SEDIMENTARY HISTORY OF THE MOYVOUGHLY AREA, COUNTY WESTMEATH, IRELAND: EVIDENCE FOR SYNSEDIMENTARY FAULT MOVEMENTS IN A MIXED CARBONATE-SILICICLASTIC SYSTEM OF COURCEYAN AGE

1991 ◽  
pp. 353-384
Author(s):  
GILL M. HARWOOD ◽  
MICHAEL SULLIVAN
Keyword(s):  
History Of ◽  
Mixed Carbonate

scholarly journals Carbon isotope chemostratigraphy and sea-level history of the Hirnantian Stage (uppermost Ordovician) in the Oslo–Asker district, Norway

2021 ◽  
pp. 1-32
Author(s):  
Mikael Calner ◽  
Johan Fredrik Bockelie ◽  
Christian M.Ø. Rasmussen ◽  
Hanna Calner ◽  
Oliver Lehnert ◽  
...  
Keyword(s):  
Sea Level ◽  
Fourth Order ◽  
Sedimentary Facies ◽  
Late Ordovician ◽  
Depositional Environments ◽  
Temporal Development ◽  
First Occurrence ◽  
History Of ◽  
Southern Norway ◽  
Mixed Carbonate

Abstract We present a δ13Ccarb chemostratigraphy for the Late Ordovician Hirnantian Stage based on 208 whole-rock samples from six outcrops in the Oslo–Asker district, southern Norway. Our data include the Norwegian type section for the Hirnantian Stage and Ordovician–Silurian boundary at Hovedøya Island. The most complete record of the Hirnantian Isotope Carbon Excursion (HICE) is identified in a coastal exposure at Konglungø locality where the preserved part of the anomaly spans a c. 24 m thick, mixed carbonate–siliciclastic succession belonging to the upper Husbergøya, Langåra and Langøyene formations and where δ13Ccarb peak values reach c. +6 ‰. Almost the entire HICE occurs above beds containing the Hirnantia Fauna, suggesting a latest Hirnantian age for the peak of the excursion. The temporal development of the HICE in southern Norway is associated with substantial shallowing of depositional environments. Sedimentary facies and erosional unconformities suggest four inferably fourth-order glacio-eustatically controlled sea-level lowstands with successively increased exposure and erosion to the succession. The youngest erosional unconformity is related to the development of incised valleys and resulted in cut-out of at least the falling limb of the HICE throughout most of the Oslo–Asker district. The fill of the valleys contains the falling limb of the HICE, and the postglacial transgression therefore can be assigned to the latest part of the Hirnantian Age. We address the recent findings of the chitinozoan Belonechitina gamachiana in the study area and its relationship to the first occurrence of Hirnantia Fauna in the studied sections, challenging identification of the base of the Hirnantian Stage.

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