As part of the master's thesis, we examined the sequence of recent marine sediments from two boreholes (ANK03 and ANK08) collected in the selected area between Koper and Ankaran. The aim of the study was to determine the mineral and geochemical composition of the selected sediment samples from the Bay of Koper. We conducted a sedimentological description of the cores, granulometric analysis of the samples, and prepared samples for further research, such as X-ray powder diffraction (XRD), X-ray fluorescence spectroscopy (XRF), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and 14C dating. Based on granulometric properties, we identified the sediment in borehole ANK03 as loosely sandy clayey silt, while the sediment from borehole ANK08 was identified as loosely clayey silty sand. In both cores, larger pieces, particles, and smaller fragments of marine snails, shells, or other organisms were observed, especially at the top and bottom of both boreholes. Using XRD, we determined the presence of quartz, calcite, dolomite, feldspar, clinochlore, halite, pyrite, and illite in the collected samples. Using SEM-EDS, we confirmed the presence of these minerals and also found K-feldspar, zircon, TiO2 mineral (likely rutile), monazite, fluorapatite, and potential carriers of toxic elements, pyrite, and Cr-spinel. XRF analysis determined the concentrations of major oxides, potentially toxic elements (PTE), and other trace elements. Silicon dioxide (SiO2) represented the highest proportion of major oxides, associated with the presence of quartz and clay minerals in the Eocene flysch. Al2O3, Fe2O3, and K2O concentrations were influenced by the occurrence of albite and clay minerals (illite, kaolinite, and clinoclase) in the bay. MgO content was linked to dolomite from the hinterland, while CaO originated from limestones in the hinterland and to some extent from inorganic remains of marine organisms (snails, shells, ostracods, and foraminifera). The gradual increase in P2O5 content throughout the borehole likely indicates the consequence of agricultural development, as it is present in fertilizers washed into the bay by meteoric water. In both boreholes, the calculated enrichment factor (EF) confirmed elevated concentrations of PTE, including copper (Cu), zinc (Zn), lead (Pb), and arsenic (As). Elevated PTE concentrations in the upper 50 cm, temporally defined up to a maximum of 2509.5 ± 83.5 calibrated years before present (BP), are likely due to anthropogenic influence. Individual enriched PTE concentrations in deeper sections of the borehole are likely a result of more intense weathering during a favorable climate with increased rainfall and temperature fluctuations and greater material input through rivers across the geological background into the Bay of Koper. Chromium (Cr) and nickel (Ni) concentrations were slightly elevated, undoubtedly influenced by the geological background of flysch rocks surrounding the bay. Absolute dating with 14C in borehole ANK03 determined the ages of sediments at specific depths, covering approximately the upper third of the Holocene sequence, with the highest age being 3499 ± 60 calibrated years BP, obtained at a depth of 187 centimeters. The unusual shape of the age model curve may be partly influenced by the deepening and displacement of marine sediments by the Port of Koper or the action of erosional currents and underwater landslides, as evidenced by a negative deviation in the curve at depths from 52,5 to 109 cm.
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