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C. R. Geoscience 335 (2003) 681689

Stratigraphie

Prsence de Palocne marin dans les Grands Causses (Fr

Bernard Peybernsa,c,, Richard Ciszakb, Marie-Jos Fondecave-Wallezb,Pierre-Jean Combesc, Hubert Camusc, Michel Srannec

a UMR 5573, Stramipal, universit Paul-Sabatier, 39, alles Jules-Guesde, 31062 Toulouse cedex 04, Franceb UMR 5563, universit Paul-Sabatier, 39, alles Jules-Guesde, 31062 Toulouse cedex 04, France

c UMR 5573, universit Montpellier-2, place Eugne-Bataillon, 34095 Montpellier cedex 05, France

Reu le 13 janvier 2003 ; accept le 20 mai 2003

Prsent par Michel Durand-Delga

Rsum

Dans les Grands Causses, des valles incises, lapiez, fissures et dolines hrites de karstifications polyphasesont t remplies de sdiments marins palocnes de lintervalle P1cP3 (Danien suprieur Slandien infrieur). Cesse rpartissent en trois facis dtritiques, conditionns par la tectonique extensive contrlant karstification et rosion. Lmarins nocrtacs identifis dans ces facis sont interprts comme remanis partir de dpts hypothtiquement pLa probable connexion palogographique avec le sillon des brches palocne pyrnen suppose lexistence dSENW traversant les aires continentales du Bas-Languedoc et drainant vers le nord-ouest la transgression marinejusqu la rgion de Rodez.Pour citer cet article : B. Peyberns et al., C. R. Geoscience 335 (2003). 2003 Acadmie des sciences. Publi par ditions scientifiques et mdicales Elsevier SAS. Tous droits rservs.

Abstract

Identification of Palaeocene marine sediments in the Grands Causses (France).In the Grands Causses, incised vallelapies, fissures and sinkholes inherited from successive polyphase karstifications were filled by Palaeocene marineoverall assigned to the P1cP3 interval (Upper DanianLower Selandian). These sediments are distributed into thrfacies, generated by extensional tectonics controlling karstic and erosional processes. Upper Cretaceous marine foswithin these facies are interpreted as reworked from hypothetically pellicular deposits. The probable palaeogeconnection with the Pyrenean Palaeocene Breccia trough supposes the presence of a SENW ria running acontinental areas of Lower Languedoc and draining towards the northwest the marine waters of the Palaeocene transfar as the Rodez region.To cite this article: B. Peyberns et al., C. R. Geoscience 335 (2003). 2003 Acadmie des sciences. Publi par ditions scientifiques et mdicales Elsevier SAS. Tous droits rservs.

Mots-cls : Palocne ; foraminifres planctoniques ; ria ; palokarsts ; Grands Causses ; France

Keywords: Palaeocene; planktonic foraminifera; ria; palaeokarsts; Grands Causses; France

* Correspondance et tirs part.Adresses e-mail : peyberne@cict.fr, peybernesb@aol.com (B. Peyberns).

1631-0713/$ see front matter 2003 Acadmie des sciences. Publi par ditions scientifiques et mdicales Elsevier SAS. Trservs.doi:10.1016/S1631-0713(03)00119-6

ous droits

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1. Introduction

The presence of bauxites and Cretaceous rocassigned to Coniacian (marine) and to CampaniMaastrichtian (continental) has been recently edenced [3,4] on the Grands Causses, filling a kartopography. In the same time, in the Pyrenean realmwas demonstrated the down cutting of a marine trouPalaeocene in age. This trough was filled by smarine breccias associated to hemipelagites coning DanianSelandian planktonic foraminifera. Cosequently, we have reviewed the supposed Uppertaceous outcrops of the Causses and discoverDanianSelandian planktonic microfauna (calledsemblage DS) within 12 of them, concluding that tCretaceous marine microfossils were here reworkedetritic clasts. The topics of this paper are: (a) to garguments for this new dating; (b) to inventory thecies of the Palaeocene series, transgressive over aviously emerged and karstified area; (c) to outlinePalaeocene ria probably joining the Pyrenean trouto the Grands Causses.

2. The Upper Cretaceous and Palaeocene series fromthe Causse de Campestre

The post-Jurassic series of the Campestre bewith bauxites (Luc-bas) gullying (surface K1) thKimmeridgian limestones. Above, the overlying dposits, either preserved within palaeokarstic cavior forming scattered rocks, can be reconstrucas following from the analysis of several localiti(3 to 9, Fig. 1). (A)The marine Upper Cretaceousdeposits seem not to exist as stratified beds, buis not excluded that some of them have been cserved in situ, separated from the Jurassic carbates by an hypothetic surface K2. Nevertheless, athonic Coniacian assemblage C1 has been recogn[3,4], either within the scattered rocks or as clareworked within Palaeocene breccias. A secondworked assemblage C2, younger but planktonic,been listed within Uppermost Cretaceous contintal and Palaeocene marine deposits. (B)The Upper-most Cretaceous continental deposits fill a karstic cav-ity (surface K3) reaching the bottom of the Virenq

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canyon (8a) [1] and consist of marls containing Capanian/?Maastrichtian pollens, characea (Peckicharacaperata) andMunieria (assemblage C3). These laalgae are abundant in limestones redeposited wiPalaeocene breccias or constituting lenses presebetween these last ones and Jurassic. (C)The Palaeo-cene marine deposits are evidenced, over K4, by thDanianSelandian assemblage DS (Fig. 5), identifrom marls (3) or within the calcareous matrix of tbreccias (4 to 8) and assigned to P1cP3. Three fa(Fig. 3), characterized by DS, have been separa(a) TheLuc-bas facies (F1) consists of a rhythmic alternation of sandy clays and microbreccias (17 mleast). Its base is underlined by a key-bed of high soncolithes. (b) TheSerre dAubanel facies (F2) con-sists of coarse breccias reworking Jurassic andMu-nieria-bearing carbonate clasts and filling lapies inJurassic limestones. Their matrix contains C1, C2DS. F2 is interpreted as a submarine stacking of bloalong fault scarps having generated the karstic cties and still active during the deposition of the brecias. The reworking of Barremian/Aptian orbitoliids within the breccias suggests the deposition ofrine Lower Cretaceous beds, unknown so far, overCevennes basement or close to them. (c) TheVirenquefacies (F3) is observed at the bottom of the preseVirenque canyon (8a); it consists of pink hemipelacarbonates and microbreccias, dated by DS, filkarstic cavities (K4) (Fig. 4). (D) Theerosional karsticpalaeosurfaces (Fig. 3) involve, successively supeposed: (a) K1, at the foot wall of the bauxite, whiis not dated between Jurassic and Palaeocenewhose main bauxitogenic period is AptianAlbiin the near PyreneanLanguedocianProvenal re(b) K2, hypothetic, which could have been locatat the base of Coniacian marine limestones (notservedin situ?) and dated of CenomanianTuron(after the genesis of the bauxites); (c) K3, which uderlines the base of the Campanian/Maastrichtian ctinental marls and corresponds to a long periodemersion; (d) K4, which is the most important awidespread of the herein studied surfaces, cuttingreworking the terms of the JurassicMaastrichtianterval, and dated Lower Danian because earlier tCampano-Maastrichtian and later than Upper Dan

B. Peyberns et al. / C. R. Geoscience 335 (2003) 681689 683

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3. Possible lateral extension towards northwest andsoutheast

The Palaeocene marine deposits have been idfied by DS on the Causse de Rodez(1,2). They con-sist of sandstones/microbreccias (F1) and clays,tercalated between Liassic limestones and Miocbasalts. Towards the southeast, on the Sranne Mtain, red microrhythmites (F3), filling cavities, are alPalaeocene in age. In the Bois de Paris (12), the CdEmbrasasse sinkhole is surrounded by Palaeomarine breccias reworking Tithonian and Valanginclasts, oncolithes,Microcodium and containing the assemblage DS within their matrix.

4. Origin of the Palaeocene sea and conclusion

We must look for the relationships that probably eisted during Palaeocene between Pyrenees and GCausses. The difficulty comes from the Palaeoccontinental facies (Vitrollian) of Languedoc. Thesrelationships could have been provided by a SENmarine ria connecting Pyrenees and Causses acthe continental Languedocian areas and running aante-P1c karstic valleys, where the marine waterthe DanianSelandian transgression have been cized from the meridional breccia trough [5].

1. Introduction

La prsence ponctuelle de Crtac suprieur msur les Grands Causses a t signale de longue[1,2]. Rcemment [3,4], ont t dcrits dans cettegion des gisements de bauxite et de Crtac sup sous diffrents facis, marins (Coniacien) et conentaux (Campano-Maastrichtien) , lis une tographie karstique post-bauxite et ant-coniaciennemme temps, dans le domaine pyrnen proche,dmontre [5] lexistence dun sillon marin palcne, grce la dcouverte de foraminifres planniques du Danien suprieurSlandien infrieur ddes hmiplagites associes des brches accles dans des canyons sous-marins. Ce sillon, adent par des les estouest et identifi de lAtltique la Mditerrane, sintercalait