Middle Triassic arc-related extensional tectonics in the western Tethys generated a complex pattern of intraand backarc basins. We studied volcano-sedimentary successions of subsided continental-margin blocks (Mts.

This paper presents the results of fractal analysis of fracture systems in upper Triassic dolomites in Žumberak Mountain, Croatia. Mechanical rock characteristics together with structural and diagenetic processes result in fracture systems that can be considered as fractals. They are scale-invariant in a specifi c range of scales. The distribution of fractures can be described with power law distribution and fractal dimension. Fractal dimension is a measure of how fractures fi ll the space. Fractal dimension can be estimated from photographs of outcrops by converting photographs to binary photographs. Binary photo display only black (rock or fractures) and white (fractures or rock). Fractal dimension is then estimated based on the box-counting method. In this paper, we present results of fractal analysis from three outcrops. The results are very similar to previously published results from outcrops of dolomites in Slovenia. The obtained fractal dimensions are in the range 2,69-2,78 and depend on how fracture systems are distributed in the outcrop. Lower values indicate a smaller number of fractures and a higher signifi cance of larger fractures. Higher values indicate the distribution of more similarly sized fractures throughout the whole outcrop. Fractal dimension is a very signifi cant parameter and in the rock fracture system characterisation sense, it describes how fractures are distributed in the outcrop. It can be used in discrete fracture network modelling if spatial distribution of fractures is represented with power law distribution.

Travertines and calcareous tufa are porous deposits formed by interactions between ambient precipitation of calcium carbonate and resident organisms under different temperature regimes. The distinctions between travertine as thermal spring deposits and calcareous tufa (Kalktuff) as deposits in the springs and rivers at ambient temperatures are fluid. Both represent end points in bio- and physico-chemical calcification processes across a broad gradient of temperature, mineral composition and ion saturation levels. Ecological preferences of micro- and macroorganisms in travertine depositional systems result in the re-distribution of water flow, modification of the landscape and its ecology. The resulting sedimentary structures include new environmental settings with different and diversified biota. They also include different microenvironments of diagenesis with different timings of the processes involved. Conditions in modern ambient temperature travertines of the Plitvice system of lakes and waterfalls are compared with the similar, ancient system of Rocchetta a Volturno, in the central Apennines. Diagenetic alterations are described and illustrated starting with biologically identified primary deposits.

Karst aquifers are important sources of thermal and groundwater in many parts of the world, such as the Alpine–Dinaric–Carpathian region in Europe. The Upper Triassic dolomites are regionally recognized thermal and groundwater aquifers but also hydrocarbon reservoirs. They are characterized by predominantly fractured porosity, but the actual share of depositional and diagenetic porosity is rarely investigated. In this research, we presented the geometric characterization of the measured microporosity of the Upper Triassic dolomites of the Žumberak Mts (Croatia), through thin-section image processing and particle analysis techniques. Pore parameters were analyzed on microphotographs of impregnated thin sections in scale. A total of 2267 pores were isolated and analyzed. The following parameters were analyzed: pore area, pore perimeter, circularity, aspect ratio (AR), roundness, solidity, Feret AR, compactness, and fractal dimension. Furthermore, porosity was calculated based on the pore portion in each image. The effective porosity on rock samples was determined using saturation and buoyancy techniques as an accompanying research method. We analyzed distributions of each parameter, their correlation, and most of the parameters are characterized by an asymmetric or asymmetric normal distribution. Parameters that quantify pore irregularities have similar distributions, and their values indicate the high complexity of the pore geometry, which can significantly impact permeability.

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Investigations of fossil algae in Croatia began in 1907 with the very first description of the Permian dasyclad Mizzia velebitana from Mt. Velebit by Austrian geologist Richard Schubert. This was followed by Julius Pia’s investigations (1920, 1925), on material given to him by Schubert. The first Croatian researcher on fossil algae was Milan Herak, Pia’s PhD student, with his first paper on Ladinian dasyclads published in 1950. He cooperated with a colleague from the Faculty of Science, Vanda Kochansky-Devidé, who published her first papers together with Herak on Permian and Carboniferous dasyclads in 1959 and 1960. While Herak focused on Triassic algae, Kochansky-Devidé investigated mostly Upper Palaeozoic algae and fusulinid foraminifera. Ivan Guši? comes from the same faculty, and his first paper was published in 1966. Mom?ilo Milanovi?, from the Institute of Geology (the present day Croatian Geological Survey), published his first paper in 1962, focusing mainly on Permian algae. The most prolific researcher Branko Soka? also came from the Institute of Geology; his first papers dated from 1964, and he is still an active researcher. Over time, papers originating from the “Zagreb Algological School” become distinguished by rich and well illustrated fossil material, making numerous contributions to the better understanding of fossil benthic algae from younger Palaeozoic and Mesozoic strata. This was possible not only because of the diligence of the authors, but was also the result of the very thick and well exposed carbonate sequence of the Croatian Dinarides Mts. Rajka Radoi?i? from Beograd (Serbia) also described some taxa from Croatia. Almost all the research refers to dasycladal algae, while other algae are only rarely investigated. Complete references to all papers are given.

Clypeina lagustensis n. sp. has been found in the Lower Tithonian deposits of Lastovo Island (Dalmatia, Croatia). It is visually similar, obviously related and in some sections appears almost identical, to Clypeina jurassica FAVRE, from which it differs by visible swellings and thinning of the central cavity, more pronounced distance between the neighbouring whorls of fertile laterals, and in the shape and structure of the interverticillate thallus parts, characterized by having well developed, hairy, sterile laterals. These, after emerging from the exit pore, divide into several bundles which form a common tuft with a calcareous envelope in the proximal part.

Montegrella? gracilis n.sp. (Dasycladales) is characterized by a thick calcareous envelope and narrow central cavity. Branches display two orders of laterals with alternate arrangement between consecutive whorls. The primaries are visibly differentiated into a thin, tendril-like stalk in the proximal part and a club-shaped or ellipsoidal inflated swelling in the distal part. The secondaries are poorly visible, of unclear shape and number, with a supposedly common starting point. In the type-locality, the alga occurs within a rich, typically Upper Barremian, algal assemblage. The validity of the genus Montenegrella, being disputed by BARATTOLO (1983), is commented upon by showing the generic attribution of the same or different species either to Suppiluliumaella or to Montenegrella by different authors.