Significance of the Badenian petroleum source rocks from the Krndija Mt. (Pannonian Basin, Croatia)

Discovery of petroleum source rocks at surface exposures of the Badenian deposits on northern slopes of the Krndija Mt.  is the first record of petroleum source rocks on a surface outcrop in the Croatian part of the Pannonnian basin. Rocks with increased organic matter content have the characteristics of the prime source rocks. Positive hydrocarbon potential is the consequence of a favorable type of organic facies. Type II kerogen is of mostly marine algal origin, but with somewhat more pronounced terrigenic lipid content. Source rocks are in the immature, diagenetic period of thermal transformation. Genesis of these rocks is related to the reductive depositional environment in a mostly shallow sea, formed in protected lagoons during the Badenian period, which was reconstructed using palaeogeomorphological, paleontological, petrographical and organogeochemical analyses. This new petrological data deserve attention as it points out the need for additional geological-geophysical-geochemical research of the petroleum potential of the Badenian deposits in the broad area around Našice.</p

Activity concentrations and distribution of radionuclides in surface and core sediments of the Neretva Channel (Adriatic Sea, Croatia)

The activity concentrations and the distribution of manmade 137Cs and naturally occurring radionuclides 40K, 238U and 232Th in surface and core sediments of the semi enclosed, river-dominated marine environment of the Neretva Channel were investigated in relation to the sedimentological characteristics and the content of the total organic carbon (TOC). The activity concentrations of radionuclides were determined by gamma spectrometry. Distinct interrelations between sediment properties and spatial distribution of radionuclides were established. The highest accumulation of 137Cs was found close to the river mouth, in the region of intensive deposition of organic matter of terrestrial origin. This finding implies that the river-borne organic material and its deposition processes should be considered as the most important factor controlling distribution of 137Cs in this transitional land-sea environment. The sediment accumulation rates, estimated from distribution of 137Cs in core sediments, were approximately 6 mm y-1 in front of the Neretva River mouth and 4 mm y-1 in the channel area. The spatial distribution of natural 40K and 232Th radionuclides indicates their distinct association with fine-grained sediments. The interrelation of 238U with fine-grained particles was somewhat weaker but still present. The results obtained indicate that the accumulation pattern of natural radionuclides in the Neretva Channel sediments is mainly governed by the deposition of fine-grained material. This study scrutinizes the baseline level for occurring radionuclides and should be used for monitoring and assessing the radionuclide pollution record in the investigated transitional land-sea environment of the Adriatic

Povratak Dinaridima: Nova strukturna koncepcija

Oduvijek su Dinaridi privlačili pozornost na sebe, ne samo zbog njihovih prirodnih ljepota, već i zbog ekonomskog iskorištavanja prirodnih resursa. INA d.d. već preko 50 godina provodi istražne aktivnosti u kopnenom dijelu Dinarida. Iako brojni površinski pokazatelji ukazuju na postojanje aktivnog naftnog sustava, kompleksna geološka građa Dinarida otežava jednostavan, lagan i jeftin istraživački pristup. Novija svjetska iskustva s potvrdama ekonomskih rezervi ugljikovodika i u vrlo složenim borano-navlačnim pojasevima daju novi poticaj u reaktivaciji istraživanja dinaridskog prostora. S obzirom da se niti jedna dosadašnja lokalna strukturno-tektonska koncepcija nije uspjela nametnuti kao primarna, tijekom preliminarnih istraživanja 2020. godine razvijena je nova koncepcija rotacijskih blokova nastalih dezintegracijom nekadašnje „Lapačke“ antiklinale. Dezintegracija je uzrokovana reaktivacijom Unskog rasjeda od oligo-miocena do danas. Kretanje rotacijskih blokova potpomognuto je permo-trijaskim evaporitima, koji osim što su klizne plohe, mogu biti i pokrovne stijene. Zamke formirane u podnavlačnim sustavima mogu sadržavati ugljikovodike migrirane prvenstveno iz gornjojurskog lemeškog facijesa, najboljih matičnih stijena šireg područja Dinarida. Ovakvo geološko okruženje usmjerava istražne aktivnosti ka multidisciplinarnom integralnom pristupu kao temelju suvremenog istraživanja ugljikovodika

Stabilization of Drill Cuttings Contaminated with Waste Mud

U hrvatskoj naftnoj industriji godišnje se proizvodi značajna količina krhotina razrušenih stijena. Krhotine razrušenih stijena zagađene su otpadnom isplakom te spadaju u heterogeni otpad koji sadrži ugljikovodike, teške metale i kloride. Trenutačno se kao metoda zbrinjavanja krhotina primjenjuje metoda stabilizacije uz pomoć vapna i pijeska. Opisan je postupak pripreme stabiliziranog otpada u laboratorijskim uvjetima na dva uzorka krhotina iz isplačnih jama s područja Dravske depresije. Prije pripreme stabiliziranog otpada u laboratorijskim uvjetima, u početnom uzorku otpada određen je udio organske tvari dobiven ekstrakcijom s organskim otapalom te sadržaj ukupno topljive tvari u vodi. Na temelju te dvije osnovne analize određena je količina vapna i pijeska potrebna za izradu stabiliziranog otpada. Fizikalno-kemijske značajke početnog i stabiliziranog otpada analizirane su primjenom standardnih laboratorijskih metoda. Rezultati su pokazali da miješanje otpada s vapnom i pijeskom omogućuje prevođenje početnog uzorka otpada klasificiranog kao opasan otpad u neopasan otpad. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.In the Croatian oil and gas industry, significant quantities of drill cuttings are produced annually. The drill cuttings are contaminated with waste mud being heterogeneous waste which comprises hydrocarbons, heavy metals and chlorides. Currently, the treatment option for these drill cuttings is stabilization method using lime and sand as binder. The procedure of stabilized waste preparation in laboratory conditions on two samples of drill cuttings from Drava Depression is described. Prior to the stabilization test under laboratory conditions, it was necessary to determine the content of organic matter in the initial waste sample using organic solvent extraction method, and the content of total soluble matter in water. On the basis of these two parameters, the amount of lime and sand required to produce stabilized waste were determined. Initial and stabilized waste samples were analysed according to standard methods. The results indicated that the process of stabilization of waste using lime and sand enabled the transformation of an initial waste sample classified as hazardous waste into non-hazardous waste. This work is licensed under a Creative Commons Attribution 4.0 International License

Correlation of upper Miocene–Pliocene Lake Pannon deposits across the Drava Basin, Croatia and Hungary

Upper Miocene to Pliocene (Pannonian) sediments of the Pannonian Basin System accumulated in the brackish Lake Pannon and the fluvial feeder systems, between 11.6-2.6 Ma. Their stratigraphic subdivision has been problematic for a long time due to the laterally prograding architecture of the basin fill and the historically independently evolving stratigraphic schemes of the neighbouring countries. We correlated the lithostratigraphic units of the Lake Pannon deposits between Hungary and Croatia in the Drava Basin, using lithological, sedimentological and palaeontological data from boreholes and outcrops, and seismic correlation. The Croatica and Medvedski breg formations in Croatia correspond to the Endrőd Fm. in Hungary, comprising shallow to deep water, open lacustrine, calcareous to argillaceous marls. The Andraševec fm. in Croatia corresponds to the Szolnok and Algyő Fms. in Hungary, consisting of sandstones and siltstones of turbidite systems and of clay marls deposited on the shelf-break slope. The Nova Gradiška fm. in Croatia is an equivalent of the Újfalu Fm. in Hungary, built up of a variety of lithologies, including sand, silt, clay and huminitic clay, deposited in deltaic environments. The Pluska fm. in Croatia corresponds to the Zagyva Fm. in Hungary, consisting of variegated clays, silts, sands and lignites, deposited in alluvial and fluvial environments. Coarse-grained (sand, gravel) basal layers are assigned to the Kálla and Békés Fms. and the Sveti Matej member of the Croatica fm. Coarse-grained intercalations within the deep-water marls belong to the Dorozsma Member of the Endrőd Fm. in Hungary, and to the Bačun member of the Medvedski breg fm. in Croatia. Sediment transport and lateral accretion of the shelf edge in the Drava Basin took place from the N, NW, and W, to the S, SE, and E, respectively. According to the biostratigraphic and chronostratigraphic analyses, the oldest shelf-break slopes in the Mura Basin are more than 8 Ma old, whereas the youngest ones in the southeasternmost part of the Drava Basin may be Pliocene in age (younger than 5.3 Ma). Thus, the 180 km long and at least 700 m deep Drava Basin was transformed into a fluvial plain during the last 3.5 million years of the Miocene.</p

Comparison between the Middle Miocene and the Upper Miocene source rock formations in the Sava Depression (Pannonian Basin, Croatia)

The Sava Depression lies at the very south-western margin of the Pannonian Basin. There are 20 hydrocarbon fields altogether and 17 are still in production. The organic geochemistry data and their statistical analysis from the 25 exploration wells, indicate source rock formations in two stratigraphic levels, an older one of Middle Miocene age (Badenian and Sarmatian) and a younger one of Upper Miocene age (Lower Pannonian). Both source rock formations are composed of marls, calcitic marls, clayey limestones and shales. Source rock intervals lay at depths from 1200 to 3362 m. The Total Organic Carbon (TOC) of analyzed samples varies from 0.39 to 4.94%, while their total generative hydrocarbon potential is from 2.40 to 37.40 mg HC/g rock. The mean thickness of the intervals is 100–150 m. There is a regular linear increase of the maturity level with depth. Source rocks are mature, in the catagenetic phase of transformation that enables hydrocarbon generation. A favourable organic facies, mostly kerogen type II, (organic facies AB and B), with good hydrocarbon potential, dominates the north-western and central part of the depression. It can be connected with the deeper parts of the depression and/or protected, anoxic to dysoxic stagnant environments with a gradual transition from marine (Badenian/Sarmatian) to brackish depositional environments (Lower Pannonian). In the south-eastern part of the depression, the dominant kerogen type is II–III, (organic facies BC), which indicates a stronger influx of terrestrial material from the uplifted parts that are generally closer to the margins of the depositional basin. The Fisher test (F-test) of the variance similarity (homogeneity), clearly indicates that the Badenian/Sarmatian samples belong to a statistically different population from the Lower Pannonian ones, due to their different depositional environments.</p

Formation of the authigenic cements in aquatic sediments through precipitation processes at the nanoscale - isotopic and FESEM study

The traditional view on carbon cycle assumes that CO2 is removed from the atmosphere by two major sinks, i.e. oceans and the biosphere. Terrestrial carbon sink in cements precipitated from groundwater, from interstitial water in recent sediments or from surface water (tufa) has been largely underestimated or neglected. Recent studies showed, however, that the magnitude of authigenic carbonate precipitation might be immense, so that it can be considered as the third major global C sink. Knowing this, the importance of identification and quantification of secondary carbonate becomes apparent on local, regional and global scale. While quantification of carbonate cements is rather simple in siliciclastic sediments, it remains challenging in carbonaceous environments. Isotopic tools were proven to be efficient for differentiation between primary (marine) carbonate and authigenic cements produced in organic-rich sediments or from terrestrial groundwater. The C isotopic composition of marine carbonate (limestone, dolostone) differs significantly from that precipitated from highalkalinity interstitial solutions where the dissolved inorganic carbon derives at least in part from the decomposition of organic matter. Namely, organic tissues are depleted in 13C compared to marine and atmospheric CO2 because of preferential uptake of isotopically light C from the environment and complex isotope fractionation accompanying biological processes. Our study deals with precipitation of authigenic carbonate in recent aquatic carbonaceous sediments formed on karstic terrains in a range of environments – from freshwater (lacustrine tufa, Krka river), transitional (Neretva river delta), to marine lakes and coastal marine sediments (islands of Mljet and Dugi otok, Croatia). We analysed isotopic, geochemical and morphological characteristics of sedimentary carbonate and organic matter, and using isotopic tools, assessed the transfer of carbon between dissolved and solid pool. The CO2 cycling in lakes and reservoirs, as well as organic rich marine sediments was largely dominated by biological and biogeochemical processes. Diagenetic degradation of sedimentary organic matter represents a complex suite of microbially-mediated and abiotic processes, that mineralise organic carbon to the CO2 or CH4, which undergo further processing by microbial communities and provide a source of dissolved inorganic carbon for precipitation of carbonate cements. However, in organic-rich sediments with multiple C sources (soil, lithic carbonate, land vegetation, aquatic biota) and changing redox conditions, the isotopic signatures of dissolved carbonate vary not only because of different C sources, but also because of complex diagenetic processes that remove or add dissolved inorganic carbon (DIC) from/to the interstitial solution, and fractionate DIC isotopes either in same or in different directions (i.e. toward more positive or more negative δ values). At the same time, the C isotope fractionation during precipitation of calcite remains rather stable irrespective of the temperature and precipitation rate and authigenic carbonate reflects the isotopic composition of DIC (δ13C) within approximately ±1 ‰. Therefore, the C isotopic composition of authigenic carbonate in organic-rich sediments is not unique or exclusive for a certain environment, but depends on the combination of processes that simultaneously or consecutively affect the concentration and δ13C of DIC. Therefore, additional identifiers of authigenic carbonate in freshwater sediments from carbonaceous settings are necessary for its unequivocal identification and quantification. Acknowledgments This study was funded by the Croatian Science Foundation (project 2504 NanoMin - Nanominerals in sediments and soils: formation, properties and their role in biogeochemical processes), Slovenian Research Agency (programme P1-0143) and European Commission (Horizon 2020, project MASSTWIN - Spreading Excellence and widening participation in support of mass spectrometry and related techniques in health, the environment, and food analysis, grant agreement No. 692241)

Formation of the authigenic cements in aquatic sediments through precipitation processes at the nanoscale - isotopic and FESEM study

The traditional view on carbon cycle assumes that CO2 is removed from the atmosphere by two major sinks, i.e. oceans and the biosphere. Terrestrial carbon sink in cements precipitated from groundwater, from interstitial water in recent sediments or from surface water (tufa) has been largely underestimated or neglected. Recent studies showed, however, that the magnitude of authigenic carbonate precipitation might be immense, so that it can be considered as the third major global C sink. Knowing this, the importance of identification and quantification of secondary carbonate becomes apparent on local, regional and global scale. While quantification of carbonate cements is rather simple in siliciclastic sediments, it remains challenging in carbonaceous environments. Isotopic tools were proven to be efficient for differentiation between primary (marine) carbonate and authigenic cements produced in organic-rich sediments or from terrestrial groundwater. The C isotopic composition of marine carbonate (limestone, dolostone) differs significantly from that precipitated from highalkalinity interstitial solutions where the dissolved inorganic carbon derives at least in part from the decomposition of organic matter. Namely, organic tissues are depleted in 13C compared to marine and atmospheric CO2 because of preferential uptake of isotopically light C from the environment and complex isotope fractionation accompanying biological processes. Our study deals with precipitation of authigenic carbonate in recent aquatic carbonaceous sediments formed on karstic terrains in a range of environments – from freshwater (lacustrine tufa, Krka river), transitional (Neretva river delta), to marine lakes and coastal marine sediments (islands of Mljet and Dugi otok, Croatia). We analysed isotopic, geochemical and morphological characteristics of sedimentary carbonate and organic matter, and using isotopic tools, assessed the transfer of carbon between dissolved and solid pool. The CO2 cycling in lakes and reservoirs, as well as organic rich marine sediments was largely dominated by biological and biogeochemical processes. Diagenetic degradation of sedimentary organic matter represents a complex suite of microbially-mediated and abiotic processes, that mineralise organic carbon to the CO2 or CH4, which undergo further processing by microbial communities and provide a source of dissolved inorganic carbon for precipitation of carbonate cements. However, in organic-rich sediments with multiple C sources (soil, lithic carbonate, land vegetation, aquatic biota) and changing redox conditions, the isotopic signatures of dissolved carbonate vary not only because of different C sources, but also because of complex diagenetic processes that remove or add dissolved inorganic carbon (DIC) from/to the interstitial solution, and fractionate DIC isotopes either in same or in different directions (i.e. toward more positive or more negative δ values). At the same time, the C isotope fractionation during precipitation of calcite remains rather stable irrespective of the temperature and precipitation rate and authigenic carbonate reflects the isotopic composition of DIC (δ13C) within approximately ±1 ‰. Therefore, the C isotopic composition of authigenic carbonate in organic-rich sediments is not unique or exclusive for a certain environment, but depends on the combination of processes that simultaneously or consecutively affect the concentration and δ13C of DIC. Therefore, additional identifiers of authigenic carbonate in freshwater sediments from carbonaceous settings are necessary for its unequivocal identification and quantification. Acknowledgments This study was funded by the Croatian Science Foundation (project 2504 NanoMin - Nanominerals in sediments and soils: formation, properties and their role in biogeochemical processes), Slovenian Research Agency (programme P1-0143) and European Commission (Horizon 2020, project MASSTWIN - Spreading Excellence and widening participation in support of mass spectrometry and related techniques in health, the environment, and food analysis, grant agreement No. 692241)

Restricted to open-marine Middle Triassic basins of the Dinarides and their radiolarian faunas

Late Anisian rifting resulted in a complex horst-and-graben paleotopography of the Adriatic continental margin. The most deeply subsided basins (e.g. Budva, Bosnian and Slovenian basins) remained sites of pelagic sedimentation until the latest Cretaceous. Shallower basins formed on structural highs, which were internally differentiated into several fault blocks. These shallow basins were short lived, limited to the interval between the Late Anisian to Ladinian or earliest Carnian, when they were completely filled in so that sedimentation of platform carbonates was again established in a wider area. The High Karst Zone in the External Dinarides preserves two types of sequences from this short pelagic episode. Both are characterized by micritic limestone and chert, generally include pyroclastic rocks (Pietra Verde), and locally contain carbonate breccia and calcarenite. The most obvious difference is the color of the rocks. The successions in the center of the High Karst Zone are dark grey to black due to the presence of organic matter, which may have been related to stratified water column and/or poor open-marine connections in a restricted intra-platform basin. In contrast, the pelagic limestone and chert at the margins of the High Karst swell are light to vivid red, in places greenish or light grey to pink. This latter lithology is comparable with the Buchenstein Formation of the Southern Alps. We investigated radiolarians from several Buchenstein type sections and from one organic-matter-rich section located at Mt. Svilaja in Dalmatia. The radiolarian assemblages of the Buchenstein type sections contain up to 80 genera and include multicyrtid nassellarians that are generally regarded as deeper-dwelling morphotypes and are also common in the sedimentary cover of Triassic ophiolites. The radiolarian assemblage of Mt. Svilaja consists of only 20 genera. Spumellarians and entactinarians are abundant but nassellarians account for only 5% and are represented exclusively by monocyrtids. A similar assemblage was described from the San Giorgio Dolomite in the westernmost part of the Southern Alps. Such impoverished assemblages with high predominance of surface-dwelling taxa are apparently characteristic of restricted oxygen-deficient basins that were separated from the open ocean by topographic barriers

Restricted to open-marine Middle Triassic basins of the Dinarides and their radiolarian faunas

Late Anisian rifting resulted in a complex horst-and-graben paleotopography of the Adriatic continental margin. The most deeply subsided basins (e.g. Budva, Bosnian and Slovenian basins) remained sites of pelagic sedimentation until the latest Cretaceous. Shallower basins formed on structural highs, which were internally differentiated into several fault blocks. These shallow basins were short lived, limited to the interval between the Late Anisian to Ladinian or earliest Carnian, when they were completely filled in so that sedimentation of platform carbonates was again established in a wider area. The High Karst Zone in the External Dinarides preserves two types of sequences from this short pelagic episode. Both are characterized by micritic limestone and chert, generally include pyroclastic rocks (Pietra Verde), and locally contain carbonate breccia and calcarenite. The most obvious difference is the color of the rocks. The successions in the center of the High Karst Zone are dark grey to black due to the presence of organic matter, which may have been related to stratified water column and/or poor open-marine connections in a restricted intra-platform basin. In contrast, the pelagic limestone and chert at the margins of the High Karst swell are light to vivid red, in places greenish or light grey to pink. This latter lithology is comparable with the Buchenstein Formation of the Southern Alps. We investigated radiolarians from several Buchenstein type sections and from one organic-matter-rich section located at Mt. Svilaja in Dalmatia. The radiolarian assemblages of the Buchenstein type sections contain up to 80 genera and include multicyrtid nassellarians that are generally regarded as deeper-dwelling morphotypes and are also common in the sedimentary cover of Triassic ophiolites. The radiolarian assemblage of Mt. Svilaja consists of only 20 genera. Spumellarians and entactinarians are abundant but nassellarians account for only 5% and are represented exclusively by monocyrtids. A similar assemblage was described from the San Giorgio Dolomite in the westernmost part of the Southern Alps. Such impoverished assemblages with high predominance of surface-dwelling taxa are apparently characteristic of restricted oxygen-deficient basins that were separated from the open ocean by topographic barriers