We present a systematic study of the petrological, mineralogical, sedimentological, and elemental geochemical characteristics of Cambrian Stage 3 red beds in the Hannan-Micangshan area of South China. The results show that red beds in the study area were mainly deposited in shallow marine environments, including the littoral and deeper neritic zones. Hematite and ferric hydroxides are the major pigmentary minerals in the red beds, and their origin is related to the contribution of iron-bearing minerals in the terrestrial fine-grained fraction during diagenetic transformation, based on evidence from many co-occurring iron-bearing terrestrial and clay minerals (e.g., ilmenite, chamosite, and glauconite), distinct diagenetically-altered characteristics, and close relationships between total Fe and Al, Mg, and Ti. The data also provide compelling evidence for presence of seawater-derived ferric hydroxides in shallow marine environments through in-situ technique analysis. Distinct lithological and sedimentological features in the study area allow the conclusion that diagenetic and hydrogenic ferric oxides/hydroxides jointly promoted the formation of the red beds. The present study found that the combination of active tectono-magmatic events, enhanced terrestrial fluxes, and improved dissolved oxygen conditions may have provided abundant iron sources and iron availability during the sedimentary and diagenetic processes, and thus facilitating the occurrence of red beds globally in Cambrian Stage 3.

Although it was Kalkowsky (1908) who coined the term "stromatolite", Freiesleben (1809) and perhaps Hausmann (1805) had described stromatolitic structures a century earlier. They had found them at the top of the Zechstein Limestone of the Upper Permian Zechstein Group around the Harz Mountains. Similar stromatolites have also been found in the Zechstein Limestone of Thuringia where they form the frame-builders of large reefs. They have been known since the middle of the nineteenth century, but were originally misidentified as fossil sponges, stromatoporoids or calcareous algae.

Conophyton(Maslov)is a cylindroidal stromatolite form-genus characterized by nested conical laminae.Well-preserved Conophyton,up to 4 m tall and with basal diameters of up to 50 cm,are exposed in the Proterozoic Atar Formation of Mauritania,where many occur together,in growth position,as fields of individual columns spaced between 5 and 70 cm apart.The uniformity of these forms and their regular dis-tribution suggest that they grew in quiet-water environments below wave base.Evidence for their pene-contemporaneous organomineralization is indicated by nearby toppled examples of undeformed Conophyton forms alongside eroded lithified Conophyton fragments in carbonate breccias.Two characteristics of Con-ophyton have been used to classify the structures-the form of the lamination and the nature of its axial structure.A mathematical/physical model provides an explanation for the growth pattern of Conophyton.It predicts that coniform structures with thickened axial zones form when upward organic growth of a biofilm moderately exceeds the rate of its mineralization.The varying characteristics of these features between different forms of Conophyton are thought to reflect biomineralization of the decaying biofilm rather than differences in the composition of microbial communities.A modern example of a syngenetic mineralization process capable of producing similar structures has been observed in the contemporary sediments of Lake Preston,Western Australia,where benthic microbial mats are being transformed into coniform lithified crusts.The initial biomineralization of the coniform mat forms magnesium silicate that first coats and permineralizes web-like microbial extracellular polymeric substances(EPS)and then coalesces into a uniform mass that provides mechanical strength to the cones.At a later stage,massive carbonate crystal growth occurs that over-prints much of this texture,leaving only small,remnant areas of the magnesium silicate phase.Many fossil Conophyton are composed of dolomite,and the remains of the microbial communities responsible for their construction are rarely found,except in areas of chert within the Conophyton.It is suggested that Proterozoic Conophyton were constructed in a tranquil environment through the accretion of microbial mats that were syngenetically permineralized by a magnesium silicate such as a smectite.Later,much of the un-stable smectite would be susceptible to diagenetic replacement by either dolomite,or chert in which rem-nants of microbes that had been coated or permineralized could,potentially,be preserved.

Widespread development of microbialites harbors a series of clues about microbial activity, environmental condition, and aquatic chemistry. The Ediacaran-Cambrian transition draws extensive attention on the co-evolution of complex life and Earth's environment but the associated microorganism development has been largely ignored. In this study, we present a high-resolution database with respect to the spatial and temporal distributions of microbialites in China through the terminal Ediacaran to the early Cambrian Period and describe morphological and petrological characteristics of stromatolites and thrombolites in detail to shed light on the evolutionary process of microbial carbonates. Microbialite development experienced two thriving intervals during the Ediacaran-Cambrian transition: latest Ediacaran to early Fortunian, and Cambrian Age 3 to middle Age 4. The columnar and domical stromatolites show no marked morphological changes in the Ediacaran-Cambrian transition, but stratiform stromatolites exhibit a notable decline in Cambrian time, likely caused by increasing bioturbation in the Cambrian shelf environments. Meanwhile, thrombolites evolved to form large and complicated structures in the early Cambrian featured by meter-level mound morphology and columnar-branching microbial forms (fan-like/dendritic structures), likely indicating an improved environmental adaptation (e.g., photosynthesis efficiency and hydrodynamic conditions). Another remarkable change in microbialites is the emergence of large numbers of calcified microbial microfossils preserved within the laminated/clotted mesostructures in Cambrian facies, compared with the Ediacaran forms that lack such unique structural features. For the main control over the Cambrian microbial calcification event, this study stresses again the essential role of seawater chemistry (Mg/Ca molar ratios and Ca2+ concentrations) in the formation and preservation of calcified microorganisms based on previous insights and elaborate characteristics of their occurrence and microstructures in China. The transition of the Neoproterozoic "aragonite-dolomite sea" to the Cambrian "calcite sea" (likely widely distributed in Age 3) may have promoted to the generation of an original calcite mineralogy in microbial fossils, which has a stronger ability to resist diagenetic dissolution and substitution (e.g., phosphatization and silicification) than that of the aragonite precursor.

A paleogeographic map has been compiled for the time slice of the last glacial maximum (15–20 kaBP) covering the Western Pacific region with emphasis laid on the marginal seas. This UNESCO/IOC map (1:20,000,000) is based on paleogeographic and paleoenvironmental data from 779 offshore and onshore sites, and about five hundred publications have been collected for this purpose. As seen from the Paleogeographic Map, the emergence of extensive continental shelves was the most outstanding geographic feature of the last glacial maximum in the West Pacific region. The sea-level induced environmental signal has been amplified in the marginal seas, giving rise to drastic changes in sea areas and configurations, and to reorganization of sea water circulation in seas of enclosed basin type. Since most of the Western Pacific marginal seas are influenced by monsoon circulation and some of these are located within the Western Pacific Warm Pool, the glacial geographic changes have produced a profound impact on regional and global climate. For example, the decrease of sea area and sea surface temperature (SST) in the marginal seas was one of factors responsible for the enhanced aridity of inland China during the glaciation. Glacial intensification of the winter monsoon and increased seasonality of SST in marginal seas might explain, at least partly, the apparent discrepancy between the tropical paleotemperature estimations based on terrestrial and open-ocean records in this region.

The widespread development of microbialites in shallow areas of the Tethys Ocean at the start of the Early Triassic reflects the deterioration of marine ecosystems in the aftermath of the extinction that marked the demise of the majority of Palaeozoic marine faunas. Here we present a study of the evolving microbialite forms and associated biotic assemblages of this pioneering microbialite interval from exposures at Chongyang, Hubei Province, China. This research provides a perspective on the effects of eustatic transgression on marine ecosystems as water depths increased at the beginning of Mesozoic, through the study of the changing forms, microfacies and distribution of microbialites. Microbialite forms evolved from stratiform stromatolites to a sequence of tabular thrombolites (with an intercalated layer of columnar stromatolites), followed by domical thrombolites that were overlain, in turn, by oolites. The stratiform stromatolites contain poorly preserved remains of calcified cyanobacteria, but microfossils with chambered structure can also be seen. Metazoan fossils increased from the base of the overlying tabular thrombolite, reflecting increasing biodiversity with deepening of seawater. The occurrence of columnar stromatolites within the tabular thrombolite may indicate a temporary sea-level shallowing. Foraminiferans and other metazoans are absent within the columnar stromatolites, but spherical cyanobacterial remains are extremely abundant. Well-preserved calcified cyanobacteria may reflect an absence of metazoan predation and/or carbonate supersaturation of seawater. As water deepened, domical thrombolites developed and the more complex seafloor relief created varied niches between and within the domes that harboured more ecologically diverse communities. During the process of transgression within the microbialite interval, carbon isotopes exhibit a negative relationship with biodiversity, implying that upwelling of anoxic deep-ocean water, if associated with the negative excursion of carbon isotope values, did not inhibit the diversification of benthic organisms at least on shallow carbonate platforms in the period immediately after the end-Permian mass extinction.

Ooids are typically spherical sediment grains characterised by concentric layers encapsulating a core. There is no universally accepted explanation for ooid genesis, though factors such as agitation, abiotic and/or microbial mineralisation and size limitation have been variously invoked. Here we examine the possible influence of microbial organomineralisation on the formation of some naturally occurring ooids. We develop a mathematical model for ooid growth, inspired by work on avascular brain tumours, that assumes mineralisation in a biofilm to form a central core which then nucleates the progressive growth of concentric laminations. The model predicts a limiting size with the sequential width variation of growth rings comparing favourably with those observed in experimentally grown ooids generated from biomicrospheres. In reality, this model pattern may be complicated during growth by syngenetic aggrading neomorphism of the unstable mineral phase, followed by diagenetic recrystallisation that further complicates the structure. Our model provides a potential key to understanding the genetic archive preserved in the internal structures of some ooids.

The concept of "Carbonate Factory" was introduced to describe areas of carbonate production and accumulation. In this paper, the "Ooid Factories" is used to analyze extensive Griesbachian (Triassic) oolite deposits in South China that, along with microbialites and lime-mud deposits from different carbonate depositional environments. Late Permian tropical shallow-water skeletal factories (dominant by calcareous algae, sponge, and other associated organisms) collapsed in pace with the most severe mass extinction event, and were rapidly replaced by mud-mound factories (microbialite and lime-mud deposits) and subsequent ooid factories in shallow-water circumstances of Griesbachian. Meantime, temporal nutrient-rich and high-temperature conditions probably delayed re-establishment of tropical shallow-water skeletal factories. As an elementary unit of ooid factories, Lower Triassic oolites have diagnostic characteristics of ooid fabrics (alternatively dark- and light-colored laminae), size ranges (1-5 mm), and grain compositions (pure ooids, and only a few gastropod and bivalve fragments). Continuous aggradational and progradational oolite sequences caused extensive oolite accumulations that significantly contribute to the development of platform architecture with the collaboration of mud-mound factories (mainly line-mud deposits) in South China, through the evolution of low-angle or homoclinal ramps in the early Griesbachian to distally steepened ramps or flat-topped shelves in the late Griesbachian. Moreover, ooid factories also developed in Western Tethyan, Cimmerian, and Arabian carbonate platforms within low latitudes of the Tethyan Ocean during the Griesbachian. It is suggested that extreme hothouse climate with (seasonal) dry conditions in low latitudes significantly facilitated the extensive carbonate production of ooid factories at that time due to the strong linear relationship between surface seawater temperature and carbonate saturation state.

Signals indicative of paleo-seawater rare earth element (REE) composition and microbial activity were identified in marine ooids from the Lower Triassic of South China using in situ laser ablation–inductively coupled plasma-mass spectroscopy (LA-ICP-MS) together with petrographic and isotope geochemical techniques. Quantitative trace element profiles were generated across successive growth laminae in the cortices of selected ooids. The shale-normalized REE and yttrium (Y) data of these layers show 1) light rare earth element depletion (mean LaSN/YbSN = 0.36 ± 0.14), 2) positive La anomalies (mean (La/La*)SN = 2.02 ± 1.25), and 3) high ratios of Y/Ho (mean 53 ± 12), which are similar to modern seawater compositions and Bahamian ooids. These findings imply that ooids in the study samples faithfully record Early Triassic paleo-seawater chemical signals such as REE + Y distributions. Petrographic observations revealed dark-colored layers with intense fluorescence containing structures that resemble microbial filaments or extracellular polymeric substances. These layers also possess more enriched REE compositions and higher concentrations of nutrient-like elements (e.g., Zn and Ba) than adjacent recrystallized light-colored laminae. Most ooid laminae contain negative Ce anomalies indicative of a well-oxygenated environment of formation, but some laminae have minimal negative anomalies suggesting the influence of suboxic porewater conditions. The present study provides a new perspective on the role of microbes in ooid genesis and on the utility of ooids as proxies for paleo-seawater chemistry.

Lacustrine microbialites record evidence of their depositional environments in their morphology, mineralogy and geochemistry. This synthesis reviews geochemical data both for microbialites and lake water for 21 modern lacustrine microbialite occurrences younger than 15,000 years. Although these data are limited, several trends and associations are identified that provide useful criteria to aid interpretation of the environmental settings of ancient analogues. These microbialites are either thrombolites or thrombolitic stromatolites. They form in diverse settings, including karst, volcanic, coastal and inland (athalassic) lakes. Surveyed lakes are mostly closed basins subject to evaporative processes. Lakes vary from stratified to totally mixed examples. The major hydrochemical types include Na-Cl, Ca-SO4, Ca-HCO3 and Soda Lakes. The salinity and alkalinity of the lakes correlates, as expected, with the mode of mineralization, which in turn is reflected in the microstructure of the microbialites. A correlation between the δ13Ccarbonate and the Ca2 +/alkalinity ratio (Ca/Alk) is observed. Generally, lakes with Ca/Alk > 1 are subject to carbonate precipitation driven by either uptake of CO2 that results in a broad range of positive and negative δ13Ccarbonate, or mineralization mediated by sulphate reducing-bacteria in saline to hypersaline environments that results in negative δ13Ccarbonate. Ca/Alk < 1 correlates with positive δ13Ccarbonate. The mineral make-up of the analysed microbialites trends with lake chemistry and place of deposition. Mg/Ca ratios < 0.8 correlate with precipitation of low-Mg calcite (LMC) and low salinity. Extremely high Mg/Ca ratios (> 39) are associated with hydromagnesite. Dolomite, high-Mg calcite (HMC) and monohydrocalcite are associated with the total aqueous concentration of Mg (cMg), occurring only in lakes with cMg > 75 meq/L. Evaporites (e.g., gypsum) are related to high lake water salinities. The absolute concentration of aqueous Si, commonly associated with dissolution of diatom tests, influences precipitation of crystalline and/or amorphous silicates/silica to form microbialites with Si concentrations above 0.54 mmol/L, either as amorphous phases or as minerals such as stevensite and kerolite. Combined, the trends observed in this survey demonstrate that modern lacustrine microbialites can preserve information symptomatic of the environments in which they formed. However, in a limited number of examples this is not the case, as subsequent diagenesis may alter the original mineralogy to a point where the geochemical evidence conserved from the depositional environment is lost. Additionally, some geochemical information may be the product of isolated microenvironments within living biofilms, and thus not necessarily directly related to the chemistry of ambient lake water. Further misleading conclusions would result if the hydrochemistry at the time of study had changed from those prevailing when the microbialites were mineralized. Thus, all the correlations developed in this work represent hypotheses to be tested rather than interpretations to be accepted. This compilation demonstrates how microbialites respond to different lacustrine hydrochemical environments, and is intended to provide a guide for future field studies and laboratory simulations. This review also highlights the general scarcity of trace-element data for lake waters and microbialites. However, some recent studies suggest that lacustrine microbialites may fractionate rare earth elements (REE) during uptake from water whereas marine microbialites appear to record the REE distribution from seawater without modification. This possible difference in REE behaviour could have implications for the interpretation of palaeoenvironmental proxies.

This work re-examines samples of modern microbialites collected in the 1980s from Lakes Clifton and Preston, two of the Yalgorup Lakes in southwest Western Australia. Lake Clifton contains the first convincing modern examples of thrombolites to have been recognized. It was known that aragonite mineralisation took place in these structures within near-surface biofilms. New research reveals that stevensite, a Mg-rich trioctahedral smectite, is the principal primary phase that establishes the initial structural rigidity of Lake Clifton thrombolites. Aragonite microcrystals then grow within the stevensite matrix. In adjacent Lake Preston, lithified, centimetre-scale, coniform structures occur that are similar to pinnacle-like microbial mats that grow intermittently in a small pond adjacent to the lake. Microstructures within the lithified cones confirm their microbial origin, but they have undergone four phases of mineralization; an amorphous Mg silicate phase (of smectite-like composition); some areas of Mg silicate were then partially transformed into authigenic serpentine (chrysotile and/or lizardite); aggregates of aragonite microcrystals then overprinted much of the fabric; and finally high-magnesium calcite grew as void fills and rims, as well as overprinting some of the remaining areas of the Mg silicate phase. It is concluded that syngenetic and early diagenetic carbonate mineralisation of microbialites may effectively obscure all traces of the original microbial communities, leaving only faint evidence for their organo-sedimentary origin. Secondary carbonate mineralisation of microbialites may thus eliminate the evidence of primary organomineralisation. Many published examples of apparently abiogenic but microbialite-like carbonates should be re-examined for traces of early silicate mineralisation. The discovery of microbial permineralisation of modern microbialites by Mg silicates in Lakes Clifton and Preston raises the possibility that phyllosilicates could have contributed to the early structural rigidity of some Proterozoic Stromatolites such as Conophyton. Reexamination of the literature on Conophyton tends supports this hypothesis. Finally, the significance of this research is considered in relation to ; clarifying the role of Mg silicates in microbialite organomineralisation; examining the evidence that apparently abiotic crystalline carbonate may be of secondary origin; understanding the nature of the supposed “microbialites” in Cretaceous pre-salt sequences of the proto-Atlantic rift; assessing the continuing relevance of the “microbialite” concept; and clarifying evidence for the recognition of the earliest signs of life on Earth.

Microbialites form the earliest macroscopic evidence of life, and have always been important in particular aquatic ecosystems. They demonstrate the remarkable ability of microorganisms to provide the foundation for structures that can rival coral reefs in size. Microbialites are generally assumed to form by microbial trapping and binding of detrital grains, by carbonate organomineralization of microbial biofilms, or by inorganic mineralization around microbial templates. Here we present a significant discovery that modern thrombolitic microbialites in Lake Clifton, Western Australia, gain their initial structural rigidity from biofilm mineralization by the trioctahedral smectite mineral stevensite. This nucleates in and around microbial filament walls when biological processes suppress carbon and Ca activities, leaving Mg to bind with silica and form a microporous framework that replaces and infills the filament web. After microbial materials are entombed, local carbon and Ca activities rise sufficiently for aragonite microcrystals to grow within the stevensite matrix and perhaps replace it entirely, with eradication of biogenic textural features. This may explain why many ancient microbialite carbonates lack clear evidence for biogenicity. Stevensite may provide the missing link between microbial organomineralization and subsequent abiotic calcification.

The application of modern methods of time-series analysis to a record of sea-level variation at Flint Cliff, Hamelin Pool, between October 1983 and April 1985, shows that astronomical tides account for only one of the following five key components of the record: a seasonal oceanic cycle; a short-term irregular cycle; the complex astronomical tidal system in the Pool; isolated major events; and less marked variations probably reflecting wind stress, still able to defeat the astronomical tide in the short-term. We have compared the inundation record with precisely surveyed elevation ranges of various microbial communities. The dominance of a seasonal cycle is the fundamental determinant of variation in the duration of immersion and exposure determining the littoral zonation of microbial mats in Hamelin Pool. The astronomical tide is not the major cause of this variation. The microbial communities fall into three zones. In Zone 3, the microbialite-forming colloform mat is virtually never exposed. In Zone 2, smooth, reticulate and mamillate mats colonise the lower littoral environment. Here, many of the exposed microbialites have been stranded by the falling sea level, and are colonised by intermittently submerged microbial communities that modify the stranded lithified microbialites. Zone 1 is inundated only under exceptional circumstances and microbial communities are ephemeral.

Franz Bruckmann schrieb 1721 seine erste Abhandlung uber Oolithe. Wir stellen hier eine Ubersetzung des lateinischen Originaltextes ins Englische vor. Bruckmann beschreibt die Herkunft des Namens Oolith und seine Synonyme; interpretiert Oolithe als Ansammlung von Fisch-Eiern; klassifiziert sie als Steine; gibt Auftreten und Haufigkeit an; erklart das Ablagerungsmilieu und Prozesse der Versteinerung und die grose Menge der gefundenen Eier; beweist ihre biologische Herkunft und ihre biologischen Beziehungen; unterscheidet die Oolithe von den Pisolithen und gibt Orte an, wo sie gefunden werden. Wir kommentieren Bruckmanns Text, besprechen die Wirkung seines Werkes und verfolgen die Forschung uber Oolithe bis zum fruhen 20. Jahrhundert. Wir schliesen, dass Bruckmanns Abhandlung am besten als Uberblick anzusehen ist, der eine Grundlage fur spatere Forschungen bildete. Sein wichtigster Beitrag war, Oolithe eher als Anhaufungen von biologischen Uberresten als „Spiele der Natur“ (lusus naturae) anzusehen. Einige von Bruckmanns Zeitgenossen, wie Da Costa und De Saussure zweifelten, dass Fischeier versteinern konnenund – obgleich sie die biologische Herkunft einraumten – zogen es vor, sie als mineralische Konkretionen zu betrachten. Grose Neuerungen in der Stratigraphie, Palaontologie, Mikrobiologie, Mikroskopie, vergleichenden Sedimentologie und Petrologie musten stattfinden, bevor im 19. Jahrhundert signifikante Fortschritte von Bruckmanns Interpretationen gemacht werden konnten.