Dario Sciunnach

Onset of major Pleistocene glaciations in the Alps

During maximum Pleistocene glacial expansions, the Alpine ice cap invaded the Central Europe uplands and Italian Southalpine foothills. Periglacial basins, such as the Po River Basin, are natural collectors of sediments that record the past biological and climatic changes that involve the waxing and waning of major ice caps. In a 200-m-long core from the central Po Plain, stratigraphic evidence for one such major glacial pulse of the nearby Alpine ice cap is recorded by a sequence boundary, termed the R surface, associated with a drastic reorganization of vegetational, fluvial, and Alpine drainage patterns. 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. MIS 22 corresponds to the end of the Mid-Pleistocene Revolution, a marked reorganization of Northern Hemisphere glaciation pattern that took place in the late early Pleistocene. We suggest that the R surface formed at Mid-Pleistocene Revolution‐MIS 22 time, during the onset of the first major Pleistocene glaciation in the Alps.

Subsurface magnetostratigraphy of Pleistocene sediments from the Po Plain (Italy): Constraints on rates of sedimentation and rock uplift

We used facies analysis to reconstruct the Pleistocene sedimentary evolution of seven cores from the central-northern Po Plain, Italy. The cores record an overall regressive sequence consisting of shallow-water marine and fl uvial-deltaic deposits overlain by fully continental sediments. We used magnetostratigraphy to date marine and fl uvial-deltaic sediments to the early Pleistocene and continental sediments to the middle–late Pleistocene. Sediment accumulation rates were ~30–40 cm/k.y. in the early Pleistocene, whereas relevant unconformities and/or an overall reduction in sediment accumulation rates characterized the middle–late Pleistocene. A simple Airy compensation model was applied to restore actual sediments elevations to elevations at times of deposition expressed in meters above current sea level. The correlation of isostatically corrected sedimentary facies to a sea-level curve obtained from classic oxygen-isotope studies shows that an event of rock uplift on the order of ~70–120 m occurred in the middle–late Pleistocene. Literature studies of vegetational cyclicity, used in conjunction with the sea-level curve, allowed us to link sedimentary facies to climate variability. We propose that the onset of fully and persistently continental sedimentation occurred in response to the waxing of the fi rst major Pleistocene glaciation in the Alps, currently correlated to marine isotope stage 22 at ca. 0.87 Ma, and that the episode of uplift occurred (at least in part) as a consequence of erosion and crustal rebound of the Alpine chain triggered by Pleistocene glacialinterglacial cycles.

Early Carboniferous onset of Gondwanian glaciation and Neo-tethyan rifting in South Tibet

At least four diamictite-bearing intervals of Early Carboniferous age, containing faceted pebbles, trapezoidal cobbles and boulders up to 1000 m3 in volume, have been recognized and traced for over 200 km along the Tethys Himalayan Zone of South Tibet, from east of Everest to west of Shishapangma. These largely glacio-marine sediments, intercalated within the Rakyang Formation, which overlies lower Tournaisian limestones and underlies lower Bashkirian black shales, were deposited during the Visean to Serpukhovian. Shore ice thus began to form in this region of northern Gondwana several tens of million years earlier than previously thought. This glacial event occurred at middle southern latitudes and was triggered by basin inversion and tectonic uplift in the first stages of Neo-tethyan rifting, as documented by the close association of diamictites with olistoliths and olistostromes in Lower Carboniferous units. After a transgressive interglacial episode in the Bashkirian, a much more widespread glaciation occurred in the latest Carboniferous, and was shortly followed by continental break-up and opening of Neo-tethys in the late Early Permian.

Pennsylvanian-Early Triassic stratigraphy in the Alborz Mountains (Iran)

Abstract New fieldwork was carried out in the central and eastern Alborz, addressing the sedimentary succession from the Pennsylvanian to the Early Triassic. A regional synthesis is proposed, based on sedimentary analysis and a wide collection of new palaeontological data. The Moscovian Qezelqaleh Formation, deposited in a mixed coastal marine and alluvial setting, is present in a restricted area of the eastern Alborz, transgressing on the Lower Carboniferous Mobarak and Dozdehband formations. The late Gzhelian–early Sakmarian Dorud Group is instead distributed over most of the studied area, being absent only in a narrow belt to the SE. The Dorud Group is typically tripartite, with a terrigenous unit in the lower part (Toyeh Formation), a carbonate intermediate part (Emarat and Ghosnavi formations, the former particularly rich in fusulinids), and a terrigenous upper unit (Shah Zeid Formation), which however seems to be confined to the central Alborz. A major gap in sedimentation occurred before the deposition of the overlying Ruteh Limestone, a thick package of packstone–wackestone interpreted as a carbonate ramp of Middle Permian age (Wordian–Capitanian). The Ruteh Limestone is absent in the eastern part of the range, and everywhere ends with an emersion surface, that may be karstified or covered by a lateritic soil. The Late Permian transgression was directed southwards in the central Alborz, where marine facies (Nesen Formation) are more common. Time-equivalent alluvial fans with marsh intercalations and lateritic soils (Qeshlaq Formation) are present in the east. Towards the end of the Permian most of the Alborz emerged, the marine facies being restricted to a small area on the Caspian side of the central Alborz. There, the Permo-Triassic boundary interval is somewhat similar to the Abadeh–Shahreza belt in central Iran, and contains oolites, flat microbialites and domal stromatolites, forming the base of the Elikah Formation. The P–T boundary is established on the basis of conodonts, small foraminifera and stable isotope data. The development of the lower and middle part of the Elikah Formation, still Early Triassic in age, contains vermicular bioturbated mudstone/wackestone, and anachronostic-facies-like gastropod oolites and flat pebble conglomerates. Three major factors control the sedimentary evolution. The succession is in phase with global sea-level curve in the Moscovian and from the Middle Permian upwards. It is out of phase around the Carboniferous–Permian boundary, when the Dorud Group was deposited during a global lowstand of sealevel. When the global deglaciation started in the Sakmarian, sedimentation stopped in the Alborz and the area emerged. Therefore, there is a consistent geodynamic control. From the Middle Permian upwards, passive margin conditions control the sedimentary evolution of the basin, which had its depocentre(s) to the north. Climate also had a significant role, as the Alborz drifted quickly northwards with other central Iran blocks towards the Turan active margin. It passed from a southern latitude through the aridity belt in the Middle Permian, across the equatorial humid belt in the Late Permian and reached the northern arid tropical belt in the Triassic.

The Mid-Carboniferous to Lowermost Permian succession of Spiti (Po Group and Ganmachidam Formation; Tethys Himalaya, Northern India): Gondwana glaciation and rifting of Neo-Tethys.

AbstractThe upper Lower Carboniferous to lowermost Permian terrigenous succession of the Spiti Valley can be subdivided into five formations (Thabo Formation, Fenestella Shale, Kabjima Quartzarenite, Chichong Formation and Ganmachidam Diamictite), here described in detail and subdivided into members or lithozones.The Po Group, overlying the platform carbonates and gypsum deposits of the Lipak Formation, records an increase of subarkosic to quartzarenitic terrigenous detritus derived from uplift and erosion of continental blocks in the south during the initial stage of Neo-Tethyan rifting. Increasing mineralogic stability through the Thabo Formation broadly coincides with a climate change from tropical arid to temperate humid conditions during the Visean-Serpukhovian. The Fenestella Shale, containing rich brachiopod associations of Bashkirian age, documents a stage of widespread subsidence and transgression, followed by the regressive Kabjima Quartzarenite, which records recycling of quartzose sedimentary ...

Reconnaissance geology in Upper Chitral, Baroghil and Karambar districts (northern Karakorum, Pakistan)

During the summer of 1992 a geological expedition crossed the northern Karakorum range in northern Pakistan, from the Chitral to Karambar valleys, from the villages of Mastuj to Imit. Some of the areas visited were geologically unknown. A number of structural units were crossed, belonging to the Karakorum block or to other crustal blocks north of it. They are: (a) the axial batholith, in which three plutonic bodies have been identified, and (b) the northern sedimentary belt (NSB), in which three major tectonostratigraphic units form thrust stacks dipping to the north. Their internal stratigraphy and structural style are partly different. The most complete contains a crystalline basement, transgressed by a marine succession during the Early Ordovician. The youngest strata are represented by the Reshun conglomerate, of inferred Cretaceous age. The northernmost unit of the NSB is tightly folded, whereas the central one forms a monocline. Vertical faults, mainly strike-slip, dissect the thrusted slabs. Metamorphic deformation is absent or reaches only the anchizone in the studied sector of the Karakorum NSB. To the north of the Karakorum proper there are several other tectonic units, separated by vertical faults. They are, from south to north: (a) the Taš Kupruk zone, with metavolcanics of basaltic to latibasaltic composition; (b) the Atark unit, mostly consisting of massive carbonate rocks of Mesozoic age; and (c) the Wakhan slates which consist of a thick widespread succession of dark slates, metasiltites and sandstones. The fine-grained elastic rocks are supposed to be Palaeozoic to Early Triassic in age. The Wakhan slates are intruded by plutons belonging to the East Hindu Kush batholith, from which a single K/Ar age on muscovite gave a Jurassic age.

The Bashkirian “Fenestella Shales” and the Moscovian “Chaetetid Shales” of the Tethys Himalaya (South Tibet, Nepal and India)

Abstract The “Fenestella shales” are a mid-Carboniferous marker unit which has long been described from classic localities of the NW Himalaya (Kashmir, Spiti). Correlative shaly units have recently been traced in central Nepal and as far as South Tibet, where they yielded varied brachiopod assemblages indicative of Bashkirian age. A second distinct interval of black shales, characterized by the abundance of chaetetids and directly underlying the widespread Gondwanan diamictites, has been dated as Moscovian in Spiti and represents the youngest fossiliferous horizon hitherto identified in the Upper Carboniferous of the Tethys Himalaya. The “Chaetetid shales” are recognized also in Manang, whereas in South Tibet the stratigraphic framework still needs improved definition. These major fossiliferous black shale units, marking repeated transgressive events in the middle part of the Himalayan rift sequence, have not only major stratigraphic significance but also represent a fundamental landmark in palaeogeographic and palaeoclimatic reconstructions of Northern Gondwana. With the onset of continental rifting, arid tropical climates at the close of the Tournaisian were replaced by temperate humid conditions in the Visean-Serpukhovian, when diamictites were deposited in South Tibet. After this first cooling stage, the “Fenestella shales” mark a widespread transgression at the very beginning of the Late Carboniferous, coupled with reduced tectonic activity and temperate to temperate-warm climates. After renewed tectonic activity during a second cooling episode, marked by local deposition of diamictites in central Nepal, the “Chaetetid shales” represent another major transgression in the Moscovian, shortly preceding the final and most intense cooling event marked by deposition of glacio-marine diamictites in the whole Tethys Himalaya from Kashmir to South Tibet during the latest Carboniferous/earliest Permian. Two fossiliferous horizons containing very similar brachiopod faunas of early Late Carboniferous age have recently been found also in North Karakorum, at lower southern latitudes, where climatic conditions always remained temperate and there is no trace of Upper Palaeozoic glacial deposits or ice-rafted debris.

The Carboniferous of the Western Karakoram (Pakistan)

Abstract The results of the study of the Carboniferous successions in the western part of the Northern Karakoram during three geological expeditions are summarized here. Rocks of that period are not uniformly preserved in the several thrust sheets forming the Northern Karakoram. In most of them only the basal part of the Carboniferous, up to the Visean, is preserved, whilst in the Karambar thrust sheet a more complete section—previously almost unknown—is preserved. Four new lithostratigraphic units, time-constrained by brachiopod and conodont biostratigraphy, are described, from bottom to top: (1) the Margach Formation: prevailing dark shales with subordinate fine subarkoses and quartzarenites, up to 300 m thick (mid-Famennian to middle Tournaisian); (2) the Ribat Formation: grey crinoidal limestones passing upwards to dark marly limestones and marls, at least 300 m thick (middle Tournaisian to Serpukhovian); (3) the Lupsuk Formation: subarkoses to feldspathic quartzarenites in thick beds, alternating with dark shales and siltstones, up to 400 m thick (Serpukhovian to uppermost Carboniferous); (4) within the Lupsuk Formation a local member, the Twin Valleys Member, up to 100 m thick, a bioclastic limestone intercalation of post-Moscovian age, is distinguished. The Carboniferous successions are invariably sealed by the arkoses to quartzarenites of the Gircha Formation, 133 m above the base of which, in the Karambar area, an Asselian brachiopod fauna was recovered. The Carboniferous succession is interpreted as recording the evolution of the passive margin of the Northern Karakoram Terrane, from early rifting stage in the Late Devonian to syn-rift events during the Late Carboniferous. The basal part of the Gircha Formation, of latest Carboniferous-earliest Permian age, is considered to have been deposited above a break-up unconformity, linked to the early drifting in the seaway bordering the Karakoram. In the palaeontological appendix the most significant brachiopod taxa (19 species, one new) are described.

Typology of detrital zircon as a key to unravelling provenance in rift siliciclastic sequences (Permo-Carboniferous of Spiti, N India)

AbstractDetrital zircon populations from Carboniferous to Permian sandstones from the Lozar Section of Spiti, northern India, were analyzed with the typology method in order to obtain complementary information on the source areas of the sediments. Zircon grains were subdivided into several groups and subgroups, according to degree of abrasion and morphological features.First appearance of detrital zircons with distinct typologic signature within successive stratigraphic intervals provided useful data about the tectono-magmatic evolution of the northern Indian margin during Late Paleozoic rifting of Gondwana and initial opening of Neotethys. The base of the studied sequence (Lower Carboniferous Thabo Fm.) is characterized by a largely cratonic provenance, seemingly from the Indian Shield to the South. In the Upper Carboniferous Chichong Fm., first occurrence of typical zircons from anatectic granites and increasing abundance of granitoid detritus suggest rapid uplift and unroofing of anatectic rocks of pro...

Sedimentary record of Late Paleozoic rift and break-up in Northern Gondwana: a case history from the Thini Chu Group and Tamba-Kurkur Formation (Dolpo Tethys Himalaya, Nepal)

AbstractQuantitative compositional data from selected sandstone samples in the Upper Paleozoic to lowermost Triassic succession of the central Dolpo Tethys Himalaya (Thini Chu Group and base of the Tamba-Kurkur Formation) are relevant to understand the tectonic and climatic evolution of the northern margin of Gondwana from continental rift to break-up and spreading in the Neotethys Ocean.In central Dolpo, where the Upper Permian is thicker than in other sections of the Northern India and Nepal Tethys Himalaya, and sandstones occur both just below and above the Permian/Triassic boundary, the Thini Chu Group rests discon- formably over Lower Carboniferous carbonates. A terra rossa paleosoil documents a major hiatus that possibly spans the Visean to Early Bashkirian (“rift unconformity”). Another major unconformity overlain by the Murgabian-Midian? “Costiferina arenites” is interpreted as indicating final break-up and initial spreading in Neotethys (“break-up unconformity”). In fact, arenite lenses mantling ...