Vlasta Ćosović’s research while affiliated with University of Zagreb and other places

Mass‐transport deposits are products of resedimentation phenomena involving a broad spectrum of gravity‐driven processes, and commonly have a high preservation potential in deep‐marine environments. This study documents various types of mass‐transport deposits that are interbedded with intensely bioturbated shallow‐marine calciclastic sediments deposited along a reflective coast during the middle and late Eocene. The sedimentary succession, located in the vicinity of Novigrad in northern Dalmatia, Croatia, comprises sediments deposited in a range of nearshore and carbonate ramp environments, and represents the infill of a thrust‐top (piggyback) basin of the North Dalmatian foreland basin. Five types of mass‐transport deposits, ranging in thickness from 13 cm to 6 m, have been identified: (i) calcilutite and calcarenite slumps; (ii) conglomeratic slump‐debrites with a ‘dough‐like’ appearance; (iii) blocky‐flow deposits bearing large blocks of beachface and/or shoreface deposits; (iv) rockfall deposits comprising scattered blocks of beachface conglomerates and shoreface calcarenites; and (v) ‘classical’ matrix‐supported debrites. Calciturbidites are rare and mainly comprise Ta and Tb divisions. Conglomeratic slump‐debrites are mostly found in association with offshore‐transition deposits, suggesting that mass flows were triggered above the storm wave base likely due to a combined effect of: (i) strong earthquakes related to the tectonic development of the basin; (ii) sediment destabilization due to pore‐water overpressure during forced regressions; and (iii) storm‐wave loading affecting the shallow seabed. Progressive deepening likely favoured mass‐flow transformations, although the overall paucity of turbidites suggests relatively short mass‐flow transport distance and turbidity current bypass to deeper realms. Multiple erosion phases and resedimentation processes from the Cretaceous to the late Eocene contributed to the diverse suite of extraformational clasts in the mass‐transport deposits studied. The mass‐transport deposits may be triggered and emplaced in shallow‐marine settings mainly during regressive stages of basin development, as the diverse gravel clast composition suggests significant tectonic influence. Although the mass‐transport deposits reported herein are relatively small, some of their peculiar sedimentary features and occurrence within shallow‐marine calciclastic deposits render them rather unique and suitable for a re‐assessment of the nature and evolutionary continuum of processes involved in subaqueous sediment mass transport, as well as the preservation potential of sedimentary features in high‐energy wave‐reworked environments.

Purpose The aim of this study was to describe the distribution and composition of foraminiferal assemblages and granulometric properties of sediment in transitional environments along the eastern Adriatic coast. Another objective was to compare the results and establish correlations (similarities and differences) between these sensitive environments. Materials and methods Sediments from transitional environments were collected in December 2019 at three geographically separate sites: the Mirna salt marsh, the Soline mud plain, and the Nin intertidal plain. A total of 18 sediment samples (top 2 cm) were collected along the land-sea transect. Micropaleontological and granulometric analyses were performed. Identification of foraminiferal genera and species, absolute and relative abundance, and ecological (biodiversity) indices were determined on standardized samples. Particle size distribution was determined, which allowed classification of the sediment. Carbonate content and organic content anaylses were performed as well. Results At the northernmost site, at the Mirna salt marsh, muddy sediments with low species diversity predominate. The Soline mud plain was characterized by greater species diversity and a uniform proportion of sandy and silty components in sediment. At the Nin intertidal plain, sediment was primarily sand with the greatest foraminiferal species diversity compared to the other two sites. The genus Ammonia dominated in all foraminiferal assemblages. Conclusions A different distribution pattern of benthic foraminifera in each environment was associated with variations in the grain size of sediment and was also influenced by the supply of freshwater from the river and karstic springs. Considering the lack of research on the transitional environments of the eastern Adriatic coast, this work provides more detailed data and emphasizes the importance of these environments and their biota.

Purpose This work highlights the sedimentary characteristics and the role of submarine sulfur-rich karstic springs in the distribution of benthic foraminifera in the northern part of the Adriatic Sea (Bay of Koper). Little is known about how local conditions such as temperature and sulfur bursts may influence sediment properties, benthic habitat variability, and composition of foraminiferal assemblages. Here we compare the distribution of total and living benthic assemblages in surface sediment samples collected from a funnel-shaped depression created by submarine sulfur springs. Materials and methods Sampling was performed at water depths between 24.6 and 32.2 m in fine-grained sandy silt to silty sand (partially washed). Sedimentological, mineralogical, and geochemical analyses of the sediment were carried out and the distribution of benthic foraminifera living around the springs was studied. Results and discussion In general, sediment characteristics (i.e., mineralogical, geochemical, and organic content) around the sulfur springs do not show prominent deviations from the marine surface sediment of the area; however, some differences exist among depressions of different depths. Deeper depressions in the lower parts probably extend to older continental sediments of Late Pleistocene age with alluvial features, while shallower depressions were formed entirely in Holocene marine sediments typical of a wider area. Only one of the five samples (M05) contained living foraminifera in sufficient abundance for biocenosis research. The benthic foraminiferal assemblages of moderate diversity are composed of opportunistic species. Elphidium translucens, Ammonia ex gr. tepida, Haynesina depressula, and Porosononion granosum dominate, while A. neobeccarii, Reussella spinulosa, and Textularia bocki are subordinate. Conclusions The distribution and diversity of foraminifera in the sediment near sulfur springs can be explained by several factors and their interactions. The intensity of the spring discharge affects the mixing/oxygenation of the sediment, the shape of spring depressions, and the granulometry of the coarser sediment around the springs. Sediment characteristics indicate different types of sediment origin. This is related to and can be explained by the depth of spring depressions.

Paleoecologic (paleoclimatologic) and biostratigraphic studies of pelagic and deep-water deposits rely on the identification of planktonic foraminifera. Here we report and compare the results of planktonic foraminiferal assemblages from the Middle Eocene indurated limestones and marls collected in the External Dinarides extracted with acetic acid of different concentrations (50%, 60%, 70% and 80%) and different reaction (exposure) times. The deposits originated within the Dinaric foreland basin, have been assigned to the so-called Transitional beds and Flysch, and are characterized by different ratio of carbonate content and degree of lithification. The aim of this paper is to compare the efficiency of the laboratory procedures for obtaining isolated specimens and to evaluate the impact of preparation procedure on the quality of tests (complete test vs. secondary dissolution effects). For each acetic concentration we assessed:(1)the effectiveness of the treatment in terms of the time required for successful extraction of planktonic foraminifera, and (2)the degree of dissolution by analyses of dissolution proxies, including the weight percentage of sieved residues after disaggregation and preservation features of the tests. Our results indicate that accurate taxonomic analysis of carbonate rocks requires the use of 60% acetic acid for a shorter reaction time, and hydrogen peroxide methods for marls.

The imbricated margin of stable Adria, which belongs to the External Dinarides, comprises a chain of islands, which follow the dominant NW-SE Dinaric trend in the northern segment, while the dominant tectonic orientation changes to WNW-ESE in the central Adriatic area, near Split. The new paleomagnetic results documented in this paper are from the islands of the latter and can be interpreted in terms of tectonics together with already published robust data sets from the Northern Adriatic Islands and stable Adria, respectively. The problems addressed are the proposed extra CCW rotation in the central Adriatic area relative to the rest of the Dinarides, the differences in the tectonostratigraphic models of the offshore External Dinarides, the relationship to Stable Adria and the reason for the arcuated shape of the thrust front between stable and imbricated Adria. From the five largest Central and Southern Adriatic Islands over 1000 independently oriented cores, representing 98 Upper Tithonian – Paleocene carbonate localities, were subjected to standard laboratory processing of the natural remanent magnetization, component analysis, and statistical evaluation on locality and between locality levels. The results lead to the conclusion that these islands moved in close co-ordination with both, the Northern Adriatic Islands and stable Adria, at least from the Albian on. The different tectonic trends characterizing the islands and reflected also in the arcuated shape of the thrust front between Stable and Imbricated Adria is explained by the dominance of one of the Late Cretaceous and younger compressional strain fields. The structures due to the Late Cretaceous strain field are dominant in Cres island (N-S trend), the ones formed during the Late Eocene-Early Oligocene prevail in the Northern Adriatic islands (NW-SE trend), SE of Cres. The WSW-ENE general orientation of the structures in the Central Adriatic area is due to the strong neotectonic deformation.

The distribution of modern benthic foraminifera is studied from offshore mixed carbonate-siliciclastic settings of Brunei Darussalam located in northwestern Borneo (South China Sea). The sediments were collected from 17 sites (i.e., shallow reefs, sunken wrecks, and two depth transects). A total of 231 species were identified from 8 to 63 m water depth. We conducted several analyses to understand the patterns of faunal composition, including: (1) Cluster analysis and Principal Component Analysis together with correlation to define relation among the sites; (2) Diversity indices, such as Shannon Index and Fisher's Alpha Index to assess diversity patterns at sites; and (3) Foram Index (FI) to determine whether the water quality indicates conditions that support reef growth. The most abundant foraminiferal groups from the reef and most wreck samples are larger benthic foraminifera (LBF), especially Calcarinidae and Amphisteginidae, whereas in the muddier sites the most abundant are smaller benthic foraminifera (SBF) with the genera Pseudorotalia and Asterorotalia. Certain species from the groups have shown patterns that do or do not correlate with depth and clay content.

The Bay of Koper is influenced by agricultural, urban, and port activities, therefore pollution from trace metals is a concern. A total of 20 sediment samples obtained from four 10-cm sediment cores were analyzed. Element concentration in the sediment of the bay was determined spatially and temporally from the recent surface to depth. The results were correlated with the composition and diversity of the benthic foraminiferal assemblages. Major element concentrations indicate natural lithogenic origin (which is also confirmed by mineralogical features). The benthic foraminiferal assemblages in sediment samples, although mainly composed of representatives of the Rotaliida, show moderate to high species diversity and are dominated by the pollution tolerant species Ammonia pakinsoniana, Haynesina sp., Valvulineria bradyana and the non-keel Elphidium sp. and subordinated by Ammonia tepida and Haynesina depressula. Canonical correspondence analysis (CCA) on foraminiferal species and trace element concentrations shows a possible control of some potential toxic elements (i.e., Cu, Ni, Pb, Zr, Cr, As) on the diversity and taxonomic composition of foraminiferal assemblages. Nevertheless, foraminiferal diversity and dominance in the bay are related to sediment characteristics such as sediment grain size, and the amount of terrigenous inflow rather than to the element concentrations of sediments. This study evaluated ecological conditions by using the Foram-AMBi and EcoQS indices. The values of the Foram-AMBI index reflect the good to moderate quality of ecological conditions, whereas high to poor ecological statuses were interpreted by calculating EcoQS.

Mass-transport deposits (MTDs) represent resedimentation phenomena triggered by the combined effect of seismic shocks of regional scale, structural tilting, basin-floor gradient, relative sea-level fluctuations, and/or excess pore-water pressure and can be useful in the reconstruction of basin development dynamics. The present study from the Dinaric Foreland Basin in Croatia documents several limestone blocks (olistoliths), carbonate debris, and associated bipartite carbonate megabeds as MTDs of exotic origin encased in deep neritic hyperpycnites, referred to as host deposits. Detailed facies and micropaleontological analyses indicate that host deposits were sourced from a fluvio-deltaic system located in the proximity of the uplifting orogen, while the MTDs originated from gravitational collapses of late Ypresian and early Lutetian limestones that were uplifted on blind-thrust anticline ridges on the opposite side of the basin. Mass wasting-produced carbonate blocks, debris, and gravity flows were probably triggered concurrently during the middle to late Eocene, but the blocks could have travelled faster downslope due to the lubricating effect of the underlying water “cushion,” overpressured mud, and the pull of gravity. Debrisflows and co-genetic turbidity currents that contributed to the formation of bipartite megabeds were likely mobilized deeper and moved slower than the carbonate blocks and could have been partly deflected by the previously emplaced olistoliths, resulting in megabed thinning along the olistoliths' down-dip edges. Those collapses were most likely triggered by the combined effect of relative sea-level changes associated with tectonic activity and seismic shocks of regional scale. The study suggests that progressive uplift of the frontal blind-thrust anticline ridge resulted in episodic emergence and collapses of progressively older limestone units, and marked the onset of development of the wedge-top basin. Conceptual models of olistolith emplacement and onset of basin development are suggested and may be applicable to both ancient and recent settings. The insights obtained from the integration of detailed facies analysis and micropaleontology may be useful in similar areas where such a level of detail cannot be obtained by conventional field methods.