Detection of the historical Askja ad 1875 and modern Icelandic cryptotephras in varved lake sediments – results from a first systematic search in northern Poland

Volcanic ash can disperse thousands of kilometres from the source volcano and provide valuable chronostratigraphic markers for palaeoclimate studies. We present new cryptotephra findings of historical and modern Icelandic eruptions in annually laminated lacustrine sediment records from several sites within a 570 km SW–NE transect across northern Poland. Sediments from the two lakes Wąsoskie and Szurpiły contain glass shards originating from the Plinian Askja ad 1875 eruption and showing bimodal, rhyolitic and dacitic affinities. A further cryptotephra finding in Lake Lubińskie suggests a potential origin from the Hekla ad 1845 eruption. These new findings extend the tephra dispersal map towards the south-east and provide valuable isochrons for the synchronisation of palaeoclimate proxy data at the termination of the Little Ice Age in central eastern Europe. Very low glass concentrations of modern cryptotephra in Lake Wąsoskie were potentially correlated with the Eyjafjallajökull ad 2010 eruption. Further findings in the uppermost sediments of lakes Szurpiły and Żabińskie in north-eastern Poland tentatively suggest other sources from either the Hekla and/or Kamchatkan volcanoes.     

Layer silicates from a rodingite and its blackwall from Przemiłów (Lower Silesia, Poland): Mineralogical record of metasomatic processes during serpentinization and serpentinite recrystallization

Summary Minute inclusions of phlogopite and a chlorite-vermiculite intergrade mineral occur in the vesuvianite from rodingite at Przemiów (Lower Silesia). The same inclusions were found in its blackwall, i.e. outer metasomatic zone formed at the expense of adjacent ultrabasic rock. These findings demonstrate that potassium was released from the rodingite protolith during the Ca-metasomatism that accompanied low-temperature serpentinization and was consumed by phlogopite formed in the rodingite blackwall. Fresh phlogopite persists as small inclusions in vesuvianite. The abundant phlogopite-derived intergrade chlorite-vermiculite in the blackwall documents the potassium-rich composition of the protolith of the rodingite, though its primary chemistry is highly modified during metasomatic processes. The rodingite blackwall can be useful as tracer of the metamorphic and tectonic episodes obscured during complex geological evolution of the ophiolite.

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Schichtsilikate von Rodingit- Blackwalls aus Przemiów (Niederschlesien, Polen): Mineralogische Dokumentation metasomatischer Prozesse während der Serpentinisierung und der Rekristallisation von Serpentinit

Zusammenfassung Winzige Einschlüsse von Phlogopit und einem K-führenden Chlorit-Vermiculit Mineral wurden in Vesuvian aus Rodingiten von Przemiów (Niederschlesien) gefunden. Dieselben Minerale treten in der sogenannten Blackwall, i.e. der äußeren metasomatischen Zone, die sich auf Kosten der angrenzenden Ultrabasite gebildet hat, auf. Diese Ergebnisse zeigen, daß Kalium aus dem Rodingit-Protolith während der Ca-Metasomatose, die die Niedrig-Temperatur 5erpentinisierung begleitete, freigesetzt wurde und von Phlogopit, der sich in der Blackwall bildete, konsumiert wurde. Frische kleine Phlogopite sind als Einschlüsse in Vesuvian erhalten geblieben. Das aus dem Phlogopit entstandene verbreitete Chlorit-Vermiculit Mineral belegt eine Kaliumreiche Zusammensetzung des Rodingit-Protoliths, obwohl die primäre Chemie durch metasomatische Prozesse stark verändert wurde.

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With 7 Figures     

Glacial–interglacial productivity and environmental changes in Lake Biwa,Japan: A sediment core study of organic carbon,chlorins and biomarkers

Temporal changes in paleoproductivity of Lake Biwa (Japan) over the past 32 kyr have been studied by analyzing bulk organic carbon and photosynthetic pigments (chlorins) in the BIW95-5 core. Primary productivity was estimated on the assumption of C/N_org values of 8 for autochthonous organic matter (OM) and 25 for allochthonous OM and using an equation developed for the marine environment. The estimate indicates that primary productivity ranges from 50 to 90 g C m^?2 yr^?1 in the Holocene, while it is ～60 g C m^?2 yr^?1 on average in the last glacial. Pheophytin a and pheophorbide a are the major chlorins. A downcore profile of chlorin concentration normalized to autochthonous organic carbon (OC) shows a decreasing trend. Chlorin productivity was corrected by removal of the effect of post-burial chlorin degradation. The temporal profile of chlorin productivity thereby obtained resembles that from autochthonous OC.The difference in primary productivity between the Holocene and the glacial for the lake is markedly smaller than that for Lake Baikal situated in the boreal zone. This difference between the two lakes is probably caused by the difference in their climatic conditions, such as temperature and precipitation. Precipitation at Lake Biwa is relatively large during the glacial and the Holocene because of the continuous influence of the East Asian monsoon. Lake Baikal precipitation is generally small as a result of control by the continental (Siberia) climate regime. In addition, a significant difference in productivity between the glacial and the Holocene for Lake Baikal may be essentially controlled by the hydrodynamic systems in the lake.Lake Biwa terrigenous OM input events occurred at least five times over the period 11–32 kyr BP, suggesting enhanced monsoon activity. Molecular examination of the layer with a large input of terrigenous OM during the Younger Dryas indicates that concentrations of terrigenous biomarkers such as n-C₂₇–C₃₁ alkanes, lignin phenols, cutin acids, ω-hydroxy acids and C₂₉ sterols are high, suggesting that soil OM with peat-like material entered the lake as a result of flooding. An enhanced sedimentation rate in the last 3000 years might have been partially caused by agricultural activity around the lake.     

The Holocene record of Alberca de Tacámbaro,a tropical lake in western Mexico: evidence of orbital and millennial-scale climatic variability

Laminated sediments in a core from Alberca de Tacámbaro, western central Mexico, provide a high-resolution record of palaeoclimatic variability for most of the Holocene. Using compositional and textural characteristics we identified 14 facies classified in biogenic, clastic and volcaniclastic groups, in which diatoms and other algal remains are the most common components. In addition to facies analysis, high-resolution geochemical data from continuous core scanning XRF and the analysis of discrete samples for organic and inorganic carbon content, provide the basis for palaeoclimatic reconstruction. The age model indicates that the record spans from 9.4 cal ka bp toad 1760. Three main phases in the sequence are identified, controlled by millennial-scale variability. During the period between 9.4 and 5.7 cal kabp , the lake is dominated by siliceous organisms. Drier conditions between 8.2 and 6.3 cal kabp are linked to decreases in summer insolation and solar irradiance. By 5.7 cal kabp , the change in sedimentation is related to the increase in El Niño Southern Oscillation frequency. Evidence of the occurrence of dry conditions during the archaeological Late Classic period (ad 600–900) and historical droughts are also documented in the Alberca de Tacámbaro record. Unprecedented changes in the landscape are recorded afterad 1520.     

A Variscan continental collision of the West Sudetes and the Brunovistulian terrane: a contribution from structural and metamorphic record of the Stronie Formation,the Orlica-Śnieżnik Dome,SW Poland

Structural, petrological and geochronological data from marbles and mica schists combined with those from highly disputable gneisses and eclogites of the Orlica-Śnieżnik Dome (OSD), gave new insights into Variscan evolution of eastern borderland of the West Sudetes. It is shown that the Variscan tectonometamorphic evolution of the OSD began with E–W oriented subhorizontal shortening (D1 stage) related to the collision of the West Sudetes terranes and the Brunovistulian terrane. The shortening led to generally upright folding, which resulted in formation of the steep N–S trending metamorphic planar fabric S1, thickening of the lithosphere and burial of the Stronie Formation under greenschist facies conditions. As a consequence of subsequent, near-coaxial gravity-controlled vertical shortening (D2), the S1 foliation was deformed in tight recumbent folds F2. The flattening strain was associated with the progression to amphibolite-facies conditions (from ca. 510 upto ca. 620°C) and uplift from depths corresponding to 9–10 kbar to depths corresponding to 7–8 kbar. On microscale, the flattening strain is documented by rotation of the mineral fabric overgrown by syn-D2 prograde garnet porphyroblasts. The Sm–Nd Grt–WR isochron age, correlated with the D2 event yields 346.5 ± 4.4 Ma. Further deformation and progressive metamorphism led to development of the subhorizontally disposed S2 axial plane schistosity, which terminated at the metamorphic temperature peak. During retrogression but still under ductile conditions of deformation, the S2 planes were reactivated during successive top-to-the-N shear movement of the OSD (D3 stage). Due to the mutual interaction of the OSD with the adjacent terranes the shear deformations were localized within marginal parts of these units. Finally, as a result of the NE–SW and the NW–SE oriented shortenings (D4 stage and D5 stage, respectively), both the structural surfaces and metamorphic isograds were regionally folded with W(NW)-ward plunges. A synthesis of new and existing data shows an overall similarity in sequence of Variscan deformations (D1–D2–D3) in the West Sudetes borderland to that observed in the eastern flank of the Moldanubian domain.     

From land to sea: provenance,composition, and preservation of organic matter in a marine sediment record from the North-East Greenland shelf spanning the Younger Dryas–Holocene

The organic matter content of marine sediments is often used to infer past changes in ocean conditions. However, the organic carbon pool preserved in coastal sediments is a complex mixture derived from different sources and may not reflect in situ processes. In this study, we combine taxonomic identification of reworked palynomorphs with pyrolysis organic geochemistry and reflected-light organic petrographic microscopy to investigate the provenance, composition and preservation of organic matter in a marine sediment core retrieved from the NE Greenland shelf. Our study reveals continuous yet variable input of land-derived organic carbon to the marine environment throughout the late Younger Dryas–Holocene, with the highest input of inert carbon in the late Younger Dryas. Although the sediments contain some recent marine palynomorphs, there is no other evidence of fresh marine organic carbon. In contrast, our results indicate that these shelf sediments represent a significant sink of recycled organic carbon. The results of pyrolysis geochemistry revealed that ~90% of the total organic carbon in the sediments is inert. The organic petrography analyses revealed that >70–84% of the organic carbon in the sediment core is terrigenous. Reworked dinoflagellate cysts showed a continuous provenance of Cretaceous land-derived material, most likely from the nearby Clavering Island. Our study points to the importance of constraining the organic matter origin, composition and preservation in marine sediments to achieve more accurate palaeoenvironmental reconstructions based on organic proxies.     

Preliminary results of a first record of gold and uranium in marble from Central Eastern Desert, Egypt: a witness for (syn- and post-?) metamorphic mineralization in metasediments

This paper records, for the first time, the mineralization of gold (0.98–2.76 ppm) and uranium (133–640 ppm) in marbles from the Arabian-Nubian Shield of the Eastern Desert of Egypt. These auriferous and uraniferous marbles are hosted by sheared and altered ophiolitic serpentinized ultramafic rocks of Gebel El-Rukham (ER), Wadi Daghbag (DG), and Wadi Al Barramiyah (BM). They occur as massive or banded in pod-like or bedded shapes. The ER and BM-mineralized marbles are impure calcitic, whereas the DG marble is impure calcitic to impure dolomitic. Their protolith are pure limestones and dolomitic limestones with probable argillaceous components (BM marble), and their metamorphism (Pan-African) was retrograde. Peaks of metamorphism were at granulite-amphibolite facies for the ER and BM marbles, forming diopside (Al₂O₃?=?0.17–1.07 wt.%) at 600–900°C and augite (Al₂O₃?=?2.45–9.40 wt.%) at 825–975°C, and at the amphibolite facies for DG marble, recrystallising the carbonate minerals and forming tremolite. The lowest temperatures of metamorphism were at the upper subgreenschist facies as chlorite (ER and BM marbles) and kaolinite (DG marble) were formed. Metamorphic fluids were, most probably, essentially binary H₂O–CO₂ mixtures with low NaCl and HF concentrations. Gold in the studied mineralized marbles occurs as native nuggets (10–35 μm) having globule, rod, crescent, and streak shapes, in pores, vugs, and fissures. The source of gold in all marbles is mostly the country ultramafic rocks. Timing of gold mineralization relative to the marblization and metamorphism of the country source ultramafic rocks was both syn- and post-metamorphic. Concerning the ER and DG marbles, it was syn-metamorphic, where Au liberation and transportation were mostly by the metamorphic fluids. The composition and temperature of these fluids were most probably inappropriate for formation of the sulfide complexes of gold. The gold mineralization of BM marble, on the other hand, was mostly post-metamorphic. The mineralising fluid was of surficial origin under oxidizing conditions. The encountered uranium minerals are of secondary origin such as autunite, uranophane, and carnotite. These minerals occur as fine oval aggregates and irregular grains (10–50 μm) usually filling fissures and vugs. The uranium mineralization can be classified as surficial of ages <1.5 Ma. It is proposed that the U was transported from its source (might be flesite and trachyte dikes for the ER and DG marbles and granite rocks for BM marble) to the marble rocks by surface and/or underground water related to the pluvial periods in Egypt. In BM marble, U and Au have mutual mineralizing fluid but different paragenesis.     

Clay minerals in sediments of Portuguese reservoirs and their significance as weathering products from over-eroded soils: a comparative study of the Maranhão, Monte Novo and Divor Reservoirs (South Portugal)

The Southern region of Portugal is subjected to several forms of over-erosion. Most leached products, mainly composed of fine particles containing nutrients, metals or pesticides, are easily transported by river flows. When these are hindered by a physical barrier such as a dam, the particulate load accumulates on the bottom of the reservoirs, often leading to a pronounced decrease of water quality. Bottom sediments from three reservoirs were subjected to grain-size analysis and a study of clay minerals by X-ray diffraction. Most sediments contain a diverse set of clay minerals, mostly illites, smectites, chlorites and kaolinites. The nature of the clay minerals reflects the nature of the parent rocks. During the cycles of transport and temporary deposition, they may undergo significant chemical and physical transformations, which lead to an increase of expandable properties and therefore, to a higher cationic exchange capacity, determining its important role as vehicles of environmental pollutants.