The seabed sediment borehole MC -2, from area between Ankaran and Koper, was investigated as part of the master's thesis. The borehole is 636 cm long and covers the entire Holocene sedimentary sequence.
Based on the analysis of sedimentological and granulometric properties, the borehole consists of sedimentary layers of different thicknesses (1-86 cm), classified as clayey silt, sandy silt, and silty sand depending on their composition. The Holocene sequence is dominated by clayey silt (85.87 %), followed by sandy clay (9,24 %) and silty sand (4.87%). The presence of snail remains, biogenic detritus and bivalves was observed in all cores.
Calcite, dolomite, quartz, pyrite, halite, illite, albite, chlorite, and kaolinite were identified. We observed an increasing trend in the proportion of quartz and dolomite with depth and a reverse trend of decreasing proportion of calcite with depth.
Based on PCA analysis, the measured geochemical, granulometric, and mineralogical parameters were classified into four main clusters according to their correlation. The first cluster includes parameters such as silicon (Si), organic carbon/total nitrogen ratio (TOC/TN), quartz, magnesium (Mg), and dolomite, which are due to terrigenous inputs from the surrounding bedrock. The values of the parameters of the first cluster increase with depth. The second cluster includes aluminium (Al), iron (Fe), potassium (K), and a proportion of silt and clay associated with clay minerals (kaolinite, illite, chlorite). The third cluster includes sulphur (S), chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), lithium (Li), cadmium (Cd), lead (Pb), calcite, pyrite, total nitrogen (TN), total organic carbon (TOC) and the isotopic composition of carbon (δ$^{13}$C$_{org}$). The origin of this cluster is not clearly defined, but it probably includes parameters related to environmental bioproduction (S, TOC), authigenic carbonates of bioclasts (calcite, TN, δ$^{13}$C$_{org}$), and the mixed influence of organic material, anthropogenic influence, and the contribution of surrounding flysch rocks (Cr, Mn, Ni, Cu, Zn, As, Li, Cd, Pb). The values of the parameters of the second cluster generally decrease with depth. The contents of Cr, Pb, Cu, Ni and Zn are higher than in the surrounding felsic material, indicating anthropogenic pollution in the upper part. The fourth group is represented by arsenic (As) and the sand fraction, whose origin can be associated with pyrite, halite, organic material, iron/manganese oxides, and oxyhydroxides.
Absolute age dating with $^{14}$C was used to define a Holocene sedimentary sequence, with the deepest sample at 640 cm depth being 10,515 ± 84 years old. In the upper part of the borehole, to a depth of 166 cm, a deviation was observed, which is attributed to anthropogenic mixing of the sediment due to dredging of the shipping corridor of the Port of Koper or the influence of erosional currents.
Two types of dominant sedimentation were identified in the borehole MC -2. At depths greater than 445 cm, high proportions of dolomite and quartz, very low values of the δ$^{13}$C$_{org}$ isotope ratio, and higher values of the TOC/TN atomic ratio were observed, which we attribute to dominant terrestrial sedimentation. In the upper part up to a depth of 445 cm, higher δ$^{13}$C$_{org}$ values and lower TOC/TN atomic ratios are measured, indicating mixing of sediments.
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