Vase-shaped microfossil biostratigraphy with new data from Tasmania, Svalbard, Greenland, Sweden and the Yukon

Abstract

The recent revision of the Cryogenian lower boundary from 850 Ma to 720 Ma has nearly doubled the duration of the Tonian Period to 280 Myrs, an interval longer than the Mesozoic and Cenozoic eras combined. Although subdivision of the Tonian will likely emphasize chemostratigraphy, the relatively rich fossil record of this time period may also be useful. In particular, vase-shaped microfossils (VSMs) occur globally and often abundantly in a variety of lithofacies, exhibit a variety of preservational modes, and are stratigraphically constrained by the two major carbon isotopic events of the Tonian Period, the Bitter Springs and Islay anomalies. VSMs have been used as informal, grade-level indicators of late Tonian age (e.g. ca. 800–700 Ma) for several decades but here, based on new data from an assemblage in northwestern Tasmania and restudy of samples from Svalbard, Greenland, Sweden and the Yukon, we report a species-level faunal assemblage indicative of the interval ca. 789 to 729 Ma. Species-level VSM biostratigraphy presents an opportunity for potential biostratigraphic subdivision of the lengthy Tonian Period and is particularly useful in successions where chemostratigraphy and radiometric age constraints are absent.Eight taxa are described from shales and early diagenetic cherts of the Black River Dolomite, Togari Group, Tasmania, including seven previously named species (Bombycion micron, Bonniea dacruchares, Bonniea pytinaia, Cycliocyrillium simplex, Cycliocyrillium torquata, Melanocyrillium hexodiadema and Palaeoarcella athanata), and one newly described genus and species Pakupaku kabin n. gen et n. sp. Study of additional units resulted in new recognition of B. pytinaia, C. simplex and C. torquata in the Draken Formation, Spitsbergen, Svalbard, B. dacruchares and P. athanata in the Ryssö Formation, Nordaustlandet, Svalbard, B. dacruchares, B. pytinaia, C. torquata and P. athanata in Bed 18 of the Eleonore Bay Group, Greenland, and B. dacruchares, B. pytinaia and Bombycion micron in the Visingsö Group, Sweden.