966 research outputs found
Environmental control on the end of the Dolomia Principale/Hauptdolomit depositional system in the central Alps: Coupling sea-level and climate changes
The Norian in the Western Tethys is characterised by the deposition of early-dolomitised inner platform facies (Dolomia Principale/Hauptdolomit, DP/HD), bordered on the landward side by terrigenous coastal deposits (Keuper) and on the seaward side by calcareous backreef and reefal facies (Dachstein Limestone) passing basinward to open-sea sediments (Hallstatt facies). The inner carbonate platform is locally (Lombardy Basin, Carnic Alps, Central Austroalpine) dissected by normal faults leading to the development of intraplatform troughs.
Close to the Norian-Rhaetian boundary, sedimentation records an abrupt environmental change both on platform top and basins all over the Western Tethys (e.g. Western Carpathians, Transdanubian Range, Alps, Central Apennine). The top of the Dolomia Principale locally emerged, reflecting a major eustatic sea-level fall. Emersion is recorded in favourable settings by the development of polycyclic paleosols up to 30 m thick. In the Norian intraplatform basins, the succession is capped by 4 to 8 m of thin-bedded, fine-grained limestones yielding abundant remnants of fishes and terrestrial reptiles. Fossil concentration as well as sedimentological features is indicative of reduced sedimentation rates due to decreased carbonate production, induced by the emersion of the platform top. The sea-level fall was followed by deposition of mixed fine-grained siliciclastic-carbonate successions (e.g. Riva di Solto Shale, Kossen beds, "Rhaetavicula contorta beds", Fatra Formation).
Stratigraphic evidence indicates a dry climate in the Western Tethys during the Norian, as indicated by the presence of evaporites (Burano, Apennine) and arid to semi-arid coastal to playa settings (Upper Keuper, Germany). In contrast, the basal layers of the basinal shales show evidence of wet climate.
The end of the Norian depositional system records two different phenomena: (1) an important sea-level fall was responsible for the emersion of the platform top and deposition of a condensed horizon in the basins: and (2) transition from dry to humid climate. The observed evolution is explained with a global cooling which caused the rapid sea-level fall responsible for the abrupt end of the DP/HD depositional system and the shift of the boundary between arid and temperate climate belts, which modified the distribution and amount of rainfall, triggering the deposition of shales along the Western Tethys margin
Encrinus aculeatus von Meyer, 1849 (Crinoidea, Encrinidae) from the Middle Triassic of Val Brembana (Alpi Orobie, Bergamo, Italy)
The Triassic crinoid Encrinus aculeatus is described from a single bedding plane of uncertain Pelsonian or early Illyrian or (less probable) late Ladinian origin from Val Brembana (Alpi Orobie, Bergamo, Italy) based on 36 more or less complete crowns and columns. The specimens represent an obrutional echinoderm lagerst\ue4tte of the Muschelkalk type. The individuals are semi-adult and juvenile; adult individuals are lacking. Morphological description and comparison with the holotype and additional material from the Lower Muschelkalk and basal Middle Muschelkalk of Upper Silesia (Poland) prove the assignment to Encrinus aculeatus. However, the species concept of genus Encrinus is critical because several characters are inconsistent. E. aculeatus occurs in the Middle Triassic (Bithynian to early Illyrian, ? early Ladinian) of the western Tethys shelf and Peritethys basins (Southern Alps, Balaton Upland, Germanic Basin). Encrinus aculeatus is regarded ancestral to the Upper Muschelkalk (latest Illyrian) E. liliiformis. Until now, E. liliiformis has not yet been proven with certainty from outside the Germanic Basin; references are based on isolated and undiagnostic material
Large-scale progradation, demise and rebirth of a high-relief carbonate platform (Triassic, Lombardy Southern Alps, Italy)
The Upper Anisian to Early Carnian succession of the Middle Val Brembana-Pegherolo Massif (Central Southern Alps of Italy) records a complete depositional cycle from platform inception to growth, demise and rebirth. The depositional architecture of this system reflects different evolutionary stages: an inception stage which postdates a previous drowning of an Anisian carbonate platform with progradation of the carbonate platform from the nucleation areas, an aggradational stage with increasing water depth in the basins, a progradational stage where steep slopes composed of margin-derived breccias develop and a final crisis corresponding to the subaerial exposure of the platform top, followed by the deposition of shales in the basin before the rebirth of a different type of carbonate factory. The record of this evolution reflects the effects of the change in accommodation space (interplay of subsidence and eustacy), which controls the type and storage sites of the sediments produced by the carbonate factory. The effects of the changes in accommodation space are recorded in the shallow water platform as well as in the intraplatform basins, where the sediments, delivered at different rates from the platform top are stored. As a consequence, the aggradational stage corresponds to reduced sedimentation in the basins (i.e. sediments are stored on the platform top) whereas during progradation resedimented limestones are more common in the basin. Subaerial exposure rapidly halted the carbonate production on the platform top, while a major input of shales (probably reflecting a climate change and/or lowering of the base level) is recorded in the basin, where shales onlap the slope of the previous carbonate system. The rebirth of the carbonate factory after subaerial exposure of the platform top is characterized by a different composition of the carbonate factory, probably reflecting changes of the environmental conditions. The step-by-step recording of the evolution of the carbonate system represents a unique opportunity to record a seismic-scale complete evolutionary cycle of a carbonate system in its different sub-environments, from the platform top to the basin
U–Pb zircon geochronology of volcanic deposits from the Permian basin of the Orobic Alps (Southern Alps, Lombardy): chronostratigraphic and geological implications
U\u2013Pb zircon ages from volcanic rocks of Early Permian age (Southern Alps, Lombardy), associated with fault-controlled transtensional continental basins, were determined with the laser ablation (LA)-ICP-MS technique. Four samples were collected at the base and at the top of the up to 1000 m thick volcaniclastic unit of the Cabianca Volcanite. This unit pre-dates the development of a sedimentary succession that still contains, at different stratigraphic levels, volcanic intercalations. Age results from a tuff in the basal part of the unit constrain the onset of the volcanic activity to 280 \ub1 2.5 Ma. Ignimbritic samples from the upper part of the unit show a large scatter in the age distribution. This is interpreted as the occurrence of antecrystic and autocrystic zircons. The youngest autocrystic zircons (c. 270 Ma) are thus interpreted as better constraining the eruption age, constraining the duration of the volcanic activity in the Orobic Basin to about 10 Ma. The new geochronological results compared with those of other Early Permian basins of the Southern Alps reveal important differences that may reflect (1) a real time-transgressive beginning and end of the volcanic activity or (2) the complex mixing of antecrystic and autocrystic zircon populations in the analysed samples
Stratigraphic evolution of the Triassic\u2013Jurassic succession in the Western Southern Alps (Italy) : the record of the two-stage rifting on the distal passive margin of Adria
The Triassic-Lower Jurassic succession of the Southern Alps is characterized by rapid thickness changes, from an average of about 5000m east of Lago Maggiore to about 500m in the Western Southern Alps. The stratigraphy reflects the Triassic evolution of the Tethyan Gulf and the Early Jurassic rifting responsible for the Middle Jurassic break-up of Adria from Europe. The succession of the Western Southern Alps starts with Lower Permian volcanics directly covered by Anisian sandstones. The top of the overlying Ladinian dolostones (300m) records subaerial exposure and karstification. Locally (Gozzano), Upper Sinemurian sediments cover the Permian volcanics, documenting pre-Sinemurian erosion. New biostratigraphic data indicate a latest Pliensbachian-Toarcian age for the Jurassic synrift deposits that unconformably cover Ladinian or Sinemurian sediments. Therefore, in the Western Southern Alps, the major rifting stage that directly evolved into the opening of the Penninic Ocean began in the latest Pliensbachian-Toarcian. New data allowed us to refine the evolution of the two previously recognized Jurassic extensional events in the Southern Alps. The youngest extensional event (Western Southern Alps) occurred as tectonic activity decreased in the Lombardy Basin. During the Sinemurian the Gozzano high represents the western shoulder of a rift basin located to the east (Lombardy). This evolution documents a transition from diffuse early rifting (Late Hettangian-Sinemurian), controlled by older discontinuities, to rifting focused along a rift valley close to the Pliensbachian-Toarcian boundary. This younger rift bridges the gap between the Hettangian-Sinemurian diffuse rifting and the Callovian-Bathonian break-up. The late Pliensbachian-Toarcian rift, which eventually lead to continental break-up, is interpreted as the major extensional episode in the evolution of the passive margin of Adria. The transition from diffuse to focused extension in the Southern Alps is comparable to the evolution of the Central Austroalpine during the Early Jurassic and of the Central and Northern Atlantic margins
Towards a Geological Information System: the CARGeo System and the Regione Lombardia Geological Database.
In the framework of the national mapping program «CARGNew
Italian Geological Map at 1:50.000 scale», Regione Lombardia is
generating a detailed map (1:10.000 scale) of its territory. Surveying
criteria have been carefully defined in order to produce homogeneous
geological maps: geological survey has been performed at the
1:10.000 scale, and data have been stored in a GIS-oriented database.
The detailed survey scale improved the geological knowledge: the
new maps represent an important tool for territorial planning requirements
of public administrations and engineering geologists (e.g. in
hydrogeological and seismic risk evaluation).
Field geologists performed data input in the geological data
base by alternating field campaigns and data input throughout the
year, taking advantage of periods when field activities are slackened
(i.e. according to climate conditions). In this way, data entry is
nearly synchronous with data collection, and field data become
quickly accessible. Data entry by the field geologists on one side
slows down the field activity, however, it guarantees a precise digitalization
of geometric data and a correct attribute assignment, allowing
to optimize working time.
To allow the data entry to non-GIS-specialized users, we developed
an ArcView®-VisualBasic®-MSAccess® application, enabling the
simultaneous acquisition of geometric and alphanumeric data. Data
base management and cartographic production are performed with
ArcInfo®, through specific procedures which, after data reorganization
and control (both alphanumeric and geometric), lead to the final
cartographic output at different scales.
The 1:10.000 geological database is migrated in the ArcSDE
structure and prepared for data view, query and download
(www.cartografia.regione.lombardia.it/cargweb) using ESRI (ArcIMS)
tools.
From the 1:10.000 geological database we derived the database
for the 1:50.000 CARG maps by both automatic and manual generalization
according to the CARG-APAT standards. During the different
phases of the project, several problems arose, due to both
project organization and data storage system (from data collection
in the field to elaboration and digitalization, and, in case, to final publication).
– Data collection: the survey activity was divided between «bedrock
» and «quaternary» specialists. The double survey provided a
high-quality geological description of the territory, but slowed the
generation of the data-flow. Based on this experience, the last assigned
areas are surveyed by a single geologist, under the supervision
of quaternary and bedrock experts.
– Users feedback: geologists are normally used to draw their
maps on paper; learning how to produce electronic maps can be difficult,
and the software tools have to be studied very carefully and
present user friendly interfaces. Nevertheless, in our experience, a
training period has to be planned, and geologists have to be supported
by a GIS expert, who can understand their needs and modify the
software accordingly.
– System architecture: the ArcView®-VisualBasic®-MSAccess®
(Windows platform) – ArcInfo® (UNIX platform) environment, revealed
problems in the client-server stability of an earlier version; some
unsolved troubles remain, mainly related to the network architecture.
The presence in the CARG-Regione Lombardia crew of consultant
geologists, experienced and trained in collection, analysis and data entry
in the final database, accelerated the critical phases of:
– Data base derivation from Regione Lombardia dataset to CARG-APAT standard
A compact light readout system for longitudinally segmented shashlik calorimeters
The longitudinal segmentation of shashlik calorimeters is challenged by dead
zones and non-uniformities introduced by the light collection and readout
system. This limitation can be overcome by direct fiber-photosensor coupling,
avoiding routing and bundling of the wavelength shifter fibers and embedding
ultra-compact photosensors (SiPMs) in the bulk of the calorimeter. We present
the first experimental test of this readout scheme performed at the CERN PS-T9
beamline in 2015 with negative particles in the 1-5~GeV energy range. In this
paper, we demonstrate that the scheme does not compromise the energy resolution
and linearity compared with standard light collection and readout systems. In
addition, we study the performance of the calorimeter for partially contained
charged hadrons to assess the separation capability and the response of
the photosensors to direct ionization.Comment: To appear in Nuclear Instruments and Methods in Physics Research,
Transition between terrestrial-submerged walking and swimming revealed by Early Permian amphibian trackways and a new proposal for the nomenclature of compound trace fossils
Exceptionally preserved Early Permian tetrapod trackways from the Orobic Basin (Central-Western Southern Alps) offer a unique opportunity to investigate in detail locomotion in fossil vertebrates that lived on continental European landmasses. Herein are reported the results of a study on several tetrapod trackways that display a large variety of behavioral, gait and substrate related extramorphologies. They clearly document the transition from terrestrial-underwater walking to swimming and are assigned to the compound ichnotaxon Batrachichnus C Lunichnium. The use of the "C" symbol is here introduced for the first time as nomenclatural indication of a Compound trace. Producers were probably small-sized temnospondyl or lepospondyl (microsaurs) amphibians. Comparisons with living urodelan anatomy and mechanics provide evidence for conservatism of locomotor mechanics in evolutionary history among amphibians. The derived model for locomotor kinematics in Early Permian amphibians provides a reference for interpreting transitional land-to-water trackways. The shift from walking to swimming behavior in early tetrapods, as in extant urodelan amphibians, is described as a complex balance between different dynamics
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