Tethyan Area Research Articles

Identification of the base of the lower-to-middle Campanian Globotruncana ventricosa Zone: Comments on reliability and global correlations

The reliability of the first appearance datum of Globotruncana ventricosa as biozonal marker for the Campanian is discussed. The taxonomy and species concept of G. ventricosa and of Globotruncana tricarinata, that has been either regarded as junior synonym of Globotruncana linneiana or of G. ventricosa, are examined to avoid misidentifications, and one species is here formally described as new, Globotruncana neotricarinata nov. sp. The tropical and subtropical planktic foraminiferal assemblages from the Bottaccione section (Gubbio, Italy), from Deep Sea Drillig Project (DSDP) Site 146 (Caribbean Sea, central Atlantic Ocean), and from Ocean Drilling Program (ODP) Hole 1210B (Shatsky Rise, northwestern Pacific Ocean) are analyzed for the presence of biostratigraphic markers. Lowest and highest occurrence data have been checked in thin sections and washed residues in the Bottaccione section. The comparative biostratigraphic analysis of the planktic foraminiferal distribution highlights: 1) the absence of G. ventricosa at the stratigraphic level at which it is supposed to first occur in the Tethyan area, 2) the presence of transitional specimens resembling G. ventricosa and thus erroneously used to identify the base of the G. ventricosa Zone, 3) the presence of a good sequence of bioevents that appear to be promising for regional and global correlations such as the appearance of Globotruncanita atlantica, Contusotruncana plummerae and the disappearance of Hendersonites carinatus. The correlation potential of these bioevents has been verified across latitudes by studying the Campanian planktic foraminiferal assemblage in pelagic sediments drilled on coastal Tanzania (western Indian Ocean), and at the deep-sea ODP Hole 762C (Exmouth Plateau, western Indian Ocean), that were located at 30°S and 47°S in the Late Cretaceous, respectively. Besides the known diachronous first appearance of G. ventricosa in the Southern Ocean sites, results confirm the difficulty in using G. ventricosa as zonal marker in the tropical and subtropical areas, and the validity of the first appearance datum of C. plummerae for regional and global correlations.

Plate tectonics of the Alpine realm

Abstract New field data on the East Mediterranean domain suggest that this oceanic basin belonged to the larger Neotethyan oceanic system that opened in Permian times. A Greater Apulia domain existed in Mesozoic times, including the autochthonous units of Greece and SW Turkey. It also included a united Adria and Apulia microplate since Early Jurassic times. This key information implies that a new post-Variscan continental fit for the western Tethyan area is necessary, where the relationships between the Adriatic, Apulian and Iberian plates are defined with greater confidence. To construct a reliable palinspastic model of the Alpine realm, plate tectonic constraints must be taken into consideration in order to assess the magnitude of lateral displacements. For most of the plates and their different terranes, differential transport on the scale of thousands of kilometres can be demonstrated. This plate tectonic framework allows a better geodynamic scenario for the formation of the Alpine chain to be proposed, where the western and eastern transects have experienced contrasting geological evolutions. The eastern Alps–Carpathians domain evolved from the north-directed roll-back of the Maliac–Meliata slab and translation of the Meliata suture and Austroalpine domain into the Alpine domain. In the western Alps, the changing African plate boundary in space and time defined the interaction between the Iberian–Briançonnais plate and the Austroalpine accretionary wedge.

High-resolution carbon isotope changes in the Permian–Triassic boundary interval, Chongqing, South China; implications for control and growth of earliest Triassic microbialites

High-resolution δ 13C CARB analysis of the Permian–Triassic boundary (PTB) interval at the Laolongdong section, Beibei, near the city of Chongqing, south China, encompasses the latest Permian and earliest Triassic major facies changes in the South China Block (SCB). Microbialites form a distinctive unit in the lowermost 190 cm above the top of the Changhsing Formation (latest Permian) at Laolongdong, comparable to a range of earliest Triassic sites in low latitudes in the Tethyan area. The data show that declining values of δ 13C CARB, well-known globally, began at the base of the microbialite. High positive values (+3 to 4 ppt) of δ 13C CARB in the Late Permian are interpreted to indicate storage of 12C in the deep waters of a stratified ocean, that was released during ocean overturn in the earliest Triassic, contributing to the distinctive fall in isotope values; this interpretation has been stated by other authors and is followed here. The δ 13C CARB curve shows fluctuations within the microbialite unit, which are not reflected in the microbialite structure. Comparisons between microbialite branches and adjacent micritic sediment show little difference in δ 13C CARB, demonstrating that the microbialite grew in equilibrium with surrounding seawater. The Early Triassic microbialites are interpreted to be a response to upwelling of bicarbonate-rich poorly oxygenated water in low latitudes of Tethys Ocean, consistent with current ocean models for the PTB interval. However, the decline of δ 13C CARB may be due to a combination of processes, including productivity collapse resulting from mass extinction, return of deep water to ocean surface, oxidation of methane released from methane hydrate destabilisation, and atmospheric deterioration. Nevertheless, build-up of bicarbonate-rich anoxic deep waters may be expected as a result of the partial isolation of Tethys, due to continental geography; release of bicarbonate-rich deep water, by ocean upwelling, in the earliest Triassic may have been an inevitable consequence of this combination of circumstances.

EOCENE LARGER FORAMINIFERAL BIOSTRATIGRAPHY IN THE SOUTHERNMOST DAUPHINOIS DOMAIN (MARITIME ALPS, FRANCE-ITALY BORDER)

The Trucco Formation and the Nummulitic Limestone (Dauphinois Domain, Maritime Alps) are characterized by abundant larger foraminifera, specifically nummulitids, orthophragminids and encrusting foraminifera. In the Maritime Alps, previous studies suggest a late Lutetian age for the Trucco Formation and a late Lutetian-Priabonian age for the Nummulitic Limestone. Biostratigraphic analysis of the nummulitids, in 11 stratigraphic sections, allowed us to distinguish 3 biozones: MALF1 Zone: defined by the presence of Nummulites brongniarti d’Archiac & Haime, N. puschi d’Archiac, N. perforatus de Montfort, N. striatus (Bruguiere), N. cf. dufrenoyi d’Archiac & Haime, N. variolarius/incrassatus and Operculina schwageri Silvestri. MALF2 Zone: defined by the presence of Nummulites perforatus de Montfort, N. striatus (Bruguiere), N. cf. dufrenoyi d’Archiac & Haime, N. variolarius/incrassatus and Operculina schwageri Silvestri. MALF 3 Zone: defined by the presence of gr. Nummulites variolarius/incrassatus , N. striatus (Bruguiere) and Operculina schwageri Silvestri. According to current larger foraminiferal biozonal schemes, the age of these local biozones corresponds to the Bartonian p.p. Moreover, the comparison with biostratigraphic schemes established for the Dauphinois Domain and for the Tethyan area evidences that several typical nummulitid species of the late Bartonian are lacking in the southern Dauphinois Domain, probably due to a paleogeographic control.

The Paleocene–Eocene Thermal Maximum as recorded by Tethyan planktonic foraminifera in the Forada section (northern Italy)

The Forada section in the Venetian Pre-Alps of northern Italy represents an expanded record of the Paleocene–Eocene Thermal Maximum (PETM) at a depositional paleodepth of about 1 km ± 0.5 km. High-resolution planktonic foraminiferal analysis of this section, in a time interval of approximately 1.3 Myr across the Paleocene/Eocene boundary, reveals striking faunal changes that allow the identification of eight phases (a–h). The late Paleocene was represented by stable, warm and oligotrophic surface water conditions (phase a). Unstable environmental conditions start well before the onset of PETM (ca. 150 kyr, phase b) and involved a change towards eutrophy, as marked by the increase of Subbotina and the concomitant decrease of Morozovella. This step is also characterized by enhanced fragmentation and dissolution. The interval corresponding to the main body of the carbon isotope excursion (CIE) is characterized by a marked increase of Acarinina, though with some differences in the species composition and relative abundance, both in high-and low-latitudes, particularly in the Tethyan area. Forada is no exception to this pattern. However, at Forada, two prominent peaks in abundance of acarininids are recorded ca. 30 kyr prior to the onset of the CIE, thus suggesting an increase in temperature heralding the onset of the PETM (phase c). Interestingly, the lower peak in abundance of Acarinina just precedes the 1‰ carbon isotope negative shift occurring below the onset of the main CIE. The basalmost Eocene, corresponding to the lower part of CIE curve, is represented by intense planktonic foraminiferal dissolution, implying an extraordinary rise of the CCD. This interval has an estimated duration of about 16 kyr (phase d). The dominance of acarininids in the lower part of the CIE (phase e, f; ca. 14 and 22.5 kyr) is interpreted as a consequence of the extreme warmth coupled with eutrophic conditions characterizing the Forada depositional environment at that time. These acarininids include at Forada also the temporally constrained Acarinina sibaiyaensis and A. africana. The morphological similarity between these peculiar species with the radially elongated chambered forms characterizing the Cretaceous anoxic events, suggests the hypothesis that depletion of oxygen in the upper water column might have been one of the factors causing their conspicuous occurrence at the PETM. The recovery in abundance of the specialized morozovellids and of other planktonic foraminiferal groups (e.g., biserials, globanomalinids, igorinids, planorotalids and pseudohastigerinids), occurring in the middle part of the CIE (ca. 30 kyr after the onset of the PETM), indicates an initial environmental recovery (phase g). A new stable state is definitely reached in the upper part of the Forada section where the relative proportions of the main component of planktonic foraminiferal assemblages move towards values similar to those of the late Paleocene conditions (phase h). However, the perturbation during the PETM produced significant changes in the ocean geochemistry that endured after the PETM event, as testified by the prominent high carbonate dissolution characterizing the marly levels, and the large variability in relative abundance among different components of the planktonic foraminiferal assemblages. These striking oscillations were not present in the latest Paleocene.

ALVEOLINA HORIZONS IN THE TRENTINARA FORMATION (SOUTHERN APENNINES, ITALY): STRATIGRAPHIC AND PALEOGEOGRAPHIC IMPLICATIONS

In late Paleocene-Eocene times, in the Tethyan area, the shallowest and most restricted carbonates deposited between the intertidal zone and the lower limit of the upper photic zones are characterized by Spirolina -dominated facies. This extremely shallow-water carbonate facies is recorded from the Cenomanian to the Miocene in the Tethyan realm with similar sedimentological characters and similar spiroliniform epiphytic taxa. All these taxa can be considered to reflect some kind of vicariance through time. In Southern Italy this peculiar facies is represented by the Trentinara Formation (Lower-Middle Eocene); in several stratigraphic sequences of this formation, three levels containing alveolinids were identified. The first is well known in the literature and allows us to assign the lowermost part of the Formation to the lowermost Ypresian (bio-chronozone SBZ 6, Alveolina ellipsoidalis zone); the second is not age diagnostic because alveolinids are rare and poorly preserved; the third allows the age of the upper part of the Trentinara Formation to be established as Early Lutetian (bio-chronozone SBZ 13, Alveolina stipes zone). The exact age of the top of the formation is still unclear, but probably falls within the Lutetian-Priabonian interval. The geographic locations of the most significant shallow-water carbonates of Early-Middle Eocene age, cropping out in the southern Apennines, have led to a first attempt to map their distribution within the central gyre of western Tethys.

Bajocian Ostracoda of Western Australia and their faunal affinities

The ostracod assemblages from the Newmarracarra Limestone Formation (Early Bajocian, Western Australia) are highly unusual in being formed exclusively by members of the superfamily Cytheroidea. They are also apparently composed dominantly of endemic taxa, with three new genera defined here (Bringocythere, Fistulosacythere, Gondwanacythere) and only three other genera known from elsewhere in the southern Tethyan area (AmicytherideaBate 1975,MandawacythereBate 1975,ParadoxorhynchaChapman 1904). Eight species represented by very limited material are tentatively compared with Northern Hemisphere genera but their real affinities are uncertain. The assemblages have little in common with the few records of Southern Hemisphere Middle Jurassic material described from Argentina and elsewhere.

The regional record of Albian oceanic anoxic events at the Apulian Platform Margin (Gargano Promontory, southern Italy)

The Gargano Promontory, located on the eastern margin of the Apulia Platform, represents a distinctive Tethyan area where the transition from carbonate platform to adjacent basin is exposed on land. The Albian stratigraphic record, represented by shallow-water, slope and deep-water deposits, provides a good opportunity to investigate the regional response to oceanic anoxic events (OAEs) in different depositional settings by using an integrated, high-resolution micropalaeontological (planktonic foraminifers and calcareous nannofossils) approach. Results show that organic matter preservation is confined to the more distal areas (Marne a Fucoidi Formation), and consists of black shale intervals from the middle and late Albian ( Ticinella primula/Prediscosphaera columnata Zones; upper Ticinella praeticinensis Subzone/ R. achlyostaurion Zone, respectively). Integrated biostratigraphic data correlate the intervals of black shale deposition to the Urbino and Amadeus levels, previously identified and named in the Umbria-Marche Basin. These black shales record the effects of OAEs 1b and 1c. The biotic changes in the pelagic Albian succession of the Apulian Platform Margin provide evidence for episodes of eutrophication that correlate to the deposition of these black shales. Genetic models for the two episodes of organic matter preservation are proposed, taking into account both global and local controlling factors.

Regional record of a global oceanic anoxic event: OAE1a on the Apulia Platform margin, Gargano Promontory, southern Italy

The Gargano Promontory of southern Italy, located on the eastern margin of the Apulia Platform, represents a peculiar Tethyan area where the transition between carbonate platform and adjacent basins is exposed on land. The Aptian stratigraphic record, represented in shallow-water, slope and deep-water deposits, provides a good opportunity to investigate the regional response to the worldwide documented climatic, biotic and palaeoceanographic changes related to Oceanic Anoxic Event 1a (OAE1a). A synthesis of data previously published (Ischitella and Coppitella sections), together with original data (Val Carbonara and Coppa della Guardia sections), from four stratigraphic sections from different depositional settings (proximal to distal) is provided, using an integrated, high-resolution micropalaeontological (planktonic foraminifera and calcareous nannofossils) and, for one section, geochemical (stable carbon and oxygen isotopes) approach. Organic matter preservation is confined to the more distal areas and consists of two thin intervals of black shales in the Aptian portion of the Marne a Fucoidi Formation. Biostratigraphic data assign the older black shale (5 cm thick) to the Selli Level equivalent (OAE1a, Lower Aptian); this carbon-rich interval is immediately followed by another black shale (7–10 cm thick) of early Late Aptian age. OAE1a is generally interpreted as a high-productivity event during a warming interval, followed by a cooling trend. In the Gargano Promontory, although the oxygen isotope curve indicates the above-mentioned climatic evolution, the micropalaeontological data do not support high fertility of the surface water, whereas micropalaeontological and geochemical data for the younger black shale do record high productivity (radiolarian increase in overall abundance, low nannofossil and foraminiferal species richness, increase in abudance of nannofossil fertility indices) associated with a cooling trend. The carbon and oxygen isotope record is in line with evidence from the curves documented elsewhere, whereas, among the biotic events, only the “nannoconid crisis” preceding OAE1a is revealed to be globally correlable. Environmental models for the two episodes of organic matter preservation are proposed, taking into account both global and local controlling factors.

A NEW EARLY JURASSIC RHYNCHONELLID BRACHIOPOD FROM THE WESTERN TETHYS AND IMPLICATIONS FOR SYSTEMATICS OF RHYNCHONELLIDS FROM THE TRIASSIC–JURASSIC BOUNDARY

A new multicostate rhynchonellid brachiopod Jakubirhynchia occurs in the Hettangian (Early Jurassic) carbonate deposits of the West Carpathians. A comparison with externally similar multicostate rhynchonellids from the Hettangian-Sinemurian carbonate deposits of the Alps shows their congeneric and conspecific status, indicating relatively wide regional distribution in the Early Jurassic of the western Tethys. Diagnostic characters include conjunct deltidial plates, divided, vertically inclined inner hinge plates forming sessile septalium, and subfalciform crura with relatively complex, serrate terminations and broad outline in lateral view. Although the shape of hinge plates and crura may vary according to shell convexity and shell orientation during serial sectioning, two-dimensional restorations of cardinalia and crura show their distinctive morphology. It is important to note that some of the cardinalia details and crural shape can be detected only with very short between-section distances. Based on external characters, Jakubirhynchia is a homeomorph to another multicostate rhynchonellid, Calcirhynchia, typical of the Hettangian and Early Sinemurian of the northwestern Europe province and reported also from the Tethyan province. This suggests that original distribution of Calcirhynchia might not be so wide and postextinction multicostate rhynchonellids were taxonomically more diverse as was previously supposed. Jakubirhynchiaconsistently occupies offshore, low-energy, micritic-rich habitats below storm wave base. It is the first reported Hettangian member of the family Basiliolidae and may bridge the gap between the Carnian Veghirhynchia and Early Jurassic basiliolids. Preextinction, Norian and Rhaetian brachiopods that are close morphologic relatives of Jakubirhynchia are known from outside the western Tethyan area only.

Coniacian–Santonian Radiolaria from the Upper Cretaceous of Bornholm, Denmark: A preliminary investigation

A moderately diverse fauna of Late Cretaceous Radiolaria are described for the first time from the Arnager Limestone and Bavnodde Greensand formations exposed on the island of Bornholm (Denmark). Our preliminary investigation suggests that the fauna from the Arnager Limestone Formation is relatively abundant and is assigned to the Orbiculiforma vacaensis Subzone (Alievium praegallowayi Zone) of Coniacian age. Relatively poor recovery from the Bavnodde Greensand Formation precludes assignment to the zonation scheme of Pessagno, although, the radiolarian taxa present indicate that the formation can be no younger than Santonian. The ages given for both formations by the radiolarian faunas compare favourably with published macrofossil and microfossil data. The radiolarian faunas described are of moderate abundance and diversity when compared to contemporaneous faunas described elsewhere, particularly the Tethyan area. Maximum radiolarian abundance and diversity is reached in the middle of the Arnager Limestone Formation equating to a level of maximum water depth from the foraminiferal data. A decline in radiolarian recovery is recognised into the Bavnodde Greensand Formation and is associated with a reduction in relative water depth to inner and (?)middle shelf conditions, as indicated by foraminiferal data.

LATE CRETACEOUS PLANKTONIC FORAMINIFERAL BIOEVENTS IN THETETHYS AND IN THE SOUTHERN OCEAN RECORD: AN OVERVIEW

The Late Cretaceous planktonic foraminiferal distribution recorded at several drill sites (Deep Sea Drilling Project and Ocean Drilling Program) in the South Atlantic and south Indian Ocean and from sediment outcrops in the Tethyan region (Gubbio and El Kef) have been analyzed in order to investigate the presence of a similar sequence of bioevents occurring at low, middle, and high latitude. Comparative analysis highlights the co-occurrence of several bioevents; some of them are isochronous bioevents occurring in the Tethys and in the Southern Ocean record, whereas others are diachronous across latitudes but can be used for correlation at regional scale, as they show the same stratigraphic distribution in the South Atlantic and Indian Ocean record. Isochronous bioevents are the first and the last occurrence of Helvetoglobotruncana helvetica , and the first appearance of Falsotruncana maslakovae in the lower-middle Turonian. The first occurrence of Heterohelix papula in the Southern Ocean sites, correlated with the first occurrence of large heterohelicids in the Tethyan area, allows the Coniacian/Santonian boundary to be identified. The most reliable bioevents useful for correlation at a regional scale in the Southern Ocean record are the last occurrence of the marginotruncanids in the upper Santonian, the first and the last occurrence of Globigerinelloides impensus from the uppermost Santonian to upper Campanian, the first occurrence of Heterohelix rajagopalani in the middle-upper Campanian, and the appearance of Abathomphalus mayaroensis in the lower Maastrichtian.

Sequence stratigraphy and correlation of late Carboniferous and Permian in the CIS, Europe, Tethyan area, North Africa, Arabia, China, Gondwanaland and the USA

Sequence stratigraphy was used to correlate the depositional chronology during Permo–Carboniferous time in various sedimentary basins of Gondwanaland, western Europe, eastern Europe, Tethyan area, North Africa, Arabia, China, and North America. During late Carboniferous and Permian, eleven second-order sequences (SOS) were recognised throughout the whole area. The sequence SI is Serpukhovian pp, Namurian A pp and Chesterian. The sequence SII is Serpukhovian pp–Bashkirian pp, Namurian A pp-B-C–Westphalian A–B pp and Morrowan. The sequence SIII is late Bashkirian–Moscovian, Westphalian B pp-C-D and Atokan–Desmoinesian. The sequence SIV is Kasimovian, early Stephanian and Missourian. The sequence SV is Gzhelian–Orenburgian, late Stephanian and Virgilian. The sequence SVI is Asselian, Autunian and Nealian. The sequences SVII–IX are Saxonian, Sakmarian–Artinskian–Kungurian and Leonardian–Hessian–Cathedralian. The sequences SX–XI are Guadalupian and Lopingian. Depending on the regional setting, different relationships exist between marine transgression and the respective effects of tectonics and of sea-level changes: in western Europe, effects of the glacial processes in Gondwanaland are partly balanced by the late compression in the Hercynian belt during Moscovian. Eastern Europe, Tethyan area, North Africa, China, and North America show a good correlation between glacial (ice melting) processes in Gondwanaland and the intensity of the transgression which is increased by the westward progradation of the orogeny in Urals and Appalachians. In Arabia, Tunisia and Tethyan area, the impact of the Neotethys opening is obvious from the Artinskian and mainly during the late Permian.

Significance of modern and ancient oceanic Mn-rich hydrothermal sediments, exemplified by Jurassic Mn-cherts from Southern Greece

Abstract This paper considers the occurrence of Mn-oxide-rich hydrothermal deposits in the modern oceans and presents a case history of Jurassic Mn-cherts from a Tethyan area in Southern Greece. Manganese-oxide hydrothermal sediments are known from a wide variety of oceanic settings, including both on and off the axis of spreading ridges, in back-arc basins, arc-related areas, rifts and in small ocean basins. These Mn-rich sediments differ markedly from the chemical composition of better known metalliferous deposits associated with high-temperature black smokers (i.e. Fe-rich ochres and Fe-Mn-rich umbers). The ancient example discussed in detail here is that of Late Jurassic Mn-rich cherts spatially associated with basic-intermediate composition volcanics within sutured oceanic units in the Peloponnese, S Greece. The Mn enrichment there is interpreted as related to hydrothermal activity associated with Late Jurassic off-axis volcanism, rather than to a spreading ridge source. The Mn is strongly fractionated from Fe and is concentrated in thin beds and laminations, interpreted as of primary depositional origin. The silica is assumed to be mainly biogenic, as reflected in an association with red radiolarian cherts. The source hydrothermal activity is likely to have been of low-temperature type. Similar Mn-oxide deposits occur elsewhere in the Mesozoic Tethyan area, including N Greece, SW Turkey, Cyprus and Oman, and in other orogenic belts (e.g. in California). There are also metamorphosed counterparts of Mn-rich hydrothermal deposits that include metalliferous pelites and cherts; e.g. Cyclades, S Greece and Franciscan Complex, California. The record of deep-sea hydrothermal deposits exposed on land following tectonic emplacement is biased towards off-axis Mn-deposits within abyssal sediments, since axial spreading ridges (including massive sulphides, umbers and ochres) are rarely preserved, owing to subduction.

Soritidés éocènes à costulation et/ou lames sous-épidermiques discrètes : les genres Spirolina, Praerhapydionina et Paraspirolina n. gen. dans le « Faciès à imperforés de l'Éocène moyen à supérieur de Grèce

In the Gavrovo-Tripolitza zone of Greece, the «Faciès à imperforés indicates a peculiar back-reef to lagoonal sedimentation episode succeeding a bauxitogenous emersion. The foraminiferal association comprises several arenaceous conical taxa, a lot of miliolids, a species close to Praebullalveolina afyonica, various Peneroplis and/or Dendritina, Spirolina and Praerhapydionina species, scarce small Orbitolites and Rhabdorites malatyaensis. The similarity of this association with others from various parts of the Tethyan area gives evidence for a generalized regressive episode linked to the terminal Middle Eocene tectonic phase. From this association, presence of a new taxon is emphasized : Paraspirolina gigantea n. gen., n. sp. is characterized by an external aspect of a large Spirolina, a single dendritic terminal aperture and the very unusual association of external ribs with sub-epidermal partitions. Both of these last features appearing as independent adaptive devices related to algal symbiosis, their conjunction seems to characterized a singular evolutionary grade in a particular lineage. A single terminal aperture, together with a common tendency to develop an uniserial evolute rectilinear final part (PRU) seems to show a link between the new taxon, several Eocene soritids of the Old World, namely various Spirolina species (devoid of sub-epidermal partitions) and various species assigned to Praerhapydionina (with sub-epidermal partitions, one of them, P. huberi, being reported as ribbed); they are thought to constitute a natural group (a plexus or a sub-family).

The presence of Dinogymnium (Dinophyceae) in Lower Cretaceous sediments from the northwest Tethys (southeast France and western Switzerland) and Gulf of Mexico areas: stratigraphic and systematic consequences

Palynological investigations of two Lower Cretaceous surface sections from the northwestern Tethyan area, Châtel-Saint-Denis (western Switzerland) and Vergons (southeast France), have yielded specimens of the fossil dinoflagellate Dinogymnium. These established in-situ occurrences in Hauterivian ammonite-dated sediments represent the first formal record of this genus in the Lower Cretaceous in the Tethyan area. A re-examination of the assemblages studied by Riley and Fenton (1984) from DSDP Site 535 in the Gulf of Mexico, has confirmed the in-situ occurrence of Dinogymnium in Upper Berriasian, Valanginian and Hauterivian sediments. Their comparison with the Tethyan material establishes the occurrence of Dinogymnium in the Lower Cretaceous of the Tethys-Atlantic area and leads us to reconsider the earliest occurrence of Dinogymnium which was previously generally accepted to be at the base of the Upper Cretaceous. Two new species are erected: Dinogymnium aerlicum and Dinogymnium vergonsense. Morphological, stratigraphical and palaeogeographical comparisons are made with other rare Early Cretaceous records of Dinogymnium, as well as with other, younger species of the genus.

Alternative tectonic models for the Late Palaeozoic-Early Tertiary development of Tethys in the Eastern Mediterranean region

Abstract A summary and discussion is given of alternative models of the tectonic evolution of the Tethyan orogenic belt in the Eastern Mediterranean region, based on recent information. Model 1 (Robertson & Dixon 1984). A single Tethyan ocean continuously existed in the Eastern Mediterranean region, at least from Late Palaeozoic onwards. The dominant influences were episodic northward subduction of Tethyan oceanic crust beneath Eurasia, and the northward drift of continental fragments, from Gondwana towards Eurasia. During the Mesozoic, the south Tethyan area was interspersed with Gondwana-derived microcontinents and small ocean basins. Ophiolites formed mainly by spreading above subduction zones in both northerly (internal) and southerly (external) oceanic basins during times of regional plate convergence, and were mainly emplaced as a result of trench-passive margin collisions. In a related model, Stampfli et al. (1991) argued for spreading along the North African margin in the Late Permian. Model 2A (Dercourt et al. 1986). Only one evolving Tethys existed. Triassic-Jurassic oceanic crust (Neotethys) formed in a single Tethyan ocean basin located north of Gondwana-related units. Spreading later formed a small ocean basin in the present Eastern Mediterranean Sea area during the Cretaceous. Jurassic and Cretaceous ophiolites formed at spreading ridges and record times of regional plate divergence. In an update version, Model 2B (Dercourt et al. 1993), spreading extended along the northern margin of Gondwana, with an arm extending through the south Aegean, splitting off a large microcontinent. Further spreading in the Cretaceous then opened the Eastern Mediterranean basin and fragmented pre-existing carbonate platforms. The Mesozoic ophiolites were seen as being mainly far-travelled from northerly (i.e. internal) orogenic areas. Model 3 (Şengör et al. 1984). Subduction in the Late Palaeozoic was dominantly southwards, beneath the northern margin of Gondwana in the Eastern Mediterranean. This subduction led to opening of Triassic backarc basins; and a rifted Gondwana fragment (Cimmeria) drifted across a pre-existing Tethys (Palaeo-Tethys) to collide with a passive Eurasian margin. In their model, a backarc basin (Karakaya Basin) rifted and then closed prior to collision of a Cimmerian microcontinent in the Mid Jurassic, and this was followed by renewed rifting of a small ocean basin in the Early Jurassic. Mesozoic ophiolites mainly formed above subduction zones; they were variously seen as far-travelled (in the ‘Greek area’), or more locally rooted (in the ‘Turkish area’). Recent evidence shows that difficulties exist in detail with all three models. However, four key elements are met in Model 1: dominantly northward subduction in the north; multiple ocean basins from Triassic onwards in the south; supra-subduction spreading of the major ophiolites; and emplacement from both northerly and southerly Mesozoic oceanic basins. Palaeomagnetism has played an important role, in setting the large-scale Africa-Eurasia relative motion framework and in providing tests for the tectonic affinities of smaller units, but such smaller-scale studies have often been compromised by the geological complexity and by the remagnetisation of tectonically thickened units.

Development of concepts concerning the Troodos ophiolite and adjacent units in Cyprus

Abstract The foundations for study of the Troodos ophiolite and adjacent units in Cyprus were laid down by systematic mapping by the Cyprus Geological Survey Department (1952–1970). Prior to the late 1950s, Cyprus geology was interpreted in classic geosynclinal terms. The first, integrated description of the Troodos was given by Gass & Masson Smith in 1963. Publication of the Vine & Matthew’s (1963) sea-floor spreading hypothesis was followed by Ian Gass’s key interpretation in 1968 of the Troodos as oceanic lithosphere formed by sea-floor spreading. During the early 1970s, the dominant view of the Troodos was of a mid-ocean ridge, formed by spreading at a narrow, linear spreading zone, fed by a single, axial magma chamber. However, early geochemical studies suggested that genesis could have taken place above a subduction zone. During the 1980s, drilling related to the International Cyprus Crustal Study Project stimulated much new field work. By 1990 a popular view of the Troodos was that it had formed above a northward-dipping subduction zone during the earlier stages of convergence within an oceanic basin, similar in some respects to the origin of SW Pacific forearcs. Others favoured an origin as a marginal basin formed by spreading above a southward-dipping subduction zone, either in the vicinity of Cyprus, or located in central Turkey. In whatever scenario, it is generally accepted that the spreading fabric was unstable and was fed by small, multiple magma chambers. The extension outpaced magma supply and this favoured extensional detachment faulting, mainly near the base of the sheeted dykes. The Troodos lithosphere was also bounded by an oceanic fracture zone to the present south. Studies of the Late Cretaceous-Recent sediment cover have documented deep-sea sedimentation and later uplift, related to Africa-Eurasia convergence. In W Cyprus, the adjacent Mamonia Complex was pieced together as a Mesozoic passive margin bordering a small ocean basin, although whether this was a Red Sea-type basin, or a backarc marginal basin is still debated. The Mamonia lavas and sediments were juxtaposed with the Troodos ophiolite by processes, variously interpreted as subduction/accretion, oceanic transform faulting, strike-slip, collision and/or palaeorotation of a Troodos microplate. The Kyrenia Range in N Cyprus also includes remnants of Mesozoic passive margin; it was emplaced in stages apparently by a combination of strike-slip and thrusting. On a regional scale, the Troodos ophiolite preserves part of one of a number of inferred small oceanic basins within the Mesozoic Tethyan area of the Eastern Mediterranean.

Late Triassic-Early Jurassic Calcareous Nannofossils of the Queen Charlotte Islands, British Columbia

Abstract. Sediments of the Kunga and Maude groups (Early Norian-Aalenian) from the Queen Charlotte Islands, British Columbia, have yielded the first records of early Mesozoic calcareous nannofossils in North America. These occurrences are the only record of Triassic nannofossils away from the recent discoveries in the Tethyan area (Austria, Indonesia, and the northwestern Australian margin). The nannofossil assemblages from the Queen Charlotte Islands are generally poor to moderately preserved, with species diversities typical for this time interval (2–10 species). The assemblages are comparable to those from northwest Europe, for the Lower Jurassic, and to those from Austria, Indonesia, and the Australian margin, for the Upper Triassic. They show compatible stratigraphical ranges, allowing the application of existing biostratigraphical zonations. Palaeobiogeographical interpretations are inconclusive and fail to positively confirm a low latitude (Tethyan) position for the Queen Charlotte Islands, as indicated by macrofossil data. However, Triassic nannofossil assemblages have yet to be described from high palaeolatitude locations. In addition, certain features of the Lower Jurassic assemblages may indicate Tethyan affinities but also distinguish these assemblages from those which have been previously documented. These features include the absence of Schizosphaerella punctulata, which occurs abundantly in the circum-Mediterranean region and was previously thought to be “cosmopolitan” in distribution; and the absence of Mitrolithus jansae which characterizes “Tethyan” assemblages in the circum-Mediterranean area. The Queen Charlotte Islands results are compared with new nannofossil data from Argentina, Timor and North America.

Les Ostracodes du Jurassique moyen-Néocomien du Bassin de Majunga (Madagascar)— Comparaison avec les autres faunes gondwaniennes

These studies concern the ostracod faunas obtained from the Mid-Upper Jurassic beds and the Neocomian of theTsaramandroso region (Majunga Basin, Madagascar). Similar studies were, made with formanifers and calcareous nannofossils in the same sediments by the author. The macrofossils (ammonites and belemnites) sampled were determined by other specialists. The systematic study has resulted in a list of different forms occuring in the Callovian to Aptian. From the species listed, considering the macrfauna when present, four distinct assemblages come out: two of them from the Jurassic (one from the Middle Callovian and the other from the Lower Oxfordian) and two others from the Cretaceous (one from the Valanginian and the other from the Hauterivian). A comparison of the faunas of these studies with those of nearby regions reveals that there are some faunal assemblages which confirm an “Ethiopian” or “Indo-Malgache” paleobiogeographic province, within the southern Tethyan area.