Middle Jurassic, Bajocian, Bathonian, Ammonitina, Biostratigraphy, Biochronology, Andes, South-America, Chile

FERNANDEZ-LOPEZ S., CHONG G., QUINZIO L.A. & WILKE H.G. 1994. The Upper Bajocian and Bathonian in the Cordillera de Domeyko, North-Chilean Precordillera : sedimentological and biostratigraphical results. [Le Ba­ jocien superieur et le Bathonien de la CordiIIere de Domeyko, PrecordilIere Nord-Chilienne : resultats sedimento­ logiques et biostratigraphiquesl.

ABSTRACT

The Jurassic ammonites of the CordiIIera de Domeyko have been studied in several monographies. The classic memoirs of Steinmann (1881), Tornquist (1898), Burckhardt (1903) and Stehn (1923) are particularly relevant. However, the biostratigraphic problems concerning stage boundaries arisen only in recent dates. New sedimentolo­ gical and biostratigraphical data have been obtained in relation to the BajocianlBathonian of this region. Several sections have been studied in two separate areas : Caracoles and Sierra de Varas. More than one thousand ammonites were collected in situ from these localities. Facies analysis shows that sedimentation during Late Bajocian and Bathonian occurs in a marine environment on a carbonate platform with abundant siliciclastic supply. Facies distribution was controlled by structural segmentation of the platform and processes of differential subsidence. The stratigraphical-sedimentological results together with taphonomical-palaeoecological observations are a diagnostic tool for sequence analysis. The successive ammonite assemblages which were found have allowed the establishment of four biostratigraphic units, spanning the interval from Upper Bajocian to Upper Bathonian. The sedimentological and biostratigraphical results indicate the existence of a regional discontinuity at the base of the Bathonian.

KEY-WORDS: MIDDLE JURASSIC, BAJOCIAN, BATHONIAN, AMMONITINA, BIOSTRATIGRAPHY, BIOCHRONOLOGY, ANDES, SOUTH-AMERICA, CHILE.

RESUME

Les ammonites du Jurassique de la CordiIIere de Domeyko ont ete traitees dans plusieurs monographies, parmi lesqueIIes les memoires classiques de Steinmann (1881), Tornquist (1898), Burckhardt (1903) et Stehn (1923) sont particulierement importants. Cependant, les problemes biostratigraphiques de limites d'etages n'ont ete evoques que recemment. Des donnees biostratigraphiques et sedimentologiques sont presentees pour la Iimite Bajocien-Ba­ thonien, a travers l'analyse de plusieurs coupes situees dans deux aires differentes de la Cordillere de Domeyko : Caracoles et Sierra de Varas. Dans I'ensemble, une importante quantite d'ammonites a ete recoItee in situ. L'ana­ lyse des facies montre que la sedimentation durant le Bajocien superieur et le Bathonien s'est developpee dans un environnement marin de plate-forme carbonatee avec d'abondants apPOrtS siliciclastiques. La distribution des fa­ cies est contr6lee par le decoupage structural de cette plate-forme et par la subsidence. Les donnees stratigraphi­ ques et sedimentologiques constituent, avec les observations taphonomiques et paleoecologiques, un argument utile permettant d'individualiser les differentes sequences sedimentaires. Les associations d'ammonites identifiees permettent d'etablir quatre unites biostratigraphiques couvrant l'intervaIIe Bajocien superieur - Bathonien supe­ rieur. Les resuItats sedimentologiques et biostratigraphiques indiquent l'existence d'une discontinuite regionale a la base du Bathonien.

MOTS-CLES: JURASSIQUE MOYEN, BAJOCIEN, BATHONIEN, AMMONITINA, BIOSTRATIGRAPHIE, BIOCHRONOLO­ GIE, ANDES, AMERIQUE DU SUD, CHILL 80' I

CJ 3024

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Figure 1 - Location maps of sections at Quebrada de San Pedro (Caracoles) and Aguada Colorada (Sierra de Varas), Cartes de situation des coupes de Quebrada de San Pedro (Caraco/es) et d'Aguada Colorada (Sierra de Varas), INTRODUCTION Epistrenoceras. Two sections have been studied in detail, bed by bed, and the results obtained are Some ammonites from the Middle Jurassic of the shown in this paper. These sections are Quebra­ Cordillera de Domeyko have been studied in se­ da de San Pedro (Caracoles area) and Aguada veral monographies at the end of the last century Colorada (Sierra de Varas), where more than a and in the first decades of this century. The stu­ thousand ammonites have been found, in situ. dies by Steinmann (1881), Tornquist (1898), Burckhardt (1903) and Stehn (1923) are particu­ larly interesting. Most of the ammonites descri­ STRATIGRAPIDC SECTIONS bed or mentioned in these studies belong to the Callovian, being less abundant the biostratigra­ QUEBRADA DE SAN PEDRO (69°00' Long. W, phic data concerning the Upper Bajocian and Ba­ 23°07' Lat. S). thonian of this region. Stratigraphical and pa­ leontological data have been recently provided by In the Caracoles area, above the volcanoclastic various authors such as : Harrington (1961) ; and metamorphic rocks from the Triassic, and Westermann (1967, 1981) ; Hillebrandt (1970, unconformably with them, there is a relevant 1972, 1973, 1977) ; Chong (1973, 1977) ; Covace­ succession of fossiliferous marine sediments from the Middle Jurassic. The best exposures of Bajo­ vich & Piraces (1976) ; Montaiio (1976) ; Baeza (1979) ; Westermann & Riccardi (1979, 1980, cian and Bathonian rocks are to be found at the 1985) ; Jensen & Quinzio (1979, 1981) ; Bogdanic Quebrada de San Pedro. In this locality, the follo­ wing stratigraphical intervals can be distinguis­ (1983) ; Groschke & Hillebrandt (1985) ; Bogda­ nic & Chong (1985) ; Hillebrandt, Groschke, hed (Fig. 2) : Prinz & Wilke (1986) ; Groschke, Hillebrandt, Prinz, Quinzio & Wilke (1988) ; Riccardi, Wester­ 4,5 to 5 m (SP1 - SP17). Conglomerates and mi­ mann & Elmi (1988, 1989, 1990a) ; Riccardi & croconglomerates, dark-brownish in the lower Westermann (1991a,b). part of the interval and whitish on the upper part, becoming sandy upwards, passing into fine­ The Upper Bajocian has been recognized in many grained sandstone. The clasts are rounded, some of them being over 20 cm long in the lower part localities of the North-Chilean Precordillera due to the presence of Megasphaeroceras and Lep· of the interval, but not so long in the upper part. tosphinctes, whereas the finding of Epistrenoceras The macrofossils are frequent and, in general re­ sedimented : solitary and colonial corals, bivalves paracontrarium (BURCKHARDT) in some outcrops has made it possible to distinguish a horizon of and gastropods. Epistrenoceras attributable to the Upper Batho­ nian (Hillebrandt 1970). However, the scarce am­ 8 to 12 m (SP17 - SP29). Calcareous sandstone monites found so far in the rocks from the Bajo­ and sandy limestones, grey or yellowish, with cian-Bathonian interval in the Chilean Precor­ thin beds of silty limestones whose lateral exten­ dillera have not allowed to make a biostratigra­ sion is not usually longer than 10 metres. There phic subdivision of the Upper Bajocian or the Ba­ are frequent macrofossils, in general resedimen­ thonian. Despite the scarce detailed biostratigra­ ted : bivalves, gastropods and ammonites. It has phic data, some authors have defended that in only been possible to identifY one fragmented the Cordillera de Domeyko there are probably se­ Stephanoceras sp. macroconch, around 25 cm in diments from Upper Bajocian and Lower Batho­ diameter. nian (Westermann 1981 ; Bogdanic & Chong 1985 ; Groschke & Hillebrandt 1985), whereas 3 to 8,2 m (SP29 - SP45). Silty limestones, bio­ other authors have stated the possibility of these clastic limestones and marls, greyish-yellowish. sediments being condensed or missing (Riccardi, The limestone beds are of variable thickness, Westermann & Ehlli 1988, 1989, 1990a). from 15 to 40 cm, and their lateral extension is usually several tens of metres. Some layers con­ The main objective of this paper is to provide taining abundant resedimented and silicified ma­ new biostratigraphical and sedimentological data crofossils, often forming lumachelles, being con­ concerning the Bajocian-Bathonian boundary in centrated in the lower part and finer-grained to­ the Cordillera de Domeyko. Over the March-April wards the top, and exhibiting sole marks, can be 1991 period we have studied several outcrops in identified as tempestites. The most abundant fos­ the Caracoles area and in Sierra de Varas (Fig. sils belong to costuled brachiopods, bivalves, am­ 1). In these outcrops there is a relevant succes­ monites, belemnites and gastropods. In the follo­ sion of carbonate sediments from the first beds = wing taxonomic lists, (M) macroconch, (m) = \vith Megasphaeroceras up to the horizon with microconch, S = specimen(s)...... Scale N • ell �:I 0 0 0 S 0 0 I� .. .. � � ...... • � .. ;:: ;:: ...... � .. w � ; •...... ;:�f: .. � •WUl••• .... �§� g .... � ...... Collection number .. ... � G � ;IJ i I 1 F:': aUE BRADA DE i�l' r I.:·d� I; SAN PEDRO I:·' t I�'F' .� I SECTION �;l�I�'.. '�

� : • Lytoctras sp. I � : • Llssoceras psilodiscum ISCHLOE NB.l.Oi -+- --; ...... ; --; ...... _____ ; ______-4 T.___ Lissoceros sp. � Phlycticer.s sp. opp.li. cf. subradiata {SOWERBY) :" .' •. Oppelia cf . flu. IBUCKMANl ; ...... Oppeli. sp. ...------+-- 0------;-...... -, ...... ' ••_ . ._ ._ ...... O.ycerites sp. � _Plro.ycerites cf. !Xoticus {STEINMANN) • Prohecticocern bl.nazense ELMI _...... Prohecticocern sp. 1 •• . • Stephanoceras chilenst HILL EBR.l.NOT Step hanoc eras sp. • ...... -••• --{, St.mmatoceras sp. " • Itinsailes sp. - I • Teloceras �p. : � ...• ------.---. � ouashno alf. undulatum {BURCKHARoT) ceras • C.domi les cf. daubenvi {GEMMELL.l.RO) " ; I . C.domit" cf. bremtri (TSERETElI) e. j . • • . . • • • • Cadomit" sp : 1 e----e Epistreno(!ras!)( 9r. p�racontrarium fBURCKHARQTI ------:. : StrenocH.S sp. i ,. Id'ORBIGNY) Hemig.ranti. cf. jUlii : ...... •... magnum RICCAROI , WESTERMANN • Megasph.erocfras magnum spissum RICCAROI , WESTERMANN •.____ �I�.�----�.� ______�.-"O·� ____ ,. Megasphaeroceras sp.: ______: Iniskiniles? p •• �----I .....• ..... • s , : • Iniskiniles sp. novo B in RICCAROI , WESTERMANN • Iniskiniles sp. novo C in RICCAROI & WESTERMANN In iskinites sp. : • • • • •••• :. lilloeHi. cf. steinmani ISPATH) • LilloeHi. Innlai IRICCARDI t ! :. • WESTERHANN . • Lilloetli. sp. • Xenocephaliles cf•• r.u·canus IBURCKHAROTl • • Xenocephaliles sp. � : Tulites IRuqif.riles) an ulicost.tus ILlSSAJOUS) • : g • ? Bullalimorphites IKher.ictrlS) sp. i! • Bullalimorphites sp. • i Leplosphinctes ILeplosphinclu) sp. ! i :. • •• Leplosphinctes I Pro rsisphin ctu) !p. • Stephanosphinctu aft. buitroni SANOOVAL , WESTERMANN ...... Lo�osphin(tu? or (obb.nilf,s? sp...... ___...... Choffatli. cf. jupiler {S TEINMAN N) • Choffali. jupit.r ISTEINMANN) ...... � ••_ .4:. --...... Choffati. sp. -: SStt-""t,.on"•. Bh. L l?trenocer. _".:le5 �LuPh�riiis-lfh'- "hi·n l- BIOZONES I MAGNUM BIOZONE a I STEINMANNI Bz.

BAJOCIAN BATHO NIA N STAGES In the lowest beds of the interval: are of variable thickness, from 30 to 40 cm, beco­ Stemmatoceras sp. (M), 1 S. ming thicker towards the top of the unit, their lateral extension is over one hundred metres and In the upper part (SP33 - SP45): they are organized in coarsening-upward sequen­ Lissoceras sp. (M?), 1 S. ces. Macrofossils are very abundant and in ge­ OppeUa cf. subradiata (SOWERBY, 1823) (M), 1 S. neral resedimented : bivalves, brachiopods, am­ Oppelia sp. (M), 2 S. monites, gastropods and belemnites. At about 8 Stephanoceras chilense HILLEBRANDT, 1977 (M), 1 m below the SP115 level, we have found two S. Stephanoceras spp. (M), 7 S. large smooth, serpulid-encrusted, ammonites Stemmatoceras spp. (M), 2 S. (D60 cm), belonging to Cobbanites? sp. The last 5 Itinsaites sp. (m), 2 S. m (SPI01 - SP115) span the most fossiliferous Teloceras sp. (M), 1 S. part of the section and some fossils are preserved Cadomites cf. daubenyi (GEMMELLARO, 1877) (M), as internal, pyritic moulds : 1 S. Oppelia cf. flexa (BuCKMAN, 1924) (M) + (m), 3 S. Cadomites sp. (M?), 2 S. Oppelia sp. (M) + (m), frequent. Megasphaeroceras magnum RICCARDl & WESTER­ Duashnoceras aff. undulatum (BURCKHARDT, MANN 1991 (M) + (m), abundant. 1927) (m), 1 S. Plate 1, figure 11. Megasphaeroceras magnum spissum RICCARDI & Strenoceras sp. (m), 6 S. Plate 1, figure 7. WESTERMANN 1991 (M), 1 S. Megasphaeroceras magnum RICCARDl & WESTER­ Leptosphinctes (Leptosphinctes) sp. (M?), 1 S. MANN, 1991 (M) + (m), abundant. Plate 1, figures 9 - 10. Within this association, it is noteworthy the rela­ Iniskinites? sp. (M), 2 S. tive abundance of Megasphaeroceras, probably Xenocephalites cf. araucanus (BURCKHARDT, 1903) monospecific, which are represented by macro­ (m), 1 S. conchs and microconchs, as well as by juvenile Stephanosphinctes aff. buitroni SAND OVAL & and adult forms. The specimens of other genera WESTERMANN, 1986 (m), 1 S. Plate 1, figure 8. belong to a:dult forms. Lobosphinctes? sp. or Cobbanites? (M), 5 S. Plate 1, figures 12ab. 2 to 4 m (SP45 - SP47). Greenish or yellowish lutites, which fray out laterally towards the NW, Within this association, noteworthy is the rela­ and contain very few resedimented macrofossils : tive abundance of Megasphaeroceras, probably bivalves and ammonites. Megasphaeroceras sp., monospecific, represented by macroconchs, micro­ fragments of shells preserved as flattened im­ conchs, juvenile and adult forms. Among the Op­ pressions. pelia the remains of adult macroconchs predomi­ nate, and the juveniles or microconchs are very 18 to 20 m .SP47 - SP87). Silty limestones, brow­ scarce. Other genera are exclusively represented nish-reddisll in color, and yellowish lutites. The by adult forms. thickness of their beds is variable, from 20 to 30 cm, and their lateral extension is usually over se­ 15 m (SP115 - SPI41). Marls, gypsiferous lutites veral tens of metres. Macrofossils are only fre­ and shales, greenish-grey in color. In the lower quent in some local levels and are resedimented, part of the interval there are several bioclastic but the remains of millimeter-sized gastropods limestones interbedded, locally ferruginous, of and bivalves are abundant. Ammonites occur as centimetric thickness, becoming thinner towards flattened impressions. Within these materials we the top of the unit. In the upper part of the inter­ have found: val there are thin, lenticular, silty limestones. Oppelia sp. (M), 1 S. Macrofossils are more frequent in the upper part Duashnoceras aff. undulatum (BURCKHARDT of the interval and they are usually resedimen­ 1927) (m), 1 S. ted. Remains of ammonites and bivalves are pre­ Cadomites sp. (M) + (m), 3 S. dominant, but in the upper part, disk-shaped co­ Megasphaeroceras sp. (M) + (m), frequent. lonial corals, up to 25 cm in diameter, are found Iniskinites? sp. (M), 1 S. locally. In the lowest beds of the interval : Xenocephalites sp. (m), 2 S. Oxycerites sp. (M), 7 S. Leptosphinctes (Prorsisphinctes) sp. (M), 4 S. Iniskinites? sp. (M), 4 S. Stephanosphinctes aff. buitroni SANDOVAL & Tulites (Rugiferites) angulicostatus (LISSAJOUS, WESTERMANN, 1986 (M?), 2 S. 1923) (M), 1 S. Plate 1, figures 6ab.

19 m (SP87 - SP115). Bioclastic limestones and In the middle part (SPI25-SP131) : lutites, brownish-yellowish in color. Their beds Oxycerites sp. (M) + (m), abundant. Cadomites ef. bremeri TSERETELI, 1968 (M), 1 S. Lytoeeras sp. (M?), 1 S. Iniskinites sp. novo B Ln RICCARDI & WESTER­ Lissoeeras psilodiseum (SCHLOENBACH, 1865)

MANN, 1991 (M), 3 S. (M?), 1 S. Iniskinites sp. novo C in RICCARDI & WESTER­ Lissoceras sp., 3 S.

MANN, 1991 (M), 2 S. Plate 1, figure 5. Phlyetieeras sp. (M), 8 S. Plate 1, figure 3. Iniskinites sp. (M), frequent. Oxyeerites (Paroxyeerites) cf. exotieus (STEINMANN, ?Buliatimorphites (Kheraieeras) sp. CM), 1 S. 1881) (M), 3 S. Oxyeerites sp. (M) + (m?), frequent. In the upper part : Proheeticoceras blanazense ELMI, 1967 (M), 1 S. Oxyeerites sp. (M), frequent. Prohecticoceras sp. (M), 6 S. Cadomites sp. CM), 1 S. Cadomites sp. (M), 2 S. Iniskinites Sp. (M), abundant. Epistrenoceras ex gr. paracontrarium (BURCK­ HARDT, Bullatimorphites sp. (M), 1 S. 1927), frequent. Plate 1, figure 2. (d'ORBIGNY, S. Choffatia sp. (M), 5 S. Hemigarantia cf. julii 1846), 1 Plate 1, figures lab. Lilloettia leanzai RICCARDI & WESTERMANN, 1991 In these marls and lutites it is noteworthy the (M), 1 S. relative abundance of adult forms belonging to Lilloettia sp. (M), 2 S. Oxyeerites and Iniskinites. The representatives of ChoffatiaJupiter (STEINMANN, 1981) (M) + (m), 4 each of these genera belong to several new spe­ S. cies. However, the presence of juveniles of any of Choffatia sp. (M) + (m), frequent. these genera is practically nil. Only in the upper part of the interval we have found some juvenile Among the different taxonomic groups of this as­ forms belonging to Oxycerites. sociation, only Epistrenoceras is represented by juvenile and adult forms. Most of the Choffatia 4 m (SP141 - SP153). Bioclastic limestones and specimens belong to adult forms, macroconchs or sandy lutites, brown-yellowish in color. The microconchs. The rest of the taxonomic groups thickness of this beds ranges from 20 to 40 cm, are more scarce and represented by adult macro­ and their lateral extension is usually several tens conchs. of metres. Macrofossils are abundant and most of them resedimented : bivalves, ammonites and AGUADA COLORADA (69° 13' Long. W, 24° 54' brachiopods. Among the ammonites we have Lat. S). identified: The oldest sediments on this outcrop are very fos­ Oxyeerites sp. (M), 6 S. siliferous and contain ammonites characteristic of Proheetieoeeras sp. (M), 1 S. the Upper Bajocian. The sediments from the Lo­ Cadomites sp. (M), 1 S. wer Bajocian are covered by quaternary sedi­ Iniskinites sp. (M), frequent. ments, but they are well represented on other Lilloettia cf. steinmanni (SPATH, 1928), 1 S. outcrops located near by. A relevant succession of Lilloettia sp. (M), 3 S. carbonate sediments, containing frequent Epistre­ Xenocephalites sp. (m), 1 S. noceras in their last metres, corresponds to the Choffatia cf. Jupiter (STEINMANN, 1881) (M) + (m), Bathonian. abundant. At this locality, sediments from the Upper Bajo­ This association is characterized by the relative cian and Bathonian show similar lithofacies. The abundance of representatives of Choffatia, among most common sediments are silty shales, which which there are macroconchs and microconchs. are associated with silty limestones and sandy However, the remains of juvenile forms from this limestones. These rocks are organized in thicke­ taxonomic group are very scarce. ning and coarsening-upward sequences, with se­ veral tens of metres in thickness and kilometer­ 6 m (SP153 - SP161). Lutites and marls, greyish sized lateral extension, which are made up of se­ in color, with thin intercaled beds of limestones diments from three successive facies (Fig. 3) : with millimeter-sized intraclasts. The thickness - in the lower part there are marly limestones of the layers range from 10 to 20 cm, but their and lime marls, becoming more shaly towards lateral extension is often around one hundred the top, greyish-whitish in color, with calcareous metres. Macrofossils are frequent and resedimen­ nodules ranging from 20 to 50 cm in diameter. Macrofossils are abundant, particularly resedi­ ted : bivalves, ammonites, brachiopods and be­ lemnites. mented shells of ammonites, and accumulated or From the biostratigraphic point of view, several 0 successive intervals can be distinguished (Fig. 4): 0° '. 0 $"0 $,,() 30 m (ACl - AC2). One sequence where marly 0 {j,,1vC "''''''Iv ""09" facies and fossiliferous nodules are predominant. - - Capping this sequence there are 4 or 6 metres of magmatic rocks, of porphyritic fabric and intru­ sive origin. Within the marly sediments we have · marly limestones ...... identified : . · lime marls ...... Liroxyites ef kellumi IMLAY, 1961 (M), 1 S. · · sllty sha les . Oppelia cf. subradiata (SOWERBY, 1823) (M), 1 S. sandy limestones .. Stephanoceras chilense HILLEBRANDT, 1977 (M), 1 ...... · calcareous concretions

· S. . . ammonites Stephanoeeras spp. (M), 7 S, ... blvalves (BoSltra. Astarte)

· Stemmatoceras spp. (M), 3 S. .. blvalves IOstrelds) . . belemnltes Teloceras sp. (M), 5 S.

· Cadomites sp. (M) + (m), 3 S. .. aptychus · brachlopods Lupherites sp. (M), 4 S.

· echlnoderms Orthogarantiana? sp. (M), 4 S. Spiroceras orbignyi (BAUGIER & SAUZE, 1843), ...... accumulated fossils .. resedlmented fossils abundant.

· reelaborated fossils Megasphaeroeeras magnum RICCARDI & WESTER­ MANN, 1991 CM) + (m), abundant. Figure Variations of lithological and paleontological fe atu­ 3 - Megasphaeroeeras magnum spissum RrCCARDI & res in carbonate sequences developed at Aguada Colorada. WESTERMANN, 1991 CM), 5 S. Plate 1, figures Variations des caracteristiques lithologiques et paleontologi­ ques dans les sequences carbonatees developpees a Aguada Co­ 14ab. lorada. Leptosphinetes (Leptosphinctes) sp. (M), 3 S.

resedimented small bivalves (including Bositra This interval span the most fossiliferous part of and Astarte). Many shells of ammonites were os­ the section. Most of the specimens from this asso­ treids-encrnsted during the biostratinomic phase. ciation correspond to adult shells, which were of­ The fossils found inside the nodules have their ten colonized by ostreids on its external surface, lower part well preserved, whilst most ammoni­ The most abundant taxonomic group is Megas­ tes have their upper part deformed due to com­ phaeroeeras, probably monospecific, which is rep­ paction during the early diagenesis, resented by macroconchs and microconchs. - the middle part of the sequences are silty shales and lutites, greyish, with intercala+,ed calcareous 125 m (AC2 - AC8). Six successive sequences, siltites and silty limestones. Calc� �'eous nodules mainly made up of silty shales and calcareous lu­ are scarce and smaller than in the previous term tites, are distinguished. Calcareous nodules and of the sequence. Macrofossils are frequent, resedi­ macrofossils are more scarce than in the previous mented in general, and they are usually crushed sequences. 4 m below AC5 level we have found: by diagenetic compaction. Remains of ostreids, . Megasphaeroceras magnum RICCARDI & WESTER­ ammonites (fragments of shells and aptychi), be­ MANN, 1991 CM), 1 S. lemnites and smooth brachiopods are predomi­ Megasphaeroeeras sp. CM), 2 S. nant, Iniskinites? sp. (M), 1 S. - in the upper part of these sequences there are Xenoeephalites sp. (m), 1 S. silty limestones and sandy limestones, arranged Leptosphinctes (Prorsisphinctes) sp. (M), 3 S. in thick layers, from 20 to 50 cm, reddish-brown Plate 1, figure 13. in color, which are more resistant to erosion than the previous materials, and whose lateral exten­ 5 m below AC8 level: sion is usually over one hundred metres. The lo­ Oxyeerites? sp. CM), 1 S. wer surface of these layers is sometimes 'irregu­ Cadomites sp. (M), 1 S. lar, whereas the top is more homogeneous. Some Iniskinites? sp. CM), 2 S. layers present low angle lamination in the lower part, which becomes parallel in the middle part. 171 m (AC8 - ACI3). Five successive sequences, Macrofossils in this term of the sequence are most of them thicker than the previous ones and highly sporadic. Mainly resedimented or reelabo­ made up mainly of silty shales, calcareous siltites rated fragments (sensu Fermindez-L6pez 1991) and sandy limestones, can be distinguished. Cal­ ostreids, costuled brachiopods, and echinoderms. careous nodules are scarce. Macrofossils are fre- � I\) 3 Scale �"')J<""«11".,<1', �R·. ( 0 1 0 � )·(,ktr.�bJ 0 ,�- 0 ...... Collection number ... I\) Co> .... Ut a> � CD ID 0 I\) w ....

0 • 0 0 0 0 0 °0 · 0 I 0 1 0 0 : 0 0 AGUADA 0 0 . 0 COLORADA .. 0 0 · - SECTION ..

• Lissoceras cf. psilouls(um (SCHLOENBACH

• Phlycticeras sp.

• liroxyites cf. kellumi IHLAY

• Oppelia cf. subradiata (SOWER BY) • Oxycerites? sp.

• •• Oxycerites sp. Prohecticoceras sp.

• Jeanneticeras sp .

• S tephanoceras chilense HILLE BRANOT ....Steph anoceras sp.

• Stemmatoceras sp.

_ Teloceras sp.

· . • Cadomites sp. _Lupherites sp. � . _ Orthogarantiana7 sp. Epistrenoceras ex gr. paracontrarium ( BURC KHA ROT ) • Spiroceras orbignyi IBAUGIER 8. SAUZE ) Parapatoceras distans (BAUGIER 8. SAUZE) •• • Hegasphaeroceras magnum RICCAROI 8. WESTERMANN • Megasphaeroceras magnum splssum RIC[AROI 8. WESTERMANN ...... ---_. : Megasphaeroceras sp . ------...... -i-.... Iniskinltes7 sp.

• • • . • •••• lniskinites sp.

• Lilloettia sp.

• • • X enocephal ites sp.

• Bomburltes aft. suevicus (ROEMER)

• • • Bul lallmorphites sp .

__ Leptosphlnctes ILeptosphinctes) sp.

• • Leptosohinctes (Prorsisphmctes) sp.

•• • Lobosphinctes7 or Cobbanites7 sp.

• Choffatia Jupiter (STEINMANN) • ••••• Choffatia sp. BAJOCIAN BATHONIAN I STAGES quent, but they are usually remains of fragmen­ thonian sediments. Biostratigraphic distribution ted shells, often silicified, and crushed by com­ of the ammonites genera and subgenera, and paction during the early diagenesis. At the bot­ their relative abundance, are shown in figure 5. tom of this stratigraphic interval: Cadomites sp. (m), 1 S. STRATlGRAPHIC BAJO(IAN BATHONIAN Iniskinites? sp. (M), 1 S. Bomburites aff. sueuicus (ROEMER, 1911) (m), 1 S. UNITS UPPER MIDDLE UPPER Plate 1, figure 4. MAGNUM BIOZONE '" Z 20 m below AC9 level : c 0 o� N 0 Oxycerites sp. (M), 1 S. (; iD � Iniskinites sp. (M), frequent. TAXA o .� a; 2 Xenocephalites sp. (m), 2 S. 0z 0 z • Scarce N N Z • Q 0 < Choffatia sp. (M?), 3 S. freQuent cc iD :; z e abundanl 10 m below AC11 level : ...W < cc V> Oxycerites sp. (M), 6 S. Iniskinites sp. (M), frequent. L ,ssoc eras ...... t----'------.,-----'-....--I Bullatimorphites sp. (M), 1 S. Phlyeloceras ...... Choffatia sp. (M), frequent. L,roxy,les O ppel,a ...... I-_�__ _..... 30 m (AC13 - AC14). One sequence made up of Dxyeer,les ...... calcareous lutites, silty shales and sandy lime­ Paroxyeer,les stones. Macrofossils are abundant but most of Proheel.eoeeras .. them are resedimented. Locally, the presence of Jeannet,eeras . Stephanoeeras pyritic fossils and nuclei of centimeter-sized am­ .. . monite shells is frequent. We have identified: Slemmaloeeras Lissoceras cf. psilodiscum (SCHLOENBACH, 1865) Teloeeras ... (M) + (m?), frequent. Duastlnoeeras '. - Phlycticeras Sp. (M), 1 S. [adom,les ...... Oxycerites sp. (M), frequent. Lupherlles . • Prohecticoceras sp. (M), 4 S. Drlhogar antlana' ... Jeanneticeras sp. (m), 1 S. Slrenoeeras ... . Cadomites sp., 1 S. E p Islrenoeer as • Epistrenoceras ex gr. paracontrarium (BURCK­ Hemlgaranlla .... . HARDT, 1927), frequent. SPI oceras ...... • Parapatoceras distans (BAUGIER & SAUZE, 1843), Par �paloeeras ...... abundant. Hegasphaeroceras ...... J--i----tl.� ---t•. Iniskinites sp. (M), frequent. Inlsk'nlles'......

Lilloettia sp., 1 S. In,sk ,n , les ...... Xenocephalites sp. (m), 2 S. L,lIoett,a ...... ChoffatiaJupiter (STEINMANN, 1981) (M), 1 S. Xenocepha Illes ... Choffatia sp. (M) + (m), frequent. Ruglferotes ...... Bullal'morphltes ...... Among Parapatoceras, remains of juvenile forms Bomburltes ...... are more frequent than those of adults. Juvenile Leptosphonctes ...... forms of Epistrenoceras are scarce_ The remaining Prors,sphoncles ...... taxonomic groups are represented by adult forms. Stephanosph,nctes ...... lobosphlnctes' ......

or (obbaniles' ...... BIOSTRATIGRAPHICAL AND (hottat ha ...... - ...... BIOCHRONOLOGICAL INTERPRETATIONS Figure 5 - Biostratigraphic distribution of the ammonites ge­ The successions of ammonite assemblages found nera and subgenera, and their relative abundance, within Up­ on the outcrops of the Quebrada de San Pedro per Bajocian and Bathonian of the Quebrada de San Pedro and Aguada Colorada. Repartition biostratigraphique des gen­ and the Aguada Colorada allow the definition of res et des sous-genres d'ammonites et de leur abondance rela­ four successive biostratigraphic units, with the tive dans le Bajocien superieur et le Bathonien de Quebrada rank of biozone, for the Upper Bajocian and Ba- de San Pedro et d'Aguada Colorada. For the Upper Bajocian only one biozone has Zone and the Rotundum Zone recognized in other been recognized (Magnum Biozone). The Batho­ Andean and North American basins (cf. Riccardi nian ammonites belong to three successive biozo­ et al. 1991a). Correlation of this biozone with the nes. The first two (Biozone A and Biozone B) Niortense Biozone established in Europe (cf. Dietl must be attributable to the Middle Bathonian, 1981) and with the Standard Subfurcatum Zone whereas the third (Steinmanni Biozone) corres­ (cf. Pavia 1985) are indicated by the presence of ponds to the Upper Bathonian. late stephanoceratids, as well as Leptosphinctes, Spiroceras and Strenoceras. In the Cordillera de MAGNUM BIOZONE (UPPER BAJOCIAN). Domeyko it is possible to distinguish three suc­ cessive subunits in the rocks from the Magnum It is characterized by the presence of Megas­ Biozone, which we call respectively : Lupherites phaeroceras magnum & WESTERMANN. RrCCARDI Biohorizon, Stephanosphinctes Biohorizon and In the Quebrada de San Pedro, this biozone is Strenoceras Biohorizon. about 50 m thick and is at least represented by the sediments between SP33 and SP115 levels. The Lupherites Biohorizon is characterized at its In Aguada Colorada, this biozone is up to 150 m base by the appearance of Megasphaeroceras thick (AC1 - AC7). Hall & Westermann (1980) magnum (incl. M. magnum spissum), and by the have formally established an "Assemblage Zone presence of the last Stephanoceras and Teloceras, of Megasphaeroceras rotundum", characterized in which are usually associated with Spiroceras or­ South Alaska and Oregon (USA) by the index bignyi, Leptosphinctes, and Lupherites. Repre­ species with Leptosphinctes, Spiroceras and the sentatives of Orthogarantiana? sp., Oppelia cf. last stephanoceratids. This assemblage zone has subradiata and Liroxyites cf. kellumi, are not fre­ also been utilized in the Andes, but its denota­ tion has been more generic because the Megas­ quent. This biohorizon is well represented in the phaeroceras rotundum IMLAY species does not Quebrada de San Pedro (SP33 - SP45) and in the seem to be represented (Westermann & Riccardi Aguada Colorada (ACl - AC2). It is partially 1979 ; Riccardi et al. 1990a,b). The Magnum Bio­ equivalent to the "Lupherites dehmi Assemblage zone, proposed for the Chilean basin in this pa­ Subzone" defined by Westermann & Riccardi per, at least partly corresponds to the Magnum (1979).

PLATE 1

(d'ORBIGNY). = = = = Fig. lab - Hemigarantia cf.julii SP159/5. D 27,0; H 9,8(0,36); E c.10,6(0,39) ; U 10,6(0,39) ; Nil2 = 16; Ne/2 = 24.

(BUCKHARDT, = = = Fig. 2 - Epistrenoceras ex gr. paracontrarium 1927). SP159/3. D 34,6 ; H 12,0(0,34) ; E 16,6(0,48) ; U = 12,3(0,35); Nil2 = 16.

= = = = = Fig. 3 - Phlycticeras sp. (M). SP159/4. D 37,5; H 17,2(0,45); E 13,0(0,34); U 9,6(0,25); Ne/2 25. Fig. 4 - Bomburites aft'. suevicus (ROEMER, 1911) (m). AC8+lIl. D = 24,0; H = 10,9(0,45) ; E = 23,2(0,96) ; U = 2,9(0,12). RICCARDI WESTERMANN, Fig. 5 - Iniskinites sp. novo C in & 1991 (M). SP130/2. (LISSAJOUS, Fig. 6ab - Tulites (Rugiferites) angulicostatus 1923) (M). SP119/4.

= H = = Fig. 7 - Strenoceras sp. (m). SP105/4. D 14,0 ; 4,2(0,30); U 6,1(0,43). SANDOVAL WESTERMANN = = Fig. 8 - Stephanosphinctes aff. buitroni & (m). SP107/1. D 23,9; H = 8,1(0,33); U 10,7(0,44); Ne/2 = 30.

RICCARDI WESTERMANN, = = Fig. 9 - Megasphaeroceras magnum & 1991 (m). SP111/l. D 30,5; H 15,1(0,49); E = 16,5(0,54) ; U = 3,9(0,12); Ne/2 = 28.

RICCARDI WESTERMANN, = = Fig. 10 - Megasphaeroceras magnum & 1991 (M). SP105/l. D 71,0; H 40,8(0,57); E = 35,9(0,50); U = 3,4(0,05). (BURCKHARDT, Fig. 11 - Duashnoceras aft'. undulatum 1927) (m). SP113/8. Fig. 12ab - Lobosphinctes? sp. or Cobbanites? sp. (M). SP109/l.

= = = = Fig. 13 - Leptosphinctes (Prorsisphinctes) sp. (M?). AC5-1/l. D 82,0; H 26,0(0,31); E c.22,8(O,27); U 37,7(0,46); Nil2 = 24.

RICCARDI WESTERMANN, = = Fig. 14ab - Megasphaeroceras magnum spissum & 1991 (M). AClIl. D 55,5 ; H 28,4(0,51) ; E = 45,4(0,81); U = 8,7(0,15); Ne/2 = 48.

= = W = = = Measurements in mm : D diameter; H whorl height; whorl width; U diameter of umbilicus; Nil2 number of primary ribs per half-whorl; Ne/2 = number of secondary ribs per half-whorl. All figures natural size.

= = The arrow indicates the end of the phragmocone. Me sures donnees en mm : D diametre ; H hauteur du tour; W = epaisseur du tour; U = diametre de l'ombilic ; Ni 12 = nombre de cOtes internes par demi-tour; Ne 12 = nombre de cotes externes par demi-tour. To utes les figures sont en grandeur naturelle. La fleche indique la fin du phragmocone. tI In the Stephanosphinctes Biohorizon, Megas­ treme rarity of non-crushed ammonites from the phaeroeeras magnum is found with the first rep­ Middle Bathonian sediments represents a serious resentatives of Iniskinites? (M) and Xenoeephali­ difficulty for the establishment of a detailed bios­ tes (m) group. The Prorsisphinetes can outnumber tratigraphic scheme. Taking into account the the Leptosphinetes. Several new species of Pror­ biostratigraphic data from different sedimentary sisphinetes, Stephanosphinetes and other smooth basins obtained by other authors (cf. Wester­ perisphinctids of large size (Cobbanites? sp.) are mann & Callomon 1988 ; Sandoval 1983 ; Man­ present. The stephanoceratids Cadomites and gold 1981 ; Galacz 1980), the specimen of Tulites Duashnoeeras are scarce. This biohorizon is well (Rugiferites) angulieostatus (LISSAJODS), found on developed in the Quebrada de San Pedro (SP69 - SP119 level in the Quebrada de San Pedro is the SP99) and can be recognized in the Aguada Colo­ only Bathonian ammonites which probably cor­ rada (AC3 - AC5). To date, Stephanosphinctes responds to the lower part of the Middle Batho­ have only been identified in Mexico, together nian. Based on these data it is possible to justify with Duashnoeeras spp. and Subeollina lueretia a first "A" Bathonian biozone. (d'Orbigny) from the "Duashnoeeras floresi Zone" (Westermann 1983 ; Sandoval & Westermann Taking into account the presence of Cadomites cf. 1986). bremeri TSERETELI, the assemblage identified be­ tween SP125 and SP131 levels, with a thickness The Strenoceras Biohorizon is characterized by from three to five metres and containing abun­ an assemblage which includes Megasphaeroeeras dant Oxyeerites and Iniskinites, belongs to youn­ and Strenoeeras. The perisphinctids identified as ger sediments and corresponds to the upper part Lobosphinetes? or Cobbanites? (Plate 1, figs 12ab) of the Middle Bathonian. The ammonite assem­ are relatively frequent, but their taxonomy re­ blage found in this sediments allow to distinguish mains dubious. The Oppelia are also frequent. In a second "B" Bathonian biozone. this biohorizon there are very few Duashnoeeras and Stephanosphinetes. Stephanoeeras, Stemma­ In the Aguada Colorada, the Bathonian encom­ toeeras and Teloeeras are virtually absent. The passes a further considerable thickness of silty best rock exposures assigned to this biostratigra­ shales with frequent but crushed ammonites. The phical unit are to be found on Caracoles. The presence of Bomburites aff. suevieus (ROE MER) in characteristic assemblage has been identified in the lowest beds of the sequence (AC8 - AC9) is a the Quebrada de San Pedro (SP101 - SP115) on biostratigraphical reason for suspecting that the the last five metres of Bajocian sediments. The Lower Bathonian is missing at this locality. AC7 - AC8 interval in the Aguada Colorada can correspond to this biohorizon, but the fossils In the two areas under study we have not found found are still very scarce. The Strenoeeras of ammonites characteristics of the Lower Batho­ this biohoriz m strongly suggest a rough paralle­ nian. The two assemblages mentioned above cor­ lism with th0 Subfurcatum Zone of Europe. respond partially to the "Cadomites-Tulitidae Mixed Assemblage", which Riccardi et al. (1988) The Southamerican perisphinctids belonging, ac­ have distinguished in the Chacay Melehue area cording to some authors, to the Lobosphinetes are (Argentina). This assemblage was identified bea­ the main biochronological criterium used to de­ ring in mind the presence of Cadomites from the fend the possibility that in the Chilean Precor­ C. orbignyi (GROSS.) and C. bremeri TSERETELI dillera the Standard Garantiana and Parkinsoni groups, together with scarce Tulites? (Rugiferi­ Zones, established in Europe, are represented. tes?) et davaiaeensis (LISS.). All these ammonites However, in the Caracoles area these perisphinc­ are characteristics of the Middle Bathonian. tids (Lobosphinetes? or Cobbanites?) ;:Ire associa­ However, in Chacay Melehue area most or all ted with Strenoeeras. It is possible that the Chi­ Cadomites are reworked and recorded in sedi­ lean representatives of Strenoeeras are not as old ments from the Upper Bathonian (Riccardi et al. as the European ones ; however, at present there 1990a). are not biochronological criteria to confirm that the Garantiana or Parkinsoni Zones are repre­ STEINMANNI BIOZONE (UPPER BATHO­ sented in the Chilean Basin. NIAN).

BIOZONES A AND B (MIDDLE BATHONIAN). The boundary stratotype of the Steinmanni Zone has been established in Chacay Melehue by Ric­ The Bathonian sediments are characterized in cardi et al. (1989a), and has been recognized in the Cordillera de Domeyko by the presence of the North of Chile and in Mexico (cf. Riccardi et Iniskinites with Oxyeerites and Choffatia. The ex- al. 1990b, Sandoval et al. 1990). To the Stein- manni Biozone correspond the Quebrada de San CHRONOSTRATlGRAPHIC UNITS Pedro sediments found between SP141 and Biostratigraphic Units SP161 levels, which are up to 10 m thick. Sedi­ STAGES ZONES

ments in the Aguada Colorada are thicker than ..,a: DISCUS 30 m (ACI3 - ACI4) and ammonites are more � � ::> RETROCOSTATUM Steinmani Biolone abundant. Apart from the other forms compara­ ------ble to the index species, it is noteworthy the rela­ Z BREMERI B c .., Biolone tive abundance of Choffatia gr. Jupiter (STEIN­ i ... ------0 c SUCONTRACTUS MANN) and Iniskinites spp. in the lower part of ..% c A Biolone--- c i this biozone. Above these levels relatively fre­ Cl) PROGRACllIS quent is the presence of representatives of Epis­ -'----- .J ZIGZAG trenoceras ex gr. paracontrarium (BURCKHARDT,

1927) and Parapatoceras distans (BAUGIER & PA RKINSONI // HIATUS SAUZE), as well as the first Oxycerites (Paroxyce­ Z er c UJ // U D. GARANTtANA rites) gr. exoticus (STEINMANN). Lissoceras are fre­ D. �� ;'///� ..,0 ::> ... S" _noc.,•• B,oho.U'on quent locally in some levels. Prohecticoceras and SUBFURCATUM S_.Dtt_no.ptltnct.. eh. Cl) Magnum 81. -jJitu.,h.,"..JL 8.,hOf'U'on-c/ - Phlycticeras are usually scarce. There are rare specimens which show a close similarity with members of the Hemigarantia julii (d'ORBIGNY) Figure 6 - Correlation chart of the Upper Bajocian and Batho­ nian biostratigraphic units recognized in the Caracoles area, group, along with Prohecticoceras blanazense scaled on the Submediterranean standard zonation. Ta bleau ELMI, in SP159 level. These ammonite assembla­ de comfflation des unites biostratigraphiques du Bajocien supe­ ges of the Steinmanni Biozone are comparable to rieur et du Bathonien de Caracoles, comparees avec la zona­ those found in the middle and upper parts of the tion Standard de la province submediterraneenne. European Retrocostatum Zone (cf. Westermann et al. 1984, 1988 ; Riccardi & Westermann 1991a). The biostratigraphic units recognized in the Ca­ Among the Upper Baj ocian and Bathonian am­ racoles area, and their suggested correlation with monites of the Cordillera de Domeyko, Eury­ the European Standard Zones, are shown in fig­ cephalitinae predominates in most of the strati­ ure 6. The presence of a stratigraphic disconti­ graphical levels. Megasphaeroceras and Iniskini­ nuity between the Upper Bajocian and the Batho­ tes are widespread fossils, among which juveniles nian in the Caracoles area is corroborated by the can outnUlllber the adult forms. These ammoni­ obtained sedimentological and biostratigraphical tes were eudemic (sensu Callomon 1985) in the data. The interval SPI0l-SP115 is a coarsening­ Chilean basin. At isolated levels, Lissoceras, upward sequence, which is bounded above by an Epistrenoceras, Spiroceras, and Parapatoceras are overall fining-upward sequence (SP115-SPI25). also locally quite abundant and consist of micro­ This boundary is a paraconfc:mity between two conchs and macroconchs, including juveniles and carbonate sequences develope ::. in a marine envi­ adult forms. These data suggest that ammonites ronment on a carbonate platform with abundant may have colonized the basin at least during two siliciclastic supply. The sequential sedimentation episodes, concerning the lower part of the Mag­ feature is more noticeable in Sierra de Varas, al­ num Biozone (Lupherites Bh.) and the Steinman­ though sediments from these meridional areas ni Biozone. present a higher concentration of siliciclastic components, attain larger thickness, and must On the contrary, Oppelia, Oxycerites, Paroxyceri­ have been the result of higher sedimentation ra­ tes, Stephanoceras, Teloceras, Cadomites, Luphe­ tes. In Aguada Colorada, the interval AC7 - AC8 rites, Strenoceras, Leptosphinctes, Prorsisphinctes, represents a coarsening-upward sequence, but it Stephanosphinctes, Cobbanites? and Choffatia, al­ is poorly fo ssiliferous. Lithology and thickness of though locally may be frequent, are almost exclu­ these sections are very variable and a lithostrati­ sively adult forms. The Phlycticeras, Liroxyites, graphical correlation is not possible. Each one of Prohecticoceras, Jeanneticeras, Duashnoceras, Or­ the two locality has a distinctive sedimentation thogarantiana?, Hemigarantia, Rugi{erites, Bulla­ pattern. In the Quebrada de San Pedro section timorphites and Bomburites are a minority, exclu­ the quick and irregular variations in thickness sively adult forms, restricted to sporadic levels. and lithology suggest a more near-shore deposi­ All these genera and subgenera probably were tion than in the Aguada Colorada section. In the ademic (cf. Fernandez-L6pez 1991) in the Chilean Caracoles area at least, there is a stratigraphic basin, and they could have been the result of break comprising the Garantiana, Parkinsoni and post-mortal dispersion of empty shells from dis­ Zigzag Biochrones. tant regions. This large hiatus filled well with the earlier be­ 30' - 25° 30' de Lat. Sur. N Congr. Geol. Chile no , lief that the Cordilleran regions of both North Antofagasta, 1 : 38-57. and South America had experienced a major re­ BURCKHARDT C. 1903 - Beitrage zur Kenntnis der gression at that time (cf. Hall 1988, 1984). Never­ Jura- und Kreideformation der Cordillere. Palaeon­ tographica, 50 1-144. theless, biostratigraphical and sedimentological : CALLOMON J.H. 1985 - The evolution of the Jurassic differences between the different areas in the ammonite family Cardioceratidae. Sp ecial Papers in Cordillera de Domeyko, for the Bajocian and Ba­ Paleontology , 33 : 49-90. thonian, are not only due to eustatic changes and CHONG G. 1973 - El Sistema Jurasico en la Cordillera processes of subsidence, but also to the platform de Domeyko (Chile) entre 24° 30' y 25° 30' de Lat. structural segmentation. Data recently obtained Sur. II Congr. Latinoam. Geol. , Caracas : 765-785. (Fernandez-L6pez, Chong & Wilke, in prepara­ CHONG G. 1977 - Contribution to the knowledge of the tion) show that this marine platform was structu­ Domeyko Range in the Andes of Northern Chile. Geol. Rundsch., 66 374-404. rally differentiated in blocks and affected by ac­ : COVACEVICH V. & PlRACES R 1976 - Hallazgo de Am­ tive fractures during the Early Bajocian. For the­ monites del Bajociano superior en la Cordillera de se reasons, other areas in the Cordillera de Do­ la Costa de Chile Central entre la Cuesta El Melon meyko, where more complete sections than those y Limache. Primer. Congr. Geol. Chileno, Con­ of Caracoles or Aguada Colorada, might exist. cepcion, 1 : 67-85. DIETL G. 1981 - Zur systematischen Stellung von Am­ monites subfurcatus ZIETEN und deren Bedeutung CONCLUSIONS fur die subfurcatum-Zone (Bajocium, Mittl. Jura).

Stuttgarter Beitr. Na turk., (B), 81 : 1-11. The obtained biostratigraphical and sedimentolo­ FERNANDEZ-LoPEZ S. 1991 - Taphonomic concepts for a gical data indicate the existence of a regional dis­ theoretical Biochronology. Revista Espafiola de Pa­ continuity at the base of the Bathonian. In all leontologia, 6 : 37-49. the outcrops studied so far, the Upper Baj ocian is FERNANDEZ-LoPEZ S., CHONG G. & WILKE H.-G. (en only represented by the Magnum Biozone, even preparacion) - Sedimentacion y volcanismo durante where the sediments from this substage are more el Jurasico medio en la Precordillera chilena entre 21°45' y 22°00'S. than 150 m of thick. It is possible to distinguish GALACZ A. 1980 - Bajocian and Bathonian ammonites three successive biohorizons : Lupherites Bh., of Gyenespuszta, Bakony Mts., Hungary. Geol. Stephanosphinctes Bh. and Strenoceras Bh. At Hung. , ser. paleont., 39 : 1-227. least in the Caracoles area there is a stratigra­ GROSCHKE M. & HILLEBRANDT Av. 1985 - Trias und phic break comprising the Garantiana, Parkinso­ Jura in der mittleren Cordillera Domeyko von Chile ni and Zigzag Biochrones. In the Quebrada de (22° 30' - 24° 30'). N. Jb . Geol. Palaont. Abh., 170 : San Pedro there are ammonites characteristic of 129-166. the Middle Bathonian. The Upper Bathonian is GROSCHKE M., HILLEBRANDT A. v., PRINZ P., QUINZlO widely represented in the Cordillera de Domeyko L.A. & WILKE H.-G. 1988 - Marine Mesozoic Paleo­ by Steinmanni Biozone sediments. geography in Northern Chile between 21° - 26° S. Lecture No tes Earth Sci. , 17 : 105-117. HALL RL. 1984 - Lithostratigraphy and biostratigra­ Acknowledgements - This research was funded by phy of the Fernie Formation (Jurassic) in the the projects "Estudio de fa cies marinas bajocienses en southern Canadian Rocky Mountains. Canadian la Cordillera de Domeyko, Chile" (DGICYT, BE90-277, Society of Pe troleum Geologists Memoir, 9 : 233-247. Ministerio de Educacion y Ciencia de Espana) and" HALL RL. 1988 - Late Bajocian and Bathonian (Mid­ Programa de Investigacion en Geologia Regional" dle Jurassic) ammonites from the Fernie Forma­ (Departamento de Ciencias Geologicas, Universidad tion, Canadian Rocky Mountains. J. Paleont. , 62 : Catolica del Norte, Chile). 575-586. HALL RL. & WESTERMANN G.E.G. 1980 - Lower Bajo­ cian (Jurassic) Cephalopod Faunas from Western REFERENCES Canada and Proposed Assemblage Zones for the Lo­ wer Bajocian of North America. Palaeontographica BAEZA L. 1979 - Distribucion de facies sedimentarias Americana, 9 (52) : 1-93. marinas en el Jurasico de Cerritos Bayos y zonas HARRINGTON H.L. 1961 - Geology of parts of Antofa­ adyacentes, norte de Chile. II Congr. Geol. Chileno, gasta and Atacama Provinces, Northern Chile. Am. Assoc. Pe trol. Geol. Bull. , 45 169-197. 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V Congr. per Bajocian Ammonite Strenoceras in Chile : first Geol. Chileno, Santiago, 2 : C415-C426. circum-Pacific record of the Subfurcatum Zone. RICCARDI A.C., WESTERMANN G.E.G. & ELMI S. 1989 - Ne wsl. Stratigr. , 9 : 19-29. The Bathonian-Callovian Ammonite Zones of the WESTERMANN G.E.G., CORONA R. & CARRASCO R. 1984 Argentine-Chilean Andes. 2nd Intern. Sy mp . Juras­ - The Andean Mid-Jurassic Ne uqueniceras ammo­ sic Strat. , Lisboa 1987 : 347-358. nite assemblage of Cualac, Mexico. Geol. Assoc. Ca­ RICCARDI A.C., WESTERMANN G.E.G. & ELMl S. 1990a - nada Sp ec. Paper, 27 : 99-112. The Middle Jurassic Bathonian-Callovian Ammo­ WESTERMANN G.E.G. & RICCARDI A.C. 1985 - Middle nite Zones of the Argentine-Chilean Andes. Geobios, Jurassic Ammonite Evolution in the Andean Pro­ 22 : 553-597. vince and Emigration to Tethys. Lecture No tes RICCARDI A.C., WESTERMANN G.E.G. & DAMBoRENEA Earth Sci. , 1 : 6-34. S.E. 1990b - Middle Jurassic of South America and WESTERMANN G.E.G. & CALLOMON J.M. 1988 - The Antarctic Peninsula. Ne wsl. Stratigr. , 21 : 105-128. Macrocephalitinae and associated Bathonian and RICCARDI A.C. & WESTERMANN G.E.G. 1991a - Middle Early Callovian (Jurassic) ammonoids of the Sula Jurassic ammonite fauna and biochronology of the Islands and New Guinea. Pa laeontographica, 203 : Argentine-Chilean Andes. Part III : Bathonian-Cal­ 1-90. lovian Eurycephalitinae, Stephanocerataceae. Pa­ laeontographica, 216 : 1-110. RICCARDI A.C. & WESTERMANN G.E.G. 1991b - Middle S. FERNANDEZ·LOPEZ Dpto. Paleontologia Jurassic ammonite fauna and biochronology of the Facultad Ciencias Geologicas Argentine-Chilean Andes. Part IV : Bathonian-Cal­ Universidad Complutense lovian Reineckeiidae. Palaeontographica, 216 : 111- 28040 Madrid, Spain 145. SANDOVAL J. 1983 - Bioestratigrafia y Paleontologia G. CHONG, L.A. QUINZIO & H.G. WILKE (Stephanocerataceae y Perisphinctaceae) del Bajo­ Dpto. Geociencias cense y Bathonense en las Cordilleras Beticas. Te sis Universidad Catolica del Norte Doct. Univ. Granada (1982) : 1-613, Antofagasta, Chile