Palaeogeographic Domains Research Articles

Facies character and evolution of a mixed carbonate–siliciclastic shelf: Upper Triassic–Lower Jurassic succession in the eastern Northern Calcareous Alps (Stumpfmauer, Austria)

Western Tethys sedimentary successions constitute fundamental archives of Late Triassic–Early Jurassic environmental, carbonate production and tectonic changes. During the Late Triassic, the Northern Calcareous Alps (Austria) belonged to the Western Tethys passive margin, characterised by the deposition of the early-dolomitized peritidal Hauptdolomit (Norian) adjacent basinward to the Dachstein carbonate shelf and passing upward to the mixed carbonate–siliciclastic Kössen Formation (Upper Norian–Rhaetian). The Kössen Fm. was subdivided into the lower shallow-water Hochalm Member and the upper Eiberg Member, accumulated in an intraplatform basin coeval to shallow-water carbonates (Upper Rhaetian Limestone). The Eiberg Mb. and overlying Jurassic strata were extensively studied as a continuous marine record across the Triassic/Jurassic boundary. In contrast, shallow-water successions, time-equivalent to the Eiberg Mb. and Upper Rhaetian Limestone, located North of the Eiberg Basin, are poorly investigated. This study focusses on the approximately 350 m thick Norian to Lower Jurassic succession cropping out in the eastern Northern Calcareous Alps (Stumpfmauer). The 32 distinguished lithofacies compose seven, vertically superimposed, sedimentary units (A–G), belonging to the Hochalm Mb. of the Kössen Fm. (Unit A peritidal cyclothems, Unit B claystone/marlstone with fossiliferous beds, Unit C coral boundstone to floatstone), Upper Rhaetian Limestone (Unit D subtidal cyclothems with claystone), shallow-water carbonate strata transitional to Lower Jurassic (Unit E ooidal coated grain peloidal grainstone with basal transgressive lag, Unit F bivalve-rich, microbialite and oncoidal lithofacies, previously attributed to the Upper Rhaetian Limestone) and Hettangian–Sinemurian Kalksburg Fm. (Unit G cross-laminated coated grain peloidal grainstone with quartz and chert). The detailed lithofacies characterisation presented in this study contributes to the knowledge on the Northern Calcareous Alps stratigraphy and depositional environments across the Triassic/Jurassic boundary. The identified sedimentary units can be framed in the evolution of Western Tethys and share similarities with depositional systems from the Western Carpathians, Transdanubian Range, Southern Alps and Dinarides suggesting coherent sedimentary response and environmental, climate and tectonic controls in different palaeogeographic domains.

A global view on the Ordovician stratigraphy of southeastern Europe

Abstract The Ordovician documented in southeastern Europe reflects different sedimentary environments, from shallow water to basin, belonging to diverse palaeogeographical domains. Some of these geological sectors and their palaeontological content have been well described for a long time such as the Carnic Alps, which represent one of the most continuous Paleozoic sequences in the world. For some other areas, the quality of the data is variable and the knowledge is less detailed, sometimes with lithostratigraphic units still to be formalized, which also reflects the fragmentary nature of the outcrops. The Ordovician stratigraphy of southeastern Europe with its diverse successions has been revised herein and integrated with new data in an attempt to develop a global scenario for this critical time interval in the evolution of life.

Distribution of rare earth elements of Tunisian margin clays

AbstractThe rare earth element (REE) content of the Tunisian Permian–Neogene shales have been studied to determine the origins of the clay minerals in these shales. The Permian–Neogene series overlies the Palaeozoic basement that has been studied via oil-drilling cores. This study of REEs was performed in various palaeogeographical domains of Tunisia, from the ‘Saharan Platform’ in the south to the ‘Nappes Zone’ in the north. In this work, those levels rich in illite (Palaeozoic, Triassic and Jurassic), smectite (Campanian–Maastrichtian) and palygorskite (continental Eocene) as well as some Miocene levels rich in halloysite are examined. The distribution of REEs in the Tunisian margin sediments is generally homogeneous, except for the Miocene levels containing halloysites. The normalization curves of REEs vs North American shale composite characterize the inherited clays regardless of the dominant minerals, except for a few cases of neoformation. The flat REE curves indicate a detrital origin of the studied clay levels.

Ostracod Response to a Major Middle Jurassic Sea-Level Fall: A Case Study from Southern Tunisia (North Gondwana) with Implications on Regional Stratigraphy and Palaeoenvironmental Reconstruction

Marginal-marine to non-marine ostracod assemblages from the Bajocian (Mid-Jurassic) of southern Tunisia, precisely from the Krachoua Formation at the Kef El Anneba section near the Beni Kheddache area, are here described and tested for their utility to improve the stratigraphic accuracy and palaeoenvironmental reconstructions. This particular microfauna consists of 11 species belonging to 6 genera and represents 2 distinct types of species-rich assemblages from this time interval, allowing the interpretation of the depositional setting of the fossiliferous horizon from which the samples derive. The first ostracod assemblage is mainly composed of the brackish to shallow marine species Fastigatocythere sp. Mette, 1995; Vernoniella aff. V. bajociana Bate, 1965b; Paracypris sp. A, Paracypris sp. B, Fabanella sarda Malz et al., 1985; Marslatourella aff. M. bathonica Andreu, 1999; and Fabanella aff. F. bathonica Oertli, 1957. This ostracod biofacies reflects marginal marine (shallow platform, restricted lagoon) conditions in the studied area. In contrast, the second ostracod assemblage is exclusively dominated by the non-marine limnic species Alicenula sp., Theriosynoecum pusilla Rohr, 1976; Theriosynoecum aff. T. aveyronensis Rohr, 1976; and Theriosynoecum sp. Such ostracod biofacies reflects the establishment of (a) permanent freshwater lake(s) in the studied area, triggered by the total emersion of the Bajocian Krachoua platform, presumably as response to the short-term sea-level fall event JBj3 of Haq (2017). The recognized ostracod species from the upper part of the Krachoua Formation at Kef El Anneba section (Medenine area) are particularly similar to those already described from the neighbouring sections of Kezzani (Dhaher area) and Krachoua (Tataouine area), facilitating a stratigraphic calibration of the Krachoua Formation, as well as regional correlations of the respective Bajocian continental event within the southern Tunisian palaeogeographic domain. Moreover, the biogeography of the studied ostracod microfauna from the Mid-Jurassic of southern Tunisia provides further arguments to support the hypothesis of significant biological exchanges between Laurasian and Gondwanan islands, as recently demonstrated by means of a charophyte microflora, indicating that Peri-Tethyan biogeography remained relatively uniform during that time interval and challenging the previous assumption of their endemism.

Back-arc underplating provided crustal accretion affecting topography and sedimentation in the Adria microplate

Supported by evidence of deep crustal sources for the observed magnetic anomalies in Central Italy and by outcropping gabbros in the Croatian archipelago, we model the observed gravity and magnetic anomalies in the Central Adriatic Sea and surroundings. We suggest that the major magnetic anomalies in the area are related to a wide underplating and propose that this volume represents the first stage of the back-arc Adria continental breakup in Early Permian times. During the Palaeotethys-Adria collision, underplating has controlled topography and palaeogeographic domains resulting in the observed asymmetrical sedimentary evolution since the Triassic across the Adria microplate. Finally, we propose that the Palaeotethys-Adria boundary in the Early Permian was similar to the current Pacific-Okhotsk plate boundary.

Taxonomy, palaeoecology and palaeobiogeography of upper Cenomanian (Upper Cretaceous) oysters and plicatulids from southern Algeria

ABSTRACT Palaeontological investigation of four lithostratigraphic sections documenting the upper Cenomanian shallow marine carbonates of three palaeogeographic domains of southern Algeria (western Saharan Atlas, Guir Basin and Tinrhert Hamada) has produced a comprehensive collection of large bivalve assemblages for taxonomic purposes. A first inventory list of late Cenomanian oysters and plicatulids from southern Algeria is now available and consists of 15 taxa as follows: Lopha syphax, Ostreidae gen. et sp. indet., Curvostrea rouvillei, Flemingostreidae gen. et sp. indet., Costagyra olisiponensis, Amphidonta obliquata, Ceratostreon flabellatum, Ilymatogyra africana, Rhynchostreon suborbiculatum, Gyrostrea delettrei, Gyrostrea sp. indet., Pycnodonte (Phygraea) vesicularis vesiculosa, Plicatula (Plicatula.) auressensis, Plicatula (Plicatula) batnensis, and Chondrodonta? sp. indet. These taxa build five distinctive oyster-facies patterns, all purportedly recognisable in the field for stratigraphic assignment and regional correlation. Scarce sclerobiontic assemblage (borings: Entobia, Gastrochaenolites and Oichnus; and epibionts: juvenile oysters, serpulid tubes and Berenicean-type bryozoa) observed within these oyster shell assemblages is also identified, briefly described and adressed. This first taxonomic analysis highlights three main palaeogeographic components within these oyster- and plicatuloid-assemblages: endemic Mediterranean, Tethyan-Atlantic and cosmopolitan taxa. Moreover, the present study on these late Cenomanian oyster assemblages provides a first inventory list and stratigraphical baseline data towards further datation and correlation at the regional scale.

Structural relationships between Helminthoid Flysch and Briançonnais Units in the Marguareis Massif: A key for deciphering the finite strain pattern in the external southwestern Alps

The structural setting and tectonic evolution of the Marguareis Massif (located at the boundary between the Maritime and Ligurian Alps) has long been matter of debate. After new meso‐ and micro‐structural studies and field investigations, the tectonic unit interplay outlines a finite structural architecture more complex than that proposed in previous interpretations. We depict a stack of Briançonnais Units stemming from the Europe continental margin, and the Helminthoid Flysch Unit, detached from its original basement whose original palaeogeographic domain is still a matter of debate. Our results highlight for the first time that each unit recorded different pre‐stacking folding events progressively developed at different structural levels. The events occurred during the stacking of the units produced shear zones with top‐to‐SW sense of movement. After the syn‐stacking tectonics achieved during the Late Eocene‐Early Oligocene collisional events, the whole stack recorded the same post‐stacking deformation history here represented by a fold system with sub‐horizontal axial planes and faults. Similar tectonic evolution was documented in other sectors of the Western Alps by previous authors.

Late Aptian to early Cenomanian dinoflagellate cysts from Agadir Basin, southwestern Morocco: Biostratigraphy and palaeoenvironment

The Agadir Basin (Moroccan Atlantic margin) is characterized by its fossil richness, including organic-walled microfossils. The palynological analysis of the middle Cretaceous succession from the Tamzargout section and EGA.1 well reveals the presence of well-preserved and diverse assemblage, rich in dinoflagellate cysts. The assemblages contain stratigraphic marker taxa and show significant chronostratigraphic events. Based on these bioevents and on the comparison with different palaeogeographic domains, a determination of age was proposed. The biogeographic characteristics of most cosmopolitan taxa in this study confirm the establishment of new oceanic communication related to the opening of the equatorial Atlantic. The Albian-Cenomanian transition has been recognized only in EGA.1 well, whereas the Aptian-Albian transition, the early-mid Albian and the mid-late Albian have been defined in both the section and the well. The recorded associations are comparable to those of neighboring deposits and those of the Tethyian and Atlantic domains. The vertical distribution of the organic matter in the sediments of the Agadir Basin and the compilation of all palaeoenvironmental proxies allowed identifying an Albian transgression with specific palaeoenvironments in each interval. Neritic marine environments alternated with short phases of continental and oceanic influence is deduced for the late Aptian-early Cenomanian in this basin. The late Aptian-early to mid Albian recorded an outer neritic palaeoenvironment under oceanic influence; the mid to late Albian showed littoral conditions during a regressive phase fluctuating to middle to outer neritic environment; finally the late Albian-early Cenomanian transition was characterized by a middle neritic palaeoenvironment under coastal influence.

Ostracods as proxies for marginal marine to non-marine intervals in the mid-Cretaceous carbonate platform of the Central Tunisian Atlas (North Africa): Response to major short-term sea-level falls

Two non-marine to marginal-marine intervals have been identified by ostracod assemblages in the mid-Cretaceous carbonate platform of the Central Tunisian Atlas, the deposits of which belong to the Orbata Formation. The first non-marine interval has been recorded within member Unit 2b of the Orbata Formation which yielded the first lower Aptian ostracod fauna composed of Alicenula? leguminella, Vecticypris polita, Cypridea ventriosa, Perissocytheridea altesulcata sp. nov., Harbinia? cf. sinuata, Hourcqia aff. bateke, Ovocytheridea nuda, Bythocypris? pythagorasi sp. nov., Paracypris lusitanicus and Paracypris chekhmai sp. nov. The assemblages indicate continental to marginal-coastal environment and lower Aptian emergence of the Orbata Platform, and are interpreted as response to an earliest Aptian 3rd-order (0.5–3 myr) sea-level fall event of major amplitude. A second lowermost Albian ostracod fauna, recorded within members Unit 5b, 6 of the Orbata Formation, is composed of Candonopsis carthaginensis sp. nov., Cypridea quadrangulata, Virgatocypris kechoulaensis, Alicenula? leguminella, Vecticypris polita, Stenestroemia mosensis, Perissocytheridea kouminiensis sp. nov., Hourcqia aff. bateke, Dolocytheridea bosquetiana, Dolocytheridea donzei sp. nov., Ovocytheridea anterocompressa, Paracypris dubertreti, Paracypris mdaouerensis, Clithrocytheridea espichelensis, Bythocypris? multagracilis sp. nov. and Bythocypris dorsogibba sp. nov. The assemblages indicate another interval of non-marine to marginal-marine depositional settings as direct response to a prominent eustatic latest Aptian to earliest Albian sea-level fall event that enhanced the quasi-total emersion of the Central Tunisian Atlas palaeogeographic domain. Hence, the two studied faunas herein allow us to define two stratigraphic key surfaces of regional utility giving new insights into the chronostratigrahic subdivision of the Orbata carbonate platform, especially in supporting a previously neglected early Albian age of its upper part (Unit 5b, 6 and 7) and allow the regional stratigraphic correlation of these key surfaces in the Central Tunisian Atlas (CTA) domain. Accordingly, our results not only disprove the previous consideration of an uppermost Aptian–lower Albian hiatus but also implicate the necessity to redefine and review the previous palaeogeographic and tectono-sedimentary schemes of the CTA as suggested for almost fourty years.

Middle–late Cambrian acritarchs of the Zagros Basin, southwestern Iran

A detailed palynological study was conducted in the lower Palaeozoic of the Zagros Basin (southwestern Iran) where the Mila and Ilbeyk formations are present in several areas. The Mila Formation mainly consists of dolostones, limestones and shales deposited in a shallow marine to outer ramp environment. It is conformably overlain by the Ilbeyk Formation, characterised by shales and sandstones with scattered limestone intervals deposited in a setting extending from shoreface to low-energy offshore environments. The palynological investigation of the Mila and Ilbeyk formations from the Chalisheh, Ghalikuh and Oshtorankuh areas allows the establishment of three palynozones. These can be well correlated with the palynozonations from adjacent areas and/or with middle–late Cambrian sections independently dated with trilobites. These correlations are useful for the age determination of the Cambrian successions from southern Iran. The Cambrian assemblages exhibit close affinities with microfloras from peri-Gondwana (including the countries belonging to the Avalonia microcontinent in the Early Ordovician) and Baltica, confirming that these palaeogeographical domains were part of the same large bioprovince, as shown in current palaeogeographical maps.

Mass-transport deposits from the Toarcian of the Umbria-Marche-Sabina Basin (Central Italy)

Mass-transport deposits (MTDs) intercalated in slope/basinal successions, produced by submarine collapses and mass flows, are generally constituted of allochthonous elements sourced from platform margins. Here we present a noticeable exception where Toarcian calciclastic deposits made of pelagic carbonate elements are embedded in other pelagic carbonates. Selected outcrops pertaining to the Rosso Ammonitico Fm of three different pelagic carbonate platform (PCP)-basin systems were studied. The pelagic successions of the study areas onlap Early Jurassic structural highs. These clastic bodies partially replace the typical Toarcian reddish marls and shales of the Umbria-Marche-Sabina palaeogeographic Domain at different stratigraphic levels. The clasts range from blocks to megablocks; extraclasts of Corniola facies (Pliensbachian) and, sporadically, of Calcare Massiccio peritidal carbonates (Hettangian) are associated with Rosso Ammonitico intraclasts.The internal architecture of the MTDs and their emplacement processes, as well as their source and accumulation areas, were identified. Three distinct lithofacies characterise the clastic bodies, each one corresponding to a different emplacement process or to a different portion of the flow. The occurrence of lithified megablocks (>20 m across) of Corniola Fm suggests the exhumation of the buried portion of the unit. Synsedimentary extensional tectonics is the most likely triggering mechanism.Sedimentological analysis, coupled with geological mapping of the study areas, reveals the key role played by PCPs in the genesis of these MTDs. The early Toarcian reactivation of Hettangian palaeofaults bounding the structural highs is inferred. These faults, characterised by moderate offsets, crosscut the onlap wedges of the hangingwall successions, exhuming the older and lithified portion of Corniola Fm. Once become inactive, the fault planes were then eroded producing palaeoescarpments. Their backstepping, coupled with seismic shocks, produced the accumulation of the study clastic bodies.

Revitalizing exploration and redevelopment of deep carbonate targets in the Southern Apennines thrust belt (southern Italy): reappraising vintage data with modern approaches

Abstract Hydrocarbon distribution in the Southern Apennines thrust belt of Italy is directly related to the geological characteristics and complex evolution of the thrust tectonic pile involving units from different palaeogeographical domains. Within this structural–stratigraphic context, the main exploration target is represented by the carbonate units of the Apulian Platform, which contain the largest and deepest oilfields in the region. By integrating different types (e.g. wells, seismic, maps, reports) of legacy public and confidential data of various vintages, the subsurface structural setting of the contractional Apulian structures around the Benevento Field in the Southern Apennines hydrocarbon province is reconstructed. The discovery dates back to the early 1970s. The reservoir consists of Cretaceous–Lower Miocene carbonates at a depth of around 3000 m below sea level bearing both oil and gas. A new digital interpretation and integration, which takes into account the most recent understanding of the evolution of this thrust belt, has allowed reconstruction of the trap style of the Benevento Field and of the prospective (undrilled) structures in the surrounding area. A history of positive inversion tectonics is interpreted from a 2D kinematic restoration; this has important implications for both the structural style and the hydrocarbon prospectivity of the Southern Apennines thrust belt.

Hybodont dentition from the Upper Jurassic of Monte Nerone Pelagic Carbonate Platform (Umbria‐Marche Apennine, Italy) and its ecological implications

Here we describe a number of articulated teeth of a hybodont shark from Upper Jurassic deposits of the Monte Nerone Pelagic Carbonate Platform, in the Umbria‐Marche‐Sabina Palaeogeographic Domain (Northern Apennines, Central Italy). The material has been referred to asAsteracanthuscf.A. magnus, a quite well‐known taxon already reported from Middle to Upper Jurassic deposits of Europe. Teeth indicate an extreme crushing feeding behaviour, suggesting as putative prey both infaunal and epifaunal hard‐shelled invertebrates dwelling the sea‐floor, such as large bivalves, brachiopods, gastropods as well as vagile crustaceans. The finding represents, to date, the first formal report of hybodont shark in the Umbria‐Marche‐Sabina Domain, throwing further light on the ecology within Pelagic Carbonate Platform settings, and on the occurrence ofAsteracanthusin the Late Jurassic of the Western Tethys.

First report of hybodont shark from the Toarcian Rosso Ammonitico Formation of Umbria-Marche Apennine (Polino area, Terni, Central Italy)

In this contribution we present the first material referable to hybodont shark from the Rosso Ammonitico Formation (Umbria-Marche-Sabina Palaeogeographic Domain). Two teeth were recovered isolated within Toarcian red marly-limestone (Bifrons Zone). The best-preserved tooth is characterized by a general structure well in accord with the classic crushing dentition typical of hybodont sharks within the Subfamily Acrodontinae. The gently domed occlusal surface of the tooth does not show any trace of occlusal crest and of wrinkles, and is characterized by densely pitted, finely reticulated ornamentation. The available characters allow a conservative classification of the material at the genus level as Asteracanthus sp. The best-preserved tooth can be referred to the most mesial area of the first row of lateral teeth, using as a reference the holotype of Asteracanthus medius. The new material represents the earliest evidence of Asteracanthus and the second one from the whole Northern Apennines (Central Italy), throwing new light on the dispersal of the genus on the Jurassic Tethys.

Relationships between the Sakarya Zone and the Ankara–Erzincan suture (central-northern Turkey): geological and petrographic data from the Ankara–Çankiri, Çorum and Amasya areas

AbstractThe study was performed in central-northern Anatolia (from Ankara to Amasya) to investigate the relationships of the Sakarya Zone units and the Izmir–Ankara–Erzincan suture (IAES) melange. It reveals that all the Sakarya Zone units are metamorphic and three main tectonostratigraphic units have been distinguished for the first time: the BAA (metasiliciclastic rocks capped by metacarbonates and varicoloured phyllite), the BKC (poly-metamorphic garnet-bearing micaschist and metabasite with a well-preserved relict HP–LT amphibole in a low-amphibolitic to greenschist-facies framework) and the AMC (meta-arkose passing vertically to carbonate–phyllitic alternations and, then, to a thick succession of prevailing acidic to intermediate–basic metavolcanites and volcanic-rich metasediments). The BAA and AMC, whose metamorphic frameworks are of Cimmerian age, underlie the Mesozoic carbonate cover sequences (e.g. t2-3, j3–k1) that often show tectonic detachments and slicing. The piling up of the BAA above the HP–LT BKC can be correlated to the tectonic superposition of two similar units (i.e. the Cimmerian Çangaldağ Complex and the Alpine Middle–Upper Cretaceous Domuzdağ Complex, respectively) defined by previous authors in other sectors of the Central Pontides front. The ophiolitic melange generally underlies the Sakarya Zone, but locally (e.g. SE of Amasya) tectonically rests above the latter, probably owing to back-thrusting that occurred during the Tertiary syn-collisional shortenings and the later strike-slip tectonics. We hypothesize that, also in these areas, the Sakarya Zone–IAES consists of a complex tectonic stack of different units, belonging to different palaeogeographic domains and orogenic events (Cimmerian versus Alpine orogenies), but originated within a single long-lived (since Late Triassic to Paleocene/Eocene times), prograding subduction–accretion system in front of the Laurasian continent.

Ammonite assemblages and chronostratigraphy of the uppermost Bajocian–Callovian (Middle Jurassic) of the Murcia Region (Betic Cordillera, south-eastern Spain)

In this paper the stratigraphy and biostratigraphy of the Bathonian–Callovian rocks of the Murcia Region, based on high-resolution sampling yielding good ammonite dating, is reported. All the ammonites analysed are from four sections located on a pelagic swell (External Subbetic palaeogeographic domain) of the External Zones of the Betic Cordillera, Murcia Region, southern Spain. These represent characteristic Bathonian–Callovian sections of the Subbetic epipelagic swells in the Betic Cordillera. The lithology consists mainly of both nodular limestones and marly limestones. Discontinuities with hiatuses of variable duration, submarine hardgrounds, Fe–Mn macrooncoids, limonite crusts, neptunian dykes, etc., occur in the Middle Bathonian–Callovian interval. Extreme condensation episodes are common, but abundant ammonite faunal records have enabled a consistent and accurate chronostratigraphy. The Parkinsoni Zone, Daubenyi and Dimorphus subzones (uppermost Bajocian), the Zigzag and Aurigerus zones (Lower Bathonian), the Sofanus and Costatus zones (Middle Bathonian), the Orbis Zone (Upper Bathonian), and the Bullatus and Gracilis Zones (Lower Callovian) are recognised and characterised. The ammonite fauna shows a typical Mediterranean character. Phylloceratina and Lytoceratina are the predominant elements within the ammonite fauna, but Lytoceratina is dominant in the Lower Bathonian whereas Phylloceratina predominates in the rest of the Bathonian and in the Callovian. Other ammonites, such as Oppeliidae, Lissoceratidae, Stephanoceratidae, Perisphinctidae, Tulitidae, and Reineckeiidae, are also common throughout the uppermost Bajocian to Lower Callovian interval. Strigoceratidae are present, but scarce.

Description et biozonation des sections de crinoïdes saccocomidés du Jurassique supérieur (Oxfordien-Tithonien) du domaine téthysien occidental

The study of several hundreds of thin sections, from dozens of outcrops in three different palaeogeographic domains: the External Rif Chain (Morocco), the Vocontian Basin (Southeastern France) and the Northern Tunisia, has helped better to characterize the stratigraphic distribution of the pelagic crinoids, roveacrinid saccocomids. The saccocomids, appearing in the Middle Oxfordian, are thriving noticeably in the three studied basins at the base of the Early Tithonian substage (Hybonotum ammonite zone) and dominate the pelagic microfauna up to the relative disappearance of the group at the top of the Late Tithonian, at the limit of the A2 and A3 subzones of calpionellids. Careful examination of the respective skeletal elements of this fossil group in thin sections lead to define 47 types of skeletal sections, divided into 6 different groups. These skeletal sections are described and named on the base of their geometric forms. Most of these sections have typical geometric shapes and occur in coeval stratigraphic levels in the three investigated basins. Several of these sections are characteristic of a specific stratigraphic interval, either by their geometric shape or by their relative frequency. The stratigraphic distribution of the investigated skeletal sections, previously considered as of limited stratigraphical value, allowed to define 7 association and relative frequency biozones for the Late Oxfordian-Late Tithonian interval. These biozones are correlated with the ammonite zones.

Middle Triassic carbonate platforms in eastern Iberia: Evolution of their fauna and palaeogeographic significance in the western Tethys

This article reports the first integrated study of the Middle Triassic of Iberia, based on the stratigraphy, sedimentology, and fossil fauna of Muschelkalk facies of the Iberian Ranges and the Catalan Coastal Ranges in Spain. On the basis of this study, new palaeogeographic reconstructions of the westernmost Tethys are proposed, and the evolution of the different palaeogeographic domains of Iberia (e.g., Iberian, Mediterranean, and Levantine–Balearic) are described.In these domains, Muschelkalk facies record the development of wide carbonate platforms that were the consequence of the first two broad marine transgressions of the Mesozoic in Iberia, respectively, late Pelsonian–early Illyrian and late Illyrian–Longobardian. Of these marine incursions, the oldest only manifested in the Mediterranean Triassic domain (Catalan Coastal Ranges and part of the Iberian Ranges), which acted as a palaeogeographic gulf opening northwards. Most of the fauna related to this first incursion show strong affinities with the Alpine/Germanic bioprovinces, related to the Palaeotethys. In contrast, the second transgressive episode took place in a new regional palaeogeographic setting related to the intra-Pangea dextral shear, and the northward movement of the Cimmerian microcontinent. A rapid sea-level rise induced generalised marine flooding of the Iberian, Mediterranean, and Levantine–Balearic Triassic domains. The resulting carbonate platforms yield fossil assemblages (ammonoids, bivalves, foraminifera and conodonts) that show affinities with those of both the Alpine and Sephardic bioprovinces related to the Neotethys. These assemblages point to a significant increase in diversity during the late Fassanian–Longobardian, possibly related to the prevailing wider connections between the sea corridors, an increased continental run-off and input of nutrients and/or a general cooling of marine waters.

Microbial-dominated carbonate platforms during the Ladinian rifting: sequence stratigraphy and evolution of accommodation in a fault-controlled setting (Catalan Coastal Ranges, NE Spain)

The Upper Muschelkalk sedimentary record constitutes a major transgressive pulse of north-eastern Iberia during the Ladinian. This record is arranged in two transgressive–regressive (T–R) sequences formed by two stepped microbial-dominated carbonate ramp systems where accommodation was mainly controlled by extensional faults. This study seeks to gain new insights into how the evolution of syn-rift subsidence controls the creation of accommodation space, the depositional styles and, especially, the palaeogeographical domains where specific microbialites developed (thrombolites and stromatolites). Thrombolite bodies (at least 40 m thick) display two types of architecture, biostromal and mud-mounded and stromatolite bodies (at least 7 m thick) consist of tabular and domed, head-shaped morphologies. Domed and mounded forms are usually developed during stages of increasing accommodation rates, low-to flat-nelief forms tend to grow in association with periods of low accommodation rates. A sea-level fall of at least 50 m occurred at the end of the Early Ladinian leaving the platform subaerially exposed. As a result, a prominent karst with significant erosional incisions and profuse collapse breccia fillings was formed in the inner and middle ramp settings. The resultant subaerial unconformity bounds T–R sequences 1 and 2. Subsidence curves display two stages of rapid/decelerated total subsidence, constituting two discrete rift/post-rift pulses in the large Triassic rifting period: (i) Buntsandstein – Middle Muschelkalk, and (ii) Late Muschelkalk – Imon Formation (Rhaetian). The second pulse is characterized by a rapid syn-rift subsidence during the Late Muschelkalk, and a decelerated post-rift subsidence throughout the deposition of Keuper facies and Imon Formation. The Late Muschelkalk rapid syn-rift pulse of total subsidence produces gains in accommodation, which controls the development of the stromatolites and thrombolites (biostromes and mud-mounds).

Planktonic foraminifer biostratigraphy as a tool in constraining the timing of flysch deposition: Gurnigel flysch, Voirons massif (Haute‐Savoie, France)

AbstractNew biostratigraphic, sedimentological and petrographic data and a thorough review of existing literature modify existing knowledge on the age, the sedimentology, the petrography and the palaeogeographic origin of the Gurnigel flysch from the Voirons massif (Haute Savoie, France). Planktonic foraminiferal biostratigraphy assigns the flysch to the upper Middle Eocene (zones P12 to P14) through to Lower Oligocene (zones P16 to P20) stages. This result contrasts with previous work, which assigned the unit to the Lower Palaeocene to upper Middle Eocene on the basis of calcareous nannofossil and dinoflagellate assemblages. The following findings suggest that the Voirons massif comprises several stacked flysch units that do not have exactly the same palaeogeographic origin: (i) the occurrence of flysch exposures in reverse stratigraphic order combined with the lack of evidence for bed overturning; (ii) the variability of palaeo‐depositional settings inferred from different flysch outcrops of similar age; (iii) the differences in the heavy mineral content; and (iv) the anomalous superimposition of distal turbidites and/or basinal contourites (Saxel Marls) over proximal turbidites (Vouan Conglomerates). The young age of these kilometre‐sized flysch slices precludes their hitherto postulated locus of deposition in the South‐Penninic Ocean, and rather indicates a provenance from the Ultrahelvetic and/or North‐Penninic (Valais) palaeogeographical domains. Finally, none of the nannofossil assemblages are contemporaneous with the observed planktonic foraminifera associations, suggesting that they have been reworked, dissolved, or just simply diluted and not found by earlier researchers. This study from the Voirons massif shows that planktonic foraminifera associations are a highly reliable biostratigraphic tool for obtaining accurate ages of flysch successions.