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Early and Middle Frasnian brachiopod faunas and turnover on the South China shelf

100%

Ma X. P., Becker R. T., Li H., Sun Y.-Y.

Acta Palaeontologica Polonica

2006

tom 51

nr 4

789-812

The first appearance of the brachiopod Cyrtospirifer and related forms in the Late Devonian of South China significantly postdates the beginning of the Frasnian and the entry of the group in other parts of the world. Scattered data from different sections suggest that its first entry, associated with the emergence of other plicate spiriferids, such as theodossid and conispiriferid brachiopods, was late in the Middle Frasnian. At the same time, many rhynchonellids disappeared or became extinct locally in South China. This brachiopod faunal overturn near the Palmatolepis punctata–Early Pa. hassi zonal boundary is the most significant event in the Early–Middle Frasnian of South China, characterized by about a 35% loss of existing species and the flourishing of the plicate spiriferids, which was coeval with the end of a major biogeochemical perturbation recently recognized in the Pa. punctata Zone. By contrast, atrypid brachiopods do not seem to show any significant diversity change. The brachiopod faunal change was probably related to a (local?) transgressive event in South China, which also brought new pelagic faunas northwards into some intra−shelf deeper water areas, such as the Shetianqiao area in central Hunan Province. Fifteen brachiopod species are described and illustrated, which include some taxa that are first recorded or recognized in South China, e.g., the spiriferid Pyramidaspirifer, which is now known from both North America and South China. One new species, Desquamatia qiziqiaoensis, is erected.

Ostracods and facies of the Early and Middle Frasnian at Devils Gate in Nevada: Relationship to the Alamo Event

80%

Casier J. G., Berra I., Olempska E., Sandberg C., Preat A.

Acta Palaeontologica Polonica

2006

tom 51

nr 4

813-828

In order to document the Alamo Event and to investigate its influence on shallow−marine environments, we undertook a study of ostracods, conodonts, and analysis of the sedimentology of the lower member of the type Devils Gate Limestone. Six major carbonate microfacies (MF1–MF6) ranging from open−marine environments below storm wave base to pre−evaporitic supratidal lagoons were recognized. The sedimentological study detected no important sedimentological changes during the Alamo Event; only an influx of detrital material and lithoclasts indicate that an unusual event had occurred. Ostracods are generally rare or absent in the lower member of the Devils Gate Limestone, and only 2,000 carapaces, valves and fragments were extracted; from these some 26 taxa were identified. Two new species, Voronina? eureka and Serenida dorsoplicata are proposed. The ostracods belong to the Eifelian Mega−Assemblage and their distribution was influenced by strong salinity variations. Because of the rarity and low diversity of ostracods and conodonts in samples collected from the lower part of the lower member of the Devils Gate Limestone it is not adequate to demonstrate conclusively an extinction event close to the Alamo Event Bed. Nevertheless the greater abundance and diversity of ostracods above this bed seems to indicate that the Alamo Event did not result in significant extinction of ostracod taxa in this shallow water setting. The ostracod fauna present in the lower member of the Devils Gate Limestone suggests faunal exchanges between Nevada and the Russian Platform via the Western Canadian platform.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

1 Becker R. T.

1 Berra I.

1 Casier J. G.

1 Li H.

1 Ma X. P.

1 Olempska E.

1 Preat A.

1 Sandberg C.

1 Sun Y.-Y.

2 2006

Wyniki wyszukiwania

Early and Middle Frasnian brachiopod faunas and turnover on the South China shelf

Ostracods and facies of the Early and Middle Frasnian at Devils Gate in Nevada: Relationship to the Alamo Event