Lower Triassic sequence stratigraphy of the western part of the

Sedimentary Geology 186 (2006) 187 – 211 www.elsevier.com/locate/sedgeo

Lower Triassic sequence stratigraphy of the western part of the Germanic Basin (west of Black Forest): Fluvial system evolution through time and space Sylvie Bourquin a,*, Samuel Peron a, Marc Durand b a

Geósciences Rennes, UMR 6118, Univ. Rennes 1, 35042 Rennes cedex, France b 47 rue de Lavaux, 54520 Laxou, France

Received 30 September 2004; received in revised form 21 October 2005; accepted 10 November 2005

Abstract The aim of this paper is to analyse the fluvial evolution of the Lower Triassic in the western part of the Germanic Basin through time and space, as well as the impact of the geodynamic and climatic setting on the preservation of fluvial deposits. The Lower Triassic crops out only in the Vosges Massif and the Black Forest, so well-log studies are required to realise sequence stratigraphy correlations and establish comparisons with others parts of the Germanic Basin. In a first step, we use well-log data analyses to characterise the electrofacies associations in the Triassic and then define the well-log signatures of each formation. In a second step, the characterisation and recognition of genetic sequences and their stacking pattern allow us to define seven minor cycles integrated into two major cycles. Finally, the quantification of the lithologies at different stages of basin evolution leads to the reconstruction of paleoenvironmental maps to illustrate facies evolution through space and time. A comparison with cycles defined in the Germanic Basin allows us to propose correlations of the Lower Triassic on either side of the Rhine Graben and leads to a discussion of the evolution of fluvial systems through time and space. During the Scythian, the fluvial style is characterised by braided fluvial systems evolving laterally into lake deposits towards the central part of the Germanic Basin. During this stage, the basin was a huge depression with very few marine connections in its extreme eastern part. The stratigraphic cycles represent rhythmic fluctuations in relative lake level that could be attributed to sediment supply and/or lake level variations in an arid setting. Four minor stratigraphic cycles are observed that are integrated within a single major stratigraphic cycle. During the period of the stratigraphic base-level rise of the major cycle, a maximum of 233 m of sediment would represent a duration of sedimentation in the Paris Basin of at least 1.8 m.y. During the period of the stratigraphic base-level fall of the major cycle, a maximum of 65 m of sediment would have accumulated over 2.5 m.y. On the western edge of the Germanic Basin, the top of the Scythian is marked by a major sedimentary break characterised by a planation surface, with preservation of the first paleosols, followed by the Hardegsen unconformity. This unconformity is tectonically deformed, leading to the development of a new sedimentation area in the west of the basin. The fluvial sedimentation above this discontinuity shows a trend towards enhanced development of floodplain or lacustrine-type environments at its western margin, with the formation of paleosols. The fluvial systems are linked with sabkhas, and then with a shallow sea connected to the Tethys Ocean. In this context, the

* Corresponding author. Fax: +33 2 23 23 61 06. E-mail address: [email protected] (S. Bourquin). 0037-0738/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.sedgeo.2005.11.018

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S. Bourquin et al. / Sedimentary Geology 186 (2006) 187–211

stratigraphic cycles are caused by variations in relative sea level and/or sediment supply. The fluvial deposits are preserved in an exoreic basin. D 2005 Elsevier B.V. All rights reserved. Keywords: Lower Triassic; Fluvial sedimentation; Sequence stratigraphy; Well-log analysis; Paris and Germanic basins; Paleoenvironmental maps

1. Introduction

2. Geological setting

The Triassic is a period of transition associated with the beginning of the break-up of the Pangean supercontinent and the development of the Mesozoic basins, in a globally warm and dry climate (Ziegler, 1990; Frakes et al., 1992; Dercourt et al., 1993; Lucas, 1998; Golonka and Ford, 2000; Reinhardt and Ricken, 2000; Boucot and Gray, 2001). Within the basins around the western part of Tethys, the Triassic succession is characterised by (Dubois and Umbach, 1974; Courel et al., 1980): (i) fluvial and playa deposits during the Early Triassic, i.e. Buntsandstein facies, (ii) evaporite and marine deposits during the Middle Triassic, i.e. Muschelkalk facies and (iii) mainly evaporite and fluvial deposits during the Late Triassic, i.e. Keuper facies. In western Europe, the Buntsandstein is mainly represented by two fluvial styles: (i) large bed-load sand sheets associated with lake deposits characterising the Lower and Middle Buntsandstein (i.e. Scythian, Ro¨hling, 1991; Aigner and Bachmann, 1992), which pass vertically up into (ii) fluvial systems bordering an evaporite sabkha or a shallow sea, typical of the Upper Buntsandstein (i.e. Upper Scythian to Middle Anisian, Durand, 1978; Courel et al., 1980; Durand et al., 1994). At the scale of the western part of the Germanic Basin, this study aims to analyse (i) the evolution of the fluvial systems through time and space and (ii) the mechanism of preservation of fluvial deposits in the geodynamic and climatic context of the Early Triassic. To investigate the relationship between the fluvial environments and the stratigraphic context, we propose (1) sequence stratigraphy correlations based on well-logs (Fig. 1) located in the western part of the Germanic Basin (Paris Basin, including Rhine Graben, and Bresse-Jura Basin), (2) to reconstruct paleoenvironmental maps from a quantification of the lithologies based on well-log and outcrops data, and (3) to compare and correlate our results with data from other parts of the Germanic Basin (Richter-Bernburg, 1974; Ro¨hling, 1991; Aigner and Bachmann, 1992; Van der Zwan and Spaak, 1992; Bachmann and Lerche, 1998).

During the Early Triassic, the Paris and Bresse-Jura basins formed the western end of the Germanic Basin. The Paris Basin only existed as an independent basin from the Middle Carnian onwards (Bourquin and Guillocheau, 1993, 1996). In the Vosges (Fig. 1B), the Lower Buntsandstein units (Senones Sandstones or Anweiller Sandstones) can be attributed to the Uppermost Permian, i.e. Zechstein equivalents (Durand et al., 1994). Whereas in the major part of the Germanic basin, the bBuntsandstein GroupQ is separated from the Rotliegends by the typical-Zechstein carbonate-evaporite facies (Uppermost Permian), in France the latter are completely lacking. This is why the French geologists place the base of their bBuntsandsteinQ at the level of a major unconformity between fanglomerate prone deposits, localised in relatively restricted basins, and widespread fluvial deposits (Courel et al., 1980). Such a concept of bBuntsandsteinQ prevailed in South Germany until the adoption of a unified lithostratigraphic scale (Richter-Bernburg, 1974). Thus, in the French sedimentary basins, deposits referred to as bBuntsandsteinQ can be attributed either to Permian or to Triassic (Durand, in press). Actually, the bLower BuntsandsteinQ of the Vosges (Senones Sandstone and Anweiller Sandstone) can be attributed to the Upper Permian, i.e. Zechstein equivalents (Durand et al., 1994). Therefore, the Middle and Upper Buntsandstein units are attributed mainly to the Lower Triassic. These facies are characterised by fluvial deposits that make up the following formations (Fig. 1C), from base to top (Courel et al., 1980): bConglome´rat basalQ, bGre`s vosgiensQ, bConglome´rat principalQ, bCouches interme´diairesQ, and bGre`s a` VoltziaQ. The bCouches intermediaiesQ Formation is commonly separated from the bConglome´rat principalQ by the bZone limite violetteQ Formation that characterises by the first occurrence of Triassic soils in this area. The bed-load fluvial systems of bConglome´rat basalQ, bGre`s vosgiensQ and bConglome´rat principalQ are attributed to braided type networks developed in an arid climatic environment, as indicated by the occurrence of reworked and in situ aeolian sand dunes and wind worn pebbles (Durand, 1972, 1978; Durand et al., 1994). The bed-load fluvial deposits of the bCouches inter-


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Fig. 1. (A) Location of the studied area and the Bockenem well (Bo). (B) Location of studied wells and transect. B: Bertray1; G: Granville 109; M: Montplone1; F: Francheville1; L: Lorettes1, S: Saulcy; J: Johansweiller; SSF: Soultz-sous-Foreˆts, K: Kraichgau; E: Embermeńil. (C) Lithostratigraphic column, sedimentary environment variations and biostratigraphic data for the Lower Triassic succession in the eastern part of the Paris Basin based on Francheville well (after Bourquin et al., 1995). (a): Durand and Jurain (1969), Gall (1971), (b): Kozur (1972), Adloff et al. (1982), Khatib-Nguyen and Thi (1977), (c): Kozur (1972), Khatib-Nguyen and Thi (1977).

me´diairesQ correspond to low sinuosity rivers with transverse bars (Durand, 1978), and are associated with hydromorphic paleosols (Durand, 1978; Durand and Meyer, 1982). The bGre`s a` VoltziaQ shows an evolution from low sinuosity fluvial systems in the bGre`s a` meulesQ, with weak marine influence, to the fluviomarine environment of the bGre`s argileuxQ (Gall, 1971; Durand, 1978; Courel et al., 1980; Durand et

al., 1994). The only biostratigraphic evidence in this Buntsandstein series concerns the bGre`s a` VoltziaQ, where macrofauna and palynoflora allow the attribution of a Lower to Middle Anisian age according to location (Durand and Jurain, 1969; Gall, 1971). The bGre`s a` VoltziaQ evolves upwards to deposits with increasingly marine influence (bGre`s coquillierQ, bComplexe de VolmunsterQ, bDolomie a` Myophora orbicularisQ), then

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into the evaporitic facies (bCouches rougesQ. . .) of the Upper Anisian and, finally, the marine deposits of the Ladinian. The vertical evolution from bCouches interme´diairesQ to the marine deposits of the Ladinian characterises a general backstepping trend, in which the maximum flooding surface (mfs) is located at the top of the bCalcaires a` Ce´ratitesQ Formation dated as Ladinian (Duringer and Hagdorn, 1987). Paleocurrent directions obtained from fluvial facies indicate a mainly eastward flow (Durand, 1978). The terminology used for the Buntsandstein formations in the Palatinate is not the same as that applied in the Paris Basin. The equivalent of the bGre`s vosgiensQ Formation is divided into three units, which are, from base to top: the Trifels, Rehberg, and Karlstal formations. These three units are characterised by increasing clay content. Recent studies of the Middle Buntsandstein fluvial deposits, based on outcrops and some well-log data, from the eastern part of the Paris Basin, have proposed that the lower Triassic includes two stratigraphic cycles (Guillocheau, 1991; Friedenberg, 1994; Bourquin et al., 1995). The first one would correspond to the evolution from the bConglome´rat basalQ to the top of bGre`s vosgiensQ, while the second would extend from the base of the bConglome´rat principalQ, considered as a major unconformity, to the Ladinian mfs (Fig. 1C). However, no correlation has been carried out (1) within the bConglome´rat basalQ and the bGre`s vosgiensQ in the Paris Basin, and (2) between the Triassic of the Paris Basin (western part of the Vosges Massif), the Rhine Graben and the Black Forest. The present study of well-log data for the Triassic west of the Black Forest (Paris Basin, Rhine Graben and Bresse-Jura Basin) allows us to propose correlations and define the stratigraphic context of the Lower Triassic units. 3. Procedure The Lower Triassic crops out only in the western part of the Paris Basin, in the Vosges Massif and in the Black Forest. The outcrops are discontinuous and if the basal unit (with Permian–Triassic boundary) or uppermost unit (bConglome´rat principalQ) are not present, it is almost impossible to determine the stratigraphic position. Only well-log data can provide a continuous record. By studying the complete set of wells in the Paris Basin, Rhine Graben and Bresse-Jura Basin, we can carry out correlations and propose paleogeographic maps for the Early Triassic. The available well-logs are gamma-ray, resistivity and sonic logs. Only one well, located in the Rhine

Graben (Soultz-sous-Foreˆts well, Fig. 1B), is entirely cored in the Lower Triassic succession. The 2D and 3D geometries established in this study are based on well-log correlations. Around 580 wells are correlated using the principles of high-resolution sequence stratigraphy, i.e. the stacking pattern of the smallest stratigraphic units (Van Wagoner et al., 1988; Homewood et al., 1992) within a sedimentary succession (parasequence, Van Wagoner et al., 1990; Mitchum and Van Wagoner, 1991, or genetic unit, Cross, 1988; Guillocheau, 1991; Cross et al., 1993). Sequence stratigraphy in continental deposits is based on the analysis of fluctuations in stratigraphic base-level (Wheeler, 1964a,b; Cross et al., 1993; Gardner and Cross, 1994; Shanley and McCabe, 1994; Cross and Lessenger, 1998; Mutto and Steel, 2000), i.e. the accommodation space combined with sediment supply. The stratigraphic units reflect the brealised accommodationQ, i.e. volume of sediment actually accumulated (Cross, 1988; Mutto and Steel, 2000). In fluvial or fluviolacustrine deposits (Legarreta et al., 1993; Olsen, 1995; Currie, 1997; Leeder and Stewart, 1997; Legarreta and Uliana, 1998; Eschard et al., 1998; Bourquin et al., 1998), each of the smallest stratigraphic units corresponds to a period of low preservation or erosion (paleosol and/or lag deposits) followed by a period of high preservation (well developed fluvial sequence up until a maximum flooding episode represented by floodplain or lacustrine sedimentation). Therefore, such cycles are bounded by two maximum flooding intervals. By observing the stacking arrangement of genetic sequences, different scales of stratigraphic cycle can be identified. With increasing scale and duration, these stratigraphic cycles are termed genetic sequence sets, minor stratigraphic cycles and major stratigraphic cycles (Bourquin and Guillocheau, 1996; Bourquin et al., 1998). The maximum flooding episodes can be readily picked out on well-logs. However, the use of gamma-ray and sonic logs alone may give rise to misinterpretation. Indeed, sandstones containing large amounts of radioactive minerals (potash feldspar, heavy minerals, etc.) may produce high gamma-ray values similar to those observed in clays (Bourquin et al., 1998). 4. Well-log facies and stratigraphic units characterisation 4.1. Triassic electrofacies By comparing well-log data with outcrops located in the eastern part of the Paris basin (Fig. 1B), we can characterise the well-log signature of the Triassic formations (Fig. 2). The Permian–Triassic boundary is

S. Bourquin et al. / Sedimentary Geology 186 (2006) 187–211 Fig. 2. Well-log signature of Triassic formations, and correlations between three successive wells based on the genetic sequence stacking pattern and ordering of stratigraphic cycles. See Fig. 1B for location. 191

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marked by a sharp transition between the Lower Buntsandstein fluvio-lacustrine environments, i.e. Permian, with high gamma-ray and sonic log values, and electrofacies with low gamma-ray values of the Middle Buntsandstein, i.e. Triassic. The Middle Buntsandstein is characterised by low to medium gamma-ray values (between 20 and 75 API), and the Upper Buntsandstein by medium to high gamma-ray values (between 50 and 170 API). Using combined well-logs and cuttings data, we can distinguish the conglomerate formations of the Middle Buntsandstein (i.e. bConglome´rat basalQ and bConglome´rat principalQ) from the bGre`s vosgiensQ sandstone Formation. At outcrop, these conglomerate formations are made up of well-cemented coarse sandstones, pebbles and cobbles. The bConglome´rat basalQ is polygenetic (mainly containing clasts of siliceous material, quartz, quartzite and lydite, but also rhyolite and granite), while the bConglome´rat principalQ contains only siliceous clasts. Consequently, the well-log signature of the conglomerate facies is characterised by low sonic values (between 55 and 80 As/f) and low to medium gamma-ray values if radioactive minerals are present (20 to 40 API for the bConglome´rat principalQ and up to 70 API for the bConglome´rat basalQ). At outcrop, the bGre`s vosgiensQ Formation is composed of sandstone, and rare conglomeratic facies, containing 80 to 95% quartz and feldspar. As a result, the sandstone electrofacies yield gamma-ray values comprised between 20 and 40 API, with sonic values between 80 and 90 As/ft (Fig. 2). At outcrop, some silty-clay or clay interbeds can be observed within the formations of the Middle Buntsandstein. Within the Lower bGre`s vosgiensQ, these interbeds are thin (less than 40 cm), characterising either floodplain deposits associated with bed-load rivers in arid climatic environments or settling deposits produced by cessation of the migration of fluvial barforms (Durand, 1972, 1978; in press; Durand et al., 1994). Within the Palatinate area (Fig. 2B), the bGre`s vosgiensQ become richer in silty-clay material upward, thus defining three formations, from base to top: the Trifels, Rehberg and Karlstal formations (Dachroth, 1985). This succession reflects a vertical evolution from fluvial bed-load rivers to the playa environments of the Karlstal Formation. At outcrop, the upper part of the Karlstal Formation becomes more fluvial (bed-load rivers with few thin floodplain deposits). The well-log data allow us to distinguish the silty-clay from the sandstone electrofacies (Fig. 2): gamma-ray (GR) values higher than 45 API and sonic (Dt) values higher than 90 As/ft for silty-clay electrofacies. The Trifels, Rehberg and Karlstal formations are well recognized from well-log data

owing to the upward increase in abundance of siltyclayey electrofacies (Fig. 2), while the top of the Karlstal Formation shows a greater development of sandstone electrofacies. Therefore, for the Middle Buntsandstein, we can define three cut-off values from well-log data (Fig. 2): – if GR N 45 API and Dt N 90 As/f = silty-clay and clay electrofacies, – if GR b 40 and 80 b Dt b 90 As/f = sandstone electrofacies – if 20 b GR b 80 and Dt b 80 As/f = conglomeratic electrofacies In the field, the transition between Middle and Upper Buntsandstein is marked by the bZone limite violetteQ, which is characterised by red-violet clays with the development of hydromorphic paleosols. The Upper Buntsandstein is characterised by two formations, namely, the bCouches interme´diairesQ and the bGre`s a` VoltziaQ (see Section 2). The former corresponds to low-sinuosity rivers associated with floodplain and lacustrine environments. The latter formation corresponds to fluvial environments with increasingly marine influence upwards into the Lower Muschelkalk, which displays marine facies (see Section 2). The Middle Muschelkalk shows the earliest evaporitic beds in the Paris basin. On well-log data, the Upper Buntsandstein is well marked by higher gamma-ray values than those observed in the Middle Buntsandstein. Moreover, the boundary between the Middle and Upper Buntsandstein is marked by one or two electrofacies with high gamma-ray values that characterise the clay facies of the bZone limite violetteQ (Fig. 2). In some cases, conglomeratic facies can be detected in the basal part of the bCouches interme´diairesQ, which could correspond to the bConglome´rat de BitcheQ defined in northern Lorraine (Meńillet et al., 1989). Within the Upper Buntsandstein, it is easy to distinguish the sandstone facies from the silty-clay or clay facies (GR N 45 API and Dt N 90 As/f). Within the Muschelkalk, the evaporite and dolomite facies can be distinguished by low gamma-ray and sonic values as well as high resistivity. However, the distinction between dolomite and anhydrite is difficult without density and porosity logs (Bourquin and Guillocheau, 1996). 4.2. Triassic genetic sequence definition and vertical stacking pattern As discussed by various authors (Legarreta et al., 1993; Olsen, 1995; Currie, 1997; Leeder and Stewart,


1997; Legarreta and Uliana, 1998; Eschard et al., 1998; Bourquin et al., 1998), genetic units in fluvial environments are usually composed of: – a condensed lower part: transit or erosion surface, well-developed paleosols, amalgamated channels representing periods of stratigraphic base-level fall, i.e. decreasing accommodation space and/or increasing sediment supply; – an aggrading upper part, with well developed fluvial preservation representing periods of stratigraphic base-level rise, i.e. increasing accommodation space and/or decreasing sediment supply. Each genetic unit is bounded by two maximum flooding surfaces characterised by regionally correlated floodplain or lacustrine sedimentation. In continental environments, it is difficult to distinguish autocyclic events (resulting from local processes such as avulsion) from allocyclic factors (climate, eustatic effects, deformation and sediment supply) that can be regionally observed and lead to stratigraphic base-level variations (Olsen and Larsen, 1993; Postma et al., 1993; Schumm, 1993; Shanley and McCabe, 1994; Dalrymple et al., 1998; Bourquin et al., 2002). From well-log data, it is possible to distinguish clay facies attributed to floodplain or lacustrine environments (Bourquin et al., 1998). The smallest unit, bounded by two clay electrofacies and correlated at the scale of the formation, is considered as a genetic unit. The vertical stacking patterns of genetic units allow us to distinguish different scales of stratigraphic cycle. In continental environments, the genetic sequences and genetic sequence sets can be correlated only at the scale of a formation (Bourquin et al., 1998; Brault et al., 2003). The minor cycles are correlated at the basin scale. The correlations here are carried out between the Variscan basement or pre-Triassic deposits and the anhydrite bed characterising the basal part of the bCouches GrisesQ Formation defined in the eastern part of the basin (middle part of the Middle Muschelkalk, Fig. 1B). The Middle and Upper Buntsandstein exhibits four orders of stratigraphic cycles (Fig. 2): (1) genetic sequence, (2) genetic sequence sets, (3) minor stratigraphic cycles (denoted B1 to B7, Fig. 2) and (4) major stratigraphic cycles (Sythian and Anisian–Carnian cycles). For the Middle Buntsandstein, characterised by fluvial bed-load rivers in an arid context, the genetic units inferred from well-log data are thicker (15 to

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40 m) than those observed within the lacustrine or marine facies of the Upper Buntsandstein (7–15 m, and even 4 m within lacustrine electrofacies). This difference is due to the lower abundance of floodplain deposits in the Early Triassic succession (Fig. 2). Each genetic unit can be correlated at the scale of the eastern part of the Paris Basin; they are recognized in all the wells log within the Triassic series. The stacking pattern of genetic units allows us to define genetic unit sets, minor cycles and major cycles. For some cycles, the location of the maximum flooding surface is uncertain. In such cases, we cannot attribute a stratigraphic base-level fall to the upper part of the cycle. The turnaround surface between rise and fall of stratigraphic base-level, characterised in fluvial environments by by-pass or erosion (amalgamated channels, erosion or paleosol), is sometimes impossible to recognize from well-log data alone (Bourquin and Guillocheau, 1996; Bourquin et al., 1998). Moreover, in the arid context of the Early Triassic, no paleosols were formed. Complementary facies analyses, based on cores and outcrop data, are in progress to resolve this question. While it is difficult to quantify the duration of cycles, a comparison with stratigraphic studies in the Germanic basin nevertheless allows us to estimate the duration of major cycles (see discussion in Section 7). 4.3. Construction of Triassic paleoenvironmental maps The paleoenvironmental maps are drawn up between two stratigraphic lines to show the fluvial system evolution in time and space. The isopach and lithological data come from well-logs and outcrops data. All the maps are bounded in the eastern part by the Rhine Graben data. For the Vosges Massif, the maps integrate the outcrop data (Durand, 1978 and Geological maps of the eastern Paris Basin, scale 1/50,000). Since the Middle Buntsandstein consists of sandstones with very few clay layers, only conglomerate percentages and isopachs are indicated on the maps. The Upper Buntsandstein paleoenvironment maps show the dominant environments over the considered time span. 5. High-resolution sequence stratigraphy correlations of the Lower Triassic The results of the correlations the 580 wells studied in the Paris basin and Rhine Grabben are summarized on a NE–SW section between the Rhine Graben

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(Soultz-sous-Foreˆts well) and the area south of Orleáns (Figs. 1B, 4, and 5). 5.1. Middle Buntsandstein cycles The Middle Buntsandstein formations (‘‘Conglome´rat basal’’, ‘‘Gre`s vosgiens’’ and ‘‘Conglome´rat principal’’) exhibit one major cycle divided into four minor cycles (noted B1 to B4, Figs. 2 and 3). The data available (gamma-ray and sonic logs combined with cutting data) allow us to quantify the occurrence of sandstones, conglomerates and clays (see Section 4.1). Within the Middle Buntsandstein, the series consists essentially of sandstones with very few floodplain deposits that, however, allow the recognition of genetic sequence (see Section 4.2). The correlations reveal the onlap of the Triassic sedimentation onto the basement (Figs. 4 and 5). The bed-load fluvial sediments, attributed to braided rivers, came from the west (present-day Armorican Massif, Durand, 1978; Durand et al., 1994) and progressively fill in the topographic depression. Floodplain deposits are rare and characterised by clay layers a few centimetres thick. The conglomerate deposits are mainly located in the western part of the sedimentation area. The four minor stratigraphic cycles (B1 to B4) can be correlated across the Paris Basin up to the Rhine Graben in the east, showing that the bConglome´rat basalQ Formation is diachronous. The B1 cycle corresponds, in the Vosges Massif outcrops and Embermeńil well, to the deposits of the bConglome´rat basalQ Formation (Figs. 3 and 4). This cycle is characterised by the vertical passage of wellpreserved fluvial conglomerates into floodplain deposits (Fig. 4). In more distal parts of the basin, the conglomerates grade eastwards into sandstones. The B2 and B3 cycles (Figs. 3 and 4) are intra-bGre`s vosgiensQ Formation, and record well-preserved fluvial sandstones to floodplain deposits, the basal conglomerate facies being located in the westernmost area (Fig. 4). From cycles B1 to B3, we observe a general backstepping of conglomerate facies. The isopach maps drawn up for each cycle (Figs. 6 and 7A) indicate the basement–sedimentation area boundary, as well as the location of conglomerate facies through time and space. The more proximal facies are located to the west. These maps show the general backstepping of conglomerate facies and their lateral eastward evolution to sandstone deposits (Figs 6A, B and 7A). The B4 cycle shows well-preserved fluvial sandstones overlain by a maximum flooding episode and

then prograding conglomerates (Figs. 4 and 5). These conglomerates migrate basinwards and grade laterally into sandstones. In the Vosges Massif outcrops and Embermeńil well, these conglomerates correspond to the bConglome´rat principalQ Formation (Fig. 3). The lithogical map of this cycle (Fig. 7B) shows that the conglomerates spread across the basin. The bConglome´rat principalQ Formation rarely occurs at outcrop north of the Vosges Massif, near the German Frontier, where it is eroded. In outcrop, the bConglome´rat basalQ and of the bConglome´rat principal’’ display the same petrographic materials, notably Silurian and Proterozoic graphitic cherts that are derived from the Armorican Massif (Durand et al., 1994; Dabard, 2000), implying same provenance. The transition between the bGre`s vosgiensQ and the bConglome´rat principalQ only reflects a progressive increasing in gravel content and then an acceleration of the prograding phase. The base of the bConglome´rat principalQ is diachronous: conglomeratic facies are younger in the western part of the basin (Cycle B4, Fig. 5). Geometrically, the correlations (Figs. 2 and 5) reveal the landward migration of the silty clay facies (attributed to playa deposits of the Karlstal Formation) into a retrogradation trend, until the maximum flooding surface of the cycle B3, and then a progradational tend of sandstone and conglomerate deposits of the bConglome´rat principalQ Formation. This evolution characterised a major cycle, where the period of the stratigraphic base-level rise is represented by the cycle B1 to B3 and the period of the stratigraphic base-level fall by the cycle B4 (Figs. 2 and 3). This cycle is located above the Permian and below the Anisian, thus it is called the Scythian cycle. The top of cycle B4 is marked by a major discontinuity, which is characterised a sedimentary break. This episode can be correlated with the forming of the bZone Limite VioletteQ that crops out in many parts of Lorraine (Fig. 2). The bZone Limite VioletteQ overlies the bConglome´rat principalQ Formation and contains paleosols (dolocrete and silcrete), providing evidence for very low sedimentation rates (Durand and Meyer, 1982). In north Lorraine, the bZone Limite VioletteQ and even the bConglome´rat principalQ are locally eroded. This is indicated locally by the occurrence of a conglomerate containing bConglome´rat principalQ pebbles mixed with pedogenic carbonate and cornelian pebbles reworked from the bZone Limite VioletteQ. This unit, known as bKarneolkonglomeratQ in the Palatinate (Reis and von Ammon, 1903), corresponds to the bConglome´rat de BitcheQ defined in northern Lorraine (Meńillet et al., 1989). In addition,


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Fig. 3. Lithostratigraphic column, sedimentary environment variations, major and minor stratigraphic cycles for the Lower Triassic succession in the eastern part of the Paris Basin based on Embermeńil well.

well-log data allow to recognize locally conglomerate facies (see Section 4.1) above the discontinuity (e.g. Saulcy and Johansweiller, Figs. 2 and 5). The erosional

surface corresponds to the bHardegsen unconformityQ expressed in many parts of the Germanic basin (Durand et al., 1994).

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The transect (Figs. 4 and 5) and the four maps (Figs. 6 and 7) allow us to quantify the 3D evolution of the Triassic series and to characterise (1) the geometries of sedimentation units infilling the basement topography, (2) the general onlapping of these series, (3) the retrogradational pattern of the playa deposits, (4) the progradation of the bConglome´rat principalQ Formation, and (5) the diachronism of the Middle Buntsandstein formations (Trifels, Rehberg, Karlstal, bConglomerat basalQ, and bConglome´rat principalQ formations, Figs. 2 and 5). 5.2. Upper Buntsandstein cycles The lithostratigraphic succession comprising the Upper Buntsandstein formations (bCouches interme´diairesQ and bGre`s a` VoltziaQ), the Lower Muschelkalk (bGre`s coquillierQ, bComplexe de VolmunsterQ, and bDolomie a` Myophoria orbicularisQ), and the lower part of the Middle Muschelkalk (bCouches rougesQ Formation) corresponds to three minor cycles (noted B5 to B7, Fig. 2). They belong to the lower part of the major Anisian–Carnian cycle. The sandstones facies of the Upper Buntsandstein correspond to low sinuosity fluvial channels (Durand, 1978; Durand et al., 1994). The well-log data allow a quantification of sandstones, floodplain and/or lake deposits and sabkha lithofacies and the expression of the genetic units in these depositional environments (see Sections 4.1 and 4.2). The well-log analyses allow to characterise the occurrence of a new depositional area in the western part of the Paris Basin (Figs. 4 and 5). Its sediments seem to be contemporaneous with those located above the discontinuity in the eastern part of the basin, where the three cycles can be correlated. In the Lorraine outcrop area and in the Embermeńil borehole, the two first cycles above the discontinuity (B5, B6) correspond to the bCouches interme´diairesQ Formation (Fig. 3). They show an evolution from sandstone to clay facies (Figs. 4 and 5) attributed, by comparison with outcrops data, to low sinuosity fluvial channel sandstones to well-developed lake or floodplain fine deposits (Durand, 1978; Durand and Meyer, 1982). The facies map of these cycles (Fig. 8A) shows the distribution of the sandstone and clay deposits. This distribution could express the location and orientation of the low sinuosity river and floodplain environments during the considered period. Cycle B7 corresponds to the bGre`s a` VoltziaQ Formation up to bCouches rougesQ Formation of Lorraine outcrops and Embermeńil well (Fig. 3). This cycle

shows a different expression in the eastern and western parts of the basin. Indeed, the correlations demonstrate that the Upper Buntsandstein formations are diachronous (Figs. 2 and 9), as previously established by biostratigraphic data across the outcrop area (Durand and Jurain, 1969; Gall, 1971). For example, the bGre`s a` VoltziaQ is located in the lower part of cycle B7 in the Johansweiller well, but in the upper part of this cycle farther eastwards (Fig. 9). Moreover, these correlations point out the lateral evolution from dolomitic and anhydritic clays, attributed to shallow marine and sabkha facies, in the eastern edge of the studied area (Gall, 1971; Durand, 1978; Courel et al., 1980; Durand et al., 1994), to sandstones in the west. Geometrically, the transect reveals the landward migration – i.e. to the west – of dolomitic clay facies (marine deposits) in a major retrogradational trend (Fig. 5). The upper part of the cycle B7 is characterised by the first occurrence of anhydritic deposits (landward equivalent of dolomitic facies observed in the Soultz-sous-Foreˆts well) overlying previous marine facies in a retrogradation trend (Fig. 5). Two detailed facies maps are drawn up for this cycle, one in its lower part, which correspond to the bGre`s a` VoltziaQ Formation of Lorraine outcrops and Embermeńil well (Figs. 3 and 8B), and the other in its upper part which corresponds to the Lower Muschelkalk formations and bCouches rougesQ Formation of Lorraine outcrops and Embermeńil well (Figs. 3 and 8C). These two maps show the westward migration of the paleoenvironments and the geographic distribution of the two facies of the bGre`s a` VoltziaQ (Gre`s a` MeulesQ: sandstone facies, Fig. 8B, and bGre`s argileuxQ: silty clay facies, Fig. 8B). The fluvial systems are localised mainly along the basin border (previous basement area) and evolved basinwards into shallow marine deposits (Fig. 8B, C). 6. Comparison with other parts of the Germanic Basin In the Soultz-sous-Foreˆts well, located in the Rhine Graben, Vernoux et al. (1995) proposed use of the Palatine terminology (Fig. 10). Therefore, in this part of the basin, the Trifels and Rehberg formations would be equivalent to the cycles B1, B2 and the lower part of the B3 cycle (Lower bGre`s vosgiensQ, Figs. 2 and 10). The Karlstal Formation would correspond to the upper part of the B3 cycle and the lower part of the B4 cycle (Upper bGre`s vosgiensQ, Figs. 2 and 10). The comparison with the Germanic Basin cycles (Fig. 10) is carried out by correlating the Soultz-sous-


Fig. 4. (A) WSW–ENE correlations of Lower Triassic stratigraphic cycles, between the south of Orleáns (Bertray well), and the Rhine Basin (Soultz-sous-Foreˆts well) in the western part of the Germanic Basin. (B) Transect location. See Fig. 1B for more details.

pp. 197–200

S. Bourquin et al. / Sedimentary Geology 186 (2006) 187–211 Fig. 5. (A) Geometries and lithology of the Lower Triassic stratigraphic cycles, along the transect between the area south of Orleáns (Bertray well) and the Rhine Basin (Soultzsous-Foreˆts well) deduced from well-log analysis: (1) geometries from Variscan basement or pre-Triassic deposits to the Hardegsen unconformity (Fig. 3), (2) geometries from the Hardegsen unconformity to the basal anhydrite bed of the 25 bCouches grisesQ Formation defined in the eastern part of the Paris Basin (middle part of the Middle Muschelkalk, Fig. 3). (B) Transect location. See Fig. 1B for more details.

201

202


Fig. 6. Isopach maps with superimposed lithology (% of conglomerate) for stratigraphic cycles B1 and B2 (see Figs. 3–5), constructed from well-log data and outcrops information (geological maps, scale 1/50,000, and Durand, 1978).

Foreˆts and Kraichgau 1002 wells and then the combined well-logs for Bockenem 1 and Bockenem A100 (Fig. 3 of Aigner and Bachmann, 1992).

The correlations with the Kraichgau well, located between the Black Forest and the Odenwald, allow us to identify the Middle Buntsandstein cycles defined in


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Fig. 7. Isopach maps with superimposed lithology (% of conglomerate) for the B3 (A) and B4 (B) stratigraphic cycles (see Figs. 3–5), constructed from well-log data and outcrops information (geological maps, scale 1/50,000, and Durand, 1978).

the Paris Basin. However, an additional stratigraphic cycle is present at the base of the Lower Triassic successions in this part of the Germanic Basin. This cycle is attributed to the Induan by magnetostratigraphy

(Junghans et al., 2002). A comparison with the combined Bockenem wells (Aigner and Bachmann, 1992) demonstrates that sequence 1, as defined in the Germanic basin (Calvo¨rde and Bernburg formations),

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Fig. 8. Paleoenvironmental maps of the Upper Buntsandstein stratigraphic cycles, drawn up from well-log data and outcrop information (geological maps, scale 1/50,000, and Durand, 1978): (A) paleoenvironmental map of the B5 and B6 minor stratigraphic cycles (bCouches interme´diairesQ Formation at Embermeńil well see Figs. 3–5), (B) paleoenvionmental map of the lower part of the B7 minor stratigraphic cycle (bGre`s a` VoltziaQ Formation at Embermeńil well, see Figs. 3–5), and (C) paleoenvionmental map of the upper part of the B7 minor stratigraphic cycle (bGre`s coquille´sQ to bCouches rougesQ formations at Embermeńil well, Figs. 3–5).

would appear to have no equivalent in the Paris Basin where only erosion and/or sediment transport occur at that time. The cycles B1, B2 and B3, corresponding to the lower part of the major cycle defined in the Paris Basin, could be equivalent to sequence 2 (Volpriehausen Formation), and cycle B4 to sequence 3 (Detfurth and Hardegsen formations). The individual sequences observed in the Germanic Basin are characterised by an evolution from fluvial sandstones to playa lake deposits. The maximum flooding episode of the major stratigraphic cycle defined in the Paris Basin appears equivalent to the mfs of sequence 2 (i.e. Volpriehausen), where more or less marine fauna is present in the central part of the Germanic Basin (Richter-Bernburg, 1974; Roman, 2004). The cycle B4, i.e. upper part of the Karlstal formation in Palatinate, would be equivalent to the Detfurth Formation. However, in this western end of the Germanic Basin, the sandstones equivalent to the Detfuth Formation do not display a basal low-relief angular unconformity as seen in the central Germanic Basin (Wolburg, 1968, 1969; Ro¨hling, 1991). In Lorraine, the top of the cycle B4 is marked by a major sedimentary break period of bypass with first development of paleosols (i.e. bZone limite violetteQ, Mu¨ller, 1954; Ortlam, 1967; Gall et al., 1977). This episode could be equivalent of Hardegsen Formation, where the evidence of biological activity (ichnites, rhizolites, palynomorphs) does not allow a correlation with the arid condition of the bConglome´rat principalQ Formation. Similarly, the discontinuity observed in the Paris Basin corresponds to the Hardegsen unconformity, representing one of the most pronounced extensional tectonic event observed in the Germanic Triassic (Trusheim, 1961, 1963; Wolburg, 1968; Ro¨hling, 1991). In the Germanic Basin, the base of the Solling Formation corresponds to the erosional episode of the Hardegsen unconformity, during which 100 m of Middle Buntsandstein deposits could be locally eroded (Aigner and Bachmann, 1992). Moreover Geluk (1998) shows that the base of the Solling Formation becomes progressively younger to the west, accompanied by a decrease in thickness. In this study, this formation appears to be missing due to non-deposition or erosion. The Solling sandstones preserved in the basin could be equivalent to an episode of sediment by-pass at the basin margin. The Ro¨t Formation, corresponding to evaporitic marine and sabkha deposits, represents the first occurrence of halite deposition in the Germanic Basin. It could be equivalent to the B5 cycle. The cycles B6 and B7 could be equivalent to the first cycle of the Muschelkalk in the central Germanic Basin. The second sequence of the


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Fig. 9. E–W correlations of the Upper Buntsandstein stratigraphic cycles showing the diachronous nature of the formations. See location Fig. 1B.

Muschelkalk in that area is equivalent to the bCouches grises–LettenkohleQ cycle in Lorraine. 7. Discussion The correlations on the western margin of the Germanic Basin and a comparison with other parts of this basin allow us to propose correlations of the Buntsandstein on either side of the Rhine Graben, and lead to a discussion of the evolution of fluvial systems through time and space. The Lower Triassic displays a succession with two general fluvial systems. The earlier system, located between the supra-Permian discontinuity and the Hardegsen unconformity, is made up of braided fluvial deposits evolving laterally into ephemeral playa lacustrine facies in the central part of the Germanic Basin. The general onlapping of the Triassic is well characterised by correlations on its western margin (Figs. 2, 5, and 6). Therefore, the Lower Triassic of the central part of the Germanic Basin would began significantly earlier than that of on the western margin. The bBro¨ckelschieferQ and the Lower Buntsandstein formations, which were deposited in sebkha or playa systems, respectively, are only found in the central basin and do not have equivalents on the western margin. These deposits characterise the regressive tendency of the uppermost Zechstein, which continues into the lower Buntsandstein (Aigner and Bachmann, 1992; Aigner et al., 1998). The angular unconformity at the base of the Triassic was caused by

non-deposition or erosion of the uppermost Zechstein cycles at the basin margin (Ro¨hling, 1991; Szurlies et al., 2003). The Scythian major cycle observed in the Paris Basin corresponds to a stratigraphic base-level rise continuing up to a maximum flooding episode, which could correspond to the deposition of the lacustrine facies of the Volpriehausen Formation in the central Germanic Basin (Fig. 10). The basal part of the Karlstal Formation would be the landward lateral equivalent of these lake deposits. Within this retrogradational pattern, three cycles (B1 to B3) can be observed on the western margin (Figs. 2, 5–7). The stratigraphic base-level fall of this major cycle corresponds to the cycle B4 and shows a progradational trend of sandstone and conglomerate deposits of the bConglome´rat principalQ Formation (Figs. 2, 5, and 7B). Geluk and Ro¨hling (1997) have made high-resolution correlations of the Lower Triassic series in the Netherlands and north-western Germany. In common with Szurlies et al. (2003), Geluk and Ro¨hling (1997) based their well-log correlations on genetic units, which are considered to represent 100 ka Milankovitch eccentricity cycles. These cycles are observed in the central part of the Germanic Basin because of the deposition of fluviolacustrine facies. On the western margin, i.e. in the Paris Basin, only fluvial deposits are present and so only the major floodings of lakes are recorded in the floodplain deposits. Consequently, these authors (op. cit.) estimate that the duration of deposition of the Lower Buntsand-

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Fig. 10. Correlation between the Rhine Graben (Soultz-sous-Foreˆts well) and the Palatinate (Kraichgau 1002 well), and comparison with stratigraphic cycles defined in the central Germanic Basin (Bockenem, 50 km SE of Hannover, from Aigner and Bachmann, 1992). See Fig. 1A and B for location.

stein (Calvo¨rde and Bernburg formations) is at least 2 m.y. (Szurlies et al., 2003), and assign it to the Induan. Geluk and Ro¨hling (1997) estimate the depositional duration of the Volpriehausen Formation at about 1.8 m.y, and the Detfurth plus Hardegsen formations at about 2.5 m.y. These three formations are attributed to the Olenekian. In the Netherlands, the sedimentary hiatus between the Volpriehausen and Detfurth formations is estimated at about 0.5 m.y. In the same area, the hiatus equivalent to the Hardegsen unconformity would have a duration of 1.5 m.y., situated within the Olenekian. Consequently, the duration of the Paris Basin sedimentation would be at least 1.8 m.y. for a maximum of 233

m of preserved sediment, taking place during the stratigraphic base-level rise, and 2.5 m.y. for a maximum of 65 m of preserved sediment during the period of the stratigraphic base-level fall. On this western margin, the Hardegsen unconformity overlain a major sedimentary break characterised by a planation surface and first development of paleosols that overlies the bConglome´rat principalQ Formation. No major erosion or angular unconformity is observed near the basal part of the bConglome´rat principalQ Formation, which is characterised only by an acceleration of the prograding phase. In the dry climatic regime of the Lower Triassic (Van der Zwan and Spaak, 1992), the first cycles could be


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Fig. 11. (A) Scythian (Olenekian) paleogeographic map of the southern part of the Germanic Basin with superimposed paleoenvironments and fluvial systems: (i) Kinematic reconstruction (Van der Voo, 1993; Besse et al., 1998; Besse, personal communication), (ii) fluvial systems: in Germany (Richter-Bernburg, 1974; Ro¨hling, 1991; Aigner and Bachmann, 1992; Wachutka and Aigner, 2001), in England and Wales (AudleyCharles, 1992), in Bulgaria (Belivanova, 1998), in Netherlands (Clemmensen, 1979; Geluk and Ro¨hling, 1997; Geluk, 1998), in the North Sea (Goldsmith et al., 2003), in Eifel basin (Mader, 1983; Mader and Teyssen, 1985), in southern Scandinavia (Olaussen et al., 1994), in France (Durand, 1978 and this study). AM: Armorican Massif, BM: Bohemian Massif, RM: Rhenish Masssf; LBM: London Braban Massif. (B) Scythian (Olenekian) paleoenvironmental reconstruction of the western part of the Germanic Basin.

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attributed to lake and sediment supply variations in an arid environment. During the Scythian, the river catchment areas are mainly located in the present-day Armorican Massif, and the paleocurrents are generally oriented towards the NNE (Fig. 11). The facies association is essentially composed of stacked channel fill facies with very few flood plain deposits (b 3%) and without paleosols. Channel fills are sometimes associated with aeolian deposits. In more distal areas of the Germanic Basin, the sedimentation corresponds to ephemeral playa lakes or aeolian deposits (Clemmensen, 1979; Clemmensen and Tirsgaard, 1990; Aigner and Bachmann, 1992; Ulicny, 2004). In this context, two hypotheses could explain the preservation of fluvial systems. According to one hypothesis, the siliciclastic sediment supply from the Hercynian- (Variscan) mountain was constant, and thus the cycles result solely from lake level fluctuations. The lake levels could be controlled by monsoonal activity, under the influence of sea-level fluctuations (Van der Zwan and Spaak, 1992). Alternatively, the basin was situated in an arid environment and the variation of the sediment supply was controlled by precipitation in the mountain ranges. To investigate the relationships between sedimentation and climate, studies are in progress to simulate Early Triassic climates. Moreover, sedimentological studies on cores and outcrops are being carried out to quantify the ephemeral character of the fluvial system and quantify the occurrence of aeolian deposits. The bConglome´rat principalQ Formation is characterised by a progradation of coarse-grained sediment. The origin of the sediment is the same as for the Vosgian sandstones. This progradation could be induced by a slowing down of subsidence or by sediment supply variations such as described by numerical modelling for short time scales (Heller and Paola, 1992; Paola et al., 1992; Paola, 2000; Marr et al., 2000). In this part of the basin, the top of Scythian major cycle is marked by a major break of sedimentation, characterising a period of very low sedimentation rate, with planation surface and the first development of paleosols (bZone limite violetteQ). Above it, the major Hardegsen unconformity is observed for the first time in the subsurface of this part of the basin (Figs. 2, 4, and 5). Above this unconformity, the Triassic series, that exhibit a major change in fluvial system style, show onlap, which implies some tectonic activity just before the renewal of sedimentation marked by the bCouches interme´diairesQ, rich in angular quartz and fresh feldspars. Some local incisions are observed in outcrops located in the north of Lorraine where the bZone limite violetteQ and the top of the

bConglome´rat principalQ are locally eroded. During the Hardegsen phase, an important structural reorganisation occurred in the NW Europe (Geluk and Ro¨hling, 1998), leading to the formation of the main rift in NW Germany (Best et al., 1983; Ro¨hling, 1991). This tectonic event gave rise to a new sedimentation area, in the south part of the Paris Basin (south of Paris, Fig. 8), where fluvial sediments could be preserved. On the western margin of the Germanic Basin (Fig. 9), sedimentation above the Hardegsen Unconformity is characterised by a major retrograding trend (Aigner and Bachmann, 1992; Aigner et al., 1998). The fluvial systems are the lateral equivalents of marine deposits. Finally, the Germanic Basin is connected with the Tethys Ocean (Dercourt et al., 1993), and the fluvial systems are developed in an exoreic basin setting. The correlations reveal the existence of maximum flooding episodes recorded in lake and/or floodplain deposits. In such fluvio-coastal depositional environments, the lakelevel fluctuations may be attributed to relative sea-level variations. In the area located south of Paris, the fluvial system appears not to be connected with the eastern part of the basin. This connection only becomes established during accumulation of the bCouches grisesQ. 8. Conclusions The correlation of the Lower Triassic succession located on the western margin of the Germanic Basin allows us to characterise the stratigraphic evolution of the fluvial sedimentation. The comparison of the stratigraphic cycles observed there with those described in other parts of the basin makes it possible to assess the duration of cycles and reconstruct the basin evolution. The early Triassic can be separated into two phases. The first phase, during the Scythian, is characterised by braided fluvial systems evolving laterally into lake deposits toward the central part of the Germanic Basin. At this time, the basin is a huge basin depression with only few marine connections in the eastern part. The stratigraphic cycles reflect relative lake-level fluctuation that could be attributed to sediment supply and/or lake level variation in an arid context. The second phase occurs after a major sedimentary break (planation surface and pedogenesis) followed by the formation of the Hardegsen unconformity. This surface is tectonically deformed, leading to the creation of a new sedimentation area to the west of the basin. Above this unconformity, the fluvial sedimentation, attributed to the Anisian, shows an enhanced development of floodplains (with preservation of paleosol) associated with lacustrine. The fluvial systems are connected with a shallow sea facies in


communication with the Tethys Ocean. In this context, the stratigraphic cycles are induced by variations in relative sea level and/or sediment supply. The fluvial deposits are preserved in an exoreic basin. Acknowledgments We are grateful for the financial support of INSU/ CNRS programme bECLIPSEQ entitled bQuantification des flux se´dimentaires au Trias: re´ponse des syste`mes se´dimentaires continentaux aux sollicitations climatiques et tectoniquesQ. We gratefully acknowledge Pr. Dr. G. Bachmann, Pr. Dr. B. W. Sellwood and an anonymous referee for their critical and constructive reviews of the paper. Dr M.S.N. Carpenter post-edited the English style. References Adloff, M.C., Doubinger, J., Geisler, D., 1982. E´tude palynologique et se´diomentologique dans le Muschelkalk moyen de Lorraine. Me´m. Sci. Terre (Nancy) 25, 91 – 104. Aigner, T., Bachmann, G.H., 1992. Sequence-stratigraphic framework of the German Triassic. Sediment. Geol. 80, 115 – 135. Aigner, T., Hornung, J., Junghans, W.-D., Po¨ppelreiter, M., 1998. Baselevel cycles in the Triassic of the South-German Basin: a short progress report. In: Bachmann, G.H., Lerche, I. (Eds.), Epicontinental Triassic, Zbl. Geol. Palaönt. Teil 1, vol. 7–8. , pp. 537 – 544. Audley-Charles, M.G., 1992. Triassic. In: Duff, P.M.D., Smith, A.J. (Eds.), Geology of England and Wales. Geological Society, London, pp. 307 – 324. Bachmann, G.H., Lerche, I., 1998. Epicontinental Triassic. Zentralbl. Geol. Palaöntol., Teil 1 7–12, 1609. Belivanova, V., 1998. Triassic in the Golo Bardo Mountain—one example for the Balkanide facial type of Triassic in Bulgaria. Zentralbl. Geol. Palaöntol., Teil I 2, 1105 – 1121. Besse, J., Torcq, F., Gallet, Y., Ricou, L.E., Krystyn, L., Saidi, A., 1998. Late Permian to Late Triassic palaeomagnetic data from Iran: constraints on the migration of the Iranian block through the Tethyan ocean and initial destruction of Pangaea. Geophys. J. Int. 135, 77 – 92. Best, G., Kockel, F., Scho¨neich, H., 1983. Geological history of the southern Horn Graben. Geol. Mijnb. 62, 25 – 34. Boucot, A.J., Gray, J., 2001. A critic of Phanerozoic climatic models involving changes in the CO2 content of the atmosphere. EarthSci. Rev. 56, 1 – 159. Bourquin, S., Guillocheau, F., 1993. Geóme´trie des se´quences de de´poˆt du Keuper (Ladinien a` Rhe´tien) du Bassin de Paris: implications geódynamiques. C. R. Acad. Sci. Paris 317, 1341 – 1348. Bourquin, S., Guillocheau, F., 1996. Keuper stratigraphic cycles in the Paris Basin and comparison with cycles in other Peritethyan basins (German Basin and Bresse-Jura Basin). Sediment. Geol. 105, 159 – 182. Bourquin, S., Friedenberg, R., Guillocheau, F., 1995. High-resolution sequence stratigraphy in the Triassic series of the Paris Basin: geodynamic implications. Cuad. Geol. Iber. 19, 337 – 362. Bourquin, S., Rigollet, C., Bourges, P., 1998. High-resolution sequence stratigraphy of an alluvial fan–fan delta environment: stratigraphic

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