New methods to reconstruct Holocene compaction and to New methods to reconstruct Holocene compaction and to New methods to reconstruct Holocene compaction and to New methods to reconstruct Holocene compaction and to
determine its effects on alluvial architecture determine its effects on alluvial architecture determine its effects on alluvial architecture determine its effects on alluvial architecture
S. van Asselen* and E. Stouthamer
*Corresponding
*Corresponding
*Corresponding
*Corresponding author author author:::: author s.vanasselen@geo.uu.nl. Department of Physical Geography, Faculty of Geosciences, Utrecht University, P.O. Box 80.115, 3508 TC Utrecht, The Netherlands.
Tel.:+31(0)30 2532779. Website: www.geo.uu.nl/fg/palaeogeography.
Background: high resolution DEM (AHN, RWS-AGI) of western Netherlands.
Abstract Abstract Abstract Abstract
Compaction due to the weight of overlying deposits of unconsolidated sediments in flood basins leads to changes in cross- and down valley gradients, local sedimentation rates and natural levee heights. These changes may initiate avulsion , which is a major control on alluvial architecture . Therefore, peat compaction might be an important factor controlling alluvial architecture. Three methods to determine the influence of peat compaction on river behaviour are proposed. Fieldwork will be carried out in the Rhine-Meuse delta (The Netherlands) and in the Cumberland marshes (Canada). Furthermore, a compaction model will be developed and incorporated in a 4D (time-space) alluvial architecture computer simulation model to determine the effect of peat compaction on alluvial
architecture.
Method 1 Method 1 Method 1 Method 1
Method 2 Method 2 Method 2 Method 2
Method 3 Method 3 Method 3 Method 3
4D COMPACTION 4D COMPACTION 4D COMPACTION 4D COMPACTION
MODEL MODEL MODEL MODEL
4D ALLUVIAL 4D ALLUVIAL 4D ALLUVIAL 4D ALLUVIAL ARCHITECTURE ARCHITECTURE ARCHITECTURE ARCHITECTURE
MODEL MODEL MODEL MODEL
Determine the amount of compaction based on the geometry of natural levee and crevasse splay deposits adjacent to channel sand bodies, assuming that the base of the levee or crevasse splay was initially horizontal in cross-valley section.
Measure elevation differences between the top of compacted peat in flood basins and peat of the same age directly overlying an incompressible surface nearby (e.g. eolian dune).
Compare the volumic weight of compacted and uncompacted peat. This should be done for different types of peat.
Data Data Data Data
•Peat characteristics:
(bulk density, compression parameters) Theory
Theory Theory Theory
•Geotechnical theory
•Peat growth
•…
MODEL INPUT MODEL INPUT MODEL INPUT MODEL INPUT
Data Data Data Data
•Sedimentary record (borehole data)
•Palaeogeography Holocene Theory
Theory Theory Theory
•Sediment transport
•Aggradation/
degradation
•Overbank deposition
•Channel belt growth
•…
MODEL INPUT MODEL INPUT MODEL INPUT MODEL INPUT
F IE L D F IE L D F IE L D F IE L D M O D E L M O D E L M O D E L M O D E L
compacted peat uncompacted peat
Rhine
Rhine Rhine
Rhine----Meuse Meuse Meuse Meuse delta delta delta delta
Incompressible substrate Eolian dune
(compaction-free)
Peat
C14 dated samples of same age
amount of compaction Clay
present surface
isochrones former level of peat formation
soil sample Pressure
poreus stone gauge to measure displacement
water
Cumberland Cumberland Cumberland Cumberland marshes marshes marshes marshes
DATA DATA DATA DATA
Borehole data &
14C/AMS dating
Holocene deposits
peat
sand (channel deposits)
Pleistocene deposits sand and gravel
sandy clay (levee deposits) amount of compaction
clay (floodplain deposits)
peat sample of same age initial base of levee
