196,752 research outputs found
Pharmacological and biotechnological in vitro approaches unveil the role of GPR17 signaling in regulating the timing of oligodendroglial differentiation
No full textBackground and Purpose - In the adult central nervous system there are many oligodendrocyte precursor cells (OPCs) that serve as the primary source of remyelinating cells in demyelinated lesions. Knowledge of the mechanisms regulating OPC maturation is needed to unveil novel pharmacological targets in demyelinating diseases. The G-protein-coupled membrane receptor GPR17, activated by both uracil nucleotides and cysteinyl-leucotrienes [1], has recently emerged as an important player in oligodendrogliogenesis [2,3]. It has been previously reported that GPR17 presence is restricted to NG2+-OPCs at early differentiation stages and is completely segregated from that of myelin proteins [4]. Here, we used purified primary OPCs from rat cortical parenchyma to assess the functional consequences of GPR17 modulation by either pharmacological or biotechnological approaches on the differentiation program of these cells.
Methods and Results - OPCs were exposed to the GPR17 agonists UDP-glucose, UDP and LTE4 for 48 hours. The degree of OPC differentiation was assessed on fixed cultures by immunostaining with an antibody against Myelin basic protein (MBP), a marker of mature oligodendrocytes. Data show that all these agonists increase the proportion of MBP+ cells compared to controls, suggesting acceleration of cell maturation by promoting receptor activation. Secondly, transfection experiments with fluorescent plasmids, enabling either silencing or over-expression of GPR17 were performed to univocally correlate the expression of this receptor with cell shape changes and phenotype acquisition during oligodendroglial maturation. Preliminary results show that suppression of GPR17 expression at early differentiation stages reduces the number of MBP+cells in culture, indicating that its silencing impairs the normal program of OPC differentiation.
Conclusions - Globally, these data point at GPR17 as a key regulator of oligodendrogliogenesis and at GPR17 ligands as extrinsic local regulators of OPCs under physiological conditions and during myelin repair.
References
[1] P. Ciana, M. Fumagalli, M.L. Trincavelli, C. Verderio, P. Rosa, D. Lecca, S. Ferrario, C. Parravicini, V. Capra, P. Gelosa, U. Guerrini, S. Belcredito, M. Cimino, L. Sironi, E. Tremoli, G.E. Rovati, C. Martini, M.P. Abbracchio, The orphan receptor GPR17 identified as a new dual uracil nucleotides/cysteinil-leukotrienes receptor. EMBO J, 19, 4615-2627, 2006.
[2] D. Lecca, M.L. Trincavelli, P. Gelosa, L. Sironi, P. Ciana, M. Fumagalli, G. Villa, C. Verderio, C. Grumelli, U. Guerrini, E. Tremoli, P. Rosa, S. Cuboni, C. Martini, A. Buffo, M Cimino, M.P. Abbracchio, The recently identified P2Y-like receptor GPR17 is a sensor of brain damage and a new target for brain repair. PloS One, 10, e3579, 2008.
[3] Y. Chen, H. Wu, S. Wang, H. Koito, J. Li, F. Ye, J. Hoang, S.S. Escobar, A. Gow, H.A. Arnett, B.D. Trapp, N.J. Karandikar, J. Hsieh, Q.R. Lu, The oligodendrocyte-specific G protein-coupled receptor GPR17 is a cell-intrinsic timer of myelination. Nature Neuroscience, 12, 1398-1406.
[4] M. Fumagalli, S. Daniele, D. Lecca, P.R. Lee, C. Parravicini, R.D. Fields,P. Rosa, F. Antonucci, C. Verderio, M.L Trincavelli, P. Bramanti, C. Martini, M.P. Abbracchio, Phenotypic changes, signaling pathway, and functional correlates of GPR17-expressing neural precursor cells during oligodendrocyte differentiation. The Journal of biology chemistry,12, 10593-10604
La seconda fase del Rift Sardo: vulcanismo ed evoluzione dei sub-bacini di Ardara-Chilivani e Bonorva (Sardegna settentrionale)
No full textI sub-bacini di Chilivani-Ardara e di Bonorva del Logudoro
orientale sono stati parzialmente colmati da una sequenza di tre
unità piroclastiche. L’Unità IC è costituita da depositi cineritici debolmente
porfirici per Pl, Bt, Cpx, Kf e Qz. L’Unità PL è pomiceo-cineritica,
porfirica per Pl, Bt ± Kf ± Qz. L’Unità CH è maggiormente
porfirica per Pl, Qz, Bt ed ha un maggior contenuto in litici. Importanti
fasi di quiescenza vulcanica sono documentate da depositi epiclastici
che si rinvengono intercalati a diversi livelli stratigrafici. La
sequenza è ricoperta da sedimenti marini del Burdigaliano sup.-Serravalliano.
I differenti caratteri petrografici e minerochimici suggeriscono
che le unità piroclastiche provengano da differenti serbatoi
magmatici localizzati in posizione alto-crostale lungo faglie attive. In
un progressivo contesto transtensionale-estensionale, tali serbatoi
magmatici favoriscono per svuotamento l’instaurarsi di collassi calderici.
I dati raccolti, indicano che le eruzioni abbiano colmato le
parti più interne dei sub-bacini subsidenti del Logudoro orientale,
favorendo il perdurare di condizioni continentali che cessano con
l’attività vulcanica. La strutturazione e l’evoluzione dei sub-bacini
descritti è caratterizzata dal progressivo sbloccamento e tilting dei
blocchi tettonici, evidenziato dalla giacitura delle ignimbriti lapidee
(WI), e dalla messa in posto di prodotti pomiceo-cineritici intercalati
da epiclastiti e conglomerati. Nel quadro dell’evoluzione polifasica
del Rift Sardo, questi sub-bacini appartengono alla seconda fase di
rifting che prelude l’inizio della tettonica estensionale nel dominio
nord tirrenico.The Oligo-Miocene Sardinian Rift (27-15 Ma; CHERCHI & MONTADERT,
1982; LECCA et alii, 1997), is a typical intra arc-massif basin
(sensu DICKINSON, 1974) made up of several sub-basins filled by
thick orogenic volcanic sequences and marine sediments. This arc is
linked to the subduction of the Neotethys oceanic plate under the
European plate and to the Africa-Europe convergence. The displacement
of the arc or, in other words, the drift of the Sardinia-Corsica
Block, is related to the orogenesis of the northern Apennine and of
the Maghrebid-Sicilian chain.
Despite the key-role played by the Sardinia Rift in the knowledge
of the geodynamic evolution of the western Mediterranean
basin, the stratigraphy of volcanic sequences is still incomplete
because large portions of this rift still require detailed mapping.
At the regional scale, the Sardinia Rift shows marked differences
with regard to volcanic and tectonic style. In northern Sardinia,
the rift is arranged into several half-graben type sub-basins,
related to tilted block and horst block systems. The basins are
schematically attributable to the relative mobility of the main blocks
with minor relative strike-slip to transtensional movements along
NE-SW trending faults among the sub-blocks of eastern Sardinia.
The Chilivani-Ardara and Bonorva sub-basins contain a poorly
known thick pyroclastic sequence buried by epicontinental marine
sediments. On the basis of field, petrographic and volcanological criteria,
the volcanic pile is constituted, from bottom to the top, by
early volcanics of broadly andesitic composition (M. Cuguttada Unit:
MC), densely welded and rheomorphic ignimbrites (WI) followed by
ash and pumice pyroclastic flow deposits named throughout this
paper Pianu Ladu (PL), Pianu de Puma (IC) and Chilivani Unit (CH).
Epiclastic deposits (EVL) are observed locally at different stratigraphic
levels (the so-called «lacustre», VARDABASSO & ATZENI,
1962; PECORINI, 1962). Marine deposits onlap the volcano-sedimentary
sequence in the upper Burdigalian-Serravallian interval. Published
K-Ar (LECCA et alii, 1997) and Ar-Ar (EDEL et alii, 2001) radiometric
data obtained for the pyroclastic flow deposits indicate a
quite narrow time span in the range of 20-18 Ma.
With regard to the regional stratigraphic picture proposed by
LECCA et alii (1997), MC andesites belong to the A1 andesites; WI are
the densely welded reomorphic ignimbrites, whereas the PL, IC and
CH ash and pumice flow-Units constitute the AP2 group.
In detail, pyroclastic units belonging to the latter group show
the following:
Pianu Ladu Unit (PL). The PL unit is a light grey-coloured ash
and pumice pyroclastic flow deposit, outcropping with continuity at
the northern edge of the Chilivani-Ardara sub-basin. It lies normally
on WI ignimbrites or locally on reddish matrix-supported conglomerates
made up of clasts of Palaezoic basement. Content of pumice
and xenoliths (accidental and cognate), ranges from 20 to 10% moving
from S. A. of Bisarcio towards M. Ladu, while size and degree of
welding decrease.
Pianu de Puma Unit (IC). The IC Unit constitutes discontinuous
outcrops in the Bonorva basin as well as in the southern part of Chilivani-
Ardara. It lies with nonconformity on the Palaeozoic basement
and/or on the WI. Locally (Pianu de Puma), it is preceded by greenish
to yellow coloured epiclastic deposits at least 5 m thick, containing
rare clasts of the Palaeozoic basement dispersed in an ashy matrix. In
the field, it is a poorly porphyritic greyish coloured ashy pyroclastic
flow deposit ranging in thickness from a few metres to 30 m the
greater thickness being observed eastward of Pranu Mannu.
Epiclastic deposits (EVL). They constitute discontinuous interbeds
among the PL, IC and CH Units; characterized essentially by ash, crystals
and pumice-fragments and containing conglomerate beds formed
at the expense of Palaeozoic basement and WI ignimbrites. In the field
they commonly show a greenish colour and typical cross and parallel
bedding structures.
Chilivani Unit (CH). This is an ash and pumice compound ignimbrite
made up of at least three different flow units well exposed in
the Chilivani-Ardara sub-basin. It represents the volumetrically most
important volcanic unit of the investigated area constituting wide
plateaux dismembered by post-depositional faulting. The thickness
of the unit CH ranges from 10 m (M. Salattu and M. Filigosu sectors),
up to 100 m in M. Cordianu-M. S. Bernardo and in the west of
Pranu Mannu (sub-basin of Bonorva). Macroscopically, it is easily
recognizable because of its high porphyritic index.
Petrographic characters suggest that the pyroclastic units recognized
may be related to different magmatic reservoirs localized in
the upper crust, along active fault zones. In a tectonic/volcanism
feedback scenario, the progressive discharge of magmatic reservoirs
gives rise to caldera-like structures favoured by a progressive extensional
regime.
Several lines of evidence indicate that the PL, IC and CH units
mark the early supply in the studied basins, predating the marine
Boll. Soc. Geol. It., 124 (2005), 3-20, 6 ff., 2 tabb.
La seconda fase del Rift Sardo: vulcanismo ed evoluzione dei sub-bacini
di Ardara-Chilivani e Bonorva (Sardegna settentrionale)
ANTONIO SAU (*), LUCIANO LECCA (**), ROBERTO LONIS (*), FRANCESCO SECCHI (***) & MARIA LUISA FERCIA (*)
(*) Progemisa S.p.A. Via Contivecchi 7, Cagliari.
(**) Dipartimento Scienze della Terra, Università di Cagliari,
Via Trentino 51; e-mail: [email protected].
(***) Istituto di Scienze Geologiche e Mineralogiche, Università
di Sassari, Corso Angioj 10.
ingression. They were erupted along regional volcanogenic faults
observable westward in Bosa sub-basin, as well as in the Chilivani-
Ardara and Bonorva sub-basins.
The whole data set suggest that the volcanic products fill the
inner regions of the subsiding sub-basins in the eastern Logudoro,
prolonging the continental conditions that end with the volcanic
activity.
The volcanic activity of the sub-basins described is tectonically
related to NE-SW trending sinistral transtensive faults which show a
more pronounced extensional character with time. The sub-basins’
evolution can be summarized as progressive fault blocking and tilting
of a block system, easily recognizable by the through the WI
cover that represents a lithostratigraphic marker for northern Sardinia.
Tectonic subsidence favoured the local deposition of fluvial
conglomerates (Pianu Ladu) and finally ash and pumice flowdeposits
(IC and PL) which mark the acme of sub-basin filling and
assume a tectonic significance. In the general picture of the multiphase
evolution of the Sardinian Rift, these sub-basins belong to the
second rifting phase sensu LECCA et alii (1997), during which the
transtensional-extensional faulting affects particularly north eastern
Sardinia at about 18 Ma and predates the beginning of the extension
in the north Tyrrhenian domain
La seconda fase del Rift Sardo: vulcanismo ed evoluzione dei sub-bacini di Ardara-Chilivani e Bonorva (Sardegna settentrionale)
No full textThe second stage of the Sardinian Rift: volcanism and evolution of Ardara-Chilivani and Bonorva sub-basins (Northern Sardinia).
The Oligo-Miocene Sardinian Rift (27-15 Ma; CHERCHI & MONTADERT, 1982; LECCA et alii, 1997), is a typical intra arc-massif basin (sensu DICKINSON, 1974) made up of several sub-basins filled by thick orogenic volcanic sequences and marine sediments. This arc is linked to the subduction of the Neotethys oceanic plate under the European plate and to the Africa-Europe convergence. The displacement of the arc or, in other words, the drift of the Sardinia-Corsica Block, is related to the orogenesis of the northern Apennine and of the Maghrebid-Sicilian chain.
Despite the key-role played by the Sardinia Rift in the knowledge of the geodynamic evolution of the western Mediterranean basin, the stratigraphy of volcanic sequences is still incomplete
because large portions of this rift still require detailed mapping.
At the regional scale, the Sardinia Rift shows marked differences with regard to volcanic and tectonic style. In northern Sardinia, the rift is arranged into several half-graben type sub-basins,
related to tilted block and horst block systems. The basins are schematically attributable to the relative mobility of the main blocks with minor relative strike-slip to transtensional movements along NE-SW trending faults among the sub-blocks of eastern Sardinia.
The Chilivani-Ardara and Bonorva sub-basins contain a poorly known thick pyroclastic sequence buried by epicontinental marine sediments. On the basis of field, petrographic and volcanological criteria, the volcanic pile is constituted, from bottom to the top, by early volcanics of broadly andesitic composition (M. Cuguttada Unit: MC), densely welded and rheomorphic ignimbrites (WI) followed by ash and pumice pyroclastic flow deposits named throughout this paper Pianu Ladu (PL), Pianu de Puma (IC) and Chilivani Unit (CH). Epiclastic deposits (EVL) are observed locally at different stratigraphic levels (the so-called «lacustre», VARDABASSO & ATZENI, 1962; PECORINI, 1962). Marine deposits onlap the volcano-sedimentary sequence in the upper Burdigalian-Serravallian interval. Published K-Ar (LECCA et alii, 1997) and Ar-Ar (EDEL et alii, 2001) radiometric data obtained for the pyroclastic flow deposits indicate a
quite narrow time span in the range of 20-18 Ma.
With regard to the regional stratigraphic picture proposed by LECCA et alii (1997), MC andesites belong to the A1 andesites; WI are the densely welded reomorphic ignimbrites, whereas the PL, IC and CH ash and pumice flow-Units constitute the AP2 group.
In detail, pyroclastic units belonging to the latter group show the following: Pianu Ladu Unit (PL). The PL unit is a light grey-coloured ash and pumice pyroclastic flow deposit, outcropping with continuity at the northern edge of the Chilivani-Ardara sub-basin. It lies normally on WI ignimbrites or locally on reddish matrix-supported conglomerates made up of clasts of Palaezoic basement. Content of pumice and xenoliths (accidental and cognate), ranges from 20 to 10% moving from S. A. of Bisarcio towards M. Ladu, while size and degree of welding decrease.
Pianu de Puma Unit (IC). The IC Unit constitutes discontinuous outcrops in the Bonorva basin as well as in the southern part of Chilivani- Ardara. It lies with nonconformity on the Palaeozoic basement and/or on the WI. Locally (Pianu de Puma), it is preceded by greenish to yellow coloured epiclastic deposits at least 5 m thick, containing rare clasts of the Palaeozoic basement dispersed in an ashy matrix. In the field, it is a poorly porphyritic greyish coloured ashy pyroclastic flow deposit ranging in thickness from a few metres to 30 m the greater thickness being observed eastward of Pranu Mannu.
Epiclastic deposits (EVL). They constitute discontinuous interbeds among the PL, IC and CH Units; characterized essentially by ash, crystals and pumice-fragments and containing conglomerate beds formed at the expense of Palaeozoic basement and WI ignimbrites. In the field they commonly show a greenish colour and typical cross and parallel bedding structures.
Chilivani Unit (CH). This is an ash and pumice compound ignimbrite made up of at least three different flow units well exposed in the Chilivani-Ardara sub-basin. It represents the volumetrically most important volcanic unit of the investigated area constituting wide plateaux dismembered by post-depositional faulting. The thickness of the unit CH ranges from 10 m (M. Salattu and M. Filigosu sectors), up to 100 m in M. Cordianu-M. S. Bernardo and in the west of Pranu Mannu (sub-basin of Bonorva). Macroscopically, it is easily recognizable because of its high porphyritic index.
Petrographic characters suggest that the pyroclastic units recognized may be related to different magmatic reservoirs localized in the upper crust, along active fault zones. In a tectonic/volcanism feedback scenario, the progressive discharge of magmatic reservoirs gives rise to caldera-like structures favoured by a progressive extensional regime.
Several lines of evidence indicate that the PL, IC and CH units mark the early supply in the studied basins, predating the marine ingression. They were erupted along regional volcanogenic faults observable westward in Bosa sub-basin, as well as in the Chilivani- Ardara and Bonorva sub-basins.
The whole data set suggest that the volcanic products fill the inner regions of the subsiding sub-basins in the eastern Logudoro, prolonging the continental conditions that end with the volcanic activity.
The volcanic activity of the sub-basins described is tectonically related to NE-SW trending sinistral transtensive faults which show a more pronounced extensional character with time. The sub-basins’ evolution can be summarized as progressive fault blocking and tilting of a block system, easily recognizable by the through the WI cover that represents a lithostratigraphic marker for northern Sardinia.
Tectonic subsidence favoured the local deposition of fluvial conglomerates (Pianu Ladu) and finally ash and pumice flowdeposits (IC and PL) which mark the acme of sub-basin filling and assume a tectonic significance. In the general picture of the multiphase evolution of the Sardinian Rift, these sub-basins belong to the second rifting phase sensu LECCA et alii (1997), during which the transtensional-extensional faulting affects particularly north eastern Sardinia at about 18 Ma and predates the beginning of the extension in the north Tyrrhenian domain
Tuning the locality of filtering with a spatially weighted implementation of random spray Retinex
No full textThe human color sensation depends on the spatial distribution of the colors in the viewed scene. This principle is at the basis of the random spray Retinex (RSR) algorithm. In this work, we modify RSR by integrating its approach with a method to weight and tune the locality of spatial image information. This modification allows for spatial control of the local effect of RSR on image color filtering. We study the performances of this spatially weighted version of RSR on a public image dataset by analyzing and comparing several image features of the output image and its local properties
Geographic Information Systems Ipotesi di applicazione per la valorizzazione dei beni Culturali
No full textMetodi GIS per a gestione del patrimonio insediativo e storico-culturale, e presentazione di due casi di studio in Sardegn
The mammalian target of rapamycin (mTOR) controls oligodendrocyte maturation by fine-tuning the activity of GPR17 receptor via G protein-coupled receptor kinases.
No full textBackground and Purpose - In the adult central nervous system (CNS), oligodendrocyte precursor cells (OPCs) dispersed throughout the parenchyma serve as a primary source of myelinating cells in demyelinated lesions. The Gi-protein-coupled receptor GPR17 is activated by both uracil nucleotides (e.g. UDP-glucose) and cysteinyl-leukotrienes (e.g. LTD4). We previously reported that GPR17 (i) is transiently expressed by early OPCs (ii) its activation by endogenous ligands promotes OPC differentiation1, and that, (iii) its forced over-expression at late differentiation stages inhibits cell maturation, suggesting that the receptor needs to be down-regulated to allow terminal OPC maturation. Physiologically, GPR17 down-regulation may occur through agonist-induced receptor phosphorylation via G-protein coupled receptor kinases (GRKs)2, and may, in turn, be controlled by the mTOR pathway, that indeed plays a pivotal role in oligodendrocyte maturation3. Here, we used primary OPC cultures to investigate the mechanisms underlying GPR17 down-regulation/desensitization. Their characterization is quite important, since alterations leading to prolonged GPR17 expression in OPCs may contribute to the limited remyelination observed in demyelinating diseases.
Methods and Results - To assess whether GPR17 desensitization occurs through agonist-induced receptor phosphorylation via G-protein coupled receptor kinases (GRKs), OPCs were pre-treated with GPR17 ligands for different time periods and GPR17 ability to inhibit forskolin-induced cAMP formation was measured with a cAMP assay. Through this assay, we demonstrated a loss of GPR17 responsiveness after prolonged exposure to both UDP-glucose and LTD4. Moreover, we also showed that the same agonists induce the direct physical association of GPR17 with GRK2, which in turn phosphorylates the receptor, suggesting a role for GRK2 in GPR17 regulation. Interestingly, we also demonstrated that inhibition of the mTOR pathway by rapamycin determines a significant reduction of GRK2 levels, with parallel increases in GPR17 expression and strong impairment of OPC maturation.
Conclusions - Globally, these data suggest that dysregulation of the pathways controlling GPR17 desensitization leads to aberrant GPR17 overexpression, which, in turn, may prematurely block OPC differentiation at a pre-immature stage. New pharmacological or biotechnological strategies able to re-normalize GPR17 function in demyelinating diseases will help implementing the reparative potential of the OPCs that are still present in the adult CNS.
References
[1] M. Fumagalli, S. Daniele,D. Lecca, P.R. Lee, C. Parravicini, R.D. Fields, P. Rosa, F. Antonucci, C. Verderio, M.L. Trincavelli, P. Bramanti, C. Martini, M.P. Abbracchio, Phenotypic changes, signaling pathway, and functional correlates of GPR17-expressing neural precursor cells during oligodendrocyte differentiation. J Biol Chem. 286(12):10593-604, 2011.
[2] S. Daniele, M.L. Trincavelli, P. Gabelloni, D. Lecca, P. Rosa, M.P. Abbracchio, C. Martini, Agonist-induced desensitization/resensitization of human G protein-coupled receptor 17: a functional cross-talk between purinergic and cysteinyl-leukotriene ligands. J Pharmacol Exp Ther. 338(2):559-67, 2011.
[3] W.A. Tyler, N. Gangoli, P. Gokina, H.A. Kim, M. Covey, S.W. Levison, T.L. Wood, Activation of the mammalian target of rapamycin (mTOR) is essential for oligodendrocyte differentiation. J Neurosci. 29(19):6367-78, 2009
The archaeological risk map in an urban context ad a Public Administration tool for city centre management
No full text
I SEDIMENTI TERRIGENO-CARBONATICI OLOCENICI DELLA PIATTAFORMA DEL GOLFO DI CAGLIARI
No full textEchographic and sedimentological investigations were undertaken on the shelf of Cagliari with the purpose of underlining the relationships between modern terrigenous and bioclastic sediments and the behaviour of the sedimentary system during the Holocene eustatic rising. The Gulf of Cagliari is a sub-tropical, semi-arid Mediterranean area located in the southern part of the NW striking Oligo- Miocene Sardinian Rift, within which the Pliocene Campidano Graben is superimposed. The Quaternary continental shelf developed transversally to this tectonic trough, being fed by terrigenous sediments derived from the Palaeozoic metamorphic basement and from Tertiary sedimentary and volcanic rocks. The new echographic survey, consisting of 11 lines performed transversally from the coast to the shelfbreak, integrated previously available data and allowed us to divide the shelf into different sedimentary environments. From shore to shelfbreak we first encounter a shoreface, gently sloped and distally seagrass-covered (close to the fair-weather wave base), which ends in a wide trough parallel to the coast. Toward the open shelf is a relief, site of the Posidonia oceanica main bank, reaching a minimum depth of 13 meters under the sea level, followed by its external slope. At a depth of about 30 meters the vegetation becomes rare, as less luminosity limits the growth of Posidonia, and starting from depths of 35÷40 meters a large belt of sand waves appears, with gradually decreasing heigths and increasing frequencies basinward. At the depth of 50 m a flat bottom prevails, followed by several reliefs stretching roughly NE–SW at 55 m depth, interpreted as submerged shore lines. Externally to such structures a narrow outer shelf occurs and the shelf break is observed at a depth of 115÷125 m. Sampling sites were located along the echographic lines and on the foreshore; 98 samples were taken with a 2 dm_ grab-sampler. Compositional and grain size analysis allowed us to identify 8 groups of facies related to present day depositional environments. Shoreface sediments are represented by almost completely terrigenous coarse to medium sands in the eastern sector, and finer mixed terrigenous-bioclastic sands on the S. Gilla shoreface.
Two distinct groups of lithic facies are present near Capo S. Elia and near P.ta Zavorra, due to sediment dispersal from the limestone and andesite outcrops along the cliffed coast. The western inner-shelf depression is characterized by mixed quartzose-bioclastic sandy muds with bivalves. Mixed facies of relict terrigenous sediments and present day biogenic production (mollusks, bryozoans, red algae, echinoids and foraminifers) are on the Posidonia oceanica bank’s fore slope, where the siliciclastic component is found between -30 and -50 meters with decreasing importance seaward. Through the sand-wave belt a transition is observed to bioclastic, poorly sorted gravely sands of red algae and foraminifers. Here the sediment is completely bioclastic with rare breakthroughs of mixed sediments in proximity to the –55 m paleo-shores. From a depth of 75 meters, sediments are represented by fine bioclastic-quartzose sands with bivalves and foraminifers. A peculiar feature of this shelf is the depression in the inner shelf that can be interpreted as the product of paleo-river erosions produced during the “Würmian” low stand (MIS 4-2), associated with terrigenous inputs insufficient to fill up the
available space during the post-glacial sea level rise. Towards the middle shelf the trough is bounded by paleo-reliefs where the Posidonia bank at present overgrows, weakly aggrading and prograding. The depositional facies described document the present day sedimentary system as of a temperate water mixed terrigenous-carbonate shelf. The sedimentation is highly siliciclastic in the inner shelf from fluvial-continental feeding, and bioclastic in the rest of the shelf with a maximum productivity along the intermediate shelf’s Posidonia bank and its foreslope. In the middle and outer shelf the siliciclastic component is related to previous eustatic phases and attributable to continental and nearshore deposits lying underneath the middle-shelf Posidonia bank. Analogous depositional contexts must be attributed to the preceding high stand phases of the Middle-Upper Pleistocene. Otherwise, during glacio-eustatic phases of falling, low-stand and rising sea level, the shelf has been affected by terrigenous continental sedimentation or shoreface sequences that are currently resedimented in the middle and outer shelf. In summary, the depositional model of this shelf is characterised by alternating
phases of terrigenous-carbonate sedimentation of middle latitude, with a poorly rainy, warm Mediterranean climate during highstanding sea-level conditions, and terrigenous phases during low stands with rather rainy, cooler Mediterranean climate
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