1,721,082 research outputs found
Evidence for a "pluvial" period Between 8-7 KA on Apuan Alps (Central Italy): Implications for the sapropel paradigm In the Eastern Mediterranean
No full textA stratigraphic and chronological study of the upper level of Renella Cave (Apuan Alps, Central Italy) reveals that two episodes of flowstone accumulation bracket a thick clastic layer deposited between ca. 8.2 and 7.1 ka. This layer, which represents a period of enhanced cave flooding, is substantially in phase with an interval of depleted oxygen isotopes values previously recorded in a stalagmite from nearby Corchia Cave, previously interpreted to have resulted from an increase in local precipitation. Combined evidence from Renella and Corchia Cave suggests that this wettest phase was shorter than the condition leading to the formation of Sapropel S1. A synchronicity between signal dominated by the advection of vapour masses from the Atlantic, as Corchia and Renella archives should record in their proxies, cannot straightforwardly correlated with events (at least in duration) dominated by the monsoon signal as could be sapropels in the Mediterranean
Stratigraphy, petrography and chronology of speleothem concretion at Tana Che Urla (Lucca, Italy): paleoclimatic implications
Full text linkIn this work we present the results of a stratigraphic and lithologic study of a flowstone from Tana che Urla Cave, Apuan Alps (central Italy) which grew intermittently between ca. 160 and 8 ka. The studied succession consists of an alternation of two different lithofacies (Lf-A, Lf-B): a brown, detrital-rich (Lf-A) and a white, inclusion-poor calcite (Lf-B). Using available growth rate data, the difference between the two lithofades is thought to be the result of different amounts of meteoric precipitation, with Lf-A related to low growth rates at times of low precipitation during phases of climatic deterioration (stadial or glacial) and a higher flux of elastic material, and Lf-B related to high growth rates due to high infiltration under conditions of higher precipitation during wetter (interstadial/interglacial) periods, with lower clastic flux. Following this interpretation and the available chronology, the flowstone investigated shows a basal portion of Lf-A that was deposited during MIS6. The flowstone then passed from Lf-A to Lf B at the MIS6-5 transition, with Lf-B lasting for the full interglacial of MIS5e. A long growth interruption (hiatus H1) can be correlated with the MIS5d stadial, with resumption of lithofacies Lf-B occurring during the climatic amelioration of interstadial MIS5c. The age profile of the upper part of the flowstone is poorly constrained, and is characterised by several growth interruptions, suggesting that the last glacial was more severe compared to MIS6
Palaeo-environmental reconstruction of the Mercure Basin (Basilicata region) during MIS 13, through a multi-proxy analysis of lacustrine sediments
Full text linkThe main purpose of this work is to make a first evaluation of the potential of the carbonate lacustrine sediment of the Mercure Basin (Basilicata region), to preserve palaeoclimatic information during the Middle Pleistocene. For this purpose a multi-proxy analysis of the lacustrine sediments from a selected section of the basin was undertaken. The selected section contains several tephra layers, which constrains the timing of deposition to MIS 13. Stable isotopes (oxygen and carbon) and element content were tentatively interpreted as linked to climatic changes giving interesting results for this poorly studied interval
Barnacle-rich facies as a tool for palaeoenvironmental reconstructions
No full textPalaeoenvironmental data are fundamental in determining the manifold impacts of climate change. This paper argues that sessile barnacles are an excellent palaeoenvironmental proxy: they are present in nearly all nearshore environments, and their shell consists of diagenetically stable low-magnesium calcite and grows fast enough to record short-term variations. To demonstrate their utility, specimens from several Western Mediterranean Pliocene and Pleistocene barnacle-rich deposits are analysed herein, using for the first time a combination of sedimentology, taphonomy, stable isotope geochemistry and detailed comparisons with modern counterparts. Within shelf carbonate systems, barnacle diversity is highest in the shallow, nearshore waters and decreases moving offshore, thus providing a good proxy for the reconstruction of water depth and distance from the coastline. Barnacle taphonomy is also informative. Well-preserved complete specimens are characteristic of protected areas, whereas less well-preserved specimens occur in high-energy areas. The presence/absence of opercular plates is also particularly relevant for evaluating hydrodynamic conditions. As regards the C and O stable isotope ratios, due to the porous and coarse-grained nature of the deposits in which barnacle remains are usually found, the shells are often exposed to meteoric water percolation during diagenesis. Among the analysed specimens, only those collected from fine-grained deposits display no evidence of alteration and have isotopic ratios in line with those of their modern counterparts. These fossils display intra-shell variations that in modern barnacles have been related to short-term environmental changes (e.g., seasonal cycles). These results demonstrate that barnacles can always be useful for detailed palaeoenvironmental reconstructions based on skeletal assemblages. Furthermore, with further research aimed at gathering more data and assessing potentially interfering signals, they could become useful proxies for palaeoseasonality
Oxygen and carbon isotopic composition of modern terrestrial gastropod shells from Lipari Island, Aeolian Archipelago (Sicily).
No full textOxygen (δ18Os) and stable carbon (δ13Cs) isotopic compositions of modern terrestrial gastropod shells from Lipari Island, in the Aeolian Archipelago (Sicily), have been analysed and compared with local meteoric water δ18O (δ18Op) and vegetation δ13C (δ13Cv) respectively. Results reveal that the δ18Os-δ18Op relationship over the study area differs from those obtained on continental Europe and Italian shells, implying that even at the scale of the Mediterranean basin different relationships may co-exist. These differences have been interpreted as the increasing influence of Mediterranean vapour water on Tyrrhenian coasts at relatively low altitude (up to ~600m asl), which compensates for the effect of the δ18Op, and possibly of temperature, on shell δ18O. The steady-state flux balance model (FBM), in agreement with previous studies, suggests that snails are active prevalently at night. Shell carbon isotope ratios reflect the δ13Cv, as predicted by the metabolic model and represent a valuable tool for identifying C3 plants with very distinct isotopic signature
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
Stratigraphic evidence for a “pluvial phase” between ca. 8200-7100 ka from Renella Cave (Central Italy)
No full textA stratigraphic and chronological study of the upper level of Renella Cave (Apuan Alps, Central Italy) reveals that two episodes of flowstone accumulation bracket a thick clastic layer deposited between ca 8.2 and 7.1 ka. This layer, which represents a period of enhanced cave flooding, is substantially in phase with an interval of depleted oxygen isotope values previously recorded in a stalagmite from nearby Corchia Cave, interpreted to have resulted from an increase in local precipitation. These data confirm that during this period of time the region experienced relatively wetter conditions, including an increase in high-magnitude events capable of invading the higher passages of Renella Cave. The timing of the clastic phase occurred when the Eastern Mediterranean experienced deposition of sapropel layer S1, which is thought to reflect the stagnation of sea water produced largely by enhanced flood activity along the Nile in response to increased monsoon intensity in northern equatorial Africa. Recent estimates suggest that S1 may have lasted from ca 10.8 to ca 6.1 ka cal BP. Combined evidence from Renella and Corchia Cave indicates that the period corresponding to the wettest phase in the Apuan Alps was much shorter than this, and suggests that there is no straightforward connection between increased advection of water vapour from the Atlantic between 8.2 and 7.1 ka, as recorded in the Corchia and Renella records, and monsoon-driven enhancement of Nile discharge and S1 deposition in the eastern Mediterranea
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
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