Streams in the Harz National Parks (Germany) — a hydrochemical and hydrobiological evaluation

Between 1995 and 2001, 16 measuring points at small and medium sized brooks in the Harz National Parks were sampled. The samples have been evaluated by means of hydrochemistry and macroinvertebrate biology. Although nearly all streams are largely uncontaminated by oxygen-consuming substances, they are settled only by a small number of macroinvertebrate species. There is a clear correlation between this number and pH. The reduction in species number with decrease of pH is mainly caused by the absence of most Ephemeroptera, some Coleoptera and Trichoptera. Comparing biological evaluation of acidity with physico-chemical measurements, a unacceptable underestimation was found. The reason could be that different sensitivities to acidification between regional populations seem to exist.

Despite of the low species number, there is a very specific macroinvertebrate fauna that emphasizes the conservation value of the Harz National Parks.     

Fluid inclusion evidence for impact‐related hydrothermal fluid and hydrocarbon migration in Creataceous sediments of the ICDP‐Chicxulub drill core Yax‐1

Fluid inclusions studies in quartz and calcite in samples from the ICDP‐Chicxulub drill core Yaxcopoil‐1 (Yax‐1) have revealed compelling evidence for impact‐induced hydrothermal alteration. Fluid circulation through the melt breccia and the underlying sedimentary rocks was not homogeneous in time and space. The formation of euhedral quartz crystals in vugs hosted by Cretaceous limestones is related to the migration of hot (>200 °C), highly saline, metal‐rich, hydrocarbon‐bearing brines. Hydrocarbons present in some inclusions in quartz are assumed to derive from cracking of pre‐impact organic matter. The center of the crater is assumed to be the source of the hot quartz‐forming brines. Fluid inclusions in abundant newly‐formed calcite indicate lower cyrstallization temperatures (75–100 °C). Calcite crystallization is likely related to a later stage of hydrothermal alteration. Calcite precipitated from saline fluids, most probably from formation water. Carbon and oxygen isotope compositions and REE distributions in calcites and carbonate host rocks suggest that the calcite‐forming fluids have achieved close equilibrium conditions with the Cretaceous limestones. The precipitation of calcite may be related to the convection of local pore fluids, possibly triggered by impact‐induced conductive heating of the sediments.     

Coastal erosion vs riverine sediment discharge in the Arctic Shelf seas

This article presents a comparison of sediment input by rivers and by coastal erosion into both the Laptev Sea and the Canadian Beaufort Sea (CBS). New data on coastal erosion in the Laptev Sea, which are based on field measurements and remote sensing information, and existing data on coastal erosion in the CBS as well as riverine sediment discharge into both the Laptev Sea and the CBS are included. Strong regional differences in the percentages of coastal erosion and riverine sediment supply are observed. The CBS is dominated by the riverine sediment discharge (64.45᎒⁶ t a^-1) mainly of the Mackenzie River, which is the largest single source of sediments in the Arctic. Riverine sediment discharge into the Laptev Sea amounts to 24.10᎒⁶ t a^-1, more than 70% of which are related to the Lena River. In comparison with the CBS, the Laptev Sea coast on average delivers approximately twice as much sediment mass per kilometer, a result of higher erosion rates due to higher cliffs and seasonal ice melting. In the Laptev Sea sediment input by coastal erosion (58.4᎒⁶ t a^-1) is therefore more important than in the CBS and the ratio between riverine and coastal sediment input amounts to 0.4. Coastal erosion supplying 5.6᎒⁶ t a^-1 is less significant for the sediment budget of the CBS where riverine sediment discharge exceeds coastal sediment input by a factor of ca. 10.     

Palaeobotanical evidence of wildfires in the Late Palaeozoic of South America – Early Permian, Rio Bonito Formation, Paraná Basin, Rio Grande do Sul, Brazil

Fossil charcoal, as direct evidence of palaeowildfires, has repeatedly been reported from several plant-bearing deposits from the Late Palaeozoic of the Northern Hemisphere. In contrast charcoal reports from the Late Palaeozoic deposits of the Southern Hemisphere are relatively rare in comparison to the Northern Hemisphere. Although the presence of pyrogenic coal macerals has repeatedly been reported from Late Palaeozoic coals from South America, no detailed anatomical investigations of such material have been published so far. Here is presented an anatomical analysis of charcoal originating from Early Permian sediments of the Quitéria Outcrop, Rio Bonito Formation, Paraná Basin, located in the central-eastern portion of Rio Grande do Sul, Brazil. This charcoal comes from two different coaly facies, and it was possible to scrutinize between three types, based on anatomical characters of the charcoal. Two of these charcoal types can be correlated to gymnosperm woods, and the other type corresponds to strongly permineralized bark with characteristic features of lycopsids. The presence of charcoal in different facies, ranging from parautochtonous to allochtonous origin, indicates that different vegetation types, i.e. plants which grew under wet conditions in the lowland as well as in the more dry hinterland, have experienced wildfires. Taking into account previous petrographic and lithological analyses from the facies in which the charcoal occurs and from the conditions of the wood and bark fragments, it was possible to speculate that the intensity of such wildfires most probably corresponds to forest-crown fires. Moreover, it is possible to state that wildfires have been a more or less common element in distinct Late Palaeozoic terrestrial ecosystems in the South American part of Gondwana. The data support previous assumptions on the occurrence of wildfires in the Early Permian of the Paraná Basin which were based solely on coal-petrographic data.     

Mediterrane Trias — Grundzüge und Probleme

Zusammenfassung Die mediterrane oder alpine Trias wurde im 19. Jh. nahezu als Standard-Typus der marinen Entwicklung dieses Systems aufgefaßt. Sie lieferte fast ausschließlich die Faunenfolgen zur biochronologischen Gliederung; Schicht- und Fazies-Bezeichnungen wurden aus dem alpinen Raum bis nach Südostasien übertragen. Eine gewisse Sonderstellung maß man nur ihren Ammonoideen-Faunen zu. Ihre Erforschung schien bald nach der Jahrhundertwende abgeschlossen.Seit zwei Jahrzehnten wird jedoch die Gliederung der mediterranen Trias mit Hilfe der Ammonoidea völlig revidiert. Darüber hinaus konnten neue biochronologische Standards von der phylogenetischen Entwicklung anderer Organismen-Gruppen (Conodonten, Ostracoden, Foraminiferen, Holothurien, Dasycladaceen, Sporen und Pollen) abgeleitet werden. Die marinen Sequenzen des Mittelmeerraumes haben dabei eine wesentliche Rolle gespielt.Zahlreiche moderne Fazies-Analysen, auf die nur kursorisch verwiesen wird, erlauben, die paläogeographischen Konturen im Westteil der triassischen Tethys schärfer zu sehen und ihre geotektonische Entwicklung plattentektonisch zu deuten. Ausgehend von permischen Vorzeichnungen öffneten sich ozeanische Arme im Norden (Vardar-Zone, wahrscheinlich mit Fortsetzung bis in die Alpen) und Süden (Sizilien, Alboran). Dabei wurden einige Mikroplatten von Afrika bzw. Europa abgespalten, von denen die Adria-Platte und ihre geotektonische Differenzierung während der Trias diskutiert werden.

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In a first period of exploration, until the beginning of our century, the Mediterranean or Alpine Triassic advanced to be a standard type of the marine development of that period. It served as well as the base for a world-wide biochronological division as for the deviation of facies types.Nevertheless the subdivision of the Triassic with the help of ammonoids was revised during the past decades, and new biochronological standards were derived from the phylogenetic evolution of other taxa: conodonts, ostracodes, foraminifera, holothuroids, dasycladacean algae, and from the palynological record. For these investigations, the Mediterranean region is again of special importance.The results of modern facies analysis which are not reviewed extensely in this paper, allow to discern the palaeogeographic contures in the western part of the Triassic Tethys with more accuracy and to sketch the outlines of a plate tectonic interpretation. Following to Permian configurations two deep branches of this oceans developed, one to the north (Vardar zone, probably to the Alps) and another in the south (Sicily-Alboran). Several microplates were split off from Africa and Europe. The geotectonic differentiation of one of them (Adria microplate) is discussed.

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Résumé Au 19ième siècle le Trias méditerranéen ou «alpin» a presque partout été considé ré comme type standard du développement marin de ce système. La subdivision biochronologique est largement basée sur ses faunes, et sa nomenclature stratigraphique fut transférée aux autres régions. Concernant les ammonoïdes, le Trias méditerranéen a, en effet, pris une position spéciale. Au début de notre siècle leur exploration semblait bientôt être achevée.Depuis vingt ans on travaille cependant à la révision de la subdivision du Trias sur la base des ammonoïdes. De plus de nouveaux standards biochronologiques ont pu être établis sur la base de l'évolution d'autres taxa (conodontes, ostracodes, foraminifères, holothuroïdes, algues, spores et pollens). Au cours de ces recherches les séries marines ont joué un rôle important.De nombreuses analyses de faciès dont il n'a été fait mention qu'en passant, permettent de voir plus distinctement dans la région de la Téthys les contours paléogéographiques et d'interpréter, selon la théorie de la tectonique de plaques, leur évolution géotectonique. Tracés déjà au Permien, deux bras océaniques s'ouvraient dans la Téthys occidentale, l'un marqué par la zône du Vardar et allant probablement jusqu'aux Alpes et l'autre dans région de Sicile et de Tunisie. Au cours de ce processus, plusieurs microplaques furent séparées de l'Afrique ainsi que de l'Europe. L'exemple de la microplaque adriatique et son évolution géotectonique au cours du Trias sont brièvement discutés.

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