Late Palaeozoic red beds elucidate fluvial architectures preserving large woody debris in the seasonal tropics of central Pangaea

Fluvial red beds containing anatomically preserved large woody debris shed new light on seasonally dry biomes of the Pennsylvanian–Permian transition and elucidate the concurrence of river depositional systems and vegetation. As a result, the occurrence, distribution and preservation of petrified large woody debris accumulations are considered crucial to understanding the role of arborescent vegetation in shaping fluvial environments. This study reports sizeable silicified trunks and corresponding fluvial architectures from the uppermost Pennsylvanian (upper Gzhelian) Siebigerode Formation (Kyffhäuser, central Germany). The origin, taphonomy and depositional environment of the fossil woods are elucidated by using a multidisciplinary approach including geological mapping, lithofacies analysis, sediment petrography, wood anatomical studies and microstructure analyses. Results reflect the gradual burial of a gentle basement elevation by sand-bed to gravel-bed braided rivers at the north-western margin of the perimontane Saale Basin. Facies architectures resulted from a complex interplay of syndepositional tectonics, repeated palaeorelief rejuvenation, high-frequency channel avulsion, seasonally dry climate and woody debris–sediment interactions. The alluvial influx and cut-bank erosion recruited trunks from adjacent semi-riparian slope habitats vegetated by up to 40 m tall cordaitaleans and conifers. High discharge in wide braids facilitated uncongested transport of large woody debris. Trunk entombment and initial preservation resulted from grounding on barforms, anchoring by attached roots and subsequent burial. The post-depositional two-phase silicification was influenced by hydrothermal hematite mineralization and determined a selective wood preservation pattern known as ‘pointstone’. Large woody debris-induced sedimentary structures (‘LWDISS’) are introduced as a class of sediment structures formed by the biogenic impact on terrestrial deposition

An andesitic sill complex in the Southern Permian Basin: volcanogenetic model and stratigraphic implications

Subvolcanic intrusions are highly variable in shape and structure, and occur in nearly all parts of the upper crust, as a result of extensive volcanic activity. Processes of subvolcanics interacting with the host rock are insufficiently understood, as they are rarely exposed. In the southernmost part of the Flechtingen-Altmark Subprovince, (sub)volcanic rocks of the Flechtingen Volcanic Complex (FVC) are exposed in several quarries. It is built up of silicic tuffs, ignimbrites and lava flows, but also of intermediate lavas and extended sill sheets. Additionally, major granitic intrusions exposed by drillings are associated with the FVC. In the Mammendorf quarry, a sill intruded in between lithified turbiditic series of early Carboniferous (Visean–Serphukovian) age at the base, and widely consolidated volcanoclastic deposits of late Carboniferous (late Pennsylvanian) age at the top. Various magma-host rock interactions were found indicating brittle and ductile deformation patterns occurring at the basal contact, and secondary fluidal mixing predominantly occurring at the top contact, most probably caused by fluids accompanying the intruding magma. We present an extended volcanogenetic model for the FVC. Volcanic activity initiated at 302 ± 3 Ma with fallout deposits represented by mostly re-deposited silicic ashfall deposits of the Flechtingen Formation, and cumulated in depositing major ignimbrite series, most likely forming a caldera. Later, the sills intruded at the rheological boundary of the lithified Mississippian turbiditic series and the partly consolidated volcanoclastic series. Finally, major granitic intrusions emplaced in the basement rocks at around 298 ± 4 Ma. The study contributes to clarify stratigraphic constraints of late Carboniferous to early Permian continental deposits and sheds light on stratigraphy of significant late Paleozoic volcanic deposits of the Flechtingen-Altmark Subprovince in the Southern Permian Basin

An andesitic sill complex in the Southern Permian Basin: volcanogenetic model and stratigraphic implications

<jats:title>Abstract</jats:title><jats:p>Subvolcanic intrusions are highly variable in shape and structure, and occur in nearly all parts of the upper crust, as a result of extensive volcanic activity. Processes of subvolcanics interacting with the host rock are insufficiently understood, as they are rarely exposed. In the southernmost part of the Flechtingen-Altmark Subprovince, (sub)volcanic rocks of the Flechtingen Volcanic Complex (FVC) are exposed in several quarries. It is built up of silicic tuffs, ignimbrites and lava flows, but also of intermediate lavas and extended sill sheets. Additionally, major granitic intrusions exposed by drillings are associated with the FVC. In the Mammendorf quarry, a sill intruded in between lithified turbiditic series of early Carboniferous (Visean–Serphukovian) age at the base, and widely consolidated volcanoclastic deposits of late Carboniferous (late Pennsylvanian) age at the top. Various magma-host rock interactions were found indicating brittle and ductile deformation patterns occurring at the basal contact, and secondary fluidal mixing predominantly occurring at the top contact, most probably caused by fluids accompanying the intruding magma. We present an extended volcanogenetic model for the FVC. Volcanic activity initiated at 302 ± 3 Ma with fallout deposits represented by mostly re-deposited silicic ashfall deposits of the Flechtingen Formation, and cumulated in depositing major ignimbrite series, most likely forming a caldera. Later, the sills intruded at the rheological boundary of the lithified Mississippian turbiditic series and the partly consolidated volcanoclastic series. Finally, major granitic intrusions emplaced in the basement rocks at around 298 ± 4 Ma. The study contributes to clarify stratigraphic constraints of late Carboniferous to early Permian continental deposits and sheds light on stratigraphy of significant late Paleozoic volcanic deposits of the Flechtingen-Altmark Subprovince in the Southern Permian Basin.</jats:p&gt