David P.G. Bond

Devonian rise in atmospheric oxygen correlated to the radiations of terrestrial plants and large predatory fish

The evolution of Earth’s biota is intimately linked to the oxygenation of the oceans and atmosphere. We use the isotopic composition and concentration of molybdenum (Mo) in sedimentary rocks to explore this relationship. Our results indicate two episodes of global ocean oxygenation. The first coincides with the emergence of the Ediacaran fauna, including large, motile bilaterian animals, ca. 550–560 million year ago (Ma), reinforcing previous geochemical indications that Earth surface oxygenation facilitated this radiation. The second, perhaps larger, oxygenation took place around 400 Ma, well after the initial rise of animals and, therefore, suggesting that early metazoans evolved in a relatively low oxygen environment. This later oxygenation correlates with the diversification of vascular plants, which likely contributed to increased oxygenation through the enhanced burial of organic carbon in sediments. It also correlates with a pronounced radiation of large predatory fish, animals with high oxygen demand. We thereby couple the redox history of the atmosphere and oceans to major events in animal evolution.

Pyrite framboid study of marine Permian-Triassic boundary sections: A complex anoxic event and its relationship to contemporaneous mass extinction

Size analysis of pyrite framboids has been undertaken on epicontinental Permian- Triassic boundary sections throughout the world in order to evaluate the intensity and duration of anoxia. Mid-paleolatitude sections from the margins of the Boreal (Spitsbergen, Greenland) and Neotethyan oceans (Western Australia) reveal intense anoxia throughout the Permian-Triassic boundary interval with euxinic conditions frequently developing, and dysoxia encountered even in relatively shallow-water settings above storm wave base. At equatorial paleolatitudes, weakly oxygenated (dysoxic) conditions are widely developed in a broad range of water depths including those shallow enough to produce oolite deposition, although euxinia was rare. Western and eastern Tethyan locations re- veal a complex and unstable redox history: anoxia in the Hindeodus praeparvus Zone was replaced by oxygenated facies in the Permian- Triassic boundary interval (H. changxingensis to H. parvus zones). Oxygen-poor deposition returned during the succeeding Isarcicella isarcica Zone. The more persistent and intense development of oxygen restriction in cooler water, mid-paleolatitude sections argues against warming and dissolved oxygen decline as the key cause of Permian-Triassic bound- ary anoxia. In higher paleolatitudes the ben- thic invertebrate extinctions occurred during a prolonged phase of oxygen-poor deposition, while in equatorial Tethyan locations benthic losses occurred at the end of the fi rst anoxic phase (in the late H. praeparvus Zone).

Volcanism, mass extinction, and carbon isotope fluctuations in the middle permian of China

Middle Permian Extinction A major extinction in the Middle Permian 260 to 270 million years ago preceded the huge end-Permian extinction. Wignall et al. (p. 1179) present a detailed analysis of the Middle Permian event from rocks in southwest China. The extinction coincided with extensive nearby volcanic eruptions. A major drop in carbon isotope values followed the extinction event, implying massive disruption of the carbon cycle. Fossiliferous rocks from southwest China show that a major extinction in the Middle Permian coincided with extensive volcanic eruptions. The 260-million-year-old Emeishan volcanic province of southwest China overlies and is interbedded with Middle Permian carbonates that contain a record of the Guadalupian mass extinction. Sections in the region thus provide an opportunity to directly monitor the relative timing of extinction and volcanism within the same locations. These show that the onset of volcanism was marked by both large phreatomagmatic eruptions and extinctions amongst fusulinacean foraminifers and calcareous algae. The temporal coincidence of these two phenomena supports the idea of a cause-and-effect relationship. The crisis predates the onset of a major negative carbon isotope excursion that points to subsequent severe disturbance of the ocean-atmosphere carbon cycle.

Recovery tempo and pattern of marine ecosystems after the end-Permian mass extinction

High-resolution sampling of more than 10,000 microfossils from seven Late Permian−Middle Triassic paleoequatorial sections in south China refutes claims for a 5 m.y. recovery delay after the end-Permian mass extinction. We show that level-bottom seafloor diversity began to recover in the early Smithian, little more than 1 m.y. after the mass extinction, while recovery of reef-building metazoans began 4 m.y. later, in the Anisian. A further mass extinction in the late Smithian, identified in the pelagic fossil record, is weakly manifest as a temporary pause in diversification among benthic communities. In the Early Triassic of south China, the offshore diversity increase began before then, in shallower settings. The recovery from the end-Permian mass extinction in south China was therefore significantly more rapid and environmentally more complex than hitherto known.

Facies analysis and sea-level change at the Guadalupian–Lopingian Global Stratotype (Laibin, South China), and its bearing on the end-Guadalupian mass extinction

Abstract: The Guadalupian–Lopingian boundary stratotype at Penglaitan, and the nearby Tieqiao section, near Laibin, South China, record a series of major environmental changes within the Jiangnan Basin during a Mid-Permian biotic crisis. The sequence-stratigraphic, petrographic and palaeontological record of these sections has been studied and the associated strontium isotopic fluctuations have been assayed. Mass extinction of fusulinid foraminifers is most clearly associated in time with onset of volcanism and a relative sea-level fall that led to the establishment of mid-ramp conditions (Laibin Limestone) in settings that were previously dominated by radiolarian mudstones. The regression also coincides with a low point of 87Sr/86Sr ratios. The lowstand deposits contain mafic scoriaceous grains that record pyroclastic volcanism probably centred in the Emeishan flood basalt province 800 km to the west of Laibin. Thus, unusually violent eruptions associated with flood basalts in this province may have contributed to the environmental stresses responsible for the extinction event. Subsequent environmental changes included transgression, spread of dysoxic waters, indicated by populations of small pyrite framboids, and a major negative C-isotope excursion. All these phenomena have been previously related to the end-Guadalupian extinction but they in fact post-date the crisis because a post-extinction fauna of foraminifers is encountered at this time.

The end-Triassic and Early Jurassic mass extinction records in the British Isles

The complex crises of the end-Triassic and Early Jurassic (Toarcian) mass extinctions are well recorded in the British Isles where they coincide with major palaeoenvironmental changes. The end-Triassic extinction occurs within the quasi-marine Lilstock Formation, the fauna of which is dominated by eurytopic bivalves. These suffered a major extinction event (77% of species), including all infaunal forms, within the basal beds of the Formation. This crisis slightly predates a series of environmental events that include, in ascending order, an intense phase of seismicity (the onset of Central Atlantic flood basalt volcanism?), sea-level fall and a negative δ 13 C org spike. The extinction is linked most clearly (i.e. closest in timing) with regression and seismicity. A further sea-level fall is recorded at the top of the Formation, followed by transgression and the spread of anoxia. These events are not associated with any further bivalve losses although conodonts disappeared at this time. The link between extinction and oxygen-poor conditions is demonstrated better by the Toarcian crisis, when a bivalve extinction event (85% species loss) coincided with the onset of intense anoxia within the middle of the Semicelatum Subzone of the Yorkshire coast sections. However, these losses are part of several extinction pulses spread over more than a million years. These began earlier, at the Pliensbachian/Toarcian stage boundary when ammonites, brachiopods and ostracods all suffered losses coinciding with regression and cooling. However, the subsequent transgression saw a brief spread of marine anoxia (represented by the Sulphur Band in Yorkshire sections) that may also be implicated in the extinctions. Black shale deposition is extremely widespread in the British Toarcian record, with the remarkable exception of the Somerset and south Dorset areas where condensed, fully-oxygenated, deep-water conditions are recorded by the Leptaena Bed and ‘Junction Bed’. Even more remarkably, severe extinction losses (of brachiopods and ostracods) are recorded in this apparently benign depositional setting.

Turbidite depositional influences on the diagenesis of Beecher's Trilobite Bed and the Hunsrück Slate; sites of soft tissue pyritization

Chemical signatures of enrichment of highly reactive iron, and framboid size distributions, are reported in turbidite sediments that host soft tissue pyritization (Beechers Trilobite Bed, Upper Ordovician, and the Hunsrück Slate, Lower Devonian). These signatures demonstrate that the sediment of Beechers Trilobite Bed was enriched in highly reactive iron prior to turbidite transport but that no enrichment was present in the Hunsrück Slate. Turbidite transport and re-sedimentation altered framboid size distributions. Small diameter framboids (< 5 μm) that formed in the sediment at the pre-transport site were lost during transport due to oxidation and/or size sorting. Larger diameter framboids (∼5 –15 μm) that formed at the pre-transport site were transported without alteration. The oxidation of the original small framboid population formed highly reactive iron (oxyhydr)oxides that were reduced during post-transport suboxic diagenesis to produce porewaters rich in dissolved iron. In some turbidites a bimodal framboid population resulted where a minor population of small diameter framboids, produced by limited sulfate reduction at the post-transport site, was added to the transported large diameter population. Soft tissue pyritization in this setting was facilitated by the presence of suboxic, iron rich porewaters where dissolved sulfide formed during soft tissue decay, confining iron sulfide precipitation to the decay site.

Radiation and extinction patterns in Permian floras from North China as indicators for environmental and climate change

Abstract: Permian continental sequences from North China contain previously unrecognized episodes of plant radiation and elevated extinction. The earliest extinction, in the Lower Shihhotse Formation (Roadian, Guadalupian), records a 45% floral species loss and is tentatively correlated with global extinctions amongst dinocephalian reptiles. Two younger extinctions are dated by correlating the Illawara Reversal and palaeomagnetic polarity sequences from Shanxi Province against global palaeomagnetic history. Missing data from the Shanxi sequence are evaluated using a novel approach estimating likely maximum and minimum sequence changes that provide age estimates for post-Illawara events in North China. The second extinction in the middle Upper Shihhotse Formation is more significant and is dated to the mid-Capitanian, with a loss of 56% of plant species coinciding with two phases of volcanism of the Emeishan Large Igneous Province in South China, previously linked to the mid-Capitanian marine mass extinction. The youngest extinction in the upper Upper Shihhotse Formation (late Capitanian to mid-Wuchapingian) is catastrophic and represents the end of range in the sequence. Changes in sedimentary facies suggest it to be related to global climatic warming and drying. Other viable causal mechanisms for the extinction episodes include plate motion and collision, global climate change, volcanism and biological competition.

Mercury anomalies associated with three extinction events (Capitanian Crisis, Latest Permian Extinction and the Smithian/Spathian Extinction) in NW Pangea

Strata of Permian – Early Triassic age that include a record of three major extinction events (Capitanian Crisis, Latest Permian Extinction and the Smithian/Spathian Extinction) were examined at the Festningen section, Spitsbergen. Over the c . 12 Ma record examined, mercury in the sediments shows relatively constant background values of 0.005–0.010 μg g –1 . However, there are notable spikes in Hg concentration over an order of magnitude above background associated with the three extinctions. The Hg/total organic carbon (TOC) ratio shows similar large spikes, indicating that they represent a true increase in Hg loading to the environment. We argue that these represent Hg loading events associated with enhanced Hg emissions from large igneous province (LIP) events that are synchronous with the extinctions. The Hg anomalies are consistent across the NW margin of Pangea, indicating that widespread mercury loading occurred. While this provides utility as a chemostratigraphic marker the Hg spikes may also indicate loading of toxic metals to the environment, a contributing cause to the mass extinction events.

Ultra-shallow-marine anoxia in an Early Triassic shallow-marine clastic ramp (Spitsbergen) and the suppression of benthic radiation

Lower Triassic marine strata in Spitsbergen accumulated on a mid-to-high latitude ramp in which high-energy foreshore and shoreface facies passed offshore into sheet sandstones of probable hyperpycnite origin. More distal facies include siltstones, shales and dolomitic limestones. Carbon isotope chemostratigraphy comparison allows improved age dating of the Boreal sections and shows a significant hiatus in the upper Spathian. Two major deepening events, in earliest Griesbachian and late Smithian time, are separated by shallowing-upwards trends that culminated in the Dienerian and Spathian substages. The redox record, revealed by changes in bioturbation, palaeoecology, pyrite framboid content and trace metal concentrations, shows anoxic phases alternating with intervals of better ventilation. Only Dienerian–early Smithian time witnessed persistent oxygenation that was sufficient to support a diverse benthic community. The most intensely anoxic, usually euxinic, conditions are best developed in offshore settings, but at times euxinia also developed in upper offshore settings where it is even recorded in hyperpycnite and storm-origin sandstone beds: an extraordinary facet of Spitsbergens record. The euxinic phases do not track relative water depth changes. For example, the continuous shallowing upwards from the Griesbachian to lower Dienerian was witness to several euxinic phases separated by intervals of more oxic, bioturbated sediments. It is likely that the euxinia was controlled by climatic oscillations rather than intra-basinal factors. It remains to be seen if all the anoxic phases found in Spitsbergen are seen elsewhere, although the wide spread of anoxic facies in the Smithian/Spathian boundary interval is clearly a global event.