Microtaphonomy of bioclasts and paleoecology of microencrusters from Upper Jurassic spongiolithic limestones (External Prebetic,Southern Spain)

Microencrusters and microtaphonomic features of the Oxfordian spongiolithic limestones of the External Prebetic were studied using thin-section analysis. The spongiolithic limestone is a bioclastic-rich packstone with common echinoderm, mollusc and brachiopod remains. The bioclasts show a high fragmentation index and frequent microborings. The encrustation index (E _i) is higher for fragments of serpulids, ammonoids and bivalves, and increases with the initial grain-size of bioclasts. The main microencrusters consist of benthic microbial communities (BMC) and nubeculariids, as well as subordinate calcareous and siliceous agglutinated foraminifera, serpulids and bryozoans. BMC are usually the first colonizers, and encrusting foraminifera mainly appear on bioclasts larger than 2 mm. BMC dominate in well-developed encrustations on upward facing surfaces of larger bioclasts that are also colonized by foraminifera (nubeculariids and Subdelloidina). Bullopora, serpulids and bryozoans are more common on lower surfaces. The fact that the values of encrustation index, encrustation thickness and diversity of the microencrusters increase with the size of bioclasts is related to a higher stability and exposure time of the available bioclastic substrate. The microencruster distribution on upper and lower surfaces of large bioclasts may be related to photic control, space competition and/or predation avoidance.     

Palaeogeographic and stratigraphic distribution of mid-late Oxfordian foraminiferal assemblages in the Prebetic Zone (Betic Cordillera, Southern Spain)

Middle-Upper Oxfordian assemblages of foraminifera in the Prebetic Zone (Betic Cordillera, SE Spain) were analysed at the genus level to determine their composition, relative abundance, diversity, and dominance, as well as the size of the specimens. A relationship has been established between lithofacies, palaeogeography and composition of foraminiferal assemblages, the former two also determining the stratigraphic record of these microfossil assemblages. Two assemblages of foraminifera serve to identify relatively distal and proximal areas in the Prebetic shelf. The distal assemblage is characterized by higher diversity, specimens of greater size, and more abundant planktic and agglutinated forms. Benthic forms include Ophthalmidium, Epistomina and colonies of encrusting foraminifera. The proximal assemblage shows lower diversity, lower abundance of planktic forms, Epistomina and encrusting nubeculariids, and a greater abundance of spirillinids and Reofax. On the whole, planktic foraminifera decrease upwards in the studied succession, which, together with decreasing nodularity, could be related to system tract conditions previously proposed for Oxfordian deposits in the southern palaeomargin of Iberia.     

Middle Jurassic (Bathonian) encrusted oncoids from the Polish Jura,southern Poland

Oncoids from two localities (Ogrodzieniec and Blanowice) of the Polish Jura, southern Poland, have been investigated with respect to their genesis and paleoecology. These oncoids occur within Middle Jurassic (Bathonian) deposits. Those from Ogrodzieniec are large, elliptical, and embedded within a presumably condensed carbonate bed. Those from Blanowice, on the contrary, are significantly smaller, irregular to box-like in shape, and occur within the ore-bearing clays. The oncoids from both localities consist of a distinct carbonate core and laminated cortex that is significantly thicker and better preserved in the Ogrodzieniec oncoids. SEM and optical microscopic investigation of the oncoid cortices revealed the presence of carbonate and silicate layers with web-like structures similar to those occurring in recent cyanobacterial microbialites. Thus, the oncoid cortices investigated may have formed in a photic zone environment with the aid of coccoid and filamentous cyanobacteria. Oxic conditions prevailed during oncoid cortex formation within the siliciclastic setting, which is manifested by low total organic carbon content, high pristane/phytane (Pr/Ph) ratio, and significant predomination of the C₃₁ homohopanes. On the cortices’ surfaces, as well as between particular laminae, various encrusting organisms have been found. The encrusters, dominated by serpulids and bryozoans, are cryptic species that inhabited the undersides and recesses of the oncoids. Their presence on both the upper and lower surfaces of the oncoids indicates that the oncoids were episodically overturned on the seafloor. The much better developed cortex lamination and much higher diversity and abundance of encrusters in the Ogrodzieniec oncoids may point to better trophic conditions prevailing in a shallower marine environment characterized by transparent waters, as opposed to a deeper siliciclastic environment with less transparent waters and probably worse trophic conditions prevailing during formation of the Blanowice oncoids.     

Environmental implications of oncoids and associated sediments from the Remoredo Formation (Lower Jurassic) Mendoza, Argentina

Lower Jurassic deposits of the middle member (19 m) of the Remoredo Formation at Arroyo Montañesito, southwestern Mendoza Province (Neuquén Basin, Argentina), and its oncoids are described. Four lithofacies constitute the lacustrine deposits of the Remoredo Formation: (1) laminated green to gray calcareous shales; (2) laminated to massive dark gray mudstones; (3) massive to upward-coarsening dark gray oncolite wackestones; and (4) massive dark gray packstones with abundant macro-oncolites. According to layer configuration, two types of oncoids were recognized: (a) those having distinctly banded, well defined concentric and continuous lamination (Type I); and (b) those having a vertical arrangement of irregular and discontinuous laminae (Type I³–I). The continuous micritic laminations suggest growth during agitated conditions, and the discontinuous laminations reflect short periods of non agitation or tranquility in the water mass. The oncolites are associated with a well preserved faunal assemblage of ostracods (Darwinula sp. and possible members of the Subfamily Iliocypridinae) and some fragments of bivalves that are indicative of shallow water conditions. The facies association is a coarsening-upward sequence interpreted as the product of deposition in a shallow nearshore lacustrine environment, and a progressive infilling by pyroclastic subaereal flows.     

Palaeoenvironmental significance of cool‐water microbialites in the Darriwilian (Middle Ordovician) of Sweden

Well‐developed oncoids and centimetre‐sized stromatolites are reported for the first time from the Darriwilian (Middle Ordovician) cool‐water ‘orthoceratite limestone’ at Kinnekulle, Västergötland, Sweden. The characteristics and stratigraphical distribution of these microbialites show an apparent relationship to fluctuations in relative sea level. The most abundant and well‐developed oncoids occur in stratigraphical intervals that are characterized by notable sea‐level lowstands. Stromatolites, which share many compositional characteristics with the oncoids, are essentially confined to a single bed associated with an especially prominent lowstand. Stromatolite‐like lamination also occurs in the uppermost part of the studied succession, but this feature may be of abiogenic origin. The microbialites appear to be originally calcareous, but synsedimentary iron‐ and/or phosphate‐enriched laminae are conspicuous, and secondary substitution by coarse calcite and barite is common. Iron staining is most prominent in poorly preserved specimens. Diagenesis has occluded the identity of the producers of these microbialites, but characteristics of associated endolithic borings suggest that they were formed in photic waters. The laminated fabrics of the documented microbialites record a depositional environment sensitive to high‐frequency environmental change. Most significantly, the microbialites have provided important information about the depositional environment of their enigmatic host limestone, and the collective observations challenge the notion that the studied strata were deposited in a deep shelf to basinal environment – rather, it appears that they are to a large extent, shallow‐water deposits, formed in waters only a few tens of metres deep.     

Mineralized microbialites as archives of environmental evolution,Laguna Negra,Catamarca Province,Argentina

Environmental fluctuations are recorded in a variety of sedimentary archives of lacustrine depositional systems. Geochemical signals recovered from bottom sediments in closed‐basin lakes are among the most sensitive paleoenvironmental indicators and are commonly used in reconstructing lake evolution. Microbialites (i.e., organosedimentary deposits accreted through microbial trapping and binding of detrital sediment or in situ mineral precipitation on organics [Palaios, 2, 1987, 241]), however, have been largely overlooked as paleoenvironmental repositories. Here, we investigate concentrically laminated mineralized microbialites from Laguna Negra, a high‐altitude (4,100 m above sea level) hypersaline, closed‐basin lake in northwestern Argentina, and explore the potential for recovery of environmental signals from these unique sedimentary archives. Spatial heterogeneity in hydrological regime helps define zones inside Laguna Negra, each with their own morphologically distinct microbialite type. Most notably, platey microbialites (in Zone 3A) are precipitated by evaporative concentration processes, while discoidal oncolites (in Zone 3C) are interpreted result from fluid mixing and biologically mediated nucleation. This spatial heterogeneity is reflected in petrographically distinct carbonate fabrics: micritic, botryoidal, and isopachous. Fabric type is interpreted to reflect a combination of physical and biological influences during mineralization, and paired C‐isotope measurement of carbonate and organic matter supports ecological differences as a dominant control on C‐isotopic evolution between zones. Laminae of Laguna Negra microbialites preserve a range of δ¹³C_carb from +5.75‰ to +18.25‰ and δ¹⁸O_carb from ?2.04‰ to +9.28‰. Temporal trends of lower carbon and oxygen isotopic compositions suggest that the influence of CO₂ degassing associated with evaporation has decreased over time. Combined, these results indicate that microbialite archives can provide data that aid in interpretation of both lake paleohydrology and paleoenvironmental change.     

The role of microbes in reef-building communities of the Cannindah limestone (Mississippian), Monto region, Queensland, Australia

Reefs in the Cannindah Limestone at Old Cannindah Homestead, Monto region, Queensland, are exceptional in Eastern Australian Mississippian (Carboniferous) build-ups because of their largest dimension and differentiated microbial fabrics. Calcimicrobes and microbial carbonates, which represent a marine reefal environment occupied by both corals and sponges, are particularly abundant in the reef framework fabrics compared to other Mississippian build-ups in the world. They contributed significantly to the rigidity of the reefs on a crinoidal bank setting. Metazoans and calcimicrobes coexisted and played different roles in reef construction. Reef-building and cavity-dwelling microbes include Renalcis, Palaeomicrocodium, Girvanella, problematic Aphralysia, Ortonella, Shamovella-like, Rothpletzella-like, Wetheredella-like, and some problematic calcimicrobes, which occur in inter-corallite infillings of fasciculate rugose corals, in thrombolitic textures, in or within deposits between microdigitate stromatolite and laminated microbialites, and in reef cavities. Some reef intervals are entirely formed by Renalcis, Palaeomicrocodium, problematic calcimicrobes, and cement. Girvanella, as an encrusting calcimicrobe, generally bound bioclasts and micrite, or together with cement, formed boundstone. Microbial carbonates, including thrombolites, microencrusters, microdigitate stromatolite, laminated and tabular microbialite, irregular layers of self-encrusting vesicles, and microbial micrite, occur commonly in reef framestone and boundstone. The role of microbes and relevant microbial carbonates in the Cannindah reef limestone highlighted a significant account of microbial facies complexes associated with the Mississippian reefs.     

Mineral evolution and processes of ferruginous microbialite accretion – an example from the Middle Eocene stromatolitic and ooidal ironstones of the Bahariya Depression,Western Desert,Egypt

Peritidal ferruginous microbialites form the main bulk of the Middle Eocene ironstone deposits of the Bahariya Depression, Western Desert, Egypt. They include ferruginous stromatolites and microbially coated grains (ferruginous oncoids and ooids). Their internal structures reveal repeated cycles of microbial and Fe oxyhydroxide laminae. The microbial laminae consist of fossilised neutrophilic filamentous iron‐oxidising bacteria. These bacteria oxidised the Fe(II)‐rich acidic groundwater upon meeting the marine water at an approximately neutral pH. The iron oxyhydroxide laminae were initially precipitated as amorphous iron oxhydroxides and subsequently recrystallised into nanocrystalline goethite during early diagenesis. Organic remains such as proteinaceous compounds, lipids, carbohydrates and carotenoids are preserved and can be identified by Raman spectroscopy. The ferruginous microbialites were subjected to post‐depositional subaerial weathering associated with sea‐level retreat and subsurface alteration by continued ascent of the Fe(II)‐rich acidic groundwater. At this stage, another iron‐oxidising bacterial generation prevailed in the acidic environment. The acidity of the groundwater was caused by oxidation of pyrite in the underlying Cenomanian Bahariya formation. The positive iron isotopic ratios and presence of ferrous and ferric iron sulphates may result from partial iron oxidation along the redox boundary in an oxygen‐depleted environment.     

新疆准噶尔盆地西北缘洪古勒楞组时代的新认识

标准地点的洪古勒楞组长期以来一直被认为是准噶尔盆地西北缘,乃至整个新疆北部以海相为主的层位上最高的晚泥盆世晚期的沉积。然而牙形类和微体脊椎动物的研究证实,该组跨弗拉阶－法门阶（Ｆ－Ｆ）界线,它至少包括了一小部分弗拉晚期和主体部分为法门早期的沉积。两个牙形类带ＬａｔｅｒｈｅｎａｎａＺｏｎｅ和ＭｉｄｄｌｅｃｒｅｐｉｄａＺｏｎｅ被识别出,它们在Ｆ－Ｆ界线附近,并分别在大绝灭事件（在ｌｉｎｇｕｉｆｏｒｍｉｓＺｏｎｅ内）之前后。另一个层位更高的牙形类带ＬａｔｅｃｒｅｐｉｄａＺｏｎｅ也可能存在。同时还证实,长期以来一直被认为“正常层序”的标准地点的洪古勒楞组的层序是倒转的。由此,含植物大化石Ｌｅｐｔｏｐｈｌｏｅｕｍｒｈｏｂｉｃｕｍ等的陆相层在下（此层可能归于该组下伏的朱鲁木特组）,而产牙形类和其它丰富的无脊椎动物的海相层在上。按牙形类年代带的年代地层时间表（Ｆｏｒｄｈａｍ,１９９２）,该组距今约３６８－３６４百万年。至于它和邻近地区和布克河组的关系,由于后者发现了更高层位的牙形类,两者还不能完全对比。     

Succession following the catastrophic eruption of Ksudach volcano (Kamchatka, 1907)

Ksudach Volcano, southern Kamchatka Peninsula, erupted in 1907 and impacted over 2000 km² of forests with air-fall pumice deposits. We identified three impact zones. In Zone I, deposits deeper than 100 cm destroyed all vegetation. Two early successional stages occur, a lichen-dominated desert and isolated patches of a pioneer herb stage. Zone II is defined by pumice deposits 30 to 100 cm deep. Deposits of 70 to 100 cm destroyed all vegetation, but left scattered snags. Here primary succession dominates recovery, but its rate varies. Isolated trees survived in deposits of 30 to 70 cm and primary and secondary successional stages form a complex mosaic termed an intermediate succession. In Zone II, the primary stages found in Zone I are joined by a dwarf shrub-herb stage and a secondary birch forest stage. Zone III occurs where thinner deposits permitted some vegetation to survive in all locations. Secondary succession dominates in deposits of 10 to 30 cm. Trees suffered damage, but survived deposits of 20 to 30 cm, while other vegetation layers were eliminated. Deposits of 10 to 20 cm eliminated mosses and lichens and but only reduced the number of dwarf shrubs and herbs. Deposits of less than 10 cm damaged herb, moss and lichen layers but did not eliminate any species. All sampled vegetation remains in a pre-climax state, having yet to recover fully from earlier eruptions. Reconstructed vegetation maps for before 1907 and for ca. 1925 are compared to the map of vegetation in 1994. Based on degree of soil formation, vegetation recovery and colonization rates at different pumice depths, and the current vegetation, we estimate that full recovery of the soil-vegetation system will take more than 2000 years.     

Oncoid growth and distribution controlled by sea-level fluctuations and climate (Late Oxfordian,Swiss Jura Mountains)

Abundant lagoonal oncoids occur in the Late Oxfordian Hauptmumienbank Member of the Swiss Jura Mountains. Four oncoid types are observed in the studied sections and classified according to the oncoid surface morphology, the structure and composition of the cortex, and the texture and fauna of the encasing sediment. Micrite-dominated oncoids (types 1 and 2) have a smooth surface. Type 1 has a rather homogeneous cortex and occurs in moderate-energy environments. Type 2 presents continuous or discontinuous micritic laminae. It is associated with a low-diversity fauna and occurs in high-energy facies. Bacinella and Lithocodium oncoids (types 3 and 4) display a lobate surface. They are dominated by microencrusters (Bacinella irregularis and Lithocodium aggregatum) and are found in low-energy facies. The stratigraphic and spatial distribution of these oncoid types shows a correlation with the sequence-stratigraphic evolution of the studied interval, and thus with relative sea-level fluctuations. It can be shown that these sea-level fluctuations were controlled by orbital cycles with 100- and 20-kyr periodicities. At the scale of 100- and 20-kyr sequences, types 1 and 2 oncoids are preferentially found around sequence boundaries and in transgressive deposits, while types 3 and 4 oncoids are preferentially found around maximum floodings and in highstand deposits. This implies that changes of water energy and water depth were direct controlling factors. Discrepancies in oncoid distribution point to additional controlling factors. Platform morphology defines the distribution and type of the lagoon where the oncoids flourished. A low accumulation rate is required for oncoid growth. Additionally, humidity changes in the hinterland act on the terrigenous influx, which modifies water transparency and trophic level and thus plays a role in the biotic composition and diversity in the oncoid cortex.     

Taphonomy of fossil macro-invertebrate assemblages as a tool for ecostratigraphic interpretation in Upper Jurassic shelf deposits (Prebetic Zone, southern Spain)

Composition and taphonomy of macro-invertebrate fossil assemblages, together with facies analysis, have been approached in order to interpret shifting paleoenvironmental conditions in the External Prebetic (S-SE Spain) during the early Late Jurassic (Middle Oxfordian). In oolitic and spongiolitic limestones, the size of fossil remains, mode of preservation, within-bed position, corrasion, fragmentation, epibiont and biogenic encrustation, disarticulation and uncoupling, allow recognition of two taphofacies, respectively. Identified ecostratigraphic events and trends accord with rapid flooding under high-energy conditions related to ecospace enlargement for cephalopods and then the persistence of lower energy, long-lasting exposure of skeletals and higher sedimentary rates. The paleoenvironmental interpretation is consistent with neritic environments shifting from shallow carbonate to hemipelagic sedimentation and enlarging of shelf ecospace for marine invertebrates.     

Microbial contribution to deposition of upper carboniferous and lower Permian seamount-top carbonates,Akiyoshi, Japan

Summary Microbial organisms significantly contributed to the accumulation of shallow-marine carbonates in an open-ocean realm of the Panthalassan Ocean during Late Carboniferous-Early Permian time. The Jigokudai plateau in the northern part of the Akiyoshidai Plateau is the study area, where the limestone of the Upper Carboniferous Kasimovian Stage to the Lower Permian Artinskian Stage is well exposed. The fusulinid biostratigraphy as well as top-bottom geopetal fabrics revealed that the rocks of the study area are overturned. The thickness of this succession is approximated to 150 m. The succession is lithologically divided into the Lower Jigokudai and Upper Jigokudai formations. The lime-stones of these formations were deposited in a lagoonal setting. The Lower Jigokudai formation (95 m thick: Kasimovian to Asselian) is characterized by sand shoal facies represented by crinoid-Tubiphytes-fusulinid peloidal pack/grainstones and oolitic grainstones. Phylloid algal grain/packstones and microbial boundstones subordinately crop out. The Upper Jigokudai Formation (55 m thick: Sakmarian to Artinskian) is characterized by shoal and tidal flat facies represented by mollusk-fusulinid peloidal grain/rudstones, and peloidal grain/rudstones and peloidal lime-mudstones, respectively. Laterally discontinuous microbial bound-stones occur intercalated in mollusk-fusulinid peloidal grain/rudstones. This formation contains pendant and meniscus cements, and flat-pebble breccia indicative of an intertidal deposition and subaerial exposure. Various types of boundstone and organosedimentary structures constructed mainly by filamentous cyanobacteria,Tubiphytes obscurus tubular microproblematicum A, and other microproblematica were recognized. Significant facies types are (1) filamentous cyanobacteria-microproblematicum A bind/framestones, (2)Tubiphytes obscurus bindstones, (3) stromatolitic bindstones, (4) microbial laminites, (5) microbially linked structures, (6) oncoids, (7) microproblematica B-C framestones. The calcimicrobes, combined with synsedimentary cementation, formed small-scale and low-relief mounds of these facies, and greatly contributed to the deposition of the Kasimovian to Artinskian Panthalassan buildup.     

Late Paleozoic stromatolites: new insights from the Lower Permian of Kansas

Carboniferous to Permian marine stromatolites are widely dispersed across the Pangaean margins and embayments and are typified by the ‘Ottonosia-grade stromatolite’ (designated herein). This stromatolite type consists of a well-laminated oncoid or domical stromatoid that developed into branching, laminated columns in the upper reaches. To develop a model for the global pattern, we investigated Lower Permian stromatolites from Kansas (Howe Limestone Member, Red Eagle Limestone). Stromatoids from the Lyon County locality typify the Ottonosia-grade stromatolites. The laminae are sharp throughout the stromatoid and are defined by an increase in cornuspirid foraminfera and algal filaments. The upper zone of the stromatoid is composed of well-laminated branching and brecciated columns (‘pseudo-thrombolitic’). Coeval stromatolites from a new exposure at the Tuttle Creek Dam spillway possess a more massive mesostructure. These stromatolites are composed of a turbinate stromatoid or oncoid base and an overlying domical stromatoid, and are rimmed by smaller meandering columns. Only the basal stromatoid, oncoids, and upper columns are well laminated. In both localities, the microbial-constructing ecosystem is dominated by cornuspirids and calcifying filamentous algae (?Girvanella). The mesostructural differences of the stromatolites are due to different environments of formation. The Tuttle Creek stromatolites formed in a shallow-subtidal to intertidal open marine setting. The coeval Lyon County stromatolites formed in a semi-restricted, marginal marine environment such as a lagoon or supratidal zone. Based on this information and independent sedimentological data, we conclude that lagoonal or supratidal zones were common features in the late Paleozoic intracratonal zones of the Pangaean supercontinent and account for Ottonosia-grade stromatolites occurring in the Laurentian mid-continent, the Zechstein Basin, Japan, Brazil, and Tunisia.     

Ammonite succession at the Bajocian/Bathonian boundary in the Cabo Mondego region (Portugal)

The Cabo Mondego outcrops exposed along the cliffs, on the western margin of the Iberian Plate, show an expanded stratigraphic section of Lower Bathonian deposits containing abundant ammonoids. Upper Bajocian deposits correspond to similar facies, of muddy limestones alternating with marlstones, although ammonoids are scarce. A detailed succession of ammonites across the Bajocian/Bathonian boundary has been recognized at Cabo Mondego, which can form a useful bio‐ and chronostratigraphic standard for the Lusitanian Basin. The revision of previous collections from the classical section and new field samplings of two other separate sections allow the recognition through up to twenty metres of thickness, the highest zone of Bajocian (Parkinsoni Zone) and the lowest zone of Bathonian (Zigzag Zone). The Parkinsoni and the Zigzag zones established for NW European areas and belonging to the Northwest European Province, can be identified in the Lusitanian Basin, although the ammonite fossil assemblages are composed of Submediterranean taxa. However, a subdivision of the Parkinsoni Zone is not possible, due to the scarcity of well preserved ammonoids. The Zigzag Zone can be recognized and characterized as composed of two subunits (Parvum and Macrescens subzones) as represented in diverse European basins of the Submediterranean Province. Ammonite fossil assemblages of the Parvum Subzone may be grouped into two successive horizons, which are biochronostratigraphically equivalent to the subdivisions of the Convergens Subzone distinguished in the Digne‐Barrême area (SE France). New biochronostratigraphic data on the Bigotitinae, youngest members of Leptosphinctinae and oldest members of Zigzagiceratinae are relevant in understanding the evolution and faunal turnover of the West Tethyan Perisphinctidae during earliest Bathonian. The ammonite succession at the Bajocian/Bathonian boundary in the Cabo Mondego region (Portugal) represents one of the most complete biostratigraphic records so far recognized on the Iberian Plate.     

Active eukaryotes in microbialites from Highborne Cay,Bahamas, and Hamelin Pool (Shark Bay), Australia

Microbialites are organosedimentary structures that are formed through the interaction of benthic microbial communities and sediments and include mineral precipitation. These lithifying microbial mat structures include stromatolites and thrombolites. Exuma Sound in the Bahamas, and Hamelin Pool in Shark Bay, Western Australia, are two locations where significant stands of modern microbialites exist. Although prokaryotic diversity in these structures is reasonably well documented, little is known about the eukaryotic component of these communities and their potential to influence sedimentary fabrics through grazing, binding and burrowing activities. Accordingly, comparisons of eukaryotic communities in modern stromatolitic and thrombolitic mats can potentially provide insight into the coexistence of both laminated and clotted mat structures in close proximity to one another. Here we examine this possibility by comparing eukaryotic diversity based on Sanger and high-throughput pyrosequencing of small subunit ribosomal RNA (18S rRNA) genes. Analyses were based on total RNA extracts as template to minimize input from inactive or deceased organisms. Results identified diverse eukaryotic communities particularly stramenopiles, Alveolata, Metazoa, Amoebozoa and Rhizaria within different mat types at both locations, as well as abundant and diverse signatures of eukaryotes with <80% sequence similarity to sequences in GenBank. This suggests the presence of significant novel eukaryotic diversity, particularly in hypersaline Hamelin Pool. There was evidence of vertical structuring of protist populations and foraminiferal diversity was highest in bioturbated/clotted thrombolite mats of Highborne Cay.     

A new study of Olenekian–Anisian boundary conodont biostratigraphy of the Tulong section in Himalaya Terrane,southern Tibet

The Himalaya Terrane of southern Tibet exposes successive shallow-marine carbonate deposits from the Lower to Upper Triassic, and is a key region for studying the Triassic conodont biostratigraphy at the northern margin of the Indian Plate. On the basis of newly collected samples from the Kangshare and Laibuxi formations at the Tulong section, 11 conodont species of 7 genera were identified, and four conodont zones were established, namely, the Novispathodus abruptus Zone (lower Spathian, first reported in Tibet), the Columbitella jubata Zone (middle Spathian), the Triassospathodus symmetricus Zone (upper Spathian), and the Chiosella timorensis Zone (lowermost Anisian) in ascending order. The first occurrence (FO) of Chiosella timorensis indicates the Olenekian–Anisian boundary (OAB) at Bed 25, upper part of the Kangshare Formation. The regional and global correlation of these conodont zones is synthesized.     

Potential causes of enhanced transfer of mercury to St. Lawrence River Biota: implications for sediment management strategies at Cornwall, Ontario, Canada

We examined factors and pathways involved in the transfer of mercury (Hg) to the food web in St. Lawrence River embayments near Cornwall, Ontario, where natural remediation of contaminated sediments (eventual burial by settling of cleaner sediments) has been adopted as a management strategy. Yellow perch (Perca flavescens) from one of the study zones (Zone 1) along the river by Cornwall contained significantly higher total mercury (THg) concentrations than perch from other equally contaminated zones. While THg concentrations in benthic invertebrates did not vary among contaminated zones, THg concentrations in yellow perch and invertebrate prey recovered from the perch stomachs were 1.5–2.5 times higher in Zone 1 than those from other zones, suggesting that prey selection affects THg accumulation more than habitat location. No significant differences were found in THg concentrations among different prey species within Zone 1, although there were significant differences in THg concentrations in the same prey species within Zone 1. In contrast, THg concentrations among different prey species increased significantly with trophic level in other contaminated and reference zones. The lack of correspondence between trophic position and THg accumulation in Zone 1 suggests two possibilities: (1) yellow perch in Zone 1 are highly mobile and are assimilating THg from a wide range of prey across Zone 1 with variable THg concentrations and (2) there may be an important non-dietary source of THg to the Zone 1 food web. Potential waterborne Hg sources to Zone 1 were investigated. Whereas THg and MeHg values in discharges from a disused canal were similar to Zone 1 surface water values (0.97 and 0.04 ng l^?1, respectively), concentrations in storm sewer and combined sewer overflows discharging in the vicinity of Zone 1 were 19–45-fold (THg) and 2–4-fold (MeHg) higher than upstream river water. Contributions of Hg to the water column from sediment–water diffusion, estimated using a simple, well-mixed reactor model, ranged 0.05–0.1% of the surface water THg concentration and 1–2% of the MeHg concentration measured in summer months in Zone 1. Although not investigated in the other zones, a strong correlation (r ² = 0.82) was found between MeHg in porewater and amphipod concentrations in Zone 1, indicating that the sediment porewater is bioavailable and likely an important pathway for transfer of sediment Hg to the foodweb. Large areas of Zone 1 contain bark deposits and produce high rates of gas ebullition, and may not provide favourable conditions for progressive burial with clean sediments and attenuation of Hg transfer to biota through natural remediation. Careful monitoring of surface sediment concentrations and biota is required in these areas. Failure to reduce concentrations of Hg in these media would indicate alternative or additional management measures are required.