Josip Tišljar

Carbonate Platform Megafacies of the Jurassic and Cretaceous Deposits of the Karst Dinarides

Platform carbonate deposits of the Karst Dinarides area have a stratigraphic range from the Middle Triassic (or even Carboniferous in some places) to the Middle Eocene, forming a belt nearly 700 km long and, (after reduction by younger tectonics) 80–210 km wide. Besides their significant thickness (4500 to 8000 m) they are characterised by frequent lateral and vertical alternations of different facies, mostly associated with shallow marine environments. Environments ranging from peritidal through low-energy shallow subtidal–lagoons, restricted inner platform shallows, high-energy tidal bars, beach and shoreface to reefal–perireefal predominate, but there are also carbonate slope deposits and those representing temporarily drowned platform facies and intraplatform troughs. The Jurassic to Cretaceous part of this carbonate succession has been subdivided into 19 megafacies units (9 for the Jurassic and 10 for the Cretaceous), the majority of which represent an inner part of the ancient Adriatic Carbonate Platform. Marginal parts of the platform are mostly buried, either by the recent Adriatic Sea along the SW margin, or younger deposits along the NE margin; at some localities such Jurassic and Cretaceous deposits are represented by debrites and/or carbonate turbidites. An additional short review of the overlying Uppermost Cretaceous and Palaeogene deposits (4 megafacies units) enabled a better insight into the post-platform evolution. The very complex vertical and lateral alternation of different megafacies units, including emerged areas which were observed throughout the studied sequence in different parts of the Karst Dinarides, indicate the significant palaeogeographic dynamics of the region. This variability resulted from interaction of the global eustatic signal and local factors, including extensive organic production on the carbonate platform and synsedimentary tectonics controlled by the specific palaeogeographic position of the platform during its geological history.

Eocene Limestones Overlying Lower Cretaceous Deposits of Western lstria (Croatia): Did Some Parts of Present lstria Form Land During the Cretaceous?

In the region of the western Istrian anticline, erosional remains of the transgressive Eocene Foraminiferal limestones overly shallow water deposits of Early Cretaceous age (Valanginian, Hauterivian and Barremian). This evidence, together with the ocurrencc of bauxite deposits and Palaeogene beds overlying Albian, Cenomanian and Senonian limestones indicate the very high relief of the land transgressed by the Palaeogene sea. Contrary to the traditional connection beetween formation of the western Istrian anticline and the Laramian tectonic phase at the end of the Cretaceous (Maastrichtian), new investigations suggest sporadic tectonic movements with constant tectonic coordinate orientation from the Hauterivian to the end of the Cretaceous. With these movements, formation of the anticline structure began in the Early Cretaceous, with the emerged apical parts representing land areas throughout most of the Cretaceous.

Carbonate facies evolution from the late albian to Middle Cenomanian in Southern Istria (Croatia): influence of synsedimentary tectonics and extensive organic carbonate production

SummaryDuring the Late Albian, Early and Middle Cenomanian in the NW part of the Adriatic Carbonate Platform (presentday Istria) specific depositional systems characterised by frequent lateral and vertical facies variations were established within a formerly homogeneous area, ranging from peritidal and barrier bars to the offshore-transition zone. In southern Istria this period is represented by the following succession: thin-bedded peritidal peloidal and stromatolitic limestones (Upper Albian); well-bedded foreshore to shoreface packstones/grainstones with synsedimentary dliding and slumping (Vraconian-lowermost Cenomanian); shoreface to off-shore storm-generated limestones (Lower Cenomanian); massive off-shore to shoreface carbonate sand bodies (Lower Cenomanian); prograding rudist bioclastic subaqueous dunes (Lower to Middle Cenomanian); rudist biostromes (Lower to Middle Cenomanian), and high-energy rudist and ostreid coquina beds within skeletal wackestones/packstones (Middle Cenomanian).Rapid changes of depositional systems near the Albian/Cenomanian transition in Istria are mainly the result of synsedimentary tectonics and the establishment of extensive rudist colonies producing enormous quantities of bioclastic material rather than the influence of eustatic changes. Tectonism is evidenced by the occurrence of sliding scars, slumps, small-scale synsedimentary faults and conspicuous bathymetric changes in formerly corresponding environments. Consequently, during the Early Cenomanian in the region of southern Istria, a deepening of the sedimentary environments occurred towards the SE, resulting in the establishment of a carbonate ramp system. Deeper parts of the ramp were below fair-weather wave base (FWWB), while the shallower parts were characterised by high-energy environments with extensive rudist colonies, and high organic production leading to the progradation of bioclastic subaqueous dunes. This resulted in numerous shallowing- and coarsening-upwards clinostratified sequences completely infilling formerly deeper environments, and the final re-establishment of the shallow-water environments over the entire area during the Middle Cenomanian.

Stratigraphy and depositionalenvironments of the lower cretaceous in the Karst region of the outer Dinarides (yugoslavia)

Abstract A detailed study of four geological columns and numerous data obtained from other localities in the Karst region of the Dinarides has been used as the base for a discussion of the stratigraphic range of determined taxa, revealing considerable differences from earlier listings. Of the stratigraphic subdivisions the biostratigraphic one seems preferable. An uniformity of biostratigraphic subdivision for the narrower Mediterranean region is proposed. A lithofacial analysis has determined that the sedimentation of the inner part of the carbonate bank (platform) occurred through alternating supratidal, intertidal, subtidal, lagoon and back-reef environments.

The Origin and Importance of the Dolomite-Limestone Breccia Between the Lower and Upper Cretaceous Deposits of the Adriatic Carbonate Platform: An Example from Cicarija Mt. (Istria, Croatia)

On the NE slopes of Cicarija Mt. (N Istria) a 120-150 m thick complex composed of dolomite-limestone breccia crops out between the Lower and Upper Cretaceous deposits. This studied breccia sequence is of post-sedimentary, tectogenic-diagenetic origin. It was formed by polyphase tectonic fracture of the Upper Albian to Lower Cenomanian early- and late-diagenetic dolomite succession with relics of recrystallized limestone, which enabled very important subsequent diagenetic alteration. This included partial dissolution, dedolomitization, recrystallization and calcitization of the fine-grained, crushed dolomite matrix, and centripetal dissolution of dolomite fragments and their cementation by calcite and ferroan calcite cements, as well as the partial collapse of fragments from the roofs of dissolution cavities and limited late-diagenetic silicification (the silica surplus originating from layers of diagenetic quartz from underlying Upper Albian deposits). Such a complex pattern of different events resulted in the high variability of breccia characteristics over relatively small distances, especially near more intensively tectonized zones. The contemporaneous stratigraphic level (Lower to Upper Cretaceous transition) in other parts of the Adriatic Carbonate Platform is also characterised by predominantly late-diagenetic dolomites with relics of limestones (including local occurrences of early-diagenetic dolomites) which are, in more tectonized areas, late-diagenetically altered into tectogenic-diagenetic breccias.

Stratigraphy of Paleogene Strata within the Mesihovina - Rakitno Area (Western Herzegovina)

The paper presents the stratigraphy of Paleogene strata from the central part of carbonate Dinarides. The carbonate and the clastic rock units were stu died. Their contact with underlying Senonian limes tone is marked by unconformity as a result of Laramian tectonic phase. The unconformity is denoted by the abundance of bauxite deposits. The abundance of calcareous nanoplancton species as well as ben tic foraminifera points at the sedimentation of Paleogene strata during the Eocene period. The succession of sediments with easily recognizeable transgressive, inundation and regres sive features has been established. Lithostratigraphical characteristics enabled the distinguishing of larger lithofacies groups. The simultaneousness of carbonate rocks with lower part of clastic succession as well as the transitionallitho· facies have been approved. The simultaneous overburden of bauxite deposits regardless of its lithology (carbonate of clastic) speaks in favour of the unite bauxitebearing phase.

The Kimmeridgian tidal-bar calcarenite facies of western Istria (Western Croatia, Jugoslavia)

SummaryThe Upper Jurassic limestones of western Istria are composed of three main facies: 1. peloid packstone/grainstone deposited in a shallow subtidal environment; 2. oolitic coated bioclastic calcarenite and 3. mudstone with desiccation cracks, originating in a near-shore environment ranging from shallow subtidal to supratidal or meteoric vadose zone. The calcarenite facies is characterized by thick-bedded to massive bioclastic grainstones/rudstones with cross-bedding and, at places, also large symmetrical wave ripples. It is composed of well-sorted tangential ooids and variable amounts of large coated bioclasts ofCladocoropsis and other hydrozoans, corals, pachydont bivalves and test of benthic foraminifers. Almost all the larger bioclasts are coated by micrite envelopes. The Kimmeridgian grainstone/rudstone facies in Western Istria has been interpreted as tidal bar and winnowed carbonate sands.ZusammenfassungIm Malm (Kimmeridgium) von W-Istrien können drei Hauptfaziestypenunterschieden werden: Peloid-Packstone-/Grainstone-Fazies des flachen Subtidals; Ooid- und Bioklasten-Gezeitenbarren-Kalkarenitfazies und Austrocknungs-Mudstone-Fazies (flaches Subtidal-Supratidal infolge von Meeresspiegelschwankungen). Im Hangenden der Gezeitenbarren-Kalkarenitfazies finden sich Brekzien aus Küstennähe oder sogar des Auftauchbereichs und/oder Bauxitlagerstätten, die die transgressive Grenze zur Austrocknungs-Mudstone-Fazies des Tithons kennzeichnen. Die wichtigsten sedimentologischen Merkmale dieser Fazies sind dickbankige bis massive Ooid-Grainstones und Ooid-Bioklasten-Grainstones/Rudstones mit klar ausgeprägter Schrägschichtung und starkwelligen Rippelmarken. Außer tangentialen Ooiden enthalten diese Schichten auch unterschiedliche Mengen von groben umrindeten Bioklasten (Cladocoropsis und andere Hydrozoen, Korallen, pachydonte Muscheln, benthische Foraminiferen). Nahezu alle Bioklasten (Rindenkörner) besitzen allseitige Mikritrinden.Die Texturen und Strukturen, insbesondere die Schrägschichtung und die Wellenrippel, beweisen, daß der Detritus aus Ooiden und Bioklasten transportiert und durch Gezeitenströme und Wellen abgelagert worden ist.

Shoreline Cross-bedded Biocalcarenites (Middle Miocene) in the Podvrsko-Snjegavic Area, Mt. Psunj, and their Petroleum Significance (Pozega Subdepression - Eastern Croatia)

The extensively distributed bioclastic sedimentary bodies in the Podvrsko-Snjegavic Area, Mt. Psunj (Pozega Subdepression, Eastern Croatia) are mostly composed of fragments of bryozoans, echinoids, lamellibranchs and corallinaceans. Apart from this, a relatively compositionally uniform, but granulometrically variable bioclastic detritus occurs, which also contains a smaller proportion (5-30%) of siliciclastic grains of medium to coarse sand, as well as sporadic pebbles up to 60 mm in diameter. These sediments are characterised by remarkably large-scale cross-bedding with erosional surfaces clearly delimiting the sets. They are interpreted as shallow-marine shoreface subaqueous dunes, sand bars and barriers formed on the nearshore - mainly shoreface area during the Late Badenian in a high-energy depositional cycle with strong synsedimentary tectonics. With regard to the petroleum-geological reservoir characteristics, the described Middle Miocene cross-bedded biocalcarenites are compared with numerous large oil and gas pools globally, and in other localities in Croatia on the margins of inselberg massifs between the Drava and Sava rivers and south of the Sava river.

Upper Jurassic (Malm) Shallow-Water Carbonates in the Western Gorski Kotar Area: Facies and Depositional Environments (Western Croatia)

Shallow-water carbonates in the Upper Jurassic of the Gorski Kotar were deposited on a carbonate ramp, in beach-barrier island-lagoonal and peritidal environments. In the continuous sequence, more than 900 m thick, several facies have been found: (A) low-energy shallow-water wackestones/mudstones of the Lower Oxfordian, (B) high-energy shallow-water grainstones of the Middle Oxfordian, (C) low-energy, above the fair-weather wave-base packstones of the uppermost Oxfordian and transition to the Kimmeridgian, (D) shallowing-upward/coarsening-upward units formed through progradation of beach-tidal bars or barriers over the peritidal deposits of the Kimmeridgian and the beginning of the Tithonian and (E) peritidal shallowing-upward units capped by storm tidal deposits of the Tithonian and beginning of the Berriasian. Fossil assemblages adapted to the environmental changes: maximum of their abundance, in the number of the taxa, as well as in the number of individuals, corresponds to the high-energy facies B (Oxfordian), while their minimum corresponds to the peritidal shallowing-upward units of facies E (Tithonian).

RESPONSE OF TRACEMAKERS TO TEMPORARY PLATFORM DROWNING: LOWER CENOMANIAN OF SOUTHERN ISTRIA (WESTERN CROATIA)

ABSTRACT The Early–Late Cretaceous transition marked the beginning of the final disintegration of the Adriatic Carbonate Platform, which eventually resulted in the formation of the Dinarides mountain belt in the Paleogene, Neogene, and Quaternary. In southern Istria (Croatia) a continuous succession crops out that shows deepening from shallow subtidal to carbonate ramp in the latest Albian followed by gradual shallowing in the early Cenomanian, including well-preserved Ophiomorpha and Thalassinoides burrow systems in sections from Cintinera Cove and Vinkuran quarry. Burrow systems that overlie hummocky cross-stratified deposits are good indicators of specific environmental conditions during deposition. During transgression, favorable conditions for suspension- and deposit-feeding crustaceans were established which resulted in complex networks of Ophiomorpha and Thalassinoides. The increase in bioturbation up-section is recorded by a gradual increase in the bioturbation index as well as the size of burrow systems during transgressive events; a completely bioturbated interval in Vinkuran quarry indicates the maximum flooding surface. Formation of burrow systems was interrupted by subsequent clinoform progradation interpreted as a highstand shedding of shallow-marine bioclasts caused by high carbonate production and intense bioerosion of rudist and chondrodont shells, causing the relatively rapid infilling of the basin and re-establishment of the shallow-marine peritidal deposition in the entire northwestern part of the Adriatic Carbonate Platform.