Sizing up the sub-Tommotian unconformity in Siberia: comment and reply

Article Abstract:

A.H. Knoll et al. were wrong in their statement regarding the stratigraphic magnitude of the unconformity at the base of the Pestrotsvet Formation in the stratotype area of the Tommotian Stage in Siberia. They mistakenly claim that this hiatus corresponds to beds in the western Anabar Region characterized by a sequence of five assemblages of small shelly fossils. There is no data which supports that claim that beds corresponding to the upper Manykai and lower Medvezh'ya Formations of the Anabar region are not found in the south Siberian sections.

Formations (Geology), Geological formations

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Biostratigraphy of the Vendian-Cambrian beds and the lower Cambrian boundary in Siberia

Article Abstract:

A general biostratigraphic scheme is presented for the Vendian-Cambrian sedimentary beds of southern Siberia that resolves them into three zones which are named after prominently occurring fossils. The prevalence of Chinese-type small shelly fossils in the zones suggests that the Aldanocyathus sunnaginicus Zone of Siberia correlates with the Siphogonuchites-Paragloborilus Zone of China. The Cambrian-Precambrian boundary should be taken to be the base of the A. sunnaginicus Zone in Siberia.

Paleontology, Cambrian period, Invertebrates, Fossil, Fossil invertebrates

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Discussion on Sm-Nd isotopic age of Precambrian-Cambrian boundary in China

Article Abstract:

The new dating technique to determine the age of the Precambrian-Cambrian boundary, which uses the Sm-Nd method on phosphatic material, has yielded doubtful statistical data. The approach is apparently inadequate for the precise dating of the Precambrian-Cambrian boundary. Moreover, the statistical analysis presents a serious underestimation of age uncertainties, particularly the isochron age calculations.

Methods, China, Measurement, Geology, Stratigraphic, Stratigraphy, Geological time, Geochronology, Archaeological dating

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