Cryptospore Assemblages from the Ordovician/silurian Boundary in the Puna Region, North-west Argentina

Palynomorph assemblages have been recovered from deposits believed to straddle the Ordovician/Silurian boundary, from the upper member of the Salar del Rincón Formation, in the Puna region of north-west Argentina. The palynomorph assemblages are dominated by terrestrial cryptospores, but also contain marine elements (acritarchs, prasinophycean algae and chitinozoans). The cryptospore assemblages are similar in composition to those described from coeval deposits worldwide, suggesting that the producers were cosmopolitan and tolerated a wide range of climatic conditions. They are correlated with the Imperfectotriletes spp. Interval Biozone (sub-biozone α) of the Imperfectotriletes spp.- Laevolancis divellomedia Assemblage Biozone, indicating a Hirnantian (latest Ordovician) age. Acritarchs include late Ordovician species such as Eupoikilosusa striata and Villosacapsula cf. setosapellicula , that coexist with the Llandovery species Dactylofusa estillis. Based on lithological and palynological evidence, an early Llandovery, or a late Hirnantian (post-glacial) age is proposed for the basal part of the upper member of the Salar del Rincón Formation.     

The microfossil record of early land plants

Dispersed microfossils (spores and phytodebris) provide the earliest evidence for land plants. They are first reported from the Llanvirn (Mid-Ordovician). More or less identical assemblages occur from the Llanvirn (Mid-Ordovician) to the late Llandovery (Early Silurian), suggesting a period of relative stasis some 40 Myr in duration. Various lines of evidence suggest that these early dispersed microfossils derive from parent plants that were bryophyte-like if not in fact bryophytes. In the late Llandovery (late Early Silurian) there was a major change in the nature of dispersed spore assemblages as the separated products of dyads (hilate monads) and tetrads (trilete spores) became relatively abundant. The inception of trilete spores probably represents the appearance of vascular plants or their immediate progenitors. A little later in time, in the Wenlock (early Late Silurian), the earliest unequivocal land plant megafossils occur. They are represented by rhyniophytoids. It is only from the Late Silurian onwards that the microfossil/ megafossil record can be integrated and utilized in interpretation of the flora. Dispersed microfossils are preserved in vast numbers, in a variety of environments, and have a reasonable spatial and temporal fossil record. The fossil record of plant megafossils by comparison is poor and biased, with only a dozen or so known pre-Devonian assemblages. In this paper, the early land plant microfossil record, and its interpretation, are reviewed. New discoveries, novel techniques and fresh lines of inquiry are outlined and discussed.     

Palaeophytogeographical and palaeoecological implications of a miospore assemblage of earliest Devonian (Lochkovian) age from Saudi Arabia

Palynological samples from two boreholes drilled in the eastern part of Saudi Arabia contain a rich assemblage of cryptospores and trilete spores. They are dated as most probably Lochkovian in age. Intriguingly, the cryptospores are very similar to those from a coeval continental palynomorph assemblage from the Old Red Sandstone Continent, whereas the trilete spores show a strong affinity with miospore assemblages from Western Gondwana. It is suggested that cryptospore-producing plants inhabited confined, damp biotopes and had a wide range of climatic tolerance. On the other hand, trilete spore-producing plants inhabited a wider variety of biotopes but were more sensitive to climatic variations. The high degree of similarity between Old Red Sandstone and Saudi Arabian cryptospore assemblages favours palaeogeographic reconstructions where there is close proximity between Western Gondwana and Euramerica and/or a land connection between these palaeoplates. Climatic differences between the Old Red Sandstone Continent and the northern part of Western Gondwana can be invoked to explain the variations in the trilete spore assemblages.     

Miospore assemblages from the Silurian–Devonian boundary,in borehole A1-61, Ghadamis Basin,Libya

Well preserved and diversified miospore assemblages have been recorded from a relatively continuous sequence in borehole A1-61 which spans the Silurian–Devonian boundary in the northwestern part of the Ghadamis Basin, Libya. The sequence is represented by early Devonian Lochkovian beds of the Tadrart Formation that transgress onto the Silurian Ludlow-Pridoli beds of the upper part of the ‘Alternances Argilo-gréseuses’ Formation. The present work demonstrates a succession of miospore assemblages from closely sampled layers that have been stratigraphically dated as Ludlow–middle Pridoli and early Lochkovian by chitinozoans and acritarchs. Over 80 species of cryptospores and trilete spores have been identified. Modified detailed morphological interpretations are given. The miospore assemblages are correlated with miospore zonation schemes established for the type sequences of the Welsh Borderland, and those previously described from Libya. Early occurrences of some species as Streelispora newportensis on the western Gondwana plate, are put forward by comparison with the Old Red Sandstone continent. Phytogeographic and palaeobotanic implications based on these observations are discussed.     

Miospore stratigraphy of Lower and early Middle Devonian deposits from Tidikelt, Central Sahara, Algeria

The Tidikelt region forms an outstanding area for subsurface Lower Devonian stratigraphy in the central Algerian Sahara. Sediments from five boreholes have revealed abundant and diverse assemblages of miospores, acritarchs, chitinozoa, scolecodont and microplant remains. The miospores are moderately well preserved. Three new miospore species (Dibolisporites saharansis nov. sp. Hassan Kermandji, Acinosporites conatus nov. sp. Hassan Kermandji and Scylaspora tidikeltense nov. sp. Hassan Kermandji) are described. Miospore assemblages vary through the regressive and transgressive sequences. Seven miospore assemblage biozones, including six new miospore assemblage biozones (Scylaspora tidikeltense-Perotrilites microbaculatus, Dictyotriletes emsiensis-Emphanisporites spinaeformis, Apiculiretusispora arenorugosa-Camptozonotriletes caperatus, Verrucosisporites polygonalis-Dictyotriletes subgranifer, Emphanisporites annulatus-Geminospora svalbardiae, Hystricosporites microancyreus-Grandispora protea, Calyptosporites velatus-Rhabdosporites langii) are proposed for the Lower and early Middle Devonian rocks of Tidikelt Plateau. The combined use of distinctive, wide distribution cosmopolitan and Gondwanan forms as biozonal and species characteristics permits accurate subdivision, dating and correlation of Tidikelt successions with other similar miospore zones of the Lower Devonian of Europe, Canada and other parts of Gondwana plate. The miospore data provide new explanations to stratigraphic relationships of regional rock units, sedimentary cycles and stratigraphic hiatus. The miospore biozones are proposed as a provincial biozonation, which may also be applied to other Palaeozoic rocks of similar miospore content.     

Miospore biostratigraphy of the Lower Mississippian clastics of the Michigan Basin, USA

Two moderately diverse, moderately abundant miospore assemblages are recorded from the Lower Mississippian Coldwater Shale and Marshall Sandstone of the Michigan Basin. The microfloral assemblage from the older Coldwater Shale is similar to assemblages of the Spelaeotriletes balteatus-Rugospora polyptycha Biozone of western Europe. This biozone is generally absent from North America. The overlying Marshall Sandstone has a miospore assemblage representative of the oldest Osagean Spelaeotriletes pretiosus-Raistrickia clavata Biozone of western Europe. Identification of these assemblages indicates the presence of the Kinderhookian-Osagean boundary within or between the two clastic units. The identification of this boundary has important stratigraphical and sedimentological implications for age relations with Lower Mississippian rocks in adjacent basins and also provides information on regional sedimentology and depositional patterns.     

Late Devonian and early Carboniferous microfloras from the Hakkarı Province of southeastern Turkey

Late Devonian and early Carboniferous miospore and microphytoplankton assemblages are described for the first time from southeastern Turkey. The preliminary data show that assemblages recorded from the upper part of the Yiginli Formation are late Famennian in age and can be correlated with the VH, LL, LE Miospore biozones of western Europe, whilst assemblages from the overlying Köprülü Formation are considered to be middle to late Tournaisian in age and are tentatively assigned to the PC Miospore biozone of western Europe. Regional palynological correlations with other sections in North Africa and the Middle East are proposed. A new species, Verruciretusispora loboziakii is described.     

Chitinozoan faunas from the Rügen Ordovician (Rügen 5/66 and Binz 1/73 wells), NE Germany

The island of Rügen (NE Germany), situated close to the Trans-European Suture Zone (TESZ), in the southern Baltic Sea is underlain by sedimentary rocks of an Early Palaeozoic age, known only from boreholes. The wells, Rügen 5/66 and Binz 1/73, were investigated for their chitinozoan assemblages to improve the earlier biostratigraphic dating (graptolites and acritarchs) and to facilitate comparisons with other chitinozoan assemblages on both sides of the TESZ. In the lower part of the Rügen 5/66 core (3794.7-3615.8m), Lagenochitina destombesi Elaouad-Debbaj is indicative of an early late Tremadoc age. In the upper part of the same well (3287.3-1709.7m), the observed chitinozoan taxa suggest an age spanning the early Llanvirn to the Caradoc. The entire sampled interval of the Binz 1/73 core (5217.6-5041.8m) is interpreted as belonging to the Siphonochitina formosa Biozone (early-early late Abereiddian, corresponding to the early Llanvirn). The chitinozoan data corroborate the earlier suggested biostratigraphic ages, based on acritarchs and graptolites. The chitinozoans from the Binz 1/73 well point to a high latitude provenance of the investigated host sediments at time of deposition.     

FTIR characterisation of the chemical composition of Silurian miospores (cryptospores and trilete spores) from Gotland, Sweden

To better understand the biological affinities of cryptospores, micro-FTIR (Fourier transform infrared) spectroscopy analysis has been carried out on isolated specimens from the Upper Silurian of Gotland. The geobiochemical results have been compared to spectra of trilete spores, chitinozoans and leiospheres from the same sample. The palynomorphs are all very well preserved as attested by their pale yellow to orange colour indicative of a low thermal maturity. Micro-FTIR spectroscopy indicates that cryptospores display very similar spectra to those of the trilete spores, which are composed of sporopollenin characterised by absorption bands from aliphatic C-H in methylene (CH₂) and methyl (CH₃) groups, aromatic (C=C and C-H) groups and C=O groups of carboxylic acids. The sporopollenin composition of the cryptospore wall observed here is additional evidence demonstrating the embryophytic affinity of the cryptospores. In addition, several variations in other bands in the spectra of the different miospore morphospecies are evidenced and may be linked to their biological affinity or palaeoecological history.     

Silurian-Devonian miospores from the western and central Algeria

The age of Rock Units B1 and B2 of the Middle Silurian-Lower Devonian of Sahara (Algeria) is assessed and confirmed as late Homerian to ?earliest Lochkovian on the basis of moderately well preserved miospore assemblages. The data upon which this age assessment is provided by recent palynological studies in the Cantabrian Mountains (NW Spain), the type Wenlock area, Shropshire (England), south and south-west Wales, the Midland Valley of Scotland and the Ghadames Basin, Libya. Quantitative study shows that cryptospores decrease in number and variety upwards, laevigate miospores are prevalent and the representatives of the rugulate, crassitate genus Scylaspora are dominant. The occurrence and range of these species as well as other miospore taxa recorded during this study provide the basis for recognizing three miospore assemblage and one interval biozones, namely Scylaspora vetusta-Scylaspora kozlica, Chelinospora sanpetrensis-Cymbosporites triangulatus, Chelinospora hemiesferica and Scylaspopra radiata-Apiculiretusispora synoria. Of these biozones, two assemblage biozones are proposed as new. Core samples of Rock Unit B1 from borehole NGS-1 of the Triassic Province contain the oldest two miospore assemblage biozones. Rock Unit B2 from the boreholes GMD-2, ISS-1 (Tidikelt Plateau) and NGS-1 (Triassic Province) comprise the youngest two miospore biozones. The assemblage and interval biozones allow inter-regional correlation with latest Middle Silurian to probably earliest Devonian strata. The inadequacy of coverage of core samples result in the absence of critical palynological evidence, to determine the exact position of the base of the Ludlow, Pridoli and Lochkovian. Comparison with the zonal and sub-zonal divisions of Mid-Palaeozoic sequences from other parts of the world shows crucial differences in the distribution of the spore flora within Gondwanan and Euramerican regions during Pridoli and early Lochkovian. Six new miospore species namely Retusotriletes delicatus nov. sp., Scylaspora cymba nov. sp., S. distincta nov. sp., S. radiata nov. sp., S. undulata nov. sp. and Cymbosporites triangulatus nov. sp. are described. Three more possibly new miospore forms are described and illustrated but not specifically named.     

Miospores in middle-upper Frasnian to Famennian sediments partly dated by conodonts (Boulonnais,France)

The middle-upper part of the Formation de Beaulieu exposed in the new railroad trench at Caffiers-Ferques and the Formation de Ferques exposed in the Tartinskal quarries contain well-preserved miospore assemblages. They are here restudied in comparison with new conodont data ranging from the middle asymmeyricus to the Ancyrognathus triangularis Zone. The conodonts allow precise correlations with the type Frasnian area as well as with the Russian Platform and Timan-Pechora provinces. The miospore assemblages of the Formation d'Hydrequent are also considered and their age discussed in term of the Frasnian/Famennian boundary.In the systematic part, two new combinations are proposed: Ancyrospora lysii (Taugourdeau-Lantz, 1960) nov. comb., and Pustulatisporites rugulatus (Taugourdeau-Lantz, 1967) nov. comb.     

Hydrodynamic control of sedimentation in the Ordovician (Arenig–Caradoc) Baltic Basin

Changes in mineralogy, geochemistry and grain size in a deep shelf succession from the Ordovician Baltic Basin are used to determine shifts in marine current direction and sea-level fluctuations. The analyses show a long-term, relatively stable interval in the Arenig–Llanvirn followed by shorter periods of perturbations and rearrangements in the early Caradoc. The Arenig deposits of the Aizpute-41 core have a high 2–10 µm terrigenous component. During the Llanvirn the proportion of this size fraction diminished. The grain size change was accompanied by mineralogical changes. In the early Caradoc the kaolinite disappeared, the muscovite content decreased, and quartz and albite increased. This and several geochemical indicators point to an input of considerable part of sediment from different sources than in the Arenig–Llanvirn. Two currents, a southwesterly for the Arenig and a westerly for the early Caradoc, are proposed. A red facies belt in the deep shelf marks the pathway of the Arenig–Llanvirn current. Smaller shifts in SiO₂/Al₂O₃ ratio in the Aizpute-41 section are interpreted as reflecting transgressions and regressions corresponding to regional stage boundaries.     

Siluro-Devonian miospore biostratigraphy of the Urubu River area, western Amazon Basin, northern Brazil

Well-preserved miospores have been observed in the Urubu River area from the western part of the Amazon Basin, northern Brazil, in rocks belonging to the uppermost Pitinga and Manacapuru Formations. A previous palynological work based on chitinozoans has dated these strata as Late Ludlow, Early Pridoli and Early Lochkovian. Although samples are relatively poor in miospores, the present study reveals the most diversified Silurian-Earliest Lochkovian palynoflora ever reported from South America, an interval where miospore information is still very rare. Sixty-four species have been identified, of which two are new (Artemopyra urubuense and Retusotriletes amazonensis). One single specimen attributed to the genus Grandispora, identical to unpublished forms identified by one of us (P.S.) in Lochkovian sections of Saudi Arabia, has been found in a Lochkovian sample from the Urubu River. These constitute the oldest geological record of Grandispora. Among the abundant acritarchs, specimens of the genus Schizocystia have been observed for the first time in pre-Devonian rocks.Although the Late Silurian-Early Lochkovian miospore biostratigraphy is still in its infancy in South America, it seems that Amazon Basin assemblages do not show significant differences in composition in comparison to coeval palynofloras from other areas of northwestern Gondwana. This is surprising since the miospore localities under consideration are widely distributed over high to low paleolatitudes, i.e. from cool temperate to dry subtropical belts. Conversely, Siluro-Devonian Gondwanan assemblages differ considerably from the contemporary palynofloras of the Old Red Sandstone Continent and adjacent areas, thus contradicting recent phytogeographic interpretations based on megafloras.     

Late Silurian trilete spores from northern Jiangsu, China

The Late Silurian is generally considered to a particular significant key period in the study of early land vascular plants. A trilete spore assemblage of the Upper Silurian is described from northern Jiangsu, China. This assemblage comprises 11 genera and 20 species of trilete spores (including laevigate, apiculate, perinotrilite, patinate, rarely distally murornate and equatorially crassitate, and three indeterminate trilete miospores forms). It has similarities to those described from coeval assemblages from around the world (e.g., England and South Wales; Tripolitania, Libya; Cornwallis Island, Canadian Arctic; Northwest Spain). The rare cryptospore, only one specimen (Tetrahedraletes sp.) had been found to be associated with the Chinese trilete spore assemblage. The discovery of the trilete spores from Late Silurian rocks indicates the existence of early land plants, some possibly vascular, at that time in northern Jiangsu, China.     

Palynofacies and spore assemblage variations of upper Viséan (Mississippian) strata across the southern North Sea

Viséan strata are penetrated by exploration wells in the southern North Sea, reaching from the Firth of Forth in Scotland to offshore northwest Germany and to Rügen Island, northeastern Germany, south of the Baltic Sea. Several wells have been studied representing different late Viséan depositional settings ranging from proximal near-shore clastic facies (Firth of Forth, Northwest of Germany) to distal carbonate platform facies (Rügen Island). Variations of the miospore assemblages from the coeval (NM and VF Miospore Biozones) parts of these sections were analyzed with respect to palynofacies, spore abundance; morphological composition; diversity and palaeobotanical/palaeoecological affinities. While assemblages from similar down-depositional dip facies settings remain similar (even over east-west distances of > 750 km), all of the above attributes show significant variations from proximal to distal depositional settings (< 200 km to the southeast). These down-depositional dip changes appear to be continuous, but the greatest degree of change is seen at the boundaries between deltaic and non-deltaic near shore facies; between near-shore coastal clastic and carbonate platform facies; and between inner-and outer-carbonate platform facies.Miospore abundances, assemblage diversities and the number of coincident genera between the sections are reduced in moving towards distal depositional settings. This reduction most effects rounded triangular and triangular miospores, while the proportion of rounded miospores increases significantly. The palaeobotanical/palaeoecological character of the miospores also clearly changes in moving from coastal clastic to carbonate platform depositional settings. These changes appear to be largely controlled by taphonomic effects such as primary input and sorting during transportation and deposition, such that a facies-related pattern is apparent. Variations in late Viséan miospore assemblages across the studied area appear to be most closely related to the different facies realms suggesting that previously identified differences in miospore assemblages from Germany and Britain reflect depositional facies rather than regional variations in parent vegetation or climate.     

Cyanobacterial macrophytes in an Early Silurian (Llandovery) continental biota: Passage Creek, lower Massanutten Sandstone, Virginia, USA

A compression macrofossil with structure consisting of mineral-replaced filaments embedded in an amorphous carbonaceous matrix is described as a macrophytic cyanobacterial colony from continental assemblages of the Early Silurian (Llandovery) Passage Creek biota, in the lower Massanutten Sandstone (Virginia, USA). Filaments are predominantly multiseriate and consist of spheroidal crystalline aggregates representing early pyrite (subsequently replaced by iron hydroxides) precipitated preferentially inside cells. Interpretation of the fossils as cyanobacteria is based on close similarities to modern organisms in terms of overall morphology and production of copious extracellular investments, filament and cell sizes, and continental epigeal (freshwater or terrestrial) habitat. This interpretation incorporates data on cyanobacterial taphonomy and mechanisms of diagenetic mineral precipitation. These fossils are part of the oldest macrofossil assemblages documenting well-developed and diverse communities on continents. They provide the earliest direct evidence for cyanobacteria in strictly continental habitats, corroborating the commonly held but poorly documented view that cyanobacteria were among the initial colonizers of continents.     

江西全南小慕泥盆-石炭系孢子组合及其地层意义

据30属57种(包含9新种)小孢子的垂直分布特征,将江西全南小慕泥盆一石炭系的小孢子划分为3个组合(自下而上):1)Acanthotriletes denticulatus-Apiculireiusispora raris(DR)组合,2) Leiotriletes macrothlis-Grandispora xiamuensis(MX)组合,uispinosa(TT)组合,3)Apiculiretusisporatera-Lycospora cf. thuispinosa(TT)组合.这3个组合分别产于三门滩组、翻下组与荒塘组-刘家塘组.据孢子资料的分析与植物、腕足类、鱼类等化石的佐证,三门滩组与翻下组的时代均属晚泥盆世晚期(Famennian),荒塘组与刘家塘组属早石炭世早期(Tournaisian).本区泥盆系与石炭系的界线置于翻下组与荒塘组之间较适合.     

Permanent dyads in sporangia and spore masses from the Lower Devonian of the Welsh Borderland

Dyads, interpreted as cryptospore permanent dyads, are reported from sporangia and spore masses recovered from fluviatile deposits of Lochkovian (Early Devonian) age from the Welsh Borderland. The morphology, anatomy and ultrastructure of the specimens have been analysed using LM, SEM and TEM. Two specimens consist of a single sporangium terminating an axis: one is cup-shaped and attached to an unbranched axis and named Culullitheca richardsonii gen. et sp. nov., the other comprises an isotomously branching axis with one sporangium preserved and is named Fusitheca fanningiae gen. et sp. nov. Two specimens show dyads adhering to cuticular fragments presumably derived from sporangia. In one the cuticle is of irregular shape, in the other it is elliptical. The final specimen comprises an elongate spore mass. In all cases ultrastructural analysis reveals that the spore walls are essentially homogeneous. Our findings suggest that cryptospore permanent dyads were produced by rhyniophytoid plants of small stature. The affinities of these plants remain conjectural, as is the relationship of the cryptospore permanent dyads with other sporomorph morphotypes (cryptospores and trilete spores). However, the production of dyads by a plant with a bifurcating sporophytic axis is evidence against affinity with extant bryophytes. The mode of formation, adaptive significance, affinities, phylogenetic relationships and stratigraphical history (including demise) of cryptospore permanent dyads is discussed.     

Llandovery sporomorphs and graptolites from the Manbo Formation,the Mojiang County,Yunnan, China

Llandovery sporomorphs and graptolites have been recovered from the Manbo Formation, Mojiang area, western Yunnan, China, which belonged to the Indo-China Palaeoplate in the Palaeozoic. The graptolite fauna, including 8 genera and 12 species, is considered Mid Telychian, Llandovery in geological age, confirming the existence of Llandovery rocks in this region. The Silurian stratigraphical sequence of this area is reconsidered as in the ascending order: Manbo Formation (Llandovery–early Wenlock), Shuiqing Formation (late Wenlock–Ludlow) and unnamed formation (Pridoli?). The sporomorph assemblage from the Manbo Formation includes seven species in five genera. The dominant members of this assemblage are Tetrahedraletes medinensis and Laevolancis chibrikovae. Based on the low diversity and low abundance, the geological age of this assemblage is considered to be approximately the Telychian, Llandovery. The parent plants of sporomorphs probably inhabited the landmass near Mojiang area, these sporomorph-producing plants probably included bryophyte-like land plants and primitive vascular land plants. The sporomorph evidence shows that the South China and Indo-China palaeoplates may have been in close proximity (maybe with some continental bridges linking them) to each other at least in the Llandovery. They were also closely related with Gondwanaland in the Llandovery.     

A Lower Silurian (Aeronian) radiolarian assemblage from black cherts of the Armorican Massif (France)

The Chalonnes-sur-Loire outcrop is the most complete Llandovery section in the Ligerian domain (Armorican Massif, NW France); it displays a ca. 10 m-thick sequence of organic-rich black bedded cherts alternating with black graptolitic shales, which were deposited above glaciomarine diamictites of the Hirnantian glaciation. It is likely the black cherts accumulated under eutrophic waters, on the outer shelf part (distal offshore) of a Gondwanan margin, situated at intermediate to high latitudes of the Southern hemisphere. Hydrofluoric acid processing allowed the extraction of radiolarians; seven species are identified in the best preserved sample discovered so far. All seven are common species in tropical assemblages known from Alaska and Nevada, which are characteristic of the Orbiculopylorum assemblage, of Aeronian to early Telychian age. This age is in good agreement with independent age control from graptolites in the Chalonnes section, suggestive of an Aeronian age for the radiolarian-yielding level.