Naslov
Microfacies analysis and stable isotope record from continental freshwater lacustrine carbonates (early-middle Miocene, Sinj basin, SE Croatia)

Autori
Vranjković, Alan ; Tišljar, Josip ; Dragičević, Ivan ; Pavelić, Davor ; Mandic, Oleg ; Sprovieri, Mario ; Harzhauser, Mathias ; Lirer, Fabrizio ; Tadej, Neven

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

Izvornik
Sedimentary environments of Mediterranean Island(s) / Pascucci, Vincenzo ; Andreucci, Stefano - Sassari : EDES-Editrice Democratica Sarda, 2009, 402-402

ISBN
978-88-6025-123-7

Skup
27th IAS meeting of sedimentology

Mjesto i datum
Alghero, Italija, 20.09.2009. - 23.09.2009

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
microfacies; lacustrine carbonates; stable isotopes; cyclostratigraphy; 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 Croatian Karst (External) Dinarides. The pre-Neogene basement is dominated by the Adriatic Carbonate Platform (AdCP) carbonates along the basin margins, ranging in age from the Upper Triassic to the Eocene. Extensive Permo-Triassic evaporites deposits with a direct sedimentary contact with the basal lake sediments occur beneath the basin. Two partially overlapping sections were logged in detail, representing together a continuous, around 500 m thick record of lacustrine deposits. Their correlation roots in sedimentary cycle pattern and marker bed correspondence. The lake sedimentation is dominated by authigenic carbonates ; the siliciclastic input was insignificant. The uppermost beds include 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. Following to previous study of the topmost, 140 m thick, coal bearing part of the succession, we concentrate now to its middle and lower parts dominated by limestone deposition and including several limestone types. Those limestones are usually light, thin to medium bedded, and commonly soft and porous. The CaCO3 content varies between 82% and 99%, and it primarily refers to the calcite. Sedimentological analysis and petrography made it possible to distinguish five main microfacies types: A – Lime mudstone – consists of very fine-grained micrites. The deposition of the fine-grained components of lacustrine carbonates is dominantly induced by the photosynthetic activity of macrophytes and microphytes. It belongs to deeper and protected lake parts . B - Detrital limestone – during low stands, much of the clastic material may be derived from cannibalizing fringing older lacustrine and/or palustrine beds, now exposed as mud flats and transported by sheet wash. The calcite crystals with organic matter impurities derived from the disintegration of calcified roots – mostly Microcodium. C - Charophycean mudstone or wackstone - contain degraded, and/or carbonized plant remains, plant encrustations, most commonly related to the stems of the submerged Charophytes and fruits and stems of Damasonium plant. Rooted submerged macrophytes indicate a vegetated littoral environment of the carbonate lake. D - Stromatolite bindstone - alternation of thin micritic laminae, and micrite to microsparite laminae containing calcite grains up to 20µm in diameter. Both laminae types contain micrite-calcified microbial filaments about 0.02mm in diameter. E - Gastropod weckstone and coquinas - the association of gastropods, bivalves, ostracods, plant encrustations and predominantly oxidized macrophyte remains suggests a calm, very shallow fresh-water environment of a carbonate lake while coquinas my represent storm deposits. G - Breccia-conglomerate might have been deposited by sporadic fluvial influence. Isotope analyses were carried out on bulk samples representative of the different microfacies. The wide range of the δ18O (-9, 39 to -2, 79 vs. VPDB) and δ13C (-4, 72 to 2, 80 vs. VPDB) values of the lacustrine system reflects the great variability of paleoenvironments and processes involved in 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 characterised by significant isotope fractionation induced by evaporation.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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