Wyniki wyszukiwania

1

Artykuł dostępny w postaci pełnego tekstu - kliknij by otworzyć plik

Skeletonized microfossils from the Lower-Middle Cambrian transition of the Cantabrian Mountains, Northern Spain

100%

Clausen S., Alvaro J. J.

Acta Palaeontologica Polonica

|

2006

|

tom 51

|

nr 2

Two different assemblages of skeletonized microfossils are recorded in bioclastic shoals that cross the Lower–Middle Cambrian boundary in the Esla nappe, Cantabrian Mountains. The uppermost Lower Cambrian sedimentary rocks represent a ramp with ooid−bioclastic shoals that allowed development of protected archaeocyathan−microbial reefs. The shoals yield abundant debris of tube−shelled microfossils, such as hyoliths and hyolithelminths (Torellella), and trilobites. The overlying erosive unconformity marks the disappearance of archaeocyaths and the Iberian Lower–Middle Cambrian boundary. A different assemblage occurs in the overlying glauconitic limestone associated with development of widespread low−relief bioclastic shoals. Their lowermost part is rich in hyoliths, hexactinellid, and heteractinid sponge spicules (Eiffelia), chancelloriid sclerites (at least six form species of Allonnia, Archiasterella, and Chancelloria), cambroclaves (Parazhijinites), probable eoconchariids (Cantabria labyrinthica gen. et sp. nov.), sclerites of uncertain affinity (Holoplicatella margarita gen. et sp. nov.), echinoderm ossicles and trilobites. Although both bioclastic shoal complexes represent similar high−energy conditions, the unconformity at the Lower–Middle Cambrian boundary marks a drastic replacement of microfossil assemblages. This change may represent a real community replacement from hyolithelminth−phosphatic tubular shells to CES (chancelloriid−echinoderm−sponge) meadows. This replacement coincides with the immigration event based on trilobites previously reported across the boundary, although the partial information available from originally carbonate skeletons is also affected by taphonomic bias.

2

Small shelly fossils from the argillaceous facies of the Lower Cambrian Forteau Formation of Western Newfoundland

88%

Skovsted C. B., Peel J. S.

Acta Palaeontologica Polonica

|

2007

|

tom 52

|

nr 4

A diverse fauna of helcionelloid molluscs, hyoliths, and other small shelly fossils is described from limestone layers within the Forteau Formation of the Bonne Bay region in western Newfoundland. The fauna is dominated by internal moulds of various molluscs and tubular problematica, but also includes hyolith opercula, echinoderm ossicles, and other calcareous small shelly fossils preserved by phosphatisation. Originally organophosphatic shells are comparatively rare, but are represented by brachiopods, hyolithelminths, and tommotiids. The fauna is similar to other late Early Cambrian faunas from slope and outer shelf settings along the eastern margin of Laurentia and may be of middle Dyeran age. The similarity of these faunas indicates that at least by the late Early Cambrian, a distinctive and laterally continuous outer shelf fauna had evolved. The Forteau Formation also shares elements with faunas from other Early Cambrian provinces, strengthening ties between Laurentia and Australia, China, and Europe during the late Early Cambrian. Two new taxa of problematic fossil organisms are described, the conical Clavitella curvata gen. et sp. nov. and the wedge−shaped Sphenopteron boomerang gen. et sp. nov.

3

Early Cambrian molluscs from glacial erratics of King George Island, West Antarctica

75%

Wrona R.

Polish Polar Research

|

2003

|

tom 24

|

nr 3-4

Ograniczanie wyników

2 Acta Palaeontologica Polonica

1 Polish Polar Research

1 Alvaro J. J.

1 Clausen S.

1 Peel J. S.

1 Skovsted C. B.

1 Wrona R.

1 2007

1 2006

1 2003

Skeletonized microfossils from the Lower-Middle Cambrian transition of the Cantabrian Mountains, Northern Spain

Small shelly fossils from the argillaceous facies of the Lower Cambrian Forteau Formation of Western Newfoundland

Early Cambrian molluscs from glacial erratics of King George Island, West Antarctica