Naslov
Orbitally-paced climate evolution from a continental freshwater lacustrine record (Sinj basin, SE Croatia)

Autori
Vranjković, Alan ; Mandic, Oleg ; Lirer, Fabrizio ; de Leeuw, Arjan ; Jimenez-Moreno, Gonzalo ; Sprovieri, Mario ; Harzhauser, Mathias ; Pavelić, Davor ; Krijgsman, Wout ; Kuiper, Klaudia ; Pelosi, Nikola

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Earth system evolution and the Mediterranean area from 23 Ma to the present / Barbieri, Francesco - Parma : Acta Naturalia de 'L'Ateneo Permense', 2009, 36-37

Skup
13th Congress of Regional Committee on Mediterranean Neogene Stratigraphy (RCMNS)

Mjesto i datum
Napulj, Italija, 02.09.2009. - 06.09.2009

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
climate change; cyclostratigraphy; long-lived lakes; Miocene; Dinaride Lake System

Sažetak
The Sinj basin belongs to the southernmost basins of the Miocene Dinaride Lake System. It was formed in a 342 km2 large, rhomboidal, NW-SE elongated pull-apart basin. The basin was initiated in the Early Miocene, following the transpressional regime related to a right-lateral movement along the major northwest-southeast-trending Adriatic strike slip fault system. The basin is located on the Croatian Karst (External) Dinarides. The pre-Neogene basement is dominated by the Adriatic Carbonate Platform rocks along the basin margins, ranging in age from Upper Triassic to Eocene. Extensive Permo-Triassic evaporite deposits with a direct sedimentary contact with the basal lake sediments occur beneath the basin. An about 500 m thick lacustrine succession was logged in the western marginal part of the basin. The section represents almost the complete infill of the Miocene basin. Only the lower- and upper-most intervals lack, due to absence of corresponding outcrops. Integrated Ar/Ar dating and magnetostratigraphic investigation proved the long-levity of the Sinj basin lake environment demonstrating Early to Middle Miocene deposition lasting for more than 2.5 my. The lake sediments are dominated by authigenic carbonates ; the CaCO3 content varies between 82% and 99% ; the siliciclastic input was insignificant. The uppermost 100 m of the section include up to 2 m thick coal seam intercalations, whereas the basal and the middle part of the infill show exclusively carbonate rocks. The whole succession is intercalated occasionally by volcanic ash layers. The initiation of the coal deposition at the top of the section shows a straightforward correlation with the Middle Miocene climate optimum. Bulk samples for stable isotope analyses have been taken at distances of 0.25 m for the organic matter rich topmost 140 m of the section and at distances of 0.5 m for the rest of the section. The results demonstrates wide range of the δ18O (-17, 21 to -1, 8 vs. VPDB) and δ13C (-15, 40 to 2, 80 vs. VPDB) values pointing to great variability of paleoenvironments and processes involved in the isotope fractionation. Particularly, the wide range in δ18O values suggests that the lake waters did vary significantly through time, what is typical of environments without continuous renewal of water and characterized by significant isotope fractionation induced by evaporation. The δ18O and δ13C show both negative excursions at intervals intercalated by lignite seams. In contrast the general upward warming trend preceding the Middle Miocene climate optimum is clearly reflected by the gradual positive shift of the δ18O values. The calibration of the stable isotope curve to the time scale, based on the magnetostratigraphic age model, allows its first order correlation with the 400ky- and 100ky-eccentricity cycles. The stable isotope record provides apparently a straightforward correlation of the identified cycles with the astronomically forced climate fluctuations altering the local balance of precipitation and evaporation. The negative excursions of the curve show thereby the phase relation to eccentricity minima, which is in accordance with the interpretation of δ18O negative shifts reflecting the humidity events and the fresh water input, respectively. Consequently the positive δ18O shifts marking the phases of dry climate and increased lake evaporation show the correlation with the eccentricity maxima. The inferred phase relation stays in perfect accordance with the pollen distribution data available for the upper, coal bearing part of the section. Hence each of the 100ky-eccentricity maxima identified therein from positive stable isotope excursions has its counterpart in one of the single warming events identified by the pollen record.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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