Magneto-lithological models for recent sediments. Examples from deltaic, lagoonal and littoral lakes

The results analysed in the article are complementary to the magnetic susceptibility and lithological data presented in a recent paper (Radan et al., 2008), in which various cases from the most important southeastern Romania wetlands have been approached. The modern sediments have been sampled from the same areas, i.e. the Danube Delta, the Razim (Razelm) Sinoie Lagoonal Complex and the Black Sea Littoral Zone. New composite models are illustrated and the correlations between the k values and the main lithological components (i.e. organic/TOC, carbonate/CAR and mineral-siliciclastic/SIL, respectively) are commented. On the basis of the entire magneto-lithological databank obtained for the lake sediments sampled in the 2006 and 2007 cruises (the data used in the above cited paper included), several correlation coefficients (r) were calculated, e.g. related to k vs TOC, k vs CAR, k vs (TOC+CAR) and k vs SIL. The graphical correlation is also taken into consideration to show and interpret the connection between the enviromagnetic parameter and the lithological characters. Generally, positive (direct) correlations characterise the magnetic susceptibility (MS) vs mineral component (SIL), whereas negative (reverse) correlations define MS vs TOC, as well as MS vs (TOC+CAR). The MS regime recorded within the various sedimentary environments located in deltaic, lagoonal and littoral lakes and the ternary diagrams showing the lithological classification (i.e. detrital fraction, carbonate fraction and organic matter) of the sampled bottom sediments are compared. Based on the MS values and the lithological contents, the models carried out for several deltaic lakes clearly emphasize the allochthonous sedimentation, predominantly detrital in the lacustrine ecosystems that are directly influenced by the River Danube, comparing with the dominantly autochthonous sedimentation in the distal zones, where the organic component is mostly present. As regards the lagoonal and the littoral lakes, the coincidence between the sedimentary areas characterised by higher MS values and those defined as dominantly siliciclastic, and by low MS intensity fingerprints and those rich in organic matter, respectively, is well reflected by corresponding maximum and minimum anomalies identified within the specific (k, SIL, TOC) maps. These connections are also shown by other magneto-lithological models and, particularly, by patterns illustrating the graphical correlation between different parameters that characterise the lake sediments. Therefore, the quality of proxy parameter of the magnetic susceptibility to reveal distinguishing features for different lithological characters and the connection with the distinct position of the lakes related to the fluvial supplies, to the hydrodynamic context or to the specific source-areas are reflected by new data, and together with the previous results (Radan et al., 2008) show that the recent sediments sampled in various aquatic ecosystems stand for high fidelity enviromagnetic archives.