Holocene Rhine reoccupation of the IJssel valley by divide dissection north of Zutphen K.M. Cohen [email protected] Dept. Physical Geography, Fac. Geosciences, Utrecht University PObox 80.115 3508 TC Utrecht, Netherlands ABSTRACT Cohen, K.M., E. Stouthamer, W.Z. Hoek, H.J.A. Berendsen & H.F.J. Kempen (2009) Zand in banen. 3rd fully revised edition. Arnhem: Provincie Gelderland. 130 pp. + CD-ROM + Digital Maps. In Dutch, with a summary in English. The Gelderse IJssel is the youngest natural distributary of the Rhine delta. When it came into existence between 300 and 700 AD, it annexed a valley that had not previously been part of the Holocene delta plain before. Understanding the drainage configuration of the valley and the position of the main divide, which separated Rhine tributaries from drainage going north prior to the formation of the IJssel, is key when reconstructing the timing and mechanics of the annexation process. The initiation of the IJssel is of archeological- historical interest, and the features from the initial stage - preserved some meters above deposits from later stages - offer a great opportunity to quantify a major flood of the Rhine. Kampen During 5 years of field campaign covering the full river valley length and width, we mapped and dated landscape features related to the IJssel diversion and the areas many dissected older elements. This allowed us to position the paleodivide between Zutphen and Deventer, and to explain how it formed. The outcomes of this research falsify former paleodrainage reconstructions that Zwolle assume the divide lay further south and that showed the rivers Berkel and Oude IJssel draining northward, instead of heading west towards the Rhine. DIVIDE CONTROL ON REOCCUPATION The channel deposits of the Gelderse IJssel show a two-staged division. The oldest stage (initial stage) saw multiple shallow channels and occupied a relatively wide belt within the valley. The younger stage (mature stage) occupies a relatively narrow channel belt of greater thickness, and showed all the phenomena of a meandering river. The river was embanked in the 14th century, continued to meander for two more centuries (still mature stage), and then lost most of its discharge due to discharge redistribution events at the upstream delta apex. Drainage and geomorphology (straightened map) BEFORE DURING AFTER divide area Early-Holocene inherited drainage situation Avulsion splay formation [350-700 AD] Gelderse IJssel channel belt maturisation GLD | OV Deventer ~768 AD OOST VELUWE WOLDBERG V V V IJsselmeer 205 210 215 205fortified 866 / 882 AD 210 215 205 210 215 ZUIDOOST V V V V (Zuiderzee) D D VELUWE V V V Cs V V V V V V V V V V VELUWEZOOM V V V V V V V V V V V V V V V V V V N Dorth V V V V V V V V V V V V V V V V V V V <1311 AD V V V V V V V V V V V V V V V KampenV V V V Arnhem V V V V V V V V V V Dt Nederrijn Hunnepe Dortherbeek V V V V V V V V V V V V V V V V V V Zutphen V V V V V V V V V V V V Olst V V Wijhe V V V V V V Deventer ZwolleV V V V Wilp Wp IJssel V V V V V V V V V V Doesburg V V V V V V V V V ~965 AD Aa V V V V V V V V V V V V V V V V V V V V V V V V activeFormer c. 40.000-20.000 valley of river yr Berkelago 10 km Oude IJssel Berkel Dortherbeek Ov. Vecht Zwarte Water KMC 09 ther e after coversand bur GLD | OV Pingo-remnant cluster: G OVERBETUWE LIEMERS ACHTERHOEK SALLAND IJSSEL DELTA paleo-seepage zone low high Veluwe periglacial fans uncovered covered 7.5 Former drainage, present former Higest coversand ridges ?? predating the IJssel channel of the river IJssel valley rim topography Berkel periglacial fan uncovered covered last active 12.500-11.700 yr ago sourced from periglacial alluvial fans ied 7.5 Annotated geological section along the axis of the IJssel valley seepage zone (FeO) Holocene V V E Lower reaches of combined Valley edge Valley edge Coversand ridges Incised lower reaches of combined Voorst Voorsterbeek < 893 AD Voorsterbeek Oude IJssel + Berkel local rivers Oude IJssel 40-25 ka Rijn Voorst-Gorssel-Wilp Salland +Veluwe-source local rivers kunstmatige bocht- afsnijding 1357 AD 14 slope and fan IJssel delta Pingo-remnant cluster: paleo-seepage zone Zutphen, since ~300 AD Berkel canals, water mill Berkel fan Veluwe fan complex complex Woldberg since 1000 yr 7.5 fortified 866 / 882 AD Arnhem river Berkel 1225-1250 AD 12 Doesburg seepage zone (FeO) Z 7.5 Holocene Berkel Nederrijn IJssel Zutphen +10 Z W Warnsveld 10 < 1121 AD Deventer (m) Olst 8 V V V V V V V V V V V V V valley Wijhe Rijndelta V V V V V V V V V V Oude IJssel 460 465 470 Withmundi 6 [since 5 ka] [25-15 ka] Zwolle 460 465 470 794 797 AD 460 465 470 [40-25 ka] [40-15 ka] Kampen [13-9 ka] IJssel 4 top IJssel natural levee ? ka] 60-25 IJs embankment Wychmoith 2 ine [ sel v top sand IJssel pointbars < 1500 AD Rh alle V nd y R v v v v Eerbeek <1096 AD rla hi v v v v ntfe ne V V V IJsselmeer Gelderse o [8 V V V V V V V v v v v NAP d-M 0- Poort on 4 V V V V V V V v v v v Brummen 794 AD R 0 v v v v v v v v NAP Rhine k V V V V V V V national RD grid (km) Netherlands a] [40-15 ka] V V V V V V V V V V [25-15 ka] V V V V V V V V -2 Zutphen Member v v v v Eemian Rhine [130-80 ka] V V V valley periglacial outwash fan Brook valleys Splays and initial multi-channel avulsion belt formation Channel belt Active channelsand moats Ov. -4 V V V V V V Vecht V V V V coversand dune ridge Brook channels, traced Crevasse channels Present river IJssel Silted-up splay floodplain Residual channels -6 V V V V [?60-40 ka] Rhine-filled glacial tongue basin: Twello Mb. V V V V Deventer coversand relative lows Brook channels projected Early Medieval fortified settlements Zutphen and Deventer Isolated breach splays Medieval cities, first dikes End of Saalian [145-130 ka], Termination II V V V V [80-?60 ka] 7.5 Minimal elevation(m O.D.) breached by crevasse channels -8 = historic church move 890 880 880 890 900 910 920 930 940 950 960 970 980 990 1000 RWS km langs geul Dortherb. All ages based on oldest (known) historic toponym mentioning; < = existed from before; = church / chapel founding 0 50 100 km downstream distance Preserved channels of the initial stage are avulsion-splay crevasse channels. They reworked lows Late Pleistocene Holocene in coversand ridges of the divide, and had splays downstream of these locations. As time progressed 130 80 40 25 15 11.7 ka 11.7 5 2 1 0 ka 0 = 2000 AD Local eolian and fluvial deposition Local deposition and repeated Rhine floods forced themselves to the divide breach, the number of active channels Eolian dunes (Wierden & Delwijnen Members) Level maintained by Early Holocene local Late glacial local drainage trunk systems drainage (top of brook channel deposits) dropped, and the width and incision-depth of the remaining channels increased. This caused the V V V Legend Veluwe periglacial alluvial fans and fan toes Peat (Nieuwkoop Formation) V V V V Gelderse IJssel to mature into a single channel meandering system. In the divide region the mature Berkel periglacial local river deposits Rhine delta deposion Overijsselsche Vecht periglacial local river deposits Boxtel Formation Floodplain and -basin deposits, clay meander belt occupies a slightly incised architectural position: the top of IJssel sand bars is Rhine deposition IJssel embankment level (situation 1995) Overbank deposits (Wijchen Member) Level of top of IJssel natural levees encountered decimeters to a meter lower than equivalent initial stage deposits. To the south and Channel deposits: sands and gravelly sands, with lateral and vertical dissective architecture indicated. Level of top of subrecent pointbar sands the north of the divide, patches of the brook valley deposits occur preserved buried between Echteld Formation Kreftenheye Formation Hippo and Mammoth skull not to scale. along Nederrijn and IJssel Rhine branches crevasse channels. They are dated and used to constrain the begin of avulsion splay formation. GEOLOGY OF DIVIDE FORMATION DATING THE GELDERSE IJSSEL Since ~40,000 years ago - after the Rhine abandoned its IJssel valley An apparent gap exists in the dated age of the IJssel upstream and downstream course between 60,000 and 40,000 years ago - local periglacial of the divide area. This is due to the (i) the static presence of the divide until ca. depositional sedimentary systems buried the valley floor. Orphaned 550 AD and (ii) the centuries necessary for the IJssel breach to mature. divide area Zutphen former Rhine tributaries built out low gradient alluvial fans from both Reaches upstream of the divide were gradually flooded by Rhine waters from 2500 sides of the valley. The fans were fed from catchments draining the Berkel yr ago onward.