Aenigmatite,sodic pyroxene,arfvedsonite and associated minerals in syenites from Morotu,Sakhalin

Aenigmatite, sodic pyroxene and arfvedsonite occur as interstitial minerals in metaluminous to weakly peralkaline syenite patches in alkali dolerite, Morotu, Sakhalin. Aenigmatite is zoned from Ca, Al, Fe³⁺-rich cores to Ti, Na, Mn, Si-rich rims reflecting the main substitutions Fe²⁺Ti⁴⁺Fe³⁺, NaSiCaAl and Mn²⁺Fe²⁺. Aenigmatite replaces aegirine and ilmenite supporting the existence of a no-oxide field in — T space. In one case aenigmatite has apparently formed by reaction between ilmenite and arfvedsonite. Titanian aegirine (up to 3.0 wt% TiO₂) and Fe-chlorite may replace aenigmatite. Sodic pyroxene occurs as zoned crystals with cores of aegirine-augite rimmed by aegirine and in turn by pale green aegirine containing 93 mol% NaFe³⁺Si₂O₆. Additional substitution of the type NaAlCaFe²⁺ is indicated by significant amounts (up to 6 mol%) of NaAlSi₂O₆. Arfvedsonite is zoned with rims enriched in Na, Fe and depleted in Ca which parallels the variation of these elements in the sodic pyroxenes.The high peralkalinity of the residual liquid from which the mafic phases formed resulted from the early crystallization of microperthite (which makes up the bulk of the syenites) leading to an increase in the Na₂O/(Na₂O+K₂O) and (Na₂O+K₂O)/Al₂O₃ ratios of the remaining interstitial liquid which is also enriched in Ti, Fe, and Mn. Bulk composition of the melt, , temperature and volatile content were all important variables in determining the composition and stability of the peralkaline silicates. in the residual liquid appears to have been buffered by arfvedsonite-aegirine and later by the arfvedsonite-aenigmatite and aenigmatite-aegirine equilibria under conditions of a no-oxide field. An increase in , above that of the alkali buffer reactions, is inferred by an increase of Ti and Mn in aenigmatite rims. The latest postmagmatic vapour crystallization stage of the syenites is marked by extremely low which may have been facilitated by exsolution of a gas phase. Low is supported by the replacement of aenigmatite by titanian aegirine, and the formation of rare Ti-rich garnet with a very low (Ti⁴⁺+Fe³⁺)/(Ti+Fe) ratio of 0.51, associated with leucoxene alteration of ilmenite.     

Bacteria—particle interactions in turbid estuarine environments

A study of the distribution of bacteria in relation to particle concentration and type was conducted over a spring-neap tidal cycle in the Tamar Estuary, southwest England. Three groups of bacteria were recognized: free-living; those attached to permanently suspended particles; and those attached to particles which undergo tidally controlled resuspension and sedimentation. The total activity and the activity of all three groups of bacteria increase in the turbidity maximum region. The bacteria associated with the permanently suspended particles, which have a larger mean size and organic carbon content than those in the resuspended sediments, contribute the major part of this increased activity. This is a significant finding as it had been previously thought that the increase in bacterial activity at the turbidity maximum was due to bacteria attached to resuspended sediments. However, resuspension still plays an important role because the increase in bacterial activity is consistently coincident with the turbidity maximum.     

Correlation between individual waves in a real sea state

The correlation between individual waves in a real sea state has a central role in existing theories of wave grouping. The attractive Kimura (1980) theory has two critical assumptions, that the sequence of individual wave heights follows a Markov process and that the joint distribution of consecutive wave heights follows a bivariate Rayleigh form. Analysis of measured water surface records suggests that sequences of individual waves can reasonably be described as a first order mixed autoregressive, moving-average or ARMA process, though a distinction among ARMA (1,0), ARMA (0,1) and ARMA (1,1) models was beyond the resolution of the data. These include the Markov or ARMA (1,0) model. The decisive detail, the joint distribution of consecutive wave heights in the sea state, was evaluated by a simulation methodology that is consistent with the Gaussian random wave model. The estimates are dependent on spectral shape and are consistently narrower and more sharply focussed at the peak than the corresponding bivariate Rayleigh estimate. The resulting predictions of run and group length statistics differ from the Kimura theory, though not by a sufficient margin to displace the Kimura theory as a pragmatic choice for wave grouping.     

Quantitative provenance of silt and clay within sandy deposits of the Lithuanian coastal zone (Baltic Sea)

A quantitative provenance approach is developed and in this study applied for the silt and clay fractions of sandy, coastal deposits. Mineralogical composition of 37 surface samples was determined by X-ray diffraction (XRD). Grain-size distributions were obtained by standard dry sieving and pipette techniques. The characterization of mineralogical provenance is based upon known compositional information of possible sources, logical models for mineral combinations related to regional geological provinces and processes, and geographical features of the documented mineral distribution in the area of investigation. These interpretations are further supported by results of correlation and principal component analyses of mineral varieties, grain-size parameters and bathymetric features of the area. Partitioning of source contributions specific for each site of deposition is derived by solving simultaneous equations. Then, the quantified mineral composition at the initial source is reconstructed in the SE Baltic Sea along the Lithuanian coast, exemplifying this new methodology for quantification of sediment sources. The main sources supplying sediment to the area are: 1) Sambian Peninsula to the south (erosion of Pleistocene till and “Blue Earth” Paleogene sediments), supplying 33% of fine-grained sediment on average, 2) Nemunas River, the discharge of which passes through Curonian Lagoon and supplies an average 17% of the coastal fine sediments, and 3) Pleistocene till, eroded on the sea floor in the north and at the Olando Kepur? shore cliff and contributing an average of 50% of the sediment. Although we use the mineralogy within the environmentally important fine-grained fraction, this mathematically simple approach could be used with any other parameters characterizing the identified sources. A quantification of the separate source contributions to each individual site of accumulation studied, using the stable, mineralogical components of the “sediment archive”, offers a time-integrated, net-effect reflection of the combined processes of an entire environmental system.     

Mountaineering incidents in France: analysis of search and rescue interventions on a 10-year period(from 2008 to 2018)

In Europe and especially in France,there is a growing enthusiasm for outdoor sports and recreation.In the meantime,the risk of both severe and frequent injuries associated with active pursuits is acknowledged,especially in mountainous areas.The effectiveness of prevention must rely on detailed knowledge of typical circumstances and scenarios but thorough understanding of the mechanisms of accidentality remains limited by the fragmentation of sources and by mostly heterogeneous methodologies.This paper aims at giving insights on victims’profiles,season,location,and circumstances of mountaineering accidents in the French Alps,through the study of rescue interventions data from 2008 to 2018.Thanks to the analysis of the exhaustive database of search and rescue interventions from the French mountain national police force,and while questioning its limitations,we strive to answer two questions:what are the characteristics of the hazardous situations leading to a rescue intervention in mountaineering?Among these situations,what are the characteristics that tend to make them more harmful?     

Optical luminescence dating of a loess section containing a critical tephra marker horizon,SW North Island of New Zealand

A new IRSL dataset is presented for the age and setting of a critical Late Glacial Maximum tephra isochron marker. The rhyolitic tephra, known as the Kawakawa Tephra, occurs as a 14 cm thick layer within a 5.9 m thick loess section overlying alluvial gravels in the Rangitikei River valley, SW North Island of New Zealand. Ages range from 21 at the base to 5 ka near the top of the loess and bracket an age of 17.0 ± 2.2 for the tephra. The new IRSL ages are in agreement with published and unpublished luminescence ages from other localities of loess, sand and ash above and below the tephra and of the tephra itself, that indicate an age of ca. 19 ka for the Kawakawa Tephra. This age is considerably younger than the generally accepted ¹⁴C 27.1 ka cal yrs BP age of the Kawakawa Tephra and highlights an unresolved discrepancy between the two dating systems.     

华南花岗岩暗色微粒包体成因研究

通过对暗色微粒包体的空间分布和形态特征以及包体矿物学、显微结构和岩石化学组成等方面的研究成果,在花岗岩“原地重熔”成因模型的基础上,建立了包体演化与熔渣演化的关系模型,证实包体的前身是捕虏体,后者代表从盖层落入岩浆中的岩块,包体则是岩块部分熔融后的残余物。不同类型、不同形态、不同基性度的包体,代表了岩石原地熔融过程中不同阶段的产物,富云包体反映了熔渣演化的最后阶段,在此基础上的进一步熔融即与寄主岩浆混成一体,完成了从岩石到岩浆的整个演化过程。     

华南花岗岩暗色微粒包体矿物组成及微结构研究

对来自华南多个花岗岩体的暗色微粒包体样品进行了系统的矿物组成和微结构研究,发现包体中不管是造岩矿物还是副矿物,均存在新、老两个不同世代;包体的微结构大部分情况下也不是“火成结构”,而是以熔融结构为主,并且常多种结构共存,揭示包体是岩石部分熔融的残余物而并非来自岩浆的结晶。不同包体或同一包体从中心到边缘的矿物组成与微结构的差异,反映原岩部分熔融程度的不同,揭示其处于不同的演化阶段。