Late Ordovician (Hirnantian) depositional pattern and sea-level change in shallow marine to shoreface cycles in central Sweden

The Upper Ordovician Kyrkås Quartzite Formation at the Nifsåsen Quarry (Jämtland, Sweden) exhibits c. 90 m of siliciclastic sedimentary rocks deposited on a shallow shelf at the craton-attached part of the Caledonian foreland basin. Five lithologies are distinguished, including claystone, mudstone, siltstone, subarkose and sublitharenite. Based on these five lithologies, sedimentary structures and biota, three marine facies associations are defined: the Mudstone association (FA1) deposited close to storm wave base, the Sandstone/mudstone association (FA2) formed between storm and fair-weather wave bases, and the Sandstone association (FA3) accumulated above fair-weather wave base. The facies associations are arranged in two sequences, c. 50 and 40 m thick, separated by a transgressive surface, indicating repeated shoreline progradation. Both sequences commence with marine heterolithic shales and siltstones, with upwardly increasing frequency of tempestites. Continued shoaling is indicated by a dominance of hummocky and trough (locally tabular) cross-stratified sandstone beds in the upper part of each sequence. Sand beds are increasingly amalgamated up-sequence, reflecting progressively diminishing accommodation space. The depositional style and sedimentary structures indicate that the study area was storm-dominated with an abundant supply of siliciclastic material. Biostratigraphic data tie the depositional changes to the globally recognized Late Ordovician (Hirnantian) glacial interval. These data suggest that the first sequence was formed during the initial phase of regression in the earliest Hirnantian. The lowermost part of the overlying sequence contains elements of a typical Hirnantia fauna followed by beds yielding Normalograptus persculptus, suggesting a second regressive cycle in the Jämtland basin during the early N. persculptus Biozone.

[1]  P. Dahlqvist,et al.  Late Ordovician palaeoceanographic changes as reflected in the Hirnantian–early Llandovery succession of Jämtland, Sweden , 2004 .

[2]  M. Whitehouse,et al.  Subduction‐flip during Iapetus Ocean closure and Baltica–Laurentia collision, Scandinavian Caledonides , 2003 .

[3]  D. Roberts.  The Scandinavian Caledonides: event chronology, palaeogeographic settings and likely modern analogues , 2003 .

[4]  J. Dowdeswell,et al.  Calibrating the Late Ordovician glaciation and mass extinction by the eccentricity cycles of Earth's orbit , 2000 .

[5]  R. Greiling,et al.  The orogenic wedge in the central Scandinavian Caledonides: Scandian structural evolution and possible influence on the foreland basin , 1998 .

[6]  T. Torsvik.  Palaeozoic palaeogeography: A North Atlantic viewpoint , 1998 .

[7]  L. Cherns,et al.  LATE ORDOVICIAN EARLY SILURIAN TRANSGRESSIVE SEDIMENTATION IN THE JAMTLAND BASIN, CENTRAL SWEDISH CALEDONIDES , 1995 .

[8]  L. Cherns.  A medusoid from the Late Ordovician or Early Silurian of Jämtland, central Sweden , 1994, Journal of Paleontology.

[9]  P. Brenchley,et al.  The role of wave reworking on the architecture of storm sandstone facies, Bell Island Group (Lower Ordovician), eastern Newfoundland , 1993 .

[10]  R. Gayer,et al.  Caledonian nappe geometry in north-central Sweden and basin evolution on the Baltoscandian margin , 1989, Geological Magazine.

[11]  B. Baarli.  Bathymetric co-ordination of proximality trends and level-bottom communities: a case study from the lower silurian of Norway , 1988 .

[12]  R. Walker,et al.  A storm and tidally‐influenced prograding shoreline—Upper Cretaceous Milk River Formation of Southern Alberta, Canada , 1986 .

[13]  P. Allen,et al.  Storm sedimentation , 1985, Journal of the Geological Society.

[14]  I. Stanistreet.  Contemporaneous faulting in the Upper Ordovician of the Oslo-Asker District, Norway, and its significance in the development of the Oslo Basin , 1983 .

[15]  R. Dott,et al.  Hummocky stratification: Significance of its variable bedding sequences , 1982 .

[16]  R. D. Kreisa.  Storm-generated sedimentary structures in subtidal marine facies with examples from the Middle and Upper Ordovician of southwestern Virginia , 1981 .

[17]  Jean Lajoie,et al.  Sand and Sandstone , 1974 .

[18]  G. Linström.  Förteckning på siluriska koraller från Jemtland, samlade af Dr G. Linnarsson , 1872 .

[19]  Jörgen Samuelsson.  Petroleum potential and thermal history of the Caledonian foreland basin, Sweden , 1997 .

[20]  D. Harper,et al.  Hirnantian Trilobites and Brachiopods in Space and Time , 1991 .

[21]  P. Brenchley,et al.  A facies analysis of upper Ordovician regressive sequences in the Oslo Region, Norway — A record of glacio-eustatic changes , 1980 .

[22]  J. Temple.  Upper Ordovician brachiopods from Poland and Britain , 1965 .

[23]  V. Jaanusson,et al.  The Cambrian, Ordovician, and Silurian in Västergötland, Närke, Dalarna, and Jämtland, Central Sweden , 1960 .