High-Reesolution Magnetostratigraphy of Speleothems from Snežna jama, Kamnik-Savinja Alps, Slovenia

Snežna jama je velika vodoravna fosilna epifreatična jama. Leži v grebenu Raduhe, V delu Kamniško Savinjskih Alp v SV Sloveniji. V bližini vhoda je v jami v okrog 3 m visok prerezu razgaljeno zaporedje plasti sig s številnimi prekinitvami rasti in izdatno terigeno komponento v spodnjem delu. V 2,4 m dolgem zveznem profilu smo vzeli zaporedne vzorce , ki smo jih proučili z termalno demagnetizacijsko metodo in metodo spreminjajočega magnetnega polja. Magnetostratigrafske analize so pokazale 7 normalnih in 6 reverznih magnetocon. Magnetne lastnosti se dobro ujemajo z litološko mejo v profilu sige. Spodnji del profila kaže večjo magnetno susceptibilnost in močnejšo remanentno magnetizacijo. Sprememba lastnosti v profilu nakazuje pomembno paleogeografsko spremembo v času nastajanja sige. Starost sige sega izven dosega datacijske metode alfa spektrometrične analize U razpadne vrste; ravnotežje U izotopov pa nakazuje starost večjo od 1,2 Ma. Najbolj verjetna starost sige, ki jo dobimo z korelacijo s primerjavo z geomagnetno časovno skalo je bodisi 3,0 do 5,0 ali 1.8 do 3.6 Ma. Starost jame lahko primerjamo z nekaterimi brezstropimi jamami na krasu v JZ Sloveniji, kjer sedimentacijo v jamah postavljamo v mesinsko obdobje. Snežna jama je bila dvignjena v sedanjo višino z mlajšimi (plio-pleistocenskimi) dvigovanji Alpskega loka.The Snežna jama Cave is located in the Kamnik-Savinja Alps, NE Slovenia, in a Raduha Ridge. The cave is a huge, more or less horizontal fossil phreatic/epiphreatic conduit. It is penetrated by vertical shafts – invasion vadose (proglacial) caves. Close to the cave entrance, there is about 3 m high wall composed of speleothems - a complex sequence of flowstone with numerous breaks in deposition, six of them are principal. The lower part of the profile (about 85 cm) contains abundant terrigenous component (terra rossa-derived clay). Stalagmites developed in several periods are completely buried by nearly horizontal younger sequences of flowstone. Continuous speleothem log was recovered from the profile in a total length of about 2.4 m. The rock column was cut to cubes in the laboratory (2x2x2 cm) and studied both by thermal demagnetisation (23 samples, 12 steps - 20 to 620 ¡C) and alternating field method (98 samples, 14 steps - 1 to 100 mT). Magnetic properties identified the lithological boundary. In contrast to the upper part, the lower one shows both higher magnetic susceptibility and higher remanent magnetisation. The turn point can indicate important palaeogeographical change. Magnetostratigraphic log is composed of 7 normal and 6 reverse polarised magnetozones. The age of speleothems detected by the U-series alpha-counting spectrometry falls outside the method range, i.e. over 350 ka. Uranium isotopic equilibria indicate the age over 1.2 Ma. The age of the fill is pre-Quaternary, clearly older than 1.77 Ma. The most probable age from correlation with geomagnetic polarity timescales is about 3.0 to 5.0 or 1.8 to 3.6 Ma. Both possibilities can indicate the growth rate of speleothems of about 1.1 to 1.3 m per 1 Ma. The age of speleogenesis can be compared to some of unroofed caves in the area of the Classical Karst (SW Slovenia) connected with the Messinian period. Snežna jama was uplifted to high altitudes by younger (Plio-Pleistocene) uplift of the Alpine chain

Cave Sediments from Postojnska–Planinska Cave System (Slovenia): Evidence of Multi-Phase Evolution in Epiphreatic Zone

The Postojnska jama–Planinska jama cave system and number of smaller adjacent caves are developed in the Postojnski kras. These caves are located between two dextral strike-slip fault zones oriented in the Dinaric direction. The caves contain lith­ologically diversified cave fill, ranging from speleothems to allo­genic fluvial sediments. The allogenic clastic material is derived from a single source, Eocene siliciclastics of the Pivka Basin. Small differences in mineral/petrologic composition between the sediments can be attributed to different degrees of weather­ing in the catchment area and homogenization of source sedi­ments. Thick sequences of fine-grained laminated sediments, deposited from suspension are common. The depositional en­vironment was mostly calm, but not completely stagnant. Sucha sedimentary environment can be described as cave lacustrine, withdeposition from pulsed flow. The homogeneity of the pa­laeomagnetic data suggests rapid deposition by a number of short-lived single-flood events over a few thousand years. This depositional style was favourable for recording of short-lived excursions in the palaeomagnetic field. The sediments were originally not expected to be older than Middle Quaternary in age (i.e. about 0.4 Ma). Later numerical dating (Th/U and ESR) indicated ages older than 0.53 ka. New palaeomagnetic data from selected sedimentary profiles within the cave system detected normal polarization in muchof the profiles studied. Reverse polarized magnetozones, interpreted mostly as short-lived excursions of magnetic field, were detected in only a few places. Therefore, we interpreted most of the sediments as be­ing younger than 0.78 Ma, belonging to different depositional phases within the Brunhes chron. Palaeomagnetic properties of two profiles in caves intersected by the artificial tunnel be­tween Postojnska jama and Črna jama had reverse polarized magnetozones and of sediments in Zguba jama, may indicate an age muchgreater than 0.78 Ma. The cave system has evolved over a long period of time, governed by the functioning of Pla­ninsko polje in the relation to the evolution of the resurgence area in Ljubljana Moor further to the east. General stabilization of the hydrological system withlow hydraulic head led to the evolution of caves in epiphreatic and paragenetic conditions over a long time-span. Individual cave segments or passages were completely filled and exhumed several times during the evolution of the cave. Alternation of depositional and erosional phases may be connected withchanging conditions within the cave system, the functioning of the resurgence area, collapse, climatic change, tectonic movement and the intrinsic mecha­nisms of contact karst

A lacustrine record of the early stage of the Miocene Climatic Optimum in Central Europe from the Most Basin, Ohře (Eger) Graben, Czech Republic.

21 pagesInternational audienceThis study reports on a ~ 150 m thick macrofossil-barren sequence of siliciclastic sediments from a Burdigalian age (Early Miocene) freshwater lake. The lake was located within an incipient rift system of the Most Basin in the Ohře (Eger) Graben, which was part of the European Cenozoic Rift System, and had an original area of ≈ 1000 km2. Sediments from the HK591 core that cover the entire thickness of the lake deposits and some of the adjacent stratigraphic units were analysed by X-ray fluorescence spectroscopy (a proxy for element composition) and magnetic polarity measurement. The element proxies were subjected to frequency analysis, which provided estimated sedimentation rates, and allowed for sediment dating by magnetostratigraphy and orbital tuning of the age model. Based on the resulting age model and the known biostratigraphy, the lake was present between 17.4 and 16.6 Ma, which includes the onset of the Miocene Climatic Optimum in the latest Early Miocene. The identification of orbital forcing (precession, obliquity and short eccentricity cycles) confirms the stability of the sedimentary environment of the perennial lake in an underfilled basin. The dating allowed the sediment record to be interpreted in the context of the current knowledge of the European climate during that period. The stability of the sedimentary environment confirms that precipitation was relatively stable over the period recorded by the sediments

Palaeomagnetic research on karst sediments in Slovenia

We have conducted palaeomagnetic and magnetostratigraphic research on karst sediments in Slovenia since 1997. More than 2,000 samples were taken and analysed in 36 different profiles at 21 locations in caves and on the surface. Standard palaeomagnetic analyses were used (thermal and alternating field demagnetisation, magnetic susceptibility measurements, etc.). There is no evidence of younger marine deposition than Eocene in the SW part of Slovenia. Younger sediments occur only in caves and very rarely on the karst surface (different soils and a few remains of terrigeneous sediments). Marine and terrestrial Tertiary to Plio–Quaternary deposition occurs in the SE and E Slovenia. Chronostratigraphy of cave sediments in SW Slovenia completed by Rado Gospodarič in the 1980s was based on Pleistocene warm/cold cycles. Later Th/U dating indicated that speleothems from different caves in Slovenia are older. New dating principally results from palaeomagnetism and magnetostratigraphy of cave sediments calibrated, in some sites, by Th/U, palaentological and geomorphological analyses. Calibrated data contributed to the reconstruction of speleogenesis, deposition in caves, and indirectly to the evolution of karst surfaces and succession of tectonic movements. The evolution of caves in the Slovenian territory took part within one post-Eocene karstification period. This period continues to the present, and can be subdivided into individual, but not well limited, phases related to Cenozoic palaeogeographical changes. The period contains distinct phases of massive deposition in caves with as yet still preserved sediments dated to about 5.4–4.1 Ma (Miocene–Pliocene), 3.6–1.8 Ma (Pliocene) and Quaternary, following the cessation of Miocene deposition in the Pannonian Basin in the central, E and SE Slovenia and post-Messinian evolution in the SW and W Slovenia

Palaeomagnetic and U-series Dating of Cave Sediments in Baradla Cave, Hungary

Drobnozrnati siliklastični sedimenti glavne galerije in gornjega nivoja jame Baradla, izkazujejo veliko homogenost v zgradbi in sedimentnih teksturah. Paleomagnetne analize kažejo normalno polarizacijo vseh vzorcev, kar pomeni starost, ki je mlajša od meje Brunhes/Matuyama pri 780 ka. Siga oz. stalagmiti, ki pokrivajo siliklaste v gornjem jamskem nivoju, vsebujejo tudi reverzno polarizirane vzorce, katerih datacije z uran torijevo metodo kažejo na starost 114-115 ka, kar nakazuje na dogodek Blake. Homogenost sedimentov lahko razložimo z enkratnim dogodkom, kjer je zapolnitev s sedimentom povzročil zastoj pretoka. Temu so lahko botrovali geološki (npr. podor) ali paleoklimatski vzroki pred približno 130-150 ka, kolikor je tudi najvišja starost sedientov v sistemu Domica-Baradla izmerjena z metodo uran-torij. Fine-grained siliciclastic sediments from the main gallery and upper cave level show nearly uniform composition and sedimentary textures. Palaeomagnetic analysis indicates normal magnetic polarisation of all samples, i.e. the age younger than Brunhes/Matuyama boundary at 780 ka. Flowstone/stalagmite covering siliciclastics in the upper cave level contains reverse polarised samples dated by U-series method to about 114–115 ka, which can be identified as the Blake Event. The uniform composition of sediments can indicate the infill of the cave during a single event caused by the blockage of drainage routes due to geological (collapse) or palaeoclimatic (ice) changes, which took part before ca 130 to 150 ka as indicating by the oldest U-series data from the whole Domica–Baradla Cave System.

Cave Fill in the Črnotiče Quarry, SW Slovenia: Palaeomagnetic, Mineralogical and Geochemical Study

V kamnolomu Črnotiče je bila izkopana s sedimenti in sigo z zapolnjena jama. Analiziran je bil 1,75 m visok del zapolnitve. Profil je sestavljen iz pasovite karbonatne kamnine z interkalacijami rdečih ilovic. Te so se odložile na erozijsko/korozijsko površino starejše, že močno prekristaljene sige. Pasovita in laminirana karbonatna kamnina profila je sestavljena iz prekristaljenega kalcilutita ter je podobna sladkovodnemu apnencu. Značilna laminiranost nakazuje nastanek iz bogatih organskih filmov. Rdeče ilovice sestavljajo kremen, smektit, vermikulit, gibbsit, pM kaolinit, goethit, atanas, rutil, haematit, kalcit, sljude in glinenec. Vsebujejo tudi pelete z več Mn hidroksioksidov. Rdeče ilovice so ostanki preperevanja, odloženi v z vodo zasičenem okolju. Za v profilu vzete vzorce so značilne srednje do visoke vrednosti Jn kar je posledica velike količine železovih mineralov. Srednja paleomagnetna smer je za skupino normalnih paleomagnetnih polaritet enaka D = 10.6°; I = 55.0°, za skupino reverznih polaritet pa D = 173.0°; I = -31.3°. Zgornji del profila kaže reverzno paleomagnetno smer, ki jo prekinjata dve normalni magnetozoni. Sodeč po razporeditvi posameznih magnetozon sklepamo, da je vrh najvišje normalno polarizirane cone primerljiv z dogodkom Olduvai (1.76/1.79 Ma) kot najmlajšo možnostjo, ostali del profila pa je lahko le starejši.A fossil cave, filled with cave sediments was open in the Črnotiče Quarry. An about 1.75 m high section was analysed. Profile consists of banded carbonate rocks intercalated by red clays which was deposited on corroded/ eroded surface of older speleothems. Banded and laminated carbonate rocks are composed of recrystallized calcilutite resemble freshwater limestones. Characteristics of lamination could indicate its origin from organic-rich films. Red clays are composed of quartz, smectite, vermiculite, gibbsite, pM kaolinite, goethite, anatase, rutile, haematite, calcite, micas and feldspar. They contain pellets with Mn hydroxyoxides. That red clays are weathering products redeposited in water-saturated environment. Samples are characterised by intermediate up to high magnetic values of Jn which is caused by the presence of high amount of Fe-minerals. Mean palaeomagnetic directions are for the group of normal palaeomagnetic polarity equal to D = 10.6°; I = 55.0°, and for the group of reverse polarity than D = 173.0°; I = -31.3°. The top part of the profile shows reverse palaeomagnetic direction interrupted by two normal magnetised zones. According to the arrangement of individual magnetozones we assume, that the top of the highest normal polarised magnetozone could be correlated with the Olduvai event (1.76/1.79 Ma) as the youngest possibility, and therefore the rest of profile must be older

Fossil Vertebrates and Paleomagnetism Update of One of the Earlier Stages of Cave Evolution in the Classical Karst, Slovenia: Pliocene of Črnotiče II Site and Račiška Pečina Cave

For the first time in the Classical Karst, paleontological data enabled to match the magnetostratigraphic record precisely with the geomagnetic polarity timescale in two studied sites: (i) a series of speleothems alternating with red clays in Račiška pečina Cave (Matarsko podolje), and (ii) an unroofed paleocave of the Črnotiče II site (Podgorski kras Plateau) completely filled by fluvial clastic sediments covered by speleothems. The later sites are also characterized by a rich appearance of fossil tubes of autochthonous stygobiont serpulid Marifugia cavatica. The vertebrate record is composed mostly of enamel fragments of rodents and soricomorphs. Absence of rootless arvicolids as well as taxonomic composition of the mammalian fauna suggests the Pliocene age of both sites. For (i) Račiška pečina (with Apodemus, cf. Borsodia) it was estimated to middle to late MN17 (ca 1.8–2.4 Ma), while (ii) the assemblage from Črnotiče II (with Deinsdorfia sp., Beremedia fissidens, Apodemus cf. atavus, Rhagapodemus cf. frequens, Glirulus sp., Cseria sp.) is obviously quite older: MN15–MN16 (ca 3.0–4.1 Ma). In respect to congruence of biostratigraphic and paleomagnetic data and a reliable sedimentary setting of the samples we propose to apply the respective datum also as the time of one ancient speleogenetic phase in the Classical Karst

Križna jama (SW Slovenia): Numerical-and correlated-ages from cave bear-bearing sediments

Križna jama is a large river cave located between Loško and Cerkniško poljes under Križna gora Mount in southern Slo­venia. It has been known since the mid-19thcentury due to numerous cave bear finds. The cave is filled by complicated sequences of cave fluvial and lacustrine sediments, whichare recently partly eroded. We studied two paleontological exca­vations and profiles in the Medvedji rov to contribute to the solution of dating of bone-bearing lithological horizons. The Križna jama I profile consists of alternation of speleothem lay­ers (flowstone sheets withsmall stalagmites, sometimes within situ cemented Ursus gr. spelaeus bones) and fine-grained silici­clastics often withbones of cave bear. It can be correlated withthe upper part of the Križna jama II profile, but witha slightly less preserved stratigraphic record. Radiocarbon and U-series dates clearly indicate two different ages of cave bear thanato­cenoses in the Križna jama I profile: those above flowstone crusts were dated to ca. 47–45 ka by radiocarbon dating; those included in speleothem layers and clay interbeds are older than 94 ka (U-series date). The details of internal lithology, low thicknesses of layers and the state of bone preservation exclude expected sandwiching of younger layers into eroded/washed spaces among flowstones. Numerical dating excludes re-depo­sition of bear bones from older assemblage to sediments above flowstones. According to the paleomagnetic parameters (pre­vailing normal polarization), the deposition took place within the Brunhes Chron (< 780 ka). There were discovered in total four short-lived reverse excursions of the magnetic field. Ac­cording to U-series data, the upper one (profile I) might be correlated withthe Blake excursion. The lower ones are older than ca 190 ka and can be correlated withsome of the Jamaica-Pringle Falls, Namaku, Calabrian Ridge, Portuguese margin or Calabrian Ridge 1 excursions. Sediments in studied profiles were deposited during the Last Glacial (Weichselian), Eemian interglacial, Saalian glacial and Holsteinian interglacial

A cave response to environmental changes in the Late Pleistocene: a study of Budimirica Cave sediments, Macedonia

Budimirica Cave is a small cave located in the southern part of the Republic of Macedonia, inthe Kamenica Valley, a tributary to the Crna Reka and part of the Vardar river drainage network.The response of the cave to Late Pleistocene environmental changes is interpreted based on adetailed study of cave sediments, with previous data being supplemented, reinterpreted andcompared to the Ohrid Lake palaeoclimate record. The oldest exposed speleothems in the Budimiricasediment profile were deposited during the MIS 5a (radiometric age of ca 83 ka). Sandsto clays in the overburden are characterized by cycles separated by short-lived interruptions indeposition. They were deposited from a number of repeated flood events likely during the MIS4 stage, the Weichselian (Wurmian) Glaciation, correlating to aggradation in the Kamenica Valley.The top flowstone is correlated with a warmer climate excursion at 45–50 ka (MIS 3) recordedfrom the Ohrid Lake deposits. The whole section was extensively eroded during the MIS 2stage, due to strong incision in the Kamenica Valley, indicated by knickpoint retreat. The erosionsurface is overlain by a fossil-bearing breccia (with Ursus spelaeus) derived from frost shatteringof the cave walls close to the entrance due to climate deterioration and enlargement of theentrance by slope retreat during the MIS 2 stage. Budimirica Cave sediments reflect changes inthe Kamenica Valley, as well as the environmental changes during the last glacial-interglacialcycle, with clastic cave sediments deposited during glacial stadials, and erosion and flowstonedeposition characteristic of the interstadials. They also allow reconstruction of the evolution ofthe Kamenica Valley during the Late Pleistocene, with a general trend of valley incision hinderedby climate influenced river aggradation, but reinforced by river knickpoint retreat.</p

Palaeoenvironments and palaeoceanography changes across the Jurassic/Cretaceous boundary in the Arctic realm: case study of the Nordvik section (north Siberia, Russia)

The Jurassic/Cretaceous transition was accompanied by significant changes in palaeoceanography and palaeoenvironments in the Tethyan Realm, but outside the Tethys such data are very scarce. Here we present results of a study of the most complete section in the Panboreal Superrealm, the Nordvik section. Belemnite d18O data show an irregular decrease from values reaching up to 1.6 in the Middle Oxfordian and from 0.8 to 1.7 in the basal Ryazanian, indicating a prolonged warming. The biodiversity changes were strongly related to sea-level oscillations, showing a relatively low belemnite and high ammonite diversity during sea-level rise, accompanied by a decrease of the macrobenthos taxonomical richness. The most prominent sea-level rise is marked by the occurrence of open sea ammonites with Pacific affinities. Peak abundances of spores and prasinophytes correlate with a negative excursion in organic carbon d13C near the J/K boundary and could reflect blooms of green algae caused by disturbance of the marine ecosystem.Web of Science33art. no. 1971