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The Norian Stage is the longest stage in the Phanerozoic, and some members of the boundary working group have been evaluating suitable Carnian-Norian boundary sections for roughly two decades. This has identified two possible candidate boundary sections, at Black Bear Ridge (British Columbia, Canada) and Pizzo Mondello (Sicily, Italy). After a formal voting procedure within the working group, ending on the 26th July, 2021, the Pizzo Mondello section was selected as the global stratotype section and point for the base of the Norian. We evaluated the global correlation potential of the two proposed primary markers, the conodont Metapolygnathus parvus and the ‘flat-clam’ Halobia austriaca. Secondary markers were also evaluated around these boundary datums for correlation potential, and the veracity of the proposed sections for GSSP status. Data and arguments for the proposed sections and datums are presented here. Through a two-stage process of option elimination in voting, conforming with ICS guidelines, the working group decided by 60% majority to propose that the first occurrence datum of Halobia austriaca in the Pizzo Mondello section at the base of bed FNP135A should become the ‘golden spike’ for the base of the Norian. A secondary biotic marker for this boundary is the first occurrence of Primatella (Carnepigondolella) gulloae, in sample NA43, ca. 0 m below FNP135A, and the FA of Dimorphites noricus (sample NA42.1) ca. 3.5 m above bed FNP135 (indicating the first subzone of the Jandianus Zone). The best physical secondary marker is the magnetozone PM5n with the proposed boundary ca.40% through the thickness of PM5n. Strengths of the chosen datum are: 1) it also maintains historical priority for ammonoid zonations, which had placed the base Norian near to this level in Europe, North America and probably NE Asia; 2) Halobia austriaca is widely distributed in all paleolatitudes and is a long-established taxon.

The 150th anniversary of the death of Albert Oppel (1831–65) provided the opportunity to celebrate this outstanding stratigrapher with a Thematic Issue dedicated to the importance of fossils for dating and correlating of sedimentary rocks. In this issue, we analyse Oppel's significant contribution to modern chronostratigraphy, before exploring the Phanerozoic through all its major fossil groups, to verify if fossils are still able to make a significant contribution to chronostratigraphy. The extraordinary merit of Oppel's work has been the demonstration that fossils can be used to sub-divide sedimentary sequences into zones, which in turn might be organized in higher chronostratigraphical units. The zone for Oppel is characterized by the distinctive fossil content, and his view strongly influenced the development of the standard chronostratigraphical scale for about one century, until the introduction, in the 1950s, of the log-based range chart as the common practice to study the fossil record of sedimentary successions. This approach forced the stratigraphers to shift the focus from the fossil content of the zones to their boundaries. This new view allowed for the introduction of new kind of zones with precisely defined boundaries based on bioevents and to the decline of the Oppel Zone. This turning point in the history of chronostratigraphy was fuelled by the International Commission on Stratigraphy programme of definition of the units of the International Chronostratigraphic Chart based on the boundary stratotype and point (GSSP) concept, which started in 1973.

The Lower-Middle Triassic Aghdarband Basin, NE Iran, consists of a strongly deformed arc-related marine succession deposited along the southern margin of Eurasia in a highly mobile tectonic context. This basin is a key-area for the study of the Cimmerian events, as the Triassic units show severe deformations, which occurred short time after the collision of Iran with Eurasia, and were sealed by the Middle Jurassic succession. In this work, we document the structural setting and evolution of this area, based on detailed mesoscopic structural analyses of faults and folds, paleostress reconstruction and revision of the Triassic stratigraphy. The Triassic sequences are deeply involved in a N-verging thrust stack interacting with an important left-lateral transpressional fault zone characterized by strike-slip faults, vertical folds and high angle reverse faults generating intricate positive flowers. Systematic folds asymmetry indicates that they developed in a left-lateral transpressional zone coeval to thrust imbrication to the south, due to a marked strain partitioning. The extent of the transpressional zone shows that important left-lateral movements developed parallel to the belt during the Cimmerian collision, in response to oblique convergence between Iran and Eurasia. Inversion of Triassic syn-sedimentary faults, possibly inherited from Palaeozoic structures of the Kopeh Dagh basement and favouring strain partitioning, is suggested by unconformities, significant differences in the sedimentary successions, repeated olistoliths, scarp-related coarse breccias and rapid tectonic drowning, occurring especially along the northern tectonic boundary of the basin. Paleostress analyses point to a complex stress pattern showing a 45° rotation of the stress field along the left-lateral fault system, related to a complete deformation partitioning in two domains respectively characterized by pure reverse dip-slip and strike-slip motions. The main direction of compression, possibly oriented NE–SW in present days coordinates, favoured the development of large shear zones disrupting the eastern portion of the Cimmerian orogen.

The Upper Carnian-Lower Norian (Upper Triassic) Luning Formation at Berlin-Ichthyosaur State Park (BISP) in central NV (USA) has been sampled using for the first time the bed-by-bed approach for ammonoids, pelagic bivalves, and conodonts, more than 60 years after its first description by Silberling (U.S. Geological Survey Professional Paper 322: 1–63, 1959). BISP is historically important for the definition of the uppermost Carnian of the North American Triassic chronostratigraphic scale and is known worldwide as one of the most important ichthyosaur Fossil-Lagerstatte because of its extraordinary record of 37 articulated, large-sized specimens of Shonisaurus popularis. Nearly 190 ammonoids were collected from two stratigraphic sections, documenting all the latest Carnian to Early Norian ammonoid faunas previously described by Silberling. Halobiids were collected from five levels, and the first report of conodonts from BISP includes faunas from 13 levels. The ~340-m thick Brick Pile section, the most complete in the study area, includes the uppermost Carnian Macrolobatus Zone, which provides conodont faunas of the lower primitia zone and Halobia septentrionalis. The 200-m thick lowermost Norian Kerri Zone, which begins 52 m above the Macrolobatus Zone, yields conodonts of the upper primitia zone in its lower part, together with H. cf. beyrichi and H. cf. selwyni. The ichthyosaur-bearing interval, whose stratigraphic position has been interpreted quite differently by previous authors, is documented in the uppermost Carnian Macrolobatus Zone and is characterized by rich Tropites-dominated ammonoid faunas and by the onset of Halobia. All models proposed by various workers to explain the unusual ichthyosaur record are discussed and an additional explanation for the main ichthyosaur-bearing bed is proposed. The new hypothesis is that a harmful algal bloom (HAB) may have been the trigger for the mass mortality recorded in this level. Although the C/N boundary in the Brick Pile section lies within a 52 m interval that presently lacks paleontologic data, this succession is included in a small group of sections that are expected to contribute to the definition of the GSSP of the Norian stage. Correlation of the Brick Pile section with the best Carnian/Norian sections in northeastern British Columbia is discussed. Compared to the British Columbia Juvavites Cove and the GSSP candidate Black Bear Ridge sections, the Brick Pile section exhibits an ammonoid and Halobia record that is slightly more similar to that of the Tethyan sections. Correlation of the Brick Pile section with the second GSSP candidate Pizzo Mondello (Sicily, Italy) well demonstrates the significant problems encountered in calibration of the Tethyan and North American scales.

We obtained bulk-sediment δ18O and δ13C data from biostratigraphically-constrained Tethyan marine sections at Aghia Marina (Greece), Guri Zi (Albania), and Brumano and Italcementi Quarry (Italy), and revised the published chemostratigraphy of the Pizzo Mondello section (Italy). We migrated these records from the depth to the time domain using available chronostratigraphic tie points, generating Ladinian–Rhaetian δ13C and δ18O records spanning from ~ 242 to ~ 201 Ma. The δ18O record seems to be affected by diagenesis, whereas the δ13C record appears to preserve a primary signal and shows values increasing by ~ 1‰ in the Ladinian followed by an ~ 0.6‰ decrease across the Ladinian–Carnian boundary, followed by relatively constant (but oscillatory) Carnian values punctuated by a negative excursion at ~ 233 Ma in the early Carnian, a second negative excursion at ~ 229.5 Ma across the early–late Carnian boundary, and a positive excursion at ~ 227 Ma across the Carnian–Norian boundary. The Norian record is characterized by a long-term decreasing trend and a negative excursion at ~ 216 Ma. Rapid increases and decreases in δ13C have been observed in the Rhaetian, but these may be at least in part due to mixing of different sources of carbonate carbon with different δ13C values. Our Triassic δ13C record has been compared to data from the literature, and a composite δ13C record spanning the last ~ 242 Myr of Earth's history has been generated. This composite record shows a sequence of dated δ13C trends and events that can be used for stratigraphic correlation as well as for a better understanding of the global carbon cycle in the Mesozoic–Cenozoic.

The Anisian succession of Nakhlak (in Central Iran) is characterized by a siliciclastic succession with minor carbonate units, with massive carbonate mounds up to 50 m thick in its upper part. The mounds, constrained in age to the late Bithynian (Ismidicus Zone) by ammonoids and conodonts, are characterized by a flat top and a lateral pinch-out marked by clinostratified slopes (about 15° in dip). Stratigraphic and microfacies analyses document an inner part of the mound characterized by massive microbial carbonates with open-space structures (stromatactis) filled with fine-grained internal sediments and marine cements. Isolated sponges (up to 5 cm), serpulids and bryozoans are present, which grew on the calcimicrobial limestone. A narrow bioclastic margin (mainly with crinoids and brachiopods) produces most of the slope facies (consisting of bioclastic grainstone and packstone, with intraclasts from the inner part of the mounds) which interfinger basinward with volcaniclastic sandstones. The demise of carbonate productivity is marked on the top of the carbonate mounds by a condensed surface, rich in ammonoids, glaucony grains, and articulated crinoids, documenting a rapid drowning. Paleolatitude data support deposition in a tropical setting, and sedimentological constraints indicate deposition close to the fair-weather wave base, within the photic zone. The late Bithynian Nakhlak carbonate mounds developed before the appearance (documented since the Pelsonian in different parts of the world) of scleractinians which, despite the favorable environmental conditions, are absent at Nakhlak. The Nakhlak mounds thus represent one of the last occurrences of the microbial factories (which developed after the Permo-Triassic extinction event and persisted for most of the Middle Triassic, but with a gradually increasing role played by scleractinians) before the first appearance of the Mesozoic corals.

The Triassic chronostratigraphic scale was built on two centuries of research on ammonoid biostratigraphy and biochronology. Two Triassic stage bases and all of the Triassic substages are currently defined by ammonoid bioevents. The study of Triassic ammonoids began during the late 1700s, and in 1895, Edmund von Mojsisovics, Wilhelm Waagen and Carl Diener published an essentially complete Triassic chronostratigraphic scale based on ammonoid biostratigraphy. This scale introduced many of the Triassic stage and substage names still used today, and all terminology of stages and substages subsequently introduced has been based on ammonoid biostratigraphy. Early Triassic ammonoids show a trend from cosmopolitanism (Induan) to latitudinal differentiation (Olenekian), and the four Lower Triassic substage (Griesbachian, Dinerian, Smithian and Spathian) boundaries are globally correlated by widespread ammonoid biotic events. Middle Triassic ammonoids have provinciality similar to that of the Olenekian and provide a basis for recognizing six Middle Triassic substages. Late Triassic ammonoids provide a basis for recognizing three stages divided into five substages. The main uncertainty for the future of Triassic ammonoid biostratigraphy is not the decline of the ammonoids as a tool for dating and correlation of Triassic strata but, rather, the dramatic decrease in the number of specialists, due to the lack of replacement of experienced palaeontologists who started their activity in the 1950s and 1960s.

New Late Ordovician and Triassic palaeomagnetic data from Iran are presented. These data, in conjunction with data from the literature, provide insights on the drift history of Iran as part of Cimmeria during the Ordovician-Triassic. A robust agreement of palaeomagnetic poles of Iran and West Gondwana is observed for the Late Ordovician-earliest Carboniferous, indicat- ing that Iran was part of Gondwana during that time. Data for the Late Permian-early Early Tri- assic indicate that Iran resided on subequatorial palaeolatitudes, clearly disengaged from the parental Gondwanan margin in the southern hemisphere. Since the late Early Triassic, Iran has been located in the northern hemisphere close to the Eurasian margin. This northward drift brought Iran to cover much of the Palaeotethys in approximately 35 Ma, at an average plate speed ofc. 7-8 cm year 21 , and was in part coeval to the transformation of Pangaea from an Irvin- gian B to a Wegenerian A-type configuration.

New structural, sedimentological, petrological and palaeomagnetic data collected in the region of Nakhlak-Anarak provide important constraints on the Cimmerian evolution of Central Iran. The Olenekian- Upper Ladinian succession of Nakhlak was deposited in a forearc setting, and records the exhumation and erosion of an orogenic wedge, possibly located in the present-day Anarak region. The Triassic succession was deformed after Ladinian times and shows south-vergent folds and thrusts unconformably covered by Upper Cretaceous limestones following the Late Jurassic Neo-Cimmerian deformation. Palaeomagnetic data obtained in the Olenekian succession suggest a palaeoposition of the region close to Eurasia at a latitude around 208N. In addition, the palaeopoles do not support large anticlockwise rotations around ver- tical axes for central Iran with respect to Eurasia since the Middle Triassic, as previously suggested. The Anarak Metamorphic Complex (AMC) includes blueschist-facies metabasites associated with discontinuous slivers of serpentinized ultramafic rocks and Carboniferous greenschist- facies 'Variscan' metamorphic rocks, including widespread metacarbonates. The AMC was formed, at least partially, in the Triassic. Its erosion is recorded by the Middle Triassic Baqoroq Formation at Nakhlak, which consists of conglomerates and sandstones rich in meta- morphic detritus. The AMC was repeatedly deformed during post-Triassic times, giving origin to a complex structural setting characterized by strong tectonic fragmentation of previously formed tectonic units. Based on these data, we suggest that the Nakhlak-Anarak units represent an arc-trench system developed during the Eo-Cimmerian orogenic cycle. Different tectonic scenarios that can account for the evolution of the region and for the occurrence of this orogenic wedge in its present position within Central Iran are critically discussed, as well as its relationships with a presumed 'Variscan' metamorphic event. The Cimmerian orogeny, affecting the southern Eurasian margin between Turkey and Thailand, is related to the collision of several microplates, most of which detached from northern Gondwana in the Early Permian during the opening of the

South canyon, located in the New Pass Range in central Nevada (Fig. 1), is one of the most important localities for Upper Triassic marine invertebrates in North America. This site yields very rich ammonoid faunas, as well as cnidarians (Muller, 1936; Stanley, 1979; Roniewicz and Stanley, 1998), foraminifers (Gazdzicki and Stanley, 1983), bivalves (Waller and Stanley, 1998, 2005; Hopkin and McRoberts, 2003), and brachiopods. The significance of South Canyon, however, derives largely from its ammonoid faunas, since it is the type locality of the Desatoyense Zone of the North American Standard Triassic Scale (Fig. 2), currently the best-defined time scale for the Triassic System. Knowledge of the South Canyon ammonoid fauna is largely based on the work of Johnston (1941) who described a rich collection containing thirteen genera, seventeen new species, two varieties, and five taxa in open nomenclature. Johnston interpreted these as a single new fauna, recognized for the first time in North America. Although he noted its strong affinities to Tethyan faunas of the Lower Carnian “zone of Trachyceras aon ,” Johnston nevertheless designated his South Canyon fauna as a new biozone, the Joannites Zone, which he dated as Early Carnian by correlation with the Aon Zone. The Joannites Zone was subsequently renamed the Trachyceras Zone by Silberling (1956), and later the Desatoyense Zone (index Trachyceras desatoyense Johnston, 1941) by Silberling and Tozer (1968). They further demonstrated the position of the Desatoyense Zone with respect to the Upper Ladinian ammonoid succession of British Columbia by the discovery of a fauna with elements of the Sutherlandi Zone at South Canyon, “some hundreds of feet” below the Desatoyense Zone. More recently, Tozer (1994) constrained the position of the Desatoyense Zone with respect to the Lower Carnian ammonoid succession of Canada by documenting elements …

The Triassic is a turning point in the evolutionary history of ammonoids, characterized by the flourishing Ceratitida and the appearance of the first heteromorphs. Following the end-Permian mass extinction, ammonoids were among the first groups to rediversify by producing many new taxa. Already in the late nineteenth century, the still currently recognized Triassic stages and substages were introduced. The historical development of Triassic ammonoid biostratigraphy is a good example of worldwide cooperation between many geographically-diverse research groups, which initially began in Germany and the European Alps. This cooperation was then extended to North America, Transcaucasia, North Indian Margin, South China, and Russia. A renewed interest in Triassic ammonoid biozonation has occurred during the last few decades, leading to the recognition of tens of ammonoid zones spanning about 50.9 Myr (leading to an average duration for ammonoid biochronozones of about 0.74 Myr), whose correlation and definition are herein synthesized.

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.

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.

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).  1998 Elsevier Science B.V. All rights reserved.

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.

Magnetostratigrapic and biostratigraphic data across the Anisian/Ladinian (Middle Triassic) boundary were obtained from the Frotschbach/Seceda section from the Dolomites region of northern Italy, and the Vlichos section from the Greek island of Hydra, where the Aghia Triada published section was also resampled. The Frotschbach/Seceda section includes two radiometrically dated (U Pb) tuff levels and covers two of the three chief candidates for the position of the base of the Ladinian, namely at the base of the Secedensis Zone or the subsequent Curionii Zone. The Aghia Triada section yields biochronological evidence for the base of the Secedensis Zone, whose significance is, however, critically discussed in the light of the magnetostratigraphic correlation with Frotschbach/Seceda. The Vlichos section can be correlated with Aghia Triada and Frotschbach/Seceda by means of magnetic polarity stratigraphy and sparse fossil occurrences. The satisfactory correlation of the magnetozones allows us to construct a composite geomagnetic polarity sequence tied to Tethyan ammonoid and conodont biostratigraphy for about a 2.4 Myr interval across the Anisian/Ladinian boundary.

An important, 2.4 km-thick Triassic succession is exposed at Nakhlak (central Iran). This succession was deformed during the Cimmerian orogeny and truncated by an angular unconformity with undeformed Upper Cretaceous sediments. This integrated stratigraphic study of the Triassic included bed-by-bed sampling for ammonoids, conodonts and bivalves, as well as limestone and sandstone petrographic analyses. The Nakhlak Group succession consists of three formations: Alam (Olenekian–Anisian), Bāqoroq (?Upper Anisian–Ladinian) and Ashin (Upper Ladinian). The Alam Formation records several shifts from carbonate to siliciclastic deposition, the Bāqoroq Formation consists of continental conglomerates and the Ashin Formation documents the transition to deep-sea turbiditic sedimentation. Petrographic composition has been studied for sandstones and conglomerates. Provenance analysis for Alam and most of the Ashin samples suggests a volcanic arc setting, whereas the samples from the Bāqoroq Formation are related to exhumation of a metamorphic basement. The provenance data, together with the great thickness, the sudden change of facies, the abundance of volcaniclastic supply, the relatively common occurrence of tuffitic layers and the orogenic calc-alkaline affinity of the volcanism, point to sedimentation along an active margin in a forearc setting. A comparison between the Triassic of Nakhlak and the Triassic succession exposed in the erosional window of Aghdarband (Koppeh Dag, NE Iran) indicates that both were deposited along active margins. However, they do not show the same type of evolution. Nakhlak and Aghdarband have quite different ammonoid faunal affinities during the Early Triassic, but similar faunal composition from the Bithynian to Late Ladinian. These results argue against the location of Nakhlak close to Aghdarband. Central Iran is geologically a very complex area, characterized by a tremendous variety of rock types ranging from Precambrian to Miocene sedimentary rocks, Palaeozoic–Cenozoic ultramafic–acid igneous rocks and Palaeozoic–Mesozoic metamorphic rocks. Such an astonishing geological diversity is related to a very long history that started with the assembly of Gondwana in early Palaeozoic times and continued to the present-day collision of the Arabian Plate with Eurasia. The unravelling of this long and complex history is challenging. The understanding of the Cimmerian system (Sengor 1984) is especially difficult as the Carboniferous–Jurassic rocks were often deformed, eroded, covered and/or metamorphosed during more recent collisional events, and their boundaries were sometimes reactivated by more recent faults and thrusts. Despite many published contributions to the geology of Central Iran, no shared interpretation has emerged at the microplate and local scales. For instance, there is no consensus on the proposal by Davoudzadeh et al. (1981) and Soffel et al. (1996) that the present-day Central Iran microplate has rotated by 1358 counterclockwise since the Triassic. This model has usually been accepted (Davoudzadeh & Weber-Diefenbach 1987; Ruttner 1993; Alavi et al. 1997; Seyed-Emami 2003), but a From: BRUNET, M.-F., WILMSEN, M. & GRANATH, J. W. (eds) South Caspian to Central Iran Basins. The Geological Society, London, Special Publications, 312, 287–321. DOI: 10.1144/SP312.14 0305-8719/09/$15.00 # The Geological Society of London 2009. test carried out by Wendt et al. (2005) on the basis of the palaeogeographical distribution of Palaeozoic facies actually failed to confirm the model. At the local scale there are often different interpretations of the stratigraphic v. tectonic relationships of several sedimentary and metasedimentary units. For instance, in the key areas of Nakhlak and Anarak, very different pictures were provided not only for the complexly metamorphic Anarak Range (e.g. Sharkovski et al. 1984; Bagheri 2007; Bagheri & Stampfli 2008), but also for the nearby unmetamorphosed Nakhlak Range (e.g. Sharkovski et al. 1984; Alavi et al. 1997). In order to clarify the general setting of Central Iran and its related Cimmerian history we selected the Nakhlak–Anarak area, which has been known since the 1970s (Davoudzadeh & Seyed-Emami 1972) for the contrast of its peculiar 2.4 km-thick mixed siliciclastic, volcaniclastic and carbonatic succession with the surrounding Triassic successions (i.e. Shotori Range, Tabas: Stocklin et al. 1965; see Seyed-Emami 2003 for a comprehensive summary). Based on lithological similarity, several authors suggested a correlation between the Nakhlak Triassic and an almost coeval succession exposed at Aghdarband (Koppeh Dag, NE Iran). Moreover, this correlation was used to support the 1358 counterclockwise rotation of Central Iran since the Triassic (Davoudzadeh et al. 1981). Despite its great significance it is worth noting that the geology and stratigraphy of the Nakhlak–Anarak area are not known in detail, as demonstrated by the rather different descriptions available in the literature (Davoudzadeh & Seyed Emami 1972; Sharkovski et al. 1984; Alavi et al. 1997; Vaziri 2001). The area was visited by a team of stratigraphers, structural geologists, palaeontologists and palaeomagnetists in 2003 and 2004. Most of the stratigraphic data are presented here, while the geological, structural and the palaeomagnetic analyses are described in separate contributions (Muttoni et al. 2009; Zanchi et al. 2009). The geology of the Nakhlak area: open

Along the eastern coast of Socotra Island (Yemen) a 220-m-thick marine Triassic succession is rather well exposed. The succession rests on a crystalline basement of Proterozoic age and is truncated by Jurassic sediments with slight angular unconformity. The Triassic of Socotra was deposited on an epicontinental setting and sedimentation was mostly controlled by sea-level changes. Its peculiar feature is the unusually rich paleontologic record consisting of conodonts, ammonoids, brachiopods and megalodontid bivalves. Three stratigraphic sections were studied at Ras Momi and Ras Falanj. The lithology is dominated by marls and limestones, often organized into shoaling upward cycles. Dolomitization occurs in the upper part of the succession. From the lithostratigraphic point of view the succession is attributed to one formation, divided into two members. The lower member is mostly calcareous, while the upper member mainly consists of dolostones. The detection of sequence boundaries, transgressive and highstand systems tracts (TST and HST) allow the identification of five depositional sequences from Olenekian to Late Carnian age. The age of the first three cycles is especially wellconstrained with conodonts and ammonoids. The five depositional sequences can be well correlated with the Sharland et al. (2001, 2004) peri-Arabian sequences Tr30, Tr40, Tr50, Tr60, Tr70. However, the high-resolution conodont and ammonoid bio-chronostratigraphic data from Socotra allow the re-calibration of the age of sequences Tr40 and Tr50.

SUMMARY Magnetobiostratigraphic data are presented from three Early/Middle Triassic HanBulog Limestone successions from Kqira, northern Albania. A total of 206 standard palaeomagnetic samples were obtained for thermal demagnetization and statistical analysis 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 (Kqln to Kq3r) in which are embedded four short polarity intervals, one at the base of Kqln and three towards the top of Kqlr. 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 Kqlr/Kq2n polarity transition. This is in good agreement with recently published magnetobiostratigraphic data from the coeval Chios (Greece) sections. The palaeomagnetic pole calculated from the Kqira 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 Kqira pole acquires a West Gondwana affinity when restored for the Neogene clockwise rotation. If the clockwise rotation was entirely related to Neogene tectonics, the Kqira area was evidently associated with West Gondwana and located at 12-16"N of the western Tethys margin.