| 1. |
- Kozik, Nevin P., et al.
(författare)
-
Rapid marine oxygen variability : Driver of the Late Ordovician mass extinction
- 2022
-
Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 8:46
-
Tidskriftsartikel (refereegranskat)abstract
- The timing and connections between global cooling, marine redox conditions, and biotic turnover are underconstrained for the Late Ordovician. The second most severe mass extinction occurred at the end of the Ordovician period, resulting in ~85% loss of marine species between two extinction pulses. As the only “Big 5” extinction that occurred during icehouse conditions, this interval is an important modern analog to constrain environmental feedbacks. We present a previously unexplored thallium isotope records from two paleobasins that record global marine redox conditions and document two distinct and rapid excursions suggesting vacillating (de)oxygenation. The strong temporal link between these perturbations and extinctions highlights the possibility that dynamic marine oxygen fluctuations, rather than persistent, stable global anoxia, played a major role in driving the extinction. This evidence for rapid oxygen changes leading to mass extinction has important implications for modern deoxygenation and biodiversity declines.
|
|
| 2. |
- Bowman, Chelsie N., et al.
(författare)
-
Integrated sedimentary, biotic, and paleoredox dynamics from multiple localities in southern Laurentia during the late Silurian (Ludfordian) extinction event
- 2020
-
Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 553
-
Tidskriftsartikel (refereegranskat)abstract
- The Silurian was a time of major climatic transition punctuated by multiple biotic crises and global carbon cycle perturbations. The most severe of these biotic events was the late Silurian (Ludfordian) Lau/Kozlowskii extinction event (LKE) and the associated Lau carbon isotope excursion (CIE). Although the extinction event and Lau CIE are globally documented, the only records thus far of local and global marine paleoredox conditions through this interval are from a single region in Scandinavia. Here we examine four sections along a bathymetric transect of mixed carbonate-siliciclastic sediments from western Tennessee, USA. A novel approach using a multi-proxy dataset combining high-resolution geochemical data and microfacies analyses from multiple localities explores the possibilities of local/regional-scale redox heterogeneities during a time of widespread environmental upheaval on a global scale. Paired positive excursions recorded in carbonate carbon isotopes and carbonate-associated sulfate sulfur isotopes support recent work from carbonate and siliciclastic successions from Scandinavia, suggesting a global enhancement of organic carbon and pyrite burial driven by an expansion of euxinic (anoxic and sulfidic water column) conditions in the oceans during the mid-Ludfordian. Furthermore, positive excursions in organic carbon isotopes and pyrite sulfur isotopes reflect the global changes in redox. Stratigraphic trends in I/Ca ratios imply a local expansion of low-oxygen conditions, with low, but non-zero values during the rising limb and peak of the CIE. The fossil assemblages vary across the shelf and through the CIE interval. Stratigraphic changes in fossil assemblages and I/Ca are closely associated with local and global changes in oxygenation and sea level during the mid-Ludfordian. The collective data indicate significant biotic reorganization in response to changes in marine redox conditions and in conjunction with sea-level variation during the LKE interval, but detailed macroscopic biodiversity is currently unconstrained for this region.
|
|
| 3. |
- Kozik, Nevin P., et al.
(författare)
-
Progressive marine oxygenation and climatic cooling at the height of the Great Ordovician Biodiversification Event
- 2023
-
Ingår i: Global and Planetary Change. - 0921-8181. ; 227
-
Tidskriftsartikel (refereegranskat)abstract
- The oxygen content of ancient seawater has been hypothesized to be a major controlling factor for biodiversity throughout Earth's history. The Great Ordovician Biodiversification Event (GOBE) represents one of the largest increases in biodiversity during the Phanerozoic, with peak rates of diversity occurring in the Middle–Late Ordovician. Multiple causal factors have resulted in this long-term adaptive radiation, but direct links to marine oxygen levels remain poorly characterized. Here we utilize a multiproxy dataset from the Röstånga-2 drillcore, Skåne (Scania), southernmost Sweden, to constrain local and global marine paleoredox dynamics using a multi-proxy approach throughout the Middle–Late Ordovician (Darriwilian–early Sandbian stages). Pyrite sulfur isotopes (δ34Spyr), iron speciation and trace metal concentrations (V, U, and Mo) all indicate pervasive locally reducing conditions, and thallium (ε205Tl) isotopic compositions indicate significant changes in global Mn-oxide burial. This is one of the first studies to utilize direct local and global paleoredox proxies to identify changes in marine oxygen associated with peak rates of biodiversification in the Ordovician. Our new thallium isotope and pyrite sulfur isotope trends from black shale are combined with previously published carbonate-based redox proxy data (δ238U and δ34SCAS–carbonate-associated sulfate) from time equivalent successions in Baltica, Laurentia and Argentine Precordillera, indicating a global shift towards enhanced Mn-oxide burial, decreased anoxic seafloor area, and decreased pyrite burial, respectively. Thus, oceanic conditions during the Middle–Late Ordovician are interpreted to have transitioned from pervasive, highly reducing conditions towards more oxygenated marine settings. These changes in global paleoredox coincide with paleotemperature proxy data that indicated an overall climatic cooling trend during this time. Significant cooling of Ordovician oceans and climate would have permitted enhanced ventilation of marine environments, that in turn likely facilitated new ecospace development/utilization and ultimately drove marine biodiversification. Our results show a protracted, yet progressive oxygenation of marine environments over an interval of ∼11 Myr coinciding with peak rates of biodiversification during the GOBE.
|
|
| 4. |
- Kozik, Nevin P., et al.
(författare)
-
Protracted oxygenation across the Cambrian–Ordovician transition : A key initiator of the Great Ordovician Biodiversification Event?
- 2023
-
Ingår i: Geobiology. - : Wiley. - 1472-4677 .- 1472-4669. ; 21:3, s. 323-340
-
Tidskriftsartikel (refereegranskat)abstract
- Fluctuations in marine oxygen concentrations have been invoked as a primary driver for changes in biodiversity throughout Earth history. Expansions in reducing marine conditions are commonly invoked as key causal mechanisms for mass extinctions, while increases in marine oxygenation are becoming an increasingly common causal mechanism invoked for biodiversification events. Here we utilize a multiproxy approach to constrain local and global marine paleoredox conditions throughout the late Cambrian–Early Ordovician from two drill core successions in Baltoscandia. Local paleoredox proxies such as manganese concentrations and iron speciation reveal that both sites in the Baltic paleobasin had persistently anoxic and predominantly euxinic (anoxic and sulfidic) bottom water conditions throughout the study interval. Corresponding trace metal datasets indicate nuanced contraction and expansion of global anoxic and euxinic conditions along continental margins during the late Cambrian–Early Ordovician. Lastly, thallium isotope data from these locally reducing sections suggest a global expansion of oxygenated shelf and deeper marine environments from the late Cambrian into the Early Ordovician. This evidence for increasingly oxic marine environments coincides with increases in burrowing depth and tiering in marine animals, as well as diversification of body fossils throughout this ~8-million-year interval. The collective geochemical datasets provide some of the first direct paleoredox evidence for an increase in marine oxygen concentrations as a key mechanism for the Ordovician radiation of marine life.
|
|
| 5. |
- Lindskog, Anders, et al.
(författare)
-
Oxygenation of the Baltoscandian shelf linked to Ordovician biodiversification
- 2023
-
Ingår i: Nature Geoscience. - 1752-0894. ; 16:11, s. 1047-1053
-
Tidskriftsartikel (refereegranskat)abstract
- Marine biodiversity increased markedly during the Ordovician Period (~487–443 million years ago). Some intervals within the Ordovician were associated with unusually rapid and prominent rises in taxonomic richness, the reasons for which remain debated. Links between increased oxygenation and biodiversification have been proposed, although supporting marine oxygen proxy data are limited. Here we present an expansive multi-site iodine-to-calcium (I/Ca) record from Lower–Middle Ordovician marine carbonates in Baltoscandia that provides a detailed account of the spatio-temporal development of oxygen conditions across this palaeoshelf. The data document progressive oxygenation of regional seafloor environments, with well-oxygenated waters sourced from the palaeoequatorward Iapetus Ocean and peak I/Ca values (that is, dissolved oxygen concentrations) coinciding with the most pronounced biodiversity increases and ecosystem reorganizations during this time interval. This occurred while the climate cooled, global sea level dropped and carbonate deposits became regionally dominant. The results suggest that ventilation of shelves played a critical role in regulating early Palaeozoic marine biodiversity via development of ecospace and aerobic–metabolic conditions.
|
|
