Search

New acritarch data from the Kistedalen Formation based on two sections with continuous exposure enable us to establish the most detailed Miaolingian acritarch biozonation in Baltica to date. Six interval zones previously established in Gondwana, the Eliasum llaniscum, Cristallinium cambriense, Adara alea, Timofeevia lancarae, Cristallinium dubium and Vulcanisphaera turbata zones, are identified, and their correlations within the Acado‐Baltic Province examined. The diagnoses of Retisphaeridium, Cristallinium, Retisphaeridium dichamerum, Retisphaeridium lechistanium, Cristallinium dubium and Cristallinium cambriense are emended and the new species Retisphaeridium rugulatum sp. nov. and Retisphaeridium minimum sp. nov. are described. The diagnosis of Retisphaeridium ovillense (Cramer & Díez) Vanguestaine is emended and the species assigned to Dictyotidium ovillense comb. nov. The main evolutionary changes of the placoid acritarchs during the Miaolingian are analysed. Comparison with previous acritarch data from the Kistedalen Formation suggests that different extraction methodologies may result in significant bias in the recovered fossil record. [ABSTRACT FROM AUTHOR]

Acritarchs, microphytoplankton of algal protists, from the Shiala and Yong Limestone formations of the Gunji village along Kali river (upstream) of Kumaon Tethyan Himalaya, Pithoragarh district, Uttrakhand, India have been examined for the first time. It aims to test the basin-wide existence and testing the reliability of already locally established biozones from the Garhwal Tethys Himalaya, Chamoli district, Uttrakhand. The study reveals moderate to poorly preserved, matured assemblages and diversified forms of acritarchs from both formations. The assemblage includes sphaeromorphs, acanthomorphs, netromorphs, polygonomorphs, diacromorphs, herkomorphs, etc. Two palynoassemblages have been recognized each from the Shiala and Yong Limestone formations. Palynoassemblage (I) from the Shiala Formation is confirmed by one productive sample which reveals a mix of Late Ordovician and Silurian forms. The acritarchs assemblage assigned to 16 genera with at least 13 species. The acritarchs from the Yong Limestone Formation are more plentiful and diverse confirming the Palynoassemblage (II) that contains biostratigraphically significant forms of typical Silurian (Ludlow) age. This Palynoassemblage is assigned to 23 genera with 16 species. The paper also describes the possible reasons for floral difference from the same formation and basin sampled at two different localities of the Tethys Himalaya, possibly due to palaeoclimatic constraints. However, detailed work on this aspect is required. The palynoassemblages from both the formations describe morphologically non-distinct, ubiquitous, wide palaeogeographic spread and uncertain stratigraphic taxa too along with biostratigraphic significant forms. [ABSTRACT FROM AUTHOR]

The Pin Formation of the northern Indian Himalaya may contain a record of the late Katian (Late Ordovician) warming event (the Boda Event). Palynological samples collected from two members of this formation are investigated in order to evaluate the biostratigraphical potential of the different microfossil groups. Acritarchs and chitinozoans are the most abundant microfossils, but fragments of scolecodonts and melanosclerites are also present. Several of the acritarchs from the Pin Formation are long-ranging through the lower Palaeozoic, but other taxa can be compared to Upper Ordovician (Katian) assemblages described from other parts of the world. The chitinozoan assemblages, consisting of 13 species (including those in open nomenclature) belonging to seven genera, are mainly recorded from two layers. The chitinozoan assemblage collected from the sample at 87.3 m in the uppermost part of the Farka Muth Member, and that collected at 184.89 m from the Takche Member, indicate a late Katian age. This age interpretation is in accordance with conodont data from the Takche Member, a positive carbon isotopic peak from the top of a shale unit in the Takche Member, and the initial part of the rapid negative shift of the Paroveja isotopic excursion related to the Boda Event of late Katian age. Further detailed studies with a higher number of samples are needed, that describe better preserved and more diversified palynomorph assemblages, which would help to more precisely refine the Upper Ordovician biostratigraphy in this area. [ABSTRACT FROM AUTHOR]

Twenty-nine core and seven cuttings samples were collected from two boreholes penetrating the Middle Ordovician Hawaz Formation in the Murzuq Basin, south-west Libya. The samples were palynologically analysed in order to determine age and depositional environment. The palynological assemblages contain abundant sphaeromorphs, rare but diverse acritarchs, rare chitinozoans, and relatively abundant cryptospores. A total of 26 acritarch species, five chitinozoan species and 17 cryptospore species have been identified. The acritarch and chitinozoan assemblages provide biostratigraphical age dating and indicate that the Hawaz Formation is Mid Ordovician and most likely mid Darriwilian (Llanvirn) in age. The cryptospore assemblage is typical of those from the Mid Ordovician–earliest Silurian and does not permit further age refinement. Based on palynofacies analysis, the depositional environment of the Hawaz Formation is interpreted as shallowing upward from nearshore marine inner shelf to marginal marine. The cryptospores provide rare evidence for Middle Ordovician terrestrial vegetation at this very early stage in its development. [ABSTRACT FROM PUBLISHER]

Borehole 2506 drilled in the northern area of the Arkhangelsk Oblast penetrated through the Paleozoic sedimentary block isolated in the Vendian thick sequence. A diverse acritarch assemblage has been established within the depth interval of 119.9–217.5 m. The assemblage comprises more than 70 taxa, including species characteristic of the boundary interval between the Volkhov and Kunda horizons of the East European Platform (the graptolite Didymograptus hirundo Zone). Stratigraphic position of host deposits was established within the Darriwilian Stage of the Middle Ordovician. The described assemblage of microphytofossils is similar to coeval assemblages from NW Russia, Baltic region, and Scandinavia, being typical of the Baltic phytoplankton province of temperate latitudes. A great number of species in common suggests that the assemblage under consideration is correlative with coeval assemblages of southern China thus offering a possibility of remote correlation. [ABSTRACT FROM AUTHOR]

As the primary producers, acritarchs represent the base of the food chain in the Paleozoic marine ecosystem which links with the evolution of acritarchs. Based on high precision quantitative research, much information about Paleozoic marine ecosystem is provided. A quantitative analysis of Early-Middle Ordovician acritarch diversity changes in the Meitan Formation, Honghuayuan section, Tongzi, Guizhou is made and the the acritarch diversity curves are compared with sea level curves. We found that acritarch diversity changes were related to sea level changes during the Early-Middle Ordovician. Whereas sea level rose, and acritarch diversity also increased. An inshore-offshore model of acritarchs best explains the relative abundance changes of some acritarch taxa in relation to sea level changes. [ABSTRACT FROM AUTHOR]

Demonstrates depth zonation of Arenigian acritarchs in South China. Details on scientists which have been puzzle by the fact that characteristics offshore acritarchs occur with nearshore ones; Information acritarchs.