http://hdl.handle.net/2122/218 Ricerca nel canale cerca http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/5961 Titolo: The metamorphic basement of Romanian Carpathians: a discussion of K-Ar and 40Ar/39Ar ages<br/><br/>Autori: Strutinski, C.; Postfach 10 28 20, 66028 Saarbrücken, Germany; Puste, A.; Department of Mineralogy, “Babeş-Bolyai” University, 1 Kogălniceanu, 400084 Cluj Napoca, Romania; Stan, R.; Geological Institute of Romania, PO Box 181, 400084 Cluj Napoca, Romania<br/><br/>Abstract: More than 600 radiometric K-Ar ages on rocks from the metamorphic basement of the RomanianCarpathians are statistically treated and discussed. The data suggest that the most pervasive Alpine rejuvenationoccurred in a belt of about 100-120 km width, within which crystalline rocks were intensely reworked, undergoinga metamorphic remobilisation of Barrovian type before Middle – Late Cretaceous. This Eo-Alpine metamorphicbelt outcrops on the flanks of the Mureş Zone, i.e., in the Rodna massif to the NE, and in the Northern Apuseni tothe west. Away from it, ages get progressively older and outline a broad Variscan metamorphic province. In themost external part of the South Carpathians preserved pre-Variscan ages point to the former extension of theMoesian Plate. Within the study area radiometric K-Ar ages, as well as recently reported fission-track data, do notsupport reheating above 300°C and corresponding regional metamorphic events during meso- and neo-Alpinetimes. http://hdl.handle.net/2122/5712 Titolo: Reassessing the biostratigraphy and the paleobathymetry of the Gonfolite Lombarda Group in the Como area (northern Italy)<br/><br/>Autori: Tremolada, F.; RPS Energy; Guasti, E.; NTO; Scardia, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia; Carcano, C.; Burren Resources Petroleum; Rogledi, ENI E&P; Sciunnach, D.; Regione Lombardia<br/><br/>Abstract: Calcareous nannofossil and foraminiferal analyses have been carried out on outcrops from the type-area of the Gonfolite Lombarda Group (Como, northern Italy). In these marine fine- to coarse-grained clastics, rapidly accumulating at the southern front of the uprising Alpine range during the Oligo-Miocene, a scarce, but reliable, sequence of calcareous nannofossil events has been observed, allowing to refine the previous age assignments. Planktonic foraminifera were found to be extremely rare and provided limited biostratigraphic information. The Villa Olmo Conglomerate and the Chiasso Formation contain the Last Occurrence (LO) of Sphenolithus distentus and the First Occurrence (FO) of Triquetrorhabdulus carinatus, which are characteristic of the nannofossil zones NP24 and NP25 (Chattian), respectively. The lower part of the Como Conglomerate was deposited during the zone NP25, whilst the upper part of the Como Conglomerate straddles the Chattian/Aquitanian boundary in zone NN1. The deposition of the Prestino Mudstones also occurred during zone NN1. However, the upper part of this formation has been dated as Burdigalian during nannofossil zone NN2. The deposition of the upper part of the Val Grande Sandstone has been assigned to the NN3 zone owing to the presence of the taxon Sphenolithus belemnos, which is restricted to NN3. The upper part of the investigated section is characterized by the deposition of the Lucino Conglomerate and its fine-grained members (Lucinasco and Lurate Caccivio Mudstones). The Lucinasco Mudstones have been dated as late Burdigalian corresponding to zone NN4, whilst the overlying Lurate Caccivio Mudstones were deposited during the Langhian part of the zone NN5, based on the presence of S. heteromorphus and the absence of H. ampliaperta. On the whole, the base and the top of the outcropping Gonfolite Lombarda Group result from our study to be younger than hitherto proposed, allowing to resolve certain previous conflicts with the few radiometric dates available for clasts from the Gonfolite Lombarda Group. The depth of deposition was upper bathyal during the Chattian and the Aquitanian and shallowed to neritic during the deposition of the Langhian Lurate Caccivio Mudstones. http://hdl.handle.net/2122/5634 Titolo: Paleomagnetic investigations on the Pleistocene lacustrine sequence of Piànico-Sèllere (northern Italy)<br/><br/>Autori: Scardia, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia; Muttoni, G.; Università di Milano<br/><br/>Abstract: The Piànico-Sèllere is a lacustrine succession from northern Italy that records a sequence of climatic transitions across two Pleistocene glacial stages. The intervening interglacial stage is represented by well-preserved varves with calcitic (summer) and clastic (winter) laminae. There is a tight coupling between climate-driven lithologic changes and magnetic susceptibility variations, and stable paleomagnetic components were retrieved from all investigated lithologies including the largely diamagnetic calcite varves. These components were used to delineate a sequence of magnetic polarity reversals that was interpreted as a record of excursions of the Earth’s magnetic field. Comparison of the magnetostratigraphic results with previously published data allows discussion of two possible models which have generated controversy regarding the age of the Piànico Formation. The data indicates that the Piànico Formation magnetostratigraphy correlates to geomagnetic field excursions across the Brunhes/Matuyama transition, and consequently the Piànico interglacial correlates to marine isotope stage 19. This correlation option is substantially consistent with K-Ar radiometric age estimates recently obtained from a tepha layer interbedded in the Piànico Formation. The alternative option, considering the Piànico interglacial correlative to marine isotope stage 11 within the Brunhes Chron as supported by tephrochronological dating reported in the literature, is not supported by the magnetostratigraphic results. http://hdl.handle.net/2122/5390 Titolo: New stratigraphic constraints for the Messinian-Pliocene transition in the Southern Alps<br/><br/>Autori: Monegato, G.; Università di Padova; Scardia, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia; Pini, R.; CNR-IDPA<br/><br/>Curatori: Iaccarino, S.; Università di Parma; D'Argenio, B.; CNR-IAMC; Lirer, F.; CNR-IAMC<br/><br/>Abstract: The Messinian succession of the Southern Alps is widely exposed in the Venetian-Friulian Basin, whilst more westwards in the Po Basin only isolated outcrops are preserved in the Lake Garda and Lake Como areas. The Alpine Messinian deposits are characterized by the lack of evaporites and Lago-Mare type sequences and, because of the lacking of marine deposits, their chronology is still loosely constrained. Pliocene marine deposits are located in very confined outcrops at the outlet of the main valleys, from Friuli to Piedmont.New investigations concerning many of these successions have yielded new chronological constraints for the stratigraphy of the upper Neogene in the Southern Alps area, as well as new provenance data, supporting the reconstruction of the drainage network evolution in response to the Messinian Salinity Crisis (MSC).In Friuli, deposits of early Messinian age exposed along the Tagliamento River show a petrographic evolution across the Messinian-Pliocene unconformity. The occurrence of clasts from the Paleozoic successions of the Carnic Alps (up to 15%), completely lacking in the Messinian deposits, pinpoints to a widening of the drainage basin during the MSC because of stream piracy and tectonic activity. Deposition continues with alluvial fan facies within the Tagliamento Valley and in the upper piedmont plain until the Late Pliocene.In the central Venetian sector, new provenance analyses on the Messinian conglomerate suggest a drastic drainage network reorganization, as a consequence of the MSC fluvial entrenchment. The Pliocene deposits at Cornuda, next to the present-day valley mouth of Piave River, indicate that the outlet of the river was still confined at that time several km to the east, and the southwestwards migration to the present location took place only later, during the Pleistocene. Westwards, in the catchment of the Brenta River an increase of crystalline rock fragments in the gross composition (from 30 to 60 %) is observed and interpreted as the enhancement of the crystalline basement exhumation, triggered by the system response to the sea level drop.In the Lake Garda area, new investigations on the Sirmione continental conglomerate, doubtfully ascribed to the Messinian, shows the existence of three superimposed units, different in petrographic composition and sedimentology. The lower body consists of poorly-sorted, matrix-supported, coarse-grained gravels, with blocks exceeding the 0.5 m size; sand and gravel petrographic analyses point to a provenance from the Adige catchment, with porphyries locally reaching the 80% of the whole petrographic composition in the pebble fraction. The middle unit displays clast-supported, crudely-bedded gravels with a better sorting and enrichment in carbonate pebbles (up to 70%). The upper body is totally characterized by well-sorted limestone and dolostone pebbles, pointing to a drainage confined in the Southern Alps. The geologic survey allowed to detect several clayey silt layers interbedded in the conglomerate lower and middle units, that have been sampled for pollen analyses.On the western bank of Lake Garda, the Mt. San Bartolomeo succession consists of Messinian?-Early Pliocene continental conglomerate with Melanopsis, overlain by Pliocene shallow-water marine clays and an upper conglomerate unit. The lower conglomerate is clast-supported and poorly-sorted and suggests alluvial fan/intra-valley deposition settings, locally confined. Calcareous nannofossil analyses allowed to refer the marine clays to the late Zanclean (biozones NN14 and NN15). Shallow-water marine settings have been inferred also for the upper conglomerate on the basis of the occurrence of marine algae (Tasmanaceae and Prasinophyceae) and stratigraphic data suggest an heteropic relationship with the marine clay. Petrographic analyses point to a local provenance for the whole Mt. San Bartolomeo succession, with dominant carbonates and subordinate porphyries and volcanoclastic rocks in the pebbles.The overall gathered data allow to cast light on the geomorphologic response of the fluvial systems to the MSC in the Venetian-Friulian Basin and on the Late Miocene paleodrainages in the Lake Garda area. In the Venetian-Friulian Basin the stratigraphic record documents the strong rejuvenation of the Tagliamento and Brenta rivers’ headwaters, leading up to a stream piracy and to the basement exhumation increase, respectively. Taking into account the post-Messinian tectonic shortening and the former Messinian coastline position, we can estimate roughly in the order of 0.1 m/yr the upstream migration of the erosional signal triggered by the MSC dramatic sea level drop (~1500 m). More westwards, in the Lake Garda area high percentage of porphyries in the Sirmione conglomerate suggests that the Adige River flowed in Late Miocene times along Lake Garda valley with likely the Chiese River as tributary of the main trunk. The huge sand-rich bodies observed in the Po Plain subsurface and related to the Garda entry-point could be therefore referred to the Adige River catchment. http://hdl.handle.net/2122/5383 Titolo: Il contributo dei pozzi perforati dalla Regione Lombardia alla conoscenza del Pleistocene lombardo<br/><br/>Autori: Scardia, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia; Muttoni, G.; Università di Milano<br/><br/>Abstract: Facies analysis applied to several up to 220-m-deep cores, taken by Regione Lombardia in the central-northern Po Plain, allowed to recognize an overall regressive sequence consisting of cyclotemic shallow marine and fluvial-deltaic deposits overlain by distal to proximal braidplain sediments. Magnetostratigraphy, coupled with calcareous nannoplankton biostratigraphy, was used to date marine and fluvial-deltaic sediments to the early Pleistocene and continental sediments to the middle–late Pleistocene. Sediment accumulation rates were of ~0.3-0.4 mm/yr in the early Pleistocene, whereas an overall reduction in sediment accumulation rates to ~0.06-0.08 mm/yr, associated to relevant unconformities, characterized the middle-late Pleistocene.Stratigraphic evidences from petrographic, sedimentologic and palynologic analyses highlight in the Regione Lombardia cores a drastic reorganization of vegetational, fluvial, and Alpine drainage patterns, associated to a sequence boundary termed the “R surface”. The “R surface”, seismically traceable across the Po Plain subsurface, was constrained magnetostratigraphically to the first prominent Pleistocene glacio-eustatic lowstand of marine isotope stage (MIS) 22 at 0.87 Ma at the end of the Mid-Pleistocene Revolution, when climate worsened globally and locally caused the onset of the first major Pleistocene glaciation in the Alps.Most marine deposits in the cores lie above sea level highstands of corresponding age, suggesting that they have been uplifted. In order to estimate the observed rock uplift, sediments were back-stripped to elevations at times of deposition (expressed in meters above current sea level) by applying a simple Airy compensation model. The correlation of the isostatically corrected sedimentary facies to a glacio-eustatic reference curve obtained from classic oxygen isotope studies highlights a positive elevation mismatch (rock uplift) in the range of 70-120 m, which occurred after the onset of the major Pleistocene glacial-interglacial cycles at rates of at least 0.15-0.09 mm/yr. Although the driving forces of the observed rock uplift cannot be unambiguously identified, but its timing of onset after the beginning of the major Pleistocene glacial-interglacial cycles and the low seismicity observed in the most of the Regione Lombardia area seem to point to an isostatic readjustment of the chain probably due to the long-term erosional removal of sediments during major Pleistocene glacial advances. http://hdl.handle.net/2122/5382 Titolo: Late Matuyama climate forcing on sedimentation at the margin of the southern Alps (Italy)<br/><br/>Autori: Scardia, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia; Donegana, M.; CNR-IDPA; Muttoni, G.; Università di Milano; Ravazzi, C.; CNR-IDPA; Vezzoli, G.; Università di Milano-Bicocca<br/><br/>Abstract: The Pleistocene history of climate control on sedimentation in the Southern Alps-Po Plain system, northern Italy, was reconstructed using an integrated magnetostratigraphic, palynological, and petrographical approach on a 47-m-deep core. The core mainly consists of lacustrine sediments pertaining to the Bagaggera sequence, deposited at the foothills of the Southern Alps during the late Matuyama subchron (0.99–0.78 Ma). At that time, climate worsened globally and locally it caused the progradation of an alluvial fan unit onto the nearby Po Plain, triggering lake formation by damming of a tributary valley. These new data are used in conjunction with data from the literature to highlight and track the effects of climate forcing on sedimentation during the late Matuyama subchron in different orographic and geodynamic settings of the Southern Alps-Po Plain system as part of the greater Alpine area. We found that the episodes of alluvial fan and braidplain progradation observed in the southern foreland of the Alps during the late Matuyama global cooling seem broadly synchronous with the deposition of most of the so-called Günz and Älterer Deckenschotter deposits in the northern forelands of the Alps as well as with the first major waxing of the Alpine valley glaciers, possibly around the Marine Isotope Stage 22 (~0.87 Ma). http://hdl.handle.net/2122/5175 Titolo: Chronology of the transition from a spreading ridge to an accretional seamount in the Marsili backarc basin (Tyrrhenian Sea)<br/><br/>Autori: Cocchi, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Caratori Tontini, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Muccini, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Marani, M. P.; ISMAR-CNR, Sezione di Geologia Marina, Via Gobetti 101, 40129 Bologna, Italy; Bortoluzzi, G.; ISMAR-CNR, Sezione di Geologia Marina, Via Gobetti 101, 40129 Bologna, Italy; Carmisciano, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia<br/><br/>Abstract: Inversion of new high-resolution magnetic data from the Marsili seamount and the surrounding basin in the Tyrrhenian Seareveals NNE–SSW magnetization stripes ranging from the Matuyama chron to the Brunhes chron, including the shortpositive Jaramillo subchron. The detailed magnetic chronology shows that from the late Matuyama (1.77 Ma), the average halfspreading rate was about 1.5 cm yr-1, with a slight decrease between the Jaramillo and the Brunhes events, when the growth of the volcanic edifice overcame lateral spreading.Analysis of spreading rate and volume of erupted lava indicates that at the beginning of the Jaramillo subchron (1.07 Ma), theMarsili basin evolved from pure horizontal spreading to a superinflated seamount as a consequence of tearing of the Ionian slab. Our data give us a snapshot of the geodynamictransition from an active backarc spreading phase to the vertical accretion of the seafloor because of a radical change inthe subduction dynamics. http://hdl.handle.net/2122/4907 Titolo: Coupled Greenhouse Warming and Deep Sea Acidification in the Middle Eocene<br/><br/>Autori: Bohaty, S. M.; School of Ocean and Earth Science, National Oceanography Centre, Southampton, UK; Zachos, J. C.; University of California, Santa Cruz, USA; Florindo, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Delaney, M. L.; University of California, Santa Cruz, USA<br/><br/>Abstract: The Middle Eocene Climatic Optimum (MECO) is an enigmatic warming event that represents an abrupt reversal in long-term cooling through the Eocene. In order to further assess the timing and nature of this event, we have assembled stable isotope and calcium carbonate concentration records from multiple Deep Sea Drilling Project and Ocean Drilling Program sites for the time interval between ~43 and 38 Ma. Revised stratigraphy at several sites and compilation of δ18O records place peak warming during the MECO event at 40.0 Ma (Chron C18n.2n). The identification of the δ18O excursion at sites in different geographic regions indicates that the climatic effects of this event were globally extensive. The total duration of the MECO event is estimated at ~500 kyr, with peak warming lasting <100 kyr. Assuming minimal glaciation in the late middle Eocene, ~4 to 6ºC total warming of both surface and deep waters is estimated during the MECO at the study sites. Maximum warming at ~40.0 Ma also coincided with a world-wide decline in carbonate accumulation at sites below 3000 m depth, reflecting a temporary shoaling of the calcite compensation depth. The synchroneity of deep-water acidification and globally extensive warming makes a persuasive argument that the MECO event was linked to a transient increase in atmospheric pCO2. The results of this study confirm previous reports of significant climatic instability during the middle Eocene. Furthermore, the direct link between warming and changes in the carbonate chemistry of the deep ocean provides strong evidence that changes in greenhouse gas concentrations exerted a primary control on short-term climate variability during this critical period of Eocene climate evolution. http://hdl.handle.net/2122/3067 Titolo: Radioisotopic age constraints for Glacial Terminations IX and VII from aggradational sections of the Tiber River delta in Rome, Italy<br/><br/>Autori: Florindo, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Karner, D. B.; Department of Geology, Sonoma State University, 1801 East Cotati Avenue, Rohnert Park, CA 94985, USA; Marra, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: Buried sedimentary aggradational sections deposited between 800 ka and 600 ka in the Tiber River coastal alluvial plain havebeen studied using borecores from around Rome. 40Ar/39Ar ages on sanidine and/or leucite from intercalated tephra layers andpaleomagnetic investigation of clay sections provide geochronologic constraints on the timing of aggradation of two alluvialsections, demonstrating that they were deposited in response to glacio–eustatic sea level rise caused by Glacial Terminations IXand VII. 40Ar/39Ar age data indicate ages of 802±8 ka (1σ full errors) and 649±3 ka (1σ full errors) for Glacial Terminations IXand VII, respectively, providing a rare test, beyond the range of U-series dating for corals and speleothems (∼500 ka), of theastronomically calibrated timescale developed for oxygen isotope records from deep sea cores. http://hdl.handle.net/2122/2749 Titolo: Field Trip Guide to Active Tectonics Studies in the High Agri Valley<br/><br/>Autori: Ferranti, L.; Università di Napoli Federico II; Maschio, L.; Università di Napoli Federico II; Burrato, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: The year 2007 is the 150 anniversary of the Great Neapolitan Earthquake which on 16 December 1857 struck a vast region of Southern Italy and was centered in the Val d’Agri (Agri River valley), one of the largest basins of the Southern Apennines mountain chain. The earthquake effects were promptly studied by Robert Mallett, an Irish engineer who published an extensive report considered a landmark in the modern Seismology [Mallet, R., 1862. The great Neapolitan earthquake of 1857. The first principles of observational seismology. Chapman and Hill (Publ.), London].Although this earthquake is one of the largest (M~7) in the national seismic catalogue, the location and geometry of the causative fault are object of a warm debate which has blazed in the last years within the scientific community. The querelle is not limited to the identification of seismogenic sources in the Val d’Agri area but, obviously, imbues models of the Quaternary tectonic evolution of the Apennines.Taking the occasion of this recurrence, the Università degli Studi di Napoli Federico II, the Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the Istituto di Metodologie per l’Analisi Ambientale del CNR (CNR-IMAA) in Tito (Potenza), with the contribution of the Università della Basilicata at Potenza, have promoted a three-day meeting in the Val d’Agri with the aim of discussing field evidences and models for active tectonics in the area.