Ljubomir Babić

Borings in Mobile Clasts from Eocene Conglomerates of Northern Dalmatia (Coastal Dinarides, Croatia)

SummaryBored clasts occur in Eocene conglomerates deposited in the upper shoreface and beachface settings of the Dinaric foreland basin. The trace fossil assemblage consists ofGastrochaenolites, Trypanites, and possibly some other ichnotaxa and may be compared to theTrypanites Ichnofacies. The preservation characteristics of the borings reflect many stages of colonisation/boring and abrasion. The removal of shells of the boring bivalves, the different depths of the abrasional truncation of borings, and the predominant preservation of the largest excavations (Gastrochaenolites) in the ichnocoenosis are related to repeated phases of abrasion, caused by the mobility of clasts. Coastal gravel is a specific variant of hard substrates, whose mobility controls the colonisation of borers, the type of assemblage and its preservation potential.

Uplifted Pleistocene marine sediments of the Central Adriatic Island of Brusnik

The Island of Brusnik, located in the Central Adriatic Sea, is mainly known for its Triassic igneous rocks. However, it also contains Pleistocene conglomerates, limestones and Neptunian dikes, as well as Holocene rock debris, soil, and beach gravels. Quaternary sediments unconformably overlie tectonically disturbed Triassic basement. The majority of Pleistocene limestones, as well as the matrix of the conglomerates, are predominantly bioclastic grainstones and rudstones. Gastropod shells in these sediments retain their original aragonite mineralogy, and may also display their original colours. The majority of the conglomerates and limestones originated in lower beachface and shoreface environments. Similar sediments have not been identifi ed in the surrounding area and the Dinarides in general. Some of the Pleistocene sediments originated during MIS 5e of the Last Interglacial based on radiometric evidence. The island experienced uplift of about 30m during the Middle and Late Pleistocene and this process probably continued in the postglacial period. The combination of uplift and cyclic sea-level changes is envisaged to have resulted in an overall downstepping pattern of the Pleistocene deposits.

Meteoric phreatic speleothems and the development of cave stratigraphy: An example from Tounj Cave, Dinarides, Croatia

Abstract Speleothems occurring in some caves of the carbonate Dinarides line all channel surfaces, and have been deposited from meteoric waters under phreatic conditions. Such phreatic speleothemic deposition modifies common experience (l) that meteoric phreatic conditions cause dissolutional widening of cave voids, and (2) that speleothems imply vadose conditions. The phreatic speleothems described here postdate an early polygenetic evolution of the cave voids, and predate the last, vadose stage. They were likely produced during the late/postglacial warming period, when dissolved carbonate was amply supplied, and when there was much water available for saturation of underground voids. Phreatic speleothems may be used as a tool for time correlation of internal deposits, both within one cave and within a karst region. They indicate an important stage in the history of the ground-water regime of an area. In general, phreatic speleothems help in better understanding of the development of subterranean voids and related karst/palaeokarst.

Variable sources of beach sands of north Adriatic islands: examples from Rab and Susak

The composition of beach sands from the Islands of Rab and Susak (northern Adriatic) has been studied in order to determine how individual beaches are supplied with detritus. The beaches on both islands are composed of quartz dominated siliciclastic sand, with subordinate carbonate content. Three end-member heavy mineral assemblages have been identified among the studied beach sands, each one associated with a specific source rock: (1) a garnet dominated assemblage and (2) a zircon, rutile and tourmaline dominated assemblage on Rab Island, as well as (3) an assemblage dominated by unstable minerals on Susak Island. Sands from individual beaches contain one of these specific assemblages or display a mixing of two varieties. The end-member assemblages are very comparable with those of Eocene and Pleistocene sediments which crop out on the two islands, identifying them as the principal sources of detritus. Cretaceous and Eocene carbonate rocks, although present to a considerable extent in the study area, has shown to be a negligible source of sandy material. Thus, the supply of detritus to the beaches is primarily controlled by erosion of siliciclastic rocks in the immediate or nearby hinterland.

Sharply-Topped Alluvial Gravel Sheets in the Palaeogene Promina Basin (Dinarides, Croatia)

The upper part of the Promina Beds at their western extent is represented by two alluvial units: the Kunovac Beds and the Upper Alluvial Unit. The Kunovac Beds contain a high proportion of fine-grained sediments, and generally lacks debris flow deposits. The principal architectural components of the Kunovac Beds are (1) complex (multilateral, multi-storey) gravel-dominated sheets, which originated by the advance of mobile-channel belts, and were terminated by sudden abandonment, (2) smaller heterogeneous gravelly-sandy sheets, which originated in fluvial belts from a combination of sheet flows and channelized flows, (3) small isolated ribbons reflecting the filling of small channels, and (4) floodplain mudstones and sandstones. The basic style by which the Kunovac Beds, as well as the most part of the Promina alluvium were built up are the repeated advances and abandonments of the alluvial belts, and related stacking of coarse-grained sheets and floodplain deposits. The most important factors responsible for the dominance of this sheet-like geometry are high sediment supply and high aggradation and subsidence rates. Deposition of the Kunovac Beds occurred on alluvial plains, situated between the basin-margin proximal alluvium (including fans) and marginal-marine zone of the Promina Basin. The alluvial Promina Beds represent a transverse type of basin-fill pattern, whereas the deepest portion of the basin experienced longitudinal palaeotransport.

An Association of Marine Tractive and Gravity Flow Sandy Deposits in the Eocene of the NW Part of the Island of Pag (Outer Dinarides, Croatia)

The Eocene clastics of the NW part of the island of Pag overlie carbonate platform deposits and are dominantly sandy. Besides minor components, they include cross-laminated and cross-bedded sandstones produced by marine tractive flows, mostly directed toward E, and ESE, and dominantly massive sandstones probably deposited by gravity flows. The area was situated close to sand-rich sources and river mouth(s). Possible settings include a delta-related shallow-marine area, and a sea strait. Structural deformation intervened very early in the history of a complex outer dinaric foreland realm and governed its subsequent evolution, in contrast to a simple foreland trough envisaged before.

The youngest stage in the evolution of the Dinaric carbonate platform: the Upper Nummulitic Limestones in the North Dalmatian foreland, Middle Eocene, Croatia

The paper provides a description of the poorly known Upper Nummulitic Limestones exposed in the North Dalmatian foreland basin of the Outer Dinarides in Croatia. This formation originated on a land-attached ramp-type platform with a temperate sediment production. It transgressively overlies older platform limestones and includes limestones deposited in very shallow, restricted settings, which subsequently evolved into carbonate platform environments typified by diversified biota. The succession terminated at a drowning unconformity, which is intra-Bartonian (Middle Eocene) in age based on biostratigraphic interpretations of the larger foraminifera present. This study demonstrates that the history of the carbonate platform of the Outer Dinarides extends into the Bartonian and that the studied limestones document the youngest, hitherto unknown stage in the platform development. The SW margin of the Upper Nummulitic platform was dissected by faults and prone to collapse, which represented the source for megabreccias deposited in an adjacent basin. This platform-basin system represents a new element in the sedimentary and tectonic evolution of the Dinaric foreland.

Climatic cycles recorded in the Middle Eocene hemipelagites from a Dinaric foreland basin of Istria (Croatia)

Climatic cycles recorded in the Middle Eocene hemipelagites from a Dinaric foreland basin of Istria (Croatia) Middle Eocene hemipelagic marls from the Pazin-Trieste Basin, a foreland basin of the Croatian Dinarides, display repetitive alternations of two types of marls with different resistance to weathering. This study focuses on the chemical composition, stable isotopes, and palynomorph content of these marls in order to better understand the nature of their cyclic deposition and to identify possible paleoenvironmental drivers responsible for their formation. The less resistant marls (LRM) have consistently lower carbonate content, lower δ18O and δ13C values, and more abundant dinoflagellate cysts than the more resistant marls (MRM). We interpret these differences between the two marl types to be a result of climatic variations, likely related to Milankovitch oscillations. Periods with wetter climate, associated with increased continental runoff, detrital and nutrient influx produced the LRM. Higher nutrient supply sparked higher dinoflagellate productivity during these times, while reduced salinity and stratification of the water column may have hampered the productivity of calcareous nannoplankton and/or planktonic foraminifera. In contrast, the MRM formed during dryer periods which favoured higher carbonate accumulation rates. This study provides new information about the sedimentary record of short-scale climate variations reflected in wet-dry cycles during an overall warm, greenhouse Earth.

Hydrologic Evolution of a Carbonate Aquifer (Dinaric Karst, Croatia)

Dinaric Karst terrains contain specific, lam inatedspeleothems, which line all surfaces of subterraneanvoids including Cretaceous bedrock limestone, and oldervadose speleothems and clastic sediments. The speleotherms may attain a thickness of one metre. Deposition of these speleothems took place during a longterm phreatic period in the Late Quaternary. This is incont rast to well-known, widespread speleothems, whichwere, and are deposited in vadose and uppermost phreaticsettings. Furthermore, the origin of these phreaticspeleothems departs from common experience by the dominant dissolutional widening of underground conduits when saturated. Phreatic speleothems can be importantstrat igraphic marker for the stratigraphy of cavesediments. This approach revealed a sequence of threehydrologic stages: (1) prephreatic stage with dominantvadose conditions and dissolution processes, (2) phreaticstage when the ground-water level was very high inthe large karst area, and when the volume of the voidsdecreased, and (3) the last, dominantly vadose stageduring which voids were enlarged for the second time,and phreatic speleothems may be covered by youngerclastics and vadose speleothems.