Ervin Mrinjek

Sedimentology and Depositional Setting of Alluvial Promina Beds in Northern Dalmatia, Croatia

Facies associations comparable with Scott- or Donjek-type facies associations have been recognised in the alluvium of the Promina beds in northern Dalmatia (Late Eocene to possible Early Oligocene). Scott-type facies associations prevail in the upper part of the studied succession whereas Donjek-type facies associations characterise its lower part. Vertical variations in sediment supply, stream gradient or base level are primarily related to south-westward thrustings followed by tectonic quiescence and erosion of the source area.

The Benkovac Stone Member of the Promina Formation: A Late Eocene Succession of Storm-Dominated Shelf Deposits

The Upper Eocene Benkovac Stone Member of the Promina Formation of northern Dalmatia, Croatia, is a thinly bedded succession of alternating carbonate sandstones and calcareous mudstones, ca. 40 m thick, exposed as a narrow, SE-trending outcrop belt near the town of Benkovac. This unit occurs in the middle part of the Promina Formation, which is a spectacular calciclastic succession of deposits of late Middle Eocene to Early Oligocene age, about 2000 m thick, showing an upward trasition from deep-marine turbidites to shallow-marine and alluvial deposits. The sheet-like sandstone beds of the Benkovac Stone Member are mainly 1–25 cm thick and have been classified into 6 facies and 3 subfacies, differing in stratification or showing various internal sequences of stratification types. The thicker and most common beds show plane-parallel stratification passing upward into hummocky cross-lamination and undulatory to flat parallel lamination (Facies S1), or consist of only the latter two divisions (Facies S2). Subordinate beds show convolute stratification (Facies S3), are amalgamated (Facies S4), or are homogenized and merely graded (Facies S6). The thinner beds have more uneven boundaries and show translatory ripple cross-lamination (Subfacies S5a), climbing ripple cross-lamination (Subfacies S5b) or pinch-and-swell lamination attributed to starved and rolling-grain ripples (Subfacies S5c). The intervening mudstone beds (Facies M) are silt-streaked and bioturbated. Trace fossils indicate a combination of Zoophycos and Cruziana ichnofacies. The sedimentary succession was deposited in a microtidal offshore transition zone characterized by muddy “background” sedimentation punctuated by discrete storm events. The observed spectrum of tempestite sandstone beds represents a wide range of storm events, varying in magnitude and in the mode of sand dispersal – from the pure action of oscillatory waves to pure geostrophic currents. The majority of tempestites are attributed to a combination of these two end-member factors, with the geostrophic currents often enhanced by a high load of sediment suspension (density-modified currents). The Benkovac Stone Member is underlain by muddy offshore deposits (Debelo Brdo Member) and covered by sandy to gravelly shoreface deposits (Otavac Member), which in turn pass upwards into braidplain deltaic and alluvial deposits. This regressive succession is considered to be a parasequence deposited as a highstand systems tract during a gradual, stepwise rise of relative sea level. The thick parasequence consists of progradational and retrogradational sets of much smaller parasequences, the record of which differs markedly in the shoreface and offshore transitional part. The difference is attributed to the underlying contrast in the physical factors controlling the supply of sand to these shallow shelf zones.

Pliocene Alluvial Sediments in the Drava Depression of the Virovitica–Slatina Area, Northern Croatia

Clastic sediments in the vicinity of Virovitica (Northern Croatia) consist of gravels, sands, silt clays and marls. Gravels with discontinuous sheet-like geometry are typical for an alluvial fan system. The most abundant sediment, quartz rich sand, originates from a sandy braided river system. Silt, clays, and marls were deposited in the flood plain. They contain fossil macroflora indicative of moderate climate conditions, including maidenhair leaves (Ginkgo), the presence of which suggests that these sediments were deposited before the Pleistocene glaciation.

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.

The Bottom Current Sediments (Contourites) in the Upper Cretaceus Deep-Water Deposits in the Northeeastern Part of Žumberak (Croatia)

The Upper Cretaceous deep marine deposits in NE parts of Žumberak contain sediments deposited by bottom currents - muddy, sandy and sandy-gravelly contourites. The complete (negative-positive) sequences and incomplete (negative-positive) sequences have been observed. Apart from the sediments that have been deposited by bottom currents, several turbidite layers reworked by bottom currents occur.