Page 26 - Studia Universitatis Hereditati, vol 13(2) (2025)

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studia universitatis hereditati, letnik 13 (2025), številka 2 / volume 13 (2025), number 2

Figure 10: Geochemical Zones (1–3) and Subzones (21 and 22) of Core OSOR 2 and Depth Profiles of TOC and TN
Concentrations, Inorganic Carbon (TIC) and C/N Weight Ratios and Insoluble Residuum (%) (elaborated by Croa-
tian Geological Survey, 2025)

Insoluble residuum follows the distribu- C/N < 10 suggests that organic carbon (TOC)
tion of TIC (carbonate) with an upward de- in Zone 1 is marine organic matter, while sedi-
cline in concentrations from the base of Zone 3 ments in Zones 2 and 3 contain a mixed source
to the boundary of Zone 2. In Zone 2 the car- of both marine and terrestrial organic carbon.
bonate (TIC) content continues to decrease The sedimentary succession at a depth of 70 cm
with the increase of organic carbon accumula- shows a ratio of 24, which indicates that most of
tion. The amount of TIC rises abruptly in Zone the organic carbon is of terrestrial origin. Zone
3 and continues to rise to the top of the core, 3 shows a gradual shift upwards towards the ma-
while the insoluble residuum follows an oppo- rine organic matter source C/N < 10 (fig. 10)
site trend in this zone (fig. 9). Smear slide in-
spection of the sediments showed that the or- Core Chronology
ganic carbon concentrations are related to the Radiocarbon measurements on three mollusc
contents of silt-sized charcoal in the sediment. shells revealed that sediment core OSOR 2 spans
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These higher TOC values are associated with at least 5.5 calibrated ka BP (table 1). C analy-
increased charcoal deposition possibly sourced sis of the mollusc shells from the part of the core
from human activities in Osor. The molar ratio where a distinct change in colour (from grey to