Showing papers in "Geologica Belgica in 2010"

Distribution and contamination status of heavy metals in estuarine sediments near cua ong harbor, ha long bay, vietnam

Abstract: The distribution, controlling geochemical factors and contamination status of heavy metals in estuarine sediments near Cua Ong Habor, Ha Long Bay (Vietnam) were investigated. 36 surface sediment samples were collected and analyzed for major elements (Al, Ca, Fe, K, Mg, S), heavy metals (As, Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn), organic matter, loss on ignition (LOI), grain size composition and pH. Spatial distribution patterns of heavy metals as well as their controlling factors were elucidated based on geochemical mapping and statistical methods such as the Pearson Product- Moment linear correlation and Factor Analysis. The results illustrated that the distribution patterns of As, Cd, Cr, Cu, Ni, Pb and Zn are mainly controlled by organic matter and clay minerals and determined by the distribution of the fine- grained fraction (Φ < 63 µm) in the sediments. In contrast, Fe and Mn compounds seem to exert some control on the distribution of Co. Carbonates partly control the distribution of Mn, but are not important with respect to the other studied heavy metals. The contamination status by heavy metals was assessed based on comparison with Canadian, Wisconsin- United States and Flemish numerical Sediment Quality Guidelines, and calculation of Geo-accumulation Index (Igeo) and Enrichment Factor (EF). The results indicated that natural processes such as weathering and erosion of bedrock are the main supply sources of heavy metals in sediments near Cua Ong Harbor. Among the studied heavy metals, only As is of concern whereas Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn seem to reflect their background concentrations in sediments of Ha Long Bay.

Rietveld refinement strategy for quantitative phase analysis of partially amorphous zeolitized tuffaceous rocks

Abstract: The Rietveld method has become one of the most popular methods in quantitative mineralogical analysis based on X-ray powder diffraction. An estimate of the amorphous phase content can be made by introducing a known amount of an appropriate internal standard. This method was applied to a selected set of zeolitized tuffaceous rocks to develop guidelines for Rietveld quantitative phase analysis in complex mixtures. A local sensitivity analysis of selected refinable parameters was performed and phase abundance results for synchrotron and laboratory based X-ray diffraction data collection were compared. The calculated amorphous phase fraction showed a very high sensitivity towards the refined amount of internal standard, in particular when small amounts of amorphous phase were encountered in the samples. Optimal reproducibility of phase abundance results was obtained when a sufficient number of background polynomials was employed and the internal standard thermal parameters were not refined. A very good correlation between laboratory and synchrotron data was achieved when the communicated refinement strategy was followed, supporting the use of laboratory equipment for routine quantitative mineralogical analysis.

hiGh-FreQuencY cYcles And Their seQuence sTrATiGrAPhic conTeXT: orBiTAl ForcinG And TecT onic conTrols on deVoniAn cYcliciTY, BelGium

Abstract: The sequence stratigraphic approach has evolved into an important tool for stratigraphic analysis and does have an element of prediction. Several sequence models have been proposed and are in use, but there have been emotive discussions in the literature over these, as well as systems tracts and key surfaces. Metre-scale cycles (parasequences) are the building blocks of sequences and are an essential component of carbonate successions throughout the stratigraphic record. Their thickness and facies patterns, reflecting the longer-term changes in accommodation that affected deposition, enable the various systems tracts in a sequence to be recognised. There have been many arguments over the origin of parasequences with orbital forcing, tectonic and sedimentary mechanisms all having their proponents. Devonian carbonates of the Ardennes-Eifel-Aachen area are dominated by a suite of parasequence types deposited in ramp and shelf-interior locations. They show thickness patterns and trends in facies, which on a broad scale can be correlated across the region, whereas individual cycles cannot. Some packaging of cycles is seen, which could indicate an orbital-forcing control. However, there is clear evidence for a tectonic control on regional thickness patterns in some parts of the succession, as a result of deposition across syn-sedimentary extensional faults. As with many areas of Earth Science, explanation involves a combination of several hypotheses and here one mechanism does not seem to have been responsible for the Devonian cyclicity.

Earthquake-induced landslide hazards in mountain regions: a review of case histories from central asia

Abstract: This paper presents a summary of the main trigger factors of earthquake-induced landslides as well as a review of case histories of major landslide-triggering earthquake events in Central Asia. The Kainama earth-flow case history of 2005 is added to document possible mid-term effects of smaller earthquakes. These events show that in the Central Asian Mountains, two types of seismically triggered mass movements may have particularly disastrous effects: massive long runout rockslides and medium-sized earth flows made of loess - or a mixture of both. These types of mass movements also significantly contributed to the largest natural catastrophe of the last century in Central Asian mountain regions: the 1949 Khait earthquake. The high impact potential of these types of mass movements is further pointed out through comparison with two worldwide known events, the 1920 Haiyuan (China) and the 1976 Peru earthquake. Case studies had been carried out on rockslides, debris slumps and earth flows triggered by the above-mentioned Kemin and Suusamyr earthquakes as well as other smaller seismic shocks in the Kyrgyz Tien Shan. Many of the investigated landslides had known a complex failure history before final collapse. To better assess the short- to long-term effects of earthquakes on slopes, landslides need to be surveyed more intensively, over mid- and long-terms.

Estimation of groundwater recharge in Bugesera region (Burundi) using soil moisture budget approach

Abstract: Groundwater recharge for Bugesera region, a potable water-scarce area in northeastern Burundi, is computed using the soil moisture budget technique. Five evapotranspiration methods including Hamon, Hargreaves, Thornthwaite and two modifications of the original Thornthwaite method are evaluated in comparison to the reference evapotranspiration method, i.e. the FAO Penman-Monteith equation for years where complete climatic data is available. The evapotranspiration calculated by the aforementioned methods along with rainfall data are used to compute the soil moisture budget. The latter is calculated using the methodology devised by Thornthwaite & Mather (1955). Recharge calculation is performed using both the Thornthwaite Monthly Water-Balance Model (henceforth TMWB model) and excel sheets wherein each term of the soil moisture budget is computed separately. The results of evapotranspiration calculations show that, while the other evaporation methods slightly to moderately underestimate or overestimate the potential evapotranspiration in comparison to the FAO Penman-Monteith method, Hargreaves equation aberrantly overestimates this parameter. Likewise, groundwater recharge estimated using Hargreaves' evapotranspiration is dramatically reduced in comparison to the other evapotranspiration methods. Moreover, this study clearly shows that the time discretisation used in recharge calculations has important consequences, the use of smaller time steps leading to enhanced recharge. This better corresponds to reality. Compared to the recharge values obtained on a daily basis with Penman-Monteith evapotranspiration, the TMWB model which is on a monthly basis, using Hamon's evapotranspiration, gives the best approximations of reality, with the advantage of needing much less data. The distribution pattern of monthly recharge features a bimodal pattern somewhat similar to that of the monthly rainfall with an important peak in April.

Geology of the cassiterite mineralisation in the Rutongo area, Rwanda (Central Africa): current state of knowledge

Abstract: The Mesoproterozoic Kibara orogen in Central Africa hosts different granite-related rare element deposits that contain cassiterite, columbite-tantalite ( coltan ), wolframite, beryl, spodumene, etc. as typical minerals. The primary deposits of these minerals are formed by pegmatites and quartz veins that have historically been related to the youngest, most evolved G4-granite generation in the northern part of the Kibara orogen. This study focuses on quartz vein-type cassiterite mineralisation in the Rutongo area in Rwanda. The Rutongo area consists of a large anticline that is characterised by the presence of cassiterite-mineralised quartz vein sets that dominantly occur in quartzites. The emplacement of the quartz veins has been related to a later phase in the deformation history of the Kibara orogeny. The mineralised quartz veins are associated with intense alteration, comprising silicification, tourmalinisation, sericitisation and muscovitisation. Cassiterite itself is associated with muscovite in fractures in and along the margins of the quartz veins. Cassiterite crystallisation is followed by the precipitation of different sulphides, such as arsenopyrite, pyrite, chalcopyrite and galena. Cassiterite mineralisation resulted from the circulation of high-temperature and moderate-salinity fluids with a H2O-CO2-(CH4-N2)-NaCl composition. The stable isotopic composition of the cassiterite mineralising fluids indicates precipitation during metamorphic hydrothermal conditions, during which the metamorphic fluids where in isotopic equilibrium with granitic rocks. The circulation of these fluids probably resulted in the remobilisation of the Sn from these magmatic rocks, as indicated by the relative low Sn concentration of the specialised G4-granites. 40Ar-39Ar age dating of muscovite associated with the mineralisation gives an integrated age of 869 ± 7 Ma, which is clearly younger than the age of the G4-granites (~986 Ma) and the pegmatites with associated columbite-tantalite mineralisation (~965 Ma) in the area. Based on this large time gap, the 40Ar-39Ar age is interpreted to reflect a hydrothermal event post-dating the emplacement of the Kigali granite, only indicating a possible minimum age for the formation of the cassiterite mineralisation. Based on the structural setting, petrographical observations, the geochemistry of the G4-granites, stable isotope geochemistry, we therefore propose a model in which Sn was mobilised from primary magmatic rocks by a metamorphic hydrothermal fluid system that was generated after crystallisation of the granites and pegmatites. Cassiterite was precipitated in structurally controlled locations, together with the alteration of the host-rocks.

Stratiform and vein-type deposits in the Pan-African Orogen in Central and Southern Africa: evidence for multiphase mineralisation

Abstract: Stratiform deposits in the Pan-African Orogen are of the Cu-Co type and are restricted to carbonates and siliciclastic sediments that are stratigraphically close above the basement. The stratiform Cu-Co deposits formed during early diagenesis (possibly around 820 Ma) and during late diagenesis/metamorphism and the Pan-African Orogeny (~580 to ~520 Ma). The early diagenetic Cu-Co sulphides were partly remobilised into the second stratabound Cu-Co mineralisation, with precipitation of Cu-Co sulphides in nodules, veins and as breccia cements. Vein-type Cu-Pb-Zn mineralisation occurs at two distinct levels, higher in the stratigraphy. The lower level vein-type deposits occur in dolomite and are dominantly of the Zn-Cu type. The higher level vein-type deposits occur at the contact between dolomite and sandstone and are dominated by Cu. The Cu-dominated deposits that have been dated, developed during the waning stage of the Pan-African Orogeny (~530 to ~500 Ma). The Zn-dominated deposits for which a mineralisation age has been established, formed after the Pan-African Orogeny. Some of these vein-type mineralisation have been remobilised after their formation, with the precipitation of massive Cu(-Ag) sulphides.

The correlation potential of magnetic susceptibility and outcrop gamma-ray logs at Tournaisian-Viséan boundary sections in western Europe

Abstract: We have measured five deep-water carbonate and carbonate-siliciclastic sections at the Tournaisian-Visean (Tn/V) boundary in western Europe, using petrophysical outcrop logging techniques (gamma-ray spectrometry /GRS/ and magnetic susceptibility /MS/). The aim was to trace correlatable log patterns across the flanks of the London-Brabant Massif from eastern Ireland to western Germany. Both GRS and MS logging proved useful for long-distance (up to ~1000 km) correlation. The log patterns can be interpreted in terms of sea-level fluctuations. A late Tournaisian regression, a sequence boundary at the Tn/V boundary, early Visean lowstand systems tract and an overlying transgressive to regressive succession can be identified from the GRS and MS logs. The Tn/V sequence boundary can be correlated with exposure features and karstic surfaces in the up-dip shallow-water settings at the boundary between sequence 4 and 5 of Hance et al. (2001, 2002). This indicates that sea-level fluctuations around the Tn/V boundary were synchronous and traceable on the flanks of the London-Brabant Massif. The GRS-based logging has a greater correlation potential than MS as it can be applied in a broad spectrum of facies and depositional settings. In certain sections, the MS signal shows an increasing trend during transgression and a decreasing during regression, which is opposite to the MS paradigm from shallow-water carbonate platform settings. These trends are assumed to result from landward/basinward facies shifts of a low-productivity carbonate ramp system. Lowstand shedding of carbonate tempestites and turbidites results in low MS values while during sea-level rise the ramp systems backstep, developing a retrograding facies succession in its distal parts, which is associated with upward-increasing MS values.

Trace element variations in the middle frasnian punctata zone (late devonian) in the western canada sedimentary basin - changes in oceanic bioproductivity and paleoredox spurred by a pulse of terrestrial afforestation?

Abstract: The 'punctata Event' (Early-Middle Frasnian transition, Late Devonian) was recently recognized as yet another episode of major geochemical perturbations associated with the Middle-Late Devonian ecosystem readjustments which culminated in the Frasnian-Fammenian (F/F) mass extinction event, one of five largest of the Phanerozoic. We report variations in total organic carbon (TOC), magnetic susceptibility (MS), major, minor and trace element proxies (for changes in detrital input, bioproductivity and redox conditions) across the P.punctata conodont biozone in the Western Canada Sedimentary Basin (Western Laurussia). Geochemical proxies and MS display similar trends, suggesting an intimate interdependence. The data is thus evaluated within 1) a regional sequence stratigraphic perspective and 2) the marine-terrestrial teleconnections model (Algeo & Sheckler, 1998), whereby the rise and expansion of arborescent vascular land plants (the first 'true' forests) results in a transient increase in pedogenesis and solute delivery (hence biolimiting micronutrients) to the oceans. The punctata Event approximately coincides temporally with the advent of archaeopterid forest expansion and rise to dominance in the Frasnian-Fammenian age. This evolutionary event is speculated to have amplified the detrital influx which was likely already elevated by conditions of sea level lowstand, early transgression, episodes of mountain building and increased weathering during Frasnian warming. Statistical correlations among proxies suggest that changes in detrital input were the main driver of a bioproductivity increase. Elevated organic matter export from the photic zone likely led to the deposition and later preservation of organic-carbon rich facies under facilitated conditions of bottom water oxygen depletion. This paper is intended to supplement the growing body of work aimed at elucidating the causes of the punctata Event and documenting ecosystem responses to major perturbations of the global carbon cycle.

Stratigraphy of an Early–Middle Miocene sequence near Antwerp in northern Belgium (southern North Sea basin)

Abstract: The lithostratigraphy and biostratigraphy of a temporary outcrop in the Antwerp area is described. The deposits can be attributed to the Kiel Sands and the Antwerpen Sands members, both belonging to the Lower and Middle Miocene Berchem Formation. Invertebrate and vertebrate macrofossils are abundantly present. The molluscan fauna compares well to former findings in the Antwerpen Sands Member. It can be concluded that the studied sequence is continuously present in the Antwerp area, and thickens in a northward direction. The study of the marine mammal fauna shows that eurhinodelphinids are the most common fossil odontocete (toothed-bearing cetaceans) in the Antwerpen Sands Member, associated here with kentriodontine, physeteroid, squalodontid, mysticete (baleen whales) and pinniped (seals) fragmentary remains. Both the molluscan fauna and the organic-walled palynomorphs indicate for the Antwerpen Sands Member deposition in a neritic, energetic environment, which shallowed upwards. The dinoflagellate cysts indicate that the Antwerpen Sands Member was deposited during late Burdigalian to Langhian times.

Fresh-salt water distribution in the central Belgian coastal plain: an update

Abstract: The 1974 map showing the depth of the fresh-salt water interface (defined by 1500 mg/l total dissolved solids concentration) in the Belgian coastal plain is a vital document for hydrogeologists. Since its publication, new data have been collected. These comprise water quality analyses and borehole measurements ordered by the Flemish Environmental Agency, the Flemish Land Use Agency or from dissertations and new lithological data synthesised by the HCOV (Hydrogeological Code Flemish Subsurface) mapping. The aim of this paper is to compare the new information with the 1974 map and provide an update for the central part of the Belgian coastal plain. This resulted in only minor differences. The main adjustments are the identification of a number of additional areas where the phreatic aquifer is completely filled with fresh water, incorporation of insights of the groundwater flow system in the dunes, shore and sea and, some small changes in the position of transition zones between fresh-water lenses and adjacent areas where salt water occurs at very shallow depth. The general conclusion is that comparison with new field data obtained in the more than 30 years after its publication, confirms and strengthens the validity of the map.

Fine-grained non-carbonate particles embedded in neritic to pelagic limestones (lochkovian to emsian, prague synform, czech republic): composition, provenance and links to magnetic susceptibility and gamma-ray logs

Abstract: Variations in non-carbonate impurities trapped in the Lower Devonian limestone stratal successions in the Prague Synform are studied, with particular emphasis on the composition and quantities of fine-mineral grain assemblages. Different assemblages are encountered for the Lochkovian, lower Emsian and Pragian. The Lochkovian (represented by the Lochkov Formation) is characterized by pyrite-pyrrhotite assemblages with lower abundance of iron oxides and oxyhydroxides (mostly goethite) whereas the Pragian (represented by the Praha Formation) shows relatively abundant iron oxides and oxyhydroxides (mostly hematite). Major changes in magnetic susceptibility and gamma-ray spectrometric logs also coincide with the Lochkovian/Pragian boundary. Maximum values of magnetic susceptibility and relatively high Th, K concentrations above the boundary correspond to the elevated amounts of barite and Ba concentrations. This level is interpreted as a significant interval with elevated delivery of impurities of aeolian origin, deceleration of sedimentation rate together with decreased carbonate productivity. REE distributions in the Lochkovian to lower Emsian are indicative of the aeolian origin of trapped impurities. Detrital zircons found in all three stages are considered to be also of aeolian origin.

Early-Middle Frasnian (early Late Devonian) sedimentology and magnetic susceptibility of the Ardennes area (Belgium): identification of severe and rapid sea-level fluctuations

Abstract: This paper focuses on the early and middle Frasnian stratigraphic interval from the Ardennes area in Belgium, with a multidisciplinary and high-resolution study, including detailed sedimentology and magnetic susceptibility study, to identify the main paleoenvironmental changes affecting this interval. Three mud mound levels are observed, in stratigraphic order, the Arche, La Boverie and Lion mounds, surrounded and separated by shales. The three mounds are characterized by the same facies and relatively similar facies evolution through time. The base of the mounds shows deep mound facies (mud, stromatactis, crinoids) and the upper part of the mounds shallow mound facies (lagoonal facies, laminites). The mound succession is interpreted as related to the following events: the base corresponds to transgressive and high stand system tracts; overlain by a sharp transition with shallow facies that correspond to a main regression; followed by the next transgressive system tracts, which corresponds to the upper part of this mound and the lower part of the next mound. Then, again a sea-level drop occurs below the top of this lithostratigraphic unit and is followed by the next transgressive stage etc. A similar transgressive-regressive history is interpreted for all three mounds. As the La Boverie mound is only 35 to 45 m-thick, compared to the 100 m-thick Arche and Lion mounds, the two sea-level fluctuations occurring at the base and top of the La Boverie mound are considered as very severe and rapid, occuring within 1 My. An important transgression is interpreted as occurring during the global negative carbon excursion, the punctata Event, recorded worldwide (synthesis in Racki et al., 2008). During this interval, strong and sharp variations are also recorded in the magnetic susceptibility curve.

The dynamic time-warping approach to comparison of magnetic-susceptibility logs and application to Lower Devonian calciturbidites (Prague Synform, Bohemian Massif)

Abstract: The effectiveness of alignment of magnetic susceptibility (MS) stratigraphic sections by means of the dynamic time warping (DTW) approach was tested with positive results. The DTW is a robust and effective tool for the alignment of the sequential MS data which is particularly sensitive to MS-log patterns, their details, successions, distortion or absence from logs. Moreover, the DTW performance proved to be appropriate for sections which involve a great deal of irregularly spread compacted or thick-bedded intervals and variously positioned and sized gaps. In view of the fact that the lateral changes in short- to medium-term sedimentation rates and local variations in diagenetic compaction are not exceptional but rather common features of the compared sedimentary sections, the DTW becomes a significant tool for stratigraphic comparison of sections with good potential of becoming an alternative to cyclostratigraphic correlation methods. Conditions governing the formation of Lower Devonian (Pragian) carbonate clinoforms obviously appear to be this case, and testing of the DTW on this type of MS sections suggests that the computationally robust results remain approximately the same, even if the importance of high values (peaks) is nonlinearly decreased or increased. In such cases the DTW outperforms the distortion-based vector quantisation (VQ), continuous density hidden Markov models (CDHMM), wavelet transformation (WT) or cross-correlation (CC) based approaches. The near absence of artificially introduced preconditions or predefined elements is also an advantage. The alignment of the sections using the DTW gives us warning about distorted intervals, thus reducing the risk of assembling quite different types of rhythmic patterns or cycles together. The overall ambition of this paper is to introduce the DTW alignment technique as an effective tool for MS log correlation. Extensive testing of the requirements for input data and constraints according to maximum differences between the compared stratigraphic segments are reserved for other studies. For the Pragian of the Barrandian area (specifically, calciturbidite-dominated clinoforms), the DTW-based interconnection between the relevant points of two sections has a resolution which is close to sampling distances (several cm) and is about two orders of magnitude higher compared to that which can be achieved by the bio-, chemo- or lithostratigraphic tools. The first results confirmed the presence of numerous visible and hidden gaps and condensations in the sections.

Magnetic susceptibility correlation of kM-thick eifelian-frasnian sections (ardennes and Moravia)

Abstract: After briefly introducing the sedimentology of two Eifelian-Frasnian carbonate sections in Belgium and Moravia, this paper focuses on the comparison of the magnetic susceptibility (MS) curves. The Ardennes section shows highly variable facies, with an alternation of ramp, platform and mound environments. Detrital inputs are locally very important. Time-equivalent facies in the area of the Moravian Karst correspond to rather pure carbonate platform facies, mostly composed of Amphipora beds. The first analysis of long-term trends in Devonian MS in Belgium and Moravia shows a remarkable similarity, despite a very different background of palaeogeographical setting, facies, sedimentary rate and retrogradation-progradation history. However, a relative independence of the MS and the distal-proximal curves, deduced either from the microfacies record (Ardennes) or from shoreline shifts (Moravia) is observed. This questions the nature of the forcing mechanisms that must at least be active at the inter-regional scale. Moravia and the Ardennes are located along the same palaeolatitude, perhaps suggesting some climatically driven mechanisms, responsible for the input of the detrital fraction responsible for the MS in these sediments. Trade winds are potentially responsible for transportation of dust and its widespread distribution in intertropical areas.

Influence of major elements on heavy metal composition of river sediments

Abstract: In the present study, the relationship between heavy metals (As, Cd, Cr, Cu, Hg, Pb, Ni, Sn and Zn) and major elements and the location and/geological substrate of 105 river sediments in Flanders was investigated. Factor Analysis was used to divide the dataset into four components: a first component including clay, organic matter, Na, Ca, K and Mg, a relationship between Fe, As and Cd, an anthropogenic factor (including Cu, Hg, Pb, Sn and Zn) and finally the pH and insoluble residue. Regression equations were constructed, using major elements such as Fe and Ca as independent variables, besides more classical explaining variables such as clay content (< 2µm fraction), organic matter content and pH. Most heavy metal concentrations could be predicted very well by the independent variables, except Zn, Se and Sn. The results from this study, performed on a dataset of 105 riverbed sediments, indicate that, besides organic matter and clay content, other variables such as the total Fe and Ca content can be relevant parameters to predict heavy metal concentrations in sediments. The more general applicability of the obtained regression equations should be verified, and the inclusion of Fe and Ca in regression equations that are applied for the standardization of total metal concentrations in soils and sediments, should be considered.

Dust – A geology-orientated attempt to reappraise the natural components, amounts, inputs to sediment, and importance for correlation purposes

Abstract: The paper deals with the recent and present-day natural components of the dust inputs to sediments, and aims to attract the attention of geologists to atmospherically mediated teleconnections among basins across the globe. Similar components as today can also be expected to exist in the pre-human history of the Earth, with capability to affect the quantity and quality of non-carbonate phases in limestones. However, a significant part of atmospheric dust sedimentation is not sufficiently covered by standard measurements. Owing to air quality regulations, most of the present research is conducted to understand the emissions and atmospheric load of PM10, and a lesser number of studies map the possible transport of coarser natural particulate matter over the large distances. With respect to the studied particle sizes and methods of their determination, the present-day aerosol science and geological approach, focused on measured sedimentation or input to sediment, show practically no overlap. We report the first evidence (or at least a well-reasoned hypothesis) that the low numbers of frequently occurring large particles, e.g. with 50-µm de or larger, must always represent a substantial mass added to mineral dust budgets. These rare and bulky particles are either transported with the super-storm dust plumes in the troposphere, or with the jet streams near the tropopause. From the geological point of view, it is important to consider all sizes of mineral-lithic particles or grains, particularly from the silt to fine-sand sizes (i.e., 4-250 µm). In atmospheric physics, only the total suspended particulates (TSP) are a partial and often unreliable counterpart. This subject is especially worth of exploring although the emerging discipline, combining the estimates of the total burden of atmosphere by every classes of the natural solid particles and their measurable 'final sedimentary inputs', is still encumbered with much imprecision, and the reported results are more concerned with the principles and rough estimates than all variants of calculations. Classifying the components by their sources, this attempt suggests that the ideal mean airborne inputs to the sediments on the present-day Earth are approximately as follows (g/m 2 /yr): terrestrial weathering ≈ 3.3; volcanic ash ≈ 0.3; biotic ≈ 0.5; cosmogenic ≈ 0.0002; wildfires ≈ 0.3; solids with ultra fine secondary aerosols ≈ 0.02, giving a total of ≈ 4.4. Therefore, a mean (ideal) input of the natural dust to the present (and possibly also Holocene) sediments of about 4-5 g/m 2 /yr should be considered. Naturally, the real inputs vary geographically to a large

An Emsian-Eifelian Calciturbidite sequence and the possible correlatable pattern of the Basal Choteč event in Western Ossa-Morena Zone, Portugal (Odivelas Limestone)

Abstract: An Emsian-Eifelian carbonate-volcaniclastic sequence in south-western Ossa-Morena Zone (Portugal) was studied in terms of reef fauna, conodont biostratigraphy, macro- and micro-facies and magnetic susceptibility stratigraphy. The results point to a bracketing between the Po. patulus and T. australis conodont biozones (uppermost Emsian - middle-late Eifelian). The field data, facies analysis and reef fauna indicate that the sequence is composed entirely of calciturbidite and debris-flow deposits (intercalated with hemipelagic tuffites) related to a (up-slope) reefal system resting on top of volcanic buildings within a large volcanic complex. The purity of the limestones does not seem to be generally influenced by volcanic contributions. Although with some uncertainties, the first part of the section seems to show pre-, syn- and post-Basal Chotec Event (BCE) beds as recorded by significant shifts in lithofacies and magnetic susceptibility signal. A tentative interregional correlation with magnetic susceptibility curves is suggested with sections in Morocco, Nevada (USA) and Uzbekistan.

Facies and palaeoecology of the upper member of the Aisemont Formation (late Frasnian, S. Belgium): An unusual episode within the late Frasnian crisis

Abstract: RESUME Facies et paleoecologie du membre superieur de la Formation d’Aisemont (Frasnien superieur, S. Belgique): un episode inhabituel dans la crise du Frasnien superieur. Le membre superieur de la Formation d’Aisemont – aussi appele “second biostrome” - correspond au dernier niveau carbonate significatif du Frasnien superieur au bord nord du Synclinorium de Dinant et dans le Synclinorium de Namur, en Belgique. Il est constitue de calcaire bioclastique a oncoides et coraux, souvent dolomitise et n’est donc pas a proprement parler un biostrome puisque seul un niveau tres peu epais est construit par des coraux. L’essentiel du membre est forme de calcaire relativement riche en oncoides et organismes dont la plupart sont des opportunistes (bryozoaires, brachiopodes, gasteropodes, spongiaires, etc.). Les coraux identifies appartiennent aux genres Phillipsastrea et Frechastraea, qui dominent aux cotes du tabule Alveolites. L’observation d’objets multi-encroutes, ainsi que des colonies effilochees de coraux, laisse penser que le milieu de depot etait un environnement difficile pour les principaux organismes constructeurs: fond meuble, eaux turbides, sedimentation fine intermittente. Le developpement d’un niveau construit par les coraux est donc un evenement important, qui correspond a la colonisation d'un fond durci. Ce dernier marque la base d’un cortege regressif et confirme le modele de la « sequence d’Aisemont » (cycle transgression-regression de troisieme ordre). Enfin, la proliferation de structures microbiennes tant dans le membre, sous forme d’oncoides, que dans son equivalent lateral, sous forme de thrombolithes et stromatolithes, dans le Membre de Petit-Mont (Formation des Valisettes dans l’Anticlinorium de Philippeville) est interpretee comme le resultat des deteriorations environnementales menant aux crises du Frasnien superieur.

A partial rostrum of the porbeagle shark lamna nasus (lamniformes, lamnidae) from the miocene of the north sea basin and the taxonomic importance of rostral morphology in extinct sharks

Abstract: A fragmentary rostrum of a lamnid shark is recorded from the upper Miocene Breda Formation at Liessel (Noord-Brabant, The Netherlands); it constitutes the first elasmobranch rostral process to be described from Neogene strata in the North Sea Basin. Based on key features of extant lamniform rostra and CT scans of chondrocrania of modern Lamnidae, the Liessel specimen is assigned to the porbeagle shark, Lamna nasus (Bonnaterre, 1788). In addition, the taxonomic significance of rostral morphology in extinct sharks is discussed and a preliminary list of elasmobranch taxa from Liessel is presented.

Palaeoenvironmental study and small scale correlations using facies analysis and magnetic susceptibility of the Mid-Emsian (Himmelbaach quarry, Luxembourg).

Abstract: The Himmelbaach quarry is located in the Wiltz Synclinorium in Luxembourg. The rocks outcropping in this quarry correspond to the mid-Emsian Clervaux Shales Formation. Three different facies have been identified in the quarry. An argillaceous sandstone facies with oblique stratifications, cross-stratifications, herring-bones and erosive bases represent the first facies; the second facies is characterized by lenticular- (with connected lenses) to wavy-bedded sandy argillites, argillaceous sandstones and quartz arenites. The last facies corresponds to a quartz arenite with oblique stratification, planar laminations and mud drapes. The base of this facies shows flaser bedding and sigmoidally curved bed surfaces. The palaeoenvironmental study of this area is rather difficult because of the structural deformation and lateral variation of the facies. Due to this deformation, six partial sections (4a to 4f) were sampled here. In order to reconstruct a reliable vertical and lateral succession of the depositional setting, facies analysis and magnetic susceptibility were used. Magnetic susceptibility (MS) is generally applied as a tool for correlation in a deepwater carbonated environment. In this paper we used the MS technique successfully in a siliciclastic proximal setting. Analysis of MS curves as well as the recognition of three marker beds ((1) the last bed of argillaceous sandstones in Facies 1; (2) a thin horizon of carbonated sandstone within Facies 2; (3) the first appearance of the characteristics massive quartzitic beds in Facies 3) allowed the correlation of sections 4a, 4b and 4c. These correlations helped us to reconstruct a vertical and lateral succession of facies, which ultimately led to the recognition of a tide-dominated marginal-marine depositional model composed respectively of tidal channels (Facies 1), a tidal flat (Facies 2) and a tidal sand ridge (Facies 3). This example also shows the usefulness of magnetic susceptibility for small scale correlation, even in a proximal environment such as a marginal-marine setting.

The Givetian- Frasnian boundary at Nismes parastratotype (Belgium): the magnetic susceptibility signal controlled by ferromagnetic minerals

Abstract: A comparison between microfacies and magnetic susceptibility (MS) curves has been performed at the Givetian-Frasnian transition in southern Belgium. The MS curve is subdivided in four magnetic sequences. Most of the section has MS and MF curves anti-correlated. Hysteresis parameters reveal a low coercivity mineral of magnetite type phase and a high coercivity mineral (i.e. hematite) in all samples. Strong correlation between ferromagnetic and low-field magnetic susceptibilities suggests that ferromagnetic minerals control almost totally the MS signal with an increasing upsection abundance of paramagnetic grains (iron-bearing clay minerals and pyrite). A decreased proportion of superparamagnetic grains, probably of diagenetic origin, is observed upsection. The hematite grains increases in the Frasnian as attested by the higher hematite contribution to the IRM 500mT . The anti-correlation between the magnetic viscosity coefficient and the hematite contribution to the IRM 500mT suggest that hematite are not associated to the superparamagnetic fraction and has a detrital origin. The opposite evolutions could be partly explained by sedimentological parameters and by an increased amount of primary detrital magnetite and hematite upsection. This detrital influx highlights the drowning of the carbonate platform at the end of the Givetian illustrating the progressive change from a Givetian rimmed platform towards a Frasnian ramp setting.

The stratigraphical architecture of the quaternary deposits as support for hydrogeological modelling of the central zone of hanoi (vietnam)

Abstract: The Quaternary deposits of the Hanoi area have been investigated in order to provide information required for the design of a groundwater-flow model. Limited sedimentological data exist from 32 destructive drillings carried out previously in the study area. The data base contains hydrographical and hydrogeological observations, but few sedimentological details. This is in contrast with the more seaward regions of the area where the Holocene deposits of the Red River plain has previously been studied. However, a comparison of the results obtained in this study with the previous studies indicates that the Hanoi sediment succession developed in an incised valley under conditions of rapid relative sea-level rise until ca. 7-6 a cal BP. The succession consists initially of alluvial floodplain deposits conformably overlain by mud deposited at the head of an estuary which filled with continuing rapid sea-level rise. Once the relative sea-level rise stabilized, fluvial deposition prograded over the adjacent estuarine mud. The development of a groundwater-flow model requires knowledge of the three-dimensional distribution of the various deposits. Despite the paucity of information with respect to sediment description, a model of the entire Quaternary sequence is presented in several lithostratigraphic crosssections and a panel diagram. The latter forms the basis for the construction of a contour map of the base of the Pleistocene and Holocene deposits, and for a sequence map of the Quaternary deposits in the study area

Earthquake-induced landslide hazards in mountain regions: a review of case histories from central asia (An inaugural lecture to the society)

Abstract: RESUME Aleas de glissements de terrain induits par tremblements de terre dans les regions montagneuses: Exemples d’Asie Centrale Nous presentons, dans cet article, les facteurs principaux qui contribuent au declenchement d’instabilites sismiques a travers des exemples de ruptures majeures en Asie Centrale S’ajoute a cela la description d’un glissement de terrain (Kainama) induit par des seismes de plus faible magnitude Ces evenements montrent que dans les montagnes d’Asie Centrale, essentiellement deux types de mouvements de masse d’origine sismique peuvent avoir un impact devastateur : il s’agit des grands ‘glissements rocheux’ et des ‘coulees de loess’ (ou eventuellement une combinaison de ces deux types) Ces types de mouvements de masse ont egalement cause les plus grands impacts de l’evenement le plus catastrophique dans les montagnes d’Asie Centrale du siecle passe: le tremblement de terre de Khait de 1949 Dans cet article, l’impact potentiel des instabilites d’origine sismique en Asie Centrale est analyse au moyen d’une comparaison avec des mouvements de masse induits par deux evenements majeurs : le seisme de Chine de 1920 et le seisme du Perou en 1976Nous avons analyse en detail les glissements rocheux, les glissements de debris et les ecoulements de terre engendres par les seismes de Kemin, de Suusamyr et des seismes de plus faible magnitude dans le Tien Shan kirghize Parmi ces mouvements de masse, beaucoup resultent d’une longue et complexe histoire de rupture Nous pensons qu’une instrumentation plus approfondie de quelques instabilites existantes permettrait de mieux comprendre les effets a moyen et a long terme des seismes sur la stabilite des versants

Stenolaemate bryozoans from the latest devonian (uppermost famennian) of western germany

Abstract: Three bryozoan species are described from the uppermost part of the Velbert Formation ("Strunian", uppermost Famennian), Velbert Anticline (Rhenish Massif, Germany), including two new species: Stenophragmidium velbertensis sp. n. and Nikiforovella gracilis sp. n., and one species in open nomenclature: Dyscritella sp. The bryozoans thrived on a shallow high-energetic clear-water carbonate ramp characterized by the microbiota Girvanella, Paracaligelloides and Quasiendothyra. The discovery of Nikiforovella suggests the existence of faunal migrations between Europe and eastern Palaeotethys realms (China, Kazakhstan).

Sources and processes in arc magmatism: the crucial role of water

Abstract: Arc magmatism distinguishes itself from magmatism in other tectonic settings by the crucial role that water plays in its petrogenesis. Water influences the geochemistry of the sub-arc mantle, by transferring fluid-soluble elements from the slab into the mantle. Water probably also carries the oxidised signature from the slab into the mantle wedge. The ubiquitous negative Ti-anomaly in arc magmas may reflect an increase of the compatibility of titanium in the solid residue during partial melting in water-bearing peridotite. Finally, water also has a strong influence on the identity of minerals involved in crystal fractionation processes, and gives rise to the low-Fe (calc-alkaline) fractionation trend by lowering the temperature at which the silicates start crystallising, without influencing the crystallisation temperature of iron-oxides.

Acritarchs from the abbaye de villers and tribotte formations in their type section of the thyle river valley (middle ordovician, brabant massif, belgium) and their stratigraphic implications

Abstract: Reinvestigation of the Thyle river section, in the southern part of the Brabant Massif, has led to a better understanding of acritarch distribution in the Middle Ordovician Abbaye de Villers and Tribotte formations, and their stratigraphical significance in the type localities of both formations The middle and upper parts of the Abbaye de Villers Formation and the lower part of the Tribotte Formation yielded an acritarch assemblage corresponding to the Frankea hamata-Striatotheca rarirrugulata Acritarch Zone of the English Lake District, demonstrating a late Arenig (late Fennian, early Darriwilian) age Two species, Adorfia firma and Arbusculidium filamentosum, not recorded in the overlying Rigenee Formation, probably have their last appearances below the Arenig-Llanvirn boundary Acritarch (late Arenig, late Fennian) and chitinozoan datings (middle Arenig, Whitlandian pro parte) of the middle part of the Abbaye de Villers Formation suggest correlation with the older part of the Frankea hamata-Striatotheca rarirrugulata Acritarch Zone The uppermost part of the Tribotte Formation shows palynological similarities with the overlying Rigenee Formation The exact position of the Arenig-Llanvirn boundary in the Thyle river section is not yet known and does not necessarily coincide with the Tribotte-Rigenee lithostratigraphical boundary

On the use of magnetic techniques for stratigraphic purposes: examples from the Lower Palaeozoic Anglo-Brabant Deformation Belt (Belgium)

Abstract: Within the Lower Palaeozoic Anglo-Brabant Deformation Belt, magnetic susceptibility on its own does not allow for a straightforward distinction between different lithostratigraphic units, except for the high-susceptibility levels of the Lower Cambrian Tubize Formation. Moreover, the variation in magnetic susceptibility within individual lithostratigraphic units is often larger than that between different units, but at the same time, this internal variation in susceptibility may show no clear relationship to features obvious in outcrop or hand specimens. Hence, the applicability of magnetic susceptibility for stratigraphic purposes in the Anglo-Brabant Deformation Belt is low. Better results are obtained using the temperature-dependent variation in terms of percentage of magnetic susceptibility within the "room temperature interval". Also the anisotropy of magnetic susceptibility allows for a better distinction between different lithostratigraphic units than does magnetic susceptibility. The best results are obtained by a comparison of thermal demagnetisation curves of magnetic remanence, used for determining ferromagnetic mineralogy. This method even allows distinguishing lithostratigraphic units in which ferromagnetic carriers do not contribute to overall magnetic susceptibility and its anisotropy. Ideally, each magnetic technique should be used for stratigraphic purposes only in combination with other magnetic techniques. Moreover, knowledge about the magnetic carriers (s.l.) facilitates this use of magnetic techniques and strongly improves the accuracy of the interpretations.

Goldius angusticalix sp. nov. (trilobita, scutelluidae) from the couvin formation (middle devonian) in belgium, with a preliminary list of scutelluid species from the ardennes

Abstract: RESUME. Goldius angusticalix sp. nov. (Trilobita, Scutelluidae) de la Formation de Couvin (Devonien moyen) en Belgique, avec une liste preliminaire d'especes scutelluidees de l’Ardenne. Les trilobites scutelluides sont rares dans le Devonien de l'Ardenne (Belgique, France). Goldius angusticalix sp. nov. et Scabriscutellum sp. A sont decrits dans la Formation de Couvin (Eifelien inferieur) de Nismes. Un apercu est presente de la repartition regionale dans l’Eifelien de Goldius de Koninck (= Brontes Goldfuss; Bronteus Goldfuss; Goldfussia Bronn; Calycoscutellum Archinal), Scabriscutellum Richter & Richter, Septimopeltis Přibyl & Vaněk et Scutellum Pusch. En outre, les analogies entre les faunes trilobites contemporaines de Nismes et Uxheim (Allemagne) sont brievement discutees.