Chert provenance analysis at the Mack Canyon Site,Sherman County,Oregon: An evaluative study

Chert is the most frequent lithic raw material in the Columbia Plateau, but archaeologists have made few attempts to link chert artifacts to their quarries in this area. The Mack Canyon Site in north-central Oregon is near a chert source, providing an opportunity to compare provenance analysis techniques. Macroscopic and microscopic visual attributes and element concentrations were determined for 26 samples from six sources in the Columbia Plateau. Additional concentration data from two other sources were included for comparison. Four artifacts were selected from the Mack Canyon Site for comparison to the nearby outcrop. Although all of the artifacts were macroscopically indistinguishable from the local material, microscopic attributes and element concentrations indicate that only one of the artifacts came from the outcrop. Linking chert artifacts and quarries through statistical analysis of element concentrations holds promise for the Columbia Plateau. © 1996 John Wiley & Sons, Inc.     

NWA 10214—An LL3 chondrite breccia with an assortment of metamorphosed,shocked, and unique chondrite clasts

NWA 10214 is an LL3‐6 breccia containing ~8 vol% clasts including LL5, LL6, and shocked‐darkened LL fragments as well as matrix‐rich Clast 6 (a new kind of chondrite). This clast is a dark‐colored, subrounded, 6.1 × 7.0 mm inclusion, consisting of 60 vol% fine‐grained matrix, 32 vol% coarse silicate grains, and 8 vol% coarse opaque grains. The large chondrules and chondrule fragments are mainly Type IB; one small chondrule is Type IIA. Also present are one 450 × 600 μm spinel‐pyroxene‐olivine CAI and one 85 × 110 μm AOI. Clast 6 possesses a unique set of properties. (1) It resembles carbonaceous chondrites in having relatively abundant matrix, CAIs, and AOIs; the clast's matrix composition is close to that in CV3 Vigarano. (2) It resembles type‐3 OC in its olivine and low‐Ca pyroxene compositional distributions, and in the Fe/Mn ratio of ferroan olivine grains. Its mean chondrule size is within 1σ of that of H chondrites. The O‐isotopic compositions of the chondrules are in the ordinary‐ and R‐chondrite ranges. (3) It resembles type‐3 enstatite chondrites in the minor element concentrations in low‐Ca pyroxene grains and in having a high low‐Ca pyroxene/olivine ratio in chondrules. Clast 6 is a new variety of type‐3 OC, somewhat more reduced than H chondrites or chondritic clasts in the Netschaevo IIE iron; the clast formed in a nebular region where aerodynamic radial drift processes deposited a high abundance of matrix material and CAIs. A chunk of this chondrite was ejected from its parent asteroid and later impacted the LL body at low relative velocity.     

Effectiveness of landscape‐based green infrastructure for stormwater management in suburban catchments

Land cover changes associated with urbanization have negative effects on downstream ecosystems. Contemporary urban development attempts to mitigate these effects by designing stormwater infrastructure to mimic predevelopment hydrology, but their performance is highly variable. This study used in situ monitoring of recently built neighbourhoods to evaluate the catchment‐scale effectiveness of landscape decentralized stormwater control measures (SCMs) in the form of street connected vegetated swales for reducing runoff volumes and flow rates relative to curb‐and‐gutter infrastructure. Effectiveness of the SCMs was quantified by monitoring runoff for 8 months at the outlets of 4 suburban catchments (0.76–5.25 ha) in Maryland, USA. Three “grey” catchments installed curb‐and‐gutter stormwater conveyances, whereas the fourth “green” catchment built parcel‐level vegetated swales. The catchment with decentralized SCMs reduced runoff, runoff ratio, and peak runoff compared with the grey infrastructure catchments. In addition, the green catchment delayed runoff, resulting in longer precipitation–runoff lag times. Runoff ratios across the monitoring period were 0.13 at the green catchment and 0.37, 0.35, and 0.18 at the 3 grey catchments. Runoff only commenced after 6 mm of precipitation at the decentralized SCM catchment, whereas runoff occurred even during the smallest events at the grey catchments. However, as precipitation magnitudes reached 20 mm, the green catchment runoff characteristics were similar to those at the grey catchments, which made up 37% of the total precipitation in only 10 of 72 events. Therefore, volume‐based reduction goals for stormwater using decentralized SCMs such as vegetated swales require additional redundant SCMs in a treatment train as source control and/or end‐of‐pipe detention to capture a larger fraction of runoff and more effectively mimic predevelopment hydrology for the relatively rare but larger precipitation events.     

Investigating a time‐shift extended imaging condition in a Kirchhoff pre‐stack depth migration algorithm

Extracting true amplitude versus angle common image gathers is one of the key objectives in seismic processing and imaging. This is achievable to different degrees using different migration techniques (e.g., Kirchhoff, wavefield extrapolation, and reverse time migration techniques) and is a common tool in exploration, but the costs can vary depending on the selected migration algorithm and the desired accuracy. Here, we investigate the possibility of combining the local‐shift imaging condition, specifically the time‐shift extended imaging condition, for angle gathers with a Kirchhoff migration. The aims are not to replace the more accurate full‐wavefield migration but to offer a cheaper alternative where ray‐based methods are applicable and to use Kirchhoff time‐lag common image gathers to help bridge the gap between the traditional offset common image gathers and reverse time migration angle gathers; finally, given the higher level of summation inside the extended imaging migration, we wish to understand the impact on the amplitude versus angle response. The implementation of the time‐shift imaging condition along with the computational cost is discussed, and results of four different datasets are presented. The four example datasets, two synthetic, one land acquisition, and a marine dataset, have been migrated using a Kirchhoff offset method, a Kirchhoff time‐shift method, and, for comparison, a reverse time migration algorithm. The results show that the time‐shift imaging condition at zero time lag is equivalent to the full offset stack as expected. The output gathers are cleaner and more consistent in the time‐lag‐derived angle gathers, but the conversion from time lag to angle can be considered a post‐processing step. The main difference arises in the amplitude versus offset/angle distribution where the responses are different and dramatically so for the land data. The results from the synthetics and real data show that a Kirchhoff migration with an extended imaging condition is capable of generating subsurface angle gathers. The same disadvantages with a ray‐based approach will apply using the extended imaging condition relative to a wave equation angle gather solution. Nevertheless, using this approach allows one to explore the relationship between the velocity model and focusing of the reflected energy, to use the Radon transformation to remove noise and multiples, and to generate consistent products from a ray‐based migration and a full‐wave equation migration, which can then be interchanged depending on the process under study.     

Development of push moraines in deeply frozen sediment adjacent to a cold-based glacier in the McMurdo Dry Valleys,Antarctica

Previous studies of push moraines have concluded that structural architecture is controlled by a combination of stress exerted by flowing ice and the rheology of the deforming sediment. However, the relationship between deformation processes and the thermal/hydrologic conditions within the sediment remains ambiguous. Using a combination of surface mapping, logging exposures and ground penetrating radar we examine the relationships between surface morphology, material properties and development of deformation structures in deeply frozen sediment that has been deformed by Joyce Glacier, a cold-based glacier in the McMurdo Dry Valleys. The structural architecture of the push moraines is characterized by a combination of brittle and ductile deformation structures that have produced a structurally complex pattern of thrust faults, low angle listric thrusts and recumbent folds that extend 400 m beyond the glacier margin. Deformation is ductile where the ice concentration exceeds c. 65% volume and predominantly brittle where the ice concentration is less than c. 65%. The change in rheology reflects transition in behaviour from the material having a predominantly frictional character when the ice is limited to pore spaces to a non-frictional character in which strength is primarily determined by the cohesive strength of the ice. This work shows that glaciotectonic deformation can occur in deeply frozen permafrost where there is no liquid pore water. We conclude that the presence of liquid porewater is not a necessary condition for the development of glaciotectonic deformation or for the formation of push moraines. © 2019 John Wiley & Sons, Ltd.     

Raman study of shock features in plagioclase feldspar from the Mistastin Lake impact structure,Canada

Plagioclase feldspar is one of the most abundant minerals on the surface of the Earth, the Moon, and Mars, and is also commonly found in meteorites. Studying shock effects in feldspar thus provides us with fundamental information about impact cratering processes on planetary bodies. In this study, plagioclase from monomict and polymict breccias, impact melt rocks, and shock‐metamorphosed target rocks, from throughout the Mistastin Lake impact structure, Canada, was examined using 514 nm laser Raman spectroscopy. As one of the very few impact structures with anorthosite in the target rocks, the Mistastin Lake impact structure provides a unique opportunity to study shocked plagioclase displaying progressive shock metamorphic features. A series of microscopic features was observed within plagioclase, including twins, needle‐like inclusions, planar features, and alteration. The lack of planar deformation features is notable. Raman spectra of these features suggest that this technique is capable of differentiating and classifying shock features in low to moderately shocked rocks. Caution should be exercised, however, as Raman spectra collected from unshocked plagioclase references with known compositions indicate that peak width and peak ratio of the Raman peaks in lower wave number region (<350 cm^?1) and the main signature peaks around 500 cm^?1 vary with chemical composition and crystal orientation. Data collected from diaplectic glass suggest that Raman features are efficient in distinguishing crystalline plagioclase and diaplectic glass. We also observed significant variations in the Raman intensities collected from diaplectic glass, which we ascribe to the localized disorder or inhomogeneity of shock pressure and temperature throughout the target.     

Multi-element otolith chemistry of juvenile sole (Solea solea), whiting (Merlangius merlangus) and European seabass (Dicentrarchus labrax) in the Thames Estuary and adjacent coastal regions

Estuaries are regarded as valuable nursery habitats for many commercially important marine fishes, potentially providing a thermal resource, refuge from predators and a source of abundant prey. To assess the extent of estuarine use by juvenile (0+) common sole (Solea solea), whiting (Merlangius merlangus) and European seabass (Dicentrarchus labrax) we: (1) developed techniques to distinguish between estuarine and coastally-caught juveniles using otolith chemistry; and (2) examined the accuracy with which multi-elemental signatures could re-classify juveniles to their region of collection.High-resolution solution-based inductively coupled plasma mass spectrometry (HB-SB-ICPMS) was used to quantify 32 elements within the juvenile otoliths; 14 elements occurred above detection limits for all samples. Some elemental distributions demonstrated clear differences between estuarine and coastally-caught fish. Multivariate analysis of the otolith chemistry data resulted in 95–100% re-classification accuracy to the region of collection. Estuarine and coastal signatures were most clearly defined for sole which, compared to bass and whiting, have low mobility and are less likely to move from estuarine to coastal habitats between larval settlement and later migration to adult stocks. Sole were the only species to reveal an energetic benefit associated with an estuarine juvenile phase. The physiological ability of bass to access upper estuarine regions was consistent with some elemental data, while the high mobility and restricted range of whiting resulted in less distinct otolith chemistries.     

Fisher's behaviour with individual vessel quotas—Over-capacity and potential rent: Five case studies

Internationally, individual vessel quotas (IVQ) have become an increasingly popular management tool. The main attraction of IVQs is the incentives they create for cost savings, autonomous capacity adjustment and, subsequently, rent generation. In this paper, the extent to which different IVQ systems have facilitated resource rent generation and capacity adjustment in five European countries—Denmark, Iceland, Norway, Sweden and the UK—is examined. The potential economic rents and the capacity reduction necessary to achieve these rents in each of the fisheries are also estimated. Reasons why IVQs have not achieved their potential economic benefits in these fisheries are also examined.