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Introduction to special issue: new developments in speleothem paleoclimate and paleoenvironmental science
No full textStudi speleogenetici e paleoclimatici su stalagmiti del Sistema carsico dei Piani Eterni, Parco Nazionale Dolomiti Bellunesi, Italia
No full textNel 2013 ha avuto inizio una fruttuosa collaborazione tra il Dipartimento di Scienze Biologiche, Geologiche e
Ambientali dell’Università di Bologna, l’Ente Parco Nazionale Dolomiti Bellunesi, la Commissione Centrale
per la Speleologia CAI, e la Federazione Speleologica Veneta per la datazione e lo studio paleoclimatico degli
speleotemi del Sistema Carsico dei Piani Eterni. A tutt’oggi, sono state campionate diverse stalagmiti
provenienti da condotti relativi a diversi livelli paleo-epifreatici. La presenza di abbondante uranio nell’Unità
Bituminosa che caratterizza buona parte del sistema ha permesso di datare le concrezioni con ottima precisione
fino a oltre i 500.000 anni.
I due campioni più interessanti sono IS1 (crescita da 390.000 a 345.000 anni) e MN1 (crescita da 105.000 a
85.000 anni). Entrambi gli speleotemi provengono da condotte paleo-epifreatiche, a quote diverse
(rispettivamente a 1340 e 860 m s.l.m.) e hanno registrato numerose fasi di allagamento dei condotti con
sedimentazione di argille e sabbie, probabilmente legate al periodo di raffreddamento e aumento dell’instabilità
climatica post-interglaciale (rispettivamente del MIS11 e MIS5). Tali speleotemi hanno registrato le ultime fasi
di allagamento epifreatico di tali gallerie e, attraverso comparazioni di quota con morfologie esterne quali
terrazzi fluviali e depositi glaciali, potrebbero fornire un’idea temporale dell’evoluzione del sistema,
sollevamento regionale, incisione e conseguente abbassamento della tavola d’acqua nell’adiacente Val del Mis.
Altri speleotemi in livelli superiori del sistema sono stati datati e risultano essere più antichi (oltre 520.000
anni), mentre alcuni speleotemi del livello paleo-freatico più elevato (Grotta Isabella) sono in corso di studio.
Sono previste inoltre analisi isotopiche degli speleotemi per ricostruzioni paleoclimatiche di specifici intervalli
del Quaternario nelle Dolomiti. Lo studio degli speleotemi e della loro relazione con la formazione dei condotti
e le oscillazioni epifreatiche, a diverse quote e in diversi periodi temporali, potrebbe fornire nuovi interessanti
spunti sull’evoluzione di sistemi carsici multi-livello come quello dei Piani Eterni
Tufa deposits in the Via Gellia, Derbyshire
Full text linkDetailed mapping, section logging, sampling and petrological description of a tufa deposit in the Via Gellia, Cromford, Derbyshire UK has enabled interpretation of the depositional and post-depositional history of the deposit. This has been interpreted in the context of the geomorphology and hydrogeology of the area
A hybrid model to evaluate subsurface chemical weathering and fracture karstification in quartz sandstone
No full textA hybrid numerical, finite differences and semi-analytical/empirical model has been developed to evaluate the
spatial and time scale of chemical weathering along a fracture in quartz sandstones. The model is based on the
diffusion transport occurring from the bedrock mass toward the fracture walls driven by the SiO2 concentration
gradient between water in the bedrock pores (high silica content) and water flowing in the fracture (low silica
content). Because of molecular diffusion, intergranular water becomes undersaturated with respect to silica. This
promotes dissolution of quartz at grain boundaries and results in a porosity profile decreasing from the fracture
walls toward the rock interior. Bedrock individual grains are released and gradually removed by the water
flowing into the fracture when a critical value of porosity is reached (Grain Release Threshold, GRT): this process
drastically increases the fracture enlargement rate.
The model outcomes establish a minimum time of 90 ka to reach the GRT. This time is independent of length,
aperture and dip of the fracture, but is controlled by parameters such as the initial fracture aperture, water
temperature, quartz grain size, and initial bedrock porosity. It is attested that the water flowing in the fracture
remains undersaturated with respect to silica over very long timescales (in the order of 105 years) and over very
long flow paths. In turn, this suggests that the extremely slow reaction between quartz and water is the keyfactor
for the formation of subterranean karst-like features in quartz sandstone, otherwise silica saturation would
be reached after short distances and deep weathering in this lithology would be prevented.
Finally, the model outcomes were compared to field data from the Gran Sabana caves (Venezuela) and other
quartz sandstone weathering landforms elsewhere, showing that dissolution/diffusion in the rock matrix is a
reliable mechanism for the formation of these peculiar karst-like features
The first multi-proxy palaeoclimate record (~115ky-110ky) from the Island of Sardinia
No full textAlthough occupying a critical position at the center of the Mediterranean Sea, the Island of Sardinia (Italy) has never been the focus of multi proxy data-based palaeoclimate studies. An excellent way to obtain information about late Quaternary terrestrial climate oscillations in the region is the study of carbonate speleothems, because they allow the reconstruction of palaeohydrology through the geochemical properties of the their growth layers (Fairchild and Treble, 2009; McDermott, 2004) and are highly suited to accurate independent chronologies (Richards and Dorale, 2003; Scholz et al., 2012).
To this end, U-Th series dating, δ18O and δ13C isotope analysis and petrographic observations have been applied to a ~30 cm long stalagmite (BMS1) sampled in the Bue Marino coastal cave (western Sardinia) providing the first palaeoclimate record for this area.
Seventeen U-Th ages attest to the formation of BMS1 during MIS5d, between ~110 and ~115 thousand years BP, a period of intense climate perturbations that followed the last interglacial peak (Dansgaard et al., 1993). A positive correlation between δ18O and δ13C, and its correspondence with carbonate fabric variations, reflects variations in drip rate, in turn related to secular variation in the rainfall quantity reaching the cave site during its formation. Furthermore, a hiatus at around 111ky BP marks the interruption of a general isotopic enrichment trend, and probably corresponds to the arrival of a short-lived arid-cold period in the region comparable to a sub-D-O cycles (Capron et al., 2010). The presence of intra millennial climate events has already been reported in Alpine speleothems (Boch et al., 2011) but never in the Mediterranean sea region. For this reason further analyses are planned in order to better understand this variability in Sardinia, that represents an exceptional opportunity to correlate existing and future palaeoclimate records from the peri-Mediterranean European and African mainland.
Boch, R., Cheng, H., Spötl, C., Edwards, R. L., Wang, X., and Häuselmann, P., 2011, NALPS: a precisely dated European climate record 120–60 ka: Climate of the Past, v. 7, no. 4, p. 1247-1259.
Capron, E., Landais, A., Chappellaz, J., Schilt, A., Buiron, D., Dahl-Jensen, D., Johnsen, S. J., Jouzel, J., Lemieux-Dudon, B., Loulergue, L., Leuenberger, M., Masson-Delmotte, V., Meyer, H., Oerter, H., and Stenni, B., 2010, Millennial and sub-millennial scale climatic variations recorded in polar ice cores over the last glacial period: Climate of the Past, v. 6, no. 3, p. 345-365.
Dansgaard, W., Johnsen, S. J., Clausen, H. B., Dahl-Jensen, D., Gundestrup, N. S., Hammer, C. U., Hvldberg, C. S., Steffensen, J. P., Sveinbjornsdottir, A. E., Jouzel, J., and Bond, G., 1993, Evidence for general instability of past climate from a 250-kyr ice-core record: Nature, v. 364, p. 218-220.
Fairchild, I. J., and Treble, P. C., 2009, Trace elements in speleothems as recorders of environmental change: Quaternary Science Reviews, v. 28, no. 5-6, p. 449-468.
McDermott, F., 2004, Palaeo-climate reconstruction from stable isotope variations in speleothems: a review: Quaternary Science Reviews, v. 23, no. 7-8, p. 901-918.
Richards, D. A., and Dorale, J. A., 2003, Uranium-series chronology and environmental applications of speleothems, Volume 52.
Scholz, D., Hoffmann, D. L., Hellstrom, J., and Bronk Ramsey, C., 2012, A comparison of different methods for speleothem age modelling: Quaternary Geochronology, v. 14, p. 94-104
A long continuous palaeoclimate-palaeoenvironmental record of the last glacial period from southern Italy and implications for the coexistence of Anatomically Modern Humans and Neanderthals
Full text linkThe first multi-proxy palaeoclimate record (~115ky-110ky) from the Island of Sardinia
No full textAlthough occupying a critical position at the center of the Mediterranean Sea, the Island of Sardinia (Italy) has never been the focus of multi proxy data-based palaeoclimate studies. An excellent way to obtain information about late Quaternary terrestrial climate oscillations in the region is the study of carbonate speleothems, because they allow the reconstruction of palaeohydrology through the geochemical properties of the their growth layers (Fairchild and Treble, 2009; McDermott, 2004) and are highly suited to accurate independent chronologies (Richards and Dorale, 2003; Scholz et al., 2012).
To this end, U-Th series dating, δ18O and δ13C isotope analysis and petrographic observations have been applied to a ~30 cm long stalagmite (BMS1) sampled in the Bue Marino coastal cave (western Sardinia) providing the first palaeoclimate record for this area.
Seventeen U-Th ages attest to the formation of BMS1 during MIS5d, between ~110 and ~115 thousand years BP, a period of intense climate perturbations that followed the last interglacial peak (Dansgaard et al., 1993). A positive correlation between δ18O and δ13C, and its correspondence with carbonate fabric variations, reflects variations in drip rate, in turn related to secular variation in the rainfall quantity reaching the cave site during its formation. Furthermore, a hiatus at around 111ky BP marks the interruption of a general isotopic enrichment trend, and probably corresponds to the arrival of a short-lived arid-cold period in the region comparable to a sub-D-O cycles (Capron et al., 2010). The presence of intra millennial climate events has already been reported in Alpine speleothems (Boch et al., 2011) but never in the Mediterranean sea region. For this reason further analyses are planned in order to better understand this variability in Sardinia, that represents an exceptional opportunity to correlate existing and future palaeoclimate records from the peri-Mediterranean European and African mainland.
Boch, R., Cheng, H., Spötl, C., Edwards, R. L., Wang, X., and Häuselmann, P., 2011, NALPS: a precisely dated European climate record 120–60 ka: Climate of the Past, v. 7, no. 4, p. 1247-1259.
Capron, E., Landais, A., Chappellaz, J., Schilt, A., Buiron, D., Dahl-Jensen, D., Johnsen, S. J., Jouzel, J., Lemieux-Dudon, B., Loulergue, L., Leuenberger, M., Masson-Delmotte, V., Meyer, H., Oerter, H., and Stenni, B., 2010, Millennial and sub-millennial scale climatic variations recorded in polar ice cores over the last glacial period: Climate of the Past, v. 6, no. 3, p. 345-365.
Dansgaard, W., Johnsen, S. J., Clausen, H. B., Dahl-Jensen, D., Gundestrup, N. S., Hammer, C. U., Hvldberg, C. S., Steffensen, J. P., Sveinbjornsdottir, A. E., Jouzel, J., and Bond, G., 1993, Evidence for general instability of past climate from a 250-kyr ice-core record: Nature, v. 364, p. 218-220.
Fairchild, I. J., and Treble, P. C., 2009, Trace elements in speleothems as recorders of environmental change: Quaternary Science Reviews, v. 28, no. 5-6, p. 449-468.
McDermott, F., 2004, Palaeo-climate reconstruction from stable isotope variations in speleothems: a review: Quaternary Science Reviews, v. 23, no. 7-8, p. 901-918.
Richards, D. A., and Dorale, J. A., 2003, Uranium-series chronology and environmental applications of speleothems, Volume 52.
Scholz, D., Hoffmann, D. L., Hellstrom, J., and Bronk Ramsey, C., 2012, A comparison of different methods for speleothem age modelling: Quaternary Geochronology, v. 14, p. 94-104
A long record of MIS 7 and MIS 5 climate and environment from a western Mediterranean speleothem (SW Sardinia, Italy)
No full textHere we present the first record of Marine Isotope Stage (MIS) 7 from Sardinia, based on a U-Th-dated
speleothem from Crovassa Azzurra cave, which also grew during MIS 5. Carbonate precipitation was
continuous during MIS 7, while two multi-millennial hiatuses interrupted growth during MIS 5. These
hiatuses occurred during times of unstable climate, but local karst-specific conditions are considered to
have played an important role as well. d13C values mostly reflect soil bioproductivity and vegetation
density. During less humid periods these values reflect bedrock d13C values, because of a semi-closed
system and/or sulphuric acid-driven bedrock dissolution. d18O changes were governed by the interplay
of rainfall amount and moisture source. Disentangling these two effects was possible by comparing d13C
and d18O values, whereby both isotopes co-vary during periods when d18O was dominated by the amount
effect. Changes in the relative proportion of Atlantic and Mediterranean moisture sources was the main
control on d18O at times when d18O was decoupled from d13C.
d18O variations during MIS 5 are synchronous with Greenland stadials (GS) and interstadials (GI) GS 26,
GI 25, GI-GS 22, GI-GS 21. With the exception of GS 22, these climate oscillations did not affect soil
bioproductivity, and d18O mirrors the relative proportion of Atlantic and Mediterranean moisture sources.
GS 22 was a prominent arid period in Sardinia, in accordance with other regional palaeoclimate
archives.
High soil bioproductivity is indicated by d13C values for MIS 7e and MIS 7c-a; the latter interval was
characterized by a 30 kyr-long time span of warm and humid conditions in Sardinia. Soil bioproductivity
decreased markedly during MIS 7d and the climate became drier. The latter period, also constrained by
d18O data, lasted significantly shorter in Sardinia than in central Europe.
As indicated by changes in d13C and d18O relationships, variations in moisture source are also recorded
for MIS 7, with Mediterranean-dominated rainfall during MIS 7e and 7c followed by a shift toward
Atlantic-dominated rainfa
Ricostruzioni paleoclimatiche del Peri-Adriatico attraverso speleotemi: primi risultati
No full textNell’ambito di una tesi di dottorato presso l’Università di Bologna e l’Université de Savoie (Francia), ed in
collaborazione con l’Università di Melbourne (Australia), si sta portando avanti un ambizioso progetto di ricerca
con l’intento di individuare dei record paleoclimatici in speleotemi campionati in grotte d’Italia e del Carso
dinarico. In questa prima fase di campionamento, grazie al coinvolgimento degli speleologi locali, sono state
raccolte stalagmiti e colate già rotte in precedenza in grotte della Puglia, dell’Emilia Romagna, del Triestino,
della Slovenia, e della Bosnia Erzegovina. I campioni sono stati tagliati longitudinalmente lungo l’asse di
accrescimento e poi lucidati. Dei campioni più promettenti (con laminazione ben visibile, calcite primaria pulita,
senza evidenti segni di ricristalizzazione) sono stati datati bottom e top per il loro inquadramento cronologico. Il
successivo campionamento a microdrilling ha permesso di ricavare le polveri utili per le analisi degli isotopi
stabili dell’ossigeno e del carbonio, effettuate tramite spettrometria di massa. Tali studi permetteranno di
ricostruire il clima del passato delle aree di campionamento, fornendo un valido contributo allo studio
paleoclimatico del Mediterraneo centrale
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