Portal de Periódicos da CAPES

The sediments of the Floian GSSP: depositional history of the Ordovician succession at Mount Hunneberg, Västergötland, Sweden

2012; Taylor & Francis; Volume: 134; Issue: 4 Linguagem: Inglês

10.1080/11035897.2012.749943

2000-0863

Sven Egenhoff, Jörg Maletz,

Geological and Geophysical Studies

The succession at Mt. Hunneberg consists of intercalated siliciclastic mudstones and carbonates of Tremadocian to Floian age. Above an unconformity with underlying Furongian shales, siliciclastic mudstones with graptolites and overlying glauconite packstones of the upper Alum Shale Formation are exposed showing a sharp top contact to the carbonates of Bjørkåsholmen Formation. Above, the Tøyen Shale Formation consisting of siliciclastic mudstones and intercalated carbonate beds forms the stratigraphically youngest Ordovician unit at Mt. Hunneberg. The Tøyen Shale Formation is characterized by a lower marl- and carbonate-rich part, exclusively present in the southwest of Mt. Hunneberg, and an upper portion consisting of siliciclastic mudstones, extending from the Tetragraptus phyllograptoides graptolite Biozone on upwards. The siliciclastic mudstones of the Alum Shale Formation represent open shelf sediments reflecting sea-level highstands of two trans- and regressions. Overlying glauconite packstones indicate a transgression of Adelograptus zone age or younger. The Bjørkåsholmen Formation reflects a relative sea-level lowstand. The Tøyen Shale Formation records a deepening of the sedimentary environment during sea-level rise initially establishing offshore conditions, with the upper Tøyen Shale Formation siliciclastic mudstones indicating open shelf deposition. Abundant burrows throughout the succession reflect hospitable living conditions in the Mt. Hunneberg area, also during deposition of the Floian black shales. A pronounced decrease in thickness of the Hunneberg succession toward the northeast reflects erosion in the proximal compared to distal Hunneberg areas. The succession shows that alternating offshore to open shelf conditions is an ideal sedimentary environment to establish a Global Boundary Stratotype Section and Point with abundant and detailed biostratigraphic information.