Węgiel we fliszu karpackim – kilka spostrzeżeń sedymentologicznych
Abstract
Occurrence of coal in the Carpathian flysch – some sedimentological observations
In the Carpathian Flysch, coal is present either as detritus of Carboniferous coal deposited together with other clastic material or as thin layers of lustrous coal. The latter is generally considered to derive as an effect of carbonisation of organic matter in flysch basin. Some authors (Birkenmajer, Turnau, 1962) suggested, on the basis of Carboniferous spores, that in the Aalen Flysch of the Pieniny Klippen Belt some coal layers are built of Carboniferous material, supplied to the basin by turbidity current.
EXOTICS OF THE UPPER CARBONIFEROUS COAL
Coal as detrital material of all fractions was supplied to the flysch basin from cordilleras, and, above all, from the land bordering the basin to the north. Transport directions of material point to the two main source areas: 1. Upper Silesia Coal Basin and its continuation to the south and 2. postulated coal basin being now under the Polish Eastern Carpathians (Bukowy, 1957, Kotlarczyk, Śliwowa, 1963). Turnau (1970) presumes that the two areas have formed one Precarpathian Coal Basin. In the external troughs of the flysch basin adjoining to these areas, coal exotics in the coarsest fractions, supplied in all the possible ways of transport, are especially frequent (Fig. 1). Activity of turbidity currents is probably responsible for spreading the fine — grained fractions far from the source areas, e. g. coal exotics in the Ukrainien Carpathians (Kopystiański et al., 1959), about 200 km away from the hipothetical Precarpathian Coal Basin.
COAL BLOCKS, PEBBLES AND GRAVELS
The coarsest coal fragments (up to 80 cm in diameter, Bukowy 1957) are found exclusively in pebbly mudstones. Exotics in these mudstones are rarely scattered (Fig. 3) and coal fragments, despite of their less density, have the same orientation as other exotics (Fig. 4). Orientation of the long axes of clasts agrees with Lindsay’s model for laminar flow, but orientation of short axes is different, pointing to the rotation of pebbles and „freezing” of mudflow during turbulent flow stage. Coal fragments of the gravel fraction were also transported by sand flow (fluxoturbidities). In this case they are arranged mostly along stream lines and form minor bodies lense-like in the cross-section (Fig. 5). Lineation of elongated clasts is parallel to the transport direction. Coal gravels have might be transported by turbidity currents in suspension. In the graded-bedded sandstones coal fragments are associated with gravel fraction. Till now, no proves for transport of coal fragments coarser than several cm were found. Coal sand is visible mostly in the laminated sandstones, where it is accumulated on some sedimentary surfaces and arranged along stream lines (Fig. 6) or it fills erosional furrows (Fig. 7). Coal silt forms an admixture in the clay shales and silts tones, coloured them black (Bukowy, 1957). Theoretically this fraction may form individual laminae in the clay-members of turbidity rhytms (Birkenmajer, Turnau, 1962).
LAYERS OF LUSTROUS COAL Discontinuous coal layers are several mm thick and several cm long, sometimes up to 30 cm thick and about 1 m long (Roth, 1962a). They are built of vitrinite. Others have physical proporties characteristic for brown coal (Schmidt et al., 1903, Horwitz, Doktrowicz-Hrebnicki, 1932, Gabiniet et al., 1977). Origin of some layers is undoubtedly connected with carbonisation of plant matter in situ (imprints of cortex, branches, fructifications etc, cf Kuźniar, 1910). Sedimentological (Fig. 8, 9, 10) and petrographic observations (lack of detrital structure) excluded their origin from coal silt. Such facts as: 1. occurrence of layers in nongraded mudflow or in sandstones formed under the upper flow regime; 2. irregular shapes of lenses in cross-section with splitted off ends; 3. occurrence of lenses on inclined sedimentary surfaces; 4. crossing of some layers — may be interpreted as an effect of fractional transport of plant remnants together with clastic material. Presence of few Carboniferous spores in some layers (Fig. 8) may be explained as a result of spore-sticking to the Cretaceous or Tertiary plant remnants during transportation. Occurrence of resedimented spores in sediments along with coarse grains and fragments of undoubtedly Carboniferous coal is quite understood. Presence of Carboniferous spores in some Aalen coal layers of the Pieniny Klippen Belt may be explained in this way.
In the Carpathian Flysch, coal is present either as detritus of Carboniferous coal deposited together with other clastic material or as thin layers of lustrous coal. The latter is generally considered to derive as an effect of carbonisation of organic matter in flysch basin. Some authors (Birkenmajer, Turnau, 1962) suggested, on the basis of Carboniferous spores, that in the Aalen Flysch of the Pieniny Klippen Belt some coal layers are built of Carboniferous material, supplied to the basin by turbidity current.
EXOTICS OF THE UPPER CARBONIFEROUS COAL
Coal as detrital material of all fractions was supplied to the flysch basin from cordilleras, and, above all, from the land bordering the basin to the north. Transport directions of material point to the two main source areas: 1. Upper Silesia Coal Basin and its continuation to the south and 2. postulated coal basin being now under the Polish Eastern Carpathians (Bukowy, 1957, Kotlarczyk, Śliwowa, 1963). Turnau (1970) presumes that the two areas have formed one Precarpathian Coal Basin. In the external troughs of the flysch basin adjoining to these areas, coal exotics in the coarsest fractions, supplied in all the possible ways of transport, are especially frequent (Fig. 1). Activity of turbidity currents is probably responsible for spreading the fine — grained fractions far from the source areas, e. g. coal exotics in the Ukrainien Carpathians (Kopystiański et al., 1959), about 200 km away from the hipothetical Precarpathian Coal Basin.
COAL BLOCKS, PEBBLES AND GRAVELS
The coarsest coal fragments (up to 80 cm in diameter, Bukowy 1957) are found exclusively in pebbly mudstones. Exotics in these mudstones are rarely scattered (Fig. 3) and coal fragments, despite of their less density, have the same orientation as other exotics (Fig. 4). Orientation of the long axes of clasts agrees with Lindsay’s model for laminar flow, but orientation of short axes is different, pointing to the rotation of pebbles and „freezing” of mudflow during turbulent flow stage. Coal fragments of the gravel fraction were also transported by sand flow (fluxoturbidities). In this case they are arranged mostly along stream lines and form minor bodies lense-like in the cross-section (Fig. 5). Lineation of elongated clasts is parallel to the transport direction. Coal gravels have might be transported by turbidity currents in suspension. In the graded-bedded sandstones coal fragments are associated with gravel fraction. Till now, no proves for transport of coal fragments coarser than several cm were found. Coal sand is visible mostly in the laminated sandstones, where it is accumulated on some sedimentary surfaces and arranged along stream lines (Fig. 6) or it fills erosional furrows (Fig. 7). Coal silt forms an admixture in the clay shales and silts tones, coloured them black (Bukowy, 1957). Theoretically this fraction may form individual laminae in the clay-members of turbidity rhytms (Birkenmajer, Turnau, 1962).
LAYERS OF LUSTROUS COAL Discontinuous coal layers are several mm thick and several cm long, sometimes up to 30 cm thick and about 1 m long (Roth, 1962a). They are built of vitrinite. Others have physical proporties characteristic for brown coal (Schmidt et al., 1903, Horwitz, Doktrowicz-Hrebnicki, 1932, Gabiniet et al., 1977). Origin of some layers is undoubtedly connected with carbonisation of plant matter in situ (imprints of cortex, branches, fructifications etc, cf Kuźniar, 1910). Sedimentological (Fig. 8, 9, 10) and petrographic observations (lack of detrital structure) excluded their origin from coal silt. Such facts as: 1. occurrence of layers in nongraded mudflow or in sandstones formed under the upper flow regime; 2. irregular shapes of lenses in cross-section with splitted off ends; 3. occurrence of lenses on inclined sedimentary surfaces; 4. crossing of some layers — may be interpreted as an effect of fractional transport of plant remnants together with clastic material. Presence of few Carboniferous spores in some layers (Fig. 8) may be explained as a result of spore-sticking to the Cretaceous or Tertiary plant remnants during transportation. Occurrence of resedimented spores in sediments along with coarse grains and fragments of undoubtedly Carboniferous coal is quite understood. Presence of Carboniferous spores in some Aalen coal layers of the Pieniny Klippen Belt may be explained in this way.