Filtern
Dokumenttyp
Sprache
- Englisch (5)
- Deutsch (1)
- Mehrsprachig (1)
Schlagworte
- Permineralisation (3)
- Raman spectroscopy (3)
- Anthracite (2)
- Anthrazit (1)
- CL Spectroscopy (1)
- CL microscopy (1)
- Cathodoluminescence microscopy (1)
- Coal rank (1)
- Pechkohle (1)
- Permineralization (1)
Samples of the permineralized tree fern Psaronius sp. from the Lower Permian Rotliegend of Chemnitz were examined to find out their chemical composition and structural behavior. The inhomogenic distribution of elementary constituents of oxides, sulfates and carbonates within the silica-matrix consisting of ?-quartz and chalcedony were formerly detected by analytical X-ray microscopy. Most of the compounds could be revealed by Raman spectroscopy. Calcite and barite developed in small fissures. Iron of different oxidation level is the prevailing pigment in the agate preserved adventitious roots. Coalified cellulose whose structure mainly corresponds to anthracite reflects the anatomical detail of the former organic tissues.
Permineralized samples of the tree fern Psaronius sp. belong to the spectacular discoveries of the Lower Permian Rotliegend Petrified forest of Chemnitz, one of the most famous palaeontological sites in the world. The cellular tissues of the 280 million years old fossil fern show a delicate three-dimensional preservation by permineralization. Moreover, anatomical detail can be distinguished very well because of the black coloured former cell walls. By means of Raman spectroscopy this fossilised tissue of the adventitious roots is revealed to be carbon which structure seems to correspond to anthracite. The aim of this work is the experimental confirmation of the carbon structure by means of thermogravimetry and Raman spectroscopy on coal samples of different rank, especially anthracite samples from different times and localities.
Coal maturation involves the sequence peatlignitecoalanthracite-microcrystalline graphite by incresasing the density and specific energy. The loss of in situ moisture (typically up to 200 °C) and volatile organic matter (up to 600 °C) has been acquired by thermogravimetry. The increasing carbon content, density resp. structure results in Raman spectra with typical band shape of the D- and G-peaks. We used these methods to characterise and compare the separated coal samples to the dispersed carbon inclusions in permineralized Psaronius.
Samples of different three-dimensionally preserved fossil plants (Medullosa sp., Dadoxylon sp., Calamodendron striatum, Psaronius sp.) from the Lower Permian petrified forest of Chemnitz were examined with regard to their chemical composition and structural order. Raman spectroscopy and cathodoluminescence microscopy are shown to be powerful tools for such investigations.
Silicified wood from ChemnitzHilbersdorf generally shows yellow cathodoluminescence (CL) of the cell walls and only weak yellow-brownish CL of the cell lumina. By time-resolved cathodoluminescence spectroscopy, a secondary mineralisation of hydrothermal origin was recognized. The latter is shown by short-lived blue CL at the cell walls extinguishing the yellow signal. Therefore, after the primary silicification step a secondary mineralisation step initiated by hydrothermal processes, seems to have taken place at probably slightly higher temperatures. The resulting silica matrix consists of phanerocrystalline and microcrystalline a-quartz as well as microcrystalline moganite, both partially associated with iron oxides.
Dadoxylon sp. is a prominent example for parallel permineralisation by a-quartz and fluorspar, which is outstanding for the Chemnitz Petrified Forest. CL on this samples shows parallel silicification and fluoritisation, followed by infiltration of iron oxides.
Permineralised samples show very low percentage of original organic remains. The seed fern Medullosa, for example, shows dispersed carbon, which is mainly restricted to the centres of the typical star-shaped vascular bundles. Raman spectroscopy revealed that these carbonaceous particles are of an anthracite structure. For experimental confirmation coal samples of different rank, especially anthracite from different geological times and localities, were studied by means of Raman spectroscopy. The remaining pith of the vascular bundles is white-coloured and consists of a-quartz and moganite, whereas surrounding tracheides exhibit white and reddish coloured parts. The reddish parts, mainly found in the rays, additionally contain a-Fe2O3 and Fe3O4 among the SiO2 polymorphs of a-quartz and moganite. Sometimes iron oxides could have dominated permineralisation processes as the peak intensities of distinct parts of the samples suggest.