ARTYKUŁY NAUKOWE Model litofacjalny stożka ujściowego Wisły jako zapis interakcji środowiska lądowego i morskiego

Abstract

Lithofacies model of the Vistula river-mouth fan as a record of the interaction of marine and terrestial environments.A b s t r a c t. The study area (20 km2) covers part of the Vistula River's delta front and prodelta, active since 1895. The Vistula river-mouth fan is a unique area of intense accumulation of clastic material, whose development can be investigated from a precisely defined moment in the history of its origin to the present day. The research has resulted in a morphodynamic model (based on bathymetric plans of the contemporary Vistula mouth area over the period of 1894–2000) and a facies model of the Vistula mouth fan. The analysis of the morphometric models shows that 105 years after the Vistula Cross-Cut was opened, the volume of the sediment accumulated in the fan was 133.39 million m3 and the rate of accretion has decreased. Facial models were created on the basis of results of lithological analysis of sediments. The Vistula mouth fan is built of delta front sediments represented mainly by sand facies (fine-, medium- and coarse-grained, locally with gravel, as well as marine and freshwater mollusc shells), only locally by silt facies. The thickness of theriver-mouth fan sands is 11–15 m. The prodelta sediments are found on the fan's forefield within a depth zone of 12–16 m, and they also underlie the fan sediment. Their thickness is up to ca. 10 m. Cluster analysis of the individual grain-size distributions made it possible to distinguish two lithofacies in the Vistula mouth fan: lithofacies A (fine-grained sand, silty sands, clayey silt) and lithofacies B (medium-grained and coarse-grained sand). This allowed reconstructing the processes which has taken place over the last 100 years, and to forecast future changes in the development of the active part of the Vistula Delta.