The Global Standard Stratotype‐section and Point (GSSP) of the Furongian Series (uppermost series of the Cambrian System) and the Paibian Stage (lowermost stage of the Furongian Series), has been recently defined and ratified by the International Union of Geological Sciences (IUGS). The boundary stratotype is 369 metres above the base of the Huaqiao Formation in the Paibi section, northwestern Hunan Province, China. This point coincides with the first appearance of the cosmopolitan agnostoid trilobite Glyptagnostus reticulatus, and occurs near the base of a large positive carbon isotopic excursion (SPICE excursion).

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Metamorphosed supracrustal rocks in the central Ross Sea sector of the Transantarctic Mountains are of Neoproterozoic age and not Cambrian. They include pillow basalts with a mantle separation age of 700–800 Ma. In the Skelton Glacier area, these rocks experienced two strong phases of deformation that produced folds and associated foliations. Both rocks and structures are cut by a 551 ± 4 Ma unfoliated quartz syenite (late Neoproterozic). The deformation and limited geochemical data suggest an active Antarctic plate margin whose late Neoproterozoic history is markedly different from that of the temporally equivalent rift to drift transition recorded along the autochthonous western margin of Laurentia. If these two cratons were ever contiguous, separation occurred by c. 700–800 Ma.

The Global boundary Stratotype Section and Point (GSSP) for the base of the Drumian Stage (Cambrian Series 3) is defined at the base of a limestone (calcisiltite) layer 62 m above the base of the Wheeler Formation in the Stratotype Ridge section, Drum Mountains, Utah, USA. The GSSP level contains the lowest occurrence of the cosmopolitan agnostoid trilobite Ptychagnostus atavus (base of the P. atavus Zone). Secondary global markers near the base of the stage include the DICE negative ! 13 C excursion, the onset of a long monotonic 87 Sr/ 86 Sr isotopic shift, and the transgressive phase of a eustatic event. Faunal turnovers close to the base of the Drumian Stage are recognized as the base of the Bolaspidella Zone (polymerid trilobites) in Laurentia, the historic base of the Floran Stage in Australia, the base of the Dorypyge richthofeni Zone (polymerid trilobites) in South China, and the base of the Gapparodus bisulcatus-Westergaardodina brevidens Assemblage-zone (conodonts) in Baltica and South China. The last occurrence of the cosmopolitan trilobite Ptychagnostus gibbus occurs in the lower part of the Drumian Stage, and the base of the Hydrocephalus hicksii Zone (polymerid trilobites) as used in Siberia and Baltica occurs near the base of the stage.Recent efforts by the ISCS to develop internal subdivisions of the Cambrian System applicable on a global scale are coming to fruition as work proceeds on horizons deemed potentially suitable for pre-

The Shackleton Limestone formed a carbonate platform that bordered part of the Greater Antarctic craton in middle and late Early Cambrian time. In the Holyoake Range of the central Transantarctic Mountains, this unit records deposition on a stable shelf on which flourished ecological reefs composed of microorganisms and archaeocyathans. Burrow‐mottled lime mudstone, wackestone and packstone with patch reefs represent accumulation in shelf areas of relatively low to moderate energy. Thick ooidal grainstone units reflect deposition in higher energy shoals and as sand sheets that were associated with extensive reef complexes. The framework of these reefs was principally the product of micro‐organisms, by inference mostly cyanobacteria. Archaeocyathans constitute as much as 30% of some reefs, but commonly they form less than 10% and are absent from some. On the basis of microbial composition, three reef types are recognized. The first type is a Renalcis boundstone that lacks archaeocyathans. Within these, abundant upward‐directed thalii of Renalcis formed a framework that trapped fine‐grained sediment. The second type, which forms the core of some larger reefs, is composed of stromatactis‐bearing, microbial boundstone. The third, yet most common, reef type is variable in composition. It is characterized by the presence of abundant Epiphyton, but may include archaeocyathans, and the microbial microfossils Girvanella and Renalcis as well as cryptomicrobial clotted micrite. In this type of reef, frame‐building organisms typically constructed highly porous structures that had small interparticle and fenestral pores and large growth‐framework cavities, as well as rare metre‐sized caverns. Within these spaces, Epiphyton and, less commonly Renalcis, encrusted framework elements, fine‐grained sediments accumulated, and pervasive sea‐floor cements were precipitated. Boundstone fabrics in the Shackleton Limestone are highly complex, with fabrics analogous to younger, more metazoan‐rich reefs, as well as deep‐water stromatactis‐bearing mud‐mounds. The Epiphyton‐Girvanella‐archaeocyathan frameworks and stromatactis‐bearing boundstones, both of which seemingly first appeared in the middle Early Cambrian, are regarded as the precursors, in structure, composition, and preferred hydrologic setting, of the more extensive reefs and complex framework styles of later Phanerozoic time.