Downslope Displacement Rates of Ploughing Boulders in A Mid-Alpine Environment: Finse, Southern Norway.

Annual and seasonal displacements of ploughing boulders were investigated at Finse, southern Norway, by traditional surveying and differential carrier-phase global positioning system measurements. Annual displacement rates were mainly below 10 mm/year, although one particular season showed rates of 26 mm/year on average. There was a tendency for larger boulders to travel faster. Seasonal displacements were restricted to the annual freeze-thaw cycle. The frost heave seems to have a significant horizontal component, which does not necessarily point in the downslope direction. Thus, the concept of frost creep is not applicable to the investigated ploughing boulders. On the other hand, due to tilting of the boulders, a momentum may be gained during thaw consolidation that could induce downslope displacements. Such a process will work together with gelifluction.     

An Introduction to Multipoint Flux Approximations for Quadrilateral Grids

Control-volume discretizations using multipoint flux approximations (MPFA) were developed in the last decade. This paper gives an introduction to these methods for quadrilateral grids in two and three dimensions. The introduction is kept on a basic level, and a brief summary to more advanced results is given. Only the O-method with surface midpoints as continuity points is discussed. Flux expressions are derived both in physical and in curvilinear space. Equations for calculation of the transmissibility coefficients are given, and an explicit solution is shown for constant coefficients. K-orthogonality, stability and monotonicity are discussed, and an iterative solution technique is presented. Two numerical examples close the paper.     

Tidal amplification and along‐strike process variability in a mixed‐energy paralic system prograding onto a low accommodation shelf,Edgeøya,Svalbard

The study describes the depositional development and sediment partitioning in a prograding paralic Triassic succession. The deposits are associated with the advance of large prism‐scale clinoforms across a shallower platform area. Approaching the platform, the limited accommodation and associated relative higher rates of deposition generated straighter clinoforms with lower foreset angles. The vertical restriction across the platform is interpreted to have amplified the tidal signature. Sediment was redistributed from the coast into increasingly sandy delta‐front deposits, compared to offshore equivalents. The deposits comprise extensive compound dune fields of amalgamated and increasingly clean sandbodies up‐section. Rapid deposition of significant amounts of sand led to differential subsidence and growth‐faulting in the delta front, with downthrown fault blocks further amplifying the tidal energy through funnelling. A mixed‐energy environment created along‐strike variability along the delta front with sedimentation governing process‐regime. Areas of lower sedimentation were reworked by wave and storm‐action, whereas high sedimentation rates preserved fluvially dominated mouth bars. A major transgression, however, favoured tidally dominated deposits also in these areas, attributed to increasing rugosity of the coastline. Formation of an extensive subaqueous platform between the coast and delta front dampened incoming wave energy, and tidally dominated deposits dominate the near‐shore successions. Meanwhile formation of wave‐built sand‐bars atop the platform attest to continued wave influence. The strong tidal regime led to the development of a heterolithic near‐shore tidally dominated channel system, and sandier fluvial channels up‐river. The highly meandering tidal channels incising the subaqueous platform form kilometre wide successions of inclined heterolithic stratification. The fluvially dominated channels which govern deposition on the delta plain are narrower and slightly less deep, straighter, generally symmetric and filled with cleaner sands. This study provides important insight into tidal amplification and sand redistribution during shallowing on a wide shelf, along with along‐strike process‐regime variability resulting from variations in sediment influx.     

Model analysis of the measured concentration of organic gases in the Norwegian Arctic

A 2-D meridional model for the chemistry and transport in the troposphere is used to study the seasonal variation of the concentration of organic gases like C₂H₂, C₂H₆, C₃H₈, C₆H₆, C₇H₈. CHCl₃ and C₂Cl₄ at high latitudes. The anthropogenic sources for these species were estimated, and the temporal and latitudinal distribution of OH and O₃ was calculated using a complex photochemical reaction system. There is fair agreement between the calculated annual variation and the measured concentrations for C₂H₂, C₂H₆, C₃H₈, C₇H₈ and C₂Cl₄ at Spitsbergen during July 1982 and March/April 1983, with a distinct late winter maximum and summer minimum. For CHCl₃, the direct anthropogenic source is minor compared to indirect anthropogenic or natural sources. For benzene, emission in car exhaust is important, but other anthropogenic sources are required for the calculations to agree with the measurements. Measured C₂H₄ and C₃H₆ concentrations are much higher than the calculated ones based on anthropogenic emissions, and show opposite seasonal trends. This indicates biogenic sources for these compounds.A buildup of PAN (300 pptv) is calculated at high latitudes during winter. This makes it the dominant source for NO_x as the temperature increases in the spring. NO_x is found to be a limiting factor for O₃ production at high latitudes during spring.     

Facies model for a coarse‐grained,tide‐influenced delta: Gule Horn Formation (Early Jurassic), Jameson Land,Greenland

Tide‐dominated deltas have an inherently complex distribution of heterogeneities on several different scales and are less well‐understood than their wave‐dominated and river‐dominated counterparts. Depositional models of these environments are based on a small set of ancient examples and are, therefore, immature. The Early Jurassic Gule Horn Formation is particularly well‐exposed in extensive sea cliffs from which a 32 km long, 250 m high virtual outcrop model has been acquired using helicopter‐mounted light detection and ranging (LiDAR). This dataset, combined with a set of sedimentological logs, facilitates interpretation and measurement of depositional elements and tracing of stratigraphic surfaces over seismic‐scale distances. The aim of this article is to use this dataset to increase the understanding of depositional elements and lithologies in proximal, unconfined, tide‐dominated deltas from the delta plain to prodelta. Deposition occurred in a structurally controlled embayment, and immature sediments indicate proximity to the sediment source. The succession is tide dominated but contains evidence for strong fluvial influence and minor wave influence. Wave influence is more pronounced in transgressive intervals. Nine architectural elements have been identified, and their internal architecture and stratigraphical distribution has been investigated. The distal parts comprise prodelta, delta front and unconfined tidal bar deposits. The medial part is characterized by relatively narrow, amalgamated channel fills with fluid mud‐rich bases and sandier deposits upward, interpreted as distributary channels filled by tidal bars deposited near the turbidity maximum. The proximal parts of the studied system are dominated by sandy distributary channel and heterolithic tidal‐flat deposits. The sandbodies of the proximal tidal channels are several kilometres wide and wider than exposures in all cases. Parasequence boundaries are easily defined in the prodelta to delta‐front environments, but are difficult to trace into the more proximal deposits. This article illustrates the proximal to distal organization of facies in unconfined tide‐dominated deltas and shows how such environments react to relative sea‐level rise.     

Nested intrashelf platform clinoforms—Evidence of shelf platform growth exemplified by Lower Cretaceous strata in the Barents Sea

Two nested clinoform set types of different scales and steepness are mapped and analysed from high-resolution seismic data. Restoration of post-depositional faulting reveals a persistent pattern of small-scale, high-angle clinoforms contained within platform-scale, low-angle clinothems, showing a combined overall progradational depositional system. The large clinoforms lack a well-defined platform edge, and show a gradual increase in dip from topset to foreset. A consistent recurring stratal pattern is evident from the architecture, and is considered a result of interplay between relative sea-level change and autocyclic switching of sediment delivery focal points that brought sediment to the platform edge. This un-interrupted succession records how intra-shelf platforms prograde. Quantitative clinoform analysis may assist in determining the most influential depositional factors. Post-depositional uplift and erosion requires restoration with re-burial to maximum burial depth. Backstripping, decompaction and isostatic correction was performed assuming a range of lithologic compositions, as no wells test the lithology. Nearby wells penetrate strata basinward of the clinoforms, proving mudstone content above 50%, which in turn guide restoration values. Typical restored platform heights are 250–300 m, with correspondingly sized platform-scale clinoform heights. Typical large-scale clinoform foreset dip values are 1.3°–2.4°. Small-scale clinothems are typically 100 m thick, with restored foreset dip angles at 4.4° - > 10°. The results suggest that intrashelf platform growth occurs in pulses interrupted by draping of strata over its clinoform profile. The resultant architecture comprises small-scale clinoforms nested within platform-scale clinothems.     

Effects of sedimentary interfaces on fracture pattern,linkage, and cluster formation in peritidal carbonate rocks

The permeability of a reservoir is particularly dependent upon the proportion of its fractures that penetrate or are arrested at interfaces such as contacts and discontinuities. Here we report on fracture penetration and fracture arrest in Lower Cretaceous peritidal deposits exposed in the Pizzicoli Quarry, Gargano Promontory, southern Italy. We measured more than 2000 fractures, in the field and using LIDAR data, of which 564 fractures from the field and 518 from LIDAR studies are the focus of this paper. Fracture arrest/deflection and penetration depend much on the effects of peritidal cycle interfaces such as paleosol horizons, laminated carbonate mudstones, and stylonodular horizons. The laminated mudstones have the greatest effect; 63–99% of the fractures are deflected or arrested at such interfaces, whereas 63–90% are deflected/arrested at paleosols, and 20–35% at stylonodular horizons. In the mudstones, many fractures are arrested at thin, internal laminae, such that few penetrate the entire laminated layer, and fewer still the boundaries between the layers. Paleosol interfaces deflect/arrest more than 60% of all fractures. However, when small-offset fractures above and below paleosols are regarded as penetrating, they are evenly spaced (non-clustered), so that fracture-related fluid transport may occur across the entire paleosol. Stylonodular horizons deflect/arrest and split some fractures, but generally have little effect compared with the other types of interfaces. We present three main mechanisms for fracture deflection and/or arrest: (1) the fracture-induced tensile stress ahead of its tip, referred to as the Cook-Gordon debonding mechanism; (2) rotation of the principal stresses at and across the interface, resulting in the formation of stress barriers; and (3) large elastic mismatch (particularly as regards Young’s moduli) between layers across an interface. All these mechanisms are likely to have operated during fracture propagation and arrest in the carbonate rocks of the Pizzicoli Quarry.     

Interpretation of well-cell pressures on hexagonal grids in numerical reservoir simulation

Peaceman’s equivalent well-cell radius for 2D square grids has been generalized to 2D grids consisting of regular hexagons. The development consists of the following steps. Firstly, the analytical solution for the pressure drop between injector and producer for wells in a seven-spot pattern is determined. Secondly, this solution is compared with the numerical solution on hexagonal grids for a sixth of a seven-spot pattern. Finally, the equivalent well-cell radius is calculated, and its asymptotic behavior for infinitely fine grids is derived. The results are valid for both steady-state and unsteady-state conditions.