The use of the magnetic susceptibility record as a proxy signature for the lithological composition of lake sediments: evidences from short cores in the Meşteru - Fortuna depression (Danube Delta)

Abstract

The paper analyses the enviromagnetic results obtained on short cores collected from Danube Delta lakes and channels. A Hydro-Bios type core sampler was used to investigate sediments up to ca. 60 - 80 cm depth from various sedimentary environments located both in the Fluvial Delta Plain (e.g., Lungu L., Cuteţchi L., Fortuna L., Crânjală Canal, Băclăneşti L., Matiţa L., Babina L., Bogdaproste L., Gorgova L., Uzlina L., Isacova L.) and the Fluvio-Marine Delta Plain (e.g., Puiu L. and Roşu L.). In this article, the results achieved for the sediment cores taken in the Meşteru - Fortuna Depression, during the 2010 - 2013 interval, are presented. The data make possible to compare, in some cases, the magnetic susceptibility (k; MS) characterisation of the bottom sediments (sampled with the grab sampler) with the MS data associated with the first 10-30 cm of sediments collected from the upper half of the cores, taken out from the same places within a lake. More interesting are the variations in the magnetic susceptibility regime along the cores. In many cases, the enviromagnetic
parameter “intensity” increased from the upper part towards the core base, but also some well-defined maximum and minimum k anomalies were detected. A clearly higher MS regime was identified along the whole short cores collected from the Crânjală mid-channel. The data demonstrate the capability of the MS parameter as a sedimentogenetic indicator, being possible to correlate the higher k values with the interception of a silted up zone or of two different sediment sequences within a core as a result of the hydrological regime changes occurred during the time. As regards the lower k values
measured at the upper part of the cores, they are usually related to the muds rich in fine vegetal (organic) detritus and/or rich in shell fragments. Based on
the values of the enviromagnetic parameter (k) and of the contents of the lithological components along the cores, several correlation coefficients (r) were
calculated, taking into consideration all the possible pairs of magnetic and/or lithological parameters. The vertical distribution of the magnetic susceptibility
associated with the cores clearly illustrates the particular characteristics of the “confined sedimentary environments” versus the “dynamic sedimentary
environments”.