Geochemical study on a well in the Western Canada Basin: relation of the aromatic distribution pattern to maturity of organic matter

Thirty-one rock samples from a Western Canada Basin well have been analysed for aromatics, using glass capillary gas chromatography with simultaneous flame ionization and sulfur-selective flame photometric detection. A uniform aromatic distribution pattern with a marked predominance of di- and tricyclic aromatic hydrocarbons was observed throughout a depth interval of 3000 meters comprising Cretaceous and Jurassic sediments. The very high relative abundance of sulfur aromatics at two narrow intervals in the Triassic and Mississippian is attributed to a major change in facies. Gradual changes with increasing depth have been observed for a series of compound ratios, which had been calculated from the isomers of methyl- and dimethylphenanthrene, and their parent compounds. These changes reflect the increasing thermal maturation of the sedimentary organic matter. A Methylphenanthrene Index (MPI) has been introduced, which exhibited a very good correlation with vitrinite reflectance data. The MPI is the first maturity parameter which is based on a series of aromatic hydrocarbons. This hydrocarbon internal maturity parameter permits the recognition and definition of maturity levels in extracts which can be compared to the maturity (e.g. vitrinite reflectance) of source rocks.     

Quasi-static and Quasi-dynamic Modeling of Earthquake Failure at Intermediate Scales

We present a model for earthquake failure at intermediate scales (space: 100 m–100 km, time: 100 m/v _shear- 1000’s of years). The model consists of a segmented strike–slip fault embedded in a 3-D elastic solid as in the framework of Ben-Zion and Rice (1993). The model dynamics is governed by realistic boundary conditions consisting of constant velocity motion of the regions around the fault, static/kinetic friction laws with possible gradual healing, and stress transfer based on the solution of Chinnery (1963) for static dislocations in an elastic half-space. As a new ingredient, we approximate the dynamic rupture on a continuous time scale using a finite stress propagation velocity (quasi–dynamic model) instead of instantaneous stress transfer (quasi–static model). We compare the quasi–dynamic model with the quasi–static version and its mean field approximation, and discuss the conditions for the occurrence of frequency-size statistics of the Gutenberg–Richter type, the characteristic earthquake type, and the possibility of a spontaneous mode switching from one distribution to the other. We find that the ability of the system to undergo a spontaneous mode switching depends on the range of stress transfer interaction, the cell size, and the level of strength heterogeneities. We also introduce time-dependent log (t) healing and show that the results can be interpreted in the phase diagram framework. To have a flexible computational environment, we have implemented the model in a modular C++ class library.     

Multi-Element Isotope Dilution Sector Field ICP-MS: A Precise Technique for the Analysis of Geological Materials and its Application to Geological Reference Materials

We present a multi-element technique for the simultaneous determination of twelve trace elements in geological materials by combined isotope dilution (ID) sector field inductively coupled plasma-mass spectrometry (SF-ICP-MS) following simple sample digestion. In addition, the concentrations of fourteen other trace elements have been obtained using the ID determined elements as internal standards. This method combines the advantages of ID (high precision and accuracy) with those of SF-ICP-MS (multi-element capability, fast sample processing without element separation) and overcomes the most prevailing drawbacks of ICP-MS (matrix effects and drift in sensitivity). Trace element concentration data for BHVO-1 (n = 5) reproduced to within 1–3% RSD with an accuracy of 1–2% relative to respective literature values for ID values and 2–3% for all other values. We have applied this technique to the analysis of seventeen geological reference materials from the USGS, GSJ and IAG. The sample set also included the new USGS reference glasses BCR-2G, BHVO-2G and BIR-1G, as well as the MPI-DING reference glasses KL2-G and ML3B-G, and NIST SRM 612. Most data agreed within 3–4% with respective literature data. The concentration data for the USGS reference glasses agreed in most cases with respective data of the original rock powder within the combined standard uncertainty of the method (2–3%), except the U concentration of BIR-1G, which showed a three times higher concentration compared to BIR-1.     

Late Miocene – Recent exhumation of the central Himalaya and recycling in the foreland basin assessed by apatite fission-track thermochronology of Siwalik sediments, Nepal

Thermochronological analysis of detrital sediments derived from the erosion of mountain belts and contained in the sedimentary basins surrounding them allows reconstructing the long-term exhumation history of the sediment source areas. The effective closure temperature of the thermochronological system analysed determines the spatial and temporal resolution of the analysis through the duration of the lag time between closure of the system during exhumation and its deposition in the sedimentary basin. Here, we report apatite fission-track (AFT) data from 31 detrital samples collected from Miocene to Pliocene stratigraphic sections of the Siwalik Group in western and central Nepal, as well as three samples from modern river sediments from the same area, that complement detrital zircon fission-track (ZFT) and U–Pb data from the same samples presented in a companion paper. Samples from the upper part of the stratigraphic sections are unreset and retain a signal of source-area exhumation; they show spatial variations in source-area exhumation rates that are not picked up by the higher-temperature systems. More deeply buried samples have been partially reset within the Siwalik basin and provide constraints on the thermal and kinematic history of the fold-and-thrust belt itself. The results suggest that peak source-area exhumation rates have been constant at ∼1.8 km Myr⁻¹ over the last ∼7 Ma in central Nepal, whereas they ranged between 1 and ∼1.5 km Myr⁻¹ in western Nepal over the same time interval; these spatial variations may be explained by either a tectonic or climatic control on exhumation rates, or possibly a combination of the two. Increasing lag times within the uppermost part of the sections suggest an increasing component of apatites that have been recycled within the Siwalik belt and are corroborated by AFT ages of modern river sediment downstream as well as the record of the distal Bengal Fan. The most deeply buried and most strongly annealed samples record onset of exhumation of the frontal Siwaliks along the Himalayan frontal thrust at ∼2 Ma and continuous shortening at rates comparable with the present-day shortening rates from at least 0.3 Ma onward.     

The Greenland Ice Core Chronology 2005, 15–42 ka. Part 1: constructing the time scale

The Greenland Ice Core Chronology 2005, GICC05, is extended back to 42 ka b2k (before 2000 AD), i.e. to the end of Greenland Stadial 11. The chronology is based on independent multi-parameter counting of annual layers using comprehensive high-resolution measurements available from the North Greenland Ice Core Project, NGRIP. These are measurements of visual stratigraphy, conductivity of the solid ice, electrolytical melt water conductivity and the concentration of Na⁺, Ca²⁺, SO₄²⁻, NO₃⁻, NH₄⁺. An uncertainty estimate of the time scale is obtained from identification of ‘uncertain’ annual layers, which are counted as 0.5±0.5 years. The sum of the uncertain annual layers, the so-called maximum counting error of the presented chronology ranges from 4% in the warm interstadial periods to 7% in the cold stadials. The annual accumulation rates of the stadials and interstadials are on average one-third and half of the present day values, respectively, and the onset of the Greenland Interstadials 2, 3, and 8, based on 20 year averaged δ¹⁸O values, are determined as 23,340, 27,780, and 38,220 yr b2k in GICC05.     

Sediment pollution in the Vågen,Bergen harbour,Norway

Recent sediments in the Vågen, Bergen harbour, are subjected to injection of untreated sewage from around 15,000 person equivalent. Here the distribution of trace elements is mapped in surface and subsurface sediments. Selected trace-element concentrations decrease from the inner towards the outer Vågen. These concentration gradients do not correlate with minerogenic grain size. Linear correlation, combined with enriched sediment trace elements, are used to infer sources for these elements and possible reasons for their enrichment. (1) Frequent use of dental amalgam might be related to the enrichments of and correlation between Ag, Cu, Hg and Sn in surficial sediments pre-1994. (2) Enrichment and correlation of Cu/Zn may be related to the commercial and private use of anti-fouling boat-paint. Further, tributyltin is suggested as a source of Sn enrichment. (3) Increased traffic in the city of Bergen with gasoline combustion and car-wheel wear-off release Pb and Zn. (4) Hg and Pb might have been atmospherically supplied due to the combustion of coal in a nearby gas plant pre-1985. (5) No correlation is observed between enriched Vågen trace metals and bedrock element composition of the surrounding mountains, indicating a minor supply from erosion.     

Deglaciation history and post-glacial mass movements in Balsfjord, northern Norway

The deglaciation history of Balsfjord, northern Norway, and post-glacial mass movement events were investigated. Radiocarbon dates indicate that the Balsfjord glacier retreated from the Tromsø–Lyngen moraines about 10.4 ¹⁴C Ky BP. Between ca. 10.3 ¹⁴C Ky BP and 9.9 ¹⁴C Ky BP, deposition of a distinct end moraine–the Skjevelnes moraine–in the central part of Balsfjord occurred. The transition from glacimarine to open marine sedimentary environment took place before 9.6 ¹⁴C Ky BP. Between ca. 9.5 ¹⁴C Ky BP and 8.4 ¹⁴C Ky BP, at least one local and three regional mass movement events occurred. After this period, no gravity flow activity is preserved in the cores. The high frequency of mass movements in the early post-glacial period is presumed to be due to fast sea level changes and/or tectonic activity induced by rapid isostatic uplift.     

A map-view restoration of the Alpine-Carpathian-Dinaridic system for the Early Miocene

A map-view palinspastic restoration of tectonic units in the Alps, Carpathians and Dinarides reveals the plate tectonic configuration before the onset of Miocene to recent deformations. Estimates of shortening and extension from the entire orogenic system allow for a semi-quantitative restoration of translations and rotations of tectonic units during the last 20 Ma. Our restoration yielded the following results: (1) The Balaton Fault and its eastern extension along the northern margin of the Mid-Hungarian Fault Zone align with the Periadriatic Fault, a geometry that allows for the eastward lateral extrusion of the Alpine-Carpathian-Pannonian (ALCAPA) Mega-Unit. The Mid-Hungarian Fault Zone accommodated simultaneous strike-perpendicular shortening and strike-slip movements, concomitant with strike-parallel extension. (2) The Mid-Hungarian Fault Zone is also the locus of a former plate boundary transforming opposed subduction polarities between Alps (including Western Carpathians) and Dinarides. (3) The ALCAPA Mega-Unit was affected by 290 km extension and fits into an area W of present-day Budapest in its restored position, while the Tisza-Dacia Mega-Unit was affected by up to 180 km extension during its emplacement into the Carpathian embayment. (4) The external Dinarides experienced Neogene shortening of over 200 km in the south, contemporaneous with dextral wrench movements in the internal Dinarides and the easterly adjacent Carpatho-Balkan orogen. (5) N–S convergence between the European and Adriatic plates amounts to some 200 km at a longitude of 14° E, in line with post-20 Ma subduction of Adriatic lithosphere underneath the Eastern Alps, corroborating the discussion of results based on high-resolution teleseismic tomography.The displacement of the Adriatic Plate indenter led to a change in subduction polarity along a transect through the easternmost Alps and to substantial Neogene shortening in the eastern Southern Alps and external Dinarides. While we confirm that slab-pull and rollback of oceanic lithosphere subducted beneath the Carpathians triggered back-arc extension in the Pannonian Basin and much of the concomitant folding and thrusting in the Carpathians, we propose that the rotational displacement of this indenter provided a second important driving force for the severe Neogene modifications of the Alpine-Carpathian-Dinaridic orogenic system.