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Bashkirian Stage
Time:2012-09-27 viewd:12524 times

The Bashkirian is the lowest  stage of the Pennylvanian, and is preceded by the Serpukhovian and is followed by the Moscovian. The Bashkirian correlates with the upper part of the Namurian and lower part of the Westphalian stages in regional western European stratigraphy. It also overlaps with the North American Morrowan and lower part of Atokan stages and the Chinese Luosuan, Huashibanian and lower Dalaan stages.

The base of the Bashkirian is at the first appearance of conodont species Declinognathodus noduliferus. The top of the stage is at the first appearance of the conodonts Diplognathodus ellesmerensis, Declinognathodus donetzianus or Idiognathoides postsulcatus, or at the first appearance of fusulinid Aljutovella aljutovica.

The GSSP for the Bashkirian is located at 82.9m above the top of the Battleship Formation in the lower Bird Spring Formation at the Arrow Canyon section near Las Vegas, Nevada. The GSSP coincides exactly with the historically stable Mississippian-Pennsylvanian boundary/Mid-Carboniferous Boundary.

The Birdspring Formation consists of limestone with subordinate mudstone, sandstone and dolostone, and is dominated by pelmatozoans, brachiopods and bryozoans. The succession comprises numerous high-order transgressive-regressive sequences that were caused by glacio-eustatic fluctuations driven by ongoing glaciations in Gondwana. 

Lithology and selected conodont, foraminifera and brachiopod ranges for the Mid-carboniferous boundary intervals at Arrow Canyon section.

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