Microbialites

The largest and longest silicate caves in the world created in arenites of the Roraima Group in Venezuela have been explored on Chimantá and Roraima plateaus (tepuis) of Guyana Highlands. Geological and geomorphological research showed that most feasible way of the caves genesis is winnowing and erosion of unlithified or poorly lithified arenites. Dissolution is also present but it probably plays neither the trigger role, nor volumetrically important role in the cave-forming processes. The strongest dissolution/reprecipitation agent is the condensed air moisture which is most likely the main agent contributing to growth of siliceous speleothems. As such, it can be active only after, not before the cave is created. Siliceous speleothems are mostly microbialites except of some normal stalactites, cobweb stalactites and flowstones which are formed inorganically. They consist of two main types: 1. fine-laminated columnar stromatolite formed by silicified filamentous microbes (either het...

Jurassic reef patterns reflect the fulminant global and regional changes initiated by the breakup of northern Pangea. The pattern of reef distribution across the Jurassic reflects a complex mix of (1) different and changing tectonic styles along the continental margins and adjacent shelf seas; (2) sea-level rise and its modulating influence on extrinsic sedimentation; (3) oceanographic and climatic reorganizations related to general sea-level rise and the new plate-tectonic configurations; and (4) evolutionary changes in the ecological demands and abilities of reef biota, which, in part, appear to have been triggered by the extrinsic changes during the breakup of northern Pangea. Rifting and onset of drift in the central Atlantic as well as in the western Tethys resulted in a distinct sea-level rise, which transformed Jurassic shelf seas along the northern Tethys margin from dominantly siliciclastic to dominantly carbonate settings. The opening of the ocean passageway from the Tethys to the Caribbean and Pacific completely reorganized global oceanic circulation patterns. During the Late Jurassic, shelf seas were considerably deep, increasing the areas of settings suitable for development of siliceous sponge mounds on the northern Tethys margin. In contrast, many parts of the southern Tethys margin underwent strong morphological changes due to rift tectonics within the Triassic carbonate platforms, which resulted in a completely different pattern in Jurassic reef distribution relative to the northern Tethys. After the end-Triassic extinction event, Jurassic reefs recuperated gradually during the Early Jurassic, with a first major reef domain developing in Morocco. Their temporal distribution through the Middle Jurassic was more balanced, but reefs occurred in scattered domains often distant from each other (e.g., Portugal, France, Madagascar, Iran). Late Jurassic reefs expanded rapidly in the course of the ongoing sea-level rise and the oceanographic reorganization, resulting in mostly interconnected domains. A pattern of waxing and waning of reef abundance and spatial reef distribution through time is superimposed on this trend. It is again, at least to a large extent, correlatable with sea-level fluctuations of greater magnitude. Jurassic reef growth had peaks during the transgressive episodes of the Sinemurian– Pliensbachian, Bajocian–Bathonian, and Oxfordian–Kimmeridgian, with superimposed higher-frequency peaks. The Jurassic represents the peak not only of development of Mesozoic coral reefs but equally of development of sponge mounds. Sponge mounds represent siliceous sponge–microbolite mud mounds, which expanded enormously during the Oxfordian along the European part of the northern Tethys. A peculiar type of bivalve reefs, the Lithiothis reefs, were widespread particularly during the Sinemurian and Pliensbachian, and they might have partially filled a potential reef-growth habitat not occupied by corals, owing to the reduced availability of coral taxa at that time. Bivalve reefs, in particular oyster reefs, also occurred scattered in Middle and Late Jurassic times, mostly representing marginal marine environments. Sea-level rise and tectonic opening of new seaways had a pronounced influence on climate and marine circulation patterns, which were the principal factors in Jurassic reef development. Particularly in the Late Jurassic, coral and stromatoporoid reefs occurred in high paleolatitudinal settings (e.g., Argentina, Patagonia, Japan) evidencing strong climatic equilibration of marine and coastal areas, despite the fact that strong seasonal contrasts should have prevailed in the Gondwana interiors. There are only a few records of low-latitude reef sites, despite the availability of carbonate platforms, which might reflect overheated waters in this area. Humidity was probably higher than previously thought. Siliciclastic influx was partially high during the Kimmeridgian, owing to fluvial runoff and renewed tectonic activity, and reduced the number of reef sites and domains considerably, despite ongoing global sea-level rise. Jurassic, chiefly Upper Jurassic, reefs not only grew within the expanding carbonate settings but also thrived in terrigeneously influenced environments. This is particularly obvious in the North Atlantic rift basins, such as the Lusitanian Basin of west-central Portugal, but it is also discernible in many other Jurassic reef domains. Occurrence of coral associations in fine siliciclastics, ratios of skeletal low-density vs. high-density banding, morphological adaptations towards sedimentation, high proportions of bioerosion, and overlap of many coral domains with proposed upwelling areas suggests that there was a considerable stock of Jurassic zooxanthellate corals with a distinct heterotrophic proportion of feeding, thus living in mesotrophic settings. In contrast, reefs on the isolated, oceanic shallow-water Apulia–Adria platforms differ considerably, being dominated by stromatoporoids, chaetetids, and corals. We propose the theory that these oceanic faunas might have already had a more advanced photosymbiotic relationship than the other forms and thus could thrive in presumably strongly oligotrophic settings. Such associations, which might have occurred similarly on oceanic platforms in the Pacific, are thought to have been the stock for Cenozoic development of coral reefs into superoligotrophic settings, whereas the more nutrient-tolerant reefs along the continental margins vanished in the course of latest Jurassic and Berriasian sea-level drop. Sediment-stressed, nutrient-rich shallow-water settings might then have been reconquered by rudist bivalves in the course of the Cretaceous. Jurassic reefs not only constitute widespread and important hydrocarbon reservoir rocks; their manifold characteristics and related dependence on basin tectonics, sea-level change, and ecological parameters makes them valuable basin-analysis tools for potential hydrocarbon plays. This preprint is identical with the final version of the paper, except for some minor layout details. Please note that only Figs. 2-4 are colored in the published version.

Dinosaur tracks are biogenic, sedimentary structures and not body fossils or biological objects in the common sense. They result from the complex interaction of the kinematics of the trackmaker, its foot anatomy, and the substrate properties, and from taphonomic processes acting prior to the incorporation of the tracks into the sedimentary record. The objective of this work is an interdisciplinary study of a large sample of dinosaur tracks and trackways linking sedimentology with vertebrate ichnology, palaeontology, and palaeoecology.

Excellent conditions are provided by the Late Jurassic (Kimmeridgian) Chevenez—Combe Ronde tracksite, which is one of several tracksites located on the future course of the Transjurane highway near Porrentruy (Canton Jura, NW Switzerland). Here, eight superimposed dinosaur track-bearing surfaces were systematically excavated level-by-level within a 0,65 m thick laminite interval, unearthing almost 1400 dinosaur tracks. The main track level, located at the base of the interval, is the most diverse ichnoassemblage composed of 14 trackways of tiny (Pes Length < 25 cm) and small (25 cm < PL < 50 cm) sauropods and 43 trackways of minute (PL < 10 cm), small (10 cm < PL < 20 cm), and medium-sized
(20 cm < PL < 30 cm) bipedal, tridactyl dinosaurs.

The main issues are: (1) identification of true tracks, undertracks, and overtracks, and their relationships with substrate properties, their link with the exposure index, and their utility in the reconstruction of the palaeoenvironment; (2) implications of the main track level ichnoassemblage for dinosaur behaviour, the terrestrial palaeoecosystem, and vertebrate ichnofacies; (3) relationships between variability in trackway patterns and configurations with locomotion speed, behaviour, and substrate properties as well as implications for locomotion capabilities; (4) Quantification and relevance of sauropod trackway gauge; and (5) interpretation of manus-dominated and pes-only sauropod trackways.

The approach is first actualistic by studying human footprints and processes acting during their formation and preservation on modern tidal-flats. In these highly structured environments, microbial mats are ubiquitous, strongly facies-specific, and occupy a key position during and after footprint formation. Undertracks readily form in biolaminated sediment, whilst underprints and deep tracks are common in unlaminated, water-saturated sediment. Most consolidated vertebrate tracks are affected by taphonomic processes, including renewed and/or repeated growth of microbial mats leading to the formation of modified true tracks, internal overtracks (track fills), and overtracks.

The sauropod tracks and the encasing laminite interval of the Combe Ronde site are then subject of detailed sedimentological and taphonomical analyses. This discloses the sediment properties at the time of track formation and reveals the processes modifying the tracks during subaerial exposure and integrating them into the sedimentary record. Track morphology, associated track features, and sedimentary features can be linked with the exposure index, identifying the palaeoenvironment as a supratidal flat not located in close proximity to a coastline. These flats were susceptible for track recording only during short periods after wetting due to a rainy period or due to occasional storms. Longer periods of subaerial exposure prior to burial are indicated by the presence of internal overtracks and/or overtracks, and rapid covering up is indicated by the lack of overtracks on top of tracks with large displacement rims. Cross-sections of sauropod tracks provide insight into the consolidation history of the substrate prior to track formation and into the walking dynamics of dinosaurs, confirming that sauropods put their hindfeet in a pronounced plantigrade way on the ground.

The level-by-level superimposition of the studied surfaces enables to identify true tracks, undertracks, and overtracks. The best-defined true tracks (anatomical morphotypes) of the main track level are then used for ichnotaxonomy and trackmaker identification, and the detailed analyses of trackway parameters, including trackway gauge, provide insight into the locomotion capabilities of dinosaurs.

The best-defined minute and small tridactyl tracks can be assigned to the ichnogenus Carmelopodus, extending it from the Middle Jurassic into the Late Jurassic. These tracks were likely left by a small theropod dinosaur similar in size to Compsognathus or Juravenator. The medium-sized tridactyl tracks of morphotype II exhibit some of the typical features of the ichnogenus Therangospodus (attributed to large and robust theropods) but also some of ornithopod ichnotaxa.

The sauropod trackways show a wide range of patterns and configurations but are all medium- to wide-gauge. Therefore, they are assigned tentatively to the ichnogenus Brontopodus attributed to derived “brachiosaurid” or “titanosaurid” dinosaurs. The variability of the trackways reflects the general locomotion capabilities of the trackmakers and is an expression of individual walking style and behaviour, which may be related to substrate properties. Trackway patterns (the degree of manus overprinting by the pes) and different trackway configurations including trackway gauge are not only related to locomotion speed, and they provide no evidence of a relationship with ontogeny.

The gauge of sauropod trackways can be quantified with the pes trackway ratio and the here defined [WAP/PL]-ratio (Width of the pes Angulation Pattern / Pes Length). Gauge is possibly related to the substrate and the behaviour of the trackmaker adapting to it, but this does not change the overall medium-gauge to wide-gauge appearance of the trackways. The manus-dominated and pes-only sauropod trackways of the Combe Ronde site are explained by trackmakers exerting more pressure on the manus than the pes, and by overprinting of the manus by the pes, respectively.

The alignment of trackways on the main track level shows no evidence of a nearby shoreline and of interactions between the different groups of dinosaurs. It indicates gregarious behaviour amongst tiny and small sauropods, and suggests that minute and small bipedal dinosaurs were frequent visitors on the supratidal flats.

The ichnoassemblage of the main track level is the first one found in the Jura Mountains displaying abundant minute and small tridactyl tracks. This is also typical for the other Ajoie ichnoassemblages, which further exhibit tracks of tiny to large (up to 1,1 m PL) sauropods, and tracks of medium-sized to large (up to 0,8 m PL) bipedal dinosaurs. Sauropod trackways include narrow-gauge and wide-gauge trackways indicating the presence of “basal” and derived sauropods. This suggests that dwarfed insular animals can be excluded as trackmakers of the tiny and small sauropod trackways of the Ajoie ichnoassemblages and the Combe Ronde tracksite and that the Jura carbonate platform was connected with the landmasses of the London-Brabant Massif and the Massif Central during periods of emersion. Dinosaurs used the Jura carbonate platform for the establishment of in situ, predominantly saurischian dinosaur populations, but also as a migration corridor between the massifs.

Because the Ajoie ichnoassemblages are dominated by small tridactyl tracks, they differ from other Jurassic tetrapod ichnofacies in carbonate settings, notably from the Brontopodus ichnofacies. In the case of those ichnoassemblages commonly attributed to the Brontopodus ichnofacies, the lack or rareness of small tridactyl tracks may indicate the absence of small trackmakers in those palaeoenvironments or unsuitable conditions for the formation and preservation of small tracks.

This study highlights the benefits of systematic and interdisciplinary analyses of dinosaur tracks, which disclose variations related to behaviour and to differences in substrate. This allows recognizing anatomical morphotypes and trackway configurations representative of typical trackmaker behaviour. The latter can then also be used in ichnotaxonomical classification. Similar approaches should be in the focus of future work and performed on the other tracksites and ichnoassemblages of the Ajoie. Together with the evidence from other tracksites of the Jura Mountains, this will contribute towards a better understanding of the terrestrial palaeoenvironments and palaeogeography, and of dinosaur palaeoecology and palaeobiogeography on the Jura carbonate platform.

The study of microbial fossils involves a broad array of disciplines and covers a vast diversity of topics, of which we review a select few, summarizing the state of the art. Microbes are found as body fossils preserved in different modes and have also produced recognizable structures in the rock record (microbialites, microborings). Study of the microbial fossil record and controversies arising from it have provided the impetus for the assembly and refining of powerful sets of criteria for recognition of bona fide microbial fossils. Different types of fossil evidence concur in demonstrating that microbial life was present in the Archean, close to 3.5 billion years ago. Early eukaryotes also fall within the microbial realm and criteria developed for their recognition date the oldest unequivocal evidence close to 2.0 billion years ago (Paleoproterozoic), but Archean microfossils >3 billion years old are strong contenders for earliest eukaryotes. In another dimension of their contribution to the fossil record, microbes play ubiquitous roles in fossil preservation, from facilitating authigenic mineralization to replicating soft tissue with extracellular polymeric substances, forming biofilms that inhibit decay of biological material, or stabilizing sediment interfaces. Finally, studies of the microbial fossil record are relevant to profound, perennial questions that have puzzled humanity and science—they provide the only direct window onto the beginnings and early evolution of life; and the methods and criteria developed for recognizing ancient, inconspicuous traces of life have yielded an approach directly applicable to the search for traces of life on other worlds.

Major, trace (Y, Zr, Pb, Th and U), rare earth element (REE) and Sm–Nd isotope analyses were carried out on microbialites and
detrital carbonate sediments collected in Upper Jurassic coral- and sponge-microbialite reef settings. Selected bioconstructions
developed in various palaeogeographic settings and depositional environments on northwestern Tethys and eastern Atlantic margins: pure carbonate lagoon, carbonate-dominated deep shelf to epicontinental basin and mixed carbonate-siliciclastic shallow ramp and lagoon. The proximity to terrigenous sources directly controlled REE patterns of carbonate samples. Lateral and intrareef sediments, and to a lesser degree stromatolitic microbial crusts, are more susceptible to contamination by terrigenous material than are microbialites of thrombolitic fabric. In mixed carbonate siliciclastic settings, microbialites display a flat shale-normalized
REE pattern. In pure carbonate lagoonal settings, microbialites have shale-normalized REE patterns similar to those of modern
seawaters with a negative Ce anomaly [(Ce/Ce⁎) up to 0.14], positive La and Gd anomalies, and light REE depletion relative to
heavy REE. These data imply that similar REE chemistry than modern seawater already occurred on the northwestern Tethys
margin at the Upper Jurassic. Strong negative Ce anomalies (b0.4) imply microbialite formation in well-oxygenated seawaters both in coral reefs of pure carbonate lagoonal environments (Pagny-sur-Meuse) and sponge bioherms of deep-shelf settings (Plettenberg). Absence of positive Ce anomalies rules out an influence of alkaline and high-pH seawaters. Thus, REE patterns and Nd isotopic signatures, which are in perfect agreement with existing results for Tethysian seawater, confirm that microbialites can be used as proxies of palaeoenvironmental seawater chemical characteristics.

L'étude sédimentologique, pétrographique et paléontologique de la coupe des Escaliers de Sommant a permis de confirmer l'hypothèse de la présence d'un mudmound dans le domaine intermédiaire des préalpes médianes (Septfontaine, 1984, fig. 5, p.22). Suite du résumé p. 4 du présent pdf.
Le présent travail est remarquable par la précision des observations et l'intérêt des interprétations pour l'histoire géologique de la marge Nord de la Thétys au Jurassique. La présence d'un mudmound véritable, de grande ampleur (hectométrique à kilométrique pour son extension le long de la marge N-briançonnaise) est un fait unique dans les Alpes. De telles structures (microbialite) ne sont connues que dans le Dévonien de Belgique.
Cette étude de diplôme a été supervisée par le Prof. Eric Davaud et le Dr Michel Septfontaine. Il n'a pas pu être publié à l'époque pour des raisons de temps, l'auteur étant entré dans la vie active. Ce pdf a pour but de combler une carence qui concerne aussi bien les sédimentologues que les géologues préalpins.

May, A. (1994i): Foraminiferen, Kalkalgen und andere Mikrofossilien aus dem Givetium und Frasnium (Devon) des Sauerlandes (Rheinisches Schiefergebirge). - Dortmunder Beiträge zur Landeskunde, Naturwissenschaftliche Mitteilungen, 28: 7-31, 19 figs., 2 tabs.; Dortmund.

Abstract: The Beisinghausen Limestone (Upper Givetian to Frasnian) from Eslohe-Reiste in the eastern Sauerland (Rhenish Massif) consists of proximal turbidites. The particles came from the Middle to Upper Devonian Massenkalk reef complex of Attendorn and Elspe and they can be attached to different parts of the reef complex. The Beisinghausen Limestone shows a remarkable rich content of microfossils, consisting of foraminifera, calcisphaeres, calcareous algae, and microproblematica. These microfossils are described. The content of microfossils of the Beisinghausen Limestone is compared with the content of microfossils of two Lower Givetian coral-limestone horizons from the northwestern Sauerland as weil as the content of microfossils of the Upper Givetian lagoonal Massenkalk from the Brilon reef complex in the eastern Sauerland (table 1-2).

Kurzfassung: Der Beisinghäuser Kalk (Ober-Givetium bis Frasnium) von Eslohe-Reiste im östlichen Sauerland besteht aus proximalen Turbiditen. Die Partikel stammen aus dem mittel- bis oberdevonischen Massenkalk-Riffkomplex von Attendorn und Elspe und lassen sich verschiedenen Bereichen des Riffkomplexes zuordnen. Der Beisinghäuser Kalk zeigt eine auffällig reiche Mikrofossilführung aus Foraminiferen, Calcisphaeren, Kalkalgen und Mikroproblematika. Die Mikrofossilführung des Beisinghäuser Kalkes wird beschrieben und sowohl mit der Mikrofossilführung von zwei Korallenkalk-Horizonten aus dem Unter- Givetium des nordwestlichen Sauerlandes als auch mit der Mikrofossilführung des obergivetischen lagunären Massenkalkes im Briloner Riffkomplex (Ost-Sauerland) verglichen (Tabelle 1-2).

1. The effects of phosphorus enrichment and grazing snails on a benthic microbial community that builds stromatolic oncolites were examined in an experiment at Rio Mesquites, Cuatro Ciénegas, Mexico. Chemical analyses of stream water samples indicated that overall atomic ratios of total nitrogen (N) to total phosphorus (P) were approximately 110, indicating a strong potential for P-limitation of microbial growth.

2. Phosphorus enrichment involved addition of 5 μmol Na2HPO4 L−1 to streamside microcosms receiving intermittent inputs of stream water while grazer manipulation involved removal of the dominant grazer, the snail Mexithauma quadripaludium. After 7 weeks, we examined responses in organic matter content, C : N : P ratios, metabolism (P removal, primary production, dark respiration, and calcification), and microbial community structure using molecular fingerprinting of 16S rRNA genes.

3. Manipulation of snails did not affect response variables measured in these treatments (organic matter, C : P ratio, P removal rate). However, P enrichment significantly decreased the C : P and N : P ratios of surficial materials in the oncolites (organic matter content was unchanged), increased net and gross photosynthesis (oxygen consumption in the dark was unchanged), increased rates of calcification, and increased diatoms relative to cyanobacteria. Heterotrophic Eubacteria and Archaea were only modestly affected. Thus, our results indicate weak grazing effects but strong impacts of P in this benthic system.

4. We hypothesise that a state of severe P-limitation is imposed on autotrophic production in this food web due, at least in part, to co-precipitation of phosphate during calcite deposition. This produces severe P-limitation of the benthic algae and cyanobacteria, resulting in high C : P ratio of microbial mats relative to the biomass of photoautotrophs (phytoplankton, terrestrial foliage) in other ecosystems. In turn, this high C : P ratio is likely to generate severe stoichiometric constraints on the herbivores, thus limiting their populations and resulting in weak overall grazing impacts.

"The natural boundary between Permian and Triassic corresponds to the maximum regression, that is the maximum basinward shifts of coastal onlap. Large shallow shelves exposure which dramatically
reduced the habitat area, oxidation of a great amount of organic carbon, release of gas hydrates give way to a hyper-weakening of the ecosystem and a devastating extinction. These events and global
change, recorded in the large d13C shift (BAUD et al. 1989), strongly affected the carbonate productivity, stratal patterns and biofacies. A bloom of disaster forms: -fungi (Eshet et al. 1995), - cyanobacteria, -blue-green algae is the intrisic biotic response to the mass extinction.
During the first step of the very rapid and large scale lowest Triassic transgression , we note in different areas (S Alps, Taurus,Turkey, S Armenia, E Elburz, Iran, Central Iran and Central Afghanistan) the growth of domal stromatolites, thrombolites and other microbial structures. At the dawn of Triassic time, the carbonate factory was dominated by non-skeletal species and by micro-organisms able to precipitate carbonate"

The sulfur-bearing limestones interbedded in the upper Miocene diatomaceous sediments (Tripoli Formation) of the Lorca Basin (SE Spain) are typified, as other Mediterranean coeval carbonate and gypsum deposits, by filamentous, circular and rod-shaped microstructures of controversial origin. These features have been interpreted both as fecal pellets of brine shrimps and/or of copepods, remains of algae or cyanobacteria and fossilized sulfide-oxidizing bacteria. To shed light on their origin, a multidisciplinary study including optical, UV and scanning electron microscopy, Raman microspectroscopy, and geochemical (carbon and oxygen stable isotopes) analyses has been carried out on three carbonate beds exposed along the La Serrata ridge. The different composition of the filamentous and circular objects with respect to the rod-shaped microstructures suggest that the former represent remains of bacteria, while the latter fecal pellets of depositor suspension-feeder organisms. Size and shape of the filamentous and circular microfossils are consistent with their assignment to colorless sulfide-oxidizing bacteria like Beggiatoa (or Thioploca) and Thiomargarita, which is further supported by the presence, only within the microfossil body, of tiny pyrite grains. These grains possibly result from early diagenetic transformation of original sulfur globules stored by the bacteria, which are a diagnostic feature of this group of prokaryotes. The development of microbial communities dominated by putative sulfide-oxidizing bacteria at Lorca was favored by hydrogen sulfide flows generated through degradation of organic matter by sulfate-reducing bacteria thriving in underlying organic-rich sediments.

Spectacular modern freshwater oncoids from the river Alz (Bavaria, Southern Germany) grow in-situ, without being regularly overturned. In order to understand growth processes, properties of Alz river waters such as nutrient balance and pH were analysed and monitored, and the biotic composition of the oncoids was examined. Key features for the understanding of the growth of the Alz oncoids include (1) the presence of subconcentric calcareous laminae; (2) the existence of extracellular polymeric substances (EPS) within the enveloping biofilm that are produced by cyanobacteria and diatoms and cover the entire oncoid except for the contact area with riverbed sediments; (3) a stratified, 'telescoping' pattern of cyanobacteria living both intertwined within the soft outer biofilm and in radial arrangement within the partially calcified cortex below; (4) the calcification pattern of individual cyanobacterial colonies; (5) the presence of an oncoidal food web; (6) the occurrence of destructive processes such as boring by endolithic cyanobacteria and EPS-burrowing of animals; (7) a lack of multicellular algae and higher plants owing to pronounced phosphate limitation. Organismic interactions important in the extant Alz oncoids are believed to be important for a more complete understanding of fossil oncoids.

Although sphinctozoans, multi-chambered
hypercalcified sponges, can be traced from the Cambrian,
their reef-building capacity in the Early Paleozoic
appears limited. The oldest sphinctozoan-coral-microbial
reef is documented here, from the Upper Sanqushan Formation
(Late Katian) of southeast China. This is also the
first report of Ordovician sphinctozoans from South China.
The sponges occur in a >120-m-thick reef that is mainly
constructed by calcimicrobes (Kordephyton, Renalcis, and
Epiphyton) with a low abundance of in situ metazoans, predominantly
sphinctozoan sponges (Corymbospongia) and
rugose corals (mostly Palaeophyllum and Streptelasma).
Tetradium is the only tabulate coral preserved in growth
position. Crinoids and brachiopods are common reef dwellers.
Dasycladacean algae are rare and probably transported
and stromatactis is abundant. Bio- and litho-facies in this
area as well as the characteristics of the microbialite suggest
that the reef developed in a deeper subtidal setting that
was unfavorable for most metazoan reef builders. In contrast
to the high-energy stromatolite-sphinctozoan reefs
from the Late Silurian, this case represents a low-energy community, indicating that the first reef-building sphinctozoans
might have originated in a relatively deep-water
environment on seamounts of a back-arc basin during the
Late Ordovician.

The Yalgorup lakes, a groundwater-fed system in south-western Australia recognized as a Ramsar wetland, hold significant scientific and conservation value due to the presence of a unique range of lake systems, resident waterfowl and, on the eastern shore of Lake Clifton, the presence of the only thrombolite reef in the southern hemisphere. Recent concern over changing physico-chemical conditions in the lakes, particularly an increase in salinity, prompted this study: the current status of the inherent thrombolite community is unknown. Salinity, total phosphorous (TP), phosphate, total nitrogen (TN), nitrate, chlorophyll-a and relative abundance of the thrombolite microflora were measured in Lake Clifton to analyse changing conditions in this lake and to determine the effect of these water parameters on the thrombolite community. Comparisons with historical data revealed a significant increase in salinity since 1985 and a possible increase in phosphorus concentrations in the lake in the recent decade, although historical nutrient data are rather sparse. The increased salinity may be due to concentration of lake water through a combination of high evaporation, long-term reduction in rainfall and increased groundwater abstraction. Comparison of the composition of the thrombolite community with historical data indicates a large reduction in relative abundance of Scytonema sp. and other filamentous cyanobacterial species, which are believed to be fundamental for the thrombolite structure. It is concluded the changing physico-chemical environment of the Yalgorup Lakes may have led to the decline in important genera in the thrombolite community; however, the mechanisms underlying this change remain unknown.

The Griesbachian part of the Marmarasar Formation (Kara Baglyar) [1] in the Zangakatun (Sovetachen) section (Armenia) is characterized by microbial build-ups, spaced from 5 to 20m and surrounded by thin-bedded platy lime mudstone in a deep ramp environment. Above a basal carbonate fan crust follows a succession of thrombolitic domal forms, some of them up to 1.5m thick. The synoptic relief of the thrombolite head is estimated at 40-60cm above the muddy sea bottom. The overturned cone-shaped build-up geometry has a top head diameter up to 8m width consisting of numerous thrombolite domes, and an usual height of up to 15m. The water depth is interpreted below storm wave base and the asymmetrical build-up growth hints to a steady bottom current. Changes in the paleo-environment at the top of the kummeli conodont zone end the thrombolite growth. The overall duration of these post-extinction microbial build-ups is estimated at 700&#39;000 years. Comparable Late Proterozoic Conophyton-Jac...

We evaluated and optimized three rapid methods for extraction of high-quality DNA from carbonate-encrusted microbial communities using modern calcifying oncolites built by cyanobacteria and diatoms in a high-calcium freshwater river. Pulverization, acid (HCl) dissolution, and chelator-mediated (EDTA) dissolution of the carbonate matrix were used and optimized to liberate microbial cells from their mineral encasing. This was followed by cell lysis and DNA extraction and isolation. HCl dissolution yielded no measurable DNA, probably due to hydrolysis, whereas pulverization and EDTA dissolution yielded averages of 3.5 and 7.8 μg per gram of sample, respectively, of high molecular weight DNA. These DNA isolates could be used successfully for PCR-amplification of 16S rRNA gene segments (alleles) and subsequent fingerprinting of the cyanobacterial (including diatoms) and total bacterial communities through denaturing gradient gel electrophoresis (DGGE) separation. Fingerprints showed no differences in microbial community composition between the pulverization and EDTA dissolution methods. While the pulverization method was faster, we demonstrate here that EDTA carbonate dissolution is superior because it preserves vertical stratification of the microbial communities lost using the pulverization method, thus allowing for spatially resolved community analyses.

Permian-Triassic boundary microbialites (PTBMs) are thin (0.05-15 m) carbonates formed after the end-Permian mass extinction. They comprise Renalcis-group calcimicrobes, microbially mediated micrite, presumed inorganic micrite, calcite cement (some may be microbially influenced) and shelly faunas. PTBMs are abundant in low-latitude shallow-marine carbonate shelves in central Tethyan continents but are rare in higher latitudes, likely inhibited by clastic supply on Pangaea margins. PTBMs occupied broadly similar environments to Late Permian reefs in Tethys, but extended into deeper waters. Late Permian reefs are also rich in microbes (and cements), so post-extinction seawater carbonate saturation was likely similar to the Late Permian. However, PTBMs lack widespread abundant inorganic carbonate cement fans, so a previous interpretation that anoxic bicarbonate-rich water upwelled to rapidly increase carbonate saturation of shallow seawater, post-extinction, is problematic. Preliminary pyrite framboid evidence shows anoxia in PTBM facies, but interbedded shelly faunas indicate oxygenated water, perhaps there was short-term pulsing of normally saturated anoxic water from the oxygen-minimum zone to surface waters. In Tethys, PTBMs show geographic variations: (i) in south China, PTBMs are mostly thrombolites in open shelf settings, largely recrystallised, with remnant structure of Renalcis-group calcimicrobes; (ii) in south Turkey, in shallow waters, stromatolites and thrombolites, lacking calcimicrobes, are interbedded, likely depth-controlled; and (iii) in the Middle East, especially Iran, stromatolites and thrombolites (calcimicrobes uncommon) occur in different sites on open shelves, where controls are unclear. Thus, PTBMs were under more complex control than previously portrayed, with local facies control playing a significant role in their structure and composition.

ABSTRACT In the Late Triassic (~ 235–201.3 Ma) scleractinian corals and hypercalcified sponges built large, diverse reef ecosystems, the most famous of which are the Dachstein reefs. This study presents a depth transect along an Upper Triassic (lower Rhaetian) Dachstein reef from the Gosausee margin of the Dachsteingebirge (Gosau, Austria). The Gosausee microbial-sponge-coral reef is a complete barrier reef with an almost continuous fore reef to lagoon transect preserved (a very rare occurrence for the Triassic), and thus provides a window into depth zonation of Dachstein-type reef facies and biotic succession. The Gosausee reef facies exhibit strong depth control and five classic reef facies or zones are identified: the fore reef, reef front, reef crest, back reef, and lagoon facies. Thin, rare microbial fabrics and a high abundance of fine-grained, mud-rich skeletal wackestones (transported reef debris) characterize the deepest fore reef. As the reef shallows, muddy sediments decrease in abundance and are replaced by microbial fabrics, corals, and cements. Abundant sponges, microbial crusts, and thick, marine cements typify the reef crest, whereas microbialite-coated phaceloid corals are dominant in the back reef facies. Heavily cemented oncoids or microbial-sponge bindstones are characteristic of the lagoon. Based on their compositional and biotic similarities, the Gosausee reef was likely part of the same barrier reef systems as the source reef for the Gosaukamm reef breccia (one of the classic Norian–Rhaetian Dachstein reefs). The reef zones of the Gosausee margin can be used to interpret the depth or reef zone of less well preserved reef fragments, can inform models of community ecology and niche utilization in the Late Triassic, and highlight the need for additional research into the environmental factors that controlled biotic distribution in Upper Triassic reefs.

Community structure and composition are dictated by evolutionary and ecological assembly processes which are manifested in signals of, species diversity, species abundance and species relatedness. Analysis of species coexisting relatedness, has received attention as a tool to identify the processes that influence the composition of a community within a particular habitat. In this study, we tested if microbialite genetic composition is dependent on random events versus biological/abiotical factors. This study was based on a large genetic data set of two hypervariable regions (V5 and V6) from previously generated barcoded 16S rRNA amplicons from nine microbialite communities distributed in Northeastern, Central and Southeastern Mexico collected in May and June of 2009. Genetic data of the most abundant phyla (Proteobacteria, Planctomycetes, Verrucomicrobia, Bacteroidetes, and Cyanobacteria) were investigated in order to state the phylogenetic structure of the complete communities as w...

Community structure and composition are dictated by evolutionary and ecological assembly processes which are manifested in signals of, species diversity, species abundance and species relatedness. Analysis of species coexisting relatedness, has received attention as a tool to identify the processes that influence the composition of a community within a particular habitat. In this study, we tested if microbialite genetic composition is dependent on random events versus biological/abiotical factors. This study was based on a large genetic data set of two hypervariable regions (V5 and V6) from previously generated barcoded 16S rRNA amplicons from nine microbialite communities distributed in Northeastern, Central and Southeastern Mexico collected in May and June of 2009. Genetic data of the most abundant phyla (Proteobacteria, Planctomycetes, Verrucomicrobia, Bacteroidetes, and Cyanobacteria) were investigated in order to state the phylogenetic structure of the complete communities as w...