The Barrême Basin and the Gévaudan diapir - an example of the interplay between compressional tectonics and salt diapirism Rod Graham¹, Lajos Adam Csicsek¹ ¹Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ, UK email: [email protected], [email protected]

1) Abstract, Regional setting 2) Stratigraphy

System/ Series/ Code/ Stage/ Regional System/ Series/ Code/ Stage/ Regional period epoch index age tectonics period epoch index age tectonics Mio-Pliocene units AR N Our understanding of the role of salt diapirism in determining the finite Ba m-pl n7 Albian Pliocene Neogene Undiff. Mio- geometry of fold and thrust belts has grown apace in the last few years, g3V AT b g3G Oligocene units Aptian g2S Chattian a n6 g2R g1S g1B

e7g1,G Colliosion but the interplay between the two remains a significant problem for n4-5 Barremian Oligocene Rupélian e7 Priabonian e6-7C

structural interpretation. The Gevaudan diapir in the fold and thrust belt Lower Eocene units n3 Hauterivian e Bartonian Subduction of the Cretaceous Paleogene eC Eocene Lutetian? European margin of the sub-Alpine chains of Haute is well known and has been Foreland basin succession Cretaceous n2c Subduction of the Upper Cretaceous units Pe n2b documented by numerous eminent alpine structural geologists. n2 Valanginian Paleocene Valais Ocean DT Ar n2a (Rifting of the Valais Ocean)

Maastrichtian of the PLO Graciansky, Dardot, Mascle, Gidon and Lickorish and Ford have all n1 Berriasian Subduction Campanian Lower Cretaceous units A D j9 Tithonian j6-9 c5 Santonian described and illustrated the geometry and evolution of the structure, BA j7-8 Kimmeridgian j5-6 j5 and Lickorish and Ford’s interpretation is figured as an example of Upper Jurassic units c3b4 Coniacian

G Upper c3 Turonian diapirism in a compressional setting by Jackson and Hudec in their text M Cretaceous c2 Upper

Jurassic Cénomanian S Ocean c1

on salt tectonics. We review these various interpretations and present Middle Jurassic units j2-4 Oxfordian Postrift succession another. Terres noires Cretaceous

Lower Jurassic units n7 Albian Ocean

The differences between the various interpretations say much about the Postrift succession j3 Callovian CA Spreading of the Piemont-Liguria Lower V j2-3 j2-3 Bathonian Jurassic complex interplay of salt diapirism and thin-skinned thrusting and have 200 km Cretaceous Triassic units Spreading of the Valais

j2-3 j1S profound implications for the way we interpret the tectonic and Bajocien

Middle j1 j1 Jurassic sedimentary evolution of the Barreme basin which lies adjacent to the Permian units j1D Sandstone l9 Aalenian diapir. l7 l6 Toarcien Conglomerates

10 km l5 Pliensbachian Ocean (PLO) The Barreme basin is a thrust-top fragment of the Provencal foreland Crystalline basement Synrift succession

Lower l3-4 Sinemurian

basin and has been described in detail from both sedimentological (e.g. Jurassic lD Chalky limestone and marl Rifting of the Piemont-Liguria Figure 1. The fold and thrust belt of the Southern Subalpine Chains comprises the Digne and Authon thrust l1-2 Hettangian Evans and Elliott, 1999) and structural (e.g. Antoni and Meckel, 1998) t10 Rhaetian Upper t7-9 sheets. The thrust system has polyphase deformational history (Graham et al. 2012.) Thrusting started before the Triassic Keuper tG,tK Evaporites Marl

points of view. Here we make the case that it is also a salt related Triassic M.Triassic t2 Muschelkalk minibasin - a secondary minibasin developed on a now welded Eocene. During the Eocene and Oligocene a series of thrust-sheet-top basins evolved one of which is the Barréme L.Triassic t1 Buntsandstein Interbedded marl basin. During the Miocene and Pliocene the mountain front reached the basin. Permian allochthonous Middle Cretaceous salt canopy. We believe that within and limestone The study area is indicated by the black rectangle. The location of the regional cross-section (Fig. 3,4) is indicated Units autochtonous Permian units the basin it is possible to interpret successive depocentres which may Autochtonous Undifferentiated

Autochtonous Cherty limestone crystalline basement by the black line. The white line indicates the edge of the Provencal platform during the Early and Middle Jurassic. Carboniferous record progressive salt withdrawal. We argue that though thrust loading AR: Argentera; D: Dôme de Barrôt; A: basin; Ar: Argens syncline: Pe: Peyresq syncline; CA: Arc; 500 m must be the fundamental driving mechanism responsible for salt 400 Limestone Bioclastic limestone DT: Digne thrust sheet; AT: Authon thrust sheet; G: Gevaudan diapir BA: Barrême basin; Ba: ; M: Majestres 300 movement late in the tectonic history of the region, thrusting has not syncline; S: St Jurs imbricates; V: Valensole basin 200 Sandstone Evaporites done much more than modify existing salt related geometry. 100 and siltstone 0 Crystalline rocks Limestone and dolomite

Figure 2. Lithostratigraphic column of the study area and the major tectonic events in the Western Alps. We refer the lithostratigraphic units as they are shown in this 3) Various interpretations of the Gévaudan diapir and the surrounding basins lithostratigraphic column.

Figure 5. A “non-salt attempt” interpretation of R. Graham around Gévaudan

Figure 3. Modified after Graham in Elliott et al. 1985, a pure fold and thrust belt interpretation

Figure 4. Csicsek 2019, one of the first attempt of a regional section during a PhD project. Note the thickness changes in the Mesozoic succession and a lot of possible, welded salt related contacts. Figure 6. Artoni & Meckel 1998, an another structural interpretation. Note the thick salt layer at the top of the basement, thickness changes in the Mesozoic succession , the steep thrust faults bounding the different units and a possible young-on-older contact between the Gévaudan-Reichard unit and the Douroulles syncline.

Middle Eocene (Bartonian) 40 Ma~ a 6.35°E 6.40°E 6.45°E West East PROVENÇ AL FORELAND Onset of flexural subsidence synchronous BARRÊME BASIN with Calcaires Nummulitiques transgression SEA LEVEL + + + + + MESOZOIC COVER + + ? Paleo-normal faults + THINNED CONTINENTAL CRUST + + + + + THRUST + + WEDGE sites of development + + + + + + + + + + + + + + of later thrust faults + + + + + + + + + + + + + + + + +++ + + + + + + + + + + St. Jacques +

Late Eocene (Priabonian) 36 Ma~

43.96°N Initial thrust front established west of Barrême BARRÊME GRÈS D’ANNOT SUB-BASINS SEA LEVEL N Barrême + + + Turbidites onlap structured basin floor + + DIGNE + + + + + + THRUST + + + + + + + Section line + + + + + 43.95°N + diapir + + + + + + + + + +? + THRUST + + + WEDGE + + + + + + + Gévaudan + + + + + + + + + + + + + + + + + + + + + mbl = blue marls, apto-albian; cN = limestones with Nummulites; mGlob = Globigerine marls from the Priabonian; + + gS = Sénez sandstone; mR = red molasse; cgC = calcareous conglomerates (top of the red molasse) + + + 0 1 km + + + + Figure 7.Gidon 1997. Cross-setion of the southern part of the Barrême basin. Late Eocene (Priabonian) 36 Ma~

Diapir overthrusts SHALLOW MARINE BASIN ST. LIONS ANTICLINE mid-Jurassic SEA LEVEL b Back-stepping shoreface of Former shale ? Calcaires Nummulitiques (CN) Allochthonous sheet C Southwest reactive Northeast AP CN PER RETA TIA UP CE buried by N N - A O EOC L PTIAN - A US diapir? DI OM BIAN A LB mid-Cretaceous Digne G IAN SHALES IA Barrême N SH EO N thrust E ALES N CO shale T AND LIMES ONES MI lateral tip HR T AN syncline U JU ST RA JURASSIC Reactivation SS IC of paleo-normal 1 TRIASSIC EVA PORITES faults as thrust faults + + + + + + + + + + + Gévaudan + + + + + + + + + + + + + + + + + 0 diapir Early Oligocene (Rupelian) 30 Ma~

-1 CONTINENTA L BASIN

ER CRETACE PP OU A U S -2 PT CN MARINE BASIN TIAN - AL Elevation (km) B N IA FILL AP IA EO N - N CO AL 0 5 km M BI NEOCO IA AN MIA -3 DI N SH N G SH ALES NE AL JU V.E. × 1 T ES RA JU H AND SS R RU L IC A ST IMESTONES SS IC Recent alluvium Tithonian limestone JURASSIC + + + + + + + + TRI ASSIC EVA PORITES + + + + + Oligocene Middle Jurassic shale Barrême thrust-sheet-top Figure 5. Sketch illustrating the regional tectonic setting of the Barrême thrust-sheet-top Eocene Liassic limestone basin between middle Eocene (ca. 40 Ma) and early Oligocene (ca. 30 Ma) time. This ~10 m.y. Upper Cretaceous limestone Triassic gypsum time interval spans the initiation of the marine thrust-sheet-top basin to the onset of nonmarine sedimentation at Barrême, the so-called flysch to molasse transition of Allen et al. (1991). Note Middle Cretaceous shale Basement that the thicknesses of stratigraphic units are not drawn to scale. Lower Cretaceous limestone

Figure 8. Schematic map of the structures of the Southern Figure 9. Cartoons shoving the evolution of the Gévaudan diapir Figure 10. Lickroish and Ford 1998. Series of cross sections, form N to Figure 11. Lickorish & Ford 1998 cross section in Jackson and Hudec 2017. Their interpretation Figure 12. Sketch showing the evolution of the Barrême Subalpine Chains, Gidon 1997. Note the strike-slip faults and the sourroundign basins. S. Their interpretation includes the eastward migration of the includes an allochthonous salt sheet buried by mid-Cretaceous shale (n7c1). The Eocene thrust-sheet-top basin. Note the generally constant thickness around the Gévaudan area. Note the relatively short period of structural evolution. Gidon 2000. depocenter in the Barrême basin and the intrusion of the Gévaudan and Oligocene units are thickening towards to east. of the Mesozoic sccession. Evans and Elliott 1999. diapir during Late Oligocene.

4) Geological and schematic structural map of the study area 5) Observations, stratal and structural geometries around the Gevaudan diapir

n2 n3 6°25' 33 27 19 n7-c1 WNW ESE NE SW e7 c1-2 n4-5 G c3 N n4-5 n6a G n1 j2-4 30 41 43 n3 35 n2 35 30 82

31 50 8 n4O 63 29 54 12 c3b4 23 c1-2 43 59 12 3 13 c3 38 70 42 42 50 c3 14

c3b4 51 e7g1 71 25 27 e7 30 87n7-c1 30 n4-5 70 40 eC 84 45 53 n3 45 41 n1 n2 84 e7 17 WNW ESE NE Steep (early normal?) faults cross-cutting the subvertical section le Clap syncline,SM SW g1B 40 Schematic boundary (weld) between g2R 81 Barrême basin,SM le Clap syncline,SM Clavoune Douroulles syncline,SM Clavoune le Clap s. and Barrême basin (projected) 75 20 c3b4 l3-4 44°00' 50 44°00' e7 l1-2 81 c3 l5-9 g1B e7 15 j2-3 j2-4 45 68 HW of the c3b4 Barrême basin,SM Digne Thrust c1-2 c1-2 c3 j6-9 eC c3 c3b4 t7-9t10 c1-2 60 c1-2 c1-2 40 n2 15 88 19 of theUndiff. Barrême Tertiary basin 10 27 n1 64 Undiff. 68 n7-c1 j6-9 16 30 c1-2 76 n7-c1 40 51 eA 58 j2-4 n1 n2 17 60 n7-c1 c3b4 Douroulles syncline,SM n1 Tertiary of the Barrême basin Terres Noires 89 j2-4 49 c1-2 27 c3b4 19 n7-c1 n4-5 j2-4 n2 65 g2S 41 61 n7-c1 n6a c1-2 n7-c1,Albo-Cenomanian 54 2 n6a j5 j6-9 g1B n3 3 89 t7-9 n3 n3 n3 40 76 c1-2 t10 j5 black shale 50 58 14 n3 18 41 9 l3-4 l1-2 j5 e7g1 21 18 86 n7-c1 Hauterivian 23 68 35 Tg+Tk 14 15 n4-5 32 26 Tg+Tk 46 j6-9 16 c1-2 40 2 l5-9 lentil? 46 n6b ? 4 c4 64 c1-2 j6-9 18 69 n6a j2-4 n6a 21 19 30 76 Fontaine Salée flap c1-2 21 44 34 38 j2-3 76 g1B 11 9 33 g2R g3G 40 58 14 33 12 j2-4 n1 c3b4 36 g2S j2-3 c2-3a Tithonian olistolithes or lentils 26 n4 n3 30 Terres Noires 14 n6a 43 42 n7-c1,Albo-Cenomanian j9 46 88 j2-4 Barremian with olistoliths n7-c1 47 44 16 j2-4 26 33 45 e7g1 61 38 42 Terres Noires black shale 18 88 87 n4-5 33 25 n7-c1 g1B 49 n6a 18 19 49 40 g2R 61 83 Tg+Tk 80 g2S j2-4 j6-9 Upper Cretaceous angular unconformities 41 73 n3 (some intraformational) g3G 74 n2 49 80 15 Tg+Tk 83 n1 Overturned/subvertical Argovian-Valanginian section below flap n3 57 45 30 n4-5 88 89 e7 49 50 n3 g3V 22 71 40 23 Figure 15. The view of the southern side of the Clavoune section. Springs where salt brine Figure 16. The view of the northern side of the Clavoune section. n6 43 21 66 c4 50 31 37 n1 53 g3G 58 19 28 70 18 flows to surface are located in the valley E of Clavoune (Morin et al. 2004). See Fig. 13 for locaction. 15 10 56 eC n7-c1 n2 35 15 n3 40 9 42 85 WNW 32 21 67 ESE NW SE NNW SSE 71 84 20 WNW ESE 26 j2-4 46 86 9 47 24 j7-8+j9 9 70 c3-4 c1-2 23 j5-6 g3V 46 g2R 9 n2 j7-8+j9 29 25 n2 24 n7-c1 j7-8+j9 1 n1 j2-4n1 tG,tKj2-4 n1 c3b4 U. Cretaceous n3 tG,tK c3 n6 j2-4 45 g3G n2 30 g1S 15 49 40 30 g2R 38 28 n4-5 43°55' l7-9 g2a 45 j2-3 80 55 l3-4 n4-5 78 e7g1 59 tG,tK 67 40 n3 10 20 30 n3 e7 25 n3 n6 e7g1 n1 j7-8+j9 n2 n4-5 n4-5 n4-5 21 l1-2 j5-6 n1 n6 e7 30 l5 j7-8+j9 eC Poudingues d’Argens l3-4 n3 eC 20 a 85 l1-2 j2-4 c3 20 n3 l7-9 l3-4 n7-c1 l5 n3b4 l7-9 n2 l5 10 Figure 17. Panorama image of the Douroulles syncline. See Fig. 13. for location. j2-3 n1 c2 n6 n2 20 n6 tG,tK j2-4 In the foreground, the minibasin infill Poudingues d’Argens conglomerates dipping towards n1 e7g1 n7-c1 j7-8+j9 j2-3 n7-c1 l3-4 5 km to the west and onlapping onto the steeply dipping Upper Creatceous limestone on the 40 n4-5 20 50 j6-9 j2-3 western flank of the minibasin (a). The Upper Cretaceous succession is partly composed of intraformational breccias (b). We suggest that the Poudingues d’Argens conglomerates may have been formed by the Figure 13. The new geological map of the study area. (Key: Fig.2) Figure 18. Tilted subvertical Poudingues d’Argens on the eastern flank of the Barrême basin. The underlying reworking of these Upper Cretaceous breccias (c) which were deposited locally in the Upper Cretaceous succession to the E is also composed of intraformational breccias. The tilting is related to b hammer for scale secondary minibasins on the top of the allochthonous salt sheet. evaucation of the allochthonous salt due to thrust loading. Paleocurrent data measured on tilted channel fill c suggest N-S flow direction, parallel with bounding salt wall of the basin. See Fig. 13 for locaction. Possible extent of the middle Cretaceous salt sheet 6) Evolutionary diagram

Figure 19. Cartoons shoving possible Early Jurassic - present day evolution of the Gévaudan area, NOT TO SCALE

1. Top Liassic 2. Top Terres Noires 3. Top Lower Cretaceous W Marine/basinal conditions E W E Digne-Montagne de Vibres Douroulles W Marine/basinal conditions E Sea level Sea level Marine/basinal conditions unit syncline -Laupe unit Sea level Gévaudan diapir Gévaudan diapir Gévaudan diapir

Digne Thrust Lower Cretaceous Terres Noires Liassic j2-3 Arg.-Kimm.-Tith, Terres Noires Tg,Tk le Clap unit Tg,Tk Liassic Tg,Tk Liassic Tip folds of the splay of ? the Digne Thrust ?

Note: The original amount of evaporite is less certain! The driving force of salt tectonics may have been the differential loading of the overburden above the salt or subsalt deformation (syn-rift normal faulting on the Ligurian passive margin, not shown here) Postrift phase 2 Synrift phase Clavoune unit 4. Albian - Cenomanian 5. Late Cretaceous 6. Paleocene (Pre-Nummulitic deformation) Sea level Marine/basinal conditions Sea level Terrestrial conditions Poudinges d’Argens alluvial fan W Marine/basinal conditions Dismembered roof fragments/lentils: E W + E originally below or above the extrusive sheet? Gévaudan diapir Local source, from underlying Upper Cretaceous infill W E (Future. Eocene-Oligocene) Barrême basin, Secondary minibasin of the secondary minibasins Douroulles syncline,SM Future Lambruisse-Laupe u. (Future. Eocene-Oligocene) Barrême basin, Secondary minibasin Bois de Lieye le Clap syncline,SM Poudingues Gévaudan diapir Lambruisse-Laupe u. Gévaudan diapir Fontaine Salée flap Note: Upper Cretaceous sediments are missing d’Argens minibasin fill Digne- Allochthonous salt sheet/canopy or reduced W of Barreme basin! le Clap syncline,SM Fontaine Salée Montagne de Vibres unit Douroulles s., SM ? Tg,Tk ? Tg,Tk Upper Cretaceous Pre-Nummulitic erosion surface flap Tg,Tk Upper Cretaceous Albian- Albian- Tg,Tk Tg,Tk Cenomanian Cenomanian eC Fontaine Salée flap Albian- Gevaudan diapir ? Lower Cretaceous Lower Cretaceous Fontaine Salée flap Cenomanian Lower Cretaceous Arg.-Kimm.-Tith, Arg.-Kimm.-Tith, Arg.-Kimm.-Tith, Terres Noires ? Terres Noires Terres Noires Tg,Tk j2-3 Tg,Tk j2-3 j2-3 Liassic Liassic Bois de Lieye Liassic Tg,Tk

Future Digne- Future la Blache-Castellane Beggining of Digne Thrust la Blache-Castellane Barrême syncline Montagne de Vibres unit unit unit Note: Width of the pedestal and stem is less certain! Castellane unit 1 la Blache- Postrift phase Collision

7. Eocene - Oligocene 8. Oligo - Miocene

g3V g3G Globigerina g2S Chattian Priabonian - Early Rupelian: Marine conditions marl g2R g3V + g1S g1B g3G “Nummulitic transgression” Globigerina g2S Chattian Gres de Ville turbidites e7g1,G Oligocene Rupélian marl g2R Late Rupelian - Chattian: Terrestrial conditions + g1S g1B Nummulitic e7 E Gres de Ville turbidites e7g1,G Terrestrial conditions limestone Priabonian E Oligocene Rupélian W ? e6-7C W Bois de Lieye Nummulitic e7 Poudinges e Bartonian Sea level limestone ? Priabonian d’Argens e6-7C Paleogene eC Rotated Poudingues Eocene Lutetian? Poudinges e Bartonian 7) Conclusions (Priabonian - Early Rupelian) d’Argens d’Argens minibasin fill Paleogene eC Gévaudan diapir Eocene Lutetian? Barrême basin, Secondary minibasin Lambruisse-Laupe u. Gévaudan diapir Lambruisse-Laupe u. Priabonian - Late Rupelian - Chattian Salt sheet molasse Early Rupelian le Clap syncline,SM j2-3 Barrême basin, Secondary minibasin Late Rupelian - Chattian le Clap syncline,SM Priabonian - molasse Bois de Lieye Salt sheet Early Rupelian • The Gevaudan area is a good example of the Tg,Tk Rotated Poudingues Upper Cretaceous Upper Cretaceous Digne-Montagne de Vibres unit eC d’Argens minibasin fill Tg,Tk eC

Albian-Cenomanian complexity and uncertainty associated with salt relat- eC Albian-Cenomanian Lower Cretaceous Lower Cretaceous Arg.-Kimm.-Tith, Arg.-Kimm.-Tith, ed geometry in fold and thrust belts, well-illustrated Terres Noires 5 km Terres Noires j2-3 j2-3 Liassic by the variety of interpretations past and present. Tg,Tk Tg,Tk Liassic Figure 14. Schematic structural map of the study area showing the occurences Digne Thrust Digne- Digne Thrust la Blache-Castellane Digne- la Blache-Castellane • Halokinetic influence in the structural and strati- Montagne de Vibres unit of Upper Triassic evaporites (black) and younger Triassic units (purple). unit Montagne de Vibres unit unit graphic evolution of the area (and many others in the The pink dashed line represents the possible extent of the middle Cretaceous Collision Haut Provence fold and thrust belt) is shown by extrusive salt sheet. anomalous stratigraphic thicknesses and structural geometries. • The well known Barreme Basin, a thrust -top Present day, SCALED SECTIONS fragment of the Provencal foreland basin, is re-inter- preted as a secondary minibasin developed on top of an allochthonous salt sheet which extruded onto the Albo-Cenomanian sea floor at a time of low sedimen- Section line 1, simplified tation rate. The probable original extent of this Section line 2, detailed canopy is suggested. Gévaudan diapir NW Barrême basin SE WNW ESE WNW ESEWSW SWENE WNE E SW NE Albian-Cenomanian • The Barreme Basin had three precursor second- Secondary minibasin + Barrême basin Gévaudan diapir Upper Digne- Secondary minibasin Digne- Cretaceous la Blache-Castellane ary minibasins which filled with Upper Cretaceous Lambruisse-Laupe u. Montagne de Vibres unit Bois de Lieye la Blache-Castellane Lambruisse-Laupe u. Montagne de Vibres unit unit Rotated Poudingues Bois de Lieye unit pelagic limestones, then, during the first wave of Undiff. Rotated Poudingues 2000 d’Argens minibasin fill Clavoune Tithonian olistholite d’Argens minibasin fill 1750 e7g1 g1B Oligocene Clavoune or lentil Globigerina m. St Lions cong. Alpine thrusting and loading in the latest Cretaceous, Nummulitic 1500 S. de Reichard Barremian olistholite or lentil 1500 n7c1c3-b4 G, Gres de n3 limestone Upper Jurassic 1250 g2R by the Palaeocene Poudingues d’Argens - a pebble, Globigerina Albian-Cenomanian 1125 Ville c3-b4 n7c1 1000 Molasse R. g3G c3b4 1000 875 j9o marl 750 g2S c3 cobble and boulder conglomerate formed entirely Terres Noires n3 n4 c1-2 U. Cret. 500 c1-2 n7c1 Alb.-Cen. e7g1 Tg,Tk n6a from Upper Cretaceous debris. eC 250 eA Liassic e7 Numm. e7 0 • As the canopy salt evacuated westwards, pre- 0 Albian-Cenomanian Lower Cretaceous j2-3 250 c3-b4 n7c1 n4 Liassic 500 n6a sumably in response to more internal thrust loading, Lower Cretaceous 750 n3 n4 Aptian-Albian 1000 n2 n2 accommodation space was created for the Eo-Oligo- Arg.-Kimm.-Tith, Arg.-Kimm.-Tith, n3 n1 1250 n2 n1 cene rocks of the Barreme Basin and the earlier Terres Noires Terres Noires 1500 n1 j6-9 j5 1750 j6-9 formed Poudingues d’Argens minibasin was strongly j5 j2-3 2000 Terres Noires j2-3 2250 Terres Noires rotated to be overlain unconformably by the younger 2500 Liassic Tg,Tk j2-3 Tg,Tk 2750 j2-3 formations. In detail there are several other uncon- Liassic Liassic (l1-2,l3-4,l5-9) 3000 Liassic 3000 formities in the section. 3250 1:1 1:1 2.5 0 2.5 KILOMETRES 3500 • Oligocene or Miocene thrusting emplaced part of the near-crest flank of the original diapir as the al- Figure 20. Section line 1. See Fig. 13,14 for location. Figure 21. Section line 2. See Fig. 13,14 for location. lochthonous structural ‘horse’ which now forms the Clavoune hill. The Gevaudan diapir is the remnant of 8) References the one-time canopy. ARTONI, A. & MECKEL, L. D. 1998. History and deformation rates of a thrust sheet top basin: the Barrême basin, western Alps, SE . Geological Society, • If these ideas are correct, useful future work London, Special Publications, 134, 213-237. might involve a re-investigation of the source to sink CSICSEK, L. A. 2019. The effects of salt tectonics in the evolution of a fold and thrust belt, Southern Subalpine Chains, France. Conference poster, TSG AGM, Bergen DARDEAU, G. & DEGRACIANSKY, P. 1990. Halokinesis and Tethyan rifting in the Alpes-Maritimes (France). of the Tertiary formations in the area. BULLETIN DES CENTRES DE RECHERCHES EXPLORATION-PRODUCTION ELF AQUITAINE, 14, 443-464. EVANS, M. J. & ELLIOTT, T. 1999. Evolution of a thrust-sheet-top basin: The Tertiary Barreme basin, Alpes-de-Haute-Provence, France. Geological Society of America Bulletin, 111, 1617-1643. GIDON, M. 1997., 2000. Extrait de GEOL-ALP. www.geol-alp.com 9) Acknowledgements GRAHAM, R., JACKSON, M., PILCHER, R. & KILSDONK, B. 2012. Allochthonous salt in the sub-Alpine fold–thrust belt of Haute Provence, France. Natural Environment Research Council (NERC) Centre for Doctoral Geological Society, London, Special Publications, 363, 595-615. Training (CDT) in Oil & Gas for funding the PhD project of Adam JACKSON, M. P. & HUDEC, M. R. 2017. Salt tectonics: Principles and practice, Cambridge University Press. Csicsek and CASP Award for funding fieldwork in 2017. Field assis- LICKORISH, W. H. & FORD, M. 1998. Sequential restoration of the external Alpine Digne thrust system, SE France, constrained by kinematic data and synorogenic sediments. tants contributed to field work in 2018 and 2019. Geological Society, London, Special Publications, 134, 189-211. Useful discussion with many colleagues about Alpine geology and MASCLE, G., ARNAUD, H., DARDEAU, G., DEBELMAS, J., DELPECH, P.-Y., DUBOIS, P., GIDON, M., DE GRACIANSKY, P.-C., KERCKHOVE, C. & LEMOINE, M. 1988. salt tectonics is also gratefully acknowledged. Salt tectonics, Tethyan rifting and Alpine folding in the French Alps. Bulletin de la Société géologique de France, 4, 747-758. MORIN, D., CATHERINE, L., FONTUGNE, M. & GUIOMAR, M. 2004 Aux origines de l'extraction du sel en Europe (VIe millénaire av. JC), La source salée de -Alpes-de-Haute-Provence. Bulletin de la Société Préhistorique Française, 341-352.