Magnetostratigraphy of a Lower-Middle Triassic boundary section from Chios (Greece)

The Marmarotrapeza Formation at Chios Island (northern Aegean Sea, Greece) is renowned for its Lower-Middle Triassic boundary sections in a marine Tethyan setting. Two sections have been sampled bed by bed to develop a magnetostratigraphic framework for the ammonoid and conodont biostratigraphy. The boundary sections occur within a lower normal (A+)-reverse (B−)-upper normal (C+) polarity sequence. The Lower-Middle Triassic boundary, placed at the first occurrence of the ammonoid genera Aegeiceras ugra Diener, Paracrochordiceras spp., Paradanubites depressus Fantini Sestini and Japonites sp., and close to the first appearance of the conodont species Gondolella timorensis Nogami, occurs in normal polarity zone Chios C+. The overall mean direction of the reversal-bearing characteristic component, whose early acquisition is suggested by a tilt test, is D = 271.2°, I = 33.2° (α95 = 11.7°, k = 112.5, N = 3). The inferred paleolatitude of the sampling sites is about 18°N, consistent with either an African or stable European affinity, although the declinations suggest large-scale counter-clockwise rotations with respect to Africa or stable Europe since the Early-Middle Triassic

UPPER SPATHIAN TO BITHYNIAN (LOWER TO MIDDLE TRIASSIC) BRACHIOPODS FROM NORTH DOBROGEA (ROMANIA)

Brachiopods obtained from several Triassic localities in North Dobrogea, in Romania, are described. Upper Spathian and Aegean Hallstatt-type red limestones have been sampled in the Deşli Caira section, proposed as the GSSP for the base of the Anisian. The Bithynian brachiopods mostly originate from the Tubiphytes-microbial buildup in the Mahmudia quarry, and also from the Hallstatt-type limestones of Agighiol and Orta Bair. Their age estimates are supported by ammonoids collected from the same beds. The upper Spathian and Aegean assemblages of Deşli Caira consist of four rhynchonellids, with one genus and two species newly described, Ortarhynchia petersi gen. n. sp. n. and Austriellula iordanae sp. n. The Bithynian assemblages comprise the most diverse fauna, with 15 species, four species of which are newly described, Ortarhynchia petersi gen. n. sp. n., Piarorhynchella kittli sp. n., Ptychomentzelia dobrogeana sp. n. and P. simionescui sp. n. In the Tubiphytes facies of Mahmudia, the assemblage is numerically dominated by mentzeliids and dielasmatids, forming 84.8 % of the whole assemblage. Spiriferinids and rhynchonellids form the minor component. Instead, rhynchonellids prevail in the Hallstatt facies at Agighiol and Orta Bair. The assemblages described here are hardly comparable with those of the western Tethys. The Bithynian assemblage is very different from its equivalent described from the substage stratotype in Turkey. In North Dobrogea, the carbonate substrate and clear and agitated water supported an assemblage with high diversity. In contrast, in Bithynia, the brachiopod community dwelled on a softer and muddier substrate, with higher density and lower diversity. The locality of Aghdarband (Iran) also delivered Bithynian brachiopods, forming another different assemblage. The recovery and radiation of brachiopods after the P/T crisis is discussed in the framework of Palaeo-Tethyan palaeogeography, making comparisons with the South China localities

PERMIAN STRATIGRAPHY AND FUSULINIDS FROM ROSH GOL (CHITRAL, E HINDU KUSH)

Chitral (Pakistan), geologically, includes the eastern termination of the Hindu Kush and its transition to the Karakorum. The position of the boundary is not precisely defined, and may be located provisionally at the Chitral Fault, or at the Tirich Mir Fault. Four main tectonostratigraphic units are identified. From SE to NW they are:1) Lun Shales (shales and slates with Devonian calcareous intercalations) and Devonian to Permian carbonates. 2) Metabasites, consisting of amphibolites and green tuffs, locally associated with carbonates. 3) Atark Group, mostly metacarbonates in which Permian, Triassic and Cretaceous intervals have been detected. 4) Wakhan Slates, a very thick terrigenous succession of dark colour, partly of Paleozoic age. Huge granitoid bodies have been intruded into this unit. This 4-fold subdivision is here proposed for the first time. A terrigenous-calcareous succession of Permian age has been measured and sampled in the Atark Group at Rosh Gol. Seven lithostratigraphic units have been identified. Six of them contain fossils, mostly fusulinids, allowing identification of Yahtashian, Bolorian, Kubergandian and Late Murgabian or Midian. The most significant species of fusulinids are illustrated; these have close affinities to the Central Pamir

PERMIAN RUGOSA FROM NORTHERN KARAKORUM AND AGHIL RANGES

A Coral fauna has been collected in the calcareous/arenitic shallow-water units of Artinskian/Kubergandian ages in Northern Karakorum (Hunza valley) and Aghil Ranges (Shaksgam valley). Most of the species collected were undescribed, but their age is fairly well constrained through fusulinids and conodonts. From the biogeographic point of view they belongs to the Lytvolasma province, with some affinities to Lhasa microplate, Himalaya Range and allochthonous Nappe in Timor

Early Permian Pangea 'B' to Late Permian Pangea 'A"

The pre-drift Wegenerian model of Pangea is almost universally accepted, but debate exists on its pre-Jurassic configuration since Ted Irving introduced Pangea 'B' by placing Gondwana farther to the east by ∼3000 km with respect to Laurasia on the basis of paleomagnetic data. New paleomagnetic data from radiometrically dated Early Permian volcanic rocks from parts of Adria that are tectonically coherent with Africa (Gondwana), integrated with published coeval data from Gondwana and Laurasia, again only from igneous rocks, fully support a Pangea 'B' configuration in the Early Permian. The use of paleomagnetic data strictly from igneous rocks excludes artifacts from sedimentary inclination error as a contributing explanation for Pangea 'B'. The ultimate option to reject Pangea 'B' is to abandon the geocentric axial dipole hypothesis by introducing a significant non-dipole (zonal octupole) component in the Late Paleozoic time-averaged geomagnetic field. We demonstrate, however, by using a dataset consisting entirely of paleomagnetic directions with low inclinations from sampling sites confined to one hemisphere from Gondwana as well as Laurasia that the effects of a zonal octupole field contribution would not explain away the paleomagnetic evidence for Pangea 'B' in the Early Permian. We therefore regard the paleomagnetic evidence for an Early Permian Pangea 'B' as robust. The transformation from Pangea 'B' to Pangea 'A' took place during the Permian because Late Permian paleomagnetic data allow a Pangea 'A' configuration. We therefore review geological evidence from the literature in support of an intra-Pangea dextral megashear system. The transformation occurred after the cooling of the Variscan mega-suture and lasted ∼20 Myr. In this interval, the Neotethys Ocean opened between India/Arabia and the Cimmerian microcontinents in the east, while widespread lithospheric wrenching and magmatism took place in the west around the Adriatic promontory. The general distribution of plate boundaries and resulting driving forces are qualitatively consistent with a right-lateral shear couple between Gondwana and Laurasia during the Permian. Transcurrent plate boundaries associated with the Pangea transformation reactivated Variscan shear zones and were subsequently exploited by the opening of western Neotethyan seaways in the Jurassic

Magnetobiostratigraphy of the Spathian to Anisian (Lower to Middle Triassic) Kçira section, Albania

Magnetobiostratigraphic data are presented from three Early/Middle Triassic Han-Bulog Limestone successions from Kçira, northern Albania. A total of 206 standard palaeomagnetic samples were obtained for thermal demagnetization and statisticalanalysis from the 42, 10 and 5m thick sections. The reversal-bearing characteristic component, carried by haematite and magnetite, defines a composite sequence of six main polarity intervals (Kçln to Kç3r) in which are embedded four short polarity intervals, one at the base of Kçln and three towards the top of Kçlr. The early acquisition of the characteristic remanence is supported by the lateral correlation of magnetozones between sections. The Early/Middle Triassic boundary, approximated by the first occurrence of the conodont Chiosella timorensis, falls close to the Kçlr/Kç2n polarity transition. This is in good agreement with recently published magnetobiostratigraphic data from the coeval Chios (Greece) sections. The palaeomagnetic pole calculated from the Kçira characteristic directions lies close to the Triassic portion of the apparent polar wander path for Laurussia (in European coordinates). However, a 40-45" clockwise rotation of the external zone of the Albano-Hellenic Belt to the south of the Scutari-Pec Line is thought to have occurred since the Early-Middle Miocene. The Kçira pole acquires a West Gondwana affinity when restored for the Neogene clockwise rotation. If the clockwise rotation was entirely related to Neogene tectonics, the Kçira area was evidently associated with West Gondwana and located at 12-16"N of the western Tethys margin

Towards a better definition of the Middle Triassic magnetostratigraphy and biostratigraphy in the Tethyan realm

Magnetostratigraphic and biostratigraphic data for the Middle Triassic (Anisian) were obtained from the Han-Bulog facies in the Nderlysaj section from the Albanian Alps and the Dont and Bivera formations in the Dont–Monte Rite composite section from the Dolomites region of northern Italy. The Nderlysaj section is biochronologically bracketed between the late Bithynian and early Illyrian substages (i.e., late-early and early-late Anisian), whereas the Dont–Monte Rite section comprises the late Pelsonian and the early Illyrian substages. The data from Nderlysaj and Dont–Monte Rite, in conjunction with already published data, allow us to construct a nearly complete composite geomagnetic polarity sequence tied to Tethyan ammonoid and conodont biostratigraphy from the late Olenekian (late-Early Triassic) to the late Ladinian (late-Middle Triassic). New conodont data require revision of the published age of the Vlichos section (Greece)

Opening of the Neo-Tethys Ocean and the Pangea B to Pangea A transformation during the Permian

We studied the stratigraphy, composition, and paleomagnetic properties of lateritic weathering profiles of Permian age from northern Iran and western Karakoram, Pakistan. A limited set of samples deemed representative yielded stable low-inclination paleomagnetic components carried essentially by hematite of chemical origin isolated in massive, fine-grained, and homogeneous ferricrete facies. These laterites originated at equatorial paleolatitudes characterized by intense weathering processes under warm and humid climatic conditions. Paleomagnetic estimates of paleolatitude from Iran, Karakoram, and north Tibet from this study and the literature, albeit sparse, provide testable constraints on the motion of the Cimmerian terranes as the result of the opening of the Neo-Tethys Ocean along the eastern margin of Gondwana during the Permian. We confirm and help refine previous suggestions that the Cimmerian terranes migrated from southern Gondwanan paleolatitudes in the Early Permian to subequatorial paleolatitudes by the Middle Permian – Early Triassic. As a novel conclusion, we find that timing, rates, and geometry of Cimmerian tectonics are broadly compatible with the transformation of Pangea from an Irvingian B to a Wegenerian A-type configuration with Neo-Tethyan opening taking place contemporaneously essentially in the Permian

AN ANOXIC INTRAPLATFORM BASIN IN THE MIDDLE TRIASSIC OF LOMBARDY (SOUTHERN ALPS, ITALY): ANATOMY OF A HYDROCARBON SOURCE

The Ladinian rocks of Central Lombardy consist of carbonate platforms (Esino Formation) subdivided by intraplatform troughs represented either by dark, well bedded limestones, marls and dolomites of poorly oxic to anoxic environment (Perledo-Varenna and Lierna Formations), or by grey nodular cherty limestones (Buchenstein Formation). Subsidence and deposition rates were high ( >100 m/MA), both on the carbonate platform and in the anoxic intraplatform troughs. Sedimentological study of the anoxic intraplatform rocks in the Grigne Mountains has identified 12 main lithofacies with mudstone/ wackestones, both massive and laminated, forming more than 2/3 of the total thickness. Packstones and carbonate breccias, all originating or fed from the neighbouring shallow carbonate platforms, represent 6 % of the total thickness in the basin. Also the dominating micrite is thought to have originated by overproduction on the carbonate platform. Concerning the depositional processes, almost 3/4 of the total thickness is interpreted x re-sedimented. Dolomitization is widespread in the marginal parts of the basin. No benthonic macrofauna is present, and only sporadically the bottom oxygen content was sufficient to support a non skeletal infauna. Two depositional sequences have been detected, both causing emersion on the carbonare platform. The younger emersion was severe and the platform/basin system ceased to exist. The Grigne Mountains are presently arranged in three main tectonically stacked sheets. Vitrinite Reflectance, Illite Crystallinity Index, and Conodont Alteration Index, all suggest an increase of temperature within the sheets, from south to north, i.e. from the geometrically deeper to the more elevated, which has reached the field of deep diagenesis or even anchimetamorphism