Grosvenor Mountains 95 howardite pairing group: Insights into the surface regolith of asteroid 4 Vesta          下载免费PDF全文

Nicole G. Lunning  Kees C. Welten  Harry Y. McSween Jr  Marc W. Caffee  Andrew W. Beck 《Meteoritics & planetary science》2016,51(1):167-194

Regolithic howardites are analogs for the surface materials of asteroid 4 Vesta, recently mapped by the Dawn spacecraft. Rigorously evaluating pairing of howardites recovered in 1995 in the Grosvenor Mountains (GRO 95), Antarctica, enables an examination of a larger, more representative regolith sample. Previous work on two of the howardites studied here concluded that GRO 95602 and GRO 95535 are solar wind‐rich surface regolith samples and that they are not paired with each other, leading to uncertainty regarding pairing relationships between the other GRO 95 howardites. Based on petrology, cosmic‐ray exposure history, and terrestrial age, four GRO 95 howardites are paired. The paired howardites (GRO 95534, 95535, 95574, 95581) were from a meteoroid with radius of 10–15 cm, a preatmospheric size comparable to that of Kapoeta, the largest known regolithic howardite. The paired GRO 95 howardites contain clasts of at least 18 separate HED lithologies, providing evidence they were assembled from diverse source materials. The total eucrite:diogenite mixing ratio (ratio of all eucrite lithologies to all diogenite lithologies) in the paired GRO 95 howardites is ~2:1. Petrographically determined basaltic eucrite:cumulate eucrite ratios in regolithic howardites, studied here and previously, vary more widely than total eucrite:diogenite ratios. Relative to eucritic pyroxene, plagioclase is depleted in these howardites, which provides evidence that plagioclase is preferentially comminuted in the vestan regolith. The extent of plagioclase depletion could be an indicator of regolith maturity.  相似文献   

Cosmic‐ray exposure age and preatmospheric size of the Bunburra Rockhole achondrite     

Kees C. WELTEN  Matthias M. M. MEIER  Marc W. CAFFEE  Matthias LAUBENSTEIN  Kunihiko NISHIZUMI  Rainer WIELER  Phil A. BLAND  Martin C. TOWNER  Pavel SPURNÝ 《Meteoritics & planetary science》2012,47(2):186-196

Abstract– Bunburra Rockhole is the first meteorite fall photographed and recovered by the Desert Fireball Network in Australia. It is classified as an ungrouped achondrite similar in mineralogical and chemical composition to eucrites, but it has a distinct oxygen isotope composition. The question is if achondrites like Bunburra Rockhole originate from the same parent body as the howardite‐eucrite‐diogenite (HED) meteorites or from several separate, differentiated parent bodies. To address this question, we measured cosmogenic radionuclides and noble gases in the Bunburra Rockhole achondrite. The short‐lived radionuclides ²²Na and ⁵⁴Mn confirm that Bunburra Rockhole is a recent fall. The concentrations of ¹⁰Be, ²⁶Al and ³⁶Cl as well as the ²²Ne/²¹Ne ratio indicate that Bunburra Rockhole was a relatively small object (R approximately 15 cm) in space, consistent with the photographic fireball observations. The cosmogenic ³⁸Ar concentration yields a cosmic‐ray exposure (CRE) age of 22 ± 3 Myr, whereas ²¹Ne and ³He yield approximately 30% and approximately 60% lower ages, respectively, due to loss of cosmogenic He and Ne, mainly from plagioclase. With a CRE age of 22 Myr, Bunburra Rockhole is the first anomalous eucrite that overlaps with the main CRE peak of the HED meteorites. The radiogenic K‐Ar age of 4.1 Gyr is consistent with the U‐Pb age, while the young U,Th‐He age of approximately 1.4 Gyr indicates that Bunburra Rockhole lost radiogenic ⁴He more recently.  相似文献   

Perylene dominates the organic contaminant profile in the Berau delta, East Kalimantan, Indonesia     

Booij K  Arifin Z  Purbonegoro T 《Marine pollution bulletin》2012,64(5):1049-1054

The geographical distributions of polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), hexachlorobenzene, and 1,1-dichloro-2,2-bis(4-chlorophenyl)ethene (4,4'-DDE) were studied in the Berau delta (East Kalimantan, Indonesia), using sediment sampling and passive water sampling with semipermeable membrane devices. High concentrations of perylene were observed in sediments (54-580 ng g(-1) dry weight), and water (1-680 pg L(-1)). Perylene accounted for about 60% of the total concentrations of PAHs in the sediment. The relative abundance of the other PAHs was indicative of petrogenic sources. Concentrations of PCBs, hexachlorobenzene, and 4,4'-DDE in sediments were below or close to the detection limit (～ 0.02 ng g(-1)). The analysis of a sediment core revealed no appreciable changes in the concentration of target compounds over the past three decades. We show that sediment sampling and passive water sampling are complementary techniques, and propose to bring the results of both methods to the same concentration scale, using locally derived sediment-water partition coefficients.  相似文献   

Seismic interferometry by tangent‐phase correction          下载免费PDF全文

Flavio Poletto  Biancamaria Farina  Gualtiero Böhm  Kees Wapenaar 《Geophysical Prospecting》2015,63(3):567-586

We present a modified interferometry method based on local tangent‐phase analysis, which corrects the cross‐correlated data before summation. The approach makes it possible to synthesize virtual signals usually vanishing in the conventional seismic interferometry summation. For a given pair of receivers and a set of different source positions, a plurality of virtual traces is obtained at new stationary projected points located along the signal wavefronts passing through the real reference receiver. The position of the projected points is estimated by minimizing travel times using wavefront constraint and correlation‐signal tangent information. The method uses mixed processing, which is partially based on velocity‐model knowledge and on data‐based blind interferometry. The approach can be used for selected events, including reflections with different stationary conditions and projected points with respect to those of the direct arrivals, to extend the interferometry representation in seismic exploration data where conventional illumination coverage is not sufficient to obtain the stationary‐phase condition. We discuss possible applications in crosswell geometry with a velocity anomaly and a time lapse.  相似文献   

Data-driven retrieval of primary plane-wave responses     

Giovanni Angelo Meles  Lele Zhang  Jan Thorbecke  Kees Wapenaar  Evert Slob 《Geophysical Prospecting》2020,68(6):1834-1846

Seismic images provided by reverse time migration can be contaminated by artefacts associated with the migration of multiples. Multiples can corrupt seismic images, producing both false positives, that is by focusing energy at unphysical interfaces, and false negatives, that is by destructively interfering with primaries. Multiple prediction/primary synthesis methods are usually designed to operate on point source gathers and can therefore be computationally demanding when large problems are considered. A computationally attractive scheme that operates on plane-wave datasets is derived by adapting a data-driven point source gathers method, based on convolutions and cross-correlations of the reflection response with itself, to include plane-wave concepts. As a result, the presented algorithm allows fully data-driven synthesis of primary reflections associated with plane-wave source responses. Once primary plane-wave responses are estimated, they are used for multiple-free imaging via plane-wave reverse time migration. Numerical tests of increasing complexity demonstrate the potential of the proposed algorithm to produce multiple-free images from only a small number of plane-wave datasets.  相似文献   

Identification and Explanation of a Change in the Groundwater Regime using Time Series Analysis     

Christophe Obergfell  Mark Bakker  Kees Maas 《Ground water》2019,57(6):886-894

Time series analysis is applied to identify and analyze a transition in the groundwater regime in the aquifer below the sand ridge of Salland in the Netherlands, where groundwater regime refers to the range of head variations throughout the seasons. Standard time series analysis revealed a discrepancy between modeled and observed heads in several piezometers indicating a possible change in the groundwater regime. A new time series modeling approach is developed to simulate the transition from the initial regime to the altered regime. The transition is modeled as a weighted sum of two responses, one representing the initial state of the system, the other representing the altered state. The inferred timing and magnitude of the change provided strong evidence that the transition was the result of significant dredging works that increased the river bed conductance of the main river draining the aquifer. The plausibility of this explanation is corroborated by an analytical model. This case study and the developed approach to identify a change in the groundwater regime are meant to stimulate a more systematic application of time series analysis to detect and understand changes in groundwater systems which may easily go unnoticed in groundwater flow modeling.  相似文献   

The CM carbonaceous chondrite regolith Diepenveen     

Marco Langbroek  Peter Jenniskens  Leo M. Kriegsman  Henk Nieuwenhuis  Niek De Kort  Jacob Kuiper  Wim Van Westrenen  Michael E. Zolensky  Karen Ziegler  Qing‐Zhu Yin  Matthew E. Sanborn  Josh Wimpenny  Akane Yamakawa  Sebastiaan J. De Vet  Matthias M. M. Meier  Kees C. Welten  Kunihiko Nishiizumi  Marc W. Caffee  Aaron S. Burton  Jason P. Dworkin  Daniel P. Glavin  Qinghao Wu  Richard N. Zare  Alexander Ruf  Mourad Harir  Philippe Schmitt‐Kopplin   《Meteoritics & planetary science》2019,54(7):1431-1461

A carbonaceous chondrite was recovered immediately after the fall near the village of Diepenveen in the Netherlands on October 27, 1873, but came to light only in 2012. Analysis of sodium and poly‐aromatic hydrocarbon content suggests little contamination from handling. Diepenveen is a regolith breccia with an overall petrology consistent with a CM classification. Unlike most other CM chondrites, the bulk oxygen isotopes are extremely ¹⁶O rich, apparently dominated by the signature of anhydrous minerals, distributed on a steep slope pointing to the domain of intrinsic CM water. A small subset plots closer to the normal CM regime, on a parallel line 2 ‰ lower in δ¹⁷O. Different lithologies in Diepenveen experienced varying levels of aqueous alteration processing, being less aqueously altered at places rather than more heated. The presence of an agglutinate grain and the properties of methanol‐soluble organic compounds point to active impact processing of some of the clasts. Diepenveen belongs to a CM clan with ~5 Ma CRE age, longer than most other CM chondrites, and has a relatively young K‐Ar resetting age of ~1.5 Ga. As a CM chondrite, Diepenveen may be representative of samples soon to be returned from the surface of asteroid (162173) Ryugu by the Hayabusa2 spacecraft.  相似文献   

Seabirds in the North Sea Demobilized and Killed by Polyisobutylene (C₄H₈)_n (PIB)     

Kees C.J Camphuysen  Hein Barreveld  Gerhard Dahlmann  Jan Andries Van Franeker 《Marine pollution bulletin》1999,38(12):677-1176

This paper reports on a mass stranding of seabirds in the North Sea in December 1998. Hundreds of birds were washed ashore alive in Zeeland (SW Netherlands), covered in a whitish, sticky substance, and were transported to a rehabilitation centre. About 10 days later, more (dead) casualties washed ashore further to the north on Texel and along the mainland coast, again covered in a glue-like substance. Common guillemots Uria aalge, northern fulmars Fulmarus glacialis and common scoters Melanitta nigra were the most numerous birds affected in this incident. Both strandings were temporarily (10 days) and geographically separated (ca. 120 km apart), but were apparently caused by a single source of pollution. The meteorology at the time was consistent with the course of a single incident. At least 1100 seabirds were affected by this substance, soon identified as polyisobutylene (C₄H₈)_n. PIB is known as a non-toxic, non-aggressive substance. Volunteers cleaning the birds in the rehabilitation centre reported serious discomfort and dizziness and the soft parts of the PIB-affected birds found dead (bill, eye, throat, feet, webs) appeared to dissolve in a few days time. Both effects cannot be attributed to PIB, and are therefore unexplained. Although the dumping of PIB in the marine environment is not explicitly prohibited under MARPOL, the effects on wildlife observed are enough to plead for counter-measures.  相似文献   

Equipartitioning is not sufficient for Green＇s function extraction     

Roel Snieder  Yuanzhong Fan  Evert Slob  Kees Wapenaar 《地震学报(英文版)》2010,(5):403-415

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Interferometric electromagnetic Green's functions representations using propagation invariants   总被引：1，自引：0，他引：1  

Evert Slob  Deyan Draganov  Kees Wapenaar 《Geophysical Journal International》2007,169(1):60-80

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