豫西寒武纪叠层石微生物化石及其钙化特征

微生物的钙化机理是当今微生物碳酸盐岩研究的热点。微观条件下,在豫西寒武纪碳酸盐岩叠层石中发现了大量微生物化石,形态特征明显,为典型蓝细菌属的丝状葛万菌(Girvanella)和球状肾形菌(Renalcis)。根据豫西寒武纪叠层石明暗纹层中微生物化石的赋存状态及相关化石证据,可以判断叠层石的钙化分为微生物的物理和化学2种作用方式,其中物理钙化有2种钙化途径,而化学钙化又有化学诱导和化学控制2种钙化模式和多种钙化途径。在扫描电镜下能够清晰地看到各种钙化方式的结果和微生物主动营造作用所留下的证据,即磨圆度较低的颗粒物和深色灰泥等。结果表明叠层石的有机成因和水动力条件对其钙化方式具有重要影响。     

Pedogenetic and diagenetic fabrics in the Upper Proterozoic Sarnyëré formation (Gourma, Mali)

Several diagenetic fabrics are described in the uppermost member of the Sarnyéré formation, an Upper Proterozoic dolomite (700-600 Ma). Micronodular micrite, microsparite showing nodulisation processes, orbicular crusts and oncoids are thought to be due to the pedogenetic alteration of an algal (Porostromata) boundstone. Further evolution in a vadose zone creates a network of cavities which are later filled by “cave stromatolites”, micropopcorn micrite and multilayered cements. A rhythmical repetition of facies evidences a polyphased pedogenetic history, leading to a 30 m thick highly complex section. Such numerous and diversified structures are rarely preserved, especially in Proterozoic rocks, but each of them have equivalents in recent examples of caliche soil profiles.     

Processes of carbonate precipitation in modern microbial mats

Microbial mats are ecosystems that arguably greatly affected the conditions of the biosphere on Earth through geological time. These laminated organosedimentary systems, which date back to > 3.4 Ga bp, are characterized by high metabolic rates, and coupled to this, rapid cycling of major elements on very small (mm-µm) scales. The activity of the mat communities has changed Earth's redox conditions (i.e. oxidation state) through oxygen and hydrogen production. Interpretation of fossil microbial mats and their potential role in alteration of the Earth's geochemical environment is challenging because these mats are generally not well preserved.Preservation of microbial mats in the fossil record can be enhanced through carbonate precipitation, resulting in the formation of lithified mats, or microbialites. Several types of microbially-mediated mineralization can be distinguished, including biologically-induced and biologically influenced mineralization. Biologically-induced mineralization results from the interaction between biological activity and the environment. Biologically-influenced mineralization is defined as passive mineralization of organic matter (biogenic or abiogenic in origin), whose properties influence crystal morphology and composition. We propose to use the term organomineralization sensu lato as an umbrella term encompassing biologically influenced and biologically induced mineralization. Key components of organomineralization sensu lato are the “alkalinity” engine (microbial metabolism and environmental conditions impacting the calcium carbonate saturation index) and an organic matrix comprised of extracellular polymeric substances (EPS), which may provide a template for carbonate nucleation. Here we review the specific role of microbes and the EPS matrix in various mineralization processes and discuss examples of modern aquatic (freshwater, marine and hypersaline) and terrestrial microbialites.     

Porphyry copper deposits of the CIS and the models of their formation

Deposits of the “porphyry” family (essentially porphyry copper and gold-porphyry copper, gold-bearing porphyry molybdenum-copper, gold-containing porphyry copper-molybdenum and porphyry molybdenum deposits) are associated in time and space with granitoid magmatism mainly in Phaerozoic volcano-plutonic belts. Whatever their age, the deposits belong to two types of belts: basaltic belts, representing axial zones of island arcs, or andesitic belts formed within active continental (Andean-type) margins.The petrochemistry of ore-bearing magmatism related to the nature of the substratum of volcano-plutonic belts, reveals a number of essential characteristics, both in composition and zonation of wallrock alteration and ore mineralization. These characterisics enabled previous researchers to establish four models of porphyry copper deposits based on their lithologic associations, e.g., “diorite”, “granodiorite”, “monzonite” and “granite”.Pophyry copper deposits are thought to be the product of self-generating “two-fluid mixing” ore-magmatic systems. Porphyry intrusions are pathways for energy and metals from deep-seated magma chambers, of which the upper mineralized parts are accessible for observation. The relationship between magmatic fluids and meteoric water participating in the ore-forming processes (dependent on the structural-petrophysical conditions of formation), provide a subdivision for the porphyry copper ore-magmatic systems into three types: “open”, “closed” and “transitional”.Concurrently, a common trend in the evolution of the systems has been established, from a nearly autoclave regime of structural-and ore-forming processes to a gradual increase in the importance of hydrothermal recycling. The completeness of the OMS (ore-magmatic system) development according to this scheme, which determines the existence of various OMS types, depends on many factors, the most important being the depth of formation of porphyry intrusive bodies, the petrophysical peculiarities of the host rocks and the palaeohydrogeological conditions of ore deposition.Although rock fracturing (especially defluidization: second boiling) and contraction are caused by the same mechanisms, the stockwork growth in “open” and “closed” systems, relative to the wall rock, takes place in opposite directions, primarily due to different petrophysical parameters of the near-stock environment.In “open” systems structural and ore metasomatic processes are finalized. Fractures extend progressively from porhyry stocks into the marginal parts of the intrusive framework and extension of large-scale recycling of magmatic and activated meteoric water, in the same direction, result in the formation of ore-bearing stockworks. These are large in all dimensions, cover mainly hanging-wall zones and are characterized by clearly defined concentric mineral zoning and extensive geochemical haloes.In a “closed” OMS with centripetal growing fractures, hydrothermal convection is stunted. The vertical extension of recycling cells is restricted and the volume of meteoric water involved in circulation during the period of ore deposition is relatively small. As a result, relatively small intra-intrusive lenticular stockworks are developed which are characterized by close co-existence of several generations of mineralization with fragmentary preservation of the earliest ones. These are characterized by the elements of “reverse” zoning, increased density of the veinlets and metal content, as well as poorly developed hanging-wall dispersion haloes.     

Magnetic overprints in granitoids and metamorphic rocks from Limousin (France): evidence for Late Variscan rotations, crustal folding and tilting

Generally, the lack of bedding criteria in basement units hampers the interpretation of paleomagnetic results in terms of geotectonics. Nevertheless, this work demonstrates that successive remagnetizations recorded in Early Carboniferous metamorphic and plutonic units, without clear bedding criteria, can be used to constrain a polyphased tectonic evolution consisting of a regional clockwise rotation, followed by a folding phase, a tilting phase and a second regional clockwise rotation.Metamorphic, ultrabasic, tonalitic and granitic rocks from different parts of Limousin (western French Massif central; 45.5°N/1.25°E), which underwent metamorphism during Devonian–Early Carboniferous or were intruded in the Early–Middle Carboniferous, were sampled in order (a) to identify the magnetic overprinting phases and the related tectono-magmatic events and (b) to constrain the regional and plate tectonic evolution of Limousin. Paleomagnetic results from 32 new and 26 sites investigated previously show that at least 90% of the magnetization isolated in rocks older than 330 Ma are overprints. In agreement with results from adjacent areas of the Variscan belt, the major overprinting phases occurred: (a) in the last stages of the major exhumation phase [332–328 Ma; mean Virtual Geomagnetic Pole (VGP) “Cp”: 37°N/70.5°E], (b) during the post-collisional syn-orogenic extension (325–315 Ma; VGP “B”: 11°N/114°E), (c) in the Latest Carboniferous and Early Permian (VGP “A1”: 27°N/149°E) and (d) in the Late Permian (VGP “A”: 48°N/146°E). The Middle–Late Carboniferous overprints “Cp” and “B” are contemporaneous with emplacement of leucogranitic, crustal derived plutons, and probably result from the hydro-thermal activity related to the magmatism. The drift from “Cp” directions to “B” directions implies that after 330 Ma, Limousin underwent a clockwise rotation by 65°, together with the Central Europe Variscides. The “Bt” components, the VGPs of which deviate from the mean apparent polar wander path (APWP) of the belt, are interpreted as “B” overprints tilted during Late Variscan tectonics, that is, in the time range 325–315 Ma. The first and most important generation of “Bt” overprints was tilted during NW–SE folding associated with NE–SW shortening, updoming and emplacement of leucogranitic plutons. The second generation reveals southeastward tilting due to NE-striking normal faulting. The drift from “B” to “A1” directions implies that Limousin has participated to the second clockwise rotation by 40° of the whole belt in Westphalian times.     

Role of cyanobacteria in Corg-rich deposits: an example from the Indidura Formation (Cenomanian-Turonian), northeastern Mexico

We present evidence of accumulation of calcareous cyanobacterial “microspheroids” as predominant components of the Cenomanian-Turonian Indidura Formation of northeastern Mexico. The unit at Parras de la Fuente includes a sequence of limestones and marls with well-defined light-dark rhythms at the decimetric to millimetric scale, in which CaCO₃ and total organic carbon vary between 43–78% and 0.3–3.6%, respectively.A distinctive feature of the section is the presence of abundant millimeter-scale microlaminae arranged in nearly even-parallel white and dark gray “varve like” dual lamination less than 3 mm thick, in which the darker units contain scattered planktonic foraminifera and radiolaria, whereas the lighter microlaminae are dominated by calcitic microspheroids (20–40 μm). The white laminae are evidently the result of recurring cycles of calcareous cyanobacterial blooms, possibly associated with fluvial dilution of surface waters.The organic carbon-rich laminated marlstones and laminated biocalcilutites of the Indidura Formation document paleoceanographic conditions favorable to unusual cyanobacterial productivity cycles that were also characterized by strong dysoxic/anoxic bottom conditions.     

Dislocation generation, slip systems, and dynamic recrystallization in experimentally deformed plagioclase single crystals

Three samples of gem quality plagioclase crystals of An60 were experimentally deformed at 900 °C, 1 GPa confining pressure and strain rates of 7.5–8.7×10⁻⁷ s⁻¹. The starting material is effectively dislocation-free so that all observed defects were introduced during the experiments. Two samples were shortened normal to one of the principal slip planes (010), corresponding to a “hard” orientation, and one sample was deformed with a Schmid factor of 0.45 for the principal slip system [001](010), corresponding to a “soft” orientation. Several slip systems were activated in the “soft” sample: dislocations of the [001](010) and 110(001) system are about equally abundant, whereas 110{111} and [101] in ( 31) to ( 42) are less common. In the “soft” sample plastic deformation is pervasive and deformation bands are abundant. In the “hard” samples the plastic deformation is concentrated in rims along the sample boundaries. Deformation bands and shear fractures are common. Twinning occurs in close association with fracturing, and the processes are clearly interrelated. Glissile dislocations of all observed slip systems are associated with fractures and deformation bands indicating that deformation bands and fractures are important sites of dislocation generation. Grain boundaries of tiny, defect-free grains in healed fracture zones have migrated subsequent to fracturing. These grains represent former fragments of the fracture process and may act as nuclei for new grains during dynamic recrystallization. Nucleation via small fragments can explain a non-host-controlled orientation of recrystallized grains in plagioclase and possibly in other silicate materials which have been plastically deformed near the semi-brittle to plastic transition.     

Messinian events in the Sorbas Basin in southeastern Spain and their implications in the recent history of the Mediterranean

The Messinian (Late Miocene) marine stratigraphic record of the Sorbas Basin (S.E. Spain) is well preserved and can be considered as being representative of the entire western Mediterranean. It exhibits a series of features relating to: (1) the composition, characteristics and evolution of coral reefs; (2) changes between temperate and subtropical climates; and (3) the extensive development of microbial carbonates (stromatolites and thrombolites) at the end of the Messinian. Each of these features has global significance.

Porites, which is the major and almost only coral component in reefs, is heavily encrusted with stromatolites. These reefs grew at the edge of the subtropical belt and were totally eliminated at the end of the Messinian because of global cooling.

Lowermost-Messinian carbonate sediments in the Sorbas Basin reflect a temperate climate, whereas those immediately above, which contain bioherms and coastal reefs, are subtropical. The shift from temperate to subtropical conditions during the early Messinian was accompanied by an important change in water circulation within the western Mediterranean. Temperate times were marked by cold surface Atlantic waters entering the Mediterranean, whereas subtropical times coincided with warm surface waters entering the western Mediterranean from the east. The subtropical waters were thermally stratified, which favoured the deposition of euxinic marls and diatomites at the centre of the basin. The upwelling of nutrient-rich water promoted stromatolite development within reefs and Halimeda growth on adjacent slopes.

Lastly, microbial carbonates (stromatolites and thrombolites) attained giant dimensions during the late Messinian, which can be regarded as a measure of their success in occupying a variety of ecological niches. This abundance of available habitats is believed to have resulted from the Messinian “salinity crisis”, which was followed by a re-colonization of the western Mediterranean. In this context stromatolite proliferation was due to opportunism of microbial communities in colonizing the new environments, rather than to a complete absence of other competitive biota. We do not believe that hypersaline conditions were a causal factor in stromatolite development because of the normal-marine biota associated with them.     

Lacustrine stromatolites: Useful structures for environmental interpretation – an example from the Miocene Ebro Basin

The significance of stromatolites as depositional environmental indicators and the underlying causes of lamination in the lacustrine realm are poorly understood. Stromatolites in a ca 600 m thick Miocene succession in the Ebro Basin are good candidates to shed light on these issues because they are intimately related to other lacustrine carbonate and sulphate facies, grew under variable environmental conditions and show distinct lamination patterns. These stromatolites are associated with wave‐related, clastic‐carbonate laminated limestones. Both facies consist of calcite and variable amounts of dolomite. Thin planar stromatolites (up to 10 cm thick and less than 6 m long) occurred in very shallow water. These stromatolites represented first biological colonization after: (i) subaerial exposure in the palustrine environment (i.e. at the beginning of deepening cycles); or (ii) erosion due to surge action, then coating very irregular surfaces on laminated limestones (i.e. through shallowing or deepening cycles). Sometimes they are associated with evaporative pumping. Stratiform stromatolites (10 to 30 cm high and tens of metres long) and domed stromatolites (10 to 30 cm high and long) developed in deeper settings, between the surge periods that produced hummocky cross‐stratification and horizontal lamination offshore. Changes in stromatolite lamina shape, and thus in the growth forms through time, can be attributed to changes in water depth, whereas variations in lamina continuity are linked to water energy and sediment supply. Growth of the stromatolites resulted from in situ calcite precipitation and capture of minor amounts of fine‐grained carbonate particles. Based on texture, four types of simple laminae are distinguished. The simple micrite and microsparite laminae can be grouped into light and dark composite laminae, which represent, respectively, high and low Precipitation/Evaporation ratio periods. Different lamination patterns provide new ideas for the interpretation of microbial laminations as a function of variations in climate‐dependent parameters (primarily the Precipitation/Evaporation ratio) over variable timescales.     

The optical features and hydrocarbon-generating model of “barkinite” from Late Permian coals in South China

Leping coal is known for its high content of “barkinite”, which is a unique liptinite maceral apparently found only in the Late Permian coals of South China. “Barkinite” has previously identified as suberinite, but on the basis of further investigations, most coal petrologists conclude that “barkinite” is not suberinite, but a distinct maceral. The term “barkinite” was introduced by (State Bureau of Technical Supervision of the People's Republic of China, 1991, GB 12937-91 (in Chinese)), but it has not been recognized by ICCP and has not been accepted internationally.In this paper, elemental analyses (EA), pyrolysis-gas chromatography, Rock-Eval pyrolysis and optical techniques were used to study the optical features and the hydrocarbon-generating model of “barkinite”. The results show that “barkinite” with imbricate structure usually occurs in single or multiple layers or in a circular form, and no definite border exists between the cell walls and fillings, but there exist clear aperture among the cells.“Barkinite” is characterized by fluorescing in relatively high rank coals. At low maturity of 0.60–0.80%R_o, “barkinite” shows strong bright orange–yellow fluorescence, and the fluorescent colors of different cells are inhomogeneous in one sample. As vitrinite reflectance increases up to 0.90%R_o, “barkinite” also displays strong yellow or yellow–brown fluorescence; and most of “barkinite” lose fluorescence at the maturity of 1.20–1.30%R_o. However, most of suberinite types lose fluorescence at a vitrinite reflectance of 0.50% Ro, or at the stage of high volatile C bituminous coal. In particular, the cell walls of “barkinite” usually show red color, whereas the cell fillings show yellow color under transmitted light. This character is contrary to suberinite.“Barkinite” is also characterized by late generation of large amounts of liquid oil, which is different from the early generation of large amounts of liquid hydrocarbon. In addition, “barkinite” with high hydrocarbon generation potential, high elemental hydrogen, and low carbon content. The pyrolysis products of “barkinite” are dominated by aliphatic compounds, followed by low molecular-weight aromatic compounds (benzene, toluene, xylene and naphthalene), and a few isoprenoids. The pyrolysis hydrocarbons of “barkinite” are mostly composed of light oil (C₆–C₁₄) and wet gas (C₂–C₅), and that heavy oil (C₁₅⁺) and methane (C₁) are the minor hydrocarbon.In addition, suberinite is defined only as suberinized cell walls—it does not include the cell fillings, and the cell lumens were empty or filled by corpocollinites, which do not show any fluorescence. Whereas, “barkinite” not only includes the cell walls, but also includes the cell fillings, and the cell fillings show bright yellow fluorescence.Since the optical features and the hydrocarbon-generating model of “barkinite” are quite different from suberinite. We suggest that “barkinite” is a new type of maceral.     

Response to Thrift's “The future of geography”

Reviews and observations about the status of the discipline of geography, no matter how positive, invariably raise programmatic concerns. These concerns have a long history that arise from geography's struggles to find an identity that embraces its many parts and yet are consistent with the logic by which the academy partitions knowledge. Pedagogy and research historically claimed by geography is currently being reinvented and relabeled under such headings as “integrated environmental science” and “spatial science”, and these developments have the potential to change the breadth of the “geographic imagination”. Several observations about dominant explanatory perspectives and substantive domains of geographic enquiry are also provided.     

Controls on microbial activity and tidal flat evolution in Shark Bay,Western Australia

Microbial deposits at Shark Bay constitute a diverse living microbial carbonate system, developed in a semi‐arid, highly evaporative marine setting. Three tidal flats located in different embayments within the World Heritage area were investigated in order to compare microbial deposits and their Holocene evolution. The stressing conditions in the intertidal–subtidal environment have produced a microbial ecosystem that is trapping, binding and biologically inducing CaCO₃ precipitation, producing laminated stromatolites (tufted, smooth and colloform), non‐laminated thrombolitic forms (pustular) and cryptomicrobial non‐laminated forms (microbial pavement). A general shallowing‐upwards sedimentary cycle was recognized and correlated with Holocene sea‐level variations, where microbial deposits constitute the younger (2360 years bp ) and shallower sedimentary veneer. In addition, sediments have been documented with evidence of exposure during the Holocene, from 1040 to 940 ¹⁴C years bp , when sea‐level was apparently lower than present. Filamentous bacteria constitute the dominant group in the blister, tufted and smooth mat types, and coccus bacteria dominate the pustular, colloform and microbial pavement deposit types. In the subtidal environment within colloform and pavement structures, microbial communities coexist with organisms such as bivalves, serpulids, diatoms, green algae (Acetabularia), crustaceans, foraminifera and micro‐gastropods, which are responsible for exoskeleton supply and extensive bioturbation. The internal fabric of the microbial deposits is laminated, sub‐laminar, scalloped, irregular or clotted, depending on the amount of fine‐grained carbonate and the natural ability of microbial communities to trap and bind particles or induce carbonate precipitation. Nilemah tidal flat contains the thickest (1·3 m) and best‐developed microbial sedimentary system; its deposition pre‐dated the Rocky Point and Garden Point tidal flats, with the most positive isotope values for δ¹³C and δ¹⁸O, reflecting strong microbial activity in a highly evaporative environment. There is an evolutionary series preserved within the tidal flats reflecting relative ages and degree of salinity elevation.     

The Genesis,Classification, Problems and Prospects of Microbial Carbonates:Implications from the Cambrian Carbonate of North China Platform

Currently, sedimentologists focus on the challenging issue of microbial carbonates, which are regarded as "one of the sedimentary rocks most difficult to study", having complicated sedimentary fabric. Their characteristic features closely related to microbial activity, distributed over a long period of geological time, and formed in diversified sedimentary environments. The main research concentrations are the calcified microbial mats and biofilms in geological records as the products of lithification and diagenesis. Starting from the origin, this paper systematically reviewed and explained the processes dwelling within two types of microbial communities, the thinner biofilm and the thicker microbial mat, which enabled them to convert into microbial carbonates through biomineralization and lithification. This study proposed that the existence of multiple microbial mats was another important cause for the diversification and complexity of microbial carbonates in addition to its complex depositional process. Moreover, the sedimentary characteristics and classification of different types of microbial carbonates were reviewed, exemplifying the Cambrian microbial carbonates in the North China Platform. These microbial carbonates are suggested to be placed under "bindstone" after Embry and Kloven, which can be further divided into 5 types, stromatolites, thrombolites, oncolites, laminites and leiolites. Dendrolite is not categorized as a separate class, instead attributed to thrombolites. The microbial carbonates may possess good source rock potential because of the enriched organic content, and may also serve as hydrocarbon reservoirs because of certain microbial textures and fabrics leading to significant porosity and permeability. Because of their biomineralization processes related to microbial activity, the microbial carbonates are not only an important window to understand the evolution of the earth's surface environment, but also capable of forming large-scale reservoirs, and their scientific and economic values are self-evident.     

Long base line tilt and strain measurement

Two types of noise afflict strain and tilt measurement. They may be categorized as “active” noise, which is due to atmospheric pressure variations, temperature variations, water-table variations and so forth; and “passive” or signal-generated noise which is a consequence of the interaction of the strain field of interest with inhomogeneities of material properties local to the measurement site.The reason why both types of noise are normally reduced by the use of long base line instruments is explained and a simple, practical long base line tiltmeter is described.     

A study of the kinetic parameters of individual macerals from Upper Permian coals in South China via open-system pyrolysis

A unique Upper Permian coal, Leping coal, is widely distributed in South China. The coal samples studied in the paper were collected from two mines in the Shuicheng coalfield of Guizhou Province, southwest China. The geochemical works including coal petrography, maceral content, Rock–Eval pyrolysis, and kinetic modelling of hydrocarbon-generating have been carried out on whole coal and individual macerals. The higher contents of volatile matter, elemental hydrogen, and tar yield, and the high hydrocarbon generation potential of the Leping coals are attributed to their high content of “barkinite”, a special liptinite maceral.The hydrocarbon generation potential of “barkinite” (S₂=287 mg/g, hydrogen index (HI)=491 mg/g TOC) is greater than that of vitrinite (S₂=180 mg/g, HI=249 mg/g TOC), and much higher than that of fusinite (S₂=24 mg/g, HI=35 mg/g TOC). At the same experimental conditions, “barkinite” has a higher threshold and a narrower “oil window” than those of vitrinite and fusinite, and consequently, can generate more hydrocarbons in higher coalification temperature and shorter geological duration. Data from the activation energy distributions indicate that “barkinite” has a more homogenous chemical structure than that of vitrinite and fusinite. The above-mentioned characteristics are extremely important for exploring hydrocarbon derived from the Leping coals in South China.     

Evidence for cyclic reactions between andalusite, “sericite” and sillimanite, mount franks area, willyama complex N.S.W

In the Mt. Franks area of the Willyama Complex, microfabric evidence suggests that the alteration of andalusite to sillimanite has taken place by a process similar to that suggested by Carmichael (1969). Andalusite is pre- to syn-S₂ in age. Alteration to “sericite” has resulted in the formation of “sericite” laths, some of which are crenulated about S₂, and some which are syn- and post-S₂. “Fibrolite” occurs in these andalusite—“sericite” aggregates within the sillimanite zone and is wholly embedded in “sericite”. “Fibrolite” is pre- to syn-S₂ in age. This evidence is interpreted as suggesting that the formation of sillimanite from andalusite took place via a “sericite” phase.Further microfabric observations are interpreted to imply constant volume for the reaction aluminosilicate → “sericite”. This suggests a situation in which Al³⁺ is relatively mobile but Al⁴⁺ is relatively immobile. This suggestion differs from Carmichael's (1969) idea of Al³⁺ immobility.     

Tepee-shaped agglutinated microbialites: an example from a Famennian carbonate platform on the Lennard Shelf, northern Canning Basin, Western Australia

Distinctive, metre‐scale antiformal structures are well developed in a Famennian carbonate platform in the Chedda Cliffs area of the Lennard Shelf reef complexes. The structures are distinguished by chevron‐shaped crests and thickened cores and contain abundant non‐skeletal allochems (ooids/pisoids, peloids and intraclasts) of silt to pebble size and variably developed laminations and fenestrae. The internal morphology and pervasive occurrence of fenestral clotted and wavy laminated fabrics suggest that these structures are microbial mounds composed of agglutinated stromatolites and thrombolites. Microbial fabrics most probably originated through sediment trapping and binding by microbial mats with early lithification involving microbial calcification and cementation of trapped sediment. The facies and stratigraphic context of the mounds support a shallow subtidal, transitional backreef to reef‐flat setting; however, alone these mounds do not provide unequivocal environmental information. Other large antiformal structures in Famennian platforms on the Lennard Shelf, previously described as tepee structures, show morphological similarities to the Chedda Cliffs mounds, which suggests that these other structures may also be microbial mounds. The presence of microbial mounds in platform successions further highlights the importance of microbial communities in the Lennard Shelf reef complexes.     

SHRIMP U–Pb zircon geochronology and geochemistry of metavolcanic and metasedimentary rocks in Northwestern Fujian, Cathaysia block, China: Tectonic implications and the need to redefine lithostratigraphic units

Northwestern Fujian Province is one of the most important Pre-Palaeozoic areas in the Cathaysia Block of South China. Metavolcano-sedimentary and metasedimentary rocks of different types, ages and metamorphic grades (granulite to upper greenschist facies) are present, and previously were divided into several Formations and Groups. Tectonic contacts occur between some units, whereas (deformed) unconformities have been reported between others. New SHRIMP U–Pb zircon ages presented here indicate that the original lithostratigraphy and the old “Group” and “Formation” terminology should be abandoned. Thus the “Tianjingping Formation” was not formed in the Archaean or Palaeoproterozoic, as previously considered, but must be younger than its youngest detrital zircons (1790 Ma) but older than regional metamorphism (460 Ma). Besides magmatic zircon ages of 807 Ma obtained from metavolcano-sedimentary rocks of the “Nanshan Formation” and 751–728 Ma for the “Mamianshan Group”, many inherited and detrital zircons with ages ranging from 1.0 to 0.8 Ga were also found in them. These ages indicate that the geological evolution of the study area may be related to the assembly and subsequent break-up of the Rodinia supercontinent. The new zircon results poorly constrain the age of the “Mayuan Group” as Neoproterozoic to early Palaeozoic (728–458 Ma), and not Palaeoproterozoic as previously thought. Many older inherited and detrital zircons with ages of 3.6, 2.8, 2.7, 2.6–2.5, 2.0–1.8 and 1.6 Ga were found in this study. A 3.6 Ga detrital grain is the oldest one so far identified in northwestern Fujian Province as well as throughout the Cathaysia Block. Nd isotope t_DM values of eight volcano-sedimentary and clastic sedimentary rock samples centre on 2.73–1.68 Ga, being much older than the formation ages of their protoliths and thus showing that the recycling of older crust played an important role in their formation. These rocks underwent high grade metamorphism in the early Palaeozoic (458–425 Ma) during an important tectono-thermal event in the Cathaysia Block.     

Algal bloom episodes and the formation of bituminite and micrinite in hydrocarbon source rocks: evidence from the Devonian and Mississippian, northern Williston Basin, Canada

Organic petrology (incident light microscopy) of Middle Devonian inter-reef laminates and Devonian-Mississippian epicontinental black shales, Williston Basin, Canada, indicates that algal bloom episodes and consequential bacterial activity played a significant role in the accumulation of amorphous, bituminite III-rich organic microfacies. Corpohuminite-like algal akinete cells produced by filamentous algae during algal bloom periods are persistent maceral inclusions within the potential hydrocarbon source rock intervals. These cells (%R_{o mean} range 0.24-0.90) are regarded as positive indicators of stressful palaeoenvironmental conditions. Unicellular Tasmanites and Leiosphaeridia marine alginite and variably degraded alginite remnants (“ghosts”) within the amorphous kerogen may be products of cell lysis, photo-oxidation and microbial alteration; these processes are characteristic of algal bloom periods. Minute (ca. 1 μm) spheroidal and coccoidal bacteria-like macerals are dispersed throughout the bituminite III network, attesting to the importance of microbial activity within the water column and sediment during and after organic matter accumulation. Dispersed granules, laminations and replacement textures of micrinite-like macerals within bituminite III are interpreted as remnants of microbial alteration rather than a residual product of thermal maturation and hydrocarbon generation.     

“Traditional” women, “modern” water: Linking gender and commodification in Rajasthan, India

In this paper, I analyze the connections made between women and water in a Rajasthani drinking water supply project as a significant part of drinking water’s commodification. For development policy makers, water progressing from something free to something valued by price is inevitable when moving economies toward modernity and development. My findings indicate that water is not commodified simply by charging money for it, but through a series of discourses and acts that link it to other “modern” objects and give it value. One of these objects is “women”. I argue that through women’s participation activities that link gender and modernity to new responsibilities and increased mobility for village women involving the clean water supply, a “traditional” Rajasthani woman becomes “modern”. Water, in parallel, becomes “new”, “improved” and worth paying for. Women and water resources are further connected through project staff’s efforts to promote latrines by targeting women as their primary users. The research shows that villagers applied their own meanings to latrines, some of which precluded women using them. This paper fills a gap in feminist political ecology, which often overlooks how gender is created through natural resource interventions, by concerning itself with how new meanings of “water” and “women” are mutually constructed through struggles over water use and its commodification. It contributes to critical development geography literatures by demonstrating that women’s participation approaches to natural resource development act as both constraints and opportunities for village constituents. It examines an under-explored area of gender and water research by tracing village-level struggles over meanings of latrines.