Seismic stratigraphy of Late Quaternary deposits in the eastern Skagerrak

Abstract

High-resolution seismic profiles from the Swedish west coast divide Quaternary deposits into six seismic sequences, containing 13 different seismic facies. Documentation of these sequences and facies and their stratigraphic and geographic variability is the first step in a basin-fill analysis to interpret depositional environments and major controlling processes. The deposits are attributed to one deglaciation cycle. The seismic sequences are: (I) bedrock, (II) coarse glacial deposits, (III) Weichselian glacimarine ice-proximal deposits, (IV) Weichselian glacimarine ice-distal deposits, (V) channel fill deposits and (VI) Holocene marine deposits. The major part of the sediment package is the Weichselian glacimarine ice-proximal deposits, deposited during the ice recession period, close to or adjacent to the retreating ice. Typical appearances for these deposits are conformably well-stratified deposits with high amplitude. The second largest sequence consists of Holocene marine deposits and these are mainly found in the southern part of the study area. They have typically a near-transparent seismic configuration with only weak parallel stratification. These two major sequences are separated by a regional nonconformity, creating a hiatus of at least 6000 years. The hiatus was formed when strong bottom currents related to the cyclonic under-water circulation in the Skagerrak started to influence the area. Later the conditions changed, reducing the erosional effect of the bottom currents, allowing new sedimentation in the southern part while the northern part is still exposed to erosion.