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Recognition of the Trans-European Suture Zone (TESZ) by the palaeobiogeographical distribution pattern of early to middle Ordovician acritarchs
Geological Magazine
Abstract
The Tremadoc to early Llanvirn is the time interval in the Ordovician
for which a global
acritarch distribution pattern can be proposed. It is possible to differentiate
a high latitude, cold- to temperate-water realm and a low latitude, warm-water
realm. The cold-water assemblages, recorded from numerous
localities at the northern border of Gondwana in the southern hemisphere,
include
some diagnostic
morphotypes, such as Arbusculidium
filamentosum, Arkonia,
Aureotesta, Coryphidium-Vavrdovella,
Dicrodiacrodium, Frankea and Striatotheca.
Assemblages related to warm-water areas are described from
Canada, the United States, northern China, Australia, and Baltica. Although
a
distinction of separate
provinces within the cold-water and warm-water realms is difficult, the
differentiation between these two
units appears evident and a distinction of the assemblages from peri-Gondwana
and the microfloras from
Baltica is possible. This enables a recognition of the Trans-European Suture
Zone in the early to middle Ordovician.
... Several of the more frequently recorded and biostratigraphically most useful Ordovician acritarch taxa from the periphery of Gondwana have been reviewed in recent years. Frankea was revised by Servais (1993), Dicrodiacrodium by Servais et al. (1997), Arkonia and Striatotheca by Servais (1997), Ampullula by Brocke (1998), Aureotesta and Marrocanium by Brocke et al. (1998) and Arbusculidium filamentosum by Fatka and Brocke (1999). So far, however, the genus Coryphidium, has not been reviewed in detail, although it is commonly used for dating sedimentary rocks or determining palaeogeographical affinities. ...
... Several of the more frequently recorded and biostratigraphically most useful Ordovician acritarch taxa from the periphery of Gondwana have been reviewed in recent years. Frankea was revised by Servais (1993), Dicrodiacrodium by Servais et al. (1997), Arkonia and Striatotheca by Servais (1997), Ampullula by Brocke (1998), Aureotesta and Marrocanium by Brocke et al. (1998) and Arbusculidium filamentosum by Fatka and Brocke (1999). So far, however, the genus Coryphidium, has not been reviewed in detail, although it is commonly used for dating sedimentary rocks or determining palaeogeographical affinities. ...
... *Coryphidium bohemicum. -Servais and Fatka 1997, p. 622. *Coryphidium bohemicum Vavrdová 1972. ...
The acritarch genus Coryphidium Vavrdová, 1972 is one of the most frequently recorded acritarch taxa in the Ordovician. The original diagnoses, stratigraphical ranges and geographical distribution of all Coryphidium species are critically evaluated in a review of published literature supplemented by studies of material from the British Isles, Belgium, the Czech Republic, Germany, Spain, Morocco, Algeria, Tunisia, Libya and China, including sections from type areas. The taxonomic concept of the genus is here rationalized: the genus Coryphidium is emended and the informal category of coryphid acritarchs is introduced to include all morphotypes with the characteristic vesicle shape of the two genera Coryphidium and Vavrdovella Loeblich and Tappan, 1976. Nine of the previously described species can be attributed to the genus, and two other species possibly belong to it. The attribution to Coryphidium of the species C. sichuanense Wang and Chen, 1987 is rejected here. Intraspecific variability is very important and the attribution of Coryphidium specimens at the specific level is sometimes difficult. The genus is found in all palaeoenvironments from nearshore to offshore settings and apparently does not occupy specific palaeoecological niches. Coryphidium is very useful biostratigraphically and palaeobiogeographically. The review indicates that the genus first appears in the uppermost Tremadocian Araneograptus murrayi graptolite Biozone and is common through the upper Lower Ordovician and the Middle Ordovician, while Upper Ordovician occurrences might be the result of reworking. Palaeogeographically, Coryphidium is an indicator of the peri-Gondwanan acritarch “palaeoprovince” during the Early/Middle Ordovician.
... Coryphidium is a common component of the peri-Gondwanan acritarch palaeoprovince (Li 1987;Servais et al. 2003;Molyneux et al. 2013), and its FAD is in the uppermost Tremadocian . To date, this taxon has not been recorded from the Baltic or Laurentia palaeoprovinces (Servais and Fatka 1997). In Avalonia (north-west England), the first occurrence of Coryphidium is in the upper part of sub-assemblage 3 of the messaoudensis-trifidum assemblage, which corresponds to the uppermost Tremadocian (upper part of stage slice Tr3 and time slice 1d by Molyneux et al. 2007). ...
... In the present study, the FAD of Coryphidium bohemicum is in the Floian Stage because it is associated with the Eremochitina brevis Biozone (stage slice Fl3 and time slice 2c of Webby et al. 2004;Videt et al. 2010). This genus and its species have not been recorded from Baltica or Laurentia (Servais and Fatka 1997). Figure 17. ...
The Lashkarak Formation (Lower-Middle Ordovician) in the Gerdkuh locality, 10 km west of Damghan city, northern Iran has been found to contain acritarchs and chitinozoans. This study aimed to understand these chitinozoan and acritarch successions as well brachiopods in this part of the Alborz Mountains, in a novel manner. Ninety-Seven surface samples from this succession were collected and analysed. Thirty samples yielded well-preserved palynomorph taxa such as acritarchs, chitinozoans, and scolecodonts, as well as graptolite remains. In total, 53 taxa were identified from acritarchs (38 species from 21 genera) and chitinozoans (15 species from 10 genera). Although scolecodonts and graptolite remains were also observed, they were not studied in detail. The palynological analyses revealed the presence of several diagnostic acritarchs in the Lashkarak Formation, including Vulcanisphaera simplex, Arbusculidium filamentosum, Coryphidium bohemicum, Dactylofusa velifera, Striatotheca mutua, Arkonia virgata, and Orthosphaeridium ternatum. These acritarchs allowed recognition of five acritarch assemblage zones. Similarly, seven chitinozoan biozones were recognised, including Eremochitina brevis, Desmochitina ornensis, Belonechitina henryi, Cyathochitina protocalix, Cyathochitina calix, Siphonochitina formosa, and Laufeldochitina clavata. These findings confirm the inclusion of the Alborz Mountains in the peri-Gondwana palaeoprovince during the Early-Middle Ordovician. The co-occurrence of the acritarch and chitinozoan taxa with previously identified brachiopods allowed for the establishment of a more detailed Early-Middle Ordovician biozonation, demonstrating their potential usefulness for global chronostratigraphy. Based on palynological and brachiopod assemblages, a shallow marine environment of inner shelf setting is suggested for the Early-Middle Ordovician at the Gerdkuh locality. Moreover, in this study, four new morphotype species were erected, consisting of one new chitinozoan (Cyathochitina gerdkuhensis sp. nov.) and three new acritarchs (Baltisphaeridium razii sp. nov., Navifusa alborzensis sp. nov., and Orthosphaeridium iranense sp. nov). However, Othosphaeridium cf ternatum. was left with open nomenclature.
... 3,4) for Ibexian (Early Ordovician) and post-Ibexian^pre-Hirnantian (Middle^Late Ordovician) time puts the neritic platforms close together in a southern latitudinal position, enabling migratory relations between Laurentia, Baltica, West and East Gondwana, but excludes Siberia, which is reconstructed in rather low northern latitudes. However, this model does not take into account the traditionally reconstructed oceanic areas such as the Iapetus Ocean between Laurentia and Baltica (e.g., Vannier et al., 1989; Erdtmann, 1991; Oliver et al., 1993) or the Tornquist Sea between Baltica and NW Gondwana ('Armorica') (same references; also Servais and Fatka, 1997) (without entering the debate on the reality of the Tornquist Sea; see, e.g., Paris and Robardet, 1990; vs. Servais and Fatka, 1997.) At the same time, in the model of Boucot et al. (1995), no oceanic area seems to have been intercalated between the various terranes of East Asia, SE Asia and East Gondwana, in agreement with the solution of Metcalfe (1999, ¢g. ...
... 3,4) for Ibexian (Early Ordovician) and post-Ibexian^pre-Hirnantian (Middle^Late Ordovician) time puts the neritic platforms close together in a southern latitudinal position, enabling migratory relations between Laurentia, Baltica, West and East Gondwana, but excludes Siberia, which is reconstructed in rather low northern latitudes. However, this model does not take into account the traditionally reconstructed oceanic areas such as the Iapetus Ocean between Laurentia and Baltica (e.g., Vannier et al., 1989; Erdtmann, 1991; Oliver et al., 1993) or the Tornquist Sea between Baltica and NW Gondwana ('Armorica') (same references; also Servais and Fatka, 1997) (without entering the debate on the reality of the Tornquist Sea; see, e.g., Paris and Robardet, 1990; vs. Servais and Fatka, 1997.) At the same time, in the model of Boucot et al. (1995), no oceanic area seems to have been intercalated between the various terranes of East Asia, SE Asia and East Gondwana, in agreement with the solution of Metcalfe (1999, ¢g. ...
Cambrian–Ordovician vertebrate and supposed vertebrate occurrences have been repeatedly claimed during recent decades, with confirmed taxa bearing mineralized tissues with a vertebrate histomorphology still relatively rare. The only biogeographic province that we can presently recognize is the Gondwana Endemic Assemblage (GEA) with possible Late Cambrian fragmentary remains from Australia but more definite Early Ordovician (Arenigian) to early Late Ordovician (Caradocian) arandaspids (i.e., Sacabambaspis, Arandaspis) and other taxa known from South America and Australia. Certain chondrichthyans (‘sharks’, at first without teeth and which might not constitute a monophyletic group) might have originated in East Gondwana province and then are found in the Late Ordovician and Early Silurian of Mongolia, Tarim, and South China. The GEA fauna proper disappears by middle–late Caradocian and vertebrates do not reappear in Gondwana until mid Late Silurian. Late Ordovician (−455 Myr or earlier) vertebrates are also known with certainty from Laurentia, viz., North America (pteraspidomorphs Astraspis, Eriptychius, and various gnathostome-like taxa including chondrichthyan-, placoderm- and acanthodian-like remains), and Siberia (astraspid-like microremains with an unusual histology, which might correspond to a new group of lower vertebrates) as well as scales from putative loganiid and thelodontidid thelodonts from North America and Russia (Timan–Pechora, the Severnaya Zemlya archipelago and Siberia). This is defined as the Laurentia–Baltica–Siberia Assemblage (LBSA). We also mention one enigmatic reference to a Late Ordovician anaspid in South Africa. There is no clear association of taxa between the GEA and LBSA despite a small overlap in time. Various recent palaeogeographic models published for the Ordovician are critically analyzed and considered within four groups: the archetypal palaeogeographic reconstructions, two alternative solutions, and a compact version. Habitats of vertebrates in mostly BA1 (marine intertidal) to BA3 (shallow subtidal) environments, and their dispersal capabilities are evaluated with regard to those models. The main feature of Ordovician vertebrate biogeography is endemism. Furthermore, the present lack of complete descriptions of most taxa, which are often represented only by isolated microremains, and the need for a thorough phylogenetic analysis preclude any phylogenetic palaeobiogeographic study. In such a framework, we also evaluate possible links between external, physical factors and the Ordovician radiation of vertebrates. The Late Proterozoic deposition of oceanic phosphate and the Early Cambrian increase in oxygen on Earth might have been the spur for vertebrate evolution before the phase when hard tissues appeared. The sharp decline of the marine strontium isotope ratio during the Middle to Late Ordovician transition, interpreted as having been controlled primarily by continental collisional tectonics and its associated erosion and weathering, has been proposed as the consequence of a possible mantle superplume event which could have caused the prominent Caradocian transgressive phase. This might have been a factor in the changeover from a Gondwanan to a Laurentian focus for vertebrates.
... In a number of publications dealing with acritarch palaeobiogeography, the method of Fortey and Mellish (1992) was criticized and acritarch workers emphasized the importance of their group for palaeogeographical studies (e.g. Tongiorgi et al. 1995;Servais and Fatka 1997). In most fossil groups, there is a wide range of different taxa, some of which are biostratigraphically useful, others are water-depth indicators, and again others are palaeobiogeographically useful. ...
Due to increasing availability of data for many fossil groups and a generally accepted palaeogeographical configuration, palaeontologists have been able to develop progressively more robust palaeobiogeographical scenarios for the spatial distributions of Ordovician marine faunas. However, most research in Early Palaeozoic palaeobiogeography centers on data derived from extensively studied localities in North America and Europe. Thus, clear patterns are emerging of regional biogeography for these areas. However, the fragmentary nature of data from other regions hinders the development of a detailed understanding of palaeogeographical schemes of many clades at the global level. Provincial patterns are now available for several fossil groups, but the global coverage remains generally fragmentary. Palaeobiogeographical investigations were traditionally focused on the better understanding of palaeogeographical scenarios and often employed quantitative analyses of faunal similarity. More recently palaeobiogeographical analyses have expanded to investigate questions such as the location and pace of speciation and macroevolution together with macroecological change. For example, studies on the evolution of speciation levels in the frame of the taxonomic radiation of the Great Ordovician Biodiversification are now available. Future investigations, including modelling, will provide more integrative, global patterns of provincialism, including the location of Ordovician biodiversity hotspots and the recognition of latitudinal diversity gradients.
... -The genus Coryphidium (Fig. 5G), reviewed by Servais et al. (2008), is a common component of acritarch assemblages from the Floian to Darriwilian stages of Perigondwana, but its first occurrence is in the uppermost Tremadocian. The genus has not been recorded from Baltica or Laurentia (Servais & Fatka 1997) and is one of the taxa used to define the Perigondwanan acritarch province (Li 1989;Servais et al. 2003;Molyneux et al. 2013). ...
First Appearance Datums (FADs) of selected, easily recognizable acritarch morphotypes are assessed to determine their potential contribution to correlation between Lower and Middle Ordovician stages and substage divisions along the Gondwanan margin (Perigondwana) and between Perigondwana and other palaeocontinents. The FADs for 19 genera, species and species groups are recorded throughout their biogeographical ranges. The taxa investigated fall into three groups. Some have FADs at about the same level throughout their biogeographical ranges and are useful for long-distance and intercontinental correlation. Among these are Coryphidium, Dactylofusa velifera, Peteinosphaeridium and Rhopaliophora in the upper Tremadocian Stage; Arbusculidium filamentosum, Aureotesta clathrata simplex and Coryphidium bohemicum in the lower–middle Floian Stage; Dicrodiacrodium in the upper Floian Stage; Frankea in the Dapingian–lower Darriwilian stages; and Orthosphaeridium spp., with FADs in the Dapingian–lower Darriwilian stages of Perigondwanan regions and at about the same level in Baltica. Other taxa, however, have diachronous (or apparently diachronous) FADs, and this needs to be taken into account when using them for correlation. A second group of genera and species, comprising Striatotheca, the Veryhachium lairdii group and the V. trispinosum group, have a recurring pattern of FADs in the Tremadocian Stage on Avalonia and in South Gondwana and West Gondwana, but in the Floian Stage of South China and East Gondwana. The third group, consisting of Arkonia, Ampullula, Barakella, Dasydorus, Liliosphaeridium and Sacculidium, have FADs that are markedly diachronous throughout their biogeographical ranges, although the global FADs of Arkonia, Ampullula, Liliosphaeridium and Sacculidium are apparently in South China and/or East Gondwana. It is possible that diachronous FADs are only apparent and an artefact of sampling. Nevertheless, an alternative interpretation, suggested by recurring patterns, is that some as yet undetermined factor controlled a slower biogeographical spread over time, resulting in diachroneity.
... As used here, Baltica consists of most of northwestern Europe (Finland, Norway, Sweden, the Baltic States, northeastern Poland) and northwest Russia to the present-day Urals ( Figure 5). Bagnoli et al. (1988), Servais & Fatka (1997), Tongiorgi et al. (2003), Servais et al. (2003Servais et al. ( , 2004, Hints et al. (2009) and Molyneux et al. (2013) reviewed the data on Ordovician acritarchs from Baltica ( Figure 5). Although most of the studies on Early Ordovician acritarchs from Baltica emphasize the taxonomic and biostratigraphic aspects of the assemblages recovered, several monographs have also been published. ...
A well-preserved and moderately diverse organic-walled microphytoplankton assemblage was recovered from the subsurface Lower Ordovician Nambeet Formation, Canning Basin, Western Australia. The microphytoplankton assemblage consists of prasinophyte phycomata (Leiosphaeridia spp.), acritarchs, cyanobacteria (Eomerismopedia maureeniae), degraded algae, chitinozoans and graptolite fragments. The acritarch assemblage comprises 13 genera, one of which is new (Aciculasphaera), 13 named species, three of which are new (Aciculasphaera interrupta, Gorgonisphaeridium martiniae and Loeblichia nambeetense), five species left in open nomenclature (sp.), and one cf. designation. The acritarch assemblage indicates an Early Ordovician (late Tremodocian through Floian) age and displays some similarities with comparable-age assemblages reported from North and South China, Australia and Laurentia. The paleogeographic distribution of the acritarch assemblage indicates that this assemblage represents a low- to mid-paleolatitude occurrence. Sedimentologic and palynologic evidence signifies deposition in a normal marine offshore environment.
... However, more detailed micropalaeontological work (e.g. Servais & Fatka 1997; suggests that the sediments were deposited in a deep-marine basin within the Ran and Tornquist oceans, which lay between Baltica and Avalonia/Gondwana (Fig. 7.7), rather than representing facies marginal to Baltica itself (Cocks & Torsvik 2005) (for detailed discussion see 'Avalonia-related terranes' section below). Baltica-related terranes. ...
The scenario of the Caledonian Orogeny is of a number of larger and smaller continental masses rifting from Gondwana and drifting north at various rates, sometimes rotating, eventually coming into contact with Laurentia and Baltica. The Gondwanan fragments formed an archipelago and moved rather like the fragments of Indonesia or the Philippines have been doing over the last 50 Ma. Furthermore, they did not all collide during the Caledonian Orogeny, but also in the subsequent Variscan Orogeny (see Kroner et al. 2008; McCann et al. 2008). A review of the present state of knowledge on the Caledonian Orogeny in Central Europe can be summarized in a number of salient points. • The existence of the terranes of Laurentia, Baltica and Gondwana has been inferred from geological studies, deep seismic profiling and potential field studies. • The main oceanic sutures are the Tornquist Suture/Caledonian Deformation Front (CDF) and the Iapetus Suture. • There is still ongoing debate concerning subduction polarity during ocean closures, or even a possible flip in subduction polarity. • A possible deep-reaching link between the CDF and the Iapetus Suture cannot be definitively proven. • The Iapetus Suture is defined across Ireland and Great Britain. • The CDF is defined in Scandinavia and between the North Sea and the Baltic Sea. • The southernmost extent of Baltica is located between the Southern Permian Basin depocentre and the Elbe Line and involves thrusting of Avalonia onto Baltica. • The thin-skinned nature of the Caledonian deformation complex is evident in the Baltic Sea area. Here, Baltica crust escaped deformation during Caledonian collision. • The longevity and regional importance of orogenic structures in the central European region is evident. Pre-existing tectonic structures of presumably Caledonian origin were reactivated during subsequent tectonic events. The physical properties of inherited lithospheric structure thus determine both the physical effects and the areal extent of processes active up to the present day. Some ongoing problems, however, still remain, including the following. • Precisely when and how did the various terranes collide? • Does surface geology indicate the exhumation of crustal roots not only in western Norway or north of Scotland, but also in other areas? • Can exhumation rates be deduced precisely enough to reconstruct the destruction of the Caledonian mountain ranges? • Was the southern Avalonia margin a passive margin formed by rifting from Gondwana in Early Ordovician time, or was it formed by later rifting? Did it face a major Rheic Ocean to the south, or a narrower mainly intracontinental basin? • Did Avalonia ride up over Baltica, or was it a sliver of crust that was obducted, leaving lower crust and mantle lithosphere to subduct? • Exactly when did Avalonia, the Armorican Terrane Assemblage and the other European peri-Gondwanan terranes leave Gondwana? • Why are the Caledonides of northern Germany buried beneath a thick covering of Mesozoic sediments? • How deep do the observed lineaments reach today? Do they exist below the lithosphere-asthenosphere boundary? • How important were strike-slip movements?
... The genus Frankea, is considered a biostratigraphical and paleobiogeographical marker for the Middle Ordovician of Gondwanan and peri-Gondwana. It has been encountered in the same interval in other areas of the world (Servais and Maletz 1992;Cooper et al. 1995;Servais and Fatka 1997;Vecoli 1999;Li et al. 2002;Rubinstein et al. 2011). ...
Based on palynological index species and other
significant taxa, subsurface Paleozoic formation can be differentiated
based on biostratigraphy. Five palynozones are recognized.
One biozone is present in the Sidi Toui Formation,
and indicates a middle ± upper Cambrian age. Four biozones
are identified in the Ordovician, Silurian, and Permian.
Permian and Triassic sediments unconformably overlie a
subcrop of different Paleozoic units. Thus, a major unconformity
has been identified in the south of Tunisia, which may be
related to the Hercynian orogeny
... The FEAAC forms a thrust sheet on Baltican crust ( Fig. 5; Winchester et al., 2002b). It was drilled in a 3130-m thick intersection on Rügen Island and consists of Tremadocian to Middle Caradocian turbidites, shales, and occasional tuffi tes with peri-North Gondwanan acritarchs (Servais and Fatka, 1997). Across the Southwest Baltic Sea, the FEAAC recurs in Northwest Poland, and docking has been shown to be pre-Middle Ashgillian for the presence of reworked North Gondwanan microfossils in Southwest Baltican sediments . ...
The Moesian Platform is a crustal block within southern Europe, located beyond the southwestern margin of the East European craton. Along this margin lie terranes that were accreted to Baltica as part of Far Eastern Avalonia during Late Ordovi- cian-Early Devonian time and terranes that already formed part of Cambrian Baltica, displaced as proximal terranes together with Far East Avalonian terranes. The tectonic history and crustal affinity of the Moesian Platform, however, remain poorly understood. A review of available tectonostratigraphic, paleontological, and geochro- nologic data suggests that the Moesian Platform comprises four distinct terranes, two with Baltican and two with Avalonian affinities. A fifth terrane, North Dobrogea, lies between the Moesian Platform and the East European craton and records Variscan (Carboniferous) accretion. This accretionary record leads to the paradox that the youngest accreted crust (North Dobrogea) lies closest to the craton, whereas the earlier accreted crust and crust derived from the craton itself are now located more externally. A review of terranes along the southwestern margin of the East European craton, between the North Sea and the Black Sea, suggests that a dextral strike-slip dominated the southwestern Baltican margin during Late Ordovician-Early Devonian accretion of Far Eastern Avalonia, much as is the case in western North America today. Variscan indentation of the Bohemian Massif led to escape-displacement of some Caledonian terranes, and strike-slip displacement during the Mesozoic opening of Mediterranean-style oceanic basins led to the current juxtaposition of Moesian ter- ranes, inverted with respect to their accretionary history.
... The northwestern parts of Central Europe belonged during the Ordovician to the microcontinent Avalonia that included the eastern seaboard of North America from Cape Cod, Massachusetts, through eastern Newfoundland, Canada, the southern part of the British Isles, Belgium, and the central European parts south of the Trans-European Suture Zone, that crosses Poland in a NW-SE direction. While Cocks et al. (1997) placed the northeastern margin of Avalonia (the Avalonia-Baltica boundary) close to the Ebbe line in central-northern Germany, it is now widely accepted that Belgium, the western and northern parts of Germany and possibly the northwestern part of Poland (western Pomerania, Koszalin-Chojnice Zone) belong to the easternmost extension of the microcontinent (Servais & Fatka 1997;Winchester et al. 2002b), but recent studies put this part on the southernmost edge of the Baltica plate (Poprawa 2006). It is also widely accepted that this microcontinent separated from Gondwana during the Early Ordovician (probably in the Arenig), and rapidly drifted northwards during the Ordovician, closing the Iapetus Ocean, but leaving behind a widening Rheic Ocean, up to the docking with Baltica during the latest Ordovician (Ashill, in terms of British series). ...
The Ordovician type sections for global correlation, that have been defined in the last decade, are situated either in Sweden (Baltica continent), North America (Laurentia) or the Yangtze Platform (South China continent). The historical sections in the British Isles have been abandoned and will serve only as regional standards in the future. The Ordovician outcrops and subsurface sections of Central Europe are, compared to the new standards, of limited value for international correlation and for the understanding of the Ordovician world. The Ordovician of Central Europe belongs to various areas with, in general, a very complex tectonic evolution. The localities described here (from Belgium, Germany, the Czech Republic, Poland and the Alpine region) are part of a vast region affected by the Variscan Orogeny and, in palaeogeographical tems, all of these areas belonged to peri-Gondanan terranes, with the exception of the northeastern part of Poland that belonged to the Baltica palaeocontinent. It is today widely accepted that, during the Ordovician, the eastern part of the microcontinent of Avalonia included Belgium, western and northern Germany, and possibly northwestern Poland. It is less clear to what entity the outcrop areas of the Rhenohercynian, Saxothuringian and Moldanubian zones belonged. It is evident that they must be attributed to Gondwana-derived terranes (such as, in palaeogeographical terms, Armorica or the Armorican Terrane Assemblage and Perunica) or to sedimentary basins in the vicinity of the Gondwanan supercontinent. However, it is still not clear whether the different areas were separate microcontinents or simply tectonically separated units (terranes) or different sedimentary basins. Ongoing and future research will possibly provide answers to these questions. Our review includes the Avalonian sequences of Belgium in the northwestern part of the investigated area of Central Europe, continues into western, northern and eastern Germany, and extends into northwestern and southern Poland. The review of the Ordovician of the Saxothuringian and the Moldanubian zones includes the outcrop areas of southeastern Germany, the Czech Republic and southwestern Poland. The Ordovician from the pre-Variscan parts of the Alpine mountain chains of Switzerland, Austria and northern Italy are also briefly discussed. For each individual area, we present the stratigraphical succession, based on the most recent results, and correlate the successions with the modern standard of Ordovician stratigraphy, including the timeslice subdivision of Webby et al. (2004). The most complete successions are those from Belgium (Brabant Massif and Condroz Inlier), from Saxothuringia (Schwarzburg Anticline) and from Bohemia (Prague Basin). Most of the other areas present generally isolated outcrops in a complex tectonic context that cannot easily be integrated in a complete stratigraphical succession. Such areas include the Ardennes (Belgium and western Germany), the Black Forest (Schwarzwald, southwestern Germany), the Ebbe Mountains and isolated outcrops in Hessen (western Germany), the subsurface Ordovician of northern Germany, many of the areas in eastern Germany (such as the Harz Mountains or the Lausitz region, for example), and most areas in Poland, but also the basement of the Alps, which is very poorly understood but includes some Ordovician fragments. Due to the complex tectonic history, most rocks are poorly preserved, and fossils are often absent in the sedimentary successions, which makes a perfect understanding of the stratigraphical succession difficult in many areas. Furthermore the development of the different sedimentary basins is mostly unknown thus far. Sedimentary analyses are absent from many areas, and the precise relationship between the different successions presented in this review remains preliminary. Fossils are absent in many sedimentary units, and the mostly siliciclastic successions, that are now attributed to cold-water environments of high latitudes in the southern hemisphere, provide, compared to the palaeocontinents at low latitudes, only few fossils. An exception is the Prague Basin, an area that is famous for its excellent palaeontological content. The development of carbonate rocks in the latest Ordovician was possibly due to a global warming event. In summary, a high number of micro- and macrofossils have been described from the various successions of the Ordovician of Central Europe, allowing not only international correlation and palaeogeographical attributions, but also a first interpretation of the palaeoenvironment.
... The Cambrian and Lower Ordovician deposits of megasequence 1 of the Brabant Massif are mostly marine and terrigenous, derived from the Gondwana continent, as witnessed by acritarchs and other fossils (Cocks & Fortey, 1982;Cocks et al., 1997;Servais & Fatka, 1997). ...
Pre-Silesian rocks in the Netherlands comprise two different units: i) a deeply buried,
moderately deformed, slightly metamorphic and scarcely known Caledonian basement of
Precambrian to Silurian age, and ii) Middle Devonian to Early Carboniferous siliciclastics and carbonates which unconformably cover this basement. The basement is best known from the Anglo-Brabant deformation belt. Its rocks, marine, shelf to deep-water clastics, were deformed during the three-plate convergence of the Caledonian orogeny (Late Silurian to Early Devonian). The Netherlands was situated on the Gondwana-derived Avalonia plate, which collided with Baltica and Laurentia. Following the last, Early Devonian, phase of the Caledonian orogeny, a horst-and-graben topography controlled the deposition, with fluvial deposits residing on the footwall blocks, and basinal deposits in the hanging-wall blocks. Horst blocks shielded a large portion of the area from siliciclastic influx coming from the Mid North Sea High, allowing a widespread carbonate platform to form during the Early Carboniferous in the central and southern Netherlands. The synsedimentary horst-and-graben faults were gradually overstepped, and gave way to the regional subsidence of a Silesian coal-bearing molasse basin in the Variscan foreland.
... The intensely tectonized Ordovician clastic successions present, e.g., in the subsurface of the island of Rügen, NE Germany, have been interpreted as an accretionary prism thrusted onto the southwestern border of the Baltic Platform during the Avalonia-Baltica collision [7, and references therein]. Palaeogeographically, the Ordovician of Rügen can be attributed to the easternmost extension of Avalonia [8,9,14]. Accordingly, it is reasonable to think that the source area of the reworked acritarchs corresponds to the Ordovician of Rügen, where Lower to Middle Ordovician acritarchs closely comparable to the reworked microflora of the Slagelse-1 and Pernille-1 boreholes occur [8], or another area, such as Pomerania (North Poland) which also formed part of the 'Danish-North German-Polish Caledonides'. ...
Profuse and well-preserved acritarchs were recovered from subsurface
Lower Palaeozoic successions cored by the boreholes Slagelse-1 and
Pernille-1 (Danish-North German Basin). Together with Llandovery in situ
microphytoplankton, reworked Cambrian and Ordovician species occur. The
reworked Ordovician acritarchs show a clear Perigondwanan
palaeobiogeographic affinity and indicate clastic sedimentary input from
a Perigondwanan-related terrane located south of the East European
Platform. Microfloral similarity enables identification of the detrital
source area with the Avalonia Terrane. The present data also suggest
that development of a foreland basin marginal to the Caledonian
Deformation Front in the Danish-North German Basin started in Early
Silurian times.
... In the NW, the Iapetus Ocean is presumed to have been situated north of the Lake District, now represented by a suture that continues through Ireland (Cocks et al. 1997). In the NE, the Tornquist Sea, which separated Avalonia from Baltica, was located in the north of Germany, with a suture crossing northern Germany and northwestern Poland (Servais & Fatka 1997). In the south of Avalonia the Rheic suture is difficult to outline and is strongly debated, because of the Variscan overprint. ...
In recent decades various research studies have focused on the reconstruction of Palaeozoic Europe, reflecting the complex geodynamic history related to the formation of the supercontinent Pangaea. It has been demonstrated that Palaeozoic Europe comprises a series of tectonostratigraphical units, or 'terranes', located between the remnants of three major palaeocontinents, Gondwana, Laurentia and Baltica. Some of these 'terranes' have been referred to as 'microcontinents', a typical (palaeo-)geographical term, and as 'microplates', a typical plate-tectonic term, giving rise to misunderstandings and a continuing scientific debate. This confusion is based primarily on an inconsistent use of different palaeogeographical terms by specialists from different scientific disciplines. Whereas large palaeocontinents such as Baltica and Siberia have been named as terranes by some workers, several peri-Gondwanan 'terranes' have been attributed to microcontinents or microplates, without conclusive reasoning. This paper is a critical review of the terminology used for three European peri-Gondwanan palaeogeographical entities: 'Avalonia', 'Armorica' and 'Perunica'. The review indicates that only Avalonia should be considered as a separate (micro-)continent on a separate (micro-)plate. Armorica has many different definitions and is commonly considered to be composed of several terranes. It is, however, not at all evident if Armorica was a separate (micro-)continent and/or an independent (micro-)plate. For Perunica, defined originally as a separate microplate, current evidence demonstrates that it can probably be considered only as a palaeobiogeographical province.
... Planktonic fossils cannot be used to indicate palaeoprovinciality but they can indicate palaeolatitudes (Cocks & Verniers 2000). The planktonic acritarchs and chitinozoans in the Middle Ordovician of the Rügen and Pomerania subsurface are clearly of a high-latitude and not of a low latitude Baltic affinity (Servais 1994; Servais & Katzung 1993; Servais & Fatka 1997; Samuelsson et al. 2000, 2001; Vecoli & Samuelsson 2001a contra Cocks et al. 1997). They indicate a southern provenance for this microplate and hence it is thought to be Gondwana-derived (Servais 1994; Vecoli & Samuelsson 2001b; Samuelsson et al. a this volume). ...
A review is given of recently published and new data on Avalonia east of the Midlands Microcraton. The three megasequences from Cambrian to mid Devonian described in Wales and Welsh Borderland are also present east of the Midlands Microcraton (Brabant Massif, Condroz, Ardennes, Remscheid and Ebbe inliers, Krefeld high). The three mega-sequences are caused by a tectonic driving mechanism and are explained by three different geodynamic contexts: an earlier phase with extensional basins or rifting and rather thick sequences, when Avalonia was still attached to Gondwana; a second phase with a shelf basin with moderately thin sequences when Avalonia was a separate continent and a later phase with a shelf or foreland basin development and thick sequences. Deformation of the megasequences 1 and 2 or 1 to 3 varies between areas. In Wales and the Lake District the Acadian phase is long-lived and active from early to mid Devonian. In the Ardennes inliers a deformation is active between the late Ordovician and the Silurian (Ardennian Phase), with a similar intensity as the core of the Brabant Massif, when present erosion levels are compared. The Brabant Massif is partly deformed by the long-lived Brabantian Phase from late Silurian till early mid Devonian. Both the Ardennes inliers and the Brabant Massif are not classic orogenic belts, only slate belts where no more than the epizone is reached at present erosion levels. Areas supposedly close to the microcraton or basement are nearly undeformed (SW Brabant Massif and central Condroz). A model of anticlockwise rotation of Avalonia of about 55° from Caradoc to Emsian is proposed to explain the deposition setting of megasequence 3 and the subsequent Acadian and Brabantian deformation. Immediately after the Avalonian microcontinent touched Baltica in Caradoc times it created a short-lived subduction magmatic event from The Wash to the Brabant Massif and soon after the magmatism ended a foreland basin developed. Possibly during and after that development a long-lived and slow compressional event occurred, leading to the deformation of the Anglo-Brabant Deformation Belt. In the early Devonian, contemporaneous with the shortening of the Anglo-Brabant Deformation Belt, extension occurred in the Rheno-Hercynian Zone, possibly caused by the same slow rotation of Avalonia. More evidence emerges that Avalonia cast of the Midlands Microcraton comprises not one but probably two terranes: the remnant of the palaeocontinent Avalonia, and what is called the palaeocontinent Far Eastern Avalonia; the latter is only occasionally observed in the few deep boreholes into the Heligoland-Pomerania Deformation Belt, in southern Denmark, NE Germany and NW Poland, with scant available indirect data in between indicating only Proterozoic basement and no Caledonian deformation. For Far Eastern Avalonia a similar palaeogeographical history is postulated as Avalonia, with rifting from Gondwana in Arenig or earlier times, collision with Baltica before the mid-Ashgill and deformation between the late Ordovician and latest Silurian. The Avalonia concept might need to be expanded to an 'Avalonian Terrane Assemblage' with cratonic cores and small short-lived oceans as in the Armorican Terrane Assemblage.
... However, the distinction between these two assemblages might not be so straightforward, as some elements of the AAL assemblage also occur in high latitudes (Vecoli, 2004;Breuer and Vanguestaine, 2004and the authors' personal observation). Acritarch associations displaying significant " mixing " of typical elements of the two assemblages have been reported from South China and Baltica, and have been interpreted as indicating a paleogeographical position at mid paleolatitudes (Bagnoli et al., 1988;Yin, 1995;Brocke, 1997;Servais and Fatka, 1997;Brocke and Fatka, 1999;Webby et al., 2004). There are significant compositional differences between Early Ordovician acritarch suites from the South China and those from North Chinese terranes (Yin, 2006). ...
... Shortly after its first appearance during the Early Ordovician, Veryhachium developed a wide paleogeographic distribution, occurring on a number of paleocontinental blocks across a range of latitudes. This is also true of Middle and Late Ordovician Veryhachium morphotypes, thereby eliminating them as paleobiogeographic indicators (Servais and Fatka, 1997;Vecoli, 1999;Servais et al., 2003 ...
Veryhachium Deunff 1954, originally described from the Ordovician of western France, is one of the most frequently recorded acritarch genera. Over 250 species and subspecies, from the Cambrian to the Neogene, have been attributed to the genus. This genus has a simple morphology; it displays a triangular, rectangular, or polygonal central vesicle, with a few, simple processes drawn out from the angles of the vesicle in a single plane, and sometimes with supplementary or auxillary processes arising from the vesicle body. Veryhachium has been
emended and revised numerous times. The number of valid species is excessive: most are probably synonyms. To facilitate effective classification, only a few morphological categories should be retained. For the Lower Paleozoic, the use of two informal groups is proposed.
These are the Veryhachium trispinosum group for triangular specimens, and the Veryhachium lairdii group for rectangular forms. Although generally abundant and widespread throughout the Phanerozoic, Veryhachium is of limited biostratigraphic, paleoecologic, or paleogeographic value. However, its First Appearance Datum (FAD) is of great importance for Ordovician stratigraphy; the first Veryhachium morphotypes appear in the Tremadocian Stage, making the genus an important biostratigraphic marker.
... However, the distinction between these two assemblages might not be so straightforward, as some elements of the AAL assemblage also occur in high latitudes (Vecoli, 2004; Breuer and Vanguestaine, 2004 and the authors' personal observation). Acritarch associations displaying significant " mixing " of typical elements of the two assemblages have been reported from South China and Baltica, and have been interpreted as indicating a paleogeographical position at mid paleolatitudes (Bagnoli et al., 1988; Yin, 1995; Brocke, 1997; Servais and Fatka, 1997; Brocke and Fatka, 1999; Webby et al., 2004). There are significant compositional differences between Early Ordovician acritarch suites from the South China and those from North Chinese terranes (Yin, 2006). ...
Acritarch assemblages are described here for the first time from the Early Ordovician Yinzhubu and Ningkuo formations of the Nanba section (Yiyang region, Hunan province, South China). Independent stratigraphical control is provided by co-occurring late Tremadocian–early Floian (early Arenig) graptolite and chitinozoan biozones. A very diverse association of 33 species attributed to 23 genera is identified, and three acritarch assemblage zones are distinguished. These are comparable to coeval assemblages from several localities worldwide. During the Early Ordovician the Yiyang area was at low latitudes. The acritarch association interestingly shows a mixed character, comprising typical taxa from both cold-water and warm-water paleobioprovinces.
... , Vavrdová , 1974 ; Paris and Robardet , 1990 ; Havlíček and Fatka , 1992 ; Havlíček et al . , 1994 ; Servais and Fatka , 1997 ; Plusquellec and Hladil , 2001 ; Álvaro et al . , 2003 ; Fatka , 2003 ; Vecoli and Le Hérissé , 2004 ; Bełka and Narkiewicz , 2008 ) . ...
New LA-ICP-MS U–Pb detrital zircon ages from Ediacaran and Paleozoic siliciclastic rocks are used to constrain provenance and paleogeographic affinities of the Teplá-Barrandian unit (TBU) in the centre of the Bohemian Massif (Central Europe, Czech Republic). The samples taken span the period from ≤ 635 Ma to ∼ 385 Ma and permit recognition of provenance changes that reflect changes in geotectonic regime. Detrital zircon age spectra of two Ediacaran, one Lower Cambrian and three Upper Ordovician samples resemble the ages known from the NW African proportion of Gondwana, particularly the Trans-Saharan belt, while three rocks from higher Lower Cambrian to Lowermost Ordovician strata contain detritus that may have been derived exclusively from local sources. The age spectrum of the Devonian rock is a combination of the NW Gondwanan and local features. These new findings in combination with a wide range of published data are in agreement with a Neoproterozoic subduction-related setting at the margin of Gondwana followed by a Cambrian/Early Ordovician rifting stage and an Ordovician passive margin setting. Furthermore the data are in favour of a position of the TBU at the Gondwanan margin throughout pre-Variscan times.
... Caryocaridids have so far been recovered from two areas in Germany, the Ebbe-Anticline in the Rheinisches Schiefergebirge (Rhenish Massif) and from the subsurface of the island of Ru « gen in the Baltic Sea. These two areas are considered to be part of the early Palaeozoic microcontinent of Eastern Avalonia (Servais and Fatka, 1997). Koch and Brauckmann (1998) summarised the previous literature and redescribed specimens (Caryocaris wrightii ( = 3) and Caryocaris sp. ( = 20) from the Rheinisches Schiefergebirge, which were found in the Kiesbert-Tonschiefer Formation (fasciculatus Biozone) and in the Plettenberger-Ba «nderschiefer Formation (lentus Biozone), both currently attributed to the Llanvirn D. artus Biozone (Eiserhardt et al., 2001b). ...
Evidence is presented here for a zooplanktonic component in Ordovician marine ecosystems, namely the caryocaridid arthropods, that add to other well-documented midwater organisms such as graptolites, cyclopygid and telephinid trilobites, orthoconic cephalopods and the microphytoplankton (e.g. acritarchs). Although the soft anatomy of caryocaridids is largely hypothetical, their carapace design and ultrastructure, and their phyllocarid-like abdominal morphology (flattened furcal rami, telescopic segments) indicate a swimming lifestyle in midwater niches. Both functional and ecological interpretations are supported by their palaeogeographical and facies distributions and by analogies with modern pelagic ostracods. Caryocaridids occur at numerous localities on the palaeo-plates of Laurentia, Baltica, Avalonia, Perunica, Gondwana and South China and are recurrent faunal components of graptolitic black shales (mainly Tremadoc to Llanvirn). Typical faunal associates are the didymograptid and isograptid graptolites, pelagic cyclopygid and deep-sea benthic atheloptic trilobites. Their depositional environments suggest that the caryocaridids and their pelagic associates (graptolites) most probably thrived in waters above the distal shelf margins, where upwelling-controlled primary productivity possibly reached its maximum. Their exact bathymetrical range within the water column cannot be inferred from fossil evidence. However, their feeding strategies may have led them to exploit food resources across the mesopelagic–epipelagic boundaries as do numerous midwater crustaceans in present-day ecosystems. Caryocaridids represent a significant step in the post-Cambrian colonisation of midwater niches by arthropods and in the construction of complex modern foodwebs.
Acritarchs, microphytoplankton of algal protists, from the Shiala and Yong Limestone formations of the Gunji village along Kali river (upstream) of Kumaon Tethyan Himalaya, Pithoragarh district, Uttrakhand, India have been examined for the first time. It aims to test the basin-wide existence and testing the reliability of already locally established biozones from the Garhwal Tethys Himalaya, Chamoli district, Uttrakhand. The study reveals moderate to poorly preserved, matured assemblages and diversified forms of acritarchs from both formations. The assemblage includes sphaeromorphs, acanthomorphs, netromorphs, polygonomorphs, diacromorphs, herkomorphs, etc. Two palynoassemblages have been recognized each from the Shiala and Yong Limestone formations. Palynoassemblage (I) from the Shiala Formation is confirmed by one productive sample which reveals a mix of Late Ordovician and Silurian forms. The acritarchs assemblage assigned to 16 genera with at least 13 species. The acritarchs from the Yong Limestone Formation are more plentiful and diverse confirming the Palynoassemblage (II) that contains biostratigraphically significant forms of typical Silurian (Ludlow) age. This Palynoassemblage is assigned to 23 genera with 16 species. The paper also describes the possible reasons for floral difference from the same formation and basin sampled at two different localities of the Tethys Himalaya, possibly due to palaeoclimatic constraints. However, detailed work on this aspect is required.
The palynoassemblages from both the formations describe morphologically non-distinct, ubiquitous, wide palaeogeographic spread and uncertain stratigraphic taxa too along with biostratigraphic significant forms.
Acritarchs and chitinozoans were documented from Ordovician strata and miospores from Lower Permian beds in the Zardkuh area. Ninety-one palynomorph species, comprising acritarchs (63 species of 31 genera), chitinozoans (16 species of 12 genera), and miospores (12 species of 10 genera) were recognized that form 10 local assemblage zones, comprising Zones A–F = acritarchs, G–I = chitinozoans, and J = miospores. Zone A occurs in the uppermost Ilebeyk Formation, indicating Late Cambrian; Zones B–E are present in the Zardkuh Formation, suggesting Early Ordovician (Tremadocian–Floian)–Middle Ordovician (Dapingian) and Zone F occurs in the Seyahou Formation, presenting Late Ordovician (Hirnantian). Likewise, three Gondwanan chitinozoan Zones G–I were established in this succession. Zones G–H occur in the Upper Shale Member of the Zardkuh Formation, supporting an Early-Middle Ordovician (Floian–Dapingian), and Zone I is restricted to the Seyahou Formation, suggesting Late Ordovician (Hirnantian) age. Finally, Zone J occurs in the Faraghan Formation, confirming Early Permian. Based on palynomorph zones, two hiatuses are present within the Paleozoic sequences of the study area. The first hiatus occurs between the Zardkuh and Seyahou formations, encompassing the Middle Ordovician (Dapingian) and much of the Late Ordovician (Sandbian and Katian). The second hiatus appears between the Seyahou and Faraghan formations, spanning the Silurian, Devonian, Carboniferous, and earliest Permian (Asselian). The palynomorph taxa, including Arbusculidium, Striatotheca, Coryphidium, Vavrdovella, Eremochitina, Velatachitina, and miospore taxa, confirm that the study area belongs to peri-Gondwana paleoprovince. Four new species are Vavrdovella mawlawii sp.nov., Vogtlandia zardkuhensis sp.nov, Pseudocoryphidium zagrosensis gen et sp.nov, and Pterospermella saadii sp.nov.
The triangular-shaped acritarch genus Frankea, which displays characteristically branched appendices, has considerable stratigraphical and palaeobiogeographical significance in the Ordovician. High intraspecific variability of terminal processes (appendices) numbers and process lengths within Frankea suggest that the genus could be suitable for use in studying the relationship between morphological characters and environmental conditions. Quantitative multivariate exploratory analyses on Frankea indicate that the length of the appendices varies according to different localities and is most probably ecologically dependent and not age diagnostic as previously suggested. Principal components analyses and discriminant analyses are used to assess the original specific classification of Frankea. The morphometric analyses suggest that usage of quantitative characters, such as the process length, should be taken into consideration during the separation of species. A comprehensive discussion of qualitative and quantitative characters is carried out and suggests there are only three species of Frankea: F. hamata, F. hamulata and F. sartbernardensis.
A main goal of this study was to understand the character of the Caledonian Deformation Front in Pomerania, NW Poland and its relationship to the adjoining Teisseyre-Tornquist Zone (TTZ), in the context of the Avalonia-Baltica early Palaeozoic collision. Since the Pomeranian Caledonides are concealed beneath 1–4 km thick platform cover of upper Palaeozoic and Mesozoic sediments, we used a combination of potential field, seismic and well data to investigate the basement architecture and structure of the lower Palaeozoic rocks. Starting from a qualitative review of gravity and magnetic data, we built a 2D gravity and magnetic model upon the PolandSPAN™ PL1-5600 seismic reflection line and applied 3D gravity inversion for a depth-to-basement study. Using well tops, a top lower Palaeozoic horizon and lower Palaeozoic isopach map were created. We found out that the Pomeranian Caledonides represent a thin-skinned fold-and-thrust belt involving Ordovician and Silurian sediments of the Caledonian foreland basin. The deformation front was developed due to the buttressing effect of a basement ramp occurring directly above the TTZ. The latter corresponds to a Precambrian suture zone overprinted by successive extensional tectonics and buried beneath the foreland basin. In northern Poland, the suture is defined by a remnant crustal keel still preserved underneath the TTZ, probably resulting from Precambrian collision during formation of the Rodinia paleocontinent. We propose that the extension of the Thor suture separating Baltica and Avalonia must exist west from the TTZ, probably in the Rügen area. In our interpretation, the TTZ represents an intra-cratonic crustal discontinuity comparable to its NW prolongation, the Sorgenfrei-Tornquist Zone that runs across the Baltic Sea, Sweden and Denmark. Consequently, the basement underlying the Palaeozoic Platform in NW Poland may be considered to have been part of Baltica in early Palaeozoic times.
Diversified assemblages of acid-resistant plant microfossils (acritarchs, prasinophytes and algal/cyanobacterial filaments) have been obtained from the so-called "Basal clastic Series" or "Devonian basal clastics". Basal clastics are predominantly coarse-grained sediments which form the lowermost portion of the Palaeozoic clastic cover of the Brunovistulicum. Excellent preservation of recovered specimens, a high density of accumulations of palynomorphs in investigated rock samples, a lack of thermal alteration of a polymeric vesicle wall (TAI about 1+) and common imprints of crystals of pyrite document the autochthonous origin of acritarch associations. Palynomorphs obtained from the three deep boreholes (Měnin-1, Němčičky-3 and Němčičky-6) represent a reliable evidence of the late Early Cambrian age (Holmia kjerulfi - Protolenus faunal zones) of fine-grained interlayers within the predominantly coarse-grained sequences as well as their marine origin. New investigation of samples from Měnin-1 borehole (depth 1565-1566 m) extends the age of the marine ingression in southern Moravia to the lowermost Cambrian (palynozone Asteridium tornatum - Comasphaeridium velvetum) Moreover, assemblages of fossil marine microplankton from southern Moravia may elucidate as yet not resolved problems of palaeogeography and of the provenance of terranes accumulated near the Baltica/Gondwana suture (Trans-European Suture Zone).
Palynomorphs (acritarchs and Chitinozoa) provide useful biostratigraphical and palaeobiogeographical information concerning the subsurface Ordovician of the Rügen Island (NE-Germany, Baltic Sea). The oldest sedimentary deposits present at Rügen, dated by acritarchs, are of late Tremadoc age. Arenig sediments have not been recorded. Most boreholes contain a succession of rocks attributed to a Llanvirn (Aberreiddian and Llandeilian) to early Caradoc age. The youngest rocks recorded in the Rügen sequence are dated by chitinozoa and can be attributed to the middle to late Caradoc and possibly to the early Ashgill. Palaeobiogeographical information from both the acritarchs and the Chitinozoa indicates that the Rügen Ordovician can be attributed to high latitudes in the southern hemisphere and most probably to Avalonia.
Geological data concerning the Early Palaeozoic sequences of northern Central Europe are compiled and interpreted concerning stratigraphy, sedimentation, palaeogeography, tectonics, metamorphism, and geochronology. Based on these data, an External Caledonian Belt can be traced from the eastern North Sea to the Holy Cross Mts. in southeast Poland with three distinct segments - the Schleswig, Rügen and Pomeranian Caledonides. In front of the Caledonian belt, a foredeep developed from Late Ordovician to Late Silurian times. Each segment of the Caledonides displays differences, above all in stratigraphic extent and degree of deformation. But the thrust-and-fold structure and their thrusting upon the foreland are common features, although the transport distances may vary considerably between the different segments. The Ordovician sequence of the Rügen Caledonides represents sedimentary environments situated far away from Baltica, whereas the Pomeranian Caledonides evolved from the Baltic epicratonic cover with overlying foredeep deposits. Beneath the External Caledonian Belt, Baltica's crust extends far to the south. Scarce data, scattered from southern Britain to southern Poland, indicate an Avalonian core within the Internal Caledonides south of the external belt. Available data allow to construct a plate tectonic model for the Early Palaeozoic evolution to the south of present Baltica, including rifting, ocean floor spreading associated with subduction, arc volcanism, obduction of oceanic crust and flysch deposition, convergence and accretion, collision and overthrusting as well as development of a foredeep on Baltica's crust.
Petrological, sedimentological and ichnological studies of cores from the Měnín-I borehole revealed episodic shallow marine influence in the terrestrial clastics underlying the Devonian clastic and carbonate rocks. The organic-walled, acid-resistant microfossils have been recovered from bioturbated beds and have allowed us to determine the age as the earliest Cambrian (most likely Platysolenites antiquissimus Faunal Zone). Several index acritarch species justify a preliminary assignment to the Asteridium tornatum-Comasphaeridium velvetum Acritarch Zone. The microfossils are very well preserved, without any noticeable thermal alteration (thermal alteration index about 1+) or mechanical damage. The ichnoassemblage contains Diplocraterion isp., Skolithos isp., and Planolites isp. The intensity of bioturbation and ichnofabric patterns correspond well to those described from the Cambrian of the East European Platform. The composition of Cambrian acritarch assemblages, of the ichnotaxa, as well the very low thermal alteration of organic-walled microfossils, link this Moravian sedimentary cover of Brunnia (Brunovistulicum in broader sense of the meaning) to the sediments of the same age which rest on other crustal segments in the southern and central part of Poland and even further on the Baltica Paleocontinent. This indicates a connection rather than separation of these Cambrian "Gondwanan parts" and Baltica by the Trans-European Suture Zone.
From the Ordovician of the Ebbe and Remscheid Anticline (Rhenish Massif, Germany) the hitherto known finds of the family Cyclopygidae are described and most of them figured. They belong to the genera Cyclopyge, Degamella, Microparia, Pricyclopyge, Ellipsotaphrus, and Psilacella. Furthermore the investigation and stratigraphy of the localities, the additional fauna as well as the palaeogeographical situation are outlined.
Borehole G 14-1/86, located in the Baltic Sea between the Tornquist Zone and the Caledonian Deformation Front/Thor Suture, penetrates a Lower Palaeozoic sedimentary succession deposited on the south-western margin of the East European Platform. Detailed palynological analysis of the Ordovician and Silurian successions enables precise dating and facilitates provenance interpretation of the sedimentary sequence. The following chitinozoan biozones are identified: Cyathochitina primitiva Biozone (early - early late Arenig); Laufeldochitina striata Biozone (late Abereiddian - late Llandeilan) and Ancyrochitina merga Biozone (Cautleyan - Rawtheyan, middle Ashgill). A further chitinozoan assemblage is possible to be correlated with the global Spinachitina maennili Biozone (uppermost Rhuddanian - lower Telychian). A relatively diversified acritarch assemblage of Ashgill age (independently dated by Chitinozoa) also occurs. This assemblage contains numerous reworked forms of Llanvirn, Tremadoc and late Cambrian ages. The reworked Llanvirn acritarchs are typical of the high-latitude Perigondwanan microphytoplankton palaeobioprovince and testify to detrital input of Gondwanan-related source during the Ashgill, suggesting that by this time the Tornquist Ocean was closed.
The pre-Devonian part of the Lohme 2/70 well was investigated for its chitinozoan fauna. All samples from the investigated interval, 3288.4 to 3345.6 m, yielded an assemblage of moderately to poorly preserved flattened chitinozoans typical of the North Gondwana Siphonochitina formosa Biozone including e.g. Cyathochitina jenkinsi NEVILLE 1974, Conochitina parviventer JENKINS 1967 but also Lagenochitina cf. cybaea (UMNOVA 1969). The recovered assemblage indicates a depositional age from the earliest to the early late Abereiddian. The presence of S. formosa corroborates the earlier palaeogeographical attribution of the Rügen Ordovician to eastern Avalonia.
Early to mid Palaeozoic marine phytoplankton are represented by acritarchs and associated forms, which had a global distribution from the early Cambrian to the early Carboniferous (Mississippian). Palaeozoic phytoplankton assemblages show varying degrees of cosmopolitanism and endemism through time. A high degree of cosmopolitanism was evidently characteristic of the Cambrian and much of the Late Ordovician, Silurian and Devonian, but provincialism was more marked in the Early Ordovician and Hirnantian (latest Ordovician), the latter at a time of major palaeoenvironmental perturbations. Distribution patterns of Palaeozoic phytoplankton are attributed to a number of interacting factors, including palaeolatitude, palaeotemperature, oceanic circulation patterns, the disposition of continents, differentiation between oceanic and cratonic (distal-proximal) assemblages, and sedimentary environments and facies. There are indications that biogeographical ranges of taxa shift over time. Moving our understanding of Palaeozoic phytoplankton biogeography forward requires (1) targeted investigation of regions and time periods for which no or little data exist, (2) quantitative analysis of data to investigate how similarity between regions varies through time and how this might correlate with other datasets such as carbon isotope stratigraphy or sea-level, and (3) rigorous application of well-defined time slices to compare coeval assemblages, at least within the limits of resolution.
The uppermost Ordovician in the Holy Cross Mountains is represented by sandy mudstones, sandstones and marls of the Zalesie Formation deposited during the Hirnantian regression. Two arcitarch assemblages were recognized in the studied Upper Ordovician succession of the southern Holy Cross Mountains. The first one is dominated by species of Baltisphaeridium, Polygonium, Exculibranchium, Orthosphaeridium, Ordovicidium, Peteinosphaeridium, Multiplicisphaeridium, which occur in the upper Caradoc deposits. Upward in the section, these taxa are replaced mainly by diversified species of Veryhachium occurring together with Domasia, Deunfia, Leiofusa, Polygonium, Cheleutochroa, Multiplicisphaeridium and Polygonium. In the Zalesie Formation (upper Ashgill) they are accompanied by the redeposited Furongian/Lower Ordovician specimens and the Middle Ordovician species of the peri-Gondwanian affinity (e.g. Frankea), which were likely replaced from Avalonia during collision of this terrane with Baltica
Acritarchs from the Lashkarak, Ghelli and Niur formations of the western part of Kuh-e-Saluk were examined to more precisely determine the stratigraphical age. This study was also undertaken to assess the palaeogeographic relationships of the northeastern Alborz Range to the Southern and Northern Hemispheres during the Palaeozoic interval represented by these formations. A total of 78 acritarch taxa were encountered. Four new species together with two species in open nomenclature are described: Multiplicisphaeri-dium iranicum, Multiplicisphaeridium sp., Veryhachium membranispinum, Stelliferidium persicum, Leiofusa sp., and Estiastra iranicum. The encountered acritarch species have been arranged in six ascending local stratigraphic Zones. Zones I-II occur in the Lashkarak Formation, suggesting an Early Ordovician age (Tremadoc-Arenig). Zones III-V are present in the Ghelli Formation, indicating a Mid and Late Ordovician age. Zone VI appears in the lower part of Niur Formation and suggests the Early Silurian age (Llandovery). The Early Ordovician acritarchs of the Lashkarak Formation were com-pared with those from other parts of world. This comparison indicates a broad similarity with those of the same age in northern Africa, southern Europe and southwestern China. This similarity suggests that the northeastern Alborz Ranges were part of the Peri-Gondwanan supercontinent during the Early Ordovician. The Mid to Late Ordovician and Early Silurian acritarch taxa were also compared with those of the same age from elsewhere. This comparison indicates a broad similarity with those of northern Africa, southern Europe, the Middle East and the United States. This similarity suggests that the Peri-Gondwanan palaeocontinent began to move toward the Northern Hemisphere palaeocontinent during the Mid and Late Ordovician and by the Silurian formed the supercontinent of Pangea. Diverse acritarch taxa in the Early Ordovician (Lashkarak Fm.), Mid and Late Ordovician (Ghelli Fm.) and Early Silurian strata (Niur Fm.) reveal a marine environment for each formation.
Trilobites and brachiopods are the two main fossil groups that allowed construction of the first palaeogeographical maps for
the early Palaeozoic. Together with the bivalves and ostracodes, the benthic elements of these fossil groups have proved to
be of great palaeobiogeographical importance. For this reason, these groups are usually considered to be ‘better’ fossils
for inferring Ordovician palaeogeography. The present study indicates that planktic and nektic fossil groups should not be
neglected in such palaeobiogeographical studies. The plotting on a palaeogeographical reconstruction for the Arenig (Lower
Ordovician, – 480 Ma) of some planktic (acritarchs, chitinozoans) and nektic (vertebrates, pelagic trilobites) fossil groups
indicates that their distribution appears in part surprisingly similar to that of the benthic trilobite faunas that are considered
to display the greatest provincialism. For example, the distribution of the ‘peri-Gondwanan’ acritarch province including
Arbusculidium filamentosum, Coryphidium and Striatotheca, and the distribution of the Eremochitina brevis chitinozoan assemblage are almost identical to the palaeogeographical distribution of the Calymenacean-Dalmanitacean trilobite
fauna. A review of the different planktic and nektic fossil groups also indicates that it is very important to carefully select
‘good’ palaeogeographical indicators, in most cases from a large number of taxa. It appears that almost all fossil groups
include some ‘good’ palaeobiogeographical ‘markers’. Therefore it is important to search for ‘better’ taxa within each fossil
group, instead of looking only for the ‘better’ fossil groups as a whole.
Central Europe consists of a complex mosaic of more or less independent terranes with varying tectonometamorphic histories, usually also of different lithological compositions and protolith, and thus it is reasonable to suppose that the majority of these blocks have experienced somewhat different palaeogeographical evolution. The present terrane juxtaposition has been interpreted in general as a result of the Variscan collision of peri-Gondwanan and peri-Baltic derived terranes, with Gondwana on one side and Baltica and/or Laurentia on the other side. However, reconstruction of the pre-Variscan development and mutual palaeogeographical relationships remains a major challenge of interpretation.
From three Rügen boreholes (G14, Rügen 5, Loissin 1) across the Caledonian deformation front four Lower Palaeozoic slate samples and three detrital muscovite concentrates from associated sandstones have been analysed by ⁴⁰ Ar/ ³⁹ Ar analysis. Microprobe analysis of the detrital muscovites show homogeneous, but distinct chemical compositions for each concentrate. Particulate organic matter reflectance and illite crystallinity indicate that all the analysed whole–rock samples have experienced anchizonal metamorphic conditions.
⁴⁰ Ar/ ³⁹ Ar analysis of the samples from the G14 and Loissin 1 wells give almost identical results. Muscovite concentrates define plateau ages of c. 830 Ma and show an isotopic rejuvenation of low–temperature increments around 440 Ma. Whole–rock slate samples give plateau ages of c. 440 Ma and c. 427 Ma. Isotopic rejuvenation in the low–temperature increments prior to 350 Ma in the Loissin 1 sample can be attributed to the Permo–Carbonifereous volcanism which is known from this borehole. In contrast, samples from the borehole Rügen 5 show a different isotope pattern. A muscovite concentrate defines a plateau age of 609 Ma. Two whole rock slate samples give internally discordant but identical ⁴⁰ Ar/ ³⁹ Ar spectra with consistent isotopic rejuvenation from high– to low–temperature increments from 510 Ma to 420 Ma.
While for the G14 and Loissin 1 sandstone samples a Baltica–derived provenance can be assumed, greywackes of Rügen 5 indicate a Cadomian–influenced Perigondwanan detrital source. According to the results of whole–rock slate samples the main Caledonian tectonothermal event in NE–Germany occurred around the Ordovician–Silurian boundary or in the early Silurian (450–425 Ma). From these data the Rügen Palaeozoic appears as an allochthonous Caledonian nappe complex which has been thrust much further onto the Baltic shield than previously thought.
During the Early Palaeozoic, Belgium was located in the eastern part of the microcontinent of Avalonia, which moved from high to low latitudes during the course of the Ordovician. In the Belgian Condroz Inlier (“Bande de Sambre-et-Meuse”), Ordovician trilobites have been reported from four formations: the early Llanvirn Huy Formation, the Caradoc Sart-Bernard and Oxhe formations, and the Ashgill Fosses Formation. These assemblages are some of the easternmost occurrences of trilobites in Avalonia, and they include aspects that are particularly interesting from a palaeobiogeographical standpoint.The trilobite faunas of the Huy and Sart-Bernard formations are revised in detail, while the others are discussed more briefly, having been redescribed in recent years. The Huy Formation belongs to a biofacies characteristic of the outer shelf/upper slope, and its faunas are typically Avalonian, almost identical to those recorded from the Skiddaw Group of northern England, and from the Ebbe and Remscheid anticlines in the Rhenish Massif, Germany. Pricyclopyge binodosa, which is inferred to be mesopelagic, is common to all these areas, and also occurs in Bohemia and Armorica. Placoparia cambriensis has a remarkably wide distribution in the early Llanvirn, and has been recorded from a range of biofacies across Avalonia, Armorica, Morocco and Bohemia. It is suggested that this species may have been epipelagic. Re-examination of the trilobites from the Sart-Bernard Formation has confirmed that all are conspecific with, or compare closely with Bohemian taxa. The trilobite assemblages of the Oxhe Formation are typical eastern Avalonian faunas, while the Ashgill Fosses Formation assemblage has much in common with those of other parts of Armorica, as well as with Baltica and Bohemia, attesting to the increasing proximity of Avalonia, Baltica and the Prague Basin during the latest Ordovician.
The Trans-European Suture Zone (TESZ) is the boundary
between ancient Precambrian lithosphere of the East
European Craton (EEC) and the younger lithosphere
beneath the latest Neoproterozoic–Palaeozoic mobile
belts of western Europe. The former is characterized by a
thick crust (c. 45 km), low heat flow and a tectono-thermal
age of about 3000 to 800 Ma, the latter by a thinner
crust (c. 30 km), higher heat flow and a tectonothermal
age of 560 to 290 Ma. These contrasting types of crust
were juxtaposed during the Caledonian and Variscan orogenic
episodes. The crystalline basement of the TESZ is
largely concealed by sedimentary basins controlled by
the reactivation of structures within the suture zone during
Permian–Mesozoic extension and Cenozoic inversion.
The pre-Permian evolution of the craton and the
mobile belts, and the location of the sutures, is inferred
from isolated outcrops, hundreds of boreholes and geophysical
evidence. Existing seismic data demonstrates
that the TESZ is rather narrow and has an expression at all
levels of the lithosphere and deep into the asthenosphere.
Teleseismic studies have demonstrated that the differences
in the velocity structure of the asthenospheric and
lithospheric mantle across the TESZ persist to depths of
c. 400 km (Zielhus & Nolet, 1994).
Conodonts have been discovered in two locations in the Lienne Valley near Chevron from low grade metamorphic siliciclastic deposits of the Stavelot Inlier belonging to the Salm Group. The conodont fauna described and illustrated in this paper has been collected from a single fossiliferous horizon within the Ottré Formation, at the transition between the Meuville Member and the Les Plattes Member. This is the first record of a conodont fauna from the Stavelot Inlier in Belgium. It is also of interest for regional stratigraphy, international correlation, as well as for palaeobiogeographic interpretations, because the Salm Group forms an epimetamorphic, comprehensive series of nearly thousand meters in thickness but is poorly dated.
The biostratigraphical comparisons suggest an Early Ordovician, tentatively latest Tremadocian age for the conodont assemblage, but a basal Arenig age cannot be excluded. The fauna is clearly dominated by typical drepanodiform elements, but there is quite some morphological variation in this small simple cone assemblage from subrectiform (of Drepanoistodus?) to reclined and recurved elements. The most common elements belong to Drepanodus arcuatus Pander 1856 ranging from the uppermost Tremadocian up into the lower Darriwilian (= uppermost Arenig). However, there are also a few elements in the fauna from the Salm Group, like some strongly recurved “Drepanodus” recurvatus Sannemann 1955, which are comparable to the latest Tremadocian ‘franconicus’ fauna, characteristic for the Frankenwald area. The species diversity is very low which is comparable to the situation in cold water areas if the Mediterranean Province of Gondwana and peri-Gondwana like the Frankenwald region, the Barrandian area and the Montagne Noire.
The discovery of this small conodont fauna enhances our knowledge not only of the chronostratigraphy of the Salm Group, but also of the palaegoegraphical situation of the Belgian Ardenne in Early Ordovician times.
Early Palaeozoic bimodal rift-related magmatism is widespread throughout much of the Variscides of Europe. It is traceable from the Polish Sudetes to NW Iberia. Granitic plutonism generally predates Cambro–Ordovician bimodal magmatism. In the N Bohemian Massif this early Palaeozoic granitic plutonism was generated by partial melting of Cadomian basement, whereas contemporaneous alkali granites with a mantle component are typical of the NW Iberian Massif. Silurian-Devonian mafic magmatism in the N Bohemian Massif, Massif Central and NW Iberian Massif is partly preserved as obducted ophiolites. Compositional diversity displayed by Cambro-Ordovician mafic magmatism can be accounted for by interaction between a spreading centre and an upwelling mantle plume. This indicates that combined tensional forces and mantle plume convection assisted the early Palaeozoic dispersal of terranes from the N Gondwana margin. Continued fragmentation resulted in development of an archipelago of related terranes separated by a network of seaways and formation of oceanic crust.
The Trans-European Suture Zone (TESZ) is a broad and complex zone of terrane accretion separating ancient lithosphere of the Baltic Shield and East European Craton (EEC) from the younger lithosphere of western and southern Europe. There is debate about the number of terranes involved, and their origins. The most significant terrane boundaries, originally oceanic sutures, are poorly exposed, and are defined using faunal provinciality. Prominent geophysical lineaments may represent sub-terrane boundaries within composite terranes. The Avalonia Composite Terrane was amalgamated to Baltica in latest Ordovician time. The provenance of the Malopolska and Moravo–Silesian terranes, whose Neoproterozoic basement is suspect with respect to Baltica, but with which they nonetheless share faunal affinities, is still debated. The extent of the Variscide Rhenohercynian Zone defines the southern limit of the early Palaeozoic-accreted terranes. Terranes within the Bohemian Massif exhibit HP metamorphism recording subduction-driven collision prior to incorporation in the TESZ collage, itself associated with a HP event. In Romania, the Saxothuringian Zone (and Rheic Suture) are directly juxtaposed with the EEC, and the crustal structure of the TESZ has been much modified by post-Palaeozoic tectonism. Deep seismic reflection data, where available, show that the oceanic sutures are frequently associated with inclined reflectivity zones (IRZ) in the lithospheric mantle, here inferred to mark relict subduction zones. Interpreting the age of subduction is complicated by offset of originally coplanar mantle and crustal segments of the IRZ, resulting from early orogenic lithospheric delamination at the Moho interface and/or post-orogenic 'reordering' processes. The mantle IRZ appear to indicate a N-directed polarity for early Palaeozoic subduction, apparently incompatible with the geological evidence, which indicates subduction of the Tornquist Sea beneath Avalonia, and a large amount of underthrusting of Avalonia by Baltica. Possible explanations for these apparently incompatible observations are evaluated. © 1999 Elsevier Science B.V. All rights reserved.
Moderately preserved early Middle Ordovician (Šárka Formation) organic-walled microfossils from the locality of Praha – Červený vrch Hill were studied and documented. The less diversified assemblage contains twelve morphotypes of acritarchs and five chitinozoan species, no cryptospores were detected. All the ascertained acritarchs and chitinozoans belong to taxa characteristic for the cold-water peri-Gondwanan localities.
The trilobite biodiversity curve for Avalonia differs markedly from the global and other regional patterns in having the peak of diversity immediately prior to the Hirnantian extinction event rather than in the Caradoc or even earlier. This reflects both the very wide spectrum of biofacies represented in this part of the succession in Avalonia and the immigration of taxa resulting from the closure of the Iapetus and Tornquist oceans. Detailed analysis of the faunas demonstrates that Avalonia exemplifies the many factors involved in provincial breakdown and their influence on biodiversity. Furthermore, it emphasises the need to understand the palaeoenvironmental context within which such changes took place.Over 90 trilobite genera are known from the mid-Ashgill (Cautleyan and Rawtheyan stages) of Avalonia with half of these making their first appearance on this microcontinent in that interval. The wide environmental spectrum reflected in the rock record not only includes the return of the deepest water (cyclopygid–atheloptic) biofacies but also marks the first recorded development in Avalonia of the pure carbonate illaenid–cheirurid association which was first established in low latitude Laurentia much earlier in the Ordovician. Its appearance in Avalonia may reflect a combination of the drift of the microcontinent towards tropical latitudes and a possible warming event. Recruitment into this and other environments was overwhelmingly from low latitudes with the largest cohort having its earlier history in Laurentia. Setting aside the ‘new’ pure carbonate environment, the marked rise in diversity and concomitant provincial breakdown resulted from the insinuation of immigrant taxa into existing communities across the shelf and upper slope rather than from any substantial replacement of the established incumbents. The peak of diversity in the mid-Ashgill made the climatically triggered Hirnantian extinction all the more dramatic in Avalonia.
A number of palaeobiogeographical models for Ordovician organic-walled microphytoplankton (acritarchs, prasinophytes, and related groups) have been published during the past 30 years. A modern synthesis of Ordovician acritarch palaeobiogeography, based on previously published acritarch ‘provinces’ and global distribution models, as well as new plots on recently compiled palaeogeographical maps is presented. Review of the literature and new plots indicate that a number of preliminary conclusions can be drawn. Following minor biogeographical differentiation of acritarch assemblages during the Cambrian, ‘provincialism’ started at the Cambrian–Ordovician boundary. In the late Tremadocian a warm-water assemblage, containing the genera Aryballomorpha, Athabascaella and Lua, but no diacrodians, seems to be limited to low-latitude localities such as Laurentia and North China. From the late Tremadocian and throughout most of the Arenig a peri-Gondwana acritarch assemblage with the easily recognisable taxa Arbusculidium filamentosum, Coryphidium, and Striatotheca is present on the southern margin of Gondwana, and its distribution corresponds almost exactly with that of the Calymenacean–Dalmanitacean trilobite fauna. It seems reasonable to consider the acritarchs of Baltica as belonging to a temperate-water ‘province’, which was probably not restricted to the palaeocontinent of Baltica but had a wider distribution at about the same latitude, as some of the elements recorded from Baltica also occur in South China and Argentina. The maximum separation of the continents during the Arenigian, reflected by a pronounced biogeographical differentiation of most Ordovician fossil groups, led to the development of geographically distinct acritarch assemblages. Data from the late Middle Ordovician and the Late Ordovician remain too poor to elucidate global palaeobiogeographical patterns. The biogeographical distribution of Ordovician acritarchs appears similar to that of the resting cysts of modern dinoflagellates, primarily controlled by latitude but also following the continental margins.
Based on the extensive literature on Ordovician acritarchs, biodiversity curves of marine microphytoplankton of the palaeocontinent Baltica have been compiled. The dataset is derived from more than 100 publications and includes over 600 species whose ranges can be used in diversity analysis. Stratigraphically well-constrained data from the Rapla and Männamaa boreholes, northern Estonia, are analysed separately in order to provide additional information on the Middle to Late Ordovician microphytoplankton evolution on shallow shelf settings.
1990.04 We review the highlights of the 1988 symposium on Palaeozoic Biogeography and Palaeogeography, and present a revised set of 20 Palaeozoic base maps,that incorporate much,of the new data presented at the symposium. The maps include 5 major innovations: (1) A preliminary attempt has been made,to describe the motion of the Cathaysian terranes during the Palaeozoic; (2) a more detailed description of the events surrounding the Iapetus Ocean is presented; (3) an alternative apparent polar wandering,path for Gondwana,has been constructed using the changing distributions of palaeoclimatically restricted lithofacies; (4) new,palaeomagnetic,data have been incorporated that places Laurentia and Baltica at more southerly latitudes, and adjacent to Gondwana, during the Early Devonian; Siberia is also placed further south in the light of biogeographic data presented at the symposium; (5) Kazakhstan is treated as a westward extension of Siberia, rather than as a separate palaeocontinent. The relationships between climatic changes, sea level changes, evolutionary radiations and intercontinental migrations are discussed. A symposium on Palaeozoic Biogeography and Palaeogeography,
A total of 129 samples from the Palaeozoic Lashkarak, Geirud and Dorud formations of the Hassanakdar area were examined palynologically in order to determine more precisely the stratigraphical age of these units. The study was also undertaken to assess the palaeogeographical relationships of the Alborz Ranges to Southern and Northern Hemispheres during the Palaeozoic interval represented by these formations. 90 palynomorph taxa were recorded including 58 acritarch, 24 spore and 8 pollen taxa, which permit the recognition of six ascending stratigraphic zones. Zones I-III represent the Lower Ordovician (Tremadoc-Arenig), Zones IV-V indicate the Upper Devonian (Frasnian) and Zone VI suggests a Lower Permian (Sakmarian) age. Two major “hiata” are recognised within the studied interval; the first “hiatus” appears between the Lashkarak Formation and Geirud Formation and extends from the Upper Ordovician through the Silurian and Lower-Middle Devonian, possibly equating with the Caledonian Orogeny. The second “hiatus” occurs between the Geirud Formation (Late Devonian) and Dorud Formation (Lower Permian) and spans the interval of Famennian, the entire Carboniferous and part of the Lower Permian. It possibly corresponds to the Hercynian Orogeny.Diverse acritarch taxa in Lower Ordovician (Lashkarak Formation), Late Devonian (Geirud Formation) and Lower Permian (Dorud Formation) indicate a marine environment for each formation. Comparison of palynomorph taxa recorded in the Hassanakdar area with those reported from other parts of world indicates that the Alborz Ranges have been part of the Gondwanan Supercontinent during the Palaeozoic Era.
A well-preserved assemblage of acritarchs (about 29 species, 3 new, listed here but described in another paper, Cramer 1968), plant spores, and chitinozoans, from the Lower Silurian Red Mountain Formation south of Birmingham, characterized by Veryhachium? carminae, contains many acritarchs in common with the Neagha and MaplewoodFormations, New York; these are remarkably different from Silurian assemblages in Ohio, Indiana, Illinois, and the Rochester Formation in New York and Ontario, all characterized by Deunffia furcata. Cramer plots the regional distribution of these assemblages and correlatives in Europe and Africa, and shows them to be roughly parallel to Silurian magnetic paleolatitudes (with the continents in different relative position), and to constitute 'palynological' provinces related to paleoclimatic zonation.
New and revised information is given for the stratigraphic distribution of fossils, especially trilobites, from outcrops of Tremadoc, Arenig, Caradoc and Ashgill rocks in southern Turkey. Tremadoc trilobites in the western Taurus are of S. European type, but those in SE Turkey resemble faunas in Iran and Afghanistan. Early Ashgill strata from three areas between the extreme SE and SW of Turkey contain trilobites of Asiatic and European affinities. Tremodoc and Arenig acritarchs comprise mainly taxa known from Peri-Gondwana; those of Ashgill age include taxa recorded from the latter region, Baltica and Laurentia. -from Authors
Lower Paleozoic palynomorphs show large morphologic diversity and are generally extremely abundant in unmetamorphosed marine sediments although the stratigraphic ranges and regional distribution of most taxa are still poorly known. Sufficient data are now becoming available to determine the distribution of palynomorphs in the Silurian System, and, to a lesser extent, in the Upper Ordovician and Lower Devonian.
A number of contrasting, worldwide, acritarch biofacies existed in the regions bordering the Atlantic, in Arctic Canada, and in Siberia during the Silurian. Megafossil evidence indicates that these biofacies were contemporaneous and are regularly and predictably time-transgressive. Regionally the biofacies are not significantly correlative with local lithofacies. However, the lineations based on differences in acritarch assemblages approximately parallel lithotope boundaries and a causal relationship between them is suspected.
On a Wegnerian palinspastic reconstruction of Atlantic Pangaea, the parallelism of biofacies lineations, lithotopes, and perhaps even paleomagnetic latitudes is conspicuous. We interpret this as reflecting regional paleotemperature differences.
In order to account for the regional distribution of palynomorph biofacies in the lower Paleozoic, we propose a model that has mobile crustal blocks and essentially stable climatic conditions from Late Ordovician into Early Devonian time. Therefore, we interpret shifts in biofacies to be correlative with amount and rate of crustal movements. Because Silurian acritarch biofacies boundaries parallel paleoisotherms, they also parallel paleolatitudes. Supporting evidence includes: (1) the epeiric sea on Atlantic Pangaea had a minimum width of at least 45 degrees and probably had a pronounced latitudinal temperature gradient, (2) regionally continuous biofacies have a simple and regular geometry, (3) lithotopes and biofacies are parallel and their boundaries follow small circles, (4) regional biofacies are independent of such ephemeral factors as islands, troughs, and local sediment source changes, (5) biofacies form a transcontinental chronological and regional homotactic arrangement, (6) the biofacies are time-transgressive and follow a polar trajectory from Ordovician to Devonian pole positions.
Species of organic-walled microphytoplankton obtained from a well core of the Eden Shale (Upper Ordovician) of Wayne County, Indiana show a reciprocally fluctuating pattern of abundance. Two phytoplankton communities can be identified: the Baltisphaeridium dasos Community, consisting of 2 species, and the Axisphaeridium cylindratum-Dicommopalla macadamii Community, consisting of 9 species. Three additional species appear to be eurytopic. The 2 communities alternate in dominance according to position in the core, while the abundances of the eurytopic taxa fluctuate independently. A model is proposed in which changing water mass boundaries produce these fluctuations. An alternative model that assumes random sampling of seasonal changes in phytoplankton abundance cannot be excluded with the limited data available. Although speculations about possible causes for the proposed water mass fluctuations are not attempted, it is possible the ancient water masses might be mappable using microphytoplankton, and it is important to biostratigraphic work to recognize such patterns.
Fossils have an important contribution to make in the reconstruction of early Palaeozoic palaeogeography. The North Atlantic regions include well-known early Palaeozoic fossil faunas, which should relate to the dispositions of continental plates during the period. However, different versions of Ordovician palaeogeography based on fossils are described in the literature, and in this paper we evaluate the influences which produce these discrepancies. The most reliable results are obtained by combining analysis of faunal similarity (especially shelf faunas) with mapping the distribution of those biofacies which relate to former deep-water sites. Planktic organisms may not be reliable palaeocontinent discriminants. Cladistic analyses of different groups of organisms living at the same (Early Ordovician) time point to the usefulness of trilobite data for palaeogeographic reconstruction. Such data indicate a three-fold division of the North Atlantic region into Baltica, Laurentia and Gondwana from the Cambrian to at least the mid-Ordovician. Paris and Robardet (1990) denied the existence of a Tornquist's Sea separating Baltica from Gondwana in the Early Ordovician, it is considered that their different reconstruction was because the planktic organisms on which they based their maps were not affected by this important oceanic separation to the same extent as shelly benthos. On the other hand, there is no evidence of deeper-water biofacies along the supposed line of Rheic Ocean separation of Avalonia from Gondwana until the Late Ordovician. However, there is some evidence of deeper biofacies along the Nantes-Sardic Line (new term) extending from southern Armorica to Sardinia.
A study of Silurian acid-resistant microfossils from the Ghadames Basin in Tripolitania (Libya) using palynological techniques revealed that the following may be used as palaeoenvironmental indicators: spores, acritarchs, chitinozoa, tasmanitids, scolecodonts, plant tissue, eurypterid cuticle, and graptolite siculae. The palynofacies were defined by quantitative and qualitative diversification of these assemblages. Sedimentological features were used to confirm these proposed facies.Six distinct types of palynofacies were identified and related to models of distance from the shoreline. It is tentatively suggested that they may relate to lagoonal, intermediate and open marine environments.
The paleolongitudinal shift of the boundaries of theDomasia-palynofacies during the Wenlockian was about 170 km along a cross-section in North America and about 90 km in West Europe. This shift probably fixes (1) the direction of drift of the reassembled Atlantic continents during the Wenlockian asN45°W± 10°to20°; and (2) the rest of continental drift as 2+ cm per year.
Palynological evidence suggests that the North Florida Lower Paleozoic block has arrived at its present position with respect to the Appalachians from a Silurian Pangean position inside the divergence of the 1000-fathom contours of the African and South American conti- nental blocks. In Silurian times, the northern part of the circum-Atlantic area was underlain by an ep- eiric sea containing numerous shoals and low- relief islands, especially in what is now western Europe and northwestern Africa; there was also a zone of plate consumption along the axis of the Appalachians and their continuation (Bird and Dewey, 1970; Dewey atd Bird, 1970). It is logical that a paleolatitude-parallel isother- mal banding existed in this sea. Limitations im- posed by the distribution of lithotopes require that the Wenlockian 25øS latitude intersect the axis of the Appalachian mountain belt at an angle of 5 ø to 15 ø. Palynological evidence fixes the latitudes much more finely, as is shown in Figure 1, which is a paleotopographic map aver- aged over the Silurian and plotted onto the basal Wenlockian isochronal surface (Cramer, 1970). In obtaining the palynological interpreta- tion, it is assumed that the compositional band- ing in the phytoplankton distribution reflects the temperature requirements of at least a fair number of phytoplankton taxa and that, therefore, the phytoplankton-facies boundaries are paleoisotherm- and paleolatitude-parallcl (Cramer, 1970; Cramer ad Dez de Cramer, 1970). (The worldwide ,sample spacing is too wide to detect expected local lobes in the straight boundaries. These are known to exist. For example, they are clearly apparent in the Middle and Upper Silurian elastics section of northwestern Spain. The lobes are probably caused by environmental factors of local im- portance such as turbidity, salinity, trace-ele- ment, and nutrient differences.)
Potential advantages to the use of Palaeozoic organic-walled phytoplankton over other fossil groups are their presence in large numbers in small samples (particularly cores) and their partial independence from lithofacies. Reasons why this potential has not been fully realized are discussed, and the history of study is briefly reviewed. The 'latitude parallel' distribution model proposed for Silurian phytoplankton does not hold up when plotted on a more recent plate reconstruction, although some important insights are forthcoming. Ordovician microfloras appear broadly consistent with proposed plate models, and the diachronous distribution of the genus Frankea can be explained by combining the plate model with a restricted, high southern latitude distribution. Ten Frasnian microfloras are compared in detail using G. G. Simpson's Index and cluster analysis. Microfloras from Brazil, Ghana and Algeria cluster together, distinct from outlying areas, while the Carnarvon Basin microflora in Australia is considered relatively endemic. The Frasnian phytoplankton data support a plate reconstruction in which a large seaway separated Africa and South America from North America and Europe.
Recent progress in the plotting of biogeographical distributions is shown to be partly due to improved base maps, some of the notable anomalies detected by earlier workers being explained and easily accommodated in the latest maps. Progress is also in part due to increasingly precise systematics, which results in more accurate biostratigraphical correlation: examples include the 'Didymograptus' bifidus controversy and its role in the definition of the Pacific and Atlantic provinces of the Arenig-Llanvirn. Analogy with modern planktonic regimes enables recognition of marker species in specific water masses; and in the distinction of neritic from open ocean plankton. Analysis at species level and lower of Wenlock graptolite assemblages has resulted in the recognition of the Rheic and Mediterranean subprovinces within a Pacific province or realm. Hydrodynamic modelling suggests directions for future research which may provide independent support for biogeographical studies.
Graptolite biogeography is examined for the late Arenig-Llanvirn when provincialism was at its greatest and the Llandeilo-Caradoc when graptolites were cosmopolitan. This examination incorporates new data from China and recently revised palaeogeographic base maps. Water-mass specificity is considered to be the primary factor affecting graptolite biogeography. On the recently revised base maps, the distribution of Pacific and Atlantic provinces in the late Arenig-Llanvirn is in general consistent with the model of water-mass specificity and the hypothesis that climate cooling associated with the onset of continental glaciation lead to the development of provincialism. However, a small clockwise rotation of South America and a slight northward shift in the position of North America is recommended. The climatic-cooling hypothesis includes the proposal that continued cooling confined graptolites to the tropics where the uniform environment precluded provincialism. The distribution of the cosmopolitan fauna of the Nemagraptus gracilis Zone in relationship to the Llandeilo-Caradoc palaeogeography is consistent with this hypothesis, except for the positions of the European platform, Britain, Armorica, and the Carpathians in the mid to high southern latitudes. Either the latitudinal positions of these areas must be shifted substantially to the north, or the climatic-cooling hypothesis mnst be in error.
World-wide distribution patterns of conodont species during the Cambrian, Ordovician, and Silurian are assessed quantitatively using a Coefficient of Similarity (CS) formula. The validity of the idea is examined that there is a correlation between CS values and the geographic distance between the sample points, and that changes in CS values may, at least in part, reflect plate motions. To minimize effects of local palaeoecological control and the varying degree of exploration of the faunas, well known faunas are used from comparable depositional environments on the several continental plates.
Conodont provincialism can be traced back to Upper Cambrian time, when there was an initial differentiation into low-latitude, warm-water (Midcontinent Faunal Region) and high-latitude, colder-water (Atlantic Faunal Region) faunas. The Lower Ordovician is characterized by great taxonomic diversification as well as striking provincial differentiation. Based on regional distribution patterns, it is possible to recognize a North American Interior Province, a Mediterranean Province, a North Chinese Province, a Siberian Province, a Baltic Province, and an Australian Province during Arenig time. A similar lateral differentiation prevailed during Llanvirn to lower Caradoc time. It is difficult to recognize a close correlation between CS values and inferred distances of plate separations in the Cambrian and Lower and Middle Ordovician.
Unlike some megafossil groups that markedly decreased in provincialism during the Upper Ordovician, the conodont faunas continued to exhibit pronounced lateral differentiation despite the fact that the Baltic, Siberian, and North American plates were then relatively closely together in the equatorial zone. Near the Ordovician-Silurian boundary (probably in the uppermost Ordovician) there was a global, quite conspicuous turn-over in the conodont faunas. During that time, the taxa characteristics of the Atlantic Faunal Region disappeared and apparently, the ancestors of virtually all Silurian taxa are to be found in the Midcontinent Faunal Region.
The Silurian conodont faunas have a cosmopolitan character although there are minor local differences that may be attributed to local environmental control. During Silurian time, the plates that have produced the best conodont faunas (North America, Baltica, Siberia) were all in the equatorial zone, and a general uniformity in environmental conditions may be one of several reasons behind the cosmopolitan character of the Silurian conodont faunas.
Many Lower Palaeozoic conodont species were capable of crossing water bodies of oceanic dimensions, and the distribution of many taxa seems to have been more closely controlled by water temperature and other ecological parameters than by potential migration barriers related to size of water bodies and emerged continental blocks. Nevertheless, because of their pronounced latitudinal differentiation during the Ordovician, the conodont faunas may be used as tools to decipher some of the positions of continental plates.
The shallow-water benthos of cratonic areas distinguish different continents, and the closure of the Iapetus Ocean during the Ordovician and Silurian can be monitored by the faunas which crossed the ocean at different geological times. Brachiopod and trilobite distributions carry different palaeobiological evidence than, for example, contemporary conodont provinces, which probably reflected a combination of temperature differences and water depths. The Celtic 'Province' is reviewed, and it is concluded that each of the island faunas should be treated separately (since many have links with adjacent continents), rather than together as a province. In Newfoundland, faunas help to locate the site of the main Iapetus closure at the Reach Fault, although a substantial island arc in the Notre Dame Bay area accreted on to America in early Caradoc times. In the late Ordovician and early Silurian of Newfoundland fossils assist in the dating of quite local fault-controlled marginal basins, some of which include large olistostromes; undisturbed assemblages of brachiopods in life position give indications of the depth of water in some basins. Authors
Fossils provide an independent criterion for testing structural hypotheses generated from field evidence or geochemistry, as well as functioning in their traditional role in the dating of rocks or determining biogeographic realms. The identification of exterior, oceanic biofacies may be of use in discriminating the course of former continental margins. The isograptid graptolite biofacies (Early to Middle Ordovician) can be distinguished from contemporary epicratonic graptolite biofacies; its worldwide occurrence corresponds with continent margins reconstructed from other criteria. Hence a new isograptid record from E New Guinea suggests that there may have been an Ordovician oceanic site there. The tectonic juxtaposition of different biofacies contributes to an understanding of tectonics and can serve to quantify displacement: the accretionary prism hypothesis for the Southern Uplands of Scotland is supported and contrasted with the rearrangement of biofacies in the Cambro-Ordovician Cow Head Group of western Newfoundland which reveals not only the original shelf-margin- slope topography, but also provides an estimate of the movement involved in the emplacement of one Taconic allochthon. Faunal evidence is used in assessing the original position of 'suspect' marginal areas. This shows that Anglesey was not greatly separated from Gondwana in the early Ordovician - but strike-slip movement cannot be disproved. Local changes in relative sea-level are determinable from sediments and faunas; in marginal belts these may differ from the global eustatic curve, and when this happens it is a measure of local tectonic activity. Particular sea-level curves may serve to define structurally coherent units within mobile belts. New sea-level curves are contrasted for a segment of N Wales with that for central SW Wales; the S Welsh area mostly responded passively to the eustatic curve, which can adequately account for shifts in facies and faunas, while N Wales had a curve often at odds with eustasy and reflecting its structural history. -after AuthorsDept. Palaeontology, British Museum (Natural History), Cromwell Road, London SW7 5BD, UK
The faunal criteria for the recognition of the relative separation of old continents are: 1, the contrast between shallow- (not deep-) water faunas off opposite shorelines; 2, the recognition of deeper-water facies surrounding the edges of continents; and 3, the recognition of the disposition of ancient climatic belts. These criteria are defined and used to assess the relative position of the various parts of what is now Britain in the Palaeozoic. The Iapetus Ocean is well characterized by faunal differences from the Cambrian until the lower Ordovician, but from Caradoc times onwards these differences dwindle, until by the latest Silurian only the distribution of the ostracods separates the two sides of the ocean on faunal grounds. In the early Ordovician, S British faunas are comparable with those from Bohemia, France and elsewhere to the S, indicating connection with Gondwanaland, and these faunas differ from those in the Baltic area, a distribution which we attribute to a true ocean, Tornquist's Sea, between N and S Europe. Tornquist's Sea probably closed in the upper Ordovician, and from Ashgill times onwards the S British and Baltic faunas remained similar. During the middle and late Silurian there is evidence of increasing faunal distinction between Britain, the Baltic area and North America on the one hand and southern Europe and Gondwanaland on the other, indicating an opening Rheic Ocean which appears to have persisted until late Carboniferous times.
A sedimentary sequence overlying a granite pluton near Ishkarwaz (upper Yarkhun valley, Chitral, Pakistan; Karakorum Microplate) contains abundant, but poorly preserved, acritarchs probably referable to the late early Arenig-early late Arenig interval. The palynological assemblages of Karakorum show a marked similarity to the cold water Peri-Gondwana assemblages; i.e. to those of Li Jun's Arbusculidium-Coryphidium-Striatotheca‘Mediterranean’ Bioprovince. Biogeographical and geological comparisons suggest that, before the accretion of Cimmerian microplates to the Eurasian continent, the Karakorum Microplate was located along the northern margin of Gondwana in a latitude intermediate between the Mediterranean region and South China (Yangtze Platform).
The geographical distribution of Ordovician acritarchs is not uniform. In Europe two main provinces can be distinguished: (1) the Baltic province, characterized by the prevalence of acanthomorphids, and (2) the Mediterranean province, characterized by the occurrence of diacromorphids.
Quantitative treatments of 168 dinoflagellate cyst assemblages from modern marine sediments were used to decipher the salient environmental and climatic features of the distribution of common living cyst-based taxa. Surface sediment samples were studied by routine palynological methods from estuarine, continental shelf, slope and rise zones, and abyssal plains between latitudes 62°N and 27°S within fourteen geographic regions of the North and South Atlantic Oceans, the Caribbean and Mediterranean Seas and from one region in the southeastern Pacific Ocean near Peru, to meet this general objective. The results were expressed as percentages of species present and statistically analyzed by multivariate Q-mode factor analysis, cluster analysis and by calculation of a diversity index, using pre-existing computerized routines.
Two faunal regions, a cool-water, Atlantic and a tropical-water, Pacific, may be distinguished among Tremadoc into Ashgill planktic graptolite faunas. The zenith of graptolite provincialism was during the Arenig-Llanvirn when Laurentia, Australia-New Zealand, North China, South China, Siberia, Argentine Precordillera, and parts of Kazachkstan were provinces within the Pacific Region. Coeval, Southern Hemisphere, Atlantic Region provinces were: England-Wales, Baltoscania, Bolivia-Peru-Northern Argentina, western Europe, North Africa, and possibly part of modern Tien Shan. South China Arenig-Llanvirn faunas include many incursions of Atlantic Region taxa, probably reflective of current circulation changes linked to development of seasonal monsoons. Mid-Ordovician plate motion included northward movement of Baltoscania into the tropics. That motion resulted in Baltoscania becoming a province in the Pacific Region in the Late Ordovician. Late Ordovician glaciation led to restriction of graptolites to the tropics (Pacific Region) during the latest Ordovician. Deglaciation was followed by re-establishment of a tropical, Pacific Region fauna and a cool-water, Atlantic Region fauna during the Llandovery and Wenlock. Graptolite faunas appear to have been only tropical from the Ludlow to their extinction in the Pragian (Early Devonian). The graptolite regions and provinces are essentially consistent with plate positions suggested by palaeomagnetic and lithofacies data.
A new base map for the Lower Palaeozoic of the Gondwanan continental plate incorporates various modifications to older reconstructions. An analysis is attempted of faunas at various times through the Lower Palaeozoic, in particular the Lower Ordovician (Arenig-Llanvirn), the middle and late Ordovician (Caradoc-Ashgill) and the early Silurian (Llandovery). Regressions and transgressions are identified and 'western' and 'eastern' Gondwanan platform faunas identified in contrast to the deeper-water peri-Gondwanan marginal faunas. The effects of climatic variation, both with time and between contemporary areas, are reviewed, and are seen to be the chief controlling factor on platform faunas, with a cline from Boreal to tropical faunas alongside the Gondwanan palaeocontinent. The biogeographical relationships of deeper-water faunas were more complex: certain distinctive taxa may be found distributed widely around the perimeters of the continent, and other faunas have taxa in common with marginal faunas around other contemporary palaeocontinents. Some older-described faunas, particularly brachiopods, trilobites and graptolites, are freshly reviewed, and new faunal data from Libya, Turkey, and Iran are presented and figured.
DURING the Lower Palaeozoic, there was a gradual increase in the similarity of the faunas between North America to the west of the Appalachians, western Newfoundland, northwestern Ireland and Scotland on the one hand, and coastal New England, southern New Brunswick, Nova Scotia, eastern Newfoundland, England and northern Europe on the other hand. The best explanation for this is that the lapetus (or Proto-Atlantic) Ocean was wide enough to separate two faunal provinces in Cambrian times, and that there was progressive migration of the more mobile components of the faunas as the old ocean closed (Fig. 1). The pelagic animals crossed first, followed later by animals (trilo-bites and brachiopods) with pelagic larval stages; but animals without a pelagic larval stage (such as benthic ostracods) were not able to cross until the ocean had closed at one point, though not necessarily everywhere along its length. Finally, faunas limited to fresh water or brackish water (like many Devonian fish) did not cross until there were non-marine connections between the continents on either side of the closing ocean.
Using as point of departure data from hundreds of localities with, essentially, Middle Silurian acritarch assemblages, logical constraints on the composition of these assemblages as they can be inferred from geological information, are discussed. It is concluded that (1) the regional composition of coeval acritarch spectra was primarily temperature controlled, and only secondarily determined by such factors as abnormally high or low salinity, turbulence, etc.; and (2) acritarch spectrum provinciation is the rule rather than the exception in the Lower Paleozoic.A palynological province model for the Wenlockian is presented, and also a tentative one for the Lower Ordovician. There is not always a perfect match between the palynological province model and observed palynofacies, the geotectonic implications of which are discussed in some detail.
The predominantly marine Lower and Middle Devonian of the Rhineland is relatively poor in phytoplankton. Moreover, the composition of the assemblages found is rather undiversified. However, the assemblages gain some interest because of their relation to the Emsian-Eifelian type-region and their close association with diversified spore floras. The composition and stratigraphic distribution of the assemblages are briefly described. Comparisons are made with more prolific phytoplankton assemblages from the Daleje shales of Bohemia (Upper Emsian) and the Nehden shales of the Eifel region (Upper Devonian). Paleoecological considerations seem to indicate that in the Devonian of Central Europe the neritic facies is connected with poor phytoplankton assemblages, the pelagic facies more often with rich and diversified assemblages.
The early Ordovician was a time of maximum continental separation and hence a time when faunal evidence can be used to assess palaeogeography in a critical way. We summarize the known trilobite occurrences (18 genera) from the Arenig–Llanvirn of the Lake District, and record some genera for the first time. Maps of the distribution of some of these forms are given. All genera except Cyclopyge were confined to the Gondwana continent at the time, and some are known from many localities; and two species are widespread in England, Wales, France, Iberia and Bohemia. The fauna is entirely distinct from those of Scandinavia and North America. All the palaeontological evidence points to the Lake District being adjacent to Ordovician Gondwana. In the earlier Ordovician it is not reasonable to suggest that the Iapetus Ocean lay to the south of the Lake District as did Allen (1987).
A rich acritarch assemblage (called HD2) from the Arenigian Dawan Formation of the Daping section (Yangtze Gorges area, Hubei Province, Southern China) is described. The new data supplied by the study of this assemblage support the previous opinion that the Upper Yangtze Region should be included within the Mediterranean (Peri-Gondwana) acritarch Paleoprovince. But, compared with this scenario, the picture resulting from the above data seems to be more complicated. Actually, the HD2 assemblages have a mixed composition, even if they show a prevalent Mediterranean character. Some Australian and Baltic affinities were also observed. The extension of the Mediterranean acritarch biofacies up to the Yangtze Platform during Arenigian times is attributed to a cool periantarctic (that is peri-Gondwana) oceanic current first flowing along the subpolar margin of Gondwana and after rising northwards up to South China. The proposed scenario implies that the above mentioned peri-Gondwana current branched northwest of Southern China, giving also origin to a progressively warmer current, then descending up to Baltica. The palaeobiogeographical implications of this oceanic current pattern are discussed. Nine new species are described: Baltisphaeridium fragile, Ordovicium yangtzeense, Peteinosphaeridium armatum, P. exornatum, P. robustiramosum, P. tenuifilosum, Pirea baculifera, P. levigata, and Striatotheca rugosa. Six previously described species are revised: Ampullula? erchunensis (Fang Xiaosi, 1986) Tongiorgi, Yin and Di Milia, comb. nov., emend., Barakella rara (Lu Li-chang, 1987) Tongiorgi, Yin and Di Milia, comb. nov., emend., Costatilobus? rhabdocladius (Lu Li-chang, 1987) Tongiorgi, Yin and Di Milia, comb. nov., emend., Costatilobus? striatum (Lu Li-chang, 1987) Tongiorgi, Yin and Di Milia, comb. nov., emend., Rhopaliophora mamilliformis Lu Li-chang, 1987, emend., and Veryhachium symmetricum Lu Li-chang, 1987, emend.
In light of recent additions to the Palaeozoic palaeo-magnetic data-base, particularly for the Ordovician era, a revised apparent polar wander (APW) path for Baltica has been constructed following a rigorous synthesis of all Late Precambrian-Permian data. The APW path is characterized by two prominent loops. Firstly, a Late Precambrian-Cambrian loop probably relating to a rifting event and secondly, a younger loop relating to a Mid-Silurian (Scandian) collision event. These features imply major change in plate-tectonic reconfiguration.
Plankton records and 25 samples of Recent sediment from Trondheimsfjord and the adjoining shelf were studied to investigate production, sedimentation, and preservation of cysts, as factors which influence the eventual composition of dinoflagellate cyst assembleges. All sediment samples were examined for dinoflagellate cysts using routine semiquantitative palynological procedures. In addition, fjord sediments were subjected to a limited sediment analysis, and, for three samples, results from preparations both with and without acid treatments were compared. For the first time, cyst assembleges from Recent sediments were directly compared with extensive plankton records from overlying waters. Results indicate that approximately 20% of the 55 locally recorded dinoflagellate species contribute cysts to bottom sediments. Once formed, cysts behave as fine silt particles in the sedimentary regime, increasing in abundance as the percentage abundance of finer sediment increases, usually with increased water depth. Cyst-forming species are almost entirely restricted to a few genera, particularly Gonyaulax and Peridinium, within the order Peridiniales. For some groups, reasonably good correspondence was found between percentage abundances of dinoflagellates in plankton and their cysts in sediment, though plankton records covering at least five years were required to establish this. Gonyaulax grindleyi Reinecke (Von Stosch 1969) appeared to be consistently overrepresented by cysts in sediment relative to available plankton evidence; possible explanations are suggested. At least 30% of the cyst species present, including most Peridinium species, were eliminated, or rendered unreliable for semiquantitative palynology, by application of routine palynological preparation treatments. Such cysts may provide useful, non-quantitative, palynological information from Recent and possibly Quaternary sediments, but their persistence would seem unlikely. Thus, factors of preservation probably further restrict the dinoflagellate fossil record. Cyst assemblages from Trondheimsfjord are comparable with those previously recorded from the northeastern coast of U.S.A., and from Scotland and northeastern England. Fjord assemblages are dominated by small, simple, spinose cysts which would be regarded as acritarchs if culture experiments had not proved that they are dinoflagellate cysts. Much potential biogeographic and palaeoenvironmental information was included within the less abundant species.Attention is drawn to the role which future culture experiments may be expected to play in helping to resolve taxonomic difficulties currently affecting dinoflagellate studies. Palynological significance of results from the present study is discussed especially with reference to recent work by Von Stosch which strongly suggests that cysts may be hypnozygotes formed routinely in sexual cycles of dinoflagellates.
The palaeobiogeographic method appears to be an attractive alternative for reconstruction of the palaeogeography of the Variscan regions during the Palaeozoic. The evolution of faunal assemblages and climatic characteristics from the Cambrian up to the end of the Devonian, demonstrates that Baltica and North Gondwana represent two major and independent palaeogeographic entities separated by a mid-European Rheic Ocean which opened as early as the Cambrian and closed progressively from the Devonian. The South Armorican Ocean, whose closure generated the so-called Ligerian Orogen, is regarded as a branch of the Rheic Ocean. Both a Tornquist's Sea, separating Baltica from its western extension (Avalonia) during the Ordovician and a Proto-Tethys Ocean, extending between southwestern Europe and north Africa during the Devonian, are excluded from our reconstructions.
A formal biozonation is proposed for the Ordovician chitinozoans of the Northern Gondwana Domain. This palaeogeographic province, located at rather high latitudes during the Ordovician, includes southwestern Europe, central Europe, Middle-East, northern Africa and Florida. The present chitinozoan biozonation is based upon the study of several thousand assemblages recovered from closely spaced samples (both outcrop and subsurface material). Each biozone is defined either by the total-range biozone or by the partial-range biozone of a taxon selected as the index species because of its distinctive morphology, its wide geographic distribution and its restricted stratigraphic range. The main chitinozoan species coexisting with the index species in each biozone are reported. Particular attention is paid to the stratigraphical calibration of these chitinozoan biozones; in spite of some difficulties with precise correlations, reference is made of the Stages and Series of the British Ordovician System, regarded as a standard. If one assumes that 55 million years separate the appearance of the first chitinozoans in the Tremadoc to the top of the Ashgill, then the average duration for each of the 22 chitinozoan biozones recognised herein is about 2 million years.