Coastal lagoon systems and sedimentary constraints on Holocene relative sea-level: Samsø, Southern Kattegat Sea

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1 1 University of Copenhagen Faculty of Science Coastal lagoon systems and sedimentary constraints on Holocene relative sea-level: Samsø, Southern Kattegat Sea Lasse Sander, ph.d. student Department of Geosciences and Resource Management, University of Copenhagen, Denmark Geological Survey of Denmark and Greenland (GEUS)

2 2 OVERVIEW A: the BRIDGES project and Holocene RSL in DK B: Coastal lagoons: Distribution and sedimentation C: Samsø Field sites & methods Results Sum-up & conclusion

3 3 U N I V E R S I T Y OF C O P E N H A G E N The BRIDGES approach Beach ridge and lagoon systems as indicator for sea-level changes PhD project (until August 2014) highstand introduction lagoons beach ridge plain & coastal lagoons island of Samsø combine surface morphology with sedimentology beach-ridges Draget, Langør, Samsø

4 Hansen et al 2011 U N I V E R S I T Y OF C O P E N H A G E N Holocene sea-level introduction ~0,3 mm/yr Påsse & Anderson 2005, modified 4

5 Holocene sea-level introduction Approx. RSL development: Samsø + 3 m RSL = ASL + IM RSL: relative sea-level ASL: absolute sea-level IR: isostatic movement 7-8 ka BP Påsse & Anderson 2005, modified 5

6 Coastal lagoons: definition introduction The term lagoon originated from the Latin lacūna, meaning gap, pond or pool (Tagliapietra, Sigovini, and Volpi Ghirardini, 2008) A lagoon is - a shallow coastal basin connected to the sea (Pisani 1960) - a body of shallow coastal water with a restricted connection but free exchange with the adjacent open sea (Postma, 1969) - the major axis is oriented parallel to the coast (Phleger, 1969) a shallow coastal water body separated from the ocean by a barrier, connected at least intermittently to the ocean by one or more restricted inlets, and usually oriented shore-parallel (Kjerfve, 1994) Working definition (inner Danish waters): A near-coastal basin that received marine sedimentation during the Holocene and that is separated from the open sea by a barrier 6

7 Coastal lagoons: distribution field site & methods 7

8 Coastal lagoons: sediment dynamics introduction H = accomodation space Ms = mass accumulated P = production 8

9 Coastal lagoons: sediment dynamics introduction Nichols & Boon, 1994 WIND H = accomodation space Ms = mass accumulated P = production 9

10 Coastal lagoons: sediment dynamics introduction H = accomodation space Ms = mass accumulated P = production 10

11 Coastal lagoons: sediment dynamics introduction H = accomodation space Ms = mass accumulated P = production 11

12 Coastal lagoons: sediment dynamics introduction OSL 14C H = accomodation space Ms = mass accumulated P = production 12

13 Coastal lagoons: sediment dynamics introduction H = accomodation space Ms = mass accumulated P = production 13

14 14 Samsø: fieldsites, methods, results

15 Samsø: Geology & surface properties field site & methods Geological map 1:25,000 Digital Elevation Model LIDAR based, 10x10 m res. Topography Position Index (TPI) calculated with focal mean (annulus), inner radius 100 m outer radius 300 m, Based on Lidar DEM 10x10 m resolution Holocene Pleistocene fresh water ridge (positive TPI) 64 m 0 depression (positive TPI) 4 km Pleistocene glacial - 2 m 15

16 Samsø: Field sites & methods field site & methods Stavns Made Mårup beach ridge system Frederiksdal Geodata and field surveys Cores (n=31) sedimentological description dating ( 14 C, OSL) grain-size analysis loss on ignition (LOI) carbon, sulphur X-ray flourescence (XRF) benthic foraminifera 4 km Kinesiske Mur 16

17 Frederiksdal: modern lagoon 180±50 a OSL quartz sand 5 m DVR90 results sandy 500 m cal a BP AMS 14 C (Marine04) Bulk sediment -1 m DVR90 silty LiDAR cal a BP AMS 14 C (Marine04) Bulk sediment orthophoto cal a BP AMS 14 C (Marine04) Cardium shell shell debris cal a BP AMS 14 C (Marine04) Bulk sediment phi scale diamict (moraine) Wikimedia commons: Wentworth-Grain-Size-Chart.pdf 17

18 18 U N I V E R S I T Y OF C O P E N H A G E N Stavns Made: sub-recent lagoon results 500 m 7484±30 cal a BP AMS 14 C (Marine04) wood 7484±30 cal a BP AMS 14 C (Marine04) wood 5250±290 a BP OSL quartz sand 6326±40 cal a BP AMS 14 C (Marine04) bulk sediment 3950±200 a BP OSL quartz sand LiDAR orthophoto 6114±65 cal a BP AMS 14 C (Marine04) bulk sediment 7814±65 cal a BP AMS 14 C (Marine04) Cardium shell 7628±50 cal a BP AMS 14 C (Marine04) Cardium shell

19 16,5 15,2 14,0 12,8 11,6 10,4 9,2 8,0 6,8 5,6 4,5 3,3 2,1 0,9-0,3-1,5-2,7 16,5 15,2 14,0 12,8 11,6 10,4 9,2 8,0 6,8 5,6 4,5 3,3 2,1 0,9-0,3-1,5-2,7 U N I V E R S I T Y OF C O P E N H A G E N Stavns Made: core SM1b results clay silt sand peb % eolian marine lagoonal + eolian phi % lagoonal? lagoonal phi 19

20 Grain-size distributions results parent population (diamict) e.g. a barrier +P sorting lagoonal population wind-blown population 6 phi 20µm SAMPLE! 2,5 phi 250µm n=400 20

21 Constraints on relative sea-level position results Hansen et al 2011, modified end of high stand? basal peat Cardium shell life position, articulated 21

22 Constraints on relative sea-level position results Hansen et al 2011, modified 22

23 Constraints on relative sea-level position results Hansen et al 2011, modified 23

24 Constraints on relative sea-level position results Hansen et al 2011, modified end of high-stand period? Clemmensen et al

25 Constraints on relative sea-level position results Hansen et al 2011, modified end of high-stand period? Clemmensen et al

26 Sum-up and conclusions conclusions 1) Small-scale coastal lagoons are a widespread feature of the coastal environment in DK 2) These lagoons are located along and across gradients of isostatic uplift 3) Marine sedimentation in the lagoons can be used to constrain the onset of transgression in the mid-holocene A period of rapid transgression occured 7,4-7,9 ka BP in coastal basins on Samsø The final infill of the lagoons coincides with evidence of a period of sea-level drop around 4,4-3,4 ka BP (Anholt, Clemmensen et al 2012) Lagoonal sedimentation further preserves signals of morphological development in the proximity of the lagoons. Coastal lagoons are small and reactive coastal environments and are thus valuable sedimentary archives for the study of dynamics and rates in transgressive coastal environments. 26

27 DYK seminar, September 19, Thank you for your attention!