IANIGLA   20881
INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
First Appearance Data of selected acritarch taxa and correlation of Lower and Middle Ordovician Stages
Autor/es:
LI, J.; WANG, WEN HUI; SERVAIS, T; RUBINSTEIN, CLAUDIA V.; MOLYNEUX, S.G.; NOWAK, H.; YAN, KUI
Lugar:
Nottingham
Reunión:
Congreso; The 50tf annual meeting of AASP - The Palynological Society; 2017
Institución organizadora:
AASP - The Palynological Society
Resumen:
The bases of the global stages of the Ordovician System are all defined on the first occurrence of either a conodont or a graptolite species. Complementing the graptolite and conodont biozonations, chitinozoan biozonation schemes have also been used in global correlation although no chitinozoan marker species is used to define any chronostratigraphical division. Acritarchs have long been used for biostratigraphical dating and correlation of Ordovician successions, often in sediments devoid of other fossils, but biozonation schemes to complement those of the graptolites, conodonts and chitinozoans have not been developed. Nevertheless, acritarchs have the potential to correlate global stages and stage slice boundaries in the Lower and Middle Ordovician. First Appearance Data (FADs) of selected acritarch morphotypes have been assessed to determine their potential contribution to correlation of Lower and Middle Ordovician stages and substage divisions along the Gondwanan margin and between Gondwana and other palaeocontinents. The FADs of nineteen genera, species and species groups are recorded throughout their biogeographical ranges. The taxa investigated fall into three groups. Some have FADs at about the same level throughout their biogeographical ranges, and are useful for long-distance and intercontinental correlation. Among these are: Coryphidium, Dactylofusa velifera, Peteinosphaeridium and Rhopaliophora in the upper Tremadocian Stage; Arbusculidium filamentosum, Aureotestaclathrata simplex and Coryphidium bohemicum in the lower?middle Floian Stage; Dicrodiacrodium in the upper Floian Stage; Frankea in the Dapingian?lower Darriwilian stages; and Orthosphaeridium spp., with FADs in the Dapingian?lower Darriwilian stages of Perigondwanan regions and at about the same level in Baltica. Other taxa, however, have diachronous FADs, and this needs to be taken into account when using them for correlation. A second group of genera and species, comprising Striatotheca, the Veryhachium lairdii group and the V. trispinosum group, have a recurring pattern of FADs in the Tremadocian Stage on Avalonia and in South Gondwana and West Gondwana, but in the Floian Stage of South China and East Gondwana. The third group, consisting of Arkonia, Ampullula, Barakella, Dasydorus, Liliosphaeridium and Sacculidium, have FADs that are markedly diachronous throughout their biogeographical ranges, although the global FADs of Arkonia, Ampullula, Liliosphaeridium and Sacculidium are apparently in South China and/or East Gondwana. It is possible that diachronous FADs are only apparent and an artefact of sampling. Nevertheless, an alternative interpretation, suggested by recurring patterns, is that some as yet undetermined factor controlled a slower biogeographical spread over time, resulting in diachroneity.