Late Pleistocene lacustrine sediments and their relation to red soils in the Northeastern margin of the Dinaric Karst

A large karst doline at section Hrastje – Lešnica in the Dolenjska region (SE Slovenia) was uncovered during the construction of Slovene highway No. A2. Its fill consists of brownish-yellow clay to silt with plant remains and ferrugineous coatings after root casts and gastropods (paleosol horizon) in the bottom, and overlying thick lacustrine laminated grey clayey sediments which were partly rubified. Brownish-yellow clay to silt contains quartz, chlorite, muscovite and feldspars transported as external clastic material from evolved karst and non-carbonate landscapes from surroundings into the site. The material is well weathered only in the area of the paleosol horizon. The strongly impoverished malacocoenosis indicates any Quaternary warm phase characterized by light semi-open forest with patches of open ground habitats. Only the last paleomagnetic sample in the bottom of sediment sequence shows reverse polarity of magnetic field and represents the geomagnetic excursion, i.e., the Blake excursion at ca 120–112 ka (MIS 5e), rather than Brunhes/Matuyama boundary at 0.78 Ma (MIS 19). Thick lacustrine laminated grey clayey sediments above are also dominated by quartz, muscovite, chlorite and feldspar. That overlying sediment was almost unweathered (content of feldspars, muscovite and chlorite); it was only slightly rubified on its surface, in middle part of the section and at the contact with the underlying karstified limestone slope of the depression. The grey sediment has a different mineralogical composition than underlying soils (e.g., lack of quartz, chlorite) and non-carbonate residue of the host limestone. Therefore, the grey sediments could not serve as a parent (source) material for terra rossa formation in the broader area (i.e., polygenetic red soils developed in paleoclimate related to current Mediterranean climatic conditions). Laminated grey sediment was deposited in a rather cold climate. Relatively poor palynospectra may indicate transport of pollen grains out of the depocentre with flowing water and/or the rapid deposition. The latter is supported by insufficiently centered paleosecular variations. Plant assemblages indicate that the dominant cover of the surrounding landscape was temperate climatic zone riparian forest with some quite humid environment as wetlands and ponds on periodically flooded plain. The regional correlation, based especially on an abundance of Fagus, indicates the deposition at the beginning of the last glacial cycle (Würmian) in its warmer substage – MIS 5c (ca 105–95 ka). All paleomagnetic samples from this part of the sediment section show normal magnetization and negligible clockwise rotation of 1.8° ± 4.7°.Key words: karst sediments, mineralogy, gastropods, palynology, paleomagnetism, paleoenvironment, Dolenjska region, Slovenia.Pozno pleistocenski jezerski sedimenti in njihova povezava z rdečimi tlemi na severovzhodnem robu Dinarskega krasa Na Dolenjskem krasu je bila med graditvijo trase A2 slovenskega avtocestnega križa na odseku Hrastje–Lešnica razgaljena večja vrtača. V spodnjem delu je bila povsem zapolnjena z rjavkastorumenim sedimentom glinene do meljaste frakcije, v zgornjem delu pa z debelim zaporedjem laminiranega sivega glinenega sedimenta, ki je bil ponekod rahlo rubificiran. Rjavkasto rumeni glineni do meljasti sediment na dnu vrtače, v katerem so posamezni rastlinski ostanki, s koreninami povezane ferigene skorje in gastropodi (paleotalni horizont), vsebuje kremen, klorit, muskovit in plagioklaze. Ti so bili preneseni v vrtačo kot klastični material z bližnjih območij razvijajočega se kraškega in nekarbonatnega (fluvialnega) površja. Dobro preperel material je le v območju paleotalnega horizonta. Močno osiromašena malakocenoza nakazuje eno od toplih faz kvartarja, ko so prevladovali svetli gozdovi z redkimi drevesi in jasami odprtih talnih habitatov. Samo zadnji od paleomagnetnih vzorcev na dnu raziskanega sedimentnega zaporedja kaže reverzno polarnost magnetnega polja. Menimo, da ta reverzna polarnost kaže na t. i. Blakeovo geomagnetno ekskurzijo pred cca 120.000 in 112.000 leti (MIS 5e) in ne meje Brunhes/Matuyama pred 780.000 leti (MIS 19). Tudi v debelem zaporedju sivih laminiranih glinastih jezerskih sedimentov prevladujejo med minerali kremen, muskovit, klorit in glinenci. Glede na ohranjenost glinenih mineralov, muskovita in klorita sklepamo, da so ti sedimenti skoraj neprepereli; rahlo so rubificirani le na površju, v osrednjem delu profila in na stiku z zakraselo podlago vrtače. Mineraloška sestava sivih sedimentov je drugačna kot v spodaj ležečem talnem horizontu, kjer je manj kremena in klorita, razlikuje pa se tudi od nekarbonatnega preperinskega ostanka apnenčaste prikamnine. Kot tak torej siv sediment ni izvorni material na sosednjih območjih pogoste terre rosse (poligenetska rdeča tla, razvita v pleoklimatskih razmerah, podobnih današnjemu mediteranskemu podnebju). Laminirani sedimenti so se odložili v razmeroma hladnem obdobju. Dokaj siromašen palinospekter lahko kaže po eni strani, da so bila pelodna zrna odstranjena iz depocentra s tekočo vodo, po drugi pa na visoko hitrost sedimentacije. V prid temu procesu pritrjujejo tudi premalo centrirane paleosekularne variacije. Rastlinske združbe nakazujejo, da je bila bližnja okolica v glavnem porasla z obrežnimi gozdovi zmernega podnebnega pasu, kjer so se v humidnih obdobjih poplavljenih ravnic občasno pojavljala tudi mokrišča in manjše ojezeritve. Regionalne korelacije, ki temeljijo predvsem na veliki količini pelodov bukve (Fagus) kažejo, da so se sivi glinasti sedimenti odlagali v toplejšem obdobju na začetku zadnjega poledenitvenega cikla (Würm) med t. i. MIS 5c pred okoli 105.000 do 95.000 leti. Vsi paleomagnetni vzorci tega dela sedimentnega profila kažejo normalno magnetizacijo in zanemarljivo rotacijo 1,8° ± 4,7° v smeri urinega kazalca.Ključne besede: kraški sedimenti, mineralogija, polži, palinologija, paleomagnetizem, paleookolje, Dolenjska, Slovenija.

Low-temperature magnetism of alabandite : Crucial role of surface oxidation

Manganese(II) monosulphide crystallizes into three different polymorphs (alpha-, beta-, and gamma-MnS). Out of these, alpha-MnS, also known as mineral alabandite, is considered the most stable and is widespread in terrestrial materials as well as in extraterrestrial objects such as meteorites. In this study, a low-temperature antiferromagnetic state of alpha-MnS was investigated using macroscopic magnetic measurements as induced and remanent field-cooled (FC) and zero-field-cooled (ZFC) magnetizations and magnetic hysteresis. Both natural alabandite and synthetic samples show (i) Néel temperatures in a narrow temperature range around 153 K and (ii) a rapid increase of the magnetization around 40 K. An anomalous magnetic behavior taking place at about 40 K was previously ascribed to the magnetic transition from a high-temperature antiferromagnetic to a low-temperature ferromagnetic state documented for non-stoichiometric alpha-MnS slightly enriched in manganese. However, our detailed microscopic observations and, in particular, oxidation experiments indicate that the anomalous magnetic behavior around 40 K is caused by a presence of oxide layer of ferrimagnetic hausmannite (Mn3O4) on the surface of alpha-MnS rather than being an intrinsic property of nearly stoichiometric alpha-MnS.Peer reviewe

Bat urea-derived minerals in arid environment. First identification of allantoin, C4H6N4O3, in Kahf Kharrat Najem Cave, United Arab Emirates

Kahf Kharrat Najem Cave is a small cave in United Arab Emirates (UAE) that hosts a bat colony which is the source of guano deposits and peculiar centimeter-long yellowish stalactites. The mineralogy and geochemistry of these deposits were analyzed using powder X-ray diffraction (XRD), energy dispersive X-ray spectroscopic microanalysis (EDX), scanning electron microscope (SEM), and stable isotope composition (δ13C and δ15N). Urea CO(NH2)2 was found to be the main compound of these stalactites, while allantoin C4H6N4O3 was found to be an accessory urea byproduct. This paper is the first to mention allantoin in a cave environment. We also identified rare sulfate minerals (aphthitalite, alunite) and phosphates that probably correspond to the archerite-biphosphammite series. The occurrence of these rare bat-related minerals is due to the extremely dry conditions in the cave, which accounts for the extraordinary preservation of the guano deposits and allows for the crystallization of these very soluble minerals.Publisher PDFPeer reviewe

Implications for behavior of volatile elements during impacts—Zinc and copper systematics in sediments from the Ries impact structure and central European tektites

This study has been funded through the Czech Science Foundation project 13-22351S. Paul Savage was supported by the Marie Curie IOF ‘Isovolc.’ Frederic Moynier is grateful to the European Research Council under the European Community's H2020 framework program/ERC grant agreement # 637503 (Pristine) and the Agence Nationale de la Recherche for a chaire d'Excellence Sorbonne Paris Cité (IDEX13C445), and for the UnivEarthS Labex program (ANR-10-LABX-0023 and ANR-11-IDEX-0005-02). Parts of this work were supported by IPGP multidisciplinary program PARI, and by Region Île-de-France SESAME Grant no. 12015908.Moldavites are tektites genetically related to the Ries impact structure, located in Central Europe, but the source materials and the processes related to the chemical fractionation of moldavites are not fully constrained. To further understand moldavite genesis, the Cu and Zn abundances and isotope compositions were measured in a suite of tektites from four different substrewn fields (South Bohemia, Moravia, Cheb Basin, Lusatia) and chemically diverse sediments from the surroundings of the Ries impact structure. Moldavites are slightly depleted in Zn (~10–20%) and distinctly depleted in Cu (>90%) relative to supposed sedimentary precursors. Moreover, the moldavites show a wide range in δ66Zn values between 1.7 and 3.7‰ (relative to JMC 3-0749 Lyon) and δ65Cu values between 1.6 and 12.5‰ (relative to NIST SRM 976) and are thus enriched in heavy isotopes relative to their possible parent sedimentary sources (δ66Zn = −0.07 to +0.64‰; δ65Cu = −0.4 to +0.7‰). In particular, the Cheb Basin moldavites show some of the highest δ65Cu values (up to 12.5‰) ever observed in natural samples. The relative magnitude of isotope fractionation for Cu and Zn seen here is opposite to oxygen-poor environments such as the Moon where Zn is significantly more isotopically fractionated than Cu. One possibility is that monovalent Cu diffuses faster than divalent Zn in the reduced melt and diffusion will not affect the extent of Zn isotope fractionation. These observations imply that the capability of forming a redox environment may aid in volatilizing some elements, accompanied by isotope fractionation, during the impact process. The greater extent of elemental depletion, coupled with isotope fractionation of more refractory Cu relative to Zn, may also hinge on the presence of carbonyl species of transition metals and electromagnetic charge, which could exist in the impact-induced high-velocity jet of vapor and melts.PostprintPeer reviewe

Chemistry and Sr–Nd isotope signature of amphiboles of the magnesio-hastingsite-pargasite-kaersutite series in Cenozoic volcanic rocks: Insight into lithospheric mantle beneath the Bohemian Massif

Amphibole phenocrysts and xenocrysts from Cenozoic volcanic rocks of the Bohemian Massif (BM) belong to the magnesio-hastingsite-pargasite-kaersutite series. Their host rocks are mostly basaltic lavas, dykes and breccia pipe fills, less commonly also felsic rocks from rift zones along lithospheric block boundaries of the BM. The calculated p–T conditions suggest that almost all amphiboles crystallized in a relatively narrow temperature range (1020–1100 °C) at depths of 20–45 km (0.7–1.2 GPa) during the magma ascent. The initial 143Nd/144Nd and 87Sr/86Sr ratios of amphiboles (0.51266–0.51281 and 0.70328–0.70407, respectively) are similar to those of their whole rocks (0.51266–0.51288 and 0.70341–0.70462, respectively). This testifies to locally elevated proportions of recycled Variscan crustal material during melting of mantle peridotites rich in clinopyroxene–amphibole veins. These veins were formed by metasomatic fluids enriched in High Field Strength Elements and are isotopically similar to EM-1 mantle type.Fenokrysty a xenokrysty amfibolů kenozoických vulkanických hornin Českého masivu (ČM) náleží svým složením do magnesiohastingsit-pargasit-kaersutitové série. Jejich hostitelské horniny jsou především bazaltické lávy, žíly nebo brekciovité výplně komínů, méně často také felsické horniny z riftových zón podél hranic litosférických bloků ČM. Vypočtené p-T podmínky ukazují, že téměř všechny amfiboly krystalizovaly v relativně úzkém teplotním rozmezí (1020–1100 °C) v hloubkách 20–45 km (0,7–1,2 GPa) během výstupu magmatu. Iniciální izotopové poměry 143Nd/144Nd a 87Sr/86Sr v amfibolech jsou v rozmezí 0,51266–0,51281 a 0,70328–0,70407. To vypovídá o lokálně zvýšeném množství recyklovaného variského korového materiálu během tavení plášťového peridotitu bohatého na klinopyroxen-amfibolové žíly. Tyto žíly vznikly z metasomatických fluid obohacených o prvky s velkým iontovým potenciálem a jsou izotopově podobné obohacenému plášti typu 1 (EM-1)

Ověření obsahu azbestu v horninách lomu Sýkořice : závěrečná zpráva

Zpráva je volně šiřitelná. Anotace: U pěti vzorků hornin z lomu v Sýkořici byl vyhodnocován možný obsah azbestu. Horniny byly podrobeny makroskopickému a mikroskopickému pozorování a studiu elektronovým mikroanalyzátorem a práškovou rentgenovou difrakcí. V žádném ze studovaných vzorků nebyly nalezeny významné akumulace azbestových minerálů, jak jsou definovány právními normami ČR