The document discusses the geology of the Western External Sierras of the Pyrenees Mountains. It describes the location and types of thrust faults in the region, including duplex, back, and roof thrusts, which formed due to the convergence of the African and Eurasian plates during the Alpine orogeny. It also examines two models of thrust belt development and discusses how different rock layers influenced the fault geometries. Overall, the document provides an overview of the structural geology and tectonic evolution of the Western External Sierras region during the Alpine orogeny.

1. Isaac Kenyon
Figure: http://upload.wikimedia.org/wikipedia/commons/3/33/Pyrenees_Catalonia.jpg

2.  Location of the Western External Sierras.
 Types of thrust faults of the Western External Sierras
and how they form i.e. Decollment mechanisms.
 Geological history of the South Central Pyrenees.
 Relation of the Western External Sierras and the
regional context of the Alpine Orogeny.

3. Figure: http://su-
thermochronology.syr.edu/_images/pyreneesmap3.jpg
Figure: Minh Nguyen (PANO_20140606_152833 ) photo from the highest peak of my mapping area

4.  Thrust faults - Are reverse faults but with a
low taper angle and have a hanging wall
block above a very low angle thrust.
 Decollment – Is a gliding plane between two
rock masses. AKA (basal detachment fault).
 Back thrusts – A thrust fault which has an
opposite vergence to that of the main thrust
system or thrust belt.

5.  Mechanically weak layers
slip in strata allowing the
development of stepped
thrusts.
 Decollment in the
Pyrenees occurs from
mechanically weak
basements i.e. Shales and
evaporites (my area).
(Vidal-Royo, Koyi and Muñoz, 2009)
Figure:
http://upload.wikimedia.org/wikipedia/commons/thumb/
3/31/Decollement_in_a_compressional_setting.pdf/page1
-1280px-Decollement_in_a_compressional_setting.pdf.jpg
It’s a deformational structure
associated with compressional
settings (fold-and-thrust belts).
Triassic Evaporites
Figure from mapping: Minh Nguyen
photo: IMG_20140604_145331

6. Model 1 - (Meigs and
Burbank, 1997)
Model 2 - (Vidal-Royo,
Koyi and Muñoz, 2009)
 Fold and thrust
development Critical-
taper wedge model.
 The thrust belt
revolves around the
critical taper angle
between basal
decollment and the
surface slope.
 Model implies that internal
deformation is modulated
by changes in the surface
slope and in material
properties within and at
the base of the wedge.
 Model depicts the ductile
 frictional contrasts of
the basal decollment of
structures through thin-
skinned shortening
tectonics (a style of
thrusting in which
sedimentary cover is
entirely removed from
underlying basement).

7. Model 1 - (Meigs and
Burbank, 1997)
Model 2 - (Vidal-Royo,
Koyi and Muñoz, 2009)
 Fold and thrust
development Critical-
taper wedge model.
 The thrust belt
revolves around the
critical taper angle
between basal
decollment and the
surface slope.
 Model implies that internal
deformation is modulated by
changes in the surface slope
and in material properties
within and at the base of the
wedge.
 Model depicts the ductile 
frictional contrasts of the
basal decollment of
structures through thin-
skinned shortening tectonics
(a style of thrusting in which
sedimentary cover is entirely
removed from underlying
basement).

8. Model 1 - (Meigs and Burbank, 1997) Model 2 - (Vidal-Royo, Koyi and
Muñoz, 2009)
 Issue: not sufficient resolution
of data.
 Limited applicability to fold
and thrust belts due to
mechanical and deformational
incompatibilities between the
geological record and the
model.
 Model depends on the
mechanical behaviour of
evaporites and it’s
interaction with the
overlying overburden.
High frictional domain
(dashed lines represent
sand)
Low frictional domain (black
areas shows the ductile layer
Source: Meigs and Burbank, 1997)

9.  Duplex thrusts (Antiformal stack duplex) – Where a
series of thrusts connects both with a floor thrust
below and a roof thrust above i.e. Back thrust.
 Form in the hanging walls of the thrust system.
 Anticlines are related to folding at the tip of basal
decollment.
 It develops as a result of thrusting to accommodate
deformation i.e. fault-propagation folds
(Vidal-Royo, Koyi and Muñoz, 2009)
Source: http://www.diggles.com/pgs/2008/Thrust_Belt_plays.jpg
Source: (McClay, 1991)
Duplex thrust – my fair copy map

10.  A thrust fault which has an opposite vergence
to that of the main thrust system
 The back thrusts in my area formed a tectonic
wedge (a body of rock that has moved between
a pair of oppositely vergent thrusts).
 The triangle zone in the South of my area is a
wedge in which a third, foreland-south vergent
thrust completes a triangle in cross section.
Figure taken from:
http://www.diggles.com/pgs/2008/Thrust_Belt_plays.jpg
Figure taken from: (McClay, 1991)
Example triangle zone from
my fair copy map.

11.  Roof thrusts – When a back thrust
cuts off the top of original thrust
vergence.
 The upper thrust surface bounds a
duplex. It can be smooth/folded by
movement on underlying thrusts of
the duplex.
Figure taken from:
http://www.diggles.com/pgs/2008/Thrust_Belt_plays.jpg
Figure taken from: (McClay, 1991)
(McClay, 1991)
Example of the Duplex, Back and Roof thrusts in
my area – my own cross-section.

12. Figure: http://all-geo.org/highlyallochthonous/wp-
content/uploads/2010/07/Cretmap.jpg

14. Figure:
http://upload.wikimedia.org/wikipedia/commons/thumb/b/b6/
Iberian_Tectonic_EN.svg/300px-Iberian_Tectonic_EN.svg.png

15. Starting
here
Ending
here

16.  Figure: Shows the change from the rifting of Africa from Eurasia after the break up
from Pangaea to compression and the movement of Africa towards Iberia and
Eurasia. This is where the thrust faults start to develop early Cretaceous.
Image:
http://geology.gsapubs.org/content/36/11/839/F4.l
arge.jpg

17. Bernd Andeweg, 2002
Africa
Iberia
Eurasia
•Not all models correspond to a
simple plate tectonic reality.
Pyrenean fold belt
Figure:
http://www.igc.cat/web/en/map
ageol_atles_evoluciopaleo.html

18.  There was a 150km
separation between
Iberia and Europe during
this time (Andeweg,
2002).
 Most of Iberia was below
sea level (subtle eustatic
sea level changes caused
significant shifts in the
position of the coastline.
Beach deposits
Source:
IMG_20140523_121540
Minh Nguyen

19. Bernd Andeweg, 2002
Africa
Iberia
Eurasia
Figure:
http://www.igc.cat/web/en/map
ageol_atles_evoluciopaleo.html
Figure:
http://d1jqu7g1y74ds1.cloudfront.net/
wp-
content/uploads/2010/11/Geologic-
time-scale.jpg

20.  Clockwise rotation of
Iberia, with partial
subduction under Eurasia
(Andeweg, 2002) with
large scale deformation.
 Rapid convergence
between Iberia and
Africa.
Iberia
Eurasia
Betics
Africa
Sardinia
Bernd Andeweg, 2002

21.  Southward thrust sheet
emplacement from rapid
convergence of Africa and
Eurasia (Andeweg, 2002).
 Inversion of previously rifted
Mesozoic basins.
 Introduction of marine
foreland deposits.
 Development of the Ebro
basin.
 Deposits of limestone
platforms due to marine
transgressions. Figures: mapping Minh Nguyen
(A) IMG_20140523_155047
(B) IMG_20140529_123447
(C) Thin section photo supplied by the
department
B
CA
Transgression

22. Bernd Andeweg, 2002
Africa
Iberia
Eurasia
Figure: http://d1jqu7g1y74ds1.cloudfront.net/wp-
content/uploads/2010/11/Geologic-time-scale.jpg

23.  Pyrenean suture becomes a compressional active plate margin
(Andeweg, 2002).
 Southward thrusting creates the first important relief of the
Pyrenees.
 Ebro foreland basin is deep marine and turbiditic at this point and
is widening to the cope with advancing load.
 The sediments derived are shelf and slope marls and sandstones.
Source: IMG_20140528_113104
Minh Nguyen

24. Bernd Andeweg, 2002
Africa
Iberia
Eurasia
Ebro
Basin
Figure: http://d1jqu7g1y74ds1.cloudfront.net/wp-
content/uploads/2010/11/Geologic-time-scale.jpg

25.  Peak collision of the Pyrenees
 Folding of a syncline separates the Pyrenean foreland basin from marine
waters (Andeweg, 2002).
 Eastern Ebro basin is now closed from the worlds oceans (endoheric).
 Lacustrine centre and alluvial fan building on the margins of the basin
occurs.
 Basement detachment faults become reactivated.
Figure taken from:
http://claymin.geoscienceworld.org/content/47/3/303/F2.large.jpg

26. Bernd Andeweg, 2002
Figure:
http://www.igc.cat/web/en/map
ageol_atles_evoluciopaleo.html
Africa
Iberia
Eurasia
Figure:
http://d1jqu7g1y74ds1.cloudfron
t.net/wp-
content/uploads/2010/11/Geolo
gic-time-scale.jpg

27.  Pyrenees is further
deformed and uplifted
 Syn-sedimentary
continental deposition
and molasse (alluvial)
sedimentation
 Influx of terrestrial
sandstone, marine
shale and rapid
exhumation.
(Andeweg, 2002)
Figure taken from:
http://upload.wikimedia.org/wikipedia/commons/3/37/Uureg_Nuur.jpg

28. Bernd Andeweg, 2002
Africa
Iberia
Eurasia
Figure:
http://www.igc.cat/web/en/map
ageol_atles_evoluciopaleo.html

29.  External Sierras
fully develops
 End of the
sedimentation cycle
and start of erosion
 Ebro basin begins
to fill with
conglomerates,
passing into
fluvial/lacustrine
sediments
(siltstones and
sandstones). Figure taken from: http://www.reditec.org/en/sortida_geotectonica
The External Sierras

30. Bernd Andeweg, 2002
Africa
Iberia
Eurasia
Figure: http://d1jqu7g1y74ds1.cloudfront.net/wp-
content/uploads/2010/11/Geologic-time-scale.jpg

31.  Convergence between Eurasia (containing Iberia) and Africa begins to slow down.
 Sedimentary break in the plate boundary reorganisation.
 Limited activity along the plate boundary (axial zone).
 External Sierras stops developing in the west
 SE verged thrusting terminates (25Ma)
 A shift to major denudation (erosion)
 Passive margin
(Andeweg, 2002)
Figure taken from: http://gent.uab.cat/ateixell/en/content/field-seminar

32.  Many of the thrust faults in the
Pyrenees are roll over thrust
anticline faults.
 Can be ideal for trapping
hydrocarbons as the anticlines
plunge create a 4-way dip
closure effect. (Possibility?)
 Impermeable evaporites (strong
competent, and crystalline)
 The marine sediments and
limestones etc. would act as
reservoirs and source rocks for
the area.
Figure: taken from the Geology of Petroleum
module from Moodle Lecture 7 - Pete Burgess
Impermeable
Source: IMG_20140602_142651
Minh Nguyen

34.  There is a wealth of geological data in the Western
external Sierras to study thrust fault geometry in relation to
the Alpine orogeny.
 The Western External Sierras supports the types of
thrusting: duplex, roof and back thrusts.
 My work reflects on a combination of both models as proof
that not all work.
 Different lithologies (mechanically speaking have variations
in tectonic stresses which produce different thrust fault
mechanisms).
 Models are useful in a small context, geology is never small.
 The thrust fault geometry has a part to play in the
depositional environment of the Pyrenees
 Places similar
 Future work

35.  Field photos – Minh Nguyen – Samsung phone
 RHUL logo – https://www.royalholloway.ac.uk/iQuad/graphics/cER/Primary/RHULMasterlogoCMYK-Cropped-550x275.jpg
 Wally - http://i.dailymail.co.uk/i/pix/2010/06/01/article-1283070-0622451D0000044D-804_306x598.jpg
 4.bp.blogspot.com, (2015). [online] Available at: http://4.bp.blogspot.com/--mh-
6Nft1iE/TlZ240s0MtI/AAAAAAAADE4/GL9HWfkr3n0/s1600/SCHELLART_2002_Pyreenes_profile.jpg [Accessed 20 Feb. 2015].
 All-geo.org, (2015). [online] Available at: http://all-geo.org/highlyallochthonous/wp-content/uploads/2010/07/Cretmap.jpg [Accessed 20 Feb. 2015].
 Andeweg, B. (2002). Cenozoic tectonic evolution of the Iberian Peninsula. [S.l.: s.n.], pp.83 - 118.
 Anon, (2015). .
 Claymin.geoscienceworld.org, (2015). [online] Available at: http://claymin.geoscienceworld.org/content/47/3/303/F2.large.jpg [Accessed 20 Feb. 2015].
 Diggles.com, (2015). [online] Available at: http://www.diggles.com/pgs/2008/Thrust_Belt_plays.jpg [Accessed 20 Feb. 2015].
 Discoveringfossils.co.uk, (2015). [online] Available at: http://www.discoveringfossils.co.uk/eocenemap.jpg [Accessed 20 Feb. 2015].
 Geology.gsapubs.org, (2015). [online] Available at: http://geology.gsapubs.org/content/36/11/839/F4.large.jpg [Accessed 20 Feb. 2015].
 Igc.cat, (2015). Paleogeographical evolution. [online] Available at: http://www.igc.cat/web/en/mapageol_atles_evoluciopaleo.html [Accessed 20 Feb.
2015].
 McClay, K. (1991). Glossary of thrust tectonic terms. Thrust Tectonics: London, Chapman & Hall, pp.419-433.
 Meigs, A. and Burbank, D. (1997). Growth of the South Pyrenean orogenic wedge. Tectonics, 16(2), pp.239-258.
 Reditec.org, (2015). Virtual field trip - Geotectonics | REDITEC. [online] Available at: http://www.reditec.org/en/sortida_geotectonica [Accessed 20 Feb.
2015].
 Stampfli, G., Borel, G., Marchant, R. and Mosar, J. (2002). Western Alps geological constraints on western Tethyan reconstructions. Journal of the Virtual
Explorer, 08.
 Su-thermochronology.syr.edu, (2015). [online] Available at: http://su-thermochronology.syr.edu/_images/pyreneesmap3.jpg [Accessed 20 Feb. 2015].
 Teixell, A., Arboleya, M., Julivert, M. and Charroud, M. (2003). Tectonic shortening and topography in the central High Atlas (Morocco). Tectonics, 22(5),
p.n/a-n/a.
 Upload.wikimedia.org, (2015). [online] Available at:
http://upload.wikimedia.org/wikipedia/commons/thumb/9/92/Tectonic_map_Mediterranean_EN.svg/400px-Tectonic_map_Mediterranean_EN.svg.png
[Accessed 20 Feb. 2015].
 Upload.wikimedia.org, (2015). [online] Available at: http://upload.wikimedia.org/wikipedia/commons/3/33/Pyrenees_Catalonia.jpg [Accessed 20 Feb.
2015].
 Vergés, J., Fernàndez, M. and Martìnez, A. (2002). The Pyrenean orogen: pre-, syn-, and post-collisional evolution. Journal of the Virtual Explorer, 08.
 Vidal-Royo, O., Koyi, H. and Muñoz, J. (2009). Formation of orogen-perpendicular thrusts due to mechanical contrasts in the basal décollement in the
Central External Sierras (Southern Pyrenees, Spain). Journal of Structural Geology, 31(5), pp.523-539.

36. Thank you for
listening!
Feel free to ask
any questions
Figure: Minh Nguyen
(IMG_20140530_120304)