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| Floian | |
|---|---|
| Name | Floian |
| Partof | Ordovician |
| Subperiod | Early Ordovician |
| Time start | 477.7 |
| Time start uncertainty | 1.4 |
| Time end | 470.0 |
| Time end uncertainty | 1.4 |
| Preceded by | Tremadocian |
| Followed by | Dapingian |
| Type section | Flo, Sweden |
Floian
The Floian is the second stage of the Ordovician Epoch broadly spanning from about 477.7 to 470.0 million years ago, succeeding the Tremadocian and preceding the Dapingian. Internationally ratified by the International Commission on Stratigraphy and defined by a global stratotype section and point, the Floian is integral to correlating Early Paleozoic successions across palaeocontinents such as Baltica, Laurentia, Siberia, and Gondwana.
The Floian stage was formalized by the International Commission on Stratigraphy with a boundary defined at the first appearance datum of a specific conodont species, tying the stage to the GSSP near Fågelsången? and stratigraphic sections in Sweden. Chronologically it is placed within the lower Ordovician and temporally overlaps regional stages such as the Arenig of traditional British stratigraphy and the Canadian early Ordovician series. The stage is used in global time scales published by bodies such as the International Union of Geological Sciences and in stratigraphic charts produced by the Geological Society of America.
Floian strata are correlated using lithostratigraphic and biostratigraphic markers that tie formations across Baltica, Laurentia, Siberia, and marginal shelves of Gondwana. Correlation relies on shared occurrences of conodonts and graptolites known from sections studied by researchers associated with institutions like the Swedish Museum of Natural History, University of Oslo, University of Copenhagen, and the Smithsonian Institution. Key international correlations reference stages such as the Arenig, the Tremadocian, and the Dapingian as defined in regional frameworks of the United Kingdom, China, and Argentina.
The stage name derives from the type locality near Flo on the western Swedish Baltoscandian margin. The naming followed stratigraphic work by paleontologists and stratigraphers affiliated with institutions including Uppsala University, the Swedish Museum of Natural History, and collaborating teams from University of Oslo and Lund University. The GSSP and type sections were proposed after comparisons with classic sections in Spitsbergen, Greenland, and Scotland examined by specialists who have published in journals tied to the Geological Society of London and the Journal of the Geological Society.
Biostratigraphy of the Floian relies heavily on conodont taxa (notably species within genera used to define the lower boundary), alongside graptolite assemblages and trilobite ranges that enable correlation with faunas described from Svalbard, Anticosti Island, Newfoundland and Labrador, Wales, and Yunnan. Key index fossils used in Floian sections include conodont elements tied to biostratigraphic zonations developed by researchers associated with the Palaeontological Association and regional surveys led by the British Geological Survey and the Geological Survey of Canada.
Absolute age constraints for the Floian combine radiometric dates from volcanic ash beds (zircon U–Pb) and chemostratigraphic ties such as carbon isotope excursions correlated with global records. Zircon U–Pb dates from ash layers in sections matched to Floian strata have been produced by laboratories at institutions like the Geological Survey of Norway, University of Aberdeen, and the U.S. Geological Survey. These radiometric anchors underpin the numeric age bracket used by the International Commission on Stratigraphy in the global time scale.
Floian paleoenvironments reflect shallow marine shelves, carbonate platforms, and slope settings across palaeocontinents including Baltica, Laurentia, and passive margins of Gondwana with faunal provinces recorded in regions such as Scandinavia, Greenland, China, and South America. Fossil assemblages and sedimentary facies indicate diverse benthic communities with trilobites, brachiopods, bryozoans, and echinoderms studied by paleontologists from Natural History Museum, London, Smithsonian Institution, and the Institute of Paleontology, Chinese Academy of Sciences. Paleoceanographic reconstructions utilize data from isotope studies published with contributions from the University of Cambridge, University of California, Berkeley, and Stockholm University.
Floian-bearing formations and regional equivalents include well-studied units such as those on Öland, Dalarna, and the Västergötland succession in Sweden; the Islay and Girvan successions of Scotland; the Anticosti Island sequences in Canada; the Yangtze Platform exposures in China; and sections in Svalbard and Greenland. Regional geological surveys and mapping by agencies like the Geological Survey of Sweden, the British Geological Survey, and the Geological Survey of Canada provide lithostratigraphic frameworks that allow integration of Floian records into continental-scale syntheses by researchers at institutions including Uppsala University, University of Oslo, and the University of Alberta.