%0 Journal Article %J Geology Magazine %D 2013 %T Reconstructing the Avalonia Palaeocontinent in the Cambrian: A 519 Ma Caliche in South Wales and Transcontinental Middle Terreneuvian Sandstones %A E. Landing %A Westrop, S. R. %A Bowring, S. A. %K Avalonia %K caliche %K Early Cambrian %K sequence stratigraphy %K South Wales %X

An Early Cambrian caliche on the St Non's Formation (emended) is the base of the Caerfai Bay Formation (unit-term changed) at Caerfai Bay, South Wales. Subaerial exposure and the caliche mean the two formations were not genetically related units. The St Non's is an older sand sheet (likely tidalitic, not delta-related) referred to Avalonian depositional sequence (ADS) 2, and the Caerfai Bay is a shallow mud basin unit referred to ADS 4A. The similar Random Formation (upper ADS 2) in North American Avalonia has a basal age of c. 528 Ma and is unconformably overlain by red mudstones or sandstones in fault-bounded basins on the Avalonian inner platform. Coeval British sandstones (lower Hartshill, Wrekin, St Non's, Brand Hills?) are unconformably overlain by latest Terreneuvian (ADS 3) or Epoch 2 (ADS 4A) units. Dates of 519 Ma on Caerfai Bay ashes give an upper bracket on the late appearance of Avalonian trilobites and suggest an ADS 2–4A hiatus of several million years. Post-St Non's and post-Random basin reorganization led to abundant Caerfai Bay Formation volcanic ashes and sparse Brigus Formation ashes in Newfoundland. The broad extent of erosional sequence boundaries that bracket lithologically similar to identical units emphasize that ‘east’ and ‘west’ Avalonia formed one palaeocontinent. The inner platform in southern Britain was larger than the Midlands craton, a tectonically defined later Palaeozoic area unrelated to terminal Ediacaran – Early Palaeozoic depositional belts. The cool-water successions of Early Palaeozoic Avalonia were distant from coeval West Gondwanan carbonate platforms.

%B Geology Magazine %V 150 %P 1022-1046 %G eng %U http://dx.doi.org/10.1017/S0016756813000228 %R 10.1017/S0016756813000228 %0 Journal Article %J Geology %D 1994 %T New Constraint on the Division of Cambrian Time %A Isachsen, C. E. %A Bowring, S. A. %A E. Landing %A Samson, S. D. %K Avalonian terrane %K Early Cambrian %K Placentian Series %K southern New Brunswick %K U-Pb zircon age %K volcanic ash %X

A U-Pb zircon age of 530.7 ±0.9 Ma for a volcanic ash in the lower Placentian Series of the Avalonian terrane in southern New Brunswick provides a precise point for calibration of Early Cambrian biologic evolution. The ash is from the middle Rusophycus avalonensis Zone in Saint John, New Brunswick. This date is on subtrilobitic, Lower Cambrian strata that may be approximately correlative with the sub-Tommotian Manykaian Stage of Siberia and the lowest Meishucunian Stage of the South China platform. This age, when combined with published geochronologic data from the Cambrian, suggests that the Manykaian Stage may have lasted approximately 13 m.y. and that the Tommotian may have been considerably shorter.

%B Geology %V 22 %P 496-498 %G eng %U http://geology.gsapubs.org/content/22/6/496.short %R 10.1130/0091-7613(1994)​022<0496:NCOTDO>​2.3.CO;2