Hirnantian (latest Ordovician) glaciations and their consequences for the Oslo Region, Norway, with a revised lithostratigraphy for the Langøyene Formation in the inner Oslofjorden area

Abstract

During the Hirnantian Age (Late Ordovician) the Oslo Region was located in a subtropical setting with siliciclastic input and carbonate production. At that time the sea level fluctuated in the Oslo Region during three regressive-transgressive episodes, some of which involved subaerial exposure and coastal valley erosion. The last major sea-level drop resulted in the formation of a conspicuous network of incised valleys that were subsequently filled with sediment during the transgression in the latest part of the Hirnantian. The continuing transgressive event rapidly flooded the exposed land areas in the central Oslo-Asker district. The areas towards the west in mainland Asker and Sylling in the adjacent Modum district were first transgressed in the late Rhuddanian (Early Silurian). Primarily eustatic processes affected the area, but synsedimentary faulting may also have been in play. There are two distinct palaeovalley trends: one at Hovedøya in Oslo more or less NW-SE, with narrow valley sides, the other at Kalvøya and surrounding areas trending approximately NE-SW, with one valley more than 10 km long. There may have been more than one filling phase. Sediment fill of the last-formed incised valleys were mapped and correlated across a large area of the Oslo-Asker district. Four new members of the Langøyene Formation are proposed: the Skaueren, Høyerholmen, Pilodden and Kalvøya members. Strata of the lateral Langåra Formation began deposition during the Katian. The rest of the formation as well as the Skaueren and Høyerholmen members contain fossils belonging to the cold-water Kosov fauna of early to mid Hirnantian age. The Pilodden and fossiliferous parts of the Kalvøya members include a mix of cold-water Kosov and warm-water Edgewood faunas of late Hirnantian age. Detailed descriptions of many incised valley fill sections in Oslo and Asker are included to show the spectrum of the sediment fill composition.

The latest Ordovician Hirnantian brachiopod faunas: New global insights

“…Marginal Laurentia: Girvan, Scotland (Harper, 1981(Harper, , 2006. Baltica: Jämtland (Dahlqvist et al, 2010), Scania (Koren et al 2003), Siljan (Suzuki et al, 2009;Ebbestad et al, 2015;Kröger et al, 2015), and Västergötland (Bergström, 1968;Bergström and Bergström, 1996), Sweden; Oslo-Asker Region, Norway (Cocks, 1982;Brenchley and Cocks, 1982;Bockelie et al, 2017); Estonia-Latvia (Harper and Hints, 2016;Hints and Harper, 2015); Holy Cross Mountains, Poland (Masiak et al, 2003). Avalonia: Meifod, C Wales (Brenchley et al, 2006;Schmitz and Bergström, 2007;Blackett et al, 2009); Bala, N Wales (Temple, 1965;Brenchley and Cullen, 1984;Vandenbroucke et al, 2008); Westmorland, N England (Temple, 1968;Wright, 1985Wright, , 1988Cocks, 2008), UK.…”

Exploring the end‐Ordovician extinctions in Hirnantian near‐shore carbonate rocks of northern Guizhou, SW China: A refined stratigraphy and regional correlation

“…In South China, Hirnantian black graptolitic shales are well developed, and shelly strata have been widely considered as being represented only by the early to mid‐Hirnantian Kuanyinchiao Formation (and its stratigraphic equivalents) deposited during the major Hirnantian glaciation, as indicated by the presence of typical Hirnantia fauna (Rong et al, ; Zhan, Liu, Percival, Jin, & Li, ). In shallow‐water carbonate platforms from low‐latitude regions, for example, Laurentia and Baltica, shelly fossils are dominant, and graptolites are either absent or very rare (e.g., Ainsaar, Truumees, & Meidla, ; Bergström et al, ; Bockelie, Baarli, & Johnson, ; Copper, Jin, & Desrochers, ; Kröger et al, ; Mauviel & Desrochers, ; Wang, Zhan, Huang, & Percival, ).…”

Plectatrypinae and other ribbed atrypides succeeding the end Ordovician extinction event, Central Oslo Region, Norway

“…persculptus Biozone or earliest Rhuddanian on the islands and coastal areas. Deposition first commenced in the Coronograptus cyphus Biozone, late Rhuddanian, inland far to the west in Asker at Olledalen (Bockelie et al, 2017). The base of the overlying Spirodden Member is correlated to the topmost part of the Lagarograptus acinaces Biozone in Asker (Fig.…”

“…The Central Oslo region also has gaps in the record, however, the gaps are quite short at some localities. The region in the beginning of Hirnantian was a coastal area with incised valleys and had a varied topography (Bockelie et al, 2017). When the sea level started to rise again at the base of the Metabolograptus persculptus Biozone near the middle Hirnantian age (Bergström et al, 2009), a rich and laterally variable brachiopod fauna was present from the beginning of the transgressive depositions already in latest Hirnantian.…”