Contaminants in sediments: Using robust regression for grain-size normalization

Sediment contaminant concentrations usually show an inverse correlation with grain size. This can cause difficulties in distinguishing real differences in contamination from artifacts caused by variations in sediment texture. To overcome this, regression analysis is frequently used to remove the dependency of concentrations on grain size. However, least squares regression lines can be affected markedly by the presence of a small number of unusual samples in the dataset. These outliers may represent samples which are more severely contaminated or which were derived from areas with different underlying geology. They can be removed semi-manually, but robust regression methods such as least absolute values provide a convenient and objective alternative. The methods are illustrated using an example dataset of metal contaminants in sediments from the Humber Estuary, United Kingdom. Least squares regression on the complete dataset yields a rather poor grain size normalization for several elements. By contrast, least absolute values regression produces results very similar to those obtained by least squares regression after careful manual removal of outliers, but it avoids the need for subjective judgments of which data points to omit from the analysis. The intercepts of several of the fitted regression lines were non-zero, indicating that regression-based normalization is preferable to methods based on ratios.     

High resolution images of Cygnus X-1

The classic black hole candidate Cygnus X-1 exhibits many similarities to Galactic jet sources (micro-quasars) in soft gamma and hard X-ray rays. This has fuelled suspicions that radio jets also may be present in Cygnus X-1. The lack of radio flaring in Cygnus X-1 has been associated with the presence of continuous jets rather than multiple plasmon ejection however no evidence for this has been observed with the VLA, or with MERLIN. Recent VLBA observations at 15 GHz have detected extended emission and further multi frequency observations are required to confirm the presence of jets on a milliarcsecond level.     

The geometry of en-echelon vein arrays

Two distinct types of en-echelon vein arrays are recognised, those which form in active ductile shear zones and those which form by the primary nucleation of fractures not connected with active shear zones. The theoretical relation between vein width and orientation in a zone undergoing progressive simple shear is examined and compared with similar data from natural arrays. It is found that many veins have undergone dilation prior to rotation during simple shear, showing that shearing occurred after the en-echelon array was established. Generally, all strongly sigmoidal veins occur in arrays in which pressure solution was also active. In non-sigmoidal arrays there is a clear relation between the amount of overlap of adjacent veins and the orientation of the veins relative to the zone containing them. Two different patterns of dilation and distortion of arrays in which pressure solution was not active are described. It is concluded that primary en-echelon veins originated as tensile fractures, whilst en-echelon veins formed in active shear zones originated as shear fractures.     

A geochemical investigation of pressure solution and the formation of veins in a deformed greywacke

Pressure solution and vein formation often occur simultaneously in shear zones during the deformation of sedimentary rocks. The mineralogical and chemical variations around a typical example of an en echelon zone of quartz veins from north Cornwall are discussed in detail. Solution of quartz is confined to the shear zone and occurs along discrete surfaces. Accumulation of insoluble minerals along these surfaces gives rise to spaced pressure solution cleavage. Petrographic data show that during pressure solution the breakdown of felspar and epidote results in the crystallisation of clay mineral, quartz and siderite. Redistribution of silica within the shear zone by pressure solution does not account for all the quartz in the veins, or for the observed increased concentration of iron and calcium. It is concluded that material was introduced from an external source into the shear zone.     

Factor analysis of stream sediment geochemical data from the Mount Nansen area,Yukon Territory,Canada

Q- and R-mode factor analytical studies were made of 158 stream sediment samples from the Mount Nansen area, Yukon Territory, analyzed for Cu, Pb, Zn, Mo, Ni, Ag, and Sb. R-mode results were more clear-cut than were Q-mode in terms of ease of interpreting geological significance of individual factors, although results of both methods were very comparable. The 3-factor R-mode model accounted for 79.9 percent of the variation in the data. Factor 1, a Pb-Zn-(Ag) factor correlated with Mount Nansen volcanic rocks and particularly with known Pb-Zn-Ag-Au veins within those rocks. Factor 2, a Cu-Mo factor correlated with porphyric intrusions known to contain Cu-Mo mineralized zones. Factor 3, an Sb-(Ag) factor is, as yet, not adequately explained in terms of geology. The main additional contribution of the Q-mode study is the communalities. Samples that depart from the norm (i.e. do not agree well with the 3-factor model) are readily apparent because of low communalities and must be considered anomalous in the general sense until an adequate explanation for this difference is found.     

Size,shape and spatial arrangement of mega‐scale glacial lineations from a large and diverse dataset

Mega‐scale glacial lineations (MSGLs) are a characteristic landform on ice stream beds. Solving the puzzle of their formation is key to understanding how ice interacts with its bed and how this, in turn, influences the dynamics of ice streams. However, a comprehensive and detailed characterization of this landform's size, shape and spatial arrangement, which might serve to test and refine formational theories, is largely lacking. This paper presents a detailed morphometric analysis and comparison of 4043 MSGLs from eight palaeo‐ice stream settings: three offshore (Norway and Antarctica), four onshore (Canada), and one from under a modern ice stream in West Antarctica. The length of MSGLs is lower than previously suggested (mode 1000–2000 m; median 2892 m), and they initiate and terminate at various locations on an ice stream bed. Their spatial arrangement reveals a pattern that is characterized by an exceptional parallel conformity (80% of all mapped MSGLs have an azimuth within 5° from the mean values), and a fairly constant lateral spacing (mode 200–300 m; median 330 m), which we interpret as an indication that MSGLs are a spatially self‐organized phenomenon. Results show that size, shape and spatial arrangement of MSGLs are consistent both within and also generally between different ice stream beds. We suggest this results from a common mechanism of formation, which is largely insensitive to local factors. Although the elongation of MSGLs (mode 6–8; median 12.2) is typically higher than features described as drumlins, these values and those of their width (mode 100–200 m; median 268 m) overlap, which suggests the two landforms are part of a morphological continuum and may share a similar origin. We compare their morphometry with explicit predictions made by the groove‐ploughing and rilling instability theories of MSGL formation. Although the latter was most compatible, neither is fully supported by observations. © 2014 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.     

Tilting of active folds and drainage asymmetry on the Manawatu anticlines,New Zealand: a preliminary investigation

The apparent southward tilting of five anticlines in the Manawatu, North Island, New Zealand, is investigated using two drainage basin analysis techniques: the transverse topographic symmetry factor (T) and the asymmetry factor (AF). The techniques are used to determine whether westward‐flowing trunk streams on the gentle western limbs of five anticlines are migrating southwards across their drainage basins, concomitant with down‐tilting of the fold axes. While results show potential for the techniques to be applied in such a tectonic setting, our findings are inconclusive. This could be due to the incipient nature of the folds (c. 0·5 Ma in age), and it would seem more appropriate to apply the techniques in concert with detailed field analyses of river migration patterns. Copyright © 2008 John Wiley & Sons, Ltd.     

Doing interdisciplinarity: motivation and collaboration in research for sustainable agriculture in the UK

This paper studies knowledge production in complex, collaborative research projects that brought together academics from different disciplines, research users and agricultural businesses. It takes a comparative approach, studying the interactions within interdisciplinary research teams from ten case studies, considering the process of collaboration from initial idea through to publication. The research developed a typology of participants in these projects, and identified the motivations and challenges of each. Our results analyse the process of research teams coming together and the relationships that are built up during the research. A particular challenge identified was the building of cooperation and trust. This issue is explored alongside issues of communication, methodology, data analysis and the process of drawing and publicising conclusions.     

Palaeozoic-Recent geological development and uplift of the Amanos Mountains (S Turkey) in the critically located northwesternmost corner of the Arabian continent

We have carried out a several-year-long study of the Amanos Mountains, on the basis of which we present new sedimentary and structural evidence, which we combine with existing data, to produce the first comprehensive synthesis in the regional geological setting. The ca. N-S-trending Amanos Mountains are located at the northwesternmost edge of the Arabian plate, near the intersection of the African and Eurasian plates. Mixed siliciclastic-carbonate sediments accumulated on the north-Gondwana margin during the Palaeozoic. Triassic rift-related sedimentation was followed by platform carbonate deposition during Jurassic-Cretaceous. Late Cretaceous was characterised by platform collapse and southward emplacement of melanges and a supra-subduction zone ophiolite. Latest Cretaceous transgressive shallow-water carbonates gave way to deeper-water deposits during Palaeocene-Eocene. Eocene southward compression, reflecting initial collision, resulted in open folding, reverse faulting and duplexing. Fluvial, lagoonal and shallow-marine carbonates accumulated during Late Oligocene(?)-Early Miocene, associated with basaltic magmatism. Intensifying collision during Mid-Miocene initiated a foreland basin that then infilled with deep-water siliciclastic gravity flows. Late Miocene-Early Pliocene compression created mountain-sized folds and thrusts, verging E in the north but SE in the south. The resulting surface uplift triggered deposition of huge alluvial outwash fans in the west. Smaller alluvial fans formed along both mountain flanks during the Pleistocene after major surface uplift ended. Pliocene-Pleistocene alluvium was tilted towards the mountain front in the west. Strike-slip/transtension along the East Anatolian Transform Fault and localised sub-horizontal Quaternary basaltic volcanism in the region reflect regional transtension during Late Pliocene-Pleistocene (<4 Ma).