Enstatite meteorite clasts in Almahata Sitta and other polymict ureilites: Implications for the formation of asteroid 2008 TC3 and the history of enstatite meteorite parent asteroids

The anomalous polymict ureilite Almahata Sitta (AhS) fell in 2008 when asteroid 2008 TC₃ disintegrated over Sudan and formed a strewn field of disaggregated clasts of various ureilitic and chondritic types. We studied the petrology and oxygen isotope compositions of enstatite meteorite samples from the University of Khartoum (UoK) collection of AhS. In addition, we describe the first bona fide (3.5 mm-sized) clast of an enstatite chondrite (EC) in a typical polymict ureilite, Northwest Africa (NWA) 10657. We evaluate whether 2008 TC₃ and typical polymict ureilites have a common origin, and examine implications for the history of enstatite meteorite asteroids in the solar system. Based on mineralogy, mineral compositions, and textures, the seven AhS EC clasts studied comprise one EH_a3 (S151), one EL_b3 (AhS 1002), two EH_b4-5 (AhS 2012, AhS 26), two EH_b5-6 or possibly impact melt rocks (AhS 609, AhS 41), and one EL_b6-7 (AhS 17), while the EC clast in NWA 10657 is EH_a3. Oxygen isotope compositions analyzed for five of these are similar to those of EC from non-UoK collections of AhS, and within the range of individual EC meteorites. There are no correlations of oxygen isotope composition with chemical group or subgroup. The EC clasts from the UoK collection show the same large range of types as those from non-UoK collections of AhS. The enstatite achondrite, AhS 60, is a unique type (not known as an individual meteorite) that has also been found among non-UoK AhS samples. EC are the most abundant non-ureilitic clasts in AhS but previously were thought to be absent in typical polymict ureilites, necessitating a distinct origin for AhS. The discovery of an EC in NWA 10657 changes this. We argue that the types of materials in AhS and typical polymict ureilites are essentially similar, indicating a common origin. We elaborate on a model in which AhS and typical polymict ureilites formed in the same regolith on a ureilitic daughter body. Most non-ureilitic clasts are remnants of impactors implanted at ~50–60 Myr after CAI. Differences in abundances can be explained by the stochastic nature of impactor addition. There is no significant difference between the chemical/petrologic types of EC in polymict ureilites and individual EC meteorites. This implies that fragments of the same populations of EC parent bodies were available as impactors at ~50–60 Myr after CAI and recently. This can be explained if materials excavated from various depths on EC bodies at ~50–60 Myr after CAI were reassembled into mixed layers, leaving relatively large bodies intact to survive 4 billion years. Polymict ureilites record a critical timestep in the collisional and dynamical evolution of the solar system, showing that asteroids that may have accreted at distant locations had migrated to within proximity of one another by 50–60 Myr after CAI, and providing constraints on the dynamical processes that could have caused such migrations.     

Field Investigation of a New Recharge Approach for ASR Projects in Near‐Surface Aquifers

Aquifer storage and recovery (ASR) is the artificial recharge and temporary storage of water in an aquifer when water is abundant, and recovery of all or a portion of that water when it is needed. One key limiting factor that still hinders the effectiveness of ASR is the high costs of constructing, maintaining, and operating the artificial recharge systems. Here we investigate a new recharge method for ASR in near‐surface unconsolidated aquifers that uses small‐diameter, low‐cost wells installed with direct‐push (DP) technology. The effectiveness of a DP well for ASR recharge is compared with that of a surface infiltration basin at a field site in north‐central Kansas. The performance of the surface basin was poor at the site due to the presence of a shallow continuous clay layer, identified with DP profiling methods, that constrained the downward movement of infiltrated water and significantly reduced the basin recharge capacity. The DP well penetrated through this clay layer and was able to recharge water by gravity alone at a much higher rate. Most importantly, the costs of the DP well, including both the construction and land costs, were only a small fraction of those for the infiltration basin. This low‐cost approach could significantly expand the applicability of ASR as a water resources management tool to entities with limited fiscal resources, such as many small municipalities and rural communities. The results of this investigation demonstrate the great potential of DP wells as a new recharge option for ASR projects in near‐surface unconsolidated aquifers.     

NMR Logging to Estimate Hydraulic Conductivity in Unconsolidated Aquifers

Nuclear magnetic resonance (NMR) logging provides a new means of estimating the hydraulic conductivity (K) of unconsolidated aquifers. The estimation of K from the measured NMR parameters can be performed using the Schlumberger‐Doll Research (SDR) equation, which is based on the Kozeny–Carman equation and initially developed for obtaining permeability from NMR logging in petroleum reservoirs. The SDR equation includes empirically determined constants. Decades of research for petroleum applications have resulted in standard values for these constants that can provide accurate estimates of permeability in consolidated formations. The question we asked: Can standard values for the constants be defined for hydrogeologic applications that would yield accurate estimates of K in unconsolidated aquifers? Working at 10 locations at three field sites in Kansas and Washington, USA, we acquired NMR and K data using direct‐push methods over a 10‐ to 20‐m depth interval in the shallow subsurface. Analysis of pairs of NMR and K data revealed that we could dramatically improve K estimates by replacing the standard petroleum constants with new constants, optimal for estimating K in the unconsolidated materials at the field sites. Most significant was the finding that there was little change in the SDR constants between sites. This suggests that we can define a new set of constants that can be used to obtain high resolution, cost‐effective estimates of K from NMR logging in unconsolidated aquifers. This significant result has the potential to change dramatically the approach to determining K for hydrogeologic applications.     

Characteristics of beaver ponds on deltas in a mountain environment

Many beaver ponds in the Rocky Mountains, that have been described in the literature, are in‐channel ponds that are relatively small and short‐lived. This paper describes floodplain beaver ponds on low‐gradient deltas in glacial finger lakes in Glacier National Park, Montana. These ponds are distinctly larger, probably fed by hyporheic flow, and stable and long‐lived. Ponds examined were, with one exception, 44 years old. Glacial discharge is present in each valley where beaver ponds occupy low‐gradient deltas, and this discharge likely sustains pond water level over the course of the summer. As glaciers recede and disappear, deltaic beaver ponds dependent on hyporheic flow may be negatively affected. Copyright © 2012 John Wiley & Sons, Ltd.     

BEAVER-POND SEQUENCE MORPHOLOGY AND SEDIMENTATION IN NORTHWESTERN MONTANA

Two adjacent beaver-pond sequences of seven ponds each were examined along the eastern boundary of Glacier National Park, Montana, to determine spatial patterns and amounts of sedimentation, both within individual ponds and along pond sequences. Dams and their associated ponds were categorized into two age groups, young versus old, based on dam morphology and surface vegetation. Old ponds contained significantly more sediment than did young ponds. However, hypothesized patterns of downstream reductions in coarse-grained sediment, both within a pond and along a sequence, were not observed, nor were there any discernible patterns in sediment texture across ponds. [Key words: beaver pond, sedimentation, Rocky Mountains, Montana.]     

Possible persistence of the morganucodontans in the Lower Cretaceous Purbeck Limestone Group (Dorset, England)

‘Triconodonts’ are relatively rare in the new Purbeck Limestone Group mammal fauna, especially in comparison with the finds made in the nineteenth century in the same beds. However, besides some remains of the already known Triconodontidae, a new possible morganucodontan of uncertain familial affinities, Purbeckodon batei gen. et sp. nov., has been discovered, extending considerably the chronological range of the order while constituting another testimony to the vitality and diversity of Mesozoic mammals.     

FeS-Induced Radical Formation and Its Effect on Plasmid DNA

Plasmid DNA was incubated at 25°C with aqueous solutions of dissolved Fe(II), S(-II), and nanoparticulate FeS with a mackinawite structure, FeS_m. At ??0.1 mM total dissolved Fe(II) and S(-II), an increase in the proportion of the relaxed plasmid DNA occurs, through scission of the DNA backbone. In solutions where FeS_m was precipitated, nanoparticulate FeS_m binds to the DNA molecules. In solutions with concentrations below the FeS_m solubility product, nicking of supercoiled pDNA occurs. Plasmid DNA appears to be a sensitive proxy for radical reactions. The reactant is proposed to be a sulfur-based radical produced from the iron-catalyzed decomposition of bisulfide, in a manner analogous to the Fenton reaction. This is further supported by experiments that suggest that sulfide free radicals are produced during the photolysis of aqueous solutions of polysulfides. Supercoiling of DNA affects nearly all DNA?Cprotein transactions so the observation of relaxation of supercoiled forms through reaction with FeS solutions has direct implications to biochemistry. The results of this experimentation suggest that genotoxicity in FeS-rich systems is a further contributory factor to the limited survival of organisms in sulfidic environments. Mutations resulting from the interactions of organisms and mobile elements, such as plasmids, in sediments will also be affected in sulfide-rich environments.     

Stream water chemistry and quality along an upland–lowland rural land-use continuum, south west England

This study examined stream water quality across a range of catchments which are representative of the key environments and land uses of rural south-west England. These catchments included: (a) an acidic upland headwater catchment, rising on the moorlands of Dartmoor, with low-intensity sheep rearing; (b) a headwater catchment rising on the weathered granite lower slopes of Dartmoor, with cattle farming; (c) a lowland headwater clay catchment with sub-surface drainage and high intensity livestock farming, fodder crop cultivation, and hard-standing/slurry storage; and (d) the main River Taw, a lowland river system receiving drainage from a range of tributaries, exemplified by the above catchment types. Variations in water chemistry and quality were observed along an upland–lowland transition, from headwater streams to the main river channel. Within the livestock-dominated headwater streams, total phosphorus (TP) was dominated by particulate phosphorus (PP). These PP concentrations appeared to be mainly linked to two sets of processes: (1) in-stream sediment precipitation with sorption/co-precipitation of phosphate and/or localised in-channel mobilisation of sediment (by cattle or channel-clearing operations) under low flow conditions, and (2) sediment erosion and transportation associated with near-surface runoff during storm events. Under baseflow conditions, in-stream and/or riparian processes played a significant role in controlling general nutrient chemistry, particularly in the headwater streams which were heavily impacted by livestock.