| 1. |
- Bergstrom, Stig M., et al.
(author)
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High-resolution δ13Corg chemostratigraphy links the Decorah impact structure and Winneshiek Konservat-Lagerstätte to the Darriwilian (Middle Ordovician) global peak influx of meteorites
- 2018
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In: Lethaia. - : Scandinavian University Press / Universitetsforlaget AS. - 0024-1164 .- 1502-3931. ; 51:4, s. 504-512
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Journal article (peer-reviewed)abstract
- The precise age of the Winneshiek Shale, a recently discovered Konservat-Lagerstätte located in a very unusual depositional setting inside the Decorah impact structure, has remained uncertain in the absence of biostratigraphically highly diagnostic fossils. This chemostratigraphical study, based on δ13Corg data from 36 drill core samples through the shale, shows that the age ranges from the upper part of a small unnamed δ13C excursion in the Dw1 Stage Slice of the Darriwilian Global Stage to the lower part of the MDICE excursion in Stage Slice Dw2 of the same stage. This Dw1-Dw2 interval has an isotopic age of ~464-467 Ma. The gradational contact between the Winneshiek Shale and the underlying, rapidly deposited, impact breccia indicates minimal time difference between the impact event and the Winneshiek Shale. New age data show that the Decorah impact event was coeval with the early Darriwilian abnormally high influx of micrometeorites and meteorites recorded in sections in Baltoscandia, Russia and China and that the Decorah crater can be included among the unusually large number of meteorite craters formed during Middle and early Late Ordovician time. As is commonly the case in black shale deposits, the partly uniquely preserved Winneshiek Shale crater fauna is impoverished taxonomically and adds numerically relatively little to the conspicuous and much discussed Darriwilian global biodiversification increase.
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| 2. |
- Bergstrom, Stig M., et al.
(author)
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Katian (Upper Ordovician) delta C-13 chemostratigraphy and sequence stratigraphy in the United States and Baltoscandia: A regional comparison
- 2010
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In: Early Palaeozoic sea level and climate - Selected papers presented at the IGCP 503 closing meeting in Lille (France), 23-31 August 2008 (Palaeogeography, Palaeoclimatology, Palaeoecology). - : Elsevier BV. - 1872-616X .- 0031-0182. ; 296:3-4, s. 217-234
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Conference paper (peer-reviewed)abstract
- delta C-13 values of numerous limestone samples from Katian (Upper Ordovician) successions in Oklahoma and the Upper Mississippi Valley document the presence of at least three of the four positive excursions that have been recognized in the lower-middle Katian interval in the Cincinnati region in Ohio. Kentucky, and Indiana. A comparison with Estonia reveals that five out of the six positive excursions now recorded through the Katian succession in the Cincinnati region are present in the coeval stratigraphic intervals in Estonia, which suggests that these represent global perturbations in the carbon cycle A study of the relations between flooding events and delta C-13 excursions shows that only some of the excursions occur in transgressive intervals whereas other excursions are in regressive strata and hence, this is in conflict with the idea that positive carbon isotope excursions are forced by rises in sea level Part of a previously published attempt to use Upper Ordovician sequence stratigraphy for trans-Atlantic correlation is shown to be seriously out of phase with the biostratigraphy and chemostratigraphy Several of the sequences recognized in the Cincinnati region do not appear to have counterparts in Estonia, which suggests that they do not reflect eustatic, but local, conditions (C) 2010 Elsevier B V All rights reserved.
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| 3. |
- Bergstrom, Stig M., et al.
(author)
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Late Ordovician-Early Silurian delta C-13 chemostratigraphy in the Upper Mississippi Valley: implications for chronostratigraphy and depositional interpretations
- 2011
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In: Earth and Environmental Science Transactions of the Royal Society of Edinburgh. - 1755-6929. ; 102, s. 159-178
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Journal article (peer-reviewed)abstract
- A pioneer study of the previously unknown delta C-13 chemostratigraphy in the Ordovician/Silurian boundary interval in eastern Iowa and northeastern Illinois resulted in the discovery of the Hirnantian Isotope Carbon Excursion (HICE). The presence of this major isotope excursion in the Mosalem Formation in Iowa and the Wilhelmi Formation in Illinois, which indicates that the excursion interval in these units is of Hirnantian (latest Ordovician) rather than Early Silurian age, necessitates a revised chronostratigraphic classification of these units. Although the precise level of the Ordovician/Silurian boundary remains somewhat uncertain in the absence of the diagnostic graptolites, it is herein placed in the upper part, but well below the top, of the Mosalem Formation and at the top of the Wilhelmi Formation. During a major regression following the deposition of the Maquoketa Shale, the upper part of the latter elastic unit was in some places deeply eroded, resulting in a topographically dissected landscape with upland areas separated by wide incised valleys. During a subsequent late Hirnantian transgression, these palaeovalleys were gradually filled with marine sediments, but the upland areas were not transgressed until earliest Silurian times. The new chemostratigraphical evidence is in good agreement with the available biostratigraphical data, especially from corals, conodonts, and brachiopods. A preliminary chemostratigraphical study of the presumably coeval Edgewood Group successions in Pike County, northeastern Missouri failed to document any heavy delta C-13 values characteristic of the HICE and some, or all, of the Hirnantian values obtained there may be diagenetically overprinted.
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| 4. |
- Bergstrom, Stig M., et al.
(author)
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Revision of the position of the Ordovician-Silurian boundary in southern Ontario: regional chronostratigraphic implications of delta C-13 chemostratigraphy of the Manitoulin Formation and associated strata
- 2011
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In: Canadian Journal of Earth Sciences. - 0008-4077. ; 48:11, s. 1447-1470
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Journal article (peer-reviewed)abstract
- delta C-13 values of 142 samples from the Manitoulin Formation and subjacent strata collected from 14 exposures and two drill-cores on Manitoulin Island, Bruce Peninsula, and the region south of Georgian Bay suggest that the Manitoulin Formation is latest Ordovician (Hirnantian) rather than earliest Silurian in age. A delta C-13 excursion identified as the Hirnantian isotope carbon excursion (HICE), which has a magnitude of nearly 2.5 parts per thousand above baseline values, is present in an interval from the upper Queenston Formation to the lower to middle part of the Manitoulin Formation in most of Bruce Peninsula and in the area south of Georgian Bay, whereas on Manitoulin Island the RICE appears to be absent. This indicates that a significant part of the Manitoulin Formation is older on the Bruce Peninsula and in its adjacent region than on Manitoulin Island. The chemostratigraphically based conclusions are consistent with biostratigraphic data from conodonts and brachiopods. The Hirnantian delta C-13 curve from Anticosti Island, Quebec is closely similar to those of southern Ontario. Traditionally, the Ordovician-Silurian boundary has been placed at the base of the Manitoulin Formation, but the new results suggest that it is more likely to be at, or near, the base of the overlying Cabot Head Formation. These new results have major implications For the interpretation of the geologic history and marine depositional patterns of the latest Ordovician of a large part of the North American Midcontinent.
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| 5. |
- Bergstrom, Stig M., et al.
(author)
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The base of the global Dapingian Stage (Ordovician) in Baltoscandia: conodonts, graptolites and unconformities
- 2009
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In: Earth and Environmental Science Transactions of the Royal Society of Edinburgh. - 1755-6929. ; 99, s. 189-212
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Journal article (peer-reviewed)abstract
- In the recently completed and formally ratified new series and stage classification of the Ordovician System, the base of the Middle Ordovician Series coincides with the base of the global Dapingian Stage. In the Global Stratotype Section and Point (GSSP) of this stage, which is located at Huanghuachang in southern China, the base of the Dapingian Stage is defined its the level of first appearance of the conodont Baltoniodus triangularis. The fact that this species, along with some other taxa present at the Dapingian GSSP, Occurs in many sections in Baltoscandia makes it possible to recognise with considerable precision the level of this global stage boundary in Sweden, Estonia, northwestern Russia, and Denmark. In several, but not all, regions, especially in the East Baltic, the global stage boundary coincides with the base of the regional Volkhov Stage and Call be tied to the base of the Megistaspis polyphemus Trilobite Zone. The regionally somewhat different relationships between the position of the global stage boundary and a very widespread hardground complex are probably due to the occurrence of local and/or regional unconformities in the upper Floian-lower Dapingian interval. Although biostratigraphically important graptolites are present in the study interval in some Baltoscandic sections, the precise graptolite correlation of the base of the Dapingian Stage remains somewhat unclear, although it appears to be near, or at, the base of the Isograptus victoriae victoriae Zone (Ca 2).
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| 6. |
- Dahlqvist, Peter, et al.
(author)
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The lowermost Silurian of Jamtland, central Sweden: conodont biostratigraphy, correlation and biofacies
- 2005
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In: Transactions of the Royal Society of Edinburgh. Earth Sciences. - 0263-5933. ; 96:1, s. 1-19
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Research review (peer-reviewed)abstract
- The Late Ordovician-Early Silurian succession in Jamtland includes the marine Kogsta Siltstone, which is unconformably overlain by the shallow-water Ede Quartzite that grades into the open-marine Berge Limestone. A Hirnantia shelly fauna dates the uppermost Kogsta Siltstone as Hirnantian, and shelly fossils indicate an Aeronian age for the Berge Limestone. Biostratigraphically highly diagnostic conodonts of the early-middle Aeronian Pranognathus tenuis Zone provide the first firm date of the Upper Ede Quartzite and the lowermost Berge Limestone. The Lower Ede Quartzite has not yielded fossils, but sedimentological data suggest it to be of Hirnantian age and reflect the glacio-eustatic low-stand. The contact between the Lower and Upper Ede Quartzite, here taken to be the Ordovician-Silurian boundary, appears to be an unconformity associated with a stratigraphic gap that at least includes the Rhuddanian Stage. The biostratigraphically important conodonts Pranognathus tenuis, Kockelella? manitoulinensis, and Pranognathus siluricus are recorded from Sweden for the first time, and these and other conodonts are used for correlations with coeval units in Europe and North America. In a regional review of Aeronian conodont faunas, three intergrading, apparently depth-related, conodont biofacies are recognised, the Jamtland conodonts representing the one characteristic of the shallowest water.
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| 7. |
- Eriksson, Mats, et al.
(author)
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Biotic dynamics and carbonate microfacies of the conspicuous Darriwilian (Middle Ordovician) 'Taljsten' interval, south-central Sweden
- 2012
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In: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 1872-616X .- 0031-0182. ; 367, s. 89-103
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Journal article (peer-reviewed)abstract
- Enclosed in the Darriwilian (Middle Ordovician) part of the reddish 'orthoceratite limestone' of Baltoscandia is a conspicuous c. 1.5 m thick unit colloquially known as the 'Taljsten' interval. It has a wide geographical distribution in the Baltoscandian paleocontinent but is particularly well exposed in south-central Sweden. The unit is characterized by its deviant gray color and beds with a mass occurrence of cystoid echinoderms. Moreover, the recent discovery of an anomalous abundance of extraterrestrial chromite grains and micrometeorites in the 'Taljsten' and immediately adjacent strata bear witness of a time of deposition correlating to an increased influx of extraterrestrial matter to Earth. In this study we analyze the faunal dynamics, based primarily on microfossils and carbonate microfacies, across this intriguing interval. Generally known as a macrolithologically monotonous succession, the 'Taljsten' proved more heterogeneous than previously believed in terms of fossil content and preservation, as well as mineral content and composition. The general texture is wackestone/packstone, but local heterogeneities are frequent. A microfaunal reorganization occurred with a transition from a trilobite- and brachiopod-dominated community to one dominated by echinoderms, which is mirrored also macroscopically by the cystoids. The latter pelmatozoans seem to have flourished and might even have aided in the formation of the numerous hardgrounds. The increase in echinoderms is linked to a Volkhovian increase in echinoderms in eastern Baltica. In the immediate post-'Taljsten' strata there is no distinct change back to the pre-'Taljsten' biota. Conodont and ostracod faunal diversity data reveal peak values in the 'Taljsten' compared to the enclosing strata, suggesting that the paleoenvironment was more suitable for higher diversity faunas of these metazoan groups. All data collectively support a regression in the beginning of the 'Taljsten', likely followed by transgression in its upper part. (C) 2012 Elsevier B.V. All rights reserved.
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| 8. |
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| 9. |
- Schmitz, Birger, et al.
(author)
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Chemostratigraphy in the Swedish Upper Ordovician: Regional significance of the Hirnantian delta C-13 excursion (HICE) in the Boda Limestone of the Siljan region
- 2007
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In: GFF. - 2000-0863. ; 129, s. 133-140
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Journal article (peer-reviewed)abstract
- Samples from the Boda Limestone and immediately overlying strata at Osmundsberget in de Siljan region have produced an excellent Hirnantian isotope excursion (HICE) curve, in which the excursion interval is about 22 m thick and the HICE reaches maximum delta C-13 values of between +5 parts per thousand and +6 parts per thousand. Both the HA and HB stratigraphic unconformities are recognized in the study succession as well as in the coeval stratigraphic interval in the Loka Formation in Vastergotland and at Meifod in central Wales. A comparison between these and some other shallow-water successions in North America and northern Europe shows striking similarities in the delta C-13 curve, the lithology, and the stratigraphic sequence development. This is taken as support for the idea that glacio-eustacy exercised a major control on the depositional pattern in shallow-water successions during Hirnantian time. This applies also to the Osmundsberget succession where the formation of carbonate mounds was stopped by the HA regression that was caused by a major glaciation in Gondwana.
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| 10. |
- Schmitz, Birger, et al.
(author)
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The middle Darriwilian (Ordovician) delta C-13 excursion (MDICE) discovered in the Yangtze Platform succession in China: implications of its first recorded occurrences outside Baltoscandia
- 2010
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In: Journal of the Geological Society. - : Geological Society of London. - 2041-479X .- 0016-7649. ; 167:2, s. 249-259
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Journal article (peer-reviewed)abstract
- The middle Darriwilian delta C-13 excursion (MDICE), one of the least known of the Ordovician delta C-13 excursions, has previously been recorded only from the Middle Ordovician of Baltoscandia. Analysis of many recently collected limestone samples from the Guniutan Formation at two Yangtze Platform localities show elevated delta C-13 values in the same biostratigraphic interval (Microzarkodina ozarkodella Conodont Subzone) as the MDICE in Baltoscandia, which justifies identification of the Chinese delta C-13 excursion as the MDICE. These occurrences, which are in strata that show striking lithological and conodont faunal similarity to the Swedish Holen Limestone and some coeval units in Estonia, indicate that the MDICE, the stratigraphically oldest of the named Ordovician delta C-13 excursions, is likely to have a world-wide distribution and to have great potential for local and long-range chemostratigraphic correlations.
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