1,721,007 research outputs found
Background values of potential toxic metals in the Pisa coastal plain: an example of integrated sedimentological and geochemical study
No full textDetailed geochemical characterization of Quaternary deposits between Serchio
and Arno river mouths enables the construction of a reliable geochemical map
for selected potentially toxic metals in the Pisa coastal plain. Following the
procedures carri ed out for the compilation of the Pedogeochemical Ma p of
Emilia-Romagna (1:250,000 scale), 60 samples, col lected at 30 selected sites
within depths of 20-30 cm and 100-120 cm, respectively, were sampled by
hand-drill ing and form the geochemical dataset. Geomorpholog ica l and
sedimentological investigations allowed the characterization of the study sites
in terms of facies associations.
Zr, Fe203, Al203, Ca O and Sr appear to represent reliable indicators of soil
alteration, allowing an obvious distinction between i) late Pleistocene units,
corresponding to the Coltano sands; ii) Holocene (pre-Roman) deposits,
including the channel-levee systems of Arno and Serchio rivers, and iii) recent
sediments of alluvial and coastal origin. Subtle geochemical indicators also
enable the differentiation of so il alteration at top of major beach-ridge systems
aligned parai lei to the present shoreline, thus providing an obvious indication of
coasta l progradation during the late Holocene. Arno and Serchio fluvial deposits
exhibit similar geochemical compositions. Ni/Y and MgO, however, appear as
valuable indicators for their distinction in terms of sediment provenance.
Systematic variability in chromium and nickel concentrations is observed in the
study area across the three major facies associations (beach-ridge sands, levee
and crevasse-splay silty sands, floodplain silts and clays), with increasing metal
contents within the finer-grained deposits. This reflects a primary contro! on
sediment composit ion by selection processes during t ransport. Beach-ridge
sands, in particular, display a high compositional variability that could reflect
an influence of transport pathways on the spatial distribution of metals. A
similar contro! of grain size o n meta l distribution is shown by zinc and,
subordinately, by copper and lead.
This study shows that a geochemical ma p constructed on a geologica! basis
may furnish a real istic depiction of spatial metal distribution within superficial
sediments, providing a powerful tool for planning environmental strategies.
Similarly to what recently documented from wide areas of Romagna coastal
pia in (Amorosi & Sammartino, 2005; 2007) and Parma alluvial plain
(Sammartino et al. , 2007), chromium (and subordinately Ni) in the Pisa coastal
plain may display very high natura! concentrations, locally exceeding the
pollution thresholds defined by law. As a consequence, evidence for
contamination should not be established before detailed geochemical
characterization of fa ci es is undertaken. Similarly, limiting values for meta l
concentrations should not ignore the actual background values, which are
primarily a function of provenance and grain size
Background levels of potentially toxic metals from soils of Pisa coastal Plain (Tuscany, Italy) as identified from sedimentological criteria.
No full textIdentification of reliable background values of
potentially toxic metals in sediments requires detailed
integration of geochemical data with accurate sedimentological
studies. Through analysis of 60 soil samples from
the Pisa coastal plain, this study shows to what extent
sediment provenance and facies characteristics may influence
the natural distribution of potentially toxic metals (Cr,
Ni, Cu, Zn, Pb) within alluvial and coastal sediments.
Metals supplied to the alluvial plain are mostly concentrated
within the finest sediment fraction (floodplain clays),
while coarser crevasse and overbank deposits exhibit
invariably lower metal contents. Beach-ridge sands display
the lowest metal concentrations. Transport of ophiolitic
detritus by the longshore drift may account for locally high
Cr concentrations within beach deposits. Geochemical
fingerprinting of individual facies associations in terms of
natural metal contents results in the construction of a
geologically-based geochemical map. This map offers a
more reliable depiction of spatial distribution of background
levels than interpolation techniques based uniquely
upon statistical methods. Matching background values
against metal concentrations from topsoil samples leads to
the reliable assessment of the pollution status of Pisa
coastal plain. Metal contents exceeding the threshold values
designated for contaminated areas (Cr) simply reflect
catchment geology, and are not the product of artificial
contamination. On the other hand, anthropogenic disturbance
may be detected even where metal contents (Pb, Cu)
lie below the threshold values. The use of sedimentological
criteria is presented here as a pragmatic tool to enhance
predictability of natural metal contents in sediments, with
obvious positive feedbacks for legislative purposes and
environmental protection
Stratigraphic control on earthquake-induced liquefaction: A case study from the Central Po Plain (Italy)
No full textStudies on earthquake-induced liquefaction tied to high-resolution stratigraphic analysis have been rarely undertaken. We report the results of a multidisciplinary study from the Quistello–Moglia area, in the central Po Plain (northern Italy). In this region, combined stratigraphic, sedimentological, geotechnical, and geochemical data allowed assessment of liquefaction potential and identification of the primary source for liquefaction, following the second main shock (Mw ~ 6) of the 2012 Po Plain earthquake. Using Cone Penetration Test (CPT)-based simplified procedures for liquefaction hazard evaluation, we assessed the highest liquefaction potential of Holocene, fluvial-channel and related (crevasse/levee) fine sand-silt facies encased in thick, mud-prone floodplain and swamp successions. The liquefaction potential, and the intensity of the manifestations induced on the ground surface, decreased for the vertically-amalgamated, sheet-like Pleistocene sandy fluvial units encountered at depths greater than 13 m. Floodplain and swamp deposits were virtually non-liquefiable. In the Quistello area, the compositional characterization of sands that were liquefied and extruded during the 2012 earthquake reveals the diagnostic geochemical fingerprint of sediment carried by the Po River, as opposed to the Apennine composition of surficial sediments. These data rule out proximity of liquefied layers to the surface, and attest the buried, meandering Po River system at depths of ~ 7–10 m most likely representing the source for the liquefied sand that vented to the surface. Similarly, at Moglia, liquefied sands were likely sourced from loose and saturated, ribbon-shaped, fluvial sand bodies encased in mud, though at shallower (4–7 m) depths. Pronounced liquefaction phenomena in alluvial plain systems are commonly believed to be associated primarily with elongate topographic ridges following paleo-river courses. Here, we document that under favorable stratigraphic conditions liquefaction may also occur away from surficial channel–levee systems, in areas dominated superficially by overbank fines. Combining subsurface stratigraphic analysis with geotechnical data, thus, is critical to investigate liquefaction patterns and delineate liquefaction hazard zones
Environmental changes in the lacustrine ancient harbour of Magdala (Kinneret Lake, Israel) inferred from ostracod, geochemical and sedimentological analyses
No full textAncient harbour areas represent a peculiar context where the cooperation between geosciences and archaeology may provide useful information about the mutual interactions involving natural settings and human society. Several multidisciplinary studies have recently focused on Mediterranean seaports evolution, furnishing a wide literature about past bio-sedimentary response to harbour activities (Marriner et al., 2010). On the contrast few geoarchaeological-palaeoecological data on strictly lacustrine harbours, where the importance of ostracods as bioindicators is enhanced by the lack of other organisms as foraminifers, are available. As a part of the “Magdala project” and in the framework of the late Hellenistic-Roman (167 BC-350 AD) sedimentary history reconstructed by Sarti et al. (in press) for Magdala harbour area (Kinneret Lake, north Israel), quantitative ostracod analyses were performed on 28 samples collected from two key stratigraphic sections excavated in front of the Roman harbour structures (docks and a flight of stairs).
Along the sections, detailed described in terms of sedimentological features and anthropogenic artifacts (Lena, 2012; Sarti et al., in press), the abundant and well-preserved ostracod fauna show a very similar faunal composition and distribution. Despite the oligotypic character of the ostracod community, strongly dominated by the opportunistic, true euryhaline species Cyprideis torosa, two different associations were distinguished. Similarly to what observed within the present-day lake basin at ca. 5 m water depth (Mischke et al., 2010), comparable proportion of smooth and noded valves of C. torosa characterize the sandy interval barren in anthropogenic artifacts and interpreted as the natural lacustrine beach at the sections bottom (pre-harbour unit). At the passage to the overlying bay silty sands, containing several late Hellenistic archaeological artifacts, a sharp increase of noded C. torosa (up to 87% of total fauna) is recorded along with the occurrence of other species preferring fine-grained substrates and high-organic stagnant waters, as Pseudocandona albicans. This diagnostic change in ostracod content is paralleled by a sharp increase in concentration (up to double concentration values) of trace metals Zn, Pb and Cu within the silty sands interval, suggesting the establishment of an anthropogenically forced semi-protected basin with high levels of heavy-metal pollution during the late Hellenistic period (sin-harbour unit).
In order to increase the quality of our palaeoenvironmental reconstructions and provide insights into the harbour water chemistry derived by human activities, ostracod geochemistry analyses (ICP-MS, ...) are in progress on C. torosa valves recovered from the pre-harbour and sin-harbour units. The integration of palaeontological and geochemical analyses will potentially differentiate unpolluted from polluted conditions, avoiding complications related to grain-size partitioning. This methodological approach may also improve our knowledge about the “factor X” (van Harten, 2000) that contributes to the development of phenotypic nodes on C. torosa within freshwater-oligohaline settings. Comparing element concentrations with the frequency of noded forms and plotting shell chemistry of smooth versus noded valves can provide new information about ostracods, including C. torosa ecophenotypical features, as bioindicators of high pollution levels within ancient lacustrine harbours
Trunk river and tributary interactions recorded in the Pleistocene–Holocene stratigraphy of the Po Plain (northern Italy)
Full text linkTributary rivers can contribute significantly to alluvial-plain construction by supplying large volumes of clastic material. Their relation to the main axial river strongly influences sediment deposition and preservation. The Po Plain is fed by the Po River and a dense network of transverse tributaries draining the nearby Alpine and Apennine chains. Stratigraphic, sedimentological, petrographic and geochemical analyses on 38 cores permitted detailed differentiation of Po and Apennine sedimentary units. Po River deposits are vertically stacked channel-belt sand bodies with high contents of quartz–feldspar and metamorphic rock fragments, combined with high chromium levels. These sand bodies, 20 to 30 km wide, are replaced southward by finer-grained deposits that represent the distal Apennine tributary-rivers system. Apennine sands, confined in narrow ribbons, show lower quartz–feldspar contents, abundant sedimentary lithics and lower chromium levels. In the last 870 kyr, the boundary between the Po and the Apennine sediment delivery systems shifted along a north–south axis in response to distinct controlling factors. A 20 km northward shift of the Po channel belt, possibly related to a tectonic event, is recorded across a regional unconformity dating to the Marine Isotope Stage 12/11 transition. High sediment supply rates during glacial-lowstand periods widened the Po channel belt southward towards the Apennine domain for a few kilometres. The Last Glacial Maximum channel-belt sand body, 30 km wide and 40 m thick, progressively narrowed northward after the glacial culmination. During the Holocene, channel patterns became avulsive and distributive. Narrow channel belts (<3 km) formed along the Po River branches, and abundant swamp and poorly drained-floodplain muds were preserved in interfluvial areas. Activation and deactivation of the Po branches resulted in sharp narrowing and widening of the area available for Apennine-rivers sedimentation. This work provides insights into tributary-trunk river relations which control grain-size distribution and compositional characters of subsurface deposits
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Detecting background values of potentially toxic metals by integrated sedimentological and geochemical studies: an example from the Cecina River Basin (Tuscany, Italy)
No full textIn order to assess unambiguously legislation limits and levels of concern for potentially toxic metals in sediments, natural concentrations (background values) should be established accurately. Through an example from the Cecina River basin, in central Tuscany (Italy), where natural Cr and Ni concentrations may locally exceed the threshold values designated for contaminated areas (150 mg/kg for Cr and 120 mg/kg for Ni) up to 20 times, we show to what extent background metal concentrations can be determined precisely by integrated sedimentological and geochemical studies.
XRF analyses of 76 samples collected by hand-drilling at 1 m depth from fluvial-channel, overbank, backswamp and beach-ridge deposits reveal distinctive sediment compositions that enable multi-element fingerprinting of individual depositional facies based upon diagnostic metal contents. Sediment provenance is the major factor controlling spatial heavy-metal distribution across the study area. Specifically, sediment supplied by Cecina River and its tributaries is characterized by remarkably high natural Cr and Ni concentrations, reflecting erosion of ultramafic complexes cropping out patchily in the drainage basin. In contrast, significantly lower contents are recorded from ophiolite-free source areas.
At the basin scale, Cr and Ni serve as valuable indicators of sediment pathways through distinct segments of the routing system. A stepwise increase in Cr concentration is recorded along the 75 km-long Cecina River, from source (100 mg/kg) to mouth (400 mg/kg). The major shifts in metal concentration are recorded close to the tributaries-trunk junctions, thus reflecting direct supply of ultramaphic detritus from the tributaries into the main river. Where headwater streams flow through large ophiolitic complexes, very high Cr (900-1600 mg/kg) and Ni (800-1100 mg/kg) concentrations are delivered to the upstream reaches of the tributaries. A remarkable decrease to 1/3-1/5 of total metal concentration is observed downstream, over very short distances (of just few kilometers), reflecting sediment dilution from non-ophiolitic sources. The highest Cr concentrations are recorded, however, close to the Cecina fluvial mouth, where huge natural metal accumulations in beach sands (commonly > 2000 mg/kg) were controlled by hydraulic selection and sorting processes.
The complex spatial distribution of Cr and Ni values across the Cecina River basin documents the inadequacy of using a single threshold value of metal concentration for legislative purposes. Detecting unique geochemical signatures for a variety of facies associations may represent a powerful tool for environmental planning that can be used pragmatically by the regulatory bodies to assess the anthropogenic impact on alluvial and coastal plain
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
