CiSncias da Terra (UNL) Numero especial n

EXCURSION B

pp. 37-56 fig. 0.1-3.9

MAINLY CONTINENTAL MIOCENE AND PLIOCENE DEPOSITS FROM LOWER TAGUS

AND MONDEGO TERTIARY BASINS R. P. B. PENA DOS RE IS 1, P. M. R. R. PROEN<;A CUNHA 1, B. P. BARBOSA 2, M.

T. ANTUNES 3 & J. PAIS 3

1 - Dept. Ciencias da Terra, Faculdade de Ciencias e Tecnologia , Univ. Coimbra, Centro de Geociencias (INIC), P-3000 Coimbra

2 - Servi~os Geol6gicos de Portugal., R. Academia das Ciencias, 19-22, P-1200 Lisboa 3 - Centro de Estratigrafia e Paleobiologia (lNIC), Faculdade de Cicmcias e Tecnologia, Quinta da Torre,

P-2825 Monte de Caparica

N

~ ~ U o

Fig. 0.1 - Tour itinerary

Coimbra ~ ",;:::' ~":'.:'::'

,,' :', •....... ~ " ~::' ::::'"

o if! .. ' ., Jt. • G6is

'0! Miranct!d~'c>-orvo 10 " I

I I I

f;:;/.-::! Neogene

• Stops

• Localities

---+- 1st. day ••••• ~ 2nd. day

~ 3rd.day

50 km

37

INTRODUCTION AND STRATIGRAPHY

This excursion is arranged to places of im­portant interest of the stratigraphycal continen- . tal neogene infilling of the western central por­tuguese continental margin. The itinerary is shown on Fig. 0.1. To describe the sedimen­tary succession the lithostratigraphic nomencla­ture has been informally used in capital letters.

The mesozoic and cenozoic sedimentary record of the western Iberian margin (Lusitanian Basin) is about 4 km thick (WILSON, 1988). In the pre-upper Aptian de­posits, several unconformity-bounded se­quences (UBS) are defined according to Wilson (1988): UBS1) upper Triassic-upper Calovian; UBS2) middle Oxfordian-Berriasian; UBS3) Valanginian-Iower Aptian.

In the post-lower Aptian record of Central Portugal, the definition of the infill episodes (ANTUNES, 1979; RIBEIRO et al., 1979; CUNHA, 1987a, 1987b; ANTUNES et al., 1987; WILSON, 1988; REIS & CUNHA, 1989; MOUGENOT, 1989; BARBOSA, et ai., 1990) led to the establishment of a recent pro­posal of synthesis (CUNHA, 1992) in which several unconformity-bounded sequences are distinguished: UBS4) upper Aptian-Iower Campanian; UBS5) upper Campanian­Maastrichtian; UBS6) Paleocene-Iower Lutetian; UBS7) upper Lutetian-Bartonian; UBS8) Priabonian-Iower Chattian; UBS9) up­per Chattian-upper Burdigalian; UBS 10) upper Burdigalian-Iower Tortonian; UBSll) upper Tortonian-Iower Messianian; UBS 12) upper Messianian-Zanclean; UBS 13) Piacenzian.

In the Lutecian, distensive faulting related to the Pyrenaic Orogeny openned up the Lower Tagus tectonic graben, and led to the separation of the Lusitanian Basin in two tertiary basins Mondego (northern) and Lower Tagus (southern). In the onshore area, the tertiary sedimentary in fill consists of main continental siliciclastic deposits; the Mondego Basin is about 370m thick and the Lower Tagus Basin the maximum thickness is about 900m.

The following paragraphs present a general caracterization, for the onshore area, of the neogenic unconformity-bound sequences (Fig. 0.2):

UBS 9 - The record exists at the vestibular area of Tagus River (Lisbon region) and in the offshore area. Not visited in this excur­sion.

38

UBSlO - The record integrates a positive fluvial succession: orange conglomeratic arkoses passing upwards to arkoses, siIt­stones with carbonated crusts and lime­stones. Smectite and kaolinite are the domi­nant clay minerals.

UBSll, UBS12 and UBS13 consists mainly of piedmont coarse alluvial deposits corre­spondent to the Portuguese Central Range, Maci~o Calcario Estremenho (Estremenho Massif) and Western Mountains uplifts.

UBS 11 - Greyish and reddish litharenites, greywackes, breccias and conglomerates, with clasts of metasedimentary rocks and milky quartz, alternating with silts tones. Smectite and illite are the most common clay minerals in sediments.

UBS 12 - Red conglomerates, litharenites and siltstones, with calcareous concretions and clasts of milky quartz and quartzite. Illite and kaolinite, in similar proportions, are the usual clay minerals. UBS 11 and UBS 12 document endorreic stages of the evolution of the Mondego and Lower Taglis tertiary basins.

UBS 13 - In the onshore area, the record is composed of continental (conglomerates, coarse sandstones and mudstones), transi­tion (lignites, diatomites, "lumachelles ") and shallow marine sediments (Fig. 0.3). The sediments, mainly of light yellow and white colour, are composed of quartz and quartzite clasts; the clay fraction contains mostly kaolinite, with illite and seldom vermiculite. In the Mondego and Lower Tagus tertiary basins, the continental de­posits have been interpreted as alluvial fans entering rivers valleys (pre-Tagus and Erg~s rivers) from the north-western mountam front (Portuguese Central Range). This siliciclastic sediments caracterized the Hesperian landscape prior to its present (quaternary) fluvial dissection, culminating the marginal piedmonts in many tertiary basins. The record of UBS 13 documents a exorreic stage in which eustasy was an im­portant control on clastic deposition. The transgressive-regressive evolution can be correlated with the 3rd order eustasy cycle nQ 3.6 of Haq et al. (1987). Near the pre­sent coast line, the UBS 13 record begin with marine sediments; the UBS 13 upper contact is made by disconformity, with a siliciclastic cover testifying another marine incursion correlated with the 3rd order cycle nQ 3.7 of HAQ et al. (1987).

MONDEGO UBS sw

A

14

NE B

TECTONIC PHASES

h;~~::o-im-al -.... =-""''''' Intra-upper Piacenzian

13

12

1 1

10

9

8

7

A - offshore B - onshore

~- hiatus

. Q -marine limestones

Intra­Pliocene

Intra­Messinian

Intra­Tortonian

Intra­Burdigalian

Intra­Chattian

,II~VV\ Intra-N Priabonian

Intra­lutetian

11

"Iberomanchega" I

"Neo-castelhana"

"Castelhana"

Pyrenaic

Pre-pyrenaic

- conglomerates D -no data x - silcrete

- sandstones and mudstones <D -stops

Fig. 0.2 - Tertiary unconformity-bounded sequences (UBS) of the western portuguese record (Mondego and Lower Tagus tertiary basins) and stratigraphic position of the stops.

39

sw - PS m '-<-

'-<-. '-c...

'< '-C---50 '--<::- '-C

'-<.... '---.-/ '-C ss.sJ "-

'-c:.-'-<-- '---G

15 ~s ss

'<--COINA '--~ '--C.

"-<-"-<-

~$.ss

'-C

25

CO '-c:: ~

'-d1 lM E

'-c. \..C.-

'-<--L.L-

B

~

~1

115

0

S,V

50

, '-<-- ~

+ +

~2 I:~ :'·:13 ~4

Is> S $16 [[[[[ll7 \8 ~9 Km 40 , ,

A

C.A ~O

Fig. 0.3 - Schematic geological sections (SW-NE), showing the upper pliocene record in the Mondego (A) and Lower Tagus (8) tertiary basins. 1 - basement (metamorphosed / granitic); 2 - mesozoic and cenozoic substratum; 3 - alluvial conglomerates; 4 - alluvial sandstones; 5 - alluvial siltstones; 6 - marish sediments (sandstones interbeded with Iignits and diatom its); 7 - marine sandstones; 8 - sedimentary discontinuity; 9 - Lousa fault; SV - Senhora da Vit6ria beach (S. Pedro de Muel); CA - Carnide; PO - Pombal; CE - Cemache (Coimbra); SQ - Santa Quiteria; GO - G6is (Carvalhal and Sacoes sections); PS - Selubal peninsula; CO - Coruche; GA - Gaviao; CB - Castelo Branco

region; SF - spanish border.

FIRST DAY

RIO MAIOR - COIMBRA REGION

In the Rio Maior - Coimbra region (Mondego tertiary basin) the neogene sedimen­tary succession was divided int the following major units:

1) Amor Sandstones and Clays (UBS 10 -upper Burdigalian-Iower Tortonian) - gen­erally startswith gravel deposits but is mainly composed of clayey sands deposited in a flood plain passing to lacustrine condi­tions to SW. The sediment has a light gray color locally reddish, it is unlithified and includes silicified levels.

2)Pombal-Redinha Sandstones and Clays -lower levels include orange coarse felds-

40

pathic sandstones and conglomerates (UBS 11 - upper Tortonian-Iower Messianian); the upper levels are composed of red sand­stones and conglomerates alternating with mud stones showing carbonate concretions (UBS 12 - upper Messianian-Zanclean). They correspond to deposition in alluvial fan systems related to Sic6 Massif uplift.

3) Upper Pliocene terrigenous sediments (UBS 13) show important lateral variations used for the definition of the following litho strati graphic units (Fig. 0.3 A).

3.1 - The Carnide Sandstones: a shallow marine fossiliferous unit; 3.2 - The Roussa Sandstones: a coastal unit (shorestring); 3.3 - The Barradio Clays: a rich in organic matter palustrine unit;

3.4 - The Morou~os Complex, a proximal and lateral equivalent alluvial fan system of the previous units.

1st STOP

FREIRIA DE RIO MAIOR

Purposes - Observation of Almoster and Santarem Upper Vallesian limestones and marls and of the infilling of the Rio Maior graben.

Description - The old quarry of Freiria de Rio Maior shows a section of the Almoster and Santarem limestones (Fig. 1.1). There is a suc­cession of mostly greyish lacustrine limestones with a few and thin intercalated clayey levels.

Some limestones are very compact and show structures that may be ascribed to algae and other plant remains. Other ones are rich in casts of gastropods (Limnaea, Planorbis, etc.),

. most of them being represented by cavities. The clayey levels are rich in Charophyte

gyrogonites and Gastropoda also. The lower one yielded further fossils: pollen and spores, Ostracoda, freshwater fishes and amphibians, besides a rhinoceras and small mammals (Perissodactyla: Cf. Aceratherium (A.) simor­rense; Rodentia: Rotundomys jreiriensis, Hispanomys peralensis, Progonomys hispani­cus; Lagomorpha: Prolagus crusajonti) , that point out to an Upper Vallesian, MNlO age (ANTUNES & MEIN, 1979). This gives a fairly accurate datation for this unit.

Corresponding environmental features would be the predominance of shallow lacus­trine fed by an influx of limy waters from res­surgences of the nearby Calcareous massif. These were surrounded by dense forest and further away by drier savannah or steppe areas. Climate would be warm and quite dry, with contrasting seasons and arid events.

The Santarem and Almoster limestones (Upper Miocene) were subjected to intensive faulting. Some grabens were developped, the most important one being that of Rio Maior. Here, an important down thrust occurred, re­lated to the ascension of the nearby Fonte da Bica salt dome.

The infilling of the Rio Maior graben be­gun with the deposition of thick accumulations of white sands of mainly eolian nature. These are actively exploited for industrial purposes. An important bye-product is the kaolin rich fraction separated through sand washing and employed as special clays in ceramics. The sands did not yield any fossils, besides a sole

(/) Q) -c E

..: 0 -en N >. (/)

~ ~g 0 E 0) (/)

c 0 Q) a.~

0 C a. 0 E (/)

..::t! Q)~ ~ '- ro "0 ..c :E cu~ Cii~ ..c Q) :t::: Rp ~~ 0 ::lE ca -l I-

I~O 2.0 ,.,.' i7

• 19

I---18 .. ..

I---17 ~ 15 0.9 •

I--

•

14 6.5

~ (!) r.;-

• I--

0 • Z « 13 2.3

• -(J) I--

W 12 1.0

f--

.....J ~~~ (!)

.....J 11 1.5

« f--10 i:!.-.-...::;!.T.: ~. > .. .. ~ . •

\8 ~ ~. • ~ ~,4 0 • er:

w a.. a.. ~Y-=r~ :J

5 7.5

~rvr0- (0)

I , 0

\/

~ (!)

MNIO 4 IF (!) • • 3 &--r-r-~ ~.o.5

2 1.8 .. I--

1 2,5 0 - -- --

Fig. 1.1 - Freiria de Rio Maior section.

41

Pallialum (L.) excisum has been found in a borehole. However, the correlation with the Caldas da Rainha - Pombal Pliocene (Lower Piazencian) seems to be valid.

In the upper part of Rio Maior sands, some small intercalations of diatomites are present. Later, the graben has been filled by a sucession of essentially lacustrine beds, mostly diatomites and lignites, that were both commercially ex­ploited in the past. These beds are particularly rich in well preserved plant macroremains, as well as pollen and spores (DINIS, 1984; PAIS, 1987). This succession ends with some algal (Botryococcus sp.) coal levels that overlie positive sequences [fine sand -+ clays rich in gastropods with some small mammals either of Uppermost Pliocene or Lower Pleistocene age (now under study) -+boghead coal; both clays and coal are gypsum rich].

Quaternary coarse sands and gravels over­lie both the diatomite-lignite series and the Rio Maior sands, through erosion surfaces.

2nd STOP

PAREDES DE VITORIA BEACH (12 km North from Nazare)

Purposes - Observation of pliocene marine mi­caceous sandstones (UBS 13) overlying juras­sic limestones.

Description - This section 25 m thick, de­scribed by CACHAO (1989) on the northern limit of Paredes de Vit6ria beach is one of the most westerly pliocene outcrops of the Lusitanian basin (Fig. 1.2 and O.4A) Over a pre-pliocene paleokarst surface with lithofagic invertebrate perforations, were deposited a micaceous fossiliferous sandstone, similar to the most frequent facies of the Carnide Sandstones. The upper part of the section pre­sents sandstone facies refered as Arenitos de Paredes equivalent to Roussa Sandstones (Pombal region).

3rd STOP

ROAD MONTE REAL-LEIRIA (lkm North from Amor)

Purposes - Observation of the langhian lacus­trine Amor Sandstones and Clays (UBS 10) presenting frequent vertebrate remains.

42

o u~

-0

c~ b «:::::;

'Arenilo de Paredes"

z .-1--+-"-'-:'-'::'-::-; UJ~

u&> oc. -::>

....J VI C3 ll.

..... --

----- ...

.·Arenito de Carnid~· .,. ... ,..

--,---

Fig. 1.2 - (1) Paredes de Vit6ria section. (2) Detail of the basal beds of the pliocene fossiliferous sediments

(CACHAO,1989).

Description - This outcrop with poor observa­tion conditions, evidences clay feldspathic sandstones rich in smectite, palygorskite and carbonate concretions. These vertebrate re­mains, were described by (ANTUNES & MEIN, 1981).

. 4th STOP

CARNIDE (12 km WSW from Pombal)

Purposes - Observation of the fossiliferous upper pliocene Carnide sandstones (UBS 13) overlying middle miocene mudstones (Amor Sandstones and Clays).

Description - This outcrop shows a section of the Carnide Sandstones (8 - 12 m). From the base to the top it comprises a lenticular fossili­ferous conglomerate (mainly Mollusca and Bryzoa), fine yellowish micaceous sandstones

o (,J

~ ..

.. • i (j) (,J

-~-

(,J C3 0:0

CII

0 Cl (,J

Z 'W

(,J 0 j

0 (,J z Co 'W <!)

ID .... ~

"Arenito de Carnide"

" "

, '" :-:-:-:-:

Cl

Fig. 1.3 - (1) Carnide section. (2) Detail of the basal beds of the pliocene fossiliferous sediments

(CACHAO.1989).

with well rounded gravel cobble lag intercala­tions and reddish coarse sandstones and con­glomerates with crossbedding structures (Fig. 1.3 and O.4A). The basal conglomerate con­tains a nannofossil assemblage (Discoaster ta­malis, D. surculus, D. variabilis, D. brouweri) indicative CN12a Zone of Okada & BuJry (lower NN16 zone of Martini) (CACHAO, 1990). The fauna (molluscs, in particular) oc­curing in the base of the Carnide Sandstones indicate a shallow marine environment not deeper than 30 m with waters of near normal salinity and r.s:latively wann temperature condi­tion (CACHAO & sa v A, 1990).

5th STOP

ROUSSA DE CIMA (9 km West from Pombal)

Purposes - Observation of the- Roussa Sandstones unit (UBS 13).

Description - This unit includes white kaolinitic coarse sandstones (15 m), showing

gentle « 10°) planar crossbedding structures (Fig. 1.4 and 0.4)) overlying by confonnity,the Carnide Sandstones. On the top the Roussa Sandstones contact conformably the Barraclio Clays composed of coarse sandstones with len­ticular greyish mud stone intercalations (BARBOSA,1983).

SECOND DAY

6th STOP

ENt - EN237 CROSS - ROADS (Pombal-Ansiao)

Purposes - Observation of the Amor and Pombal-Redinha units (UBS 10 -11-12).

Cl)

a:::

t E

M I

N

J-.-E

Lf"I.

_ili~~

E o

•

Fig. 1.4 - Roussa section (SOARES. 1984). RS - Roussa Sands tones; BC - Barracao Clays.

43

Description - The Amor unit overlays paleo­gene sediments and is composed of arkoses with silicified pedogenetic crusts rich in palig­orskite. Pombal-Redinha unit contacts, by angular unconformity, the older units. At the bottom includes orange coarse feldspathic sandstones and conglomerates; the upper levels are composed of red sandstones and conglom­erates alternating with mudstones showing car­bonate concretions.

7th STOP

REDINHA (10 km North from Pombal)

Purposes - Observation of the Barradio Clays (UBS 13).

Description - The pliocene sediments overlaies the Pombal-Redinha unit. The Barracao Clays (Fig. 0.3A) include a negative aluvial suces­sion: greyish mudstones pass up to coarse yel­lowish quartz arenites and redish heterometric conglomerates on the top.

8th STOP

CERNACHE AERODROME (about 5 km South from Coimbra)

Purposes - Observation of the pliocene Cruz de Morou~os Complex (UBS 13).

Description - This outcrop is located over an important NS vertical fault (Pombal - Cernache fault) which separates upper cretaceous mud­stones (Taveiro Claystones and Sands) in the western block from lower cretaceous sand­stones and conglomerates (Belasian Sandstones) in the eastern block. These sedi­ments are overlaid in disconformity by the Cruz de Morou~os Complex, showing conglomer­ates with sandy lenses interpreted as pliocene alluvial fan deposits. They are considered to be the distal equivalents of Santa Quiteria Conglomerates (CUNHA & REIS, 1991; CUNHA, 1992) (Fig. 0.3).

EAST OF COIMBRA REGION

In the Coimbra eastern region the post -Paleocene sedimentary succession (Mondego Tertiary Basin) has been divided into several major units (DA VEAU et ai., 1985-1986;

44·

CUNHA, 1992), separated by regional de­scontinuities (Fig. 2.1 and 2.2):

1) C6ja Arkoses - arkoses and gravel con­glomerates rich in smectite, related to a gravel fluvial system (UBS7 and UBS8 -upper Lutetian-lower Chattian).

2) Lobao Arkoses - coarse arkosic sandstones deposited in a proximal portion of a gravel fluvial system (UBS 10 - upper Burdigalian­lower Tortonian). This neogene unit is not seen in this excursion.

3) Sac6es Grup - consisting of alternating shale and quartzitic conglomerates and massive siltstones. Includes piedmont ac­cumulations correspondent to the Portuguese Central Range and Western Mountains uplifts. 3.1) Campelo Formation (UBS11- Upper Tortonian-Lower Messianian). This forma­tion can be subdivided in two members; the Arro~a Member greyisch or yellow clayey deposits are the distal equivalent of the Folques Member con glomera tic facies. 3.2) Telhada Conglomerates (UBS 12 - up­per Messianian-Zanclean) - red conglomer­ates with slate and vein quartz clasts. 3.3) Santa Quiteria Conglomerates CUBS 13 - Piacenzian) - coarse ocre conglomerates mainly with quartzitic clasts.

9th STOP

SERRA DE SANTA QUITERIA (about 22,5 km East from Coimbra)

Purposes - Campelo Formation, Telhada Conglomerates, Santa Quiteria Conglomerates observations and also a geomorphological scenery (UBS 11-12 -13).

Description - In a open pit located near the Arro~a village outcrops the base of the Arr09a Member (Campelo Formation). Lutites alternat­ing with lenticular beds of small slate and quartz vein pebbles are seen (SQ-Norte column of figure 2.2 and 2.1). Here this unit overlays the BU9aco Group.

At about 350 m of altitude the Telhada unit contacts, by disconformity, the Campelo Formation. Along the road badly exposed red conglomerates outcrops, showing alternating massive unsorted cobble and boulder gravel, with few parallel-laminated coarse sands.

The contact with the Santa Quiteria Conglomerates overlying unit is a disconfor­mity located near the chapell at about 400m of altitude. They integrate clast-supported boulder conglomerates, with some lenses of sandstones (Fig. 0.3A).

t222] ,

NNW

~5 ~ ES]6 ~7 ~8 ~

~~~::::":"':':""" //71 .-.

Fig. 2.1 - Geological section of the Santa Quiteria - G6is region). I - metamorphic basement (slates); 2 - metamorphic basement (quartzites); 3 - BuCaco Group (Cretaceous); 4 - Bucaqueiro Sandstones (Upper Cretaceous); 5 - C6ja Arkoses; 6 - Campelo Formation (a - Folques Member; b - Arroca Member); 7 - Telhada Conglomerates; 8 - Santa

Quiteria Conglomerates; 9 - Lousll fault (CUNHA, 1992).

A

B

m SSE E sporao Carvalhal NNW 600 J-:;:....,.-_~---,-

Portela ,~--1-----~~~~---' ,/ / ''''' 'I

400 , ,

" / " " ..... /

"- " - /' -- , 200

,

5 6 7 km

o 2 3 ;,., i .~....,

Fig. 2.3 - The overthrust of Portela de G6is. A - after DELGADO (1895-98); B - after DAVEAU et al., 1985-1986. 1 - basement; 2 - cretaceous and cenozoic sediments; 3 - alluvium.

45

~m

•

•

• • •

SO-Norte SQ-Sul • • • • •

• •

• • •

•

• • • •

•

[~om :f-

ALA

~1

CSB

CTE

FCA

1:"0·012 (:-:::,:13

•

• •

•

CXG

04

• •

• •

_5

SAL

~t~1 ~;~~.~~~~~ ,i:\/:\ .:.:.:.:-:.:.1

I~ ';:L}~;I •

't1

• 6

Fig. 2.2.- Stratigrafic columns of the Coimbra eastern region. 1 - basement; 2 - horizontally bedded clast-supported conglomerates; 3 - muddy matrix-supported conglomerates; 4 - sandstones; 5 - siltstones; 6 - maximum particle size (mean); CXG - "Xisto-Grauvaquico" Complex GBU - Bu~aco Group; ALA, ACH and CPI - Bu~aco Group formations; ABU - Bu~aqueiro Sandstones; ACO - Coja Arkoses; mCAS - Casalinho de Cima Member; mMON - Monteira Member; FCA - Campelo Formation; CTE - Telhada Conglomerates; CSQ - Santa Quiteria Conglomerates

(Cunha, 1992).

•

•

\0

"'"

From the top (492 m of altitude), a geo­morphological scenery can be seen over the cretaceous and tertiary sediments, and palaeo­zoic basement. Looking eastwards is a palaeo­zoic quartzite relief. Looking southwards, the southern tectonic block (Portuguese Central Range horst) is seen.

10th STOP

PORTELA DE GOIS

Purposes - Observation of the Portela de G6is overthrust.

Description - This stop shows the Shale­Greywacke Complex (Precamb.-Camb.) over­thrusting the Santa Quiteria Conglomerates (UBS 13) (Fig. 2.3 and O.4A). The heteromet­ric quartzitc pebbles and blocs of caotic fabric came from the Penedos de G6is quartzitic ridge. This overthrust proves that after the de­position of the Santa Quiteria Conglomerates (considered ofpiacenzian age) occurred another· compressional stage of the Lousa fault.

THIRD DAY

VILA DE REI REGION

The neogene continental deposits situated at Vila de Rei region are located close to or­dovician quartzite ridges of the Amendoa­Envendos syncline, in Central Portugal. They include main continental siliciclastic sediments of the Lower Tagus Basin northeastern border. In the region they are controled by a complex fault system related to the uplift of the southern border of the Hesperic Massif, mainly during the neogene final stages (Fig. 3.1).

The neogene column presents six lithos­tratigraphic units, from bottom to top:

1) Monsanto Sandstones (UBS8 Priabonian-Iower Chattian) - an alluvial conglomeratic sandstones;

2) Ota Sandstones and Tomar Claystones (UBS 10 - upper Burdigalian-Iower Tortonian) - fluvial sandstones grading up to clays tones and lacustrine limestones;

3) Ulme Sandstones and Serra de Almeirim Conglomerates (UBS 13 - Piacenzian) - a prograding alluvial sucession (BARBOSA & REIS, 1989) and (Fig. 0.3);

4) Vila de Rei Conglomerates (UBS14) - a quaternary border alluvial fan conglomer­ates (BARBOSA & REIS, 1991a).

11th STOP

MATAGOSA (6,5 km SSW from VHa de Rei)

Purposes - Geomorphological panoramic view of neogene sediments overlying palaeozoic basement.

Description - Northward view of the neogene pediment gently tilted up towards the quartzite ridges on the horizon. The sediment thickness covering the palaeozoic quartzites and schists is afected by a complex faulty blocky system. Looking southwards, pliocene pediplain is a little raised compared with the northern by a WNW-ESE trending fault parallel to the Codes stream. Eastward the neogene basin limit by the palaeozoic quartzite relief is seen.

Old open pits (possibly old Roman gold works) and huge dump of rounded boulder quartzites, can be seen looking towards NE, over the quartzites, on the opposite river mar­gin. Serra de Almeirim Conglomerates is the main collector unit, although some quaternary terraces of Codes stream, seen from here, have been exploited too. This great scars and dumps are geographically named "conheiras".

12th STOP

MACIEIRA TO VILAR ROAD (6 Kms SW from VHa de Rei)

Purposes - Observation of a tertiary complete section, integrating four litho strati graphic units, named from base to top: Monsanto Sandstones (UBS8), Ota Sandstones.and Tomar Claystones.(UBS 10); Serra de Almeirim Conglomerates (UBS 13). Only the upper four units are neogene.

Description - Here the Monsanto Sandstones (UBS8) contact the palaeozoic slates by fault. It is a whitish coarse sandstone with reddish to pink subvertical stains, columnar structure and local carbonate crusts. Palygorskite is the dominant clay mineral. The contact with the upper unit is not well exposed.

Ota Sandstones and Tomar Clays tones (UBS 10) correspond to a positive miocene megasequence, integrating coarse to fine red­dish arkosic microconglomerate sandstones grading up to fine sandstones and mudstones. The upper part is a speckled reddish (marmorized) massive mud stone belonging to Tomar Claystones. An unconformity separates the Toinar Claystones from the following unit.

47

[:

~

~ ~ ~

, :><

~ ~ ~ --y" ~ ~ ~ 3

\. -",

... ,

/ \ lJl ~ ~ I 0+ * r I \ ' .... \ 11 ++ J J

..... ..... ..... ~z: N ..... 0 .0 00 ~ 0- VI of:"' I.IJ N .....

Fig. 3.1. - Geological sketch of the Lower-Tagus Basin norther border in the Vila de Rei area and stop locations. 1 - Terrace deposits; 2 - Vila de Rei Conglomerates (Quaternary); 3 - Serra de Almeirim Conglomerates (piacenzian); 4 - Ota Sandstones and Tomar Clays tones (Miocenc); 5 - Monsanto Sandstones (Paleogene); 6 - Shales and quartzites (Palaeozoic basement); 7 - Normal fault; 8 - Reverse / thrust fault; 9 - Old open pit; 10 - 11 th, 12 th and 13 th A.M. stops; 11 - Villages; 12 - Way to the stops; PQ - Plio-quaternary; P - Pliocene conglomerates SI - Silurian schists; Od - Ordovician shales and quartzites; Xg - Ante-ordovician "Xisto-Grauvaquico" Complex PC - Precarnbrian gneisses.

48

7 Km

;] [!] Sre. Almeirim cg1.

~ Ulme sst.

~ ~

E Monsento sst.

~ Peleeozoic besement

11 th stop

~ 7

450

350

250

150

50

(m)

Fig. 3.2. - Stops and geological profile location of the continental siliciclastic sediments and tectonic scketch of the Lower Tagus Basin northern border (modified from BARBOSA & REIS, 1991b).

Serra de Almeirim Conglomerates (UBS 13) are highly rounded quartzite con­glomerates, matrix supported, with MPS=35 cm.

13th STOP

LOUSA VILLAGE (6,5 kms ESE from VHa de Rei)

Purposes - Lousa thrust, "Conheiras" and profiles (Fig. 3.4).

Description - Palaeozoic slates thrust, towards north, over Serra de Almeirim Conglomerates is visible in the Lousa wall road. In front, the other side of the Codogoso stream, another big "conheira" can be seen. Some meters ahead, Lousa "conheira" is crossed by the road, start­ing up a positive macrosequence: from the massive quartzite boulders conglomerates of MPS=50 cm passing up to conglomerates bar­forms with MPS = 20 cm quartzites clast sup­ported, interbbeded with planar cross bedded sandstones. The third part of the profile ends

49

FIg. 3.3 Home: lIaaioira Coord: 1= 195.0 km Y- 287.2 km

~T~ l j ~ I ~ Graln oIse Uedlm. struct. I ~ 11 P S IWIIII Seq I I Obe. I lhm lIudo Sol C&I Pale ....... et.c 0 am 60 pAy ntACT Bas

... .(4.Qt.SA)

28·

28.

m D °00 D ~ • (4.Qt.SA)

Q) 84- lie I=l Sm 0 ..., m

"d I=l ItS

22-m 00 ID 0

ItS Sm ..., 4.Qt.Bro.SA) 0 , 225 20· 000 0 i"

Bed

Cl C ...... Jkar

IB - · .. · Sm !.QtJlrc.SA)

IB-00 000

14- · . ~ !oQt Bro • .B4

· lie · '. Sm · . · . B.Qt.Bro.SA) 12 .. · o 0

00 . lO-

aD 0 ID B.QtJlrc.SA)

o o· 0 · Sm

B- ~ -?- ~D-

\.,# 8.QtJlrc.SA)

...; B- Sm

l~~ ru'

m V!st m UdIte 0 ;i!L ..., I=l 4-ItS m I=l . :il G ... '0' fecII !llI;It.!IO

2_~ : J F Iht

~ I~t.m Fill.

B[ Sm • ..r,-~ &Yf C ...... ~lI!l I I/Qz 3D!), 0- ~~

Qt ....

FIg. 3.3 (cont.) Ham.: IIaclelra (conL)

..... OJ 0°00000 J 00. 0 .00 o 0 et 0 ooQO 00 coOO 0

o 0 8 Cl 00 0 00

000•

o 0 00 0 °20, dJ 0 CooO 0 o 0 8 0 00

~I I 11-.:.!~. ';'~ ooC:o·oo o o 0 0 ID 0000

. 0:>0 <>'00°0 \ o 0 8 0 00

o 0 00 0 0 20 62- rOO _. 0 Co

~ I:} Sm •

I 48-

~I I j 48-0 ...,

!I I i44~: 1111 .l ItS a 0

E-<I I ...l42-

",A1{~ 3B-~ ~

~lI=1 Jlo 0 ~

32-, ID 0 0

3D_lSm

Fig. 3.3. - Macieira profile.

Coord: 1- 195.0 km Y- 281.2 km

liPS ~

le ...... . --

Yell

kelll (35.IIz.!B) I ~A

I 15f.Qt. SA)

k Bed

I I 1=

r l!edl(4.Qt.SA)

y,

~

o I..()

FIe. a.. Name: Louaa Coord: X- 200.& kmY· 29U km Fig. 3.4 (cont.) Name: Louee (cant.) Coorcl: X- 200.B km Y- 29U km

JD 5OIv .... ~_v.I--1 Ok I 0l1li. I

" " 18 Qz. SR . YeU' Coaree

25 Qj. SR Ar«ar . 42-

Y~~' • 00 0 a C?o -° 00

~ . 40- Gp·(])ooo'°.o'QO . C>o;c, .

.. ~ .q •. ~.~

38-I I I I I I I .

1 u-~I I

138-, 11

~ "-~ _'V 'Ye

~ ID

1 '"' CD

~ 12 to>

1\ I 134

1 ~ I ~ 4 17~90"'S! ~ 0

~ Co)

S' I -l32 • .... ? , , .~

CD 11 ~30_lm~ 6

1 ~ Aq

~0.6

IYal &-1 1 I I. '1 1\1

I Iied/ coers

CD ArKar 'd ID

8-1 11 I. '1 1 1 1 t:: -l28-CD

YeUI 50 Qz. R 1 ~A~ -¥ I

rn

l I I IGt~ 17~90"'S!

28-

i I I I I ~I I I ri:~ I I I ~+ -"7 --"'2~ _ GC"

IYel14~.70".8R 24-

50 Qz. R

10Qt.A

l~e • , , -l22-

U1 Fig. 3.4 - Lousa 1 profile . .....

with trough crossbedding sandstones with few lag conglomerates. The paleocurrents trend to WNW.

On the top, the Yila de Rei Conglomerates outcrop along the road, showing planar accre­tion surfaces towards SW, overlying the Serra de Almeirim Conglomerates over which the highest topographic (270 m) conheiras are built (Fig. 3.5). Yila de Rei Conglomerates,with MPS = 35 cm, are matrix supported massive conglomerates of angular quartzite clasts in­terbbeded with red coloured mud stones, showing prismatic soil disjunction and iron ce­mentations. They represent debris flows / mud flows alluvial fans controled by the tectonic uplift of the neighbouring quartzites (BARBOSA & REIS, 1991a).

Red

12, Q .. ' . Red IIIty

mu .... 12, Qs,A

Red

12, QI, A . Flno lit

36, QI, ~

i

SQ, Qs, sa . YoU 50, Qz, R

Fig, 3.5 - Lousa 2 profile.

52

14th STOP

ULME VILLAGE (7 km SE from Chamusca)

Purposes - Ulme Sandstones and Serra de Almeirim Conglomerates observations.

Description - The observation starts on the Miocene Tomar Claystones (Fig.3.6). They are normally reddish brown massive mudstones, sometimes with carbonate concretions and Fe­Mn nodules. Some calcrete horizons may oc­cur. The Ulme Sands tones overlie uncon­formably this unit.

The Ulme Sandstones correspond to mu 1-tistory bodies of trough crossbedded yellowish and reddish feldspathic medium to coarse sandstones. They include quartz extraclasts and mudstones intraclasts underlin­ing limits of the sets. Ulme Sandstones defines with Serra de Almeirim Conglomerates a nega­tive macrosequence.

The Ulme lateral outcrop, close the top of the profile (Fig.3.7A), show a section subparallel to the palaeoflow. Ten diferent lithosomes integrating conglomerates and sandstones can be separated, corresponding to accretion barforms towards SW. At the outcrop base, Ulme Sandstones passing up to Serra de Almeirim Conglomerates shows reactivation surfaces. Quartzite c1ast supported fabric, and a(t) and b(t) imbrications, has been used for palaeoflow determinations (see panel A of Fig. 3.7). Quartzite c1ast MPS is 16 cm rising to 20 cm to the top.

15th STOP

VALE DE CAVALOS VILLAGE (13 km NE from Almeirim)

Purposes - Yale de Cavalos profile and exten­sive road section.

Description - This outcrop show the same stratigraphic units (Tomar Claystones and Ulme Sandstones) of the previous stop (Fig. 3.8).

In the Yale de Cavalos outcrop (Fig. 3.7B), the observation is normal to the deduced palaeoflow which trends to WSW. Six main bodies showing trough bedforms of conglom­erates and sandstones (quartzite MPS = 16 cm) are separated by erosion concave surfaces.

01 C;J

42-

l~--+-' I I 38-

11.1 11.1

ILl Si I -138-.--. P

~

~ L'IS

'0 I-< L'IS 8 o

E-<

I I I 34

32·

80-1 30-

28-

26-

22-

Name: U1me

.... 20 D "'="'"1

~

Coord: X- 280.1 km Y-173.8 km

~.QU..jSA

YeIll

YeIll ~.Qt,A.JSA

~.Qt,A/SA

eo­!kat

Coarse !kat

8- I YellI5.Qt.A./SA •

miCIl

Red'

Obs.

8-AI

Fig. 3.6 - Ulme profile.

Fig. 3.6 (cont.) Name: U1me (cont.)

11.1

~ o ...., rtJ

'd I:l L'IS rtJ

ILl

S S

uU

A

-b

Ise~ b

Coord: X- 280.1 km Y- 179.8 km

I V.I...atY iC'l __ I Obs.

'eel

I I 6. OU/SA

Coarse ° !km.

Ye,

5, ut, A/SA D-AIC

C-Int

5, ut,A/SA Iclasta

eU'°I2.Oz. 91 • 12.0z,91 •

Coarse !km.

5, ut,A/SA · 6. ut,A/SA ·

IYeu

6. ut,A/SA • Coarse !k 1st

I lYe

VALE DE CAVALOS

{N=93

~- a (t) R=o,90

~~o~ 0: ~

"-

330·

7,5

2,5m

{

N:10

b (j) R=O,91

v = 251·

B AZ=150·

7,Sm

Sm

2,Sm

o I I 0 o 5

230· ULME

4)5

3m

1,5m

o

10m 15 20m 25 30m 35 40m 45 ·50m 55 60m 65

~-1

~ -2

/ -3

{ N=80 ~/ ,;,:: a (t)

A R=o.8B

AZ =40· r=40 , Bm b (i)

R=O,90

'ii =228·

/ -$-b L4,5m

" .. , - .. , - ~'.

"' I 3m )'t_"r.··1 .... ·b>l~~. a

------- ~,-:: --~~{~~~ 1,5 m

5m 10 15m 20 25m 30 35m

Fig. 3.7. - Ulme panel ( A ) and Vale de Cavalos panel ( B). 1- Vector mean for clast imbrications, b (i); 2 - Clast ma­jor axis orientation, a (t); 3 - Paleocurrent trends; 4 - Conglomerate and sandstone sedimentary lithosomes;

.5 - Outcrop limits.

40

~

Fig. 3.8 Neme: VlIle de Ca"faloB

~ 42- J2< ,.....;

t:I.O 25 Ye 15. Qz. SR ()

.~ • El Red

..... 126 40- 15. Qz. SR COIll"II8 .~ J2<-Q) • El 20 At_ -~'C:7

Q)

< I=l 15. Qz. SR

..... «S

Q) • ~ "C

1 rn ~ 13. Qz. SR •

122 36- 4r Ye 13. Qz. SR • Red

D

34

118 32· 'C .....; rIl rn ~ Q) at.

COIll"II8 El 30- ~ YeU .- At_ ~ "---

14 2B- ~ '---"'"

A

.....; 28- 1 rIl I>-. CCI Ye -()

J ~ Sanely

M 110 24- mudat. CCI

El 0 l E-I

22-

Fig. 3.8 • Vale de Caval os profile.

55

Name Coord: X .. y ..

a ~ III YAmMl c z z ~ llATRIX 0 III 0 III GRAIN SIZE " SEDIMENTARY § PARTICLE liIe.> ~

I~ i ~ ~ Dr.i STRUCTURES SIZE " ~~ t= 5 ~ MUDS I SST I CGL I PALEOC. ETC. 0 CM PS) CLAY FRAC'l ~1::tI ~ to)

o cm. 50 iI I::tI 0

~30- 44-I -, ~ o CUI 0

- 42- st J2< COll1'se t' ::--- or AkBBt.

oL 25 ~ 15. Q:.l. SR I ~

• ~

Red J

Gt ~26- 40- ~/)...p~~~ ~ 15. Qz. SR

r--. ....... ~ ~ • - -.....;;,

STRUCTURES LITHOLOGIES '--C:.......- . TROUGH (t) I

DIMENTION CH TROUGH ~ PLANAR(p)

'=/5 lIII MUDSTONES (r)

HORIZONTAL (h) g CUST IMBRICATION CJ SANDSTONES (S)

MASSIVE (m) - INTRACLASTS

~ loobcfobl CONGLOMERATES (G)

~ RIPPLES (r) ROOTLETS

PALEOCURRENTES ABBREVIATIONS

~ PLANAR Qz - Qu.art.zite . mm - marmorized

Qt. - Quartz A - AneWIl1'

t{ Ak - Arkose- R - Rounded TROUGH Sst - Smdstone SR - Sub rounded

I IlIBRlCATION Cal • Conglomerat.e SA - ~bangular

.15 Qz. SR - Quartzit.e of 16 cm (lIPS) sub rounded

Fig.3.9 - Sections legend.

REFERENCES

Seepage 67.

56