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Evaluation of bulk carbonate delta C-13 data from Triassic hemipelagites and the initial composition of carbonate mud
No full textBulk carbonate samples of hemipelagic limestone–marl alternations from the
Middle and Upper Triassic of Italy are analysed for their isotopic
compositions. Middle Triassic samples are representative of the Livinallongo
Formation of the Dolomites, while Upper Triassic hemipelagites were sampled
in the Pignola 2 section, within the Calcari con Selce Formation of the
Southern Apennines in Southern Italy. Triassic hemipelagites occur either as
nodular limestones with chert nodules or as plane-bedded limestone–marl
alternations which are locally silicified. In the Middle Triassic Livinallongo
Formation, diagenetic alteration primarily affected the stable isotopic
composition of sediment surrounding carbonate nodules, whereas the latter
show almost pristine compositions. Diagenesis lowered the carbon and oxygen
isotope values of bulk carbonate and introduced a strong correlation between
d13C and d18O values. In the Middle Triassic successions of the Dolomites,
bulk carbonate of nodular limestone facies is most commonly unaltered,
whereas carbonate of the plane-bedded facies is uniformly affected by
diagenetic alteration. In contrast to carbonate nodules, plane-bedded facies
often show compaction features. Although both types of pelagic carbonate
rocks show very similar petrographic characteristics, scanning electron
microscopy studies reveal that nodular limestone consists of micrite (< 5 lm
in diameter), whereas samples of the plane-bedded facies are composed of
calcite crystals ca 10 lm in size showing pitted, polished surfaces. These
observations suggest that nodular and plane-bedded facies underwent
different diagenetic pathways determined by the prevailing mineralogy of
the precursor sediment, i.e. probably high-Mg calcite in the nodular facies and
aragonite in the case of the plane-bedded facies. Similar to Middle Triassic
nodular facies, Upper Triassic nodular limestones of the Lagonegro Basin are
also characterized by uncorrelated d13C and d18O values and exhibit small, less
than 5 lm size, crystals. The alternation of calcitic and aragonitic precursors in
the Middle Triassic of the Dolomites is thought to mirror rapid changes in the
type of carbonate production of adjacent platforms. Bioturbation and
dissolution of metastable carbonate grains played a key role during early
lithification of nodular limestone beds, whereby early stabilization recorded
the carbon isotopic composition of sea water. The bulk carbonate d13C values
of Middle and Upper Triassic hemipelagites from Italy agree with those of
Tethyan low-Mg calcite shells of articulate brachiopods, confirming that
Triassic hemipelagites retained the primary carbon isotopic composition of the
bottom sea water. A trend of increasing d13C from the Late Anisian to the Early Carnian, partly seen in the data set presented here, is also recognized in
successions from tropical palaeolatitudes elsewhere. The carbon isotopic
composition of Middle and Upper Triassic nodular hemipelagic limestones
can thus be used for chemostratigraphic correlation and palaeoenvironmental
studies
Aragonite dissolution, sedimentation rates and carbon isotopes in deep-water hemipelagites (Livinallongo Formation, Middle Triassic, northern Italy)
No full textHemipelagic nodular limestones are a widespread facies in the Triassic of the Tethys, often considered as being deposited at
rather constant sedimentation rates. The aim of this paper is to investigate the sedimentation rate variability in a case-study from
the Middle Triassic of the Dolomites, northern Italy, and to suggest possible causes. The nodular cherty limestones of the
Livinallongo Fm. and correlated units were studied in four stratigraphic sections and compared to classical successions from the
literature. Correlations between sections are based on ammonoid biostratigraphy and tephra stratigraphy. Correlation highlighted
conspicuous changes in sedimentation rates through time and between sections, associated with sedimentological
evidence of deep-water aragonite dissolution. Deep-water dissolution is believed to have resulted in small hiatuses and in a bias
of ammonoid assemblages towards taxa with more resistant shells. Carbonate petrography and geochemistry provide evidence
of differential diagenesis of the Livinallongo Fm. Carbonate nodules were lithified at the water–sediment interface, and their C
isotope composition is regarded as a proxy of the d13C of Middle Triassic bottom seawater. The onset of nodular cherty
limestones, occurring contemporaneously at the basin scale, and the coeval carbonate platform drowning events are tentatively
explained by the inflow and local upwelling of cool deep water from Panthalassa into the western Tethys
Corrosion morphology and cave wall alteration in an Alpine sulfuric acid cave (Kraushohle, Austria).
No full textWhereas most karstic caves worldwide are formed by carbonic acid, a small but significant number of sub-surface cavities are the product of sulfuric acid speleogenesis (SAS). In the Eastern Alps, no cave has so far been attributed to this type. In this multidisciplinary study we demonstrate that Kraushöhle in northern Styria was indeed formed by SAS. The cave pattern shows individual chambers, 3D-mazes and blind galleries, as well as typical SAS morphologies such as cupolas, gypsum replacement pockets, corrosion notches and convection niches. “Ceiling pendants drip holes” are described here for the first time and these corrosion features are fully consistent with the SAS model. Other features of Kraushöhle include thick gypsum deposits with strongly depleted δ34S values and other minerals - mostly sulfates - indicating highly acidic conditions.
We also studied acid-rock interaction processes giving rise to widespread corrosion and concomitant replacement by gypsum. Petrographic and geochemical analyses reveal the presence of a distinctive alteration layer of highly increased porosity at the interface between the host limestone and the secondary gypsum. Dissolution and replacement of the limestone was fast enough to prevent the development of C and O isotopic alteration halos but resulted in selective leaching of elements. This stable isotope signal is thus different from the pronounced isotope gradient commonly observed in CO2-dominated hypogenic caves. Petrographic observations reveal that the limestone-gypsum replacement was a nearly constant volume process
Aragonite dissolution, sedimentation rates and carbon isotopes in deep-water hemipelagites (Livinallongo Formation, Middle Triassic, northern Italy) - Reply
No full textReply to the discussion of Preto et al., 2005, [Maurer, F., Brack, P., in press. Aragonite dissolution, sedimentation rates and carbon isotopes in deep-water hemipelagites (Livinallongo Formation, Middle Triassic,
northern Italy) — Comment. Sedimentary Geology doi:10.1016/j.sedgeo.2006.09.003
Holocene climate variability in Sicily from a discontinuous stalagmite record and the Mesolithic to Neolithic transition
No full textFabric and stable isotopic composition of a Holocene stalagmite (CR1) from a cave in northern Sicily record changes in paleorainfall in the early Holocene. High δ13C stable isotope values in the calcite deposited from ca. 8500 to ca. 7500 yr ago are interpreted as reflecting periods of high rainfall. The wet phase was interrupted by two periods of multi-century duration characterized by relatively cool and dry winters centered at ca. 8200 and ca. 7500 yr ago, highlighted by low δ13C and δ18O values. A high variability of δ13C values is recorded from ca. 7500 to ca. 6500 yr ago and indicates that the transition from a pluvial early Holocene to the present-day climate conditions was punctuated by decadal-scale periods of relatively dry winters. In northern Sicily, the traditional elements of the Neolithic appear at ca. 7700 yr ago. It is possible that changes in rainfall influenced the passage from hunter-gathering to farming and sheep-herding economies
Climate variability in the SE Alps of Italy over the past 17000 years reconstructed from a stalagmite record.
No full textThe European Alps is a region very sensitive to Dryas (YD) marked the end of the Palaeolithic painclimatic
change (Beniston & Jungo 2002), and it is terso A better insight into the climate evolution of the
important to extend the existing climate records as far SE European Alps from the Last Glacial Maximum
back in rime as possible to detect any anthropogenic would greatly improve our understanding of Alpine
climate signals. At present, there is a large set of history. Rere we present an exceptional c. 17 kyr
palaeoclimate and climate data from the CentraI and speleothemr ecord from the southeasternm argin of the
Western Alps, but a fragmentary record from the ltalian Alps.
Eastern Alps (cf. Davis et al. 2003 and references
therein). A stalagmite record from northem ltaly
(McDermott et al. 1999) suggested that the CentraI. .
Alps had a similar Rolocene climatic evolution as the Samplmg and analytlcal procedures
JUTa Mountains and the French Alps. The eastern sec- G h. l tI ' tor of the ltalta..ne oAglrpasp ltes at the boundary between the lca se mg
CentraI and Southern European climate regions as The 27-cm-high, candle-shaped, stalagmite SVI was
defined by pollen data (Davis et al. 2003) and, there- sampled in Grotta Savi, a cave located at 441 m a.s.l.
fore, may show different climate evolution with north of Trieste (4S03ios"N, 13°S3'10"E) (Fig. l).
respect to the CentraI and Western Alps. The Eastern The outer surface of the stalagmite was whitish,
ltalian Alps bave great pre-history importance, which translucent and wet, a typical feature of active
is documented by abundant archaeological evidence stalagmites from the southem watershed of the Alps.
for both indigenous and imported cultural 'packages' At the time of removal, SVI was fed by a constant
(Mithen 2003). In the Dalmeri Shelter site, at 1240m drip (c. 10drops/min) from a stalactite growing about
a.s.l. in NE ltaly, a unique finding of painted stones 30m above the stalagmite. The Savi cave is cut in
dated at c. 13cal.kyr BP, which show lberian fissuredlimestoneoverlainbythin«SOcm)grassland
naturalistic influence (Dalmeri et al. 2004), seems to soil cover, a situation which optimizes the potential for
support Mithen's (2003) hypothesis that the Younger Dryas (YD) marked the end of the Palaeolithic painters. A better insight into the climate evolution of the SE European Alps from the Last Glacial Maximum would greatly improve our understanding of Alpine history. Here we present an exceptional c. 17 kyr speleothem record from the southeastern margin of the Italian Alps
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
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
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