Abstract

The Sukharikha River section contains more than 800 m of fossiliferous Vendian and Lower Cambrian carbonate rock deposited in ramp, shelf, and slope environments. A diverse fauna of small shelly fossils, calcibionts, brachiopods, trilobites, and archaeocyaths has allowed us to develop a multi-taxa biostratigraphic framework for this section. A dearth of distinctive fossils low in the Sukharikha Formation prevents us from determining the position of the Vendian-Cambrian boundary. Abundant small shelly fossils and archaeocyaths in the uppermost Sukharikha Formation and low in the Krasnoporog Formation provide ample biostratigraphic control near the base of the Tommotian Stage, but the Nemakit-Daldynian - Tommotian boundary, as defined at Ulakhan-Sulugur on the Aldan River, is temporally ambiguous. For this reason there is no precise definition of this boundary. In the Sukharikha River section we have provisionally placed the base of the Tommotian Stage at the first occurrence of Nochoroicyathus sunnaginicus Zone archaeocyaths, about 1.5 m below the top of the Sukharikha Formation. However, we suppose that this horizon actually predates the deposition of nominally basal Tommotian taxa in the Aldan region. A new global stratotype section for the Nemakit-Daldynian - Tommotian boundary should be selected, and this section may turn out to be a good candidate. The paleontological richness (especially small shelly fossils and archaeocyaths), the apparent absence of long depositional hiatuses, and the presence of well-preserved limestones suggest that the Sukharikha River section contains the combination of paleontological, sedimentological, and isotopic data to resolve some fundamental problems in Early Cambrian stratigraphy.

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