Search publications of the members of the Royal Belgian institute of natural Sciences
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Shallow-rooted mud volcanism in Lake Baikal
- Lake Baikal is the only freshwater basin containing sediments with gas hydrate accumulations, some of which are associated with mud volcano activity. Twenty-two mud volcanoes have already been identified in different areas of Lake Baikal, but the formation process and source depth remained unknown due to a lack of conclusive evidences. Here we discuss a set of geological and geophysical data to report the discovery of the hydrate-bearing Akadem mud volcanic complex (AMVC) on the Academician Ridge in central Lake Baikal. The obtained results allowed for the first time to concretely estimate the source depth of the mobilized fluids and sediments. Analysis of diatom skeletons present in the mud breccia revealed that the oldest diatom specimen is Cyclotella Iris et var. This specie is characteristic for a short age interval ranging between 4.8 and 5.6 Ma. The same diatom was also detected between 230 and 310 m below the lake floor (mblf) in the borehole BDP-98 drilled near the AMVC. Combining biostratigraphic correlation and seismostratigraphy, it is estimated that the same interval is located at 200–300 mblf below the mud volcanic field. The elevated heat flow measured at AMVC indicates that the original bottom gas hydrate stability (regionally located at ∼212 mblf) is currently shifted upwards of ∼100 m. The acquired data are consistent with a scenario envisaging the rise of warm fluids throughout the mud volcano complex zone. We suggest that deep fluids migration could have initiated the gas hydrate dissociation and, in turn, rapidly generated over pressured shallow mud chambers. The ultimate piercing and triggering of the mud volcanoes activity resulted in the eruption of mud breccia and formation of densely packed crater sites in the study area. The depicted scenario can be applied to many mud volcanoes in Lake Baikal where similar anomalous heat flow conditions have been measured. These findings also emphasize that the genetic association between gas hydrate dissociation and the initiation of eruptive activity explains numerous peculiarities of the “Baikal” sedimentary volcanism (e.g. lack of lithified rocks among mud breccia clasts, gas hydrates, moderately elevated heat flow). This type of mud volcanism differentiates from the typically deeply rooted piercements observed worldwide in mature (marine) sedimentary basins. Ultimately our findings open a new prospective for mud volcano research worldwide, emphasizing that gas hydrates are not just one of the common features for sedimentary volcanism, but may have an active role as a triggering mechanism for the process itself.
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Unravelling the high-altitude Nansen blue ice field meteorite trap (East Antarctica) and implications for regional palaeo-conditions
- Antarctic blue ice zones, the most productive locations for meteorite recovery on Earth, contain old ice that is easily accessible and available in large quantities. However, the mechanisms behind these meteorite traps remain a topic of ongoing debate. Here, we propose an interdisciplinary approach to improve our understanding of a meteorite trap in Dronning Maud Land (East Antarctica) on the Nansen blue ice field meteorite trap (2600–3100 m above sea level), where more than half of the Asuka meteorites have been collected. Based on 185 surface blue ice samples, one of the largest observed spatial patterns in oxygen isotopic variation to date is found. Relying on meteorites for which the terrestrial ages are determined using 14C and 36Cl, this surface ice is interpreted to date from the Last Interglacial up to the present-day. By combining state-of-the-art satellite derived surface velocities, surface mass balance modelling and ice flow modelling, we estimate that about 75–85% of the meteorites found on the ice field were supplied by ice flow after entering the ice sheet in an accumulation area of a few hundred square kilometres located south (upstream) of the ice field. Less than 0.4 new meteorites per year are supplied to the ice field through ice flow, suggesting that the hundreds of meteorites found 25 years after the first visit to this ice field mostly represent meteorites that were previously not found, rather than newly supplied meteorites. By combining these findings, the infall rate of meteorites from space is estimated, which is in line with values from the literature, but situated at the higher end of the range. A comparison of the oxygen isotopic variation of the surface blue ice to that of the European Project for Ice Coring in Antarctica (EPICA), Dronning Maud Land (EDML) ice core (located 750 km to the west, at the same elevation), suggests that the regional changes in topography have been relatively limited since the Last Interglacial, supporting theories of an overall stable East Antarctic Ice Sheet (EAIS) over this time period.
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Intense aqueous alteration on C-type asteroids: Perspectives from giant fine-grained micrometeorites
- This study explores the petrology of five giant (>400 μm) hydrated fine-grained micrometeorites from the Transantarctic Mountain (TAM) micrometeorite collection. For the first time, the extent and mechanisms of aqueous alteration in unmelted cosmic dust are evaluated and quantified. We use a range of criteria, previously defined for use on hydrated chondrites, including phyllosilicate fraction, matrix geochemistry and micro textures. Collectively, these micrometeorites represent ∼2.22 mm2 of intensely altered hydrated chondritic matrix (with petrologic subtypes of <1.2 in the scheme of Howard et al. (2015)) and reveal a range of alteration styles. Two particles are found to contain pseudomorphic chondrules with thick fine-grained rims, while another micrometeorite contains several aqueously altered CAIs. Their outlines range from well-defined to indistinct, demonstrating that the advanced stages of aqueous alteration progressively remove evidence of coarse-grained components. The remaining two micrometeorites entirely lack coarse-grained components but are similarly altered. Thus, the combined chondrule-to-matrix ratio among these giant micrometeorites is extremely low (6.45 area%), and significantly below the average ratio found in typical CM or CR chondrites (∼20%, Weisberg et al., 2006). Our findings are consistent with previous analyses from smaller Antarctic micrometeorites, which suggest that chondrules (and CAIs) derived from hydrated carbonaceous chondrite parent bodies are underrepresented among the micrometeorite flux, even when considering contributions from coarse-grained micrometeorites. Therefore, to explain the relative paucity of anhydrous material, we propose that the flux of fine-grained micrometeorites is primarily derived from intensely aqueously altered, primitive C-type asteroids, which have lost the majority of their refractory coarse-grained components by replacement with secondary phyllosilicate minerals.
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How the larval traits of six flatfish species impact connectivity
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Digital mapping of coastal boulders – high-resolution data acquisition to infer past and recent transport dynamics
- Coastal boulder fields provide clues to long-term frequency-magnitude patterns of coastal flooding events and have the potential to play an important role in coastal hazard assessment. Mapping boulders in the field is time and labour-intensive, and work on intertidal reef platforms, as in the present study, is physically challenging. By addressing coastal scientists not specialized in remote sensing, this contribution reports on the possibilities and limitations of digital applications in boulder mapping in Eastern Samar, Philippines, where recent supertyphoons Haiyan and Hagupit induced high waves, coastal flooding and boulder transport. It is demonstrated how satellite imagery of submetre resolution (Pléiades, WorldView-3) enables efficient analysis of transport vectors and distances of larger boulders, reflecting variation in latitudes of both typhoon tracks and approaching angles of typhoon-generated waves. During the investigated events, boulders with a-axes of up to 8 m were clearly identified to have been shifted for up to 32 m, mostly along the seaward margin of the boulder field. It is, however, hard to keep track of smaller boulders, and the length of a-axes and b-axes including their orientation is often impossible to map with sufficient accuracy. Orthophotographs and digital surface models created through the application of an unmanned aerial vehicle and the ‘Structure from Motion’ technique provide ultrahigh-resolution data, and have the potential to not only improve the results of satellite image analysis, but also from field mapping and may significantly reduce overall time in the field. Orthophotographs permit unequivocal mapping of a- and b-axes including their orientation, while precise values for c-axes can be derived from the respective digital surface models. Volume of boulders is best inferred from boulder-specific Structure from Motion-based three-dimensional models. Battery power, flight speed, and altitude determine the limits of the area covered, while patches shielded by the boulders are difficult to resolve. For some tasks field mapping remains mandatory and cannot be replaced by currently available remote sensing tools: for example, sampling for rock type, density and age dating,recording of lithological separation of boulders from the underlying geological unit and of geomorphic features on a millimetre to decimetre-scale, or documentation of fine-grained sediment transport in between the boulders in supratidal settings. In terms of future events, the digital products presented here will provide a valuable reference to track boulder transport on a centimetre to decimetre-scale and to better understand the hydrodynamics of extreme-wave events on a fringing reef coastline.
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Long-term trends of land use and demography in Greece: a comparative study
- This paper offers a comparative study of land use and demographic development in northern and southern Greece from the Neolithic to the Byzantine period. Results from summed probability densities (SPD) of archaeological radiocarbon dates and settlement numbers derived from archaeological site surveys are combined with results from cluster-based analysis of published pollen core assemblages to offer an integrated view of human pressure on the Greek landscape through time. We demonstrate that SPD can be a useful approach to outline differences between regions and a useful complement to archaeological site records, evaluated here especially for the onset of the Neolithic and the Final Neolithic/Early Bronze Age transition. Pollen analysis highlight differences in vegetation between the two subregions but also several parallel changes. The comparison of land cover changes between two sub-regions of Greece further demonstrate the significance of the bioclimatic conditions of core locations and that apparent oppositions between regions may in fact be two sides of the same coin in terms of socio-ecological trajectories. We also assess the balance between anthropogenic and climate related impacts on vegetation and suggest that climatic variability was as an important factor for vegetation regrowth. Finally, our evidence suggest that the impact of humans on land cover is amplified from the Late Bronze Age onwards as more extensive herding and agricultural practices are introduced.
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Description of Chicoreus (Triplex) franzettiae n. sp. (Gastropoda: Muricidae) from the Philippine Islands
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A little-known German naturalist: Konrad Miller (1844-1933) and his malacological contributions
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A review of Stenostylus Pilsbry, 1898 and Drymaeus Albers, 1850 (Mollusca: Gastropoda: Orthalicoidea: Bulimulidae) from Colombia, with description of new species
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Reconstructing science networks from the past: eponyms between malacological authors in the mid-19th century
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Charles Hippolyte Crosse (1826-1898) and his contributions to malacology: a biography and bibliography
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Obsessed with shells: John L. Staid-Staadt (1886-1969) as a life-long and ardent collector
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Enkele onbekende Nederlandse schelpenverzamelingen uit de 19e eeuw
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A candid view of relations between malacologists in the second half of the nineteenth century: the correspondence of Henri Drouët with Hippolyte Crosse
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Bridging the Atlantic: the correspondence of Thomas Bland and William Binney with Hippolyte Crosse, between 1863 and 1885
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Notes on Drymaeus species from Peru (Mollusca, Gastropoda, Bulimulidae), and description of a new species
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Herman Roeters van Lennep (1820-1879) and the auction of his collection.
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More than just a name: Colonel Messager and his correspondents
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Faunal report. In: Jimenez Serrano, A. et al. Proyecto Qubbet el-Hawa: Trabajos arqueólogicos en las tumbas QH32, QH33, QH34aa, QH34bb, QH122, QH35p y QH36. Novena Campaña (2017)
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Indice de minéralisation sulfurée (Fe, Zn, Pb, Cu, Ni, Co) liée aux strates du Frasnien (limite F2-F3) dans le sondage d'Heibaart (Loenhout, province d'Anvers).
