microfacies and organic geochemistry of the Late Triassic Tor formation (Stože, NW Slovenia)

Profil Stože se nahaja ob gorski cesti od Loga pod Mangartom proti Mangartskemu sedlu, ki poteka tik ob slovensko-italijanski meji. V profilu Stože je razgaljen srednji in zgornji del zgornjekarnijske Tor formacije in spodnji del Portella dolomita. Raziskoval sem mikrofacies, organsko geokemijo, stabilne ogljikove in kisikove izotope karbonatnega matriksa. Na podlagi litoloških značilnosti sem profil razdelil na 4 deleod spodaj navzgor si sledijo: litofacies 1 % bioklastični apnenci z glinavci, litofacies 2 % mikritni bioturbirani apnenci, laporasti apnenci, laporovci in glinavci, litofacies 3 % bioklastični apnenci in laporovci in litofacies 4 % debeloplastnati do masivni dolomit - Portella dolomit. Bioklastični apnenci v litofaciesu 1 so tipa rudstonesestavljajo jih školjčni drobir, ehinodermi in foraminifere. V litofaciesu 2 prevladujejo bioturbirani apnenci tipa mudstone do wackestone ter redke plasti apnencev tipa grainstone, ki so dobro sortirani in so sestavljeni iz peloidov in prekristaljenih zrn. V litofaciesu 3 dobimo apnence tipa wackestone do packstone, ki jih grade večinoma školjčni drobir, gastropodi in ostrakodi ter posamezne apnence tipa grainstone. Tor formacija se je odlagala na mešano karbonatno-siliciklastični rampi. Prevladovala je večinoma mirna sedimentacija, ki so jo prekinjali nevihti dogodki. Diagenetski vpliv v profilu Stože je glede na vitrinitno odsevnost 0.5% nizek. V določenih primerih so se odložili organsko bogati glinavci. Organska snov je nezrela oziroma polzrela. Na podlagi biomarkerjev sem ugotovil, da je bil prisoten znaten terestrični dotok. Kisikove izotopske vrednosti se gibljejo med -5 in -1.5 % (VPDB) in kažejo na diagenetsko preobrazbo tekom pozne diageneze. Druge triasne izotopske vrednosti, ki imajo vrednosti okoli 0 % (VPDB), so precej višje v primerjavi z vrednostmi profila Stože in nosijo primarni izotopski signal. Vrednosti ogljikovih izotopov imajo konstantne vrednosti med 2.5 in 3 %. Izjema je negativni odklon pri 55. metru. Konstantne vrednosti kažejo, da ni bilo višjega organskega vnosa v sedimentacijsko okolje.The Stože section is located at the mountain road from Log pod Mangartom towards the Mangart saddle near the Slovenian-italian border. The Stože section exposes middle and upper part of the Late Carnian Tor Formation and the lower part of the Portella Dolomite. Microfacies, organic geochemistry, stable oxygen and carbon isotopes of the bulk carbonate matrix were investigated. On the basis of lithological characteristics the whole section was divided into 4 parts: lithofacies 1 % bioclastic limestone and shale, lithofacies 2 % micritic bioturbated limestone, marly limestone, marl and shale, lithofacies 3 % bioclastic limestone and marl and lithofacies 4 % bedded to massive dolomite % the Portella Dolomite. The Lithofacies 1 is characterized by rudstone, which is composed of bivalves, echinoderms and foraminifera. The Lithofacies 2 is dominated by bioturbated mudstone to wackestone. They are rarely intercalated with grainstone, which is composed of peloids and recrystallized grains. Lithofacies 3 is characterized by wackestone to packstone, composed of bivalves, gastropods and ostracods. Some grainstone occurs as well. The Tor Formation was deposited on a shallow mixed siliciclastic-carbonate ramp. It was characterized by calm sedimentation, which was interrupted by storm events. Siliciclastic rocks have terrestrial source, which is also evident in the terrestrial organic input - biomarkers. The diagenetic overprint of the Stože section is low in respect to vitrinite reflectance of approximately 0.5%. Organic rich shales have been deposited in cases. Organic matter is of immature to submature stage. Oxygen isotope values ranging from -5 to -1.5% (VPDB) point to a deep burial alteration. Other Triassic isotope data (primary isotope signal) have values around 0%, which are higher compared to values of the Stože section. The oxygen values of Stože section have been depleted during the deep burial. Carbon isotope values are ranging between 2.5 and 3 % (VPDB) with a significant negative excursion at the 55 metre. The constant carbon values indicate that there has been no significant organic input in the depositional environment