The Micrhystridium and Veryhachium Complexes (Acritarcha: Acanthomorphitae and Polygonomorphitae): A Taxonomic Reconsideration

Sarjeant, William A. S.; Stancliffe, R. P. W.

doi:10.2307/1485800

Cited by 104 publications

(48 citation statements)

References 48 publications

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“…Although Permian acritarch diversity is considered low, an overview of Permian phytoplankton by Lei et al (2013a) showed a richness of about 20-30 genera during most of the Permian, with acritarchs belonging to the genera Micrhystridium and Veryhachium being the most common (Lei et al, 2013a, b;Sarjeant and Stancliffe, 1994). Since cysts are generally small in size it is difficult to study them under the light microscope and identification at species level can be difficult (Sarjeant, 1970).…”

Section: Aquatic Palynomorphsmentioning

confidence: 99%

“…Since cysts are generally small in size it is difficult to study them under the light microscope and identification at species level can be difficult (Sarjeant, 1970). Several revisions and simplifications have been proposed for the genera (Lei et al, 2013b;Sarjeant and Stancliffe, 1994). We follow the simple classification scheme proposed by Lei et al (2013b), in which different species of acritarchs are grouped together, based on ge- ometrical shape of the acritarchs.…”

Section: Aquatic Palynomorphsmentioning

confidence: 99%

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Salinity changes and anoxia resulting from enhanced run-off during the late Permian global warming and mass extinction event

2018

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Abstract. The late Permian biotic crisis had a major impact on marine and terrestrial environments. Rising CO 2 levels following Siberian Trap volcanic activity were likely responsible for expanding marine anoxia and elevated water temperatures. This study focuses on one of the stratigraphically most expanded Permian-Triassic records known, from Jameson Land, East Greenland. High-resolution sampling allows for a detailed reconstruction of the changing environmental conditions during the extinction event and the development of anoxic water conditions. Since very little is known about how salinity was affected during the extinction event, we especially focus on the aquatic palynomorphs and infer changes in salinity from changes in the assemblage and morphology. The start of the extinction event, here defined by a peak in spore : pollen, indicating disturbance and vegetation destruction in the terrestrial environment, postdates a negative excursion in the total organic carbon, but predates the development of anoxia in the basin. Based on the newest estimations for sedimentation rates, the marine and terrestrial ecosystem collapse took between 1.6 and 8 kyr, a much shorter interval than previously estimated. The palynofacies and palynomorph records show that the environmental changes can be explained by enhanced run-off and increased primary productivity and water column stratification. A lowering in salinity is supported by changes in the acritarch morphology. The length of the processes of the acritarchs becomes shorter during the extinction event and we propose that these changes are evidence for a reduction in salinity in the shallow marine setting of the study site. This inference is supported by changes in acritarch distribution, which suggest a change in palaeoenvironment from open marine conditions before the start of the extinction event to more nearshore conditions during and after the crisis. In a period of sea-level rise, such a reduction in salinity can only be explained by increased run-off. High amounts of both terrestrial and marine organic fragments in the first anoxic layers suggest that high run-off, increased nutrient availability, possibly in combination with soil erosion, are responsible for the development of anoxia in the basin. Enhanced run-off could result from changes in the hydrological cycle during the late Permian extinction event, which is a likely consequence of global warming. In addition, vegetation destruction and soil erosion may also have resulted in enhanced run-off. Salinity stratification could potentially explain the development of anoxia in other shallow marine sites. The input of freshwater and related changes in coastal salinity could also have implications for the interpretation of oxygen isotope records and seawater temperature reconstructions at some sites.

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Section: Aquatic Palynomorphsmentioning

confidence: 99%

Section: Aquatic Palynomorphsmentioning

confidence: 99%

Salinity changes and anoxia resulting from enhanced run-off during the late Permian global warming and mass extinction event

2018

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“…Já para SARJEANT & STANCLIFFE (1994), os principais critérios utilizados são o número de espinhos ou processos, sua natureza, se são sólidos ou ocos, e, nesse último caso, se as suas cavidades estão ou não ligadas ao interior da vesícula.…”

Section: Generalidades E Aspectos Morfológicosunclassified

“…TURNER 1984, com ausência completa daquelas mais comuns nas associações pré-carboníferas. Contudo, a variedade de formas incluídas nesses dois gêne-ros é extremamente grande, de modo a induzir a aceitação do conceito de "complexos" para neles serem abarcados diversos morfotipos (SARJEANT & STANCLIFFE 1994, FÉLIX 2012.…”

Section: Classificação Sistemáticaunclassified

“…Dessa forma, constata-se que as classificações do grupo têm caráter efêmero e estão sujeitas a mudanças e, por outro lado, há dificuldades no estabelecimento de padrões diagnósticos que evidenciem o significado biológico de cada táxon. De maneira geral, os 13 subgrupos instituídos por para o Grupo Acritarcha abarcam a grande parcela de variação morfoló-gica destes cistos, representados por dezenas de gêneros e centenas de espécies (SARJEANT & STANCLIFFE 1994), cuja maior diversidade foi registrada entre o Cambriano e o Devoniano.…”

Section: Introductionunclassified

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Acritarcos (grupo acritarcha evitt 1963): conceitos gerais, aplicações e importância na análise estratigráfica do intervalo pennsilvaniano e permiano da Bacia do Paraná

Félix

Souza

2012

Rev. Inst. Geol.

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RESUMOEmbora 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 interpretações 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.Palavras-chave: palinologia, Paleozóico Superior, fitoplâncton, Bacia do Paraná, Gondwana. ABSTRACTDespite their uncertain biological affinity, the palynomorphs known as acritarchs are commonly used for biostratigraphic and paleoenvironmental interpretation, particularly of Cambrian to Devonian deposits. This paper presents an updated review of the morphology, classification and stratigraphic distribution of organicwalled microfossils included in this group, as well as their application in Geosciences. Brazilian records from Paleozoic intracratonic basins, especially from Pennsylvanian and Permian deposits of the Paraná Basin, are discussed. The main results of the analysis of this interval in the basin are (i) many of the taxa identified as acritarchs are related to species of prasinophyceae and zygnemataceae algae, and (ii) the record of intervals with abundant association of specimens assigned to the genera Micrhystridium and Veryhachium, which corroborates previous interpretations of a Permian stratigraphic marker of marine nature at the top of the Palermo Formation and base of the Irati Formation. The taxonomic review supports the idea of a worldwide decrease in diversity of these taxa during the Pennsylvanian and Permian interval (phytoplankton blackout), especially considering richness at the generic level, which was much lower than that observed in pre-Carboniferous deposits in Brazil and in other parts of the world.

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An Ordovician age for the Muggort's Bay Lower Palaeozoic inlier, County Waterford, Ireland—the southernmost exposure of the Irish Caledonides

Bruck

Vanguestaine

2005

Geol. J.

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The most southerly exposed Lower Palaeozoic strata in Ireland occur on the southwest coast of County Waterford along a 2.5 km long coastal section at Muggort's Bay where they are surrounded by Devonian rocks. Five formations can be distinguished which, in ascending order, are: the Ballycurreen, Carrickbrean, Rathnameenagh, Moanbrack and Killinoorin formations. The total thickness of the succession is over 1800 m. No macrofossils are present, but the lithologies are largely fine-grained turbidites and subordinate volcanic rocks which closely resemble the Ribband Group seen elsewhere in southeast Ireland and have previously therefore been classified with it. Palynological analysis was undertaken on 25 samples collected from Muggort's Bay, of which eight were productive. Diagnostic microfossils, comprising acritarchs, chitinozoans and scolecodonts, indicate an Early to Middle Ordovician age for both the Rathnameenagh and the Moanbrack formations. These ages confirm that the strata are part of the Ribband Group which elsewhere has been biostratigraphically dated as ranging from Mid-Cambrian to Mid-Ordovician. Reworked mid-Middle Cambrian acritarchs occur in the Moanbrack Formation and reworked late Middle to early Late Cambrian acritarchs in the Rathnameenagh Formation. Despite generally poor preservation of the organic matter, some 20 acritarch species have been distinguished. Among these, three species belong to the herein revised genus Retisphaeridium for which an emended diagnosis is proposed together with two new combinations, Retisphaeridium capsulatum (Jankauskas, 1976) Vanguestaine nov. comb. and Retisphaeridium pusillum (Moczydlowska, 1998) Vanguestaine nov. comb.

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The Micrhystridium and Veryhachium Complexes (Acritarcha: Acanthomorphitae and Polygonomorphitae): A Taxonomic Reconsideration

Cited by 104 publications

References 48 publications

Salinity changes and anoxia resulting from enhanced run-off during the late Permian global warming and mass extinction event

Salinity changes and anoxia resulting from enhanced run-off during the late Permian global warming and mass extinction event

Acritarcos (grupo acritarcha evitt 1963): conceitos gerais, aplicações e importância na análise estratigráfica do intervalo pennsilvaniano e permiano da Bacia do Paraná

An Ordovician age for the Muggort's Bay Lower Palaeozoic inlier, County Waterford, Ireland—the southernmost exposure of the Irish Caledonides

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