Ruyang Group Research Articles

Oxidizing atmosphere and life on land during the late Paleoproterozoic outset of the “boring billion”

The so called “boring billion” (1800–800 Ma) of Late Paleoproterozoic and early Mesoproterozoic time can now be reassessed from the evidence of diverse paleosols in the Ruyang Group (1749–1561 Ma) in Henan Province, China. Widespread marine sulfidic facies is the reason for the term “boring billion”, but terrestrial facies and paleosols were far from uniform or anoxic at that time. The Ruyang Group in Henan has 12 distinct kinds of paleosols, with 5 distinct pedotypes in alluvial fan facies of the Bingmagou Formation, 6 in fluvial facies of the Yunmengshan Formation, 3 in coastal plain facies of the Baicaoping Formation, and 4 in the coastal to intertidal Beidajian Formation. These paleosols are evidence of hyperarid climate that was cool temperate despite proximity to the paleoequator. These ancient soils were alive with iron- and manganese-fixing bacteria that created desert varnish and vesicular structure, as well as sulfur-oxidizing bacteria creating desert roses of gypsum. The paleosols may also have supported cyanobacteria, algae and fungi, known from palynomorphs in shales of the Baicaoping and Beidajian formations. Consumption of alkali and alkaline earth elements in the paleosols are evidence of 1700–20,600 ppm (6–73 times preindustrial level or PAL) of atmospheric CO2, consistent with the amount needed for a greenhouse effect to offset a faint young sun. A comparable model based on iron and manganese oxidation in the paleosols indicates 318–16,623 ppm (0.002–0.08 PAL) O2. This was enough to support animals (0.005 PAL O2), considering that these are minimal estimates of O2 diluted by some soil respiration. Animals had not yet evolved, but that evolutionary process may not have been limited by atmospheric composition.

Raman spectroscopy and structural heterogeneity of carbonaceous material in Proterozoic organic-walled microfossils in the North China Craton

Raman spectroscopy is a minimally intrusive and minimally destructive technique that has played an important role in analyzing Precambrian carbonaceous microfossils and microstructures. Previous studies have shown that heterogeneities in structural order of carbonaceous material (CM) as revealed by Raman spectroscopy can be preserved in Proterozoic silicified cyanobacterial fossils. However, such heterogeneities have not been documented in Proterozoic eukaryotic microfossils preserved as carbonaceous compressions. In this study, we used Raman spectroscopy to investigate the structural characteristics of organic-walled microfossils, including eukaryotes preserved as carbonaceous compressions, from the late Paleoproterozoic Ruyang Group and the early Neoproterozoic (Tonian) Liulaobei Formation in the North China Craton. Raman geothermometers indicate that CM experienced low-grade metamorphism with apparent peak metamorphic temperatures of ~200 °C for both the Ruyang and Liulaobei microfossils. Heterogeneities in structural characteristics of CM in eukaryotic microfossils were found among different subcellular structures of Shuiyousphaeridium macroreticulatum and among different taxa from the same stratigraphic horizon. We suggest that these heterogeneities can be attributed to differences in precursor organic compounds; thus, the importance of organic precursors should be considered in CM Raman geothermometry studies, especially in environments where heating events occurred quickly. The Raman data presented here are also consistent with hypotheses that the Ruyang microfossils Dictyosphaera delicata and S. macroreticulatum are biologically conspecific taxa with their vesicle walls having similar CM Raman features, and that the Liulaobei microfossils Leiosphaeridia jacutica and L. tenuissima are distinct taxa despite their similarities in morphologies other than vesicle wall thickness. Although more data are needed to verify the consistency of interspecies, intraspecies, and intraspecimen variability, this study indicates that Raman spectroscopy may have the potential to provide an independent test of early eukaryote taxonomy, which has been traditionally based only on morphological features, and to reveal heterogeneities of CM of early eukaryotic organisms.

Tectono-sedimentary evolution of the Mesoproterozoic basins in the southern Yan-Liao and Mianchi-Queshan areas: insights from stratigraphic pattern and detrital zircon geochronology

The widespread Mesoproterozoic successions around the world have recorded the breakup of the ancient supercontinent Columbia. In the North China Craton (NCC), the Mesoproterozoic basins in the Yan-Liao and southern NCC are the important evidence to study the nature and evolution of the Mesoproterozoic basins. In this study, we scrutinized the stratigraphic pattern and detrital zircon U–Pb geochronology in the southern Yan-Liao and Mianchi-Queshan areas in the southern NCC, to investigate the evolutionary relationship between the Mesoproterozoic basins in the north and south of NCC. Detrital zircons from the Mesoproterozoic sequence in the southern Yan-Liao areas showed monotonous source with age peak at ca. 2500 Ma, corresponding well with the ages of the Neoarchean complex in the central NCC. However, the Mesoproterozoic sequence in the Mianchi-Queshan areas, which is represented by the Ruyang Group, exhibited significantly different characteristics with influx of much younger zircons. The southern Yan-Liao and Mianchi-Queshan areas showed distinct similarity in the stratigraphic pattern, reflected by the Mesoproterozoic successions in these two areas being both bracketed by two sequence boundaries and further divided into two sequences under a uniform sea-level change. The Mesoproterozoic strata in these two areas probably possessed a correlative relationship in the stratigraphic patterns and basin evolutionary history.

Geochemistry and detrital zircon records of the Ruyang-Luoyu groups, southern North China Craton: Provenance, crustal evolution and Paleo–Mesoproterozoic tectonic implications

Paleo- to Mesoproterozoic sedimentary rocks in the southern margin of the North China Craton (NCC) are represented by the Ruyang and Luoyu groups. We studied the sedimentary rocks from the Yunmengshan and Beidajian formations of the Ruyang Group and the Cuizhuang and Sanjiaotang formations of the Luoyu Group. Detrital zircon grains from these formations have U–Pb age populations of 3.64–3.31 ​Ga, 2.96–2.86 ​Ga, 2.72–2.59 ​Ga, 2.56–2.47 ​Ga, 2.45–2.0 ​Ga, 1.99–1.85 ​Ga and 1.84–1.65 ​Ga. The geochemical features of the sedimentary rocks suggest that some of the sediments were sourced from intermediate to felsic magmatic rocks. The age groups of the detrital zircon are roughly consistent with the tectono-thermal events in the southern margin of the NCC. The Hf isotopic compositions of detrital zircon from the sedimentary rocks in Ruyang and Luoyu groups suggest that significant crustal growth and reworking of the NCC took place during the Neoarchean and early- to mid-Paleoproterozoic, while crustal reworking at the Paleoarchean and late-Paleoproterozoic, and crustal growth at the Mesoarchean. We suggest the depositional times of the Ruyang Group and Luoyu Group are constrained to no older than 1.75–1.7 ​Ga and 1.7–1.65 ​Ga, respectively. Formation of late-Paleoproterozoic basins related to the strike slip and extrusion tectonics that cross-cut the NCC during the late Paleoproterozoic (<1.75 ​Ga), and the late Paleoproterozoic sedimentation once isochronous developed in the southern margin of the NCC through the Taihang region of the interior NCC and linked the Yanshan–Liaoxi regions of the northern NCC.

Sedimentary environment and depositional evolution of the Mesoproterozoic Bingmagou Formation on the southern margin of the North China Craton

The Precambrian sedimentary strata on the southern margin of the North China Craton are well developed and widely exposed, making the region ideal for the study of depositional processes. However, because of the length of the depositional history and the lack of biogenic criteria, interpretations of the sedimentary environments of the Precambrian strata are often based on the tectonic background, geographical environment, rock type and sedimentary structures, resulting in controversies in the literature. In this study of the Bingmagou Formation in the Ruyang Group on the southern margin of the North China Craton, analysis of petrologic features, palaeocurrents and sedimentary facies is combined with regional correlation of relevant strata and the reconstruction of ancient landforms to explain the depositional environments and environmental transitions. Dominated by marine deposits on the southern margin of the North China Craton, the sedimentary strata of the Ruyang Group unconformably overlie the Archean crystalline basement or Proterozoic Xionger Group. As the lowermost unit of the Ruyang Group, the Bingmagou Formation, which was depositionally controlled by topography and faults and received abundant detrital material, is a highly distinctive set of sedimentary strata and represents an environmental transition from alluvial fan to sandy coast.

Diversity of organic-walled microfossils from the early Mesoproterozoic Ruyang Group, North China Craton – A window into the early eukaryote evolution

Mesoproterozoic Era was an important time for initial diversification of eukaryotic clades and appearance of the earliest complex cell morphologies. Shales and siltstones of the Ruyang Group, Shanxi Province, North China Craton, record such diverse organic-walled microfossils, in addition to novel morphotypes. Recently, the depositional age of this succession has been constrained to 1744±22 to 1411±27Ma via zircon U-Pb and Hf isotopic dating. This dating extended back the time of the first appearance of complex eukaryotic characters (e.g. processes, sculpture, layered wall structure) in the fossil record. We have conducted a biostratigraphic investigation of the samples throughout the fossiliferous Ruyang Group to provide an estimate of the relative early eukaryotic diversity in the Mesoproterozoic. Light- and scanning electron microscope observations have documented 26 species, including several that are reported for the first time, and some that were previously known only from younger, Neoproterozoic strata. Diversity was high in the upper Baicaoping Formation, declined in the middle and reached its peak in the upper Beidajian Formation. Novel morphologies among the unicellular Ruyang biota included a variety of processes, from tube-like extensions to hirsute spines, vesicles with velutinous outer membranes, as well as numerous specimens with internal bodies of varying sizes. We have also recorded the globally distributed Mesoproterozoic taxa Dictyosphaera and Tappania, and several morphotypes of Shuiyousphaeridium. Key characters displayed by the Ruyang biota are consistent with reproductive structures (especially cysts) like those among modern protists. These microfossils provided an additional evidence for the ongoing first radiation of Eukarya by at least 1400Ma.

A biomechanical analysis of the early eukaryotic fossil Valeria and new occurrence of organic-walled microfossils from the Paleo-Mesoproterozoic Ruyang Group

The Paleo-Mesoproterozoic Ruyang Group of North China hosts early eukaryotic fossils such as Dictyosphaera, Shuiyousphaeridium, and Valeria, and thus offers valuable insights into the early evolution of single-celled eukaryotic life. In this paper, we report several additional forms of organic-walled microfossils from the Ruyang Group, including Plicatidium latum, Spiromorpha sp., and an unnamed form. V. lophostriata from the Ruyang Group is investigated using transmitted light microscopy, scanning electron microscopy, transmission electron microscopy, and biomechanical analysis. V. lophostriata is reconstructed as a spherical vesicle with two hemispherical halves bearing concentric striations resembling latitudinal circles. The formation of striations could be explained using the Belousov-Zhabotinsky reaction model or the Turing reaction-diffusion model. A biomechanical analysis using the thin-walled spherical pressure vessel model suggests that the concentric striations of V. lophostriata may have functioned as a mechanism to guide biologically programmed excystment through medial split. Our analysis provides essential paleontological data to better understand the functional biology and life cycles of early eukaryotes such as Valeria.

Affinity, life cycle, and intracellular complexity of organic-walled microfossils from the Mesoproterozoic of Shanxi, China

AbstractLight microscope and scanning electron microscope observations on new material of unicellular microfossilsDictyosphaera macroreticulataandShuiyousphaeridium macroreticulatum,from the Mesoproterozoic Ruyang Group in China, provide insights into the microorganisms’ biological affinity, life cycle and cellular complexity.Gigantosphaeridium fibratumn. gen. et sp., is described and is one of the largest Mesoproterozoic microfossils recorded. Phenotypic characters of vesicle ornamentation and excystment structures, properties of resistance and cell wall structure inDictyosphaeraandShuiyousphaeridiumare all diagnostic of microalgal cysts. The wide size ranges of the various morphotypes indicate growth phases compatible with the development of reproductive cysts. Conspecific biologically, each morphotype represents an asexual (resting cyst) or sexual (zygotic cyst) stage in the life cycle, respectively. We reconstruct this hypothetical life cycle and infer that the organism demonstrates a reproductive strategy of alternation of heteromorphic generations. Similarly inGigantosphaeridium,a metabolically expensive vesicle with processes suggests its protective role as a zygotic cyst. In combination with all these characters and from the resemblance to extant green algae, we propose the placement of these ancient microorganisms in the stem group of Chloroplastida (Viridiplantae). A cell wall composed of primary and secondary layers inDictyosphaeraandShuiyouisphaeridiumrequired a high cellular complexity for their synthesis and the presence of an endomembrane system and the Golgi apparatus. The plastid was also present, accepting the organism was photosynthetic. The biota reveals a high degree of morphological and cell structural complexity, and provides an insight into ongoing eukaryotic evolution and the development of complex life cycles with sexual reproduction by 1200 Ma.

Depositional age, provenance and tectonic setting of the Proterozoic Ruyang Group, southern margin of the North China Craton

Late Paleoproterozoic rifting and accompanying magmatism and sedimentation, which occurred widely in the North China Craton, are interpreted to be related to the breakup of the supercontinent Columbia. The Ruyang Group, overlying the Xiong’er Group in the southern margin of the craton, is a typical fluvial-marine sedimentary sequence mainly composed of sandstone with minor shale and dolostone. Sandstones from the Ruyang Group exhibit high contents of SiO2 (86.8–98.7wt.%) but relatively low contents of Al2O3, K2O, Na2O, TiO2 and MgO, typical of mature siliceous clastic rocks. Trace elements of these rocks indicate that the sequence was deposited in a passive continental margin environment and that the sedimentary detritus was derived from a Paleoproterozoic silicic-intermediate source, similar to other Paleo-Mesoproterozoic sedimentary sequences in the region.Detrital zircons from three sandstone samples of the Ruyang Group yield 207Pb/206Pb ages ranging from 1.70Ga to 2.70Ga with two pronounced peaks at ca. 2.10Ga and 1.86Ga. A weighted mean age at 1744±22Ma from nine young zircon ages between 1.80Ga and 1.70Ga can constrain the maximum depositional age of the Ruyang Group. Most detrital zircons exhibit negative ɛHf(t) values ranging from −15.6 to 0 and old TDMC ages ranging from 2.50Ga to 3.60Ga, implying reworking of Archean crust. A close match between the U–Pb ages and TDMC(Hf) ages, as well as the positive ɛHf(t) values for some detrital zircons, indicate a contribution of juvenile materials. The detrital zircon grains have TDMC(Hf) ages clustering between 3.00Ga and 2.60Ga with a peak at around 2.80–2.70Ga, indicating a major period of crustal growth at this time.

The nature and origin of nucleus‐like intracellular inclusions in Paleoproterozoic eukaryote microfossils

The well-known debate on the nature and origin of intracellular inclusions (ICIs) in silicified microfossils from the early Neoproterozoic Bitter Springs Formation has recently been revived by reports of possible fossilized nuclei in phosphatized animal embryo-like fossils from the Ediacaran Doushantuo Formation of South China. The revisitation of this discussion prompted a critical and comprehensive investigation of ICIs in some of the oldest indisputable eukaryote microfossils-the ornamented acritarchs Dictyosphaera delicata and Shuiyousphaeridium macroreticulatum from the Paleoproterozoic Ruyang Group of North China-using a suite of characterization approaches: scanning electron microscopy (SEM), transmission electron microscopy (TEM), and focused ion beam scanning electron microscopy (FIB-SEM). Although the Ruyang acritarchs must have had nuclei when alive, our data suggest that their ICIs represent neither fossilized nuclei nor taphonomically condensed cytoplasm. We instead propose that these ICIs likely represent biologically contracted and consolidated eukaryotic protoplasts (the combination of the nucleus, surrounding cytoplasm, and plasma membrane). As opposed to degradational contraction of prokaryotic cells within a mucoidal sheath-a model proposed to explain the Bitter Springs ICIs-our model implies that protoplast condensation in the Ruyang acritarchs was an in vivo biologically programmed response to adverse conditions in preparation for encystment. While the discovery of bona fide nuclei in Paleoproterozoic acritarchs would be a substantial landmark in our understanding of eukaryote evolution, the various processes (such as degradational and biological condensation of protoplasts) capable of producing nuclei-mimicking structures require that interpretation of ICIs as fossilized nuclei be based on comprehensive investigations.

Thermally‐induced structural and chemical alteration of organic‐walled microfossils: an experimental approach to understanding fossil preservation in metasediments

The identification and confirmation of bona fide Archean-Paleoproterozoic microfossils can prove to be a challenging task, further compounded by diagenetic and metamorphic histories. While structures of likely biological origin are not uncommon in Precambrian rocks, the search for early fossil life has been disproportionately focused on lesser thermally altered rocks, typically greenschist or lower-grade metamorphism. Recently, however, an increasing number of inferred micro- and macrofossils have been reported from higher-grade metasediments, prompting us to experimentally test and quantify the preservability of organic-walled microfossils over varying durations of controlled heating and under two differing redox conditions. Because of their relatively low-intensity natural thermal alteration, acritarchs from the Mesoproterozoic Ruyang Group were chosen as subjects for experimental heating at approximately 500°C, with durations ranging from 1 to 250 days and in both oxic (normal present day conditions) and anoxic conditions. Upon extraction, the opacity, reflectivity, color, microchemistry, and microstructures of the heated acritarchs were characterized using optic microscopy, scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The results differ for acritarchs prepared under oxic vs. anoxic conditions, with the anoxic replicates surviving experimental heating longer and retaining biological morphologies better, despite an increasing degree of carbonization with continuous heating. Conversely, the oxic replicates show aggressive degradation. In conjunction with fossils from high-grade metasediments, our data illustrate the preservational potential of organic-walled microfossils subjected to metamorphism in reducing conditions, offer insights into the search for microfossils in metasediments, and help to elucidate the influence of time on the carbonization/graphitization processes during thermal alteration.

Novel application of focused ion beam electron microscopy (FIB-EM) in preparation and analysis of microfossil ultrastructures: A new view of complexity in early Eukaryotic organisms

Coupled dual-beam focused ion beam electron microscopy (FIB-EM) has gained popularity across multiple disciplines over the past decade. Widely utilized as a stand-alone instrument for micromachining and metal or insulator deposition in numerous industries, the submicron-scale ion milling and cutting capabilities of FIB-EM systems have been well documented in the materials science literature. These capacities make FIB-EM a powerful tool for in situ, site-specific transmission electron microscopy (TEM) ultrathin foil preparation. Recent advancements in the field-emission guns (FEGs) of FIB-EM systems have provided spatial resolution comparable to that of many high-end scanning electron microscopes (SEM), thus providing enhanced imaging capacities with material deposition and material removal capabilities. More recently, FIB-EM preparation techniques have been applied to geological samples to characterize mineral inclusions, grain boundaries, and microfossils. Here, we demonstrate a novel method for analyzing three-dimensional (3D) ultrastructures of microfossils using FIB-EM. Our method, FIB-EM nanotomography, consists of sequential ion milling, or cross sectioning, and concurrent SEM imaging. This technique with coupled dual-beam systems allows for real-time, 3-D ultrastructural analysis and compositional mapping with precise site selectivity and may provide new insights in fossil ultrastructures. Using the FIB-EM nanotomography method, we investigated herkomorphic and acanthomorphic acritarchs (organicwalled microfossils) extracted from the $999 Ma Mesoproterozoic Ruyang Group of North China. The 3-D characteristics of such important but controversial acritarch features as processes and vesicularly enclosed central bodies are described. Through these case studies, we demonstrate that FIB-EM nanotomography is a powerful and useful tool for investigating the three-dimensionality of microfossil ultra- and nanostructures.

Organic-walled microfossils from the Proterozoic Vindhyan Supergroup of Son Valley, Madhya Pradesh, India

Well-preserved and diversified organic-walled microfossil assemblages are recorded from the Vindhyan sediments of Son Valley and DMH-A well, in Madhya Pradesh. The microfossils include acritarchs, coccoid and filamentous taxa that suggest a Meso-Neoproterozoic age for the Vindhyan Supergroup which, hitherto, was assigned a Late Paleoproterozoic to Early Paleozoic age, based on fossil evidences and radiometric datings.&#x0D; The Kajrahat Limestone, within the basal Semri Group, recorded abundant filamentous microfossils, viz. Polythrichoides, Karamia, Arctacellularia and Siphonophycus along with simple unornamented sphaeromorph acritarchs (Leiosphaeridia spp.), suggesting ca. 1500-1450 Ma age of Early Mesoproterozoic. The microfossil assemblage of Deonar Formation also includes the above taxa; however, Satka, Eomicrocystis and acanthomorph acritarchs, Tappania spp., appear within this formation along with abundant polygonomorph acritarchs referable to Octoedryxium. The Deonar microfossil assemblage resembles the assemblage of Roper Group (northern Australia) and suggests ca. 1450-1350 Ma age of Early to Middle Mesoproterozoic.&#x0D; The sediments of Kheinjua Subgroup are marked by the appearance of various species of Navifusa, Simia and Pterospermopsimorpha in the Koldaha Shale with overall abundance of Tappania, Satka, Eomicrocystis, Kildinosphaera and Leiosphaeridia. The presence of Middle to Late Mesoproterozoic marker taxa, viz. Tappania plana, T. tubata and Navifusa segmentata helps to correlate the Koldaha Shale and Salkhan Limestone assemblages with the assemblage of the Ruyang Group (China), suggesting an Ectasian-Stenian (ca.1350-1050 Ma) age. In additon to the above taxa, the appearance of Early Neoproterozoic marker taxa, such as, Vandalosphaeridium, Bavlinella, Melanocyrillium and budding leiosphaerids in the Rampur Formation indicates a Late Stenian-Tonian age (ca. 1050-850 Ma) for this formation.&#x0D; The microfossil assemblage of the Rohtas Subgroup is quite distinct as the marker taxa of the Kheinjua Subgroup, viz. Tappania spp.and Navifusa spp. disappear. The presence of Trachysphaeridium laufeldi, Vandalosphaeridium reticulatum, Bavlinella faveolata and Stictosphaeridium spp., and the disappearance of Eomicrocystis, Satka and budding leiosphaerids within this formation allow its correlation with Middle Neoproterozoic Miroyedikha (Siberia) and Husar-Kanpa (central Australia) assemblages, suggesting an Early Cryogenian (ca.850-750 Ma) age for the Rohtas Subgroup.&#x0D; The microfossil assemblages from the Kaimur and Rewa groups are represented by the species of Symplassosphaeridium, Synsphaeridium and Leiosphaeridia. The occurrence of B. faveolata, T laufeldi and Octoedryxium truncatum in their assemblages suggest a Middle to Late Neoproterozoic (Late Cryogenian; ca.750-650 Ma) age. The sediments of the Bhander Group also include the above taxa. However, the appearance of Ediacaran (Vendian) marker species of Obruchevella, viz. O. parva and O. valdaica in the Ganurgarh Shale, and their abundance in the overlying Nagod Limestone and Sirbu Shale, suggests a Late Cryogenian-Early Ediacaran (ca. 650-570 Ma) age for the Bhander Group. Yet, the appearance of Obruchevella delicata, Lophosphaeridium tentativum and Cymatiosphaera sp. in the Nagod Limestone, and Obruchevella parvissima, Cristallinium sp. and Dictyotidium sp. in the Sirbu Shale suggest that the age of the Bhander Group extends into the Late Ediacaran (ca.570-544 Ma).&#x0D; The record of Calymmian (ca. 1500 Ma) to Late Ediacaran (ca. 544 Ma) organic-walled microfossil assemblages categorically suggests an Early Mesoproterozoic to Terminal Proterozoic age-range for the Vindhyan Supergroup. The occurrence of well-developed Middle and Late Mesoproterozoic microfossil assemblages in the Deonar Formation and Kheinjua Subgroup negates the Late Paleoproterozoic (ca. 1630 Ma) age assignment to them, based on radiometric datings. The presence of Ediacaran (Vendian) marker species of Obruchevella and the absence of distinctive Early Cambrian acritarchs in the Bhander Group brackets the upper age limits of Vindhyan Supergroup to the Late Ediacaran, and does not encompass the Lower Paleozoic.

Protists of the Upper Mesoproterozoic Ruyang Group in Shanxi Province, China

Organic-walled microfossils described in this paper have been obtained from the Beidajian Formation of the Mesoproterozoic Ruyang Group (ca. 1300 Ma) in southern Shanxi Province, China. They are characterized by many eukaryotic organisms, such as acanthomorphic acritarchs, sphaeromorphic acritarchs with a distinct circular excystment, acritarchs with multilayered walls and ornamentation, and multicellular filaments and algal thallose. Recently, more eukaryotic microfossils have been found and the triaromatic dinosteroid biomarker was extracted from the whole rock sample containing abundant acritarch specimens of Dictyosphaera delicata and Shuiyousphaeridium. One acritarch form, Spiromorpha segmentata, shows morphological similarities to the extant green alga Spirotaenia. It means that sexual reproduction by conjugation probably arose in the late Mesoproterozoic. A new genus Spiromorpha is proposed here. In combination with known Mesoproterozoic microfossil assemblages from the Roper Group of Australia and the Bahraich Group of Ganga Basin, India, we infer that marine protests had a rapid development during the Mesoproterozoic Era.

Combined micro-Fourier transform infrared (FTIR) spectroscopy and micro-Raman spectroscopy of Proterozoic acritarchs: A new approach to Palaeobiology

Micro-scale analytical techniques permit correlation of chemistry with morphology of individual Proterozoic acritarchs (organic-walled microfossils), and thus provide new approaches for elucidating their biological affinities. A combination of micro-Fourier transform infrared (FTIR) spectroscopy and laser micro-Raman spectroscopy was used to investigate the organic structure and composition of individual acritarchs. Well preserved Neoproterozoic acritarchs from the Tanana Formation, Australia (ca. 590–565 Ma), and Mesoproterozoic acritarchs from the Roper Group (1.5–1.4 Ga), Australia, and Ruyang Group, China (1.4–1.3 Ga, age poorly resolved but certainly >1000 Ma and <1625 Ma) have thermal maturities that range from immature to oil window. FTIR spectra of Tanarium conoideum from the Tanana Formation contain intense aliphatic C H stretching bands in the 2900 cm −1 region relative to the C C aromatic ring stretching band at 1600 cm −1. This FTIR spectrum is consistent with the FTIR spectra obtained from algaenans isolated from extant chlorophyte and eustigmatophyte microalgae. FTIR spectra of Leiosphaeridia sp. from the Tanana Formation contain a less intense aliphatic C H stretching band relative to the C C aromatic ring stretching band. By comparison, the spectra acquired from the Mesoproterozoic acritarchs were dominated by C C aromatic ring stretching bands at 1600 cm −1 relative to moderate-weak CH 3 terminal groups (1345 cm −1), C H aliphatic stretching (3000–2700 cm −1), and C O (1710 cm −1), although some differences in biopolymer composition occurred between species. Curve-fitting of the aliphatic C H x stretching region provides greater insight into the aliphatic structures of the acritarchs. The CH 2/CH 3 intensity ratio can be used to assess the relative chain length and degree of branching. Organic material in the Tanarium conoideum consists of straight long chain hydrocarbons, while the other acritarchs contain hydrocarbons consisting of short chains that are highly branched. In this study it was found that Raman spectroscopy does not provide additional information about biopolymer composition of Proterozoic acritarchs, but rather offers complementary data regarding the aromaticity and degree of saturation of the macromolecular structure of acritarch cysts.

Discovery of branched tubular algae and microscopic tubes with annular-helical thickening from the Mesoproterozoic Ruyang Group of Shanxi, North China

Most previously reported Mesoproterozoic (1600—1000 Ma) fossils are from silicified carbonates, and they are commonly small in size (15—20 mm), ranging from coccoids to filaments in morphology. Many of them can be interpreted as cyanobacteria. Carbonaceous shales represent another source of palaeontological information of the Mesoproterozoic biosphere. Sphaeromorphic and acanthomorphic acritarchs, as well as filamentous fossils, are common in many Mesoproterozoic shales. Here we report an unusual assemblage of tubular fossils from the Meosproterozoic Ruyang Group in Shanxi, North China. Some of these tubes are branched. Others bear annular-helical thickening that might be represented by one extinct algae to adapt to a desiccating environment.

Acanthomorphic acritarchs from Meso-Neoproterozoic shales of the Ruyang Group, Shanxi, China

The wide-spread non-metamorphic shales of the Ruyang Group (1150-950 Ma) in southern Shanxi, China contain abundant and well-preserved acritarchs and filamentous microfossils, suggesting a shallow-marine depositional environment. Acanthomorphic acritarchs obtained from both the Baicaoping Formation and the Beidajian Formation of the Ruyang Group include Shuiyousphaeridium Yan, emend. and a new genus Tappania Yin Lei-ming, gen. nov. In addition, Shuiyousphaeridium macroreticulatum (Du) Yan is emended and two new species Tappania plana Yin Lei-ming, sp. nov. and T. tubata Yin Lei-ming, sp. nov. are described.

Neoproterozoic fossils in Mesoproterozoic rocks? Chemostratigraphic resolution of a biostratigraphic conundrum from the North China Platform

Siliciclastic rocks of the Ruyang Group, southern Shanxi, and the broadly equivalent Gaoshanhe Group, Shaanxi, contain exceptionally well-preserved, large (Ø ≈ 150 μm) acanthomorphic acritarchs recently interpreted as late Neoproterozoic (Sinian, c. 800-544 Ma) in age. This biostratigraphic interpretation is based on the presence of large acanthomorphs in Sinian successions of South China and elsewhere and the perceived absence of comparable forms in older rocks; it casts doubt on the long-accepted interpretation of Ruyang and correlative rocks as Mesoproterozoic in age (1600-1000 Ma). In contrast, thick marine dolomites in overlying units contain abundant radial fibrous fabrics and a narrow range of δ 13C values (c. 0 ± 1‰ vs. PDB), features which characterize unambiguously Mesoproterozoic carbonates elsewhere on the North China Platform and on other continents. Age estimates based on petrofabrics and chemostratigraphy are corroborated by a UPb zircon age of 999 Ma (no recorded error) for granites which intrude overlying carbonates. Thus, in combination, the available data constrain the Ruyang siliciclastics and overlying carbonates to be older than about one billion years, making Shuiyousphaeridium Yan and other large process-bearing acritarchs from these units among the oldest known distinctly ornamented eukaryotic microfossils.

Vermiform trace fossils from the Precambrian Ruyang Group, western Henan

THE origin and evolution of Precambrian lives has been a long-standing controversial problem. It is now generally accepted by most paleontologists that the origin of metazoa can be traced back to more than 1000 Ma, because the Ediacara and latest pre-Ediacara fauna, such as the Huainan fauna, are featured by their diversification of forms, complicated structures and