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

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<ul><li><p>THE TOARCIAN AAI,ENIAN BOUNDARY IN THE BETIC CORDII,I,ERA </p><p>(SOUTHERN SPAIN) </p><p>RAFAEL GARCILA-GOMEZ, ANTONIO P. JIMENEZ, ASUNCION LINARES, PASCUAL RIVAS &amp; JOSE SANDOVAL. </p><p>GARC~A-G(~MEZ R., J IMI~NEZ A.P., LINARES A., RIVAS P. &amp; 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. </p><p>ABSTRACT </p><p>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. </p><p>KEY-WORDS : SUBBETIC, SOUTHERN SPAIN, TOARCIAN - AALENIAN BOUNDARY, AMMONITE - FAUNA, BIOSTRATIGRAPHY. </p><p>RI~SUMt~ </p><p>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 &amp; 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. </p><p>MOTS-CL]~S : SUBBt~TIQUE, SUD DE L'ESPAGNE, TRANSITION TOARCIEN - AALt~NIEN, AMMONITES, BIOSTRATIGRAPHIE </p></li><li><p>212 </p><p>TOJ AEN </p><p>O </p><p>TO GRANADA </p><p>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. </p><p>INTRODUCTION </p><p>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 &amp; Rivas 1981 ; Garc ia Gdmez &amp; Rivas 1981a,b ; E lmi et al . 1989 ; Goy &amp; 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 ; </p><p>Henr iques 1989 ; E lmi &amp; Rul leau 1991 ; Cresta 1991 ; Goy &amp; 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. </p><p>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 </p></li><li><p>213 </p><p>E I= </p><p>_ +.+ '--+ + t,++ .++++++ +.+ _+++ ++++ + .+, I+ " + ++--'+++ +++++ ram++ +'+_+ +." =+=-+.0 . - .= . = ++ '+</p></li><li><p>214 </p><p>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. </p><p>GEOGRAPHICAL AND GEOLOGICAL SETTING </p><p>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). </p><p>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. </p><p>LITHOLOGY AND FACIES </p><p>SIERRA DE RICOTE (Fig. 2) </p><p>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. </p><p>CERRO Mt~NDEZ 1. (Fig. 3) </p><p>A preliminary note about the biostratigraphy of this section has been published by Linares &amp; 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. </p><p>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. </p><p>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. </p><p>CERRO MI~NDEZ 2 (Fig. 4) </p><p>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). </p><p>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. </p><p>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. </p></li><li><p>215 </p><p>CM-1 ~ + ~ .- </p><p>. _ . . _+ +., ++ ~+ ++ </p><p>+ + + + .+- .++, + -+ .+- '+ o j++ +++ .+ , </p><p>I I I I I I I I I </p><p>i I i </p><p>r </p><p>[ </p><p>i </p><p>I </p><p>I </p><p>1 I , i 6 </p><p>I . 1 I </p><p>I I I </p><p>I t </p><p>I I </p><p>I 0 </p><p>i I t l </p><p>t I </p><p>r I </p><p>61.6 </p><p>1 </p><p>+ J </p><p>I </p><p>I </p><p>go </p><p>+ I </p><p>+ ,o I t i </p><p>I l I t I I , ,* </p><p>I I </p><p>I I </p><p>, ? !+ i l l I I i </p><p>t I I </p><p>I </p><p>i </p><p>{ </p><p>I </p><p>+ l I u </p><p> + + I t lD I </p><p>' ; t+ +' + l l l l l </p><p>I I t l ~ I I </p><p>I ' ' </p><p>~, I ' P+</p></li><li><p>216 </p><p>E </p><p>CM- 2 + + </p><p>I ,M ,,~ ~ ~. - o =.% ~ ~. -~ - ~ E t </p><p>' 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 </p><p>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 </p><p>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 ' </p><p>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 </p><p>- - i , I t , ~ , , , ' '= i 1 1 1 l t I i , i i I I @0 [ t </p><p>l ~ ' ' I ' I I I I I ~ I I I I r </p><p>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 </p><p>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 </p><p>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 </p><p>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 </p><p>, I I I ~ I I '+_ + I I I I I I I I I t I I I l l Ill </p><p>I I 1% I ' I ' ' ' I ' ' ' ~ ' ~ ' ; i I ' { lrl i , </p><p>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 " </p><p>'~ 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 </p><p>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 </p><p>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 ' </p><p>" ' I I ' ~ i ' ' ' ' I I I ' i [ l I ! lp ~ i , I , , , t l ' I i l ' </p><p>I ~ I I I I ~ I i , i 0 35 ' , , I ' ' ' , ,' ' I ' , I r ' , I , </p><p>I [ </p><p>I , I [ I .~ n i t , , l r , ' l ' ' r l i , , , [ , l </p><p>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 </p><p>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 </p><p>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 </p><p>. . . . . . ~0~[~= ~ : , , , , , I ' , ' , , , ' ;~ ', ,,~.'' ' ' ' ' ' , I ,+ , - - " , I I J I ' I ' I~ I I I~ I </p><p>, , . , , , , , , , , , </p><p>_'</p></li><li><p>217 </p><p>TOARCIAN i =o [ m O ' . ,g l , I -&lt; I t - i r" I I ~ i rn~ </p><p>I I~ I C I </p><p>AALENIAN r </p><p>MURCHISONAE </p><p>STAGE </p><p>ZONE </p><p>SCALE </p><p>i j - I I _ I _ . LEVEL </p><p> 0 - - 0 0 0 - 0 - - - ~ - 0 - - - </p><p>0 - . . . . . . . . . . . . . . . . . . . . . . . . O0 . . . . . . - 0 - - 0 00- . . . . . . . . . - - - -O . . . . . . . . . . . . </p><p>O -O </p><p> - - -O - - - -0 . . . . . . . . . . . . </p><p>0 - 0 - O-- . . . . 0 - - </p><p>0 - - - -O -O </p><p>0-0 - - </p><p>0-- O-- </p><p>0 - - - </p><p>N m </p><p>i </p><p>m </p><p>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 </p><p>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). </p><p>ZEGRI NORTE (Fig. 5) </p><p>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- </p><p>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. </p></li><li><p>TI - IE AMMONITE ASSOCIAT IONS AND THEIR CONNEXION WITH FACIES TYPE (Fig. 2-4 ; P1. 1) </p><p>In mar ly and grey marly- l imestone fa...</p></li></ul>

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