20 research outputs found
Holocenska sedimentacija u solinskom kanalu (Mljetska jezera, Jadransko more)
A 103 cm long core from the Soline Channel (Mljet Island, Adriatic Sea), which is at present a surface connection between the peculiar marine Mljet Lakes and the open sea, indicates substantial changes of the sedimentary environment in the Holocene. In the layer dated to 4,600 B.P., 25–30 cm below the bottom (which is at 2.8 m depth), freshwater algae represented by species of Chara/Nitella were found along with the gastropod Limnea stagnalis. This dominantly brackish sediment extends from 10 to 60 cm below the bottom. Above that interval marine sediment was found and below it quartz dominated the subareal or freshwater sediment. This indicates that the surface marine connection between Mljet Lakes and the sea was established after deposition of freshwater/brackish sediments i.e. not earlier than ca. 4 kyr B.P.Jezgra dugačka 103 cm izvađena iz kanala Soline (otok Mljet, Jadransko more), koji je danas površinska veza između jedinstvenih morskih Mljetskih jezera i otvorenog mora, ukazuje na bitne promijene taložnog okoliša u holocenu. U sloju čija je starost procijenjena na 4,600 godina, 25–30 cm ispod dna (koje se nalazi na dubini od 2.8 m), nađene su slatkovodne alge iz roda Chara/Nitella zajedno s puževima Limmnea stagnalis. Ti pretežno bočati sedimenti protežu se od 10 do 60 cm ispod dna. Iznad njih nalaze se marinski sedimenti a ispod kopneni ili slatkovodni sedimenti. To ukazuje da je površinska veza morem između Mljetskih jezera i otvorenog mora uspostavljena nakon taloženja slatkovodnih/bočatih sedimenata tj. ne prije oko 4 tisuće godina
Hydrologic Evolution of a Carbonate Aquifer (Dinaric Karst, Croatia)
Dinaric Karst terrains contain specific, laminated speleothems, which line all surfaces of subterranean voids including Cretaceous bedrock limestone, and older vadose speleothems and clastic sediments. These speleothems may attain a thickness of one metre. Deposition of these speleothems took place during a long-term phreatic period in the Late Quaternary. This is in contrast to well-known, widespread speleothems, which were, and are deposited in vadose and uppermost phreatic settings. Furthermore, the origin of these phreatic speleothems departs from common experience by the dominant dissolutional widening of underground conduits when saturated. Phreatic speleothems can be important stratigraphic marker for the stratigraphy of cave sediments. This approach revealed a sequence of three hydrologic stages: (1) pre-phreatic stage with dominant vadose conditions and dissolution processes, (2) phreatic stage when the ground-water level was very high in the large karst area, and when the volume of the voids decreased, and (3) the last, dominantly vadose stage during which voids were enlarged for the second time, and phreatic speleothems may be covered by younger clastics and vadose speleothems
Palaeoenvironmental reconstruction of the Milna valley on the island of Vis (Central Adriatic) during the late Holocene.
This study provides a reconstruction of the 1.5 ka palaeoenvironmental evolution of the small, and presently dry, Milna valley on the island of Vis. Sediments from the valley were studied using multi-proxy approach, applying sedimentological, mineralogical, petrological, anthracological, malacological, 14C and land cover analyses, in regard to climatic, vegetation, and hydrological changes. The mineral composition of the siliciclastic detritus from the Milna valley points to the Dinaride Ophiolite Zone in Bosnia as its dominant source of origin, eroded by the Neretva River, and deposited in the form of alluvial sediments in the Central Adriatic area. However, Cetina and Drin Rivers may have also contributed some of the sediments. Regional aeolian resedimentation of the material occurred during Pleistocene, which later accumulated and became preserved in the Milna valley. Beside the Dinaride Ophiolite Zone, part of the mineral composition is influenced by minerals from the Alpine region and by neutral to basic volcanism, probably of Italian origin. During the Dark Age Cold Period (DACP) the Milna valley was covered by forests of the Pinus sylvestris group, within which cold-resistant and closed forest habitat preferring species (molluscs) lived. This forested environment probably lasted until the Little Ice Age (LIA) period when fires occurred in the 15th and 16th centuries. The opening of the landscape corresponded to the resettling of the population from the interior to the coast and to the expansion of vineyards on the island. The deforestation enabled the formation of torrential flows and deposition of unsorted sediments. Most of the pebbles are rounded clasts of the Middle Cretaceous (Cenomanian) dolomite in which the valley is formed. However, pebbles which are not present in outcrops of the Milna valley have also been identified. After the LIA, the valley became dry again and has been continuously under anthropogenic impact ever since. Different cartographic sources enable the further tracing of land cover changes from the beginning of the 19th century to present day. The analysis revealed that the highest anthropogenic impact on the landscape occurred in the second part of the 19th century, after which afforestation started. Moreover, the major issue today relates to changes influenced by the current relative sea level rise. This study adds to the knowledge on coastal fluviokarst valley evolution in typical Mediterranean conditions, relating our understanding of Holocene deposition, human activity, and land cover changes on the island of Vis
Glaciochemical investigations of the ice deposit of Vukušić Ice Cave, Velebit Mountain, Croatia
The 3H activity and the concentration of 23 metals and metalloids have been analysed in cave ice samples from the perennial cave ice deposit of Vukušić Ice Cave, Velebit Mt., Croatia. The results of tritium measurements exclude a secular age for the upper 2.4 m of ice deposition, and provide clear arguments that the sampled ice sequence consists of frozen post-1950 precipitation. Measured concentrations of most of the analysed elements have largely surmounted reported concentrations of similar elements from local precipitation or Alpine snow/firn/ice records, whereas three metals (Cr, Cu, Pb) show concentrations comparable to them. Principal component analysis was used to select three groups of elements. The Ca-Mg-governed group (PC1) encompasses the bedrock-related components; their fluctuation might thus reflect the past intensity of dissolution in the epikarst. PC2, with the most characteristic elements being Na, Cr and Pb, probably preserved an atmospheric depositional signal. PC3 is governed by Al and Fe. This probably carries the distal, non-karstic crustal signal and hence might be related to atmospheric circulation (i.e., wind direction and speed)
Isotope analyses of groundwaters of the North African Plain.
Isotope analyses of 36 groundwater samples were performed as part of an extensive hydrogeological study in Tripolitania, Libya. The stable isotope ratios 2H/1H, 18O/16O, and 13C/12C, and the radioactive isotope ratios 3H/1H and 14C/12C were measured which reflect mixing, vertical and horizontal flow as well as the individual recharge conditions of the various aquifers. The majority of water samples showed very low 14C as well as 3H concentrations corresponding to reliable conventional 14C ages exceeding 11,000 yrs. The results of the isotope analyses confirm, complete, and refine the hydrogeologically derived concepts of the study area
Hydrological and Ecological Controls on Autochthonous Carbonate Deposition in Lake Systems: A Case Study From Lake Wuliangsu and the Global Perspective
Based on similar to 150-year of sedimentary records, we identify that autochthonous carbonate deposition in Lake Wuliangsu, in the upper reaches of the Yellow River, was independent of both hydrological and ecological variations before 1965, influenced by hydrological changes due to agricultural activities during 1965-1990, and slightly impacted by higher productivity under the eutrophication process after 1990. By comparing with data from lakes across the globe, we find that lake size and lake stratification control the contribution of recycled organic carbon to autochthonous carbonate deposition. Continuous mixing and aeration in shallow lakes facilitate the transformation of organic carbon into 29-45% of sedimentary carbonate, different from large and deep lakes (2-25%). Organic carbon recycling in lakes remains generally stable or decreases under the pressure of lake eutrophication, requiring further investigations on whether more organic carbon will be buried in the carbonate form