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Felix Gradstein, Harald Brunstad, Mike Charnock and Øyvind Hammer

31 May 2011 FORCE Sequence Stratigraphy Meeting Mega-Scale Sequence Stratigraphy of Slumped Chalk and Sand complexes (MTC) in the southern Norwegian Sector (Quadrants 1 and 2): Application of the NORLEX database. Felix Gradstein, Harald Brunstad,

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Felix Gradstein, Harald Brunstad, Mike Charnock and Øyvind Hammer

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  1. 31 May 2011 FORCE Sequence Stratigraphy MeetingMega-Scale Sequence Stratigraphy of Slumped Chalk and Sand complexes (MTC) in the southern Norwegian Sector (Quadrants 1 and 2): Application of the NORLEX database. Felix Gradstein, Harald Brunstad, Mike Charnock and Øyvind Hammer

  2. NORLEX OBJECTIVE: A multi company consortium and alliance with the University of Oslo to improve our understanding of lithostratigraphic units in the Norwegian Sector.

  3. STRATIGRAPHIC SCHEMES Chronostratigraphy - Lithostratigraphy - 'Sequence' Stratigraphy P80 SB Vidar Olistolith P20 SB Base siliclastics Top Chalk

  4. VIDAR ‘FM’ : NPD FACT PAGES Current Published Knowledge Status

  5. STRATIGRAPHIC SCHEMES dark grey to grey brown very fine grained sandstones, remarkably clean (<0.1% detrital clay), rounded glauconite pellets common 82m thick in type well

  6. VIDAR MEMBER (TYPE) New nannofossils, palynology, micropaleo analysis by Jackie Lees, Felix Gradstein, Dirk Munsterman. • WELLS • 2/1-4 • 1/3-5 • 1/3-7 NOTE the Maastrichtian dating for the 63m thick Vidar Member.

  7. VIDAR MBR: POOR COVERAGE Core only in well 1/3-7 (lower part, distal equivalent) to determine sedimentary facies interpretation.

  8. VIDAR MBR: DISTRIBUTION Vidar Distribution of Vidar Member and Line of well correlation W-E, Wheeler diagram and seismic section E W

  9. P80 SEQUENCE ELEMENTS NOTE Vidar Escarpment and Vidar Olistolith units (to W)

  10. VIDAR MBR v FORTIES MBR NOTE Relationship of Vidar onlapping Forties Member

  11. REGIONAL WELL CORRELATION Vidar Mbr Olistolith (P90 lowstand) Top Balder Fm (P90) P80 HST Fiske- bank Datum: P80 Sequence SB (base Vidar Olistolith) NOTE 1) truncated P50 to P70 (Forties Mbr) below P80 SB. 2) See also thick P80 HST (prograding Fiskebank Mbr)

  12. WHEELER DIAGRAM OF W-E LINE IMPORTANT DIAGRAM TO CONSTRUCT FOR UNDERSTANDING SEQUENCE STRATIGRAPHIC RELATIONSHIPS. 1/3-7 1/3-1 2/1-4 2/2-2 8/11-1 9/11-1 1/2-1 NOTE: Rapidly deposited P70 Forties sands and P80 olistolith. Stratigraphic time-gap Thin but time-extensive background muds

  13. DIAGRAMMATIC GEO-MODEL P70 P80 SB From Brunstad et al. (in prep.)

  14. PROGRADING FISKEBANK MBR 8/12-1 (updip well) Top Balder Top Chalk Prograding Clinoforms during P80 Highstand (Fiskebank Mbr)

  15. VIDAR MBR THICKNESS NOTE the Vidar Member Olistolith only represents the lower part of the of the P80 Sequence Olistostrome.

  16. Chaotic basal unit on seismic Slumped chalks (Vidar Mbr) Slumped Fiskebank sequence P80 LOWSTAND PALAEOGEOGRAPHY Well defined scar on seismic Note apparent relationship between scar feature and underlying salt structures - ?partial causal mechanism associated with an unstable shelf margin Extent uncertain (no well control) Thin prograding shelfal shelf

  17. ?uncertain setting Sequence truncated or absent Sand bar forms defined on seismic ?thin, back barrier setting Only late stage, thin, muddy transgressive sequence Progradation direction Note: Collapsed scar buried by prograding Fiskebank sequence in this area B basin floor muds Condensed shelfal sequence associated with condensed parallel reflectors. Some minor progradational units Progradation direction Thick Fiskebank sandstones associated with prograding clinoforms A thick muddy prograding slope Base slope P80 HIGHSTAND PALAEOGEOGRAPHY

  18. SUMMARY AND CONCLUSIONS • A multi-disciplinary study improves understanding of the Vidar Member. • The Vidar Member is interpreted as an olistolith, and part of a large scale Mass transport Complex (MTC) developed in Quads 1 and 2. • The Vidar mass transport event is likely Late Paleocene in age. • The overlying Fiskebank Member (Prograding shelf sands) is considered genetically linked to the Vidar Mbr and was deposited in areas with increased accomodation space and in the fault scar /collapse area during the earliest Eocene P80 Highstand. • What is the causal mechanism of shelf edge instability ? ? Tectonics related to Norw.Sea break-up. ? Salt movement below the chalk. • Mass Transport Complexes (MTC) poorly documented in North Sea.

  19. We thank the organisers of this FORCE workshop for the attractive opportunity to present this study

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