Reed Wicander

Gloeocapsomorpha prisca Zalessky, 1917: A new study: Part I: Taxonomy, Geochemistry, and paleoecology

Abstract Gloeocapsomorpha prisca Zalessky , 1917 is emended and redescribed and a neotype is designated from Middle Ordovician kukersites of the Baltic Shale Basin, Estonia. Gloeocapsomorpha was a colonial, probably cyanobacterial organism and its fossil remains are represented by at least three morphotypes. These morphotypes result from growth and life cycle stages which are overprinted by post-mortem changes. Gas chromatography of hydrocarbons from pyrolysed kukersite yields a diagnostic low molecular weight, odd-dominated suite of n-alkanes, maximizing at C19. The emended diagnosis of Gloeocapsomorpha incorporates these biogeochemical criteria. Morphological and biogeochemical characteristics of Gloeocapsomorpha show strong similarities with certain species of the modern Entophysalidaceae cyanobacteria. Entophysalis major, a mat-forming, and sometimes stromatolite-forming, cyanobacterium, is suggested as a modern analogue for G. prisca.

Acritarchs and Spores from the Upper Devonian Lime Creek Formation, Iowa, U.S.A.

A well-preserved acritarch and spore assemblage is described from an 18.3 m section of the Upper Devonian (upper Frasnian, Palmatolepis gigas conodont zone) Juniper Hill and Cerro Gordo members of the Lime Creek Formation, Floyd County, Iowa, USA. The palynomorph assemblage comprises 23 genera and 43 species of acritarchs, and 12 genera and 12 species of spores. We propose two new acritarch genera, Centrasphaeridium and Pratulasphaera; nine new acritarch species; and two new spore species. In addition, one new combination, Dictyotidium craticulum (=Cymatiosphaera craticula Wicander and Loeblich 1977) is proposed. The palynomorph assemblage indicates a nearshore, normal marine environment, consistent with the interpretation provided by the associated shelly fauna. Comparison with other Frasnian palynomorph assemblages indicates similarity mostly in terms of long-ranging and cosmopolitan acritarch species while of the 12 miospore species present, only Geminospora lemurata and Laiphospora membrana have been previously reported.-Authors

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.

The use of microphytoplankton and chitinozoans for interpreting transgressive/regressive cycles in the Rapid Member of the Cedar Valley Formation (Middle Devonian), Iowa

Abstract With only minor exceptions, the paleoenvironmental interpretations using microphytoplankton diversity and microphytoplankton/spore ratios are in agreement with previous ecological and depositional interpretation for the Rapid Member (Middle Devonian, upper Givetian) exposed at the River Products Conklin Quarry, Johnston County, Iowa. Analyses of acritarch morphotype variability, fluctuations in acritarch species diversity and the ratio of microphytoplankton (acritarchs and prasinophytes) to spores were compared to known paleoenvironmental interpretations based on sedimentology and megafossil content. The greatest microphytoplankton diversity occurs in the lower 14 m of the Rapid Member, suggesting deposition in a near- to offshore marine environment; whereas, the increase in relative abundance of spores in the upper 6 m suggests a closer proximity to the paleoshoreline. Chitinozoan diversity trends (greater diversity in ‘deeper-water’ depositional settings) indicates the same shallowing trend. The combined palynomorph (microphytoplankton, chitinozoan and spore) data appear to provide a fine resolution for paleoecological interpretation of the Rapid Member, particularly in relation to paleoshoreline fluctuations. The acritarch assemblage consists of 40 species distributed among 28 genera. The new genus Luscinasphaera Wicander et Wood, gen. nov. and the new species Ammonidium iowaensis Wicander et Wood, sp. nov., Cymatiosphaera cladora Wicander et Wood, sp. nov.,? Gorgonisphaeridium adjunctum Wicander et Wood, sp. nov., G. parvispinosum Wicander et Wood, sp. nov., Luscinasphaera indistincta Wicander et Wood, sp. nov., Multiplicisphaeridium segregatum Wicander et Wood, sp. nov., Solisphaeridium laevigatum Wicander et Wood, sp. nov. and Villosacapsula compta Wicander et Wood, sp. nov. are established. The chitinozoan assemblage consists of ten species, including Ancyrochitina fruticosa Wicander et Wood, sp. nov. .

GLOBAL PATTERNS OF ORGANIC-WALLED PHYTOPLANKTON BIODIVERSITY DURING THE LATE SILURIAN TO EARLIEST DEVONIAN

Abstract 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 Přídolí) 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 Přídolí 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.

Gloeocapsomorpha prisca Zalessky, 1917: A new study part II: Origin of Kukersite, a new interpretation

Abstract Kukersite is the name given to exceptionally carbon-rich Middle Ordovician oil shales found in the Baltic Shale Basin of Estonia. The organic component of these sediments consists mostly of accumulations of the microfossil Gloeocapsomorpha prisca which, we propose, was an intertidal, marine, mat- forming benthonic cyanobacterium similar to, but not identical with, the extant cyanobacterium Entophysalis major. Kukersite beds are formed in situ or occur as allochthonous deposits resulting from transport of G. prisca from large intertidal areas by water or wind currents into anoxic offshore environments. It is proposed that the cyclical nature of sediments containing kukersite and marine carbonate facies in the Baltic Shale Basin results from changes in relative sea level, probably caused by both local tectonism and eustatic sea level changes.

Chapter 23 Biogeography of early to mid Palaeozoic (Cambrian–Devonian) marine phytoplankton

Abstract 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.

Lower devonian (Gedinnian) acritarchs from the haragan formation, Oklahoma, U.S.A.

Abstract A diverse and prolific acritarch assemblage consisting of 54 species was recovered from eight composite samples of the Lower Devonian (Gedinnian) Haragan Formation of southern Oklahoma, U.S.A. Two new species, Lophosphaeridium bulbosum n.sp. and Uncinisphaera tribulosa n.sp. are described and illustrated and two new combinations, Diexallophasis tappana (= Tylotopalla tappanae Kirjanov 1978) n.comb. and Multiplicisphaeridium raspa (= Baltisphaeridium raspa Cramer 1964b) n.comb. are proposed. Several diagnostic Lower Devonian acritarchs are present, including Baltisphaeridium cravattense, Demorhethium lappaceum, Evittia cymosa, Fimbriaglomerella divisa, Oppilatala vulgaris, Pterospermella circumstriata, P. verrucaboia, Riculasphaera fissa , and Thysanoprobolus polykion . Many of these forms have also been reported from Spain, France, and Algeria. Other taxa present in European and/or African assemblages, such as Cymbosphaeridium and Quadraditum , do not occur in the Haragan samples, perhaps indicating an environmental parameter was present that did not allow migration between these two regions.

Acritarchs: proterozoic and paleozoic enigmatic organic-walled microfossils

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.

An Early Ordovician organic-walled microphytoplankton assemblage from the Nambeet Formation, Canning Basin, Australia: biostratigraphic and paleogeographic significance

A well-preserved and moderately diverse organic-walled microphytoplankton assemblage was recovered from the subsurface Lower Ordovician Nambeet Formation, Canning Basin, Western Australia. The microphytoplankton assemblage consists of prasinophyte phycomata (Leiosphaeridia spp.), acritarchs, cyanobacteria (Eomerismopedia maureeniae), degraded algae, chitinozoans and graptolite fragments. The acritarch assemblage comprises 13 genera, one of which is new (Aciculasphaera), 13 named species, three of which are new (Aciculasphaera interrupta, Gorgonisphaeridium martiniae and Loeblichia nambeetense), five species left in open nomenclature (sp.), and one cf. designation. The acritarch assemblage indicates an Early Ordovician (late Tremodocian through Floian) age and displays some similarities with comparable-age assemblages reported from North and South China, Australia and Laurentia. The paleogeographic distribution of the acritarch assemblage indicates that this assemblage represents a low- to mid-paleolatitude occurrence. Sedimentologic and palynologic evidence signifies deposition in a normal marine offshore environment.