Characteristics of Deformation Bands and Relationship to Primary Deposition: an Outcrop Study from the Wirral, North-West England

Characteristics of deformation bands and relationship to primary deposition: an outcrop study from the Wirral, north-west England

Ed Hough*, Oliver Wakefield, Cath Cripps, Joanna Thompson British Geological Survey, Nottingham, UK

* [email protected]

A talk of three halves: Primary sedimentology: Fluvial/Aeolian sandstone- lithology and environments of deposition

Secondary processes: geometry, style and properties of deformation bands – the Wirral …but not their formation and timing

Consequence: potential impacts on subsurface management

Bolton Sandstone Group Fl • Onshore extent of B Manchester Liverpool southern East Irish Sea Runcorn Basin Ae Chester Fl WALES ENGLAND • Preserved geology-

Wrexham Stoke-on- fluvial and aeolian

E Trent Ae W n

g a

l a

e n

10 km Llangollen s d terrestrial dryland

Aeolian dune Fluvial Dry crossbed interdune

Channel lag

A Outer braid bands B

1 cm Cataclasite B

1 cm C

Thurstaston Hill

Planar zones of crushing of framework grains, fusing and grainsize reduction; commoner in ‘clean’

• Mapped out and measured- thickness, lateral and vertical extents where possible; host lith and facies • Allocated to one of 4 morphological classes • Permeability measured in the field and from cores- mini-permeameter • A field portable instrument • Probe measures resistance of gas flow by formation • Correction factor translates to permeability estimate

© NERC All rights reserved ...... 9 . . . . Facies control on occurrence; influence of primary deposition Facies type Individual bands All other facies 8% Aeolian 72 crossbed 74 Dry interdune 2 Aeolian crossbed Upperplain beds 1 92% Channel lag 2 4 Fluvial crossbed 1 Fluvial massive 0

Individual bands 80 70 Conjugate set 60 50 40 30 20 10 0 Aeolian Dry Upperplain Channel Fluvial Fluvial crossbed interdune beds lag crossbed massive Grange Road © NERC All rights reserved ...... 7 ...... Morphology of deformation bands

• Individual ‘thread’ • Conjugate set • Braid • Composite

C D A 35 - 300 cm Sometimes discontinuous 0.8 - 82.3 cm 3 - 240 cm

0 - 0.9 cm

Class Perm min (mD) Perm max (mD) Thread 2.10 25.97 Braid 2.41 49.43 Conjugate 3.47 50.11 Composite 4.73 25.46 Undeformed host 69 5100 (Bloomfield et al., 2006)

Permeability60 vs. thickness

50 Thurstaston Hill

40 ) D m (

y t i l

i 30 b a e m r e P 20

10 Permeability Permeability (mD) 0 0.1 1 10 100 1000 Cataclasite thickness (mm) Deformation band thickness (mm)

• Wood Report- maximise production in the depleting North Sea- compartmentalise where reservoir pressures are lower • Aquifer management- enhance production; inform contaminant models • Effect on monitoring and testing in the regions subsurface- NERC Energy Security Innovation and Observation System (ESIOS) • Identification in cores/seismic reflection problematical • Potential lateral and vertical extent informed by understanding facies geometries © NERC All rights reserved ...... 11 . . Conclusions

• Supports influence of lithology on development: More common in grain fall and grain flow (dune) facies; less common in interdune and channel/channel lag • 4 distinct classes proposed, based on morphology • Permeabilities up to 2 orders of magnitude lower than undeformed host • Primary sedimentology as a tool for prediction

… a factor in extending the life of mature basins? …relevance to groundwater fluid flow models- better aquifer management; a consideration for ESIOS?

Thanks for listening

Any questions?

Ed Hough*, Oliver Wakefield, Cath Cripps, Joanna Thompson British Geological Survey, Nottingham, UK

[email protected]