The Labyrinthodontidae Beds in the Holy Cross Mountains (Poland) occur in the middle part of the Middle Buntsandstein in the northern marginal Triassic belt around the basement core. The predominantly sandy sequence is laid down in channels and flood-plains of a mainly moderately- to weakly-braided river system with generally moderately- to widely-spaced streams enclosing moderately wide to extensive overbank plains. The main watercourses are surrounded by a levee belt of proximal crevasse splays which laterally pass into shallow little channels and sheets of distal crevasse splays that intersect the floodplain. The diversification of bedding plane features in both main stream and crevasse-splay watercourse sands testifies to a wide spectrum of depositional, erosional, deformational and biogenic processes accompanying and punctuating the general sedimentary mechanisms of channel bar migration and sand sheet accumulation. Bröckelbank carbonate breccias within the substratum sequences document formation of mainly submature palaeosols in emerged parts of streams and overbank plains during occasionally longer periods of subaerial exposition. Secondary-erosional removal of overbank fines is the main mechanism to trigger the origin of multistorey channel deposits by superimposition of successive stream sands, whereas primary-sedimentary restriction of formation is the control of the original distribution of palaeosols prior to their complete secondary destruction. The inverse relationship between widespread accumulation of suspension fines and rare origin of palaeosols is the result of persistent inundation of the overbank area by extensive floods giving rise to long-term drowning of large parts of the topstratum flats. The evolution of fluvial style is restricted to the range of a narrow spectrum within the general facies model, with the two end members of a continuous sequence of patterns being moderately-braided streams with partially well-drained floodplains and weakly-braided rivers with poorly-drained overbank areas which correspond to the lower and upper part of a fluvial megacycle, respectively. Laterally and longitudinally, both types of channel network coexist forming occasionally a zoned braidplain, but in most cases, the second type of alluvial pattern is generally very subordinate in comparison to the dominant river type and is mainly present in some reaches of the stream belt. The evolutionary trend of decreasing braiding of the channel system and increasing width of floodplains leads to passage from substratum-dominated cyclothems in the lower part of the sequence to progressively increasing importance of overbank sedimentation towards the top of the succession, initiating the transition to the mainly silty-clayey topstratum deposition in the following members. The Labyrinthodontidae Beds in the Holy Cross Mountains are assigned to the medial zone II within the sedimentary model of the whole Mid-European Triassic Basin, representing an almost entirely alluvial plain with some pedogenesis in temporarily abandoned and emerged parts of the channel and floodplain fabric. The Labyrinthodontidae Beds have a key position in the overall evolution of fluvial depositional environment in the Buntsandstein of the Holy Cross Mountains by being the transition from the gravelly braidplain complex of the Czerwona Gora and Stryczowice Beds to the overbank system of the Hieroglyphic Beds and the Pseudooolithic Beds. The particular significance of the Bröckelbank carbonate breccias is the documentation of a change from arid to semi-arid climate during course of the sedimentological evolution which comprises a fluvial magnacycle owing to tectonic stability of the source area that is undergoing progressive denudation after initial uplift and creation of relief. The possibility of correlation with the evolution in the Eifel underlines the importance of the Labyrinthodontidae Beds for linking of the depositional history of several parts of the Mid-European Triassic Basin.
The Plains Of Passage Epub Download
The Permo-Scythian series in the Drauzug (Gailtal Alps and Lienz Dolomites) in Carinthia and Eastern Tyrol (Austria) represents a transgressive facies with transition from the denudated Variscan mountain chain via a restricted fluvial flat with braided river belts to an intertidal seam at the margin of a shallow epicontinental sea. The alluvial-fan and fluvial conglomerates and sandstones in the lower part of the sequence are progressively replaced by coastal sabkha and intertidal clastic and carbonate sediments in the upper part that pass into muddy and carbonate shallow marine deposits in the following members. Within the Permo-Scythian series which successively includes Laas Formation, Gröden Formation, Alpine Buntsandstein and Werfen Formation, the Alpine Buntsandstein records the passage from fluvial gravel and sand plains to a coastal sabkha with evaporation and a marine intertidal belt. In the littoral seam, reworking of the fluvially transported and deposited detritus by coastal near-shore currents takes place. The same general setting of the transition between Permian and Triassic is present in the Northern Calcareous Alps. In the context of the whole Upper Austroalpine Unit, the depositional framework of the Scythian series in the Eastern Alps reflects the progradation of delta complexes. Successive periods of progradation produced separate delta lobes that form a complex upon stacking and coalescence. Evaporation in fluvial and sabkha flats starts with dolomite cement in alluvial sandstones in the Early Scythian and increases towards the Middle Triassic with development of gypsum beds and magnesite-bearing sandstones and mudstones. The characteristic rauhwacke layers represent collapse breccias that originated from leaching of evaporites by percolating meteoric waters in the intertidal zone. In the Scythian series of the Eastern Alps (especially in the Alpine Buntsandstein), the fluvial system is mainly active in the western and northwestern part and gives way towards the south and southeast to an intertidal and beach plain belt at the margin of the prograding Tethys Sea. 2ff7e9595c
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