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Robson B.E.,Royal Holloway, University of London | Collinson M.E.,Royal Holloway, University of London | Riegel W.,Geowissenschaftliches Zentrum Gottingen | Wilde V.,Senckenberg Forschungsinstitut und Naturmuseum | And 2 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2015

Wildfire activity in early Paleogene greenhouse conditions can be used as an analogue to gauge the effect of future warming trends on wildfire in the current climate system. Inertinite (fossil charcoal in coal) from 11 autochthonous early Paleogene lignite seams from the Schöningen mine (Germany) was quantified using macerations, in situ pillars and industry standard crushed samples. A new three transect method was developed to quantify in situ charcoal. The combination of in situ pillars and crushed samples accounts for temporal and spatial variation in charcoal through a stratigraphically oriented pillar, whilst maintaining comparability with industry standards and previous work. Charcoal occurs as a range of randomly distributed particle sizes, indicating that fires were burning locally in the Schöningen peat-forming environment and in the surrounding areas, but according to petrological data, not in an episodic or periodic pattern. Although charcoal abundance is low (relative to previous high fire worlds such as the Cretaceous), three quantitative and semi-quantitative methods show increased wildfire activity (relative to the modern world) in the warmest parts of the early Paleogene. As atmospheric oxygen levels stabilised to modern values and precipitation and humidity became the main control on wildfire, increased rainfall followed by drier intervals would have created an environment rich in dry fuel in which wildfires could easily propagate if humidity was low enough. In the later part of the Early Eocene (Ypresian) charcoal abundance fell to levels similar to those found in modern peats. This indicates that the transition to the modern low fire world occurred within the Early Eocene, earlier than previous records suggest. © 2015 The Authors. Published by Elsevier B.V.

Muller A.,Geological Survey of Norway | Leiss B.,Geowissenschaftliches Zentrum Gottingen | Ullemeyer K.,University of Kiel | Breiter K.,Academy of Sciences of the Czech Republic
International Journal of Earth Sciences | Year: 2011

The lattice-preferred orientation (LPOs) of two late-Variscan granitoids, the Meissen monzonite and the Podlesí dyke granite, were determined from high-resolution time-of-flight neutron diffraction patterns gained at the diffractometer SKAT in Dubna, Russia. The results demonstrate that the method is suitable for the LPO analysis of polyphase, relatively coarse-grained (0. 1-6 mm) rocks. The Meissen monzonite has a prominent shape-preferred orientation (SPO) of the non-equidimensional minerals feldspar, mica and amphibole, whereas SPO of the Podlesí granite is unapparent at the hand-specimen scale. The neutron diffraction data revealed distinct LPOs in both granitoids. The LPO of the non-equidimensional minerals feldspar, mica and amphibole developed mainly during magmatic flow. In the case of the Meissen monzonite, the magmatic flow was superimposed by regional shear tectonics, which, however, had no significant effect on the LPOs. In both samples, quartz shows a weak but distinct LPO, which is atypical for plastic deformation and different in the syn-kinematic Meissen monzonite and the post-kinematic Podlesí granite. We suggest that, first of all, the quartz LPO of the Meissen monzonite is the result of oriented growth in an anisotropic stress field. The quartz LPO of the Podlesí granite, which more or less resembles a deformational LPO in the flattening field of the local strain field, developed during magmatic flow, whereby the rhombohedral faces of the quartz crystals adhered to the (010) faces of aligned albite and to the (001) faces of zinnwaldite. Due to shape anisotropy of their attachments, the quartz crystals were passively aligned by magmatic flow. Thus, magmatic flow and oriented crystal growth are the major LPO-forming processes in both granitoids. For the Meissen monzonite, the solid-state flow was too weak to cause significant crystallographic re-orientation of the minerals aligned by magmatic flow. Finally, the significance of our results for the evaluation of the regional tectonic environment during magma emplacement is discussed. The discussion on the regional implications of the more methodologically oriented results provides the basis for future, more regionally aimed studies in view of the fabric characteristics of such plutons and their developing mechanisms. © 2010 Springer-Verlag.

Lenhardt N.,TU Darmstadt | Lenhardt N.,University of Pretoria | Bohnel H.,National Autonomous University of Mexico | Wemmer K.,Geowissenschaftliches Zentrum Gottingen | And 3 more authors.
Bulletin of Volcanology | Year: 2010

The volcaniclastic Tepoztlán Formation (TF) represents an important rock record to unravel the early evolution of the Transmexican Volcanic Belt (TMVB). Here, a depositional model together with a chronostratigraphy of this Formation is presented, based on detailed field observations together with new geochronological, paleomagnetic, and petrological data. The TF consists predominantly of deposits from pyroclastic density currents and extensive epiclastic products such as tuffaceous sandstones, conglomerates and breccias, originating from fluvial and mass flow processes, respectively. Within these sediments fall deposits and lavas are sparsely intercalated. The clastic material is almost exclusively of volcanic origin, ranging in composition from andesite to rhyolite. Thick gravity-driven deposits and large-scale alluvial fan environments document the buildup of steep volcanic edifices. K-Ar and Ar-Ar dates, in addition to eight magnetostratigraphic sections and lithological correlations served to construct a chronostratigraphy for the entire Tepoztlán Formation. Correlation of the 577 m composite magnetostratigraphic section with the Cande and Kent (1995) Geomagnetic Polarity Time Scale (GPTS) suggests that this section represents the time intervall 22.8-18.8 Ma (6Bn.1n-5Er; Aquitanian-Burdigalian, Lower Miocene). This correlation implies a deposition of the TF predating the extensive effusive activity in the TMVB at 12 Ma and is therefore interpreted to represent its initial phase with predominantly explosive activity. Additionally, three subdivisions of the TF were established, according to the dominant mode of deposition: (1) the fluvial dominated Malinalco Member (22.8-22.2 Ma), (2) the volcanic dominated San Andrés Member (22.2-21.3 Ma) and (3) the mass flow dominated Tepozteco Member (21.3-18.8 Ma). © 2010 Springer-Verlag.

Jeffery A.J.,Keele University | Gertisser R.,Keele University | Jackson R.A.,Keele University | O'driscoll B.,Keele University | And 2 more authors.
Mineralogical Magazine | Year: 2016

The rare potassium zirconium silicate dalyite has been identified for the first time on Terceira, Azores, within syenitic ejecta of the Caldeira-Castelinho Ignimbrite Formation. New quantitative analyses of this dalyite were combined with the small number of published analyses from various locations worldwide to evaluate the mineral's compositional variability. Additionally, solid-state modelling has been applied to assess the site allocations of substituting elements. The new analyses yield the average formula (K1.84Na0.15)Σ=1.99(Zr0.94Ti0.012Hf0.011Fe0.004)Σ=0.967Si6.03O. Model results predict the placement of substituting Hf and Ti in the octahedral site, and highlight the overall complexity in the incorporation of Fe, Mg and Ba. The combined dataset reveals that dalyite found within peralkaline granites and syenites is generally defined by higher Na?K substitution and lower Ti?Zr substitution relative to dalyite from highly potassic rocks. The Terceira dalyite exhibits a bimodal variation in the degree of Na?K substitutionwhich is attributed to a K-enrichment trend induced by late-stage pore wall crystallization and albitization, coupled with the control of pore size upon the degree of supersaturation required to initiate nucleation of dalyite in pores of varying size. © by Walter de Gruyter Berlin/Boston 2016.

Inglis G.N.,University of Bristol | Collinson M.E.,Royal Holloway, University of London | Riegel W.,Geowissenschaftliches Zentrum Gottingen | Riegel W.,Senckenberg Forschungsinstitut und Naturmuseum | And 4 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2015

Sphagnum moss is the dominant plant type in modern boreal and (sub)arctic ombrotrophic bogs and is of particular interest due to its sensitivity to climate and its important role in wetland biogeochemistry. Here we reconstruct the occurrence of Sphagnum moss - and associated biogeochemical change - within a thermally immature, early Paleogene (~55Ma) lignite from Schöningen, NW Germany using a high-resolution, multi-proxy approach. Changes in the abundance of Sphagnum-type spores and the C23/C31 n-alkane ratio indicate the expansion of Sphagnum moss within the top of the lignite seam. This Sphagnum moss expansion is associated with the development of waterlogged conditions, analogous to what has been observed within modern ombrotrophic bogs. The similarity between biomarkers and palynology also indicates that the C23/C31 n-alkane ratio may be a reliable chemotaxonomic indicator for Sphagnum during the early Paleogene. The δ13C value of bacterial hopanes and mid-chain n-alkanes indicates that a rise in water table is not associated with a substantial increase in aerobic methanotrophy. The absence of very low δ13C values within the top of the seam could reflect either less methanogenesis or less efficient methane oxidation under waterlogged sulphate-rich conditions. © 2015 The Authors.

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