Speleogeneza špilje u kamenolomu Debeljača (Lovinac, Lika)

U radu su izneseni rezultati speleomorfoloških i geoloških istraživnja špilje te rezultati fazne analize uzoraka sedimenata iz špilje. Usporedbom dobivenih rezultata s dosadašnjim spoznajama o geologiji, hidrogeologiji i strukturno-tektonskim odnosima šireg područja dane su osnove speleogeneze istraživane špilj

Speleothem growth intervals reflect New Zealand montane vegetation response to temperature change over the last glacial cycle

Flowstone speleothem growth beneath Mount Arthur, New Zealand shows a clear relationship to vegetation density and soil development on the surface above. Flowstone does not currently form beneath sub-alpine Nothofagus forest above ca. 1000–1100 m altitude but U-Th dating shows it has formed there during past intervals of warmer-than-present conditions including an early–mid Holocene optimum and the last interglacial from ca. 131–119 ka. Some flowstones growing beneath ca. 600 m surface altitude, currently mantled with dense broadleaf-podocarp forest, grew during full glacial conditions, indicating that local tree line was never below this altitude. This implies that Last Glacial Maximum annual temperature was no more than ca. 4 °C cooler than today. Flowstone growth appears to be a robust indicator of dense surface vegetation and well-developed soil cover in this setting, and indicates that past interglacial climates of MIS 7e, 5e, the early–mid Holocene and possibly MIS 5a were more conducive to growth of trees than was the late Holocene, reflecting regional temperature changes similar in timing to Antarctic temperature changes. Here, flowstone speleothem growth is a sensitive indicator of vegetation density at high altitude, but may respond to other factors at lower altitudes

Holocene hydroclimate changes in continental Croatia recorded in speleothem δ13C and δ18O from Nova Grgosova Cave

We present the first stable isotope (δ13C and δ18O) speleothem record from continental Croatia retrieved from two coeval stalagmites from Nova Grgosova Cave. U-Th dates constrain the stalagmite growth history from 10ka to the present, revealing coeval growth between 7.8 and 5.6ka. We interpret δ18O as an autumn/winter hydrological proxy related to changes of vapor source, precipitation amount, and/or seasonal rainfall distribution, while δ13C predominantly responds to spring/summer vegetation status and soil microbial activity. We identify several centennial to millennial-scale hydroclimate oscillations during this period that result from multiple forcing factors. Along with amount and source effect, it appears that some centennial variations were governed also by seasonal moisture balance. From 9.2 to 8.8ka BP, the local environmental setting was characterized by enhanced vegetation activity, while during the 8.2ka event the main feature was a change in precipitation seasonality. The most prominent change, identified in both δ13C records, is a sudden decline of vegetation and soil biological activity around 7.4 ka, indicating a precipitation decrease at a time of maximum plant growth in spring and summer and likely also reduced precipitation in autumn and winter. Although small in magnitude in these speleothems, a peak in δ18O and δ13C values at 4.3–4.1ka suggests that both summer and winter conditions were substantially drier during the 4.2ka event, in accordance with increased Mediterranean aridity and consistent with other global climate changes reported at this time. Compared to the present North Atlantic Oscillation (NAO) influence, we assume that millennial Holocene NAO-like variations were persistent through the Holocene via their effect on modifying local/regional air temperature, vapor origin, and inter- and intrannual precipitation distribution. Anthropogenic deforestation, which was the first major human impact on the environment during the Neolithic agricultural revolution, is excluded as a leading factor in δ13C variability since the first sedentary settlements were established further to the east in more arable locations along river valleys. However, the impact of intensive mining around the cave site during the last millennium is evident, with substantial deforestation driving an increase in δ13C

A time-space window between Eocene karst bauxite genesis and the first molasse deposition in the Dinaric Foreland Basin in the North Dalmatia, Croatia

Karst bauxite deposits in the North Dalmatian piggyback basin (NDPGB) are a part of the Mediterranean bauxite belt, which is the largest European bauxite deposit zone; however, there is a general lack of information regarding the genesis, age, and precursor of the bauxite deposits in this region. In this study, we combined detrital zircon U–Pb geochronology with compositional, mineralogical, and morphological data from four bauxite locations in the NDPGB to provide a new palaeogeographical and palaeoenvironmental evolution model for the Lutetian–Rupelian timeframe of the NDPGB. The Eocene climatic conditions began with the Palaeocene–Eocene Thermal Maximum event (∼56 Ma), followed by the Early Eocene Climatic Optimum (∼49 Ma) and Middle Eocene Climatic Optimum (∼40 Ma), and were completed as a cooling trend culminating around the Eocene/Oligocene boundary (∼34 Ma), with a shift towards an icehouse climate. These events were coeval with the continuous drift of the African continent towards Eurasia and the subsequent closure of the western part of the former Neo-Tethys Ocean associated with massive volcanic activity. Based on the bauxite deposits of the NDPGB, Early Eocene limestones formed in the last phase of the long-lasting Adriatic Carbonate Platform. The Middle Eocene orogenic activity resulted in an elevation in this area. High average temperatures, accelerated hydrological cycles and precipitation, and intensive continental weathering with increased volcanic carbon input resulted in favourable conditions for the development of karst bauxites at this time. Further Upper Eocene tectonic deformation of the NDPGB area resulted in the development of bauxite traps and enabled redeposition of the initial bauxite material. Subsequently, the bauxite deposits were covered with clastic carbonate molasse derived from the intensive erosion of the young Dinaric orogeny. The implications of this study are as follows. First, it provides new information on the timing of bauxitisation in the area by providing the first radiometric zircon geochronology, which refined and restricted the time window for bauxite formation in this region. Additionally, our results provide a new perspective on the possibility of aeolian precursors in karst bauxite formation and provide new constraints on the first tectonic marks of the initial Dinaric orogeny

A time-space window between Eocene karst bauxite genesis and the first molasse deposition in the Dinaric Foreland Basin in the North Dalmatia, Croatia

Karst bauxite deposits in the North Dalmatian piggyback basin (NDPGB) are a part of the Mediterranean bauxite belt, which is the largest European bauxite deposit zone; however, there is a general lack of information regarding the genesis, age, and precursor of the bauxite deposits in this region. In this study, we combined detrital zircon U–Pb geochronology with compositional, mineralogical, and morphological data from four bauxite locations in the NDPGB to provide a new palaeogeographical and palaeoenvironmental evolution model for the Lutetian–Rupelian timeframe of the NDPGB. The Eocene climatic conditions began with the Palaeocene–Eocene Thermal Maximum event (∼56 Ma), followed by the Early Eocene Climatic Optimum (∼49 Ma) and Middle Eocene Climatic Optimum (∼40 Ma), and were completed as a cooling trend culminating around the Eocene/Oligocene boundary (∼34 Ma), with a shift towards an icehouse climate. These events were coeval with the continuous drift of the African continent towards Eurasia and the subsequent closure of the western part of the former Neo-Tethys Ocean associated with massive volcanic activity. Based on the bauxite deposits of the NDPGB, Early Eocene limestones formed in the last phase of the long-lasting Adriatic Carbonate Platform. The Middle Eocene orogenic activity resulted in an elevation in this area. High average temperatures, accelerated hydrological cycles and precipitation, and intensive continental weathering with increased volcanic carbon input resulted in favourable conditions for the development of karst bauxites at this time. Further Upper Eocene tectonic deformation of the NDPGB area resulted in the development of bauxite traps and enabled redeposition of the initial bauxite material. Subsequently, the bauxite deposits were covered with clastic carbonate molasse derived from the intensive erosion of the young Dinaric orogeny. The implications of this study are as follows. First, it provides new information on the timing of bauxitisation in the area by providing the first radiometric zircon geochronology, which refined and restricted the time window for bauxite formation in this region. Additionally, our results provide a new perspective on the possibility of aeolian precursors in karst bauxite formation and provide new constraints on the first tectonic marks of the initial Dinaric orogeny

Persistent influence of obliquity on ice age terminations since the Middle Pleistocene transition.

Radiometric dating of glacial terminations over the past 640,000 years suggests pacing by Earth's climatic precession, with each glacial-interglacial period spanning four or five cycles of ~20,000 years. However, the lack of firm age estimates for older Pleistocene terminations confounds attempts to test the persistence of precession forcing. We combine an Italian speleothem record anchored by a uranium-lead chronology with North Atlantic ocean data to show that the first two deglaciations of the so-called 100,000-year world are separated by two obliquity cycles, with each termination starting at the same high phase of obliquity, but at opposing phases of precession. An assessment of 11 radiometrically dated terminations spanning the past million years suggests that obliquity exerted a persistent influence on not only their initiation but also their duration

Quaternary environmental evolution in the South Carpathians reconstructed from glaciokarst geomorphology and sedimentary archives

The Carpathian island-type glaciokarst has a great potential of preserving signals of past environments, archived in cave deposits like speleothems and clastic infills. We present here the geomorphology and structural control of several relict alpine caves and the surrounding glaciated marble karst in the Făgăraș Mountains. Four truncated and partially unroofed caves remained on the ridge-top of Mușeteica Mountain, above the glacial cirque, while a ponor cave that developed on the cirque bottom could be related to the Last Glacial Period. Structural measurements and cave morphology showed that the conduits formed at the intersection of foliation planes and tectonic fractures on the NE-SW and NW-SE directions. Cave development reflects three speleogenetic stages: 1) texture- and fabric-controlled dissolution and distension; 2) structurally-controlled breakdown; and 3) truncation, unroofing, and cave infilling with sediments. Slow diffuse dissolution was typical for the ridge-top caves, whereas M1 Cave developed by pressure flow

The SISAL database: a global resource to document oxygen and carbon isotope records from speleothems

Stable isotope records from speleothems provide information on past climate changes, most particularly information that can be used to reconstruct past changes in precipitation and atmospheric circulation. These records are increasingly being used to provide “out-of-sample” evaluations of isotope-enabled climate models. SISAL (Speleothem Isotope Synthesis and Analysis) is an international working group of the Past Global Changes (PAGES) project. The working group aims to provide a comprehensive compilation of speleothem isotope records for climate reconstruction and model evaluation. The SISAL database contains data for individual speleothems, grouped by cave system. Stable isotopes of oxygen and carbon (δ 18O, δ 13C) measurements are referenced by distance from the top or bottom of the speleothem. Additional tables provide information on dating, including information on the dates used to construct the original age model and sufficient information to assess the quality of each data set and to erect a standardized chronology across different speleothems. The metadata table provides location information, information on the full range of measurements carried out on each speleothem and information on the cave system that is relevant to the interpretation of the records, as well as citations for both publications and archived data. The compiled data are available at https://doi.org/10.17864/1947.147

Geochemical investigations of Corchia speleothems: implications for past climate change

© 2016 Dr. Petra BajoThis PhD thesis addresses three research questions using speleothems from Corchia Cave (Italy). An outline of the major findings follows. The first question concerns glacial-interglacial cycles. The greatest obstacle in resolving the question of which orbital parameter (or combination thereof) forces Earth’s climate to switch between glacial and interglacial states is a lack of radiometrically dated records of glacial terminations. In this study, three stalagmites (CC8, CC119 and CC122) were precisely and accurately dated using the U-Pb dating method, and a composite age-depth model developed. The speleothem chronology was then transposed to a series of deep-sea sediment records, allowing three glacial terminations during the Middle Pleistocene Transition (MPT) to be radiometrically dated. The results reveal that Terminations XII and X are separated by two obliquity cycles, and that Marine Isotope Stages 25 to 22 are not part of a 100-kyr cycle as previously thought. Both terminations started at the same phase of obliquity but show an inconsistent relationship with precession-driven maxima in summer insolation intensity. This implicates obliquity as the major forcing parameter, while the role of precession is less conclusive. The second question concerns the integrity of speleothems for radiometric dating. Speleothems are considered as one of the most suitable materials for U-series dating. High-resolution U-Th dating of Corchia Cave stalagmite CC26, however, revealed a number of age outliers, which was unexpected due to the otherwise pristine appearance of the speleothem. The aim was to explore the potential causes for these outliers. By using a multi-aliquot approach, analytical problems were eliminated. Micro-CT analyses revealed a limited number of micro-voids, and it is proposed that these were pathways for small (localised), but significant (in terms of dating implications) U loss. Uranium-loss modeling constrains the possible timing of the diagenetic processes. These results show that such “invisible” diagenesis has implications for the accuracy of U-Th based chronologies for speleothems and suggests a need for a more careful approach, particularly in studies which are based on low-resolution dating. The third and final question relates to the drivers of stable carbon isotope (δ13C) changes in Corchia Cave speleothems at the onset of interglacials. The ‘dead carbon proportion’ (DCP) record from stalagmite CC26 was used to develop a more robust interpretation of the factors driving carbon isotope variation. High DCP (44.8 to 68.8%) was interpreted as a result of two processes: closed-system dissolution and sulphuric-acid dissolution. A ~parallel decrease in δ13C and DCP during the Holocene provides support for the previous interpretation of δ13C as reflecting long-term post-glacial soil recovery. Additionally, short-term changes in DCP are compared to the Mean Anomaly Index based on the trace element and stable isotope record from the same specimen (Regattieri et al., 2014), which reveals that DCP is also sensitive to millennial-scale changes in recharge hydrology

Plan upravljanja istraživačkim podacima - UNLOCK-CAVE

Dokument pod nazivom "Plan upravljanja istraživačkim podacima - UNLOCK-CAVE" daje informacije o podacima prikupljenim za vrijeme provedbe uspostavnog istraživačkog projekta "UNLOCK-CAVE - Istraživanje paleoklimatske varijabilnosti visoke rezolucije pomoću posrednih pokazatelja u sigama iz Nove Grgosove spilje (UIP-2020-02-7355)" te načinu na koji se isti obrađuju i pohranjuju