121,923 research outputs found
Geological Evidences For Late Paleozoic Intra-pangea Dextral Shear
No full textThe Wegenerian configuration of Pangea at Jurassic times, also known as Pangea A, is not questione damong Earth scientists. Debate exists on its pre-Jurassic configu- ration since Ted Irving (1977 Nature) introduced twenty-five years ago Pangea B by placing Gondwana to the East by 2500km with respect to Laurasia on the basis of paleomagnetic data. Pangea B is mainly necessitated by paleolatitude discrepancy be- tween Africa (Gondwana) and North America (Laurasia), which would overlap by about 1700km if reconstructed in a Pangea A configuration at Early Perian times. West Gondwana/Adria poles support Pangea B in the Early Permian, but allow transi- tion to Pangea A by the end of the Permian in the late. stages of the Variscan/Hercynian orogeny (Muttoni et al., 1996 EPSL). Importantly, some of the Early Permian pale- opoles are in igneous rocks and/or from low paleolatitude sites (e.g., Adria), hence making inclination error less likely as an explanation for Pangea B as envisaged by Rochette and Vandamme (2001 Annali di Geofisica). A few Earth scientists tried to seek geological evidence for the pre-Jurassic dextral mega-shear between Gondwana and Laurasia necessary to go from Pangea B or similar configuration to the Pangea A configuration at the time of Atlantic opening in the Jurassic (e.g., Ricou, The Ocean Basins and Margins, Vol. 8, Plenum Press, 1996). Nevertheless, it is fair to say that Pangea B and its tectonic implications have not been broadly accepted but this leaves the problem of the supportive paleomagnetic data unresolved. The ultimate option is to abandon the geocentral axial dipole (GAD) hypothesis by introducing a non-dipole component in the Late Paleozoic paleomagnetic field to explain
the paleolatitude dis- crepancy between Africa and North America (Van der Voo and Torsvik, 2001 EPSL). We are not so distressed by the geological consequences of Pangea B to abandon the GAD hypothesis which has been the basis for virtually all tectonic interpretations us- ing paleomagnetic data. We present new paleomagnetic data from Adria (i.e., West Gondwana) to verify whether Pangea B is paleomagnetically defensible, and review recent geological data from the literature in support of any pre-Jurassic intra-Pangea dextral mega-shear which could be reconciled with the necessary Pangea B to A tran- sition. Relevant geological lines of evidence for Gondwana vs. Laurasia Pangean mo- tions which build on the interpretations of late Hercynian faults sensu Arthaud and Matte (1977 GSA Bulletin) are as follows: (i) Late Paleozoic mantle-scale dextral 1 shear with simultaneous emplacement of orogen-scale granitoids characterized late Hercynian Pyrenees
D2 deformation (e.g., Leblanc et al., Tectonophysics, 261, 1996; Gleizes et al., J. Struct. Geol., 20, 1998, Druguet and Hutton, J. Struct. Geol., 20, 1998). (ii) The Hercynian orogen of Gondwanan France and Iberia has been recently interpreted as the result of the juxtaposition of far-travelled terranes bounded by Late Paleozoic mainly dextral transpressive faults with up to 2000km of dextral displace- ment (Shelley and Bossiere, J. Struct. Geol., 22, 2000). (iii) the Alps preserve evidence for an orogen-scale Permian (trans)tensional event characterized by the emplacement of mafic and ultramafic rocks at the crust-mantle boundary (the Ivrea-Verbano Zone: e.g., Handy and Zingg, Geol. Soc. Am. Bull., 103, 1987; Handy and Streit, Earth Pl. Sc. Lett., 165, 1999; the Malenco Unit: e.g., Trommsdorff et al., Ofioliti, 24, 1999). A similar scenario characterized also the northern Apennines (Marroni et al., Tectono- physics, 292, 1998). Permian magmatic underplating is accompanied by coeval em- placement of granitic and rhyolitic magmatism in shallower levels of the (southern) Alpine crust (e.g., Bozen porphyrites), and volcanosedimentary sequences deposited in dextral pull-apart basins (i.e., Collio Fm.). (iv) central Europe is occupied by ca. 48000km3 of Permian volcanics erupted in a general trans(tensional) regime proba- bly along mantle-scale faults (Beneck et al., Tectonophysics, 266, 1996). These and other geological evidences suggest that docking of Gondwana to Laurasia occurred in a general dextral tectonic regime involving lithosphere-scale processes such as ana- tectic melting and/or magma channeling along shear zones, terranes tectonics, as- thenosphere unroofing and magma underplating which we reconcile with Pangea B to Pangea A transformation in the Late Paleozoic (and therefore not in the Triassic as proposed by Torcq et al. (1997 EPSL). Finally, we would point out that where de- formation is known to be dominated by continental large-scale transcurrent motions (e.g., San Andreas fault system, N. America Cordilleran terranes, New Zealand Alpine fault), it is difficult to find field evidence for more than half of the total displacement of juxtaposed plates/terranes (Umhoefer 2000 Tectonophysics)
Punti di fermi in materia di Comunità montane? Prime note a Corte cost. sent. 24 luglio 2009, n. 237
No full textBio-chronostratigraphic calibration of the Upper Carnian-Lower Norian magnetostratigraphic scale at Pizzo Mondello (Sicani Mountains, Sicily)
No full textPizzo Mondello section is known since 15 years because
of the continuous Late Triassic pelagic record of great
significance for the establishment of an integrated chronostratigraphy
of the Late Triassic (Gullo et al. 1996;
Muttoni et al. 2001, 2004).
During the last 4 years, Pizzo Mondello section has been
studied in detail to provide a new and high resolution integrated
bio-chronostratigraphy for the calibration of the
magnetostratigraphy and chemostratigraphy proposed by
Muttoni et al. (2001, 2004), and now it is one of the GSSP
candidates for the definition of the base of the Norian.
The lowest 143 m of the Cherty Limestone, straddling the
C/N boundary have been studied in detail. The preliminary
data of the ongoing research have been presented in all the
meetings of the STS from Albuquerque 2007 and here we
summarize the final results.
The key correlation to the standard marine Triassic Scale
is provided by the ammonoids. They are relatively rare,
however the available collections document the Upper
Carnian Discotropites plinii and Gonionotites italicus
Subzones, from meter 15 to meter 80 from the base of the
section. The following 15 meters are poor in ammonoids,
while higher up the lower part of the Lower Norian Guembelites
jandianus Zone is documented by Dimorphites cf.
n. sp.1 of Krystyn, 1980.
Conodonts are very abundant and have a great potential
as practical tool for global correlations. The abundance
of specimens at Pizzo Mondello gave the opportunity to
point out clear relationships among the five most widespread
Upper Camian/Lower Norian conodont genera
(Paragondolella, Carnepigondolella, Metapolygnathus,
Epigondolella and Norigondolella) and to identify trends
of the generic turnovers (Mazza et al. 2010). The two biomarkers
so far proposed as possible marker events for the
GSSP were the FAD of E. quadrata (sample FNP88A) and
the FAD of M. communisti (sample NA35). However, the
FAD of E. quadrata occurs within the Gonionotites italicus
Subzone, while the FAD of M. communisti is on its top.
Halobiids are extremely common in the Cherty Limestone
and they have also a great potential for large scale correlations.
Nine species of Halobia have been recognized:
Halobia carnica, H. lenticularis, H. simplex, H. superba,
H. cf. rugosa, H. radiata, H. austriaca, H. styriaca and H.
mediterranea. The best possible marker for the base of the
Norian is the first occurrence of Halobia austriaca, that is
recorded in the middle of the interval between the record
of the Gonionotites italicus Subzone and the Guembelites
jandianus Zone.
Radiolarians were found in few samples but with high
diversity assemblages. In the upper Gonionotites italicus
Subzone to the Guembelites jandianus Zone there is an
overlap of species previously considered Late Carnian
with species usually regarded as Early Norian. About 4 m
above the FAD of E. quadrata, in the Gonionotites italicus
Subzone, the first assemblage with Capnuchosphaera
deweveri Kozur & Mostler, Capnuchosphaera tricornis
De Wever, Kahlerosphaera norica Kozur & Mock and
Xiphothecaella longa Kozur & Mock, usually referred to
Early Norian, occurs.
These integrated bio-chronostratigraphic studies lead to
identify some possible GSSP marker events especially on
conodonts and halobiids, which occur in the upper part of
magnetozone PM 4n, within PM 4r and in the lower part
of PM 5n.
Possibly the most suitable magnetostratigraphic event to
recognize the basal Norian is the base of magnetozone
PM 5n, as already suggested by Krystyn et al. 2002 and
Muttoni et al. 2004
Paleomagnetism of latest Anisian (Middle Triassic) sections of Prezzo Limestone and Buchenstein Formation, Southern Alps, Italy
No full textA paleomagnetic study was carried out at six stratigraphic sections (309 specimens) in the latest Anisian (Middle Triassic) Prezzo Limestone and the overlying Buchenstein Formation. These units outcrop over a wide area in the western Southern Alps, although most of the sampled sections are in the vicinity of the Late Eocene-Early Oligocene Adamello batholith. Three sites suffered a complete remagnetization induced by the Adamello, whereas a characteristic component with a positive fold test has been isolated at the three other sites. The mean pole of the characteristic component (Lat. 63.2-degrees-N, Long. 229.3-degrees-E, N = 3, A95 = 8-degrees, k = 236) is in agreement with the Triassic portion of the West Gondwana apparent polar wander path (APWP), supporting the use of paleopoles from well-dated rocks in the Southern Alps as useful proxies for the African APWP. The characteristic component, where isolated in the sampled sections, is of normal polarity only, corresponding to the latest Anisian on the basis of well-defined ammonoid and conodont biostratigraphy, but the present results suggest that there are good opportunities for extending Middle Triassic magnetostratigraphy in these Southern Alps rock units. The mean pole of the Adamello-induced component (Lat. 74.5-degrees-N, Long. 172.1-degrees-E, N = 4, A95 = 7.6-degrees, K = 145) lies close to the Early Tertiary portion of the APWP for stable Europe. The post-folding, Adamello-induced directions confirm that the 30-42 Ma Adamello batholith intruded after Alpine deformation and that no further deformation apparently occurred in post-emplacement times
Il decreto legislativo c.d. sanzione e premi. Riflessioni critiche in attesa del verdetto della Corte costituzionale
No full textIl d.lgs. 6 settembre 2011, n. 149, reca “Meccanismi sanzionatori e premiali relativi a regioni, province e comuni” e costituisce l’ottavo decreto di attuazione della l. 5 maggio 2009, n. 42 (in ispecie degli artt. 2, 17 e 26), con la quale il Parlamento ha delegato al Governo, nell’ambito del c.d. federalismo fiscale, la realizzazione concreta dei principi di cui all’art. 119 Cost.
Il testo si caratterizza per un certo disequilibrio tra le previsioni a carattere sanzionatorio e quelle di natura premiale a tutto vantaggio delle prime e per uno spiccato interesse del legislatore delegato per i disavanzi sanitari.
Notevole è, poi, la scelta di individuare come unici destinatari delle suddette sanzioni gli enti territoriali periferici, dimenticando di porre una disciplina analoga, nel medesimo testo o altrove, per il livello di governo centrale.
Inoltre, mentre la scelta di disciplinare le sanzioni e i premi in un unico provvedimento sia per le Regioni sia per gli Enti locali può, al massimo, definirsi inopportuna, criticabile sembra essere l’estensione della disciplina dettata a Regioni a statuto speciale e Province autonome.
Questi sono solo alcuni dei profili in relazione ai quali dubbi di legittimità sono stati posti alla Corte costituzionale, le cui decisioni in merito sono attese per il prossimo autunno.
In ogni caso la disciplina posta, soprattutto con riferimento all’istituto più importante, ossia quello del c.d. fallimento politico degli organi di vertice della gestione territoriale periferica, è sembrata a molti già poco chiara, a tratti lacunosa, certamente inadeguata a giungere a concreti accertamenti di responsabilità da sanzionare (o premiare) e, dunque, inefficace rispetto all’obiettivo di raggiungere in tempi brevi una buona accountability a livello regionale, in particolare, ma anche provinciale e comunale. La funzione del d.lgs. n. 149/2011 appare, per questo, prevalentemente di marketing, da spendere soprattutto sotto il profilo politico
Jurassic monster polar shift confirmed by sequential paleopoles from Adria, promontory of Africa
No full textJurassic paleomagnetic data from North America have long been contentious, generating ambiguities in the shape of the global-composite apparent polar wander path. Here we show from a restudy of two subdivisions of the Late Jurassic Morrison Formation at the classic locality at Norwood on the Colorado Plateau that the derived paleopoles reflect variable overprinting probably in the Cretaceous and are of limited value for apparent polar wander determination. We instead assembled an updated set of Jurassic paleopoles from parauthocthonous Adria, the African promontory, using primary paleomagnetic component directions derived from stratigraphically superposed intervals and corrected for sedimentary inclination error. These paleopoles are found to be in superb agreement with independent igneous paleopoles from the literature across the so-called Jurassic monster polar shift, which in North American coordinates is a jump of ~30° arc distance from the 190- to 160-Ma stillstand pole at 79.5°N 104.8°E to a 148 ± 3.5-Ma pole at 60.8°N 200.6°E defined by four Adria sedimentary paleopoles and the published Ithaca, Hinlopenstretet, and Swartsruggens-Bumbeni igneous paleopoles. The implied high rate of polar motion of ~2.5°/Myr across the monster shift is compatible with maximum theoretical estimates for true polar wander. We include a critique of published Jurassic paleomagnetic data that have been variably used in reference APWPs but that as a result of their low quality muted the real magnitude of the Jurassic monster shift. Finally, we provide paleocontinental reconstructions to describe examples of the bold signature that the monster polar shift left in the distribution of climate-sensitive sedimentary facies worldwide
A detailed record of the C34n/C33r magnetozone boundary for the definition of the base of the Campanian Stage at the Bottaccione section (Gubbio, Italy)
No full textWe provide an updated and detailed magnetostratigraphy across the C34n/C33r polarity reversal boundary at the Bottaccione section (Gubbio, Italy) that represents a candidate GSSP for the base of the Campanian Stage (Late Cretaceous). The position of the C34n/C33r boundary is stratigraphically located at 221.525 +/- 0.075 m in agreement with previous estimates from the literature. Following a critical review of data from the literature, we assign a nominal age of 83.06 +/- 0.18 Ma to the observed C34n/C33r polarity reversal boundary and an average rate of deposition of the Santonian/Campanian boundary Scaglia Rossa Formation of 1.09 +/- 0.25 cm/kyr (similar to 11 m/Myr). We also assess the paleolatitude of deposition of the Scaglia Rossa at Bottaccione by correcting the characteristic remanent magnetization component directions for sedimentary inclination flattening, obtaining a value of 21.1 degrees N (+/- 1.6 degrees)
Modulation of Late Cretaceous and Cenozoic climate by variable drawdown of atmospheric <i>p</i>CO<sub>2</sub> from weathering of basaltic provinces on continents drifting through the equatorial humid belt
No full textThe small reservoir of carbon dioxide in the atmosphere (pCO2) that modulates climate through the greenhouse effect reflects a delicate balance between large fluxes of sources and sinks. The major long-term source of CO2 is global outgassing from sea-floor spreading, subduction, hotspot activity, and metamorphism; the ultimate sink is through weathering of continental silicates and deposition of carbonates. Most carbon cycle models are driven by changes in the source flux scaled to variable rates of ocean floor production, but ocean floor production may not be distinguishable from being steady since 180 Ma. We evaluate potential changes in sources and sinks of CO2 for the past 120 Ma in a paleogeographic context. Our new calculations show that decarbonation of pelagic sediments by Tethyan subduction contributed only modestly to generally high pCO2 levels from the Late Cretaceous until the early Eocene, and thus shutdown of this CO2 source with the collision of India and Asia at the early Eocene climate optimum at around 50 Ma was inadequate to account for the large and prolonged decrease in pCO2 that eventually allowed the growth of significant Antarctic ice sheets by around 34 Ma. Instead, variation in area of continental basalt terranes in the equatorial humid belt (5° S–5° N) seems to be a dominant factor controlling how much CO2 is retained in the atmosphere via the silicate weathering feedback. The arrival of the highly weatherable Deccan Traps in the equatorial humid belt at around 50 Ma was decisive in initiating the long-term slide to lower atmospheric pCO2, which was pushed further down by the emplacement of the 30 Ma Ethiopian Traps near the equator and the southerly tectonic extrusion of SE Asia, an arc terrane that presently is estimated to account for 1/4 of CO2 consumption from all basaltic provinces that account for ~1/3 of the total CO2 consumption by continental silicate weathering (Dessert et al., 2003). A negative climate-feedback mechanism that (usually) inhibits the complete collapse of atmospheric pCO2 is the accelerating formation of thick cation-deficient soils that retard chemical weathering of the underlying bedrock. Nevertheless, equatorial climate seems to be relatively insensitive to pCO2 greenhouse forcing and thus with availability of some rejuvenating relief as in arc terranes or thick basaltic provinces, silicate weathering in this venue is not subject to a strong negative feedback, providing an avenue for ice ages. The safety valve that prevents excessive atmospheric pCO2 levels is the triggering of silicate weathering of continental areas and basaltic provinces in the temperate humid belt. Excess organic carbon burial seems to have played a negligible role in atmospheric pCO2 over the Late Cretaceous and Cenozoic
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