( Ciencias da Terra (UNL) Lisboa N. o 14 pp.277·288 2000 J 7 Figs. The Neogene of Algarve (Portugal) J. Pals"-'', P. Legoinh a'':", H. Elde rfi eld(b,3), L. 80 U53(8,4) & M. Estevensv-" Work supported by the Praxis XXI Project "Necgenicc e Quatemaric da margem aua nuce da Iberia e trans fonnao;&s globais" (FCT, MeT), a - Centro de Estudos Geol6gicos, Faculdadede Cienciase Tccnologia. Quinta da Torre, P·2825·114Caparica,Portugal. b- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK. t, [email protected]; 2 . [email protected];3 · helOl@csc,cam.ac.uk; 4 . 1 S@fct.urd,pt; S- eslevens@telcpac_pl A BST RACT Key-word s: Neogene; Stratigraphy; Algarve; Portugal. A synthesis abour rhe Neogene and Quaternary of Algarve (Southern Portugal) is presented. New isot op ic ages as well as biostratigraphic data about the Miocene deposits allow to present a new stratigraphic frame for the previously characterized units. The Lagos-Pcrtimao Formation corresponds to deposits of "temperate carbonate platform" sedimentological type, developed dur- ing a long time span (Lower Burdigalian to Upper Serravallian). A major change in sed imentation conditions (carbonate to silic iclastic environments) occurred in the Lower Tortonian with the depos ition of yellowish sands. Spongoliths rich in microfossils are rep resented in Algarve inland. Their age is not well estab lished; calcareous nannofossils indicate the CN5a l one (Upper Serravallian) while foraminifera point out at least Nl6 zone (Lo wer Tortonian). In the Upper Tortonian, the sedimentation is widespread in Eastern Algarve, related with the Guada lquivir Basin infill. The deposits begin with detrital limestones, locally very rich in Heterostegina , passing to fossiliferous conglomerates and siltstones (Cacela Fo nnation). Coarse-grained conglomerates at Galvana (Faro) pose some age problems. K/Ar age on glauconite indicates 6.72±O.17 Ma. However, glauconites may be reworked from older deposits (Cacela Form ation ). The Galvana Conglomerate could be related to Pliocene deposits arc not well characterized. Olhos de Ague sands, with a thin marine intercalation rich in marine vertebrates (fishes, a crocodile, cetaceans, sircnians), may be Upper Pliocene; however, the vertebrates point out to a Serrav allian to Tortonian age. ages on oysters from above the level with vertebrates point out to 3.0(+2.5-1.0) Ma. Similar sand deposits occur at Morgadinho (Luz de Tavira). These sands are overlain by marls, lignite clays, lacustrine limestones and a silty calcareous crust. A small mammals association indicate an age span between Upper Pliocene and Lower Middle Pleistocene (M N 17.MN20). A Biharian mammal fauna (Lower Pleistocene) was collected at Algoz in similar deposits. In the present stale of knowledge, Morgadinho and Algoz deposits may be correlative. RESU MO Palav ras-chaver Neogenico; Bstratigrafia; Algarve; Portugal. Apresenta-se uma sintese sobre 0 Neoge nico do Algarve. Dataeccs de bern como dados biostratigraficos de unidades miocenicas, pe nnitiram 0 estabelecimento de urn novo quadro estratigrafico para as unidades liticas algarvias. A Formacao de Lagos-Portimao corrcsponde a depositos sedimentares de tipo "plataforma carbonatada temperada" que se dcscnvolveu durante urn longo intervalo de tempo ( Burd igaliano inferior a Serravaliano superior). Uma mudanca maie r na scdirnentacao (ambie nres silici clasticos) deu-se no Tortonian o inferior com a deposicao de areias finas amarel adas . No interior do Algarve ocorrem espongolitos rieos de microfosseis. A idade nao este pe rf eitamente d efinida. Foraminiferos indieam a zona N16 (Tortoniano inferior) e os Nanofosseis calce nos a zona CN5a (Serravaliano superior) . No Tortoniano superior a sedimcntacao foi mais significativa no Algarve Oriental, em retacac com 0 enchimento da bacia do Guadalquivir. Os depositos iniciam-se por calcarios detriticos, locahnentc multo ricos de Ileterostegina, que passam a conglomerados e siltitos muito fossilifcros (Formacao de Caccia). 277
Transcript
( Ciencias da Terra (UNL) Lisboa N.o 14pp.277·288
2000 J7 Figs.
The Neogene ofAlgarve (Portugal)
J. Pals"-'', P. Legoinh a'':", H. Elde rfi eld(b,3), L. 8 0 U53(8,4) & M. Estevensv-"
Work supported by the Praxis XXI Project "Necgenicc e Quatemaric da margem aua nuce da Iberia e trans fonnao;&s globais" (FCT, MeT),a - Centro de Estudos Geol6gicos, Faculdade de Cienciase Tccnologia. Quinta da Torre, P·2825·114 Caparica,Portugal.
b - Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK.t , [email protected]; 2 . [email protected];3 · helOl@csc,cam.ac.uk; 4 . [email protected],pt; S- eslevens@telcpac_pl
A synthesis abou r rhe Neogene and Quaternary ofAlgarve (Southern Portugal) is presented. New isot opic ~7S rj86Sr ages as wellas biostratigraphic data about the Miocene deposits allow to present a new stratigraph ic frame for the previously characterized units.The Lagos- Pcrtimao Formation correspo nds to depo sits of "temperate carbonate pla tform " sedimentological type, develope d during a long time span (Lower Burdigalian to Upper Serravallian). A major change in sed imentation conditions (carbonate to silic iclasticenvironments) occurred in the Lower Tortonian with the depos ition of yellowish sands.
Spongoliths rich in microfossils are rep resented in Algarve inland. Th eir age is not well estab lished ; calcareous nannofo ssilsindicate the CN5a l one (Upper Serravall ian) whi le foraminifera point out at least Nl6 zone (Lo wer Tortonian).
In the Upper Tortonian, the sedimentation is widespread in Easte rn Algarve, related with the Guada lqui vir Basin infill. Thedeposits begin wi th detrital limestones, locall y very rich in Heterostegina , passing to fossiliferous co nglomerates and siltston es(Cacela Fonnation).
Coarse-grained conglomerates at Galvana (Faro) pose some age problems. K/Ar age on glauconite indicates 6.72±O. 17 Ma.However, glauconites may be reworked from older deposits (Cac ela Formation). The Galvana Con glomerate could be re lated toPliocen e deposits arc not well characterized . Olhos de Ague sands, with a thi n marin e intercalation rich in marine vertebrates(fishes, a crocodile, cetaceans, sircnians), may be Upper Pliocene; howeve r, the verte brates point out to a Serravallian to Tortonianage. "Sr~Sr ages on oysters from above the level with vertebrates point ou t to 3.0(+2.5-1. 0) Ma. Similar sand deposits occur atMorgad inho (Luz de Tavira). These sands are ove rlain by marls, lign ite clays, lacustrine limestones and a silty calca reous crust. Asmall mammals association indicate an age span between Upper Pl iocene and Lower Middle Plei stocene (M N 17.MN20). A Biharianmammal fauna (Lower Pleistocene) was collect ed at Algoz in similar depos its. In the present stale o f kno wledge, Mo rgad inho andAlgoz deposits may be correlative.
RESUMO
Palavras-ch a ver Neogenico; Bstratigrafia; Algarve; Portugal.
Apresenta-se uma sintese sobre 0 Neoge nico do Algarve. Dataeccs de "Sr~6Sr, bern como dad os biostratigrafico s de unidadesmiocenicas, pennitiram 0 estabe lecimento de urn novo qua dro estratigrafico para as unidades liticas alg arvia s. A Formacao deLagos -Portimao corrcsponde a depositos sedimentares de tipo "plataforma carbonatada tempera da" que se dcscnvolveu durante urnlongo intervalo de tempo (Burdigal iano inferior a Serravaliano superior). Uma mudanca maie r na scdirnentacao (ambie nressilici clasticos) deu-se no Tortonian o inferior com a deposicao de areias finas amarel adas .
No interior do Algarve oco rrem espongolitos rieos de microfosseis. A idade nao este perfeitamente definida. Foraminiferosindieam a zon a N16 (Tortoniano inferior) e os Nanofosseis calce nos a zona CN5a (S erra valia no superior) .
No Tortoniano superior a sedimc ntacao foi ma is significativa no Algarve Oriental, em re tacac com 0 enchi me nto da bacia doGuadalquivir. Os depositos iniciam-se por calcarios detriticos, locahnentc multo ricos de Ileterostegina, qu e passam a conglomeradose silt itos muito foss ilifcros (Formacao de Caccia).
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I" Ccogressc sobre 0 Cenozcico de Portugal
o conglomerado grossciro de Galvana (Faro) poe alguns problemas. uatecees KJAr de glauconite indicam 6.72±O. 17 Ma.Todavia, a glauconi te podc tcr sido remobilizada a partir de niveis mais antigos (Formacao de Cacela). Parecem ester relacio nadoscom memento de forte instabilidade tectcruca como 0 da instalacao do olistostroma do Guadalquivir.
o Pliocenico nao csta bern caracrcrizado . As areias de Olhos de Ague com uma intcrcalacao marinha pouco espcssa , rica devertebrados marinhos (peixes, urn crocodile. cetaceos, sircnidoos) possivelmcntc redepositados, pede corrcs pondcr ac inicio doPfiocenico superior; eontudo , os pcixcs, marnlferos marinhos e 0 crocodile apontam para 0 Serravaliano a Tortoniano inferior.Datacces 17SrJ1"Sr cfecruadas em ostras e em dentes de pcixc fomcccram vatores de 3.0(+2.5-1.0) Ma. Arcias do mesmo tipoocorrem em Morgadinho {Luz de Tavira). Sao sobrepostasper margas, argilites lignitosos, calcarios lacustres e uma crcsta carbonatada.Os argilites lignitoscs fomeceram fauna de pcqucnos mamiferos corrcspondcnte eo intervale Plioccnico superior a parte inferior doPlis roccnico medic (tvrN 17-MN20). Em Algoz foi recolhida uma fauna datada do Pllstocenlco inferior (Bihar iano) em depos itossernelhantes. Epossivcl que as jazidas de Morgadinho e de Algoz sejam correlat ives.
FOREWORD
The first studies about the Cenozoic of Algarve dealtonly with some fossil localities and deposits (Pereira daCosta , 1866 ; Dollfus et at., 1903·1904; Bourcan &Zbyszcwski, 1940; Chavan, 1940; Zbyszewski, 1948;1950).
In 1979, M.T. Ant unes and 1. Pais, carried outstratigraphic studies on the Neogene ofAlgarve (Researchline n" I of the former "Centro de Estratigrafia cPaleobiologia da Universidade Nova de Lisboa"}, Somesynthetic interpretations have been published (Antunes etaI., 1981; Antunes et aI., 1990; Antunes et al., 1992). Newdevelopments have been achieved concerning mainly 87Srl!IIISr isotopic dating at the Department of Earth Sciencesof Cambridge University (Table 1, Fig. 1). A revision isunder way taking into account all the available data, andspecially isotopic ages, micropaleontology and sequencestratigraphy analysis.
At the present status of knowledge, the Neogene unitscharacterized so far are mainly of Miocene age and mostlymarine. They range from Lower to Uppermost Miocene.However, there are lithological differences. Olhos de Aguasands could be ascribed to the Pliocene based on ~7Srfl6Sr
dating, bu t this needs to be con fir med . T hose ofMorgadinho (Antunes et at.; 1986e) may (at least in part)be Pliocene in age.
The Neogene units so far recognized in Algarve areshown in the Fig. 7, and will be discussed by chronological order.
Pereira de Sousa (1917; 1918; 1922) admitted the presence of Miocene igneous rocks in Algarve although thesewere not found later. In 1971, a small basanite outcropenclosed by Miocene biocalcarcnites was detected, showing clear evidence of low grade thermal effects on the sedimentary rocks along the contact with the igneous dike.This rock represents the latest volcanic activity in Portugal(Pin to Coelho & Bravo, 1983). However, Cenozoicvolcanic activity is well known in Southern Spain, sinceLanghian-Scrravallian till the Quaternary.
Tectonic struc tures concerning the Mesozoic andCenozoic deposits of the Algarve basin allow to recognize the following alpine orogenic events : Jurassic (UpperTriassic at least) - Lower Cretaceous N-S distension;E·W distension during Lower to Upper Cretaceous; N-Scompression during the setting -up of the Monchiqucsyenite dome at the uppermost Cretac eous; Paleogene
278
compression (only locally? - at the Albufeira salt dome);Lower and Middle Miocene N-S and E-W distension;Tortonian N-S co mpress ion; post -Messini an E·Wcompression; N-S compression during the Quaternary.
rs Mem Moo;z Fo" m 12.5(_1.1+0.7) 0.7088)1 0.000016,
-';" .j!i!
' ~
/},'<,,".]
Fig I - Geological schematic map of Algarve.Numbers - Sr isotopes sampling localities.
Cuncias do Terra (UNL). 14
The NE-S W fract ures a ffecting th e Pa leozo icbasement are related to the first distension phases . Th emesozoic N-S distension is the main cause of the twoE-W flexures so far recognized . Th e tectonic inversi onoccurred after the setting up of the Monchique syenite. Ifth e Lo wer Cre taceous - Lo we r Mioc en e Albu feira 'sunconformity is a loca l effect of halokinesis, then the truetectonic invers ion o f the Algarve basin only took place inthe Lower to Middle Tortonian.
Th ese events corre late well with those known 10
southern Spa in and Morocco (Ku llberg et af., 1992).
L.AG OS - PORTIl\-1AO FORMATION
Th is Formation, first described by An tunes er al.(198 1), is the most evi dent M iocene unit in westernAlgarve. It makes up a sizable portion of the costal seacliffs, and is of considerable sce nic interest. It overliesCarboniferous, J urassic, Cretaceo us an d possib lyPaleogene units. In some places a very cle ar angu larunconformity can be obse rved, whereas stratigraphicalhiatuses or paraconformities may be recognized elsewhere.
The whole successi on has been much affec ted by karstphenomena.
The Lagos- Portimao Formation comprises yellow orpink massive and very foss iliferous biocalcareni tcs o f" warm temperate" platform type . Th e unit ends by anerosion surface , and is overlain by laminated sandstones,poor in foss ils.
At Olhos de Agua-Praia de Santa Eulal ia, a lenticularbody of sands tones with sand waves outcrop. I'Sr/uSrisotopic ages give 15.5(±OA) Ma taken for biocalcaren itesund er th e sands to nes (San ta Eu lali a beach ),14 .6(+0 .5-0.6) Ma for the sands tones and, above it,14.4(+0 .5-0.6) Ma.
In the lower part, well expose d at Praia do Cana vial(Fig. 3), mol luscs are p lentiful. As for the upper part, thereare many sea-urchins, Bryozoa, pcctinids and fishes. Thelocality of Cerro das Mos (Lagos), from where a largecrocodilian (Tomistoma) tooth was collected long ago(Antunes. 1961; Antunes er al., 198 1), has also producedsome Odontoceti teeth . These may be dated from theSerravallian, which, cons titute the oldest marine mammalocc urrence in Algarve (Estevens, 2000).
Pla nktic Foraminifera from the upper levels includ eGlobigerinoides trilobus, G subquadratus. G bisphericus,Gfoboquadrina baroemoenensis and cr. Praeorbulinatransttoria , which po int o ut to N7-N8( ? ) (U ppe rBurdigalian to Langhian) (A ntune s et 01., 198 1). Thepresence of Orbulina in b iocalcareni tes at the Faroborehole indicate that the Serravallian is also rep resen tedthere (Antunes er aI., 1984; Antunes & Pais, 1992 ).
A 17Srf'liSr isot opic age indicate 19.5(+0 .2.0.3 ) Ma(Lower Burdigalian) at Arrifiio (lower deposits, ove rlyingth e Cre tac e o us ) a nd 11.3 (+0 .9 - 1.3 ) Ma (Uppe rSerravaHian) at Praia da Gale (upper part) (Fig . 2). At Praiado Canavia l (Fig . 3), 17Srj86Sr from oyster and/or pcctin idshe lls indicates ages ofl7 .5(±O.7) Ma, 16.3(+0.5-0.3) Ma
279
1° Ccngressosobre 0 Cenozcico de Portugal
and 14.3(±0.5) Ma (Burdigalian to Lower Serravallia n).The upper beds at Praia da Rocha (Fig. 4) gave a 17 Srfl~Sr
age of 12.2(+1.2-1.3) Ma and 11 .5(+0.8-0.5) Ma (UpperSerravallian). At Aljezur, the lower levels (sands withoyes tcrs, outcroping at the "P avilhac Gimnodesportivo'')ind icat e 19.5(+0.3·0.2) and 18.5(±0.3 ) Ma, thuscorresponding to the Lower Burdigalian. At Igreja Nova,marls with biocalcarenites gave 16.9(±0.3) Ma and upperlevels. silstoncs and marls at Fuma Amarela, gave valuesbetween 12.6 and 9.8 Ma (Table 1).They may correspondto the great Serravallian transgression .
Nannoplankton (Reticulofenestra pseudoumbilicus andCalcidiscus p remacin tyrez) from the upper part of the unit(Albardeira, Lagos), also points out to a Serravallian age(NN6 or CN5 a) (Cachao, 1995).
On the other hand, this unit is older than the K-Ar datedglauco nite fine sands from Praia da Gale (10. I±O.25 Ma),as well as the sandstones from Praia da Rocha [' 7SrJl6Sr:10.7(+0.8- 1.2) MaJ.
MEM MONIZ SPONGOLITIIS
Overlying the Cretaceous in the inner Algarve there isan outc rop of white spongo liths virtu all y de void ofmacro fossils but containing microfauna. These depositswere originally described by Romariz et al. (1979. 1980b).They are unknown elsewhere in Portugal, but closely similar ones are widespread around the Mediterranean. Theyseem to have accumula ted in upwelling conditions in atrough related to tectonic events .
The rock is composed essentially of skeletal elementsof sponges. They also yielded some fish remnants alongwith large numbers of microfossi ls, including diatoms,calc areous nann ofossils (among others, Helicospheracarteri, Recticulof enestra pseudoumb ilicus, Coccolithuspelagicus, Cyclococcolithus macintyrei, Sphenolithusabies. Discolithin a multip ora ) (Antunes et al .• 1981 ;Cacbao, 1995) benthic (Nonion boueanum, Ammon ia,Bu!iminids , Bolivi nids, U viger inids ) and plan kticForaminifera, and Os trac oda (Au rila zby sze wskii,Nonurocythereis seminulum, Carinocythereis ga lilea)(Antunes et al., 1981; 1990; 1992).
Pl anktic foraminifera (Gl obigerina bulloides, G.quinqueloba , G. druryi, G. glutinata, Neogloboquadrinaacostoensis, Globigerinoides bulloideus) date these bedsat least fromN 16(LowerTortonianHAntunes etal. , 198 1;
. 1990; 1992). Ca lcareous nannoplancton indicate zone
CN5a of Bukry (upper Serravallian) (Cecbao, 1995). I7Srl" Sr age on planktic foraminifera is 12.5(+0.7-1. 7) Ma(Upper Serravallian) . Hence , the accurate age of thesedeposits is still open to discussion, albe it between rathernarrow limits.
Benth ic Foraminifera point out to shallow environments, rich in organic matter, and to low oxygen conte nts.
Such facies are quite alike some Upper Miocene onesin Sou t hern Spa in th at ove r ly th e Guada lquivirolistostrome.
FINE SANDS AND SANDSTONES
Th is unit is sepa rated from the Lagcs-P ortlmsoFormation through a disconformity,
It marks a major change from carbonated to siliciclasticsedimentation. Taking into account the isotopic ages from thelower levels, this change can becorrelated. with the begginingof the eustatic 2nd order cycle TB3 (Haq et al ., 1987).
The lowermost level at Praia da Rocha (Fig. 4) is aconglomerate with phos pha tic c lasts and gla uconite.Ostrea shells gave a 87SrJl6Sr isotopic age of 10.7(+0.81.2) Ma (Lower Tortonian).
Fine sands at the Hot el Auramar bea ch [l7SrfUSrisotopic age 9.5(+1.0-0.5) Ma] are considered correlativeof the unit Fine sands and sandstones.
At Praia da Gale. glauconite-ricb fine sands allowedK-Ar dating (1O.1±0.25 Me, Lower Tortonian) (Antuneset aI., 1984). Boski et al. (1995) obtained K-Ar ages fromthe same region 8,15±O,29 and 7,54±O,27 Ma.
CACELA FORMATION
The uppermost Miocene deposits arc wcll representedineastern Algarve, but they also outcrop near Lagos (westem Algarve) .
At Campina de Faro and Quelfes there are fossili ferouscarbonate rocks rich in detrital quartz; in some places thesedeposits grade into microconglomerates (Faro limestoneswith quartz pebbles and conglomerates).At the upper partof the Auramar Hotel beach there is a lower level of eonglomerates with oysters t hat gi ve a 17Sr/ IiiSr age of8.3(+2.2-3 .3 ) Ma. T hi s is in ag re emen t wi th th ebiostratigraphic datation ofthe lower levels ofCacela river(NI6-N I7) which begin by a conglomerate d irectlyoverlying the Triassic (Fig. 5). The Auramar conglomerate
Biocalcareme with bivalves (pedinids and ostreids) and echink1s(less abundart than the bivalves. except lor the last meter whereechinids predominate).
_14.3(~.5)Ma
• • • :0.,,;, .
arcceeereone. more compact than the previous levels, withbryozoans, bivalves (peclinids and oslreids ), gastropods andfragments of BChinids . ReddiSh ferrug inous concretions.
co10Et1.o.mEt:~
'"oj
Fig. 3 - Praia do Canavial section (Antunes et at., 1997).
281
1°Congresso sobre 0 Cenozcicc de Portugal
Praia da Rocha section
Fine yellow sandstone, with thin greyish, carbonaled crossed beds.h contains very scarce fragments of pectinids and echinids.
Reddish biocalcarenite.
Biocalcarenite with echinids, pec1inids , balanids and abundant largeostre lds.
Yellowish sandstone.
Compact greyish biocalcarenite, with more rossns than the previouslevel (balanids and pectin Ids more abundant; large echinids), but inlesser numbers than at the basal level. Ther e are yellowishsandstone Intercalations
Fine yellowish-orange, carbonate-cemented sandstone , withscattered and scarce fossils (pectinid and echinid fragme nts , balan idsand bryozoans).
Compact , yel lowish-orange biocalcarenite with abundant fossils :large pecti nids and echinids (fhe latter reaching 15 em in diameter) ,ostreid s, vertebra le ocoee, corals, gastropods, etc. It also showsbiOturbations and some ferruginized bivalve shells.
...._....
.'. .' .
· .. .'
· . ....
Fine yellow sandstone, with fossi ls similar to those of the secoodlevel but less frequent.
::::::::%:;:::::::::;.:::::: Fine yellowish-orange sandstone with intercalated ferrugi nous beds.: : :::;:::::::: : : :::.:::::~:: h contains pectinids and scattered small echinid fragments.
illl i·lllllfd:::I - 12.~+1.2-1.3)Ma
"-. Cong lomerate with phosphatic nodules and glauconite
1~ili.m: - 10.7(+O.S-1.2)Ma
_ Biocalcarenite with echinids and large sized pectinids.
10
20
1 5
,..".!!J::01Cj 5 _.
•. ~ .
m · . ' ;
" C ·8 .!!..:ii 01~ '6., ~
~ "III....
m25.,
e.,"" ~0 c:ii 0
~ 1::.,0eL t-eL
:>
. .
Fig. 4 - Praia da Rocha section (Antunes et al., 1997).
282
is interpre ted here as correlative ofthe lowermost depositsof Caccia Formation, which comprise mainly yellow,orange, or green glauconite silts.
The lower conglomerates at Cacela (Fig. 5) and thedirectly overlying silts yielded the richest and best preserved Miocene mollusk fauna in Portugal. Th is fauna wasdescribed by Pereira da Costa (1866, 1867) and Dollfus etal. (19 03, 1904), and revised by Chavan ( 1940) andBourcart & Zbyszewski (1940). Glycym eris, Cardium,Megacardita , Panopea, Pelecyora, Callista , Turritellids,Naticids, and Conus are common. There are also someVertebrata. Among the selacians,Carcharocles megalodonhas been recorded but no Carcharodon carcharias (bothspecies coexist in Pliocene when the latter appears for thefirst time, this association being known in Southern Spain- Elche, etc.) (info rm . of M. T. Antunes). Also, a fewprevio usly unr eported cetacean remains have beenco llecte d long ago at Caeela supposedly from theyellowish silt levels. These consist of vertebrae , rostrumand mandible fragments of large-sized Myst iceti, whichare deposited at the Geological and Mining Institute.
Olho s de Ague and Cerro das Mas occ urrences(refe rred to elsewhere), are the on ly localities in Algarvethat yielded fossils of marine mammals. Moreover, Cacciais one of the youngest records of marine mammals inPortugal; it is on ly a little older than the late Messinianremains from the Esbarrondadoiro Formation in AlvaladeBasin, Alentejo (Antunes et al., 1986).
As no accurately dated post-lower Tortonian miocenedeposits are known in the Lower Tagus Basin (where theremainder of the series is very well represented), theimportance of the Cac ela reco rd becomes obv ious .Foraminifera and Ostracoda [Audia (Cy mbaurila) diecci,A . gr. semilun ata, Cartn ocyihereis g alilea a ndNonuracythereisseminulum] are plentiful.
Pl ankt ic foram inifers a re suita ble fo r dating:Glo big e rina bullo ides , Globorotalia scuuta , G.pseudomiocenica, G menardii, G humerosa, G altisp iraand Neogloboquadrina acostaensis indicate N16-17 zonesof Blow (U pper Torton ian-Lower Messin ian). Thepresence of Sp iroplectam ina ca rinata (a ben thi cforaminifer) excludes a Messinian age for the lower levelsof the Cacela Formation (Antunes et al. , 1981;1990; 1992).
Calcareous nannoplancton from the lower beds includeDiscoaster berggrenii, Heli cosphaera sta lls, Miny lithaconvalis and Triquetrorhabdu lus rugosus (?) that also pointto the same Upper Tortonian age (CN9a zone of Bukry)(Cachao, 1995).
Somewhat higher levels (at Fabrica) yielded calcareous nanno pla nc ton (Coccoli thus p elag icus ,Reucu lof enestra pseudoumbilica, R. minuta , R. minuuda,R. haqii, Diayococcnes antarct icus, Sphenolithus abies,S. morifo rmis , He licosp hae ra ca rteri, Eudiscoastersurculus , E. icarus, E. intercalaris, E. pseudovariabilis,Triquetrorhabdulus rugosus) and plankt ic Foraminifera[Glob igerina bulio ideus , G. ap ert ura , G. dru ry i, G.quinqueloba, Globigerinoides extremus, G seigliei, Gquadrilobatus, Globigerinita gl utinata, Orbulina universa,O. su turalis , Globoq uadrina glo bosa , Globorotalia(Hirsutella) scitula, Neogloboquadrina acos taensis sin.]
Cu nctas da Terra (UNL), 14
that may be ascribed to Late Tortonian-Messinian (Antuneset al. , 1990) . Be nt hic Foram in ife ra (B olivi nids ,Buliminids) indicate oxigen-poor environments (Antunesetal., 1990).
These beds are overlain by si lty or fine sand beds instratigraphical continuity with scarce , poorly preservedfossils including some plant remnants. Upper beds maybe Messinian in age .
The middle, also silty, levels of Cacela Formation areric h in gla uconite that gave ages of 6.90±0. 18 Ma(Galvana) , 6.88±O.5 (Quelfes)and 7.03±O.4 Ma (near Luzde Tavira), uppermost Tortonian (Antunes et al., 1984,1986d ; 1990; 1992). i
7Srl"Sr ages from the Quelfes siltsare 5.3(+4.3 -0.7); 5.2(+4.4- 1.1) and 5.2(+4.4-0 .6) Ma(Fig. 7) . At Q uelfe s, above the glauco nite level, theoccurrence of Globorotalia men ardii (100% dext.) andGloborotalia miotumida (100% sinist.) allow correla tionwith the event 3 from the Guadalquivir basin (Sicrro etal., 1985, 1993, 1996). This event has been correlated withtheTortonian/ Messi nian bo undary. Glo borotaliaconorniozea (FAD7 .12 Ma, Messinian) was found at theuppermost levels from Quelfes region.
The upper deposits of the Cacela Formation overlieferruginous hardgr ound. They correspond to confinedmarine environmen ts, fossi ls being scarce and poorlypreserved. The age may be Messinian to Lower Pliocene.
',G ALVAN A CONG LOM ERAT E
The stratigraphic position of the spectacular Galvanaconglomerate, with striate blocks exceeding one meter,and interbedded glauconiferous silts (Antunes et aI., 1984),is not clear. Glauconiferous silts indicate a K-Ar age of6.72±0. 17 Ma; however, the glauconite may have beenreworked from the Campina de Faro silts (Antunes et al.,1984; 1990; 1992).
Conglomerates are related to strong tectonic instabili tyand were prob ab ly form ed in the sub-masine slopesassociated to the Algarve southern flexure. The K-Ar ageis compatible with that of the Guada lqu ivir basinolistostrome, although this is far away and corresponds toSouth-North sediment mass movements (the Galvana conglomerate has been generated by North-South sedimentmovements).
Conglomerates overlying glauconitic silts in a boreholeat Campina de Faro, may correspond to the Galvanaconglomerate. If so , this is younger than the silts and itsage could be Messinian or Pliocene.
OLIIOS DE AGUA SA NDS
A thick sand series outcrops ncar Olhos de Aguebetween the Sandsto nes with sand waves and the FaroQuarteira Fonnation .
The Olhos de Ague section originally described byRomariz er er. (1979-1980a), was recently revised (Fig.6) . The successi on starts by alternating sandy and peliticlayers (flaser facies) overlain by cross-bedded brownishsands and followed by feldspathic, fluviatile white sands .Locall y, the brownish sands outcrop in water-erode d
gullies and are covered by red pel ites. The latter areoverlain either by white sands or by the Faro-QuertciraFormation (Quaternary). Over these white fluviatile sandsthere are beach sands and conglomerates with abradedremnan ts of aquatic Verteb rata (fish vertebrae and teeth,cetacean bones, Sirenian teeth and bones). The majorityof the fishes a re marine, often very large in s ize(Carcharocles megoiodon.lsurus hastalis, Odontaspis cftaurus, Hemipristis serra, Carcharhinus sp.). The degreeof abrasion of the vertebrate remnants suggests that theywere rolled by waves in shallow, sandy bottoms at a beach.The Sirenians (Metaxytherium medium) point out to warmshallow seashore environments, rich in aquatic vegetation (algae, vascular plants) . The prese nce of fish likeLares,also frequent in fresh water facies suggests (as wellas the feldspathic sands) the existence of a large riverwhose mouth was quite close by. The presence of largecrocodil ians as Tomistomacf lusitanicacorroborates theseviews and indicates tro pical to sub-tropical conditions(Antunes, 1979; Ant UReS et al., 1981; 1990, 1992).
Above these levels there are sands rich in oysters andscarce pectinids - includi ng the rare Paliol/um(Lissochlamys) excisum. Molluscs indicate estuarine. evenbrackish environments.
Vertebrata are compatible with a post-Langhian age;they are certainly pre-Plioce ne and they may correspond
to the Serravallian or to the Tcrt onian. The mollusks arenot chronologically charac teristic. However, Palio/lum(Lissochlamys) exctsum is known both in Upper Mioceneand Pliocene (Demarcq, 1979) (it is common in UpperPliocene in western Portugal). 11S rl"Sr age obta ined fromoysters gave 3.0(+2.S· 1.0)Ma. However this value has tobe taken caut iously since it corresponds to a brackishenvironme nt, with broad errors.
M ORGADI NIIO AND ALGOZ DEPOSITS
This unit comprises thick sandy deposits in assoc iation (towards the lop) with marls, lignite clays, lacustrinelimestone and a silty calcareous ernst This unit is poorlyexposed in outcrop, for which most observations have beencarried out during the excavat ion of water wells.
At Morgadinho and Luzde Tavira these sands overly theCaccia Formation and arc overlain by the Faro--Qliart:eirasands, as at Algoz (where the basement is not known).
At Morgadinho, the lignite clays yielded a few smallmammals (Ga/emys Icormosi, Prolagus cf catpensis,Mimomys sp. and Muridae undetermined), fres hwatersmall cyprinid fisbes, gastropods, Ostracoda, pollens andspore s (including Anthoceros , Kesette rta . Pinus.Cupressacea and Ericaceae) (Antunes et aI., 1986c). Th e
284
Ciencias da Terra (UNL) , 14
Olhos de Agua sect ion
on-ec..on..~
01...m-eonos:5
Very thn sands wiltl pelllic layers,
Dal1< red sands wiIh cross stratification and pebble layers ,
Dark reddiSh d ays.
- 3.0(+2.5-1.0)Ma
.. .~~ jbi White sands with crossstratification.. : ' : .: ' l" ~ '
Fig. 7 - Stratigraphic frame of the Algarve Cenozoi c .
286
mammalian fauna ind ica tes an age span between the Upper Pliocene and the lower Mi dd le Ple istocen e (MN 17 toMN 20 mammal units).
In the present state of knowledge. M orgadinho andAlgoz deposits seem to be co rrelat ive . The Al goz mam-
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