Quaternary Depositional Environments in the Vrgoračko Polje/Lake (SE Croatia)

The Vrgoračko polje is a karst field with a surface area of 37 km2 and an altitude of between 20 and 28 m above sea level, situated at the southern edge of the Dalmatian Zagora. During the Quaternary the polje was flooded for variable periods of time and a lacustrine environment was established. A multidisciplinary study of drill-cores, outcrops and geoelectric measurements recognised five main sedimentary facies: laminated sediment, redeposited sediment, coarse grained carbonate debris, littoral clay and lacustrine chalk. Based on the facies analysis, depositional environments developed during the Holocene include aquatic lacustrine littoral and deeper-water environments. The terrestrial environment is represented by a desiccated lake phase. The littoral clay facies (filling depressions and caverns in the karst relief) is laterally equivalent to the deep-water laminated facies (varves?). A stratigraphic break between littoral claya nd lacustrine chalk could be time-equivalent to disturbed laminated sediments deposited in deeper-water and to local intercalations of coarse-grained carbonate debris in shallow-water facies sediments. These features could have been the result of a neotectonic event (earthquake), which triggered debris flows of colluvial material from slopes around the lake, and this could also have changed the hydrological regime of the Vrgoračko polje and affected subsequent depositional facies. According to 14C dating, deposition of the lacustrine chalk started at the beginning of the Mid-Holocene Warm Period (7686±36 aBP) with a sedimentation rate of approximately 0.51 mm a-1 during the Middle, and 0.58 mm a-1 during the Late Holocene to today. Calculated carbonate production was estimated at 1050 gm-2 a-1. A temporary phase of subaerial exposure of the lake is indicated by desiccation cracks and two bioturbated palaeosol horizons. The described depositional environments and sediment facies found in the Vrgoračko polje could be considered to represent a typical Quaternary lacustrine sedimentation pattern for other Dinaric karst poljes.  </span

Incoming research project: Abrupt climate changes – Evidence from Quaternary sedimentary sequences in Croatia (ACCENT)

“Abrupt climate changes–Evidence from Quaternary sedimentary sequences in Croatia” is a four-year investigation project that is funded by the Croatian Science Foundation and started on April 1st 2021. We propose a fundamental and multidisciplinary approach to produce meaningful data on past abrupt climate changes (CC) Interpretation of these data can help create the basis both for comparison of paleo- and modern climate changes and for predicting their dynamics in the future. The specific geological, pedological geomorphological and climatic diversity of Croatia enables to study in high- resolution study the parallel development of abrupt CC during the Late Pleistocene and Holocene at four locations only 300 km apart. A stepwise fieldwork approach will be applied. Initial fieldwork is required to investigate four different geological successions and harmonize terminology and research approaches in different scientific fields and among various experts. Further, dedicated and focused fieldwork will be exercised including outcrop and core sampling. Several analytic methods will be applied to characterise soils and sediments, together with their paleoenvironmental significance and age: micromorphology and stable isotope analysis, granulometry, radiocarbon and optically stimulated luminescence dating. Gathered data will be subjected to geostatistical analysis. For selected sites, digital elevation model analysis and geoelectrical soundings will be performed. The loess–palaeosol sequences of NE Croatia show great potential in reconstructing the Upper Pleistocene climate and environmental changes. The cumulic horizons are mentioned in descriptions of the sections and geochronologically framed by IRSL- dating as weakly developed incipient soils representing the sedimentological record of short- term warming that preceded the long-term cooling and sedimentation of loess (Fig. 1a). The lower parts of the horizons are bioturbated, indicating intensive life in cumulic horizons (soils), while the silty texture and pale color indicate short exposure to pedogenic processes. 14 horizons represent paleoclimate archives of 14 CC episodes. Preliminary studies on dune sands (Đurđevac Sands) were conducted in the Podravina area. Within the dunes sets, two paleosoils, type arenosol, were discovered. Preserved bioturbations confirm their in situ formation (Fig. 1b). Radiocarbon analysis of charcoal from the paleosoils showed that they developed before the very beginning of the Holocene, and, consequently, the oldest dune sediments were already formed before the end of the Pleistocene. Glacial features and forms in karst indicate different ages of glaciations on the Velebit Mountain. Presumably fluvioglacial features can be observed (Fig. 1c) 1 m above the sea level. Their properties and age of formation will be the subject of detailed analysis. Finally, the Vrgoračko Polje is a karst field situated at the southern edge of the Dalmatian Zagora. During the Quaternary, the polje was flooded for variable periods and a lacustrine environment was established. The multidisciplinary study of drilling cores, outcrops and geoelectric measurements recognized five main sedimentary facies: laminated sediment, redeposited sediment, coarse-grained carbonate debris, littoral clay and lacustrine chalk. A stratigraphic break between littoral clay and lacustrine chalk could be time- equivalent to the disturbed laminated sediments deposited in deeper water (Fig. 1d). According to radiocarbon dating, deposition of the lacustrine chalk started at the beginning of the Holocene and lasts until today. The described depositional environments and sediment facies found in the Vrgoračko Polje are considered to represent a typical Quaternary lacustrine sedimentary pattern for other Dinaric poljes. So far, preliminary investigations and a short literature survey suggest that the four proposed Croatian sites represent meaningful archives in the context of Late Pleistocene and Holocene CC. The main objectives of the project are: 1) Understanding of the spatial extent and differences in appearance of paleoclimatic events in the Pannonian and Dinaric areas ; 2) Determine teleconnections in SE Europe and compare it with abrupt CC in the European Sand Belt, and 3) Correlate it with climate archives from the Adriatic Sea. Reaching the set objectives and goals will help researchers to identify and map critical ecological conditions during the Quaternary, where major geomorphological, hydrogeological and pedological changes had occurred and where current ecotones can be expected to exist in the future in different climatic regions. Ultimately, the outcomes can be applied by land-use planners and stakeholders to check whether the present land-use will be sustainable any longer under changing conditions and, if not, to suggest alternative management of land-use changes, especially concerning geohazards like landslides, slumps, debris flows, floods and drifting dunes

Abrupt climate changes – Evidence from Quaternary sedimentological sequences in Croatia (ACCENT)

A fundamental and interdisciplinary approach to investigate abrupt climate change enables us to obtain valuable data and interpret the dynamics of these changes. These data and their interpretation can form the basis for both comparing paleoclimate changes with modern ones and predicting the dynamics of these changes in the future. These insights can make it easier for humankind to adapt to changes that will affect all aspects of life on Earth. Because of the fast and unquestionable climate change and threats that have emerged, geologists have been trying, based on records in Quaternary sediments, to identify the process of change. The exploration is focused on loess/paleosoil sequences and the Đurđevac Sands in the Pannonian area (continental climate) and fluvioglacial sediments in the foothills of the Velebit Mt. and lake sediments from Lake Vrgorac in the Dinaric area (Mediterranean climate). Firstly, explorations of loess-paleosoil sequences revealed the existence of 14 cumulic horizons, which evolved just above well-developed paleosoils. They represent paleoclimate archives of the dynamics of 14 climate changes. The research is focused on analyzing cumulic horizons in NE Croatia, providing detailed descriptions of transitions from the warm to the glacial period in the Late Pleistocene. Next, the investigation of paleosoils and geomorphological/sedimentological features in the dunes of the Đurđevac Sands may help to determine the nature of the Pleistocene- Holocene transition in this area, as well as potential Holocene climate-related paleoenvironmental changes. Those terrestrial archives in the south of the Carpathian Basin provide insight into the magnitude, timing, and spatial variability of climate changes. In addition, fluvioglacial sediment successions in the foothill of the Velebit Mt. are crucial for describing abrupt climate change during the Late Pleistocene, as it will reveal the magnitude, timing, and spatial variability of climatic transitions and correlate them with transitions in a continental climate as based on the other archives outlined above. Finally, the depositional environments and sediment facies found in Vrgoračko polje are considered to represent a typical Quaternary lacustrine sedimentation pattern for other Dinaric karst fields in a Mediterranean climate. The dynamics of all mentioned facies transitions in all proposed sections are a consequence of past climate change. The specific geological and pedological diversity, geographical position, geomorphology and climate diversity of Croatia enable the parallel high- resolution study of the development of abrupt climate changes at locations only 300 km apart. This research will improve our understanding of the spatial extent and differences in the occurrence of paleoclimatic events in the Pannonian and Dinaric areas. That will yield insight into eolian-fluvioglacial-lacustrine teleconnections in SE Europe. In turn, this forms the basis for supraregional correlations with the European Sand Belt (NW Europe) and the Adriatic Sea

The Đurđevac sands: First dating results and preliminary palaeogeographical reconstruction

“Abrupt climate changes–Evidence from Quaternary sedimentary sequences in Croatia” is a four-year research project that is funded by the Croatian Science Foundation and started on April 1st 2021. A fundamental and multidisciplinary approach is producing meaningful data on past abrupt climate changes (CC). Interpretation of these data helps to create the basis both for comparison of paleo- and modern climate changes and for predicting their dynamics in the future. The specific geological, pedological, geomorphological and climatic diversity of Croatia enables us to study in high-resolution the parallel development of abrupt CC during the Late Pleistocene and Holocene. Four investigated locations are only 300 km apart: loess/palaeosoil sequences and dunes in the Pannonian area (continental climate) on the one hand, and fluvioglacial sediments and karst lacustrine sediments in the Dinaric area (Mediterranean climate) on the other hand. The Đurđevac Sands form a unique terrestrial dune landscape that covers Late Pleistocene loess deposits and Holocene river Drava fluvial and associated marshy deposits. Based on the superposition principle, in the Guidebook of the geological map for the Đurđevac sheet 1:100.000, the Đurđevac Sands are Holocene in age. Samples were taken in an abandoned sand quarry, Draganci, in the town of Kalinovac. The quarry is carved out into what seems to have been a massive (hummocky) dune, bordering a partially degraded large-scale parabolic dune created by northern winds. Samples were taken after clearing the excavation wall, turning it partially into a staircase. Within the dunes sets, two palaeosoils were discovered. Preserved bioturbations confirm that the palaeosoils are found in situ. Several analytic methods were applied to characterise soils and sediments, together with their age and paleoenvironmental significance: radiocarbon and optically stimulated luminescence dating, digital elevation model, geoelectrical, pedological, sedimentological, modal and grain-size analyses. According to the grain-size measurements, the sand fraction dominates in all analysed samples, mostly between 95 and 100 %. Medium and fine sand grains represent equally the sand fraction. Therefore, most of the samples are classified as sand, or less frequently as fine sand. The dunes are composed of high spherical sand grains with quartz dominating in the light mineral fraction. The heavy mineral fraction contributes with 22-46%, and garnet is dominating. Recent radiocarbon dating results of charcoal suggests that the older palaeosoil (14 659 ± 498 cal yr BP) developed at the beginning (peak), and the younger palaeosoil (13 566 ± 229 cal yr BP) developed in the middle part of the Bølling–Allerød warming (BA). They represent an abrupt interstadial period, roughly between 14.7 and 12.9 ka BP, just before the Younger Dryas cooling, the final stadial of the Pleistocene. Optically stimulated luminescence (OSL) dating was applied to verify those recent findings using the aeolian sands covered by and covering the palaeosoils. The two lowermost samples below the palaeosoils yield OSL ages of around 14.5 ka, while the uppermost sample above the upper palaeosoil has an age of around 8 ka. It thus seems that at this site, aeolian activity has been registered during the period just before the BA warming, and later in the Holocene, but not during the Younger Dryas. A detailed sampling campaign with additional analyses is foreseen, together with digital elevation surveys, in order to refine the palaeoenvironmental history of the Đurđevac Sands

Dynamics and intensity of climate change recorded in palaeosoils

A fundamental and multidisciplinary approach to investigate abrupt climate change enables us to obtain valuable data and interpret the dynamics of these changes. The aim of the CSF project ACCENT is the exploration of palaeosols intercalated in (i) loess (Baranja), (ii) the Đurđevac Sands in the Pannonian area (continental climate), (iii) fl uvioglacial sediments in the Privlaka and (iv) lacustrine sediments of the Vrgorac Lake in the Dinaric area (Mediterranean climate). Investigations of loess- palaeosoil sequences enabled to reveal the warming intensity of archived interstadials (chernozem, brown forest soil or terra rossa), as well as postpedogenetic alterations (hydromorphy). Comparison with modern soils, developed from similar parent materials and on similar reliefs, indicate much longer and more intense warmings than in present climates. Additionally, loess-palaeosoil sequences revealed the existence of thick, uniform (cumulic) horizons, evolved just above welldeveloped palaeosoils. They are meaningful archives in the context of Late Pleistocene and Holocene climatic oscillations. Accordingly, this analytical approach will enable exploring the dynamics of the various facies transitions mentioned above and correlate them in other proposed sections. This research will improve our understanding of the spatial extent and diff erences in appearing of abrupt climate changes in the Pannonian and Dinaric areas, and correlation with the European Sand Belt and the Mediterranean

Soil erosions as indicator of abrupt climate changes during Quaternary

“Abrupt climate changes–Evidence from Quaternary sedimentary sequences in Croatia” is a four-year research project that is funded by the Croatian Science Foundation and started on April 1st, 2021. A fundamental and multidisciplinary approach is producing meaningful data on past abrupt climate changes (CC). Interpretation of these data helps to create the basis both for comparison of paleo- and modern climate changes and for predicting their dynamics in the future. The specific geological, pedological, geomorphological and climatic diversity of Croatia enables us to study in high-resolution the parallel development of abrupt CC during the Late Pleistocene and Holocene. Four investigated locations are only 300 km apart: loess/palaeosol sequences and dunes in the Pannonian area (continental climate) on the one hand, and fluvioglacial sediments and karst lacustrine sediments in the Dinaric area (Mediterranean climate) on the other hand. In all those environments, warm periods (interstadials) are archived in geological successions as palaeosols. The ages of these palaeosols and overlying sediments indicate time gaps (hiatuses) in sedimentary succession. Since the upper parts of soil profiles are missing, it can be concluded that the ends of warm periods were characterized by strong soil erosion during the investigated period (last 120 ka). Such events are preserved in each investigated location with different recent and palaeoclimate conditions

Evidence of abrupt climate change preserved within Quaternary sedimentological sequences in Croatia – methodological approach

Aiming to identify and describe the evidence of Late Quaternary abrupt climate changes, preserved four different pedo-sedimentary complexes in Croatia will be investigated. They are Zmajevac loess-palaeosol sequence and Đurđevac Sands, located in the Pannonian region, and fluvioglacial sediments of Privlaka and karst lacustrine sediments of the Vrgoračko polje in the Croatian Dinaric region. The planned methodology implies geophysical surveying, utilization of remote sensing techniques drilling, and sampling, as well as carrying out various laboratory analyses to determine textural, geochemical, palaeobotanical, micromorphological, mineralogical, and geochronological properties of the marker horizons (MH). The MH of this study is considered those that indicate the change in climatic conditions, e.g. horizons formed by sediment cumulization synchronously to the vegetation regression upward on the top of well-developed paleosols, as markers of progressive aridization. The locations for sampling were selected based on previous field experience and supported by the results of geoelectrical sounding and drilling campaigns that delimited the lateral and vertical extent of the MH. The mineralogical and geochemical properties of several MH have already been described through previous research. The age of each MH will be established by radiocarbon dating, optically stimulated luminescence (OSL) dating or existing geochronological information [1] [2] [3] [4]. The results of micromorphological analysis and geochemical indicators [5] will provide information about the pedogenetic development of the palaeosols and will ultimately be translated into dynamics of climate change during the Late Quaternary

Evidence of Late Quaternary environmental changes preserved within the Privlaka pedo-sedimentary complex at the eastern Adriatic coast, Croatia

The Privlaka pedo-sedimentary succession (Eastern Adriatic coast, Croatia) is a promising archive of palaeoenvironmental changes as it shows a clear alternation of (a) palaeosol(s) and glacio-fluvial deposits. The objective of this study is to describe the palaeosols and sediments, and unravel the nature, magnitude and timing of environmental change preserved within this terrestrial record. To this end, a more than 12 m thick section was investigated in detail, which is divided into four different units of which one is represented by a reddish palaeosol, and the other three by sediment packages, each indicating a different pedosedimentological context. For the purpose of delineating the absolute thickness and lateral extent of the complex, geoelectrical soundings and remote sensing techniques were deployed. The profile was thoroughly described and sampled for the purpose of conducting high-resolution palaeoenvironmental research using mineralogical, geochemical, pedophysical and micromorphological properties. Preliminary results will be presented and discussed in the light of the Late Quaternary palaeoenvironmental evolution of the region and surroundings. The research is funded by the Croatian Science Foundation under the projects ACCENT (IP-2020-02-3274) and DOK-2021-02-9476