engleski

Upper Palaeozoic sedimantary rocks from Gorski kotar, Croatia: New sedimentological and palaeontological data

Based on the new sedimentological and paleontological data from the region of Gorski kotar, an obvious heterogenity of facies of the Upper Paleozoic rock record has been recognized. The investigated area is located between the well known Paleozoic sediments of the Velebit mountain and Paleozoic rocks of Outer Dinarides in Slovenia. The stratigraphy of the Permian clastic assemblage in Gorski kotar, as well as the interpretation of facies, have long been the matter of the different opinions. During our investigations we recognized up to 300 m thick clastic sequence with thin-bedded blackish shales and micaceous siltstones ; thick-bedded sandstones and quartz rich conglomerates. Limestone rich conglomerates and breccias also appear, but have unraveled position within the investigated sedimentary complex. Permian clastic sedimentary rocks have features of the alluvial fan delta facies, occurring after the uplift, probably in the Saalian phase. Fossiliferous limestones are incorporated in some of the clastic successions in form of the stratified biocalcarenites, or as large blocks, and pebble to cobble sized clasts in limestone rich conglomerates and breccias. The dominating microfossil groups in biocalcarenites and limestone clasts are: foraminifers, algae, calcisponges, echinoids and bryozoans. Determined fossils range from the Upper Carboniferous to the Permian. Among 71 species, 22 are strictly Carboniferous, while 29 show Carboniferous to Permian age, and 20 are Permian in age (most of them typical for the Rattendorf Beds). Nevertheless, we have not found Middle Permian genera typical for the Trogkofel Beds, which have been reported earlier. Fossils younger then Permian have not been found. Although all skeletal fragments have been redeposited, some stratigraphic conclusions can bee inferred. Stratified biocalcarenites reflect the age of the clastic facies they intercalate with, and the whole clastic sequence is surely younger then the youngest fossil found in biocalcarenites. The age of the late Middle Permian, or the beginning of the Upper Permian has been suggested. This proposal is supplemented by the character of sedimentary rocks, which record molase-type sedimentation occurred after the Saalian uplift. Sedimentologically, clastic sediments from Gorski kotar can be compared to the similar clastic Trogkofel succession in Slovenia (Middle Permian in age). Fossil genera determined from clasts in limestone rich conglomerates and breccias show the same age (Carboniferous to Lower Permian), but the recent palynological research of black shales which appear to be matrix, indicates even Carnian age. This presumption is supplemented by signs of at least twice resedimented clasts. This facies need to be more thoroughly investigated.

Permian clastic sedimentary rocks; Alluvial fan delta facies; Carboniferous to Lower Permian fossil association; Gorski Kotar;

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