( Cie ncias da Terra (lINL) Lisboa N." 14pp. 19 1-202

2000 121 Figs.

Miocene sediments from Foz da Fonte and Penedo sections(Lower Tagus basin): clay minerals and isotopic data

A.P. Stlva'!', F. Rocha'!', P. Legotnha'" , J . Pais'", M. Telles Antunes?' & C. Gomes'"

I - Departamento de Geociencias. Universidade de Aveiro , 3810 Aveirc , Portugal2 • Centro de Estudos Geotogicos. Fac.Ciencias Tec nologia, Quinta da Torre, 2825-114 Caparica, Portugal.

3 - Academia das Ciencias de Lisboa; Centro de Estudos Geo16gicos, Fac.Ciencias Tecnologia , Quinta da Torre, 2825- 114 Caparica, Portugal.

ABSTRACT

Key-word s: Clay minerals; Isotopic data; Mioce ne; Lower Tagus Basin; Paleoenvironmental reconst ruction.

Eight depositional sequences (DS) delimited by regional disconformities had been recognized in the Miocene of Lisbon andSerubal Peninsula areas . In the case of the western coast of the Setu bal Pen insula, outcrops consisting of Lower Burdigalian toLower Torto nian sed iments were studied. The strat igraphic zonography and the environmental considerations are main ly supportedon data concerning to foraminifera, ostracoda, vertebrates and palynomorphs.

The first mineralogical and geochemical data determined for Foz da Fonte, Penedo Sui and Penedc Norte sedimentary seque ncesare presented. These analyt ical data mainly correspond to the sedi ments' fine fractions. Mineralogical data are based on X-raydiffraction (XRD), carried ou t on both the less than 3811m and 2 11m fractio ns. Qualitative and semi-quan titative determinations ofclay and non-clay minera ls were obtained for both fractions . The clay minerals asse mblages complete the lithos tratigra phic andpaleoenvironmental data obtai ned by stratigraphic and palaeontological stud ies. Some palaeomagnetic and isotopic data are discussedand correlated with the mineralogical data . Multivariate data analys is (Principal Components Analysis) of the mineralogical datawas carried out using both R-mode and Q-mode factor analysis.

RES UMO

Patavras-c have: mincrais das argiles: dados isotop icos: Miocenico: Bacia do Baixo Tejo; reconsttnncao paleoambiental.

No Miocenico das regioes de Lisboa e da Peninsula de Senibal haviam side reconhecidas o tto sequenctes depos icionais (OS)limitadas par disconfonnidades. A zonacao e as reconsnrutcoes paleoambientais foram obndas, essencialmente, atraves do estudode foraminiferos, ostracodos, vertebrados e palinomorfos.

No prcsentc trabalho aprcsentam-se os primeiros resultad os referen tes amincralogia e geoqulmicadas frac~es finas des depositosmiocemcos de Foz da Fonte, Pcnedo SuI e Penedo Norte. Os dados mineralogicos foram obtidos atraves de d i frac~il.o de raios -X dasfracr;oes < 38J.lm e < 2 pm. Foram feitas determinacoes semi-quantitativas e qualitativas dos minerais argilosos e nao argilosos. Asassocia coes de mmerais argilosos foram utilizadas como com plemento dos dados litos rratigra ficos e paleoarnbientais anter ionncntedefinidcs atraves de estudos de estratigra fia e paleontologia . Estabe lecem-se correlacocs com dado s paleomagneticos e de isotopesestaveis (C, 0 ) anterionnentcobtidos de alguns dos nlvcis estudados. Foi levada a efeito analise multivariada (analise de componentesprincipals] dos dados mineralogicos recorrendo aos facto res "R-mode" e "Q -mode".

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I" Congresso sobre0 Cenoz6ico de Portugal

~ RESULTS AND DIS CUSSION

GEOLOGI CAL SETTING

INTRO DUCTION

Antunes et al. (199 9) point out a I'S rfl6Sr age of 20Maapproximately, for the lower beds. Disconformitie s canbe observed in the inte rmediate part of the sec tion.The isotopic data (0180 and Ol lC values) show clearchanges between depositiona l sequences BO and BI(Fig. 4).

.L. illite + smectite + kaol inite (15K );b illite + kaol inite + smec tite (IKS);L smectite + illite + kaolinite (SIK);~ smectite + illite + kaolinite (SIK).

Foz da Fonte Sec tio n (Figs. 2 - 5)

Fine fractions of Lower Miocene (lower Burdigalian,depositional sequence BO) sediments from Foz da Fontesection consists o f non-clay minerals (quartz ,phyllosil icates, calcite, plagioclase and K-feldspar), andclay minerals (illite, smectite, kaolinite and rare chlorite).The deposi tiona l seq uence B I mineral co mposi tionappears to be richer in carbonates and in opal ClCT. Itshows sharp oscillations as far as smectite is concernedand slight oscillations in illi te and kaolinite contents.Variations on the relative contents of the clay minerals(Fig. 3) allowed the definition offour mineralogical unitsin the Fe z da Fonte section (the most represented clayminerals arc underli ned) :

Fifty one samples, collected at the Foz da Fonte,Penedo Sui and Penedo Norte outc rops (Fig. 1), werestudied.

Th e mineralogical co mposition of the sediments,particularly of their fine fractions, was determined throughXcrey diffraction (XRD) patterns correspondi ng to lessthan 38 11m and 2 11m fractions. Qualitative and semi-quan­titative determ ination of clay and non-clay minerals wascarried out on both stud ied fractions.

Palaeomagnetic and isotopic previously obtained(Antunes et al., 1996; 1998; 1999; 2000) are correlatedwith mineralogical data.

Mul tivar iate data analyses (Principal Com po nentsAnalysis) of the mineralogical data were carried out (R·mode and Q-mode factor analys is).

M ATERIALS AND M ETHODS

Norte section with the classical units "Helvetian" Vla-bwhich occur in the Lisbon region. There is an erosionsurface between beds 5 and 6, on which lies a conglomeratewhose elements main ly consist of very abraded bivalvecasts with a black, phosphate-rich pa tina (L. Gaspar,Marine Geology Lab., Portuguese Geological Survey). Theconglomerate corresponding to bed 8 contains glauconiteand fragments of phosphate crusts.

-

Ir-~-0.• ••

..~ATLANTIC OCE AN

The oldest Miocene sediments outcrop on the cliffs atFoz da Fonte beach. Mioce ne sediments directly overlieCretaceous limestones at a low angle unconfonnity. Theyconsist essentialy of fossili ferous biocalcaren ites andmarls. The lowermost beds include cobbles and pebb lesof Cretac eous volcan ites and limestones. In the lower partof the section, a sandy bed corresponds to a regressionevent. The middle section presents detrital shallow faciesand eroded surfaces. One of the se is overlain by aremarkable concentration of oyster shells. The upper partof the section shows a marl/marly clay cyclic character.

Penedo Sui outcrop is exposed on the cliff at Bicasbeach . Basa l beds (fossil iferous biocalcarenites andsands tones with sedimentary discontinuities) are the sameas in the intermediate part of Foz da Fonte section.

Penedo Norte outcrop is located about lKm to the northof Penedo Sui. Zbyszewski (1967) correlates the Penedo

Fig. 1- Geographic setting of the area under study.

Detailed stratigraphic studies have been carried on inLisbon and Set ubal Peninsula regions. Eight Miocenedepos itional sequences (DS) delimited by regionaldisconformities had been established. In the western coasto f the Setuba l Peninsula, Lowe r Bu rdigalian toLower Tortonian outcrops were studied. Environmentalconsiderations that could be put forward were mainlysupported by data on foraminifera, ostracoda, verteb ratesand palynomorphs.

In the present work, the firs t minera logical andgeochemical data for Fozda Fonte, Pencdo Sui and PenedoNorte sedimentary sequences are presented « 38 11m and< 2 11m fraction s) (Fig. I). The clay mineral assemblageswere used as lithostratigraphic markers for correlationand paleoenvironmental reconstruction.

192

Ciencias da Terra (UNL), 14

•,•,,,,,

!•v:" .,,,,,-'

,,

.• -, 0 ,

> o- p-...,). -6 0.-0

."0 ..... . "c ......

-4 ~ •• •, 0 1

-8 .s -4 ~>.o"c._::- -.''(: . 0.->

• . e-.,.,o II>

"'- 11>, ,~

•

,i

. '-.0'_ """Fig. 4 - Foz da Fonte Sect ion. C and 0 isotopic composition

(Antunes et aI., 1997).

,,a

, .

Fig. 2 - Foz da Fonte Section. Composition of the < 38J,1msedimentary fraction.

•..'.o

II' '.:=£:J-:T.<l' HI-.=.:- I l~;;~:..1t~- I-:::~ 'JG,:=£:" l' II -= IffilIl! III -=' 1I I '"::::- ~::::.:= :';::Ij ~:;,<' ~ liT''--'-'--'---'--'---'--'--~

I "".- ' I 11"'" I:"" . ..

I ·· I""" ",.. ... ~ 3

I z,_".z ,..Ill., 'I(

• 0..e

~ I0 '

I,""".

Once again, the isotopic curves (O I ~O and oUCvalues )show clear changes between depositional sequences BOand B I and between B I and B2 (Fig. 7).

Pcncdo Sui Section (Figs. 6 - 9)

Penedo Nor te Sec tion (Figs. 10 - 13)

Lillite + kaolinite (IK) ;bsmectite + illite + kaolinite (SIK);.l.smectite + illite + kaolinite (SIK );:lillite + smcctite + kaolinite (ISK).

The mineral composition (fine fractions) ofthe LowerMiocene (Burdigalian ) depos itio na l sequence BO atPenedo Sui consis ts in calcite, quartz, phyllosilicates,plagioclase and Kcfeldspar, and clay minerals such assmectite, illi te , kaolinite and rare chlorite . Mineralcomposition, on the passage to depositi onal sequence BI-,becomes richer in detrital minerals (quartz, phyllosilicatesand plagioclase) and, in much less degree, in dolomiteand opal C/CT. The calcite content diminishes; there areslight oscillations in smectite, illite and kaolinite contents .Variations of the relative conten ts of clay minerals (Fig.8) were used to recognize four mineralogical zones:

.2 ... _ ....."'"

","­,.;,. -- "..'.oo . - _ _ ~~

- ----

[-':'l'_.,~;:

...... :: mffiillll:~:-::::::::-:::-~'S\,-'­- " f.i""fF · . . ~.-~~"",,'S..~_ I

" m - -" J....~""-~'II !

, .

I" lll-·- II II - I

,,a

...,.......

.......~ "

,..:~ ...

l" ~:=...

"

z ,..':':...."..•

I ~-

Fig. 3 - Foz da Fonte Section. Composition of the < 2 urnsedimentary fraction.

The fine fractions of the lower beds of Pcnedo Nortedepos itional sequence B2 (Burdiga lian) essentially consist

193

I" Congressc sobre 0 Cenozoico de Portugal

_ 0 :1ai'." j ,I, I, ,1,1 ,1,1, ,I," ',I, ',>GlE

- 51:: : : : : : : : : : : : : : : ' : : :1- ;:11 , , , " "" I , , , , , ,x.

. :~'~'I : : : ::: :::, : : : : : : :1

••

-

! " "'~.:-'

~ ,, ---

" ..'~~.., ... , NT ..

I,..1"""1,..·U.;·...

••"••o•o•

UNIT 1

UNIT 2

";

.."~ .

'" -.

0.5 1

/

.. ....- - / <"',0..: ,,- - - - - - - --

..12 -:-.............'>I 1

"I. "....819 .........

.........8

7/ 8

7

5

4

3

2

Io

Fig. 6 - Penedo SuI Section, -c 381lm sedimentary fraction.Fig. 5 - Foz da Fonte: variations on the relative conte nts of themain clay minerals K1J. Kaolin ite/Illite ; SII · Smectite/Illite.

of quartz, phyllosilicatcs, plagioclase and K-feldspar, andopal ClCT and calc ite as accesso ry minerals . Smectite,illite and kao linite are the clay minerals. The Burdigaliansection becomes enriched in calc ite and (much less) inillite. The medium levels (Langhian, depositio nal sequenceL I) are characterised by a strong incre ase in do lomite inthe fin e frac tions, and by minor changes in the clayminerals associations (slight increase in illite and loss ofsmectite). The Scrravallian part of the section (depositionalsequences SI , S2 and T I) becomes much richer in calcite(almost monomineralic), with a strong increase of illite .The relative contents of clay minerals were used tocharacterize four mineralogical zones (Fig . 11) on PenedoNorte outc rop:

±.,. smectite + illite + kao linite (SIK);i,illite + smecti te + kaolinite (ISK );2.,.i llite + kaol inite + smecti te (IKS);Lsmectite + illite + kaolinite (SIK).

Pectinid shells from bed 8 were 87Srf':l6Sr dated (H.

Elderfield, Cambridge University) from 11.5 to 13Ma. Bed9 is a medium grained, glauconite rich sandstone; K-Arage (C . Regenc io Macedo, Coimbra University) isIO.97±0.25 Ma (Lower Tortonian) . Isotopic data (ol80 andolle values) do not show so sharp d isconformitiesbetween the depositional sequences as in the precedingoutcrops.

l~11l=_1 ~~ -;;::,. ~]I '.""", w -I:

. - -

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

••,•,0

•0 "• ,,

•

Fig. 7 • Pencdo Sui Sectio n. Com position of the <Zumsedimentary fraction.

194

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..~-- [;1' 'J1l:I' _ _ ~'l_f"oI_ . _ .

.',_ 0 ," _ ll!l5_ I'!!'I...-- ---- ..",",_ ;:t;~ __ -.~_

II

---I II I

-1 .....":'

I

I 00 -I

,~ •.".~., ...."i •

I "

T """'......,, • •

Fig. 10 • Pcncdo Norte Section, < 38JJ rn sedimentary fraction.

i1

,

-2 . , 0 2

>.6"0. _). . 6" O-0\'S0In

•1 :

•

,"

·.,•

,

·5 .~ ·3

".> ' 6''c -_> ' 6''c .~

fl iti l

• . _op. ' _ ... 2.--

••,

I~ I I.- -- If -"""":i:.:'a,

••

(..'~T <f '" •"'

•","•••••

Fig. 8 • Penedo SuI Section, C and 0 isotopic composit ion(Antunes et at., 1997).

Fig. I I - Penedo Norte Section, < 2 p m sedimentary fraction .

[--J'_..~ ..._.._ _ ,. 'c

l"-i _

<.2"", _

II

---

"

r

II

.' ."'...... It ..

_..----~,

Ii 00_,

~ •• t~"., ......

t •

I i

UN IT 2

0,' 1,5

.••.•.\

- - '~ - - - -

lI97 \.

P• • IOVNfT 4"- -- ---- --------

Pc . 7\,

Pn ' \

Po. 3 •.~ UNIT3 I

I e.~ 1

Fig. 9· Penedo Sui: variations on the relative contentsofthe main clay minerals. K1I . Kaolin ite/Illite;

SII - Smectite/Illite.

195

Facto r 3 expresses the alternation of more or lessmarine environments (with events characterized by anintense detri tal sup ply) with other ones marked bychemical sedimentation. Factor I stresses that there weretransitions towards more proximal environments oflagoontype, under a more tempe-rate climate; Factor 2 explainspost-depositional parameters .

The vertical evolution of the Factor scores shows theimpact of each Factor on the characterized zones andallows to recognize a paleoenvironmental evolution.AlongUnit I, the analysis of the evolution of the three Factorsscores points out to a transition from a distal marineenvironment to a more proximal one, with some lagoonepisodes. In Unit 2 oscillations of the relative impact ofeach Factor can be detected.This points out to an evolutiontowards more distal marine environments. The evolutionof the Factors along Unit 3 reveals the occurrence oflagoon and fluvial episodes, alternating with marine ones.During the deposition of the sediments of the Unit 4,environment was again a more distal marine one.

The B-modc factor analysis of the mineralogical dataof the Penedo Sui section fine fractions (Fig. 14) allowsthe following conclusions:

• Factor I shows zeolites (Zeo l), pyrite [Pyr] andsiderite (Sid) in front of Kcfeldspar (K.F);

• Factor 2 shows hematite (Hem), opal C/CT (Opal),plagioclase (Plag) and dolomite (Dol);

• Factor 3 shows calcite (Calc) in front of thequartz (Qz) and phyllosilicates (Kaol, Sm, 111).

• Factor I shows calcite (Calc) in front ofquartz (Qz),phyllosilicatcs (Kaol, Sm, lJI), K-feldspar (K.F),plagioclase (Plag), anhydrite (An), opal Clcr (Opal)and dolomite (Dol);

• Factor 2 shows siderite (Sid) in front of halite (Hal);• Factor 3 shows pyrite (Pyr) in front of zeolites

(2<01).

Sta tis tical a nalysis

The P -mode factor analysis of the Foz da FonteMiocene profile fine fraction mineralogical data (Fig. 12)supports the following conc lusions:

lHT 6

Fig. 12 • Pencdo Nolte section , C and 0 isotopic compositio n(AnlUncs et al., 1996).

1°Congresso sobre 0 Cenczoicc de Portugal

--II - t I iI - - G'"O_6''C_......."'.._..I - I I- - • ., • ,

, ,,, , ,, , ,

I , •, , , , , , ,,,, ,•,

• • • , , • •, ,E , ,, , , •, •

I • ,, • • ,,, , ,, , • , ,, ,,,, ,,, , , , , ,,, , , , , , , ,E • ,, , , ,,,, ,

1, , , • ,, ,, , ,

i ,,,,• • , • ,,,• ,, , ,, , , ,, ,, ,,, • ,,• ,,. , , , ,, , • ,,,, ,, ,, , • • , ,,"

, , ,, , , ,,,·, ,,,, ,

I, , • , ,, ,,,,,, , • , , • ,,l ,,, , ,, , • ,

> , ,, , , , , •,I "l_~ ,• , ;r,,• t • , , , ... 1

· '1*,"'" ", • ,

~: • •,•, , , , ,,, • ,, • .. • ,l ' '• , ,, , ; .; ,• , ,, , , , , , ,,, • , , , ,, , " ,

• • ' I , . ', , ; ." ,I '1 _ !

" • ;/ '\1 ,i , ;I, ' .. !, , , -, ' ~, !i 1 i,

• " ~)' '100.... 1ol , • , , ,1 . I- - ;; i ; .

- > .. • • •..- ...-. ) . • ~O_·; ••~_..- ...-.'..- ..,..-.. ) •• ~O()ooOool .... .~()ooOooI

lHT S

.. 2

Fig. 13• Penedo Nolte: main clay minerals. KII • Kaolinite!Illite ; sn . Smecntezlttne.

Factor 1 expresses depositional environments of lessmarine influence, that are more prox imal and moresiliciclastic. Continental influence has been greater, witha few lagoon episodes, characterised by some chemicalsedimentation. Factor 2 expresses an evolution towardslagoon environments; Factor 3 expresses a sharp evolutionof the conditions expressed by Factor 2.

Once again, the vertical evolution of the Factor scores(Fig. 15) shows the role of each Factor on the distinctivezones being established; it allows the definition of theirpaleoenvironmental evolution . Along Unit I the evolu­tion of the three Factor scores points out that sedimenta­tion took place in a distal marine environment. In Unit 2we can detect oscillations of the relative impact of each

196

Ciencias da Terra (UNL). 14

"':- .. ­• • ••- Ilol U .........~

••

.,

F3

•• "~ -•u ..

~

i: -IW •

~ •"': ~-,~ .,•

-r

Fig. 14 · Foz da Ponte profile : R-mode factor analysis of the fine fraction mineralogical data .

3

L

L

•

-'._ F3

-0- F2

..-0" Fl

..-'E"

UNIT 3

: ~: {\: f \• I ,. ,, ,

-..... it r.--<>-.....t::;\-., "

\ D " 'C]'"" .

e-e/Do

Lc

UNIT 2

... ..." 'fj'p

,H

f\\I\\\

7 7f8 8 819 10 11 12 16 16.l 16.2 18 19 20 21s

(C)

. up

~\· '.\

\.,'qf"• !." .j '

43

•p

UNIT 1

a

I•••.df ,..a

Q ' . ' []o '

1

Jo

o

·1

,

.'

Fig. 15 - Foz da Fonte : vertical evolution ofthe Factor scores O. C - Co ntinental; 0 - Marine, Distal ; P - Marine, Prox imal;L -Lagoon.

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10 Congresso sobre 0 Cenoz6icode Portugal

Factor, pointing out a gradual evo lution towards a moreproximal marine environment, with lagoon events. Theevo lution of the three Factors along Unit 3 reveals thepersistency ofalternating lagoon and marine events . Dur­ing the deposition ofUnit 4 environments became clearlymarine.

The applica tion of g -mode factor analysis to the finefraction minera logical data of Pe nedo Norte section (Fig.17) allo ws us to recognize :

• Facto r 1shows ca lcite(Calc) in front ofquartz (Qz),phyllosilicates (Kaol, Sm., lIl), plagioclase (Plag),opal ClCT (Opal ). hematite (Hem) and anhydrite

(An);

• Factor 2 shows siderite (Sid) in front of Kcfeldspar(K -F) and pyrite (Pyr) ;

• Factor 3 shows dolomite (Dol) in front of hal ite(H.I).

.21

.31

0"" P,oc.s

Sid . ~al •

-e.s","0 .

..Q .~ Sidbol.• -8 . ~

- I - I

Fig. 16 - Pencdo SuI profile: R-mode factor analysis of the fine fraction mineralogical data.

-o- F2

···O···F3

- e - FI

-u•••••••PID

UNIT 3-'-

r,'.PIDL

UNIT 2

DIP -

p -:- p

.'?iO.... ~ " . - -~0 ..... I~ " 1: I ~ fJ 1

: , .. 1

f \ rl...I-'-N ,

;>.. ! ,. -- \-q f,' \

.0 ······0 " o./. . J\ ., -,q, . ~ .,-, / p PIL '0

"

\

Pent 14 8197 7197 6194 5197 4197 2194 Pen3 Pen S Pe n7 PentO

-0.5- 1 D"

-1.5 ....E-<--2 Z;:>

2

1.5

1

0.50..

'1;a.-.0..•.

-0.5'0

Fig. 17 · Pencdo SuI: vertical evolution of' the Factor scores. D - Marine, Distal; P ,... Marine, Proximal; L ~ Lagoon.

198

Cienciu da Terra (UNL), 14

'"•

F3I

-0. . DoN

F2,

u

'i'... '"•b: - I •

-0,

-0.' ~-•'"

-,

Fig. 18 - Pcncdo Norte profile: Rcrncde factor analysis of the fine fraction mineralogical data.

3,-- - - - - - - - - - - - - - - -----,

2

1

o

-I

-2

PlLo.. , , ,

-0- FI

-0- F2

o

UNIT 7..•.. F3

14342123

UNIT 6

9252

UNIT S

6.1

UNIT 4 L

1

Fig. 19 - Penedo Norte: vertical evolution of the Factor scores O. D - Marine, Distal ; P - Marine, Proximal;L- Lagoon.

Factor I expresses a depositional enviro nmentcharacterized by marin e influence. comprising episodesof intensive detrital supply. Th e presence of hematite inthis association (more clearly than in the other outcrops)may reflect some events of sub-aerian (fluvio-deltaic?)sedimentation. Factor 2 expresses a transition towardslagoon environments. Factor 3 explains post-deposit iona lvariables typical of marin e environments.

The vertical evolution of the Factor scores (FIg. 17)shows the impact of each Factor in thecharacterizedzones

recognized in the Penedo Norte section. It provides addi­tional data about pa leoenvironmental evolution. AlongUnit 4 the evolution of the three Facto r scores points outto a transition from a proximal marine to a lagoon envi­ronment. In Unit 5, osci llations of the relative impact ofeach Factor show an evolution towards a more marineenvironment. The evo lution of the Factors along Unit 3reveals a distal marine environment. During the deposi­tion of the sediments from Unit 4, environments revertedto more proximal mari ne ones.

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, 0 Congresso sobre 0 Cenozcico de Portugal

CONCLUSIONS

I . Sedimentsof Foz da Fonte section are characterizedby th e follow ing fe atu re s: illi te predominat es oversmectite, and kaol inite appea rs in significant amountsalong all the section . Clay minerals and non clay mineralassemb lages po int out to source areas on which asemi-arid climate may have prevailed.

2. Sediments of Penedo SuI section arc charac terizedby predominance of smectite over illite. Kaolin ite becomessignificant in the lower strata of the section (chlori te isbut vestigial).

3. Sediments ofPenedo Norte section are characterizedby smectite predominance. However, illite becomes a majorclay mineral in the upper strata of the sect ion just wheredolomite contents increases. Compared to those ofthe othertwo sections, these sediments display features that are cha­racteristic of sedimenta tion in a deeper sea environment.

4 . Clay mineral assemblages allow to recogn ize sevenmineralogical units (Fig. 19). The vertical evolution ofthe factor scores for eac h of the outcrops confirms theestablished zon ing. It also reveals the impact of eachFactor on the different d ist inctive zones, and thereforecontributes to the characterization ofa paleoenvironmentalevolution (Fig. 20).

5. The time span of Unit 1 (Foz da Fonte and PenedoSui sections) deposition is characterized by temperateclimate and weak hydrolysing conditi ons in the sourceareas. Environment was infralittoral.

6. Unit 2 ( Foz da Fonte an d Penedo Sui) timespan is charac terized by some cl ima te cha nges andcircalittoral deposition en vironments that evolve to aninfralittoral one .

7. Sedime nts of the Unit 3 (Fez da Fonte and PenedoSui) reveal a sub tropical climate and a so mewhat moredista l infrali ttoral deposition environment.

8. Sediments of the Unit 4 (a ll sections) also reveal asubtropical clima te and an infrali ttoral environment thatchanges to circalittora l.

9 . Uni t 5 ( Penedo Norte) ind icate a dep osit ionenvironment similar to that for Unit 3 but under mildertemperate conditions.

10. Un it 6 (Pened o Norte) re vea l a c irca litto raldep osi t ion environme nt character ized by still moretemperate conditions.

I I . Finally, Un it 7 (Penedo Norte) is re lated to a rnorcdistal, infrali ttoral environment. Climate cond itions in theso urce a reas w ere typica l of more contrasting andhydrolysing conditions that were in favour ofsmect ic soilsformation.

[I]itll , soz 0 ... PONT I!

n S IK.. .."

n r. ""oIo NOM

5 " uNIT ,H

"':ii' "

I " uNIT6

•n I

"is"

PI!N IlDO SUI. 1 5 < UNIT ,

..~,J.. .,I 5 , UNIT .. 5 I ,

"NIT"

S I K

·-\v··f-- - - - - - --1- - +!

I "

5 1 , UNIT 3

UNIT 2

1'.;1.•.f- --1_ - +I

1 5<I , UNIT t

I -ILLITE

S - SMECTITE

K • KAOLINITE

Fig. 20 - Clay mineral assemblages of the m.ineralogical units defined in the studied sections.

200

:

Ciencias da Terra (UNL), 14

FOZDA FONTE PENEDOSUL PENEDO NORTE

Units Marine Hidrolysls Marine Hldrolysis Marine Hidrolysls

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Fig. 21 • Paleoenvironmental evo lution.

20 1

10 Congresso sobre 0 Cenozoicc de Portugal

REFERENCES

Antunes , M. T.; Civis, J.; Gonzalez-Delgado, 1.A.; Legoinha. P.; Nascimento, A. & Pais. J. (1996) - Miocene stable isotopes (011(),~1lC), biostratigraphy and environments in the southern limb ofAlbufeira syncline (SetUbal Peninsu la, Portugal). Geogacera,Madrid. 2 1: 2 1 ~24, 4 figs.

Antunes, M. T.; Civis, J.; Gonzalez-Delgado, I.A.;Legoinha. P.; Nascimento, A. & Pais, J. (1997) - Lower Miocene stable isotopes(SI 'O, S"C), biostratigraphy and environments in the Foz da Fonte and Penedo sections (SetUbal Peninsula, Portugal). Geogaceta23: 7-10 .

Antunes, M. T.; Elderfield , H.; Legoinha, P.; Nascimento,A. & Pais,1. (1999) - AStratigraphi c framework for the Miocene from theLowerTagus Basin (Lisbon, Setubal Pen insula, Portugal). Depositiona l sequences, biostratigraphy and isotopic ages. Bol. Soc.oeot. Espana,Madrid , 12( 1): 3- 15.

Antunes, M. Telles; Legoinha, P.; Cunha. P. & Pais, 1. (2000) ~ Estratigra fia de alta resolu~io e correteeao de facies do Aqui tanianoao Tortoniano inferior (Lisboa e Peninsula de Senibal, Bacia do Baixo Tej o). 10 Congresso sobre 0 CerIOZO;CO de Portugal,Monte de Caparica: 159-160.

Schultz, L.G (1964) - Quantitative interpretat ion of mineralogical compositio n from X-ray and chemical data for the Pierre Shale.U.S. Geol. Surv.Prof Paper, 391-C , 1 ~3 \.

Thorez, 1. (1976) - Practical identificationofclay minerals. 90pp. (Ed. G. Lelotte, Belg ique) .

Zbyszewski, G (1967) - Contributions al'etude du Miocene de la serra da Arribida. Com. Servo GeotPormgal, Llsboa, LI: 37-148.

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