Confined shallow-water environments are encountered many places along the coast of the inner Danish waters. Despite their common occurrence, these environments have rarely been studied as sedimentary archives. In this study we set out to trace back changes in relative sea-level and associated geomorphological responses in sediment cores retrieved from coastal lagoon systems on the island of Samsø. In the mid-Atlantic period, the post-glacial sea-level rise reached central Denmark. Waves, currents and tides began to erode the unconsolidated moraine and melt-out deposits. This initiated the formation of coastal barriers and marine lagoonal sedimentation. Until present day, the ongoing isostatic uplift caused a gradual drop of relative sea-level resulting in shoreline accretion and lagoonal infilling. Stratigraphy, grain-size distribution, fossil and organic matter content of cores retrieved from the lagoons were analyzed and compared. Age control was established using radiocarbon and optically stimulated luminescence dating. Our data produced a surprisingly consistent pattern for the sedimentary successions found in the lagoons. The period of initial transgression can be identified as the onset of deposition of fine-grained, organic-rich sediments. However, radiocarbon dates evidence a punctuation of these deposits further upcore. Grain-size analysis suggests that the reworking and abrasion of the lagoon sediments resulted from the gradual lowering of the wave-base. The core sequence is topped off-by marine sands and wind-blown deposits. Based on these findings, we suggest a conceptual model that allows inferring age and elevation of transgressive and regressive stages from the lagoon cores. The common occurrence of similar environments distributed along gradients of isostatic uplift/subsidence (approximately +0.7 to -0.5 mm/yr) in the south-western Baltic, makes coastal lagoon systems a valuable archive for the reconstruction of Holocene sea-level and coastal evolution.

Coastal lagoon sediments as a recorder of Holocene landscape evolution and sea-level development: Samsø, southern Kattegat Sea, Denmark.

MORIGI, CATERINA;
2014

Abstract

Confined shallow-water environments are encountered many places along the coast of the inner Danish waters. Despite their common occurrence, these environments have rarely been studied as sedimentary archives. In this study we set out to trace back changes in relative sea-level and associated geomorphological responses in sediment cores retrieved from coastal lagoon systems on the island of Samsø. In the mid-Atlantic period, the post-glacial sea-level rise reached central Denmark. Waves, currents and tides began to erode the unconsolidated moraine and melt-out deposits. This initiated the formation of coastal barriers and marine lagoonal sedimentation. Until present day, the ongoing isostatic uplift caused a gradual drop of relative sea-level resulting in shoreline accretion and lagoonal infilling. Stratigraphy, grain-size distribution, fossil and organic matter content of cores retrieved from the lagoons were analyzed and compared. Age control was established using radiocarbon and optically stimulated luminescence dating. Our data produced a surprisingly consistent pattern for the sedimentary successions found in the lagoons. The period of initial transgression can be identified as the onset of deposition of fine-grained, organic-rich sediments. However, radiocarbon dates evidence a punctuation of these deposits further upcore. Grain-size analysis suggests that the reworking and abrasion of the lagoon sediments resulted from the gradual lowering of the wave-base. The core sequence is topped off-by marine sands and wind-blown deposits. Based on these findings, we suggest a conceptual model that allows inferring age and elevation of transgressive and regressive stages from the lagoon cores. The common occurrence of similar environments distributed along gradients of isostatic uplift/subsidence (approximately +0.7 to -0.5 mm/yr) in the south-western Baltic, makes coastal lagoon systems a valuable archive for the reconstruction of Holocene sea-level and coastal evolution.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11568/491077
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