Rhine-Meuse Delta studies

Faculty of Geosciences - Department of Physical Geography, Universiteit Utrecht

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Neotectonics

Figure 1 Epicentra of known earthquakes in the southern Netherlands and adjacent areas in Belgium and Germany.

Figure 2 Rupture in a dike along the River Meuse, as a result of the 1992 earthquake (picture by KNMI).

Figure 4 Rate of tectonic movements during the Holocene (in cm/100 14C yr), according to Stouthamer & Berendsen (2000).

Neotectonic movements occur in the southern part of the Netherlands, especially at the faults bordering the Peel Horst and the Roer Vally Graben (Figure 1). In 1992 a major earthquake occurred near Roermond at a depth of 17 km, with a magnitude of 5.9 on the Richter scale. The earthquake was felt in a large area, from Denmark to the Vosges in France. This earthquake led to minor damage to roofs and churches. One person died as a result of a heart attack. In the Netherlands, a rupture occurred in a dike along the River Meuse (Figure 2). The Rhine and Meuse have crossed this faultzone while it was active and this makes the area a natural laboratory for studying the interaction of rivers and tectonics in a basin setting.

The influence of neotectonic movements on Holocene river systems in the Rhine-Meuse delta was first demonstrated by Stouthamer & Berendsen (2000). They found that gradient lines of the top of channel belt sands (GTS-lines) are deformed, where channel belts cross the Peel Horst (Figure 3) and the Peel Boundary Faultzone. Avulsion locations are aligned to the Peel Boundary Faultzone. Such observations indicate continued influence of neotectonic activity.

Figure 3 Deformation of gradient lines of the top of channel belt sands (after Stouthamer & Berendsen 2000).

The evidence for tectonic deformation is particularly strong in buried valley floors from the end of the Last Glacial (Cohen, Stouthamer & Berendsen, 2002), that form the subsurface of the Holocene delta. Deformation can also be detected in the longitudinal profile of the Laacher See reworked-pumice bed within these deposits (Verbraeck 1990, Figure 5). The tectonic deformation of Late Weichselian gradient lines are partly syn-depositional and partly post-depositional: when the deposits were laid down, the valley gradient was steeper over the Peel Horst, and after deposition, differential subsidence continued causing the gradient lines to oversteepen locally (Cohen, 2003). Deformation in the younger delta channel belts is smaller. The youngest active channel belt (River Waal) shows virtually no deformation: the river is able to maintain an equilibrium profile. The deformation seems to increase for older channel belts, suggesting an essentially post-depositional effect. Stouthamer & Berendsen (2000) used the differences in deformation of the GTS-lines to calculate the rate of tectonic movements during the Holocene (Figure 4). However, according to Cohen (2003) some of the irregularities in the Holocene gradient lines may not have a tectonic origin.

Figure 5 Longitudinal profile showing the reworked Allerød-interstadial Laacher See pumice layer, that occurs within the Kreftenheye Formation (originally after Verbraeck 1990; from Cohen, Berendsen & Stouthamer 2002). The Laacher See eruption and admixing of pumice to the Lower-Rhine sediment occurred at the end of the Allerød-interstadial (~13,000 cal yr BP).

Using hand-cored sections in flood basins, steps in the top of Late Glacial deposits have been mapped that mark the presently most-active faults of the Peel Boundary Faultzone. Vertical offsets up to 1.5 m occur in 15,000 year old buried surfaces and provide a measure for displacement rates. Vertical movement could also be reconstructed from the deformations in the Late Weichselian gradient lines and using peat dates from Holocene floodbasins (Cohen, Stouthamer & Berendsen 2002; Cohen, 2003; Cohen, Gouw & Holten, 2005). Rates of vertical movement along the Peel Boundary Faultzone indicate that rates are non-linear. Over the past 15,000 years, the Peel Boundary Faultzone appears to have been more active from 15,000-5000 yr BP, than from 5000 yr BP till the present (Cohen, 2003).

Figure 6 Asymmetrical meander belt between Rhenen and Amerongen, suggesting tectonic tilting Horst (Stouthamer & Berendsen 2000).

Other indications for tectonic movements are:

• The occurrence of an asymmetric meander belt between Rhenen and Amerongen (Figure 6). The Peel Block is tilted here to the northeast, and the River Rhine is forced in that direction, resulting in a number of successive meander cutoffs along the ice-pushed ridge that borders the area to the northeast.
• A preference for the main Late Glacial and Early Holocene meandering Rhine and Meuse channels, to position themselves along the northern rim of the wider valley floors created by braided predecessors in the Weichselian. This occurs across several tectonic blocks and indicates regional warping.
• The relative abundance of crevasse splays immediately downstream of the most active faults, and the relative lack of such splays immediately upstream.
• Conservative behavior of Holocene channels that cross the least subsiding blocks in the central delta. These are relatively straight channels that, despite deltaic aggradation and frequent partial and full avulsions upstream, remained located at the same position for many thousands of years.
• Nodal avulsion sites mark the downstream ends of these conservative reaches (Figure 7). A combination of active tectonics (upstream conservatism, downstream increasing relative subsidence), antecedent tectonic effects (subsurface deformation) and autogenic amplifying effects (Late Holocene compaction of Middle Holocene peat) explains the position of avulsion nodes in the central delta (Figure 7).

Figure 7 Location of avulsion nodes, on faults bordering the Peel Horst (Stouthamer & Berendsen 2000).

Figure 8 Basal peat samples, plotted relative to gradient lines of Van Dijk et al. (1991). The deeper peat samples show a ~2 m elevation difference, more than can be attributed to former groundwater-surface gradients (Törnqvist et al. 1998).

More indications come from groundwater rise studies. Basal peat data (Figure 8) and curves of groundwater rise from sites across the central delta show post-depositional effects of differences in tectonic subsidence. This has been used to map differences in subsidence during the Holocene (Törnqvist et al., 1998; Cohen 2003; Cohen, Gouw & Holten, 2005; Cohen, 2005). The landward shifting of Holocene onlap as the Rhine delta backfilled its former valley during the Middle Holocene (Figure 9), stalled when the terrace intersection migrated through the Peel Horst region and was forced to bury the at that time already significantly deformed Pleniglacial terrace (Cohen, Stouthamer & Berendsen, 2002).

Figure 9 Shifting of the terrace intersection between Holocene and Late-Weichselian deposits (Berendsen & Stouthamer 2000).

The Rhine-Meuse delta record can be used to map faults, map differences in subsidence rates (tilting blocks, subsiding blocks), to identify changes in the rates at which faults move, and to study the response of river valleys and delta’s to active tectonics. To study what drives neotectonics in the area, the Rhine-Meuse fluvial record needs to be complemented with insights from other areas and disciplines. Tectonic activity and related fluvial response in the Late Glacial and Holocene was mainly driven by glacio-isostasy (collapse of a so-called forebulge; Cohen, 2003; Wallinga et al., 2004; Busschers et al. 2005), with ‘normal’ tectonics operating in the background and providing the structural framework along which neotectonics are expressed. Our current research regarding neotectonics and river sedimentary response further explores that concept.

Literature

1. Berendsen, H.J.A. (2004), De vorming van het land. Inleiding in de geologie en geomorfologie. Fysische geografie van Nederland. Assen: Koninklijke Van Gorcum. Vierde, geheel herziene druk, met CD-ROM.
2. Berendsen, H.J.A. & E. Stouthamer (2000), Late Weichselian and Holocene palaeogeography of the Rhine-Meuse delta, The Netherlands. Palaeogeography, Palaeoclimatology, Palaeoecology 161 (3/4), p. 311-335.
3. Stouthamer, E., & H.J.A. Berendsen (2000), Factors controlling the Holocene avulsion history of the Rhine-Meuse delta (The Netherlands). Journal of Sedimentary Research 70 (5), p. 1051-1064.
4. Berendsen, H.J.A., K.M. Cohen & E. Stouthamer (2000), Het ontstaan van de Rijn-Maas delta. Aarde & Mens 4, p. 3-10.
5. Berendsen, H.J.A., & E. Stouthamer (2002), Palaeogeographic evolution and avulsion history of the Holocene Rhine-Meuse delta, the Netherlands. Netherlands Journal of Geosciences / Geologie en Mijnbouw 81 (1), p. 97-112.
6. Berendsen, H.J.A., & E. Stouthamer (2001), Palaeogeographic development of the Rhine-Meuse delta, The Netherlands. Assen: Van Gorcum. 270 p.
7. Busschers, F.S., H.J.T. Weerts, J. Wallinga, C. Kasse, P. Cleveringa, H. de Wolf & K.M. Cohen (2005), Sedimentary architecture and optical dating of Middle and Late Pleistocene Rhine-Meuse deposits - fluvial response to climate change, sea-level fluctuation and glaciation. Netherlands Journal of Geosciences 84-1, p. 25-41.
8. Cohen, K.M. (2003), Differential subsidence within a coastal prism. Late-Glacial - Holocene tectonics in the Rhine-Meuse delta, the Netherlands. Netherlands Geographical Studies 316, 172 p. KNAG/Faculteit Ruimtelijke Wetenschappen Universiteit Utrecht.
9. Cohen, K.M. (2005), 3D Geostatistical interpolation and geological interpretation of paleo-groundwater rise in the Holocene coastal prism in the Netherlands. In: Giosan, L. & J.P. Bhattacharya (Eds.), River Deltas - Concepts, models, and examples. SEPM Special Publication 83, p. 341-364.
10. Cohen, K.M., E. Stouthamer & H.J.A. Berendsen (2002), Fluvial deposits as a record for neotectonic activity in the Rhine-Meuse delta, The Netherlands. Netherlands Journal of Geosciences / Geologie en Mijnbouw 81 (3-4), p. 389-405.
11. Cohen, K.M., M.J.P. Gouw & J.P. Holten, (2005), Fluvio-deltaic floodbasin deposits recording differential subsidence within a coastal prism (central Rhine-Meuse delta, the Netherlands). In: M.D. Blum, S.B. Marriott & S.F. Leclair, Eds. (2005), Fluvial Sedimentology VII. Special Publication 35, p. 295-320. International Association of Sedimentologists. Blackwell Scientific.
12. Törnqvist, T.E., M. van Ree, R. van 't Veer & B. van Geel (1998), Improving Methodology for High-Resolution Reconstruction of Sea-Level Rise and Neotectonics by Paleoecological Analysis and AMS 14C Dating of Basal Peats. Quaternary Research 49, p. 72-85, Article no. QR971938
13. Van Dijk, G.J., H.J.A. Berendsen & W. Roeleveld (1991), Holocene water level development in The Netherlands' river area; implications for sea-level reconstruction. Geologie en Mijnbouw 70, p. 311-326.
14. Verbraeck, A. (1990), De Rijn aan het einde van de laatste ijstijd: De vorming van de jongere afzettingen van de Formatie van Kreftenheye. Geografisch Tijdschrift Nieuwe Reeks XXIV (4), p. 328-340.
15. Wallinga, J., Törnqvist, T.E., Busschers, F.S. & Weerts, H.J.T., (2004), Allogenic forcing of the late Quaternary Rhine-Meuse fluvial record: the interplay of sea-level change, climate change and crustal movements. Basin Research, 16, p. 535-547.

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Design: René Berendsen --- Programming and layout: Arnoud Berendsen --- Scientific content: Henk Berendsen --- Sandwiches and milkshakes: Helen Berendsen --- Last updated: April 14, 2007