Depositional architecture and evolution of progradationally stacked lobe complexes in the Eocene Central Basin of Spitsbergen

The down‐dip portion of submarine fans comprises terminal lobes that consist of various gravity flow deposits, including turbidites and debrites. Within lobe complexes, lobe deposition commonly takes place in topographic lows created between previous lobes, resulting in an architecture characterized by compensational stacking. However, in some deep water turbidite systems, compensational stacking is less prominent and progradation dominates over aggradation and lateral stacking. Combined outcrop and subsurface data from the Eocene Central Basin of Spitsbergen provide a rare example of submarine fans that comprise progradationally stacked lobes and lobe complexes. Evidence for progradation includes basinward offset stacking of successive lobe complexes, a vertical change from distal to proximal lobe environments as recorded by an upward increase in bed amalgamation, and coarsening and thickening upward trends within the lobes. Slope clinoforms occur immediately above the lobe complexes, suggesting that a shelf‐slope system prograded across the basin in concert with deposition of the lobe complexes. Erosive channels are present in proximal axial lobe settings, whereas shallow channels, scours and terminal lobes dominate further basinward. Terminal lobes are classified as amalgamated, non‐amalgamated or thin‐bedded, consistent with turbidite deposition in lobe axis, off‐axis and fringe settings, respectively. Co‐genetic turbidite–debrite beds, interpreted as being deposited from hybrid sediment gravity flows which consisted of both turbulent and laminar flow phases, occur frequently in lobe off‐axis to fringe settings, and are rare and poorly developed in channels and axial lobe environments. This indicates bypass of the laminar flow phase in proximal settings, and deposition in relative distal unconfined settings. Palaeocurrent data indicate sediment dispersal mainly towards the east, and is consistent with slope and lobe complex progradation perpendicular to the NNW–SSE trending basin margin.     

The mobility of U and Th in subduction zone fluids: an indicator of oxygen fugacity and fluid salinity

The solubility of U and Th in aqueous solutions at P-T-conditions relevant for subduction zones was studied by trapping uraninite or thorite saturated fluids as synthetic fluid inclusions in quartz and analyzing their composition by Laser Ablation-ICPMS. Uranium is virtually insoluble in aqueous fluids at Fe-FeO buffer conditions, whereas its solubility increases both with oxygen fugacity and with salinity to 960 ppm at 26.1 kbar, Re-ReO₂ buffer conditions and 14.1 wt% NaCl in the fluid. At 26.1 kbar and 800°C, uranium solubility can be reproduced by the equation: log\textU = 2.681 + 0.1433logf\textO₂ + 0.594\textCl, \log {\text{U}} = 2.681 + 0.1433\log f{\text{O}}_{2} + 0.594{\text{Cl,}} where fO₂ is the oxygen fugacity, and Cl is the chlorine content of the fluid in molality. In contrast, Th solubility is generally low (<10 ppm) and independent of oxygen fugacity or fluid salinity. The solubility of U and Th in clinopyroxene in equilibrium with uraninite and thorite was found to be in the order of 10 ppm. Calculated fluid/cpx partition coefficients of Th are close to unity for all conditions. In contrast, D^fluid/cpx for uranium increases strongly both with oxygen fugacity and with salinity. We show that reducing or NaCl-free fluids cannot produce primitive arc magmas with U/Th ratio higher than MORB. However, the dissolution of several wt% of oxidized, saline fluids in arc melts can produce U/Th ratios several times higher than in MORB. We suggest that observed U/Th ratios in arc magmas provide tight constraints on both the salinity and the oxidation state of subduction zone fluids.     

Mud‐rich delta‐scale compound clinoforms in the Triassic shelf of northern Pangea (Havert Formation,south‐western Barents Sea)

In recent years it has become clear that many shallow‐marine heterolithic and mudstone‐dominated successions are deposited as mud belts forming part of subaqueous deltas that are related to major fluvial sources either upstream or along shore. Here the Havert Formation is presented as an ancient example of this kind of system. The Havert Formation in the south‐western Barents Sea represents shelf margin clinoforms consisting predominantly of heterolithic deposits. Sediments were mainly derived from the east (Ural Mountains), but a smaller system prograded northward from Fennoscandia. The Havert Formation holds a lot of interest due to: (i) its stratigraphic position, directly above the Permo–Triassic boundary and contemporaneous to the emplacement of the Siberian Traps; (ii) the fact that it represents the first siliciclastic input in the south‐western Barents Sea and it shows interaction between Uralian‐derived and Fennoscandian‐derived sediments; and (iii) its hydrocarbon potential. This study is focused on a detailed sedimentological analysis of cored intervals of the (Ural‐derived) Havert Formation, in combination with seismic interpretation, well‐log correlations and palynological analysis of the Havert and overlying Klappmyss formations. The cored intervals belong to the shelf environment of the Havert shelf‐margin clinoforms (300 to 500 m thick). This sedimentological analysis distinguishes six facies associations, spanning from tidally‐influenced channels at the shoreline to mud‐rich subaqueous platform and foresets of the subaqueous delta. Seismic lines and well‐log correlations show the larger‐scale evolution of the Ural‐derived Havert Formation, characterized by episodes of low‐accommodation and high‐accommodation. The palynological analyses provide the first detailed study of the Havert Formation in the Nordkapp Basin, revising its depositional age in the region as Induan to early Olenekian (Smithian). Furthermore, they strengthen the environmental interpretation; palynofacies present on the shelf record flora of tidally‐influenced coastal plains, whereas the palynofacies in the deep‐water slope contain only amorphous organic matter.     

Transport and sedimentation of Cu in a microtidal estuary, SE Norway

The transport and sedimentation of copper in the Glomma estuary, SE Norway during a period of 90% reduction in the industrial input of Cu, was studied from sediment trap material and compared to samples of the bottom sediments. Traps were deployed at four stations for several monthly periods during 1990, 1994 and 1995. Trapped material was analysed for suspended particulate matter (SPM), total organic carbon (TOC) and nitrogen (TN), Cu, and Al. Only about 10% of the Cu from the river is trapped in the estuary. Still there was a moderate but significant reduction in Cu concentration in the trap SPM from 1990 to 1994, reflecting the industrial reductions, but only if excluding summer samples apparently influenced by antifouling Cu from boat paint. Settling matter therefore seems appropriate and sensitive for monitoring changes in the Cu load. The results supported the view that TOC is the main carrier of Cu to the sediments.     

Characterisation of a Natural Quartz Crystal as a Reference Material for Microanalytical Determination of Ti,Al, Li,Fe, Mn,Ga and Ge

A natural smoky quartz crystal from Shandong province, China, was characterised by laser ablation ICP‐MS, electron probe microanalysis (EPMA) and solution ICP‐MS to determine the concentration of twenty‐four trace and ultra trace elements. Our main focus was on Ti quantification because of the increased use of this element for titanium‐in‐quartz (TitaniQ) thermobarometry. Pieces of a uniform growth zone of 9 mm thickness within the quartz crystal were analysed in four different LA‐ICP‐MS laboratories, three EPMA laboratories and one solution‐ICP‐MS laboratory. The results reveal reproducible concentrations of Ti (57 ± 4 μg g^?1), Al (154 ± 15 μg g^?1), Li (30 ± 2 μg g^?1), Fe (2.2 ± 0.3 μg g^?1), Mn (0.34 ± 0.04 μg g^?1), Ge (1.7 ± 0.2 μg g^?1) and Ga (0.020 ± 0.002 μg g^?1) and detectable, but less reproducible, concentrations of Be, B, Na, Cu, Zr, Sn and Pb. Concentrations of K, Ca, Sr, Mo, Ag, Sb, Ba and Au were below the limits of detection of all three techniques. The uncertainties on the average concentration determinations by multiple techniques and laboratories for Ti, Al, Li, Fe, Mn, Ga and Ge are low; hence, this quartz can serve as a reference material or a secondary reference material for microanalytical applications involving the quantification of trace elements in quartz.     

The contribution of urban runoff to organic contaminant levels in harbour sediments near two Norwegian cities

The main aim of the present study was to compare the quality of particle emissions (urban runoff and settling particles in rivers and harbours) to the quality of top-layer bed sediments, for two Norwegian harbours (Oslo and Drammen). A sub-aim was to investigate whether non-industrial urban runoff contributed to the organotin load of sediments, apart from leaching from ship hulls. Time-integrated samples of stormwater runoff were obtained in an innovative manner, by sampling man-holes in the stormwater system. Settling particles were sampled with sediment traps. The study focused on PAHs, PCBs and organotin compounds. Contaminant levels were generally a factor of 2-10 (PAHs) and 3-30 (TBT) lower in emitted riverine and runoff particles than in top-layer bed sediments, except for PCBs in Oslo harbour (only 20-30% lower). Significant levels of tributyltin (TBT; median 140mug/kg) were shown in runoff particles, showing that TBT can also be emitted via urban sources, since the sampled man-holes were not in areas where dry-docking activities take place. Possible land-based TBT sources include long-lasting house paint and use of TBT as PVC stabilizer and timber preservative. Since there are ongoing emissions into the two studied harbour areas, it is concluded that the addition of an actively sorbing capping material such as activated carbon might be the best remediation alternative.     

Quantitative analysis of melt and fluid inclusions by LA-ICP-MS: Practical aspects and selected results

Quantitative analysis of melt and fluid inclusions by LA-ICP-MS: Practical aspects and selected resultsAudétatA.,GüntherD.,andHeinrichC.A.1998.Formation of a m agm atic- hydrothermal ore deposit:Insights withL A-ICP-MS analysis of fluid inclusions.Science,279:2091～2094 AudétatA .,GüntherD.,andHeinrichC.A.2000 a.Causes for large- scale m etal zonation around mineralized plutons:FluidinclusionL A-ICP-MS evidence from theMoleGranite,Australia.EconomicGeology,(in press) …     

The Svalbard Eocene‐Oligocene (?) Central Basin succession: Sedimentation patterns and controls

A synthesis has been undertaken based on regionally compiled data from the post early Eocene foreland basin succession of Svalbard. The aim has been to generate an updated depositional model and link this to controlling factors. The more than kilometer thick progradational succession includes the offshore shales of the Gilsonryggen Member of the Frysjaodden Formation, the shallow marine sandstones of the Battfjellet Formation and the predominantly heterolithic Aspelintoppen Formation, together recording the progressive eastwards infill of the foredeep flanking the West Spitsbergen fold‐and‐thrust belt. Here we present a summary of the paleo‐environmental depositional systems across the basin, their facies and regional distribution and link these together in an updated depositional model. The basin‐margin system prograded with an ascending shelf‐edge trajectory in the order of 1°. The basin fill was bipartite, with offset stacked shelf and shelf‐edge deltas, slope clinothems and basin floor fans in the western and deepest part and a simpler architecture of stacked shelf‐deltas in the shallower eastern part. We suggest a foredeep setting governed by flexural loading, likely influenced by buckling, and potentially developing into a wedge top basin in the mature stage of basin filling. High‐subsidence rates probably counteracted eustatic falls with the result that relative sea‐level falls were uncommon. Distance to the source terrain was small and sedimentation rates was temporarily high. Time‐equivalent deposits can be found outbound of Stappen High in the Vestbakken Volcanic Province and the Sørvestsnaget Basin 300 km further south on the Barents Shelf margin. We cannot see any direct evidence of coupling between these more southerly systems and the studied one; southerly diversion of the sediment‐routing, if any, may have taken place beyond the limit of the preserved deposits.     

Relationships between morphological and sedimentological parameters in source‐to‐sink systems: a basis for predicting semi‐quantitative characteristics in subsurface systems

The study of source‐to‐sink systems relates long‐term variations in sediment flux to morphogenic evolution of erosional–depositional systems. These variations are caused by an intricate combination of autogenic and allogenic forcing mechanisms that operate on multiple time scales – from individual transport events to large‐scale filling of basins. In order to achieve a better understanding of how these mechanisms influence morphological characteristics on different scales, 29 submodern source‐to‐sink systems have been investigated. The study is based on measurements of morphological parameters from catchments, shelves and slopes derived from a ∼1 km global digital elevation model dataset, in combination with data on basin floor fans, sediment supply, water discharge and deposition rates derived from published literature. By comparing various morphological and sedimentological parameters within and between individual systems, a number of relationships governing system evolution and behaviour are identified. The results suggest that the amount of low‐gradient floodplain area and river channel gradient are good indicators for catchment storage potential. Catchment area and river channel length is also related to shelf area and shelf width, respectively. Similarly to the floodplain area, these parameters are important for long‐term storage of sediment on the shelf platform. Additionally, the basin floor fan area is correlative to the long‐term deposition rate and the slope length. The slope length thus proves to be a useful parameter linking proximal and distal segments in source‐to‐sink systems. The relationships observed in this study provide insight into segment scale development of source‐to‐sink systems, and an understanding of these relationships in modern systems may result in improved knowledge on internal and external development of source‐to‐sink systems over geological time scales. They also allow for the development of a set of semi‐quantitative guidelines that can be used to predict similar relationships in other systems where data from individual system segments are missing or lacking.