pp.199-208.. ·4 Figs., ·1PI.

Upper Miocene planktonic foraminifera from Algarve.Chronostratigraphical implications

Paulo Legoinha

Work supported by the Project "Studies on Portuguese Paleontology (Post-Paleozoic)" (POCTl/CYT/3635 1/99-00)Centro de Estudos Geolegicos (FCTIMCT), Universidade Nova de Lisboa, Faculdade de Cienc ias e Tecnologia , Quinta da Torre, P-2825-114

Caparica , Portugal ; pal@fct.unl.pt

Abstract

Key-words: Planktonic foraminifera; biostratigraphy; isotopic ages; chronostratigraphy; Upper Miocene; Algarve (Portugal).

New data on the planktonic foraminifera from the Upper Miocene Cacela Formation and Mem Moniz spongoliths are presented.The coiling type of Globorotalia menardii from Cacela and Quelfes and the occurrence at Quelfes of G. miotumida allow

correlation with the bio-events I to 3 (7,512 to 7,24 Ma; Sierro et al., 1993; 2001) that have been recognized in the GuadalquivirBasin (Spain). The presence of Neogloboquadrina acostaensis and N. humerosa at Mem Moniz points out to the Upper Miocene(Tortonian, upper N16, or even NI7). Mem Moniz spongoliths are correlated with the Cacela Format ion.

Some 87Srj86Sr isotopic ages ofmollusc or foraminifera shells don't fit well with finer biostratigraphic record and present wideerror margins.

Resumo

Palavras-chave: Foraminiferos planct6nicos; biostratigrafia; idades isot6picas; cronostratigrafia; Miocenico superior; Algarve(Portugal).

Sao apresentados novos dados acerca da biostratigrafia do Miocenico superior do Algarve (Formacao de Cacela e espongolitosde Mem Moniz). Os foraminiferos planct6nicos de Cacela e Quelfes, em especial 0 tipo de enrolamento de Globorotalia gr. menardiie a ocorrencia de Globorotalia miotumida (em Quelfes) permitem correlacoes com os bio-eventos 1 a 3 caracterizados na Bacia doGuadalquivir (7,512 to 7,24 Ma; Sierro et al., 1993; 2001). Neogloboquadrina acostaensis e Neogloboquadrina humerosa nossedimentos de Mem Moniz permitem data-los do Miocenico superior (Tortoniano , parte superior de N16 ou mesmo N17) ecorrelaciona-los com a Formacao de Cacela.

Verifica-se desfasamento entre a inforrnacao biostratigrafica, mais fina, e datacoes 87Sr/86Sr, que evidenciam grandesmargens de erro.

Introduction

A comprehensive study ofthe chronostratigraphy oftheMiocene ofPortugal has been carried on. A synthesis on theNeogene ofAlgarve has been presented (Pais et ai., 2002) .

The author has studied the Miocene planktonic foraminiferafrom the Lower Tagus Basin and Algarve (Legoinha,200 I). In this paper new data are presented on planktonicforaminifera from the Upper Miocene ofAlgarve, especiallyfrom Cacela Formation and Mem Moniz spongoliths.

199

Ctsncias do Term (UNl. ), 15

The Cacela Formation (Antunes in Ribeiro et 01. , 1979)is exposed in eastem Algarve (Cacela, Quelfes). Basal levelsare conglomcrates and limeston es with pebbles. Upwards,there are muddy or calcareous, often glauconite-rich sands.This Formation contacts by angular unconform ity withthe Triassic and by disconformity with the Lower to MiddleMiocene, Lagos-Port imao Formation.

W hi te spo ng o li ths w it h d iatoms , c al careou snann op lankton , foramini fera, ostracoda and fishes out cropat Mem Moni z (Espcngolitos de Mem Moni z; Romari z etal. , 1979) . T hese deposits fill a tectonic depre ssion . Theconce rne d un it was ascribed to the Serra va lian o rTortonian . However, several different age values had beenproposed. Chronology can be sett led now . Sediments likethese are unknow n elsewhere in Portugal.

The aims o f this study are:

a) to review the published data concerning the planktonicbiostratigraphy ofCace la, Quelfes and Mem Moni z;

b) to discuss new pla nktonic fora minifera data and" SrfMSr ages;

c) to improve the Upper Miocene chronostratigraphicknowledge ofthe Algarve;

d) to esta blish correlations with the bio-events definedin the Guadalquivir Basin (Sie rro et al.; 1996).

Samples for foraminiferal study were disaggregatcdwith a HP 2solution , and washed in a 125 urn sieve.

CacelaLocation

Outcrops near Cacela (Fig. I). GPS coordinates: N 37"09' 46" , W 7" 32' 48 ,6". The upper part can be observedat the locality named Fabrica.

Geological setting

Cong lomerates and fine yellowish-gray sands tonesout crop at Ribei ra de Caccia, corresponding to the basallevels ofthe Caccia Formation, Lower member.At Fabrica ,there arc fine yello wish-orange sands intercalated withlevels of carbonate concretions, the upper membe r o f thesame Format ion (Antunes et 01., 198 1).

Cacela yield ed the richest and best preserved Miocenemollusk fauna in Portugal. Th is fauna was described byPereira da Co sta (1866; 1867), Cotter (1879 ; in Do llfus et01. , 1903- 1904; in Cho ffat, 1950), Chavan in Bour cart &Zbysz ewski (1940), Frencix ( 1957) and Brebio n (1957).

In the last 30 years, a systematic study ofthe Algarve'sNeogene have been carried on by resea rchers ofthe Centrode Estudos Geologicos , often in co llabora t io n wit hforeign co lleagues. T he knowled ge on paleont ology,stratigraphy and chronology has been impro ved (essentialdata concerning Cacela, Antunes et 01. , 1981; Antunes etal., 1990 , 1997; Go nza lez-Delgado et al., 1995; Pais et01. 20 00;G onzal e z- Delgado & Civ is, 2000 ; Civi set al., 2000).

200

Fig. I - CacetaFormation (Geological Map of Algarve, 1:100000;Manuppella, 1992): Ribcira de Cacclaand Fabrica outcrops.

Bizon (in Antunes et aI., 1981) found Globigerinoidesextremus, Globorotalia aff conomiozea, Globorotaliapseudomiocenica, Globotalia menardii, Globorotaliaacostaensls (sinist. ) and Globorotalia humerosa (sinist.)that ind icate the top ofN I6 or, probably, N 17.

Sicrro (in Antunes et aI., 1990) identified abundantp lanktonic foramini fera a t Fabrica, among othe rsGtob igerinoides extremus, Globigerinoides seigliei eNeogloboquadrina acostaensis (sinist.) . The presence ofthe benthic Spiropleclammina carinate, which disappearsin the basa l Messini an, wa s remarked . The foraminiferalassemb lage poi nts out to the Up per Tortonian.

According to Nasci mento (in Antunes et al., 198 1),the Ostracoda indicate a Messin ian age.

P lankton ic Foraminifera and biost ratigraph ic analysis

Th e samples Ribci ra Cacela 2 and Fabri ca 2 (Fig . 2)gave add itional important dat a.

Ribei ra Caeela 2 y ie lde d s inis tral menardi formGloborotalia. In the Guadalquivir Basin , Sierro (19 85)and Sic rro et al. (1993) charac terized a succession ofbio-events . The fi rst one is th e sharp reduction ofGloborotalia menardii g roup I (s inis t.). The secondone is marked by th e appearance o f Globoro ta liamenardii gro up II (dext.). Between these events, thetemperate waters of No rth Atlantic and Medite rraneanwere almost deprived of keeled Globorotalia (Sierro eta/., 1993, p.l 43).

Fabrica 2 yielded a rich and diversified planktonicassemblage, that does not include keeled Globorotalia.This assemb ladge comprises (Antunes et 01., 1990) :Globigerina bulloides, Globtgerlna apertura, Globigerinad ruryi , Globigerinita glutinala, Glo bigerinoidesbulloideus, Gloh igerin oides extremus, Globigerinotdesseigliei, Globigerinoides immaturus, Orbulina universa,Orbulin a sutura lis , Globig er in a q uinq ueloba ,G loboqua dr ina globo/ a , Globorotalia scit ula,Neogloboquadrinaacostaensis (s inist.).

a:Inozoa::r:u

m

10

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...: ~ ... .. .. .. - ... .... .. .- .• • • • • • M _ • • • • • • ••

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Ciencias da Terra (UNLJ, 15

Lit hostratigraphy

Yellowish sandstone.

~N

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...CIl CQ. .!!!Q. c:::::J 0 I'­

t:: ~

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co0>Zo

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Fine, yellowish-orange sandstone withcarbonate concretions. Scarce fossils .

Fine yellowish-gray sandstones with abundantforaminifera. bryozoa, bivalves, gastropods andfishes.

5.7{+3.9-1.1)MaFine yellowish-grey sandstone.

Conglomerates wrth abundant fossils: mostlytarqe-sized molluscs, cirripeds.

c:::o

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Fig. 2 - Cace la sec tion: chronostratigraphic framework; correlation with bioevents from the Guada lquivir Basinand I7Srl'6Sr ages .

Cace la 2 and Fab rica 2 age is between that of the events1 and 2 ofthe Guadalquivir Basin (respectively 7,512 and7,35Ma astronomic ages; Sierro et al., 2001).

Isotop ic ages

17SrJ'6Sr age ofa biva lve mollusc gave 5,7 (+3,9 -1,1)M a. T his age seems too young in comparison withbiostrat igraphic da ta. Furthe rmore the margin of error isvery wide. This could suggest that the calibration curve isnot well established for this span of time,

Q uelfesLocation

Samples were collected at some outcrops near Quelfes(Fig .3). GPS coo rdinates: N 37° 03' 18,3"; W 7° 49' 52,6".

Fig. 3 - Quelfes (Geological Map of Algarve, 1: I00 000;Manuppella, 1992): the arrow points out to the location of the

studied outcrops.

201

Ciencias da Terra (UNL). 15

Geological sctt ing

San ds and marl y s ilts , o ften with bi o turba tionstructures, are ex posed. A g lauc on ite-ric h leve l wasrecognised in the upper part. Basal bed s are co nglomerat iclimeston es wi th siliceo us pebb les and limestone boulders.

Th ese de pos its belong to the Cace la Fo rm at ion.Neogloboquadrina acostaensis (si nist. predom ina nce ),Globigerinoides extremus and some keeled Globorotalia(dext. predom inance) point out to the Upper Tortoni an .S ierro (ill Antunes et al., 1990) stressed the possibilitythat the upper levels could be Messin ian in age. Incomparison with Guadalquivir Basin, the age ofconcerneddepo sits is sometime between events 2 and 3 (Sierro, 1985;Sierro et 01., 1993).

Pla nktonic Fo ra min ifera and biostra tigr aphic ana lysis

Sa mples Q2 and Q4 are the richest in p lank ton icfo ra mini fer s, w hil e Q3 is the less rich (Fig.4) . T hefollowing spec ies were identified:

Q 1 - Dentog lobigerina altisp ira , Globigerinoidesbulloideus, Globigerinoides conglobatus , Globigcrinoidesex /rem us, Neoglo bo q ua drina humerosa, Orbulinauniversa.

Q2 - Dentoglobigerina altisp ira , Globigerina bu lloides,Glob igerina p raecalida , Glob ig erinoides bulloideus ,Glob igerinoides conglobatus, Globigerinoides extremus,Globigerinoides se igliei, Neogloboquadrina humerosa,Orbulina sutura lis, Orbulina univers a.

Q3 - Globigerinoides bulloideus, Globigerinoidesseiglie i, Orbulina suturalis, Orbulina universa .

Q4 - Globigerina bu lloides , Globigerina concina,Globigerino ides bulloideus, Globigerinoides elongatus,Globigeri no ides ex tremus, Glo bigerino ides seigliei,Globo ro la lia g r. men ardii (de xt. ) , Glo bo ro ta liam io t urnld a ; Neogloboquadrina a c os t aens is ,Neogloboquadrina humerosa, Orbulina uni versa.

Q5 - Globigerina bulloides, Globigerina dru ry i ,Globigerinoides bulloideus , Globige rinoides trilobus,Globorotalia cono miozea , Orbu lina sutura lis, Orbu linauniversa.

Biostratigraphi c interpretation is shown (Fig. 4) . In thelower pa rt, N. humerosa e G conglobat us ind icate theUpper Tortonian (prob ab ly N 17). In the upp er part Gmi otum ida an d G. co nomiozea poin t o ut to theMess ini an (N 17) . Glo bo rota lia gr. men ard ii (dext.)is st ill present in the Q4 sample . Thi s suggests th atthe co ncerned levels may be correlated to the event 3 ofth e G uad alqu ivi r Basin , marked by the repl acem entof the G menardii group by the G miotumida gro up(Si erro et 01., 1993).

202

Isotopic ages

Shells of mollu scs from different Icve ls were date d" Sr/"Sr: 5,3 (+4, 3-0,7 ) Ma, 5,2 (+4 ,4 -1 ,1 ) Ma, 5,2(+4 ,4 -0 ,6) Ma. T hese agcs seem too m uch youngerthan the ex pec ted age 7 (+1 - 1) Ma as established byBerggren et 01. (1995) for N17 . Let us recall that KlArg lauconite age for two samples from Lu z de Tavira(co rrelative of Quelfes) is 6,88±0,4 Ma and 7,03±0,4 Ma(Antunes et 01., 1986). Age of event 3 is 7,24 Ma (Sierroet 01.,2001).

Me m Mo nizLocat ion

Outcrops at Mem Moniz (Fig. 5) tha t border thenational road EN395.

Gcologica l setting

Withish sediments wi th some teleostean fish remnan ts(bo nes and sca les) and high abundance o f microfossil s(spo nge ske leta l ele men ts , d iatoms , ca lca re o usnannofossi ls, planktonic foraminifera and ostraco ds). Thelowercon tact is an angularunconformity over Cretaceousunits (Romariz et 01., 1979; Antunes et 01., 198 1). Th estra tig raphic posi tion has been object of controversy.Sediments like these are unknown elsew here in Portugal.In Sp a in, s imilar sed iment s are kn own to overlie theGuadalquiv ir olistostrome.

Prates (ill Romariz et 01., 1979) ascribed the MemMo niz dep osits to the Up per Burd igali an o r LowerLanghian (N8 or N9) on plank tonic foramin ifera.

Ac cordi ng to Bizon (ill A ntune s et 01., 1981 ),Glo borota lia ac os tae ns is (s inis tra l) po in ts out to aTor tonian , N 16 age.

Sierro (ill An tunes et 01., 1990) stressed that the pre­do minance of Globigerina bulloides in association withNeogloboqua drina acostaensis , Glob igerino idesbu llo ideus , Globigerina druryi, Globige rina quinquelobaand Globigerinita glutina ta ind icates at least N 16.

T he se sed ime nts were a sc r ib ed to th e M idd leSerrava lli an (CN5a) o n calca reo us nan nop la nkt on(Cachao , 1995).

" Srl" Sr age on plank tic foraminifera wa s ob tained:12.5 (+0.7- 1.7) Ma, Upper to Middle Serrava llian (Ant uneset 01., 1997).

Planktonic Foraminifera and biostratigraphic anal ysis

Four samples were s tud ie d. T he p lankton icforamin ifera frequence dec reases from the lower to themiddle part of the succession . They are more abunda ntaga in in the upp er par t. Foraminifera are well preservedbut are sm aller than usual.

The foll ow ing spec ies were identified : Globigerinaangustiumbiltcata, Globigerina bulloides, Globigerinaconcina, Glob igerina dru ryi , Globigerina falconensis ,

Cicncios da Terra (UNLi. 15

>- Planktonic ForaminiferaIn, >- "« J: $ ;ia: e, .!!] CD

o « :g CD :2-I- a: CD e :es s-c C:l '" " CD CD ca: i= 8 E ~ E c: ~ ~ (jj iii

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Fig.4. Chronostratigraphic framework of the Quelfes section; occurrence of planktonic markers, correlation withbioevents from the Guadalquivir Basin, and 11S rJS6Sr ages.

203

Ciencias da Terra (UNLJ, 15

MemMoniZspongoIiths:

sampled_ crops

Iso top ic ages

The " Srl'''S r p lankto nic fo raminife ra she ll age isseemingly too old - 12.5 (+0 .7·1.7) Ma (Midd le to UpperSerravall ian). This age is not supported by biostra tigraphicinforma tion and should be rej ected.

Con cl us io ns

I) Planktonic foraminifera and espec ially the coi ling typeof Globorolalia menardii gro up and the occurrence ofGloborotalia miotumida at Quelfes a llow corre lation withthe I to 3 bio-events in the Gu adalq uivir Basin (Sie rro et01., 1993).

2) Cacela and Fabrica may thus be da ted from the timespa n between Guada lquiv ir basin's events I and 2 (7.512and 7.35 Ma; Sierro et 01. 200 I).

Fig. 5 • Spongolithsat Mem Moniz (Geological Map ofAlgarve, 1:100000; Manuppella, 1992).

Globigerinella aequilateralis, Globigerinoides bulloideus ,Globoquadrina baroemoenensis, Neogloboquadrinaacostaensis (si nist.), Neogloboquadrina humerosa(sinist.).

N. acostaensis and N.humerosa point out to uppermostN 16 or even N 17. This age should be older than 6 Ma(Upper Messi nian), as the N. acostaensis co iling directionchanged to dex tral coiling. The absence of ca rinateGloborotalia do no t a llow a better biostratigraph icacc uracy.

The presen ce o f Glob ig erina drury i co uld beproblema tic. T he last appearance dat um is genera llyregarded as Upper Serrava llian (NI4), but Sierro (1984)has shown that it still occurs in the Guadalquivir Basin inthe Upper Miocene and Lower Pliocene.

This assemblage undoubtedly is Upper Miocene inage. Hence the Mem Moni z sed iments are of the someage as the CaccIa Formation. The correlation betweenQuc lfes ( lower part) and Cacc ia is most likely. Thischrono logy is ncar the same as that of similar deposits inperi-medi terranean area, i.e. Spain, Ita ly and Argelia.

References

3) At Quelfes , Glob orotalia miotumida and G menardii(dex t.) may be co rrelated to event 3 (7 .24 Ma) .

4 ) In th e upper part of th e outc rop , Globorotaliaconomiozea suggests a Messinian age (FA D 7. 12 Ma;Berggren et al., 1995).

5) Glauconite KiAr ages from Luz de Tavira sed iments,that can be correlated to those of'Quelfes, yielded 6.88±OAMa and 7 .03±OA Ma; these ages fit well with theplanktonic biostratigraphy.

6) Mcm Moniz spo ngol iths can be asc ribed to the UpperMiocene, Tortonian, upper part ofN I6 or N 17.

7) There arc im portan t differences between thebiostratigraphic information and the S<'"/Sr" ages whoseerror marg ins are quite broad.

Acknowledgements

I am gra teful to Prof. M. Telles Antunes for helpfulreview of this paper. I thank Prof. Joao Pais for aid andcooperation on field work and SEM photography.

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Antunes, M. T.; Odin, G & Pais, J. (1986) . Ages KIM de glauconies des environs de Luz de Tavira, Algarve. Ciencias da Terra(UNL). Lisboa, 8: 22·30.

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Pais, 1.; Lcgoinha, P.; Blderfield, H.; Sousa. L. & Estevens , M. (2000) - The Neogene of Algarve. Ciincias da Terra (UNL),Lisboa,14: 277-288.

Pereira da Costa, F. A. (1866) - Molluscos fcsseis/gasterepcd es dos depositos terciarios de Portugal. Comissao Geologica dePortugal. 10 Cademo, 116 p.

Pereira da Costa, F. A. (1867) - Mclluscos fessei s/gasteropodes des depcs uos terciarios de Portugal. Comissao Geologica dePortugal. ZO Cademo: 117· 252.

Ribeiro, A.; Antunes, M. T.; Ferreira, M. P.; Rocha, R.; Soares, A F.; Zbyszewski, G ; Moitinho de Almeida, F.; Carvalho, D. &Monteiro, 1. H. (1979) - Introduction ala Geologie genm.le du Portugal. Serv. Geol. de Portugal. Lisbca; 114 p.

Romariz, C.; Correia, F. & Prates, S. ( 1979) . Contributions to the geology ofAlgarve, Portugal. III - Un nouveaux [sic] facies duMiocene. Bol. Mus. Lab. Min . Geol. Fae. Ciene. Lisboa , 16 (I): 265-27 1.

Sierro, F.J. (1985) - The replacement ofthe Globorotalia menordii group by the Globorotalia miotumida group: an aid to recogniz ingthe Tortonian-Messinian boundary in the Mediterranean and the adjacent Atlant ic. Marine Micropaleon/ology , 9: 525-535 .

Sierro, F. J.; Flores, 1. A.; Civis, J.; Ijonzalez-Delgado, J.A. & Frances, G ( 1993) · Late Miocene globorotaliid event-stratigraphyand biogeography in the Ng-Atlantic and Mediterranean. Marine Micropaleon tology, 21: 143-168.

Sierro, F. J.; Hilgen. F.J.; Krij gsman, W. & Flores, 1.A. (2001) - The Abad composite (SE Spain): a Messinian reference sect ion forthe Mediterranean and theAPTS. Paleogeography. Paleoclimalology, Paleoecology, 168: 141-169.

205

Cibu:ias cia Tara (UNL), IS

Plate 1

Planktonic foraminifera. Scale. 100 um,

Fig. 1 - Globorotalia miotumida Jenkins, 1960; Quelfes section.

Fig. 2 - Globorotalia gr. menardii (Parker. Jones & Brady, 1865); Quelfes section.

Fig. 3, 6 - Neogloboquadrina humerosa (Takayanagi & Saito, 1962) ; Mem Moniz section.

Fig. 4. 5 - Neogloboquadrina ocostaensis (Blow. 1959); Mem Moniz section.

Fig. 7, 8 - Globorotalia (G) conomiozea Kennett, 1966; Quelfes section.

Fig. 9. 10 - Globigerinoides euremus Bolli. 1965; Quelfes section.

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Ciencias da Terra (UNL ), 15

PLATE 1

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