These papers arise from the conference in Bristol, England, of the above international Working Group, which was held in the University of Bristol conference centre from 9–13 May, 1983. Forty-five persons attended; thirty-two were members of the Working Group (about a third of the total membership which is drawn from about twenty countries in many parts of the world from Australia to Argentina and from Korea to western Canada.)

Relevant points of general principle and special application to the problem under discussion are quoted selectively from the recently published time scale by Harland et al. (1982) and critically considered. Most of the principles and the resulting names for divisions of the Precambrian–Cambrian transition used in it are accepted. The unique significance of the transition from dominantly chronometric to dominantly chronostratic boundaries based on the ‘biostratigraphic sequence’ is an additional justification for the higher ranks previously given to the Vendian (Era) and its constituent divisions: Varangian (or Varangerian) and Ediacaran (or Ediacarian) Periods. The historic transition begins with the latest of the Proterozoic glaciations (the earlier ones started about 950 m.y. ago) and ends with the exponential diversification of the Metazoa. The causal linkage of the two events is hypothetical. Their stratigraphic sequence is demonstrable on the East European platform where the type section of the Vendian is located, and on the Yangtse platform. Normative, operationally designated boundaries are required for the stratigraphic divisions. The history of life in which there are no sharp initial and terminal boundaries shows clearly a rapid transition from widespread but generally rare occurrences of Vendian, particularly Ediacaran, fossils to ubiquitous, generally ‘shelly’ Palaeozoic (initially Cambrian) faunas of unquestioned biostratigraphic importance. This biohistoric transition is the beginning of the Phanerozoic division of a unique historic process. For the Eon of the stratigraphic scale comprising Palaeozoic to Cainozoic Eras the new term Holozoic is therefore proposed.

Being located in Jinning County, Yunnan Province, approximately 103° E, 25° N, the Meishucun section has a long history of study, convenient accessibility, mild spring-like climate all the year round and good exposures of the relevant strata. In the particular area there occur monofacial transitional carbonate deposits of marine origin, yielding in great abundance both small shelly fossils and trace fossils, which are present in close association and in some cases on the same bedding surface. The sequence of biotic assemblages is clearly evident and can be used for wide intercontinental correlation.

In the lower part of the Qiongzhusi Stage, stratigraphically higher, there appear the oldest trilobites, archaeostracods and Baltisphaeridium characteristic of the Early Cambrian.

During the last six years great progress has been made in the study of the particular section through lithostratigraphic, biostratigraphic, geochronological, magnetostratigraphic and seismostratigraphic approaches, thus making the Meischucun Stage and the Sinian–Cambrian boundary stratotype section in the Meishucun area a Chinese candidate for global stratotype section and point for the Precambrian–Cambrian boundary.

The Sinian and Cambrian systems within the Yangtze stratigraphic province represent continuous deposits, and the strata above and below the Sinian–Cambrian boundary are rich in fossils. From all the relevant boundary sections, the Meishucun section in Jinning County, Yunnan Province serves as the stratotype section for the Sinian–Cambrian boundary and is the Chinese candidate for the global stratotype section and point for the Precambrian–Cambrian boundary. The present paper, with the various charts and tables, elaborates on several typical Sinian–Cambrian boundary sections and the distribution of fossils in them.

In accordance with the characteristics of biological evolution, three biotas can be recognized for the period from the Late Sinian to the Early Cambrian. The first biota appeared in the Late Sinian, characterized by the presence of the soft-bodied metazoans; the second biota occurred during the Meishucun Stage of the early Cambrian, and is characterized by the appearance and prevalence of small shelly fossils from many different phyla; and the third biota came into existence during the Qiongzhusi Stage of the Early Cambrian; it is characterized by the first appearance and prevalence of trilobites.

The Meishucun Stage of the Lower Cambrian can be divided into three fossil zones. The Sinian–Cambrian boundary is placed at the base of the first Anabarites–Circotheca–Protohertzina zone. According to isotopic dating by the Rb–Sr whole-rock isochron technique, the age of the Sinian–Cambrian boundary is inferred to be 610±10 Ma.

In this paper the author describes the results of the Rb-Sr isotopic dating of black shale at the Sinian (Precambrian)–Cambrian boundary at the Meishucun section, Jinning County, Yunnan Province, China. The Sinian and Cambrian strata in eastern Yunnan are well developed, the Sinian–Cambrian boundary section in the vicinity of Meishucun Village in Jinning County being representative. These well developed strata provide excellent conditions for research on the radiometric age of the Precambrian–Cambrian boundary. An Rb-Sr isochron age of 579.7 ±8.2 Ma has been obtained on black shale from the Badaowan Member of the Early Cambrian Qiongzhusi Formation, which occurs at 20 m above the Sinian–Cambrian boundary. So an inferred age of 610±10 Ma is given for the Sinian (Precambrian)–Cambrian boundary.

The Cambrian and Precambrian sedimentary strata in the centre and west part of the Yangtze Platform are in continuous successions, in which the Tiantzushan Member and the Meisuchun Formation are exceedingly rich in shelly fossils. In Co-operation with the stratigraphic study in depth and in order to determine the isotopic age for the Precambrian–Cambrian boundary in the Yangtze Platform, a number of isotopic age determinations by different techniques have been made in the laboratories of the Yichang Institute of Geology and Mineral Resources and the Research School of Earth Sciences, Australian National University, mainly on the sequences in the Yangtze Gorges area together with those from some other areas in the Yangtze Platform. In this paper, the authors summarize all of these results and infer 610±10 Ma as an age for the Sinian–Cambrian Boundary in the Yangtze Platform if the ‘golden spike’ is considered to be placed at the bottom of the Meishucun Stage.

Well-preserved, silicified Obruchevella from the earliest Cambrian (Meishucun Stage) sequence from Meishucun section in Yunnan Province, China contains distinct cross-partitioning. This suggests that this helically coiled microfossil represents the remains of an oscillatorialean cyanophyta. Obruchevella is a microfossil that exhibits a variety of form that may be produced through degradation. Obruchevella identified in the Meishucun section includes O: parva, O. parvissima, O. delicata, O. meishucunensis and several other morphs which are yet to be identified.

The appearance of the first abundant skeletal organisms in the earliest Cambrian was a quantum leap in the evolutionary history of life. It provided the foundations of the animal kingdom from Cambrian times onwards. This paper demonstrates that this evolutionary process resulted from a combination of environmental and biological factors. The author maintains that the appearance of the oldest shelly fossils is a reasonable criterion for defining the Precambrian–Cambrian boundary. This arises not only from the viewpoint of taking the Cambrian Period as the first period in the Palaeozoic Era, but is also a logical extension of regarding the history of life as being divisible into a series of developmental stages.

Four sedimentary sections seen in continuous exposures along the Lena River on the Siberian Platform in Yakutia contain a record of the geomagnetic field during the Tommotian and Atdabanian stages of Early Cambrian time. The direction of the stable remanent magnetization indicates that the Siberian platform was located on the equator, and the corresponding palaeomagnetic pole provides a well-dated extension of the Siberian apparent polar wander path. A belt of archaeocyathid bioherms which separates two major facies zones in the lower Cambrian was positioned on and aligned more or less parallel with the palaeoequator. The geographical position of this belt appears to have tracked the southward motion of the Siberian platform during post-Tommotian time. These palaeomagnetic results combined with the extensive biostratigraphy of the Siberian Platform provide a provisional geomagnetic polarity time scale for this part of Early Cambrian time. Comparison of these results with data of similar age from Central Australia suggests that strata of Tommotian and lower Atdabanian age are not present in the Amadeus Basin of Australia.

Calcareous algae make their first appearance near the base of the Tommotian. The oldest confirmed occurrences are of ?Gemma, Obruchevella and Renalcis in the Nemakit-Daldyn Horizon and late Yudomian of Siberia. A little higher in the sequence, in the Aldanocyathus sunnaginicus Zone of the earliest Tommotian, Angulocellularia, Bajanophyton, Batenevia, Botomaella, Girvanella, Hedstroemia, Korilophyton, Proaulopora, Subtifloria, and Tarthinia appear. Immediately above this, in the Dokidocyathus regularis Zone of the middle Tommotian, Chabakovia appears with the epiphytacean genera Epiphyton, Gordonophyton and Tubomorphophyton. There are only minor subsequent additions to this flora before the end of the Atdabanian. Kordephyton appears in the Dokidocyathus lenaicus Zone of the late Tommotian and Razumovskia in the early Atdabanian.

These fossils constitute three calcareous algae assemblages (CAA 1, 2, 3) characteristic of the Nemakit-Daldyn Horizon/late Yudomian, early Tommotian, and middle Tommotian/Atdabanian respectively. Most of the genera are long-ranging, but their rapid appearance and diversification near the base of the Tommotian repesents an important event in the history of calcareous algae and augments faunal data concerning evolution and biostratigraphy near the Precambrian/Cambrian boundary.

The Precambrian–Cambrian boundary problem is being studied in an areno-argillaceous sequence in the Kashmir and Spiti Valley, Northwest Himalaya, India. In Kashmir, a rich and diversified microbiota – cryptarchs and algae of the Late Precambrian, and low Lower Cambrian trace fossils are recorded. In the Spiti Valley, the yield of microbiota is poor and the trace fossils are late Lower Cambrian.

This paper comprises the first palaeontological correlation between the Upper Proterozoic–Lower Cambrian Series of Ossa-Morena, Luso-Oriental-Alcúdica and Galaico-Castellana Zones of the Iberian Peninsula.

The authors show the palaeontological events on acritarchs, stromatolites, cyanophyta, soft-bodied metazoa, trilobites, archaeocyathans and skeletal microfossils from three representative sequences of the above mentioned zones and discuss the position of the Precambrian–Cambrian boundary in the sequences. The Sierra de Córdoba general Series (Ossa-Morena Zone) has an erosive discontinuity between the rocks with the first record of Cambrian metazoan activity (Skolithos sp., Monomorphichnus sp., Phycodes pedum and Rusophycus sp.) and the rocks with a palynological association (Bavlinella faveolata, Protosphaeridium flexosum, Trachisphaeridium sp., aff. Octoedryxium truncatum, Phycomicetes? sp. and cf. Ooidium sp.) which suggests a Lower–Middle Vendian age. For this reason we suggest that the Precambrian–Cambrian boundary be placed at this unconformity.

The upper part of the Sierra de Guadalupe Series (Luso-Oriental-Alcúdica Zone) includes detrital beds with Phycodes pedum, Planolites sp. and Treptichnus sp. which are also the first record of Cambrian metazoan activity. In the middle part of the sequences, acritarchs attributed to the genus Micrhystridium are found at the top of the Calcareous Beds. This is taken to indicate an early Cambrian age. Vendotaenids and Bavlinella faveolata are found in abundance, thus indicating a Late Vendian age for the middle part of this unit. Thus, we propose the Precambrian–Cambrian boundary be located in the upper part of the Calcareous Beds.

In the Rio Uso Series (Galaico-Castellana Zone), the Azorejo Sandstones contain Rusophycus gr. radwanskii, Planolites sp. and Gordia sp. Trace fossils produced by trilobite-like arthropoda (Monomorphichnus) have been cited in the upper part of the underlying Pusa Shales. Moreover, Octoedryxium truncatum and Bavlinella faveolata are found in the lower part of this unit which suggest that the Precambrian–Cambrian boundary could be situated in the Pusa Shales.

Calcareous microfossils related to annelid polychaetes are found associated with Upper Vendian acritarchs in the Calcareous Beds of Sierra de Guadalupe. They are the oldest record of skeletal metazoa in the Spanish Series.

The medusoids found are associated with a Vendian flora and they are also the oldest non-skeletal metazoa record known in the Iberian Peninsula.

The Lower Cambrian sequence at Nuneaton is outlined, paying particular attention to the 2 m thick Home Farm Member (including the Hyolithes Limestone) and its faunal succession at the type locality, Woodlands Quarry, Hartshill. There follows the first modern description and illustration of microfossils and small shelly fossils from this member. Of thirty-two species covered here, twenty are described and illustrated from Nuneaton for the first time and eight of these are new records. The varied fauna includes phosphatic and calcareous microproblematica (especially Coleoloides typicalis), protoconodonts, agglutinated foraminifera, cap-shaped molluscs, primitive bivalves, hyoliths, inarticulate brachiopods and sponges. The fauna has affinity with fossils in the top Tommotian to lower Atdabanian rocks from Siberia and China, from the Baltic area and the belt from southeast Newfoundland to Massachusetts.