Lucia Angiolini

Tethyan oceanic currents and climate gradients 300 m.y. ago

We reconstruct the oceanic circulation pattern of the Tethys Ocean 300 m.y. ago by placing Late Carboniferous–Early Permian climate-sensitive biotic associations from Gondwana and Laurasia on a Pangea paleogeography constrained by selected paleomagnetic data. Warm-climate fossils and facies from Iran, located at that time along the Gondwanan margin of Arabia, are compatible with the existence in the Tethys Ocean of a warm subtropical surface current gyre, whereas cold surface currents swept the glaciated Gondwanan margin at higher southern latitudes, redistributing cold biota toward the tropics. This Tethyan surface current system and the associated narrow zonal barrier show similarities to recent glacial climate patterns. When placed on a large-scale paleogeographic reconstruction of Pangea of the B type, it neatly explains the otherwise problematic observation that the Carboniferous–Permian biota of Iran and northern Arabia is dominated by warm Euramerican and/or Russian taxa that are strikingly different from typical cold Gondwanan associations.

Gondwanan deglaciation and opening of Neotethys: the Al Khlata and Saiwan Formations of Interior Oman

Abstract New stratigraphic, petrographic and paleontological data from the Lower Permian of southeastern Arabia help to elucidate the still debated timing of Neotethys rifting and the climatic evolution following the Gondwanan glaciation. The transition from the Al Khlata to the Saiwan Formation, here described in detail, is interpreted to record continental break-up and onset of Neotethyan spreading between northern Gondwana and the Cimmerian terranes at mid-Sakmarian times, as constrained by brachiopod assemblages. The eastern Oman arm of the Neotethyan rift-system instead failed, and sea-floor spreading of the Indo–Madagascar trough was delayed until final fragmentation of Gondwana in the Late Jurassic. Petrographic composition of Lower Permian sandstones documents a distinct change from transitional to dissected rift-shoulder provenance, and widespread exposure of granitoid basement rocks at a late syn-rift to early post-rift stage. Very abundant pore-filling celestite at the Al Khlata/Saiwan transition may have precipitated from circulating brines related to remobilization of Proterozoic salt due to rift tectonics. The sharp base of the Saiwan Formation records a major transgression related to the onset of Neotethyan spreading, final deglaciation and consequent global sea-level rise, as indicated by ravinement surfaces associated with lag deposits with tree trunks, reworked ferruginous pedogenic concretions and phosphate, and by paleoecological analyses. The basal bed of the Saiwan Formation is characterized by the pioneer Pachycyrtella paleocommunity, with Pachycyrtella omanensis>85%), suspension feeding, rapid rates of reproduction and growth (r-strategy), early maturity, high mortality rates in the juveniles. The more mature secondary ecological succession developed higher in the Saiwan Formation records maximum flooding and significant climatic amelioration. The Saiwan Formation, at the beginning of the Late Sakmarian, finally sutures the irregular rift-related topography in the rim basin of Interior Oman, and records a shift towards warmer temperate conditions after the end of the Gondwanan glaciation.

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.

Permian climatic and paleogeographic changes in Northern Gondwana: the Khuff Formation of Interior Oman

Abstract Detailed stratigraphic, paleontologic, and petrographic data from the Middle Permian Khuff Formation exposed in the Haushi–Huqf area of Interior Oman provide new insight into the Permian climatic evolution of the northern Gondwana margin, and on the still debated timing of Neotethys opening between Gondwana and the Cimmerian blocks. The Khuff Formation is interpreted to record a major transgression of Neotethyan waters in Wordian times (Middle Permian), at a stage of full oceanization and tectonic quiescence, when thermal subsidence caused final drowning of rift shoulders and deposition of marine carbonates onto vast portions of stable Arabia. The petrographic composition of Middle Permian sandstones indicates a post-rift stage, and documents a long-term increase in mineralogic stability ascribed to a shift toward warm–humid climatic conditions, coupled with reduced relief and longer transit times of detritus from source to basin. Raising temperatures and northward latitudinal drift towards lower tropic latitudes throughout the Permian are fully documented by rich transitional marine faunas and available paleomagnetic evidence.

How cold were the Early Permian glacial tropics? Testing sea-surface temperature using the oxygen isotope composition of rigorously screened brachiopod shells

Abstract: Brachiopod carbonate from Early Permian brachiopod shells from low palaeolatitude north Iran and higher palaeolatitude Pakistan Karakorum were screened for diagenesis and analysed for oxygen isotope ratios to derive seawater palaeotemperatures. Screening techniques employed included SEM ultrastructural analysis, cathodoluminescence (CL), image analysis of CL images, trace-element (Sr, Mn, Fe) determinations, and carbon and oxygen stable-isotope determinations. The Karakorum shells were found to be diagenetically altered, but those from north Iran were judged to be pristine. Using data from pristine material, two distinct time slices were analysed: the early and middle Asselian. Two contrasting δ18O values for seawater (0‰ and +1.0‰ V-SMOW) were used to account for different extensions of the Gondwanan ice caps. The δ18O data from north Iran indicate a range of seawater temperatures from +24.3 to +30.3 °C (for δ18Oseawater = 0‰ V-SMOW) or from +30.3 to +35.4 °C (for δ18Oseawater = +1.0‰ V-SMOW) for the early Asselian. Results for δ18O from the middle Asselian indicate seawater temperatures of +24.4 to +28.0 °C (for δ18Oseawater = 0‰) or +29.2 to +32.8 °C (for δ18Oseawater = +1.0‰). The maximum calculated temperatures in the middle Asselian are about 2 °C lower than those for the early Asselian. The average temperature for both time slices is similar to modern tropical sea-surface temperatures, indicating that low-latitude Early Permian ocean waters in Iran did not undergo significant cooling during the final Glacial III episode of Gondwanan glaciation. This confirms other evidence based on biotic provinces, which suggests that during the Permo-Carboniferous glaciation, the low-latitude warm belt became narrower and confined to the western Tethys and Cathaysian provinces, and was not subject to a reduction in temperature, but rather a reduction in size.

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 ...

Palaeocopida (Ostracoda) across the Permian–Triassic events: new data from southwestern Taurus (Turkey)

The Palaeocopida have been considered as an entirely Palaeozoic group and their disappearance as a marker for the Palaeozoic–Mesozoic boundary. Despite this, 11 Palaeocopida species have been recorded in the Early Triassic. New data obtained in southwestern Taurus at the Permian– Triassic section of Çürük daǧ, permit an assessment of this problem. This paper synthesizes the data on lowermost Triassic ostracodes and revises the youngest Palaecopida occurrences. A new Early Triassic Palaeocopida species is described (Reviya curukensis n. sp.).

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.

Taxonomy and quantitativebiochronology of Guadalupian brachiopods from the Khuff Formation, Southeastern Oman

Abstract The Guadalupian Khuff Formation of the Huqf area (Sultanate of Oman) is composed of marine marls and bioclastic limestones which yield a rich brachiopod fauna associated with conodonts, foraminifers, ostracods, bivalves, gastropods, and cephalopods. The brachiopod fauna of the Khuff Fm. includes Perigeyerella raffaellae nov. sp., Derbyia sp. cf. D. diversa Reed , 1944 , Neochonetes (Sommeriella) arabicus ( Hudson & Sudbury , 1959) , Celebetes manarollai nov. sp., Haydenella sp., Chonetellini ? gen. and sp. indet., Dyschrestia rugosa nov. sp., Kozlowskia tescorum ( Hudson & Sudbury , 1959) , Calliprotonia sp., Juresania omanensis Hudson & Sudbury , 1959, Bilotina yanagidai nov. sp., Linoproductus sp. aff. L. kaseti Grant , 1976, Grandaurispina ghabaensis nov. sp., Magniplicatina sp., Cyclacantharia sp., Acritosia sp., Orthotichia sp. cf. O. bistriata Reed , 1944, Cleiothyridina sp. cf. C. seriata Grant , 1976, Pennospiriferinoidea genus and species undetermined, Dielasma sp. A, Dielasma sp. B, Dielasma sp. C, D. sp. aff. D. minor Waagen , 1882 and Hemiptychina sp. This fauna shows strong affinities with that of the Amb Fm. (Salt Range, Pakistan) and that of the Rat Buri Limenstone of southern Thailand. Analysis of the brachiopod data of the Khuff Fm by means of the Unitary Association method (Guex 1991) leads to the construction of a local biochronological sequence of eight faunal associations. Strictly based on a bed rock-controlled sampling, this result provides a firm basis and a first step for future correlations with other Guadalupian brachiopod sequences. It also suggests that species diversity and rates of faunal turnovers are only partly controlled by the vertical succession of depositional environments, which reflects an intra-Khuff asymmetric transgressive-regressive cycle. A full evaluation of the biochronologic component of the Guadalupian brachiopod faunas still requires further tests against other similarly well-documented sequences.

Lower and Middle Triassic foraminifera from the Eros Limestone, Hydra Island, Greece

The systematics and stratigraphic ranges (constrained by conodont dating) of abundant and well preserved foraminiferal faunas from six sections in the Lower and Middle Triassic Eros Limestone of central and western Hydra (Argolis Peninsula, Greece) are described. A joint analysis of the conodonts, foraminifera and bivalves has enabled the Scythian and Anisian stages to be recognized with some certainty within the Eros Limestone carbonate platform. The foraminifera have affinities with those of many other Tethyan localities, in particular the Dinarides, Balkans, Carpathians and the Southern Alps.