Sequence stratigraphic and genetic aspects of the Tournaisian "Liegender Alaunschiefer" and adjacent beds

Abstract

This study reports the results of interdisciplinary investigations of Tournaisian deposits from the German Rheinisches Schiefergebirge and provides a genetic and sequence stratigraphic interpretation. Microfacies and geochemical data confirm normal marine outer shelf to slope environments for the Lower Tournaisian Hangenberg Formation. In contrast, data from the condensed, phosphatic "Liegender Alaunschiefer" black shale indicate low current energy and anoxic conditions in the sediment and the water column. We suggest that anoxia was caused by eutrophication and high organic productivity due to factors such as upwelling, a climaterelated improvement of oceanic ventilation, and volcanic nutrient input. The Hangenberg Formation represents the lowstand through the early transgressive systems tract of a third-order depositional sequence, while the "Liegender Alaunschiefer" is a late transgressive systems tract and maximum flooding deposit. The Richrath Limestone was deposited during the highstand systems tract. Thus, quickly rising sea level and eutrophication may account for the peculiar and uniform facies of the "Liegender Alaunschiefer".

The Kulm Facies of the Montagne Noire (Mississippian, southern France)

“…The transition into that facies was gradual, as evidenced by the progressive dissociation of the nodular limestone beds and the increase of shale interbeds in the uppermost Montagne Noire Griotte Group. This scenario has to be put in context with the important global sea-level rise at the end of the early Tournaisian (Lower Alum Shale Event, Siegmund et al, 2002), which leads to the characteristic formation of dark shales with phosphatic nodules. A further important sea-level highstand (Avins Event, Poty, 2007) is connected to an extensive transgression in the late Tournaisian, and thus deposition of the Faugères Fm starts in the Ecailles Succession concordant on late Devonian rocks.…”

Petrophysical and geochemical signature of the Hangenberg Events: an integrated stratigraphy of the Devonian-Carboniferous boundary interval in the Northern Rhenish Massif (Avalonia, Germany)

“…The siliciclastic succession is capped by the Stockum Limestone, a marly nodular limestone horizon of the kockeli Zone to basal sulcata Zone age, which is missing at Oberrödinghausen. The overlying early Tournaisian Hangenberg Limestone (sulcata to quadruplicata Zone) is mainly composed of grey nodular limestones with thin shaly interbeddings, which has been interpreted as the lowstand system tract deposits (Van Steenwinkel 1993, Siegmund et al 2002. Its microfacies and diagenesis was studied by Van Steenwinkel (1984) and Siegmund et al (2002).…”

“…The overlying early Tournaisian Hangenberg Limestone (sulcata to quadruplicata Zone) is mainly composed of grey nodular limestones with thin shaly interbeddings, which has been interpreted as the lowstand system tract deposits (Van Steenwinkel 1993, Siegmund et al 2002. Its microfacies and diagenesis was studied by Van Steenwinkel (1984) and Siegmund et al (2002). The uppermost studied unit is represented by the Kahlenberg Formation (crenulata to cuneiformis zones).…”

“…Famennian; e.g., Becker 1992, Becker et al 2004, Racka et al 2010, Hartenfels 2011, the Dasberg Events/Crisis (late Famennian; e.g., Hartenfels & Becker 2009, Hartenfels 2011, the Hangenberg Events/Crisis (latest Famennian to earliest Tournaisian; e.g., Walliser 1984;Marynowski & Filipiak 1997;Kaiser et al 2006Kaiser et al , 2009Marynowski et al 2012) and mid-Tournaisian Lower Alum Shale Event (e.g., Becker 1993b, Zhuravlev 1998, Siegmund et al 2002. Although the possible triggers of many Late Devonian events are numerous and hotly debated, an intimate link between the Gondwana glaciation (e.g., Veevers & Powell 1987;Isaacson et al 1999Isaacson et al , 2008Streel et al 2000a;Almond et al 2002;Caputo et al 2008;Fielding et al 2008) and the multiphase Hangenberg Events is generally accepted in the literature (Caplan & Bustin 1999;Streel et al 2000bStreel et al , 2013Streel 2002;Streel & Marshall 2007;Isaacson et al 2008;Wicander et al 2011;Myrow et al 2013).…”

“…The decrease towards the top of the Hangenberg Limestone could be the result of such bounding of light organic carbon with a probable source in overlying organic-rich shales of the Kahlenberg Formation (Siegmund et al 2002, Kerschke & Schulz 2013.…”