Late Paleozoic volcanism in the central part of the Southern Permian Basin (NE Germany, W Poland): facies distribution and volcano-topographic hiati

Abstract

Based on facies analysis of more than 5,500 m cores of 45 deep wells, three large sub-provinces have been defined for the Lower Rotliegend volcanic rocks in the central Southern Permian Basin (SPB) in northeastern Germany and western Poland. Additional data came from unpublished descriptions of more than 200 wells. The three sub-provinces are: (a) the Mecklenburg–Vorpommern Sub-Province (MVSP) dominated by silica-rich lava domes and subvolcanic intrusions, (b) the Eastern Brandenburg Sub-Province (EBSP) dominated by a Mg-andesite shield volcano complex, which extends into western Poland, and (c) the Flechtingen–Altmark Sub-Province (FASP) with prominent ignimbrite sheets punctuated by lava domes and flows. Whereas in NE Germany thickness of up to 2,300 m have been found in places, in western Poland ignimbrites and other pyroclastic deposits as well as andesitic and silica-rich lava complexes accumulated successions of a few hundreds of meters. A hiatus of up to 30 Ma occurs between the Lower Rotliegend volcanic and sedimentary rocks (Asselian–Sakmarian), and Upper Rotliegend II sediments (Upper Wordian–Capitanian). Upper Rotliegend I deposits are known from a few wells and outcrops, only. Previous studies postulated solely intrabasinal tectonics to account for this major unconformity. However, under semiarid to arid conditions as assumed for the Rotliegend of the SPB both SiO2-rich lava complexes and silica-poor shield volcanoes can be expected as being extremely resistant to weathering and erosion. Most probably these bodies “drowned” in a regolith formed by physical weathering, rarely removed by torrential rain. Thus, the silica-rich lava complexes and the shield volcanoes in the Central European Basin System (CEBS) can be viewed as long-living morphological highs, with intervolcanic depressions in between. In these intervolcanic depressions, syn- to postvolcanic successions of conglomeratic to sandy alluvial fan sediments and lake to mud flat deposits accumulated during the Upper Rotliegend I. They show numerous pedogenic horizons representing times of non-deposition. During the Upper Rotliegend II, the remaining volcano-topography was filled up with alluvial, eolian and playa deposits. In some places in western Poland, covering was not complete until the Zechstein (Latest Permian). At the same time, soil formation and/or erosion in the upper part of SiO2-rich complexes and shield volcanoes remained subordinate. Consequently, the volcano-topographic hiatus on top of the volcanic complexes comprises the maximum period of time, whereas in the intervolcanic depressions this time splits into periods of deposition and numerous minor intraformational hiati. Intrabasinal tectonic activity cannot be ruled out as one major control of the Rotliegend depositional evolution in the subsiding SPB. However, the presence of weathering-resistant volcanic edifices led to the formation of long-lasting depositional gaps in many regions of the central SPB.