A practical review of geostatistical processing applied to geophysical data: methods and applications

Nowadays, geostatistics is commonly applied for numerous gridding or modelling tasks. However, it is still under used and unknown for classical geophysical applications. This paper highlights the main geostatistical methods relevant for geophysical issues, for instance to improve the quality of seismic data such as velocity cubes or interpreted horizons. These methods are then illustrated through four examples. The first example, based on a gravity survey presents how a geostatistical interpolation can be used to filter out a global trend, in order to better define real anomalies. In the second case study, dedicated to refraction surveying, geostatistical filtering is used to filter out acquisition artefacts and identify the main geological structures. The third one is an example of porosity being integrated geostatistically with a seismic acoustic impedance map. The last example deals with geostatistical time to depth conversion; the interest of performing geostatistical simulations is finally discussed.     

SELDI-TOF MS analysis of alkylphenol exposed Atlantic cod with phenotypic variation in gonadosomatic index

Proteomics is a new and promising approach to evaluate potential effects of pollution. In order to investigate if there is a direct link between the protein expression profiles obtained by the SELDI-TOF MS technology and effects observed at the organism level in fish, plasma samples from unexposed and 20 ppb alkylphenol exposed female Atlantic cod (Gadus morhua) with high phenotypic variation in gonadosomatic index (GSI) were analyzed by SELDI-TOF MS. Principle component analysis (PCA) showed that the major proteomic variation present in the dataset (i.e. 23.6%) could be significantly correlated to the individual variation in GSI, which indicates that SELDI-TOF MS data can reflect effects observed at higher levels of organization in fish. Further exploration of the other principal components revealed an additional proteomic pattern specific for the alkylphenol exposed females. Hence, this study supports the usefulness of SELDI-TOF MS as a proteomic tool in ecotoxicological research.     

The REE-Ti mineral chevkinite in comenditic magmas from Gran Canaria,Spain: a SYXRF-probe study

The REE-Ti silicate chevkinite has been recognised previously in Miocene ignimbrites from Gran Canaria, and in correlative offshore syn-ignimbrite turbidites. We have estimated the partition coefficients of REE, Y, Zr and Nb for chevkinite and co-existing peralkaline rhyolitic (comendite) glass using synchrotron-XRF-probe analyses (SYXRF) in order to evaluate the role of this mineral in the REE budget of felsic peralkaline magmas. The Zr/Nb ratio of the chevkinite is 1.55–1.7, strongly contrasting with Zr/Nb of 6.5 in the associated glass. Zr shows a three-fold enrichment in chevkinite relative to the residual melt, whereas Nb is enriched by a factor >10. The enrichment of Ce and La in chevkinite is even more significant, namely 19 wt(%) Ce and 12 wt(%) La, compared to 236 ppm Ce and 119 ppm La in the glass. Chevkinite/glass ratios are 988±30 for La, 806±30 for Ce, 626±30 for Pr, 615±40 for Nd, 392±50 for Sm, 225±30 for Eu, 142±25 for Gd, 72±20 for Dy. For trace elements, we derived Kd_TE of 74±25 for Y, >8 for Hf, >50 for Th, 15±5 for Nb and 3.55±0.4 for Zr. Mineral/glass ratios for co-existing titanite are 28±10 for La, 86±20 for Ce, 98±30 for Pr, 134±35 for Nd, 240±50 for Sm, 50±20 for Eu, 96±25 for Gd, 82±25 for Dy, 99±30 for Y, 45±10 for Nb and 3±0.5 for Zr. Based on these data, the removal of only 0.05 wt% of chevkinite from a magma with initially 300 ppm Ce would deplete the melt by 93 ppm to yield 207 ppm Ce in the residual liquid. Chevkinite thus appears, when present, to be the controlling mineral within the LREE budget of evolved peralkaline magmas.Editorial responsibility: I. Parsons

---

Three‐dimensional texture of natural pseudotachylyte: Pseudotachylyte formation mechanism in hydrous accretionary complex

Melt‐origin pseudotachylyte is the most reliable seismogenic fault rock. It is commonly believed that pseudotachylyte generation is rare in the plate subduction zone where interstitial fluids are abundant and can trigger dynamic fault‐weakening mechanisms such as thermal pressurization. Some recent studies, however, have discovered pseudotachylyte‐bearing faults in exhumed ancient accretionary complexes, indicating that frictional melting also occurrs during earthquakes in subduction zones. To clarify the pseudotachylyte generation mechanism and the variation of slip behavior in the plate subduction zone, a pseudotachylyte found in the exhumed fossil accretionary complex (the Shimanto Belt, Nobeoka, Japan) was re‐focused and microscopic and three‐dimensional observations of the pseudotachylyte‐bearing fault were performed based on optical, electron, and X‐ray microscope images. Based on the patterns contained in the fragment, the pseudotachylyte is divided into four domains, although no clear domain boundaries or layering structures are not found. Three‐dimensional observation also suggests that the pseudotachylyte were fragmented or isolated by cataclasite or carbonate breccia. The pseudotachylyte was rather injected into the surrounding carbonate breccia, which is composed of angular fragments of the host rock and a matrix of tiny crystalline carbonate. The pseudotachylyte volume was extracted from the X‐ray microscope image and the heat abundance consumed by the pseudotachylyte generation was estimated at 2.18 MJ/m², which can be supplied during a slip of approximately 0.5 m. These observations and calculations, together with the results of the previous investigations, suggest hydrofracturing and rapid carbonate precipitation that preceded or accompanied the frictional melting. Dynamic hydrofracturing during a slip can be caused by rapid fluid pressurization, and can induce abrupt decrease in fluid pressure while drastically enhancing the shear strength of the shear zone. Consequently, frictional heating would be reactivated and generate the pseudotachylyte. These deformation processes can explain pseudotachylyte generation in hydrous faults with the impermeable wall rock.     

Biodiverse rotifer assemblage(Rotifera: Eurotatoria) of floodplain lakes of the Brahmaputra basin of lower Assam,northeast India: composition and ecosystem diversity

The study aims to ascertain the hypothesis on the rich rotifer biodiversity of the floodplain lakes(beels) of the Brahmaputra river basin and to use these metazoans to assess trophic status or to characterize habitat variations of wetlands. The plankton samples collected from four beels of lower Assam revealed 160 Rotifera species belonging to 35 genera and 19 families. The richness is of biodiversity value as ~38.0% and ~57.0% of the rotifer species known till date from India and northeast India(NEI), respectively. One species each is new to the Oriental region and NEI, and three species are new to Assam; 23 species merit global biogeography interest and several exhibit distribution values in the Indian sub-region. The diverse Lecanidae Brachionidae Lepadellidae Trichocercidae and speciose littoral-periphytic L ecane Lepadella Trichocerca, and richness of Brachionus spp. following removal of aquatic macrophytes are noteworthy. Overall rotifer composition showed homogeneity amongst beels while lower monthly richness and community similarities affirmed heterogeneity within individual beels. We propose L/B quotient based on L ecane : Brachionus species ratios to characterize habitat variations of the sampled wetlands. Sláde?ek's B/T quotient based on B rachionus : T richocerca species ratios affirmed general 'meso-trophic' status of diff erent beels. Our results provided little insight on the influence of individual abiotic factors but the canonical correspondence analyses asserted higher cumulative influence of ten abiotic parameters on Rotifera richness in each beel.     

宁武天池干海湖泊沉积物的部分非磁滞剩磁研究

应用部分非磁滞剩磁(pARM)谱,对山西宁武天池干海湖泊沉积物携带的磁信息研究表明,粗磁铁矿颗粒(MD)是主要载磁矿物颗粒,其pARM谱在低矫顽力区间(AF20 mT)达到最高值;而细磁铁矿颗粒(PSD-SD)为次要载磁颗粒,其pARM谱在高矫顽力区间(AF20 mT)稍有突起。但是,剖面三个层位具有不同特征,上层(大约7.3~4.0 ka)的粗磁性矿物颗粒含量最高,下层(大约12.0~13.0 ka)次之,而中层(大约12.0~7.3 ka)相对最低;中层的细磁性颗粒含量最高,下层和上层的细磁性颗粒含量次之。pARM谱分析结果与磁滞曲线测量获得的磁畴结果一致。在较高的交变磁场区间获得的pARM可以有效地压抑粗磁颗粒的信息,进而使细磁颗粒的信号增强。应用pARM谱分析,能有效判别样品中磁性矿物的磁畴状态,有助于沉积物的古气候、岩石磁学和古地磁学研究。