Was Delayed Intercontinental Seas' Euxinia A Vital for Eukaryotes to Survive During the Statherian PaleoProterozoic?

Delayed euxinia in Paleoproterozoic intracontinental seas: Vital havens for the evolution of eukaryotes?

Authors:

Spinks et al

Abstract:

Increased flux of sulfate to the oceans in the aftermath of the Great Oxidation Event (GOE) ∼2.4 billion years ago (Ga) caused major changes in seawater chemistry, which eventually contributed to the cessation of iron formation deposition ∼1.8 Ga. It is generally accepted that this engendered heterogeneous stratified redox conditions, with anoxic and sulfidic (euxinic) conditions in shallow open-marine environments and anoxic ferruginous conditions in deeper environments. However, the redox evolution of intracontinental marine basins following the cessation of iron formation deposition remains poorly understood.

Here, we report contrasting paleoredox conditions in two shale units of the lower McArthur Basin, northern Australia, soon after the cessation of iron formation deposition ∼1.84 Ga. Our data shows that the ∼1.78 Ga McDermott Formation was deposited in a sulfur-limited, anoxic shallow-marine environment, whereas the younger ∼1.73 Ga Wollogorang Formation was deposited in a euxinic shallow-marine environment. This implies a delay in the development of euxinia in a shallow intracontinental basin following the onset of euxinia in the open marine realm. Since bioessential metals are sequestered by pyrite deposition under euxinic conditions, protracted low-sulfidic conditions in 1.78 Ga intracontinental shallow environments could have provided vital niches for nitrogen-fixing prokaryotes and eukaryotes. Thus the ability for localized Paleoproterozoic intracontinental basins to remain non-euxinic after the onset of euxinia in shallow open-marine shelves highlights the importance of intracontinental environments to the evolution and diversification of microbial life, perhaps throughout the wider Proterozoic.

Evidence of High Surface Ocean Productivity During the Middle Permian

Proliferation of shallow-water radiolarians coinciding with enhanced oceanic productivity in reducing conditions during the Middle Permian, South China: evidence from the Gufeng Formation of western Hubei Province

Authors:

Shi et al

Abstract:

The Middle Permian is a critical period when a possible cooling regime prevailed and massive deep-water cherty sediments were deposited in the South China Craton. An integration of radiolarian paleoecologic and geochemical studies from the Middle Permian Gufeng cherty succession of western Hubei Province, South China tests the relationships among oceanic productivity, redox conditions, and radiolarian responses as well as origin of the cherts. A total of 21 species and six undetermined species in 10 radiolarian genera are identified from the Gufeng Formation in the northern margin basin of the Yangtze Platform of the South China Craton. Three radiolarian Pseudoalbaillella globosa, Follicucullus monacanthus, and Follicucullus scholasticus zones were established and constrained the Gufeng Formation as Roadian to Middle Capitanian in age. The Gufeng cherts embrace a biologic and hydrothermal origin in the northern marginal basin and southern margin basin (the Nanpanjiang Basin) of the South China Craton, respectively. The high oceanic primary productivity in surface oceans resulted in the widespread reducing conditions in the bottom water column. Such high oceanic productivity event slightly predated the Middle Permian Kamura cooling event of the Panthalassian Ocean. Both the elevated continent weathering due to pre-eruptive crustal uplift of the Emeishan flood volcanism and active oceanic upwelling may have stimulated high oceanic productivity and facilitated the deposition of the Gufeng cherts. All radiolarians bloomed in relatively oxic conditions. Only shallow-water radiolarians, mainly spherical forms, proliferated in the reducing conditions, which also coincided with an enhanced oceanic productivity. The abundance of spherical radiolarians therefore is an ideal proxy indicating oceanic primary productivity.

Electricity Generating Bacteria Produce "Firewall" Against Euxinia

Cable bacteria generate a firewall against euxinia in seasonally hypoxic basins

Authors:

Seitaj et al

Abstract:

Seasonal oxygen depletion (hypoxia) in coastal bottom waters can lead to the release and persistence of free sulfide (euxinia), which is highly detrimental to marine life. Although coastal hypoxia is relatively common, reports of euxinia are less frequent, which suggests that certain environmental controls can delay the onset of euxinia. However, these controls and their prevalence are poorly understood. Here we present field observations from a seasonally hypoxic marine basin (Grevelingen, The Netherlands), which suggest that the activity of cable bacteria, a recently discovered group of sulfur-oxidizing microorganisms inducing long-distance electron transport, can delay the onset of euxinia in coastal waters. Our results reveal a remarkable seasonal succession of sulfur cycling pathways, which was observed over multiple years. Cable bacteria dominate the sediment geochemistry in winter, whereas, after the summer hypoxia, Beggiatoaceae mats colonize the sediment. The specific electrogenic metabolism of cable bacteria generates a large buffer of sedimentary iron oxides before the onset of summer hypoxia, which captures free sulfide in the surface sediment, thus likely preventing the development of bottom water euxinia. As cable bacteria are present in many seasonally hypoxic systems, this euxinia-preventing firewall mechanism could be widely active, and may explain why euxinia is relatively infrequently observed in the coastal ocean.

Detection of the Devonian Hangenberg Event in an Open Oceanic Island Arc

Climate instability and tipping points in the Late Devonian: Detection of the Hangenberg Event in an open oceanic island arc in the Central Asian Orogenic Belt

Authors:

Carmichael et al

Abstract:

Sedimentary petrology and trace element geochemistry indicate that the Late Devonian to Early Carboniferous Heishantou Formation near Boulongour Reservoir (NW Xinjiang, China) was deposited on a steep slope, mid-latitude accreting island arc complex in an open oceanic system. Bulk 87Sr/86Sr ratios show excursion patterns that are consistent with excursions at the Devonian-Carboniferous (D-C) boundary in epicontinental margin sediments. Sedimentation rates for the Boulongour Reservoir sediments show highly variable rates that range from 0.5 cm/ky to 10 cm/ky, consistent with other Late Devonian sections and modern arc environments. Multiple whole rock geochemical proxies for anoxia and the size and distribution of pyrite framboids suggest the presence of the Hangenberg Event in the sediments associated with the D-C boundary, despite the lack of visible black shale. The presence of anoxia in an open ocean, island arc environment cannot be explained by upwelling of anoxic bottom waters at this paleolatitude, but can be explained by the global infliction of oceanic shallow water eutrophication on to a climate system in distress.

Awesome Triassic-Jurassic Mass Extinction Picture

Credit Victor Leshyk.

 The related paper.

Episodic Photic Zone Marine Euxinia During the Triassic-Jurassic Mass Extinction

Episodic photic zone euxinia in the northeastern Panthalassic Ocean during the end-Triassic extinction

Authors:

Kasprak et al

Abstract:

Severe changes in ocean redox, nutrient cycling, and marine productivity accompanied most Phanerozoic mass extinctions. However, evidence for marine photic zone euxinia (PZE) as a globally important extinction mechanism for the end-Triassic extinction (ETE) is currently lacking. Fossil molecular (biomarker) and nitrogen isotopic records from a sedimentary sequence in western Canada provide the first conclusive evidence of PZE and disrupted biogeochemistry in neritic waters of the Panthalassic Ocean during the end Triassic. Increasing water-column stratification and deoxygenation across the ETE led to PZE in the Early Jurassic, paralleled by a perturbed nitrogen cycle and ecological turnovers among noncalcifying groups, including eukaryotic algae and prokaryotic plankton. If such conditions developed widely in the Panthalassic Ocean, PZE might have been a potent mechanism for the ETE.

Evidence of Euxinia During the Frasnian–Famennian Devonian Mass Extinction

Geochemical evidence for euxinia during the Late Devonian extinction events in the Michigan Basin (U.S.A.)

Authors:

Formolo et al

Abstract:

Several mass extinction events occurred in the Late Devonian, but the trigger for these events remains elusive. In this study, geochemical evidence in the Late Devonian Antrim Shale, Michigan Basin, U.S.A., records episodic euxinia contemporaneous with these extinction events. Diagnostic changes in iron proxy data and elevated trace metal enrichments correspond to the Kellwasser Crisis. In this study, carbon, sulfur, iron and trace metal geochemistry preserved in the Antrim Formation validates the establishment and expansion of euxinic conditions associated with the Kellwasser Crisis and the Frasnian–Famennian boundary. The strength of the sequential extraction iron mineral data presented here, in concert with trace metal and sulfur isotope proxies, provides definitive signatures of euxinia when other data may be more ambiguous in regard to paleoredox conditions. During the time of the Frasnian–Famennian boundary extensive sulfide oxidation at the chemocline, the result of Fe-limiting conditions within the basin, provides an alternative explanation for the oceanic decline in δ34SSO4 during, and following, the Frasnian–Famennian event. Our geochemical evidence, indicating the presence of anoxia in the Michigan Basin, is consistent with data from other globally distributed locations. Euxinia should be considered a key driver for these global extinction events, and possibly others such as the Hangenberg Event in the Late Devonian.

Cenomanian/Turnonian Cretaceous Ocean Anoxic Event 2 had a More Complex Carbon Cycle Than Suspected

Decoupling of the carbon cycle during Ocean Anoxic Event 2

Authors:

Eldrett et al

Abstract:

The Cenomanian to Turonian boundary transition (ca. 95–93 Ma) represents one of the most profound global perturbations in the carbon cycle of the past 140 m.y. This interval is characterized by widespread deposition of organic-rich fine-grained sediment marked by a globally recognized positive carbon isotope excursion (CIE) reflecting the widespread removal of 12C-enriched organic matter in marine sediments under global anoxic greenhouse conditions. However, the exact timing and trigger of this inferred global phenomenon, termed Oceanic Anoxic Event 2 (OAE-2), is still debated, with recent studies showing diachroneity between the deposition of the organic-rich sediment and the CIE, and conflicting interpretations on detailed redox analyses in several of these inferred anoxic settings. Here we present the first evidence for widespread and persistent oxygenation during OAE-2 based primarily on the distribution of redox-sensitive trace metals and biota preserved in sedimentary rocks from the Western Interior Seaway of North America. Our data indicate anoxic-euxinic conditions in the mid- to late Cenomanian, but improved bottomwater oxygenation prior to and during the CIE. Trace metal enrichments support large volumes of mafic volcanism possibly from the High Arctic large igneous province (HALIP), which occur within the middle of the CIE indicating that the emplacement of LIPs was not the primary trigger of the Cenomanian-Turonian CIE. The apparent paradox of an oxygenated phase within OAE-2 suggests a much more complex carbon cycle during these global perturbations than previously thought. These findings have important implications for greenhouse carbon cycle changes over time scales of 0.1–10 m.y.

The Global Extent of the Turonian Cretaceous Anoxic Event

Sulfur isotopes track the global extent and dynamics of euxinia during Cretaceous Oceanic Anoxic Event 2

Authors:

Owens et al

Abstract:

The Mesozoic Era is characterized by numerous oceanic anoxic events (OAEs) that are diagnostically expressed by widespread marine organic-carbon burial and coeval carbon-isotope excursions. Here we present coupled high-resolution carbon- and sulfur-isotope data from four European OAE 2 sections spanning the Cenomanian–Turonian boundary that show roughly parallel positive excursions. Significantly, however, the interval of peak magnitude for carbon isotopes precedes that of sulfur isotopes with an estimated offset of a few hundred thousand years. Based on geochemical box modeling of organic-carbon and pyrite burial, the sulfur-isotope excursion can be generated by transiently increasing the marine burial rate of pyrite precipitated under euxinic (i.e., anoxic and sulfidic) water-column conditions. To replicate the observed isotopic offset, the model requires that enhanced levels of organic-carbon and pyrite burial continued a few hundred thousand years after peak organic-carbon burial, but that their isotope records responded differently due to dramatically different residence times for dissolved inorganic carbon and sulfate in seawater. The significant inference is that euxinia persisted post-OAE, but with its global extent dwindling over this time period. The model further suggests that only ∼5% of the global seafloor area was overlain by euxinic bottom waters during OAE 2. Although this figure is ∼30× greater than the small euxinic fraction present today (∼0.15%), the result challenges previous suggestions that one of the best-documented OAEs was defined by globally pervasive euxinic deep waters. Our results place important controls instead on local conditions and point to the difficulty in sustaining whole-ocean euxinia.

Evolution of the Lower Cambrian Oceanic Enviroment in China

Depositional environments for stratiform witherite deposits in the Lower Cambrian black shale sequence of the Yangtze Platform, southern Qinling region, SW China: Evidence from redox-sensitive trace element geochemistry

Authors:

Dao-Hui Pi, Shao-Yong Jiang, Li Luo, Jing-Hong Yang and Hong-Fei Ling

Abstracts:

Very large stratiform witherite mineralization occurs in Lower Cambrian black shales and siliceous rocks in the southern Qinling region of SW China. Two types of witherite ores are divided according to their colours, i.e., the white ores and the dark-gray ores. We analyzed a number of redox-sensitive trace elements in both the white and dark-gray ores from various witherite deposits. The redox-sensitive metal concentrations and the distribution of the two types of ores provide good evidence for their depositional redox conditions in the Early Cambrian ocean in the southern Qinling region. Our geochemical data suggest that both the dark-gray and white witherite ores may have been deposited in reducing environments, with the dark-gray ores deposited in an anoxic-euxinic environment, whereas the white ores deposited under a suboxic-anoxic condition.

Euxinia in the Devonian Mass Extinctions, an Australian Data Point

Biomarkers reveal the role of photic zone euxinia in exceptional fossil preservation: An organic geochemical perspective

Authors:

1. Ines Melendez (a)
2. Kliti Grice (a)
3. Kate Trinajstic (a,b)
4. Mojgan Ladjavardi (a)
5. Paul Greenwood (a,c)
6. Katharine Thompson (a)

Affiliations:

a. Western Australian Organic and Isotope Geochemistry Centre, Department of Chemistry, Curtin University, Perth, WA 6845, Australia

b. Department of Earth and Planetary Science, Western Australian Museum, Perth Cultural Centre, James Street, Perth, WA 6000, Australia

c. Centres of Exploration Targeting and Biogeochemistry, School of Earth and Environment, University of Western Australia, Perth, WA 6009, Australia

Abstract:

Photic zone euxinia (PZE) has proven important for elucidating biogeochemical changes that occur during oceanic anoxic events, including mass extinction and conditions associated with unique fossil preservation. Organic geochemical analyses of a 380 Ma invertebrate fossil, which included well-preserved soft tissues, from the Gogo Formation (Canning Basin, Western Australia) showed biomarkers and stable isotopic values characteristic of PZE and a consortium of sulfate-reducing bacteria, which lead to exceptional fossil and biomarker preservation. The carbonate concretion contained phytoplankton, green sulfur bacteria (Chlorobi), and sulfate-reducing bacteria biomarkers with an increasing concentration toward the nucleus where the fossil is preserved. The spatial distribution of cholestane unequivocally associated with the fossilized tissue and its high relative abundance to the total steranes suggest that the fossil is a crustacean. The presence of an active sulfur cycle in this Devonian system, including sulfate reduction and the resulting PZE, played a pivotal role in the preservation of soft tissue from the fossil and its associated low-maturity biomarker ratios.

Pop sci write up.  The write up generalizes waaaay beyond the paper covers.