşaul Lake case is firstly discussed. The highest k values (up to 490.97×10-6 SI) were recorded on the sediments sampled in the north-western extremity, in the Casimcea river solid discharge area. This is followed up by the influence zone of the green schists quarries from Sibioara (SW of the lake). The lowest k values (e.g., 22.83×10-6 SI) cover the central–south-eastern part of the lake, i.e. where the organic-rich sediments prevail.
With regard to the Siutghiol Lake, a possible anthropogenic impact of the Poarta Albă – Năvodari Canal construction works is inferred from the recent sediments sampled in the northern area, with MS values reaching 403.44×10-6 SI. High and very high k values (up to 949.19×10-6 SI) were also recorded on the samples collected from the NW-W area, where the input of the high border could be responsible for this magnetic regime, but a presumable anthropogenic impact caused by the Ovidiu village vicinity must not be neglected.
Similar cartographic images were obtained for the distribution of the SIL and MS values relating to the sediments of the Techirghiol Lake. The highest k values (up to 206.38×10-6 SI) and SIL contents (up to 76.8%; average value: 54.1%) follow up the banks of the two southern arms of the lake, the sediments being predominantly siliciclastic, often visibly sandy. The significance of the ancient water streams which supplied the liman should be also considered. The dominantly organic sediments are mainly placed in the central-northern area of the Techirghiol Lake, where zones of maximum TOM contents (up to 65.1%) and of minimum MS values, respectively, are recorded; correspondingly, the bottom sediments in this area are poor in the siliciclastic material.
As concerns the Mangalia Lake, the SIL and MS maps are very well correlated, as well: the k values are increasing upstream to downstream, along with the enrichment of the sediments in siliciclastic material and the decreasing of the organic substance contents. The M-C-O ternary diagram shows the major role of the detrital mineral fraction within the lake sediments.
This integrated magnetic susceptibility and lithological study represents an interesting enviromagnetic approach of some lacustrine ecosystems that are located in the Black Sea Littoral Zone.