Geologisch-tektonische auswertung von ERTS-1 und SKYLAB-aufnahmen von nord-und mittelitalien

Multispectral satellite imagery, in conjunction with aerial photography and field work, offers new possibilities for the recognition and interpretation of overregional geological and tectonic systems. All three methods in geologic work were applied to Northern and Central Italy. In the Northern and Central Apennines two stress directions were recognized. The various stages in the evolution of the mountains and of the whole peninsula were evaluated and interpreted under new aspects. The tectonic features are explained by a clockwise rotation of various blocks along left-handed transform faults. These faults can be interpreted as resulting from shear due to a main stress directed north-eastwards. The lineations of the Southern Alps are traced through the Po Valley into the Northern Apennines.

Zusammenfassung

Multispectral satellite imagery, in conjunction with aerial photography and field work, offers new possibilities for the recognition and interpretation of overregional geological and tectonic systems. All three methods in geologic work were applied to Northern and Central Italy. In the Northern and Central Apennines two stress directions were recognized. The various stages in the evolution of the mountains and of the whole peninsula were evaluated and interpreted under new aspects. The tectonic features are explained by a clockwise rotation of various blocks along left-handed transform faults. These faults can be interpreted as resulting from shear due to a main stress directed north-eastwards. The lineations of the Southern Alps are traced through the Po Valley into the Northern Apennines.     

Paleomagnetic evidence for large en-bloc rotations in the Eastern Alps during Neogene orogeny

We present new paleomagnetic data from the Northern Calcareous Alps and the Central Alps of Austria. All new data are overprint magnetizations and can be subdivided into two groups: In rocks older than earliest Rupelian, two remagnetizations reflecting both clockwise and counter-clockwise rotation were detected. In rocks of late Rupelian and younger ages, only a counter-clockwise rotated remagnetization was found. Our results together with results from previous paleomagnetic studies from the Eastern and Southern Alps suggest two main phases of vertical axis rotation. The first, clockwise rotation affecting the Northern Calcareous Alps was active between earliest to Late Rupelian. We propose a model where the Northern Calcareous Alps are segmented into individual blocks. Within a dextral shear corridor these blocks rotated clockwise due to the counter-clockwise rotation of the Southern Alps and Central Alps. The second, counter-clockwise rotation occurred in the Late Oligocene to Middle Miocene, affecting Eastern and Southern Alps. In this stage of orogeny, the internal massifs of the Western Alps were already accreted to the upper plate and therefore included in counter-clockwise rotation. This rotation is contemporaneous with counter-clockwise rotation in the Apennines and opening of the Balearic basin, and a genetic relationship is suggested. A second step of counter-clockwise rotation, reconstructed from published data, is observed in the sedimentary basins at the southeastern margin of the Eastern Alps, where counter-clockwise rotated Miocene and Pliocene sedimentary rocks are present. This rotation is seen in connection to a young counter-clockwise rotation of the Adriatic plate.     

Organic matter characterisation of the Selli Level (Umbria-Marche Basin, central Italy)

The Selli Level is a marker-bed in the Umbria-Marche Apennines that represents the regional sedimentary expression of the Lower Aptain Oceanic Anoxic Event 1a. This one to three-metre-thick interval shows a remarkable uniformity on a regional scale, with a green to grey marly lower part overlain by black shales. Bulk geochemical studies and an examination of palynofacies were carried out on three sections in order to characterise the distribution and nature of the organic matter in the Selli Level which has been poorly known hitherto. The organic content is medium (0.5 to 2.9% TOC) in the basal part and higher (4.5% on average, and up to 18% TOC) in the black shales. Pyrolysis and palynological data indicate that the organic matter is mainly of marine origin. The geochemical characteristics of the Selli Level are compared to other, more or less organic-rich marker-beds in the Cretaceous succession of the Umbria-Marche Apennines.

Abstract

Le Niveau Selli est un niveau-repère des Apennins d'Ombrie-Marches qui correspond à l'enregistrement régional de l'événement anoxique océanique 1a. Ce niveau, épais de un à trois mètres, présente une remarquable uniformité à l'échelle régionale avec une partie inférieure argileuse, verdâtre à grise, surmontée par des black shales. Des analyses géochimiques et l'examen des palynofacies ont été entreprises sur trois coupes afin de caractériser le contenu en matière organique du niveau Selli, jusqu'à présent mal connu. Les teneurs en carbone organique sont moyennes (0,5 à 2,9% COT) dans la partie basale et élevées (4,5% en moyenne et jusque 18% COT) dans les black shales. Les résultats de pyrolyse et des observations palynologiques indiquent que la matière organique est essentiellement d'origine marine. Les caractéristiques géochimiques du niveau Selli sont comparées aux autres niveaux repères, plus ou moins riches en carbone organique, qui émaillent la série du Crétacé du basin d'Ombrie-Marches.     

Albian oceanic anoxic events in northern Tunisia: Biostratigraphic and geochemical insights

Albian pelagic successions of the Nebeur area in northwestern Tunisia consist of radiolarian-bearing and organic-rich black shale beds, which represent the lower part of the Fahdene Formation. The carbonate content of the organic-rich beds ranges between 40 and 48%. Total organic carbon (TOC) analyses via Rock Eval pyrolysis yielded values ranging between 0.7 and 2.8% and a mixed marine/terrestrial origin. T_max values vary between 424 and 450 °C, indicative of submature to mature organic matter. High resolution planktic foraminiferal and radiolarian biostratigraphy suggest that the black shales beds span the mid- to late Albian, confined to the middle part of the Ticinella primula zone, upper Biticinella breggiensis zone and lower appeninica + buxtorfi zone. Episodes of organic-rich deposition in the “Tunisian Trough” are interpreted as being the sedimentary record of the global oceanic anoxic events OAE1b, c, and d respectively. Age-diagnostic radiolarian assemblages recovered from late Albian organic-rich black shales lie within the UA13–UA14 boundary biochronozones. The abundance of radiolarian and calcispheres (i.e. pithonella) within the black shales suggests high productivity periods and eutrophic conditions probably triggered by upwelling currents.     

Exceptionally favourable life conditions for macrobenthos during the Late Cenomanian OAE-2 event: Ichnological record from the Bonarelli Level in the Grajcarek Unit,Polish Carpathians

Pelagic and hemipelagic sediments of the Bonarelli Level (uppermost Cenomanian) in the Sztolnia section (Grajcarek Unit, Polish Carpathians) contain trace fossils of the Zoophycos ichnofacies, including (in descending order of abundance): Chondrites (smaller and larger forms), Planolites, Thalassinoides, Palaeophycus, Taenidium, Teichichnus, and Zoophycos. They occur in thick bioturbated layers, which are interbedded with rare, thin layers of unbioturbated black shales. The black shale layers mark the Bonarelli Level and are interpreted as a record of anoxia or dysoxia. Coeval sections in the Western Tethys contain similar trace fossils but they are less abundant and these sections are characterized by thicker unbioturbated black shale layers and thinner bioturbated layers. This confirms the exceptionally favourable life conditions in sediments of the Sztolnia section, which do not record strong global anoxia during the OAE-2 event. Such favourable conditions were probably caused by effective oxygenation of pore waters and deep burial of organic matter, which are a consequence of high rates of accumulation and the palaeogeographical location of the section on a flank of a submarine high, under strong circulation.     

Reflection and refraction seismics in areas of complex geology. An example in the Northern Apennines

An experimental survey, employing refraction wide-angle reflection seismic techniques (DSS: deep seismic soundings) was carried out in the Northern Apennines (North Italy). The main objective of the experiment was the application of DSS to better-define the structure of the upper crust, down to about 15 km depth, in the crucial Alps–Apennines boundary zone. A second objective was to understand the potential of DSS as a complementary tool in areas of complex geology, where the results of near vertical reflection (NVR) are generally poor. The results of the experiment show that DSS, if properly planned, can continuously follow deep markers, and therefore impart a greater significance to faint and discontinuous NVR, as well as data on the P– wave velocity of the seismic units.     

Albian oceanic anoxic events in northern Tunisia: Biostratigraphic and geochemical insights

Albian pelagic successions of the Nebeur area in northwestern Tunisia consist of radiolarian-bearing and organic-rich black shale beds, which represent the lower part of the Fahdene Formation. The carbonate content of the organic-rich beds ranges between 40 and 48%. Total organic carbon (TOC) analyses via Rock Eval pyrolysis yielded values ranging between 0.7 and 2.8% and a mixed marine/terrestrial origin. T_max values vary between 424 and 450 °C, indicative of submature to mature organic matter. High resolution planktic foraminiferal and radiolarian biostratigraphy suggest that the black shales beds span the mid- to late Albian, confined to the middle part of the Ticinella primula zone, upper Biticinella breggiensis zone and lower appeninica + buxtorfi zone. Episodes of organic-rich deposition in the “Tunisian Trough” are interpreted as being the sedimentary record of the global oceanic anoxic events OAE1b, c, and d respectively. Age-diagnostic radiolarian assemblages recovered from late Albian organic-rich black shales lie within the UA13–UA14 boundary biochronozones. The abundance of radiolarian and calcispheres (i.e. pithonella) within the black shales suggests high productivity periods and eutrophic conditions probably triggered by upwelling currents.     

Contribution of the SISCam Web-based GIS to the seismotectonic study of Campania (Southern Apennines): an example of application to the Sannio-area

In this article the implementation and potential of the Seismotectonic Information System of the Campania Region (SISCam) are described, in particular an application of this Web-based GIS system to the seismotectonic analysis of the Sannio area (Southern Apennines) is performed. WEB-GIS technologies greatly contribute to both the environmental monitoring and the disaster management of areas affected by high natural risks. Specifically the SISCam system has been developed with the aim of providing easy access and fast diffusion, through Internet technology, of the most significant geological, geophysical, and territorial data relative to the Campania Region. The Sannio area has been selected as our application example because it is among the most active seismic regions in Italy. This portion of the Southern Apennines which was hit by the June 5, 1688 strong earthquake (M _W = 6.7, CPTI 1999) and by some low- and moderate-energy seismic sequences (1990–1992, 1997), is characterized by a complex inherited tectonic setting and low-tectonic deformation rates that hide the seismogenic sources position. Since this case study turned out to be complicated, the use of the SIScam WEB-GIS has become indispensable because it allowed us to visualize, integrate and analyze all the data available, in order to obtain an accurate and direct picture of the seismotectonic setting of the area. Moreover, a different approach of data analysis was necessary, due to the lack of up-to-date neotectonic and structural data; therefore, the operation of this GIS system enabled us to process and generate some original informative layers, through image analysis, such as new structural lineaments represented on a map of the potential active faults of the area, which has been the final result of our application, as a contribution to new knowledge about the local seismic risk parameters.     

Paleomagnetic evidence for non-apenninic origin of the sila nappes (Calabria)

The magnetization of Lower Permian rocks from Sila has a mean direction D = 56.5°, I= +20.4° with ₉₅ = 9.1° after correction for Upper Neogene tilting. A further correction for the attitude of the nappes after their Middle Miocene emplacement establishes paleolatitudes consistent with those from the Lower Permian Tethys. The remarkable internal consistency of the data has not supported the distinction of units with opposite vergences within the Sila crystalline nappes. The declination indicates that the Sila massif has rotated counter-clockwise by about 90° relative to the Apennines, Sardinia and the Southern Alps and therefore the well-known Apenninic rotation alone does not account for the total change of direction in tectonic transport. Accordingly, the structural trends of tectonic phases older than the emplacement time of the Calabrian nappes should no longer be referred to present-day geographic coordinates. The post-Late Cretaceous motion relative to the north Calabrian Apennines enhances the geotectonic role of the northern boundary of the Calabrian—Peloritan arc, since its sinistral-shear character permits both tectonic transport from the west and counter-clockwise motion during tectonic transport.     

A comparison of radiolarian and foraminiferal paleoecology in the Southern Indian Ocean: New evidence for the interhemispheric timing of climatic change

The deglacial transition between oxygen-isotope Stages 6 and 5e (about 127,000 yr B.P.) is marked by both oxygen isotopic depletion and estimated sea-surface temperature (SST) increase in two subantarctic Indian Ocean cores. The data show synchroneity between warming of foraminifera-based SST estimates and depletion of δ¹⁸O, but an earlier warming trend on the basis of radiolarian SST estimates. These data have been previously interpreted to indicate that the high-latitude Southern Ocean warms prior to significant melting of glacial-age ice sheets. Comparison of core-top assemblages with surface and subsurface conditions in the Southern Indian Ocean reveals that (1) a three-part foraminiferal zonation reflects the surface hydrographic regime, with abrupt faunal transitions at two major fronts: the Subtropical Convergence (STC) and the Antarctic Polar Front (APF); and (2) a two-part radiolarian zonation coincides with a two-part subsurface hydrographic regime, with an abrupt faunal transition corresponding to the southern terminus of subtropical lower water (STLW) between the STC and the APF. It is suggested that shifts of these surface and subsurface regimes are recorded by these foraminiferal and radiolarian assemblages. In this interpretation, the observed lead of radiolarian SST with respect to δ¹⁸O indicates an early response to a southward shift of STLW, while the later foraminiferal SST warming indicates a southward shift of the STC. Thus, the origin of the Southern Hemisphere SST lead may be related to STLW, which emanates from the subtropical gyres, rather than the polar regions.     

Carbon-isotope records of the Early Jurassic (Toarcian) oceanic anoxic event from the Valdorbia (Umbria–Marche Apennines) and Monte Mangart (Julian Alps) sections: palaeoceanographic and stratigraphic implications

The Toarcian oceanic anoxic event ( ca 183 Ma) coincides with a global perturbation marked by enhanced organic carbon burial and a general decrease in calcium carbonate production, probably triggered by changes in the composition of marine plankton and elevated carbon dioxide levels in the atmosphere. This study is based on high-resolution sampling of two stratigraphic successions, located in Valdorbia (Umbria–Marche Apennines) and Monte Mangart (Julian Alps), Italy, which represent expressions of the Toarcian oceanic anoxic event in deep-water pelagic sediments. These successions are characterized by the occurrence of black shales showing relatively low total organic carbon concentrations (compared with coeval strata in Northern Europe), generally < 2%, and low hydrogen indices. On this basis, they are similar to other Toarcian black shales described from the Tethyan region. The positive and negative carbon-isotope records from the two localities permit a high-resolution correlation such that ammonite biostratigraphy information from Valdorbia can be transferred to those parts of the Monte Mangart section that lack these fossils. Spectral analyses of δ¹³C_org values and of CaCO₃ percentages from the sedimentary records of both the Valdorbia and Monte Mangart sections reveal a strong cyclic pattern, best interpreted as an eccentricity signal which hence implies a duration of ca 500 kyr for the negative carbon-isotope excursion. Based on the carbon-isotope curves obtained, the high-resolution correlation between the Italian successions and a section in Yorkshire (Northern Europe) confirms the supposition that the apparent mismatch between the dating of the Toarcian oceanic anoxic event in the Boreal and Tethyan realms is an artefact of biostratigraphy.     

“大洋板块地层”的重建与意义——以藏南仲巴地区为例

混杂岩是古增生楔存在的标志之一,一般由枕状玄武岩、灰岩、放射虫硅质岩、硅质页岩、砂岩等混乱无序组成。目前"大洋板块地层"(OPS)运用放射虫地层学方法对混乱的增生楔断片进行重建取得了良好效果,并清晰地展示了大洋板块俯冲和洋底物质连续增生的历史。在西藏仲巴地区填图过程中,结合放射虫年代学分析鉴定结果,以OPS重建的思路和理论作为指导,重建了仲巴地区混杂岩的大洋板块地层,并恢复了该区域特提斯洋在洋中脊大洋板块增生至消亡的岩石序列,自下而上分别为侏罗纪海山玄武岩、海山覆盖物侏罗系—白垩系碳酸盐岩、海山周围沉积的侏罗系—白垩系放射虫硅质岩和硅质页岩,以及海沟附近的白垩系陆源碎屑岩等,为特提斯洋大洋板块俯冲的方向、持续时间和古大地构造环境提供了信息。     

Early Eocene Radiolarian Fauna from the Sangdanlin, Southern Tibet: Constraints on the Timing of Initial India-Asia Collision

This is a new report on the early Eocene radiolarian fauna from the Sangdanlin section in the Gyirong region, along the southern margin of the Yarlung Zangbo Suture Zone. The Sangdanlin section measured in this study is divided into three lithostratigraphic units from bottom to top: the Zongzhuo, Sangdanlin, and Zheya formations. Abundant radiolarian fossils were obtained from the Sangdanlin section and 54 species of 30 genera were identified and assigned as follows: Cryptamphorella conara-C. macropora the late Cretaceous Zone and Amphisphaera coronate, Buryella tetradica-Bekoma campechensis, and B.bidartensis-B. divaricata the Paleocene-early Eocene Interval Zones. The Paleocene–early Eocene radiolarian zones are comparable to the radiolarian zones RP4-RP8 in New Zealand. Based on the data of radiolaria and lithofacies, it is suggested that the Zongzhuo Formation should be deposited along the base of the north-facing, continental slope of the Greater Indian continental margin, and the Sangdanlin Formation should be a deep marine, sedimentary sequence located in a foreland basin. The early Eocene radiolarian fauna in the Sangdanlin Formation constrains the initial age of the India-Asia collision to no later than 53.6 Ma.     

Bio- and chronostratigraphy of the Middle Triassic Reifling Formation of the westernmost Northern Calcareous Alps

New finds of fossils including bivalves, ammonoids, brachiopods and palynomorphs from the Middle Triassic Reifling Formation significantly improve the age assignment for this unit in Liechtenstein and Vorarlberg. The lower part of the Reifling Formation is tentatively referred to the Late Anisian Paraceratites trinodosus Zone and somewhat older levels, whereas the uppermost part reaches the Ladinian Protrachyceras archelaus Zone (ammonoid zonation). The Middle Triassic successions of the study area are correlated with the coeval South Alpine reference section at Bagolino (Brescian Prealps), which also bears the Ladinian GSSP. The comparison shows that the Reifling Formation in the study area is age-equivalent with the South Alpine Prezzo Limestone and the Buchenstein Formation. A volcanoclastic layer in the upper part of the Reifling Formation at Flexenpass yields a U-Pb zircon age of 239.3 +/- 0.2 Ma. This value is slightly older than previously published minimum ages from equivalent horizons in the Southern Alps; the difference is thought to be mainly due to improved pre-treatment of zircons (annealing/chemical abrasion), which significantly reduces the effects of Pb loss. The new radio-isotope age further constrains the stratigraphical age of the Reifling Formation and supports the proposed biostratigraphy-based correlation of Middle Triassic successions in the Eastern and Southern Alps. Editorial handling: E. Erba & J.-P. Billon-Bruyat     

The lithosphere－asthenosphere： Italy and surroundings

The velocity-depth distribution of the lithosphere-asthenosphere in the Italian region and surroundings is imaged, with a lateral resolution of about 100 km, by sur-face wave velocity tomography and non-linear inversion.Maps of the Moho depth, of the thickness of the lithos-phere and of the shear-wave velocities, down to depths of 200 km and more, are constructed. A mantle wedge, iden-tified in the uppermost mantle along the Apennines and the Calabrian Arc, underlies the prmctpat recent votca-noes, and partial melting can be relevant in this part of the uppermost mantle. In Calabria, a lithospheric dou-bling is seen, in connection with the subduction of the Ionian lithosphere. The asthenosphere is shallow in the Southern Tyrrhenian Sea. High velocity bodies, cutting the asthenosphere, outline the Adria-lonian subduction in the Tyrrhenian Sea and the deep-reaching lithospheric root in the Western Alps. Less deep lithospheric roots are seen in the Central Apennines. The lithosphere-asthenos-phere properties delineate a differentiation between the northern and the southern sectors of the Adriatic Sea,likely attesting the fragmentation of Adria.     

Seismotectonics of strike–slip earthquakes within the deep crust of southern Italy: Geometry, kinematics, stress field and crustal rheology of the Potenza 1990–1991 seismic sequences (Mmax 5.7)

We present a revision and a seismotectonic interpretation of deep crust strike–slip earthquake sequences that occurred in 1990–1991 in the Southern Apennines (Potenza area). The revision is motivated by: i) the striking similarity to a seismic sequence that occurred in 2002  140 km NNW, in an analogous tectonic context (Molise area), suggesting a common seismotectonic environment of regional importance; ii) the close proximity of such deep strike–slip seismicity with shallow extensional seismicity (Apennine area); and iii) the lack of knowledge about the mechanical properties of the crust that might justify the observed crustal seismicity. A comparison between the revised 1990–1991 earthquakes and the 2002 earthquakes, as well as the integration of seismological data with a rheological analysis offer new constraints on the regional seismotectonic context of crustal seismicity in the Southern Apennines. The seismological revision consists of a relocation of the aftershock sequences based on newly constrained velocity models. New focal mechanisms of the aftershocks are computed and the active state of stress is constrained via the use of a stress inversion technique. The relationships among the observed seismicity, the crustal structure of the Southern Apennines, and the rheological layering are analysed along a crustal section crossing southern Italy, by computing geotherms and two-mechanism (brittle frictional vs. ductile plastic strength) rheological profiles. The 1990–1991 seismicity is concentrated in a well-defined depth range (mostly between 15 and 23 km depths). This depth range corresponds to the upper pat of the middle crust underlying the Apulian sedimentary cover, in the footwall of the easternmost Apennine thrust system. The 3D distribution of the aftershocks, the fault kinematics, and the stress inversion indicate the activation of a right-lateral strike–slip fault striking N100°E under a stress field characterized by a sub-horizontal N142°-trending σ1 and a sub-horizontal N232°-trending σ3, very similar to the known stress field of the Gargano seismic zone in the Apulian foreland. The apparent anomalous depths of the earthquakes (> 15 km) and the confinement within a relatively narrow depth range are explained by the crustal rheology, which consists of a strong brittle layer at mid crustal depths sandwiched between two plastic horizons. This articulated rheological stratification is typical of the central part of the Southern Apennine crust, where the Apulian crust is overthrusted by Apennine units. Both the Potenza 1990–1991 and the Molise 2002 seismic sequences can be interpreted to be due to crustal E–W fault zones within the Apulian crust inherited from previous tectonic phases and overthrusted by Apennine units during the Late Pliocene–Middle Pleistocene. The present strike–slip tectonic regime reactivated these fault zones and caused them to move with an uneven mechanical behaviour; brittle seismogenic faulting is confined to the strong brittle part of the middle crust. This strong brittle layer might also act as a stress guide able to laterally transmit the deviatoric stresses responsible for the strike–slip regime in the Apulian crust and may explain the close proximity (nearly overlapping) of the strike–slip and normal faulting regimes in the Southern Apennines. From a methodological point of view, it seems that rather simple two-mechanism rheological profiles, though affected by uncertainties, are still a useful tool for estimating the rheological properties and likely seismogenic behaviour of the crust.     

Cosmogenic <Superscript>10</Superscript>Be-derived denudation rates of the Eastern and Southern European Alps

Denudation rates from cosmogenic ¹⁰Be measured in quartz from recent river sediment have previously been used in the Central Alps to argue that rock uplift occurs through isostatic response to erosion in the absence of ongoing convergence. We present new basin-averaged denudation rates from large rivers in the Eastern and Southern European Alps together with a detailed topographic analysis in order to infer the forces driving erosion. Denudation rates in the Eastern and Southern Alps of 170–1,400 mm ky⁻¹ are within a similar range to those in the Central Alps for similar lithologies. However, these denudation rates vary considerably with lithology, and their variability generally increases with steeper landscapes, where correlations with topographic metrics also become poorer. Tertiary igneous rocks are associated with steep hillslopes and channels and low denudation rates, whereas pre-Alpine gneisses usually exhibit steep hillslopes and higher denudation rates. Molasse, flysch, and schists display lower mean basin slopes and channel gradients, and, despite their high erodibility, low erosion rates. Exceptionally low denudation rates are also measured in Permian rhyolite, which has high mean basin slopes. We invoke geomorphic inheritance as a major factor controlling erosion, such that large erosive glaciers in the late Quaternary cold periods were more effective in priming landscapes in the Central Alps for erosion than in the interior Eastern Alps. However, the difference in tectonic evolution of the Eastern and Central Alps potentially adds to differences in their geomorphic response; their deep structures differ significantly and, unlike the Central Alps, the Eastern Alps are affected by ongoing tectonic influx due to the slow motion and rotation of Adria. The result is a complex pattern of high mountain erosion in the Eastern Alps, which has evolved from one confined to the narrow belt of the Tauern Window in late Tertiary time to one affecting the entire underthrust basement, orogenic lid, and parts of the Southern Alps today.     

Shear in the tethys and the Permian paleomagnetism in the Southern Alps, including new results

To verify paleomagnetic proof for megatectonic translation in the Tethys a large collection of samples from a key area, the Bolzano Quartz Porphyry Plateau in the Southern Alps, was examined. Their natural remanent magnetization was analyzed with thermal, and mainly alternating field demagnetization. The result is a well-established paleomagnetic direction of D: 150° and I: −19.5° (₉₅ = 4.9), obtained from 152 samples from 39 sites distributed over 12 volcanic units. It is argued that the inclination of this result is not significantly different from that which can be extrapolated for the Southern Alps from Early Permian paleomagnetic directions of the stable European shield. Consequently it is concluded that a paleomagnetic indication for megatectonic translation of the Southern Alps is virtually absent. But a large counterclockwise deviation of the declination is evident, and is easily explained by a counterclockwise rotation of 50° of the Southern Alps with respect to stable Europe. Since the paleomagnetic direction of the Early Permian volcanics of the Southern Alps fits in reasonably well with the (poorly known) Early Permian paleomagnetic pattern of Africa, a coherence between both regions is presumed.     

New concepts on the composition, structure, and age of the Lower Amur fragment of the Late Jurassic-Early Cretaceous accretionary prism, Russian Far East

On the basis of geological observations and the study of conodont and radiolarian microfauna, a new stratigraphic scheme was proposed for the Mesozoic deposits of the Komsomolsk district of the Amur region. The lower Khorpy Group (T₂-J₃) consists of two units: the Boktor (T₂-J₂) and Kholvasi (J_2–3). The Boktor Sequence (400 m thick) is represented by pelagic cherts with an admixture of cherty-clayey shales and volcanic rocks. The Kholvasi Sequence (500 m thick) is built up of the predominant siltstones and clayey shales with rare intercalations and lenses of clayey cherts and cherty-clayey shales. The upper Komsomolskaya Group (K₁) has a terrigenous composition and includes the Gorin, Pionerskaya, and Pivan formations of 5 km total thickness. It is made up of intercalated sandstones, siltstones, mudstones, and often turbidites (proximal to distal). The rocks contain abundant buchia fauna of Volgian-Valanginian age, as well as carbonized plant detritus and flora of the Early Cretaceous habit. The described complex is characterized by a nappe-fold structure typical of the accretionary prisms in the ocean-continent convergence zones. The predominance of the coherent type of accretionary prisms reflects the simple morphology of the oceanic plate.