1. Unconformable contact between
Hercynian Basement and Erillcastell
Volcanics marked by abundant slate
clasts in lower basltic andesitic lapilli
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Pont de Suert horst structure
composed of a series of overturned
wedges bounding a folded region
of gypsiferous marl
Progressive overturning of Buntsandstein
Formation to the south suggesting foreland
rotation of oblique thrust sheets swinging
during detachment on Triassic evaporites
Palaeohigh
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Alternation in dip direction and brecciation
across road section suggest faulted contact
Large scale ductile deformation
observed in evaporites - inferred
association with ophitic intrusions
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El Pont de
Suert
Syndepositional palaeotopographic half grabens.
Greatest displacement in Upper Carbonfierous casuing
significant thinning of Erillcastell and Malpas Formations
Evidence for cross
stratified meandering
channel sands bounded
by flood plain silts
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Malachite veins and
chert lenses - evidence for
hydrothermal geyserite deposits
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Legend
s
Overturned Bedding
¹
Pervasive S1 Cleavage
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Right Way Bedding
³
Crenulation S2 Cleavage
á Slickensides
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S3 Kink Bands
P
S
Palaeocurrent
Rivers
Roads
Folds
), Synform
Boundaries
Inferred Geological Boundary
Observed Geological Boundary
Unconformity
Contours
Faults
*
Inferred Backthrust
"
Inferred Normal Fault
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Inferred Thrust Fault
Inferred Strike Slip fault
Observed Normal Fault
Observed Thrusted Contact
Thrust Bounded Unit
Lithologies
Hercynian Basement
Ophite
Peranera Formation
Pont de Suert Gypsum
Pont de Suert Limestone
Upper Bunter Formation
0 0.25 0.5 0.75 1
Miles
S
P
Structural Data
Infrastructure
Towns
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" "
Sedimentary
Erillcastell Volcanics
Metamorphic
Igneous
P
S
P
S66
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Section lines
A A’
B B’
Main Cross Section
N-S Cross Section
49
Malpas Formation
Mesozoic Limestone
Lower Bunter Formation
Ventola
Gotarta
CLAY
SILT
SAND
GRANULE
PEBBLE
COBBLE
BOULDER
DEPTH(m)
LITHOLOGY
MAPPINGLITHOLOGY
28
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42
182
168
154
140
126
112
98
196
224
210
252
238
294
280
266
vf f m c vc
Schematic Sedimentary log
1:1400 Scale
Based on unit thicknesses along Gotarta Road
Key
Shale
Silt
Sand
Matrix-supported
conglomerate
Volcaniclastics
Volcanic breccia and tuff
Metamorphic basement
Reduction spots
Planar cross stratification
Trough cross stratification
Planar laminae
Coprolites
Skeletal fragments
Fossil fumaroles
Pillow structures
Preserved plant matter
Intermediate and silicic blocks and bombs
Accretionary lapilli
Variable interbedded sequence of low grade greenschist facies phyllites, slates and marbles
with marked differences in carbonate contents attributed to relict pelitic layers. Bioturbation
and fossilised bioclasts are most strongly preserved in phyllites and calcareous slates.
Overprinted pervasive, crenulated and kinked foliations as well as kiolmetre scale folds highlight
a minimum of four deformation episodes corresponding to both Variscan and Alpine orogenesis.
Hercynian basement
Erillcastell Volcanics
Complex series of sub-lithological pyroclastic lapilli tuffs, mass flow breccias and rhyolitic and
basaltic lava flows underlain by a thick basaltic andesite lapilli tuff sheet marking the large scale
unconformable contact with deformed basement metamorphics. Eroded normal graded ashfall
deposits and sequences of poorly cemented stratified epiclastics exhibit strong lateral
discontinuity. Evidence for fossilised and mineralised plant material and graphite bearing
bedded tuffs highlight multiple eruption events and variable emplacement temperatures
producing an upper welded ignimbrite succession comprised of basal silicic pillows, fossil
fumaroles and flattened accretionary lapilli. The latter are commonly associated with malachite
precipitation in areas of preserved cryptocrystalline quartz laminae representing hydrothermal
fluid injection.
Stratigraphic Column
1:1400 Scale
Malpas Formation
A sequence of dark grey fissile laminated silts and shales with evidence for preserved plant
material interbedded with competent normal graded yellow to beige coarse silt to
medium-grained sandstones exhibiting normal grading.
Peranera Formation
Conformable sequence of fissile muds and silts exhibiting strong red colouration with variable
concentrations of subrounded beige calcareous derbis flow nodules subparallel to bedding.
Evidence for vertebrae and abundant coprolites suggests the presence of tetrapods prevailing
in a semi-arid environment. Interbedded sequences of andesitic tuffs concentrated towards
the base of the succession.
Lower Bunter Formation
Upper Bunter Formation
Pont de Suert limestone
Pont de Suert Formation
This unit represents the incompetent Keuper marl series of the Triassic evaporite succession
comprised of impure calcareous vividly-coloured beige, red and greenish-grey gypsiferous marl.
Bedding is indistinct but may form contorted sub-horizontal isoclinal folds exhibiting
boudinage. Interbedded dark grey to black gypsum laminae reflect organic preservation with
localised red crystalline manganese reduction zones. Marl dominated regions exhibit
asymmetrical ripples up to 2 cm with evidence for fossilised tetrapods footprints and preserved
raindops. The combination of brittle and ductile deformation forms an important detachment
horizon along which thrusts have propagated.
Mesozoic Limestone
Calcareous nodules
Unconformity
CARBONIFEROUSPERMIAN
LOWERMIDDLEUPPER
TRIASSICJURASSIC
Unconformable deposition marked by a poorly sorted clast supported basal conglomerate up to
2 m in thickness transitioning into weakly graded brown - maroon fine to
coarse-grained sands and minor interbedded sequences of micaceous mudstone and
siltstones. Evidence for longitudinal and transverse bars and laterally discontinuous bank
collapse pebble conglomerates are concentrated within regions of coarser sand
fractions.
Overlying series of strongly red and maroon authigenic massive fissile laminted silts and muds
interbedded with sequences of fine and medium-grained sands grading into a poorly exposed
upper shale succession. Sedimentary structures are well developed dominated with preserved
centimetre-scale asymmetrical ripples. Large scale trough cross stratification, groove casts and
load structures are associated with meandering channel sands. Localised green
reduction concretions are sparsely distributed throughout silt layers.
Dark to light grey silt grade calcareous imbricates forming projecting ridges bounded by the
Pont de Suert Gypsum. Unit exhibits variable sparry and micritc natures with weakly developed
cross stratification and laminae. Fossilsed material is sparse forming bioclastic shell fragments
and burrowing trace fossils. Evidence for horizontal and poorly developed oblique styolites
suggests subjection to both sedimentary loading and structural compression.
Massive light grey argillaceous calcareous unit exhibiting variable sparry and micritic natures
conformably overlying the Triassic evaporites. Towards the base of the unit, dark grey medium to
coarse grained dolomites dominate with a transition into interbedded sequences of sparry
resistant beds and dark grey fissile marls overlain by breccious intercalations. Semi-continuous
calcite veins up to 2 cm in width occur throughout with sparse bioclasts present as fragmented
bivalve shells concentrated in clusters.
Observed Upper Bonansa and Prada sequences in the mapping area.
A A’
Backthrusted Mesozoic Limestone detaching on top of
evaporites following reinversion of normal faults
Hercynian basement wedge marking the
degree of overturning - isoclinal S1 faults are
likely sub-horizontal following inversion
Hercynian basement forming
core exposed due to erosion
Convergence of low angle
floor thrusts detaching on
top of Triassic evaporites
SW NE
Foreland Hinterland
Inferred thrust shallowing towards
Hinterland. Dominant basement
forming eroded core of the
Axial Zone Floor thrust propagating from
Axial Zone core along which
thrust sheets have converged
following detachment on
Keuper marls
Cross Section along line of section A-A’
1:10000 Scale
Regional Schematic Cross Section
IBERIA EUROPE
Sierra
Marginales
FORELAND BASIN
AXIAL ZONE
Progressive deformation
produced foreland rotation of
thrust sheets - mapping
area location
50 km
NS
Eroded Palaeozoic
core
Backsteepening of
ramp-flat series
Montsec BoixolsEBRO BASIN AQUATINE BASIN
Adapted form Saura & Teixell, 2006
NOGUERES
ZONE
Geological Map of El Pont de Suert
Charles Singer
Imperial College London
Ü
Thickening of Upper Carboniferous -
Permian strata could be attributed to
inversion of north verging sub-bedding
parallel extensional faults
Pont de Suert Gypsum
UPPER
Ophite
Dark greenish grey to brown holocrystalline porphyritic tholeiitic dolerites characterised by an
ophitic texture with tabular plagioclase enclosed within pyroxene phenocrysts.
Upper Palaeozoic strata exhibit significant lateral thinning and restriction
to localised extensional basins - Bunter represents more uniform deposition
LOWERLOWER
1 km 1 km
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Elevation(m)
Foreland rotation of thrusts with progressive deformation to the SSW.
Region marks boundary between axial zone and fold thrust belt with
younging of faults towards the foreland
Faulted contact along weak
evaporitic detachment horizon
Inverted bed dips shallow to the NE representing
greater overturning towards the centre of
imbricate stack
Detachment of Mesozoic Limestone
capping foreland rotated thrusts
producing duplex
Strongly deformed Herycnian Basement marking the transition of
overturning. Unit comprised of discontinuous interbedded
metasediments including slates marbles and phyllites. Evidence for
multiple deformation episodes during Variscan orogeny and
reactivation during Alpine.
Discontinuous imbricates of limestone
in the Pont de Suert Formation forming
thrusted wedges of a ramp flat structure representing
a thrust bound duplex within a larger duplex structure
Weak, ductile Triassic evaporites provide detahcment horizon along which thrusts converge
Undulating contact provides evidence for
unconformable deposition of Erillcastell volcanics
inflling palaeotopographic graben induced by
basin rifitng
313245
4697190
317500
4699471
Basic tholeiitic dolerite ophite intrusions
in the Pont de Suert Formation - occur as
intermittent outcrops through series of
imbricates
Inclined
non-overturned
strata
A A’
Inferred
repetition
of Palaeozoic
cover
rocks
0
UPPER
PERMIAN
Deposition of marine carbonates and
pelite protoliths on the continental shelf of
Laurussia subject to Hercynian orogeny.
TRIASSIC
Post-orogenic volcanism orginiating from
crustal delamination and production of
peraluminous calc-alkaline magmas.
Deposition of fluvial sediments within
terrestrial half grabens associated with
Pangaea rifitng marked by basal angular
unconformity with extensive erosion and
relief rejuvination in Permian.
Underlying E-W trending half grabens
likely controlled later fault orientations.
Syndepositional half grabens associated
with thermal subsidence extending
through Upper basement producing
strong lateral discontinuity in sediments.
Interpreted Tectonostratigraphy
CARBONIFEROUS
LOWERLOWER
JURASSIC
Extension associated with Atlantic and
Tethys rifting. Thermal uplift producing
regression and Upper Jurassic
unconformity (Vergés et al., 2002).
Alpine orogeny characterised by the
foreland rotation of thrust sheets and
inversion of pre-exisiting Cretaceous
extensional faults.
CRETACEOUS
MIDDLEUPPER
Transgressional shallow marine limestones
and sea-adjacent playa lakes.
Late Triassic tholeitiic dolerites associated
with Pangaea rifting spreading laterally
beneath poorly consolidated incompetent
gypsiferous marls.
Second main phase of extension
(Barremian to Albian) producing E-W
trending extensional faults through
substantial thinning of crust.
UPPER