Detrital zircon geochronologic tests of the SE Siberia-SW Laurentia paleocontinental connection

Strikingly similar Late Mesoproterozoic stratigraphic sequences and correlative U-Pb detrital-zircon ages may indicate that the Sette Daban region of southeastern Siberia and the Death Valley region of southwestern North America were formerly contiguous parts of a Grenville foreland basin. The Siberian section contains large numbers of detrital zircons that correlate with Grenville, Granite-Rhyolite, and Yavapai basement provinces of North America. The sections in both Siberia and Death Valley exhibit west-directed thrust faults that may represent remnants of a Grenville foreland thrust belt. North American detrital-zircon components do not occur in Siberian samples above a ~600 Ma breakup unconformity, suggesting that rifting and continental separation blocked transfer of clastic sediment between the cratons by 600 Ma. Faunal similarities suggest, however, that the two cratons remained within the breeding ranges of Early Cambrian trilobites and archeocyathans.

Lower Cambrian halkieriids from Oxfordshire, UK

Lower Cambrian sediments from the Withycombe Farm borehole (Oxfordshire) yield isolated halkieriid sclerites. All bear prominent ridges, and most appear to be either cultrates or palmates, although distinction between the two in the available material is generally difficult. Two other sclerites are more elongate: one may represent a spinose sclerite, while the other is possibly derived from the siculate zone of the original scleritome. Adjacent horizons of the Withycombe Formation yield disc-like fossils, superficially similar to hyolith opercula or monoplacophorans. These are tentatively identified as deriving from the same halkieriid scleritome. Two main types are identified, and these may correspond to the anterior and posterior shells of Halkieria evangelista from the lower Cambrian Sirius Passet fauna of North Greenland. The age of the Withycombe Formation within the Cambrian is not entirely resolved, but faunal evidence suggests an equivalence to the Cuslett Formation of southeast Newfoundland, which corresponds to either the upper Tommotian or lower Atdabanian of the standard Siberian section.