Bollettino SPI Vol. 38 - Issues 1, 2-3
Issue 1
Published in May 1999
- Cherchi A. & Schroeder R. (1999)
Late Barremian orbitolinid Foraminifera from northern Somalia
pp. 3-13
The lower part of the Early Cretaceous shallow marine deposits in the eastern Ahl Medo Range (Bosaso, northern Somalia) is characterized by three associations of orbitolinid foraminifers (from bottom to top): (1) Valserina transiens n. sp., (2) Palorbitolina lenticularis (Blumenbach), (3) Dictyoconus arabicus Henson and Palorbitolina lenticularis. This sequence of associations indicating a Late Barremian age is identical with that one in the central Oman Mountains. Valserina transiens n. sp. is regarded as the phylogenetic link between the genus Valserina and the Palorbitolina lenticularis group.
- Papazzoni C.A. & Sirotti A. (1999)
Heterostegina papyracea Seguenza, 1880 from the upper Miocene of Cessaniti (Vibo Valentia, Calabria, southern Italy)
pp. 15-21
Several specimens of Hererostegina papyracea Seguenza were collected near Cessaniti (Vibo Valentia) in upper Tortonian sandstones with abundant Clypeaster spp. and small pectinids.
The biometric analysis of the inner features of the specimens of H. papyracea leads us to insert it into the H. complanara lineage. In the
Mediterranean area H. papyracea probably represents the last species of this group. The H. costata lineage is instead represented at similar stratigraphic levels in Spain by H. gomezangulensis Perconig.
- Di Bella L. (1999)
Biostratigraphical and paleoecological evidences in non-costate Bulimina group of Pliocene-Pleistocene sediments (Latium – Southern Umbria, Central Italy)
pp. 23-38
In the context of a main study on foraminiferal assemblages ftom the Plio-Pleistocene sediments of central Italy aimed at a paleoenvironmental reconstruction of the Neogene basins of Latium and Umbria, morphological variations and stratigraphical evidence of the non-costate Bulimina group are studied. The foraminiferal assemblages show a gradual increase in abundance of the non-costate buliminids from the Upper Piacenzian to the Lower Santernian either in circalittoral environment, or infralittoral at the transition between circalittoral and infralittoral environments. The highest concentration and intraspecific and specific morphological variation of the non-costate Bulimina group were recorded in more sheltered areas of the basin characterised by a fine sedimentation (area between M. Soratte – M. Cornicolani structural high and M. Sabini). Each species shows our main morphological trends: 1) greater development of the Bulimina marginata undercut as far as the N/Q boundary; 2) not aligned chamber arrangement starting from the Upper Pliocene, with the appearance of Bulimina elegans marginata; 3) reduction of the undercut and vertical aligned chambers starting ftom the base of the Pleistocene (Bulimina etnea); 4) development of elongate and slender forms. The presence of these morphotypes allows us to date the sediments of this area, which in general are devoid of planktonic markers.
- Vaiani S.C. & Venezia P. (1999)
Quantitative analysis on benthic and planktic foraminiferal associations in the Lamone section (lower Pleistocene, Romagna Apennines, Nonhern Italy)
pp. 39-57
Quantitative analysis on benthic and planktic foraminiferal assemblages from the lower Pleistocene succession of the Argille Azzurre Formation in the Lamone valley type area (Romagna Apennines), provides the basis for a detailed reconstruction of the paleoenvironmental evolution of this sequence.
The biostratigraphic data, combined with previous age attributions based upon strontium isotope stratigraphy, indicates an age ranging from the Pliocene/Pleistocene boundary to the Emilian substage. In the lower part of the sequence, the first occurrence of “boreal guests” molluscs as Arctica islandica and Pseudamussium septemradiatum, confirms this age attribution.
The following world-wide and/or Mediterranean foraminiferal events are recognised in the lower and middle parts of the succession: 1) FO of left coiled Neogloboquadrina pachyderma; 2) FO of Globoturborotalita tenella; 3) FO of Bulimina etnea; 4) FO of Hyalinea balthica; 5) FO of Bolivinita quadrilatera; 6) FO of Saidovina karreriana. In contrast, the upper part of the sequence lacks diagnostic foraminiferal events.
Quantitative analyses on 37 benthic foraminiferal species or taxonomic units show high frequencies of opportunistic species throughout the study succession. These species are tolerant to stress environments characterised by strong variations of oxygen concentration and/or organic matter content at the sea bottom. In the uppermost part of the sequence, two short intervals, with a benthic foraminiferal assemblage consisting predominantly of Brizalina spathulata and B. alata, are tentatively correlated to sapropelitic layers found in several sections from southern ltaly.
In the lower and middle parts of the sequence, relatively high frequencies of upper bathyal and circalittoral species, such as Cassidulina laevigata carinata and Bulimina ex gr. B. marginata, are recorded in association with deep-water species, such as Cibicidoides kullenbergi, Gyroidinoides altiformis, and G. soldanii. This assemblage is consistent with an upper bathyal bathymetric zone. In the upper part of the sequence these deep-water species are generally absent. A decrease in Uvigerina peregrina peregrina and a considerable increase in C. laevigata carinata suggest shallower water depths and are consistent with a circalittoral bathymetric zone.
Quantitative analyses of 26 planktic foraminiferal taxonomic units show a cyclic variation of cold and warm water conditions in the lower
part of the succession; higher in the sequence this cyclic variation cannot be recognized, owing to the sharp increase in species diagnostic of environments with poor water circulation.
- Bonaduce G., Barra D. & Aiello G. (1999)
The genus Henryhowella Puri, 1957 (Crustacea, Ostracoda) in the Atlantic and Mediterranean from Miocene to Recent
pp. 59-72
The systematics, the ecology and the paleoecology of the plicate forms of the genus Henryhowella Puri, 1957 from the Miocene to Recent of the Mediterranean basin and Atlantic are investigated. The research allowed the finding in both Atlantic and Mediterranean of H. parthenopea n. sp. which is described and illustrated, the systematic definition of H. sarsii sarsii (G.W. Muller, 1894) and the related subspecies H. sarsii profunda n. ssp., both of which are described and illustrated. All the previous taxa are compared with the type species H. asperrima (Reuss, 1850) and each other. Another form found in Late Tortonian of Sicily is dubitatively attributed to H. asperrima and compared with topotypic specimens of the type-species. The ecological and paleoecological data allowed to define the bathymetrical range of the 3 forms found as follows: H. parthenopea n. sp. ranges from 40 to 170 m depth, H. sarsii sarsii from 110 to about 400 m and H. sarsii profunda n. ssp. which pertains to the bathyal environment. The age distribution of all the forms identified and illustrated is given.
- Bonaduce G., Barra D. & Aiello G. (1999)
Tanzanicythere levantina n. sp. (Ostracoda, Cytheruridae), first finding of the genus in the Mediterranean area
pp. 73-75
The occurrence of the genus Tanzanicythere Ahmad, 1977, represented by T. levantina n. sp., here described and illustrated, is cited for the first time from the Mediterranean basin. The new species has been found in the Upper Tortonian sediments of Greece, from a shallow marine environment, not deeper than 30-40 m.
- Kafanov A.I. (1999)
Neogene Macoma (Bivalvia, Tellinidae) migration from the Pacific to the Atlantic through the Bering Strait: taxonomic and biogeographic remarks
pp. 77-85
Modern North Pacific shells traditionally ascribed to Macoma obliqua (Sowerby, 1817) from European Neogene belong to a distinct, although related species, M. golikovi Scarlato & Kafonov, 1988. The latter may be considered the ancestor of M. obliqua. It is likely that the migration of Macoma golikovi – M. obliqua species-complex from the Pacific to the Atlantic through the Bering Strait occurred in the Late Miocene or in the earliest Pliocene.
- Croitor R. (1999)
On systematic position of “moldavian sambar deer” from the Pliocene of Moldova
pp. 87-96
The systematic position of the species “Cervus (Rusa)” moldavicus Janovskaya 1954 is discussed in this paper. The critical revision of the holotype of Cervus moldavicus (the so called ”moldavian sambar deer”) revealed mistakes in the skull reconstruction that caused a wrong systematic allocation of the discussed species. The skull and dentition morphology suggest that the ”moldavian sambar deer” is a fossil roe deer of the genus Procapreolus. C. moldavicus is considered here as a senior synonym for Procapreolus wenzensis (Czyzewska,
1960).
Some ecological and morpho-functional peculiarities of the deer under study, as well as its phylogenetical links, are discussed in the paper.
- Azzaroli A. (1999)
Notes on some middle and late Pleistocene Equids of Italy
pp. 97-108
Contrary to a widespread belief horses (Equus ferus Boddaert) of large size occur in the late Pleistocene of Europe. The present paper provides evidence from Central and Sothern Italy, but similar horses may possibly occur in other areas.
Measurements of bones are given and are compared with those of a wild ass from Tuscany, Equus graziosii Azzaroli, and with the still poorly known Equus hydruntinus Regalia, a humerus and radius of which are figured for the first time.
- Reggiani P. (1999)
The elephant Archidiskodon meridionalis (Nesti, 1825) from the Lower Pleistocene of Steggio (Possagno, Treviso, north-east Italy)
pp. 109-119
During the last season of excavations carried out in 1993, the fossil beds at Steggio (Possagno, Treviso) yielded many fossil bones including various elephant remains. Lithologically, the Steggio succession belongs to a unit informally known as the “Argille di Steggio”, composed of clayey layers alternate with gravelly layers. The elephant bones found at Steggio mainly belong to juvenile individuals. The biometric values of the molars fall within the range attributed to Archidiskodon meridionalis. The examination of the carpals and comparisons with the material found at Pietrafitta and in the Valdarno made it possible to highlight some of the typical characteristics of this species.
Issues 2-3
Published in December 1999
- Connery C. & Higgs K.T. (1999)
Tremadoc-Arenig acritarchs from the Annascaul Formation, Dingle Peninsula, Co. Kerry, Ireland
pp. 133-153
The Annascaul Formation occurs in the southeast part of the Dingle Peninsula and occupies a narrow outcrop strip running from Minard Bay northeastwards to Caherconree Mountain. It comprises the oldest rocks in the peninsula and is composed of a >500 m succes- sion of deep marine mudrocks, siltstones, turbiditic sandstones, and mud-matrix melange deposits. The formation was traditionally considered to
be Silurian in age; however lithological, structural, and metamorphic evidence indicated a much older age, although, diagnostic palaeontological evidence was lacking. Preliminary palynological study in 1996 revealed the presence of Early Ordovician acritarchs in two samples from Minard Bay. In the present study, acritarchs are recorded from 15 samples from the formation at Minard Bay and from inland exposures around Annascaul. Despite high thermal maturity, the acritarchs are moderately well preserved. The majority of the taxa are well-established species; one new species, Cymatiogalea vanguestainei, is erected. Four distinctive but low-diversity acritarch assemblages are described; these indicate an age range of early Tremadoc to early-mid Arenig for the Annascaul Formation.
- Dorning K.J. & Harvey C. (1999)
Wenlock cyclicity, palynology, and stratigraphy in the Buildwas, Coalbrookdale, and Much Wenlock Limestone formations, Shropshire, England
pp. 155-166
In the type area of the Wenlock series in Shropshire, England, carbonate/mudstone ciclicity is recognizable at five different orders of magnitude. The first order cycle covers the Silurian, with a general decline in carbonate following the late Ordovician glaciation, a carbonate maximum represented by the Much Wenlock Limestone Formation, and decreasing carbonate in the late Silurian. The second order of cyclicity is represented by conspicuous carbonate intervals in the Buildwas and Much Wenlock Limestone formations. Minor increases in carbonate which represent third order cycles are noted at intervals within the Apedale and Farley members of the Coalbrookdale Formation. The second and some third order cycles are comparable in magnitude to Primo and Secundo episodes and events. The Farley Member of the Coalbrookdale Formation at Farley Dingle, contains 176 couplets in 20 m of nodular argillaceous limestone and calcareous mudstone. Variations of nodular limestone thicknesses in the couplets enable subdivision of the Farley Member into 16 fourth order cycles possibly related to orbital obliquity or precession cycles. Fifth order cycles within the Farley Member are considered to represent dilution cycles deposited over 1650 to 3300 years. The type Wenlock succession contains palynomorph assemblages of low geothermal alteration with diverse, well preserved acritarchs together with chitinozoans. A new acritarch species, Tunisphaeridium farleyense described herein forms up to 15% of the Farley Member’s acritarch assemblage. Quantitatively the palynological assemblages reflect alternations in acritarch abundance for all orders of cyclicity; significant qualitative palynofloral changes are evident in the second and third orders of cyclicity.
- Górecka-Nowak A. (1999)
Miospore associations as indicators of the origin of coal seams in the Intrasudetic Basin (southwest Poland)
pp. 167-175
Palynological profiles of coal seams of the Zacler Formation (Westphalian A) in the Intrasudetic Basin (southwest Poland) have been studied. Two palynological assemblages are recognizable in profiles of seam 430 in the northwestern part of the basin. In the first, very monotonous assemblage, Lycospora exceeds 60%. The second, much more diverse assemblage includes as its main components Lycospora, Calamospora, Cyclogranisporites, Savitrisporites, Raistrickia, and Lophotriletes. In the first assemblage, the abundance of Lycospora reflects a vegetation composed of arborescent lycopsids. The second assemblage reflects a mixed plant community, including arborescent lycopsids, calamitaleans (sphenopsids), and ferns. Seams 409 and 412/413 in the southeastern part of the Lower Silesian Coal Basin host quite different miospore assemblages with Densosporites and related crassicingulate genera being the main components. They were produced by herbaceous and/or sub-arborescent lycopsids. These coal palynological assemblages enable recognition of three distinct floral associations: the arborescent lycopsids and mixed associations, occurring in seam 430; and the herbaceous and/or sub-arborescent lycopsid association of seams 409 and 412/413. Coals representing the first two associations are believed to have been deposited in conditions of planar rheotrophic mire; the herbaceous and/or sub-arborescent lycopsid association developed in an ombrotrophic domed mire situation.
- Hennessy D. & Higgs K.T. (1999)
Palynological zonation of the Late Devonian and Early Carboniferous of the Avon Gorge, southwest England
pp. 177-186
Well-preserved miospore assemblages are recorded from the upper Portishead beds, and the base of the Lower Limestone Shales in the classic Avon Gorge section, which displays a continuous transition from continental to marine environments. The palynofloras are assigned to the miospore zonation scheme established for the Late Devonian-Early Carboniferous of southern Ireland. The miospore assemblages from the upper part of the Portishead Beds are assigned to the Retispora lepidophyta–Knoxisporites literatus (LL) Biozone; an assemblage from the Rhacophyton Bed at the base of the Shirehampton Beds is atrributed to the Retispora lepidophyta–Verrucosisporites nitidus (LN) Biozone. Both of these biozones are latest Famennian in age. Miospore assemblages from the main part of the overlying Shirehampton Beds are assigned to the Early Carboniferous Cristatisporites hibernicus-Umbonatisporites distinctus (HD) Biozone. An assemblage from the base of the overlying Lower Limestone Shales is also assigned to the HD Biozone but is distinguished from the preceding HD assemblages by the appearance of Umbonatisporites distinctus Clayton, 1971. The Devonian-Carboniferous boundary is placed within a 4 m interval above the Rhacophyton Bed in the basal part of the Shirehampton Beds.
- Higgs K.T. (1999)
Early Devonian spore assemblages from the Dingle Group, County Kerry, Ireland
pp. 187-196
The Dingle group is the lowest lithostratigraphic division of the continental Old Red Sandstone magnafacies in the Dingle Peninsula of southwest Ireland. It is generally considered to be Late Silurian (Ludlow) to Early Devonian in age, but to date has yielded no unequivocal faunal or floral evidence of age. This paper describes two small but distinctive Early Devonian spore assemblages from the Dingle Group in the southwestern part of the Dingle Peninsula. The older assemblage is from the Eask Formation at Dunmore Head and is assigned to the D. wetteldorfensis (W) Interval Zone of early late Pragian age. The younger assemblage is from the Slea Head Formation and is assigned to the E. annulatus–B. bellatulus (AB) Oppel Zone of early to middle(?) Emsian age. The stratigraphic significance of these newly inferred early Devonian datings is discussed, particularly with reference to the contact with the underlying Sharian Dunquin Group. The palynological evidence now shows that the bulk of the Dingle Group belongs to the Early Devonian and the most likely position for the Silurian-Devonian boundary is within the basal Bulls Head Formation.
- Kozur H.W. (1999)
A review of the systematic position and stratigraphic value of Muellerisphaerida
pp. 197-206
The Muellerisphaerida are pelagic microfossils that are morphologically similar to spherical spinose acritarchs and, particularly, to spherical radiolarians. However, their diameter (including spines) is generally 5-20 times larger than that of acritarchs, and the double-layered shell consists of calcium phosphate with some organic matter that may be absent in muellerisphaerids from metamorphic rocks. A pylome, often closed by a cap, may be present (only in Papinochium Ters & Deflandre, 1966). Most similar are radiolarians which are of similar size and may have a double-layered shell and pylomes; however, radiolarians with phosphatic test are unknown. Late Precambrian spin spherical microfossils with secondarily phosphatized organic shells are morphologically very similar but distinct in shell composition and distribution (not present in the Cambrian, wherein phosphatized microfossils are common). Muellerisphaerida are known from Ordovician-Lower Devonian rocks of North America, Greenland, Sweden, Great Britain, France, Germany, Czech Republic, Austria, Hungary, Turkey, and Tasmania. Muellerisphaerida are stratigraphically useful, especially for dating metamorphic cherts; and have been used for stratigraphic determinations in tectonically complex areas of Turkey. In the Karaburun Peninsula, Silurian Muellerisphaerida occur in distal turbiditic cherts within a turbidite-olistostrome sequence. These beds (“Karareis Formation”) were previously assigned to the Scythian-Anisian (Lower-Middle Triassic). In the Bolkardag Unit of the Taurides, similar cherts from a turbidite-olistostrome unit were dated by Muellerisphaerida as Late Silurian to earliest Devonian, thus providing evidence of a Caledonian instead of Variscan orogeny.
- Moczydłowska M. (1999)
The Lower-Middle Cambrian boundary recognized by acritarchs in Baltica and at the margin of Gondwana
pp. 207-225
Acritarch assemblages recorded throughout the Cambrian successions change taxonomically in relatively short time intervals and have wide palaeogeographic distribution. They have been used for establishing several formal zones in the Lower Cambrian and some informal zones in the Middle and Upper Cambrian; these can be traced between shelf areas of various palaeocontinents regardless of faunal provinces. The most pronounced change in Cambrian acritarch diversity is observed in the Lower-Middle Cambrian boundary interval; this is evident in the global cumulative record and recorded in several particular geological sections. Replacement of the Lower Cambrian Volkovia-Liepaina assemblage by the Middle Cambrian Eliasum–Cristallinium assemblage is interpreted as marking the Lower-Middle Cambrian boundary. This slightly precedes the first appearance of trilobite species diagnostic of the Acadoparadoxides oclandicus Superzone, and in otherwise unfossiliferous interval of strata, and it is suggested to be incorporated into the said superzone. The acritarch-based boundary is recognizable in the transitional Lower-Middle Cambrian succession in the Łopiennik IG-1 borehole of the East European Platform, Poland, reported herein, and in the previously studied succession in the Barstad 2 borehole of the Baltoscandian Platform, Sweden. Both are continuous siliciclastic sequences deposited in shallow marine (Bårstad) or in offshore to slope (Łopiennik) environments and they contain age-diagnostic trilobites and acritarchs. The acritarch-based series boundary is considered in the context of regional trilobite zonations, and enables correlation between Baltica and terranes at the margin of Gondwana, including Avalonia and Armorica.
- Nestor V. (1999)
Distribution of chitinozoans in the Llandovery of the Oslo region
pp. 227-238
Llandovery chitinozoans of the Oslo region are identified and discussed. The species ranges in nine sections are illustrated. The distribution of chitinozoans in all studied formations of the Oslo region is documented, with establishment of a sticcession of nine chitinozoan biozones, named as follows: Ancyrochitina laevaensis, Belonechitina postrobusta, Conochitina electa, Spinachitina maennili, Conochitina alargada, Eisenackitina dolioliformis, Angochitina longicollis, Conochitina proboscifera, and Margachitina margaritana (continuing in the lower Wenlock).
- Pereira Z., Piçarra J.M. & Oliveira J.T. (1999)
Lower Devonian palynomorphs from the Barrancos region, Ossa Morena Zone, Portugal
pp. 239-245
The stratigraphic succession of the Barrancos region has been considered as a reference for understanding the Palaeozoic geology of the Ossa Morena Zone. The succession consists of: Cambrian to Ordovician terrigenous sediments; a black shale/lidite interval of Silurian age; a thin-bedded carbonate unit of Early Devonian age; and a poorly dated flysch interval. Palynological study reveals the presence of Lower Devonian spores in three distinct lithostratigraphic units (“Xistos Raiados”, Russianas, and Terena Formations). Acritarchs and chitinozoans are also present. The palynological data enable refinement of previous age determinations based on macrofossils and are fundamentally important in
structural and palaeogeographic syntheses.
- Raevskaya E.G. (1999)
Early Arenig acritarchs from the Leetse Formation (St. Petersburg region, northwest Russia) and their palaeogeographic significance
pp. 247-256
The Leetse Formation of Early Ordovician (Arenig: Hunneberg and Billingen) age consists of quartzose glauconitic sand, greenish-grey clay, and argillaceous glauconitic limestone with clayey intercalations. Palynological studies conducted on samples from four sections along the Baltic-Ladoga Glint within the St. Petersburg region of northwest Russia reveal the presence of three acritarch assemblages containing over 35 diagnostic acritarch taxa. These occur within an interval corresponding to the upper Paroistodus proteus through Oepikodus evae conodont Zones of Baltoscandia. The acritarch assemblages are correlative with those of Britain, South China, and Australia. Preliminary palaeogeographic assessment of the identified taxa suggests that the Baltic microflora (sensu Vavrdovd, 1974) appeared in Baltica after the early Arenig, because the Billingen acritarch associations reported herein exhibit closest similarities with coeval suites from the Yangtze region, South China.
- Rubinstein C.V. & Brussa E.D. (1999)
A palynomorph and graptolite biostratigraphy of the Central Precordillera Silurian Basin, Argentina
pp. 257-266
This work integrates palynological and graptolite studies of the Silurian La Chilca and Los Espejos formations for correlation purposes within the Central Precordillera Basin. Palynomorphs from these two formations have been grouped into five assemblages. In the Normalograptus persculptus graptolite Zone (Hirnantian), acritarchs are scarce, poorly preserved, and have no stratigraphic value. This stratigraphic interval is dominated by short-spined acritarchs. The upper Stimulograptus sedgwickii-lower Spirograptus turriculatus Zones (upper Aeronian-lower Telychian) contain acritarchs, prasinophytes and less abundant cryptospores. Tylotopalla caelamenicutis and Tylotopalla digitifera appear to be potentially useful for regional correlations of the middle-upper Llandovery boundary. The lower portion or the Los Espejos Formation yielded a highly diversified and well-preserved assemblage of acritarchs, prasinophytes, cryptospores and miospores, but unfortunately no reliable graptolite data are available. The upper third of this formation, referred to as the Neodiversograptus nilssoni–Lobograptus scanicus Zones (Gorstian), contains a single diversified palynological assemblage of typical Ludlovian age.
- Rubinsten C.V., Toro B.A. & Waisfeld B.G. (1999)
Acritarch biostratigraphy of the upper Tremadoc-Arenig of the Eastern Cordillera, northwestern Argentina: relationships with graptolite and trilobite faunas
pp. 267-286
Biostratigraphic results and palaeogeographic inferences have been obtained from an integrated study of acritarchs, graptolites, and trilobites of late Tremadoc to middle Arenig age, from the Eastern Cordillera, northwestern Argentina. One new acritarch species Eisenackidium orientalis Rubinstein is proposed, together with two new combinations Polygonium akrochordum (Rasul) Rubinstein, and Ammonidium multipugiunculatum (Cramer & Diez) Rubinstein. A biostratigraphic scheme, based on acritarchs and graptolites, is established for the interval upper Tremadoc-middle Arenig in the studied sections. Acritarch assemblages appear to relate to the cold-water to temperate Peri-Gondwana Province, based on the occurrence of Striatotheca, Coryphidium, and Arbusculidium.
- Sergeev V.N. (1999)
Silicified microfossils from transitional Meso-Neoproterozoic deposits of the Turukhansk Uplift, Siberia
pp. 287-295
Diverse assemblages of silicified microfossils occur in black chert lenses within carbonates of the Mesoproterozoic Sukhaya Tunguska and the Neoproterozoic Burovaya and Shorikha formations, Turukhansk Uplift, northeastern Siberia. These assemblages comprise numerous species of simple filamentous and coccoidal microfossils, multicellular trichomes, thick-walled sphaeromorphic acritarchs, and less abundant, but biostratigraphically important, morphologically complex acanthomorphic acritarchs. The discovery of phytoplanktonic microorganisms in cherts of the Subhaya Tunguska, Burovaya, and Shorikha formations contributes significantly to understanding of compositional changes in silicified microfossil assemblages across the Meso- Neoproterozoic boundary. These data enhance the biostratigraphic potential of late Precambrian silicified microbiotas and fill the gap in the microfossil succession of the Turukhansk Uplift, which is a possible location for the GSSP (Global Stratotype Section and Point) of the Meso-Neoproterozoic boundary.
- Tongiorgi M. & Di Milia A. (1999)
Differentiation and spread of the Baltic Acritarch Province (Arenig-Llanvirn)
pp. 297-312
The taxonomic composition and the palaeogeographic and chronostratigraphic distribution of the Ordovician Mediterranean and Baltic acritarch provinces are compared and a more precise circumscription of the Baltic Province is proposed. Both southern Perigondwana and the East European Platform appear to be characterized by Mediterranean acritarch assemblages during the Billingen, while differentiation of the oldest elements of the Baltic Province commenced in South China at the base of the Volkhov. The Baltic taxa became dominant and diversified only from the uppermost Volkhov, seemingly at the same level in both Baltoscandia and South China. Starting from the same level, isolated elements of the Baltic Province also migrated into southern Perigondwana (Bohemia, Belgium, Spain, Tunisia). A possible South China origin of some Baltic taxa is suggested, even though a polycentric origin (South China and Baltoscandia) of the assemblages comprising the Baltic Province cannot be excluded. Changes in provincial affinity at middle to low latitude since the lower Volkhov are hypothesized as being controlled primarily by trophic level fluctuations, which in turn depended on sea level changes.
- Tripathi A. (1999)
Talcheridium indicum a new acritarch with dinoflagellate-like features from the Permian Barakar Formation of India
pp. 313-316
Talcheridium indicum gen. et sp. nov., from shales of the coal-bearing Barakar Formation, Talcher Coalfield, Orissa, India, encompasses the thin-walled, ornamented acritarchous cysts referred to as “Type A” by Tripathi (1993). Many specimens show polar symmetry, and commonly have a peripheral fold, sometimes also a meridional fold. At one pole a pylome with an irregular (angular) edge is present, but there is no definite evidence of neither an archeopyle or operculum nor tabulation of the cyst wall. The affinity of the new fossil – whether it is a dinoflagellate or is best considered as an acritarch or dinoflagellate – is discussed. Talcheridium indicum is associated with Leiosphaeridia, Navifusa, and Foveofusa in an assemblage dominated by striate bisaccate pollen of late Early Permian age.
- Vanguestaine M., Pardo-Trujillo A., Coen-Aubert M., Roche M. & Boulvain F. (1999)
Evolution of organic debris and palynomorph preservation in two late middle Frasnian sections, southern Dinant Synclinorium border, Belgium
pp. 317-330
The palynofacies content of two successive calcareous shaly units [Boussu-en-Fagne Member (= Boussu) and Neuville Formation] of late middle Frasnian age has been investigated in two coeval Belgian localities at the southern margin of the Dinant Synclinorium
(La Boverie and Lion quarries, 60 km apart). The two units are differentiated by an abrupt increase in calcareous nodule concentration, which marks a sequence boundary between a transgressive and a high stand systems tract. Despite difficulties associated with differential thermal alteration, the organic matter in both areas shows very similar trends. At both localities, the Boussu Member contains higher concentrations of organic debris and sporomorphs than the Neuville Formation, while the relative proportion of black (oxidized) debris compared with brown damaged fragments progressively increases upsection in both the investigated sections. Moreover, the shale which is grey and pyritic at the base, becomes grey-green, nodular, and bioturbated towards the top. Therefore, the relative increase of opaque debris (1 which is considered the fraction most resistant to oxidation processes) suggests a change in the preservation of organic matter during the Boussu-Neuville interval. This alteration affects mainly the degraded and infested organic debris and, more or less equally, the most abundant microfossils (acritarchs and spores). Concurrently, acritarch concentration decreases while the number of broken specimens increases. The possibility of differential alteration of acritarch taxa is considered but is not confirmed by a concomitant relative increase in other palynomorphs. Moreover, the acritarch and prasinophycean assemblage succession, combined with the Shannon diversity index data, suggest similarities with Staplin’s distribution model. If so, significant differential alteration of acritarchs and prasinophytes is unlikely and the observed assemblage successions are probably due to changes in water depth that have induced variations in the reefal environment.
- Vecoli M., Tongiorgi M., Abdesselam-Roughi F., Benzarti R. & Massa D. (1999)
Palynostratigraphy of Upper Cambrian-upper Ordovician intracratonic clastic sequences, North Africa
pp. 331-341
Detailed palynological study of subsurface sections in the Algerian Sahara (boreholes Nl-2 and Uc-101) and southern Tunisia (boreholes Sn-1 and St-1) enables precise dating and intrabasinal and extrabasinal stratigraphic correlation. Most of the study samples proved palyniferous, yielding abundant, well preserved acritarchs (148 species) together with infrequent prasinophytes (2 species). Seven acritarch assemblage zones are recognizable, ranging in age from late Cambrian to late Ordovician (Ashgill) as follows: Timofeevia lancarae–Cristallinium randomense (Late Cambrian), Timofeevia phosphoritica-Dasydiacrodium caudatum (latest Cambrian), Acanthodiacrodium simplex- Arbusculidium destombesii (basal Tremadoc), Acanthodiacrodium angustum-Vulcanisphaera britannica (early Tremadoc), Arbusculidium
filamentosum-Coryphidium bohemicum (late Arenig), Frankea sartbernardensis-Vogtlandia ramificata (Llanvirn), and Evittia remota-Villosacapsula setosapellicula (Ashgill) zones. Lower Tremadoc assemblages appear to be at least partially affected by environmental factors; as a consequence, the Tunisian assemblages differ somewhat from the Algerian ones. Notably, the important index species Acantodiacrodium angustum is not present in the Algerian Tremadoc suites. Two important regional hiatuses are recognizable in the study area: one corresponding to the upper Tremadoc through upper Arenig, and the other to the entire Caradoc. The Tremadoc and Llanvirn represent periods of maximum abundance and diversity of the microphytoplankton.
- Vecoli M., Tongiorgi M. & Playford G. (1999)
The Ordovician acritarchs Frankea breviuscula, F. longiuscula, and F. sartbernardensis: a new study
pp. 343-358
Detailed observations and biometric analysis, based upon numerous specimens, facilitate enhanced morphological characterization of the Ordovician acritarchs Frankea breviuscula, F. longiuscula, and F. sartbernardensis. These species are readily distinguishable providing a sufficiency of well-preserved specimens is available for study. The nature and distribution of microsculptural elements are detailed, and the method of excystment (via epityche) in the genus Frankea is documented for the first time. Stratigraphic ranges of F. breviuscula, F. longiuscula, and F. sartbernardensis are critically re-evaluated on the basis of known records and new age-constrained biostratigraphic data. F. sartbernardensis first occurs in uppermost Arenig-basal Llanvirn strata, and constitutes an important component of lower Llanvirn (Didymograptus artus graptolite Zone) acritarch assemblages. The inception of both F. breviuscula and F. longiuscula is within the D. murchisoni graptolite Zone (Llanvirn). In the stratigraphic sections examined (from Tunisia, Spain, and Belgium), the introduction of F. breviuscula precedes that of L. longiuscula, which is more common in stratigraphically higher levels.
- Verniers J. (1999)
Calibration of Chitinozoa versus graptolite biozonation in the Wenlock of Builth Wells district (Wales, U.K.), compared with other areas in Avalonia and Baltica
pp. 359-380
The Wenlock sections around Builth Wells, recently used to establish a revised Wenlock graptolite biozonation have been here studied for Chitinozoa. Fifty-five samples have been collected from four sections containing three to five graptolite biozones; samples were taken from the same slabs of rocks used for the redefinition of the graptolite biozonation. The index species of three globally recognised chitinozoa biozones are present, Margachirina margaritana, Cingulochitina cingulata, and Conochitina pachycephala, together with several other characteristic species. These global biozones can be divided into several local biozones. In levels with the centrifugus and murchisoni graptolite biozones, a local margaritana biozone is defined; within the riccartonensis graptolite biozone two biozones are defined, the mamilla and burdinalensis biozones with a third, the tuba biozone at the top. The cingulata biozone starts at the base of the dubius graptolite biozone; the pachycephala biozone commences halfway up the rigidus graptolite biozone and at the base of the (newly defined) lundgreni graprolite biozone, is the subcyatha biozone. Halfway through the lundgreni graptolite biozone the cribrosa biozone begins and continues into the uppermost samples which are referred to the nassaludensis graptolite biozones. In five areas of Avalonia and Baltica a calibration between chitinozoa and graptolite biozonations has been established for the Wenlock: Builth Wells district (U.K.), Brabant Massif (Belgium), Estonia and northern Latvia, Gotland (Sweden) and mainland Sweden. For the chitinozoa a similar succession of nine biozones and two interzones (as the expression of extinction events) is present in at least three of the five areas. From bottom to top: the Wenlock part of the local margaritana biozone coincides with the centrifugus and murchisoni graptolite biozones. The mamilla and burdinalensis biozones are present respectively in the lower and upper part of the riccartonensis graptolite biozone. The lower extinction event is either located in the topmost part of the riccartonensis graptolite biozone (Builth Wells district) or in the dubius graptolite biozone (other areas). The main part of the tuba biozone and the cingulata biozone are found in the dubius graptolite biozone and the lagena and pachycephala biozones in the rigidus graptolite biozone. The subcyatha and the cribrosa biozones are found in the lundgreni graptolite biozone. An interzone and the indecora/lycoperdoides biozone starts within the nassa biozonal complex. The apparent minor difrences between the calibrations of biozonations of the two groups could be explained by differences in sample density, by the discontinuous or condensed sedimentation in the sections or differences in biozone definition. Eight new taxa are described, named Cingulochitina angusta, C. bouniensis, C. burdinalensis, C. dreyensis, C. pitetensis, Eisenackitina amulifera, E. causiata, and E. ithoniensis.
- Wauthoz B. & Gerard P. (1999)
Biometric study of some Domasia species (Acritarcha) from the Silurian of the Brabant Massif, Belgium
pp. 381-395
Morphological variation within the genus Domasia hampers species determinations. As most species have a short stratigraphic range, it is important to differentiate them. The studied specimens belong to a morphon whose morphological end members are D. elongata (sensu
Downie, 1960), D. limaciformis (sensu Cramer, 1971), D. symmetrica (sensu Cramer, 1971), and D. trispinosa (sensu Downie, 1960). A biometric study, based on 16 variables and a statistical analysis created four clusters. Cluster 2 and cluster 4 are close to D. limaciformis (sensu Cramer, 1971) and D. symmetrica (sensu Cramer, 1971) respectively. A discriminant analysis showed the validity of these clusters (98% of correct reallocation); and accordingly, these two species, which had been placed in synonymy, are considered to be differentiable. A classification law is presented to assist identification of specimens of the particular species. This study demonstrates the potential of multivariate statistical analysis for the solution of systematic problems.
- Wetherall P.M., Dorning K.J. & Wellman C.H. (1999)
Palynology, biostratigraphy, and depositional environments around the Ludlow-Pridoli boundary at Woodbury Quarry, Herefordshire, England
pp. 397-404
Late Silurian palynomorphs and palynodebris from Woodbury Quarry, Herefordshire, are recorded in the contexts of their biostratigraphic utility and depositional facies. The upper Whitcliffe Formation is dated as late Ludlow based on its low-diversity acritarch assemblage that includes Visbysphaera whitcliffensis, Rhacobrachion mala, and Elektoriskos brevispinosa. The overlying Downton Castle Sandstone Formation contains the stratigraphically important sporomorphs Synorisporites tripapillatus, S. verrucatus, Perotrilites sp., and Cymbosporites echinatus. On palynodebris and sedimentological grounds, the upper part of the Whitcliffe Formation clearly accumulated in a shallow marine, high energy shelf environment; palynomorph assemblages here are almost entirely marine in origin with acritarchs, chitinozoans and scolecodonts consistently present. The Downton Castle Sandstone Formation represents a fresh water lagoon/delta front environment with terrestrial palynomorphs (miospores, cryptospores, cuticle, and tubular structures) predominant. The absence of chitinozoans and scolecodonts, and reduced acritarch abundance and diversity in these beds, are also consistent with a proximal, fresh water influenced environment.