Niebuhr, Birgit , Puerner, Thomas , Goetz, Annette E. , Holzfoerster, Frank , Wilmsen, Markus
2024 ZEITSCHRIFT DER DEUTSCHEN GESELLSCHAFT FUR GEOWISSENSCHAFTEN 2024 175(卷), 4(期), (627-657页)
A revised stratigraphic, palaeoenvironmental and geodynamic interpretation of the continental Hessenreuth Formation is presented, based on integrated analyses of numerous new outcrops and shallow core sections as well as the 250-mlong core Friedersreuth 10/1990. The coarse-grained and highly immature siliciclastic succession reflects the inversion phase in the depositional history of the Danubian Cretaceous Group in the Albenreuth-Parkstein Depression (APD) along the Franconian Lineament, the northernmost segment of the staggered boundary fault system of the Bohemian Massif. Lithofacies and stratigraphic architecture of the Hessenreuth Formation allow for a distinction of five consecutive subunits, i.e. the Glash & uuml;tte, Parkstein, Glasern, Friedersreuth and Hesserberg members. The basal Glash & uuml;tte Member comprises more than 63 m of vividly coloured fluvial strata. The following ca. 78-m-thick conglomeratic sandstone packages of the Parkstein Member are interpreted as gravel-bed river deposits sourced from the N-NE (Fichtelgebirge, Saxothuringian Zone). Its terminal vividly coloured, fine-grained Red Clay-Iron Sandstone unit, indicates intermittent dryer conditions on the alluvial plain reflected by the Glash & uuml;tte and Parkstein members. The ca. 100-m-thick Glasern Member is predominantly composed of conglomerates and breccia conglomerates and subdivided into a lower cyclic and an upper chaotic subunit, interpreted as deposits generated by repeated debris-flow to flood-flow events on an alluvial fan. The polymictic coarse fraction indicates the immediately adjacent Zone of Erbendorf-Vohenstrau ss as major source area. The ca. 67-m-thick, fine-grained Frie dersreuth Member, containing fossil plant debris, reflects an intermittent base-level-rise accompanied by finer grained alluvial fan deposition while the abrupt change to the >150-m-thick, poorly-sorted, mica-rich cobble-to-boulder conglomerates of the Hesserberg Member indicates a proximal alluvial fan environment, close to a rapidly rising source area. According to our new palynological data, the marker Complexiopollis christae confirms a Turonian age for the Glash & uuml;tte to lower Friedersreuth members, while in the uppermost Friedersreuth Member and Hesserberg Member a Coniacian assemblage including Minorpollis minimus is identified; thus, the Turonian-Coniacian boundary is placed in the middle to upper Friedersreuth Member. The palynological data also indicate an alluvial plain vegetation, representing Normapolles-related gallery forests with herbaceous angiosperms and fern-dominated undergrowth. This vegetal palaeocommunity has now been identified in all Cretaceous basins around the Bohemian Massif. Lithofacies analysis revealed three different facies associations (FAs) namely alluvial plain-/overbank deposition of fines (FA 1), within channel deposition (FA 2) and debris-/mudflow deposition (FA 3), reflecting a distal-proximal gradient of a prograding warm-subhumid to semiarid alluvial fan depositional system. Petrographic data indicate that the bedrocks in the source area were deeply chemically weathered. A detailed stratigraphic correlation of the Hessenreuth Formation of the APD with the contemporaneous succession in the Bodenw & ouml;hr Depression (BWD) is presented, deposited to the south in the foreland of the Pfahl Fault. It is based on several bio-/ecostratigraphic tie points, cyclic sedimentation, and sequence stratigraphic interpretation. A comparable tectono-sedimentary evolution in both areas is detected. In the Early-Middle Coniacian boundary interval, the BWD was rapidly filled with shallow-marine sands while the Hesserberg Member in the APD reflects an abrupt increase in topography across the Franconian Lineament. We suggest that this striking change in depositional style marks the transition from basement folding in the Turonian to the formation of a frontal thrust fault with a concomitant fault scarp in the Coniacian. The Hessenreuth Formation, thus, provides a unique opportunity to study syntectonic deposition immediately in front of an active thrust fault system that accommodated Late Cretaceous crustal shortening in Central Europe.