Biostratigraphy of the Vendian-Cambrian Sukharikha River section, northwestern Siberian Platform

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.

Chronology of early Cambrian biomineralization

“…2). Archaeocyaths were also reported from the basal Pestrotsvet Formation at Selinde in the southeastern Siberian Platform (Korshunov, Repina & Sysoev, 1969;Khomentovsky & Karlova, 2002) and the uppermost Sukharikha Formation in the Igarka region of the northwestern margin of the Siberian Platform , but see Luchinina et al 1997 andRowland et al 1998). In the latter two localities, carbonates display δ 13 C oscillations with high positive peaks characteristic of the lower Tommotian boundary beds, although the position of these peaks with respect to this boundary has been questioned (Kouchinsky et al 2001(Kouchinsky et al , 2005(Kouchinsky et al , 2007.…”

“…2). Pentactines of Sulugurella sulugurica Fedorov in Pel'man et al 1990 were originally attributed to the Calcarea and reported from the Nochorojcyathus sunnaginicus Zone of the Tommotian (Pel'man et al 1990) and from the probably slightly older uppermost Sukharikha Formation of the Sukharikha River section (Rowland et al 1998), but their hexactinellid affinity is more plausible (A. Zhuravlev, pers.…”

Carbon isotope stratigraphy of the Precambrian–Cambrian Sukharikha River section, northwestern Siberian platform

“…One of these sections at the northwestern margin of the Siberian platform is exposed from 67 • 12.516 N, 87 • 21.567 E (see arrow A in Fig. 1) along ∼ 3 km upstream the Sukharikha River, a right tributary of the Enisej River Rowland et al 1998; Fig. 1.…”

Early Cambrian chronostratigraphy and geochronology of South Australia

“…Tannuolina sp., halkieriid sclerites, Torellella, and the micromolluscs Aldanella and Bemella (Rowland et al, 1998; see also Kouchinsky et al, 2010). Similar shelly fauna occur through the Sellick Hill Formation on the Fleurieu Peninsula (WANG/WANG-S and SHL/FTL)…”