Quantitative study of the distributary braidplain of the Preboreal ice‐contact Gardermoen delta complex, southeastern Norway

• Published in: Boreas
• Main Authors: TUTTLE, KEVIN J., ØOUSTMO, SVElN ROAR, ANDERSEN, BJ ÖRN G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1997
• Subjects: Norway; Ice cap
• Online Access: http://dx.doi.org/10.1111/j.1502-3885.1997.tb00660.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1502-3885.1997.tb00660.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1502-3885.1997.tb00660.x

This raised delta structure is an ice‐contact deltaic complex with a volume of c. 4.4.10 9 m 3 , deposited c . 9500 yr BP in a shallow wide ‘fjord’ during the retreat of the Scandinavian ice cap. The delta plain lies at an altitude of 200–223 m. It aggraded c . 20 m above the contemporaneous sea level during a regional marine regression. The braidplain palaeochannel characteristics indicate a peak meltwater discharge of 7–9 10 3 m 3 /s. Calculations based on a glacial ablation model indicate a mid‐summer discharge of c . 5.5 10 3 m 3 /s. However, the fluvial topset of the delta has an erosive base whose altitude decreases upstream and indicates stream incision by more the 6 m below the contemporaneous sea level. The deep scour is ascribed to episodic floods over the relatively short delta plain, which exceeded direct ablation‐associated discharges. The depositional time‐span of the delta is assessed to have been 70 years, calculated from coastal gradient and shoreline displacement curves. The average sedimentation rate of the delta is thereby inferred to have been extremely high, c . 6. 10 7 m 3 /yr. The sedimentation is thought to reflect ‘extreme’ ice‐margin conditions, where the sediment and water discharge was maximized by full‐scale ablation, with simultaneous subglacial, englacial and supraglacial sediment and water supply. These conditions might further coincide with an abundant rainfall in the catchment area or the drainage of dammed waters, initiating episodic floods which eroded deep beneath sea level. As a whole, the study illustrates the hydrological conditions of proglacial sedimentation at the front of the rapidly retreating last Scandinavian ice cap.