Naslov
Resedimented Carboniferous and Lower Permian radiolarians in Roadian (Middle Permian) deepwater clastic complex of Gorski Kotar Region (Croatia)

Autori
Aljinović, Dunja ; Kozur, W. Heinz

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

Izvornik
: 22nd IAS Meeting of Sedimentology - Opatija 2003: Abstracts / Vlahović, Igor - : Institut of Geology Zagreb, 2003, 4-4

Skup
22nd IAS Meeting of Sedimentology - Opatija 2003

Mjesto i datum
Opatija, Hrvatska, 17.09.2003. - 19.09.2003

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
Carboniferous and Lower Permian radiolarians; Roadian (Middle Permian); petromyctic conglomerats; gravelly mudstones coarse-grained sandstones;

Sažetak
The Permian sedimentary complex in central part of Gorski Kotar region (near Mrzla Vodica) consists of orthoquartzitic and petromyctic conglomerate types, coarse-grained sandstones, gravelly mudstones and occasionally calcirudites that exchange vertically with thin-bedded, partly turbiditic sandstones and shales (occasionally calclithite) composing meter-scale fining upward cycles. Several conglomerate and coarse-grained sandstone types can be found in the lower part of cycles, predominantly as massive clast-or matrix-supported and normally graded conglomerates. Orthoquarzitic types consist mostly of well-rounded quartzite grains. Petromyctic conglomerates embraced clasts of various rock types: limestone, sandstone, chert and older conglomerates as well as rafts of shale. Sandstones are quartz-rich, thick-bedded and massive. Gravely mudstones appear randomly in the lower part of the cycles and contain chaotic distribution of badly sorted mostly limestone and lesser sandstone and quartz detritus that range from granule to boulder size, scattered in shale. Granule size material usually forms contorted, slump-likestructures. In muddy matrix abundant crinoid fragments have been found. Calcirudites occurred occasionally as lensoid beds and are characterised by tightly package of partly rounded limestone clasts in lower part of the beds and gradual increase of pelitic matrix (shale) upwards.Coarse-grained clastic sediments were deposited as a consequence of redepositon and unstable environmental conditions linked with the tectonic activity at an active margin of a deep water basin. Sediment characteristics suggest deposition due to emplacement of mud rich debris flows or high-density turbidity flows that prograded to a deeper part of the basin.Channel-like shape of calcirudites permits the assumption of chutes formed at the steep slope adjacent to the exposed land areas from where the coarse grained material has been derived. The deposition of coarse material was probably restricted to chutes and scarps formed due to sliding while sandstone-shale association could be considered as a background sediment deposited aside the chutes and in flattened slope toe. The slump-like contortion in the gravelly mudstones indicate steep palaeorelief. The complete succession exceeds the thickness of 1000 m, characterised by an upward shallowing of the environment. In the upper part of the section the abundant fairly preserved large plant stems or scattered plant detritus accumulated sporadically suggest coastal environments. In shale interbeds crinoid ossicles and ammonites can be found. The ammonoids, among them Bamyaniceras sp.indicate a Roadian age of the discussed sequence (determination and age assignment Dr.sc.Leonova, Mos- cow, pers.com.). Among large clasts (blocks)from gravelly mudstones some micritic limestone types contain pyritised radiolarians of Carboniferous and Early Permian age. Several taxa have been documented: the Late Pennsylvanian to Asselian Parafollicucullus ?annulata (Ishiga), the Asselian Curval-baillella uforma (Holdsworth &Jones) morphotype 1, the Sakmarian Curvalbaillella n.sp.(=C .uforma, morphotype 2), the Sakmarian Pseudoalbaillella simplex (Ishiga & Imoto), and Phaenicosphaera sp. Asselian and Sakmarian radiolarian faunas were surely present, but faunas which consists only of P. annulata probably belong to the Late Pennsylvanian. Radiolarians have also been found in calcilithites. All radiolarian faunas from reworked clasts are strongly dominated by Albaillellaria. Such faunas indicate water depth below 500 m. Black cherts yielded thermally altered (CAI 5) Lower Carboniferous conodonts, among them Gnathodus bilineatus (Roundy). The discovery of radiolarians and conodonts have wider implications to the geodynamic evolution of the western part of Palaeotethys during Early Carboniferous to early Middle Permian (Roadian)time. The Mississippian cherts indicate oceanic sedimentation below the CCD. The Late Pennsylvanian to Sakmarian Albaillellaria-dominated limestones indicate deep pelagic environments below 500 m water depth but above the CCD. Deep water, but distinctly shallower, are the ammonoid faunas of the Roadian shales. In the trace fossil association all those ichnotaxa are absent which dominate the Palaeotethyan abyssal to bathyal upper Artinskian to Kungurian deep-sea flysch of western Sicily (e.g., Agrichnium, Megagrapton, Paleodictyon). Ammonoids do not occur in water depths below 500 m. On the other hand, all ammonoid shells are dissolved, indicating water depth below the Aragonite Compensation Depth. Water depths around 300 m are assumed for the ammonoid-bearing Roadian shales.The long-lasting deep water conditions and the sedimentologic character indicate that not a short-lived rift basin was present in the Gorski Kotar area. We interpret the Permian sequence of Gorski Kotar as deposits of the northern active margin of the Palaeotethys, possibly a forearc basin. As around the entire Apulian promontory, from western Sicily to Gorski Kotar, the Palaeotethys closed at the end of the Roadian (Middle Permian).This was accompanied by a shallowing and final disappearance of the forearc basin.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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