Radiocarbon Dating of Lake Sediment from Two Karst Lakes in Yugoslavia

Abstract

ABSTRACT. Samples of sediment cores from two lakes in the karst area of northwest Yugoslavia were analyzed. Both Lakes Kozjak and Prosce are in the Plitvice National Park, Central Croatia. 14C dating, sedlimentologic, seismic, and isotopic studies, and distribution of diatoms are presented.14C dating of lake marl revealed a uniforn sedimentation rate in Lake Prosce as opposed to Lake Kozjak. Both lake sediments belong to the Holocene period. 14C dating of lake sediment is in agreement with seismic profiles, sedimentologic analysis, and diatom frequency measurements both in an undisturbed as well as in a disturbed lake sediment. INTROI)UCTIONA comprehensive study of aquatic chemistry, hydrobiology, and hydrogeology of the Plitvice Lakes included coring of lake sediment and a subsequent systematic analysis of cores. Samples of cores taken every 5 to 50cm (depending on the type of analysis) were analyzed for pollen, diatom, and ostracode content, followed by sedimentologic, trace element, x-ray diffraction, stable isotope, and 14C analyses. The 14C, stable isotope, and diatom population analyses are presented here, along with a brief description of seismic and sedimentologic work.Lake Kozjak core was retrieved from 24m water depth. Even though a surprisingly thick lake sediment prevented the extraction of all core material overlaying bedrock, the first 12m of sediment gave very useful and, to a certain extent, unexpected data. Radiocarbon ages of an acoustically wellstratified top section indicated a fairly constant sedimentation rate of 0.8mm/a for the last 1800 years. Lake Prosce core was retrieved from 17.2m water depth and reached the clayey residual layer overlaying bedrock. Radiocarbon dating of lake sediment revealed a uniform sedimentation rate(1.4mm/a) as opposed to Lake Kozjak sediments. Both lake sediments belong to the Holocene.The x-ray diffraction analyses showed that the sediments consist of calcite with traces of dolomite, indicating that the sediments were formed by decomposition of dissolved calcium bicarbonate without any significant contribution from detrital limestone or dolomite. This was substantiated by b' 3C data, ranging between -8.5%o and -8.8%o, which is typical of sediments of biogenic origin. Geologic SettingAccording to Polsak (1979) the Plitvice Lakes are surrounded by Triassic, Jurassic, and Cretaceous beds. The whole area is gently folded and intersected by numerous faults. Two most prominent faults run in a north-

Towards a Deeper Understanding of How Carbonate Isotopes (14C, 13C, 18O) Reflect Environmental Changes: A Study with Recent 210Pb-Dated Sediments of the Plitvice Lakes, Croatia

“…These values agree well with previous δ 13 C measurements of 12-m-long sediment cores from the same lakes (SrdoË et al 1986a), as well as with δ 13 C of the top 30 cm of sediments collected in 1990 . In contrast, a significant change in δ 13 C towards 1-3‰ more positive values in the upper sediment layers is observed in the small lakes Gradinsko (-6.7 ± 0.2‰, top 15 cm) and Kaluerovac (-6.8 ± 0.2‰, top 10 cm).…”

“…Below 15 cm, the sediment cores were more compact and the water fraction remained relatively constant (PR 61%, GR 41%, K1 51%, K2 75%, and KA 35%). Therefore, the (linear) sedimentation rate obtained for deeper layers can be compared with the sedimentation rates obtained earlier from 12-m-long cores in lakes Kozjak and ProšÊe (SrdoË et al 1986a).…”

“…The lakes receive water from 2 main springs (Bijela Rijeka and Crna Rijeka springs) and 2 tributaries (RjeËica and Plitvica). The lakes are characterized by intense calcium carbonate precipitation from the water, forming tufa barriers and fine-grained lake sediments mainly composed of authigenic calcite (SrdoË et al 1985(SrdoË et al , 1986aObeliÊ et al 2005). The surrounding area is covered largely with deciduous forests.…”

“…Determination of the initial 14 C activity of DIC in water and tufa/lake sediments (Krajcar BroniÊ et al 1986 as well as carbon isotope exchange processes in downstream flow (SrdoË et al 1986b;HorvatinËiÊ et al 2003) were completed in connection with the 14 C dating of carbonate deposits. Results of 14 C dating of the 12-m-long lake sediments from the 2 biggest lakes, ProšÊe and Kozjak (SrdoË et al 1986a), and of 14 C and 230 Th/ 234 U dating of tufa deposits from the Plitvice Lakes (SrdoË et al 1985HorvatinËiÊ et al 2000) were used to study paleoclimatic conditions in this area. An anthropogenic influence on 14 C activity and on the concentrations of some aliphatic and polycyclic aromatic hydrocarbons was observed in the sediments of 2 big lakes, Kozjak and ProšÊe ).…”

Isotope analyses of the lake sediments in the Plitvice Lakes, Croatia

“…For this study we selected two biggest lakes from the Plitvice Lakes system (Figure 1b,c): the uppermost Lake Prošće (0.68 km 2 , maximal depth 39 m) which is fed by water from Matica stream, and Lake Kozjak (0.82 km 2 , maximal depth 46 m) fed by water from the upper lakes. The seismic records of both lakes showed 10−12 m thickness of lacustrine deposits below which the pre-lacustrine base can be easily identified [17].…”