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Lake District Mapping Vol. II

Lake District Mapping Vol. II. Leo M L Ritchie. Strategic. ~10 2 km area covered Access Youth Hostel at one end of my area Topography 80m to 650m elevation Poor sediment outcrops Weather Mentally unprepared for sun in UK. Where I mapped?. In the Lake District. NW of Coniston.

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Lake District Mapping Vol. II

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  1. Lake District Mapping Vol. II Leo M L Ritchie

  2. Strategic • ~102km area covered • Access • Youth Hostel at one end of my area • Topography • 80m to 650m elevation • Poor sediment outcrops • Weather • Mentally unprepared for sun in UK

  3. Where I mapped? In the Lake District NW of Coniston

  4. Geology of wider area Mapping Area

  5. Dark Siltstone (ds) Pale Siltstone (ps) Lever’s Water Limestone & calcareous siltstone (lcs) N Lithic-rich Tuff (lrt) Volcaniclastic siltstone and sandstone (vs) Lapilli Tuff (lt) More vs Interbedded Siltstone and Tuff (ist) More vs Rhyolitic Welded Tuff (mwt) Andesitic Welded Tuff (dwt) Porphyritic Intrusion (pi) Map & stratigraphic column Coniston

  6. 700 600 500 400 300 lt 200 100 ps lcs vs ist pi mwt vs vs lrt ds Succession

  7. 700 600 500 400 300 lt 200 100 ps lcs vs ist pi mwt vs vs lrt ds Rhyolitic Welded Tuff (mwt)

  8. VolcanicRhyolitic Welded Tuff (mwt) • Oldest unit • Quartz rich • homogeneous • >200m • Caradoc (Ordovician)* *Millward D. et al Geology of the Ambleside district. Memoir for 1:50 000 Geological Sheet 38 (England & Wales) British Geological Survey H.M.S.O. 2000 2nd Session Sheet 38

  9. 700 600 500 400 300 lt 200 100 ps lcs vs ist pi mwt vs vs lrt ds Volcaniclastic sandstone and siltstone (vs)

  10. VolcanicVolcaniclastic sandstone and siltstone (vs) • ~1km thickness in three separate units • Siltstone – conglomerate

  11. 700 600 500 400 300 lt 200 100 ps lcs vs ist pi mwt vs vs lrt ds Interbedded siltstone and tuff (ist)

  12. VolcanicInterbedded siltstone and tuff (ist) • ~200m thickness • Dacitic welded lapilli tuffs • And volcaniclastic siltstones

  13. 700 600 500 400 300 lt 200 100 ps lcs vs ist pi mwt vs vs lrt ds Lapilli Tuff (lt)

  14. VolcanicLapilli Tuff (lt) • ~50m thickness • Only un-welded tuff in the succession • dacitic

  15. 700 600 500 400 300 lt 200 100 ps lcs vs ist pi mwt vs vs lrt ds Lithic-rich tuff (lrt)

  16. VolcanicLithic-rich tuff (lrt) • ~400m thickness • Dacitic welded tuff • Larger lithics were rhyolitic • Columnar jointing

  17. Unconformity between vs-lrt

  18. Unconformity between vs-lrt lrt U/C vs

  19. 700 600 500 400 300 lt 200 100 ps lcs vs ist pi mwt vs vs lrt ds Limestone & calcareous siltstone (lcs)

  20. SedimentLimestone & calcareous siltstone (lcs) • ~150m thickness • Ashgill (Ordovician)* • Fossiliferous…

  21. 700 600 500 400 300 lt 200 100 ps lcs vs ist pi mwt vs vs lrt ds Pale siltstone (ps)

  22. SedimentPale siltstone (ps) • ~30m thickness • Llandovery (Silurian)* • Bioturbated…

  23. 700 600 500 400 300 lt 200 100 ps lcs vs ist pi mwt vs vs lrt ds Dark siltstone (ds)

  24. SedimentDark siltstone (ds) • >500m • unfossiliferous

  25. 700 600 500 400 300 lt 200 100 ps lcs vs ist pi mwt vs vs lrt ds Porphyritic Intrusion (pi)

  26. Intrusive IgneousPorphyritic Intrusion (pi) • ~250m • Plagioclase phyric • Interesting jointing patterns…

  27. Lever’s Water N And finally…VolcanicAndesitic welded tuff (dwt) • >200m thickness • Pyroxene and amphibole rich

  28. Structure • Predominant cleavage throughout units • Faulting (big & small)

  29. Structure - cleavage A predominant cleavage was apparent in most of my units

  30. Normal faulting in lithic rich tuff (lrt) Structure – faulting (big)

  31. Lever’s Water N

  32. Lever’s Water N

  33. Lever’s Water N

  34. Lever’s Water N 72/108

  35. Small scale faulting in volcaniclastic sand/siltstone (vs) Structure – faulting (small)

  36. Small scale faulting in volcaniclastic sand/siltstone (vs) Fine grained laminations displaced on cm-scale Structure – faulting (small)

  37. Small scale faulting in volcaniclastic sand/siltstone (vs) Fine grained laminations displaced on cm-scale Structure – faulting (small) 67/328

  38. Lever’s Water N Structure - faulting (strike-slip?) In Eastern corner of my area

  39. Lever’s Water N x

  40. dwt ds ps lcs lrt

  41. Interpretation • Eruption of tuffs and deposition of volcaniclastic sediments • Deposition of shallow then deeper marine sediments • Strike slip faulting – bringing andesitic welded tuff southward • Compression causes cleavage

  42. Problems • Does compression or strike-slip faulting take place first? • Why does pi intrudes within rock types? And when did it intrude.

  43. Plans • Find out more about tuffs and intrusions from thin sections • Provinence study of two vs units • Investigate fossils more closely to refine ideas about age

  44. Any Questions?

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