Abstract
In conjunction with the extensive archaeological projects conducted at the current outlet of Sweden’s second largest lake, Lake Vättern, macrofossil, pollen and diatom records have been studied from 14C-dated lake and river sediments from River Motala Ström in Motala and Lake Boren. These investigations have revealed sedimentary evidence of the Yoldia Sea regression, the Ancient Lake Vättern transgression, and the following stepwise river formation process. Around 9000 cal BC, two small kettlehole basins at Strandvägen and Kanaljorden became isolated from the Baltic basin. As the ice sheet retreated further north, the isostatic uplift isolated the Vättern basin from the Baltic basin. Due to the uneven isostatic uplift, the basin tilted toward the south, and the Ancient Lake Vättern transgression started in Motala. The threshold in Motala at 92.5 m a.s.l. was reached around 7200 cal BC, and River Motala Ström was formed. 14C-dated diatom records from Lake Boren, and shoreline deposits in Motala, confirm this event. The water level in Lake Vättern initially fell around 1.5 m, and around 5800 cal BC, a second erosional event cut down the threshold to modern day level. At this time, the Late Mesolithic settlements in Motala were established and expanded.
Highlights
River formation in formerly glaciated areas, where isostatic uplift and shore displacement is a dominating component of the postglacial landscape development, is a relatively poorly researched area cf [1,2]
In the case of the Lake Vättern basin, which extends over 120 km from north to south (Figure 1), the differential isostatic uplift had a direct effect on the drainage, and a new river was formed during the early Holocene
In zone 3, freshwater taxa decrease, and indifferent taxa increase, especially Staurosira construens, Staurosirella lapponica and Pseudostaurosira brevistriata. These taxa are known as opportunists, i.e., they flourish during periods of pronounced changes in the environment, e.g., in water chemistry cf [55,56] This situation is likely to have occurred when water from Lake Vättern started to flow into the Lake Boren basin from the west, lowering the pH values in Lake Boren
Summary
River formation in formerly glaciated areas, where isostatic uplift and shore displacement is a dominating component of the postglacial landscape development, is a relatively poorly researched area cf [1,2]. Few river valleys in southern Scandinavia have been the stage for such intense Mesolithic activity as the river sites in Motala (Figure 1). To understand why this place has been such a focal point, the landscape and river development needs to be understood.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
