Textural provinces and transport interpretations with fine-grained sediments in the Skagerrak

Abstract

The particle-size characteristics of 181 bottom samples from the Skagerrak and northernmost Kattegat have been evaluated with statistical and graphical approaches. Regional provinces, defined by trends in distribution parameters, triangle-plot clustering and frequency-curve shapes, vary in their inferred sedimentation processes. The partitioning of particle-size distributions is based upon the observed tendency for fine silt and clay to have limited sorting due to their deposition from aggregated suspensions. These partitioned subpopulations further allow the consideration of sequential changes in distribution parameters along possible transport paths. The methodology for deriving sediment transport paths is reviewed and modified with consideration of fine-grained sedimentation, including the complications induced by aggregation and the existence of both traction and suspension mechanisms. The partitioned fine fractions gave the most reliable trends, perhaps because of the consistency of suspension transport with respect to the large distances between sites. Fining trends with increased sorting and coarse skewness are documented toward deeper or more sheltered sites, especially in the Norwegian Trench. The coarse-fraction trends are more variable and, like the distribution of the total sample, may be highly vulnerable to the conflicting influence of suspension and traction mechanisms, imperfectly isolated in this fraction. Transport vectors are valuable additions to basin modelling, but the assumptions involved in their interpretation suggest that additional information will normally be necessary to confidently interpret the details of sediment dynamics and transport directions. Because of their interdependency with many environmental parameters, textural characteristics and sedimentologic provinces provide a framework for evaluation of both large- and small-scale processes.