Naslov
Evaporitic-carbonate deposits of Komiža diapiric structure (Island of Vis, Croatia): their palynostratigraphy and sedimentological features

Autori
Koch, Georg ; Belak, Mirko

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

Izvornik
22nd IAS Meeting of Sedimentology - Opatija 2003 / Vlahović, Igor - Zagreb : Institut za geološka istraživanja, Zagreb, 2003

Skup
22nd IAS Meeting of Sedimentology

Mjesto i datum
Opatija, Hrvatska, 17.09.2003. - 19.09.2003

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
palynostratigraphy; sedimentology; evaporitic-carbonate deposits; Komiža diapiric structure; Vis; Croatia

Sažetak
Komiža - diapiric structure, with its variety of chaotically distributed sedimentary and volcanic rocks, is in the course of investigation within the research project "Basic Geological Map of Republic of Croatia 1:50000". The investigation of Komiža - diapiric structure, being in the past rather controversially interpreted by many researchers, is directed towards the solution of stratigraphical, petrological, sedimentological and structural problems. The investigation is initiated by palynological and sedimentological study of evaporitic-carbonate deposits from the southern part of the structure. In Pištica Bay, an approximately 80m thick section of evaporitic-carbonate deposits is exposed. Lower interval (12m) consists of bituminous, tuffitic, finely laminated dolomicrite, dolomitic limestone, clayey dolomicrite, dolomitic limestone with thin layers of bituminous shale and dolomitic marl and tuffite ; all lithotypes contain secondary gypsum and relicts of anhydrite. Middle interval (48m) is represented by breccia built up of blocks of gypsum with fragments of early diagenetic dolomites, relicts of anhydrite and barite as accessory mineral. Upper interval (20m) is characterized by clayey dolomite, dolomitic marl, tuff, tuffite, dolomitic limestone, siltite ; all lithotypes contain relicts of anhydrite, secondary gypsum and barite as accessory mineral. The whole section is characterized by enterolytic structures and diapiric fracturing. Lower and upper interval contain Late Ladinian palynoflora consisting of Sellaspora rugoverrucata, Kyrtomisporis ervii, Aulisporites astigmosus, Heliosaccus dimorphus, Falcisporites stabilis, Minutosaccus crenulatus, Samaropollenites speciosus, Striatoabieites aytugii, Staurosaccites quadrifidus, Ovalipollis pseudoalatus, Partitisporites novimundanus, Duplicisporites granulatus, Camerosporites secatus and Acritarchs. Reworked palynomorphs are also present: Nuskoisporites sp. (Permian), Densoisporites nejburgii (Scythian-Early Anisian) and thermically more altered Acritarchs than the Late Ladinian ones indicating the source from older sediments. Middle interval is characterized by a transitional, Late Carnian-Early Norian palynoflora consisting of Porcelispora longdonensis, Enzonalasporites vigens., Patinasporites densus., Samaropollenites speciousus, Ovalipollis pseudoalatus, Froelichsporites traversei, Pseudenzonalasporites summus, Camerosporites secatus, Corollina mayeriana and Granuloperculatisporites rudis. This palynorflora reveals higher frequencies of xerophytic elements than the Late Ladian one, thus indicating comparatively somewhat dryer semi-arid climate. According to the described lithological and palynological features, at present two informal lithostratigraphical units may be discerned, i.e. Late Ladinian "Uvala Pištica" and Late Carnian-Early Norian "Uvala Nova Pošta". "Uvala Pištica" unit was deposited within a tidal flat environment where both terrestrial and open sea influences have mixed. Periodical pluvial events enabled the influx of fine organic and inorganic debris into supratidal to intertidal settings where evaporites and carbonates alternate dependent on repeated closures from seawater and evaporation, respectively. "Uvala Nova Pošta" unit was deposited in intertidal, lagoon settings with low terrestrial influence. Conclusion: According to the results obtained from the initial stage of the investigation, evaporitic-carbonate deposits of Pištica Bay section may be divided into two informal lithostratigraphic units, i.e. Late Ladinian "Uvala Pištica" and Late Carnian-Early Norian "Uvala Nova Pošta". Lithologically and palynologically corresponding successions of these two units have been penetrated in deep off-shore exploration well Vlasta-1 (20 km SE from Island of Vis). However, in Vlasta-1 well a thick Latest Ladinian-Middle Carnian salt (halite) body occurs within a continuous Late Ladinian-Norian succession. It is, therefore, suggested that this very salt body has caused the piercing of the diapir up to the surface in the area of Komiža. The salt (halite) deposits must have been also brought out, but on the surface they are easily dissolved and washed out by the action of atmospheric water. This may explain why they are not at present traceable. The chaotically distributed volcanic rocks (predominantly andesites), yet in some places of the Komiža - diapiric structure closely associated with evaporitic-cabonate deposits and other sediments, may well be contemporaneous with the tuff and tuffite bearing "Uvala Pištica" unit. This is consistent with the "aborted rifting" phase of the western Tethys region during the Ladinian period.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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