The paper is a study of sedimentary processes and the environment in a fjord basin in Ullsfjorden, northern Norway. The objective of the study is to elucidate and quantify sediment supply originating from glacier margin oscillations during deglactation. It is based on lithology and age calibration with seismostratigraphic profiles. The fjord basin is located between the Skarpnes moraine (c. 12.2 14C ka BP) and the Tromsø-Lyngen ice front deposit (c. 10.5 14C ka BP). It contains glacimarine and marine sediments with a total thickness of up to 150 m. Four major seismostratigraphic units have been correlated with a dated lithostratigraphy. A lowermost unit A occurs as infill in basement depressions, and reflects a high sediment accumulation rate in an ice proximal environment during the earliest deglaciation. Unit B was deposited during the Allerød glacial recession and the Younger Dryas re-advance. It is characterised by draping of laminated clayey silt with gravity flow layers. We observe a higher sedimentation rate during the Allerød than during the Younger Dryas. Unit C was deposited during the Younger Dryas/Preboreal glacial retreat. It is characterised by clayey silt with ice rafted debris (IRD), in addition to sandy turbidites. The sedimentation rate was slightly higher during the Younger Dryas/Preboreal withdrawal than during the Younger Dryas re-advance. Between 10 and 9.8 14C ka BP the sedimentary regime changed, from being tidewater glacier dominated to one receiving sediment supply from onshore glaciers. About 9.5 14C ka BP, open marine conditions commenced. The uppermost unit D reflects slow accumulation of sandy sediments in a bottom current affected environment.
Sedimentary processes and the environment during deglaciation of a fjord basin in Ullsfjorden, North Norway