Functional diversity of marine ecosystems after the Late Permian mass extinction event

Article can be accessed from http://www.nature.com/ngeo/journal/v7/n3/full/ngeo2079.htmlThe Late Permian mass extinction event was the most severe such crisis of the past 500 million years and occurred during an episode of global warming. It is assumed to have had significant ecological impact, but its effects on marine ecosystem functioning are unknown and the patterns of marine recovery are debated. We analysed the fossil occurrences of all known Permian-Triassic benthic marine genera and assigned each to a functional group based on their inferred life habit. We show that despite the selective extinction of 62-74% of marine genera there was no significant loss of functional diversity at the global scale, and only one novel mode of life originated in the extinction aftermath. Early Triassic marine ecosystems were not as ecologically depauperate as widely assumed, which explains the absence of a Cambrian-style Triassic radiation in higher taxa. Functional diversity was, however, significantly reduced in particular regions and habitats, such as tropical reefs, and at these scales recovery varied spatially and temporally, probably driven by migration of surviving groups. Marine ecosystems did not return to their pre-extinction state, however, and radiation of previously subordinate groups such as motile, epifaunal grazers led to greater functional evenness by the Middle Triassic

Emplacement of inflated Pāhoehoe flows in the Naude’s Nek Pass, Lesotho remnant, Karoo continental flood basalt province: use of flow-lobe tumuli in understanding flood basalt emplacement

Physical volcanological features are presented for a 710-m-thick section, of the Naude’s Nek Pass, within the lower part of the Lesotho remnant of the Karoo Large Igneous Province. The section consists of inflated pāhoehoe lava with thin, impersistent sedimentary interbeds towards the base. There are seven discreet packages of compound and hummocky pāhoehoe lobes containing flow-lobe tumuli, making up approximately 50% of the section. Approximately 45% of the sequence consists of 14 sheet lobes, between 10 and 52-m-thick. The majority of the sheet lobes are in two packages indicating prolonged periods of lava supply capable of producing thick sheet lobes. The other sheet lobes are as individual lobes or pairs, within compound flows, suggesting brief increases in lava supply rate. We suggest, contrary to current belief, that there is no evidence that compound flows are proximal to source and sheet lobes (simple flows) are distal to source and we propose that the presence of flow-lobe tumuli in compound flows could be an indicator that a flow is distal to source. We use detailed, previously published, studies of the Thakurvadi Formation (Deccan Traps) as an example. We show that the length of a lobe and therefore the sections that are ‘medial or distal to source’ are specific to each individual lobe and are dependent on the lava supply of each eruptive event, and as such flow lobe tumuli can be used as an indicator of relative distance from source

Cyanobacterial blooms tied to volcanism during the 5 m.y. Permo-Triassic biotic crisis Comment

Widespread but episodic deposition of cyanobacterial mats occurred during the 5 m.y. Permo-Triassic biotic crisis, providing a critical record to decipher the long-term stressful environmental conditions and thus a linkage with the killer. Here we document the timing and duration of these blooms, indicated by lipid biomarkers and microbialites, throughout South China and compare them to the timing of volcanic activity. The initial cyanobacterial bloom has the longest duration and is associated with a prominent Eu anomaly in southwestern China, where the most intensive volcanism has been proposed to occur, suggesting a causal relationship. Subsequent cyanobacterial blooms in the Early Triassic are associated with known volcanic events in South China and also with the most voluminous Siberian flood basalts, and with the largest negative carbon isotope excursions. Thus, it appears that volcanic activity has had a significant impact on microbial development in South China. South China volcanism around the Permian-Triassic boundary (PTB) could have played a much larger role in biotic changes of both bacterial and calcified faunal ecosystems than previously thought. The well-known Siberian volcanism is proposed herein, on the basis of the current compilation of dating data, to protract the Early Triassic faunal recovery rather than to cause the end-Permian extinction.</div

New Estimates on the Basalt Volume of the Tarim (Not So Large) Igneous Province, NW China

The early Permian basalts of the Tarim Basin of NW China are geographically widespread, covering over 200,000 km2 and are in places up to 1-km thick and hence frequently referred to represent a Large Igneous Province (LIP). Available volume estimates are based on average lava thickness multiplied by area, using these values results in volumes exceeding 100,000 km3, and is commonly cited as being evidence of LIP status. Using a database of 58 boreholes, field sections, and seismic data we calculate a range of basalt isopach maps, and use these to estimate new, more refined overall eruption volumes. These volumes are significantly smaller than previously reported estimates. We demonstrate that the thickness distribution of erupted basalts is nonuniform and strongly skewed, indicating that volume estimates using an arithmetically averaged thickness of input data will result in overestimation of total volumes. We find that even with the addition of an estimated nonerupted volume component, representing cumulates and intrusions, that the total volume of the Tarim volcanics is significantly below the minimum threshold of a LIP. Using a simple Monte Carlo model we demonstrate that even while accounting for uncertainty and error in the input data, the probability of the total volume exceeding 100,000 km3 is very low. The new volume estimates imply a revision of the climate and environmental impact of the Tarim volcanism. We therefore suggest that the term Tarim Igneous Province should be used instead of Tarim Large Igneous Province.Plain Language SummaryThe early Permian (287–267 million years ago) basaltic rocks of the Tarim Basin in Northwestern China are geographically widespread, and can be up to 1 km in thickness. This has led to the hypothesis that these rocks represent a period of significantly voluminous igneous activity across the area, in what is known as a Large Igneous Province (LIP). LIP are defined by a set of criteria including area, volume, and a short-duration of emplacement. In this study, we have collated all available data to test whether the basalts within the Tarim Basin meet the minimum criteria to be classified as a LIP. In this study, we demonstrate that when integrating a large number of geographically widespread boreholes and outcrops, regional seismic data and published age data that the Tarim basalts represent a significant period of igneous activity, but do not meet the threshold of a LIP. This finding is important as the volume of igneous rock formed during periods of intense igneous activity is used in geological and climate models to infer past climatic effects and extinctions. We also demonstrate that relatively simple calculations of the volume of LIPs will typically overestimate their volume and thus environmental impact, and therefore suggest that all future studies of this nature should aim to integrate all available data and consider uncertainty and probability when estimating eruption volumes.</div

Increasing the permeability of hydrothermally altered andesite by transitory heating

Changes in permeability can impact geological processes, geohazards, and geothermal energy production. In hydrothermal systems, high-temperature heat sources drive fluid convection through the pore network of reservoir rocks. Additionally, thermal fluctuations may induce microfracturing and affect the mineralogical stability of the reservoir rock, thus modifying the fluid pathways and affecting permeability and strength. This study describes the results of thermal heating events lasting several hours on a “moderately altered” plagioclase-clinochlore-calcite-quartz andesite and a “highly-altered” plagioclaseclinozoisite- quartz-clinochlore andesite from the Rotokawa geothermal field, New Zealand. We use a low thermal gradient (~ 1.2 °C/min) in an H2O-saturated, 20 MPa pressure environment to constrain changes in petrophysical properties associated with transitory thermal phenomena between 350 °C and 739 °C. As the treatment temperature increases, the mass reduces, while porosity and permeability increase. These effects were greater in the “moderately altered” andesite than in the “highly altered” andesite. Microfracturing is responsible for these changes at lower temperatures (e.g. up to 400 °C). At higher temperatures (e.g. > 400 °C), microfracturing remains partially responsible for these rock property changes (e.g. higher permeability); however, these changes are also a product of clinochlore, quartz, and (when present) calcite reacting out of the altered andesite, and increasing porosity. We propose that at temperatures > 400 °C, volumetric phase changes associated with heat driven reactions in a wet environment can contribute to micro-cracking and porosity/permeability changes. Our data support observations where high-temperature conditions at the margins of magma bodies can be associated with substantial increased permeability and decreased strength