Submarine and vadose cements in Pleistocene Bermuda reef rock

Well-rounded pebbles and cobbles of reef rock, which in bio- and lithofacies closely resembles the Recent algal cup reefs, occur in the basal conglomerate of the Pleistocene Devonshire Formation cropping out along Grape Bay on the south shore of Bermuda. The framebuilders of this rock include coralline red algae, vermetid gastropods, and barnacles. Study by petrographic microscope, electron microprobe, and SEM revealed aragonite-needle and spherulitic cements, high-Mg calcite micrite and palisade cements including calcified algal filaments. Two or three generations of these may occur in a given pore. By analogy with the Recent cup-reef material, on the basis of their composition (high strontium content of aragonite, high magnesium content of calcite) and of circumstantial evidence, these are considered submarine cements.In addition, a vadose blocky low-Mg calcite cement occurs, which never precedes any, but frequently succeedes one, two, or three of the above cements. Its fabrics vary: it may exhibit an increase in crystal size toward the center or not, it may or may not be bounded by the meniscus outline characteristic of the vadose diagenetic environment. The limitation of cement precipitation by a meniscus gives rise to a large diversity of forms determined by respective combinations of solution supply, permeability of the micro-environment, and substrate morphology. To illustrate the diversity, the meniscus cement is shown in relation to sediment particles, aragonite-needle cement, and calcified filaments.From the blocky low-Mg cement, selective neomorphism extends into some aragonitic gastropod shells; it is controlled, in part, by original shell structure. The resulting low-Mg calcite mosaic is characterized by relic structures and plane crystalline boundaries. Aragonite needles between blocky calcite cement and neomorphic calcite were not affected by the process of mineralogic alteration.This study shows that cements recognized earlier in Recent Bermuda cup reefs can be traced into the past and that additions to the diagenetic sequence can be distinguished. Knowledge of these features and their sequences should help decipher the diagenetic history of other fossil reefs.     

Phosphatic precipitates associated with actinomycetes in speleothems from Grand Cayman, British West Indies

Calcitic speleothems from a cave located on the north central coast of Grand Cayman commonly include corrosion surfaces that developed when calcite precipitation ceased and corrosion mediated by condensates became the operative process. Dissolution features associated with these surfaces, including etched crystal surfaces, microcavities, and solution-widened boundaries between crystals, are commonly occupied by microbes and microbial mats that have been replaced by calcium phosphate and/or coated with calcium phosphate. No mineralized microbes were found in the calcite crystals that form the speleothems. The morphology of the mineralized hyphae (eight morphotypes) and spores (nine morphotypes) are indicative of actinomycetes, a group of microbes that are ideally adapted to life in oligotrophic cave environs. Superb preservation of the delicate hyphae, aerial hyphae, and delicate ornamentation on the hyphae and spores indicate that the microbes underwent rapid mineralized while close to their original life positions. Although these actinomycetes were extremely susceptible to replacement by calcium phosphate, there is no evidence that they directly or indirectly controlled precipitation. Nevertheless, the association between the P-rich precipitates and microbes shows that the use of phosphorus as a proxy for seasonal climate changes in paleoclimate analyses must be treated with caution.     

3.46 Ga Apex chert ‘microfossils’ reinterpreted as mineral artefacts produced during phyllosilicate exfoliation

Filamentous microstructures from the 3.46 billion year (Ga)-old Apex chert of Western Australia have been interpreted as remnants of Earth's oldest cellular life, but their purported biological nature has been robustly questioned on numerous occasions. Despite recent claims to the contrary, the controversy surrounding these famous microstructures remains unresolved.Here we interrogate new material from the original ‘microfossil site’ using high spatial resolution electron microscopy to decode the detailed morphology and chemistry of the Apex filaments. Light microscopy shows that our newly discovered filaments are identical to the previously described ‘microfossil’ holotypes and paratypes. Scanning and transmission electron microscopy data show that the filaments comprise chains of potassium- and barium-rich phyllosilicates, interleaved with carbon, minor quartz and iron oxides. Morphological features previously cited as evidence for cell compartments and dividing cells are shown to be carbon-coated stacks of phyllosilicate crystals. Three-dimensional filament reconstructions reveal non-rounded cross sections and examples of branching incompatible with a filamentous prokaryotic origin for these structures.When examined at the nano-scale, the Apex filaments exhibit no biological morphology nor bear any resemblance to younger bona fide carbonaceous microfossils. Instead, available evidence indicates that the microstructures formed during fluid-flow events that facilitated the hydration, heating and exfoliation of potassium mica flakes, plus the redistribution and adsorption of barium, iron and carbon within an active hydrothermal system.     

Plant species as indicators of geochemical anomalies: Experiences onIlex aquifolium (holly)

The distribution of Zn, Cd, Pb, and Cu, in plants growing in mineralized and sterile areas of Tuscany has been studied to verify if and to what extent metalaccumulating species represent evidence of geochemical anomalies in soils. Samples of leaves and twigs from trees were collected, and analyzed by means of differential pulse anodic stripping voltammetry (DPASV). Hollies, brambles, and Holm oaks in particular were considered in the mineralized area of Bottino, and the special aptitude of hollies in concentrating Cd with respect to the other metals has been verified. Cadmium has been previously recognized as a pathfinder for zinc ore bodies; the results of this investigation appear to point out the relevance of holly as a bioindicator of geochemical zinc anomalies. Lower metal concentration characterizes the same species from other mineralized and sterile zones, with the exception of the urbanized area of Florence, where relatively higher Zn concentrations in hollies appear to be due to atmospheric pollution.     

安徽沙溪含和不含铜(金)矿斑岩斜长石斑晶粒度统计及其岩浆结晶动力学和成矿意义

通过对沙溪矿区含矿与不含矿斑岩中斜长石斑晶的粒度统计，计算出平均矿物粒度（Ｓ）、矿物分布密度（Ｄ）及矿物分布均匀度（Ｈ）；再根据晶体大小分布理论（ＣＳＤ），计算出斜长石的晶体生长速率、成核密度及成核速率等岩浆结晶动力学参数；发现含矿斑岩较无矿斑岩有高的成核密度和成核速率，而晶体生长速率则较低；指出成分相近的斑岩在岩浆结晶动力学特征上的极细差别可能造成岩体含矿性明显不同     

Modes of pre-Ediacaran multicellularity

A multicellular grade of organization is widely distributed among extant organisms and widely represented in the pre-Ediacaran fossil record. A review of the pre-Ediacaran record identifies nine general categories of multicellular organization: (1) simple clonal colonies; (2) integrated coenobial colonies; (3) simple uniseriate filaments; (4) simple multiseriate filaments; (5) simple coenocytic filaments; (6) branched coenocytic filaments; (7) complex multicellular filaments; (8) complex multicellular vesicles; and (9) problematic macrofossils. A small subset of these fossils can be assigned to extant lineages based on taxonomically diagnostic patterns of cell division, including compelling evidence for chroococcacean, oscillatoriacean and pleurocapsalean cyanobacteria, bangiophycaceaen red algae and hydrodictaceaen green algae. The identification of pre-Ediacaran vaucheriaceaen xanthophyte algae and siphonocladalean green algae is almost as secure, whereas the case for early multicellular nostocalean/stigonematalean cyanobacteria and fungi requires further corroboration; a distinctively patterned acritarch is tentatively identified as an early Neoproterozoic poriferan. Despite this breadth of early multicellular experimentation, there is no evidence for organ-grade differentiation prior to the Ediacaran. Indeed, it is the absence of eumetazoans and embryophytes that distinguishes the pre-Ediacaran world from the fundamentally richer and more dynamic biosphere of the Phanerozoic.     

印度尼西亚索林帕萨铜多金属矿成矿流体地球化学和矿床成因

文章对印度尼西亚索林帕萨铜多金属矿含矿石英脉流体包裹体进行了显微测温与氢氧同位素测定,发现石英脉中含有3种类型的流体包裹体:A.纯液相水溶液包裹体;B.富液相气液两相水溶液包裹体和C.富气相气液两相水溶液包裹体,其中以B类为主.三种流体包裹体同时出现,表明石英脉形成时流体可能发生过沸腾作用.成矿流体均一温度为198.9℃～356.4℃,冰点温度为-0.6℃～-2.3℃,相应流体盐度变化范围为0.94%～3.76%NaCleq..质谱测定显示成矿流体的氢氧同位素组成分别为占δDH2O=-61.0‰～-81.0‰,δ18OH2O=-3.08‰～0.17‰,表明成矿流体主要为大气降水,不排除有少量岩浆水加入.根据成矿流体地球化学与围岩蚀变类型,初步推断该矿属于酸性-硫酸盐(高硫)型的浅成低温多金属矿床,沸腾作用是成矿物质沉淀的主要因素.     

Iron biomineralization by anaerobic neutrophilic iron-oxidizing bacteria

Minerals formed by bio-oxidation of ferrous iron (Fe(II)) at neutral pH, their association with bacterial ultrastructures as well as their impact on the metabolism of iron-oxidizing bacteria remain poorly understood. Here, we investigated iron biomineralization by the anaerobic nitrate-dependent iron-oxidizing bacterium Acidovorax sp. strain BoFeN1 in the presence of dissolved Fe(II) using electron microscopy and Scanning Transmission X-ray Microscopy (STXM). All detected minerals consisted mainly of amorphous iron phosphates, but based on their morphology and localization, three types of precipitates could be discriminated: (1) mineralized filaments at distance from the cells, (2) globules of 100 ± 25 nm in diameter, at the cell surface and (3) a 40-nm thick mineralized layer within the periplasm. All of those phases were shown to be intimately associated with organic molecules. Periplasmic encrustation was accompanied by an accumulation of protein moieties. In the same way, exopolysaccharides were associated with the extracellular mineralized filaments. The evolution of cell encrustation was followed by TEM over the time course of a culture: cell encrustation proceeded progressively, with rapid precipitation in the periplasm (in a few tens of minutes), followed by the formation of surface-bound globules. Moreover, we frequently observed an asymmetric mineral thickening at the cell poles. In parallel, the evolution of iron oxidation was quantified by STXM: iron both contained in the bacteria and in the extracellular precipitates reached complete oxidation within 6 days. While a progressive oxidation of Fe in the bacteria and in the medium could be observed, spatial redox (oxido-reduction state) heterogeneities were detected at the cell poles and in the extracellular precipitates after 1 day. All these findings provide new information to further the understanding of molecular processes involved in iron biomineralization by anaerobic iron-oxidizing bacteria and offer potential signatures of those metabolisms that can be looked for in the geological record.     

新疆西准噶尔西南部加里东期成矿斑岩体的发现及意义

过去一般认为西准噶尔西南部的侵入岩均为海西中晚期,但近年在玛依勒及巴尔鲁克等构造带发现了一些早古生代侵入岩体,部分岩体显示有铜(金)矿化。本文对其中的占贝勒成矿斑岩体,利用LA-ICP-MS法进行锆石U-Pb同位素测年,结果获得425.3±2.6 Ma的年龄,揭示西准噶尔西南部地区存在有加里东期中酸性侵入岩,进而说明西准噶尔西南部地区存在加里东期斑岩型铜金成矿事件。该研究成果不仅对分析本地区地质构造演化具有重要意义,且对西准地区成矿规律的总结和进一步找矿预测具有重要意义。     

下三叠统鲕粒灰岩中微生物矿化组构特征及意义 ——以川东北地区飞仙关组为例

PTB全球最大生物灭绝事件后,早三叠世被认为是微生物发育繁殖的黄金时期,浅水环境是微生物活动及微生物岩形成的最有利环境。借助高分辨率扫描电镜和能谱分析,在川东北地区开江—梁平海槽西侧下三叠统飞仙关组浅水碳酸盐岩台地边缘的鲕粒灰岩中发现了三种微生物矿化组构:空腔状微生物矿化组构、显微瘤状微生物矿化组构和纤状微生物矿化组构;通过沉积学、岩石学及地球化学的综合分析,认为显微瘤状微生物矿化组构是微生物新陈代谢时形成的纳米球状云质颗粒,纤状微生物矿化组构是微生物的胞外聚合物,而空腔状微生物矿化组构则属于微生物个体。这些微生物矿化组构的发现,为早三叠世微生物大爆发提供了一定的直观证据;推测大量的微生物活动是早三叠世碳酸盐快速沉积现象的直接诱因,并导致于二叠纪末发育的克拉通内裂陷——开江—梁平海槽在早三叠世被快速填平。     

太行山北段多金属矿床地球化学特征

太行山北段多金属矿床有3个金属元素富集带:1.中心(铜)钼矿带,形成斑岩型矿床;2.过渡带铁-铜、银-铜、铁和锌成矿带,形成矽卡岩型矿床;3.外带铅-锌-银带,形成脉状矿床.这种分带出现于多个矿区,但不同矿区显示出独特变化.一般以其中一个矿带最发育,其它两矿带次之,但有时也有两矿带相对发育.围绕花岗岩的金属元素区域分布,流体包裹体温度测定及H、O和S同位素分析结果,表明岩浆热液与冷的大气降水(含少量源于围岩的CO₂和H₂S)之间的混合作用可以解释金属元素沉淀及时空分带的形成.     

湖北利川晚二叠世长兴期生物礁中的鹦鹉螺化石及其生态意义

川东、鄂西碳酸盐台地东缘,较广泛地发育着以海绵动物为骨架的生物礁。礁中有许多附礁生物,其中鹦鹉螺类化石在利川见天坝礁体中局部富集,共有8属9种,包括3个新种。根据现代鹦鹉螺的生态特征及当时区域沉积物的分布规律分析,工作区长兴期沉积环境是处在台地边缘,并接近斜坡相和盆地相。     

Hydrothermally altered hyaloclastites at the Earth’s surface in the rift zone of Iceland: Problem of the biochemogenic accumulation of trace elements

Results of the mineral and chemical study of surface-altered hyaloclastites from the Theistareykir and Nämafjall geothermal zones, the North Iceland rift, are considered. The paper scrutinizes the composition of hydrothermally altered rocks mainly consisting of clay minerals related to the transformation of bedrock hyaloclastites. The clay minerals also make up slope talus or proluvial deltas around highlands. The major clay minerals in areas of the present-day fumarole activity are kaolinite and smectite, while the redeposited talus-proluvial sediments are mainly composed of smectites. The studied rocks contain framboids, globules, rods, and other structures with morphology and size similar to those of mineralized bacteria. The local concentration of Ag in proluvial deposits is attributed to the intense bacterial activity. It is supposed that elevated contents of some trace elements could be related to an intense microbiotic influence.     

Epifauna on ammonites from the Lower Jurassic of the Severn Basin,southern England,and their palaeoenvironmental and taphonomic significance

Ammonites with bivalves or worm tubes attached are relatively rare among the abundant specimens in the Lower Jurassic (Sinemurian) mudstones at Bishop's Cleeve, Gloucestershire, UK, but provide evidence for ammonite taphonomy, environmental conditions and biological interactions between ammonites and epifauna. Epifauna attached only to one side or within the body chambers of ammonites usually indicate post-mortem attachment. Epifauna on both sides of, or overgrown by, ammonites attached in vivo. One large example of Oxynoticeras has at least 51 encrusting bivalves attached exclusively to one side indicating it formed a ‘benthic island’. Four, presumably annual, bivalve cohorts are recognized, with variation in preferred orientation in each cohort suggesting that current direction varied. Both the ammonite and its epifauna were buried by a single sedimentation event. Other informative examples include a Cheltonia that overgrew an epifaunal bivalve, and an example of Bifericeras which bears two clusters of four worm tubes, one of which apparently attached in vivo, the other post-mortem. Other examples bear too few specimens to be certain of the timing of attachment, but most probably attached post-mortem.     

Biomorphic textures in the ferruginous-siliceous rocks of massive sulfide-bearing paleohydrothermal fields in the urals

The work is dedicated to first finds of bacteriomorphic and microfaunal textures in the ferruginous-siliceous rocks that are widespread among volcanosedimentary complexes of the massive sulfide-bearing paleohydrothermal fields in the Urals. The bacteriomorphs are represented by: (1) single filaments with a diameter of 8–10 μm across and 80–90 μm long; (2) fascicles of branched or twisted-fibrous hematitequartz filaments 1–4 μm in diameter and up to 100 μm long; (3) microtubular textures, 20–30 μm across and up to 500 μm long, closely interlaced with thin hematite-quartz filaments (3–5 μm in diameter); (4)and hematite-quartz filaments (with the axial channel 1 μm across) formed by chains of elongated-oval lumps. These textures closely associate in the ferruginous-siliceous rocks with the fossilized tubular organisms (60–120 μm in diameter), tentaculites, remains of radiolarian skeletons, foraminifers, and others. It has been established that accumulation of various elements, such as Fe, Si, Ca, P, Mn, Ba, Ti, and K that are associated with biomorphic structures, was accompanied by the formation of their own mineral forms. Biomorphic textures in the gossanites (ferruginous-siliceous rocks forming haloes around destroyed massive sulphide mounds) differ from jasperites (not associating with sulfide ores ferruginouse-siliceous rocks), in terms of abundance, diversity, and development of tubular organisms and tentaculites. Biomineralization of different degrees of preservation in the Paleozoic ferruginous-siliceous rocks can indicate the microbial influence on geochemical processes during the decomposition of initial hyaloclastic sediments, which contain an admixture of sulfides and carbonates, under low-temperature conditions accompanied by the formation of iron and silica.     

Carbonaceous filaments from North Pole,Western Australia: Are they fossil bacteria in Archaean stromatolites?

A sample of chert from North Pole in the Archaean Pilbara block of Western Australia contains carbonaceous filaments that resemble microfossils. These occur in alternating light and dark laminae that look stromatolitic. However, the filaments are too simple in form for their origin to be determined, so they should be regarded as dubiofossils, perhaps biogenic, perhaps inorganic. Their host laminae were inorganically precipitated in a concordant fissure and thus cannot be stromatolitic. This fissure is younger than the surrounding silicified sediments of the ca. 3500 Ma old Warrawoona Group and possibly formed towards the end of the uplift and associated fracturing of the North Pole Dome, perhaps ca. 2750 Ma ago. The filaments are therefore contaminants in secondary chert.The filament-bearing rock was collected less than a metre from one of the localities (B) from which Awramik et al. reported early Archaean microfossils and possible microfossils. Their filaments from this locality were almost identical to those described here and were found in similar laminae. This suggests that their locality B filaments may also be contaminants in secondary chert. Other filaments found by Awramik et al. at North Pole come from an imprecisely located sample site (locality A) where the rock relationships are unknown. Since the host laminae of these filaments are not demonstrably primary and as cryptic concordant fissures filled with secondary minerals are common in locality A rocks, the filaments from this sample site could be contaminants too. Those that were assigned to Archaeotrichion should be treated as dubiofossils. Thus, the filaments described by Awramik et al. may not be fossil bacteria in ca. 3500 Ma old stromatolites, as they proposed, and are not necessarily the oldest known fossil organisms, as has been claimed.     

On the experimental silicification of microorganisms II. On the time of appearance of eukaryotic organisms in the fossil record

On the basis of ultrastructural, biochemical and genetic studies, bacteria and blue green algae (Kingdom Monera, all prokaryotes) differ unambiguously from the eukaryotic organisms (Fungi, plants sensu stricto) and protists or protoctists, (Copeland, 1956). The gap between eukaryotes and prokaryotes is recognized as the most profound evolutionary discontinuity in the living world. This gap is reflected in the fossil record. Fossil remains of Archaean and Proterozoic Aeons primarily consist of prokaryotes and the Phanerozoic is overwhelmingly characterized by fossils of the megascopic eukaryotic groups, both metazoa and metaphyta. Based on the morphological interpretation of microscopic objects structurally preserved in Precambrian cherts, the time of appearance of remains of eukaryotic organisms in the fossil record has been claimed to be as early as 2.7 · 10⁹ years ago, (Ka?mierczak, 1976). Others suggest chronologies varying between 1.7 to 1.3 · 10⁹ (Schopf et al., 1973) or a time approaching 1.3 · 10⁹ years (Cloud, 1974).There is general agreement that many of the Ediacaran faunas, which have been dated at about 680 m.y. are fossils of megascopic soft-bodied invertebrate animals. Since all invertebrates are eukaryotic, the ca. 680 m.y. date for deposition of these animal assemblages may represent the earliest appearance of eukaryotic organisms. But the question remains as to whether there is definitive evidence for eukaryotic cells before this “benchmark” of the late Precambrian.An excellent discussion of this particular problem as especially relating to acritarchs extending from rocks of Upper Riphean through Vendian and into the basal Cambrian is presented in recent studies by Vidal (1974, 1976) in Late Precambrian microfossils from the Visingsö rocks of southern Sweden.Previous work on the laboratory silicification of wood and algal mat communities (Leo and Barghoorn, 1976) suggested that further analysis of “artificial fossils” might be of aid in the interpretation of fossil morphology toward the ultimate solution of this problem. Thus the procedure developed by one of us (ESB) for laboratory wood silicification was adapted to various smaller objects.By successive immersions of wet cellular aggregates, colonies of various organisms and abiotic organic microspheres in tetraethyl orthosilicate, silicified cells and structures are produced which bear an interesting resemblance to ancient chert-embedded microfossils. Our observation of these microorganisms and proteinoid microspheres silicified in the laboratory as well as of degrading microorganisms, both eukaryotic and prokaryotic, have led us to conclude that many, if not all, of the criteria for assessing fossil eukaryotic microorganisms are subject to serious criticism in interpretation. We studied a large variety of prokaryotic algae, some eukaryotic algae, fungi, protozoa, and abiotic organic microspheres stable at essentially neutral pH. In some cases, degradation and/or silicification systematically altered both size and appearances of microorganisms. By the use of monoalgal cultures of blue-green algae, features resembling nuclei, chloroplasts, tetrads, pyrenoids, and large cell size may be simulated. In many cases individual members of these cultures show so much variation that they may be mistaken as belonging to more than one species. The size ranges for silicified prokaryotic and eukaryotic algae overlap. Several prokaryotes routinely yielded spherical or filamentous structures that resembled large cells. Because of genuine large sizes (e.g., Prochloron), shrinkage, systematic alteration or congregation of unicells to form other structures we find sizes to be of very limited use in determining whether an organism of simple morphology was prokaryotic or eukaryotic. Although some “prebiotic proteinoid microspheres” (of Fox and Harada, 1960) are impossible to silicify with our laboratory methods, those stable at neutral pH (Hsu and Fox, 1976) formed spherical objects that morphologically resemble silicified algae or fungal spores. Many had internal structure. We conclude that even careful morphometric studies of fossil microorganisms are subject to many sources of misinterpretation. Even though it is a logical deduction that eukaryotic microorganisms evolved before Ediacaran time there is no compelling evidence for fossil eukaryotes prior to the late Precambrian metazoans.     

From bone to pixel—fossil restoration and reconstruction with digital techniques

Fossils represent the only physical evidence for the existence of extinct life, and hold a vast potential to reconstruct organisms and ecosystems vanished a long time ago. Yet fossils are not as complete as they might appear in museum exhibits, documentaries or Hollywood blockbusters. Millions of years of fossilization have left their marks on the fossils, which might no longer resemble the condition of the organism when it was alive. A key challenge in palaeontology is therefore to restore and reconstruct the morphology of fossils. Luckily, novel digital visualization and reconstruction techniques offer powerful tools to bring extinct organisms back to life in unprecedented detail.     

The plant fossil record reflects just two great extinction events

Five great taxonomic extinctions (the so‐called ‘Big Five Mass Extinctions’) are widely recognized in life history, at the end of the Ordovician, Frasnian (Late Devonian), Permian, Triassic and Cretaceous. All of them were originally identified in the marine fossil record and have been interpreted as the result of abrupt global environmental changes. Previous evidence has suggested that terrestrial biota were also subjected to ecological disruption during these events, but it is unknown whether they suffered the same level of large‐scale taxonomic disruption as marine organisms. Here we show that the plant fossil record in fact only provides evidence of two mass taxonomic extinction events, one through the Carboniferous‐Permian transition, the other during middle‐late Permian times. This differs significantly from the mass extinctions recognized in the marine realm and suggests that vascular plants have a special capacity for surviving abrupt environmental changes.     

西藏土则雪山铜多金属矿带地质特征

对西藏昆仑山南坡1∶20万化探工作中圈出的土则雪山HS16综合异常查证中,发现宽850 m,长约4 km,由8个铜、铜锌、铜铅锌和2个铜矿化体组成的大型铜多金属矿带,其矿床成因类型为兼具沉积砂岩型铜矿和中低温热液型多金属矿床的沉积改造型矿床.该调查区铜的找矿潜力极大,具备有发现矿田级铜矿产的前提.作为铜矿的伴生,共生银、铅、锌矿也具有相当的找矿潜力.