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 2
Tectonic-sedimentation relationships on passive margins Syntectonic sedim. Stage «rift» Axial lake (restricted) M.O. preserved thermal anomaly Outward drainage => Starved basin Lithosphere stretching 3
Model: East African rift 4
Tectonic-sedimentation relationships on passive margins Transgression => evaporites Stage «break-up» Young (hot) ocean. lithosph. Sub-horizontal basement Thermal anomaly cooling cooling => densification => subsidence Oceanic accretion => Extensional stress stops => Fault activity stops 5
Model: Afar & Red Sea Red Sea/ Afar triple Junction Rift Marge continentale d Aden 6
Tectonic-sedimentation relationships on passive margins Sed = Accom => aggradation Stage «young margin» Differential Subsidence => tilting Gravitational Tectonics Differential accomm. Proximal->distal facies 7
Tectonic-sedimentation relationships on passive margins Flexural uplift Terrigenous sediment flux Stage «mature margin» progradation Reduced thermal subsidence Deep-sea fan Added sediment load => Subsidence (flexure) 8
Synthetic log of passive margins - 0 marin + - + Break-up unconf 0 lacustre Water depth Sed > Acc Acc >> Sed Acc = Sed Sed > Acc Acc > Sed Thermal postrift Subsidence Synrift subsidence Subsidence 9
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 Rust & Summerfield 1990, Anka 2004 Congo deep-sea-fan 4.5km 4 3 2 1 0km Congo Orange 10
Long-term evolution of W. Africa deep-sea fans 0km 5km 10km Congo-Angola: Cenozoic deep-sea-fan 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, 11
Onset of deep-sea-fan deposition in Oligocene 0.5 s SW Condensed surface 1 km SB Progradation of Tertiary DSF Down lap NE Miocene latest Base Oligocene Top Turonian On lap Aptian salt Top Oc. Cr. Tur. 12
? Rust & Summerfield 1990, Anka 2004, Leturmy & Lucazeau 200313? Condensed interval
terrigeous Continental erosion terrigenous marls carbonates Evaporites Reduced continental erosion terrigenous = syntectonic sedimentation 14
Record of Climate change on passive margins Climate change (icehouse) => increased continental erosion => increase terrigenous flux 15
Oceanic crust Amazon example Terrigenous sediments over oceanic crust Huge depocenter => burial + gravitational tectonics Large sediment flux => large watershed and intense erosion Sedimentation rate increases in Miocene 10-25Ma 0-10Ma Continental crust Lopez, 1996 Gravitational tectonics DSF load 40-65 Ma 65-10 0Ma 100-120Ma Oceanic crust Rifted Continental Crust 20km 16 Deep sea fans on mature margins
Flexural loading of Amazon DSF Characterizing and computing the extra-subsidence due to the lithosphere flexure in response to the load of the Amazon DSF Flexural uplift (<40m) around the load Watts, 2009 Extra-subsidence (>2km at the center of load) 17
Congo Turbidite deep-sea-fan (800 km) Angola ent Escarpem Deep-sea fan : Congo (Lopez, 2000) 18 Margin
Geometry of Congo DSF Isopach map of Oligocene - Present (Anka, 2004) 19
Effect of Congo DSF on the passive margin medio-atlantic ridge Niger fan Congo fan Sedimentary load => flexure of the oceanic lithosphere Congo watershed Modifié d après Uchupi, 1992 20
Flexural loading of Congo DSF Te=20km (Anka, 2004) Subs. >2km 21
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) 22
Source-to-sink Yellow River / Bohai Sea NASA 23