Earth Sciences and Geography

The Neoproterozoic was characterized by an extreme glaciation, but until now there has been no consensus as to whether it was a complete glaciation (snowball Earth) or a less severe glaciation (slushball Earth). We performed sensitivity experiments with an Earth model of intermediate complexity for this period of dramatic global cooling. Our simulations focus on the climate response on a cool versus a cold ocean, on a desert versus a glacier land surface, and on a lower versus a higher CO2 concentration. All Neoproterozoic model experiments represent much colder conditions than today and widespread glaciation. In case of an initial forcing representing a snowball Earth, the model maintains its complete glaciation, and temperatures are as low as –45 °C in equatorial latitudes. At the poles, the snowball experiments demonstrate annual average temperatures of <–70 °C. If the initial model forcing is more moderate (slush-ball Earth), polar temperatures are <–50 °C, but temperatures in low latitudes stay well above the freezing point of water, and therefore ice-free ocean areas remain. Based on our simulations, we are able to observe that global climate reacts less sensitively to reductions of atmospheric CO2 during times with increased glaciations. Our results suggest that the development of glaciers on land contributes significantly to intense ice coverage of the oceans. Because simulations initialized without complete ice cover do not reach the global glaciation condition, we conclude that our simulations support the rather moderate scenario of a slushball Earth than the extreme snowball Earth hypothesis. The experimental design and the model might, however, limit the interpretation of our results.

Keywords: Neoproterozoic • snowball Earth • climate modeling • climate modeling sensitivity experiment

Of the several vein types with elongate crystals, we distinguish a class of veins with well-developed fibres, exposed at Oppaminda Creek (South Australia). These calcite veins are characterised by very limited competition between growing crystals, which leads to the development of fibrous crystals with smooth boundaries and which can attain extreme length–width ratios. Fibres are often curved and track the opening trajectory. The veins are also characterised by their outwards, antitaxial growth, starting from a narrow median zone. These median zones contain wall rock inclusions and a distinctly different, non-fibrous internal microstructure. Such veins continue growing as long
as extension is suitably oriented relative to the vein orientation. Multiple, cross-cutting vein sets can thus grow simultaneously and can together track over 908 rotation of the fibre growth direction.
The veins formed by calcite precipitation on both their outer surfaces. We suggest that the term ‘antitaxial’ should be redefined as applying only to those veins that have two simultaneous growth planes at their outer surfaces. Antitaxial veins grow without further fracturing, which sets them apart from other veins that grew by precipitation inside a crack, and which only have one single growth plane at the time.
The veins at Oppaminda Creek are about 585 Ma in age, and therefore formed at an estimated 4–6 km depth. Scanning electron microscope observations revealed about 1-mm-sized structures, which we interpret as fossils of microbes that lived inside the veins at the time of their formation, and which may even have played a role in the vein formation. These structures would represent the first finds of fossilised life forms of such a combined age and depth.
(c) 2004 Elsevier Ltd. All rights reserved.
Keywords: Fibrous veins; Antitaxial veins; Fossil microbes; Flinders Ranges; Neoproterozoic

Extremophile microbes are currently known to inhabit the surface and upper kilometres of the Earth's crust. Although deep microbial life may date back to the beginning of life on Earth, fossil evidence for deep life remains virtually non-existent. A main problem is the difficulty to find and recognise micron-sized fossil remains in the vast volume of rock.

We analysed 585 My old antitaxial fibrous calcite veins that formed at about 4-6 km depth in dark carbonaceous shales, found near Arkaroola, northern Flinders Ranges, South Australia [1]. The veins contain micron-sized biomorph structures, such as coccus- and globular structures, indications of cell division (wall bands, meridian constriction) and thin (0.1 µm) fibres with knots. The combined morphological evidence indicates that these constitute fossil microbes. These microbes must have lived during vein growth and, therefore, possibly played a role in the formation of the veins. The microbes bear some resemblance to the modern-day hyperthermal Archaea, such as Pyrodictium, which thrive at temperatures of about 80-120°C and have been found in hot springs and oil wells. Living by sulphur-metabolism, these Archaea typically alter carbonate solubility, leading to calcite precipitation, as well as minor pyrite as a by-product. Minor sulphides were found inside the veins. XRF and LA-ICPMS analyses of the veins and their immediate wall rock showed mobilisation of Ca, Fe, Mg, Na, Mn, P, S, Sr, Y, Sc, Pb, Zn, U, Cu, and Mo, some of which may indicate microbial activity.

The fossil microbes from Arkaroola indicate that life had penetrated deeper rocks at least at the end of the Proterozoic. If there is a link between the distinct antitaxial fibrous texture of the veins and microbial activity, this type of veins may help in the search for more, and possibly older evidence for deep microbial life in the geological record.

Keywords:

atmospheric oxygen;
charcoal;
Late Triassic;
palaeo-wildfire;
permineralization;
SW Germany

Abstract

So far only very few reports deal with Triassic (especially macro- or mesofossil) charcoal in detail. Here we present the first results of a detailed study of fossil charcoal from Late Triassic sandstones of the Tübingen Sandstein (Exter-Formation, haetian) in the vicinity of Tübingen in SW Germany. The discovery of charcoal at this locality can be regarded as direct evidence of wildfires in the hinterland of the Rhaetian sea and all charcoal fragments studied so far represent gymnosperm woods. At the moment nothing can be stated about the frequency and extent of such fires, although the occurrence of charcoal in different sandstone-bodies points to more than one fire event. The charcoal content of the marginal marine deposit probably represents a larger region and not only the vegetation in the direct vicinity of the shore. A considerable amount of transport is indicated by abrasion of some of the charcoal fragments and the taphonomic sorting, leading to the selected accumulation of woody fragments. Some charcoal fragments are permineralized by goethite and we assume that in this case the goethite is the primary permineralization agent. Our data support the assumption that during the Late Triassic atmospheric oxygen concentrations were high enough to sustain larger wildfires. Copyright © 2010 John Wiley & Sons, Ltd.

Silicified schwagerinids (superfamily Fusulinoidea v. Moeller 1878) from the Upper Carboniferous (Carnic Alps, Austria and Italy) were isolated from cemented carbonate rocks using hydrochloric acid. The shells show details of the wall texture and of internal structures in three dimensions which are illustrated with SEM pictures. Thin sections from hand specimens provided two-dimensional sections of the shell for comparison. The functional significance of fusulinoidean internal structures is discussed and compared with verbeekinoideans and alveolinids. Particular attention is paid on the disposition of the different openings within the shell and from the chamber lumen to the outside which reflects the direction of protoplasmic flow. Based on the knowledge of the nature of protoplasm ultrastructure in Recent foraminifera and its biological significance we draw some conclusions about the nature of protoplasm in fusulinoideans and its change within the Permian verbeekinoideans.

Keywords Larger foraminifera - Fusulinoidea - Verbeekinoidea - Alveolinidae - Structural elements - Functional morphology - Carnic Alps - Upper Carboniferous

ABSTRACT. Galeate acritarchs are a major component of Late Cambrian and Early Ordovician palynological assemblages. The populations of galeate acritarchs from the Cambrian–Ordovician transition section in borehole Nl-2 of the Algerian Sahara show a gradual increase in process length and in complexity of the process structures through the succession. While the number of striate elements at the process base, the number of distal ramifications, and the number of membranes between the processes increases progressively, the central body diameter shows only minor variation within the succession. The galeate acritarchs are here interpreted as probably being resting cysts of a microorganism similar to modern dinoflagellates. Published laboratory culture experiments on living dinoflagellates
document a considerable morphological variation with respect to the process morphology of the resting cysts that can be produced by a single biologically defined species. Based on these experiments, it is possible to interpret the morphological changes in the galeate acritarchs as being possibly related to changing ecological conditions. By analogy to the cyst distribution of modern dinoflagellates, changing salinity may have played an important role. Depending on environmental parameters, and perhaps on the maturity attained before rupture of the outer membrane during cyst formation, the galeate acritarchs may show a wide variety of process morphologies that have to date been used to describe four genera (morphogenera) and 84 species (morphospecies).

KEYWORDS: acritarchs, dinoflagellates, ecophenotypism, Cambrian–Ordovician, Algeria.

Abstract

The Black Forest (southwestern Germany) comprises two phyllite-bearing low-grade metasedimentary units, which are separated by the Central Schwarzwald Gneiss Complex. Both zones have been subjected to palynological investigation. In the north, the phyllites of the zone of Baden-Baden—Gaggenau, until now believed to be unfossiliferous, yielded a poorly preserved acritarch assemblage, indicating an age ranging from the Upper Cambrian to the Lower Ordovician. These phyllites may be equivalent to the Villé slates of the Vosges mountains (eastern France). In the south, the phyllites of the zone of Badenweiler—Lenzkirch contain chitinozoans of Silurian age.
Résumé

Datations palynologiques (acritarches et chitinozoaires) de phyllites du Paléozoïque inférieur de la Forêt-Noire (Sud-Ouest de l'Allemagne). La Forêt-Noire (Sud-Ouest de l'Allemagne) comprend deux unités métasédimentaires phylliteuses, séparées par le complexe gneissique du Schwarzwald central. Des recherches palynologiques ont été réalisées dans ces deux unités. Au nord, les phyllites de la zone de Baden-Baden—Gaggenau, jusqu'à présent considérées comme azoïques, ont livré un assemblage d'acritarches mal préservés, dont l'âge est compris entre le Cambrien supérieur et l'Ordovicien inférieur inclus. Ces phyllites seraient plus ou moins contemporaines des schistes de Villé du Nord des Vosges (Est de la France). Au sud, les phyllites de la zone Badenweiler—Lenzkirch contiennent des chitinozoaires du Silurien.

Author Keywords: palynology; acritarchs; chitinozoans; Black Forest; Variscan Belt; GermanyAuthor Keywords: palynologie; acritarches; chitinozoaires; Forêt-Noire; Chaîne varisque; Allemagne

Abstract

The metasediments of the low-grade metamorphosed Baden-Baden–Gaggenau zone of the northern Schwarzwald (southwestern Germany) have been analyzed palynologically. From 133 samples representing different metasedimentary units, only three samples of the upper part of the Traischbach Serie provide extremely poorly-preserved palynomorphs. The assemblage consists of the galeate acritarch genera Caldariola, Cymatiogaleaand Stelliferidium, as well as specimens of diacromorph and polygonomorph acritarchs. Although determinations are difficult at the generic level and essentially impossible at the specific level, the assemblage can be attributed to an interval between the Late Cambrian and Early Ordovician. This is the first biostratigraphical age assignment for the metasediments of the Baden-Baden–Gaggenau zone, which can possibly be correlated with the Villé Unit of the northern Vosges Mountains (eastern France).

Author Keywords: acritarchs; Cambrian; Ordovician; Schwarzwald; Germany; biostratigraphy

Copyright © 2000 Elsevier Science B.V. All rights reserved.

 In the northern Schwarzwald (Moldanubian Zone of the Variscan belt), paragneisses drilled from approximately 2500 m depth at the Bühl-1 drilling site have experienced amphibolite-facies metamorphism and were later partly transformed to mylonites under greenschist-facies conditions. Completely graphitised acritarchs and chitinozoans were recovered from these paragneisses and mylonitic gneisses. Whereas both groups of palynomorphs give evidence of a marine depositional environment, only the chitinozoans are stratigraphically useful in this case and indicate a Paleozoic age. Previous findings of acritarchs in a different high-grade metamorphic gneiss unit within the Schwarzwald indicate an Upper Proterozoic marine sedimentation age. The spectrum of palynomorphs found thus far in the Schwarzwald in combination with petrological data suggests that within the Moldanubian domain of the Armorican microplate, rocks with different sedimentary records later experienced diverging prograde metamorphic histories. In general, the results reveal that palynological studies in combination with petrological data are a promising tool for reconstructing pre-orogenic settings in collisional belts.

Key words Palynology - Sedimentation age - Amphibolite-facies gneisses - Schwarzwald - Variscan belt

Abstract

Shallow-water carbonates from the Lower Permian of Sonora, northwest Mexico, have yielded small organic-walled microfossils that show several features characteristic of inoflagellates. The oldest unequivocal dinoflagellate fossils, however, presently known come from the Middle Triassic. Earlier reports of microfossils with possible dinoflagellate affinity from the Paleozoic and Neoproterozoic, together with dinoflagellate-specific biomarkers found in Early Cambrian rocks and molecular phylogenetic analyses, suggest the presence of an intermediate stage of evolution, or protodinoflagellate group in pre-Mesozoic times.

Author Keywords: Microfossils; Dinoflagellata; Lower Permian; Mexico

The metasediments of the low-grade metamorphosed Baden-Baden–Gaggenau zone of the northern Schwarzwald (southwestern Germany) have been analyzed palynologically. From 133 samples representing different metasedimentary units, only three samples of the upper part of the Traischbach Serie provide extremely poorly-preserved palynomorphs. The assemblage consists of the galeate acritarch genera Caldariola, Cymatiogaleaand Stelliferidium, as well as specimens of diacromorph and polygonomorph acritarchs. Although determinations are difficult at the generic level and essentially impossible at the specific level, the assemblage can be attributed to an interval between the Late Cambrian and Early Ordovician. This is the first biostratigraphical age assignment for the metasediments of the Baden-Baden–Gaggenau zone, which can possibly be correlated with the Villé Unit of the northern Vosges Mountains (eastern France).

Author Keywords: acritarchs; Cambrian; Ordovician; Schwarzwald; Germany; biostratigraphy

The Black Forest (southwestern Germany) comprises two phyllite-bearing low-grade metasedimentary units, which are separated by the Central Schwarzwald Gneiss Complex. Both zones have been subjected to palynological investigation. In the north, the phyllites of the zone of Baden-Baden—Gaggenau, until now believed to be unfossiliferous, yielded a poorly preserved acritarch assemblage, indicating an age ranging from the Upper Cambrian to the Lower Ordovician. These phyllites may be equivalent to the Villé slates of the Vosges mountains (eastern France). In the south, the phyllites of the zone of Badenweiler—Lenzkirch contain chitinozoans of Silurian age.
Résumé

Datations palynologiques (acritarches et chitinozoaires) de phyllites du Paléozoïque inférieur de la Forêt-Noire (Sud-Ouest de l'Allemagne). La Forêt-Noire (Sud-Ouest de l'Allemagne) comprend deux unités métasédimentaires phylliteuses, séparées par le complexe gneissique du Schwarzwald central. Des recherches palynologiques ont été réalisées dans ces deux unités. Au nord, les phyllites de la zone de Baden-Baden—Gaggenau, jusqu'à présent considérées comme azoïques, ont livré un assemblage d'acritarches mal préservés, dont l'âge est compris entre le Cambrien supérieur et l'Ordovicien inférieur inclus. Ces phyllites seraient plus ou moins contemporaines des schistes de Villé du Nord des Vosges (Est de la France). Au sud, les phyllites de la zone Badenweiler—Lenzkirch contiennent des chitinozoaires du Silurien.

Abstract. - Within the Mid-European Variscan Belt, Heterocorallia have been described from the Rhenohercynian, the Saxothuringian and the Upper Austro-Alpine. A section from the Early Carboniferous of the Moldanubian Southern Vosges Mountains has yielded Heterocorallia, which are here described for the first time: Hexaphyllia sp. 1, Hexaphyllia sp. 2, Heterophyllia sp. and Heterophyllia aff. ornata M'Coy 1849. Their occurrence in calciclastic turbidites is an evidence for a Moldanubian Carbonate Platform. The fragile character of the heterocoral polypars in general might be an indication for low energy evironments within the platform. A comparison from Rhenohercynian, Saxothuringian and Moldanubian Heterocorallia results in good correspondence of the occuring taxa. Together with smaller benthic foraminifera it is possible to date the Heterocorallia bearing sediments from the Southern Vosges as Arundian (Visean).

Kurzfassung. - Aus dem Mitteleuropaeischen Variszikum sind Heterokorallen bisher nur von Lokalitaeten beschrieben worden, die innerhalb der rhenoherzynischen Zone, der saxothuringischen Zone und dem Oberostalpin liegen. Ein Profil aus dem Unterkarbon der moldanubischen Suedvogesen hat Heterokorallen geliefert, die hier erstmals beschrieben werden: Hexaphyllia sp. 1, Hexaphyllia sp.2, Heterophyllia sp. und Heterophyllia aff. ornata M'Coy 1849. Sie treten dort in calciclastischen Turbiditen auf, die auf eine moldanubische Karbonatplattform hinweisen. Die Zerbrechlichkeit der Heterokorallen-Polupare laesst auf niedrig-energetische Bereiche innerhalb der Platform schliessen. Ein Vergleich der Heterokorallen-Formen aus den drei Zonen zeigt, dass keine grossen Unterschiede hinsichtlich der auftretenden Taxa bestehen. Zusammen mit benthischen Kleinforaminiferen lassen sich die Heterokorallen-fuehrenden Sedimente aus den Suedvogesen in das Arundian (Vise, Unterkarbon) einstufen.

Resume. - Des Variscides de'Europe centrale, des Heterocorallia sont decrits jusqu'a present de localites situees dans les zones rhenohercynienne, saxothuringienne et du "Oberostalpine". Une section dans le Carbonifere inferieur des Vosges meridionales moldanubiennes a fourni des Heterocorallia qui sont decrits ici pour la premiere fois: Hexaphyllia sp. 1, Hexaphyllia sp. 2, Heterophyllia sp. et Heterophyllia aff. ornata M'Coy 1849. Ils sont issus de gisements calciclastiques turbiditiques qui indiquent une platforme carbonatee moldanubienne. La fragilite des polypares des Heterocorallia en general indique la presence de domaines de basse energie, Une comparraison entre des taxa Rhenohercyniens, Saxothuringienes et Moldanubiens des Heterocorallia ne revele pas des differences majeur. Il est possible, grace a de petites foraminiferes benthiques, de dater comme Arundien (Viseen, Carbonifere inferieur) les sediments a Heterocorallia des Vosges du sud.

(c) 2002 E. Schweizerbart'sche Verlagsbuchhandlung Stuttgart.

Abstract: The acritarchs are considered to form the oldest marine organisms with an eukaryotic cell organization. They are of great biostratigraphic, palaeoecological and palaeo-biogeographic importance for the Precambrian and Early Palaeozoic. The present study provides a survey of their possible biological affinities. The main morphological characteristics of the acritarchs and their palaeogeographic and palaeoecological distribution are described and evaluated. Regarding the genesis of eukaryotes, the serial endosymbiosis theory (SET), the archaezoa theory, the fusion hypothesis and the hydrogen hypothesis are briefly described, compared and discussed. Significant differences of the evolutionary acceleration of the proterozoic acritarchs (negative acceleration of vesicle diameters and simultaneous positive acceleration of diversity) are described and interpreted in the light of the SET as an evidence for major reorganizations of the cell compartments.

Keywords: Acritarcha, biological affinities, serial endosymbiosis
theory, archaezoa theory, fusion hypothesis, hydrogen hypothesis, evolutionary acceleration, cell compartments

Kurzfassung: Die Acritarchen bilden die aeltesten marinen Organismen mit mutmasslich eukaryotischer Zellorganisation.
Sie besitzen ftir die Zeitraeiume des Prakambriums und des tieferen Palaeiozoikums hohen biostratigraphischen Wert und eine grosse palaeio6kologische und palaeiobiogeographische Aussagekraft.
In der vorliegenden Studie wird eine kurze Ubersicht ueber moegliche biologische Beziehungen der Acritarchen gegeben and ihre wichtigsten morphologischen Merkmale sowie ihre palaeotoekologische und palaeobiogeographische Verbreitung dargestellt und diskutiert. Ftir die Entstehung der Eukaryoten werden neben der Seriellen Endosymbionten Theorie (SET) die Archaezoa-Theorie, die Fusions-Hypothese und die Wasserstoff-Hypothese komprimiert vorgestellt und vergleichend diskutiert.
Markante Akzelerationsunterschiede proterozoischer Acritarchen (negative Akzeleration der Vesikeldurchmesser
unter gleichzeitiger positiver Akzeleration der Diversitaeit) werden beschrieben und anhand der Prinzipien der SET als Hinweise auf bedeutende Reorganisationen der Zellkompartimen-tierung interpretiert.

Schluesselwoerter: Acritarcha, biologische Beziehungen, Serielle
Endosymbionten Theorie, Archaezoa-Theorie, Fusions-
Hypothese, Wasserstoff-Hypothese, evolutive Akzeleration,
Zellkompartimentierung

The metabolism of a variety of microbes is known to induce the precipitation of minerals, in particular calcite and opaline silica. This can, for example, be observed in hot springs, such as those in Yellowstone and Waikiki. Water-filled pores between sediment grains are filled with cement during diagenesis and this cementation can also be driven by microbial activity. If microbes at or near the Earth’s surface play a role in precipitation of minerals, it is likely that microbes that live deeper down inside rocks do the same. The present existence of microbial life down to several kilometres is well established. However, the type(s) of biomineralisation it may produce is largely unknown.
Antitaxial fibrous calcite veins from Arkaroola, South Australia, were found to contain fossil microbes, encased within the vein calcite [1]. The microbes lived inside the developing veins at a depth of 4-6 km in the late Proterozoic (585 Ma). The fact that the microbes lived inside the veins during calcite precipitation strongly suggests that they – at least in part – played a role in that precipitation. The calcite veins are therefore partly or wholly biomineralisations. These are currently by far the oldest known biomineralisations formed by deep microbial life.
To determine whether the microbial activity left a chemical fingerprint in the calcite we analysed the vein calcite and the adjacent carbon-rich shale with XRF [2] and LA-ICPMS.
These analyses showed enrichment of Cu close to the vein compared to the distant host rock and mobilisation of Ca, Fe, Mg, Mn, P, S, Sr, Y, Sc, Pb, Zn, Cu, and Mo, some of which may result from microbial activity.
The calcite veins have a particular fibrous texture, also known from microbial pore cementation, which is common in gypsum veins, but may also occur in quartz veins, such as the Palaeoproterozic quartz (tiger’s eye) veins from the banded-iron formations in the Hammersley Ranges. It is therefore possible that the fibrous texture is indicative of a microbial origin, which may help us in finding more, and older, remains of deep microbial activity.

Keywords: hyperthermophiles, fibrous veins, microbes, archaea

Extremophile microbes are known to currently inhabit the surface and upper kilometres of the Earth’s crust. Although deep microbial life may date back to the beginning of life on Earth, fossil evidence for deep life remains virtually non-existent. A main problem is the difficulty to find and recognise micron-sized fossil remains in the vast volume of rock.
We analysed 585 My old [1] antitaxial fibrous calcite veins that formed at about 4-6 km depth in dark carbon-rich shales, found near Arkaroola, northern Flinders Ranges, South Australia. SEM analysis shows that the veins contain micron-sized biomorph
structures, such as coccus-shaped and globular structures, indications of cell division (wall bands, meridian constriction) and thin (0.1 μm) fibres with knots [2]. The combined morphological evidence indicates that these constitute fossil microbes. These
microbes must have lived during vein growth and, therefore, possibly played a role in the formation of the veins, and making these veins wholly or partly biomineralisations.
The absence of known very old fossil deep life has led the scientific community towards seeking the origin of life at the Earth’s surface. However, the fossil microbes from Arkaroola indicate that life had penetrated deeper rocks at least at the end of the Proterozoic, and probably well before that time. It may well be possible that life originated within the crust, not at the surface. If there is a link between the distinct antitaxial fibrous texture of the veins and microbial activity, this type of veins may
help in the search for more, and possibly older evidence for deep microbial life in the geological record. In the end it may aid in resolving the enigmatic origin of life itself.