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Biogeography of Late Silurian and Devonian acritarchs and prasinophytes
Abstract
The palaeobiogeography of Late Silurian-Devonian acritarch and prasinophyte microfloras is assessed using qualitative data, similarity indexes and cluster analysis. Based on the recent palaeogeographic reconstructions, the northwards movement of Gondwana initiated during the Ludlovian with the progressive narrowing of the Rheic ocean, resulted in North Africa and south European regions being closer to the equatorial zone and hence in a warmer climate. An apparent homogeneity of Late Silurian assemblages from regions of southern Baltica and the North Gondwanan margin could be explained by such a configuration. The phytoplanktonic associations could also have benefited from the equatorial currents system for trans-Rheic connections. In addition, the qualitative study and the cluster analysis allow for delineation of a biogeographic unit, including part of South America, North Gondwanan and perigondwanan regions, which is comparable to the cold Malvinokaffric realm of the southern hemisphere, based on invertebrates. During the same time, major differences recognized in the distribution of acritarchs from near shorelines to deep oceans, emphasize the potential of mazuelloids (previously referred to as acritarchs) as indicators of deep-water facies and outer margin sites. The Early Devonian shows a geographic restriction of several acritarch genera and species, with a pronounced lateral differentiation between North Gondwanan and eastern North American microfloras, that seems to have been controlled by physical barriers rather than climatic differences. The similarities in acritarch assemblages between northern Europe and the North Gondwanan margin argue for a decrease in acritarch provinciality on both sides of the Rheic ocean, and precludes the presence of a wide Devonian ocean north of western Gondwana.
... Colbath (1990) also summarized several intrinsic advantages, such as easy preservation, large quantity, slow floating rates, and rich variety, of organic-walled phytoplankton over other types of fossils for the study of palaeobiogeography. Le Hérissé et al. (1997) analyzed the palaeobiogeography of Late Silurian to early Early Devonian (Lochkovian) acritarch and prasinophyte microfloras and found out that the provincialism of phytoplankton seems to have been controlled by the physical barriers rather than the climatic differences. Le Hérissé et al. (2000) reviewed the biostratigraphical, palaeogeographical, and palaeoenvironmental knowledge of Devonian acritarchs and related forms, and compiled the stratigraphic range and geographical distribution of some 180 selected species. ...
... More recently, Molyneux et al. (2013) summarized the current status of research on marine phytoplankton palaeobiogeography of the early to middle Palaeozoic (Cambrian-Devonian). It is clear that, like for other fossil groups, the palaeobiogeographical study of phytoplankton greatly depends on the quantitative and qualitative descriptions from each sampled locality (Le Hérissé et al., 1997). In the past decades, the study on acritarchs and related phytoplanktonic forms has made significant progress, with a number of new papers published on the description of new phytoplankton assemblages and their biostratigraphical implications. ...
... The northward movement of Gondwana was initiated during the Late Silurian (Ludlovian) (Le Hérissé et al., 1997), resulting in the progressive narrowing of the Rheic Ocean. The precise timing of the closure of the Rheic Ocean, however, remains highly controversial (e.g., Fortey and Cocks, 1992;Colbath, 1990;Steemans et al., 2007;Paris and Robardet, 1990;Le Hérissé et al., 2009;Linnemann et al., 2007;Nance and Linnemann, 2008;Nance et al., 2010;Qiao and Shen, 2014). ...
Acritarchs and prasinophytes have generally been considered as organic-walled phytoplankton, and their distribution patterns play a significant role in palaeogeographical and palaeoclimatical reconstructions. In this paper the palaeobiogeography of Late Devonian phytoplankton (mainly Famennian) is quantitatively analyzed based on a global database consisting of 95 genera from 15 geographical units. The data are analyzed using cluster analysis, nonmetric multidimensional scaling, and minimum spanning tree analysis using the Jaccard, Ochiai, Kulczynski, and Yule's Y similarity coefficients. The results show that there was provincialism in the Late Devonian and three phytoplankton palaeobiogeographical realms could be identified: the West Gondwana, East Gondwana, and Boreal realms. There is a high degree of similarity between phytoplankton assemblages in East Gondwana (especially those in Australia and Iran) and Euramerica. Portugal (of the Iberian-Armorican block) was situated to the north of Algeria and probably acted as a stepping stone between Euramerica and West Gondwana. The closed oceanic surface circulation pattern in the Proto-Tethys Ocean between Euramerica and East Gondwana might have hindered the exchange of phytoplankton between East and West Gondwana. The phytoplankton province that had been typically confined to the higher latitudes was still present, while its characteristic genera gradually dispersed into the lower latitudes in the Late Devonian. There is a high similarity between phytoplankton assemblages from the western Junggar of Xinjiang, NW China and Euramerica. Latitude- and current-influenced palaeotemperature and oceanic circulation patterns are considered to have been the major determinants of the geographical distribution and evolution of marine phytoplankton in the Late Devonian.
... Because the majority of acritarchs are probably cysts produced by marine, motile, phytoplanktonic unicellular algae (Martin, 1993), they have the potential for wide geographical distribution. Although a lot of species show a cosmopolitan distribution pattern during the Llandovery and Wenlock (García Muro et al., 2016), many others have specific tolerances in terms of paleolatitude, paleotemperature etc., thus confining them to the North Gondwanan margin, Baltica or Laurussia, during a large part of the Silurian, as previously described in a series of papers by Cramer (1968Cramer ( , 1969Cramer ( , 1970, Cramer and Díez (1972, 1974a,b, 1979, Le Hérissé and Gourvennec (1995) and Le Hérissé et al. (1997). ...
... During the late Silurian, and particularly the late Ludfordian and Přídolí, Rubinstein (1995), Le Hérissé et al. (1997), Le Hérissé (2002), Rubinstein et al. (2008), and Rubinstein and García Muro (2011) previously reported a drop in provinciality and a notable morphological similarity of stratigraphically significant taxa with assemblages from Baltica, East European platform and Gondwana, on both sides of the Rheic Ocean. The phytoplankton assemblage from Saudi Arabia described herein are quite comparable to those from Pomerania in Poland (Jachowicz, 2000), the Netherlands (Van der Meer and Wicander, 1992), Libya and Spain. ...
... Numerous Palaeozoic palynological studies have used CS (e.g. Le Hérissé et al., 1997;Samuelsson et al., 2002). This simple and straightforward approach is expressed by the formula: ...
A rare occurrence of a rich and diverse palynological assemblage from the Tawil Formation is described from well JLMD-EW-8 in northwestern Saudi Arabia. The composition of this assemblage strongly indicates a middle Přídolí age. The assemblage encountered contains very characteristic chitinozoans, acritarchs, tasmanitids, freshwater algae, scolecodonts, eurypterid cuticle and other organic remains. Land-derived miospores are also common and two new cryptospore species (Cymbohilates jalamidensis and Gneudnaspora sordida) are herein formally described. Most taxa of taxonomic interest and useful for regional and intercontinental correlation are illustrated. The palaeogeographic distribution of this assemblage is also discussed as organic-walled microphytoplankton, chitinozoans and miospores encountered in the studied samples correlate well with similar assemblages from various Algerian, Libyan, and Ibero-armorican localities (i.e. Ibarmaghian regions). This corresponds to what is considered as a transgressive middle Přídolí event in the Algerian Sahara, with non-marine intervals bracketing this brief marine sea-level rise. This event is likely to have extended into all of north Gondwana, including Arabia, and can be correlated to the S50 Maximum Flooding Surface from the sequence stratigraphic framework defined in the Neftex Geodynamic Earth Model.
... In the Silurian, tentaculitoids only occurred in the southern hemisphere. This distribution could have resulted from the tropical counterclockwise circulation of the Paleo-Tethys Ocean (Hérissé et al., 1997) and the geographic barriers stretching from South Laurentia to West Gondowana. By the latest Ordovician and Early Silurian, Eastern Avalonia had become faunistically indistinguishable from Baltica, and by the Early Silurian, Avalonian-Baltic faunas themselves merged with those of Laurentia (Cocks and Fortey, 1990). ...
... By the latest Ordovician and Early Silurian, Eastern Avalonia had become faunistically indistinguishable from Baltica, and by the Early Silurian, Avalonian-Baltic faunas themselves merged with those of Laurentia (Cocks and Fortey, 1990). The closure of the Iapetus Ocean, as well as the progressive narrowing of the Rheic Ocean due to the northward drift of North Gondwana initiated during the Ludlow (Hérissé et al., 1997), formed a vicariance which probably prevented equatorial migration (Nestor, 1990). ...
... The shift isolated them from the northern margin of the recently closed Paleo-Tethys Ocean (Poncet, 1990), having become detached plates where the environment is speculated to be open and inhospitable for the tiny conical tentaculitoids. Owing to their isolation, the circulation in the former Paleo-Tethys Ocean (Hérissé et al., 1997), as a significant impetus for tentaculitoid dispersal, could have been weakened or redirected. Furthermore, the northward movement of those plates would have shifted the tentaculitoids away from the tropics and towards the temperate zone where the environment would have been inadaptable for them. ...
... However, climatic realms can be recognized and correspond roughly to the latitudinal climatic belts that existed during the Devonian (Le Hérissé et al., 1997). In Early Devonian, differences in acritarch assemblages were pronounced between North America (Laurentia) and Gondwana, although Rubinstein et al. (submitted) suggest a cosmopolitan nature of numerous Early Devonian acritarchs. ...
... Palaeogeographic reconstructions seem to indicate that the observed acritarch provincialism was not mainly caused by water temperature differences, but rather influenced by physical barriers as emerged land areas between the two regions. These barriers prevented dispersal and interchange of acritarchs and related forms (Le Hérissé et al., 1997). The level of endemism among acritarchs at generic and specific levels permits the recognition of at least two distinct acritarch biogeographic units: the eastern North American unit and the Gondwanan unit divided into the northwestern Gondwanan subunit and the high southern latitude subunit. ...
... The level of endemism among acritarchs at generic and specific levels permits the recognition of at least two distinct acritarch biogeographic units: the eastern North American unit and the Gondwanan unit divided into the northwestern Gondwanan subunit and the high southern latitude subunit. The isolation of eastern North America on the basis of the spatial distribution of acritarchs is consistent with similar biogeographical differences between the North American and European provinces based on the distribution of faunal groups such as brachiopods, corals, or ostracodes (Le Hérissé et al., 1997). Unfortunately, based only on acritarch evidence, the duration of the units defined cannot be estimated because there is no indication whether this high level of endemism in acritarch assemblages persisted after the Early Devonian. ...
Devonian miospore assemblages from 16 sections in Saudi Arabia and North Africa are studied in order to characterize the palynostratigraphy of the northern margin of western Gondwana which remains poorly known in Saudi Arabia. The preliminary taxonomic work identifies more than 200 miospore species, including a lot of new species endemic to western Gondwana. Numerous species have still to be more precisely circumscribed because of their large morphological variability. Others show continuous intergrading morphological variation. The morphological variability of each taxon is one of the main problems in any palynological study. It is due to phylogenetic evolution, ontogeny (maturation of sporangia) and taphonomic factors.
Although the standard Devonian miospore zonations established in Euramerica (Richardson & McGregor, 1986; Streel et al., 1987) are commonly used in most of the palynological studies, they are not always easily recognizable in western Gondwanan localities because of the endemic nature of the assemblages. Therefore, a new local/regional biozonation based on the characteristics of the miospore assemblages described here was needed for a more accurate correlation. The new established biozonation consists of 9 assemblage zones, 8 interval zones and 2 acme zones, extending from the late Pragian to the late Givetian and possibly the early Frasnian. The new defined biozones are compared to other coeval biozones defined in the literature. Thanks to this new local/regional biozonation, reliable correlations are established between sections.
Numerous oilfields occur in the Devonian from western Gondwana. A biozonation based on the first down-hole occurrence of species is developed for oil exploration. Thanks to this type of biozonation, only the top of a biozone has to be reached in order to be identified. The use of this biozonation is facilitated by the choice of easily recognizable and common index species. This provisional downward biozonation consists of 8 interval zones. Although it seems relatively reliable by comparison with the previously defined upward biozonation, it needs to be further tested on other drilled sections.
The review of the Emsian-Givetian miospore assemblages from the literature allows to evaluate the provincialism of assemblages on a worldwide scale during this interval. Coefficient of similarity is calculated between palynofloras from northern Euramerica, southern Euramerica, eastern Gondwana, southwestern Gondwana and northwestern Gondwana. The resulting low values correspond to low to moderate similarity of miospore assemblages between the considered regions in the Emsian-Givetian interval. The provincialism may be explained by a latitudinal climatic gradient as no palaeogeographic barrier is known during this time interval. Indeed, both Euramerican and Gondwanan land masses were very close as soon as the earliest Devonian. Despite a certain degree of provincialism, floristic interchanges existed. Northwestern Gondwana constituted an intermediate warm temperate region with shared taxa mainly from more arid Euramerican localities in the North, and cooler southwestern Gondwanan localities in higher latitudes. However, it seems that a progressive homogenization of the vegetation took place in Middle Devonian as the standard Euramerican biozones are more easily recognized in Givetian than in Eifelian and Emsian. This transition from provincialism to cosmopolitanism during the Devonian is not only shown by palynofloras but also by the palaeogeographic distribution of many other fossil groups. It is likely due to a decrease of the latitudinal climatic gradient in Middle Devonian.
... unconstrained. Recent relative-age estimates based on palynomorph data in select regions in Antarctica, South America and the Falkland/ Malvinas Islands suggest that the Malvinokaffric Realm persisted from the Late Pragian-Early Emsian to Late Eifelian (Kemp, 1972;McGregor, 1984;de Almeida-Burjack and Paris, 1989;le Hérissé et al., 1997, le Hérissé, 2001Grahn and Melo, 2005;Grahn et al., 2000Grahn et al., , 20022013;Troth et al., 2011;Marshall, 2016). ...
... Further taxa that have been demonstrated to be endemic in the Malvinokaffric Realm include certain ostracods (Becker et al., 1994;Lethiers et al., 2001;Racheboeuf et al., 2012;Salas et al., 2013), in addition to certain acritarchs, palynomorphs and chitinozoans (de Almeida-Burjack and Paris, 1989;Wood, 1995;le Hérissé et al., 1997;le Hérissé, 2001;Grahn and Melo, 2005;Troth et al., 2011). Although hyoliths are common faunal elements in the Malvinokaffric Realm, detailed taxonomic appraisals in recent years are limited to work by Marek and Isaacson (1992) and Malinky and Racheboeuf (2011) on material form Bolivia. Marek and Isaacson (1992) suggests that certain orthothecids, previously identified as 'Orthotheca', may be unique to the Malvinokaffric Realm. ...
... Important geochemical changes (e.g. Azmy et al., 1999;Saltzman, 2002;Stricanne et al., 2006), as well as paleogeographical and paleooceanical changes (Le Hérissé et al., 1997;Jeppsson, 1998) are also known to have occurred during this time. To analyze biodiversity changes during this approximately nine million year period (Ludlow, Prídolí, Early Lochkovian), a database of acritarch and prasinophyte phycomata occurrences was developed. ...
... It should be noted that the applicability of acritarchs in paleogeographic reconstructions does not always coincide with other nektic fossils (Cocks and Fortey, 1988;Cocks and Verniers, 1998). However, during the time interval considered, analysis of the coefficient of similarity values (Le Hérissé et al., 1997), and more recent studies (Le Hérissé, 2002), have demonstrated the value of acritarchs in discussing the timing of the closure of the Rheic Ocean, and proposing a near closure in the Late Silurian. The most recent data suggest again of the closure in the Early Devonian (Linnemann et al., 2007). ...
Numerous environmental factors as well as oceanic circulation patterns and geographic constraints all contribute to the abundance, distribution, and diversity of present‐day marine phytoplankton assemblages. These same factors presumably affected the Paleozoic marine phytoplankton, which was dominated by organic‐walled acritarchs and prasinophytes. During the Late Silurian (Gorstian, Ludfordian, and Prídolf) and earliest Devonian (Lochkovian), important paleogeographic, paleooceanographic, and geochemical changes were occurring as well as major compositional changes and diversity fluctuations in the marine organic‐walled phytoplankton. Innovative morphologies appeared during the Late Silurian, in both low and high latitude assemblages, but with significant quantitative differences. This was followed by a turnover in assemblage composition during the Silurian/Devonian transition, and an initial radiation of new acritarch and prasinophyte taxa in the Early Devonian.Observed changes in total phytoplankton diversity during the Gorstian through earliest Lochkovian are based on organic‐walled microphytoplankton data derived from published and unpublished key stratigraphic sections where independent age control has been firmly established. These key sections are from: Missouri and Oklahoma, U.S.A. and western Newfoundland, Canada (Laurentia); Gotland, Sweden, and Podolia, Ukraine (Baltica); the Welsh Basin and Borderland (Avalonia); northern France and northern Spain (Armorica); and Libya in northern Africa, and Argentina and Bolivia, South America (Gondwana). Regional biodiversity changes for the organic‐walled microphytoplankton were determined for the warm low latitude areas (Baltica, Laurentia, and Avalonia) and temperate to cool higher latitude areas (northern and southern Gondwana).The Late Silurian‐earliest Devonian organic‐walled phytoplankton was divided into three major categories to facilitate comparison of compositional fluctuations, both within stratigraphic sections as well as between geographic areas. The three categories, based on overall morphology, are marine chlorophytes and prasinophytes, marine acritarchs, and nonmarine types, including coenobial forms. This triparate grouping is both broad and detailed enough to mark critical changes in both the phytoplankton assemblages, as well as the paleoenvironment. In general, high phytoplankton diversity peaks occurred during the Early and Late Gorstian in the warm low latitude areas, followed by varying fluctuations during the Ludfordian and Prídolí for both the warm low latitude and cool high latitude areas. An initial radiation of new phytoplankton taxa and the appearance of more cosmopolitan assemblages mark the beginning of the Lochkovian.
... The biogeography of Upper Silurian and Lower Devonian acritarchs was further examined by Le Hérissé et al. (1997), who noted the similarities between the acritarchs from North Gondwana and Baltica. This was related to the northward advance of Gondwana, which was initiated in the Ludlow Epoch, and the narrowing of the Rheic Ocean. ...
... This was related to the northward advance of Gondwana, which was initiated in the Ludlow Epoch, and the narrowing of the Rheic Ocean. However, Le Hérissé et al. (1997) also found that some provinciality remained among Late Silurian acritarchs, and that the acritarch assemblages from the northern hemisphere appeared to be less varied taxonomically than those from the southern hemisphere. They also noted apparent migrations of warm water acritarchs into cold high latitudes during the Late Silurian (Le Hérissé et al., 1997, pp. ...
The acritarchs and prasinophyte algae from the type lower Ludlow Series of the Goggin Road section, Ludlow, England, are resolved into seven recurrent associations comprising taxa with similar environmental preferences. Endemic and environmentally sensitive associations of acritarchs and prasinophytes are identified and high-resolution fluctuations in the early Ludlow palaeoenvironment are established. An early Ludlow crisis in the acritarchs is recognized in the lower part of the Middle Elton Formation, when an abrupt palaeoenvironmental change in the Ludlow area resulted in a large decline in the abundance of the acritarchs, but allowed Tasmanites and retiolitid graptolites to flourish briefly. Cymbosphaeridium sp. A, Pulvinosphaeridium ludlowense and Multiplicisphaeridium arbusculum forma A are taxa possibly specialized, or produced as a response, to a stressed palaeoenvironment, as they are most abundant when other acritarchs and prasinophytes are uncommon. The low abundance of acritarchs and prasinophytes in the Upper Elton Formation may be related to high sedimentation rates and to the slumping of sediments caused by instability on the shelf of the Welsh Basin, or to lower plankton productivity.
... Regarding the phytoplankton, it is generally considered that paleolatitudes, paleocurrents, paleoecologic conditions (such as water temperature, water chemistry, water depth, distance from shoreline, etc.) and physical barriers may have affected the composition of organic-walled phytoplankton assemblages (Tyson, 1995;Le Hérissé and Gourvennec, 1995;Tongiorgi et al., 1995;Le Hérissé et al., 1997;Li et al., 2004;Playford, 2003;Molyneux et al., 2013;Shen et al., 2019). Even in the contemporaneous sequences, the composition of phytoplankton in different regions may not be the CONODONT ZONATION (Ziegler and Sandberg, 1990) rhomboidea crepida triangularis MIOSPORE ZONATION EASTERN EUROPE (Avkhimovitch et al., 1993) (Richardson and McGregor, 1986;Streel, 2009) same, which is the result of dissimilar paleoecologic or paleoenvironmental conditions, or disparate taxonomic and nomenclatural interpretations among different authors (e.g., Wicander and Playford, 2013). ...
Palynological investigations have been carried out on samples from the Upper Devonian Hongguleleng Formation of Western Junggar, Xinjiang, NW China. In total, 26 miospore species belonging to 19 genera and 28 acritarch species assigned to 19 genera have been recognized from the lower member of the Hongguleleng Fm. in the Bulongguoer section. The palynofloral assemblages, in particular the miospore taxa, are similar to those from the eastern European early Famennian Corbulispora vimineus–Geminospora vasjamica (VV) and Cyrtospora cristifer–Diaphanospora zadonica (CZ) miospore biozones, albeit quantitatively and qualitatively depauperate. The miospore assemblage zone is also consistent with the previous zonal schemes in light of brachiopod and conodont fauna assemblages, as well as carbon isotope geochemistry, that indicates a correspondence to the Palmatolepis crepida conodont Biozone. Part of the earliest Famennian Corbulispora vimineus–Geminospora vasjamica (VV) (more or less equivalent to the Palmatolepis triangularis conodont Biozone) miospore Biozone is most likely to be missing in the Hongguleleng Fm. of the Bulongguoer section. The palynostratigraphy and sedimentary sequence in Western Junggar are very similar to those from some other regions of western and eastern Europe, which increases the knowledge of the evolution of the paleoclimate, paleogeography and regional sedimentary environment of the Central Asian Orogenic Belt (CAOB), Eastern European Platform, and Laurussia.
... We agree with other authors (e.g., Eisenack 1934;) that mazuelloids are large acanthomorphic acritarchs close to Baltisphaeridium that have been subject to post−mortem, early diagenetic phosphatization. The most plausible hypothesis about their phylogenetic relationship is that of Le Hérissé et al. (1997), Porębska & Koszowska (2001), and , who presume close rela− tionship to the cysts of deep−water dinoflagellates. Hypertrophic conditions, which are thought to be the cause of mazuelloids' enormous size compared to other acritarchs, are indicated by sharp increase of dispersed organic matter in the black shale sediment at the onset of the Kacak Member. ...
... These measures have been used previously in Paleozoic palynological applications (e.g. Le Hérissé et al., 1997;Wellman, 2018b;Wellman et al., 2013). In all cases, taxa with only a generic assignment and those designated "?" have been excluded from the calculations, while those designated "cf." have been treated as valid identifications where appropriate following individual assessment. ...
Chitinozoans were recovered from the Naranco, Huergas and Gustalapiedra formations of northern Spain, which yielded a diverse assemblage including 29 taxa in 9 named genera. The deposits are of early Givetian age, a time when Iberia was isolated from large continents as part of the Armorican Terrane Assemblage. The formations studied here consist of a large clastic unit interrupting carbonate deposition, with large limestone formations positioned above and below the formations analyzed here. This clastic unit includes the Kačák Event, an important global extinction event associated with anoxia in the marine realm. In this paper, the relatively well-preserved chitinozoan assemblage is described and considered from a biogeographical and stratigraphical perspective. The chitinozoan community was deposited in a short space of time and includes various taxa not previously known from the Middle Devonian, though the assemblage as a whole is attributable to the period. Only moderate similarity is seen with assemblages reported from Laurussia and Gondwana, with a slight bias towards the latter. This report adds to our knowledge of chitinozoan paleobiogeography and to other recent studies of Middle Devonian palynology in northern Iberia.
... These latter two measures have been used previously in Palaeozoic palynological applications (e.g. Le Hérissé et al., 1997;Wellman, 2018;Wellman et al., 2013). In all cases, taxa assigned only to genera and those designated "?" have been excluded from the calculation, while those designated "cf." have been treated as valid identifications where appropriate. ...
Diverse microphytoplankton assemblages, including 72 taxa belonging to 27 genera of acritarchs and prasinophyte phycomata, have been recovered from Middle Devonian rocks in northern Spain, revealing an endemic flora dissimilar to coeval assemblages. These deposits are of early Givetian age and consist of the laterally equivalent Naranco, Huergas and Gustalapiedra formations of Asturias, León and Palencia provinces. At the time, Iberia was part of the Armorican Terrane Assemblage, a comparatively isolated island chain positioned between Laurussia and Gondwana. The studied formations represent a marine transect across a nearshore–offshore gradient and consist of a large clastic unit sandwiched between extensive carbonate deposits. This clastic unit incorporates the Kačák Event, an important global extinction event associated with marine anoxia. Herein, the suite of generally well-preserved microphytoplankton assemblages is described and their stratigraphical and biogeographical importance are considered. The microphytoplankton represents a single assemblage deposited in a short interval and is interpreted as being endemic. The assemblage is only moderately similar to contemporary assemblages from Laurussia and Gondwana and, although certain characteristic Middle Devonian taxa are present, other common species such as Arkonites bilixus and Tyligmasoma alargada are absent. While no unique taxa are found here, the taxa which are present represent a particular combination of species not seen elsewhere. Certain taxa appear which may have discordant temporal ranges, though no major inferences can be made from them as only two taxa both occur in significant numbers and have a confident identification. This assemblage adds to our knowledge of phytoplankton paleobiogeography, representing a significantly endemic assemblage within the generally cosmopolitan microphytoplankton flora of the Middle Devonian.
... Although graptolites likely had some control over their vertical position in the water column ) they probably were mainly carried passively in surface currents, so that their distribution might also have been determined by those currents. Thus, five to six oceanic gyres, depending on the time interval, were designated based on reconstructions from the literature (Wilde 1991;Le Hérissé et al. 1997;Herrmann et al. 2004). These gyres also include the large epicontinental seas covering much of the continents in the lower Paleozoic. ...
The last few decades have seen rapid expansion of large-scale paleontological databases that have allowed a much more methodologically rigorous approach to macroevolutionary patterns over geologic timescales. Studies have included insights into extinction, speciation, geographic range, ecological diversification, and the effects of climate change among others. However, these databases are heavily biased towards benthic shelly invertebrates, no doubt a reflection of their proportional contribution to the fossil record as a whole. Because of this it has not been clear how general observed patterns are to other groups, particularly planktic organisms which may face very different evolutionary pressures. Here, I examined some common correlates of extinction risk identified previously, apply them to a group of planktic organisms, graptolites, and compare the significance and effect size to results from benthic taxa. Of the properties associated with extinction risk geographic range is the most widely used and consistent. This property can be measured in a variety of ways that may impact results but there is relatively little published literature comparing different methods of measuring geographic range despite its widespread use. I explore how six measures of geographic range respond to changes in sample size as well their utility as correlates of extinction risk in the context of three disparate datasets. Finally, graptolites are of practical use in biostratigraphy and form the bulk of the global geologic timescale for the Ordovician and Silurian periods. Automated techniques have been developed to incorporate ever larger biostratigraphic datasets but the uncertainty in results has been difficult to characterize. I use a graptolite occurrence dataset assembled from the literature to build a novel ordinal composite for the Middle to Late Ordovician with the recently developed Horizon Annealing (HA) technique. From this composite I explore the limits and advantages of HA, with a particular focus on characterizing the uncertainty within and across the solution space of the ordinal composite.
Analyses of 1114 graptolite species with general linear models found that all factors commonly associated with extinction risk in benthic taxa were also significant in this planktic clade. However, the magnitude of the effect of geographic range was much lower than typically reported. This is most likely because the relationship between geographic range and extinction risk is non-linear with the greatest gains in extinction risk between taxa with small geographic range values and those with moderate ranges. As graptolites generally have large geographic ranges, even substantial increases in geographic range only provide a modest decrease in extinction risk. Different measures of geographic range also varied substantially in their explanatory power, and unidimensional measures were particularly poor. When the covariance among factors was accounted for by the use of partial least squares regression the strongest correlate of extinction risk was overall commonness, which reflects the interdependent effects of sampling and geographic range. Among analyses overall commonness explained 12-30% of the total variance in extinction risk. Because these two properties reinforce one another they are essentially impossible to disentangle in fossil datasets where the number of occurrences per taxon is typically low. After taking account of the correlation geographic range and sampling, the individual contributions of either variate alone were either very low (<5%) or not significant at all. The second strongest correlates of extinction risk were clade and age cohort, which are strongly correlated in graptolite evolutionary history. These two variates individually explained as much as an additional 18% of the variance.
While all individual measures of geographic range were significant correlates of extinction risk in graptolites their individual magnitudes varied substantially. To explore the cause of these differences I examined how six measures of geographic range (minimum spanning tree distance, convex hull area, maximum pairwise great circle distance, latitudinal range, longitudinal range, and equal area cell count) responded to sample size using three datasets: a simulated dataset with two differently shaped distributions of equal area, a fossil dataset of 381 brachiopod genera from the Paleobiology Database, and a set of 1152 modern bird species from the eBird database. Results showed that measures could be classified into two groups based on how their accuracy and precision responded to sampling. Group 1 measures (maximum pairwise distance, latitudinal range, and longitudinal range) rapidly became accurate and precise as sample size increased while Group 2 measures (minimum spanning tree, convex hull, and cell count) became accurate at a much slower rate, with one notable exception. In one of the simulated distributions the convex hull, as expected, became more precise as sample size increased, but unexpectedly, became less accurate at the same time. Group 2 measures also often showed a humped pattern where the lowest precision occurs at low, but not the lowest, sample sizes. This feature reflects the fact that variance at very small sample sizes is limited by either the method (cell count) or clustering of occurrences (minimum spanning tree and convex hull). Whereas the rank order of the value taxon geographic ranges was robust to variation in sample size across all measures, Group 1 measures had lower values at the smallest sample sizes.
I further examined the six measures as correlates of extinction risk in the PBDB dataset using both logistic regression and general linear models. Logistic regression of the duration of generic survival beyond their stage of first occurrence showed that all measures of geographic range were significant and relatively robust to differences in how large versus small ranges were classified. General linear models of extinction risk also found that all measures of geographic range were significant but that the magnitude of effects varied significantly. Group 1 measures were relatively poor correlates of extinction risk in comparison to Group 2 measures. The relatively poor performance of Group 1 measures probably reflects that fact that these measure are not able to capture the complex nature of real distributions and because of methodological biases in these measures that make them vulnerable to outlier points and make some values more likely than others. The convex hull also suffers from vulnerability to outlier points and consistently overestimates geographic range. The minimum spanning tree method performs well as a correlate of extinction risk but is computationally expensive while equal area cell count performs even better and is not computationally expensive. For these reasons I advise the use of equal area cell count as a measure of geographic range in most cases, with minimum spanning tree as a supplement if the number of point occurrences is not too great. I also advise against the use of Group 1 measures and CH as measures of geographic range for extinction risk analyses.
Finally, although previous automated biostratigraphic methods of ordination have proven powerful, the amount of uncertainty in solutions remains unclear, partially because such characterization is time-consuming. This is especially true for the Horizon Annealing (HA) approach, which uses more data than other methods. I examined how HA performed using a large dataset of 109 stratigraphic sections containing 136 graptolites species, one event bed, and three K-bentonites across 1549 horizons. The resulting composite generally agrees with published biozonations and independently developed composites affirming HA scales up effectively. To test for a previously hypothesized methodological bias (greater influence of first appearances than last appearances on determining the ordination of events in the composite), I ran the solution in reverse but did not find any evidence of this bias in the system. To reduce the initial burn-in time of searching in HA, I tested the use of a quasi-Bayesian scaffolding approach that starts the solution closer to traditional biozonations and found that it did significantly improve the penalty score of the solution, without any apparent bias. I further examined how effective the different ways of mutating the composite solution were at improving the solution during the search procedure. Mutations that allow changes in the spacing of collection levels within sections relative to the composite were much more effective than those that did not. I characterized uncertainty in the solution with three methods (vice, jackknife, and an island search). Vice was the fastest and most conservative measure, and it indicates an uncertainty range of 40 horizons on average, which corresponds to a temporal resolution of ~373 Kya. Finally, I characterized the uncertainty based on differences between three independent runs and found that although the global first and last occurrences of taxa were robust, the position of individual horizons varied more than was implied by any of the within-run uncertainty metrics. This result suggests that using HA composites to test dynamics based on patterns of occurrence within the temporal range of individual taxa should be done with caution.
Although the accelerating pace of quantitative approaches to macroevolution have yielded more robust results than was previously possible there are substantial gaps in taxonomic coverage and methodological issues which have often been downplayed. The studies presented here attempt to address some of those issues. First, a large proportion of macroevolutionary studies have been based on patterns in shelly benthic invertebrates and the results then treated as if they apply to all groups of organisms. I demonstrate that while the same factors are often significant between these shelly benthic invertebrates and planktic graptolites the magnitude of relationships vary substantially. These contrasts in magnitude are reflective of the groups’ ecological strategies and can provide further insight into macroevolutionary processes that uniquely effect each one. Therefore, studies should be careful to interpret their results with regard to the ecology of the particular organisms being examined and to not be overly broad in claims about how generalizable a pattern is. Second, the treatment of geographic range in macroevolutionary studies has been inconsistent and the field of macroevolution would be well-served by some standardization. Here I found that unidimensional measures of geographic range, particularly the commonly used maximum pairwise distance, should not be used due to serious biases and limitations. More complex methods, minimum spanning tree distance and equal area cell count, were found to have the most desirable qualities as measures of geographic range and should be used in most macroevolutionary analyses. Finally, the use of ordinal composite built from biostratigraphic data for analyses of turnover, extinction, colonization, or other patterns requires a knowledge of the uncertainty in the system that was lacking. I demonstrated three methods of quantifying uncertainty in an ordinal composite as well as refining search methods that should allow for this powerful approach to be more widely utilized and understood.
... Extends to include areas south of the Central Canadian Shield (i.e. Michigan and Appalachian Basins, Venezuela and Colombia) and much of North America east of the transcontinental arch (Boucot, 1974;Boucot et al., 1980;Oliver, 1990;le Herisse et al., 1997). ...
We present an interim Devonian bioregionalisation in which previous zoogeographical and biogeographical areas of Devonian taxa are reviewed. This review has been long overdue, as Devonian bioregionalisation has become poorly constrained since the foundational work of Arthur J. Boucot in the late 1960s. A systematic review of over 100 areas and amendments is completed for the first time with addition of three new areas: the Mardoowarra and the Late Devonian Eastern Australasia region, and Western Gondwana realm. This interim regionalisation is the first to be completed and standardised, made in preparation for future palaeobiogeographic studies and as a prelude to rigorous testing. By standardising the 1969 bioregionalisation of Boucot et al. Devonian biogeography can begin to assess if the proposed bioregionalisation is representative of true natural areas.
... The comparison of the marine phytoplankton from both sections of the Los Espejos Formation with coeval assemblages (Table 1, Fig. 4) indicates that more than half of the species are shared with Avalonia (e.g., Mullins 2001 and references therein; Richards and Mullins 2003) and Baltica (e.g., Porębska et al. 2004;Stricanne et al. 2006). Around 20% of the species are common to Armorica (e.g., Cramer 1964a) and Laurentia (e.g., Cramer 1970; Mullins 2001 and references therein), and almost 30%, to other Gondwanan regions (e.g., Le Hérissé et al. 1997;Cardoso 2005). On the other hand, the miospore assemblages of the Precordillera share more species with coeval assemblages from other Gondwanan and peri-Gondwanan areas such as North Africa, Brazil, and Spain (e.g., Richardson et al. 2001;Rubinstein and Steemans 2002;. ...
The palynological content from the Cerro La Chilca and Quebrada Ancha sections of the Wenlock? to Přídolí Los Espejos Formation, in the Argentinean Precordillera is studied. The marine palynomorphs exhibit higher relative abundance and diversity in almost all the productive samples, except for the uppermost ones from both sections, in coincidence with the shift towards more proximal facies in this part. The Los Espejos Formation yielded a total of 114 species of marine organic walled-phytoplankton, 52 species of miospores and two non-marine phytoplankton species. The lower part of the Los Espejos Formation, dated as Ludfordian, displays the highest phytoplankton diversity and the better-preserved palynomorphs of the studied samples in both sections. Diversity tends to diminish towards the upper part of the Los Espejos Formation, dated as late Ludfordian–Přídolí, in coincidence with the transition to storm-dominated shelf and shoreface environments and subaerial exposures that probably hinder the preservation of palynomorphs. Comparisons with coeval phytoplankton assemblages from Gondwana and other palaeoplates such as Laurentia, Baltica, and Avalonia result in strong similarities, which suggest a cosmopolitan distribution pattern during the Ludlow and the Přídolí. Conversely, the trilete spores display more similarities with those from Gondwana and thus suggest a lesser dispersive potential in comparison to phytoplankton. A new trilete spore species Emphanisporites? tenuis is described.
... The former is widely used in bioprovincialism evaluation of extant biotas and has been applied in numerous Palaeozoic palynological studies (e.g. [50]). It can be expressed as CS(a,b) ¼ 2jaPbj/ja þ bj (where a and b are the total number of species in assemblage a and b, respectively). ...
The remarkably preserved Rhynie chert plants remain pivotal to our understanding of early land plants. The extraordinary anatomical detail they preserve is a consequence of exceptional preservation, by silicification, in the hot-springs environment they inhabited. However, this has prompted questions as to just how typical of early land plants the Rhynie chert plants really are. Some have suggested that they were highly adapted to the unusual hot-springs environment and are unrepresentative of ‘normal’ plants of the regional flora. New quantitative analysis of dispersed spore assemblages from the stratigraphical sequence of the Rhynie outlier, coupled with characterization of the in situ spores of the Rhynie chert plants, permits investigation of their palaeoecology and palaeophytogeography. It is shown that the Rhynie inland intermontane basin harboured a relatively diverse flora with only a small proportion of these plants actually inhabiting the hot-springs environment. However, the flora of the Rhynie basin differed from coeval lowland floodplain deposits on the same continent, as it was less diverse, lacked some important spore groups and contained some unique elements. At least some of the Rhynie plants (e.g. Horneophyton lignieri) existed outside the hot-springs environment, inhabiting the wider basin, and were indeed palaeogeographically widespread. They probably existed in the hot-springs environment because they were preadapted to this unstable and harsh setting.
This article is part of a discussion meeting issue ‘The Rhynie cherts: our earliest terrestrial ecosystem revisited’.
... The defined endemic fauna was later expanded to include certain phacopidid trilobites of which calmoniids and particular homalonotiids are unique (Richter, 1941;Richter and Richter, 1942;Eldredge and Ormiston, 1979;Cooper, 1982;Chulp ac, 1993;Adrain and Edgecombe, 1996;Meyerhoff et al., 1996). Several gastropods ( Blodgett et al., 1990), ostracods (Becker et al., 1994;Lethiers et al., 2001;Racheboeuf et al., 2012;Salas et al., 2013), palynomorphs, acritarchs and chitinozoans ( de Almeida-Burjack and Paris, 1989;le H eriss e et al., 1997;le H eriss eA, 2001;Grahn and Melo, 2005;Troth et al., 2011) and gnathostome fish (Janvier and Maisey, 2010) are additionally suspected to be endemic to the Malvinokaffric Realm. ...
Documentation of the palaeontological heritage of the Early to Middle Devonian Bokkeveld Group of South Africa has been recorded as far back as the early nineteenth century with the arrival of the first European settlers, merchants and explorers to the Cape region. Anecdotal evidence suggests that indigenous peoples had knowledge of fossils in the Bokkeveld Group from as early as the Middle-to-Late Stone Age. Within the first hundred years of the expansion of the Cape Colony the first geological maps of the Bokkeveld Group were produced alongside the first description of fossils as well as their Devonian age and marine origin. These early investigations provided a foundation for establishing faunal endemism common to South Africa, South America and the Falkland Islands. During the early twentieth century considerable progress was made in the description of fossil fauna of the Bokkeveld Group, most notably of invertebrates and plants. This research demonstrated that invertebrate fossils from the Bokkeveld Group, as well as those from time equivalents in South America and the Falkland Islands, were distinct from the Devonian Period elsewhere (e.g. Europe and North America). The role of fossils from the Bokkeveld Group proved critical in the formal designation and delineation of a broad region of endemism, the Malvinokaffric Realm that persisted at high subpolar-to-polar palaeolatitudes in southwestern Gondwana and extended from South Africa, Bolivia, Brazil, Argentina, Antarctica and the Falkland Islands with possible elements in Guinea-Bissau, Senegal and Ghana during the Emsian-Eifelian Stages. In the latter half of the twentieth century developments in understanding the sedimentology and stratigraphy of the Bokkeveld Group lead to the premise that the succession accumulated in a storm-and-wave dominated deltaic palaeoenvironment, and enabled inferences on the palaeoecology of the fossil taxa. During this period detailed revisions of numerous invertebrate and plant taxa were undertaken as well as the first descriptions of fossil fish. Research in the twenty-first century has shown a general decline in palaeontological interest, but developments are currently underway in refining the taxonomy of fossil echinoderms and fish from the Bokkeveld Group as well as understanding the Group's palaeoenvironmental history, geochronology and understanding the decline of the Malvinokaffric Realm in South Africa and its causation.
... Whereas many probably represent the resting stage (cyst) of marine phytoplanktonic algae, various forms have now been assigned to the division Prasinophyta of the green algae. Morphology has been used to define informal groupings (Downie, 1973;Fensome et al., 1990;Martin, 1993;Colbath and Grenfell, 1995), which are useful for Precambrian and Paleozoic biostratigraphy (Martin, 1993;Vidal and Knoll, 1993;Molyneux et al., 1996) and paleobiogeography (Le H eriss e et al., 1997;Servais et al., 2003Servais et al., , 2004. Acritarchs reached their acme in the Paleozoic and are largely but not exclusively marine. ...
Because of their small size and vast abundance in various types of sedimentary rocks, microfossils have found a multitude of applications in geology, especially regarding biostratigraphy, correlations, and paleoenvironmental analysis. Organic-walled microfossils such as pollen, spores, and various organic debris derived from terrestrial plants are especially useful when studying terrestrial deposits. This chapter presents the many different groups of organic-walled microfossils, collectively called palynomorphs, and the different methods palynologists use to study and extract them from sediments and rocks. We present a biostratigraphic application, the use of the pollen and spore record across the Cretaceous-Paleogene boundary, which has proven to be one of the most precise and reliable means for pinpointing this major transition within terrestrial deposits.
... Although graptolites likely had some control over their vertical position in the water column , they probably were mainly carried passively in surface currents, so that their distribution might also have been determined by those currents. Thus, five to six oceanic gyres, depending on the time interval, were designated based on reconstructions from the literature (Wilde 1991;Le Hérissé et al. 1997;Herrmann et al. 2004). These gyres also include the large epicontinental seas covering much of the continents in the lower Paleozoic. ...
Although extinction risk has been found to have a consistent negative relationship with geographic range across wide temporal and taxonomic scales, the effect has been difficult to disentangle from factors such as sampling, ecological niche, or clade. In addition, studies of extinction risk have focused on benthic invertebrates with less work on planktic taxa. We employed a global set of 1114 planktic graptolite species from the Ordovician to lower Devonian to analyze the predictive power of species’ traits and abiotic factors on extinction risk, combining general linear models (GLMs), partial least-squares regression (PLSR), and permutation tests. Factors included measures of geographic range, sampling, and graptolite-specific factors such as clade, biofacies affiliation, shallow water tolerance, and age cohorts split at the base of the Katian and Rhuddanian stages.
The percent variance in durations explained varied substantially between taxon subsets from 12% to 45%. Overall commonness, the correlated effects of geographic range and sampling, was the strongest, most consistent factor (12–30% variance explained), with clade and age cohort adding up to 18% and other factors <10%. Surprisingly, geographic range alone contributed little explanatory power (<5%). It is likely that this is a consequence of a nonlinear relationship between geographic range and extinction risk, wherein the largest reductions in extinction risk are gained from moderate expansion of small geographic ranges. Thus, even large differences in range size between graptolite species did not lead to a proportionate difference in extinction risk because of the large average ranges of these species. Finally, we emphasize that the common practice of determining the geographic range of taxa from the union of all occurrences over their duration poses a substantial risk of overestimating the geographic scope of the realized ecological niche and, thus, of further conflating sampling effects on observed duration with the biological effects of range size on extinction risk.
... Cramer (1971) and Cramer and Díez (1972, 1974a, 1974b) provided a model for the distribution of Silurian acritarchs, represented by six principal acritarch biofacies. Le Hérissé and Gourvennec (1995) reevaluated four principal acritarch biofacies (the Neoveryhachium carminae facies, the Deunffia facies, the Domasia facies, and the Pulvinosphaeridium-Estiastra facies) of Cramer's model, and subsequently Le Hérissé et al. (1997) analysed the acritarch biogeography of the Late Silurian. More recently, Molyneux et al. (2013) 2 Supplementary data are available with the article through the journal Web site at http://nrcresearchpress.com/doi/suppl/10.1139/cjes-2015-0215. Fig. 3. Overview of Chinese localities and stratigraphy from which Silurian acritarchs have been reported. ...
The present paper reviews all investigations of Silurian acritarchs in China. Since Silurian acritarchs were first reported in China in 1978, significant progress has been made in Chinese Silurian acritarch research. A total of 30 scientific articles and theses have been published on Silurian acritarchs from China. The majority of these papers recorded acritarchs from South China, and most Silurian acritarch studies concentrated on the Llandovery. Two papers describing material thought to be Silurian have since been shown to be Ordovician acritarch assemblages. We have updated the systematics of the taxa in these reported assemblages and documented their biostratigraphic distribution within China. Investigations of Silurian acritarchs, however, are still very limited, and more research is needed for systematic, biostratigraphic, and palaeoecological interpretations.
... Using assemblages of Ludlovian to Pridolian acritarchs, prasinophytes, and mazuelloids, Le Hérissé et al. (1997Hérissé et al. ( , 2009 summarized the global patterns of phytoplankton distribution for the Late Silurian. Cluster analysis of well-dated associations indicated the presence of high latitude microfloras along the western margin of Gondwana, forming a biogeographic unit that roughly coincides with the Malvinokaffric province of Boucot (1971Boucot ( , 1975. ...
Distinctive palynomorph associations have been recovered from selected samples in the Ananea and San Gabán formations in southern Peru. A total of 38 genera and 71 species of acritarchs and prasinophytes have been identified, with several forms in open nomenclature. Palynomorph vesicle walls are affected by slight metamorphism, and thermal alteration indices range from 3 to 3+. Age-diagnostic species, such as Chutecloska athyrma Loeblich & Wicander, 1976, Domasia elongata Downie, 1960, Riculasphaera fissa Loeblich & Drugg, 1968, and Thysanoprobolus polykion Loeblich & Tappan, 1970 are present in the Ananea Formation. The species Hoegklintia visbyensis (Eisenack) Dorning, 1981, recovered from the San Gabán Formation, supports its Early Silurian age. Palynomorphs of terrestrial origin, such as miospores and resistant plant tissues, are either completely absent or extremely rare. Despite the rather sparse record and low number of productive samples, palynology allows assignment of an Early Silurian (late Llandovery to early Wenlock) age to the San Gabán Formation, and a possible Late Silurian to early Early Devonian (late Ludlow to early Lochkovian) age for the Ananea Formation at this location. The recovered acritarch and prasinophyte assemblages show close affinities to coeval microfloras known from Appalachian basins and northern Argentina microplankton assemblages, which suggest a connection between Central Andean and North American basins during the Silurian-Devonian transition. Integration of the biostratigraphic data herein obtained allows for regional basin correlations and paleogeographic reconstructions within the mid-Paleozoic Central Andes, and an interpretation of the overall geodynamic context of the basin in relation to the Proto-Andean active margin of western Gondwana.
... (e.g., Paris et al. 1981; Fatka 1999; ChluPáč 1999 and references therein, Frýda et al. 2002). As regards the phytoplankton groups, like chlorophytes and acritarchs, relatively few and geographically limited publications have been carried out in reference to this limit and, in general, the recorded palynological assemblages are badly preserved and poor in abundance and diversity (e.g., le hérissé et al. 1997a; BroCke et al. 2006; Molyneux et al. 2013 ). During the Late Silurian and Early Devonian , the proliferation of land plants took place. ...
... No estudo realizado por esses autores foi proposto um modelo baseado na distribuição de Umbellasphaeridium saharicum no Devoniano Superior, que diferenciou e caracterizou uma comunidade de microplâncton de altas latitudes entre o Frasniano e o Famenniano no Reino Malvinocáfrico, em regiões do Gondwana ocidental e Laurussia meridional. LE HÉRISSÉ et al. (1997) observaram que os processos de provincialismo são dependentes do arranjo continental, das flutuações climáticas globais e, provavelmente, de mudanças geoquímicas e na circulação oceânica. Os autores constataram que os principais aspectos da paleogeografia do intervalo Siluriano-Devoniano, entre eles o fechamento do Oceano Iapetus, e consequentes mudanças ambientais, foram suficientemente fortes para influenciar na distribuição das associações do fitoplâncton . ...
Embora constituam palinomorfos de natureza biológica incerta, os acritarcos são comumente utilizados para fins bioestratigráficos e de interpretação paleoambiental, principalmente para os depósitos de idade entre o Cambriano e o Devoniano. Este trabalho apresenta uma revisão atualizada sobre os aspectos morfológicos, classificação, distribuição estratigráfica e aplicações dos microfósseis de parede orgânica alocados neste grupo no âmbito das Geociências. Registros brasileiros são exemplificados, principalmente de bacias intracratônicas paleozoicas, com destaque para os depósitos pennsilvanianos e permianos da Bacia do Paraná. Como principais resultados obtidos para este intervalo na bacia, destacam-se: (i) muitos dos táxons identificados como acritarcos possivelmente têm parentesco com algas prasinofíceas e zignematáceas e (ii) a constatação de intervalos com associações abundantes em espécimes atribuídos aos gêneros Micrhystridium e Veryhachium, corroborando in terpretações prévias sobre um marco estratigráfico permiano de natureza marinha, incluindo depósitos da porção superior da Formação Palermo à porção mais inferior da Formação Irati. A revisão taxonômica revela um período de declínio acentuado da diversidade de espécies (blackout fitoplanctônico) para o Carbonífero e Permiano em nível mundial, principalmente considerando a riqueza em nível genérico, muito menor que aquela observada para os depósitos pré-carboníferos no Brasil e em outras partes do mundo.
... We agree with other authors (e.g., Eisenack 1934;) that mazuelloids are large acanthomorphic acritarchs close to Baltisphaeridium that have been subject to post−mortem, early diagenetic phosphatization. The most plausible hypothesis about their phylogenetic relationship is that of Le Hérissé et al. (1997), Porębska & Koszowska (2001), and , who presume close rela− tionship to the cysts of deep−water dinoflagellates. Hypertrophic conditions, which are thought to be the cause of mazuelloids' enormous size compared to other acritarchs, are indicated by sharp increase of dispersed organic matter in the black shale sediment at the onset of the Kacak Member. ...
... Eight quantitative measures of geographic range were calculated including latitudinal range, longitudinal range, maximum pairwise distance, length of minimum spanning tree, convex hull area, number of 58 £ 58 cells occupied, number of oceanic gyres occupied and number of regions occupied. The gyres were designated by reconstructions from the literature (Wilde 1991;Le Hérissé et al. 1997;Herrmann et al. 2004). Regions were designated as nine paleocontinents or distinct areas (Baltica, Avalon, Laurentia, Siberia, Kazakhstan, north-west Gondwana, south-west Gondwana, north-east Gondwana, and south-east Gondwana). ...
A set of 137 Ordovician graptolite species were used to examine the associations among geographic range, sampling, biofacies and species longevity. Model-choice using general linear models combined with partial least-squares regression analysis found seven distinct predictive variables. The dominant factors were overall commonness, biofacies, geographic range and sampling in decreasing order of variance explained. However, the data-set is biased toward particularly well-sampled and widespread taxa. Region (represented as a set of discrete geographic areas) was a strong factor in extinction risk, whereas latitudinal range and endemicity were poor predictors. Results suggest that other factors besides just geographic range and biofacies need to be considered when understanding extinction dynamics.
... al and paleoenvironmental information , in particular between the Ordovi - cian and Devonian . An acritarch provincialism is particularly obvious in the Early – Middle Ordovician ( e . g . , Li and Servais , 2002 ; Servais et al . , 2003 ) , but also present in the Silurian ( e . g . , Le Hérissé and Gourvennec , 1995 ) and Devonian ( e . g . , Le Hérissé et al . , 1997 , 2000 ) . On the other hand , inshore – offshore variations of acritarch assemblages and paleoenvironmental changes have been discussed for many years , and it is generally accepted that highest abundances and diversities are recorded on the shelves , with lower diversity acritarch assemblages present in nearshore and offshore environm ...
... 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; Vecoli and Le Hérissé, 2004). Silurian and Devonian species of Veryhachium were also cosmopolitan (Le Hérissé and Gourvennec, 1995; Le Hérissé et al., 1997; Le Hérissé et al., 2000, table 1). Li, Cao et al. (2004, fig. 3) plotted all Permian localities with the Micrhystridium–Veryhachium assemblages on a paleogeographic map, and demonstrated that Veryhachium occurred across a wide range of latitudes, indicating a cosmopolitan distribution. ...
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.
... The failure of applications of quantitative methods to acritarch assemblages for palaeogeographic reconstructions (Fortey and Mellish, 1992) probably reflected an incomplete acritarch taxonomy at the time, hence depended solely on the use of strongly biased and inconsistent taxonomic databases. It has been clearly shown by later studies that when applied to taxonomically sound databases, quantitative methods such as cluster analysis and/or similarity indexes on acritarchs (as well as on chitinozoans ) give useful results for palaeogeographic reconstruction (e.g., Le Hérissé and Gourvennec, 1995; Le Hérissé et al., 1997; Vecoli and Samuelsson, 2001; Samuelsson et al., 2002). We give here a brief summary of the current state of knowledge on acritarch palaeobiogeographic distribution especially for what concerns our study area. ...
Acritarchs, the fossilizable, resting cysts of phytoplanktonic algal protists, are the dominant component of marine organic-walled microfossils in the Palaeozoic. The majority of acritarchs show strong similarities with dinoflagellate cysts in morphological and biogeochemical features, as well as distributional patterns in the sediments. The production of these organic-walled microfossils and their distribution and survivorship in the sediments were controlled by differences in ecological tolerances and life cycle (autecology) of the planktonic parent organisms.
... continental landmasses or deep oceans can separate different biogeographical units (e.g. Le Hérissé et al., 1997). Comparing sedimentological data from both regions (Belgium and the HCM) it is obvious that their palaeoenviroments were different during early Famennian time (Thorez et al., 2006;Szulczewski, 1995). ...
A rich phytoplankton assemblage and low diversity miospore microflora is described from the Lower Famennian deposits of the Kowala Quarry, Holy Cross Mountains, Central Poland. This assemblage is assigned to the Pw acritarcha zone, which is correlated with the late triangularis–crepida standard conodont zones based on appearance of the acritarch Puteoscortumwilliereae. Comparison of the present palynological results with well-documented data from Belgium clearly indicates differences in marine microflora composition in both regions. The important taxa Visbysphaera (?) occultata, Ephelopallamedia, and Palacanthustripus in Belgium are absent in the samples from the Holy Cross Mountains and by contrast, the phytoplankton frequent in Poland (Lophosphaeridium, Dictyotidium or Cymatiosphaera) are rare in Belgium. The taxonomical difference between the Holy Cross Mountains and Belgium palynoflora may probably reflect environmental differences: offshore and more proximal environmental conditions respectively. Three new species (Leiofusa turnauae sp. nov., Lophosphaeridiumirregularis sp. nov. and Veryhachium?kowalae sp. nov.) have been formally instituted and two new taxa (Centrasphaeridium sp. A and Centrasphaeridium sp. B) are left in open nomenclature.
... Important geochemical changes (e.g. Azmy et al., 1999;Saltzman, 2002;Stricanne et al., 2006), as well as paleogeographical and paleooceanical changes (Le Hérissé et al., 1997;Jeppsson, 1998) are also known to have occurred during this time. To analyze biodiversity changes during this approximately nine million year period (Ludlow, Prídolí, Early Lochkovian), a database of acritarch and prasinophyte phycomata occurrences was developed. ...
The acritarch Teleostomata rackii gen. et sp. nov. is described and illustrated from the Middle Devonian Skały Beds that outcrop at Miłoszów (Holy Cross Mountains, Poland). At the type locality, its stratigraphical range extends strictly to the “Geminospora” extensa (Ex) Miospore Zone (= hemiansatus–varcus Conodont Zones, which correspond to the early and middle Givetian). The same acritarch has been illustrated from the Eifelian sediments of the Gondwanan shelf in Tunisia, but it was unnamed. This acritarch from Miłoszów is distinctive from other phytoplankton genera of tetrahedral shape because of its broad processes with distal pore-like openings.
A diverse and abundant organic-walled microphytoplankton assemblage is reported from two measured sections of the Lower Devonian (Lochkovian) Ross Formation in Benton and Decatur counties, Tennessee. The palynoflora comprises 24 genera and 34 species of acritarchs, including one new genus and species (Caulissoma gordonii); and five genera and 11 species of prasinophyte phycomata (excluding Leiosphaeridia and Tasmanites). Other components include chitinozoans, miospores, and scolecodonts. This is the first Early Devonian acritarch/prasinophyte assemblage to be described from Tennessee, and is assigned a Lochkovian age based on marine invertebrate faunas, stratigraphic relationships, and the palynomorph assemblage. A high degree of similarity (67% commonality) exists between this palynoflora and that from the stratigraphic and age-equivalent Haragan and Bois d’Arc formations of Oklahoma. Appreciable numbers of the microphytoplankton taxa identified herein are common to the Haragan and Bois d’Arc formations and are, moreover, restricted to the Lochkovian and endemic to Laurentia. Additionally, a number of species are widely distributed and confined to the Early Devonian, and three species, Demorhethium lappaceum, Riculasphaera fissa, and Thysanoprobolus polykion – all cosmopolitan – are constrained to the Lochkovian. With increasing knowledge of Early Devonian palynofloras, the apparent degree of provincialism is progressively declining as seemingly endemic taxa are reported from more regions in both hemispheres. The Ross Formation sediments were deposited in a low-energy, offshore, normal marine environment, punctuated by intermittent episodes of shallow-water current and storm deposition.
A detailed study of organic facies and palynological assemblages was carried out on 11 samples of potential hydrocarbon source rocks of the Pimenteiras Formation, an outcropping at the western edge of the Parnaíba Basin, Brazil. The main objectives are to characterize the depositional paleoenvironment and hydrocarbon source potential. The selection of this outcrop occurred in the function of its preservation and accessibility, and the samples collection observed 1 m of vertical spacing. Generally, the organic matter and the palynomorphs showed a good state of preservation and fluorescence. The most notable spores and acritarchs and phycomates species were discussed in light of international biozones, and the chronostratigraphic range defined as Late Eifelian - Latest Frasnian in age. TOC results show ranges from 0.40 to 2.91%, with most samples showing greater than 1%, thereby holding a high potential generation. The S1 values were virtually null, and the S2 peak ranged from 0.9 to 5.33 mg/g. The kerogen 435 °C, and the ICE between 4.0 and 4.5 demonstrating the material immaturity. For the palynofacies associations definition, only 10 out of the 25 total quantified of subgroups of kerogen categories were considered in the counting of 300 particles. A dendrogram constructed based on these results through cluster analysis, revealed four palynofacies, as follows: I constituted mainly by palynomorphs (acritarchs, prasinophytes and sporomorphs); II – Dominance of Translucent organic matter (cuticles, epidermal tissue and translucent phytoclasts with and without structure); III - Dominance of Opaque/non-fluorescent (opaque phytoclasts and non-fluorescent AOM) and IV - Dominance of AOM fluorescent (amorphous organic matter with fluorescence). The palynomorphs are the most abundant constituents of all studied kerogen. Quantitative analysis based on the distribution of palynomorphs groups throughout the section indicates the dominance of sporomorphs in the palynological assemblages from the Middle Devonian aged samples. On the other hand, occurred the predominance of microplankton elements in the Late Devonian aged samples. Thus, the depositional paleoenvironment was established as a distal oxic mud-dominated shelf with the deltaic influence of the Late Eifelian to Late Givetian, and there is a tendency distal (dysoxic-anoxic ‘shelf’) from the Frasnian, which indicates the maximum flooding surface.
Morphology Classification Acritarch Affinities and Biology Acritarch Ecology General History of Acritarchs Applications of Acritarchs Phylum Prasinophyta Further Reading Hints for Collection and Study
The late Givetian and early Frasnian of a Herzyn Limestone section in the Harzgerode Zone is characterised by a reduced carbonate sequence. During the falsiovalis to Early hassi Zone entirely condensed phosphorites have been accumulated. Phosphorites are embedded in styliolinid sparites and laminated bioclastic micrites containing a pelagic fauna. The beds record very low net sedimentation (∼ 5-200 mm Ma-1). The reduced sequence was accumulated on top of a pelagic carbonate platform under influence of strong current activity. The very youngest Muellerisphaerida hitherto known were found in one sample of this section. More than ten species of the genera Aldridgeisphaera, Oraveczisphaera and Papinochium were found. Seven species are studied in detail. Two new species (Aldridgeisphaera katzungi sp. nov. and Oraveczisphaera ruchholzi sp. nov.) are described. The total stratigraphic range of this group existing since the Caradocian can now be extended to the Upper Devonian (Frasnian).
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 palynological assemblages of the upper part of the Los Espejos Formation and the lower part of the Talacasto Formation, in the northern outcrops of San Juan Precordillera, Argentina, were studied. This section spans the Silurian/Devonian boundary. Therefore the palynological analysis
helps to constrain the age and to identify the position of the system boundary. This age interval has been much discussed owing to the scarcity of stratigraphically valuable fossils. The miospores and marine phytoplankton present in the upper part of the Los Espejos Formation, point to a Late
Ludlow/ Přídolí? to early Lochkovian age. The occurrence of relevant biostratigraphic species such as Dictyotriletes cf. emsiensis Morphon, Cymbosporits proteus, Amicospopites streeli and the possible presence of Streelispora newportensis,
permit the identification of the Silurian/Devonian boundary within the Los Espejos Formation. This system boundary is recorded for the first time in the Pre-cordillera based on palynological assemblages. The position of this limit coincides with that established based on faunal data. A Lochkovian
age is also confirmed in the lower part of the overlaying Talacasto Formation in the studied section, thus supporting previous palynological and fauna data.
SILURIAN MARINE ORGANIC-WALLED PHYTOPLAKTON AND MIOSPORES OF THE LOS ESPEJOS FORMATION, IN THE RIO DE LAS CHACRITAS SECTION, SAN JUAN PRECORDILLERA, ARGENTINA. Marine organic-walled phytoplankton (acritarchs and chlorophytes) and miospores were recorded from nine productive levels of the lower to middle section of the Los Espejos Formation, in the Río de Las Chacritas stratigraphic column, Central San Juan Precordillera. The marine phytoplankton is highly diversified and dominates the palynological assemblage through the section, with many species recorded for the first time in the Silurian of Argentina. Trilete spores and cryptospores assemblages are poorly diversified. In spite of the fact that most of the species display long stratigraphic ranges, palynological assemblages allow constraining the age of the Los Espejos Formation to the Ludlow. The presence of miospores, which first appeared in younger strata in other regions, could be interpreted as related to particular palaeoenvironmental conditions of this basin. The fitoplankton shows a strong correlation with coeval assemblages from Great Britain and important similarities with assemblages from Sweden, Spain and North Africa; thus demonstrating the lack of important biogeographic barriers and supporting a more cosmopolitan character of the late Silurian assemblages. The relationship between the acritarch and chlorophyte relative abundances shows important fluctuations throughout the studied section. Levels with greater abundance of clorophytes match the more prominent changes of sedimentary facies. Consequently, variations in the phytoplankton distribution could be revealing a strong dependence on local palaeoenvironmental factors.
Diverse and well preserved acritarch and prasinophycean phycomata assemblages were recovered from the late Silurian to Lower Devonian strata of well A161 in western Libya, and four distinct acritarch biozones are recognized, based on the stratigraphic distribution of 156 species. The palynoflora is independently dated by means of chitinozoans, and allows discussion of the evolution of acritarchs and prasinophyte phycomata across the Ludlow^Pr ›| ¤dol| ¤ boundary in relation to probable major climatic change, as well as in the early and middle Pr ›| ¤dol| ¤, and the lower Lochkovian. Correlations are proposed with the British Isles, Baltica, and Algerian Sahara. Sedimentation occurred in shallow high-energy conditions throughout, but with periodic rise of sea level. The changes in marine to terrestrial palynomorph ratios through the section document the relationship between marine palynomorph assemblages and sea surface conditions in these marginal marine environments. The major drift of Gondwana towards low latitudes during the Ludlow^Pr ›| ¤dol| ¤ transition seems to have been the driving force behind homogenization of assemblages on the two sides of the Rheic ocean, and explains the similarities between phytoplanktonic assemblages of the north Gondwanan margin and the South of Baltica. The data suggest that the Rheic ocean was almost closed by the late Silurian, and had become restricted to a moderately deep sea. In the Lochkovian the microflora are strongly facies-dependent and delineate more restricted provinces such as the Ibarmaghian domain in the sense of Plusquellec (1987) including the Maghreb and Ibero^Armorican areas. Nine new species are described: Arkonia nova, Arkonia paulumstriata, ?Cymatiosphaera florida, Cymatiosphaera nimia, Dactylofusa hispidusa, Disparifusa quasibernesgae, Evittia areolata, Multiplicisphaeridium verticisum, and ?Villosacapsula steemansii. In addition, three new combinations are suggested: Visbysphaera bonita (Cramer) comb. nov., Visbysphaera jardinei (Cramer) comb. nov. and Visbysphaera albanega (Cramer et al.) comb. nov. ß 2002 Elsevier Science B.V. All rights reserved.
Acritarchs are organic-walled cysts of unicellular protists that cannot be assigned to any known group of organisms. Most acritarchs are probably the resting cysts of marine eukaryotic phytoplankton. Some acritarchs are thought to be dinoflagellate cysts but lack the requisite morphology to make a positive attribution. Others, however, can be confidently assigned to the chlorophytes (green algae), but for convenience, are still commonly included in the acritarchs. Thus, acritarchs are a heterogeneous, polyphyletic collection of organic-walled microfossils of unknown or uncertain origin. Acritarchs vary in size from < 10 microns to more than 1 mm, but the majority of species range from 15 to 80 microns. Because of their small size, abundance and diversity, as well as widespread distribution, acritarchs are very useful in biostratigraphic correlation, as well as paleobiogeographic and paleoenvironmental studies. Acritarchs are found throughout the geologic column but were most common during the Late Proterozoic and Paleozoic. Because they represent the fossil record of the base of the marine food chain during the Proterozoic and Paleozoic, acritarchs played an important role in the evolution of the global marine ecosystem.
Rich palynological assemblages have been obtained from the Middle Devonian Chigua Formation (Chinguillos Group, San Juan Province), western Precordillera, Argentina, at two new localities (Del Chaco and Don Agustín creeks). From the palyniferous levels at Del Chaco Creek, there are two assemblages: one is very rich in microplankton (assemblage 1) whereas the other is dominated by spores (assemblage 2). The level obtained from Don Agustín Creek, poorest in overall taxa, is also rich in microplankton (assemblage 3). Compared with coeval microfloras elsewhere, a late Emsian-early Eifelian, and an early Givetian age are proposed for the first and the second assemblages respectively. A third assemblage (assemblage 3) tentatively represents a timespan around the Givetian-Frasnian boundary. The proposed age based on the palynomorphs reinforces previous palaeontological records. Variation in the microplankton diversity, fluctuations in the microplankton/spore ratio and differences in acritarch morphology are used here to interpret changing proximity to palaeoshoreline and so to recognize fluctuations in relative sea level that occurred during the deposition of the Chigua Formation.
Rich phytoplankton assemblages have been obtained from Late Devonian and Early Carboniferous deposits, from a trench and three boreholes in the Holy Cross Mountains (HCM, central Poland). Almost all samples contain both acritarchs and prasinophytes. Three phytoplankton assemblages are distinguished. The first one is from the Upper Famennian, the second from the Tournaisian and the third, poorest in specimens and taxa, is from the Viséan. The assemblages are compared with coeval phytoplankton records elsewhere in the world.Some taxa from the Holy Cross Mountains are recorded for the first time in Europe. A new species Gorgonisphaeridium aesculum sp. nov. is described, and Cavatisporites microreticulatus Jachowicz is assigned to the genus Dictyotidium and renamed Dictyotidium jachowiczii sp. nov.
Investigation of mixed carbonate-siliciclastic Lower Devonian deposits have been carried out in the Ivanye Zolote and Ustechko sections in Podolia, Ukraine. Based on palynomorph evidence, the age of the samples studied is late Lochkovian, not older than the NM Oppel miospore Zone, specifically the Si Lineage Zone. The presence of acritarchs and chitinozoans points to dominantly marine depositional conditions. However, a regressive environmental change toward more brackish conditions is indicated by a decrease in the taxonomic diversity of acritarchs in the topmost samples, the simultaneous disappearance of chitinozoans, and an increase in leiosphaerid frequency. Furthermore, evolution of limestone microfacies demonstrates a progressive transition from a shrinking marine basin toward a brackish, storm-affected muddy lagoon, manifested by recurrent profusion of impoverished, mostly opportunistic and euryhaline shelly benthos (nuculanid bivalves, leperditicopids and other ostracods, terebratulid brachiopods), chaetetid demosponges and diverse ichthyofauna. The association of plant (mainly nematophytes and some tracheids) and animal (eurypterid, ?scorpion and possibly other arthropod) remains points to the presence of nearby Early Devonian wetland vegetation, providing food and shelter for various semi-aquatic and other terrestrial arthropods.
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.
Quantitative analysis of assemblage similarity among chitinozoan and acritarch associations recovered from various sedimentary sequences across the Trans European Suture Zone (TESZ; southern Baltic Sea and northern Germany region), permits evaluation of changes in microplankton palaeobiogeography during the Ordovician in the study area. The present data confirm strong palaeobiogeographic differences between the lower Ordovician of the Rügen area, and the coeval domains of the East European Platform (EEP), corroborating the idea that the subsurface of Rügen should be considered palaeogeographically as the eastern extension of Avalonia.
Studies of the spores/pollen of living plants began in the 17th century, but it was not until the 19th century that scientists began to investigate fossil spores/pollen. At about the same time, the first remains of fossil microphytoplankton were described. However, detailed palynological analysis of the Palaeozoic only began in earnest in the 20th century, when a number of scientists commenced serious study on spores and pollen, and also “hystrichospheres” (later named acritarchs) and chitinozoans. For much of the 20th century, the major objectives of Palaeozoic palynology were primarily based on the needs of the coal industry and (since the 1950s) the petroleum industry. Thus, studies predominantly involved the description (taxonomy) and the temporal distribution (biostratigraphy) of the identified microfossils. More recently, however, more diverse aspects of Palaeozoic palynology have been investigated. The General Meeting and Workshops of the “Commission Internationale de Microflores du Paléozoı̈que” (CIMP), held at Lille in September 2002, reflected current palynological research in the Palaeozoic. This paper summarizes the evolution of Palaeozoic palynology and documents the history of the CIMP, before looking ahead to new directions in Palaeozoic palynology that will dominate the 21st century.
Diverse and well preserved acritarch and prasinophycean phycomata assemblages were recovered from the late Silurian to Lower Devonian strata of well A161 in western Libya, and four distinct acritarch biozones are recognized, based on the stratigraphic distribution of 156 species. The palynoflora is independently dated by means of chitinozoans, and allows discussion of the evolution of acritarchs and prasinophyte phycomata across the Ludlow–Přı́dolı́ boundary in relation to probable major climatic change, as well as in the early and middle Přı́dolı́, and the lower Lochkovian. Correlations are proposed with the British Isles, Baltica, and Algerian Sahara. Sedimentation occurred in shallow high-energy conditions throughout, but with periodic rise of sea level. The changes in marine to terrestrial palynomorph ratios through the section document the relationship between marine palynomorph assemblages and sea surface conditions in these marginal marine environments. The major drift of Gondwana towards low latitudes during the Ludlow–Přı́dolı́ transition seems to have been the driving force behind homogenization of assemblages on the two sides of the Rheic ocean, and explains the similarities between phytoplanktonic assemblages of the north Gondwanan margin and the South of Baltica. The data suggest that the Rheic ocean was almost closed by the late Silurian, and had become restricted to a moderately deep sea. In the Lochkovian the microflora are strongly facies-dependent and delineate more restricted provinces such as the Ibarmaghian domain in the sense of Plusquellec (1987) including the Maghreb and Ibero–Armorican areas.
Devonian Acritarch Distribution and Palaeolatitudes
Chitinozoans are a major component of the Lower Ordovician to Upper Devonian palaeoplankton. They are used for testing the respective position of northern Africa and of different European regions during the Early Palaeozoic. The relative remoteness of each area is evaluated with a coefficient of similarity calculated for the chitinozoan assemblages from each couple of regions tested. The results are in agreement with the existence of a large mid-European ocean (Rheic Ocean) which opens as early as the Lower Ordovician and started to close in the Early Devonian. Chitinozoan data, on the other hand, do not support the concept of a south European ocean (Prototethys Ocean) for the Early Devonian. There is an abridged English version. -English summary
Cette étude représente un inventaire des spores et des Acritarches des échantillons du Siegénien moyen du Cotentin dont la microfaune de Chitinozoaires a déjà été l'objet d'une description antérieure. Neuf genres de spores, cinq genres et quinze espèces d'Acritarches sont décrits et figurés.
The microplankton found in the middle to upper section of Los Espejos Formation (Upper Silurian) in the Quebrada de las Aguaditas, SW of Jachal are described. The distribution of the species in the column section and the chronological range are given. The acritarch assemblages are compared with other assemblages of similar age from the same region and from the world. The palynofacies distribution, parallel to the paleolatitudes, proposed for the Silurian is discussed. The microplankton has been assigned to the Upper Ludlovian-Pridolian? The relation between the paleoenvironment of deposition and the distribution and preservation of the palynomorphs is analyzed. -from English summary
Subsurface Paleozoic strata of northern Aquitaine are studied as a section of the 'Geologie Profonde de la France' programme. Three main geological units are distinguished, based on stratigraphical, structural, metamorphic and geophysical evidence. The significance of this N Aquitanian Paleozoic basement is discussed with regard to other components of the W part of the Variscan Belt.-English summary
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.
Preliminary results of recent parallel investigations on late Silurian and Devonian palynomorphs and macrofaunas from Bolivia provide new stratigraphic data and improved correlations. The Bolivian Devonian succession ranges from the Lochkovian to the Famennian with some gaps, or condensed levels in the Pragian and the Emsian. The palynological data allow, for the first time, the standard Devonian time-scale to be applied to the Bolivian succession and confirms some of the ages previously suggested by the macrofauna. There is an abridged English version. -English summary
From oil drillings, it is possible to propose an accurate stratigraphy, firstly for the transition Upper Silurian (Pridolian)/basal Devonian and, secondly, for the Lower Devonian (Lochkovian/Pragian/Emsian). In this paper, new palynological data will be developed. -English summary
There is increasing marine to continental regression from the latest Silurian until the latter half of the early Devonian, when a major transgressive trend is initiated which achieves its maximum in the later middle Devonian and late Devonian. Arid climate evidence (marine evaporites, calcretes) shows a well-developed arid belt. Coal deposits are lacking before the late Devonian. Palaeogeography of the time interval is disputed, largely owing to the use of different classes of data - remanent magnetic, lithological, biogeographical. A pangaeic reconstruction is employed in this study. Rate of phyletic evolution of marine benthos speeds up during the time interval owing to a steadily increasing level of provincialism, that is, cutting up biogeographical entities into smaller entities with consequent smaller populations. There are no major marine adaptive radiations, nor evidence for any marked extinction events during the interval. Such units as the halysitid corals, pentamerinid brachiopods, and graptoloid graptolites are exceptional. Few adaptive radiations, such as those of the ammonoids and terebratuloids occur during the interval. The absence of other major biotic events during the interval is consistent with its position well within ecologic-evolutionary unit VI. from Author
The marine basin which covered almost the whole area of Poland during the Silurian had left thick and unusually diversified sediments with very rich fauna. The marine sedimentation that continued during the lowermost Devonian was limited only to the area of Central Poland, but it represents one of the best palaeontologically evidenced examples of sedimentation sequence between the Silurian and the Devonian. The palaeontological study, summarized below, comprises not only graptolites but also some groups of benthic fauna, including tabulate corals, brachiopods, gastropods, bivalves, tentaculites, trilobites, ostracodes, conodonts, and floral remnants occurring in Wenlockian to Siegenian deposits. -from Author
The first part of the paper gives a general and schematic overview of the palaeogeography of the present-day peri-Atlantic regions from the early Ordovician to the late Devonian. The second part focuses on the outstanding problems concerning the relations that have existed between the different parts of western Europe. In both cases, diverging interpretations are discussed by comparing the results of sedimentological and palaeontological studies with those coming from other branches of Earth Sciences. -English summary
Seven new species of microfossils from the Buildwas Shales (Wenlockian) of England are described. They are grouped with the hystrichospheres and assigned to two new genera, Deunffia and Domasia. Veryhachium monacanthum Deunff is transferred to Deunffia.
Fossil phycomata of prasinophycean green algae are here described for the first time from the Silurian Bainbridge Formation of southeastern Missouri. Two new species, Melikeriopalla fistulosa and Pterospermella scruposa, are described. Four new combinations, Cymatiosphaera retieulosa (Kir'yanov, 1978), Dietyotidium coaretatum (Kir'yanov, 1978), Dictyotidium venulosum (Playford, 1981), and Dictyotidium cataphractum (Martin, 1978) are also made. The genus Melikeriopalla Tappan & Loeblich, 1971 is revised. A late Pridolian age for the upper part of the Bainbridge Formation is indicated by the prasinophycean flora. A comparison of fossil and recent phycomata illustrates the extreme evolutionary conservatism of the phycomaphase of the prasinophycean life-cycle. Fossil evidence suggests that the modern genus Pterosperma Pouchet, 1893 can be divided into two or more genera based on phycoma morphology.
