Mesoscale and microscale shock effects in the LL6 S4 chondrites Saint‐Séverin and Elbert: A tale of two breccias

Saint‐Séverin and Elbert, two LL6 chondrite breccias, were systematically studied to evaluate multiple deformation effects on spatial scales ranging from thin section (mesoscale) to micron‐submicron (microscale) using optical microscopy, electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The different techniques provide consistent results but have complementary strengths, together providing a powerful approach to unravel even complex impact histories. Both meteorites have an S4 conventional shock stage, but interclast areas are more deformed, and clasts are more deformed in Elbert than in Saint‐Séverin. TEM and EBSD data provide compelling evidence that Saint‐Séverin experienced significant shock deformation while already hot, and cooled rapidly afterward, as a result of a major, possibly disruptive impact on the LL chondrite parent body ~4.4 Ga ago. In contrast, Elbert was shocked from a cold initial state but was heated significantly during shock, and cooled in a localized hot impact deposit on the LL asteroid. Both meteorites probably were shocked at least twice; data for Saint‐Séverin are best reconciled with a three‐impact model.     

Using Mesoproterozoic sedimentary geochemistry to reconstruct basin tectonic geography and link organic carbon productivity to nutrient flux from a Northern Australian large igneous Province

The Beetaloo Sub-basin, northern Australia, is considered the main depocentre of the 1,000-km scale Mesoproterozoic Wilton package of the greater McArthur Basin – the host to one of the oldest hydrocarbon global resources. The ca. 1.40–1.31 Ga upper Roper Group and the latest Mesoproterozoic to early Neoproterozoic unnamed group of the Beetaloo Sub-basin, together, record ca. 500 million years of depositional history within the North Australia Craton. Whole-rock shale Sm–Nd and Pb isotope data from these sediments reveal sedimentary provenance and their evolution from ca. 1.35 to 0.85 Ga. Furthermore, these data, together with shale major/trace elements data from this study and pyrolysis data from previous publications, are used to develop a dynamic tectonic geography model that links the organic carbon production and burial to an enhanced weathering of nutrients from a large igneous province. The ca. 1.35–1.31 Ga Kyalla Formation of the upper Roper Group is composed of isotopically evolved sedimentary detritus that passes up, into more isotopically juvenile Pb values towards the top of the formation. The increase in juvenile compositions coincides with elevated total organic carbon (TOC) contents of these sediments. The coherently enriched juvenile compositions and TOC the upper portions of the Kyalla Formation are interpreted to reflect an increase in nutrient supply associated with the weathering of basaltic sources (e.g. phosphorous). Possible, relatively juvenile, basaltic sources include the Wankanki Supersuite in the western Musgraves and the Derim Derim–Galiwinku large igneous province (LIP). The transition into juvenile, basaltic sources directly before a supersequence-bounding unconformity is here interpreted to reflect uplift and erosion of the Derim Derim–Galiwinku LIP, rather than an influx of southern Musgrave sources. A new baddeleyite crystallisation age of 1,312.9 ± 0.7 Ma provides both a tight constraint on the age of this LIP, along with its associated magmatic uplift, as well as providing a minimum age constraint for Roper Group deposition. The unconformably overlying lower and upper Jamison sandstones are at least 300 million years younger than the Kyalla Formation and were sourced from the Musgrave Province. An up-section increase in isotopically juvenile compositions seen in these rocks is interpreted to document the progressive exhumation of the western Musgrave Province. The overlying Hayfield mudstone received detritus from both the Musgrave and Arunta regions, and its isotopic geochemistry reveals affinities with other early Neoproterozoic basins (e.g. Amadeus, Victoria and Officer basins), indicating the potential for inter-basin correlations.     

Bakken Stratigraphic and Type Well-Log Learning Network for Transparent Prediction and Rigorous Data Mining

Natural Resources Research - A Bakken formation learning network is established based upon type well-log data (seven petrophysical variables) and a discrete stratigraphic index (Str) comprising...     

Factors influencing biodeposit production by the New Zealand freshwater mussel Echyridella menziesii

Laboratory experiments on the New Zealand freshwater mussel Echyridella menziesii were used to investigate the short-term effects (7–8 days) of food type on rates of biodeposition and benthic substrate respiration. Post-feeding biodeposition rates ranged from 0.34 to 1.52?mg?g^?1?h^?1 (mean?=?0.50?mg g^?1?h^?1) and were unaffected by the addition of toxin-producing Microcystis. Addition of suspended sediment (30?mg?L^?1) visibly altered substrate composition, and increased total and inorganic biodeposit production rates by 24–33% compared to mussels fed commercial phytoplankton stock. Biodeposition rates of mussels in lake bed substrates were 38% higher than those in silica sand for identical feeding regimes, suggesting that a significant proportion of material produced in this experiment could have been derived from feeding on organic matter in the lake bed sediments. Respiration rates were higher in treatments with Microcystis but were unaffected by the presence of mussels. This laboratory study suggests that biodeposition by E. menziesii is resilient to short-term exposure to Microcystis, and highlights the ability of mussels to alter benthic substrate composition by incorporating suspended sediment into substrates.     

Private rights,public benefits: Industry-driven seabed protection

New Zealand has a large exclusive economic zone (EEZ) that contains a variety of marine habitats and commercially-important species. The commercial fishing industry operating within New Zealand's EEZ is of significant value to the economy and fisheries resources are managed through the extensive use of Individual Transferable Quotas (ITQs). One of the benefits of ITQs has been to better align some of the private incentives of quota owners with the public interest. These incentives contributed to an initiative proposed by the fishing industry to close large areas of New Zealand's EEZ to protect the seabed from trawling. These closed areas are termed benthic protection areas (BPAs) and protect the benthic biodiversity of about 1.1 million square kilometres of seabed—approximately 30% of New Zealand's EEZ. A significant proportion of New Zealand's known seamounts and active hydrothermal vents are protected by these closed areas. We describe and discuss the criteria used to select BPAs and some of the criticism of this marine protection initiative. We argue that the assignment of strong property rights in fishing resources was an important precondition to an industry initiative that has a significant public benefit. Where private and public interests are well aligned, government can adopt an enabling and facilitation role, ceding direct control of processes in order to get the results the align with the public interest.     

Non-equilibrium flocculation characteristics of fine-grained sediments in grid-generated turbulent flow

Results are presented from a series of settling column experiments investigating temporal variations in the flocculation characteristics of purely cohesive (kaolin clay) sediment suspensions and cohesive (kaolin) and non-cohesive (fine sand) sediment fraction mixtures. Experimental runs were conducted under controlled hydrodynamic conditions generated by a rigid array of in-phase oscillating grids. The results indicated that rapid initial floc aggregation occurred under low turbulent shear rates, with peak maximal and root-mean-square (r.m.s.) floc sizes (∼ 400 μm and ∼ 200 μm, respectively) attained after relatively short time periods, before reducing with time. By contrast, lower aggregation rates and smaller floc sizes were observed under higher shear conditions, with flocs retaining suspended in the settling column for longer time scales due to the increased turbulence. The mud input concentration displayed some correlation with maximal and r.m.s. floc sizes at higher shear rates but no correlation was apparent at low shear rates. This observed floc behaviour may be attributed to the differences in concentration gradients at high and low shear rates that affect both floc settling rate and time required for flocs to attain equilibrium size. The addition of the fine sand fraction to the kaolin clay suspension reduced both the initial floc formation (i.e. aggregation) rate and the maximal and r.m.s. floc sizes attained throughout the experiments. The reduction in maximal floc sizes appeared to be enhanced by an increase in the ratio of fine sand to kaolin clay content within the mixture.     

Mineralogy and petrogenesis of lunar magnesian granulitic meteorite Northwest Africa 5744

Lunar meteorite Northwest Africa (NWA) 5744 is a granulitic breccia with an anorthositic troctolite composition that may represent a distinct crustal lithology not previously described. This meteorite is the namesake and first‐discovered stone of its pairing group. Bulk rock major element abundances show the greatest affinity to Mg‐suite rocks, yet trace element abundances are more consistent with those of ferroan anorthosites. The relatively low abundances of incompatible trace elements (including K, P, Th, U, and rare earth elements) in NWA 5744 could indicate derivation from a highlands crustal lithology or mixture of lithologies that are distinct from the Procellarum KREEP terrane on the lunar nearside. Impact‐related thermal and shock metamorphism of NWA 5744 was intense enough to recrystallize mafic minerals in the matrix, but not intense enough to chemically equilibrate the constituent minerals. Thus, we infer that NWA 5744 was likely metamorphosed near the lunar surface, either as a lithic component within an impact melt sheet or from impact‐induced shock.     

Estimating Solar Flux Density at Low Radio Frequencies Using a Sky Brightness Model

Sky models have been used in the past to calibrate individual low radio frequency telescopes. In this article we generalize this approach from a single antenna to a two element interferometer, and formulate the problem in a way that allows us to estimate the flux density of the Sun using the normalized cross-correlations (visibilities) measured on a low resolution interferometric baseline. For wide field-of-view instruments, typically the case at low radio frequencies, this approach can provide robust absolute solar flux calibration for well characterized antennas and receiver systems. It can provide a reliable and computationally lean method for extracting parameters of physical interest using a small fraction of the voluminous interferometric data, which can be computationally prohibitively expensive to calibrate and image using conventional approaches. We demonstrate this technique by applying it to data from the Murchison Widefield Array and assess its reliability.     

Taxonomic Studies on a New Marine Ciliate, Apocoleps magnus gen. nov., spec. nov. （Ciliophora, Colepidae）, Isolated from Qingdao, China

The morphology and infraciliature of a new marine colepid ciliate, Apocoleps magnus gen. nov., spec. nov., are described based on living observations and silver impregnations. The new genus Apocoleps is characterized by having 8 (vs. 6 in most other related genera) armour tiers, spines at both ends of the cell, 3 adoral organelles and plates with 4 reniform uni-windows. Apocoleps magnus spec. nov. is defined by the following features: body elongated and slightly curved, about 100–120μm× 35–45 μm in vivo; an...     

运用nrDNA ITS 数据研究角叉菜属(Chondrus)在红藻门中的系统进化地位

测定了角叉菜属(Chondrus)5个代表种的核糖体DNA内转录间隔区(ITS)及5.8SrDNA基因序列。结果表明,角叉菜属ITS区(含ITS1、5.8SrDNA和ITS2)序列长度范围为704—714bp,G+C含量为44.6%—45.7%,变异位点69个,信息位点16个;其中,ITS1和ITS2的长度范围分别为147—149bp和398—404bp。5.8SrDNA长度为158bp,没有变异和信息位点。由MEGA3构建的系统进化树(ME和MP)显示:在进化尺度上,真红藻纲的松节藻科(Rhodomelaceae)与红毛菜纲(Bangiophyceae)亲缘关系较近。在真红藻纲内,杉藻目(Gigartinales)的进化地位相对较高,其次是海膜科(Halymeniaceae)、石花菜科(Gelidiaceae)、红叶藻科(Delesseriaceae)和粉枝藻科(Liagoraceae)等,而松节藻科进化地位相对较低。在杉藻目内,杉藻科(Gigartinaceae)和胶黏藻科(Dumontiaceae)进化关系密切,而形态学特征相似的角叉菜和马泽藻(Mazzaella)亲缘关系非常近。