Views
5 years ago

Chapter 4

Chapter 4

Chapter

4 Vecht region 4.1 GeoloGy and palaeoGeoGraphy of the Vecht reGion 4.1.1 IntroductIon This paragraph discusses the relevant geology and palaeogeography of the Neolithic sites at Swifterbant (various sites), Schokland-P14, Schokkerhaven-E170, Urk-E4 and Emmeloord-J97, located in eastern Flevoland and the Noordoostpolder. Figure 4.1 shows the location of the sites and the elevation of the Pleistocene subsurface. In the northern part of the Noordoostpolder the Pleistocene subsurface consists of aeolian coversands (Boxtel Formation, cf. Schokker et al. 2007). In the southern part of the Noordoostpolder and in the northern part of Eastern Flevoland the coversands are generally lacking. In the Pleniglacial, Late Glacial and Early Holocene (c. 40.000-8.000 BP) the river Overijsselse Vecht dissected and reworked Pleistocene Rhine deposits (Kreftenheije Formation; Busschers et al. 2007). The Geldersche IJssel as a Rhine branch became active only in the Late Holocene. Under the Periglacial climate, the Vecht and the tributaries draining the IJssel valley carried considerable discharge (Huisink 1999; Van Huissteden et al. 2001). In contrast to the coversands, the sands of the Vecht are calcareous, contain gravel and have a loamy top. Aeolian inland dunes (river dunes) of Late Glacial age border former channels of the Vecht in the southwestern part of the Noordoostpolder (top at c. 4 m -NAP, Kreftenheije Formation). Outcrops of glacial till stand out at Schokland, Urk, Tollebeek and Vollenhove (Gieten Member of Drenthe Formation; Ente 1976; Ente et al. 1986; Gotjé 1993; Weerts et al. 1998). These Pleistocene deposits were present at the surface in the region during the Late Mesolithic. The Holocene sequence, consisting of detritus-gyttja, peat and clay (Nieuwkoop Formation and Naaldwijk Formation), buried the Pleistocene subsurface in the last c. 7500 years. A gradual rise of the ground water level, owing to sea level rise downstream, resulted in the development of marshes and sedimentation of peat. This started at c. 5500-5000 BC at the studied sites at c. 8 m -NAP. The Vecht valley became submerged and the river discharged into a lagoon. At short distance from former river channels the marshes were eutrophic, while at larger distance from the rivers the marshes were increasingly oligotrophic. The extent of oligotrophic vegetation increased during the second half of the Holocene. Peat growth was continuous in the north. In the south, it was interrupted locally by periods of clay deposition. Part of the clay was delivered by the rivers Vecht and IJssel, but tidal channels from the west are considered as the main source (discussed below). Deposition of detritus-gyttja mainly took place in the deepest incised submerged river channels (Ente et al. 1986; Wiggers 1955). A tidal inlet was present during the Middle Holocene west of the study area, resulting in marine influence in the region. The inlet connected the fresh to brackish lagoon to the sea. As groundwater level rose and peat formation continued, tidal and salt water influence in the study area decreased. Three phases of marine calcareous clay deposition are registered in the Noordoostpolder. During the first phase at c. 5200-4000 BC clay was deposited in the southern and south-central area of the Noordoostpolder (Older Unio clay; see fig. 4.2). 1 During that phase the environment was comparable with a freshwater tidal system, and consisted of levees and backswamp areas. From c. 4200-4100 BC onwards, both marine influence and influence of the eutrophic river water decreased, resulting in a mesotrophic freshwater environment. From 3800 BC onwards, river discharge further decreased, resulting in peat formation. A second phase of marine clay deposition occurred at c. 3700- 3400 BC. It is synchronous with the presence of a lake in the central part of the Noordoostpolder (Younger Unio clay). A third phase of clay deposition occurred in the southern part of the Noordoostpolder at c. 2500-1800 BC (Cardium clay). During this phase marine influence appears to be the result of single events (stormfloods) rather 1 This unit probably is diachronic, and as a result the quoted age only applies to its inland limit in the study area. 163

Flex 3 in Action Sample Chapter 4 - Manning Publications
Chapter 4: The cell nucleus
Chapter 4 - Department of Business
Chapter 2.3 Automated online sequential isotope labeling for protein ...
Motion in Two Dimensions Chapter 4 - electron.rmutphysics.com
chapter 4 preventive maintenance
Download a Sample Chapter - Measuredreason.com
Insights into Book III Chapters 3, 4, and 5
Chapter 4: The Building Architectural Design - EERE
Chapter 4 PA-RISC Computer Systems - OpenPA.net
LALP Consultation Version Chapters 1 to 4
Chapter 4