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The Cambrian Bio-Radiation Event

Lupe

A multidisciplinary Approach to Bio-Earth-System Evolution, geophysiology of the Yangtze Platform, P.R. China

There is "...the ontogenetic significance of three great macroevolutionary patterns. The first is the Cambrian radiation, in which the diverse body plans that we call phyla first make their appearance in the fossil record. This sudden appearance of the phyla seems to correspond to a rapid evolutionary radiation of the animals, not merely to the vagaries of the geologic record. The Cambrian event poses an enormous and dramatic problem because so many phyla arose so rapidly." - Rudolf A. Raff (1996) in "The Shape of Life"

Summary

PREAMBLE

Recently two new documents were submitted by the DFG-Geokommission, 1) "geo-biologische und paläobiologische Prozesse als Antrieb der Evolution des Systems Erde"("Geobiological and paleobiological processes as inducement of the evolution of the System Earth") and 2) "Geotechnologien: Das System Erde: Vom Prozeßverständnis zum Erdmanagement" ("Geotechnologies: The System Earth: From process comprehension to Earth management"), which i. al. referred to the interaction of geoenvironmental and geobiological processes at critical intervals of Earth History. The mutually interactive Bio-Earth System processes are referred to as "geophy-siology". Furthermore, both programmatic conceptual papers (DFG) quoted above identify the transitional period between the latest Precambrian (Neoproterozoic III) and the earliest Cambrian as one of such critical intervals during which - seemingly "explosively" - perturbations in the Earth-Ocean-Atmospheric System are documented and radically "new" forms of Life, i.e. the so-called "autolocomobile metazoans", developed. Many years ago this bio-radiation event or "phenomenon", which is coupled with environmental perturbations, was phrased as the unfortunate term of the "Cambrian Explosion" - which actually would imply a sudden evolutive process in a time span of probably less than 2 million years bringing nearly all animal phyla into existence. The biologically generated trackways which are accompanied by first enzymatically produced skeletal remains or "hard parts", the so-called "small shelly fossils", were said to document such an explosive process. However, several lines of evidence point toward an origin of the metazoans deep in the Proterozoic, mainly from molecular biology but also from the Proterozoic fossil record of South China (see Nature, vol. 391, 1998). Results from previous DFG-supported projects by Erdtmann and coworkers (unpubl. reports Er 96/7-1 to 3 and Er 96/16-1 to 3), ), which lead to the current multidisciplinary approach, present evidence and fossil data which also point to earlier pathways of metazoan evolution during the Neoproterozoic.

INTRODUCTION

During the past two decades sharply increasing scientific attention is being paid to the "enigma" of this "Cambrian Explosion". Major national and international efforts (e.g. IGCP projects) are being undertaken to elucidate the as yet unexplained processes leading to this apparently rapid biological radiation at the dawn of the Cambrian Period, ca. 544 million years ago. However, there is sufficient "cryptic" fossil evidence now to disengage from the concept of "punctualism" with regard to the earlier pathways of animal evolution during the latest ca. 60 million years of the Proterozoic Eon. Additional support stems from precise geochronology providing an accurate absolute time frame for calibrating early animal evolution.

Conformable or quasi-conformable successions of uppermost Neoproterozoic (Vendian or "Sinian") to basal Cambrian sedimentary and fossil-bearing rocks are well known from many distant locations, such as from the Burin Peninsula, eastern Newfoundland (Chapel Island Fm., where the boundary GSSP is currently located), from Namibia and adjacent South Africa, from eastern Finnmark in northern Norway, the Barents Sea coast in the North of Russia, from Morocco, Yakutia, South Australia, and from many other regions. Virtually all these fairly well-preserved sedimentary successions represent shallow marine shelf facies, albeit each possessing their own distinctive lithogenetic character and usually their characteristic set of body and trace fossils. Therefore, no definitive isochronous time-marker permits a reliable worldwide correlation of the PC/C boundary point (GSSP) for all these sections, instead every section has their idiosyncritically defined PC/C boundary. The selection of the trace fossil Phycodes (Trichophycus) pedum as the "global" boundary marker is of limited value because the first appearance of this rather long-ranging burrow may be quite heterochronous depending on the diachronous first appearances of its distinct paleoethological facies at different locations.

Investigations of initial appearances of metazoan vestiges have, therefore, been focussed on either biomineralized skeletal evidences (i.e. "cloudinids" and "Small Shelly Fossils") or on the direct documentation of autolocomotive activities, i.e. on trace fossils. However, both these metazoan vestiges, the enzymatically formed shells or the traces, occur evidently from top Vendian strata, but they derive exclusively from such shallow-water environments as those listed above. These types of environments, however, were the unlikely "homes" of "pioneer" metazoans because they represent most rigorous high-stress environments as compared to the more stable deep-water habitats which are not represented by those celebrated sections in Siberia, in the Ediacara Hills of South Australia or elsewhere. Moreover, submarine oceanic vents apparently were the sites of the most ancient settlements of archebacterial chemo-autotrophic life forms since more than 2 billion years prior to the advent of metazoan life forms. These "cryptic" deep oceanic non-phototrophic communities persist until today and now include very "bizarre" metazoan organisms (for example pogonophorans, etc.) which derive their nutrients from a symbiosis with chemoautotrophic bacteria of the indigenous mats. It is, therefore, quite reasonable to suggest that metazoans first evolved in this type of environment - before they (supported by biomineralized "shells") successfully invaded the more rigorous photic near-shore shelf environments.

The geologic record of deep continental backarc basins or ocean floor sequences crossing the PC/C boundary is naturally very tenuous due to processes of subduction and tectonism which obliterated practically most of this deep oceanic type of facies. Therefore, the geodynamic development of postglacial Sinian to Middle Cambrian sedimentary and volcanogenic sequences on the South China Plate ("Yangtze Platform" s.l., see Figs. 1 and 2) has documented a unique succession of sedimentary rocks ranging from shallow-marine carbonates and phosphorites to deep-water black shales and cherts. Within deep water facies this sequence is fully conformable across a narrow Neoproterozoic III / basal Cambrian interval, whereas in coeval shallow water sections critical omission of strata may occur. Along a narrow but extensive zone (ca. 5 km wide only!) stretching between the Provinces of Yunnan in the SW and Zhejiang in the NE, these "boundary beds" are affected by a network of fault displacements which are impregnated and conformably overlain by sulfide ore beds, and by black shales containing extraordinary enrichments of Fe, Ni, As, Mo, V, Zn, U and PGE at the base. These faults usually terminate within the basal Cambrian Niutitang Fm. and cut and "fracturize" the top Neoproterozoic carbonates (Dengying Fm.) or coeval black cherts (Liuchapo Fm.) in coeval deeper water strata. The ore-rich basal Niutitang beds (probably of Tommotian or slightly earlier age) also contain mass occurrences of hexactinellid sponge spicules and sclerotized bivalve arthropods which provisionally have been ascribed to Perspicaris.

The unique mineral association of these "boundary beds" and their association with synchronous tectonism and diffuse venting in association with the first confirmed metazoa have given rise to a preliminary "working hypothesis" of in-situ preservation of contemporary chemoautotrophic bacterial mats which may have supplied nutrients to the metazoan "symbionts". The "pilot" fossil communities may then have decoupled from chemoautotrophic mats to photoautotrophic nutrients as recorded in the successive Lower Cambrian shallowing upwards sequence. The critical physical and atmospheric perturbations, which may have triggered this biotopic change, may be related to an impact event (which is indicated i.al. by extraordinarily high Ir values in the basal horizon of the Niutitang Fm.) or other large scaled geological processes driven by geotectonics. The rapid biotic development then culminated in the first highly diverse metazoan fauna, the so-called "Chengjiang Biota" as documented not only SE and SW of Kunming, Yunnan Province, but also in other areas of the neighbouring Provinces of Guizhou, Sichuan, Hunan, Hubei, southern Shaanxi and southern Anhui. In these regions most sections have not yet been sampled nor fossil and geochemical material been investigated.

Based on the current stage of knowledge, i.e. upon data from the previous DFG-sponsored projects by the TUB team and upon work by Chinese and other foreign scientists, a number of scientific questions emerge, for which only a few examples may be presented here.

The "unique" undisturbed geological record of Neoproterozoic to Early Paleozoic strata extending over both shallow and deeper marine facies regions, replete with a (fault-bounded) narrow but ca. 1.600 km long zone of hydrothermal activities at and below the critical Neo-proterozoic/Cambrian boundary sets the stage for an integrated investigation of Bio-/Earth-System analysis relevant to the following topics:

  1. What biodiversity patterns may be extracted from the Neoproterozoic sequences a) within shallow-water carbonate environments, b) within gravity-induced "slope" and c) within condensed deep-basinal environments, especially with reference to the hydrothermally active zone? It should be noted that, despite a uniquely complete record, macrofossil evidence within the post-Varanger (post-Nantuo) glacial Sinian interval is as yet limited and that palynofossils and trace fossils must be incorporated into this analysis. The potential "ancestral" relationships of most fossils to metazoans is as yet unknown and must be scrutinized including by means of organic geochemistry ("biomarkers").
    A critical investigation of biodiversity over the proposed interval may unravel regional patterns and the exact timing of the Early Cambrian life diversification.
  2. The potential of a terminal Neoproterozoic extinction event should be investigated, especially with reference to a regionally or globally effective impact event. It should be noted that most typical Vendobionta (Ediacara-type fossils) are virtually unknown from the Yangtze Platform and that no overlap of typical Sinian and basal Cambrian fossil associations has as yet been observed from continuous homotaxial sequences anywhere in the world.
  3. The Early Cambrian macrofossil associations should be followed upsection between the first occurrences at the level of the basal Niutitang Fm. (Nemakit-Daldynian?) to the diverse "Chengjiang-type" fauna (upper Atdabanian) and further into the "Kaili-type" fauna at the base of the Middle Cambrian. New and undescribed sections in Central Guizhou Province are available and of great potential for this study (e.g. "Zunyi biota", which were discovered in 1998 by the TUB team). Biodiversity trends in this stratigraphic interval may prove or disprove the pre-existence of multiple metazoan lineages downsection (into the Neoproterozoic).
    The tracing of changes in bodyplans within the Early Cambrian metazoans will allow to answer the question, if large genetic changes or preservational artifacts are responsible for the obvious Lower Cambrian fossil mass radiation.
  4. The unequivocal evidence for either impact or short-term hydrothermal activity at the base of the Niutitang Fm. (basal Cambrian) has to be demonstrated by geochemical and paleo-volcanological investigations. Initial studies on hydrothermalism (by E. Wallis, TUB) have to be continued and supplemented by impact-oriented studies.
  5. There are no modern (latest state-of-the-art) radiometric (zircon-based) analyses of the post-glacial Sinian to Middle Cambrian time interval from the region available as yet. Dating of e.g. intercalated tuff layers into the sediment sequences are necessary for an absolute time calibration of the investigated strata and fossils. In combination with a modern and revised biostratigraphy of the South Chinese succession radiometric dating will provide an ideal tool for international correlation. An international correlation of Neoproterozoic to Cambrian strata of the Yangtze Platform could be achieved by means of biostratigraphy so far, but the resolution is not very high largely due to the lack of zonal fossils.
  6. Modern geochemical investigations (stable isotope and trace element / REE studies) are needed to characterize the paleoenvironments at distinct time slices within the projected stratigraphic interval. This enables the reconstruction of the system interactions of the bio-, atmo- and hydrosphere at the critical time interval of rapid life diversification. High-resolution chemostratigraphy might further support correlation schemes which will be developed to firmly link strata from the Yangtze Platform with others world-wide.
  7. Modern sedimentological studies have never been carried out for the Sinian to Middle Cambrian interval on the Yangtze Platform. Apart from a "synoptical" sequence analysis of the late Neoproterozoic no detailed sequence analytical study has hitherto been carried out for the Neoproterozoic to Middle Cambrian interval on the Yangtze Platform.

PURPOSE OF PROJECT AND WORKING APPROACHES

The potentially intensive interaction of the biotic conditions with either volcanogenic, hydrothermal or "impact-related" mineralization, sedimentary environments, water-mass-dynamics and atmospheric perturbations have been documented worldwide. Appropriate successions for this critical time interval on the Yangtze Platform in South China will be subject to an integrated scientific investigation by means of a cooperation project between German and Chinese geoscientists which will be supported by DFG on the German and NSFC, CAS and CAGS (and possibly other agencies) on the Chinese side. Collaboration with other international teams will be sought and actively pursued.

The German team of geochemists, sedimentologists, economic geologists and geobiologists, together with their Chinese counterparts, will agree to identify a well-defined set of exposed (and cored borehole) sections traversing both the critical geographic region and the critical stratigraphic interval (postglacial Sinian to basal Middle Cambrian). These sections (both in outcrop and as core sections) will be measured and marked by a metric reference grid which will be binding to all project participants and work teams with regard to sample location and later correlative work.

Based on these reference sections and the stratigraphic grid new radiometric dating will be attempted at various pertinent levels of these sections which, together with a new sequence analysis, may serve as essential reference framework for subsequent paleoenvironmental analyses. These analyses will include, but not be limited to stable isotope, REE and trace element analysis, biomarker and other well-introduced techniques relevant to contemporary watermass, pore water and atmospheric constituent determination as well as to diagenetic and thermal overprint aspects. Special attention will be paid to the sampling of micro- and macrofossils and of trace fossils from all levels of these reference sections.

During joint field work together with our Chinese counterparts discussion sessions will be arranged (f.e. in the new "Sino-German Science Centre" in Beijing), in which the laboratory, methodological approaches, final data exchanges and interpretations will be discussed. Furthermore, during subsequent meetings of the German project participants in Berlin or elsewhere in Germany, further joint elaboration of research results will be worked out and final publication in form of a proceedings volume together with our Chinese counterparts is intended.

CONCEPTUAL ASPECTS OF THE PROJECT

1. GEOCHEMISTRY

Profound geotectonic, climatic and biological changes characterize the Precambrian-Cambrian transition, resulting in distinct variations of oceanic and atmospheric composition. They are reflected in the isotope signatures of carbon, oxygen, sulfur and strontium. These geochemical fingerprints frequently provide unequivocal evidence for specific processes affecting ocean/atmosphere chemistry, provided they have not been obliterated by secondary alteration. In addition, temporal records of isotopic compositions reflect the interaction of atmosphere, hydrosphere, biosphere and lithosphere and, thus, the temporal aspect of the "System Earth" through time. Prime sources of information are marine chemical sediments and biogenic minerals, such as micritic carbonates, inorganic cements, or biogenic calcites for C, O, Sr, sedimentary organic matter for C, sulfates, phosphorites, carbonates and sedimentary sulfides for S.

Isotope proxy signals of tectonic and biological evolution

The strontium isotopic composition of seawater is affected by inputs from the continental crust or the mantle. Thereby, variations in 87Sr/ 86Sr record varying fluxes resulting from continental weathering or the interaction between seawater and basalt at ocean ridge systems. The riverine input supplies radiogenic strontium from continental weathering to the ocean with a present day value at 0.712 ± 0.001. In contrast, a less radiogenic 87Sr/ 86Sr value of 0.704 ± 0.002 characterizes the mantle strontium input into the sea. Both sources of strontium respond to geotectonically driven processes, making the 87Sr/ 86Sr an ideal tracer of plate tectonics, uplift and erosion of mountains and continental weathering on time scales of 107 to 108 years. In addition, silicate weathering on the continents represents a sink for atmospheric carbon dioxide, linking the strontium isotopic composition of seawater ultimately also to the atmospheric evolution and to paleoclimate.
Long-term secular variations of the carbon isotopic composition of seawater record overall changes in net organic carbon burial. This, in turn, is governed by sedimentation rate, bottom water oxygenation, and/or bioproductivity. Again, geotectonic processes triggering sea level changes and/or sediment supply, climatic changes affecting ocean circulation patterns and nutrient supply, and biological processes (i.e. extinction/radiation events) regulating the organic carbon pool, control the carbon isotopic composition of the ocean/atmosphere system. Respective signatures can be detected in (bio-)chemically precipitated carbonate as well as in organic matter. Furthermore, biologically mediated processes (e.g. photosynthetic carbon fixation) are associated with substantial isotope effects. These are dependent and, thus, reflect environmental parameters.
The oxygen isotopic composition of seawater is controlled by 18O-exchange during reactions with the lithosphere and by climatically induced changes in the water cycle, i.e. glaciation, growth of ice sheets and variations in ocean temperature. Thereby, high-temperature circulation of seawater at ocean ridge systems results in an increase in 18O in the seawater, whereas low-temperature processes and weathering supplies 16O. These variations regulate delta18Oseawater on time scales of 107 to 108 years. Whether these processes effectively buffered the oxygen isotopic composition of Paleozoic seawater at 0 permil (SMOW), or whether the seawater composition became gradually enriched in 18O during Phanerozoic time is still subject of discussion. The second important parameter affecting the oxygen isotopic composition of seawater is ice volume / sea level / temperature. For the Pleistocene glaciation, e.g., the ice volume / sea level effect has been quantified at +0.1 permil per 10m sea level drop. Both, ice volume and sea level stand are linked to temperature, thus, recording a climatic signal on time scales of 105 to 106 years.
Variations within the global sulfur cycle are documented through the sulfur isotopic composition of seawater. The cycle is controlled by a redox balance which links it, among others, to the carbon cycle and the atmospheric oxygen budget. The oxidative part of the sulfur cycle is governed by continental weathering, riverine transport and evaporite deposition, while the reduced part is controlled, e.g., by bacterial sulfate reduction and fixation of "reduced" sulfur-bearing compounds in the sediment column. Again, diverse environmental parameters affect these latter (biologically mediated) processes which is expressed in the isotopic composition of reaction products. An additional parameter of global significance appears to be the high-temperature reaction of seawater at ocean ridge systems and the input of mantle sulfur. Again, the sulfur isotopic composition of seawater documents long-term geotectonic processes (i.e. uplift and erosion, mantle input) and aspects of bioevolution (e.g. bacterial sulfate reduction).

Correlation of isotope proxies - a unified signature of Earth System Evolution

Average values for temporal records of the strontium, oxygen, carbon and sulfur isotopic compositions of Phanerozoic seawater show strong correlations at any geologically reasonable time resolution, i.e. between 1 and 40 Ma. Statistical evaluation suggests that all systems are driven by three factors. The first one links the oxygen and strontium isotopic evolution (negative correlation) and the second one strontium and sulfur (positive correlation). Both are tentatively interpreted to reflect tectonic processes. The third factor links the carbon and sulfur isotopic evolution (negative correlation). It is interpreted as a biologically mediated redox linkage of both geochemical cycles. On geological time scales (i.e.= 1 Ma), the Earth operates in a unified exogenic system (litho-, hydro-, atmo-, biosphere) which is driven by tectonics via its control of (bio-)geochemical cycles.

2. SEDIMENTOLOGY

The lithologies and lithological successions of the Sinian to Middle Cambrian interval have been intensively worked out during the past 30 years by numerous "Regional Geological Teams" under the guidance of the Ministery of Geology and Mineral Resources (MGMR) and the Chinese Academy of Geological Sciences (CAGS) and many individual researchers, but the depositional analysis or respective basin-analytical framework for the Yangtze Platform has only begun to emerge. For current basin-historical models many questions remain unanswered. For example, evidence for a backarc basin in the southern to central part of the Yangtze Plate is as yet uncontested as is the "rift model". Even the conventional partitioning of the Yangtze Plate into "platform (Yangtze), slope (Jiangnan) and basin (Huyiang) facies regions" from NW to SE does not deliver a fully satisfactory model for the lithofacies distribution because "depressional" sedimentation occurs within platformal (carbonate-dominated) regions and large mound-like build-ups occur within the fine-clastic dominated basinal regimes.

Furthermore, the evidently abrupt vertical changes from f.e. the Nantuo Tillite to stromatolitic (dolomitized) mounds directly above (at the base of the Doushantuo Fm.) or between organic-rich black shales and carbonates, have not been explained. In many respects, modern analogues fail to give a fair model for the depositional history, whereas in other cases there are no apparent contradictions.

In general, there does not yet exist a consistent database for interregional (inter-Province) depositional or genetic basin history for the Sinian of the Yangtze Platform nor a reliable database for interregional stratigraphic correlation. Therefore, a careful stratigenetic analysis should be worked 3-year phase of this project.

3. PALEOBIOLOGY

The study of early life forms, of their evolution during the Proterozoic and of the coelomate Metazoa during the Early Cambrian still belongs to the "frontiers" of geoscientific research. Within a relatively short interval of ca. 50 Ma, between the Varanger Glaciation ("Snowball Earth") and the far-reaching Early Cambrian (Tommotian) black shale transgressions there occurred a complete "turnover" of the Proterozoic ecosystems and of the biosphere involving major extinction and radiation events for the acritarchs, vendobionts which possibly also affected the bacterial and protoctistan communities. Intensive paleontological research during the last decades failed to fully unravel the evolutionary and paleoecological patterns responsible for those tremendous changes within the terminal Neoproterozoic biosphere. The understanding of those complex interactions of the Bio-Earth System may be only expected to be achieved by an integrated multidisciplinary Earth Science investigation. Changes characterize the Precambrian-Cambrian transition, resulting in distinct variations of oceanic and atmospheric composition. They are reflected in the isotope signatures of carbon, oxygen, sulfur and strontium. These geochemical fingerprints frequently provide unequivocal evidence for specific processes affecting ocean/atmosphere chemistry, provided they have not been obliterated by secondary alteration. In addition, temporal records of isotopic compositions reflected, on one hand, to the distinctive facies distribution of the Yangtze Platform into a carbonate platform, a back-arc basin, island-arc and an open-oceanic basin and, on the other hand, to a favorable tectonic evolution after the consolidation of the Yangtze Plate during the terminal Neoproterozoic Jinning Orogeny. Based on this scenario Neoproterozoic sediments of different facies were recorded, which over extensive regions were later on only affected by burial diagenesis, weathering and fault displacements. This particular geologic history also facilitated the fairly good preservation of a comparatively rich and diverse fossil record.
During the past decades numerous exceptional fossil associations were discovered and analysed by several Chinese and international research teams from this critical time interval - as for instance the Late Proterozoic "Wengan Biota", which include presumed metazoan embryos and the Neoproterozoic "Miaohe Biota" documenting highly specialised Protoctista and fossils displaying morphological similarities to Ediacara-type fossils and, from the carbonate facies, first shell-forming organisms such as f.e. cloudinids or enigmatic carbonaceous vase-shaped fossils. From Lower Cambrian beds much greater and more diverse associations of organisms, especially distinct metazoan affinity forms, could be documented - as for instance three rich "Small Shelly Fossil" associations, Early Cambrian metazoan embryos (from Shaanxi Province), the spectacular Atdabanian "Chengjiang Fauna" which included preservation of soft-parts and sensational anatomical details as well as the early Middle Cambrian "Kaili-Biota" from the Balang-Lagerstätte in Guizhou Province. The above mentioned rich Cambrian fossil associations were secured from mostly shallow-marine sedimentary sequences, which probably contain numerous stratigraphic gaps and depositional discontinuities. It must, therefore, be assumed that also the fossil record is incomplete. Exceptional fossil records from deepwater successions were for the first time discovered by the TUB team during cooperative Sino-German DFG-sponsored field investigations in 1991 (DFG Projects Er 96/7-1 to 3 and Er 96/16-1 to 3). The faunas include Tommotian hydrothermal vent communities containing new arthropod and sponge associations which were connected to local syngenetic hydrothermal activities.
All up-to-date Chinese and international paleontological treatises have brought about considerable manifestations of the Proterozoic and Early Cambrian fossil associations of the Yangtze Platform, but on the other hand, these did not manage to go beyond solitary inventarisation of individual assemblages. The decoding of the phenomenon of the Cambrian radiation event requires, however, the total comprehension of the biodiversity of the terminal Neoproterozoic and its transition to the Early Cambrian; this could only be worked out by a team of specialists. A prerequisite for the exemplary documentation of the biodiversity for this time interval and for the Yangtze Platform would be the sorting and, respectively, the revision of the published material as well as the additional inclusion of material from uninvestigated facies regions. Once this task has been accomplished a comprehensive database for an integrated analysis of the Cambrian bioradiation event would be generated. Furthermore, chemofossils have not yet been included into paleontological investigations for this critical time interval and would open new perspectives for this project. The following selected groups of fossils are of special significance to the projected research of biodiversity for the critical time interval: Extinct Proterozoic fossils, such as vase-shaped shells, bacterial mats and sediment-grain interstitial ("meiofauna") as well as tube-shaped bacterial colonies, protoctista, acritarchs, stromatolithic build-ups, sponges incl. archaeocyathids, arthropods and "small shelly fossils". 

3. THE CAMBRIAN BIORADIATION EVENT

The Cambrian radiation event of the metazoa was since the 1970ties comprehensively included in the misnomer "Cambrian Explosion". This concept implies a cataclysmic sudden origin for at least most of the metazoan phyla during the basal Early Cambrian. This phenetic phenomenon of the "instant" appearance of fossilized remains or traces contradicts the current biological hypodigms on the evolution of higher life forms and still belongs to the great enigmas of the development of life on Earth.
Most up-to-date state of knowledge, especially of molecular biology, indicates that the evolutionary pathways of metazoans derive from deep into the Proterozoic ages. New impulses leading to the decoding of the earliest metazoan development based on paleontological data are to be found from critical remains of tiny vase-shaped shells, stacked tubular shells, various types of cloudinids and similar enzymatic or agglutinated mineralized "shells". Furthermore, new knowledge may be expected from a critical revision and analysis of these fossil remains, from a critical re-investigation of cryptic facies types and from the application of modern biogeochemical methods and techniques.
A full comprehension of the phenomenon of the Cambrian (and infra-Cambrian) bioradiation may only be attempted via a quantitative approach of this radiation and an intensive application of biodiversity research methods. This approach is essentially to be incorporated into an integrated geochemical, sedimentological and paleobiological database and research concept. Deduced from such an approach and based upon a reliable data network of biostratigraphic successions (backed up by radiometric dating) one has to approach a real-time sequence and timing of bioradiation events and their apomorphic relationships. References to the timing of the earliest Cambrian radiation may also be expected from a detailed analysis of the "Baupläne" and of their functional-morphogenetic evolutive stages. "Small Shelly Fossils" are of great importance in this context because these earliest skeletal bodyparts possessed a key role in the functional morphology of first automobile life forms during this transitional interval. A better biological assignation and improved functional interpretation will eventually lead to a better systematic classification and to the overcoming of the current "artificial" typological taxonomy for these forms. In this context one has also to consider the apparent contradictory "conservativism" and persistence of many of the recorded fossil groups as seen between the Lower Cambrian Chengjiang, lowermost Middle Cambrian Kaili and upper Middle Cambrian Burgess Lagerstätten. The slow pace or near-stasis of evolutionary processes after Chengjiang seems to document a strongly reduced rate of evolutionary processes during this long interval of time as compared to the pre-Chengjiang development. The post-Chengjiang bioradiation appears to have developed at a similar pace as non-vertebrate metazoa during the Late Phanerozoic. By means of a detailed analysis of the pre- and post-Chengjiang "Fossillagerstätten" in South China (including the newly discovered Zunyi-Lagerstätte as well as of Chengjiang and of the virtually non-analyzed Kaili-Lagerstätte) a quantitative approach must be taken - for the first time - to evaluate the evolutionary rates involved and at which point in time (and in connection with which type of environment) this evolutionary rate changed pace from fast to slow - or whatever occurred - during the Early to Middle Cambrian interval.
Due to its uniquely diverse record of both litho- and biofacies and its excellent fossil record the Yangtze Platform would be ideally suited for this binational cooperative scientific venture.

 

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