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the system currently has no formally agreed internationally recognized divisions. Since the IUGS Commission on Stratigraphy requires the definition of Global Boundary Stratotype Sections and Points (GSSPs), it has become the prime objective of the International Subcommission on Cambrian Stratigraphy to commence to document suitable biostratigraphic horizons within the system which might assist in achieving this goal. In this paper we suggest the consideration of fourteen late Early Cambrian-terminal Cambrian levels, and document their stratigraphical and biogeographical distributions. Once agreement within the Subcommission is reached on which are the most suitable, it will be necessary to search for appropriate stratotype sections, bearing in mind the necessity to calibrate the biostratigraphy by way of non-biological correlation techniques, such as chemostratigraphy and magnetostratigraphy.

The Henson Gletscher Formation of North Greenland yields moderately diverse trilobite faunas which bracket the Cambrian Series 2-Series 3 boundary interval. A number of the trilobite taxa permit correlation into other parts of Laurentia and to other Cambrian continents, thus enhancing correlation within this stratigraphical interval of the traditional Lower-Middle Cambrian boundary. In particular, the occurrence of Ovatoryctocara granulata and O. yaxiensis substantially improves the intercontinental recognition of the O. granulata level, a prime GSSP candidate. In contrast, the level with Oryctocephalus indicus cannot be located in a number of Cambrian continents with sufficient precision, making this level unsuitable for the definition of a GSSP for the base of the Cambrian Series 3 and Stage 5. Further support for the correlation potential of the base of the range of Ovatoryctocara granulata comes from recent carbon isotope studies that indicate a striking negative excursion in sections of South China (ROECE event) that probably coincides with similar excursions in Laurentia. Four new trilobite species are described: Zacanthopsis blakeri sp. nov., Protoryctocephalus arcticus sp. nov., Eoptychoparia pearylandica sp. nov. and Onchocephalus? freucheni sp. nov.

The replacement of the late Precambrian Ediacaran biota by morphologically disparate animals at the beginning of the Phanerozoic was a key event in the history of life on Earth, the mechanisms and the time-scales of which are not entirely understood. A composite section in Namibia providing biostratigraphic and chemostratigraphic data bracketed by radiometric dating constrains the Ediacaran-Cambrian boundary to 538.6-538.8 Ma, more than 2 Ma younger than previously assumed. The U-Pb-CA-ID TIMS zircon ages demonstrate an ultrashort time frame for the LAD of the Ediacaran biota to the FAD of a complex, burrowing Phanerozoic biota represented by trace fossils to a 410 ka time window of 538.99 ± 0.21 Ma to 538.58 ± 0.19 Ma. The extremely short duration of the faunal transition from Ediacaran to Cambrian biota within less than 410 ka supports models of ecological cascades that followed the evolutionary breakthrough of increased mobility at the beginning of the Phanerozoic.

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Volcanic zircons from three ashes give a U-Pb date of 511 ± 1 Ma on trilobite-bearing, upper Lower Cambrian (upper Branchian Series) strata of southern New Brunswick that correlate into the Siberian middle Botomian - Toyonian Stage interval. This very young age on the late, but not latest, Early Cambrian of Avalon is consistent both with a 519 ± 1 Ma age on the older Caerfai Bay Shales of south Wales that are tentatively correlated into strata with the oldest Avalonian trilobites (lower Branchian) and with a 517 ± 1.5 Ma age on the Antatlasia gutta-pluviae Zone (trilobites) of Morocco. Determination of a 522 ± 2 Ma zircon age on the Moroccan subtrilobitic Lower Cambrian Lie de vin Formation is consistent with an earlier reported 521 ± 7 Ma age from the Lie de vin but suggests that a 526 ± 4 Ma age on Australian trilobite-bearing Lower Cambrian rocks may be too old. A 33+ Ma duration of the Avalonian Early Cambrian and an 8+ Ma length of the Avalonian trilobite-bearing Lower Cambrian support proposals that most Cambrian time was Early Cambrian and the majority of the Early Cambrian was pretrilobitic.

The International Subcommission on Cambrian Stratigraphy has introduced a number of internal subdivisions (i.e., series and stages), but most of the explanatory publications lack reliable data on the correlation between all Cambrian key continents. A comprehensive correlation chart is presented here to review and document correlatable biostratigraphic horizons within the system and correlation of biostratigraphic zones and regional series and stages, accompanied by explanatory remarks. The chart also presents important available non-biological correlation data, such as carbon isotope signatures and radiometric ages.