Master1 Réservoirs Géologiques Architecture des Bassins - Michel Séranne

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Tectonic-sedimentation relationships at passive margin scale Outward drainage Bordering Alluvial fans rift Axial Lake (restricted => Preserved OM)

(evaporites) Sedimentation is controled by continental margin geodynamic evolution Break-up Young margin Mature margin Uplift & erosion Sed = Accomm

2 Tectonic-sedimentation relationships at passive margin scale Outward drainage Bordering Alluvial fans rift Axial Lake (restricted => Preserved OM) Transgressive seq.(evaporites) Sedimentation is controled by continental margin geodynamic evolution Break-up Young margin Mature margin Uplift & erosion Sed = Accomm => aggrad. Sed >> Accomm.=> prograd Shallow (carbonate) platform Decaying thermal subsidence Young (hot) oceanic lithosph. => Sub-horizontal basement Fast thermal subsidence Differential subsidence => Tilting => onset gravit.tecto. Deep-sea-fan Extra subsidence (load -> flexure) 2

3 Tectonic-sedimentation relationships on passive margins Stage «!rift!» Syntectonic sedim. Lake (M.O.) thermal anomaly Outward drainage => Starved basin Lithosphere stretching 3

4 Tectonic-sedimentation relationships on passive margins Transgression => evaporites Oceanic lithosphere accretion => Extensional stress stops => Fault activity stops Stage «!break-up!» Thermal anomaly!!cooling cooling => densification => subsidence 4

5 Tectonic-sedimentation relationships on passive margins aggradation of carbonate platform Stage «!young margin!» Differential Subsidence => tilting Gravitational Tectonics Differential accomm. Proximal->distal facies 5

6 Tectonic-sedimentation relationships on passive margins Terrigenous sediment flux progradation Stage «!mature margin!» Reduced thermal subsidence Deep-sea fan Added sediment load => Subsidence (flexure) 6

7 - 0 marin Sed > Acc 0 lacustre Water depth Acc >> Sed Acc = Sed Sed > Acc Acc > Sed Thermal postrift Subsidence Synrift subsidence Subsidence 7

8 Signature of global changes progradation Eocène Néogène Senonien Cenomanien Albien Aptien Neocomien Sud Gabon Séranne et al, 1992; Thèse Nzé Abeigne, 1997 synrift aggradation 8

9 Worldwide Stratigraphic architecture Neogene prograding clinoforms Oligocene unconf. Pre-Oligocene Aggrading sequence Aggradation/Unconformity/Progradation Séranne,

Stratigraphic record of global climate change " 18 O increase = cooling of oceans Radiogenic strotium isotope increase = signature of terrigenous flux to

10 Stratigraphic record of global climate change " 18 O increase = cooling of oceans Radiogenic strotium isotope increase = signature of terrigenous flux to oceans = increased erosion " 18 O "1.8 => polar ice sheets Terrigenous progradation E. Oligocene unconformity Agradation (Mostly Carbonate) Séranne,

11 Ocean circulation and global climate during Neogene Opening of Drake passage Pre-Oligocene: Meridian currents!!thermal equilibration!!hot currents from Equator!!Warm polar region As from Early Oligocene: circum-polar currents -> thermal insulation -> ice-cap formation Rifting of Tasman Sea Kenneth

high seasonality NO polar ice-sheets => Milankovitch cycles => HF sea-level change

12 Strata geometry & amplitude of HF sea-level changes Polar ice-sheets => growth & decay according to Milankovitch cycles => HF sea-level change m amplitude AND high seasonality NO polar ice-sheets => Milankovitch cycles => HF sea-level change +/-10m amplitude AND slugish clmate Séranne, 1999 Oligocene - Presenet Cretaceous-Eocene 12

13 Erosion driven by instabilities Intensive deforestation in the watershed => erosion => Terrigenous flux to margin Part played by vegetation panache de sédiments terrigènes Zone déboisée = érosion Couverture initiale NASA 13

14 Climate periodicities control on erosion dry time Precipitations arid Vegetation Erodability Sediment Production Climate change max min max min max min erosion Punctuated clastic production from Knox,

15 Integrated study of passive margins «!source-to-sink!» Watershed - depocentre relationship Angola: thick and focused deposits extensive continental watershed Africa SW: distributed and thin deposits little continental erosion Oligocene-Present isopachs 4.5km km Rust & Summerfield 1990, Anka 2004 Congo deep-sea-fan Congo Orange 15

16 Long-term evolution of W. Africa deep-sea fans Congo-Angola: Cenozoic deep-sea-fan 0km 5km 10km synrift Cont. crust Oceanic crust 50km South-Africa : late Cretaceous margin + deep-sea-fan seamount Oceanic crust Syn-rift+SDR Cont. Cr. 50km Séranne &Anka 2005, 16

17 Onset of Cenozoic deep-sea-fan deposition SW NE Miocene latest 0.5 s Condensed surface 1 km SB Progradation of Tertiary DSF Down lap Base Oligocene Top Turonian On lap salt 17 Tur.

18 ? Rust & Summerfield 1990, Anka 2004, Leturmy & Lucazeau ? Condensed interval

19 terrigeous terrigenous Continental erosion marls carbonates Evaporites Reduced continental erosion terrigenous = syntectonic sedimentation 19

20 Climate change Climate change (icehouse) => increased continental erosion => increase terrigenous flux 20

Deep sea fans on mature margins Oceanic crust

Large flux => large watershed, intense erosion

21 Deep sea fans on mature margins Oceanic crust 0-10Ma 10-25Ma 40-65Ma Ma Ma Terrigenous sediments over oceanic crust Huge depocenter => burial + gravitational deformation Large flux => large watershed, intense erosion Sedimentation rate increase in Neogene Continental crust Lopez, km 21

22 Margin Congo Turbidite deep-sea-fan (800 km) Angola ent Escarpem Deep-sea fans : Congo (Lopez, 2000) 22

23 Geometry of Congo DSF (Anka, 2004) 23

24 Flexural loading of Amazon DSF Watts,

25 Driscoll & Karner, 1994 Pb: the Amazon DSF cannot be separated from the margin depocenter Sedimentary load = DSF load + margin load 25 Flexural loading of Amazon DSF

26 Effect of Congo DSF on the passive margin Niger fan medio-atlantic ridge Congo fan Congo watershed Sedimentary load => flexure of the oceanic lithosphere Modifié d! après Uchupi,

27 Flexural loading of Congo DSF Te=20km (Anka, 2004) 27

28 Interactions Margin-DSF!!DSF sedimentary record complements that of the margin;!!dsf depocentres are as big as margin s depocentre,!!loading increases subsidence in mature margins AND flexural uplift of oshore margin;!!continental drainage concentrates in few major rivers!!dsf record processes active on continent (Seranne Anka, 2005) 28

29 Source-to-sink Yellow River / Bohai Sea NASA 29

Sedimentation on passive margins. Master1 Géologie de l Exploration et des Réservoirs Dynamique des Bassins Michel Séranne

Sedimentation on passive margins 1 Tectonic-sedimentation relationships at passive margin scale rift Break-up Young margin Sedimentation is controled by continental margin geodynamic evolution Mature margin