The Toarcian Aalenian boundary in the Betic Cordillera (Southern Spain)

  • Published on
    14-Sep-2016

  • View
    219

  • Download
    4

Transcript

  • THE TOARCIAN AAI,ENIAN BOUNDARY IN THE BETIC CORDII,I,ERA

    (SOUTHERN SPAIN)

    RAFAEL GARCILA-GOMEZ, ANTONIO P. JIMENEZ, ASUNCION LINARES, PASCUAL RIVAS & JOSE SANDOVAL.

    GARC~A-G(~MEZ R., J IMI~NEZ A.P., LINARES A., RIVAS P. & SANDOVAL J. 1994 - The Toarcian Aalenian boundary in the Betic Cordil lera (Southern Spain) [La transit ion Toarcien-Aal~nien dans les Cha~nes B~tiques (Sud de l'Espagne)]. GEOBIOS, M. S. 17 : 211-222.

    ABSTRACT

    The Toarcian-Aalenian boundary has been studied accurately for the first time, in three areas of the Subbetic domain (Southern Spain). The successive ammonite assemblages have permitted to dist inguish the uppermost Toarcian, Aalensis Zone (Mactra, Aalensis and Buckmani Subzones), and Lower Aalenian, Opal inum Zone, (Opali- num and Comptum Subzones). In the Aalensis Zone, ammonite fauna is mainly represented by Pleydellia together with some Catulloceras and Hamrnatoceras. Lytoceratidae and Phylloceratidae also occur. In the lower Opal inum Zone, the fauna is always scarce ; on the contrary, Comptum Subzone has yielded an abundant fauna of Leioceras, Tmetoceras, Erycites, Hamrnatoceras, Spinamrnatoceras, Phylloceras and Lytoceras.The l imit Toarcian-Aalenian is clearly defined by the replacement of Pleydellia and Catulloceras by Leioceras and Tmetoceras.

    KEY-WORDS : SUBBETIC, SOUTHERN SPAIN, TOARCIAN - AALENIAN BOUNDARY, AMMONITE - FAUNA, BIOSTRATIGRAPHY.

    RI~SUMt~

    On a ~tudi~ la transit ion Toarcien - Aaldnien dans quatre coupes de diffdrentes rdgions du Subb~tique Moyen : Cerro M~ndez (deux coupes) et Zegr Norte (Province de Granada) et Sierra de Ricote (Province de Murcia). Le passage Toarcien - Aal~nien montre des facies marno ca]caires dans deux coupes, tandis que ]es deux autres montrent des faci6s "ammonitico rosso". I1 n'existe pas de discontinuit6s strat igraphiques apparentes, bien que les sediments du Toarcien sup6rieur - Aal6nien inferieur peuvent ~tre tr~s condensds, voire m~me manquer par suite de lacunes strat igraphiques dans d'autres points du Subb6tique (Subb~tique externe). Les associations d'ammoni- tes trouv6es permettent une identif ication claire de la zone h Aalensis (sous-zones h Mactra, Aalensis et Buckma- ni), du Toarcien sup~rieur et de la zone h Opal inum (sous-zones h Opal inum et Comptum) de l 'Aal6nien infdrieur. La faune de la zone g Aalensis est dominde par des formes pla~yc6nes appartenant au genre Pleydellia, encore que la faune soit tr~s pauvre dans la sous-zone fi Buckmani ; de plus, on trouve de fr6quentes formes serpenticSnes du genre Catulloceras, et quelques Hammatocerat inae, Erycitinae, PhyUoceratinae et Lytoceratinae. Remarquons que dans les faci6s ammonitico rosso la faune est moins abondante. Dans les premiers niveaux de l'Aal~nien (sons- zone & Opal inum) la faune est tr~s peu abondante. On ne trouve que quelques Leioceras et de rares Hammatocera- tidae, ainsi que des Phyl loceratidae et Lytoceratidae. Dans la sous-zone h Comptum, la faune devient tr~s abon- dante mais tr6s peu vari6e, domin~e par des formes oxycSnes du genre Leioceras, coexistant avec des platyc6nes (Tmetoceras et Hammatocerat inae) et avec des Phylloceratinae et des Lytoceratinae. La l imite Toarcien - Aal~nien se trouve clairement d~fmie par le remplacement des derniers Pleydellia et Catulloceras par les premiers Leioce- ras et Tmetoceras.

    MOTS-CL]~S : SUBBt~TIQUE, SUD DE L'ESPAGNE, TRANSITION TOARCIEN - AALt~NIEN, AMMONITES, BIOSTRATIGRAPHIE

  • 212

    TOJ AEN

    O

    TO GRANADA

    Figure 1 - Geographical and geological location of the studied sections : A. Sierra de Ricote. B. Cerro M6ndez. C. Zegri Norte. 1, Guadalquivir Unit ; 2, Postorogenic and volcanic rocks ; 3, Nevado-Filabride ; Alpujfirride ; Malfiguide and Rondaide ; 4, Campo de Gibraltar Complex ; 5, Hercinian Massif ; 6, Tabular cover ; 7, Prebetic ; 8, Intermediate Units ; 9, External Subbetic ; 10, Middle Subbetic ; 11, Internal Subbetic ; 12, Penibetic. Localisation gdographique et gdologique des sections dtudides : ,4, Sierra de Ricote ; B. Cerro Mgndez ; C. Zegri Norte ; 1, Unitd du Guadalquivir ; 2, Postorogdnique et roches volcaniques ; 3, Nevado- Fildbride ; Alpujdrride ; Maldguide et Rondaide ; 4, Flysch du Champ de Gibraltar ; 5, Massif hercynien ; 6, Couverture tabulaire 7, Prdbdtique ; 8, Unitds Intermgdiaires ; 9, SubbOtique externe ; 10, Subbdtique rnoyen ; 11, Subbgtique interne ; 12, Penibgtique.

    INTRODUCTION

    There have been many studies about the Upper Toarc ian b iost rat igraphy and ammoni te fauna in the Med i te r ranean and Submedi ter ranean pro- vinces and specifically in the Betic Cordil lera. Among the most recent it is worth ment ioning those by Rivas 1972 ; J im6nez & Rivas 1981 ; Garc ia Gdmez & Rivas 1981a,b ; E lmi et al . 1989 ; Goy & Mart inez 1990 ; Goy et al. 1988, etc. The- re are also several notes on the Betic Aalenian, such as L inares 1972 ; L inares et al. 1987, etc. L ikewise recent studies of the Toarcian-Aalenian boundary have been carr ied out by Ohmert 1985 ;

    Henr iques 1989 ; E lmi & Rul leau 1991 ; Cresta 1991 ; Goy & Ureta 1991 ; Ohmert et al . 1991. However, apart from a short and little known pa- per by Linares and Rivas 1973 on the Cerro M6ndez 1 section, (in which dupl icat ions of the series by fault ing was not noticed), other data on the Toarcian-Aalenian boundary ne i ther exist in tlie Betic Cordil lera nor in other typical ly Medi- te r ranean areas. Therefore a study about this li- mit seems very necessary.

    In this paper we study for f irst t ime the Toar- c ian-Aalenian boundary in the Betic Cordi l lera by means of careful sampl ing, bed by bed, of four

  • 213

    E I=

    _ +.+ '--+ + t,++ .++++++ +.+ _+++ ++++ + .+, I+ " + ++--'+++ +++++ ram++ +'+_+ +." =+=-+.0 . - .= . = ++ '+

  • 214

    stratigraphic sections and the detailed analysis of their successive ammonite assemblages. This in turn will also allow us to determine more clearly the behaviour of the Lower-Middle Jurassic boundary in the Mediterranan cordilleras.

    GEOGRAPHICAL AND GEOLOGICAL SETTING

    After a general view of different localities where the Toarcian and Aalenian materials outcrop, we have selected four stratigraphic sections (Fig. 1) in three areas of the Subbetic domain (Southern Spain) on the base of their stratigraphic continui- ty, bedding, exposition and faunal content. In this way they display the most adequate condi- tions to carry out a fine stratigraphical study ba- sed on ammonite fauna vertical range. These are : Northern Zegri (Province of Granada), two sec- tions in Cerro M~ndez (Alamedilla, province of Granada) and the Sierra de Ricote (province of Murcia).

    From the paleogeographic point of view (Fig. 1), all the sections belong to the Middle Subbetic (the central part of the external zones of the Be- tic Cordillera), this being the only Betic domain with a more or less continuous pelagic sedimen- tation during the Upper Toarcian-Lower Aale- nian. Data from other sectors of the Middle and the External Subbetic have been added. In this last domain and in the Internal Subbetic the Up- per Lias and Lower Dogger sections are very con- densed : the Upper Toarcian-Lower Aalenian may even coincide with a sedimentary gap.

    LITHOLOGY AND FACIES

    SIERRA DE RICOTE (Fig. 2)

    In the Sierra de Ricote section (Fig. 1,2) the ma- terials belonging to the Reynesi Zone are 8 to 10 m thick ; where grey marls predominate over marly-limestones. The beds vary in thickness from 10 to 50 cm. The Aalensis Zone is composed of alternating beds of marls and grey marly-lime- stones. At the beginning of the Zone marly-lime- stones predominate over marls, while the reverse is true for the upper part of the zone.

    CERRO Mt~NDEZ 1. (Fig. 3)

    A preliminary note about the biostratigraphy of this section has been published by Linares & Ri- vas 1973, which located the Toarcian-Aalenian boundary between beds 50-58. In Cerro M~ndez 1, the materials belonging to the Upper Toarcian are rather uniform. The Reynesi Zone is approxi- mately 5 m thick with regularly alternating grey marls and marly-limestones in beds varying in thickness from 20 to 70 cm. The Aalensis Zone is about 15 m thick and calcareous beds may predo- minate locally over detritic ones.

    The transition from the Toarcian to the Aalenian comes about in facies similar those of lower beds; if we examine them more closely, we find how- ever that they contain a great amount of Zoophy- cos. Calcareous beds are more de tritic than at lo- wer levels.

    In the upper part of the Opalinum Zone (Comp- tum Subzone) we note a sharp transition to "am- monitico rosso" facies where a subsequent change in the faunal content can be seen.

    CERRO MI~NDEZ 2 (Fig. 4)

    This section is located approximatively 1,5 km to the SW of the previous one, within the same pa- leogeographical context. However, both thickness and facies of the Upper Toarcian-Lower Aalenian materials are completely different in the two sec- tions. The materials from the Reynesi Zone (Pseudoradiosa Zone from the Sub-Mediterranean zonations) reveal marly "ammonitico rosso" fa- cies, with a total thickness of 2,5 m, which is much less than the thickness of the materials of the same age in Cerro M~ndez 1. The Aalensis Zone is made up of little more than 1 m of par- tially nodulose limestone with resedimented fau- na, where the Aalensis and Buckmani subzones, at least, are condensed. At the base of the Opali- num Zone (which is thicker than in Cerro M~ndez 1) we find beds with aboundant Zoophy- cos. The upper nodular limestones (Figs. 3,4) oc- curs in the Murchisonae Zone while in Cerro M~ndez 1 they are in the Opalinmn Zone (Comp- turn Subzone).

    The Aalenian begins with similar facies to those of the uppermost Toarcian, but with a great amount of Zoophycos. In the lower part of the Comptum Subzone the sequence becomes more Calcareous with laminated limestones, becoming more detritic again in the upper part of this subzone and at the base of the Middle Aalenian.

    These sharp differences, both in thickness and fa- cies between two paleogeographic locations lying so close together may be explained by the exist- ence of an important distensive phase within the Betic basin, together with the effects that vulca- nism (very frequent at this age) could have had on the sea floor marine sedimentation.

  • 215

    CM-1 ~ + ~ .-

    . _ . . _+ +., ++ ~+ ++

    + + + + .+- .++, + -+ .+- '+ o j++ +++ .+ ,

    I I I I I I I I I

    i I i

    r

    [

    i

    I

    I

    1 I , i 6

    I . 1 I

    I I I

    I t

    I I

    I 0

    i I t l

    t I

    r I

    61.6

    1

    + J

    I

    I

    go

    + I

    + ,o I t i

    I l I t I I , ,*

    I I

    I I

    , ? !+ i l l I I i

    t I I

    I

    i

    {

    I

    + l I u

    + + I t lD I

    ' ; t+ +' + l l l l l

    I I t l ~ I I

    I ' '

    ~, I ' P+

  • 216

    E

    CM- 2 + +

    I ,M ,,~ ~ ~. - o =.% ~ ~. -~ - ~ E t

    ' t " ' I . . . . . t ~ J I = ~ ' i i ; I i ~ r ' ' ' ; I I ' { I I t ' I r ] I I I I I I l i I I I I t I I I J I J I

    l i I I I I l l i + I I l I J ; I I ' , I I I I [ I I I r I I I i ' i I I i I I I I I I I I

    I I I J t J I i ~ I I I ~ I I I t ; I I I I I I I I I I I I 55 s ; I I I I I l I , i, ' i 1 i i I I i I l l i ' l I I J I l l '

    f I I J I I I I 1 I I ' I I I I I ~ , I I Ip I I I + I ; I I I ; I I I I I I

    - - i , I t , ~ , , , ' '= i 1 1 1 l t I i , i i I I @0 [ t

    l ~ ' ' I ' I I I I I ~ I I I I r

    l I I I I f I " ,I 'l ,I , II r l ' ' ' i i l i I I i i r I , I I I I I [ + I r I i I i I I [ I I I I I I I I I I I l l l I I I I I I I

    I , I I l , I i I , ' I I ' I I ~ ' I i ~ I l I T I I ~ I I I i I ' i I + ~ r i I I j r , I l i I I i ' I I I I I

    J I [ r I r I I l I i i i I I I ' I I i i _ 1011 (~: + ' I , I I I . . . . . 45 , I j r r I I i j I I i r

    l I lp t , I , , i , , ' , ~ n ' , , , + II i Ip ~P I~ I + I J I + I I I i l + I I I I I I I J. I

    , I I I ~ I I '+_ + I I I I I I I I I t I I I l l Ill

    I I 1% I ' I ' ' ' I ' ' ' ~ ' ~ ' ; i I ' { lrl i ,

    8 40__ ~ i ~ - ~ I ' 1 ~ ' , I I " ' I i ; I " ' I I l+ I I , , I I O , , I ,' , I,, + , ,'i ,' , , 1 1 'i rll II + ' ' t ' l i l t 111 1 1 ' lII I I " " ~ ' ~I :0 l i iII "

    '~ I I ' r [ l ~ I i , I I l I j ,,==I: . . . . . ~ I ' I ' I [ , I r I II I I i I I l , , I I ,I ' I I t I I r l

    i I l I I I I i , [ i i i ' r I I + t I I I I I i I I I I I I Ii l l ( , { l ' l ' I I I I i I l I I l I I

    I I I + - I ' I i I I i t~ , , I i i i l ' , I I I I ' r i I I I I i 'r '

    " ' I I ' ~ i ' ' ' ' I I I ' i [ l I ! lp ~ i , I , , , t l ' I i l '

    I ~ I I I I ~ I i , i 0 35 ' , , I ' ' ' , ,' ' I ' , I r ' , I ,

    I [

    I , I [ I .~ n i t , , l r , ' l ' ' r l i , , , [ , l

    I ; I t I '[ I I ' r , ' I I , i i I i i l l i l l~ i I I I I r l I r , , , I i ~ i ~ ~ D ~ I I , l t ~ + I I I i t I I ' l 0 r 4, I I r I 11 ' I I I ' ' I I , @pO

    I I I ' l l , I I ' I I l j I i i r I l I I r I J l I I J l I J I I

    I I , I I I l ' r I l I I i I , I i I i 'I I ~ ' t' ' ' , I ' I , I I I , I I

    . . . . . . ~0~[~= ~ : , , , , , I ' , ' , , , ' ;~ ', ,,~.'' ' ' ' ' ' , I ,+ , - - " , I I J I ' I ' I~ I I I~ I

    , , . , , , , , , , , ,

    _'

  • 217

    TOARCIAN i =o [ m O ' . ,g l , I -< I t - i r" I I ~ i rn~

    I I~ I C I

    AALENIAN r

    MURCHISONAE

    STAGE

    ZONE

    SCALE

    i j - I I _ I _ . LEVEL

    0 - - 0 0 0 - 0 - - - ~ - 0 - - -

    0 - . . . . . . . . . . . . . . . . . . . . . . . . O0 . . . . . . - 0 - - 0 00- . . . . . . . . . - - - -O . . . . . . . . . . . .

    O -O

    - - -O - - - -0 . . . . . . . . . . . .

    0 - 0 - O-- . . . . 0 - -

    0 - - - -O -O

    0-0 - -

    0-- O--

    0 - - -

    N m

    i

    m

    Pseudogrammoceras sp Calliphylloceras sp Phylloceras sp Calliphylloceras beatricis Dumortieria latiumbilicata Catulloceras meneghmii Alocolytoceras sp Lytoceras sp Alocolytoceras ophioneum Catulloceras sp Pleydellia subcompta P. aalensis Dumortieria rhodanica Tmetoceras sp Erycites rotundi formis E. fallifax Leioceras sp Leioceras comptum Spinammatoceras sp Sp. tenax Sp. shindewolfi Ludwigia haugi Abbasitoides modestum Pianammatoceras planifo,me Pseudographoeeras umbilicatum Brasilia bradfordens is Brasilia similis Malladaites sp Graphoeeras sp

    F igure 5 - Litholog~cal succession and ammoni tes vertical range of Zegr~ Norte section, Middle Subbetic. province of Granada. Succession lithologique et rdpartition stratigraphique des ammonites dans la section du Toarcielz supdrieur - AaIdnien infdrieur de Zegri Norte, province de Grenade (Subbdtique moyen).

    ZEGRI NORTE (Fig. 5)

    In the Zegr/Norte section, both the Upper Toar- cian (Reynesi and Aalensis Zones) and the Lower and Middle Aalenian are of "ammonitico rosso" facies, which are typical of a talus edge. The ma-

    terials from this age, in beds ranging from 10 to 40 cm, are, in all, barely 6 m thick. Resedimented and reworked fauna is common in the Aalenian. From the Middle Aalenian onwards sedimenta- tion reestablished with alternating marls and marly-limestones.

  • TI - IE AMMONITE ASSOCIAT IONS AND THEIR CONNEXION WITH FACIES TYPE (Fig. 2-4 ; P1. 1)

    In mar ly and grey marly- l imestone facies the ma- terials of the Reynesi Zone (the base of which is determined by the first record of Osperleioceras gr. reynesi (MONESTIER) contains predominant ly semioxycone sl ightly ornamented forms, belon- ging to the genus Osperleioceras : O. reynesi (Mo- NESTIER), O. carezi (MONESTIER), O. wunstor f i (MONESTIER) and O. subbet icum RIVAS. Together with these , we find serpenticones belonging to the Dumort ie r ia : D. rhodanica (HAUG), D. la- t iurnbi l icata GECZY ; Lytocerat ina (Alocolytoceras ophioneurn (VACEK) and a few Phyl loceratina and Hammatoceras s. 1.

    In those sections (e. g. Cerro M6ndez 2) where the mater ials from this age contain "ammonitico rosso" facies, the faunal associations are rather

    218

    different from those which exist in marl and grey marly-l imestones. It is, sometimes, difficult to es- tablish chronostratigraphic correlations between both types of sections even within the same sedi- mentary basin. In this facies type, the faunal as- semblages are dominated by Phylloceratina, and evohite platycones belonging to the genus Ham- matoceras : H. meneghin i i BONARELLI, H. victorii BONARELLI, H. porcarel lense MERLA, Erycites e laphus MERLA ; serpenticones [Durnortiera leves- quei (D'ORBIGNY)] are sometimes locally frequent and there are very few oxycones. We should point out the presence of forms such as Pseudol i l l ia (see Garcia G6mes & Rivas 1980b), a genus which appears hardly in grey facies. The Reynesi Zone is corresponding with the Pseudoradiosa Zone sensu Goy & Martfnez (1990) and with XXII & XXIII horizons of Elmi & Rulleau (1991).

    On the sections with grey marls and mar ly lime- stones facies there is a relatively sharp fauna

    PLATE 1

    Fig. 1 - Osper le ioceras subbet icum RIVAS. CM1 - 42-2 ; Upper Toarcian, Aalensis Zone, Mactra Subzone ; CM1. section, Cerro M6ndez area, Granada prov. Toarcien supgrieul, zone it Aalensis, sous-zone & Mactra ; section CM1, secteur de Cerro M6ndez, prov. de Grenade.

    Fig. 2 - P leyde l l ia mact ra BUCKMAN. CM1 - 39-5 ; Upper Toarcian, Aalensis Zone, Mactra Subzone ; CM1 section, Cerro M6ndez area, Granada prov. Toarcian supdrieur, zone h Aalensis, sous-zone & Mactra ; section CM1, secteur de Cerro Mdndez, prov. de Grenade.

    Fig. ~ - P leyde l l ia aft. arcuata (BuCKMAN). CM1 - 45-3 ; Upper Toarcian, Aalensis Zone and Subzone ; CM1 section, Cerro M6ndez area, Granada prov. Toarcien supdrieur, zone et sous-zone it Mactra ; section CM1, secteur de Cerro Mdndez, prov. de Grenade.

    Fig. 4 - P leyde l l ia subcompta (BRANCO). CM1 - 43-1 ; Upper Toarcian, Aalensis zone and Subzone ; CM 1 section, Cerro M6ndez area, Granada prov. Toarcien supdrieur, zone et sous-zone h Aalensis ; section CM1, secteur Cerro M~ndez, prov. de Grenade.

    Fig. 5 - P leyde l l ia aa lens is (ZIETEN). CM1 - 46-2 ; Upper Toarcian, Aalensis Zone and Subzone ; CM1 section, Cerro M6ndez area, Granada prov. Toarcien supdrieur, zone et sous-zone it Aalensis ; section CM1, secteur Cerro M~ndez, prov. de Grenade.

    Fig. 6 - PIeydel l ia fa lc i fer MAUBEUGE. CM2 - 29-2 ; Upper Toarcian, Aalensis Zone ; CM2 section, Cerro M6ndez area, Granada prov. Toarcien supgrieur, zone it Aalensis ; section CM2, secteur Cerro Mdndez, prov. de Grenade.

    Fig. 7 - Leioceras costosum (QUENSTEDT). SRil - 61-1 ; Lower Aalenian, Opalinum Zone, Comptum Subzone ; SRil section, Sierra de Ricote area, Murcia prov. Aaldnien infdrieur, zone & Opalinum, sous-zone it Cornpturn ; section SRi, secteur Sierra de Ricote, prov. de Murcie.

    Fig. 8 - P leyde l l ia fa lc i fer MAUBEUOE. CM 1 - 56-3 ; Upper Toarcian, Aalensis Zone, Buckmani Subzone ; CM1 section, Cerro M6ndez area, Granada prov. Toarcien sup~rieur, zone it Aalensis, sous-zone it Buckmani ; section CM1, secteur Cerro Mendez, prov. de Grenade.

    Fig. 9 - Leioceras opa l inum (REYNECKE). CM2 - 33-1 ; Lower Aalenian, Opalinum Zone and Subzone ; CM2 section, Cerro M6ndez area, Granada prov. Aal6nien infdrieur, zone et sous-zone it Opalinum ; section CM2, secteur Cerro Mdndez, prov. de Grenade.

    Fig. 10 - Le ioceras opa l inum (REINECKE). SRil - 56-1. Lower Aalenian, Opalinum Zone and Subzone ; SRil section, Cerro M6ndez area, Granada prov. Aaldnien infdrieu~, zone et sous-zone it Opalinum ; section SRi l , secteur Sierra de Ricote, prov. de Murcie.

    Fig. 11 - Anco l ioceras opal ino ides (MAYER). SRil - 72-1 ; Middle Aalenian, Murchisonae Zone, Haugi Subzone ; SRil section, Sierra de Ricote area, Murcia prov. Aaldnien moyen, zone it Murchisonae, sous-zone h Haugi ; section SRi l , secteur Sierra de Ricote, prov. de Murcie.

    Fig. 12 - Le ioceras comptum (REINECKE). SRi -64-14 ; Lower Aalenian, Opalinum Zone, Comptum subzone ; SRil section, Sierra de Ricote area, Mnrcia prov. Aaldnien inf~rieur, zone it Opalinum, sous-zone h Comptum ; section SRi l , secteur Sierra de Ricote, prov. de Murcie.

    Fig. 13 - Eryci tes fa l l i fax ARKELL. CM1 -75-1 ; Lower Aalenian, Opalinum Zone, Comptum Subzone ; CM1 section, Cerro M6ndez area, Granada prov. Aaldnien infdrieul, zone it OpaIinu m, sons-zone & Cornptum ; section CM1, secteur Cerro Mdndez, prov. de Grenade.

  • Geob ios P1. 1 M.S. n 17 R. Garc ia -Gomez et al.

    ~-~_- : " ~

    i - - - -~:~. !1

    i /:N~

  • 220

    transition between the Reynesi and Aalensis zo- nes (the base of the Aalensis Zone is determined by the first record of the genus Pleydellia). We observe the massive appearance of forms belon- ging to the genera PleydeUia and Cotteswoldia while Osperleioceras, limited to the lower part of the Zone, becomes a minoritary genus. The va- rious forms of the genera Pleydellia and Cottes- woldia supersede each other over time, but they are always the dominant ammonite fauna, reaching their "acm~" in the Aalensis Subzone with heavely ornamented forms belonging to the species PleydeUia foUeata BUCKMAN and P. ar- cuata Buckman, together with P. fluens BUCK- MAN and P. aalensis (ZIETEN).

    The different assemblages of Pleydellia allow us to identify the Mactra, Aalensis and Buckmani Subzones. The Mactra Subzone is characterized by the presence of Pleydellia mactra (DUMOR- TIER), P. subcompta BRANCO, Cotteswoldia bifax BUCKMAN, Paradumortieria tectiforme ELMI & CALOO-FONIER together with abundant Ospeleio- ceras subbeticum RIVAS, O. wunstorfi (MONES- TIER), Dumortieria rhodanica (HAUG), Phyllocera- tina (Calliphylloceras y Holcophylloceras) and Ly- toceratina (Alocolytoceras ).

    The Aalensis Subzone coincides with the height of Pleydellia and Cotteswoldia. Together with P. aalensis (ZIETEN) we find P. arcuata BUCKMAN, P. burtonensis (BUCKMAN), P. falcifer MAUBEUGE, P. fluens BUCKMAN, P. folleata BUCKMAN, P. sub- compta (BRANCO), Cotteswoldia bifax BUCKMAN, C. crinita BUCKMAN and C. limatula BUCKMAN ; Catulloceras dumortieri (THIOLLIERE), C. insigni- similis (BRAUNS) and C. perroudi (DUMORTIER), are likewise frequents.

    Hammatoceras, Parammatoceras, Erycites, Calli- phylloceras, Holcophylloceras, Ptychophylloceras and Alocolytoceras are more scarce, but they oc- cur throughout the Aalensis Subzone. This faunal association is similar to those from Northern Spain by Goy & Martinez 1990, Goy & Ureta 1991.

    The ammonite fauna is scarce in the Buckmani Subzone, and the involute and slightly oranmen- ted Pleydellia such as P. falcifer MAUBEUGE and P. buckmani MAUBEUGE are the more repre- sentative forms. In addition of PleydeUia, we find frequent CatuUoceras ans scarce Parammatoce- ras, Bredyia, Phylloceratina (Calliphylloceras, Holcophylloceras and PtychophyUoceras) and Ly- toceratina (Alocolytoceras). In materials belonging to the Aalensis Zone, the ammonite fauna is more scarce in facies "ammonitico rosso" (Zegr/ Norte) than in grey marls and marly-limestones

    facies ; but diferences do not seem to exist be- tween the ammonite assemblages present in dif- ferent types of lithology.

    In the Subbetic domain the Toarcian-Aalenian boundary is established at the first record of Leioceras and Tmetoceras which approximately coincides with the last records of Pleydellia and Catulloceras. It is not easy to distinguish, mor- phologically, the last Pleydellia (P. falcifer MAC- BEUGE, P. buckmani MAUBEUGE) from the first Leioceras [L. opalinum (REINECKE)]. Leioceras opalinum (REINECKE) is finely ribbed, and has a relatively large umbilicus, smooth sides and a rounded umbilical edge : these characteristics make these examples similar in appearance to Pleydellia buckmani MAUBEUGE, and some speci- mens of P. falcifer MAUBEUGE.

    At the base of the Aalenian (Opalinum Subzone) the ammonite in general and the Leioceras, in particular, are usually scarce. In the Upper part of the Lower Aalenian (Comptum Subzone) the fauna is usually more aboundant and varied : we have identified grooved, fasciculated and pseudo- ribbed forms of Leioceras. The last Leioceras in this Subzone have thick ribbing and a larger um- bilicus. Associated with these Leioceras we find a few Plananmatoceras, Parammatoceras and Ery- cites fallifax ARKELL, especially in the "ammoniti- co rosso" facies (Cerro M~ndez 1 and Zegrl Norte). Tmetoceras scissum (BENEKE) and Spi- nammatoceras tenax (VACEK), S. pugnax (VACEK) are often found together with the previous ones, and are sometimes abundant.

    The boundary between ~.he Lower and Middle Aalenian can easily be traced. At almost all the points studied it coincides with a marked faunal transition. The graphoceratids replace most of the leioceratids, the genus Ludwigia (L. haugi DOUVILLE, L. crassa HORN) appears, and we find Ancoleioceras for the first time, which are typical of th first subzone of the Murchisonae Zone.

    CONCLUSIONS

    The study of the Toarcian-Aalenian boundary has been made in three different areas of the Middle Subbetic : Sierra de Ricote, prov. of Murcia (1 section), Cerro M~ndez (2 sections), and Zegr/ Norte (1 section), prov. of Granada.

    In two sections ; Sierra de Ricote and Cerro M~ndez 1, the beds corresponding to the mentio- ned boundary are made up of well stratified al- ternances of marls and marly limestones, whe- reas "ammonitico rosso" facies also occur in the

  • 221

    other two sampled sections (Cerro M~ndez 2 and Zegr/Norte).

    The successive ammonites assemblages clearly allow to dist inguish the uppermost Toarcian, Aalensis Zone (Mactra, Aalensis and Buckmani Subzones) and the Lower Aalenian, Opal inum Zone (Opal inum and Comptum subzones).

    In the Aalensis Zone, the ammonite fauna is do- minated by platycones belonging to the genus Pleydellia, espacially with regard to the Mactra and Aalensis Subzones ; in the Buckmani Subzone the fauna is very scarce as a rule, ser- penticones of the genus Catulloceras together with Phyl loceratina being dominant.

    Hammatocerat inae, Erycitinae, Phylloceratidae and Lytocerat idae are likewise present and they range throughout the complete Aalensis Zone.

    The ammonite fauna is very scarce in the initial beds of the Aalenian (Opalinum Subzone) where only few Leioceras and Tmetoceras together with Lytoceratinae, Phylloceratidae and rare Hamma- toceratidae occur.

    The fauna is very abundant, but scarcely varied, in the Comptum Subzone ; here the ammonites assemblages are dominated by oxycones belon- ging to the genus Leioceras, which coexist with platycones (Tmetoceras and Hammatocerat idae), Phylloceratidae and Lytoceratidae.

    The replacement of the last Pleydellia and Ca- tulloceras by the first Leioceras and Tmetoceras, clearly defines the Toarcian-Aalenian boundary in the Subbetic domain. Except for Lytoceratina and Phylloceratina, the ammonite-associations here recorded are similar to those from Northern Spain, South-Eastern of France and Portugal (Submediterranean province).

    Zoophycos is very abundant in the last beds of the Toarcian and the first ones of the Aalenian, precisely where the ammonite are rare.

    In the Internal and External Subbetic, the Upper Lias and the Aalenian sections are generally very condensed and the Upper Toarcian-Lower Aale- nian may even coincide with a sedimentary gap.

    REFERENCES

    CRESTA S. 1991 - Lithostratigraphic and Biostratigra- phic features of the Middle Jurassic sequence in the Monte Nerone area (Apennines, Italy). In N. NORTON (ed.) : Conference on Aalenian and Bajo-

    cian Stratigraphy Isle of Skye, Scotland. Birbeck College, Univ. of London: 7-31.

    ELMI S., GoY A., MOUTERDE R., RIVAS P. & ROCHA R. 1989 - Correlaciones bioestratigr~ficas en el Toar- ciense de la Peninsula Ib~rica. Cuad. Geol. Ibdrica, 13 : 265-277.

    ELMI S. RULLEAU L. 1991 - Le Toarcien des carri~- res Lafarge (Bas-Beaujolais, France) : Cadre bios- tratigraphique de r~f~rence pour la R~gion Lyon- naise. Geobios, 24/3 : 315-331.

    GARCIA GOMEZ R. & RIVAS P. 1980a - Pseudogrammo- ceras (Hildoceratacea, Ammonoidea) del Toarciense medio y superior de las Cordilleras B~ticas (Anda- lucia, Espafia). Estudios Geol., 36 : 263-274.

    GARCIA GOMEZ R. & RIVAS P. 1980b - E1 g@nero Pseu- dolillia en las Cordilleras B~ticas. Cuad. Geol. Univ. Granada, 11 : 195-207.

    GOY A., JIMENEZ A.P., MARTINEZ G. & RIVAS P. 1989 - Difficulties in correlating the Toarcian ammonite succession of the Iberian and Betic Cordilleras. In R. ROCHA & A. SOARES (eds.) : 2nd International Symposium on Jurassic Stratigraphy, Lisboa, 1 : 155-178.

    GoY A. & MARTINEZ G. 1990 - Biozonacidn del Toar- ciense en el ~rea de la Almunia de Dofia Godina. Ricla. Sector Central de la Cordillera Ib~rica, Cuad. Geol. Ibdrica, 14 : 11-53.

    GOY A. & URETA M.S. 1991 - The lower boundary of the Aalenian in the Fuentelsaz section (Iberian Range, Spain). In N. NORTON (ed.) : Conference on Aalenian and Bajocian stratigraphy Isle of Skye, Scotland. Birbeck College, Univ. of London : 33-47.

    HENRIQUES M.H. 1989 - O limite Lias - Dogger no Baixo Mondego (Portugal) : Ensaio de Caracteriq~o Biostratigr~fica. Publ. Lab. Mineral. Geol. Univ. Coimbra, 107 : 37-42.

    JIMENEZ A. P. RIRTAS P. 1981 - E1 Jur~sico de las Zonas Externas de las Cordilleras B~ticas. III. Zona Subb~tica. III. 4 E1 Toarciense. Cuad. Geol. Univ. Granada, 10 : 397-411.

    LINARES A. 1979 - E1 Jur~sico de las Zonas Externas de las Cordilleras B~ticas III. Zona Subb~tica III. 5. El Aaleniense. Cuad. Geol. Univ. Granada, 10 : 107-119.

    LINARE$ A. & RIVAS P. 1973 - La transiciSn Lias - Dogger en el sector de Alamedilla, Zona Subb~tica. Cuad. Geol. Univ. Granada, 4: 155-160.

    LINARES A. & SANDOVAL J. 1986 - Malladaites nov. gen. et Spinammatoceras (Hammatoceratidae, Am- monitina) de l'Aal~nien de la Zone Subb~tique, Sud de l'Espagne. Geobios, 19, 2 : 207-224.

    LINARES A. & SANDOVAL J. 1988 - Asthenoceras y Fon- tannesia (Grammoceratinae ?, Ammonitina) del tr~nsito Aaleniense - Bajociense de la Zona Subb~- tica (Sur de Espafia). Rev. Espafil. Paleontol., 3 : 3-11.

    LINARES A., URETA M.S. & SANDOVAL J. 1987 - Compa- rison between the Aalenian ammonite associations from the Betic and Iberian Cordilleras : elements of correlations. In R. ROCHA & A. SOARES (eds.) : 2nd International Symposium on Jurassic Stratigraphy. Lisboa, 1 : 193-208.

    OHMERT W. 1985 - Problems at the Toarcian/Aalenian boundary. In O. MICHELSEN & A. ZEISS (eds) : Inter- national Symposium on Jurassic Stratigraphy. Er-

  • 222

    langen 1984. Geol. Surv. Denmark. Copenhagen, I : 259-266.

    OHMERT W., PRAUSS M. WEISS M. 1991 - The Toar- cian-Aalenian boundary at Wittnau (Oberrhein area, South West Germany), a possible boundary Stratotype for the Aalenian. In N. NORTON (ed.) : Conference on Aalenian and Bajocian stratigraphy Isle of skye, Scotland. Birbeck College, Univ. of London : 7-31.

    RIVAS P. 1973 - Estudio Paleontol6gico - Estratigr4fico del Lias en el sector Central de las Cordilleras B6ti-

    cas. Resdmenes Tesis Doct. Univ. Granada, 29 : 1 87.

    R. GARCIA-GOMEZ, A.P. JIMENEZ, A. LINARES, P. RIVAS & J. SANDOVAL

    Departamento de Estratig-rafia y Paleontologia Universidad de Granada

    Avda Fuentenueva s/n. 18071

Recommended

View more >