Stratigraphy and mineralostratigraphy of the Kimmeridgian in the central Jura mountains of Switzerland and eastern France
Autor(en): Mouchet, Philippe O.J.
Objekttyp: Article
Zeitschrift: Eclogae Geologicae Helvetiae
Band (Jahr): 91 (1998)
Heft 1
PDF erstellt am: 04.10.2021
Persistenter Link: http://doi.org/10.5169/seals-168408
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http://www.e-periodica.ch 0012-9402/98/010053-16 $1.50 + 0.20/0 Eclogae geol. Helv. 91 (1998) 53-68 Birkhäuser Verlag. Basel. 1998
Stratigraphy and mineralostratigraphy of the Kimmeridgian in the central Jura mountains of Switzerland and eastern France1
Philippe O. J. Mouchet2
Key words: Kimmeridgian. microfacies, mineralostratigraphy. kaolinite. major discontinuities. Jura mountains Mots clefs: Kimmeridgien. microfaciès, mineralostratigraphic kaolinite. discontinuités majeures. Jura
ABSTRACT RESUME
The microfacies, micropaleontologv. mineralogy and sedimentology of the Les séries kimméridgiennes. très pauvres en éléments biologiques de datation series of the Reuchenette Formation (Kimmeridgian), introduced by Thalmann ont été étudiées sous leurs aspects microfaciologiques. micropaléontologiques. (1966) to replace the Kimmeridgian auctorum. have been studied and minéralogiques et sédimentologiques. L'étude inclut la localité-type de la compared with other series in the Swiss and French Jura Mountains. The studied Formation de Reuchenette. introduite par Thalmann (1966) pour remplacer le area corresponds to a shoal environment separating the Tethys (S) and the Kimmeridgien auctorum. Ces séries, principalement calcaires, ont été ensuite Paris Basin (N). The depositional environments represent three major comparées avec les séries du Jura suisse et français. Le domaine étudié domains: intertidal/supratidal domain, internal platform and external platform correspond à un haut-fond séparant la Téthys (S) du Bassin de Paris (N). Les (margin and slope). Field observations and microfacies analysis revealed two environnements de dépôt représentent trois domaines majeurs: domaine major discontinuities. Clay-mineralogy data show that kaolinite can be used as margino-littoral. plate-forme interne et plate-forme externe (bordure et talus a stratigraphical marker. Both methods, microfacies and clay-mineralogy, externe). L'analyse des microfaciès a permis de mettre en évidence deux allowed to establish correlations in an area where the biochronological markers discontinuités majeures. L'analyse minéralogique a permis d'identifier la kaolinite are extremely rare. The two major discontinuities can be correlated with series comme marqueur minéralostratigraphique. Grâce à l'étude combinée des described by Bernier (1984). Chevallier (1989) and Strohmenger et al. (1991) microfaciès et des minéraux argileux, il a été possible d'établir des corrélations in the Jura of SE France (Jura méridional) and can be tied to the global eustatic fiables pour l'ensemble du domaine étudié. Les deux discontinuités majeures curve established by Haq (1991). se corrèlent avec les séries du Jura méridional décrites par Bernier (1984). Chevallier (1989) et Strohmenger et al. (1991) et peuvent être reliées avec la courbe eustatique globale de Haq (1991
Introduction Heim (1919) subdivided Rollier's Kimmeridgian in Ptero- cerian and Virgulian. Heim's Kimmeridgian corresponds to Thurmann (1832) introduced the name Kimmeridgian as one the Lower Kimmeridgian of England, as described by Arkell of the stratigraphie subdivisions of the Jura Mountains' Upper (1956). finishing with the Aulacostephanus pseudomutabilis Jurassic by naming "Kimeridgian Marls" the "Beds with Ptero- Zone. In England, the Middle Kimmeridgian starts with the ceras". These were placed as 2nd division in the lower part of Gravesia sp. Zone, which, however, following the continental the Portlandian Group (Fig. 1). European tradition, defines the base of the Portlandian. The Marcou (1848) divided Thurmann's Portlandian Group Kimmeridgian sensu gallico corresponds thus to the Lower into two members: the "Kimmeridge marls" (or "Banné Kimmeridgian in England. Recent studies of Amoeboceras Marls") and the "Kimmeridge Limestones", both considered faunas (Atrops et al., 1993) have shown that the lower part of as purely lithostratigraphic units. the Submediterranean latest Oxfordian Planula Zone correlates Rollier (1888, 1893, 1898), for the first time, published a with the lower part of the Subboreal Kimmeridgian complete section of the Malm in the Jura Mountains of the Baylei Zone and that the lower part of the Submediterranean canton Bern. He recognized and delimited three stages: Kimmeridgian Platynota Zone correlates with the upper part Sequanian (top represented by the "St.-Verena Oolith"), of the Subboreal Baylei Zone (Fig. 2). This indicates that the Kimmeridgian (top represented by the "Banc à Nérinées" or the boundary between the Oxfordian and Kimmeridgian is actual- "Exogyra virgula Marls") and Portlandian.
1 Ph.D. Thesis. Université de Neuchâtel. projets Fonds National de la Recherche Scientifique n"21-29909.90 & 20-35878.92 : PO Box 306. Tennant Creek 0861. Northern Territory. Australia
Kimmeridgian central Jura Mountains 53 | Thurmann (1832) Marcou (1857-60) Heim (1919) ARKtLL(l956) i Thalmann (1966)
— PORTLANDIEN ~ - Twannbach- 1. Division 5 _- formation Calcaires Gravesia spp. porti andiens Z Aulacostephanus. < autissiodorensis 5 Y. VIRGULIEN __ _- A. eudoxus Reuchenette- | ^ A. mutabilis formation Cale, du Banne __ 2. Division Mames Marnes du Banne PFEROCERIEN Rasenisi cvmodoee kimméridiennes s __ Pictiona baylei D Rinsta edia Verenaschichten Z -_ pseudocordata __ Ç 3. Division Calcaires ii y- Z SEQUANIEN < C < Astartes SEQUANIEN a Fig. 1. Subdivisions of the Malm from Thurmann (1832) to Thalmann (1966).
ly drawn at a higher level in the Submediterranean zonal meridgian age for strata classically placed in the earliest scheme than in the Subboreal one. The Kimmeridgian of this Portlandian. It appears thus that, in the Jura Mountains, both study is used in the classical sensu gallico. Kimmeridgian and Portlandian were never precisely dated with Biological markers (ammonites, foraminifera) are very rare biostratigraphic markers. The names Oxfordian, Kimmeridgian in these series and. therefore, precise chronostratigraphical and Portlandian have classically been used in an approximate correlations are difficult to establish. One ammonite (Phylloceras chronostratigraphical sense. The conventional boundaries cf. tenuisculptum) of Kimmeridgian age was found at of these "stages" correspond to lithological markers Morillon (Fig. 3, 4). The charophytes (Echinochara pecki, which are supposed to be more or less isochronous and to Porochara sp.) indicate also a Kimmeridgian age for these correspond to the international stage boundaries. series but are of no use for more accurate correlations. The Thalmann (1966) introduced the name of "Reuchenette combined first appearance of Clypeina jurassica and Campbelliella Formation" for the Kimmeridgian strata of the Swiss Jura striata in the studied series can be used as a complementary mountains. This formation is defined by the same lithostratigraphical tool for correlations (Strohmenger et al. 1991). According to boundaries as used by Rollier (1888) nearly a century Gygi (1995) a find of Aspidoceras cf. acanthicum just above ago. the Virgula Beds at Alle (canton Jura) indicates a late Kim- Bernier (1984) and Chevallier (1989) recognized and described several formations of Kimmeridgian age (sensu gallico) in France. Most of these (like "Calcaires et Marnes de Europe Europe Chargey". "Calcaires et Marnes de Matafelon". etc.) are not Subboreal Submediterranean easily recognizable in the field outside road cuts. They have no Autissiodiorensis Beckeri direct equivalent in Switzerland. Only the following formations or layers are clearly and easily
Kimmeridgian gallico recognizable by their lithology (Fig. 1): the "St.-Verena Eudoxus Eudoxus Oolith". the "Banné Marls", the "Banc à Nérinées" and the sensu "Exogyra virgula Marls". The "Reuchenette Formation" does Upper not possess a characteristic lithological content (Gygi 1995) bui Mutabilis Acanthicum its limits are clearly identifiable, in a part of the studied region. e cd Divisum Persoz & Remane (1973. 1976) analysed the microfacies '5) •o c; in 'C and the mineralogy (by X-ray diffraction) series extending -c:.i; o Mountains £ a Cymodoce Hypselocyclum from the Dogger to the Malm in the central Swiss Jura S (Canton Neuchâtel). Persoz (1982) based his Oxfordian *2 s S î. and Kimmeridgian correlations on the variations of the kaolinite s o Baylei Platynota content. For this author, the kaolinite variations reflect changes in the sedimentary input and are thus independent Fig. 2. Comparison between the Submediterranean and Subboreal ammonite from facies changes. This allows kaolinite to be used as a Zones. chronostratigraphical marker.
54 P.O.J. Mouchet Coupe des Gorges de la Ixsue Coupe de Morillon N Porrenlrov Coupe de Fontine-le-Bas 1 ia Champagnole (F) * * »U Coupe du Haul-de-la-Tour ls* l3 2.Pontarlier (F) Coupe de Noirvaux ' 4^5 I, I Moutier 3.Le Locle (CH) - 'S Coupe des Gorges de l'Areuse 4Neuchâtel (CH) c Coupe de la Combe-Girard ; 8 J6":""* Forage de Neuchâtel 5.Bienne (CH) S.'' <¦¦¦:¦¦-¦¦ "•• 4» 7ft^TNeuchâtel Coupe de Reuchenette 6Moutter(CH) Champagnole Forage de Tramelan 7.Porrentruy (CH) Coupe de Monthautier 12 Forage de Grailerv 0 Mil m 13 Forage du Raimeux 14 Cssupe de Vabenau /*/< 15 Forage du Banné Vi: Forage de Bure
Fig. 3. General situation of the studied area. Fig. 4. Location of outcrops and drillholes.
The purpose of this work is to revisit Kimmeridgian terizing each mineral (clay or grain) present in the fraction stratigraphy of the Central Jura Mountains by using microfacies, (e.g. mica, kaolinite, mixed-layers, quartz) are given in raw clay-mineralogy and sequence stratigraphy (correlations values (CPM. coups par minute). Content in swelling (% smectite through major discontinuities). in mixed layers) is estimated by using the method of Moore & Reynolds (1989). The five most representative sections (presenting different Regional settings formations, variations in the microfacies curve and the Sixteen outcrops and diamond drillcores located in the Jura mineralogical content) were selected for this paper: Morillon. mountains of NW Switzerland and E France (Fig. 3. 4) have Gorges de la Loue. Gorges de l'Areuse. Reuchenette and been analysed. The studied area corresponds paleogeographi- Vabenau. cally and sedimentologically to a carbonate shelf separating the Tethys (S) from the Paris Basin (N). This shelf is influenced by two major islands: the Massif Central (SW) and the Sedimentology Ardennes-Vosges-Black Forest (NE). The climate is tropical The terminology used for the description of the thin sections is to subtropical according to Auboin et al. (1988). derived principally from Folk (1959, 1962). Dunham (1962). Flügel (1982) and Tucker & Wright (1990). Material and methods-
Samples were taken at irregular intervals in order to document Microfacies changes in lithology. Additional samples were taken to ascertain The study of thin sections allowed to recognise four major an appropriate coverage of lithologically monotonous depositional environments (slope, platform margin, internal intervals. This procedure resulted in a mean sampling distance of platform and intertidal/supratidal domain) on this carbonate shelf. 40 cm. All samples (nearly 1700) have been studied in thin These four domains are represented by sixteen microfacies section to determine the microfacies. The mineralogy (whole rock (Fig. 5). The microfacies FT corresponds to the "faciès de and clay mineralogy) of almost 550 samples has been analysed transgression" mixed facies) described by Arnaud-Vanneau at the Geochemistry Laboratory of the University of Neuchâtel (1980). It occurs above discontinuities. This microfacies is using a Scintag™ 2000 diffractometer. The methods of arbitrarily placed in the external platform (platform margin) mineralogical analysis and principally those of clay minerals because of its similarities with the other microfacies representing are based on the works of Brindley & Brown (1980), Adatte & this environment. Rumley (1984, 1989). Adatte (1988) and Moore & Reynolds (1989). Each sample was decarbonated, separated into two Slope (external platform) fractions (< 2 urn and 2-16 |im). and then analysed by X-ray diffraction (Scintag™) following the procedure described by Five microfacies numbered Fl to F5 represent this environment. Kübler (1987). The two grain size fractions (< 2 urn and 2-16 Although differing in details, they belong all to a urn) were obtained using a timed settling method (based on relatively calm environment, characterized as open marine by its Stokes law) described by Rumley & Adatte (1983). XRD analysis fauna (especially echinoderms). Mudstones. and more rarely was made on oriented clay samples (< 2 |jm and 2-16 (im wackestones, containing spicules, large angular fragments of fractions). The samples were first dried at room temperature echinoderms and shells, serpulids and foraminifera like Alveosepta and placed in ethylene-glycol solvated conditions after the first sp. and Lenticulina sp. characterize this domain, (refer to XRD analysis. The intensities of selected XRD peaks charac¬ Fig. 6, pict. a, b for microfacies Fl and F5).
Kimmeridgian central Jura Mountains 55 SE inter.-/ NW internal supra.- internal external external platform platform tidal platform platform
slope i margin domain HiO
— Ol r<-,-r i/-. sC m f, xt in Os— — —— l"ig. 5. Location of the different microlacics on ü_ ___, _u U. U. - ______toU.U. U-U-Ü-U- the Kimmeridgian carbonaie shelf.
Platform margin (external platform) Microfacies analysis
Three microfacies (F6 to F8) represent this environment. Rapid and important variations in the vertical succession of Grainstones and packstones containing mainly ooids and/or microfacies reveal major discontinuities. These discontinuities peloids indicate high energy environments, small rounded are then used for a tentative sequence stratigraphie interpretation fragments of echinoderms and shells, foraminifera like sensu Vail et al. (1977. 1987). Nautiloculina oolithica characterise this domain as open marine, By definition (Arnaud & Arnaud-Vanneau 1994). a discontinuity (refer to Fig. 6, pict. c for microfacies F7). is located between two layers if there is a lack in sedimentation due to non-deposition, alteration, dissolution or Internal platform erosion. In this study, three types of discontinuities have been distinguished. This domain is separated in an outer part and an inner part. The outer part is represented by two facies (F9-F10). Major discontinuities Grainstones and packstones containing small echinoderm debris, foraminifera and algae indicative of shallow waters They are lithologically well marked (erosional surfaces forming (Cayeuxia, Marinella) characterize this domain. a hard-ground, karstification). The microfacies show rapid The inner part is represented by two microfacies (Fl 1— and important variations across the discontinuity. A good F12; refer to Fig. 6. pict. d for microfacies Fil). Wackestones example is given by the outcrop of Gorges de la Loue where containing oncoids, foraminifera (miiiolids. Siphovalvulina karstification is remarkably developed. The deposit overlying sp.), dasycladacean algae (Campbelliella striata, Salpingoporella the discontinuity is a limestone containing black pebbles and annidata, Clypeina jurassica) characterize this domain. showing graded bedding (Fig. 9). Echinoderm debris are absent, which indicates more or less restricted environments. Minor discontinuities
Recognisable only in the outcrop, minor discontinuities are Intertidal/supratidal domain generally represented by uneven hard-grounds underlining Four microfacies (F13-F16; refer to Fig. 7. pict. e, f, g for relatively minor lithological changes. The succession of microfacies microfacies F14 and F16) represent this environment. Grainstones does not show significant changes. with keystone-vugs and mudstones with birds-eyes, charophytes (Echinochara pecki, Porochara sp.) and/or ostracods Emersive horizons characterize this domain. This third type of discontinuity is represented by intertidal to supratidal limestones with charophytes. ostracods. birds-eyes "Faciès de transgression" mixed facies, FT) and/or algal mats. They show no traces of erosion and are rarely This facies is represented by grainstones containing rounded linked to important lithological changes and/or variations in and angular black pebbles and many micritized rounded the microfacies curves. Emersive horizons present rhythmic echinoderm debris (Fig. 7. pict. h). intercalations in the outcrops of Gorges de l'Areuse and Refer to Figure 8 for the paleoecological distribution of Reuchenette. foraminifera. algae and other elements characterising each environment.
56 P.O.J. Mouchct >> ' • y w .._¦ t- 1 «
c «tys -
; iS s,
•>.
a) b)
S-*^
s **#£ \ c,
Vi? • t ______c) d)
Fig. 6. Microfacies of the Kimmeridgian shelf, (bar 1 mm). Picture a Fl marly micrite. shell debris and foraminifera (Alveosepta sp.). Texture: mudstone/wackestone. Picture b F5 biomicrite with large shell debris, echinoderms. serpulids and foraminifera (Alveosepta sp. and Lenticulina sp.). Texture: wackestone/packstone. Picture c F7 oosparite. echinoderms. micritised shells and foraminifera (Nauliloculina oolithica). Texture: grainstone. Picture d Fl 1 biomicrite rich in dasycladacean algae (Campbelliella striata. Salpingoporella annulata. Clypeina jurassica) and micritised shell remains. Few for¬ aminifera (miliolids. Siphovalvitlma sp.). Texture: wackestone.
Kimmeridgian central Jura Mountains 57 « « .»¦%
-»a i • / } *
5 y
f) ____¥. n_V. ry rTfJ • asi .Cl ¦1 » :-i-.3_-Vfrfif • •_- »• «. \ \ '..> h. W•» ./ v, ï*i$v&ifj «rf * ?>'< L*Œ
»•; xy§&_ » „, .:.¦«. » CS
g) h) __?
Fig. 7: Microfacies of the Kimmeridgian shelf, (bar 1 mm). Picture e F14 algal laminated micrite with fenestral structures. Bioclasts very rare. Texture: mudstone/boundstone. Picture f F16 micrite. ostracods. Texture: mudstone/wackestone. Picture g F16 micrite. charophytes (Echinocliara pecki. Porochara sp.) and/or ostracods indicating fresh water deposits. Texture: mudstone/wackestone. Picture h FT= sparite, black pebbles and micritised echinoderm debris. Texture: grainstone.
58 P.O.J. Mouchet external platform - erosion - internal platform. This discontinuity is in the external platform internal platform inter./ supratidal placed Divisum-Acanthicum Zone by Chevallier domain slope margin (1989). The level of D2 is not attained in this section.
Morillon
is 25 S Microfaciés FT 8 1011 12 13 14 IS 16 The road cut situated about km ol Champagnole rrudstone (France), alongside the road N5 to Morez. The total visible wackestone thickness is about 70 m and the Oxfordian-Kimmeridgian packstone represents grainstone transition. The upper part of the profile shows tectonic birds-eyes complications. As the different French formations are not very keystonevugs black pebbles clearly defined, it was not possible to recognize the formations dolomitization stromatokthes described in the Gorges de la Loue section. The microfacies charophytes de la ostracods curve shows, as at Gorges Loue, external facies in the lower of the series, with minor and discontinuities. intraclasts part major green algae The similarities between the microfacies curves in the Gorges dasycladacean. Igae oncoids de la Loue and Morillon, supported by the variations of the micritized remains miliolids kaolinite content, suggest to place Dl at the top of bed n° 25 in Siphovalvul/na Valvulina the Morillon series. As at Gorges de la Loue, internal facies Nautiloculina abundant above D2 is in Morillon Atveœepta are more Dl. not present the Lenticulina section. peloids m rxxt. spicules serpulids Gorges de l'Areuse
The is situated about 15 km W of Neuchâtel (Switzerland), Fig. X. Distribution of the different elements, foraminifera and algae on the outcrop Kimmeridgian carbonate platform. The darker zones show the characteristic near the power-station of Combe-Garot (cord. locations of the different elements. The brighter /ones show the total distribution 551.300/201.450. CN 1:50.000 n° 242 Avenches). The total of the elements on the theoretical carbonate platform during Kimmeridgian thickness of the series is about 170 m (stratigraphie interval time. Note that a microfaciés is rarely defined by a single criterion. Oxfordian-Portlandian). This outcrop has already been studied by Meia (1965) and Persoz & Remane (1973). The Ste-Verena Oolith is not as well developed as at its type-locality or in the Microfacies curves and description of sections Reuchenette quarry. The top of the "Kimmeridgian" is given by the Banc à Nérinées. The microfacies curve shows a The microfacies curves from five selected sections (Morillon, predominance of external facies in the lower part of the series, up Gorges de la Loue, Gorges de l'Areuse, Reuchenette and Va- to a zone covered by a rockslide and vegetation. Minor and benau) are represented in Figure 10. For reasons of presentation major discontinuities and also emersive horizons have been only the discontinuities used in regional correlations recognized in the Gorges de l'Areuse series. The dasycladacean (named Dl and D2) are described in this paper. association Campbelliella striata - Clypeina jurassica appears for the first time in bed n° 42. Dl has not been located precisely Gorges de la Loue in this section but could be concealed by the rockslide. The The Gorges de la Loue section is situated about 20 km N of internal facies are strongly represented above this covered Pontarlier (France), alongside the road N67 to Ornans. This zone, analogous to the above described sections of Gorges de profile was already measured and described by Chevallier la Loue and Morillon. D2 is placed at the top of bed n° 56. The 1989). The total thickness of the series is about 80 m. showing microfacies curve shows a rapid change from the supratidal the Oxfordian-Kimmeridgian transition. The microfacies curve domain to the outer part of the internal platform. D2 is located shows external facies in the lower part of the succession, up to below a Cladocoropsis mirabilis-nch bed and the Banc à the "Calcaires de la Loue". Internal facies are more dominant Nérinées. in the upper part, especially in the "Tidalites d'Arc-sous- Cicon" and the of the "Calcaires et Marnes de Sa- upper part Reuchenette voyeux". Minor and major discontinuities have been recognized in the Gorges de la Loue series. Discontinuity Dl is The section is situated about 10 km N of Biel/Bienne (Canton located at the top of bed n° 14 and is indicated by a strongly Bern. Switzerland), in the cement-quarry of Péry-Reuchenette eroded surface forming a hard-ground (karstification), overlain (cord. 585.900/226.100. CN 1:50,000 n° 233 Solothurn). The by limestones representing mixed-facies (black pebbles total thickness of the series is about 210m (stratigraphie interval breccia showing graded bedding, see Fig. 9). The microfacies Oxfordian-Portlandian). This outcrop has already been curve shows an important and rapid change across this level: studied by Rollier (1888). Baumberger (1915). Ziegler (1956)
Kimmeridgian central Jura Mountains 59 SR U
— ~ < —
'5 — -S ~ M w ¦s fire -Ì Dl ^ '-/ * \ R — à* s r» ^ — -- t -*K3
$& >
' Ä •? '«r <<^**~ Fig. 9. Gorges de la Loue, major discontinuity DI overlain by pebbly graded limestones. Gorges de la Loue, top ofthe Calcaires de la Loue, karst filling on top ofthe major discontinuity Dl Gorges de la Loue, top ofthe Calcaires de la Loue, detail ofthe first black pebble graded breccia (bed n' 15) overlying the major discontinuity Dl. and Thalmann (1966) who renamed the Kimmeridgian auc- Formation is defined here by the Exogyra virgula Marls. Minor torum as Reuchenette Formation. The Ste-Verena Oolith is and major discontinuities and also emersive horizons have well developed giving the limit between the Sequanian auc- been recognized in the Reuchenette series. The microfacies torum Upper Oxfordian) and the Kimmeridgian auctorum curve shows a predominance of external facies in the lower Reuchenette Formation), the top of the Reuchenette part of the series, up to Dl and the scree covered zone. Inter 60 P.O.J. Mouchet nal facies are predominant in the upper part of this section. able rate of interstratification (between 5-20% smectite) and The succession of emersive beds, between Dl and D2. looks are irregular. Among grain minerals, quartz, feldspar, pyrite similar to what was observed in Gorges de l'Areuse (at Combe- and goethite are present, as already observed by Persoz (1982) Garot). The dasycladacean association Campbelliella striata - and Gygi & Persoz (1986). Rectorite (regular mixed-layer, Clypeina jurassica appears for the first time in bed n° 27. Dl is illite-smectite type) has been observed here for the first time. located at the top of bed n° 19. The microfacies curve shows a The distribution of the observed minerals across the rapid variation from the supratidal domain to the outer part of Kimmeridgian carbonate shelf is given in Figure 11. It was the external platform. The overlying beds are covered by obtained by linking the diffraction patterns to microfacies and scree. D2 is located at the top of the bed n 41 (dolomicrite then averaging the peak intensities ofthe minerals (after Adatte. with birds-eyes). The microfacies curve shows a rapid change 1988). from the supratidal domain to the outer part of the internal Mica and kaolinite are the principal constituents of the platform and then to the external platform. This discontinuity <2 urn fraction, together with mixed-layers and chlorite. D2 is located just below a Cladocorospsis mirabilis-rich bed as Quartz is rarely present in this size fraction, but is more abundant in the Gorges de l'Areuse. in the 2-16 urn fraction. Occurrences of smectite are rare and do not follow a regular pattern. Rectorite is more common Vabenau on the external platform. The greatest vertical variations are observed in the kaolinite The section is situated about 10 km SE of Porrentruy. near intensities (from 0-3000 CPS). The kaolinite intensity drops Courgenay (Canton Jura. Switzerland), in a quarry (cord. sometimes nearly to zero while the intensities of mica, mixed- 574.800/248.200, CN 1:50,000 n° 222 Clos du Doubs). The total layers and chlorite remain rather constant. There is no obvious thickness of the series is about 25 m (representing the lower link between lithology (microfacies) and kaolinite content. part of the Kimmeridgian and the Banné Marls). The limit The variations ofthe kaolinite content seem indeed to be Oxfordian-Kimmeridgian is not visible. The Banné Marls are very independent from the facies and should therefore reflect changes well developed, below them we recognize the Calcaires à in the original bulk composition of the insoluble residue. The ptérocères inférieurs. The series above the Banné Marls are studied area is not too vast so that the presence/absence of this eroded. Aspidoceras cf. acanthicum was found in the limestone mineral can be considered as isochronous. Therefore kaolinite just below the Banné Marls near Courgenay (Gygi & Persoz can be used as a chronostratigraphical marker. 1986, Gygi 1995). The microfacies curve shows only small variations within the external platform. Dl is located at the top of bed n° 6, underlying the Banné Marls. D2 is not present in Rectorite these series. This regular mixed-layer mineral occurs in the < 2 urn size The microfacies of the different outcrops often correlate fraction. The main reflections are observed (on ethylene-glycol well. Detailed correlations between different sections are solvated samples) at 26.6  (001*). 13.3  (002*) (* nevertheless very difficult for two reasons. The first is the frequent superstructures). The presence of a reflection at 13.3 A means that lack of biological markers. Only the joint appearance of the the illite-smectite mixed-layer is ordered (Rl ordering. Moore dasycladacean algae Campbelliella striata and Clypeina jurassica & Reynolds. 1989). Ordering causes the appearance of new can be used as a chronostratigraphic marker (Strohmenger reflections containing components of the 001 series of the et al.. 1991). The second reason is that the different formations superstructure. of the French Jura Mountains are very difficult or impossible Content in swelling (% smectite in mixed-layers) is to recognize outside the type-localities, as their limits and estimated by using the A001/002-002/003 method in °29 CuKa, lithological content are not clearly defined. Fortunately, (Moore & Reynolds. 1989). The two next diffraction patterns mineralogical analyses of the series allowed to complete and confirm (Figs. 12 & 13) show the peaks of mica, mixed-layers and the proposed correlations. rectorite near 10°28 CuKai. and between 16-17.7°26 CuKoti. A°29 16.88 - 9.60 7.28°, illite percentage is nearly 70% (estimation after Moore & Reynolds 1989. p. 251 Mineralogy Rectorite is mainly found in micritic and bioclastic Several mineralogical studies, covering parts of the Upper limestones of the external platform. The intensity of the 002* peak Jurassic and the Lower Cretaceous have been carried out by is generally weak (< 80 CPS). The origin of this mineral can be Thalmann (1966): Persoz (1982): Viéban (1983). Adatte & diagenetic or detrital. Theoretically, rectorite could result from Rumley (1984); Gygi & Persoz (1986). However, until now. the diagenetic transformation of smectite but, according to Ramseyer Kimmeridgian was not analysed in detail. (1984), the sedimentary cover was not thick enough to The clay-minerals recognized here are: mica, kaolinite, allow this transformation. It appears thus that rectorite is of mixed-layers (IS), smectite, chlorite, rectorite. The mixed-layers detrital origin like mixed-layers (IS) with low content of are generally interstratifications of illite and smectite and swelling layers and smectite. form a broad peak on Xray-diffractograms. They have a vari¬ Kimmeridgian central Jura Mountains 61 1 2 Gorges de la Loue : kaol <2pni (CPS) Mmilloii: I kaot <2pm C l'S -3. G II 1 n M J! 34 H c 10 ^ ¦ ¦1 E î M —_. 1) 1)1 1 m! — * —» i» • » •v, A K U t. - * _____ 1 — * — «¦ Ns- -- 6 Kaolinite ___, =1 Kaolinite S turni ssy C 0 2000 Porrentrui N (Jorges de la Loue M< ulier Morillon ¦ i; Font mt le Uns flauttiela-Tour Noirvaux I UC (Jorges de l'Areuse cm Combe-Girard 'l.ilel Neuchâtel (n^09) Pontarlier Reuchenette 10 Tramelan Champagnole < 11 Mnntbaulier Gratter. 13. Raimeux snkrv 14. \ ;ihi n.m 15 Hanne 16 Bure ln°5) 62 P.O.J. Mouchet Curges de l'Areuse iCumbe-Garotl : Kcuclunctlc kastl <_um (ï>Si 9 D2 D2-. c _ sX N « t T ^dasycladacean kaol <2^m iCI'Si 14 » 2 Yabenau, is kassl <2pm 2- S (CPS) covered /une ¦D1+ Dif? Dl-HpSJN V- 9 r 'i f- & E 0 1000 P ^ br Kaolinite 1 I S 5 0 3000 Kaolinite Fig. 10. Correlations based on microfacies evolution and kaolinite distribution (fraction < 2 pm) at Morillon. Gorges de la Loue (A Calcaires de Besançon. B Calcaires et Marnes de Chargey. C Calcaires à stromatoporides de Matafelon. D Calcaires des Fins, E Calcaires de la Loue. F Tidalites d'Arc- sous-Cicon. G Calcaires et Marnes de Savoyeux). Gorges de l'Areuse (Combe-Garot). Reuchenette and Vabenau. (bar 10 m). 0 2000 Kimmeridgian central Jura Mountains 63 intertidal/ external platform internal supratidal slope n platform domain C — fs| CO ^ W. sC _._._._._._._._.¦— N r, Ttu-, scr-f— ___.ZZZZZZZ.cos Sin mixed-layers mica 001 (SKI kaolinite 001 11 XI chlorite 002 UHI quartz 100 (2-16pm) Fig. 11. Distribution of minerals on the Kimmeridgian shelf. Kaolinite distribution and correlation linked with great changes in microfacies or mineralogical composition. Mineralostratigraphic correlations are based on variations of Diagenetic alteration of the series, due to recristallization the kaolinite content. Kaolinite distribution profiles present of carbonate in the presence of meteoric water may be indicated significant analogies in the different sections (Fig. 10). Correlations by a covariance of carbon and oxygen isotopes (Jenkyns & based on kaolinite seem to confirm the proposed microfacies Clayton, 1986). When plotted as 813C-S180 graph, the carbon correlations. The discontinuity Dl is underlined by a and oxygen isotope data show no evident covariance (nb. of sharp decrease in kaolinite content. samples 38, r2 0.312). This suggests that the isotopie Kaolinite content appears to be independent from the composition of the analysed sediments has not been significantly different lithologies and depositional environments which is a altered by diagenesis. Stable isotopes can thus provide another strong argument for its detrital origin. The variations observed tool for correlations in the Upper Jurassic. in the kaolinite pattern reflect therefore variations ofthe detrital supply. The variations in kaolinite content might reflect climatic Correlations, sequence stratigraphy and cyclostratigraphy changes. An analysis of stable isotopes (bulk rock. ETH Correlations Zürich) of samples of the Gorges de la Loue section supports this hypothesis. Values of Ô13C are generally between 1 and The different profiles are correlated by using variations of 2.5%o (PDB). ôlxO between -4 and -2%o (PDB). A major microfacies and of kaolinite content. Moreover, short distance isotopie negative excursion is measured in both 5I3C and 5180 correlations have been established, using the joint appearance (%oPDB) at discontinuity Dl (Fig. 14). These shifts are not of the dasycladacean algae Clypeina jurassica and Campbelli- 64 P.O.J. Mouchet FN: M0N8G2.NI ID: MONTBEAUTIER 8 <2 GLYCOLE SCINTAG/USA DATE: OB/31/93 TIME 06 33 PT: 1 .80000 STEP: 0 .03000 WL: 1 .54060 PK# 2-THETA PK-HGT FWHM 1 8.7926 437 0.397 2 9.1833 214 0.555 3 9.6087 96 0.529 4 8.3845 64 0.249 o \ rl/ ° \ s u• 1 /lmsI ° \ — \ _ II _ \^~\ ° in \ 4> \ u Iteration 15 Error 9.68 \ Line Two-theta Sigma Peak (CPS) Sigma ESD Fwhm ESD Exd Area (CPM) 1 8.7926 0.0348 437.10 149.91 0 0594 5 44 11317 86 2 9.1833 0.1116 213.73 92.4 4 0 4196 6.51 7736.69 Fig. 12. diffraction presenting 3 8.3B45 0.0324 64.13 15.40 0 0402 17 .63 1040.70 X-ray pattern reflections and rectorite 4 9.6087 0.1996 96.50 112.38 0 1474 9.53 3402.46 of mica 001, mixed-layers (IS) near !0"28CuKai. FN:M0N8G2.NI ID: MONTBEAUTIER 8 <2 GLYC0LE SCINTAG/USA DATE: 08/31/93 TIME: 06: 33 PT: 1.80000 STEP: 0.03000 WL: 1 .54060 PK# 2-THETA PK-HGT FWHM 1 17.6933 231 0.414 2 16.8799 95 0.515 3 17.3277 90 0.533 u j / N \ 4 16.5479 49 0.092 u J ° \ *r / 1 n \ 5 16.0081 41 0.060 Si / / o t 6 16.2925 37 0.194 U f\j E 1 v/ \ / w / \ Iteration 15 Error IB.41 Line Two-tneta Sigma Peak (CPS) Sigma ESD Fwnm ESD Exp Area (CPM) 1 17.6933 0.0690 231.12 170.96 0.0924 3 30 6416 16 2 17.3277 0.2365 90.44 131.49 1.1111 23 74 3202 42 3 16.8799 0.2462 95.39 117.00 0.3977 15 71 3237.62 4 16.2925 0.0284 37.47 13.09 0.0705 46 09 473. 10 Fig. 13. X-ray diffraction pattern presenting 5 16.0081 0.0093 40.73 12.10 0.0249 69 06 155 79 reflections of mica 002. mixed-layers (IS) and rectorite 6 16.5479 0.0166 4B.68 24.75 0. 1226 0 41 681.76 between 16-17.7°26 CuKai. ella striata, as proposed by Strohmenger et al. (1991). Two de l'Areuse or "Exogyra virgula Marls" at Reuchenette) major discontinuities are correctable over the whole studied between "Kimmeridgian" and "Portlandian". just below a bed area: Dl and D2. enriched in Cladocoropsis mirabilis Felix. This discontinuity is Dl is located at Gorges de la Loue at the top of the recognized in all profiles and drillholes. For Meyer (1994) the Calcaires de la Loue and marked by a strong erosion (Fig. 9). The Banc à Nérinées near Solothurn is to be placed in the Autissio- top of the Calcaires de la Loue is dated as Acanthicum Zone diorensis Zone, whereas the Virgula Beds of Alle are rather to by Chevallier (1989). This major discontinuity is recognized at be placed in the preceding Eudoxus Zone Gygi (1995). Morillon. Reuchenette and Vabenau (below the Banné Marls) and in all other sections and drillholes covering this strati- Tentative sequence stratigraphy and cyclostratigraphy graphic interval. The Dl discontinuity is generally marked by the absence of kaolinite or a low kaolinite content. A tentative interpretation of the successions in terms of The D2 discontinuity is located a few meters below the sequence stratigraphy, as defined by Vail (1977. 1987), Haq lithostratigraphic boundary ("Banc à Nérinées" in the Gorges (1991) has been carried out. Sequences are made up by three Kimmeridgian central Jura Mountains 65 cumulated Gorges de la Loue : thickness (ml )13C%.(PDB) .)ieO%4P->EI) 70 - 3 * 1)2 (iorges de l'Areuse Ml « î 1)1 r l dc T E kil-u.' 411 t skills s/ VsMsl y Mi 'i II 2(1 -6 -4 -2024 Reuchenette Fig. 14. Gorges de la Loue. 5"C (%.. PDB) and 5'*0 (%. PDB) variations. Note important shift above major discontinuity Dl. kinds of systems tracts: lowstand systems tracts, transgressive systems tracts and highstand systems tracts. But on the sf^sN Kimmeridgian shelf, sequences sensu Vail (1977. 1987). Haq (1991) "Kimmeridgian" "Portlandian" and Arnaud & Arnaud-Vanneau (1994) are never complete due to emersion and erosion. Lowstand systems tracts are absent and transgressive systems tracts are rarely represented. Fig. 15. Comparison of the Fischer-plots representing the upper part of the a The two major discontinuities (Dl and D2) delimit series at Reuchenette and Gorges de l'Areuse. sequence sensu Vail. Dl is well marked by karstification underlying a pebbly graded limestone and marly sediments representing mixed-facies in the Gorges de la Loue section. This level probably represents a transgressive systems tract. Otherwise, assuming invariant cycle period and subsidence rate (average the deposits between the two major discontinuities (Dl cycle thickness/period), by plotting the thickness and and D2) correspond mainly to a highstand systems tract, but subsidence of successive cycles versus time. In constructing such the limit between the transgressive systems tract and the diagrams, the thickness of a long and supposedly continuous following highstand systems tract is not easily recognizable. In sequence of cycles is divided by sequence duration to arrive at a conclusion, application of sequence stratigraphy is very difficult long-term rate of regional subsidence. Total duration is then in the sense that the identification of sedimentary bodies evenly shared out among all cycles. The thickness of each cycle in terms of transgressive system tracts, highstand desposits etc. records the amount of accommodation space that is filled during is often impossible. Nevertheless, two major discontinuities are cycle deposition. Cycle thickness less subsidence should well recognizable and very helpful in establishing regional reflect changes in the rate of accommodation space creation. If correlations. the regional subsidence rate is constant, then such long-term Goldhammer (1987) and Goldhammer et al. (1987) use changes could reflect global eustasy. Drumond & Wilkinson Fischer-plots (cycle thickness diagram. Fischer. 1964) to correlate (1993) doubt of the liability of this method because the series in the Italian Triassic. They recognize eustatic fluctuations sedimentation is considered as continuous and erosion or of the sea-level corresponding to Milankovitch 1941 compaction of the series are not taken in account. Nevertheless, a cycles. Cycle thickness diagrams have been constructed (Fig. 15). tentative comparison between Gorges de l'Areuse and Reu- 66 P.O.J. Mouchet tances, thus allowing lithostratigraphic correlations: Ste-Verena c Oolith. Banné Marls. Banc à Nérinées and Exogyra virgula ¦M £ 1 s Marls and the Banc à Cladocoropsis mirabilis Felix. The latter is located just below the classical lithostratigraphic markers of Ç 3 C .3 Calcaires the Kimmeridgian auct.-Portlandian auct. limit (Fig. 16). a. en plaquettes The correlations made here are mainly the result of field Banc à Exogyra virgula observations, microfacies analyses and the kaolinite distribution. Nérinées / Maris Two major discontinuities corresponding to sequence E Cladocoropsis/ mirabilis Bed D2 boundaries have been recognized in Kimmeridgian strata l_3 enabling us to propose chronostratigraphic correlations for the U 3 studied area. Dl is located in the Acanthicum Zone (Chevallier, 73 C 1989, Gygi 1995). D2 corresponds to SB 140 determined by -3 OJJ Strohmenger et al. (1991) located in the Autissiodiorensis T3 Banné Maris 'C Dl Zone (Meyer. 1994. Gygi 1995). s Acknowledgments § S Ste-Verena Oolith This work is a summary of my Ph. D. Thesis about the Kimmeridgian of the 11 Central Jura. I thank Dr. Jürgen Remane. Dr. Bernard Kübler and Dr. Thierry Adatte for stimulating discussions, field trips and the detailed critical VUtr 3y many joint review of early versions of the manuscript. 1 thank also Dr. Reinhard Gygi for the determination of the ammonite and Pierre-Olivier Mojon for the determination of charophytes. This study was supported by the Fonds National Fig. lb Recognizable Kimmeridgian formations and discontinuities Suisse de la Recherche Scientifique (credits n 21-29909.90 et 20-35878.92). REFERENCES chenette's upper parts of the sections was made. The two Adatte. Th. 1988: Etude sédimentologique. minéralogique. micropaléontolo¬ sections show a of emersive between the cyclic repetition layers gique et stratigraphique du Berriasien-Valanginien du Jura central. Thèse. two major discontinuities Dl and D2. Both Fischer-plots are Neuchâtel. very similar (Fig. 15) and some peaks could be correlated. This Adatte. Th. & Rimley. G. 1984: Microfaciès, minéralogie, stratigraphie et confirms the correlation based on microfacies and kaolinite évolution des milieux de dépôts de la plate-forme berriasio-valanginienne des de Ste-Croix (Vaud), Cressier et du Landeron (Neuchâtel). distribution. However, without data, all these régions biochronological Bull. Soc. neuch. Sci. nat. 107. 221-239. correlations remain hypothetical. Note that the general aspect 1989: Sedimentology and mineralogy of the Valanginian and Hauterivian of the Fischer-plot curve is very similar to the Exxon curve in the Stratotypic Region (Jura Mountains. Switzerland). In: Cretaceous (Vail et al.. 1987) supporting the assumption that the cyclicity of the Western Tethys: Proc. 3rd Int. Cretaceous Symp.. Tübingen. 329-351 (Ed. by Wiedmann. J.). Schweizerbart. Stuttgart. is due to eustasy. Arkfll. W. J. 1956: Jurassic Geology of the World. Oliver & Boyd. Edin¬ burgh: 80. d-Vanneai A. 1980: et sedimen¬ Conclusions Arnai Micropaléontologie, paléoécologie tologie d'une plate-forme carbonatée de la marge passive de la Téthis: du Vercors de la Chartreuse. Geol. mém. The Reuchenette Formation was introduced by Thalmann l'Urgonien et alp. (Grenoble), 11. 3 vols. (1966) to replace the auctorum without changing Kimmeridgian Arnald, H. & Arnai d-Vanneai A. 1994: Stratigraphie séquentielle et pla¬ its boundaries. This formation is. however, only defined by tes-formes carbonatées. Université Joseph Fournier. Institut Dolomieu. its boundaries. Lithology and its fossil content are not Grenoble. F.. Gycìi. R.. B. A. & Wierzbowski. A. 1993: The Amoebo¬ characteristic. The Reuchenette Formation is. thus, difficult to map Atrops. Matya. ceras faunas in the Middle Oxfordian-lowermost Kimmeridgian. and does not seem to be a good for the Swiss type-formation Submediterranean succession, and their correlation value. Acta geol. pol.. Jura mountains. 43/3^t. The same is true for the formations established by Bernier At BOIN. J.: Broi sse. R. & Lehmann. J.P. 1988: Précis de géologie: vol. 2. (1984) and Chevallier (1989) in the French Jura Mountains. Stratigraphie. Dunod Université. Bai mberger. E. 1915: Beiträge zur Geologie der Umgebung von Biel und Many of them are not recognizable by their lithology or fossil Grenchen. Verh. natf. Ges. Basel. 26. boundaries often obvious. content. Moreover, their are not Bi rmer, P. 1984: Les formations carbonatées du Kimmeridgien et du Port¬ Only some of these formations are recognizable over short dis- landien dans le Jura méridional. Stratigraphie, micropaléontologie, sédi- Kimmeridgian central Jura Mountains 67 mentologie Thèse Univ. Lyon I. Doc. Lab. Géol. Fac. Sci. Lyon 92/1-2. Moore. D. M. & Reynolds Jr.. R. C. 1989: X-ray Diffraction and the Identi¬ 803 pp. fication and Analysis of Clay minerals. Oxford University Press. Brindley. G. W. 68 P.O.J. Mouchet