Total sediment budget of a transgressive barrier-spit,Skallingen, SW Denmark: A review     

Christian Christiansen  Troels Aagaard  Jesper Bartholdy  Merete Christiansen  Jørgen Nielsen  Niels Nielsen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):107-126

Average sea-level rise in the northern part of the Danish Wadden Sea has been 1.3 mm a^?1 during the last 100 years but during the last 25 years a rise of 4.2 mm a^?1 was observed. Concurrent with the recent sea-level rise the Skallingen barrier spit has migrated landward by 3–5 m a^?1. Long term sediment budgets for each of the morphological units involved in the migration are reviewed (e.g. onshore in the shore face +90.000 m³ a^?1, longshore -641.000 m³ a^?1, foredunes +65,000 m³ a^?1, overwash fan including shorenormal dunes +11,000 m³ a^?1, spit terminus -96,000 m³ a^?1, tidal flat + 10,000 m³ a^?1 and backbarrier salt marsh +33,000 m³ a^?1) and used to establish the relative importance of sediment transport processes involved in barrier migration. Strong interannual variations exist in the long term budget making evaluation of barrier behaviour based on short term measurements doubtful. In a cross shore sense the barrier spit is accreting in spite of the sea level rise. This is specially pronounced at an active overwash fan. However, due to substantial sediment losses to longshore transport the barrier, gets narrower and shorter during its transgressive behaviour. This may indicate that preservation of barriers in the geological record during rapid sea level rise is promoted when sediment loss to longshore transport is insignificant.  相似文献   

Comparing spatial grain-size trends inferred from textural parameters using percentile statistical parameters and those based on the log-hyperbolic method   总被引：1，自引：0，他引：1  

Jesper Bartholdy  Christian Christiansen 《Sedimentary Geology》2007,202(3):436-452

The Folk&Ward (F&W) and the log-hyperbolic methods are applied to a small - and easy to overlook - number of typical sand sized grain-size distributions from the Danish Wadden Sea. The sand originates from the same source, and the pattern of change in the grain-size distributions is, therefore, exclusively linked to dynamic sorting. In general, the F&W parameters reflect the observed grain-size trends far better than the corresponding log-hyperbolic parameters. The log-hyperbolic “typical log grain size”, ν, is sensitive to changes in skewness and cannot replace mean grain size, Mz, in grain-size trend analysis. The four log-hyperbolic parameters describing dispersion δ, τ^− 1, κ^− 1 and ζ are not able to give an unambiguous picture of spreading trends. The F&W sorting parameter, Sd, can therefore not be replaced by any of the log-hyperbolic parameters in grain-size trend analysis. In skewed grain-size distributions, there seems to be a general defect in the log-hyperbolic approximation of the best represented tail. This makes χ less sensitive to indicate the correct sign of slightly skewed grain-size distributions than Sk. However, when examining trends, the relative change between χ and Sk by and large seems to be the same. The log-hyperbolic peakedness parameter, ξ, is preferable to the F&W peakedness (kurtosis) parameter, Kg, because the latter is hypersensitive to small, insignificant variations in a grain-size distribution. By contrast, the concept of peakedness as defined by ξ, seems to relate more directly to sedimentary environmental conditions. In conclusion, the log-hyperbolic method has both advantages and disadvantages when compared with the F&W method. It is thus suggested that a sensible combination of the two methods could be advantageous to sediment trend analysis.  相似文献