The marine stratigraphy of the Hanö Bay, SE Sweden, based on different sediment stratigraphic methods

Abstract

The stratigraphy of the Hanö Bay was studied with corings, and seismic and geomagnetic methods. Combined with results from mapping of bottom deposits a stratigraphic model was set up to explain the complexity of strata down to water depths of 80 m. No finegrained sediments occur at depths less than 60–70 m. Here the bedrock is only covered by a clayey diamicton and sandy deposits. Occasional finds of peat deposits and pine stumps are found on top of the diamicton. At depths greater than 75 m the most complete stratigraphies are found. The clayey diamicton is overlain by grey varved clay and reddish varved clay. It is covered by non-varved clay. This glaciolacustrine deposition probably occurred during the Baltic Ice Lake (BIL) stage and possibly also during the earliest part of the Yoldia stage. The final drainage of the BIL is seen as sandy, silty layers in the clay. The overlying thin gyttja clay, often FeS-coloured, was possibly deposited between the saline ingression at c. 10,000 and the maximum regression at 9600–9500 ¹⁴C yr B.P. It is not yet clear if sediments were deposited during the Ancylus transgression (c. 9500–9100 ¹⁴C yr B.P.), but the cored clay gyttja, covering the gyttja clay, does presumably represent at least most of the post-Ancylus time. The variation of the distribution of the stratigraphic units shows that significant water level changes in combination with the locally intense bottom current conditions have played a major role in creating the varying stratigraphy with its extensive hiatuses found in the Hanö Bay.

Key Words:

• Late Weichselian
• Holocene
• Baltic sediments
• seismic stratigraphy
• lithostratigraphy
• magnetic susceptibility
• Hanö Bay
• south Sweden
• southern Baltic