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Faunal composition and dynamics in unconsolidated sediments: a case study from the Middle Ordovician of the East Baltic
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology, Palaeontology group.
Institute of Geology, University of Tartu Estonia.
Institute of Geology, University of Tartu Estonia.
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2003 (English)In: Geological Magazine, ISSN 0016-7568, Vol. 140, no 1, 31-44 p.Article in journal (Refereed) Published
Abstract [en]

The Volkhov Regional Stage (Middle Ordovician) in the East Baltic preserves diverse fossil assemblages dominated by epibenthic suspension feeders. Brachiopods, ostracodes, conodonts, echinoderms and bryozoans are the main components of palaeocommunities obtained from clay horizons in the Putilovo section (St Petersburg region, Russia), whereas trilobites, machaeridians, hyolithids, graptolites, benthic foraminifers and gastropods are rare or occur sporadically. Brachiopod bioclasts volumetrically dominate the debris of the studied sediments. Quantitative faunal data are used to assess species diversity patterns, as expressed by the species richness (total number of species in the standardized sample size) and by the evenness or equitability of the community. The numerical abundance of particular taxa in each standardized sample was used to evaluate the density of the fauna. The communities in the Volkhov Stage in Putilovo Quarry reveal a remarkable stability throughout the studied interval and are characterized by high density (1000–6000 specimens per 100 g), relatively moderate species richness (10–15 species) and a moderately variable equitability (0.3–0.7) for the dominant fossil groups (conodonts, ostracodes and brachiopods). Ostracodes significantly increase in numbers within the upper part of the section. This confirms a shallowing of the basin during the late Volkhov interval. Small-scale variability of the diversity estimates does not correlate with the small-scale sea-level changes reconstructed for this part of the basin. It may be connected with error in diversity measurement, or the result of undetected environmental parameters. Variability estimates for different faunal groups are poorly correlated because particular groups have different environmental tolerances.

Place, publisher, year, edition, pages
2003. Vol. 140, no 1, 31-44 p.
Keyword [en]
diversity, Conodonta, Brachiopoda, Ostracoda, Ordovician, Baltoscandia
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-91910DOI: 10.1017/S001675680200701XOAI: oai:DiVA.org:uu-91910DiVA: diva2:164790
Available from: 2004-05-14 Created: 2004-05-14 Last updated: 2013-04-29Bibliographically approved
In thesis
1. Ordovician (Billingen and Volkhov stages) Brachiopod Faunas of the East Baltic
Open this publication in new window or tab >>Ordovician (Billingen and Volkhov stages) Brachiopod Faunas of the East Baltic
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lower-Middle Ordovician (Arenig) successions in the East Baltic have been investigated for more than one hundred and fifty years. Nevertheless detailed sampling still yields new species and better knowledge of the environment in which these organisms lived. The successions are well suited for bed by bed sampling because of the lack of tectonic disturbance and because the sequences are well documented.

This study analyses collections of Billingen-Volkhov age mainly from the St. Petersburg region, but also from Estonia. A great deal of the material was obtained from the marly to clayey, soft sediment that intercalates the compact packstones and wackestones in the succession. Twenty-nine of these clay horizons were used for diversity estimates on the fauna through the succession. The most thoroughly investigated groups for this investigation were rhynchonelliformean brachiopods, conodonts and ostracodes. The results indicate that variances in diversity and abundance levels for these groups were not correlated, either to each other or to the small-scale sea level fluctuations that have been suggested for the region. However, diversity dynamics of brachiopods and ostracodes confirm the large-scale upward shallowing of the basin into the Upper Volkhov. Comparison with fossils from the limestones did not reveal any differences in faunal composition between the two preservation modes.

The detailed sampling, coupled with sampling of the recently described mud mounds that occur in several outcrops, yielded large numbers of specimens. This enabled revision of earlier poorly known rhynchonelliformean genera such as Ujukella Andreev, as well as better known genera such as Porambonites Pander. In total the examined faunas include 31 genera assigned to 53 species of rhynchonelliformean brachiopods. Of these Leoniorthis and Eoporambonites are defined as new genera, and the following new species are described: Neumania paucicostata, Ranorthis rotunda, Orthidium gambolovensis, Orthidium lavensis, Skenidioides minutus, Tetralobula peregrina, Idiostrophia prima and Idiostrophia tenuicostata.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 30 p.
Keyword
Earth sciences, Early Middle Ordovician, Billingen Regional Stage, Volkhov Regional Stage, Diversity, Brachiopoda, Conodonta, Ostracoda, Estonia, Russia, Geovetenskap
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-4303 (URN)91-506-1756-7 (ISBN)
Public defence
2004-06-04, Lecture Theatre, Palaeontology building, Norbyvägen 22, SE-752 36 Uppsala, 13:00
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Available from: 2004-05-14 Created: 2004-05-14 Last updated: 2011-02-17Bibliographically approved

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Holmer, Lars E.

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