Comun. lnst. Geol. e Mineiro, 2002, t. 89, pp. 155-178
Overview of microfossil assemblages and palaeoecological signatures
in the Middle-Upper Jurassic transitional successions from
the Lusitanian Basin, Portugal
ANA c. AzEREoo*; M. CRISTINA CABRAL *; MIGUEL M. RAMALHO** & R. PEREIRA ***
Key-words: Micropalaeontology; palaeoecology; facies; Middle-Upper Jurassic; Lusitanian Basin; Portugal.
Abstract: The successions across the Middle-Upper Jurassic disconformity in the Lusitanian Basin (Portugal), in particular those belonging to the Oxfordian Caba~os formation, have rich microfossil assemblages, comprising mainly ostracods and charophytes, but also benthic foraminifera, dasyclads, cyanobacteria, lncertae-sedis and palynomorphs. Recent detailed studies referring to many localities in the basin allowed a significant improvement of the systematical knowledge of different groups, in particular of the ostracods and charophytes, and the recognition of associations with palaeoecological significance, from the base upwards the sequences. The identified microfossil assemblages show variations in abundance and in diversity ranges, which seem to primarily relate to salinity ranges and changing frequency. Matching of the micropaleontological results with facies analysis, at a basinal scale, showed that the clearly linked regional palaeoecological signatures and evolution of palaeodepositional settings define two basic trends across the basin, one typical of the western successions and the other typical of the eastern successions.
An overview of the main data concerning ostracods, foraminifera, dasyclads and charophytes is presented, including palaeobiogeographical and biostratigraphical remarks. A brief mention to facies associations and their distribution over the basin is also made.
Palavras-chave: Micropaleontologia; paleoecologia; facies; Jurassico Medio-Superior; Bacia Lusitanica; Portugal.
Resumo: As series associadas a desconformidade Jurassico medio-Jurassico superior na Bacia Lusit3.nica (Portugal), em especial as da forma~ao de Caba~os (Oxfordiano), contem ricas associa~Oes de microf6sseis. Estas sao constitufdas, especialmente, por ostracodos e car6fitas, mas tambem por foraminfferos bent6nicos, dasicladaceas, cianobacterias, lncertae-sedis e palinomorfos. Estudos pormenorizados recentes, abrangendo diversas zonas da bacia, permitiram melhorar significativamente os conhecimentos relativos a Sistematica dos diferentes grupos, em particular dos ostracodos e das car6fitas, bern como reconhecer associa~oes corn significado paleoecol6gico, da base para o topo das sequencias. As associa~Oes reconhecidas mostram varia~Oes na diversidade e na abundancia relativa, as quais parecem estar relacionadas corn o teor e a frequencia de varia~ao da salinidade e corn o grau de exposi~ao subaerea. A conjuga~ao dos resultados micropaleontol6gicos corn os da analise de facies, a escala bacinal, demonstrou que a evolu~ao dos paleoambientes e as assinaturas paleoecol6gicas regionais, claramente relacionadas, definem dois padrOes, urn caracterfstico da regiao oeste e outro da regiao leste da bacia.
Neste trabalho apresenta-se urna sfntese dos principais resultados relativos a ostracodos, foraminfferos, dasicladaceas e car6fitas e fazem-se considera~Oes paleobiogeograficas e biostratigraficas. As associa~oes de facies e respectiva distribui~ao na bacia sao tambem sucintamente referidas.
INTRODUCTION the basin or on systematic and palaeocological aspects of
any particular group (RUGET-PERROT, 1961; RAMALHO, The successions across the Middle-Upper Jurassic discon- 1970, 1971a, b, 1981; HELMDACH, 1971, 1972; LEINFELDER, formity in the Lusitanian Basin (west-central Portugal), in 1983; GRAMBAST-FESSARD & RAMALHO, 1985; CABRAL et particular those belonging to the Oxfordian Caba<;os for- at., 1998, 1999, 2001; CARAPITO, 1998; PEREIRA et at., illation, have rich microfossil assemblages, comprising mainly 1998, 1999, in press; BARR6N et at., 1999; AzEREDO et ostracods and charophytes, but also benthic foraminifera, at., 2000; COLIN et at., 2000; MARTINS et at., 2001;
dasyclads, cyanobacteria, Incertae-sedis and palynomorphs. CABRAL & COLIN, 2002; PEREIRA, 2002; BARR6N &
The micropalaeontological record of such successions AZEREDO, in press).
was either briefly or locally reported in previous studies, In this paper, a first overview of the most significant focused either on other main subjects, on specific areas of Oxfordian micropalaeontological signatures at a wider,
* Departamento de Geologia and Centro de Geologia, Faculdade de Ciencias, Universidade de Lisboa, Campo Grande, Ed. C2, 5.0 piso, 1749-016 Lisboa, Portugal ([email protected] [email protected])
** Instituto Geol6gico e Mineiro, Estrada da Portela, Zambujal, 2720 Alfragide, Portugal ([email protected])
*** PARlEX, OIL & GAS -Av. Republica, 50, 4.0, Lisboa and Centro de Geologia da Universidade de Lisboa, Campo Grande, Ed. C2, 5.0 piSQ, 1749-016, Lisboa, Portugal ([email protected])
156
basinal scale is presented, coupled with more localized STRATIGRAPHICAL SETTING references to Middle Jurassic assemblages in order to
complete the stratigraphical setting. This reappraisal is It is well known that, in the Lusitanian Basin, the based on recent detailed studies referring to many locali- Middle Jurassic is separated from the Upper Jurassic by ties in the basin (Fig. 1), undertaken within the scope of a disc:onformable basinwide hiatus which, according to the research project PRAXIS XXI/PCNA/C/6/96 "Pas- ammonite biostratigraphy (RUGEf-PERROT, 1961; MOUlERDE sagem Jurt:2ssico Medio-Jurt:2ssico Superior na Bacia et al., 1979; ROCHA et al., 1996), spans at least from the Lusiti1:nica: caracterizar;iio paleoclimt:2tica, sedimentar e uppermost Callovian (Lamberti Zone is not recognized) estratigrt:2fica" (AZEREDO et al., 2000). These studies to the end of the Lower Oxfordian (Mariae and Cordatum focused both on micropalaeontology and on facies and zones are not recognized). It is not possible to rule out the palaeodepositional settings; a detailed description and in- possibility that some of the undated deposits, which are terpretation of these, as well as a model for the events not prone to have ammonites, may be of latest Callovian- associated with the Middle-Upper Jurassic boundary in Early Oxfordian age, though the same stratigraphical the Lusitanian Basin, within the scopec of the Atlantic hiatus is recorded in many other Atlantic-margin basins margin basins, is presented elsewhere (AzEREDO et al., in (AzEREDo et al., 1998, 2000, and references therein). In press). The micropalaeontological study did not cover places (namely at Serra dos Candeeiros) the disconformity loose specimens from Cabo Mondego, though field and is developed on Upper Bathonian limestones -dated by petrographical data from this section was also considered the foraminifera species Meyendorffina bathonica in the broader work. Some foraminiferal and ostracod AUROUZE & BIZON, 1958 (AZEREDo, 1993) -and may be assemblages from the Callovian-Oxfordian of Cabo associated with an angular unconformity. In the west and Mondego were mentioned by CARAPITO (1998). south of the basin (namely, at Cabo Mondego, Pedr6gao, The palynomorphs will not be addressed here, because Serra d'El-Rei and Serra de Montejunto), the deposits the significant data basically refer to a single locality (Pe- immediately below the disconformity are dated as Upper dr6gao) and a specific work on this palynological content Callovian, reaching the Athleta Zone only at Pedr6gao is in publication (BARR6N & AzEREDO, in press). -(RUGET-PERROT, 1961; MOUTERDE et al., 1979; ALMERAs
et al., 1991; ROCHA et al., 1996).
N The Middle Jurassic carbonate deposits immediately
t ~I below the disconformity correspond either to shallow-
marine facies (mostly to the east of the basin) or to open- marine facies (mostly to the west). The former represent what has been often informally named "Candeeiros ',"
,j formation", and the latter what has been informally named
"Brenha formation"; however, these broad designations actually correspond to several lithostratigraphical units
v (see, for instance, the 1: 500 000 Carta aeol6gica de
" Portugal, sap, 1992), but this issue will not be discussed
" here. The Upper Jurassic deposits above the discontinuity
;0: correspond to continental, transitional and restricted-ma-
'. ..
\ nne facies and belong to the Caba~os formation (though
'~~ often quoted as a Formation, it is not formally described),
; l' Legend which basically corresponds to the originally named
j) ~ :~:I~;oPS Caba~os Beds (sensu CHOFFAT, 1893a, b, followed by
"-Local;,;es JOkm RUGET-PERROT 1961; RAMALHO, 1971a, b), sometimes , , , ,
Jtj also mentioned as Caba~os Limestones (MOUTERDE et
y al., 1979). The Caba~os formation lacks good biostrati-
, graphical markers but, over the whole of the basin, the
lower to intermediate part of the successions are typified
by the presence of the dasycladacean alga Heteroporella
lusitanica (RAMALHO, 1970), which is attributed to the
Fig. I -Location map, including the studied field sections and oil ex- Middle Oxfordian in Portugal, because this species was
ploita!ion wells (Lusitanian Basin, W-Central Portugal). also found in the Torres Vedras region (Caba~os), in levels
157
apparently equivalent to, or just below, those where a few indicate a late or latest Callovian to early Oxfordian ammonite findings (not precisely located) attributed to slightly decreased sea-level rise (HAQ et at., 1987, 1988;
the Transversarium Zone had been recorded by P. Choffat HARDENBOL et at., 1998), prominent (HALLAM, 1988), or (vide RUGET-PERROT, 1961; RAMALHO, 1970, 1971a, b). incipient (NORRIS & HALLAM, 1995) sea-level fall, In other places, Middle Oxfordian, Plicatilis Zone (Serra followed by a rapid sea-level rise. The discussion of the de Montejunto -RUGET-PERROT, 1961; MOUTERDE et at., possible role of global and regional processes related to 1979; ROCHA et al., 1996) or Upper Oxfordian (RUGET- this major discontinuity is beyond the scope of this paper, PERROT, 1961; FERREIRA, 1962) ammonites are documen- but the reader may refer to AzEREDO et at. (in press) and ted from levels high above those containing H. lusita- references therein.
nica, which reinforces the validity of the age assigned to this species.
It is also worth mentioning that, over the whole of the MAIN FACIFB TYPES AND TYPICAL SUCCESSIONS basin, the lituolid forarniniferaAlveoseptajaccardi (SCHRODT,
1894) and/or Pseudocyclammina parvula HOTI1NGER, 1967 FACIES TYPES always appear in the more marine influenced facies which
gradually succeed, or laterally replace, the restricted Most of the data dealt with in this paper refer to depo- lagoonal facies with H. lusitanica. A. jaccardi has been sits attributed to the Oxfordian Caba~os formation, as the placed in the Middle Oxfordian-Kimmeridgian, and R Middle Jurassic formations were not the main subject of parvula in the Upper Oxfordian- Tithonian (HoTTINGER, the research project. On the other hand, an updated facies 1967; RAMALHO, 1971a, 1981, 1985; LEINFELDER, 1983; analysis approach is made elsewhere (AZEREDO et al., in LEINFELDER et al., 1988). However, according to our press), thus only a brief report of the main facies types recent data (see below), R parvula may also be locally recognized in the studied formations is made here. The found in the Middle Oxfordian. study was mainly based on original field sections coupled The Middle-Upper Jurassic disconforrnity is coincident with formerly existing material from C. P. P. sections, and with the tectonic record of compressional movements in also used a few borehole material (Petrogal and Shell the Portuguese Mesozoic Basins (TERRINHA, 1998) and wells) -Fig. 1. The preexisting material is deposited at with eustatic short regressive events, according to most the IGM (Lisbon). The key to symbols used in the lithos- published global sea-level curves for the Jurassic, which tratigraphical columns is presented in Fig. 2.
I, I I I, I, I Limestone I III Mudstone, Wackestone, Packstone/
I , I , I
Dol..
I.M W PfF GIR /Floatstone, Grainstone/RudstoneI', I ,1 omltlc lmestone
Iii II 11t:!;1 Ferruginous limestone/Fer. breccia
~ !:=:r !:=:r !:=:r ~ Marly limestone --
11...1...1...1.' 1 ~-~ .=-~ Clays and marls w/ ferruginous crusts
,..,i...:j...:j...:, Detrital limestone
rxxxXXx:::l <> Anhydrite/evaporite moulds
~.: ;-!--'-;' !, ;-d Bioclasticlimestone
IV V VVVl Dyke
~ 01 b !j! b !j! b !j! d Litho/intraclastic limestone
~ Irregular or undulating surface
~ "', b !!I b !!I b !!I d Oolitic limestone ~~1 Highly irregular ferruginous surface/
:"""i"' ~ "i"' ~ "i"' ~ "i': Oncolitic limestone ferrugInous surface
1.-=- -=- --,
M lsl I -v-v-v- Desiccation cracksI --=- ~ ar cays
= Fenestrae
~ .,. , ., ., ~ Black-pebble limestone O Euhedral/detrital quartz
~~ Microbiallaminiiesl .-Siliceous noduleslbeds
microbial laminite clasts P all II
..
IO~c;)c-j == ar e-amlnatlon
~'---='8c. -:;=::1 Pedogenic conglomerate -LL- Cross-lamination I ~ -:- '- ~ ~ ~ ~ Limestone with pedogenic clasts , Bioturbation
Lignitic marlslclays F Fault
Fig. 2 -Symbols used in the lithostratigraphical columns throughout the paper.
158
The "Brenha-type" successions are composed of often -Sandstone-Iignite facies association (Cabo Mondego).
bioturbated, fossiliferous
.-IUmarls and limestones, with nor-
M ed. m/th IC -e . k b dde d non-manne . IImestone-mar . 1- mal-manne. fauna (ammo~ites, brachiopo~s,. corals, bi- lignite facies association (at all the localities stu-valves, ech1OOderms, hyal1Oe-walled foramlmfera, ostra-
dl . ed .th ... h M .
I , WI a mInOr expressIon 10 t e onteJunto cods, p~lynom.orphs). In the st~died .su~cessions, it is Rocha-Forte region).
present Immedlately below the dIscontInuIty at Pedr6gao
(Fig. 3) Serra de Montejunto and Benfeito-l well (Fig -Th1O-bedded fosstllferous marly llmestone-mlcro- 4); and below the "Candeeiros-type" sandbody, which i~ biall.a~inite-~vaporite fa~ies asso~iatio? (at all the then capped by the discontinuity, at Cabo Mondego l~cal!tIes studIed).. In partl.cular, thl~ facIes associa- (WRIGHT, 1985; AzEREoo et at., in press). These topmost tIon 1Ocludes marg1Oal manne deposIts, the restricted
"Brenha-facies" sediments are of Late Callovian age (cf. lago.ona~ Heteropo~ella lusi~anica beds ~nd. more RUGET-PERROT 1961. MOUTERDE et at. 1979. ALMERAS manne-1Ofluenced 1OtercalatIons, as ech1Oold/bra-
et al., 1991). ' , , , chiopod-bearing limestones (for instance at Pedr6-
With regards to the studied sectionslboreholes, the gao) and, probably, the ammonite levels at Torres
"
C
an eelros-typed ."
successIons..
Immed
late ye.
1 b 1ow the Vedras . discontinuity (Figs. 4 and 5) are represented by skeletal,oolitic and intraclastic grainstones and packs tones TYPICAL SUCCESSIONS (Amibida, Rocha-Forte, PO-18ISerra d'EI-Rei, Vermoil-l,
PO-9/Barrocal/Pombal, Cabo Mondego) and by oncolitic, A synthetic mention to the typical vertical arrange- peloidal and fenestral mudstones to wacke-packstones ment of the main facies types recognized in the studied (PO-6ICaba~os, Rocha-Forte, PO-16/Nataria, Valverde, successions is made below, with simplified logs of the Vale de Ventos, Mem6ria/Cabe~o Gordo, PO-9/Bar- field sections most relevant to this paper.
rocal/Pombal). These facies types may be intercalated In the west of the basin, the sediments just below the with each other, range in age from Bathonian to disconformity usually correspond to the open-marine Callovian and show rich assemblages of large, imperfo- "Brenha facies", except for Cabo Mondego as mentioned rate-walled benthic foraminifera, calcareous algae, (see WRIGHT, 1985; AzEREoo et at., in press). At Pedr6- porostromates and other shallow-marine benthos gao (Fig. 3), the topmost levels of that formation are (AZEREoo, 1993, 1999; AZEREoo et al., 2000). lignitic marls and limestones containing both marine and The Caba~os formation, whose typical thickness ranges a few reworked, non-marine microfossils. The presumed from 40-50 m to 100-150 m (locally 200 m?), is stratigraphical boundary between the Callovian and the composed of pedogenic limestones, ferruginous or lignitic Oxfordian may correspond, according to AzEREoo et at.
marlslclays, lacustrine, restricted lagoonal and marginal- (in press), to a 0.5 m thick couplet of two reddish ferru- marine to shallow-marine marls and limestones, and, ginous and charophytic limestone beds (PI. 1/1), locally, oyster-coral rich mudstones and deltaic separated by a highly irregular ferruginized surface.
sandstones (see also RAMALHO, 1971a; WILSON, 1979; Above the discontinuity surface, the successions are WRIGHT, 1985; WRIGHT & WILSON, 1987; AZEREoo et al., typically composed of non-marine limestones, marls and 1998, in press). Recently, AZEREoo et at. (in press) lignites, with desiccation cracks, ferruginous surfaces defined six facies associations within the Caba~os forma- capping some beds, some detrital or authigenic quartz, tion and documented their basinal distribution, as follows abundant ostracods and charophytes, gastropods, bival-
(see also Figs. 3 to 5): ves, plant remains (including diverse palynomorphs) and
rarer reptile teeth. Locally (Cabo Mondego), oyster-coral -Erosional palaeosurfaces and ferruginous deposits sandstones and sandy limestones are found above the
facies association (Arrabida, Montejunto, Serra dos disconformity. Further upwards, the non-marine units Candeeiros, Pedr6gao, Cabo Mondego). (locally pedogenic) are interbedded with restricted-marine -Pedogenic and black-pebble limestone-conglomerate fossili~erous (ostracods, charophytes, gastropods, bivalves,
facies association (Arrabida, Serra d'EI-Rei Rocha- serpultds, dasyclads, agglutinate-walled foraminifera, -Forte!Montejunto, Caba~os, Serra dos Ca~deeiros, ~nclud!ng lituolid~, low-diversity spore assemblage,
Pedr6gao). 1Oclud1Og planktomc protozoans) and bioturbated marly
limestones and limestones (including the H. lusitanica -Heterolithic oyster-coral sandstone-Iimestone facies beds); microbiallaminites, evaporites, pedogenic conglo-
association (Cabo Mondego). merates and minor bioclastic or oolitic-intraclastic pack-
160
Cesareda/Serra d'El-Kei Benfeito-l
Above Up Oxfardian ammonites ( I) ':I (mare anhydiite':1
(m) + Montejunto (m); above) \\\
Above Middle / '\
Oxfardian ,1 '\
~ ammonites (:1) ,I \\
" ~ , ,
Q !0 15 ; "
~ ~ , ,
0 [ "I,
.; \
:a 11 ~ \', Caba~os
J ~ ~ ~ ',\ Above Middle
~ 1 ] CC '\ Oxfardian ~
~ o 5 ~~ Roeha-Forte 100 (m)\, ammamtes (I) #
: f ~ ',;, ~I~b !'. ,!! --'::, \'\\ ,,~
-" S ' 4 ,
" ~ ~ ,- '\\ ii' \
~ ., 100<), \ c ~ ;
~-g~ '" e ',',~--- " " j !,. .'1lSllallIca ~lI l
" i~ '\,\~\ ii'! f~Q '" ] ':c--"
.= ~ 'i; ~ i \ ~ 5 lusllanlca
~ J 1 ;\,~" 1,!i" '\\,~~ -":' ".'"
., ~ " So ~ i
.!; ~ So \,;\ --J'f
"""""""-" Up "" ?
" ~ Call avian', ")
'= § 1 -","'
~ ." ~ 0 ammamtes(-J ,"
" , ,
S .§ ~ MWPIFGIR 0
~ " '"" MWP
., U ., :e ' S 0
~ =- ~
~e: ~
Middle Callavian an1manites .MWP (I)
Fig, 4 -Synthetic lithostratigraphical columns and correlation of several sections (Cesareda/Serra d'EI-Rei, Rocha-Forte, Montejunto, Caba~os) and a borehole (Benfeito-l) in the south/southeast of the Lusitanian Basin (Middle-Upper Jurassic transitional successions, mainly focusing on the Oxfordian Caba~os formation). Ammonite dating according to: (I) RUOET-PERROT, 1961 and FERREIRA, 1962; (2) RUOET-PERROT, 1961 and ROCHA et al., 1996.
MICROPALAEONTOLOGICAL SIGNATURES duals in most facies types (pI, ll/1-14 and PI, llI/1-8). The
AT A BASINAL-SCALE identified faunas show different diversity ranges, which seem
primarily related to salinity variations (see below). Several This section presents the broad, basinwide, palaeoe- associations with palaeoecological significance have been cological trends recognized in the identified microfossil recognized in different sections of the basin (CABRAL et al., assemblages, particularly from the Caba~os formation 1998, 1999, 2001). Subsequent matching of those assem- (though a brief mention to the assemblages of the im- blages showed them to distinguish two basic trends across the mediately underlying deposits is made). At the same basin, one typical of the western successions and the other time, the occurrence of the most important species is typical of the eastern successions, though intermediate highlighted, within a palaeobiogeographical framework. situations occur. Systematical study is only possible on loose
specimens, therefore it covers those sections/boreholes from
OSTRACODS which loose sediment samples could be obtained (except for
Cabo Mondego): Pedr6gao, Vermoil-1, Vale de Ventos, This is the most abundant microfossil group in the studied Valverde and Mem6ria/Cabe~o Gordo (from the latter, formations, being represented by a high number of indivi- only rare identifiable loose specimens were obtained).
161
Callovian 1972),1: levis (HELMDACH, 1972), Darwinula n. sp. 1 and
.D. n. sp. 2, Sinuocythere pedrogaensis CABRAL & COLIN, The ostra~od faunas are completely d.lfferent from those 2000, Ind. Gen. n. sp. 0-16, Ind. Gen. n. sp. 1 and Klieana of the Oxfordlan, a.s could be expected, S1Oce the f~rmer are n. sp. 1. Towards the middle part of the successions (Fig. 3), mostly n~rmal-marlne faunas and th.e latter ~ domInated by characterized by intercalations of the previous lithologies non-marIne ostracods. The Callovlan marIne faunas were with the lagoonal deposits with Heteroporella and a few identified in fossiliferous marls from the lawermost part of foraminifera, the euryhaline S. pedrogaensis becomes the ~edr6giio section (Fig..3); r:arer and poorly ~reserv~ dominant relative to the other species. This group of speclmen~ were also ~ound 10 residues from Ve~otl-l. This species defined the associations 2 of the Pedr6giio section fauna maInly compnses: Cytherella cf. fullomca JONES & in CABRAL et al. (1998) and 2 and 3 of the same section SHERBORN, 1888, sensu MErrE, 1995; Cytherella cf. index in BARR6N et al. (1999), interpreted as having developed OERn-I, 1959, sensu MErrE, 1995; Cytherelloidea cf. C. aff. from a fresh-brackish water setting into a variable, jugosa (JONES, 1884) in MEITE, 1995; Patellacythere n. sp. 1, hyposaline to hypersaline environment.
Bythoceratina ( Praebythoceratina) n. sp. 1, Procytheridea cf. Further upwards, the increasing presence of desiccation gublerae BIZON, 1958, .Polycope n. sp. 1, Neurocyt~re surfaces, evaporites, pedogenic conglomerates and micro- (Neurocythere)cf.composita(WIENHOIz, 1967), Praeschuleridea bial laminites and the foraminifera genera Pseudocy- aff. s~btri~ona magna BATE: 1964, Virgulacytheridea aff. clamminalAlveosepta (see below) is accompanied by a sherifensls OERTLI & DEpECHE, 1987 and Rutlandella marked change in the ostracod population: it shows the n. ~p. 1. At Ped.r6~iio, this marine assemblage was referred highest number of individuals, diversity decreases, Therio- to 10 the assoclatlon-l of CABRA~ et al. ( 1 ~98). synoecum disappears, S. pedrogaensis dominates and is
Towards the top of the Callovlan deposIts, a few non- associated with Galliaecytheridea n. sp. 1 (marine species, marine species also occur, as Theriosynoecum fluxans only found in the west of the basin), Schuleridea sp. (only at spiculata (HELMDACH, 1972), 1: levis (HELMDACH, 1972) Vermoil-l ), Klieana n. sp. 2 and Darwinula n. spp.. Towards
and Darwinula n. sp. 2. the top, almost exclusively S. pedrogaensis occurs,
commonly in monospecific coquinas (ostracodites), usually
O
~d
o within microbiallaminites. These two types of assemblagex lor Ian
cover the associations 3 and 4 in CABRAL et al. (1998) The study of material from different sections over the and 4 and 5 in BARR6N et al. (1999), corresponding to a basin has allowed the identification of twelve genera and marginal-marine, frequently subaerially exposed setting.
twenty-two species, including at least 2 new genera (des- In the east of the basin (Vale de Ventos, Valverde and cribed in COLIN et al., 2000 and CABRAL & COLIN, 2002), Mem6ria/Cabe~o Gordo, Serra dos Candeeiros; Fig. 5) and 16 new species (of which, 6 were already described -the clearly continental deposits in the lower part of the COLIN et al.. 2000 and CABRAL & COLIN, 2002). Several Upper Jurassic successions display limnic ostracod ostracod associations may be distinguished, coupled with populations of variable abundance and diversity. In the other palaeontological and sedimentological data, either deposits immediately above the disconformity, with mar- from the base upwards the successions or between the ked subaerial exposure, the mainly freshwater family western (typically Pedr6giio) and the eastern (typically Vale Candonidae may be the dominant ostracod fauna (at Vale de Ventos)successions AZEREoo&CABRAL,in press. Most of de Ventos), namely Septacandona ramalhoi CABRAL &
this Oxfordian fauna is limnic (sensu CARBONEL et al., 1988). COLIN, 2002, S. azeredae CABRAL & COLIN, 2002, S.
In the west of the basin (Pedr6giio, Fig. 3; and Ver- multicostulata CABRAL & COLIN, 2002 and Candona ? moil-l), most of the levels attributed to the Oxfordian parvissima CABRAL & COLIN, 2002. Other species present Caba~os formation display abundant ostracod assembla- are Sinuocythere candeeirosensis CABRAL & COLIN, 2000, ges, in which diversity and dominant components are Klieana n. sp. 1, Darwinula n. sp. 3, D. n. sp. 1 and D. n.
clearly different and compare well with other micropa- sp. 2 (both rare and only at Vale de Ventos) and rare laeontological and sedimentary features (CABRAL et al., Theriosynoecum spp. This assemblage corresponds to the 1998; BARR6N et al., 1999; AZEREDO et al., 2000). The associations-l of Vale de Ventos and Valverde in CABRAL lowermost Oxfordian deposits contain very abundant et al. (1999, 2001), interpreted as representing a very fresh-brackish water ostracods, but the diversity is lower shallow, freshwater (?) setting. At Mem6ria/Cabe~o than in the Callovian marine assemblages: Theriosynoe- Gordo section, the identifiable individuals are rare, but cum gr. wyomingense (BRANSON, 1935), 1:fluxansfluxans Candonidae (S. ramalhoi, S. azeredae, C.?parvissima), (HELMDACH, 1972), 1: fluxans spiculata (HELMDACH, Darwinula n. sp. 3, S. candeeirosensis, Theriosynoecum
163
dasyclads and agglutinated foraminifera (see below), The shallow-marine limestones deposits ("Cande- typical of restricted lagoonal settings. This assemblage is eiros-facies") bear rich assemblages of complex, large very rich in S. candeeirosensis and in Klieana n. sp. 3, benthic foraminifera, associated with calcareous algae, increasingly abundant towards the top, with rarer occur- porostromates and other organisms (see AZEREDO, 1993, rences of the genera Darwinula and Theriosynoecum. 1999; MARTINS et al., 2001). At Nataria, Mem6ria/Ca-
be~o Gordo, Vale de Ventos and Valverde sections (Fig. 5), the presence of Meyendo1ifina bathonica AUROUZE &
Palaeobiogeographical and palaeoecological remarks BIZON, 1958, indicates a late Bathonian age for the last Middle Jurassic preserved deposits, while at most other Both the Callovian marine and the Oxfordian limnic locations a Callovian age is usually admitted for these ostracod faunas recognized in the Lusitanian Basin are, at limestones. Other common species in the uppermost the generic level, broadly similar to the faunas described Middle Jurassic of the studied sections are Chablaisia from deposits of equivalent or close age, in the Atlantic chablaisensis (SEPTFONTAINE, 1977), Pseudocyclammina and Tethyan marginal basins (BODERGAT, 1997; COLIN, maynci HOTTINGER, 1967, Praekurnubia crusei 1997). Also worth mentioning concerning both palaeoe- REDMoND, 1964, Mesoendothyra croatica GUSIC, 1969, cology and palaeobiogeography, is the good representa- Nautiloculina oolithica MOHLER, 1938, Trocholina spp.
tion of the Candonidae, namely a new genus with three and Valvulina lugeoni SEPTFONTAINE, 1977.
new species. This is interesting because there are very The open, normal-marine sediments ("Brenha-facies") few data on the Cypridacea (superfamily that includes comprise mostly the hyaline-walled Nodosariidae, as the Candonidae) during the Oxfordian and even during could be expected, but other small benthic foraminifera all the Jurassic (see COLIN, 1997; CABRAL & COLIN, occur (Epistominidae, Textulariidae, Milioliidae}. This 2002). During this period, the assemblages of limnic assemblage is associated with marine ostracods, marine- ostracods were clearly dominated by genera from other influenced palynofacies and normal-marine macrofauna.
superfamilies, namely Cytheracea (Theriosynoecum, Identifiable loose specimens were obtained only from Timiriasevia} and Darwinulacea (Darwinula}. This fact Pedr6gao, and their study is not yet completed. However, is also recorded in Portugal, particularly in the western preliminary results show that the populations are clearly part of the Lusitanian Basin (HELMDACH, 1971, 1972; dominated by Lenticulina spp. (several morphogenera, CABRAL et al., 1998; SCHUDACK, 2000). sensu RUGET, 1985), as documented for the European Jurassic in general (e. g. RUGET & NICOLLIN, 1997): Len- ticulina sp. mg. tricarinella (REuss, 1863), L. gr. polo-
FORAMINIFERA nica, Lenticulina sp., Citharina sp., Spirillina sp., Fron-
dicularia sp. and Vaginulina sp. were identified. At This group is much less common in the Caba~os for- Pedr6gao (Fig. 3), the topmost marine Callovian beds mation than the ostracods and charophytes, though local- comprise corals, oysters, brachiopod clusters and fer- Iy relatively abundant populations may be found. Howe- ruginous surfaces, overlain by levels bearing mixed mari- v.er, .the occurrence ?f some species. have a ~egion~1 ne and non-marine, probably reworked, ostracods and slgm~cance, concernl~g palaeoecologlcal a~d blostrat~- charophytes, plant remains and detrital quartz (AzEREDO graphical aspects. A bnef reference to the typical foraml- et al., in press). Thus, it clearly reflects a rapid shallowing, niferal population of the Middle Jurassic deposits just interpreted as related to a forced regression, for which below the disconformity is also made. evidence from other locations in the basin also exists
(AzEREDO et al., in press). Within those levels, the presence of simple agglutinated foraminifera and Milio- Upper Bathonian-Callovian liidae is more common, though never abundant. Ammo-
..baculites sp., Reophax sp., small Textulariidae and Ver- As stated, the topmost Middle Jurassic below the neuilinidae are present.
disconformity is mostly of shallow-marine (inner-mid
ramp) facies to the east, and of open-marine (outer ramp) Oxfordian facies to the west of the basin, though in places (particu-
larly to the south of the basin; Fig. 4) intermediate situa- In this case, the foraminifera are always studied in tions occur or both types of facies interfinger with each limestone thin-sections, so it covers material from all of
other. the field sections and boreholes. The most significant
164
foraminifera species within the Caba~os formation below. These lituolids were also identified in material belong to the Lituolidae, and have been well documented from the offshore wells 13C-I, 14A-2 (Pedr6gaoNieira in previous works (RAMALHO, 1971a, b,1981; LEINFELDER, de Leiria) and MO-l (Cabo Mondego/Figueira da Foz).
1983; AZEREDO et at., 1998, 2000).
In the more continentally influenced facies, rich in Palaeobiogeographical and biostratigraphical remarks charophytes and fresh-brackish water ostracods, there are
no foraminifera. These begin to appear further upwards The Jurassic assemblages dominated by simple agglu- in the successions, in the transitional deposits correspon- tinated forms like Ammobaculites spp., small textularids ding to brackish/restricted lagoonal settings, always with and vemeuilinids, have been usually assigned to restric- abundant ostracods and charophytes but also with Hete- ted-marine facies, to shallow brackish settings or to mar- roporella lusitanica (PI. IV/I). However, these first ginal-marine and pro-deltaic settings, with direct ter- assemblages are not rich, neither in number of indivi- rigenous influence (NAGY & JOHANSEN, 1991). Genera duals neither as regards to diversity: Pseudocyclammina like ReophaxJSubreophax and Ammobaculites, observed sp., Kumubia palastiniensis HENSON, 1948, Vemeuilini- in the Recent and in the Ancient, are considered endoben- dae, small Textulariidae. thic organisms typical of moderate water depth, showing
Towards the top of the successions, as said, less res- non-calcareous, simple tests and whose elongated mor- tricted, more marine influenced facies interfingers with, photypes are prone to rapidly colonize the substrate under and gradually overlies, the lagoonal/marginal-marine facies oligotrophic conditions (KUHNT & KAMINSKI, 1993). Thus, allover the basin. In these deposits, in which Heteroporella the occurrence of these type of assemblage in the topmost only occurs very rarely in the lowermost levels, the fora- Callovian from Pedr6gao is in accordance with evidence minifera are more common, even locally abundant (though mentioned above for shall owing and influx of nearby the populations are never as numerous as compared to the coastal sediment (oysters, reworked non-marine ostra- other microfossil groups referred to here), and their diver- cods and charophytes, plant remains, detrital quartz), la- sity increases. This assemblage comprises (PI. IV/2-4): ter followed by the on setting of a paralic depositional common Vemeuilinidae, locallyabundantAlveoseptajaccardi setting in the early Oxfordian.
(SCHRODT, 1894), PseudiJCyclarrunina palVula HarnNGER, The lituolids, which are large benthic foraminifera 1967 and P. maynci HO1TINGER, 1967, rarer P. sp., with imperforate walls and usually complex inner struc- Ammobaculites sp., Reophax sp., Kumubia palasti- tures, are common in the Jurassic shallow-marine, mainly niensis, Valvulina sp., Nautiloculina oolithica MOHLER, carbonate-platform environments of the peri-Atlantic and
1948, N. sp., Placopsilina sp., Conicospirillina basiliensis peri-Tethyan realms, being increasingly abundant and MOHLER, 1938, Glomospira sp., small Textulariidae and diversified from the Lower into the Middle and Upper very rare Milioliidae. These deposits also contain ostracods, Jurassic (HO1TINGER, 1967; RAMALHO, 1971a, 1981, Lenticulina sp. and other hyaline-walled foraminifera, 1985; SEPTFONTAINE, 1981; PELISSIE et at., 1984;
frequent bivalves, gastropods and echinoids, rarer crinoids, BASSOULLET et al., 1985; SEPTFONTAINE et at., 1991;
corals and brachiopods, porostromates, Aeolissacus sp., BASSOULLET, 1997). The lineage PseudocyclamminalAl- Koskinobullina socialis CHERCHI & SCHROEDER, 1979, etc. veosepta has also adapted well to shallow marine settings
The higher abundance of individuals of the genera with terrigenous influx (e. g. BASSOULLET et at., 1985;
Pseudocyclammina and/or Alveosepta in some levels is BASSOULLET, 1997).
locally associated with a predominant orientation of the As regards to the two most significant species in the tests, which may indicate that these tests were transported Caba~os formation, Alveosepta jaccardi has been widely by a sporadic current and suddenly redeposited altogether reported in the Tethyan domain, namely from: Portugal, (event deposits). The preferred orientation could have both in the Lusitanian and Algarve basins (RAMALHO, also resulted from lateral advection of constant currents, 1971a, b, 1981, 1985; LEINFELDER, 1983; LEINFELDER et al., though in this case more frequent effects of such process 1988), Spain (BASSOULLET et al., 1985), France (PELISSIE should be expected. The fact that thesarne deposits exhi- et at., 1984; BASSOULLET et al., 1985; BASSOULLET, bit fenestral structures and bridge-like cements indicates 1997), Morocco (HO1TINGER, 1967; SEJYfFONTAlNE, 1981;
a partially subaerial exposed original sediment; these BASSOULLET et al., 1985; PEYBERNES et al., 1987), the Ita- levels are recorded, for instance, at PO-9/Barrocal (PI. lian-Dinaride region (BASSOULLET et al., 1985), Israel IV/4) and Mem6ria/Cabe~o Gordo. (DERIN & REISS, 1966) and Turkey (TASLI, 1993); by Late
The most significant species are Alveosepta jaccardi JurassicitiiIso reached the American margins (BASSOULLET
(PI. IV/2) and Pseudocyclammina parvula(Pl. IV/3); see et al., 1985; BASSOULLET, 1997). Pseudocyclam:mina
165
parvula is basically known from Portugal and Morocco CHAROPHYTES (HOlTINGER, 1967; RAMALHO, 1971a, 1985), but was also
cited in Turkey (TASLI, 1993). A. jaccardi is known from As mentioned, the charophyte algae are, next to the Middle Oxfordian to the Upper Kimmeridgian; P. ostracods, the most typical fossil group in the Caba¥os parvula or gr. parvula is generally reported from the formation, being represented by several species, abun- Upper Oxfordian to the Kimmeridgian, but we have dant number of gyrogo~ites and less abundant stems, locally found it (Vale de Ventos; Fig. 5) in levels still over the whole of the basIn (PI. 1/1, 2; PI. 111/9-17).
attributable to the Middle Oxfordian on the basis of H. Though present either in marls or limestones, in simi- lusitanica, and in Algarve it reaches the Tithonian larity to ostracods the systematic identification of charo-
(RAMALHO, 1985). phytes demands loose specimens of gyrogonites. There-
K b . 1 t ...
ges . n age from the Ox fore, the taxonomic study covered the same four fieldurnu la pa as mIens IS ran I -..
fordian to the Tithonian (RAMALHO, 1971a; SEPrFONTAINE, sectlo~S- from which marly be?~ could be sampled 1988) and the other identified species have wider strati- (Pedrogao, Vale de Ventos, Memona and Valverde). The
h .
Is specimens in residues from Vermoil-1 borehole are still
grap Ica range .
under study, but current data point out to assemblages similar to those from Pedr6gao and Mem6ria/Cabe¥o
DASYCLADACEANS Gordo sections. The main results of the detailed systema-
tic study are the subject of a Master's thesis, recently Apart from a few occurrences of Salpingoporella sp. presented (PEREIRA, 2002) and of a thematic paper and unidentified dasyclad fragments in the Upper Batho- (PEREIRA et al., in press). Preliminary data had been nian lagoonallimestones just below the disconformity at presented in PEREIRA et al. (1998, 1999).
Serra dos Candeeiros (AzEREoo, 1993), this group of algae The abundance of charophyte specimens in the sam- is solely represented by one species, Heteroporella pled sediment and the well-known high intraspecific lusitanica (PI. IV /1 ), in the successions here concerned diversity of the gyrogonites led us to try a twofold approach, with. However, as previously mentioned, this alga has a integrating both morphological analysis and comparative major importance as regards to the Caba¥os formation, as populational analysis. These studies revealed the it represents the best biostratigraphical constraint for this presence of several Porocharaceae species, some pre- unit, as shown in the logs of Figs. 3-5. H. lusitanica was viously recognized in Portugal, as Porochara raskyae recognized in all of the studied localities, except in (MAOLER) SHAIKIN, 1976, P. minima (MAoLER) SHAlKIN, BarrocallPombal (PO-9) and in Vermoil-l well. In the 1976, P.fuscaMAoLER, 1955,P. sulcataGRAMBAS[-~ARD, offshore wells, it was found in 14A-2 (Pedr6gaoMeira 1985 and P. kimmeridgensis MAoLER, 1955, but others
de Leiria). unknown, as Auerbachichara cf. saidakovskyi KISELEVSKY
The fact that H. lusitanica occurs in very restricted, & SAIOAKOVSKY, 1967, and a new species (Porochara locally brackish lagoonal sediments, implies that this spe- n. sp. 1). In addition, some specimens were left in open cies has an higher level of tolerance for salinity variations nomenclature (Porochara sp. and an Ind. Gen.) and one than usually accepted for dasyclads. However, it must be species of Characeae was also identified (Aclistochara noted that in those sediments it is rarely abundant, whe- longiformis WANG & YANG, 1983).
reas in the deposits from less restricted (though always In the typically freshwater facies, the charophyte very shallow) settings, with more frequent marine incur- assemblages are richer, both in abundance and diversity, sions, it is much more abundant, even forming coquinas with gyrogonites and stems occurring together. The main as at Pedr6gao (AZEREoo et al., 1998, 2000). These species are Porochara raskyae, P. minima, P. sulcata, P.
coquinas are associated with concentrations ofthick-shelled n. sp. 1, P. fusca, Auerbachichara saidakovskyi, Aclisto- bivalves and with serpulid bioherms on bedding surfaces; chara longiformis and Ind. Gen.. However, the brackish whether these represent condensation or simply accumu- lagoonal and marginal-marine facies also bear significant lation horizons is still an open question. A concentration assemblages of these algae, showing lower diversity and of Heteroporella stems in thin-section had also been higher number of gyrogonites relative to stem remains.
previously recognized by M. Ramalho, in samples from a These assemblages are dominated by Porochara kimme- small limestone outcrop in Ota region mentioned by ridgensis, locally associated with P. fusca.
LEINFELOER et al. (1988), but not directly studied by us. Two particular features recognized in the studied suc-
Heteroporella lusitanica was never found in the cessions are worth mentioning: one is ~he fact that the
Algarve Basin (RAMALHO, 1985). charophyte remains often form coquinas, either on bed
166
tops or as stratified laminae within microbial laminites, -In the east of the basin, inner-marine deposits and very much in common with the ostracodites, including (at assemblages of late Bathonian-Callovian age below Pedr6gao) in layers intercalated with evaporite-bearing the discoI}formity are succeeded by Oxfordian limestones. This recalls the examples of co-occurrence of deposits and assemblages sucessively suggesting charophytes and evaporites in modern deposits from erosion, very shallow, dominant freshwater condi- coastal saline lakes of Australia (BURNE et al., 1980). tions with marked subaerial exposure, freshwater- Another interesting fact is the already mentioned charo- oligohaline lacustrine setting gradually interfinge- phytic ferruginous limestone truncated by a discontinuous red with, and overlain by, restricted lagoonal, more palaeosurface draped by charophyte stems (mostly) and marine influenced environment.
gyrogonites (Fig. 3; PI. 1/1), assigned to the Middle- Upper Jurassic boundary at Pedr6gao (AzEREoo et al.,
2000, in press). Other examples of particularly high num- ACKNOWLEDGEMENTS bers of stem remains were observed inthin-sections, namely
from Pedr6gao, Cabo Mondego, Valverde, Vale de Ventos, These studies were developed within the scope of the Mem6ria/Cabe~o Gordo and Montejunto limestones. research project PRAXIS XXI/PCNA/C/6/96, funded by the FCT (Portugal). We sincerely thank Prof. Reinhold Leinfelder (University of Mtinchen, Germany) and an
CONCLUSIONS anonymous referee for their constructive review of the
manuscript, and Dr. Jose Miguel Martins (Instituto Geo- The successions across the Middle-Upper Jurassic 16gico e Mineiro, Lisboa) for kindly assisting with com- disconformity in the Lusitanian Basin, in particular those puter drawings.
belonging to the Oxfordian Caba~os formation, have rich microfossil assemblages, comprising mainly ostracods and
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170
PLATE I
Fig. 1 -Photomicrograph of the ferruginous charophytic limestone (charophyte stem coquina) featuring the presumed Middle-Upper Jurassic boundary at Pedrogao; Lower (?) Oxfordian. X36.
Fig. 2- Photomicrograph of an ostracodite, also showing a charophyte gyrogonite (top-centre of the picture) and textularid foraminifera (one clearly visible towards the right). Middle Oxfordian, Pedrogao section. X49.
172
PLATE II
Fig. I -Theriosynoecum gr. wyomingense (BRANSON, 1935): example from the Lower (?) to Middle Oxfordian of Valverde section, female left valve, lateral view, X50.
Fig. 2 -Theriosynoecum jllaans spiculata (HELMDACH, 1972): example from the Lower (?) to Middle Oxfordian of Pedrogao section; female left valve, lateral view, X50.
Fig. 3 -Theriosynoecum jllaans fluxans (HELMDACH, 1972): example from the Lower (?) to Middle Oxfordian of Pedrogao section; male carapace, right view, X50.
Fig. 4 -Theriosynoecum levis (HELMDACH, 1972): example from the Lower (?) to Middle Oxfordian of Pedrogao section; right valve, lateral view, X50.
Fig. 5 -Sinuocythere pedrogaensis CABRAL & COLIN, 2000: example from the Middle to Upper (?) Oxfordian of Pedr6gao section; female carapace, right view, X75.
Fig. 6 -Sinuocythere candeeirosensis CABRAL & COLIN, 2000: example from the Lower (?) to Middle Oxfordian of Vale de Ventos section; female carapace, right view, X75.
Fig. 7 -7imiriasevia sp.: example from the Lower (?) to Middle Oxfordian of Memoria section; carapace, left view, X75.
Fig. 8 -Klieana n. sp. 1: example from the Lower (?) to Middle Oxfordian of Vale de Ventos section; female left valve, lateral view, X75.
Fig. 9 -Klieana n. sp. 2: example from the Lower (?) to Middle Oxfordian of Valverde section; female left valve, X75.
Fig. 10- Klieana n. sp. 3: example from the Middle Oxfordian of Vale de Ventos section; male? carapace, left view, X75.
Fig. II -Klieana n. sp. 4: example from the Lower (?) to Middle Oxfordian of Valverde section; male? carapace, left view, X75.
Fig. 12- Ind. Gen. n. sp. 0-16: example from the Lower (?) to Middle Oxfordian of Pedrogao section; female? left valve, lateral view, X75.
Fig. 13- Galliaecytheridea n. sp. 1: example from the Middle Oxfordian of Pedr6gao section; male? carapace, left view, X75.
Fig. 14- Ind. Gen. n. sp. 1: example from the Lower (?) to Middle Oxfordian of Pedrogao section; carapace, left view, X50.
The Scanning Electron Microscope photographs were taken in the Centro de Biologia Ambiental (Faculdade de Ciencias da Universidade de Lisboa) by Drs. Monica Martins and Telmo Nunes.
