The Transversarium-Bifurcatus Zone boundary at Rocha (Peral area, East-CentralAlgarve, Portugal)

B.MARQUES * F. OLORIZ ** F. J. RODRIGUEZ-TOVAR ** P. S. CAETANO *

* - Centro Estratigrafia e Paleobiologia da UNL, Faculdade de Ciencias e Tecnologia, Quinta da Torre, P-2825 Monte de Caparica, Portugal ** - Dpto. Estr. Paleont., Fac. Ciencias, Univ. Granada and Inst. And. Geol. Mediterranea (LA.G.M.) 18002 Granada, Spain

pp. 109-125 Ciencias da Terra (UNL) Lisboa NQll 1992 3 figs., 2 pI.

zones Bifurcatus/Bimammatum a ete reconnue une autre discontinuite, correspondanta celledu type II quisepareles RESUMO cycles 4.3-4.4 de HAQ et al. (1987); cette discontinuite avait deja ete individualisee sur la marge sud de I'Iberie. Palavras-chave: Amonites - Macroinvertebrados Dans I' intervalle entre la partie superieure de la zone bentonicas - Biostratigrafia - Ecostratigrafia ­ a Transversarium et la partie inferieure de la zone a Descontinuidades-s--Jurdssico superior-Oxfordiano-:-­ Bimammatum,l'analysedel'evolutionecostratigraphique, Algarve- Sui de Portugal. faite a partir des spectres de la faune, a montre que dans I'ensemble des cephalopodes, les ammonites sont les Este trabalho representa 0 primeiro estudo organismesles plus tolerantsau stressecologique,provoque, pormenorizado do limite das Zonas de Transversarium­ soitparla diminution del'ecospace, soitpardes arrivees de Bifurcatus no Algarve. Este limite esta associado, na area materiel terrigene; dans ces conditions, la faune benthique do Peral, a uma descontinuidade estratigrafica cujo hiato diminue considerablernent. Dans l'ensemble de la faune afecta, parcialmente, as Zonas de Transversarium e de recoltce on signale la presence, relativement abondante et Bifurcatus. Uma outra descontinuidade foi reconhecida no diversifice, desDichotomoceras,auparavantpascommuns. limite das Zonas de Bifurcatus-Bimarnrnatum que, nesta area, coincide com a descontinuidade doTipo II que separa osciclos4.3-4.4 de HAQet al. (1987);esta descontinuidade tinha ja sido individualizada na paleomargem do suI da ABSTRACT Iberia. Uma analise da evolucao ecostratigrafica feita no Key-words: Ammonites-Benthic macroinvertebrates­ intervalo entre a parte superiorda Zona de Transversarium Biostratigraphy - Ecostratigraphy, Discontinuities ­ e a parte inferior da Zona de Bimammatum com base nos Upper I urassic - Oxfordian - Algarve - South Portu­ espectros de fauna obtidos revela que as amonites sao os gal. cefalopodes mais tolerantes ao stress ecologico causado pelo aumento dos acarreios de material e pela dirninuicao This paper represents the first detailed study of the do ecoespaco da plataforma. A fauna ben tonica diminuiu Transversarium-Bifurcatus Zone boundary in the Algarve. consideravelmente nestas condicoes. Ede notar uma fauna The boundary studied in the Peral area is associated with a relativamenteabundantee diversificada deDichotomoceras stratigraphic discontinuity, whose hiatus partially affects entre as amonites recolhidas, ja que este genero era, theTransversarium-Bifurcatus Zones. A discontinuity was anteriormente, raro no Algarve. also recognized in the Bifurcatus-Birnammatum Zone boundary, which can be correlated with the traces ofa Type II unconformity, which separates cycles 4.3 - 4.4 in HAQ RESUME et al. (1987), present on the South Iberian palaeomargin. An analysis was made of the ecostratigraphic evolu­ Mots-des: Ammonites - Organismes benthiques ­ tion in the interval between the uppermostTransversarium Biostratigraphie- Ecostratigraphic- Discontinuites-:-: Zone and the lower part of the Bimammatum Zone on the lurassique superieur - Oxfordien - Algarve - Sud du basis of the faunal spectra obtained. We conclude that Portugal. ammonites are the most tolerant cephalopods to the eco­ logical stress caused by the increase of inflows and the Cette note presente les premieres donnees dctaillccs decrease of the shelf's ecospace. Benthic fauna decreased sur la limite des zones Transversarium/Bifurcatus en Al­ considerably in theseconditions. A relativelyabundantand garve. Dans la region de Peral, cctte limite est associee a diversified fauna ofDichotomocerasis noteworthy among unediscontinuitesedimentairequi affectepartiellementles the ammonites collected, as this genus waspreviously little zones a Transversarium et a Bifurcatus, A la limite des known in the Algarve.

HI

INTRODUCTION bonate-terrrigenous platform can be recognized on land in relationto the generaloutcroppingofhercynian During the Jurassic the South West margin materials of the Iberian Meseta, whereas high car­ oftheIberiansubplate was subjected to the Mediter­ bonate bottoms limited the platform to West and ranean Tethys. This region was occupied by an South (off-shore data summarized in MARQUES & epicontinental sea during the Upper Jurassic. At OLORIZ, 1989a). In the deeper areas the sediments present the outcrops on land allow us to recognize were marls and more or less clayey limestones, in two platform systems (Fig. 1): a carbonate platform which cephalopods were frequent (studied by system in the westernpartofthe Algarve (area West MARQUES, 1983) as too were benthic organisms of Lagoa belonging to the Southern Sector of the (especially brachiopods, bivalves and gastropods). Algarve, cf. MARQUES & OLORIZ, 1989a) and a On the high bottoms buildups were frequent, set on carbonate-terrigenous platform system towards the raised blocks linked to fractures and folds probably easternpart(areabetweenLagoa and Tavirabelong­ related to halokinetic activity (MANUPPELLA & ing to the Northern sector of the Algarve, cf. al.,1988). Duringthe UpperJurassicthese reefal and MARQUES & OLORIZ, 1989a). The block struc­ parareefal facies developed more orless discontinu­ turing ofthe Algarve during the Upper Jurassic can ously from the Oxfordian on (MARQUES, 1983). also be recognized, the main features ofwhich were The carbonate-terrigenous platform system was re­ caused by the activity of deep, generally inherited placed by more or less clastic, basically carbonate fractures. The carbonate-terrigenous platform sys­ sedimentation during the Upper Kimmeridgian (s. tem coincided with a large depressed region of gallico) and was in part close to emersion during the Tethyan orientation. The northern limits ofthe car- Upper Tithonian and Berriassian.

Vale Burra

o 10Km i..-.---J [)

Fig. 1-Location and geological sketch for exposed outcrops in the Algarve. Paleozoic in vertical broken lines; black for the Triassic "Gres de Silves"; horizontal ruling for carbonate platform system; Eastern Algarve Basin in crossed framework; stippled for Cretaceous; Cenozoic in white.

113 OXFORDIAN STAGE

MIDDLE SUBSTAGE

TRANSVERSARIUM ZONE

LEVEL

LITHOLOGY

o 1 m ~

AMMONOIDES

Phyfloceras sp. Holcophyfloceras sp, H. mediterraneum (NEUM.) Lytoceras neumayrei Lissoceratoides erato (d'ORB.) 50werbyceras tortisulcatum (d'ORB.) Glochiceras sp. G. (G.) subclasum (OPPEL) Ochetoceras canaliculatum (BUCH.) O. hispidum (OPPEL) O. marantianum(d'ORB.) Campylites (Neoprionoceras) sp. Campylites (Neoprionoceras) lautlingensis (ROLL.) Trimarginites sp. T. arolicum (Oppa) T. stenorhynchum (OPPEL) T. trimarginatus (Oppa) Taramelliceras. sp. T. (T.) costatum (QUENST.) T. (T.) costatum (QUENST.) laterinodosum CORV. T. (T.) pichleri.(OPPEL) T. (T.) argoviense (JEAN.) T. (T.) callicerum (OPPEL) T. (Metahaploceras) kobyi(CHOFFAn T. (M.) pseuoowenzeli (WEG.) T. (5trebliticeras) externodosum (DORN.) Passendorferia sp. P. (Perisphinctes) sp. P. (Otosphinctes) nov. sp. A (MARQUES) . P. (Oichotomosphinctes) rotoides ROCH P. (D.) dobrogensis (SIEM.) P. (D.) wartae (BUKOW.) P. (D.) elisabethae de RIAZ P. (D.) luciae de RiAl P. (D.) luciaeformis ENAY P. (Oichotomoceras) sp. P. (D.) bifurcatus (QUENST.) P. (D.) bifurcatoides (ENAY) P. (D.) aft. aassus (ENAY) P.(O.)s~nocydmdesRONCHADZE Mirosphinctes bukowskii CHOFFAT Microbiplices sp. 5ubdiscosphinctes (5.) aenas (GEMM.) 5. (5.) mindowe (SJEM.) 5. (5.) ludngae (FAVRE) 5. (5.) gr. rhodanicuslcastroi Orthosphinctes sp. O. (0.) aft. delgadoi(CHOFFAn O. (Praeataxioceras) virgulatus (QUENST.) O. (Ardescia) sp. O. (Pseudorthosphinctes) sp. Euaspidoceras sp. E (E) paucituberculatum ARKELL E costatum (DORN.) E oegir(Oppa) E (E) perarmatum (SOW.) E (Neaspidoceras) sp, Gregoryceras'riazi (GROSS.) G. (G.) gr. transversarium (QUENST.) G. aft. fouquei (KILLIAN)

Present ~4 Probably Present _1 ITIJ] 2 EEEE 3 Faunal Mixture

Fig. 2 - The studied section with vertical distribution of ammonite species. I - Marls; 2 - Limestones; 3 - Bioclastic limestones; 4 - Sponge buildups; 5 - Discontinuities.

114 During the Middle and Upper Oxfordian, stratigraphic gap should be related with"phenomenes successions of marls and clayey limestones with erosives en phased'hautniveau eustatique". Accord­ occasional small developments of buildups (Peral ing to these authors this discontinuity is a case of Fm., MARQUEs, 1983) were predominantly in the tectonics-eustasy interaction. deeper areas of the carbonate-terrigenous platform The recent opening of quarries in the system (traditionally known as the Eastern Algarve bioconstructed facies with Spongiaria in the areas of Basin). Theonlyimportantbuildupwas that ofNossa Barracha and Rocha has created favourable condi­ Senhorada Rocha, which developed in the upperpart tions for the analysis ofthe materials belongingto the of the Upper Oxfordian (the base is assigned to the transition between the Transversarium Zone and the Bimammatum orPlanula Zones, cf. MARQUES, 1983). BifurcatusZone.Thisstudy contributes to ourknowl­ Apartfrom the limestone-marl rhythmite ofthe Peral edge ofboth the lithostratigraphicand biostratigraphic Fm., there are othercarbonate facies whose develop­ characteristics of the boundary between these two ment is more local: the poorly known "Calcaires chronozones. Hydrauliques de Loule' (CHOFFAT, 1887), which MARQUES (1985) tentatively assigned to the Mid­ dle Oxfordian, and the "Calcaires de Sao Romao" which, according to RAMALHO (1985), represent a THE SECTION AT PERAL thick internal shelf succession begun in the Upper Oxfordian. The section studied by us (Fig. 2) belongs to the A study of the most significant discontinuities lower part of the outcropping succesion ofthe Peral recorded in the Oxfordian of the Eastern Algarve Fm: whose top seems to be restricted to the Lower forms part of the paper by MARQUES & OLORIZ Kimmeridgian (MARQUES & OLORIZ, 1992). The (1989b). On the basis ofthe biostratigraphic charac­ limestone beds in this section are more orless clayey terization by MARQUES (1983), these authors inter­ mudstones or wackestones. Some levels show traces preted the scarceammonite record in the upperpart of of bioturbation (Thalassinoides of 2-4 em in diam­ the Transversarium Zone and the lower part of the eter) and, since their development is very localized Bifurcatus Zone as being connected with a disconti­ (levels 20, 42 and 48), they may represent sporadic nuity (D4 in MARQUES & OLORIZ, 1989b), whose reduction in the sedimentation rate. Other benthic

'It Brachiopods Perisphinctidae LI') l2J EJ e Belemnites Aspidoceratidae Q; Gastropods •m Phyllocerataceae > •0 Ammonites I!!lI Haplocerataceae Q) ....J

['J Brachiopods N r;] Perisphinctidae LI') Belemnites e Aspidoceratidae IIID Bivalves Q; • Phyllocerataceae Gastropods m > I!!lI Haplocerataceae Q) •0 Ammonites ....J

0 Brachiopods Perisphinctidae LI') l2J EJ §I Belemnites Aspidoceratidae Q; IIID Bivalves m• Phyllocerataceae Ammonites >Q) 0 I!!lI Haplocerataceae ....J

Fig. 3 - Faunal spectra of levels 50, 52 and 54.

115 macroinvertebrates also have a discontinuous record AMMONITE BIOSTRATIGRAPHY (brachiopods, crinoids, echinoids, gastropods and bivalves), which could be interpreted as the result of intermittent colonizations of the bottoms during The ammonite assemblage found in the section favorable phases (lesserdepositional rate 1).Ammo­ studied is that known from Submediterranean Eu­ nites were also found in bed 48. rope, although there are deviations in comparison In general, the upper and lower surfaces of the withmore northern areas (MARQUES, 1983). Fig. 2 beds are not irregular, except in those cases in which shows the ammonite distribution bed-by-bed: bioturbation had developed. The marly levels are Phylloceras sp., Holcophylloceras sp., H. better developed in the upper part of the section in mediterraneum (NEUM.), Lytoceras neumayrei, connection with, or close to, discontinuities on the Lissoceratoides erato (d'ORB.), Sowerbyceras Transversarium-Bifurcatus and Bifurcatus­ tortisulcatum (d'ORB.), Glochiceras sp.. G. (G.) Bimammaturn boundaries. Inside the lower-middle subclasum (OPPEL), Ochetoceras canaliculatum part of the marly levels carbonate concretions and (BUCH.), O. hispidum (OPPEL), O. marantianum sponge remains were observed. (d'ORB.), Campylites (Neoprionoceras) sp., The sponge buildups, which are ephemeral and Campylites (Neoprionoceras) lautlingensis (ROLL.), small (Fig. 2), are irregularly distributed in the sec­ Trimarginites sp.. T. arolicum (OPPEL), T. tion. Their development clearly indicates ecological stenorhynchum (OPPEL), T. trimarginatus (OPPEL), alterations which discontinuously affected the shelf Taramelliceras sp.. T. (T.) costatum (QUENST.), T. bottoms, permitting their colonization during short (T.) costatum (QUENST.) laterinodosum CORV., T. intervals of time. Decreases in detrital inflows may (T.) pichleri(OPPEL). T. (T.) argoviense (JEAN.). T. have played an important role in the colonization (T.) callicerum (OPPEL), T. (Metahaploceras) kobyi events. This interpretation is coherent with the fact (CHOFFAT). T. (M.)pseudowenzeli (WEG.), T. that the disappearance ofthe sponge buildups coin­ (Strebliticeras) externodosum (DORN.), cides withthe increaseofmarlysedimentationduring Passendorferia sp., P. (Perisphinctes ) sp., P. the Upper Oxfordian (Bimammatum Zone, cf. (Otosphinctes) nov. sp. A (MARQUES), P. MARQUES, 1983). (Dichotomosphinctes) rotoides ROCH, P. (D.) dobrogensis (SIEM.), P. (D.) wartae (BUKOW.), P. In the section studied here, two discontinuities (D.) elisabethae deRIAZ,P. (D.) luciae deRIAZ,P. have been recognized (Fig. 2). The first of these is (Dichotomoceras)sp.,P. (D.) bifurcatus (QUENST.), associated with a level containing Spongiaria. This is P. (D.) bifurcatoides (ENAY), P. (D.) aff. crassus a condensed level with a ferruginized upper surface (ENAY), Mirosphinctes bukowskii CHOFFAT, and glauconite remains. The bioclasts are partially Microbiplices sp., Subdiscosphinctes (S.) aenas mineralized. The fossils are mainly found in the (GEMM.), S. (S.) mindowe (SIEM.), S. (S.) lucingae uppersurfaceofthe bed,placed in horizons which are (FAVRE). S. (S.) gr. rhodanicustcastroi, parallel and subparallel to bedding. In general, the Orthosphinctessp..O. (0.) aff.delgadoi(CHOFFAT), ammonites are fragmented, except the smaller ones O. (Praeataxioceras) virgulatus, O. (Ardescia) sp., which are irregularly distributed. Implantation of O. (Pseudorthosphinctes) sp., Euaspidoceras sp., E. serpulids and ostreids is frequent in the uppersurface (E.) paucituberculatum ARKELL, E. costatum of the bioclasts. Traces of Thalassinoides are fre­ (DORN.), E. oegir (OPPEL), E. (E.) perarmatum quent in the lower part ofthe bed. This discontinuity (SOW.), E. (Neaspidoceras) sp., Gregoryceras riazi is attributed to the Transversarium - Bifurcatus Zone (GROSS.). G. (G.) gr. transversarium (QUENST.), boundary and we interpret it as the resultofa decrease G. affJouquei (KILLIAN). in sedimentation rate which favoured stratigraphic Concerning the biostratigraphic data obtained condensation. Ammonites predominate among the by MARQUES (1983), attention should be drawn to fauna found here, and belemnites, brachiopods, the following: a) the more abundant and diversified bivalves, gastropods, echinoderms (echinoids, record ofGregoryceras; b) the absence or scarcity of crinoids), and aptychi are also present (Fig. 3). Larcheria is confirmed, as too is the scarcity of A second discontinuity was detected in a grain Passendorjeria; c) Dichotomoceras is relatively fre­ selected bioclastic level with a ferruginized upper quent and diversified; d) Haploceratids are rare in the surface. Thislevelisrelated to the end ofthe Spongiaria Bifurcatus Zone; and e) Epipeltoceras seems to be record and the interval attributed to the Bifurcatus rare in the lower part ot the Bimammatum Zone Zone. In the upper beds the ammonites therefore according to its absence ofthe ammonite record. belongto the Bimammatum Zone.Ooids, intraclasts, At the level of ammonite assemblages, quartz grains, sponge fragments, brachiopods, Perisphinctids and Phylloceratids are recognized to echinoderms, bivalves, sepulids and, of course, am­ be clearly predominant in the Transversarium and monite remains were observed in thin section. The Bifurcatus Zones, otherammonites beingminorities. interpretation of this horizon as a product of In the lower part of the Bimammatum Zone resedimentation is coherentwith the mixed and frag­ Haplocerataceae share predominance with the previ­ mented character of the fossil remains. ously mentioned groups.

116 Comparison with the biostratigraphic distribu­ Haplocerataceae, Euaspidoceratinae and tions in other epicontinental areas of Iberia (Iberian Peltoceratinaeare practicallyaccidentalcomponents. Range, cf. MELENDEZ, 1989) is particularly inter­ In the lowermost part of the Bimammatum zone the esting as the absence of Larcheria in the Algarve previously predominant groups (perisphinctids and would seem to indicate that the upper part of the Phylloceratids) decrease in number and share pre­ Transversarium Zone is missing (Schilli Subzone of dominance with Haplocerataceae, which show a MELENDEZ, 1989). Another possibility is that marked increase. Euaspidoceratinae also increase Larcheria may not have developed in the Algarve during this interval, despite the scarcity of and was substituted by Subdiscosphinctes. Since the Peltoceratinae. . higher preserved levels ofthe Transversarium Zone Interpretation ofthe alterations observed in the in the Algarve seem to be always linked to a discon­ faunal spectra is not easy and must be undertaken tinuity, the first of these hypotheses seems more paying attention to the eco-sedimentarycontext. Fol­ likely, although the second cannot as yet be dis­ lowing the proposal of a sequential organization by counted. MARQUES &al. (1991), the sucessionstudied here As regards the discontinuity of the at least partly corresponds to the 4.3 cycle and the Transversarium-Bifurcatus boundary in the Algarve lowerpartofthe 4.4 cycle in supercycleLZA-4 in the and the record ofa condensation level in the section chart by HAQ & al. (1987). In other words, the studied in the Peral area, the appearance of significant increase in marlstowardstheupperpart of Dichotomoceras bifurcatoides and Dichotomoceras the section must be related to the tectonic pulse crassus in the same stratigraphic level is significant. affecting the Algarve during part of the Accordingto MELENDEZ(1989), these two species Transversarium and Bifurcatus Zones (MARQUES belong to different subzones in the Iberian Range. & OLORIZ, 1989b), and also to the progradation In comparison to the Iberian Range, the scarcity caused by the development of the Shelf Margin ofPassendorferiinae and related forms in the Middle Wedge System Tract (SMWST) during part of the and Upper Oxfordian in the Algarve seems to be Bimammatum Zone. confirmed according to the data obtained from the Given the context described above, we may studied section at Peral. Finally, it can not be estab­ expecta deteriorationinlife conditionsfor the benthos lished whether any biostratigraphic differences exist and a reduction of the ecospace during the as regards the first appearance ofPraetaxioceras in Bimammatum Zone. The record of benthic the Algarve and the Iberian Range. macroinvertebrates is coherent with this hypothesis, as the Spongiaria do not persist significantly into the Bimammatum Zone, and the other bentic fauna un­ dergo a significant decrease. The slight difference REMARKS ON THEFAUNALASSEMBLAGES between the corresponding spectra in the sampled levels of the Transversarium and Bifurcatus Zones The abundance offaunal assemblages related to coincides with a relatively small change in the vol­ the record ofbuildups, irrespective ofwhat the origin ume of the ecospace in this sector of the platform of these was, is a well known fact (ENAY, 1966; during the evolution of the transgressive interval BARTHEL & al., 1971; GAILLARD, 1983; ROLIN & (TST) and the developmentofthe HighStandSystem al., 1990; GYGI, 1990). In the case studied here the Tract(HSST), both ofwhichwere subjectedto a large predominantmacrofauna is made up ofmolluscs and rate of inflows. The slight increase in benthic fauna brachiopods; echinoderms were also found. towards the Bifurcatus-Bimammatum Zone bound­ Ammonoids are predominant, amongst which the ary may perhaps be due to taphonomic noise majorgroups are eitherthatcomposed exclusively of (resedimented bioclasts in bed 52). The ammonites Perisphinctids and Phylloceratids, or that made up of do not seem to have suffered from the slight change Perisphinctids, Haploceratids and Phylloceratids. in environmental volume and the composition ofthe "Aspidoceratoides" are always minorities. Aptychi spectra is practically identical towards the upperpart are rare (Laevaptychus). Bivalves (ostreids) and gas­ ofthe TST (Transversarium Zonep.p.) and the HSST tropods (Pleurotomaria) are rare among (Bifurcatus Zone p.p.). Phylogenetic evolutionary macroinvertebrates. Echinoderms are represented by events did not alterthe balance betweenthe groupsof remains of crinoids (fragments of slightly ammonites represented in the faunal spectra. disarticulated peduncles in the condensed horizons) Thedevelopmentofthe SMWSTalso increased and some echinids. Serpulids are frequent and only ecological stress for cephalopods during the interval two fish teeth were found. of the Bimammatum Zone analyzed here. Ammo­ Fig. 3 shows the stratigraphic evolution of the nites were the least affected cephalopods (see the macroinvertebrate assemblages and the composition decrease ofbelemnites in the spectra ofFig. 3). The of the ammonite assemblages. Towards the upper new ecological conditions were favourable for ap­ part of the Transversarium and Bifurcatus Zones, parently "more balanced" spectra, but all the ammo­ Perisphinctidae and Phyllocerataceae together pre­ nite groups show a decrease in taxonomic diversity dominate the ammonite spectrum, while (Perisphinctids, Euaspidoceratinae);eitheroneofthe

117 components is clearly predominant in its group dominant in the Bifurcatus Zone as was previously (Sowerbyceras in Phylloceratidae), or bothtrends are thought. combined(Euaspidoceras in"Aspidoceratoids").The - The materials ofthe Bifurcatus Zone reach a only group showing a clear increase is thickness of approximately 1m in the area studied. Haplocerataceae, particularly after the increase of This small thickness is the greatest presently known one ofits taxa (Metahapioceras). for this chronozone in the Algarve, which contrasts The increase ofHaplocerataceae during an eco­ with the much greater thicknesses of the other sedimentary situation of reduction of the ecospace Oxfordian chronozones identified in-this region. A and progradation (SMWST) is particularly interest­ possible biostratigraphic condensation has been de­ ing, since these ammonites have traditionally been tected in the lowerand middle parts ofthe Bifurcatus interpreted as being related to sufficiently deep areas Zone. (ZIEGLER, 1967; GYGI, 1986). However, the data - On the boundary between the Bifurcatus and obtained allow us to consider that the sector studied Bimammatum Zones, a discontinuity linked to a here evolved towards comparatively more proximal bioclastic level was detected for the first time. This and presumably shallower positions during the de­ discontinuity coincides with a Type II sequence velopmentoftheSMWSTin the BimammatumZone. boundary and can be correlated with the traces recog­ The reinterpretation of the Haplocerataceae record nized in the rest of the South-Iberian margin has already been suggested by OL6RIZ (1987). (MARQUES& al., 1991). - In the context ofthe sequential organization proposed for the South-Iberianmargin(MARQUES& ai., 1991), the changes detected in the macroinvertebrate assemblages are coherentwiththe CONCLUSIONS eco-sedimentary evolution recognizable in the east­ ern Algarve, and they permit the interpretation of - It has been possible to analyze the transition significant features ofthe ecostratigraphic evolution. between the Transversarium-Bifurcatus Zones in the - Evidence of correlation was recognized be­ Algarve for the first time. Both Zones seem to be tween the increase in clayey inflows, the decrease of incomplete, especially the Transversarium Zone and the ecospace on the shelf, and the deterioration oflife very probably the lowermost part of the Bifurcatus conditions for macroinvertebrates (particularly Zone. brachiopods and molluscs). -A relatively abundant and diversified - The reactions of cephalopods to ecological Dichotomoceras fauna has been found for the first stress are varied. As a group, belemnites are less time in the Algarve. tolerant than ammonites and their representation de­ - Theabsenceor extremescarcity ofLarcheria creases with the increase in the recognized environ­ in the Algarve cannotas yet be interpreted unequivo­ mental deterioration. Accordingto the recorded spec­ cally. Although it seems clear that there is a general­ tra, the ammonites adapted to the new conditions by ized stratigraphic gap in the upper part of the changes in the global composition of the assem­ Transversarium Zone, which would explain the al­ blages, reduction oftheirtaxonomic diversity and/or most complete absence of Larcheria, we cannot changes in the predominant component(s) of the discount the possibility that this taxon had a less different groups. specialized substitute among the Subdiscosphinctes. - As regards the previous biostratigraphic data (MARQUES, 1983), a more representative record of ACKNOWLEDGMENTS Gregoryceras has been obtained, and the relative scarcity of Passendorferia has been confirmed; This paper was made possible thanks to the financial Epipeltoceras seem to be rare in the lower part ofthe support of the Integrated Action ner6.33/37 between the Bimammatum Zone; Haplocerataceae are not pre- Universities Nova de Lisboa and of Granada.

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