| 1. |
|
|
| 2. |
- Bowman, Chelsie N., et al.
(författare)
-
Linking the progressive expansion of reducing conditions to a stepwise mass extinction event in the late Silurian oceans
- 2019
-
Ingår i: Geology. - 0091-7613. ; 47:10, s. 968-972
-
Tidskriftsartikel (refereegranskat)abstract
- The late Ludlow Lau Event was a severe biotic crisis in the Silurian, characterized by resurgent microbial facies and faunal turnover rates otherwise only documented during the "big five" mass extinctions. This asynchronous late Silurian marine extinction event preceded an associated positive carbon isotope excursion (CIE), the Lau CIE, although a mechanism for this temporal offset remains poorly constrained. Here, we report thallium isotope data from locally reducing late Ludlow strata within the Baltic Basin to document the earliest onset of global marine deoxygenation. The initial expansion of anoxia coincided with the onset of the extinction and therefore preceded the Lau CIE. Additionally, sulfur isotope data record a large positive excursion parallel to the Lau CIE, interpreted to indicate an increase in pyrite burial associated with the widely documented CIE. This suggests a possible global expansion of euxinia (anoxic and sulfidic water column) following deoxygenation. These data are the most direct proxy evidence of paleoredox conditions linking the known extinction to the Lau CIE through the progressive expansion of anoxia, and most likely euxinia, across portions of the late Silurian oceans.
|
|
| 3. |
- Cramer, Bradley D., et al.
(författare)
-
Testing the limits of Paleozoic chronostratigraphic correlation via high-resolution (<500 k.y.) integrated conodont, graptolite, and carbon isotope (delta C-13(carb)) biochemostratigraphy across the Llandovery-Wenlock (Silurian) boundary: Is a unified Phanerozoic time scale achievable?
- 2010
-
Ingår i: Geological Society of America Bulletin. - 0016-7606. ; 122:9-10, s. 1700-1716
-
Tidskriftsartikel (refereegranskat)abstract
- The resolution and fidelity of global chronostratigraphic correlation are direct functions of the time period under consideration. By virtue of deep-ocean cores and astrochronology, the Cenozoic and Mesozoic time scales carry error bars of a few thousand years (k.y.) to a few hundred k. y. In contrast, most of the Paleozoic time scale carries error bars of plus or minus a few million years (m. y.), and chronostratigraphic control better than +/- 1 m. y. is considered "high resolution." The general lack of Paleozoic abyssal sediments and paucity of orbitally tuned Paleozoic data series combined with the relative incompleteness of the Paleozoic stratigraphic record have proven historically to be such an obstacle to intercontinental chronostratigraphic correlation that resolving the Paleozoic time scale to the level achieved during the Mesozoic and Cenozoic was viewed as impractical, impossible, or both. Here, we utilize integrated graptolite, conodont, and carbonate carbon isotope (delta C-13 carb) data from three paleocontinents (Baltica, Avalonia, and Laurentia) to demonstrate chronostratigraphic control for upper Llandovery through middle Wenlock (TelychianSheinwoodian, similar to 436-426 Ma) strata with a resolution of a few hundred k.y. The interval surrounding the base of the Wenlock Series can now be correlated globally with precision approaching 100 k.y., but some intervals (e. g., uppermost Telychian and upper Shein-woodian) are either yet to be studied in sufficient detail or do not show sufficient biologic speciation and/or extinction or carbon isotopic features to delineate such small time slices. Although producing such resolution during the Paleozoic presents an array of challenges unique to the era, we have begun to demonstrate that erecting a Paleozoic time scale comparable to that of younger eras is achievable.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Ebbestad, Jan Ove R., et al.
(författare)
-
Terminal Ordovician stratigraphy of the Siljan district, Sweden
- 2015
-
Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 137:1, s. 36-56
-
Forskningsöversikt (refereegranskat)abstract
- Integration of new isotopic data and earlier biostratigraphic information from eight sections through the terminal Ordovician (Pirgu and Porkuni stages) of the Siljan district, Sweden, allows a more precise correlation of sections in terms of biostratigraphy and carbon isotope dating. Four levels with positive delta C-13 excursions are identified (from bottom) - the Moe, an unnamed excursion, Paroveja and Hirnantian Carbon Isotope Excursion (HICE). The delta C-13 values through the Boda Limestone are 1-2 parts per thousand higher than usual in Baltica, only the values for the HICE remains within what is expected. Background values increase from 1.5 parts per thousand in the bottom of the core of the Boda Limestone up to 3 parts per thousand in the top of it. The HICE is identified in five of eight sections and the main peak falls according to inferred correlation within the Metabolograptus persculptus Biozone, at or close to the Hindella beds in the Upper Boda Member. The late Katian (Pirgu) age of Holorhynchus in the Siljan district is clear and its co-occurrence with the chitinozoan Belonechitina gamachiana in Estonia supports a Katian age for this zone. The base of the Ozarkodina hassi Biozone may occur within units B-C of the Upper Boda Member and in the upper part of the Loka Formation and most likely is correlated with the M. persculptus Biozone. The Hirnantia-Dalmanitina faunas reported from the lowermost part of the Loka Formation and units B-D of the Upper Boda Member seem to range through all the Hirnantian, but detailed morphological studies allow to distinguish an older (=extraordinarius) and a younger (=persculptus) fauna.
|
|
| 7. |
- Ebbestad, Jan Ove R., 1967-, et al.
(författare)
-
Upper Ordovician carbon isotope records in the Siljan district, Sweden
- 2009
-
Ingår i: <em>Absolutely final meeting of IGCP 503: Ordovician palaeogeography and palaeoclimate - Copenhagen 2009 - August 31 – September 4</em>. - Copenhagen : Geological Museum, Natural History Museums. ; , s. 23-24
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Upper Ordovician Boda Limestone and the unconformably overlying Glisstjärn Formation in the Siljan district, Sweden, were sampled for carbon isotope analysis. The aim is to combine chemo- andAbsolutely final meeting of IGCP 503: Ordovician palaeogeography and palaeoclimate - Copenhagen 2009 - August 31 – September 424biostratigraphy for detailed regional correlation. This may help further studies of the time interval spanning the two-phased end Ordovician extinction. Expanding upon the study by Schmitz & Bergström (2007), five quarries, eight sections (669 samples) were studied; two sections each in Kallholn, Osmundsberget, and Solberga, and one section each in Östbjörka and Jutjärn. The Glisstjärn Formation is exposed only in one section at Kallholn, both sections at Osmundsberget, and possibly at one section in Solberga. A cephalopod event bed is recognized in one section in Kallholn and the two sections in Osmundsberget. Additionally, a thick coquina consisting of the brachiopod Hindella is found in all quarries except Solberga. The Hirnantian Isotope Carbon Excursion (HICE) was positively identified in seven of the eight sections. The peak occurs at the Hindella bed in all sections. The beginning of the excursion in Osmundsberget is placed slightly higher than in the previous study, at about 14 m from the top of the Boda Limestone, which means it is above the level with the brachiopod Holorhynchus (identified both in Osmundsberget and Solberga). In Osmundsberget, Östbjörka and Jutjärn, sampling of the deeper parts of the Boda Limestone yielded δ13C values between + 1 and + 3 ‰, with two or three peaks higher than + 3 ‰, that may be correlated between the sections
|
|
