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The Mesozoic Evolution of South-Western Portugal – Algarve and Alentejo Basins, Portugal. Field-trip Guide, III Conjugate Margins Conference, 48 pp. PIPCo RSG Ltd, Dublin.

Abstract

This volume corresponds to a field-trip guide for a 3-day visit to South-West Portugal, as part of the III Central & North Atlantic Conjugate Margins Conference (Dublin, 2012). The field-trip starts in the Algarve Basin, a south facing Atlantic Basin, close to the Mediterranean and the former Tethys influence. In the western part of the basin, most of the Upper Triassic to Upper Jurassic sequence can be seen. We opted to look in detail at a restricted number of outcrops, representing the main facies and events of that time interval. Cretaceous deposits also occur and will be seen, although they are better exposed towards the East and are mostly covered by Tertiary deposits. The first day will take us through the Jurassic evolution of the basin and the second day through the Cretaceous and Tertiary evolution. The main elements and moments of the petroleum system will also be addressed, although the best potential of this basin lies in the offshore area to the South-East. The second day will take us to the Alentejo Basin, facing the Atlantic to the west. The only outcrops are around Santiago village, where an uplifted block has brought up the base of the Mesozoic sequence. The Upper Triassic to Lower Jurassic sequence is well exposed, whereas the Middle and Upper Jurassic may be seen only in small windows below the Tertiary cover, between Santiago and the coastline. The third day will be dedicated to the southern edge of the Lusitanian Basin, which extends for over 200 km to the North and for over 100 km offshore to the West. This edge of the basin corresponds to the Arrabida chain, showing intense alpine uplift related to the Tertiary inversion. Jurassic and Cretaceous facies will be seen, as well as the effects of the extensional and compressive regional tectonics. This field trip is intended to give an overview of the main geodynamic phases and sedimentary infill packages, leading to discussions about basin evolution and regional petroleum systems. We hope you’ll enjoy the geology, the landscapes, and especially the places and the moments to take with you in your memories!
ALGARVE AND ALENTEJO BASINS, PORTUGAL  FIELD TRIP GUIDE
www.conjugatemargins.ie
“The Mesozoic Evolution of South-Western Portugal”
CENTRAL & NORTH ATLANTIC
CONJUGATE MARGINS CONFERENCE
DUBLIN 2012
THIRD
CONJUGATE
MARGINS
CONFERENCE
2012
2
Rui Pena dos Reis & Nuno Pimentel
(Field Trip Leaders)
The Mesozoic Evolution
of South-Western Portugal
FIELD TRIP GUIDE
Financial
support
FOREWORD
This volume corresponds to a field-trip guide for a 3-day visit to South-West Portugal, as part of the III Central & North
Atlantic Conjugate Margins Conference (Dublin, 2012).
The field-trip starts in the Algarve Basin, a south facing Atlantic Basin, close to the Mediterranean and the former
Tethys influence. In the western part of the basin, most of the Upper Triassic to Upper Jurassic sequence can be seen.
We opted to look in detail at a restricted number of outcrops, representing the main facies and events of that time
interval. Cretaceous deposits also occur and will be seen, although they are better exposed towards the East andare
mostly covered by Tertiary deposits. The first day will take us through the Jurassic evolution of the basin and the
second day through the Cretaceous and Tertiary evolution. The main elements and moments of the petroleum system
will also be addressed, although the best potential of this basin lies in the offshore area to the South-East.
The second day will take us to the Alentejo Basin, facing the Atlantic to the west. The only outcrops are around
Santiago village, where an uplifted block has brought up the base of the Mesozoic sequence. The Upper Triassic to
Lower Jurassic sequence is well exposed, whereas the Middle and Upper Jurassic may be seen only in small windows
below the Tertiary cover, between Santiago and the coastline.
The third day will be dedicated to the southern edge of the Lusitanian Basin, which extends for over 200 km to the
North and for over 100 km offshore to the West. This edge of the basin corresponds to the Arrabida chain, showing
intense alpine uplift related to the Tertiary inversion. Jurassic and Cretaceous facies will be seen, as well as the effects
of the extensional and compressive regional tectonics.
This field trip is intended to give an overview of the main geodynamic phases and sedimentary infill packages, leading
to discussions about basin evolution and regional petroleum systems.
We hope you’ll enjoy the geology, the landscapes, and especially the places and the moments to take with you in your
memories!
Rui Pena dos Reis & Nuno Pimentel (Field-trip Leaders)
3
Contents
INTRODUCTION
- Itinerary & Stops
- Correlation of the W Algarve, Alentejo and S Lusitanian basins
- Palaeogeographic reconstruction of the Iberia microplate
- Regional framework of the SW Iberian basins
- Offshore structure of the Algarve and Alentejo basins
- Geodynamic framework of the Algarve Basin
- Simplified geological map of the Algarve region, southern Portugal
- Lithostratigraphy of the Algarve Basin
- Palæotemperatures in the Algarve Basin
- The CAMP record in West Iberian basins
- Atlantic NW Morocco Agadir-Essaouira Basin
- Jeanne d’Arc Basin Stratigraphic Chart
- THE LUSITANIAN BASIN - simplified petroleum systems
- THE ALGARVE BASIN - simplified petroleum systems
STOPS PRESENTATION
- Daily chronogram
- Stops overview
- STOP 1 Carrapateira
- STOP 2 Telheiro
- SAGRES area
- STOP 3 Tonel
- STOP 4 Mareta
- STOP 5 Zavial
- STOP 6 Luz
- STOP 7 Piedade
- STOP 8 Santiago
- ARRÁBIDA area
- STOP 9 Palmela
- STOP 10 São Luís
- STOP 11 Sesimbra
- STOP 12 - Espichel
4
DUBLIN
LISBOA
LAGOS
SAGRES
5 ZAVIAL
6 - LUZ
7 - PIEDADE
1 CARRAPATEIRA
2 TELHEIRO
3 TONEL
4 MARETA
1
2
3 4
5
6 7
LISBOA
SETÚBAL
9
10
11
12
9 PALMELA
10 SÃO LUÍS
11 SESIMBRA
12 - ESPICHEL
FARO
LISBOA
8
8 - SANTIAGO
DUBLIN
LISBOA
HALIFAX
A
B
A
B
N
N
N
Days
1 & 2
Day 3
Days
1 & 2
Day 3
NORTH ATLANTIC
CENTRAL ATLANTIC
Itinerary & Stops
5
S Lusitanian Basin
The Western Algarve Basin
presents a late Triassic to Early
Cretaceous Mesozoic infill, which
may be correlated with the infill
of the onshore Alentejo Basin
and the southern Lusitanian
Basin.
The main depositional
sequences and hiatus may be
recognised in all these basins,
with some regional
unconformities
Offshore Onshore
1
1
2
3 4
5
6
8
8
10
11
12
2
Stratigraphical position
of the field trip stops
Correlation of
the W Algarve,
Alentejo and S
Lusitanian Basins
6
(adapted from Pereira & Alves, 2011)
Palaeogeographic reconstruction of the Iberia microplate
The change from a Triassic/Jurassic Tethys realm to a Cretaceous Atlantic realm (Ziegler, 1999).
7
Regional framework of the SW Iberian basins
ARRABIDA
STC
Alentejo
Basin
Algarve Basin
LAGOS
Lusitanian
Basin
Andeweg, 2002
8
Seismic lines used to compose the sketch of Fig. G (see inset for location). Lines 1 and 2 =
Fig. 12 and Fig. 8, in Pereira & Alves (2011); Line 3 = Fig. 6.5, in Matias (2007).
Sketch of the basement structures and Meso-Cenozoic infill of the Alentejo Basin (ALB)
and Algarve Basin (AGB), based on the composition of three interpreted seismic lines (see
inset for location). ALB Alentejo Basin; ABG Algarve Basin; GB Guadalquivir Bank.
(Pimentel & Pena dos Reis, 2012).
Offshore structure of the Algarve and
Alentejo basins
9
Geodynamic framework of the Algarve Basin
The Algarve Basin’s Mesozoic evolution is
controlled mainly by the extension related
with its position between the western
Tethys and the Central Atlantic opening,
causing differential movement of Africa with
respect to Eurasia.
This tectonic framework promoted a left
lateral transtension shear-zone and the
extensional re-activation of NE-SW late-
Variscan faults.
During Mesozoic extension, N-S to NW-SE faults acted
as right lateral transfer faults, separating elongated
tectonic blocks. These two directions, NE-SW dip-slip
faults and NNW-SSE transfer faults, may also be
recognised in the palaeogeographic evolution of the
Algarve Basin during the Jurassic and Cretaceous.
10
(Terrinha, 1998)
(Terrinha, 1998)
Simplified geological map of the Algarve region,
southern Portugal
(Borges et al., 2012)
The Algarve presents a broad monoclynal structure dipping to the south.
At the northern margin, Upper Triassic units overlie Palaeozoic basement, followed by Lower to Middle Jurassic and
Upper Jurassic units, outcropping mostly in the western and central parts of the Basin. Cretaceous units outcrop mainly
in the central part of the basin. A Cenozoic basin covers the southern margin of the Algarve Basin.
11
Lithostratigraphy of the Algarve Basin (Terrinha, 1998)
12
Palaeotemperature vs. dept profiles for the
Western Algarve (Sagres), Central Algarve
(Albufeira) and eastern Algarve (Faro and
Tavira). Palaeotemperature values have
been calculated from %Ro data, according
to the empirical equation of Barker (1988).
In Fernandes et al., 2012 acessed at
http://www.associacaodpga.org/vi_alen_alg_moura.html
Palaeotemperatures
in the Algarve Basin
The palaeotemperature studies in the
Algarve Basin (Fernandes et al., 2012)
point to a higher geothermal gradient in
the Western Algarve (c. 60ºC).
In the Sagres area, palæotemperatures
around 90ºC at present-day surface,
point to uplift and erosion of more than
1 km of sediments.
These facts underline the importance of
local and regional tectono-thermal
evolution to understand the maturation
of potential source rocks in this basin .
13
0 m
Lusitanian
Basin (North)
Lusitanian
Basin (South)
Red Clays
with Gypsum
Massive
Dolomites
Fine-grained
sandstones
Platy Dolomites
Massive
Dolomites
Platy Dolomites
Massive
Dolomites
Red Clays
with Gypsum
Extrusive
Volcano-
Sedimentary
Platy Dolomites
Massive
Dolomites
Red Clays
with Gypsum
Extrusive
Volcanics 100m 50m
20m
Extr./Explosive
Volcano-
Sedimentary
Red Clays
w. Gypsum
Alentejo Basin Algarve Basin
HETTANGIAN
RHETIAN ?
Platy Dolomites
Massive
Dolomites
Extrusive
Volcanics
Red Clays
with Gypsum
SINEMURIAN
HETTANGIAN
(c.198-196 Ma)
CAMP-related
MAGMATIC EVENT
The CAMP record in
West Iberian Basins
(Pena dos Reis & Pimentel, 2011)
14
The onshore geological record of Late Triassic to
Early Jurassic on the West Iberian Margin may be
studied in three different basins: the Lusitanian
Basin (to the North), the Alentejo Basin (to the
SW) and the Algarve Basin (to the South). The
CAMP event, largely recorded in Morocco and
Western Canada, is also present in these basins.
Atlantic NW Morocco Agadir-Essaouira Basin
Central Atlantic Rifting
Central Atlantic spreading,
and thermal subsidence
D
R
I
F
T
Eur-Africa collision and
basin’s mild inversion
Tertiary infill and intense
compressional folding
Transgression;
Marine platform
development;
Berriasian-
Barremian
regression.
REGIONAL EVOLUTION
(Hafid et al., 2010)
Davison et al., 2010
15
Petroleum Exploration Opportunities in Jeanne d’Arc Basin,
Call for Bids NL 09 -1. On Behalf of NL DNR, October 2009
Michael E. Enachescu, Euxinic Exploration
http://www.nr.gov.nl.ca/nr/invest/jeanne_d_arc_presentation.pdf
accessed 26/07/12
Jeanne d’Arc Basin
- Stratigraphic Chart
after Enachescu, 1987 & 1994
16
THE LUSITANIAN BASIN
simplified petroleum systems
Silurian Carboniferous Late
Triassic
Early
Jurassic
Middle
Jurassic
Late
Jurassic
Early
Cretaceous
Late
Cretaceous
Tert. STRATIGRAPHY
Conraria C. Viegas Dagorda Coimbra V.Fontes Candeeiros Cab/Mtj Abadia Lour. T.Vedras F. Foz Cacém Taveiro
LITHOSTRAtT.
UNITS
SOURCE
ROCK
MATURATION
MIGRATION
Si l iciclastic
RESERVOIR
Carb onate
SEAL
Identified
onshore
Probable
offshore
17
THE ALGARVE BASIN
simplified petroleum systems
Silurian Carboniferous Late
Triassic
Early
Jurassic
Middle
Jurassic
Late
Jurassic
Early
Cretaceous
Late
Cretaceous Tert. STRATIGRAPHY
Silves Dagorda Picavesa Belixe Mareta Tonel Sagres Luz P.Mós LITHOSTR.
UNITS
SOURCE
ROCK
MATURATION
MIGRATION
Si l RESERVOIR
Carb RESERVOIR
SEAL
A.Nova Lagos
P.Branco
Identified
onshore
Probable
offshore
18
DAY 1
Lagos Hotel dep. 8.30 am
Lagos-Carrapateira = 35 km = 35 min.
STOP 1 (9.30h - 12.30h) CARRAPATEIRA
1A - Bordeira beach
1B , 1C - Pontal
1D - Três Angras
1E Amado beach
LUNCH (12.30h - 13.30h)
Carrapateira-Telheiro = 30 km = 30 min.
STOP 2 (14.00h 15.30h) TELHEIRO
TelheiroS.Vicente Cape = 10 km = 15 min
(+ 30 min. landscape stop)
STOP 3 (16.30h - 17.30h) TONEL
STOP 4 (17.30h - 18.30h) MARETA
Mareta Lagos = 35 km = 35 min.
Lagos Hotel 19.30h
Dinner 20.30h
DAY 2
Lagos Hotel dep. 8.30 am
Lagos-Zavial = 25 km = 30 min.
STOP 5 (9.30 10.30) ZAVIAL
Zavial Luz = 15 km = 30 min
(+30 min. landscape stop)
STOP 6 LUZ BEACH (11.30 - 12.30)
LUNCH (12.30 - 13.30)
Luz Lagos = 10 km = 15 min.
STOP 7 (14.00 15.00) PIEDADE
Lagos Santiago do Cacém = 200 km
= 2h15min (mostly highway)
STOP 8 (17.30 - 19.00) SANTIAGO
Santiago Hotel 19.30h
Dinner 20.30h
DAY 3
Santiago Hotel dep. 8.30 am
Santiago Palmela = 110 km = 1h15min.
STOP 9 (10.00h 10.45h) PALMELA
Palmela São Luís = 10km = 15 min.
STOP 10 SÃO LUÍS (11.00 11.30)
São Luís Setúbal Arrábida = 30 km
= 30 min (+30 min landscape stops)
LUNCH (12.30 - 13.30)
Arrábida Sesimbra = 20 km = 25 min
STOP 11 (14.00 15.30) SESIMBRA
Sesimbra Espichel = 20 km = 25 min
STOP 12 (16.00 - 17.30) ESPICHEL
Espichel Lisboa = 60 km = 1h
Lisbon Hotel area 19.00h
DAILY CHRONOGRAM
19
1
CRP
2
TEL
3
TON
4
MAR
5
ZAV
6
LUZ
7
PD
8
SC
9
PAL
10
SL
11
SES
12
ESP
Tertiary/
U. CRET.
-
Up-lifted
littoral
platform
- -
Miocene
Fossiliferous
marls
-
Miocene
Fossiliferous
marls
-
Miocene
Fossiliferous
marls
(cuesta)
- -
Up-lifted
littoral
platform
Lower
CRET. - - - -
Coastal
Dolomitic
silts and
marls
Coastal
sands and
transitional
marls
- - Eroded
fluvial sands
- -
Fluvial
sands
and
transitional
marls
Upper
JURASSIC
Marly
Limestones
(SR)
- Marly
Limestones
Marly
Limestones
(SR)
- - - -
Limestones
Orogenic
intraform.
Conglomer.
-
Shallow
marine
marls
M. JUR.
Marine Marls
Marine
Marls
Marine
marls - - - - - - - -
Lower
JURASSIC
Dolomites
Dolomites
- - - - -
Volcanics
and
Dolomites
- -
Volcanics
and
Dolomites
-
Upper
TRIASSIC
Aeolian and
sabkha
Red-beds
Aeolian and
sabkha
Red
-
beds
- - - - - Alluvial
Red-beds
- - Sabkha
Evaporitic
clays
-
Etc.
Border
outcrop of
the Alentejo
Basin
Erosional
Unconform.
on
Carbonif.
shales
U. Jurassic
unconform.
sealing M.J.
faulting
Exposed
Reef
Miocene
Erosional
Unconform.
Igneous
intrusion
Coastal
Karstic
landscape
CAMP
volcanics
(Alentejo
Basin)
Alpine
deformation
Duplex
structure
U. Jurassic
up-lift of
basement
Diapiric and
CAMP
volcanics
(Lusitanian)
Alpine
up-
lift
20
STOP’S OVERVIEW
UPPER JURASSIC
Volcanic tuffs and breccias
Marly limestones (*dolom)
Limestones and Dolomites
MIDDLE JURASSIC Dolomites
L. JURASSIC Marls & dolomites
HETTANGIAN Red clays & marls
UPPER TRIASSIC Redbeds
E
A B D
A
B
C
D
E
A
B
21
Feio et al., 1985
STOP 1
CARRAPATEIRA
Along the Carrapateira promontory a Late Triassic to Late
Jurassic sequence can be seen.
Late Triassic redbeds comprise fluvio-aeolian sands with
trough cross-bedding. The Hettangian comprises alternating
red clays and marly reduced dolomites, deposited in a sabkha-
like environment.
Early and Middle Jurassic carbonates are mainly shallow-
water deposits with intense dolomitisation.
Upper Jurassic deposits are the result of renewed orogenic
instability and subsidence, with signs of uplift, emersion,
karsification and erosion. Some restricted lagoonal facies
contain significant organic matter.
Magmatic intrusions
may be observed,
mainly related to the
Late Jurassic doleritic
Alentejo-dyke.
N
1 km
D
C
C
E
Carboniferous basement U. Triassic
redbeds
Middle
Jurassic (?)
dolomites
Basin’s
tectonic
border
The Carrapateira promontory shows most of the Jurassic sequence of the western Algarve Basin.
The Mesozoic basin is controlled and affected by NNE-SSW bordering faults and defines a broad faulted syncline.
Upper Triassic redbeds and Hettangian red clays and marls overlie Carboniferous metasedimentary basement.
The Lower and Middle Jurassic units show intense dolomitization and dating is very uncertain.
22
Laminated
dolomites
N
STOP 1
CARRAPATEIRA
Kimmeridgian marls with
Source-rock potential
23
Upper Jurassic interbedded limestones and marls at Três Angras.
Calciclastic marls and bioclastic limestones pass into interbedded grey
marls and limestones. The uppermost limestone beds are rich in
macrofossils including well preserved corals in life position.
Corals and foraminifera, as well as dinoflagellates indicate an Early
Kimmeridgian age (Ribeiro et al., 1987; Borges et al., 2011).
Borges et al., 2011
N STOP 1
CARRAPATEIRA
24
Middle Upper
Jurassic
unconformity
Upper Triassic
aeolian like redbeds
Tithonian (?)
calciclastic
conglomerates
Hettangian red
clays & dolomites
N N
S S
STOP 1
CARRAPATEIRA
WESTERN ALGARVE BASIN
SAGRES LAGOS AREA
TELHEIRO
TONEL
MARETA
ZAVIAL
LUZ PIEDADE
LAGOS
SAGRES
The western Algarve Basin presents a broadly ENE-WSW
monoclinal configuration, affected by numerous NNE-SSW faults.
Upper Triassic redbeds unconfomably overlie Carboniferous
metasedimentary basement and are overlain by Hettangian red
clays and volcano-sedimentary layers.
Lower and Middle Jurassic units are mainly dolomitic carbonates,
with some marly Callovian layers.
Upper Jurassic units include limestones and dolomites.
Cretaceous units include dolomitic siltstones and marls.
25
Rocha et al., 1979
Rocha et al., 1983
N
5 km
STOP 2
TELHEIRO
Carboniferous basement Upper Triassic Hettangian Sinemurian Sinemurian
Toarcian
NNE SSW
(Terrinha, 1997)
The Telheiro beach probably shows one of the best exposed outcrops of
the Triassic unconformity in Europe, exposed along a 60 metre high
coastal cliff.
Late Triassic sandstones , dipping around 20º SE, overlies upright chevron
folds in black shales and greywackes of Carboniferous age, deformed
during the Variscan orogeny.
The unconformity is overlain by red and yellow fluvio-aeolian
sandstones with abundant large-scale trough bedding.
This 2-5 meters thick package is overlain by well bedded planar clays
with marly intercalations, deposited in a sabkha-like environment.
The first dolomitic layers, of probable Sinemurian age, represent the
marine invasion of the basin, which continued throughout most of the
Jurassic.
The whole area comprises a well developed
planation surface, associated with Cenozoic marine
abrasion and neotectonic uplift.
Quaternary consolidated aeolian-sands, with cross-
bedding and rhizoconcretions, overlie a
palaeovalley, incised in Hettangian marls, between
resistant sandstones hard dolomites.
26
27
U.Triassic
redbeds
Carboniferous
metasedimentary
basement
Hettangian red
clays and marls
Pliocene marine abrasion surface
This major unconformity between Carboniferous shales and Triassic redbeds resulted from a long geological evolution:
i) deposition of deep marine clays and sands in a distal turbiditic environment, c. 360 My ago;
ii) intense orogenic subsidence, heating and ductile deformation at depths of around 5 km, c.310 My ago;
iii) post-orogenic gradual uplift and erosion of thousands of meters, until exposure and weathering, c.260 My ago;
iv) deposition of the first layers of fluvio-aeolian sands lying unconformably on top of the deformed Carboniferous shales.
N
STOP 2
TELHEIRO
Carboniferous
metasedimentary
basement Hettangian red
clays and marls
U. Triassic
redbeds
Carboniferous
metasedimentary
basement
U. Triassic
redbeds
28
Hettangian red
clays and marls
Hettangian red
clays and marls
Quaternary
consolidated
aeolian dunes
Sinemurian
dolomites
Pliocene abrasion surface S. Vicente
Cape
S
N
STOP 2
TELHEIRO
Sagres is the “Promontorium Sacrum”, considered by the
Romans as “the western end of the inhabited world”. It is only
when you catch sight of the grey ramparts of the fortress
blocking off the massive plateau of Sagres point and cast your
eye around the 10 km arc of sheer cliffs to the lighthouse at
Cape St. Vincent that you get a real feeling for the tremendous
historical importance of this place.
It was at least as important during the Age of Discovery as Cape
Canaveral was during the early years of space exploration.
It was to this place that Prince Henry the Navigator, came in the
15th century to work on his obsession to push back the
frontiers of the known world, and opened the phase in
Portuguese history called The Discoveries.
29
SAGRES AREA
N
1 km
Rocha et al., 1979
STOP 3 TONEL
This beach is one of the best places to see the
Callovian-Oxfordian unconformity in the
Algarve Basin. The Callovian external platform
marly limestones are overlain by a hard-ground
with ferruginous concretions and a 1.5m thick
limestone, with late Callovian to early
Oxfordian reworked ammonites and
phosphatic nodules.
This situation points to an important uplift,
exposure and erosion, before the deposition of
the middle Oxfordian oolitic limestones in
shallow water conditions.
The marly Callovian strata show folds and
thrusts with NE-SW oriented compressive
evidences, cut by the Callovian unconformity;
both the Callovian and Oxfordian units present
extensional geometries with a NE-SW
orientation (Terrinha, 1997).
30
(Terrinha, 1997)
N
31
Karstic features are an important part of the Algarve’s coastal geomorphology, related to the Tertiary inversion,
uplift and exposure. Karstification is believed to have been a long lived process, with multiple dissolution,
collapse and infill events. It affects not only the Mesozoic carbonate units, but also the Miocene fossiliferous
marls, such as in Piedade (see Stop 7). In many places, the vertical collapse structure is filled by Pliocene and/or
Quaternary sands, which once covered the whole littoral abrasion platform.
STOP 3 TONEL
STOP 4 MARETA
EAST
WEST
(Terrinha, 1997)
This beach shows a thick sequence of Middle to Upper
Jurassic marine carbonates.
The stratigraphic sequence starts with a Bathonian reefal
dome with signs of exposure and karstification. The karst
cavities are filled and covered by onlapping Upper Bajocian
sandy limestones with abundant Zoophycus.
(Rocha, 1976)
32
Early Bajocian
reef, with karstic
cavities filled-up
by Late Bajocian
onlapping sands.
33
Towards East, the cliff exposes Middle Bathonian to mostly Callovian grey marls, containing belemnites
and ammonites, as well as syn-sedimentary slump structures. These external platform facies have a good
source rock potential.
At the eastern end of the cliff, the Callovian unconformity gives way to more compact limestones and
dolomites of Oxfordian to Kimmeridgian age.
NE
Borges et al., 2011
Dark grey Callovian marls with source rock potential (TOC and maturation).
Slump
SW
NE
STOP 4 MARETA
STOP 5 ZAVIAL
This beach shows a graben of Cretaceous yellowish
dolomites, bounded on both sides by Late Jurassic pinkish
limestones and dolomites.
The Cretaceous succession is folded into an anticline,
exposing along the beach most of its east dipping flank,
crossed by late Cretaceous intrusive dykes with a NNE-SSW
orientation.
Inside this graben, we can see an unconformity separating
the Cretaceous marly limestones from the Miocene
fossiliferous sandy marls. This unconformity and the
Miocene deposits are folded in a compressional syncline
with a NE-SW axis.
This structure is related to the alpine orogenic inversion of
the Algarve Basin, with middle Miocene NW-SE oriented
compression.
34
(Terrinha, 1997)
N
1 km
Rocha et al., 1979
The Cretaceous succession is composed of decimetric layers of
alternating silty dolomites and marly dolomites, deposited in a
coastal environment. Towards east, these units give place to
reddish clays representing lagoonal to transitional
environments with sub-aerial exposure.
These are interrupted by a 3 metre thick package of quartzic
sands, cemented by carbonates, with cross-bedding, pointing
to some kind of coastal siliciclastic environment, such as a
beach-barrier.
After this sandy intercalation, clays with different colourations
appear and grade into marly limestones, within trangressive
pattern.
This sequence may be assigned to the Upper Hauterivian to
Lower Aptian, based on lithostratigraphic correlation of the
sandy intercalation (Barrancão Formation).
35
Miocene
Lower
Cretaceous
Lower Cretaceous
silty dolomites
N Rey, 2010
STOP 5
ZAVIAL
STOP 6 LUZ
36
The cliffs along this beach expose a thick Lower Cretaceous sequence, covering the
whole Aptian interval.
West of the beach, a broad rocky platform is composed of yellowish fine sandstones
with carbonate cementation, dipping gently to SE. These layers show undulated
geometries and cross-bedding, suggesting hummocky structures and deposition in
shallow coastal environments with intense wave action during storms.
Another striking feature is the concentration, in specific layers, of abundant fossils
of Nerinea algarbiensis. These fossils are mostly oriented N-S, perpendicularly to the
interpreted palaeocoastline.
The Albian sequence shows an overall transgressive pattern, with continental red and purple mottled clays with carbonate paleosoils.
Towards the top, some bioclastic sands appear intercalated in reduced grey clays and carbonates, suggesting a coastal environment.
The top of the cliff shows a thick package of shallow marine limestones. Dark rocks appears on the eastern promontory, corresponding to
a Late Cretaceous igneous intrusion.
E W
37
A. Continental red and purple clays
with paleosoils.
B. Continental to transitional clays
with sandy bioclastic intercalations,
affected by normal faulting, with large
igneous intrusion to the right.
C. Cliff exposing the upper part of the
transitional clay deposits (“Luz Marls”)
and the lower shallow-marine
carbonates (“Marly limestones” of
Porto de Mós).
A
B
C
W W
W
STOP 6 LUZ
STOP 7 PIEDADE
This tourist spot shows well developed karstic erosion in Miocene limestones.
After the Mesozoic infill of the Algarve Basin, intense inversion resulted in uplift and
erosion during the Late Cretaceous and Paleocene in the present day onshore areas.
In Neogene times, a flexural basin developed along this region, in relation to
secondary extension around the Gibratltar arc (Terrinha, 1997). Sedimentation
resumed in Middle Miocene with deposition of rhythmic fossiliferous limestones and
marls in coastal environments.
This coastal landscape is also a result of the the post-Miocene uplift of the Western
Algarve during the Plio-Quaternary. Karstic features are partially filled up by Pliocene
red sands, which after collapse of the karstic vertical wall give place to the present-
day holes and arches.
38
N
STOP 8 SANTIAGO
39
The Santiago do Cacém area is the only place where the Mesozoic Alentejo
Basin outcrops onshore. It is therefore a crucial site to study this basin and its
position between the Algarve and the Lusitanian basins. Uplifted basin
bordering blocks expose most of the Upper Triassic and Lower Jurassic
sequence, dipping to the West.
The Carboniferous Palaeozoic
basement is overlain by coarse-
grained continental redbeds,
deposited in proximal to distal
alluvial fans. Upwards, these
deposits grade into red clays and
platy dolomites, deposited in a
sabkha-like environment.
This sequence is overlain by a
volcano-sedimentary complex with
tholeitic basalts, related with the
Central Atlantic Magmatic Province
(CAMP), also recognised in
Southern Portugal.
Sinemurian opening to shallow
marine influences promoted the
deposition of massive marly
dolomites.
Middle Jurassic carbonates are
separated from Upper Jurassic
intraformational conglomerates by
a regional unconformity.
A-CASTLE
C-QUARRY
N 1 km
N
Santiago do Cacém
is a medieval city,
built in front of the
to the Roman city
of Mirobriga (with
ruins of a shrine,
baths and houses).
The castle has
Moorish origins
and was rebuilt by
the Crusaders and
dedicated to Saint
James.
B -BASE
40
100m
CARBONIFEROUS
basement (shales)
UPPER TRIASSIC
coarse redbeds
Hettangian volcanics
Hett. platy dolomites
T/J red clays
LOWER JURASSIC
marly dolomites
MIDDLE JURASSIC
Oolithic limestones
Limestones
UPPER JURASSIC
Calciclastic limestones
Marls
Conglomerates
NEOGENE sands
STOP 8A - Santiago Castle: the main monoclinal
structure can be seen, with the Lower Jurassic
dolomites marking the flattened hill tops dipping to
West; to the North, the Arrabida Chain in the horizon.
STOP 8B Close to the Hotel, a small outcrop shows
the contact between the folded Carboniferous meta-
ssedimentary basement and the overlying Upper
Triassic conglomeratic redbeds.
STOP 8C South of the town, an extensive area
occupied by numerous quarries shows the Upper
Triassic to Lower Jurassic sequence including:
conglomeratic redbeds, red clays, platy dolomites,
pinkish dolomites and CAMP-related volcanics.
Geological cross section from Santiago towards NW
NW
N
W S
Volcanics
Pink
dolomites
Red clays
Platy dolomites
Basement
Red beds
STOP 8 - SANTIAGO
41
ARRÁBIDA AREA
ESPICHEL
SESIMBRA
SÃO LUÍS
PALMELA
LISBOA
N
5 km
X
Y
(Manuppella et al., 1994)
The Arrábida chain is an alpine structure, related to the
Cenozoic inversion of the Lusitanian Basin. Several uplift related
unconformities may be identified, namely in the Late Cretaceous
and Upper Miocene.
The overall structure is an assymetrical anticline, with an ENE-
SSW oriented axis and thrusting towards South, as seen at
Espichel Cape and Arrábida hill.
This simple structure becomes more complex towards East, with
the duplication of the thrusting anticline in a duplex structure,
with two parallel axis the São Luís and the Viso hills.
This inversion structure is related to the alpine N-S compression,
reactivating the Mesozoic lystric NNE-SSW faults as strike-slip
transfer faults.
Gravimetric data and models suggest the role of uplifted
basement blocks controlling the movements along a
detachment layer of Hettangian evaporitic clays.
42
X
Y
(Manuppella et al., 1994)
GRAVITY (mGAL)
DEPTH (km)
(Silva, 1992) (in Kullberg et al., 2000)
STOP 9
PALMELA
43
CASTLE
Miocene cuesta
São Luís anticline
Arrábida
The view from Palmela Castle shows a
landscape cross section of the alpine
Arrabida chain.
From right to left we can see:
i) the elongated “cuesta” with
Miocene fossiliferous limestones;
ii) the valley with Paleogene clays;
iii) the hill of Upper Jurassic
conglomerates;
iv) the top of the hill with Lower and
Middle Jurassic limestones defining
the São Luís anticline.
Quick stop at the Arrabida chain: alpine
inversion and Miocene deformation
Paleogene clays
Upper Jurassic
STOP 10
To the East of the castle’s hill, a broad
lowland extends towards south,
covered by Cenozoic deposits. These
deposits lie directly on Paleozoic
basement, with no signs of Mesozoic
units. This situation indicates that
Palmela represents the eastern limit of
the Mesozoic basin, probably an up-
lifted basement block. Cenozoic
tectonic inversion promoted the up-lift
of the Arrabida chain and the
subsidence of the eastern areas.
N S
S N
N
5 km (Manuppella et al., 1994)
View from the castle
N
STOP 10 SÃO LUÍS
Late Kimmeridgian
Intrafornmational
conglomerates.
Erosion of L-M Jurassic carbonates
(Lower & Middle Jurassic)
(Middle Jurassic)
Erosion of basement
greywakes, etc.
(Middle Jurassic)
(Middle Jurassic)
(BASEMENT)
(BASEMENT)
(BASEMENT)
Late Jurassic
eustatic drop
Early Cretaceous
siliciclastic input
Morphological scarp
(BASEMENT)
Kullberg et al., 2000
The Late Kimmeridgian to
Tithonian Arrabida conglomerates
show an interesting vertical
evolutive pattern, with a
calciclastic composition at the
base and gradually increasing
siliciclastic component (Palaeozoic
clasts of quartz, chert, jasper, etc.)
towards the top. This situation
results from the exhumation of
uplifted basement blocks, related
to the Late Kimmeridgian basin
reorganisation.
44
N
STOP 11
SESIMBRA
45
Sesimbra is an ancient fishing village,
now surrounded by summer houses.
East of the village, the California Hills
expose the Lower Jurassic sequence,
begining with stratified volcanics. These
basaltic rocks correspond to the CAMP
event and represent its most northerly
occurrence in Western Iberia.
They are overlain by Lower Jurassic
dolomites with intense (hydraulic?)
fracturation. Upwards in the sequence,
some marly layers are time-equivalent
of a important Lower Jurassic source
rock of the Lusitanian Basin (Vale das
Fontes Formation). However, due to its
bordering paleogeographic position, its
source potential is low.
Looking eastwards from the castle, the
houses occupy the valley with Upper
Jurassic and Lower Cretaceous
siliciclastics, whereas the facing
California Hills correspond to a diapiric
inversion structure, bringing up
evaporites and Lower and Middle
Jurassic units.
N
(Manuppella et al., 1994)
CASTLE
(Manuppella et al., 1994)
(Kullberg et al., 2000)
Arrábida
California
Pedreiras
Sesimbra
STOP 12 ESPICHEL
46
Several dinosaur fossil trackways are exposed in some of the now tilted Upper Jurassic
strata which form the cape's cliffs. Local superstition interpreted the track ways as the
path taken by the Holy Virgin ("Nossa Senhora") when riding a giant mule from the ocean
and up the cliffs, which led to the eventual construction of the convent at that location.
To the North of the small chapel (a former medieval arab “morabit”), the cliff bordering
the tiny beach exposes the transition to the first Lower Cretaceous continental deposits,
related to the beginning of the opening of the North Atlantic. These siliciclastics , of
Berriasian age, correspond to the first breakup surface of this basin.
Cape Espichel is located 50 km S of Lisbon. Tourists are drawn there due to breathtaking
views of its cliffs facing the Atlantic Ocean.
The location is famous for the sanctuary complex (lSantuário de Nossa Senhora do Cabo
Espichel), built extremely close to the edge of the tall cliffs, which includes a church still
in use today. Every year, a pilgrimage takes place with blessing of fishermen boats.
47
Upper Jurassic
The Lower Jurassic
sequence shows a
succession of fluvial to
shallow coastal marine
deposits, resulting from
an overall transgressive
Berriasian - Hauterivian
second-order eustatic
cycle (Rey, 2010).
The tilting resulted
from the Late Miocene
uplift, prior to the
Pliocene abrasion
surface (also uplifted).
(Rey & Dinis 2004)
N
Basemen
t
Evaporites
Pre-
inversion
sedimentary
infill
Detachment
Arrabid
a fault
Arrabida fault
Cenozoic
syncline
“Swan neck” fold
Espichel structure. 1 Present day; 2a - pre-inversion;
2b post-inversion (Kullberg et al., 2000).
STOP 12 -ESPICHEL
Main References
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48
ISBN: 978-0-9573517-0-7
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Published by PIPCo RSG Ltd.
Copyright © 2012 Rui Pena dos Reis & Nuno Pimentel
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Article
The Cretaceous series from the Eastern Algarve consists of fourteen formations between the Berriasian and the Cenomanian. Ten of those are peculiar to this area. These last lithostratigraphic units are formally defined. The lithologic compositions, the main palaeontologic associations and the boundaries of each formation are described from a reference section, precisely located and illustrated with mean of photographic plates. The dating of these units is argued. The major facies changes are mentioned. A correlation with the formations of the Central and Western Algarve is proposed.
Carta Geológica de Portugal, na escala de 1:50 000. Folha 48-D (Bordeira)
  • M Feio
  • A Ribeiro
  • M M Ramalho
  • P Fernandes
  • V Matos
  • B Rodrigues
  • M Borges
Feio, M.; Ribeiro, A.; Ramalho, M.M. (1985) -Carta Geológica de Portugal, na escala de 1:50 000. Folha 48-D (Bordeira). Serviços Geológicos de Portugal, Lisboa Fernandes, P.; Matos, V.; Rodrigues, B.; Borges, M. (2012) -História Térmica da Bacia Meso-Cenozóica do Algarve: Implicações para a Prospecção de Hidrocarbonetos. VI Encontro de Profs. Geociências Alentejo e Algarve. http://www.associacaodpga.org/vi_alen_alg_moura.html