Latest Bajocian-early Bathonian Research Articles

Bajocian–Bathonian dinoflagellate cyst assemblages from the Middle Atlas, Morocco: Palynostratigraphic and paleoenvironmental implications

The Bajocian–Bathonian transition has been identified for the first time in the Skoura syncline of the folded Middle Atlas of Morocco based on dinoflagellate cyst and palynofacies analysis of the Ich Timellaline/Bou Akrabene Formation carbonates. This palynological study involved 109 samples of marls and limestones whose organic content yielded diverse and well-preserved dinoflagellate cyst assemblages comprising 68 taxa including stratigraphic marker taxa. Two association biozones have been defined for the late Bajocian–early Bathonian interval. The Cribroperidinium crispum-Ctenidodinium cornigerum (CC/CC) biozone is defined between the base of the Recifa Formation (Upper Bajocian) and the Ich-Timellaline / Bou Akrabene Formation (Upper Bajocian–Lower Bathonian). The second association biozone of Ctenidodinium combazii and Dichadogonyaulax sellwoodii (CC/DS) corresponds to the upper interval of the FD section (top of the Ich-Timellaline / Bou Akrabene Formation and the base of the El Mers I Formation). These two biozones were correlated with the late Bajocian–early Bathonian biozones defined in the Sub-Boreal (northwest Europe), Tethyan, and Australian domains. Close similarity between the Moroccan Middle Atlas, the Tethyan, and the Sub-Boreal domain associations has been noted. Quantitative analysis of organic matter constituents has allowed the paleoenvironmental reconstruction of the late Bajocian–early Bathonian. The organic residues of the studied samples recorded an increased land-derived phytoclasts dominance compared to amorphous organic matter and palynomorphs, indicating a proximal oxic shelf depositional environment with high terrestrial and freshwater influx during the late Bajocian–early Bathonian. During the Late Bajocian, the depositional environment corresponds to a proximal continental shelf with fluctuations from a distal to a marginal/stagnant environment.Below the Upper Bajocian–Lower Bathonian boundary, a significant marine incursion, or rather a transgression, is recorded in the studied sediments attested by an important marine fraction and dinoflagellate cysts abundance, which probably corresponds to the last Bajocian Maximum flooding surface (MFS).During the early Bathonian, the depositional environment evolved towards a distal continental shelf with an increasing marine fraction including dinoflagellate cysts and high species diversity. This may be related to the rising sea level which corresponds to the first Bathonian eustatic elevation. The proximal /marginal conditions are restored at the uppermost part of the section.

Ammonites and infrazonal stratigraphy of the lower bathonian besnosovi zone of the Russian plate

Ammonites and deposits of the Lower Bathonian Besnosovi Zone of the central and southern regions of the Russian Plate are studied. The paper discusses the infrazonal stratigraphy and correlation of two reference sections: the Pletnyovka Quarry in the north of the Penza oblast and the Sokur Quarry near the city of Saratov. The successive biohorizons Oraniceras issae, O. calvum, and O. besnosovi are recognized on the basis of ammonites of the genus Oraniceras (family Parkinsoniidae) in the Besnosovi Zone. Provisional O. mojarowskii and O. scythicum biohorizons are proposed below the above-mentioned biohorizons, whereas the O. cf./aff. besnosovi Biohorizon is proposed above them. The Besnosovi Zone corresponds to the middle part of the Western European Zigzag Zone. The Michalskii Zone underlining the Besnosovi Zone apparently corresponds to the Bajocian–Bathonian boundary interval. It is suggested that only one A. excentricum migrational biohorizon, corresponding to the upper part of the O. besnosovi Biohorizon and correlating with the lowermost part of the Ishmae Zone of the Boreal scale, can be established on the basis of Boreal ammonites of the genus Arcticoceras in the Sokur Section. Central Russian representatives of the genera Oraniceras [M] and Sokurella [m] are assigned here to the subfamily Pseudocosmoceratinae that is eudemic to the Central Russian late Bajocian–early Bathonian sea. It is suggested that the above-mentioned genera evolved from Pseudocosmoceras [M and m] that is cryptogenic neoendemic of the East European Peritethyan marine basin. New species are described: Oraniceras issae sp. nov. [M], O. calvum sp. nov. [M], Sokurella pletniovkae sp. nov. [m], and S. elshankae sp. nov. [m].

New evidence of xiphosurids from the Middle Jurassic of Morocco: Palaeoenvironmental, palaeoecological and palaeobiogeographical implications

Horseshoe crabs (Chelicerata, Xiphosura) from Mesozoic deposits are extremely rare in the fossil record of the African continent. Here we report new evidence of the occurrence of xiphosurans in North Africa. These are horseshoe crab traces, including the ichnogenera Kouphichnium (repichnia) and Selenichnites (fodinichnia and/or domichnia), which have been discovered in Middle Jurassic strata of the Imilchil area (Central High Atlas, Morocco). They are preserved on upper and lower bed surfaces of sandy limestones and marls in the upper parts of the Tislit and Imilchil formations (late Bajocian-early Bathonian).The Selenichnites traces, measuring up to 30 cm in width, co-occur with theropod and birdlike tracks. The reported Kouphichnium is the first record from Mesozoic deposits of Morocco, while Selenichnites is the second occurrence in Jurassic strata of Africa. These ichnogenera evidence different behaviour of horseshoe crabs, i.e. Selenichnites is the result of burrowing activity when searching for food in the sediment, and Kouphichnium is a regular locomotion trace left on the sediment surface, occasionally leaving an impression of the telson.The combination of sedimentological data and ichnological analysis indicates a shallow-water subtidal depositional environment preceding the Bathonian regression of the Atlas domain.Palaeobiogeographically, the discoveries indicate the presence of horseshoe crabs at the southern margin of the Tethys. Furthermore, they enhance our knowledge of their previously scarcely documented distribution in Gondwana during the Mesozoic.

Gabaleryon, a new genus of widespread early Toarcian polychelidan lobsters

Polychelidan lobsters are decapod crustaceans with a unique anatomy: a dorsoventrally flattened carapace, four to five pairs of chelate appendages and a completely reduced rostrum. These crustaceans, like most other malacostracans, are mostly preserved in outcrops in which exceptional preservation occurs, Fossil-Konservat-Lagerstätten. Unfortunately, Lagerstätten are rare, and therefore disjointed both geographically and stratigraphically. This study focuses on a new genus of polychelidan lobster, Gabaleryon gen. nov., with the description of two new Toarcian species, Gabaleryon coquelae sp. nov. from France and G. garassinoi sp. nov. from Italy. The long-standing question of the generic assignment of Eryon moorei (Toarcian, UK) is resolved and the species is ascribed to Gabaleryon. The occurrences of these three species and a fourth, Gabaleryon sp. 1 (Toarcian, Germany), provide a first palaeobiogeographical indication that the Fossil-Lagerstätten in which they occur were linked during Toarcian times. The occurrence of a possible fifth species of Gabaleryon in the late Bajocian–early Bathonian of France may extend the stratigraphical distribution of the new genus. Finally, these new species increase our knowledge of fossil polychelidans and place the Toarcian as their second peak of palaeobiodiversity, after that at the Kimmeridgian–Tithonian boundary.http://zoobank.org/urn:lsid:zoobank.org:pub:073513BD-A0D8-4A5B-B9DE-1C61781077DC

Biostratigraphy and sedimentary settings of the Upper Bajocian-Lower Bathonian in the vicinity of Saratov (Central Russia)

This paper presents the results of a detailed study of the Bajocian-Bathonian sections in the “Sokur” Quarry near the city of Saratov and of a borehole drilled in the same quarry. The study of these Bajocian-Bathonian boundary beds, unique for the Boreal-Tethyan ecotone, offers a solution to the much-debated problem of the Middle Jurassic Boreal-Tethyan correlation. The BajocianBathonian boundary beds of this section contain both Peri-Tethyan and Boreal ammonite species, allowing recognition of the Boreal ammonite zones and associated “Boreal” Bathonian zones based on belemnites, bivalves, and foraminifers. This integrated biostratigraphy allows correlation of the Late Bajocian-Early Bathonian boundary interval of the Boreal Jurassic scale with the Submediterranean standard scale.

New age data from the tectonostratigraphic units of the Istranca “Massif” in NW Turkey: a correlation with SE Bulgaria

Abstract The Istranca Crystalline Complex in NW Anatolia and SE Bulgaria includes structural units that differ in lithostratigraphy, metamorphism, age and structural position. They are collectively named as the “Istranca nappes” comprising from bottom to top the Sarpdere, Mahyadağ and Doğanköy Nappes. The Sarpdere Nappe consists of Lower Triassic arkosic metasandstones with slate interlayers, followed by Middle to Upper Triassic carbonates and an alternation of Upper Triassic clastics and carbonates. The Mahyadağ Nappe comprises a low-grade metamorphic Late Paleozoic- Triassic carbonate-siliciclastic sedimentary succession. The Doğanköy Nappe includes Precambrian?-Paleozoic metasediments, intruded by Late Carboniferous-Early Permian calc-alkaline granitoids. Its Triassic cover comprises metaclastics and metacarbonates. The Istranca nappes were juxtaposed at the end of the Triassic and transgressively covered by Lower Jurassic coarse clastics, followed above by Middle to Late Jurassic carbonates, black shales and carbonate-siliciclastic sedimentary succession. The phosphate concretions in black shales yielded radiolarian assemblages indicating Late Bajocian-Early Bathonian, Early Bathonian and Early Kimmeridgian ages. These nappes and their Jurassic cover are unconformably overlain by the Cenomanian-Santonian volcano-sedimentary successions intruded by Santonian-Campanian Dereköy-Demirköy intrusive suite. The preliminary data suggest that the Variscan basements of the Mahyadağ and Sarpdere Nappes were juxtaposed prior to the Triassic and overridden by the Doğanköy Nappe of possible Rhodopean origin from S to N during the Cimmerian compressional events

RADIOLARIAN AGES FOR THE SEDIMENTARY COVER OF SEVAN OPHIOLITE (ARMENIA, LESSER CAUCASUS)

Age data of Armenian ophiolites are of great importance for understanding the palaeogeographic and geodynamic evolution of Tethys in the Caucasus area and for lateral correlations of Tethyan ophiolitic belts in the Middle East area. Moderately well-preserved radiolarian assemblages obtained during this study from the Sarinar section of eastern Armenia allow to investigate the sedimentary and volcanic history recorded in a ca. 30 m-thick radiolarite sequence associated with spilitic lavas of the Sevan ophiolitic suture zone. The latest Bajocian-early Bathonian assemblage yielded from a sample situated close to the base of the studied sequence suggests that radiolarian ooze accumulation took place on oceanic crust of late Middle Jurassic age (probably Bajocian). Several tuffite levels are intercalated within the lower to middle part of the radiolarite sequence; a late Bathonian-early Oxfordian assemblage from a sample taken just below the uppermost tuffitic bed, suggests that during this time the oceanic domain of Sevan ophiolites was close to subaerial volcanic activity.

OPHIOLITES FROM THE GRAMMOS-ARRENES AREA, NORTHERN GREECE: GEOLOGICAL, PALEONTOLOGICAL AND GEOCHEMICAL DATA

The Grammos-Arrenes ophiolites crop out between the Pindos Flysch to the East and the Meso-Hellenic basin to the West and represent the northernmost exposure of the Pindos Ophiolite belt in Greece. Field work and sampling on key outcrops of the Sub-ophiolitic Melange provided new data on the oceanization age and on the geochemistry of the effusive products. The basalts samples show a N-MOR affinity and are associated with latest Bajocian-early Bathonian radiolarian cherts. Emplacement of the ophiolites onto the continental margin is preceded by mass flow deposition of ophiolitic material in the basins facing the advancing ophiolitic nappe. Ophiolite-bearing debris flow deposits and slide blocks are recognized in the Early Cretaceous deep water sediments of the Beotian Unit and in the upper portion of the Tertiary Pindos Flysch. The intercalations of ophiolitic material in the Beotian Flysch first, and in the Pindos Flysch, later, are interpreted as the forerunners of the Ophiolitic Nappe which derived from the Vardar Ocean to the east, and was emplaced westwards onto the Adria continental margin. The collected data allow consolidating the constraints for the timing and mechanism of ophiolite emplacement in the Pindos-Grammos area. In addition, taking into consideration the geometry of the tectonic stack in the Grammos-Arrenes area and the ages of the involved sedimentary deposits it is possible to reconstruct a geodynamic history comparable to that of the other zones studied along the Dinaric-Hellenic Chain.

The upper Bajocian-Lower Bathonian of Pechora River basin and Boreal-Tethyan correlation

Distribution of ammonites in the Bajocian-Bathonian boundary beds of the Izhma River basin is considered. A new scheme of zonal subdivisions suggested for the Pechora basin includes the Arctocephalites arcticus Zone of the upper Bajocian and the Arctocephalites greenlandicus-Arcticoceras ishmae Zone of the lower Bathonian. The Dreshchanka Formation age (late Bajocian-early Bathonian) and the commencement time of the Boreal sea transgression (Late Bajocian) are specified. Correlation of the Bajocian-Bathonian boundary strata of the northern Caucasus, central and northern Russia with stratigraphic scales of Western Europe and East Greenland are discussed. New infrazonal subdivisions, i.e., the faunal horizons, are described. As is shown, the parkinsoni-zigzag zonal boundary accepted to be the Bajocian-Bathonian boundary in standard scale corresponds to boundaries separating the michalskii and besnosovi zones in the Lower Volga region and the arcticus and greenlandicus zones in the Boreal areas.

NEW DATA ON THE AGE OF THE SIMONI MELANGE, NORTHERN MIRDITA OPHIOLITE NAPPE, ALBANIA

In the Albanian sector of the Dinaric-Hellenic Chain, the ophiolites have been subdivided into two parallel belts: the Western Belt (WB) and the Eastern Belt, due to their different stratigraphical, petrological and geochemical characteristics: WB represents oceanic lithosphere generated at a mid-oceanic ridge (MOR ophiolites), EB represents an oceanic basin developed over a subduction zone (SSZ ophiolites) (ISPGJ-IGJN, 1990; Beccaluva et al., 1994; Bortolotti et al., 1996, and bibl. therein). EB overthrust westwards WB. The radiolarian cherts (Kalur Cherts) covering the volcanites of both the successions have the same ages, comprised between latest Bajocian-early Bathonian (UAZones 5 of Baumgartner et al., 1995) and middle Callovian-early Oxfordian (UAZones 8) (Chiari et al., 2004, and bibl. therein). Thin levels of radiolarian cherts intercalated in the basalts of EB have late Bajocian to latest Bajocian-early Bathonian ages (UAZones 4-5) (Chiari et al., 1994 and Chiari et al., 2004). A “blocks in matrix-type” sedimentary melange, the Simoni Melange, unconformably covers both the successions, indistinctly lying on the radiolarian cherts or on the upper portions of the underlying volcanites (Bortolotti et al., 1996; Carosi et al., 1996). It grades upwards to the Firza Flysch (latest Tithonian-Valanginian age after Shallo 1991; Gardin et al., 1996), a pelagic sediment with frequent ophiolitebearing polimict pebbly sandstones and mudstone intercalations. The melange includes blocks of different sizes (up to several hundred meters) of continental derived (predominant) and ocean derived rocks, in a shaly matrix. It can be interpreted as “syn-orogenic....deposited after the inception of ophiolite deformation” (Bortolotti et al., 1996). The age of the melange was indirectly determined, being comprised between middle Callovian-early Oxfordian, the more recent age found at the top of the Kalur Cherts (Marcucci and Prela, 1996), and the latest Tithonian-early Berriasian?, found at the base of the Firza Flysch (Gardin et al., 1996). The aim of this note is to present new biostratigraphical data that define a more precise age of the Simoni Melange, dating a cherty-silty level found at the top of the Kalur Cherts near the Lumi i Zi (northern Albania).

Bathonian radiolarians from an ophiolitic melange of the Alpine Tethys (Gets Nappe, Swiss-French Alps)

The determination of radiolarite ages of supraophiolitic rocks date the expansion age of oceanic crust. Radiolarites from the Gets nappe, a decollement cover nappe, provide the means of dating selected localities of outcropping oceanic crust based on their radiolarian faunas. Some studied samples from the ophiolitic melange (Perriere series) have a very well preserved and highly diverse radiolarian fauna of biochronological significance. The age of the radiolarites is established by correlation with the biozonation of Baumgartner et al. (1995b), which indicates a Bathonian age for the oldest radiolarian assemblages. Accordingly, these radiolarites represent remains of the oldest sediments recorded after the opening of the Piemont-Ligurian Ocean. This age is in agreement with those recently established by isotopic methods (166 ± 1 Ma U-Pb and 165.9 ± 2.2 Ma 40 Ar/ 39 Ar) in the associated gabbros from the ophiolitic melange. The isotopic age and paleontological results are important because they represent the oldest dating of the oceanic crust of the Piemont-Ligurian Ocean, proving a Late Bajocian-Early Bathonian age for the oceanization in the western Tethys. The systematic part presents a complete Bathonian radiolarian assemblage from two of the best preserved samples; the illustrated assemblage contains 180 species attributed to 66 genera (44 nassellarians, 22 spumellarians and 1 entactinarian). Twenty new species and three new genera ( Helvetocapsa, Plicaforacapsa and Theocapsomella ) are formally described.

Downhole magnetic measurements of ODP Hole 801C: Implications for Pacific oceanic crust and magnetic field behavior in the Middle Jurassic

Downhole horizontal and vertical magnetic field measurements within the 474 m thick Jurassic crustal section drilled at ODP Hole 801C in the western Pacific show anomalies that are “in phase,” indicating that this site formed in the southern hemisphere and moved across the paleoequator to its present location at 18.6°N. The inclination computed from the horizontal and vertical anomaly logging data varies significantly downhole and can be explained by progressive rotation of the lava sequence as it is buried during accretion. This is compatible with the observed dips in the Formation Micro Scanner (FMS) data, which show up to 42° of rotation toward the fossil spreading axis. We restore the magnetic inclination to prerotated values and obtain an estimated pretilt inclination of 39.9° ± 6.6°, corresponding to a paleolatitude of 22.7° ± 5°S. The magnetic logging data document six polarity units within the drilled volcanic extrusive crust. The upper 132 m thick logged section of lavas contains four polarity units, which apparently formed 7 Myr after the formation of the underlying basement. The lower 212 m logged section of the hole is reversely magnetized with an intervening normal polarity zone. More than one reversal downhole would indicate a rapid reversal rate given the time it takes to form the extrusive section of oceanic crust: ∼45,000 years at a fast spreading rate of 66 km/Myr. Previous results from a contemporaneous section in Spain suggest rapid reversals throughout the late Bajocian–early Bathonian Stage (170–165 Ma). Nevertheless, the complicated formation history prevents quantification of the geomagnetic reversal rate for the 801C crustal section.

RADIOLARIAN ASSEMBLAGES FROM THE JURASSIC CHERTS OF ALBANIA: NEW DATA

We examined Radiolarian assemblages of Jurassic age in four sections of cherts from the sedimentary cover of the Mirdita ophiolites (Kalur Cherts) and in two sections of chert levels intercalated in carbonate successions of the Mesozoic Albanide continental margin. In the Kalur Cherts the ages of the radiolarian assemblages range from latest Bajocian-early Bathonian (UAZ. 5), to middle Bathonian - middle Callovianearly Oxfordian (UAZ. 6-8). In the sections from the carbonate successions the ages range from middle Bathonian (UAZ. 6), to late Bathonian-early Callovian - middle Callovian-early Oxfordian (UAZ. 7-8).

Pacific microplate and the Pangea supercontinent in the Early to Middle Jurassic

New biostratigraphic data based on radiolarians recovered from deep within the oceanic crustal section of Ocean Drilling Program Hole 801C in the western Pacific, along with existing radiometric information, date this oceanic crust as late Bajocian–early Bathonian (170–165 Ma). The overlying basal sediments at Hole 801C are essentially identical in age (middle Bathonian, 164–162 Ma) to the basal sediments at Deep Sea Drilling Program Hole 534A in the central Atlantic. We estimate the time of formation of the Pacific plate as 175–170 Ma and the time of initial separation of the Pangea supercontinent in the central Atlantic as 190–180 Ma. We also identify a time of extensive subduction-zone magmatism (175–159 Ma) at the eastern and western edges of Pangea. We suggest that the initial plate separation of Pangea increased subduction rates at its outer margins and altered the plate boundaries in the Pacific superocean, leading to formation of the Pacific plate.

JURASSIC RADIOLARIAN BIOSTRATIGRAPHY OF THE SEDIMENTARY COVER OF OPHIOLITES IN THE MIRDITA AREA, ALBANIA: NEW DATA

Radiolarian assemblages of Jurassic age were determined in six sections sampled of Kalur Cherts (siliceous sediments on the top of the Mirdita ophiolites) in the Mirdita area (Northern Albania). The studied sections are: Kalur, Lumthi, Bukemira, Stalosi, Simoni and Perlati i Eperm. The radiolarian assemblages indicate that the age of the bottom of the section ranges from late Bajocian-early Bathonian to late Bathonian-early Callovian. These ages are compared with those of other sections of the Kalur Cherts in Northern Albania.

Evolution of a Middle Jurassic volcanic arc: stratigraphic, isotopic, and geochemical characteristics of the Harrison Lake Formation, southwestern British Columbia

The Harrison Lake Formation is an Early to Middle Jurassic volcanic-arc assemblage unconformably overlying Triassic oceanic basement in the eastern Coast Belt of southwestern British Columbia. The formation is subdivided into four members including, in ascending order, the Celia Cove Member (conglomerate), the Francis Lake Member (fine-grained strata), the Weaver Lake Member (flows and breccias), and the Echo Island Member (pyroclastic and epiclastic strata). New biostratigraphic constraints pinpoint the initiation of volcanism to late early Toarcian. U–Pb geochronology demonstrates the arc was active until at least late Bajocian–early Bathonian time (166.0 ± 0.4 Ma), and that the timing of arc volcanism strongly overlaps emplacement of both hypabyssal intrusions (Hemlock Valley stock) and deep-seated plutons (Mount Jasper pluton) within and adjacent to the arc. Geochemical data indicate the arc is of medium- to high-K calc-alkaline affinity, and is strongly light rare earth element enriched (LaN/YbN = 1.5 – 2.5). Nd and Sr isotopic data from primary volcanic rocks demonstrate the juvenile nature of the magmatic system, but isotopic data from associated fine-grained sedimentary rocks suggest temporally controlled variations in isotopic composition interpreted to represent two-component mixing between juvenile volcanic detritus and a more evolved detrital component. The succession of facies in the Harrison Lake Formation records initial basin subsidence in the Early Jurassic, initiation of explosive volcanism in the late early Toarcian, a change to effusive volcanism in the early Aalenian, and late-stage explosive volcanism in the late Bajocian. The Harrison Lake Formation contains mesoscopic folds and overturned bedding that are absent in the overlying Callovian Mysterious Creek Formation, strongly suggesting the existence of a regional Bathonian deformational event in the southern Coast Belt.