Lithology Distribution in the Zechstein Supergroup and ... Salt techtonics seminar, 13... ·...
Transcript of Lithology Distribution in the Zechstein Supergroup and ... Salt techtonics seminar, 13... ·...
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Lithology Distribution in the Zechstein Supergroup and Controls on Rift Structure: Greater South Viking
Graben, Northern North SeaChristopher Jackson 1, Elisabeth Evrard1,Christopher Jackson 1, Elisabeth Evrard1,
Gavin Elliott1, Robert Gawthorpe2,
1 Basins Research Group (BRG), Department of Earth Science & Engineering, Imperial College, Prince Consort Rd, London, SW7 2BP, UK
2Department of Earth Science, University of Bergen, Allégaten 41, 5007 Bergen, Norway
email: [email protected]
Seismic data:
Funding:
Software:
FORCE Salt Tectonics Seminar14th November 2014
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• Carbonate-evaporite basin subjected to complete drawdown
Salt Deposition
After Tucker (1991)
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Analogues
modified from Peterson and Hite (1969), Hite and Buckner (1981) and Stroud (1994)
Pennsylvanian Paradox Formation, Utah, USA
• Basin physiography can control lithology distribution in salt basins• Post-depositional salt flow may modify primary lithology distribution• Does present (post-flow) lithology distribution reflect primary distribution?
Trudgill (2010)
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Rationale and Previous Work• Lithology distribution in Zechstein
Supergroup (ZSG) ‘well known’ in UKNorth Sea; mapping based on onvariations in structural style with sparse(published) well calibration…
• Four depositional zones; carbonate-richat basin margin (Z1-2) and halite-rich incentre (Z3-4)
x’• Lithology distribution in Norwegian North
Sea poorly understood
• Well and seismic data from theNorwegian North Sea are used toinvestigate lithology variations in theZSG and how these variations affect theevolution of rift systems
• Lithology variations may impactreservoir/seal potential, heat flow, etc
x
x’
Clark et al. (1998)
modified from Stewart (2007)
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Study Area
wells with no cuttings
wells with cuttings
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Salt Thickness and Structure
ZSG thick in basin centre; abundant diapirsThin on basin margin and intra-basin highs; few dia pirs
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100
m
50 m
• Five lithologies identified based oncuttings from 10 wells: (i) halite; (ii)anhydrite; (iii) carbonate; (iv)carnallite; and (v) shale
• Cuttings-calibrated petrophysicaldata cross-plotted to determinelithology identification in wells lackingcuttings
Lithology Identification
cuttings
16/7-3
15/12-3
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misidentification
Lithology Identification
misidentification misidentification
misidentification
• Anhydrite-Halite : relatively dense clustering; easy to discriminate between on logs• Carbonate-Shale : relatively weak clustering; difficult to discriminate between on logs• Anhydrite denser and slightly ‘slower’ than carbonate and shale
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Lithology IdentificationCarbonate cannotbe differentiate fromshale based onpetrophysicalcharacteristics alone
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Lithology Distribution - UHBasin margin
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Lithology Distribution - UH
top ZSG
base ZSG
25/10-4R 25/10-2R 16/1-2 16/7-2
• Relatively thin ZSG (up to 120 m)• Anhydrite, carbonates and shales; no halite
ZSG
16/1-2 16/7-2
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Lithology Distribution – ST -LG
Basin margin-to-basin centre
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Lithology Distribution – ST -LG
top ZSG
• ZSG thin (up to 50 m) and anhydrite-,carbonate- and shale-rich on basin margin
• ZSG and thick (>1000 m) and halite,-rich
15/9-16 15/9-13 16/7-3 16/8-2 16/9-1
15/9-16 15/9-13 16/7-3 16/8-2 16/9-1
ZSG
in basin centre
• Note across-fault thickness and lithologychange
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Lithology Distribution – LG -SHBasin centre-to-basin margin-to-basin centre
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Lithology Distribution – LG -SH
• Fault-controlled
16/10-1 16/11-15 17/11-1 17/12-2 17/12-1R
top ZSG
16/10-1
ZSG
16/11-1S 17/11-1 17/12-2 17/12-1R
• Fault-controlledchanges in ZSGthickness andcomposition
base ZSG
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• Lithology zones observed:• ‘Proximal’ (Zone 1) – Carbonate-dominated• ‘Intermediate’ (Zones 2 & 3) – Mixed evaporite-
non-evaporite• ‘Distal’ (Zone 4) – Halite-dominated
• Lithology transitions partly fault-controlled
ZSG Lithology Distribution
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Basin -Scale Context
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Controls on Lithology Distribution
Model 1 : no Early Permian rifting; ZSGdeposited before Late Jurassic rifting;erosion and carbonate-dominatedcaprock develops on structural highs dueto post-depositional footwall uplift
What controls lithology distribution in the ZSG in the Norwegian sector of the North Sea?
Model 2: ZSG deposited acrossunderfilled Early Permian rift-relatedrelief; LST halite deposition in basins andHST carbonate/anhydrite deposition onmargins
Model 3: deposition of ZSG during LatePermian rifting; lithology variability wascontrolled in the same way as for Model2.
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Late Permian Relief?
• northernEgersund Basin
• NE margin of thepan-EuropeanZSG salt basin
• Salt pinch-outonto present-daystructural high
• Is relief rift-related? If so, towhich event? Jackson & Lewis (2013)
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Late Permian Relief?
salt pinch-out
furrows?
Jackson & Lewis (2013)
basin-bounding fault
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Late Permian Relief?• Low-relief (few tens of
metres) erosion surfacedeveloped along base salt)(top Rotliegend/LowerPermian)
• Erosional ‘furrows’ up to afew kilometres long andwide
• Only developed in footwall
salt
furrows?
salt
furrows? Jackson & Lewis (2013)
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Pre-ZSG Rifting?• Stage 1 (Early Permian) – SFS
active?
• Stage 2 (Mid-Permian to earliestLate Permian) – SFS active; faultscarp relief developed and eroded;by fluvial systems; onset of ZSGonlap on fault scarp
• Stage 3 (Late Permian) – Onlapof ZSG onto and preservation of
Jackson & Lewis (2013)
of ZSG onto and preservation offault scarp relief
• Evidence for pre-ZSG (EarlyPermian) rifting?
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Influence of ZSG on Rift Structure
Seismic data reveals influence of ZSG lithology variations on rift structural style across the South Viking Graben and NE
margin of the Central Graben
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Northern South Viking Graben
• No salt-related deformation on basin margin; ZSG too thin and immobile• Updip thin-skinned extension due to hangingwall tilting; formation of salt rollers
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Ling Graben
• Diapirism in basinal areas comprised of thicker more mobile ZSG• Reactive diapirism driven by thin-skinned extension?
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Ling Graben
• Diapirism in basinal areas comprised of thicker more mobile ZSG• Subtle thin-skinned extension and minor diapirism on structural highs
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Conclusions• Petrophysical and cuttings data allow construction of a
lithology framework for the ZSG in Norwegian sector of theeastern North Sea
• Seismic mapping and stratigraphic correlations revealprominent regional thickness and lithology variations in ZSG
• Four depositional ‘zones’ (sensu Clark et al. 1998) identified:• Four depositional ‘zones’ (sensu Clark et al. 1998) identified:• Basin margin – carbonate- anhydrite- and clastic-dominated (Zones 1 and 2)• Basin centre – halite-dominated (Zones 3 and 4)• Lithology transitions locally fault-controlled• Other lithology transitions controlled by subtle base salt relief
• Triassic and Jurassic rift structural styles linked to ZSGlithology:
• Depositional Zone 1 – no diapirism or low-relief diapirs• Depositional Zones 2 and 3 – thin-skinned extension• Depositional Zones 3 and 4 – high-relief diapirs and minibasins
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A Trick of the Light?
• Does present lithology distribution reflect primary lithologydistribution?
• Post-depositional erosion and dissolution (Model 1) cannot be ruled-out; however, unlikely to be dominant control because basin-centresuccessions contain almost no carbonate and relatively littleanhydrite, suggesting basin margin/intra-basin structural highsuccessions not simply anhydrite- or carbonate-enriched versions ofthose encountered in basin-centrethose encountered in basin-centre
• Differential expulsion of halite unlikely to be dominant control; thinbasin margin/intra-basin structural high successions are not flankedby large salt structures
• Evidence for Early Permian faulting and dramatic changes inthickness and lithology of the ZSG across basement-involvednormal faults, but no independent evidence for a phase of LatePermian extension, making it problematic to discriminate betweenModel 2 and 3.
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• Stage (i) – pre-thinning salt• Stage (ii) – salt thinning; preferential expulsion of low-
viscosity halite• Stage (iii) – (apparent) welding; complete evacuation of
halite; remnant non-halite (high-viscosity) lithologies• Diapir grows in response to preferential addition of low-
viscosity halite (cf. ‘differential purification bymovement ’ (sensu Kupfer, 1968)
(i) Primary salt layer
(i-iii) Salt inflation
Differential Salt Flow
(i) Primary salt layer
(ii) Salt thinning
(iii) Salt welding
iii) Salt inflation
33.20.29
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Differential Salt Flow
modified from Wagner & Jackson (2011)
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Ling Graben
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Southern South Viking Graben
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• http://written-in-stone-seen-through-my-lens.blogspot.co.uk/2013_05_01_archive.html