2 research outputs found
The Lower Cambrian of the Salair and Gorny Altai (Siberia) revisited
This paper discusses the fossil record, stratigraphy and sedimentary environments of lower Cambrian sequences that crop out in the Salair and Gorny Altai, southern part of western Siberia (Russia).
Numerous and well-preserved archaeocyaths and a few small shelly fossils (SSF) have been discovered in carbonate sequences that crop out nearby the Gavrilovka village, Salair. The presence of the Gordonicyathus howelliarchaeocyath Zone is established for the first time in this thick sequence of biogenic carbonates, in addition to the Nochoroicyathus mariinskii Zone, which was known previously from the Gavrilovka Formation. Both of these zones are Atdabanian in age. It is likely that accumulation of the Gavrilovka Formation took place in relatively shallow waters, along reef buildups surrounded by lagoons with archaeocyaths.
In the Ak-Kaya section of the Gorny Altai, the trilobite species Alacephalus contortus and Poliellaspis rotundata, known previously from the upper Atdabanian, were discovered, only a few meters above horizons bearing lower Botoman trilobites. We may consider that the previously known age range of these two species is slightly longer and should be extended up to the lower Botoman. Alternatively, on the basis of their paleoecological affinity for agitated waters, these trilobites may be interpreted as reworked in lower Botoman strata
Chapter 19 Global Cambrian trilobite palaeobiogeography assessed using parsimony analysis of endemicity
<p>Palaeobiogeographical data on Cambrian trilobites obtained during the twentieth century are combined in this paper to evaluate
palaeoceanographic links through <em>c.</em> 30 myr, once these arthropods biomineralized. Worldwide major tectonostratigraphic units are characterized at series intervals
of Cambrian time and datasets of trilobite genera (629 for Cambrian Series 2, 965 for Cambrian Series 3, and 866 for the Furongian
Series) are analysed using parsimony analysis of endemicity. Special attention is given to the biogeographical observations
made in microcontinents and exotic terranes. The same is done for platform-basinal transects of well-known continental margins.
The parsimony analysis of endemicity analysis resulted in distinct palaeogeographical area groupings among the tectonostratigraphic
units. With these groupings, several palaeobiogeographical units are distinguished, which do not necessarily fit the previously
proposed biogeographical realms and provinces. Their development and spatial distributions are broadly controlled by Cambrian
palaeoclimates, palaeogeographical conditions (e.g. carbonate productivity and anoxic conditions) and ocean current circulation.
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