The Pliocene and Quaternary fluvial archives of the Rhine system

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Quaternary Science Reviews 25 (2006) 550–574

The Pliocene and Quaternary fluvial archives of the Rhine system Wolfgang Boenigka, Manfred Frechenb, a

Geologisches Institut, Universita¨t zu Ko¨ln, Zu¨lpicher Str. 49a, D-50674 Ko¨ln, Germany Leibniz Institute for Applied Geosciences (GGA), Geochronology and Isotope Hydrology Section, Stilleweg 2, D-30655 Hannover, Germany

b

Received 28 June 2003; accepted 19 January 2005

Abstract The River Rhine is one of the few major fluvial systems that connect the areas of the Alpine glaciers and Scandinavian ice sheet and so provides a key for correlating the two glacial areas in northern and middle Europe. The fluvial sequences of the Rhine Valley include at least 11 Pleistocene terraces in the Lower Rhine area, 2 Pliocene and 12 Pleistocene terraces in the Middle Rhine area resulting in 15 different Pliocene and Pleistocene terraces based on the correlation between Lower and Middle Rhine. The formation of fluvial terraces is significantly influenced by climatic and tectonic processes. The terrace staircases are a result of uplift in the Middle Rhine area and the southern part of the Lower Rhine area, whereas subsidence in the northern part of the Lower Rhine area resulted in buried stacked sequences. Magnetostratigraphic data provide chronological constraints for the terrace deposits in the Lower Rhine embayment and Middle Rhine region. The Matuyama/Brunhes boundary is a reliable marker horizon for the Upper Terrace fluvial deposits exposed in the Ka¨rlich clay pit in the Middle Rhine area. The first appearance of volcanic heavy mineral grains in the terrace sediments, in loess and soils can be correlated from the Middle Rhine area through the Lower Rhine embayment to the Netherlands. The first occurrence of Nordic components in terrace sediments of the Lower Rhine area is known from gravel on top of the KempenKrefeld beds and so are younger than the Holsteinian but older than the penultimate glaciation. In the lower Middle Rhine area, 40Ar/39Ar dating of tephra layers intercalated in the aeolian and fluvial sediments provide age constraints. The Upper Pleistocene aeolian sediments overlying the terrace deposits have been dated by luminescence methods, and the tephra from the Laacher See eruption (12,860 BP) is present in the Younger Lower Terrace deposits. r 2005 Elsevier Ltd. All rights reserved.

1. Introduction The Rhine is one of the few fluvial systems that connects the areas of Alpine and Scandinavian glaciation. The fluvial sequences and the sediments underlying the terraces are excellent archives of climate and environmental change and provide an important framework for late Cenozoic terrestrial stratigraphy. These sediments record changes in fluvial system dynamics and also contain important palaeo-ecological information, for example, pollen and plant macrofossils, vertebrates, including hominid remains, as well as molluscs and insects. The Middle and Lower Rhine areas (Fig. 1)

Corresponding author. Tel.: +49 511 643 2537; fax: +49 643 2537.

E-mail addresses: [email protected] (W. Boenigk), [email protected] (M. Frechen). 0277-3791/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2005.01.018

discussed here are one of the best investigated parts of the Rhine system. The fluvial deposits along the 1320 km of the River Rhine from the Alps to the North Sea have been extensively studied and mapped since the late 19th century. The Rhine system includes at least 16 terraces, providing a documentation of the Pliocene and Quaternary fluvial record. The sediments underlying the terraces yield detailed information on the distribution, lithology, sedimentary petrography, sedimentology and morphology of the fluvial sediments. The Middle Rhine area and the southern part of the Lower Rhine area (Fig. 1) were regions of significant tectonic uplift during the Pliocene and Pleistocene, resulting in well-developed terrace staircases with the higher terraces older than the lower ones. These staircases were formed by cyclic downcutting and aggradation as a result of progressive uplift and climate forcing.

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the Pliocene and Quaternary fluvial archive of the Rhine River. 1.1. Definitions 1.1.1. Terms The term river terrace used in this paper encompasses both river landform and river sediments.

Fig. 1. The study area in the Middle Rhine Valley and the Lower Rhine basin. For more details see Figs. 3 and 5.

The terraces are poorly developed in areas of subsidence, e.g., the Neuwied basin (Frechen, 1996) and the northern part of the Lower Rhine embayment (Brunnacker, 1978; Boenigk, 1991, 1995). Due to different tectonic movements it is difficult to compare and correlate the terraces along the Rhine. However, detailed sedimentological and petrographic studies provide sufficient data to distinguish terraces (Bibus and Semmel, 1977; Brunnacker, 1978; Bibus, 1980; Boenigk, 1978a, 1995; Klostermann, 1992; Hoselmann, 1994, 1996; Boenigk and Hoselmann, 2003). The first studies of the terrace stratigraphy of the River Rhine were published in the late 19th century and concerned the Middle Rhine area (Pohlig, 1883; Kaiser, 1903, 1906, 1908). Stratigraphic and chronological studies since the mid-1980s have improved our knowledge of the terrace stratigraphy and the correlation between the Middle and Lower Rhine area, including the Netherlands (Zagwijn and de Jong, 1983; Zagwijn, 1985; Schirmer, 1990a; Boenigk, 1990, 1991, 1995; Boenigk and Frechen, 1995; van den Berg and van Hoof, 2001). This paper reviews the fluvial sequences in the Middle and Lower Rhine area in Germany, the terrace chronostratigraphy and the deposition history of

1.1.2. Chronostratigraphic boundaries The boundary between the Tertiary and the Quaternary is defined in this paper by the top of the Reuverian, which has been estimated by palaeomagnetic methods to about 2.4 Ma BP, slightly younger than the polarity change of the Gauss/Matuyama boundary dated at 2.58 Ma BP (Boenigk et al., 1979; Cande and Kent, 1995). In the Lower Rhine Area, the Reuver Clay is an excellent marker horizon owing to distinct lithological and biostratigraphical changes (Fig. 2). The Reuver Clay, which correlates with the Neogene Mammal Zone NM16 (Kolfschoten et al., 1998; Mo¨rs et al., 1998), is subdivided on the basis of pollen spectra into Reuverian A, B and C. This layer also contains a species-rich Pliocene mollusc fauna that could be used to define the transition to the Quaternary. A marked petrographic change occurs from the Kieseloolite Formation to the Tegelen Formation within the upper part of the Reuverian sequence (Boenigk, 1970; Boenigk et al., 1972). The Gauss/Matuyama boundary is within the upper part of the Reuver Clay, Reuverian C according to palynological findings, in the Lower Rhine embayment (Boenigk et al., 1974a; Brunnacker and Boenigk, 1976; Boenigk, 1979). Within the sediment sequences along the River Rhine, the position of the Olduvai event, which defines the boundary between the Tertiary and Quaternary in the international literature, is not clear, although there may be evidence that the Olduvai event is in the upper part of the Tegelen Formation (Zagwijn, 1985). The end of the Olduvai, the transition from normal to reverse magnetic polarity was determined in ‘‘Clay B1’’ in the Lower Rhine embayment (Brunnacker and Boenigk, 1976; Boenigk, 1978a). ‘‘Clay D’’ has a normal magnetization and so correlates with the Jaramillo event (Brunnacker and Boenigk, 1976; Boenigk, 1978a). The Matuyama/ Brunhes boundary was determined within fluvial deposits of the River Rhine, for example, in unit B at the Ka¨rlich section in the Middle Rhine area (reverse magnetization within the lower part and normal magnetization in the upper part of unit B) (Boenigk et al., 1974a; Brunnacker et al., 1976; Boenigk, 1978a; Fromm, 1987; Boenigk and Frechen, 1998). The boundary between the Lower and the Middle Pleistocene is defined by the magnetic polarity change of the Matuyama/Brunhes boundary, which is within the Upper Terrace sediments. Thus, the Upper Terrace

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Fig. 2. The stratigraphic position of the Tertiary/Quaternary boundary based on different methods. Palynological evidence indicates a clear boundary between the Reuverian C and the pre-Tiglian. On the basis of lithological evidence, there is a clear boundary between the Kieseloolite Formation and the Tegelen Formation within Reuverian B. Palaeomagnetic studies indicate that the Gauss/Matuyama boundary is within the Reuverian C. Mammal fossils place the boundary between MN 16a/MN 16b within the Reuverian B. The mollusc fauna indicates a boundary between ‘‘Tertiary’’ and ‘‘Quaternary’’ species within the uppermost Reuverian C.

sediments include part of the Lower to Middle Pleistocene record. The Middle and the Lower Terraces are considered to correlate with part of the Middle Pleistocene and the Upper Pleistocene.

2. The Rhine system In the Middle and Lower Rhine area two Pliocene and 13 Pleistocene terraces can be distinguished (Figs. 4 and 6). For the Middle Rhine area these consist of: two Pliocene terraces, at least one Lower Pleistocene terrace, four upper terraces of Early to Middle Pleistocene age and five middle terraces of Middle Pleistocene age. For the Lower Rhine area they consist of three upper terraces of Early to Middle Pleistocene age, and six middle terraces of Middle Pleistocene age. Two lower terraces of Late Pleistocene age and the Holocene floodplain terrace are common to both regions.

levels are additionally used to distinguish terraces. Although scour hollows can be deep and irregular, the erosional base level is very helpful to distinguish terraces along the Middle Rhine area owing to the presence of rock-cut surfaces. In the Middle Rhine area, the differences in elevation between the Upper Terraces are small and local differences in the amount of uplift and/or tilt must be taken into consideration. Furthermore, deep channels are incised into bedrock below the general base level of the terrace deposits and so it is difficult to distinguish different gravel beds. Because of this variation, the morphological position of a terrace is a reliable criterion only for distinguishing between Upper Terrace sediments and Middle Terrace sediments and between Middle Terrace and Lower Terrace sediments in the lower Middle Rhine area and the Lower Rhine area (Figs. 4 and 6).

2.2. Petrography 2.1. Geomorphology The surface of a terrace deposit can have been altered by erosion or accumulation of younger sediment. Therefore, in this paper, elevations of erosion base

Because the percentage of quartz decreases as the age of the fluvial sediments becomes younger (Boenigk, 1970; Schnu¨tgen, 1974), clast lithological content is a stratigraphic tool that can be used to distinguish

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between Oligocene/Pliocene and Lower Pleistocene terrace deposits. Another stratigraphic tool that can be used for correlating terrace deposits is the heavy-mineral spectrum. Three major events and changes can be recognized in the heavy-mineral spectra of samples from the Rhine terraces (Boenigk, 1978a, 1990, 1995; Klostermann, 1992): a. change of the heavy-mineral spectrum from a predominance of resistant zircon, tourmaline, staurolite, rutile and anatase in the Pliocene fluvial sediments to a predominance of less resistant garnet, epidote, green hornblende and alterite in the Lower Pleistocene fluvial sediments; b. appearance of saussurite (alterite), as the predominant mineral in the terrace deposits of Upper Terrace 2 (UT 2), owing to the capture of the Aare fluvial system by the Rhine (Boenigk, 1982, 2001); c. predominance of volcanic heavy minerals from Middle Terrace 1 (MT1) onwards owing to the onset of the East Eifel volcanism, starting with brown hornblende in the terrace and loess deposits and followed by predominance of clinopyroxene (Boenigk, 1978a, 1990, 1995; Klostermann, 1992).

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dated by the 40K/39Ar and 40Ar/39Ar methods (Fuhrmann, 1983; Bogaard and Schmincke, 1990). 2. Aeolian, fluvio-aeolian and fluvial sediments have been dated from the Middle Rhine area by luminescence methods (Frechen, 1992; Perkins, 1995), organic material by the radiocarbon method, bone and teeth from the section at Ka¨rlich by the uranium-series and the electron-spin-resonance dating methods.

3. Middle Rhine area

In the Lower Rhine area, clay and peat are intercalated in the sediment sequence. The Tertiary/ Quaternary boundary at the top of the Reuver Clay is defined by plant remains (Fig. 2). The overlying Tegelen Clay is thus a temperate/cold complex or even an interglacial/glacial complex formed during the Early Pleistocene. Fine-grained deposits are rare in this area for the period ranging from the Eburonian to the Cromerian. Several sections containing floral and faunal remains have been described for the Holsteinian to Holocene in the Lower Rhine area. However, precise age constraints are difficult to obtain for these horizons because they do not provide a clear chronostratigraphic interpretation. In the Middle Rhine area, only coarse-grained fluvial sediments containing no fossils were deposited. The chronostratigraphic interpretation is based on faunal remains in the sediments overlying the fluvial deposits, such as for example, in the loess/palaeosol sequence in the sections in the Ka¨rlich and Ariendorf pits (Boenigk and Frechen, 1997, 1998, 2001a, b).

The Middle Rhine is defined as the stretch between the towns of Bingen and Bonn (Fig. 1). The areas of most interest are the Neuwied basin north of Koblenz and the lower Middle Rhine north of the Neuwied basin (Fig. 3). The Neuwied basin began to subside during the Eocene and contains a sequence of Oligocene marine clay, marl and sandstone through Pliocene terrestrial sediments to Pleistocene deposits. Because of the smaller uplift in the Neuwied basin relative to the lower Middle Rhine area, the terrace sequences along this stretch of river display smaller vertical intervals than upstream or downstream. In the lower Middle Rhine area, a series of terraces along the Rhine and its tributaries (Fig. 4) document alternating incision and aggradation (Jungbluth, 1918; Kaiser, 1961; Bibus and Semmel, 1977; Bibus, 1980, 1983; Boenigk, 1990, 1995; Boenigk and Hoselmann, 1991, 2003). The Rhenish Massif, an area of strongly folded Palaeozoic bedrock, was uplifted to just above sea level during the Early Tertiary. The oldest fluvial deposits, named the ‘‘Vallendar Gravel’’, are of Oligocene age or Eocene age and were deposited by small pre-Moselle and pre-Rhine rivers (Mordziol, 1908). The oldest terrace of river Rhine is the Pliocene ‘‘Kieseloolite Terrace’’ (in German: ‘‘Kieseloolith-Terrasse’’, Jungbluth, 1918). Such fluvial sediments were deposited in a broad, shallow valley by the early Rhine system during the late Miocene and Pliocene. The ‘‘kieseloolites’’ are siliceous oolites derived from Jurassic and Triassic rocks in the Lorraine region. The heavy-mineral spectra of the terrace deposits show a predominance of resistant heavy minerals, such as tourmaline, zircon, rutile, anatase and a high content of staurolite (Boenigk, 1979). There is evidence for two subunits of the Kieseloolite Terrace (Boenigk and Hoselmann, 2003).

2.4. Absolute age dating

3.1. Lower Pleistocene Terraces

1. Tephra marker horizons are intercalated in the Middle Pleistocene deposits at the sections at Ariendorf, Miesenheim and Ka¨rlich and have been

Towards the end of the Pliocene, the Rhine extended its catchment to the Alps (Boenigk, 1970, 1990), as evidenced in the pebble spectrum of the Upper Terrace

2.3. Palaeontology

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Fig. 3. The study area along the Middle Rhine with the Neuwied basin and the localities of interest.

complex by (i) a change to a more heterogeneous mixture of sand and gravel, (ii) the first appearance of garnet, epidote, green hornblende and alterite (Boenigk, 1970), as well as radiolarite in the gravel fraction (Schnu¨tgen and Brunnacker, 1976), and (iii) a decreasing content of quartz. The transition from the Pliocene to the Pleistocene is not exposed in the Middle Rhine area. In the Middle Rhine area, the time between the deposition of the Miocene to Pliocene Kieseloolite Terraces and the Upper Terrace 1 (UT1) is documented by thin, coarse-gravel deposits at different elevations. These deposits are considered to be Lower Pleistocene terraces (LPT) following Hoselmann (1994). The base of these gravels varies from 228.0 to 251.3 m asl within short distances. This considerable range is due to localscale tectonic movement (Boenigk and Hoselmann, 2003). Bibus and Semmel (1977) and Bibus (1980) subdivide the gravel deposits into three terrace units: tR1, tR2 and tR3. As chronological data are not available for the individual exposures, the morphological position is the only criterion for stratigraphic interpretation. Morphological position is not an appropriate stratigraphic approach for the older terrace deposits in the lower Middle Rhine area owing to a complex history of tectonic uplift and subsidence (Boenigk and Hoselmann, 2003), and so a reliable subdivision is not possible at present. Semmel (2001) questioned whether tectonic activity occurred during the time of deposition of the

Fig. 4. Idealized sketch of the terrace staircase in the Middle Rhine area, including Tertiary terraces and gravel beds, the Lower Pleistocene terraces (LPT), the Upper Terraces (UT1-4), the Middle Terraces (UMT-LMT2) and the Lower Terraces (Older LT and Younger LT).

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Upper Terrace sediments in the upper Middle Rhine area. No independent dating is available for these rockcut benches, which are overlain by a thin layer of gravel. Therefore, it is recommended that the LPT should be considered as a terrace complex deposited from the time of the Gauss/Matuyama boundary to that of the Jaramillo event without further subdivision to the level of individual units. An excellent exposure of Lower Pleistocene terrace deposits is in the section at Leilenkopf (northing: 559435, easting: 259260; Gauss–Kru¨ger coordinates, as determined from German 1:25,000 scale Topographical Maps) (Bibus, 1980; Boenigk and Hoselmann, 2003). Palaeomagnetic studies indicate that these terrace deposits belong to the Matuyama epoch and are older than the Jaramillo event (Fromm, 1987). 3.2. Upper Terraces The Upper Terrace complex consists mainly of braided river deposits in a valley up to 8 km wide. The distribution of these terraces has been investigated in the Middle Rhine area by Jungbluth (1918), Mordziol (1951), Kaiser (1961), Bibus and Semmel (1977), Bibus (1980) and Hoselmann (1994, 1996) and this work has included detailed mapping. Tectonic maps have been published by Boenigk and Hoselmann (2003), Meyer et al. (1983) and Meyer and Stets (1998). After the deposition of the Upper Terrace sediments in the present Middle Rhine Valley, the broad valley began to be modified into a steep-sided valley, related to increasing uplift of the Rhenish Massif. The Upper Terraces are characterized by a dominance of the heavy mineral assemblage epidote, garnet, green hornblend and alterite. The sediments from below the UT2/3 show a large variation in the heavy mineral assemblage owing to different weathering intensities (Hoselmann, 1994). Volcanic heavy minerals are not present in the sediments from below UT1-2 but are found as accessory minerals in the sediments from below UT3-4. The Upper Terrace sediments were deposited from the Jaramillo event about 1 Ma ago to about 600 ka BP, during the Brunhes epoch. The Middle Terrace sediments were deposited during the volcanic activity in the eastern Eifel area after 600 ka BP. The Upper Terrace complex can be subdivided as follows: UT4

UT2/3 UT1

Upper Terrace 4 (‘‘Unterstufe der ju¨ngeren Hauptterrasse’’) Upper Terrace 2/3 (‘‘Ju¨ngere Hauptterrasse’’) Upper Terrace 1 (‘‘A¨ltere Hauptterrasse’’)

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3.2.1. UT1 The UT1 is found only along the eastern side of the Rhine valley (Hoselmann, 1994). It can be subdivided into a lower part of coarse sand and gravel and an upper part of well-sorted fine to medium sand, the latter called ‘‘Ho¨nninger Sande’’ (Bibus, 1980; Hoselmann, 1994). The type section is at Bad Ho¨nningen (Fig. 3). The base and top are at elevations of 218 and 223 m asl, respectively (northing: 559,994, easting: 259,526) (Bibus, 1980; Boenigk and Hoselmann, 1991). In the northern Middle Rhine valley the base level of this terrace slopes continuously to the north from 218 to 199 m asl. In the southern Middle Rhine area, this terrace is considered equivalent of the tR4 of Bibus and Semmel (1977). Reverse magnetization was determined for sediments from below the UT1 in the section at Werlau (Fig. 1, northing: 555,846, easting: 340,655, base and top of gravel body at 220 and 240 m asl, respectively), most likely indicating deposition during the Matuyama epoch (Fromm, 1987). The sediments overlying UT1 in the Werlau section have normal magnetization and a pollen spectrum considered to indicate the younger part of the Cromerian (Semmel in Bibus and Semmel, 1977). The section at Ka¨rlich (Table 1) includes gravel of Unit Ba that has reverse magnetization and correlates with UT1 (Boenigk et al., 1974b; Hoselmann, 1994). Sediments from all younger terrace sediments have normal magnetization. 3.2.2. UT2/3 The Upper Terrace 2/3 (UT2/3) is the most prominent terrace along the Middle Rhine and so is named the ‘‘Hauptterrasse’’ (main terrace). The UT2/3 is composed of two gravel bodies with the same terrace surface level. In the upper Middle Rhine Valley, the base of this gravel body has a constant elevation of about 200 m asl. In the lower Middle Rhine Valley, the base of this gravel body slopes from 220 to 170 m asl from south to north. The base of the terrace deposit in this area has two erosion levels with a vertical difference of 10 m. The sediment sequence from below UT2/3 is complex. There are excellent exposures at Bruchhausen (northing: 560874, easting: 258804) with a base and top at 194 m asl and 199 m asl for the upper erosion base and with a base and top at 182 m asl and 194 m asl for the lower erosion base, respectively. The UT2/3 is also exposed as a rockcut bench covered with a thin gravel layer at the section at Loreley (194 m asl) and Erpeler Ley (191 m asl). 3.2.3. UT4 The Upper Terrace 4 (UT4) is well exposed only north of the confluence of the rivers Rhine and Ahr, and north of the village of Linz (section at Leidenberg, northing: 560,825, easting: 258,810; base of the gravel deposit at 175 m asl and top at 184 m asl). The UT4 is not exposed south of Linz or along the upper Middle Rhine Valley.

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Table 1 Correlation of loess/paleosol sequences from Ka¨rlich and Ariendorf and the terrace sediments from the Lower Middle Rhine Valley. dating of intercalated tephra is from Bogaard and Schmincke (1990), discussion of dating results is from Boenigk and Frechen (2001b) MIS

Ka¨rlich unit

40

Ar/39Ar

Ka¨rlich

Middle Rhine Terraces

Ariendorf

1 2

Brown forest soil Loess

Holocene LT

6 7

Hiatus

LMT 2

Reworked loess Ka¨rlich interglacial 2 (Peat) Tephra Ka¨rlich interglacial 1 (Brown forest soil) Loess Tephra
450 ka Brown forest soil

LMT 1

Brown forest soil Loess Hiatus Loess Tephra
215 ka Brown forest soil Loess Brown forest soil

J

11

H

12

G 16

F C–E

19 20

B A

MMT 2

MMT 1

UMT Brown forest soil Loess Soil Soil Floodloam Gravel Floodloam Gravel Tertiary sediments and tephra

Petrographically, the terrace deposits are very similar to those of UT2/3. Morphologically, the UT4 marks the transition from a broad valley to an entrenched valley, the latter characterized by the Middle Terraces. Due to a similar elevation with UT2/3 and similar lithology and petrography except the presence of accessory volcanic heavy minerals, the UT4 is attributed to the Upper Terrace complex. 3.3. Middle Terraces The Middle Terraces are present as narrow steps along the entrenched valley. The morphological change from the broad plateau valley documented by UT1-4 to the entrenched valley is due to uplift of the Rhenish Massif. The most rapid uplift was between approximately 600 and 350 ka BP, as evidenced by intercalated tephra from the re-activated volcanism in the east Eifel area (Bogaard and Schmincke, 1990). The tectonic activity resulted in downcutting of 150 m into the Palaeozoic bedrock, forming steep valley sides with minor terrace relicts. These terraces along the entrenched valley are named ‘‘Middle Terraces’’ (‘‘Mittelterrassen’’) by Kaiser (1903). There is general agreement that three terraces (Upper Middle Terrace, Middle Middle Terrace and Lower Middle Terrace) can be distinguished in the Middle Rhine Valley (Jungbluth, 1918; Kaiser, 1961; Quitzow, 1974; Bibus and Semmel,

Loess Ariendorf Interglacial (Brown forest soil) Tephra
410 ka Gravel Devonian bedrock

UT 4 UT 2/3 UT 1

1977). However, Kaiser (1961) and Quitzow (1974) divided the Upper Middle Terrace into two subunits. Schirmer (1994, 1995) distinguished 4–5 Middle Terraces, however, without naming type region or elevation. Petrographically, the Middle Terrace deposits are characterized by pebbles with a high percentage of volcanic rocks and a heavy-mineral spectrum with a high percentage of minerals from the Eifel volcanism, neither of which are present in the Upper Terrace sediments. The following subdivision is generally accepted and listed from the oldest (UMT) to the youngest (LMT): LMT Lower Middle Terrace (‘‘Untere Mittelterrasse’’) MMT Middle Middle Terrace (‘‘Mittlere Mittelterrasse’’) UMT Upper Middle Terrace (‘‘Obere Mittelterrasse’’)

The Middle Terraces are poorly preserved and consist mainly of rock-cut surfaces with only a few exposures of river deposits. However, in contrast to the Upper Terraces, the Middle Terraces can be distinguished on the basis of their elevations, because there is less faulting. 3.3.1. UMT Near the village of Feldkirchen north of Neuwied (Fig. 3), fluvial sediments of the UMT, about 1 m thick, are exposed (Heide, 1967; Frechen and Heide, 1969) in

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the Hu¨llenberg pit at an elevation of about 145 m asl. Just west of this pit, the present valley floor has an elevation of about 59 m asl, the mean river level is at 54 m asl. The heavy-mineral spectrum of the exposed sediments is dominated by volcanic brown hornblende. In the northern part of the Lower Middle Rhine valley, rock-cut terraces without overlying sediment correlate with the UMT terrace (Bibus, 1980). Owing to the predominance of brown hornblende in the heavymineral spectrum, the UMT can be correlated with the loess of unit G in the section at Ka¨rlich (Boenigk and Frechen, 1998, 2001b). Tephra horizons intercalated in the loess deposits of unit H have been dated by 40 Ar/39Ar to about 450 ka (Schmincke, 1994), indicating a slightly older deposition age of the sediment from below UMT. We do not accept the reasoning for further subdivision of UMT as previously suggested by Bibus (1980) because only one exposure with sediments was found and the likely tectonic displacement makes reconstruction difficult. The UMT is considered to be equivalent to the ‘‘obere Mittelterrasse’’ of Mordziol (1912). 3.3.2. MMT The deposits from below MMT are up to 30 m thick and exposed in a gravel pit at Ariendorf with a top at 130 m asl. The base of the terrace deposit is at about 100 m asl, the present river level is at an elevation of about 52 m asl (Kaiser, 1961; Brunnacker et al., 1975; Bibus, 1980; Boenigk and Frechen, 1997). This terrace deposit correlates with MIS 12 on the basis of the overlying loess/palaeosol sequence and the tephra layers at the top of the terrace gravel and intercalated in the loess/palaeosol sequence (Boenigk and Frechen, 1998). 40 Ar/39Ar dating of the tephra at the top of the gravel yielded an age of 419718 ka (Fuhrmann, 1983) and about 490 ka (Bogaard and Schmincke, 1990). The heavy mineral content of the terrace sediments is, in contrast to those of UMT, dominated by clinopyroxene from the renewed Eifel volcanism. Therefore, these deposits correlate with unit H of the sediment sequence in the section at Ka¨rlich. Radiometric ages of about 45278 and 45377 ka and about 480 ka were determined for the upper and lower pumice tephra layers of Unit H in the Ka¨rlich section, respectively (Fuhrmann, 1983; Bogaard and Schmincke, 1990; Schmincke, 1994). MMT is a well-developed terrace in the Lower Middle Rhine Valley. The MMT is considered to be equivalent to the ‘‘Apollinaris Terrasse’’ sensu Kaiser (1903) and the ‘‘Mittlere Mittelterrasse’’ sensu Gurlitt (1949). There is some evidence for a subdivision of the MMT. In the lower Middle Rhine valley at the section at Arienheller (northing 559,791, easting 259,479) the base and top of the gravel body is at 83 and 115 m asl, respectively. The present river is at 53 m asl. Therefore, MMT can be subdivided into a MMT1 at 78 m

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(Ariendorf) and an MMT2 at 62 m (Arienheller) above the present river. 3.3.3. LMT LMT is the ‘‘Lower Middle Terrace’’ (‘‘Untere Mittelterrasse’’). This terrace is well developed between the Lower Terrace and the valley slope. The gravel body is about 20 m thick. The heavy-mineral spectrum is dominated by clinopyroxene, similar to that of MMT. The LMT is well-exposed in the Remagen-Schwalbenberg section (northing: 560,356, easting: 258,823). The fluvial terrace deposits are overlain by a loess/palaeosol sequence considered to belong to the Upper Pleistocene (Schirmer, 1990b). The LMT is considered to be from the penultimate glaciation (Schirmer, 1990b). At this site, the base and top are at 58 m and at about 79 m asl, respectively. The present river has an elevation of 51 m asl. At the section at Koblenz-Metternich (northing: 558,110, easting: 339,720), a Lower Middle Terrace of the river Moselle is exposed about 5 km from the confluence of the Rhine and the Moselle. The top and the base of the terrace deposit are at 79 m and at about 64 m asl, respectively. The present level of the River Rhine has an elevation of 61 m asl (Boenigk et al., 1994). This terrace is assessed to be an equivalent of LMT; the fluvial sediments are overlain by Upper Pleistocene loess and intercalated with several palaeosols (Boenigk and Frechen, 2001a, b). Schirmer (1990c) described the LMT with the top of the gravel body at 75 m asl near Neuwied. The Rhine is at an altitude of 56 m asl. The terrace is well-exposed downstream until Bad Ho¨nningen. There is evidence for a subdivision of the LMT into an LMT1 at 30 m (area near Remagen and Linz) and an LMT2 at 20 m (area between Neuwied and Bad Ho¨nningen) above the present river. 3.4. Lower Terraces The youngest deposits are those of the Lower Terraces and the Holocene sediments. The Lower Terrace can be subdivided into two terraces: Younger LT

Younger Lower Terrace

Older LT

Older Lower Terrace

(‘‘Ju¨ngere Niederterrasse’’), Younger Dryas (‘‘A¨ltere Niederterrasse’’), Pleniglacial, MIS 2

The thickness of the Older LT sediments ranges from 39 to 63 m asl in the section at Sinzig-Remagen. The present-day river level is at an elevation of about 51 m asl. The Older Lower Terrace is of Pleniglacial deposition age and is overlain by a widespread layer of tephra, the Laacher See tephra, which provides an excellent tephrochronological marker horizon. The surface of the

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Younger LT—the terrace deposits correlate with the Younger Dryas—is about 2 m lower than that of the Older LT in the study area. The Younger LT sediments contain reworked Laacher See tephra. Independent age constraints are available for this tephra horizon by several dating methods: a. 12,860 calendar years BP by varve chronology and calibrated 14C-AMS data (A. Brauer, pers. com.), b. 12,9007560 calendar years BP by 40Ar/39Ar singlegrain dating (Bogaard, 1995), c. o13,500 calendar years BP by luminescence dating (Frechen, 1992). The fluvial sediments of Younger LT are in general underlain by those of Older LT. Schirmer (1990c) distinguishes a third lower terrace in the Neuwied basin, which is considered to be older than the Older Lower Terrace. 3.5. Holocene The youngest terrace including the floodplain deposits of the River Rhine was formed during the Holocene. The terrace in the sections at Bad Ho¨ningen and SinzigRemagen is at 59 and at 57 m asl, respectively. Jungbluth (1918) described this terrace as an island terrace (‘‘Inselterrasse’’). The sediment is fine-grained, silty to sandy. This terrace does not have the same significance as the LT because it is not isolated from present-day river activity. The same interpretation can be applied to the Holocene ‘‘floodplain terraces’’ of Schirmer (1995), which are not separated by definite steps.

4. Lower Rhine area The Lower Rhine area (Lower Rhine embayment) (Fig. 5) is an area of subsidence, block faulting and tilting within the Rhenish Massif and opens towards the northwest into the southern North Sea basin. It is part of the European rift system in Western Europe (Cloetingh et al., 2005). There were three main areas of subsidence in the Lower Rhine region: the Rur graben, the Erft basin and the Venlo graben. There were also two areas in which the subsidence was less than in the other three areas: the Cologne and Krefeld blocks. During deposition, each of the areas of subsidence was tilted to the northeast, resulting in a higher zone in the southwest of each area with a reduced sediment thickness due to erosion and sediment transport into the area of greater subsidence in the northeast with a greater sediment thickness. The higher ground forms a number of horsts—the Ville horst west of Cologne, the Viersen horst west of Krefeld and

Fig. 5. Geological map showing the distribution of pre-Quaternary and Pleistocene sediments in the Lower Rhine area and sections of interest. Abbreviations: A Alsta¨dten, Be Bergheim, Br Bru¨hl, Er Erkelenz, Fr Frechen, Fri Frimmersdorf, Ga Garzweiler, Gl Glehn, Go Gohr, Gr Grevenbroich, Ho Holzweiler, Ju¨ Ju¨lich, Li Lingsfort, P Ko¨ln-Porz, Roe Roermond.

the Jackerath and Bru¨ggen-Erkelenz horsts further to the west. Erosion and accumulation have alternated in the two areas of less subsidence: the Cologne and Krefeld blocks, since the Middle Pleistocene, resulting in the formation of terrace steps which are best developed where the Ville and the Viersen horsts form the western side of the Rhine valley. In the Erft basin in the centre of the Lower Rhine embayment, the Tertiary and Quaternary have a combined thickness of 600 m. This sequence is partly exposed in the large lignite mines like Hambach, Garzweiler and Fortuna, providing detailed information about the fluvial regime of the Rhine system during the Tertiary and Quaternary (Boenigk, 1978a, 1979). Fluvial sediments were deposited from the Late Miocene to Middle Pleistocene (Boenigk, 1978a, 1979). The deposition history became more complex, owing to intensive block faulting after the Pliocene. The western part of the Lower Rhine embayment, especially the Rhine/Maas system in the Netherlands, has been studied in detail by van den Berg (1995) and Tebbens (1999). The Cenozoic sediments in this area attain a maximum thickness of 1200 m and provide an excellent terrestrial archive. The fluvial record in the Lower Rhine embayment is more complete than that in the Middle Rhine area owing to subsidence. The Early and the Middle Miocene

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sediments were deposited by the pre-Rhine fluvial system. At that time the catchment area was mainly the Rhenish Massif. The depositional environment of the Lower Rhine embayment was marine in the north and lacustrine and fluvial in the south, where extensive lignite deposits also formed. During the Late Miocene and Pliocene, Kieseloolite gravel up to 280 m thick was deposited in large fans. The fluvial sediments are intercalated with lacustrine sediments, mainly clay of Brunssumian and Reuverian type. Some minor marine transgressions took place, with deposition of only thin sediment layers (Boenigk, 1979). The heavy-mineral spectrum of these deposits is dominated by stable heavy minerals like zircon, tourmaline, staurolite, rutile and anatase. 4.1. Reuver Clay The Reuver Clay is an important stratigraphic marker horizon, as evidenced by sedimentological, petrographic and palaeontological evidence. The top of the clay forms the boundary between the Pliocene and Pleistocene in the study area (Fig. 2). The Pliocene/Pleistocene boundary in the Lower Rhine embayment is defined as being at the top of the Reuver Clay on the basis of the pollen spectra—with Sequoia, Taxodium and Nyssa as typical Tertiary genera (Fig. 2). A palaeomagnetic boundary in the ‘‘Reuverian C’’ correlates with the Gauss/Matuyama boundary (Boenigk et al., 1974a, b; Brunnacker and Boenigk, 1976). This clay contains mammal bones and teeth, which provide a correlation with Mammal Zones NM16a and NM16b of the Neogene terrestrial mammal stratigraphy (Kolfschoten et al., 1998; Mo¨rs et al., 1998). The Reuver Clay is characterized by a significant change in the petrographic content. The first appearance

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of Alpine material in Rhine sediment is observed in the Reuverian B sediments, as evidenced by the palynological remains which they contain (Boenigk, 1970, 1976, 1978b). 4.1.1. Pleistocene Pleistocene fluvial deposits overlie the Reuver Clay (Reuverian A–C) in normal stratigraphic sequence. Although the upper part of this sequence is referred to as ‘‘Upper Terrace’’ (UT2 and 3), morphological terraces or terrace steps have not formed. The sediment sequence can be subdivided as shown in Table 2. More recently, a lithostratographical subdivision has been created (Mulder et al., 2003; Weerts et al., 2003) to avoid confusion between lithostratigraphic and biostratigraphic results. Sediments from the River Rhine are defined as ‘‘Formatie van Waalre’’; sediments from the River Maas were defined as ‘‘Formatie van Beegden’’; and terrestrial sediments of local origin were defined as ‘‘Formatie van Stramproy’’. These new definitions cannot be applied to the fluvial sequences in Germany and therefore are not applied in this review paper. Tables 2 and 3 include a new interpretation of the Tegelen Formation, which concerns the deposits between the Koo-Formation and the Sterksel Formation. 4.2. Tegelen formation The type region of the Tegelen Formation is in the area of the Venlo graben (Fig. 5), the ‘‘Tegelen’’ type section is between east of the Dutch village of Tegelen and the Dutch/German border. The Tegelen Formation is defined on the basis of petrographical and lithological characteristics. These sediments were deposited by the River Rhine, as evidenced by their heavy-mineral spectra, dominated by garnet, epidote and green

Table 2 Stratigraphy of the lower Rhine area for the period ranging from the Reuverian to the Cromerian including type localities and references Stratigraphy of the lower Rhine area Reuverian—Cromerian

Type localities

References

Upper Terrace 4

UT 4

Alsta¨dten

Quitzow (1956) Kowalczyk (1969) Schnu¨tgen (1974)

Upper Terraces 1–3

UT 3 UT 2 UT 1

Frechen

Burghardt and Brunnacker (1974) Schnu¨tgen (1974) Boenigk (1978a)

Holzweiler formation

Holzweiler Garzweiler

Boenigk (1978a, 2001)

Tegelen formation

Tegelen

Dubois (1905) Zagwijn (1960) Zonneveld (1947)

Reuver clay Kieseloolite formation

Reuver

Reid and Reid (1915) Florschu¨tz and Someren (1948) Zagwijn (1960)

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Table 3 Stratigraphy of the Lower Rhine area from the Reuver clay to the upper terraces MP

Southern lower Rhine Erft Basin

Central lower Rhine Rur graben Jackerath horst

Northwestern lower Rhine Venlo graben, Bru¨ggen-Erkelenz horst

R

Clay E Gravel UT1 Clay D Gravel d Clay C Gravel c Clay B2 Gravel b2

Upper Terraces (Rhine sediments)

Upper Terraces (Rhine sediments)

Frechen Interglacial I–III (Rhine deposits)

Holzweiler Formation (Maas deposits)

Kedichem Formation (deposits of other rivers)

R N

Clay B1 Gravel b1

Fortuna Interglacial (Rhine deposits/reworked sediment)

Tegelen Formation (Rhine deposits/reworked sediment)

Tegelen Formation (Rhine deposits/reworked sediment)

R N

Clay A2 Clay A1+A2

N R R

Reuver clay

MP: magnetic polarity, N: normal polarity, R: reverse polarity.

hornblende (Zonneveld, 1947). According to the petrographic and lithologic definition of the Tegelen Formation, it begins in the Reuver Clay (Fig. 2). Because the term ‘‘Tegelen’’ is considered to apply to Pleistocene units, the following subdivision is made here: Tegelen Formation sensu strictu Tegelen Formation Oebel Beds The Oebel beds are defined as the lower part of the Tegelen Formation with floral and faunal evidence of Pliocene age (Fig. 7). The Tegelen Formation sensu strictu is defined as upper part of the Tegelen Formation with floral and faunal remains indicating a Pleistocene age. 4.2.1. Oebel beds The lithology of the sediments overlying the Kieseloolite Formation in the upper part of the Reuverian does not differ from the lithology of the Tegelen Formation (Boenigk, 1970). Whether the sediments are Tertiary (i.e., Reuverian) or Pleistocene (i.e., Pretiglian and Tiglian) can be determined only on the basis of the flora and fauna in them. If there is no fossil record, no distinction is possible. In order to give the Tertiary sediments a name that is not associated with the Pleistocene, they were given the name ‘‘Horrem Beds’’ (Boenigk, 1982), after a village near the type section in the Frechen and Fortuna lignite mines west of Cologne. These pits have been filled and the exposures are no longer accessible. Klostermann (1992) proposed the name ‘‘Boisheim Beds’’ on the basis of sediments near Bru¨ggen. This name is not acceptable for reasons given in Boenigk

(1998) because the name ‘‘Boisheim Beds’’ is given to sediments that are equivalent to the Reuverian C, confusing a lithostratigraphic unit with a palynological unit. The boundaries are not identical (Fig. 2). Moreover, the type section is in a borehole and not easily accessible. Thus, the name ‘‘Oebel Beds’’ is introduced here, defined as sediments that are younger than the Kieseloolite Formation and which belong to the Tegelen Formation on the basis of their sedimentological characteristics, to the Reuverian B and/or C on the basis of palynological evidence (Zagwijn, 1960), and to Zone MN 16 on the basis of mammal fossil evidence. The lower boundary is defined by the first appearance of the heavy minerals garnet, epidote, and green hornblende from the Alpine region. The fine-grained fraction is calcareous and mica-rich. This boundary lies within the Reuverian B (Zagwijn, 1960, Boenigk, 1970). The Pleistocene portion of the Tegelen Formation is designated ‘‘Tegelen Formation s.s.’’. If palynological evidence is not available because the exposure contains no fossils, the sediment is assigned to the Tegelen Formation without differentiation. The type section is the exposure in the clay pit near Bru¨ggen-Oebel. The Oebel Beds near Bru¨ggen correspond to the Clay II sensu Boenigk (1970), near the Ville horst to the Clay A2 sensu Boenigk et al. (1972), and in the Belfeld area to the Clay III with underlying sands sensu Boenigk (1970). 4.2.2. Tegelen formation sensu strictu The sand and gravel deposits in the Tegelen section are overlain by a clay horizon. The ‘‘Tegelen Clay’’ is palynologically assigned to the Tiglian (Zagwijn, 1963) and palaeontologically assigned to NM17 Zone, following the small mammal stratigraphy (Tesakov, 1998). In the Rur graben area, sediments that correlate with the

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Tegelen Formation s.s. show an alternating sequence of sediments derived from the source areas of the rivers Maas and Rhine. In the Erft basin, lithological units 12 and 13 of Schneider and Thiele (1965) and Gravel b1 and Clay B1 of this study (‘‘Fortuna Interglacial’’, Table 3) are likely to be equivalents of the Tegelen Formation in the Venlo graben (Boenigk et al., 1974a, b; Boenigk, 1978a; Urban, 1978). Palynological analysis of Clay B1 by Urban (1978) yielded pollen spectra with insufficient evidence for climatic oscillations. Sedimentological and petrographic evidence indicate that the Clay B1 layer is most likely only part of unit 13 (sensu Schneider and Thiele, 1965).

4.3. Holzweiler formation In the central part of the Lower Rhine embayment on the Jackerath horst (Fig. 5), the Tegelen Formation is overlain by the Holzweiler Formation (Boenigk, 2001). These sediments are very coarse gravel intercalated with silt and sand horizons derived from the source area of the River Maas flowing from the SW (Boenigk, 1978a, 2001). Due to numerous coarse blocks or boulders and cryoturbation features at the upper boundary of the unit, deposition of the gravel during a glacial stage is most likely. However, the intercalated clays have not been investigated palynologically or palaeomagnetically. The Holzweiler Formation correlates with the Kedichem Formation of the Dutch stratigraphy or parts of it in the Venlo graben. The sediments of the Holzweiler Formation, which are related to the eastern Maas, correlate with older sediments including the Simpelveld terrace sensu Pru¨fert (1994) (cf. van den Berg and van Hoof, 2001). In the southern Lower Rhine embayment, the equivalent of these deposits consist of alternating clay and gravel layers exposed in the Frechen open cast mine. These clay and gravel beds are considered to have been deposited during temperate and cold intervals, respectively. The sediments deposited during the glacial intervals are denoted by ‘‘Gravel b2’’, ‘‘Gravel c’’, and ‘‘Gravel d’’ from bottom to top. Each of these gravel layers is overlain by a clay horizon, named ‘‘Clay B2’’, ‘‘Clay C’’ and ‘‘Clay D’’; ‘‘Gravel b2’’ is overlain by ‘‘Clay B2’’, etc. These clay horizons correlate with Lower Pleistocene temperate climate periods, called the ‘‘Frechen Interglacial Complex I–III’’ ( ¼ ‘‘Clay B2’’, ‘‘Clay C’’ and ‘‘Clay D’’) (Table 2). The chronostratigraphy of these Lower Pleistocene deposits is based on floral and palaeomagnetic evidence. To summarize: in the Lower Rhine embayment, there are three areas with different stratigraphic sequences of Lower Pleistocene age (Table 3). These sequences are difficult to correlate. However, in all three areas, the Reuver Clay can be identified at the base of the

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sequence, and the Upper Terrace can be identified at the top. In the eastern part of the Lower Rhine embayment, remains of Pleistocene terraces—Ho¨sel terrace and Dru¨fel terrace—were described by Breddin (1928) and Kaiser (1961). The stratigraphic interpretation of these terraces is difficult, but a Lower Pleistocene age is likely. The subsidence of the Lower Rhine embayment resulted in a stacked stratigraphic sequence and lateral erosion of the Rhine River forming the terraces on the slope of the Rhenish Massif. 4.4. Upper Terraces The term ‘‘Upper Terraces (UT)’’ is also applied to the fluvial record in the Lower Rhine area, although some periods are not recorded by sediments. The UT2-3 and the UT4 can be followed from the Middle Rhine area into the Lower Rhine area. However, in the Lower Rhine area, UT1 is not a terrace according to the definition but a buried sediment stack. UT3 is a gravel body, which accumulated in a channel cut into the gravel/sand body below. UT3 is at exactly the same level as UT2. In the Netherlands, the Sterksel Formation includes all Upper Terraces. The sediments from below the Upper Terraces are characterized by the ‘‘Rhenish’’ mineral assemblage including garnet, epidote, alterite and green hornblende. The different percentage of these heavy minerals enables a differentiation and correlation of these deposits to the sediments from below UT1, UT2 and UT3. The heavy mineral spectrum of the Upper Terrace sediments indicates that there was a complete restructuring of the drainage pattern in the Lower Rhine embayment. Initially the sediment supply was from SW to NE from the river Maas (Holzweiler Formation). Afterwards the fluvial system returned to an SE to NW drainage direction with a sediment supply only from the River Rhine in the whole Lower Rhine area (Boenigk, 2001). 4.4.1. Upper Terrace 1 The fluvial deposits are called UT1 and consist of at least eight coarse-grained/fine-grained cycles rich in blocks and boulders near the base. The sequence is overlain by ‘‘Clay E’’ (Brunnacker and Boenigk, 1983), which correlates with the Lower Pleistocene because of its likely reversed magnetic polarity (Boenigk, 1978a) and therefore represents the uppermost part of the Matuyama chron. In the Frechen brown coal pit, the stratigraphic equivalent of ‘‘Clay E’’ is represented by a weathering horizon of interglacial origin (Boenigk, 1978a). The sediments correlate with the Sterksel Mineral Zone and the Woensel Mineral Zone of the Sterksel Formation in the Netherlands. In the southern

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Lower Rhine embayment, it is difficult to estimate the duration of the deposition period of these sediments. Temperate climate deposits found in the Waardenburg core (Zagwijn, 1996) indicate a hiatus in normal deposition between UT1 and UT2. 4.4.2. Upper Terrace 2 The Upper Terrace 2 (UT2) forms the first and laterally most extensive terrace in the Lower Rhine basin. Detailed sedimentological studies are available for the sediments from below UT2 (Boenigk, 1978a, 1995). These terrace deposits can be correlated on morphological, sedimentary and petrographic (high content of alterite and saussurite) evidence with the Weert zone of the Sterksel Formation in the Netherlands and therefore correlates with Glacial B of the Cromerian Complex (Boenigk, 1978b; Zagwijn, 1985). Although there is evidence for this correlation, it is likely that this interpretation applies to the terrace only. The gravel body from below UT2 ( ¼ Ju¨ngere Hauptterrasse) forms a massive sediment accumulation. In the middle part of the Lower Rhine embayment between Geilenkirchen and Du¨sseldorf, these deposits extend more than 60 km in east—west direction, with an average thickness of 10 m. It is unlikely that this sediment mass was only deposited in parts of Glacial B of the Cromerian complex. It is more likely that these sediments were deposited during an extended period of time in which there was tectonic inactivity with infilling the basin including lateral erosion and re-deposition of sediments. 4.4.3. Upper Terrace 3 The Upper Terrace 3 (UT3) consists of well-bedded fluvial sediments, layers of large boulders, cryoturbation features and intra-formational ice-wedge casts, indicating cold climatic conditions (Brunnacker et al., 1978). The UT3 is exposed in erosional channels within UT2 only (Boenigk, 1978b) and so demonstrating the reactivation of tectonic uplift in the Lower Rhine basin followed by an incision of the Rhine into the UT2. The first occurrence of few, but typical, heavy minerals from the Eifel volcanism is found in the sediments from below UT3. This terrace can be correlated with the Rosmalen zone of the Sterksel Formation in the Netherlands (Boenigk, 1978a, 1990, 1995; Zagwijn, 1985), as indicated by its morphological position and heavymineral content. There is no evidence of reverse magnetization in the UT3 sediments. The reverse magnetic polarity, as described for these sediments by Boenigk (1978a), was based on the correlation with the sediment record from the section at Ka¨rlich, where reversed magnetization was determined. However, this correlation is no longer valid because the gravel in the Ka¨rlich section is found to correlate with UT1 (Hoselmann, 1994). Consequently, the correlation of

UT3 with the Matuyama chron is unlikely. Furthermore, the correlation of UT3 and UT2 with the Rosmalen zone and the Weert zone of the Sterksel Formation, respectively, is striking owing to the heavy mineral content (Boenigk, 1978a, Zagwijn, 1985). The UT3 terrace deposits are overlain by a temperate climate palaeosol (Schnu¨tgen et al., 1975). Due to increasing tectonic activity during the Middle Pleistocene, including subsidence in part of the area and relative uplift in other parts, the Rhine changed its course to east of Ville horst. 4.4.4. Upper Terrace 4 Quitzow (1956) described an ‘‘Unterstufe der ju¨ngeren Hauptterrasse’’, the Upper Terrace 4 (UT4) in the southern Lower Rhine. Kowalczyk (1969) and Schnu¨tgen et al. (1975) studied this terrace in several sections. This terrace is about 10 m lower than the UT3. In the opencast mine Fortuna near Niederaussem (northing: 565,155, easting: 254,405) for example, the terrace deposits are 6–8 m thick. Base and surface of the terrace sediments are at 80 m and 88 m asl, respectively. It represents a morphological transition to the Middle Terraces. Petrographically the sediment belongs to the Upper Terraces, but morphologically the sediments from below UT 4 are often in the same level as those of MT1 (Fig. 8; Kowalczyk, 1969). 4.5. Middle Terraces Our subdivision of the Middle Terraces follows the interpretation of terraces MT I-IV from Brunnacker et al. (1978). Klostermann (1992) subdivided the Middle Terraces on the basis of gravel bodies. However, in the northwestern Lower Rhine area only a remnant terrace staircase is exposed, and so the definition as landforms is applied here (Jansen, 1995, 2001; Klostermann, 1997). Our study is limited to the terrace sequence south of Du¨sseldorf. MT IIa sensu Brunnacker et al. (1978) is, for example, not a terrace but an older gravel body from below MT II. In contrast to this subdivision sensu Brunnacker et al. (1978), the uMT3 (sensu Klostermann, 1992) is only a gravel body. The subdivision of terraces and terrace bodies into subunits ‘‘a’’ and ‘‘b’’ has to be rejected because the chronological position of the gravel bodies, especially from below MT III and MT IV, is not clear, and the subunits are not in agreement with the definition of a terrace in this paper. But the differentiation of the terrace surfaces, which was already described in Brunnacker et al. (1978), will be applied in more detail (Table 4, Fig. 6). The Middle Terrace complex forms a terrace staircase in the southern Lower Rhine embayment around Cologne (Fig. 6), as described by Brunnacker et al. (1978). The most complete sequence of the Middle

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Table 4 Middle terrace staircase of the southern central lower Rhine basin. Elevations are for the type localities in the area around Grevenbroich and related to the modern Rhine level Terraces

Localities

Brunnacker et al. (1978)

This study

Near Grevenbroich

[m]

oNT

oNT

Gohr: Top Base

7 23

MT IV

MT III

MT 6

MT5

MT 4

MT II

MT 3

MT 2

MT I

MT 1

Dyck: Top Top Interglacial ‘‘Rinnenschotter’’ Base Frimmersdorf: Top Top Interglacial Base

13 4

20 13 2

25 7/2

Broich: Top Base

31 7

Niederaussem: Top Top interglacial Base

33 29 13

Sinsteden: Top Base

44 34

4.5.1. Middle Terrace 1 Middle Terrace 1 (Middle Terrace I sensu Brunnacker et al., 1976) is the oldest and uppermost Middle Terrace in the southern Lower Rhine area. There are only few remains of the MT1. The sediment from below the MT1 has a predominance of brown hornblende in the heavymineral spectrum. In the north of Cologne, the base and surface of the sediments from below the MT1 are at about 70 and 80 m asl, respectively. Cold climate indicators are often found in the sediments from below MT1 (Brunnacker et al., 1978). In contrast to the interpretation of Klostermann (1992), who suggested a correlation of the ‘‘Frimmersdorf Interglacial’’ (sensu Brelie et al., 1959) with sediments from below MT1, the clay of the ‘‘Frimmersdorf Interglacial’’ correlates with

Bru¨hl: Top Base

[m]

15 1

19

Gohr: Top Base

Terrace complex is exposed in the type area on the west side of the Rhine valley between Cologne and Grevenbroich near Du¨sseldorf, where the Middle Terraces can be subdivided into four units with the oldest designated as MT I and the youngest as MT IV (sensu Brunnacker et al., 1976).

South of Cologne

Porz: Top Top interglacial ‘‘Rinnenschotter’’ Base

North of Grevenbroich

[m]

Weetze: Top Top Moers Interglacial

5 0

Krefeld: Top Top Fluvioglacial Top ‘‘Rinnenschotter’’ Base

16 2 11 21

23 4 19

sediments from below MT5 (see Table 4 and Fig. 6). This means that the Middle Terrace 1 cannot be subdivided into three Upper Middle Terraces. 4.5.2. Middle Terrace 2 and 3 Following the interpretation of Brunnacker et al. (1978) MT II can be subdivided into a higher level (MT2) and a lower level (MT3) (Fig. 6). The sediment from below MT2 can be subdivided into two gravel bodies, separated by an discontinuous clay horizon of temperate-climate origin. This clay horizon is called ‘‘Niederaussem Interglacial’’ and exposed in the Fortuna opencast mine (Brunnacker et al., 1978; Boenigk, 1995; northing: 565,161, easting: 254,450). Brunnacker et al. (1978) and Klostermann (1992) correlated the ‘‘Niederaussem Interglacial’’ with the ‘‘Frimmersdorf Interglacial’’, exposed at the Frimmersdorf open cast mine (now ‘‘Garzweiler-Nord’’). This interpretation is incorrect because the difference in elevation is more than 17 m between the two outcrops. The present difference in the level of the Rhine between the locations of these two outcrops is only about 2 m

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Fig. 6. Idealized sketch of the terrace staircase in the southern Lower Rhine embayment around Cologne. The altitudes are related to the region south of Grevenbroich, except the sequence at section P (Ko¨ln-Portz). The Lower Middle Terrace and the ‘‘Rinnenschotter’’ from this section are altitude-corrected for the sequence of this figure.

(Boenigk, 1995). The Frimmersdorf Interglacial is interbedded with a younger gravel accumulation and is therefore younger than the Niederaussem Interglacial. The gravel below the Niederaussem temperate climate deposits (‘‘Niederaussem Interglacial’’) is characterized by a high content of brown hornblende, whereas the gravel on top of the clay has a predominance of clinopyroxene in its heavy-mineral spectrum. Near the village of Niederaussem, the base and surface of the terrace deposit are at about 50 and 70 m asl, respectively. In the west of Broich the MT3 is exposed. The top of the gravel body is at 64 m asl (Fig. 6). MT3 covers a gravel body with an erosional base at 40 m asl. Pumice is intercalated into the gravel deposits about 8 m below the surface. Owing to lateral erosion the MT3 overlaps the previously described gravel body and older gravel deposits (Fig. 6). 4.5.3. Middle Terrace 4 and 5 The MT III sensu Brunnacker et al. (1978) is subdivided into two terraces: an upper terrace at about 58 m asl (MT4) and a lower terrace at about 53 m asl (MT5). The sediments from below the Middle Terraces 4 and 5 are also characterized by a high pyroxene content

in the heavy-mineral spectrum (Brunnacker et al., 1978). The sediments from below MT5 can be subdivided into two gravel deposits, separated by a temperate climate clay horizon called ‘‘Frimmersdorf Interglacial’’ (northing: 566,140, easting: 253,840; Brelie et al., 1959), the upper part of which is rich in peat (Brunnacker et al., 1978; Klostermann, 1992; Boenigk, 1995) (Fig. 6). This terrace deposit is completely exposed in the Garzweiler Nord (Frimmersdorf, Fig. 5) brown coal pit, where the base and surface of this terrace deposit are at about 35 and 53 m asl, respectively. In the west of the villages Gohr and Broich, the MT4 is exposed at 58 m asl. The elevation of the base of the terrace sediments following Brunnacker et al. (1978) rises from 38 m near the village of Broich (northing: 566,118, easting: 255,028) to 45 m asl near the village of Gohr (northing: 566,555, easting: 254,985). Results from sediment cores in that area indicate that the base of the gravel body is at about 40 m asl. Gravels from below the MT4 near Broich are intercalated with several thin layers of pumice described by Paas (1961), Brunnacker et al. (1978) and more recently found by the authors at about 8 m below surface. A more detailed investigation showed that the pumice layers are exposed until about 63.5 m asl and therefore are intercalated into

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sediments from below MT3. The pumice enables a correlation with the Eifel volcanism and the terrace stratigraphy from the Middle Rhine area. MT4 overlaps older sediments owing to lateral erosion (Fig. 6). In the area around Broich and Gohr, the MT4 and MT5 are called Lower Middle Terrace by Quitzow (1956) or Lower Middle Terrace 1 by Klostermann (1992). The Lower Middle Terrace, following the interpretation of Klostermann (1985, 1992), is subdivided into five lower middle terraces. The stratigraphic units listed in Table 5 are gravel bodies. The ‘‘uMT1’’ sensu Klostermann is an equivalent of sediments from below MT5 of this study. The ‘‘a¨uMT2’’and ‘‘juMT2’’ exposed in the northwest of Cologne (Klostermann, 1992) are an equivalent of the ‘‘Krefelder Mittelterrasse’’ in the vicinity of Krefeld (Winter, 1968) or the sediments from below MT6 of this study. The ‘‘uMT3’’ sensu Klostermann (1992) is a glaciofluvial gravel horizon equivalent to the fluvial deposits from below MT6 (Maarleveld, 1956) (Fig. 6). South of Cologne, on the right bank of the Rhine river in the area of the Cologne-Bonn airport and in the north of this airport, a terrace is exposed at 64 m asl, which is 23 m above the present river. Kaiser (1961) named this terrace ‘‘untere Mittelterrasse’’. This terrace can be correlated with the MT5 further north owing to its altitude about 20 m above the present Rhine. The gravel body from below MT5 has a base at 22 m asl and can be subdivided by clay-rich deposits including peat with temperate climate flora at about 45 m asl, which is about 4 m above the present river. The gravel from below this interglacial horizon is defined as ‘‘Rinnenschotter’’ by Quitzow (1956), who believed that these gravels are an equivalent of the Middle Middle Terrace in the Middle Rhine area. Following Quitzow’s interpretation, Klostermann (1992) described this gravel as a separate terrace (Middle Middle Terrace). In this paper, this gravel body represents the lower part of the sediment accumulation from the deposits from below MT5.

4.5.4. Middle Terrace 6 The Middle Terrace 6 (MT IV sensu Brunnacker et al., 1976) can be distinguished from the older terraces by its morphological position. It is the lowest terrace of the Middle Terraces. North of Grevenbroich near the village of Glehn (Dyck core, northing: 566,790, easting: 253,913), Table 5 Subdivision of the Lower Middle Terraces sensu Klostermann (1985, 1992).

uMT 2

uMT 4 uMT 3  juMT 2 € auMT 2 uMT 1

Lower Middle Terrace 4 Lower Middle Terrace 3 Younger Lower Middle Terrace 2 Older Lower Middle Terrace 2

Youngest

Lower Middle Terrace 1

Oldest

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the base and top of MT6 are at about 12 m asl and at about 44 m asl, 13 m above the modern Rhine (Fig. 6), respectively. There is no significant difference between its heavy-mineral spectrum or gravel petrography and that of the older terrace deposits. The gravel from below MT6 south of Cologne is called ‘‘Lower Middle Terrace’’ by Quitzow (1956), north of Cologne it is called ‘‘Krefeld Middle Terrace’’ by Steeger (1925), and ‘‘Lower Middle Terrace 4’’ by Klostermann (1985) (Table 6). The gravel deposits from below the interglacial clay in the Dyck core (MT6) are called ‘‘Rinnenschotter’’ (gravel channel fill) by Quitzow (1956), like the gravel in the channels from below MT5. These gravel deposits are found only in channels. If these channels are not present, the base of gravel from below the MT6 is at a significantly higher level. For example, south of Cologne near Bru¨hl (northing: 563,652, easting: 256,442) the MT6 gravel has a top and base at 57 m and 43 m asl, respectively. The top level is in good agreement with the observations of the Dyck core near the village of Glehn (Table 4, Fig. 6), where the top of the terrace and the top of the interglacial was found at 44 m and 34 m asl, respectively. The top of the terrace deposit is at about 15 m (Bru¨hl) or at 13 m (Dyck) above the present river. Clay-rich sediment was found at 34 m asl; about 4 m above the present Rhine, in the Dyck sediment core. This is exactly the same altitude above the modern Rhine as the temperate climate sediments intercalated in the gravel from below MT5 at the Cologne-Bonn airport. There is debate whether the new deep erosional channels were formed and subsequently filled with gravel and younger organic deposits after MT 5 or whether this is the same temperate climate interval as described from below MT5 and subsequently covered by a younger gravel body. The gravel from below the MT6 is intercalated by several clay and peat layers of possibly different ages. They are of temperate climate origin and exposed at similar elevations (Fig. 6). As the floral and faunal remains do not provide a clear chronostratigraphic interpretation, various names have been given for these deposits in the German literature, for example ‘‘Krefeld Table 6 Stratigraphy of the Lower Terraces and the Holocene deposits north of Cologne Holocene deposits Younger LT Older LT Older LT deposits Moers Interglacial Older gravel

Top at 35 m asl, incised down to 8 m, present river at 33 m asl Top at 40 m asl, no base down to 12 m asl determined Top at 40 m asl, base at 10 m asl, present river at 33 m asl

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Beds’’ (Bertsch and Steeger, 1927), ‘‘Kempen Beds’’ (Bertsch et al., 1931), ‘‘Kempen-Krefeld Beds’’ (Kempf, 1966a, b), ‘‘Krefeld Interglacial’’ (Urban, 1980), ‘‘Holstein I and II’’ (Klostermann, 1989, 1992) and others. In this paper, we define the stratigraphic name ‘‘KempenKrefeld Beds’’ as a number of different temperate climate deposits above the ‘‘Rinnenschottern’’ either below MT5 or below MT6 that cannot be distinguished by terrace stratigraphy (Fig. 6). Between the late Elsterian and the early Saalian glaciation, there are a number of temperate climate episodes that may have interstadial or interglacial status. These are well-known from other parts of Europe, for example the Scho¨ningen site in Lower Saxony (Urban, 1991; Thieme et al., 1995) and Britain (Bridgland, 1994). There is evidence that the complex terrace sediment sequence in the Lower Rhine area is the result of climate change. However, it has not been possible to establish a reliable terrace stratigraphy for this part of the sequence in the Lower Rhine area. Differences in pebble content and heavy-mineral spectra were caused by reworking and thus cannot be used for correlation. Pollen analysis is also stratigraphically ambiguous. To summarize: there is no reliable evidence for the detailed subdivision of the ‘‘Lower Middle Terrace’’ proposed by Klostermann (1992). It is important to mention the occurrence of glaciofluvial gravel including Nordic pebbles stratigraphically between the ‘‘Rinnenschottern’’ or the Kempen-Krefeld beds and the gravel from below the MT6 (Fig. 6). Schirmer (1995) proposed an ‘‘MT5’’ younger than MT6 of our study. Unfortunately, no information was provided about the location and type section. 4.6. Lower Terraces The Lower Terraces can be subdivided into two units, an older Lower Terrace and a younger Lower Terrace. In the southern part of the Lower Rhine embayment, south of Cologne, the two terraces have a difference in elevation of about 2 m (Thoste, 1974). From Grevenbroich northwards, there is no difference in elevation between these two terrace levels. The German terms ‘‘a¨ltere Niederterrasse’’ and ‘‘ju¨ngere Niederterrasse’’ are equivalents of the Older Lower Terrace and the Younger Lower Terrace distinguished by Ahrens (1930). The terrace deposits of the Older Lower Terrace (Older LT) are intercalated with fine-grained sediments with temperate climate pollen and are thus subdivided into two gravel beds. These organic-rich deposits correlate with the Eemian (MIS 5e) and are named Moers Beds (‘‘Moerser Schichten’’, Bertsch and Steeger, 1927) or Weeze Beds or Weeze Interglacial (‘‘Weezer Schichten’’, Klostermann, 1992) in the German literature. The gravel on top of the interglacial sediments that form the terrace surface is considered to be of

Weichselian Pleniglacial age and covered by alluvial loam. This terrace is not covered by loess, in contrast to the Middle Terraces. The Younger LT contains pumice lapilli with an age of 12,860 calendar years, the time of the Laacher See eruption (Bogaard, 1995). The volcanic event is documented in the heavy-mineral spectrum of the Younger LT by elevated contents of sphene and brown hornblende. The Younger LT correlates with the Younger Dryas on the basis of cold climate indicators. Schirmer (1990d) described an ‘‘oldest’’ lower terrace near Hoisten, which he called NT1. However, this NT1 has the same altitude like the MT6 of our study and cannot be distinguished morphologically from the MT6. In the Lower Rhine Basin, no significant incision occurred since the deposition of the ‘‘Rinnenschoter’’. Thus, it is likely that there are older deposits (‘‘Rinnenschotter’’) below the Lower Terraces. 4.7. Holocene floodplain deposits The floodplain of the Rhine is lower than the Lower Terraces. The Holocene deposits occur as island-like sand and gravel deposits of different ages, separated by channels and oxbows. These terrace deposits are called ‘‘Reihenterrassen’’ or ‘‘floodplain terraces’’ (Schirmer, 1995). It is still under discussion whether periods of erosion and deposition can be distinguished regionally.

Discussion The fluvial sequences of the River Rhine include at least 16 major terrace units in both the Middle and Lower Rhine areas, providing a considerable record of Pliocene and Quaternary deposition. The terrace stratigraphy is based on differences in elevation of terrace deposits, biostratigraphy, heavy-mineral spectra, clast lithology, palaeomagnetism, dating of tephra horizons by the 40Ar/39Ar method, and luminescence dating of aeolian, fluvioaeolian and fluvial sediments. The following marker horizons can be correlated from the Middle Rhine through the Lower Rhine and to the Netherlands (Fig. 7): a. first presence of Alpine material in the Middle and Lower Rhine area, b. reactivation of the East Eifel volcanism, as evidenced in the heavy-mineral spectra. Owing to these two significant changes in petrography, the terrace sediments can be subdivided into three major units: 1. Sediments containing no Alpine material: the Vallendar Beds and the Kieseloolite Formation: The Kieseloolite terraces of Late Miocene and Pliocene age

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represent the highest terraces deposited by the early fluvial system in the Middle Rhine area. Due to its petrography and heavy-mineral spectrum, the sediments from below this terrace can be correlated with the ‘‘Kieseloolite Formation’’ in the Lower Rhine area and in the Netherlands. In these two areas, a typical Tertiary flora of Susterian to Reuverian age has been described (Zagwijn, 1960), including Sequoia, Taxodium, Nyssa and Liquidambar (Boenigk et al., 1974a, b), which are found in clay horizons intercalated in gravel. 2. Sediments containing Alpine material but no material from the eastern Eifel volcanism: The LPT and the Upper Terraces in the Middle Rhine area, and the Tegelen Formation and the Upper Terraces in the Lower Rhine area can be identified by the presence of Alpine material. Volcanic components from the eastern Eifel region are not present. The Holzweiler Formation, between the Tegelen Formation and the Upper Terrace deposits, is made up mainly of sediments from the Maas catchment. 3. Sediments with detritic material and minerals from both the Alps and the East Eifel Volcanic Field: These sediments are found in deposits of the Middle Terraces and Lower Terraces in both the Middle and Lower Rhine areas. Although this subdivision is clear, a detailed correlation of the sediments yields a major uncertainty. A more detailed correlation between the Tegelen Formation and the Holzweiler Formation along the Lower Rhine with the LPT along the Middle Rhine is not possible at present. A correlation of the younger terraces from the Middle and Lower Rhine is shown in Fig. 8. The UT deposits correspond on the basis of their stratigraphic position and lithological composition to the Sterksel Formation of the Dutch stratigraphy. Correlation of the UT is difficult in the Lower Rhine embayment owing to uplift and block faulting in the lower Middle Rhine area. The uplift rate increased significantly during part of the Middle Pleistocene, the time period ranging from 600 to 350 ka (Fig. 7) (Westaway, 2001). A correlation of the UT1 in the Middle and Lower Rhine areas is evidenced only by the petrographic similarity of the terrace sediments in the two areas (Hoselmann, 1994). Excellent evidence for correlation is available for the UT2 (‘‘Hauptterrasse 2’’) of the Lower Rhine embayment and the UT2/3 (‘‘Ju¨ngere Hauptterrasse’’) of the Middle Rhine area (Hoselmann, 1994). The two terraces form a single morphological unit. Owing to its morphology, and the predominance of saussurite (alterite) in the heavymineral association, the UT2 is considered to correlate with the Weert zone of the Sterksel Formation in the Netherlands (Boenigk, 1978a, 1990; Zagwijn, 1985). On the basis of the presence of few typically volcanic heavy

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minerals, the UT3 can be distinguished from the UT2 in the Lower Rhine and correlated with the Rosmalen zone in the Netherlands. In the Middle Rhine area, the UT3 is part of the UT2/3, as evidenced by its morphological position. The low content of volcanic minerals in the heavy mineral spectra cannot be used to separate the UT3 in the Middle Rhine area, because post-depositional translocation of these minerals occurred downward from the surface. UT4 is characterized by its petrography and a distinct terrace step in the Middle and Lower Rhine areas. The morphology is the most important criterion for distinguishing among the terraces of the Middle Terrace complex. However, the uppermost Middle Terraces in both areas, UMT along the Middle Rhine and MT1 along the Lower Rhine, correlate, as evidenced by their similar morphological position and the predominance of brown hornblende in their heavy-mineral spectra. Furthermore, this terrace can be correlated with the Lingsfort beds in the Netherlands by its heavy-mineral spectrum. The younger Middle Terraces are similar in petrographic content in both areas. The differences in the heavy-mineral spectra, determined by Klostermann (1992), are most likely due to sorting. In the Lower Rhine basin, MT2 to MT6 correlate with the Urk Formation in the Netherlands. The youngest Middle Terrace, LMT, of the Middle Rhine correlates with the Lower Middle Terrace of the Lower Rhine area on the basis of its morphologic position. In both areas, this terrace can probably be subdivided. In the Middle Rhine area and the Lower Rhine area, the top of these terrace deposits forms two distinct levels, LMT1 and LMT2 as well as MT5 and MT6, respectively, indicating a correlation of LMT1 with MT5 and LMT2 with MT6. Thus, a correlation between MMT1 and MT3 is most likely, as evidenced by their morphological position within the terrace stairs and the morphological position in relation to the drainage system of the River Rhine. It is not necessary to correlate the MMT (‘‘Mittlere Mittelterrasse’’) along the Middle Rhine with the ‘‘Rinnenschotter’’ sensu Quitzow (1956) along the Lower Rhine. The correlation of MMT1 and MT3 is supported by the presence of pumice in the fluvial sediments from both Lower and Middle Rhine area. In the East Eifel regions three main periods of pumice eruption are known: a. Rieden period (500–400 ka). b. Hu¨ttenberg period (250–170 ka). c. Laacher See eruption (12,860 a BP). The pumice of the Laacher See eruption is intermingled into the sediments of the Younger Lower

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Fig. 7. Summary of the chronostratigraphic interpretation and correlation of terraces in the Middle Rhine and Lower Rhine area with the Dutch stratigraphy.

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Fig. 8. Idealized sketch of the terraces between Koblenz and Du¨sseldorf. Line: terrace exposed as terrace stair; interrupted line: isolated exposures of terrace exposures. The base and top of the sediments from below UT 2/3 and UT 4 is presented. In the Lower Rhine embayment, base and top of the sediment from below UT 4 is shown by small circles. In the Neuwied basin, the gravel bodies from below the younger terraces are shown.

Terrace. At the section at Ariendorf, pumice from both the Rieden and Hu¨ttenberg periods are intercalated into the fluvial and aeolian sequences, respectively. The eruption ages were determined by 40Ar/39Ar dating. The correlation of the pumice from below MT3 with the Rieden period is in agreement with the morphological position in the terrace sequence. In addition, the large volume of pumice ejected during that eruption makes preservation in the sediments more likely. 40 Ar/39Ar dating yielded an age of 451–410 ka for MMT1 and MT3, and therefore a correlation with MIS 12. During the Middle and Upper Pleistocene, the lowermost erosion base was formed in the Lower Rhine area prior to the deposition of the ‘‘Rinnenschotter’’, the sediments from below MT5. The Drenthe glacial maximum of the Saalian glaciation is confirmed by glaciofluvial gravel below the Krefeld Middle Terrace gravels. The surface of the Krefeld Middle Terrace correlates with MT6 (Fig. 6). The Lower Terrace complex of the Rhine system can be subdivided into at least two terrace units by the presence of Laacher See tephra in the fluvial deposits. The sediment from below the Older LT is tephra-free, the Younger LT contains tephra, and both can be identified in the Middle and Lower Rhine areas. Independent age estimates by radiocarbon and luminescence dating methods are available for fluvio-aeolian deposits of the Pleniglacial (MIS 4-2) and Holocene Maas terraces in eastern Belgium and southeastern Netherlands (Frechen et al., 2001; Frechen and Berg, 2002). Because there is little independent age control of the terrace deposits of the Rhine system, it is difficult to correlate these terrestrial deposits with the marine magnetostratigraphy and marine oxygen isotope record

(Martinson et al., 1987; Heller and Evans, 1995). The following correlation is suggested: The Lower Pleistocene is represented by the Tegelen Formation and the Holzweiler Formation in the Lower Rhine area, which correlate with the Tiglian Formation and the Kedichem Formation, respectively, of the Dutch stratigraphy (Fig. 7). ‘‘Clay B1’’ (‘‘Fortuna Interglacial’’) correlates with the final part of the Olduvai about 1.67 Ma or slightly older [Olduvai: 1.87–1.67 Ma]. The two subsequent interglacial deposits, ‘‘Clay B2’’ and ‘‘Clay C’’, which are called ‘‘Frechen Interglacial Complex I and II’’, have reverse magnetization. The next palaeomagnetic marker horizon is found in ‘‘Clay D’’ (‘‘Frechen Interglacial III’’), which has a normal magnetization and thus most likely correlates with the Jaramillo event about 1 Ma ago, considered to be an equivalent of marine oxygen isotope stage (MIS) 23. The UT1 of the Lower Rhine embayment (Fig. 9) and the Middle Rhine area correlates with the end of the Matuyama chron (MIS 20-19) because of reverse magnetic polarity in the overlying ‘‘Clay E’’. The terrace units above ‘‘Clay E’’ show normal magnetic polarity and so these sediments are younger than 790 ka and the Matuyama chron. In the Ka¨rlich section, too, the gravel layers showing reverse magnetization are considered to correlate with UT1 (Ka¨rlich Unit B) and older deposits (Ka¨rlich Unit A). In the Middle Rhine area, Fromm (1987) determined reverse magnetization in sediments overlying a lower Pleistocene terrace of the Leilenkopf section (Fig. 3) and within sediments of UT1 in the Werlau section (Upper Middle Rhine). The UT2 and UT3 of the Lower Rhine correlate with the UT 2/3 of the Middle Rhine area and correlate with the Brunhes chron. The onset of volcanism in the eastern Eifel about 600 ka ago correlates with the beginning of deposition of

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Fig. 9. Correlation of Pleistocene terraces from the Lower and Middle Rhine area with the marine oxygen isotope stages (Bassinot et al., 1994).

the gravel from below UMT ( ¼ MT1), an equivalent of the Lingsfort Beds in the Netherlands. These sediments correlate with MIS 14. The volcanic activity of the West Eifel Volcanic Field started already about 800 ka ago, as evidenced at the section at Ka¨rlich owing to the presence of volcanic minerals in the upper part of the gravel of Ka¨rlich Unit B, which correlates to UT1. MT2 contains an intercalated clay horizon, named ‘‘Niederaussem Interglacial’’, in the Lower Rhine embayment. This clay horizon is most likely an equivalent of the palaeosol overlying Unit G in the loess/palaeosol sequence in the section at Ka¨rlich, which is considered to be an equivalent of MIS 13 (Boenigk and Frechen, 1998). However, an equivalent of MT2 is not known from the Middle Rhine area. The sediments from below MT3 and/or MMT1 correlate with the about 500–400-ka old Rieden period of the East Eifel volcanism owing to the intercalated tephra and therefore correlate with MIS 12. Both the Ariendorf Interglacial and the Ka¨rlich Interglacial 1

correlate most likely with MIS 11. The Frimmersdorf Interglacial sediments intercalated in MT4 (Lower Rhine) are considered to correlate with Ka¨rlich Interglacial 1. LMT2 in the Middle Rhine correlates with MIS 6 on the basis of the sediments overlying the terrace (Boenigk et al., 1994; Frechen et al., 1995). Along the lower Rhine, the fluvial sediments of MT5, which correlate with the LMT 1, are intercalated by interglacial deposits, the ‘‘Kempen-Krefeld Beds’’. Sediments with Nordic components from below the MT6 (Fig. 6) correlate with the Drenthe substage of the Saalian glaciation. Luminescence age estimates and the occurrence of reworked tephra from the Laacher See eruption at about 12,860 calendar years indicate that the upper part of the Lower Terrace complex correlates with MIS 2. Although only a few horizons are well dated, the fluvial sequences of the Rhine system provide an excellent considerable terrestrial record of the Pliocene

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and Pleistocene. However, independent age control by a multiple dating approach of the Middle and Lower Terrace sediments along the River Rhine will continue to be a challenging task for the future.

Acknowledgments Phil Gibbard, Chris Green, Meindert van den Berg and Jim Rose are thanked for their valuable comments on an early version of the manuscript. Frank Chambers, Terry Hill, Clark Newcomb and Rick Oches improved the English of the manuscript significantly. This is a publication of IGCP 449 ‘‘Global Correlation of Late Cenozoic Fluvial Deposits’’.

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