Phosphatic Fossils Research Articles

Phosphorus sources for phosphatic Cambrian carbonates

The fossilization of organic remains and shell material by calcium phosphate minerals provides an illuminating, but time-bounded, window into Ediacaran–Cambrian animal evolution. For reasons that remain unknown, phosphatic fossil preservation declined significantly through Cambrian Series 2. Here, we investigate the phosphorus (P) sources for phosphatic Cambrian carbonates, presenting sedimentological, petrographic, and geochemical data from the Cambrian Series 2–3 Thorntonia Limestone, Australia, some of the youngest Cambrian strata to display exceptional phosphatic preservation of small shelly fossils. We find that within Thorntonia sediments, phosphate was remobilized by organic decay and bacterial iron reduction, with subsequent reprecipitation largely as apatite within the interiors of small shelly fossils. We discuss the merits of bioclastic-derived, organic matter–bound, or iron-bound P as potential sources to these strata. Petrographic observations suggest that the dissolution of phosphatic skeletal material did not provide the P for fossil preservation. In contrast, high organic carbon contents imply significant organic fluxes of P to Thorntonia sediments. Sedimentology and iron-speciation data indicate that phosphorus enrichment occurred during times of expanded anoxic, ferruginous conditions in subsurface water masses, suggesting that phosphorus adsorption to iron minerals precipitating from the water column provided a second significant P source to Thorntonia sediments. Simple stoichiometric models suggest that, by themselves, neither organic carbon burial nor an iron shuttle can account for the observed phosphorus enrichment. Thus, we infer that both processes were necessary for the observed phosphorus enrichment and subsequent fossil preservation in the Thorntonia Limestone.

Testing the phylogenetic position of Cambrian pancrustacean larval fossils by coding ontogenetic stages.

The study of ontogeny as an integral part of understanding the pattern of evolution dates back over 200years, but only recently have ontogenetic data been explicitly incorporated into phylogenetic analyses. Pancrustaceans undergo radical ontogenetic changes. The spectacular upper Cambrian "Orsten" fauna preserves phosphatized fossil larvae, including putative crown-group pancrustaceans with amazingly complete developmental sequences. The putative presence and nature of adult stages remains a source of debate, causing spurious placements in a traditional morphological analysis. We introduce a new coding method where each semaphoront (discrete larval or adult stage) is considered an operational taxonomic unit. This avoids a priori assumptions of heterochrony. Characters and their states are defined to identify changes in morphology throughout ontogeny. Phylogenetic analyses of semaphoronts produced possible relationships of each Orsten fossil to the crown-group clade expected from morphology shared with extant larvae. Bredocaris is a member of the stem lineage of Thecostraca or (Thecostraca+Copepoda), and Yicaris and Rehbachiella are probably members of the stem lineage of Cephalocarida. These placements rely directly on comparisons between extant and fossil larval character states. The position of Phosphatocopina remains unresolved. This method may have broader applications to other phylogenetic problems which may rely on ontogenetically variable homology statements.

Paleoenvironmental conditions and strontium isotope stratigraphy in the Paleogene Gafsa Basin (Tunisia) deduced from geochemical analyses of phosphatic fossils

Fossil shark teeth and coprolites from three major phosphorite occurrences in the Gafsa Basin (southwestern Tunisia) were investigated for their geochemical compositions to improve local stratigraphy and to better assess paleoenvironmental conditions. 87Sr/86Sr isotope ratios of shark teeth from the Early Maastrichtian El Haria Formation and from the Early Eocene Métlaoui s.s. Formation yielded Sr isotope ages of 68 ± 1 and 47.9 ± 1.3 Ma, respectively, which accord with the expected stratigraphic positions of these sediments. Conversely, shark teeth from the Paleocene–Eocene Chouabine Formation have large variation in Sr isotope ratios even within individual layers. After statistical treatment and then elimination of certain outlier samples, three age-models are proposed and discussed. The most reasonable solution includes three subsequent Sr ages of 61.8 ± 2.2 Ma, 57.2 ± 1.8 and 54.6 ± 1.6 for layer IX, layers VIII–V and layers IV–0, respectively. Three scenarios are discussed for explanation of the presence of the outliers: (1) diagenesis, (2) re-working and (3) locally controlled seawater Sr isotope ratio. The most plausible account for the higher 87Sr/86Sr ratios relative to the global ocean in some fossils is enhanced intrabasinal re-working due to low sea level. Conversely, the sample with lower 87Sr/86Sr than the global seawater may link to diagenesis or to seawater influenced by weathering of Late Cretaceous marine carbonates, which latter is supported by model calculation as well. The εNd values of these fossils are very similar to those reported for Paleogene and Late Cretaceous Tethyan seawater and are compatible with the above interpretations. The relatively low oxygen isotope values in shark teeth from the topmost phosphate bed of the Chouabine Formation, together with the Sr isotope results, point toward recovering better connections with the open sea. These δ18O data reflect elevated ambient temperature, which may link to the Early Eocene Climatic Optimum.

A first report of Sphenothallus Hall, 1847 in the Cambrian of Variscan Europe

Ten specimens of two phosphatic fossils have been recently discovered in lower and middle portions of Middle Cambrian Jince Formation in the Czech Republic. They are attributed to the genus Sphenothallus Hall, 1847 and described as two separate species; comparatively small conchs are described as S. kozaki sp. nov., the much larger specimens characterized by its smooth and partly flexible organo-phosphatic walls of shell are determined as ?S. kordulei sp. nov. Sphenothallus is known to range from Cambrian to Permian and accommodates numerous species. However, its Cambrian distribution is considerably restricted. Generally rare specimens have been described from Lower to Middle Cambrian of Laurentia and from the Lower Cambrian of Gondwana and peri-Gondwana. The new record of Sphenothallus from the Jince Biota represents a notable extension of their geographic range.

Silicified tubular microfossils from the Upper Doushantuo Formation (Ediacaran) in the Yangtze Gorges area, South China

The ediacaran Doushantuo Formation in the Yangtze Gorges area (Fig. 1.2) contains abundant silicified cyanobacterial coccoids and filaments (Y. Zhang et al., 1998), acanthomorphic acritarchs (Zhou et al., 2007), multicellular algae (Xiao, 2004), and possible animal embryos (L. Yin et al., 2007). These silicified fossils are taxonomically similar to the phosphatized fossils in the Doushantuo Formation of the Weng'an area, South China (Y. Zhang et al., 1998). However, the Weng'an assemblage contains tubular microfossils that have not been previously documented in the Yangtze Gorges area. Here we report the occurrence of secondarily silicified tubular microfossils—Sinocyclocyclicus guizhouensis(Xue et al., 1992) andYangtzitubus semiteresnew genus and species—from lenticular cherts in the upper Doushantuo Formation in the Yangtze Gorges area. Of the two named taxa,Sinocyclocyclicus guizhouensiswas previously known from the Weng'an area (Liu et al., 2008). The new data extend the geographic, taphonomic, and environmental distribution of Doushantuo tubular microfossils. A fuller documentation of the Doushantuo biodiversity is also important to the evaluation of possible taphonomic or environmental biases among the three exceptional taphonomic windows—carbonaceous compression (Xiao et al., 2002), phosphatization (Xiao and Knoll, 1999), and silicification (Y. Zhang et al., 1998)—in Doushantuo black shales, phosphorites, and cherts, respectively.

Constraints on Miocene oceanography and climate in the Western and Central Paratethys: O-, Sr-, and Nd-isotope compositions of marine fish and mammal remains

The Paratethys evolved as a marginal sea during the Alpine–Himalayan orogeny in the Oligo-Miocene. Sediments from the northern Alpine Molasse Basin, the Vienna, and the Pannonian Basins located in the western and central part of the Paratethys thus provide unique information on regional changes in climate and oceanography during a period of active Alpine uplift. Oxygen isotope compositions of well-preserved phosphatic fossils recovered from the sediments support deposition under sub-tropical to warm-temperate climate with water temperatures of 14 to 28 °C for the Miocene. δ 18O values of fossil shark teeth are similar to those reported for other Miocene marine sections and, using the best available estimates of their biostratigraphic age, show a variation until the end of the Badenian similar to that reported for composite global record. The 87Sr/ 86Sr isotope ratios of the fossils follow the global Miocene seawater trend, albeit with a much larger scatter. The deviations of 87Sr/ 86Sr in the samples from the well-constrained seawater curve are interpreted as due to local input of terrestrially-derived Sr. Contribution of local sources is also reflected in the ε Nd values, consistent with input from ancient crystalline rocks (e.g., Bohemian Massif) and/or Mesozoic sediments with ε Nd < − 9. On the other hand, there is evidence for input from areas with Neogene volcanism as suggested by samples with elevated ε Nd values > − 7. Excluding samples showing local influence on the water column, an average ε Nd value of − 7.9 ± 0.5 may be inferred for the Miocene Paratethys. This value is indistinguishable from the ε Nd value of the contemporaneous Indian Ocean, supporting a dominant role of this ocean in the Western and Central Paratethys.

Microborings in Early Cambrian phosphatic and phosphatized fossils

A small proportion of phosphatic and phosphatized fossils, mostly microfossils, extracted from Lower Cambrian (Qiongzhusian) lime mudstones of deeper water aspect, belonging to the Yu'anshan and Shuijingtuo formations of South China, is perforated by microborings. These microborings are present in bradoriid and phosphatocopine arthropod carapaces, lingulid brachiopod valves, Microdictyon plates and tommotiid sclerites. Their absence in co-occurring phosphatized eodiscid trilobite exoskeletons and palaeoscolecid worm trunk fragments indicates a substrate specificity that suggests the boring microorganism was heterotrophic, extracting particular residual organic compounds present in only certain bioclast types. Microborings occur as meandering tunnels and grooves on bioclast surfaces, and most are 10–20 µm wide and circular in cross-section. The euendoliths were thus able to live partly exposed as well as within the substrate. Tunnel and groove walls bear a distinct longitudinal sculpture of straight striae separated by cuspate ridges 1–2 µm apart that parallel the microboring, never twisting. The microborings accord with the ichnotaxon Microptychoites fuquanensis Dong in Dong et al. (Dong, Y., Ji, Q., Wang, S., 1984. The discovery of microscopic trace fossils in the Sinian Doushantuo Formation in southwestern China. Scientia Geologica Sinica 346–347 [in Chinese]). The fluted sculpture appears to have no modern analogue, but may have arisen by localized secretions at the tip of a bundle of filaments. This kind of microboring had been previously reported from phosphatic substrates of Ediacaran, earliest Cambrian, Middle Cambrian and probably Early Devonian age, but appears to have no Recent counterpart.

Preservation and fluorescence of the microfossils from Neoproterozoic Doushantuo formation

The phosphatized microfossils from Doushantuo Formation, Southeast China show us the biodiversity about 600 million years ago, which is a unique window for the evolution of the early life on earth. However, the process of phosphatic fossilization in detail still remains unknown. Here we report our study on the preservation state of the fossils by using confocal laser scanning microscopy. We found that fluorescent signal of the fossil could reflect the preservation state when compared with the transmission light microscopy. First, we found the fluorescent signal of the decayed cells of the fossil was weaker than that of the nondecayed part. Second, we found that the three-dimensional reconstruction of the fluorescent signals could help to judge the degree of mineralization of the fossil cells, compared with the observation by transmission light microscope. Third, we found that almost all of the fossil specimens we observed could fluoresce more or less when excited by laser light. Therefore, the fluorescent microscopy provides a useful method for the study of the preservation state of the phosphatic fossil cells.

AN EARLY CAMBRIAN ORGANOPHOSPHATIC BRACHIOPOD WITH CALCITIC GRANULES

Abstract: The linguliform brachiopod Eoobolus from the Early Cambrian Mural Formation (Jasper National Park, Canadian Rocky Mountains) exhibits various calcitic features in its otherwise apatitic shell. It is argued here that the decomposition of the organic matter within the shell led to a microenvironment similar to those resulting in the phosphatization of soft tissues. This diagenetic regime encouraged the initial precipitation of apatite cements followed by calcite cements. By fully coating primary structures early apatite cements separate primary structures from the later precipitation of calcite cement. Round calcareous grains, about 3 µm in size, that occur in the centre of apatite botryoids must therefore represent original components of the shell. The equivalent pits of such calcareous granules are seen in the larval shells of many Palaeozoic linguliform brachiopods. This suggests that mixed organophosphatic‐calcareous shells were relatively common at that time but that they have been overlooked owing to the obliteration of original calcareous structures by traditional acid preparation methods for the extraction of phosphatic fossils. The Eoobolus shell structure is intermediate between purely organophosphatic and calcitic shells. Although one such genus is not sufficient to reconstruct the ancestral composition of the brachiopod shell, it provides a means of recognizing other transitional forms that are needed to understand fully the shift in shell mineralogy.

The Lower Cambrian brachiopod Kyrshabaktella and associated shelly fossils from the Harkless Formation, southern Nevada

A fauna of brachiopods and small shelly fossils from the Lower Cambrian Harkless Formation of Esmeraldina County in southern Nevada is described. The brachiopod Kyrshabaktella sp. provides the first unequivocal record of lingulids in the Lower Cambrian of the Great Basin. The shells of Kyrshabaktella sp. are fragmentary, but otherwise well preserved and an acrotretid-like columnar shell structure is demonstrated. The phosphatic tubular fossil Hyolithellus insolitus is described from North America for the first time and Sphenothallus sp. provides the oldest record of this problematic genus in Laurentian strata. Other faunal elements include two additional linguliform brachiopods, echinoderm ossicles and sponge spicules.

EARLY CAMBRIAN METAZOAN EGGS, EMBRYOS, AND PHOSPHATIC MICROFOSSILS FROM NORTHWESTERN CANADA

Three-dimensionally phosphatized, spherical fossils, interpreted as metazoan eggs and embryos on the basis of taphonomic features and cleavage patterns, are reported for the first time from the Cambrian of North America. These microfossils occur with a phosphatized biota of skeletonized fossils, including specimens indicative of the earliest Cambrian Anabarites–Protohertzina Zone in the Wernecke Mountains of eastern Yukon Territory, northwestern Canada. They range in size from 0.25 mm to more than 1.0 mm in diameter and can be referred to two genera, Olivooides Qian, 1977 and Archaeooides Qian, 1977. The North American discovery extends the biogeographic range of earliest Cambrian eggs and embryos from coeval successions in China and Siberia, suggesting a wide geographic distribution of these taxa, and emphasizes the crucial role of local environmental and taphonomic conditions in preserving this phosphatic window into the record of early animal evolution. In addition to previously reported taxa, the phosphatized biota also include indeterminate spheroids, fused clusters of Protohertzina siciformis Missarzhevsky, 1973, the enigmatic rodlike fossil Zhejiangorhabdion comptum Yue and Zhao, 1993, phosphatized fossils, including Paradoxiconus typicalis Qian et al., 2001, protoconularid Carinachites sp., and phosphatic tubes assigned to Hyolithellus cf. H. isiticus Missarzhevsky, 1969, cf. Pseudorthotheca sp., and ?Rugatotheca sp.

Precambrian animal life: Taphonomy of phosphatized metazoan embryos from southwest China

Phosphatized fossils from the Neoproterozoic Doushantuo Formation have provided valuable insight into the early evolution of metazoans, but the preservation of these spectacular fossils is not yet fully understood. This research begins to address this issue by performing a detailed specimen-based taphonomic analysis of the Doushantuo Formation phosphatized metazoan embryos. A total of 206 embryos in 65 thin sections from the Weng'an Phosphorite Member of the Doushantuo Formation were examined and their levels of pre-phosphatization decay estimated. The data produced from this examination reveal a strong taphonomic bias toward earlier (2-cell and 4-cell) cleavage stages, which tend to be well-preserved, and away from later (8-cell and 16-cell) cleavage stages, which tend to exhibit evidence for slight to intense levels of organic decay. In addition, the natural abundances of these embryos tend to decrease with advancement in cleavage stage, and no evidence of more advanced (beyond 16-cell) cleavage stages or eventual adult forms were found in this study. One possible explanation for this taphonomic bias toward early cleavage stages is that later cleavage stages and adult forms were more physically delicate, allowing them to be more easily damaged during burial and reworking, allowing for more rapid decay. The spectacular preservation of these embryos was probably aided by their likely internal enrichment in phosphate-rich yolk, which would have caused their internal dissolved phosphate levels to reach critical levels with only miniscule organic decay, thereby hastening phosphatization. If internal sources of phosphate did indeed play a role in the phosphatization of these embryos, it may explain their prolific abundance in these rocks compared to other phosphatized fossils as well as indicating that metazoans lacking such internal phosphate sources were likely much more difficult to preserve. The phosphatic fossils of the Doushantuo Formation, therefore, provide an indispensable, yet restricted, window into Neoproterozoic life and metazoan origins.

First Middle Ordovician biota from southern New Brunswick: stratigraphic and tectonic implications for the evolution of the Avalon continent

A limestone boulder in the Triassic Lepreau Formation near Saint John, New Brunswick, has yielded the first diverse marine fauna from the sub-Caradoc Ordovician of the western Avalon continent. This fauna includes the first Arenig conodonts recovered from Avalon and represents an unexposed interval in southern New Brunswick. Association of the conodonts Drepanoistodus and Baltoniodus and the trilobites Neseuretus, Nileus, and Stapeleyella emphasizes the faunal dissimilarity of Avalon and Laurentia through the late Middle Ordovician. Extension of the ranges of Neseuretus cf. Neseuretus parvifrons and Stapeleyella from Britain into New Brunswick further emphasizes that "eastern" and "western" Avalon were confluent parts of a unified, insular Avalon continent that originated in the latest Precambrian. This fauna correlates with the lower Amorphognathus (Lenodus) variabilis Zone (Kundan Stage) of Baltica and the terminal Arenig (upper Middle Ordovician; lower Darriwilian Stage) of Avalonian Britain. Available evidence suggests that an Arenig cover sequence with local shallow-water hematitic iron ore, quartz arenite, and rare limestone extended across the Avalonian marginal and inner platforms from eastern Newfoundland to the Boston, Massachusetts, region. This "western" Avalonian Arenig shows the greatest similarity with the Arenig of the Welsh Borderlands. Phosphatic fossils from the boulder have a thermal alteration index much lower than that of nearby lower Paleozoic outcrops and suggest derivation of the boulder from a weakly heated Avalonian succession brought into the Bay of Fundy region by post-Ordovician transcurrent faulting.

Early Cambrian lobopodian sclerites and associated fossils from Kazakhstan

A low diversity fossil assemblage dominated by Mongolitubulus spines, from the Early Cambrian Geres Member of the Shabakhty Formation at Koksu, Malyi Karatau, Kazakhstan, enables identification of its sclerite variability within the scleritome. No other sclerotised structures could be matched with the spines, indicating that these were the only sclerotised part of the body and were periodically shed. The prominent spines of Mongolitubulus have a scale–like external ornamentation and fibrous internal structure. Possibly they armed the body of a lobopodian similar to Xenusion. The Mongolitubulus spines belong to a series of Cambrian phosphatic fossils, the other end members of which are sclerites of Microdictyon, the second most abundant component of the Koksu assemblage. The latter superficially resemble schizochroal trilobite eyes, but in life covered the dorso–lateral sides of the body segments, as is evident from complete specimens from the Chinese Chengjiang locality. A pair of sclerites of Microdictyon, representing uncompleted exuviation, from Koksu show that each hole originally contained a non–phosphatised lenticular body. This makes a compound eye nature of the Microdictyon sclerites likely, and even their homology with arthropod eyes cannot be excluded.

Nd isotope composition of early Cambrian discrete basins

A Nd isotope map of early Cambrian epeiric basins has been inferred from the Nd isotopic signature recorded in phosphatic Small Shelly Fossils. The most radiogenic εNd(t) values characterize water reservoirs along the Avalonian and Cadomian belts, while εNd(t) values of −10 to −20 were obtained in Laurentia and East Gondwanan Australia and China. Such a distribution of Nd isotope signatures results from the different provenance of early Cambrian epeiric seas: juvenile magmatic arcs and/or cordilleran for Mongolia, Siberia, Iberia and adjacent terranes, and cratonic sources for Laurentia and East Gondwana. Biogenic apatite of Small Shelly Fossils may be a useful tool for mapping of Nd isotope composition and documenting water mass exchange between discrete basins.

Weird things from the Middle Ordovician of North America interpreted as conulariid fragments

Small phosphatic fossils recovered from acid residues of the Galena Group Middle (Ordovician) of Wisconsin were recently described by Clark et al. (1999) as weird things. Here, we report that specimens identified by those authors as Thing 3 and Thing 6 are fragments of conulariids belonging to two species that occur widely through Middle Ordovician strata of eastern North America. Similarly disintegrated, conspecific specimens from the Trenton Limestone of northwestern Indiana, and articulated, conspecific specimens from Ohio and New York, are introduced for comparison.

WEIRD THINGS FROM THE MIDDLE ORDOVICIAN OF NORTH AMERICA INTERPRETED AS CONULARIID FRAGMENTS

Small phosphatic fossils recovered from acid residues of the Galena Group Middle (Ordovician) of Wisconsin were recently described by Clark et al. (1999) as weird things. Here, we report that specimens identified by those authors as Thing 3 and Thing 6 are fragments of conulariids belonging to two species that occur widely through Middle Ordovician strata of eastern North America. Similarly disintegrated, conspecific specimens from the Trenton Limestone of northwestern Indiana, and articulated, conspecific specimens from Ohio and New York, are introduced for comparison.

The optimal acetate buffered acetic acid technique for extracting phosphatic fossils

When extracting or cleaning phosphatic fossils using acetic acid, the solutions must be buffered with calcium acetate to a pH greater than 3.6 for conodont and many fish taxa, and to a slightly greater pH for some conulariid, shark, and some fish taxa. Diagrams of the changes in pH and density during dissolution, rate of dissolution, and productivity per liter of acid provide a means for selecting the economically optimal process, monitoring the progress, and adjusting the composition of the solution when necessary.

Fossil preservation in the Neoproterozoic Doushantuo phosphorite Lagerstatte, South China.

Phosphorites of the late Neoproterozoic Doushantuo Formation exposed in the vicinity of Weng'an, Guizhou Province, and Chadian, Shaanxi Province, South China, contain exceptionally well-preserved algal thalli, acritarchs, and globular microfossils interpreted as animal embryos. Combined optical microscopic and SEM observations provide insights into the taphonomy of phosphatized fossils. Algal cells and tissues are variably resistant to decay, and within preserved populations permineralization began at varying stages of degradation. In consequence, there is a spectrum of quality in cellular preservation. Algal cell walls, acritarch vesicles, and embryo envelopes are commonly encrusted by an isopachous rim of apatite, with cell interiors filled by collophane and later diagenetic dolomite. In contrast, blastomere surfaces of animal embryos are encrusted primarily by minute phosphatic spherules and filaments, possibly reflecting an immediately postmortem infestation of bacteria that provided nucleation sites for phosphate crystal growth. Thus, the same processes that gave rise to Phanerozoic phosphatized Lagerstatten--phosphatic encrustation, and impregnation, probably mediated by microbial activity--effected soft-tissue preservation in the Doushantuo Lagerstatte. It remains unclear how phosphatic ions and organic macromolecules interact at the molecular level and to what extent specific microbial metabolisms or microenvironmental conditions control the phosphatization of soft tissues. New observations of phosphatized Doushantuo fossils include: a second locality (Chadian) for Wengania globosa, interpreted as an algal thallus and previously known only from Weng'an; microtunnels in Weng'an phosphorites interpreted as pyrite trails; and new taxa described from Weng'an: Meghystrichosphaeridium reticulatum (acritarch), Sarcinophycus radiatus (algal thallus), and one unnamed problematic form.

Variations in Sr and C isotopes and Ce anomalies in successions from China: evidence for the oxygenation of Neoproterozoic seawater?

Samples of marine carbonates, phosphatic fossils, phosphorites and manganese deposits were systematically collected from the Neoproterozoic Sinian System in the Yangtze Region, South China, and data of C and Sr isotopes and Ce anom values were obtained and investigated. These data, combined with Nd isotopic data (Yang et al. 1997a, Chem. Geol. 135, 127–133; Yang et al. 1997b, Chinese Sci. Bull. 42, 2072–2075), provide a detailed record of isotopes and Ce anomaly variations in Chinese seawater during the Sinian and early Cambrian periods, and show significant changes: δ 13C: −4∼+6‰; ϵ Nd (T): −4.5∼−7.6; 87Sr/ 86Sr: 0.7077∼0.7087; Ce anom: +0.20∼−0.65 , respectively. The changes exceed or match the largest in seawater throughout the Phanerozoic. The generally high values of δ 13 C during the Sinian may reflect an increase in the C org burial rate. It, in turn, may be attributed to high productivity at the surface of the ocean and a rise in the sedimentary rate, which resulted from enhanced tectonism and a global temperature rise. A trend of declining Ce anom values may also reflect an increase in organic productivity at the ocean surface and a rise in O 2 concentration in the atmosphere and the upper oceans. The most important point revealed by the Nd and Sr isotopic studies is that the strongest and most widespread tectonism took place towards the end of the Proterozoic. The tectonism caused a paleogeographic reordering, rapid rise in the global sedimentary rate and great changes in ocean chemistry, and ultimately led to the variations in C, Sr and Nd isotopes and Ce anomaly in the Sinian seawater.