Jurassic boundary and Hettangian biostratigraphy in the area of the Utcubamba valley (Northern Peru)

THE TRIASSIC/JURASSIC BOUNDARY AND I-ERTTANGIAN BIOSTRATIGRAPHY IN THE AREA OF THE UTCUBAMRA VALLEY (NORTHERN PERU)

AXEL V. H I L L E B R A N D T HILLEBRANDT A.v. 1994. The Triassic/Jurassic Boundary and Hettangian Biostratigraphy in the Area of the Utcubamba Valley (Northern Peru). [La limite Trias/Jurassique et la biostratigraphie de l'Hettangien dans la r~gion de la vall~e d2Jtcubamba du P~rou]. GEOBIOS, M.S. 17 : 297-307.

ABSTRACT In the area of the Utcubamba Valley continuous sections containing sediments of Late Triassic (Rhaetian) to Early Jurassic (Hettangian) age were investigated. The facies changes from north to south and thickness of sediments decreases in the same direction. Vertical facies changes are less important than horizontal ones. The northern part of the investigated area is characterized by sediments of the Aramachay formation, in the middle part strata of the Suta formation predominate and the southernmost part is mainly developed in the facies of the Chilingote formation. Ammonites are the most frequent fossils found in all three facies types. The finebedded siltstones yielded only crushed ammonites whilst the calcareous concretions, some limestone beds and mainly the tempestites contained well preserved ammonites. The Rhaetian is characterized by Rhabdoceras and Peripleurites in the lower part and different species of Choristoceras in the upper part. Psiloceras tilmanni, a species similar to P. planorbis and P. psilonotum, is found in the lowernmst beds of the Hettangian. Above these layers appears a new species of Psiloceras which is transitional to P. prirnocostatum. The upper part of the Early Hettangian did not yield any ammonites. The Middle Hettangian is mainly characterized by Discamphiceras reissi and Curviceras. The Late Hettangian contained species of the genera Badouxia, Sunrisites, Alsatites and Schlotheirnia. KEY-WORDS : NORTHERN PERUI TRIASSIC/JURASSIC BOUNDARY, FACIES CHANGE, AMMONITINA, HETTANGIAN BIOSTRATIGRAPHY,CORRELATIONAMERICA -EUROPE.

RESUME Dans la r~gion de la vallfie d'Utcubamba des couches d'~ge Trias sup6rieur (Rh6tien) ~ Jurassique inf~rieur (Hettangien) sont ~tudi6es. Le facies change du Nord au Sud et l'~paisseur des sediments decroit' dans la m~me direction. Les changements verticaux de facies sont moins importants que les changements horizontaux. La partie nord de la r6gion 6tudi~e est caract6ris~e par les s~diments de la Formation Aramachay, dans la partie centrale les couches de la Formation Suta dominent, et la partie sud est surtout constitu6e par le facies de la Formation Chilingote. Les fossiles trouv~s le plus frfiquemment dans les trois types de facies sont les ammonites. Les siltstones finement stratifies ne livrent que des ammonites comprim~es, tandis que les concr~tions calcaires, quelques bancs calcaires et surtout les tempestites renferment des ammonites bien conserv~es. Le Rh~tien est caract~ris6 dans sa partie inf6rieure par Rhabdoceras et Peripleurites et dans sa pattie sup~rieure par difffirentes esp~ces de Choristoceras. Psiloceras tilmanni, une esp~ce semblable ~ P. planorbis, et P. psilonotum, a ~t6 trouv~e dans les couches les plus inf~rieures de rHettangien. Au,dessus de ces couches apparait une nouvelle esp~ce de Psiloceras, repr~sentant une forme de transition avec P. primocostatum. La partie sup~rieure de rHettangien inf6rieur ne renferme aucune ammonite. L'Hettangien moyen est surtout caract~ris~ par Discamphiceras reissi et Curviceras. L'Hettangien sup~rieur contient des esp6ces des genres Badouxia, Sunrisites, Alsatites et Schlotheimia. MOTS-CLI~S : PI~ROU DU NORD, LIMITE TRIASSIQUE/JURASSIQUE, CHANGEMENT DE FACIES, AMMONITINA, BIOSTRATIGRAPHIE DE L'HETTANGIEN, CORRELATIONSAMERIQUE-EUROPE.

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S e c t i o n e a s t o f L e v a n t o (Fig. 1, loc. 1, 2a) About 3 km east of Levanto a section is exposed along the road from Chachapoyas to Levanto. Mostly the strata are strongly weathered and decalcified. Finebedded siltstones and m a r l y argillites of the Aramachay formation predominate. Only a few horizons (Fig. 2a) with ammonites were found which are always crushed. Additionally a loose siltstone bed with Peripleurites was found. The Triassic Jurassic boundary is situated at the place of the watershed between the valleys of Chachapoyas and Levanto. The biostratigraphic content includes at least Rhaetian, Hettangian and part of the Lower Sinemurian. The sequence is followed by well bedded micritic limestones of the Condorsinga formation (?Pliensbachian).

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INTRODUCTION In the area of the Utcubamba Valley between Chachapoyas and Leymebamba (Fig. 1) different sections of uppermost Triassic (mainly Rhaetian) and lowermost Jurassic age (mainly Hettangian) were investigated. In part it was possible to collect voluminous ammonite faunas which complete and expand the knowledge hitherto existing (Tilm a n n 1917 ; Jaworski 1922 ; Geyer 1979 ; Prinz 1985) for this area. Up to now unknown transitional sections from the uppermost Triassic to the lowermost Jurassic were found in different facies regions.

DESCRIPTION OF SECTIONS AND LOCALITIES WITH AMMONITES Beside transitional Triassic Jurassic sections, smaller outcrops with sections of restricted strati-

Section along t h e r o a d f r o m M a g a d a l e n a to Maino (Fig. 1, loc. 2 ; 2b ; 3) - The section was measured at the fourth hairpin bend from Maino to Magdalena. Outside of this section a limestone bed with Oxytoma was found near the first hairpin bend and a well preserved Choristoceras (P1. 1, fig. 19a,b) with loosely coiled whorls. The sequence is composed of finebedded siltstones and marly argillites with rarely intercalated finebedded, more or less calcareous beds up to 5 cm thick. In the upper part limestone concretions occur. Below the measured section (Fig. 3) an additional Choristoceras was found near to a sandy limestone bed (0,7 m thick) (Fig. 2). Most ammonites are crushed. The specimens of Oxytoma above the last Choristoceras are found in other sections only in the Rhaetian. 5 horizons with crushed Psiloceras tilrnanni occur. Outside the measured section some well preserved specimens of this species were found. The section continues (not shown on Fig. 2,3) with similar facies along the road to Magdalena. Arietidae of the Lower Sinemurian are rare.

Section along the road from Tingo to Kuelap (Fig. 1, loc. 3 ; 2c) - This section was described and figured by Prinz (1985, Fig. 10). The sequence is overturned and contains horizons with limestone concretions yielding ammonites. The section starts with finebedded siltstones and shales which contained two horizons yielding crushed Psiloceras tilmanni. Well preserved specimens of this species were found in the next two

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Outcrop 1,7 to 1,8 k m s o u t h of T i n g o (Fig. 1, loc. 4) - At this locality finebedded siltstones and calcareous siltstones are exposed. Well preserved Psiloceras tilrnonni were found. Outcrop 3,5 k m south o f T i n g o (Fig. 1, loc. 5) From this outcrop Geyer (1979) figured Psiloceras tilmanni. More or less calcareous siltstones (0,10 to 1 m thick) with lutitic intercalations and calcareous concretions are exposed. Fallen blocks of this steep outcrop contain a limestone bed (30 cm thick) with mostly small P. tilmanni. Closely coiled specimens predominate. Section 3,5 k m south o f Chillo (Fig. 1, loc. 6) At this locality the sequence is composed of well

bedded, rarely calcareous siltstones. Limestone concretions are rare. Only crushed ammonites were found. The lowest part of the section yielded Oxytoma and a species of Choristoceras (P1. 1, fig. 18) with a slowly growing whorl height. 30 to 40 m above these horizons was found Choristoceras cf. marshi (P1. 1, fig. 21). The upper part of the section yielded once more Choristoceras (fragments) and P. tilmanni. S e c t i o n s o u t h of S u t a (Fig. 1, loc. 7 ; 2d) Jaworski (1922) described from this locality ammonites of Early Rhaetian age. Tilmann (1917), Geyer (1979) and Prinz (1985) figured from Suta ammonites of Early Jurassic age. The lower part of well bedded, more or less calcareous siltstones directly south of Suta yielded Monotis and Oxytoma. The specimens of Oxytoma correspond with those found in the Rhaetian of other sections. Above the steep slope (about 100 m above the valley) and directly south of Suta are found fields with loose stones yielding rarely Choristoceras and more frequent Sunrisites? peruvianum (P1. 1, fig. 10, 11) and Schlotheimia cf. marmorea (P1. 1, fig. 9). In continuation of the Inca trail to La Jalca and 200 to 300 m above the

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Coupes hettangicnnes pros de Chillingote (pour la Wgende voir Fig. 1). near Chilingote (Fig. 1, loc. 8, 9 ; 2e ; 3 ; 4 ; 5) - Chilingote is the type locality of Psiloceras tilmanni LANGE and Sunrisites? peruvianum (LANGE) (Tilmann 1917). Sections

On the left side of the valley at different localities sections with Upper Triassic and Lower Jurassic sediments are exposed. Approximately 250 m north of a farmehouse (near the bridge crossing the Utcubamba river) an Upper Triassic Lower Jurassic boundary section (Fig. 4) was measured. The lower part of this section is formed by thickbedded limestones containing debris of undeterminable fossils. The uppermost beds yielded pelecypods with both valves, siliceous sclerites of sponges and radiolarians.

0 Figure 4 - R h a e t i a n ] H e t t a n g i a n b o u n d a r y section n e a r Chilingote (legend Fig. 1). Coupe de la limite Rhdtien/Hettangien

pros de Chilingote (pour la Idgende voire Fig. 1).

Suta is the type locality of the Suta formation (Weaver 1942). Form this locality also ammonites of the Lower Sinemurian were described.

The first ammonite horizon with Psiloceras tiImanni (P1. 1, fig. 15) lies with an irregular bedding plane above a limestone bed without ammonites. The first ammonite horizon yielded also a fragment of Choristoceras (P1. 1, fig. 20a,b) which probably was reworked from Triassic beds. The ammonites of the first horizon and those following are often irregularly bedded and these horizons probably are tempestites. Loosely and closely coiled ~D. tilmanni are found in the same beds. A second section (Fig. 5a, b) was measured at the

302

PLATE 1 Fig. la,b - A l s a t i t e s sp., Chilingote (section Fig. 3), Upper Hettangian, last whorl body chamber (internal mold with shell remains), phragmocone mostly with shell (TUB 900928/6/1). Dernier tour, loge d'habitation (moule interne avec restes du test), phragmoc6ne presque enti~rement pourvu du test.

Fig. 2a,b - S e h l o t h e i m i a cf. m o n t a n a (W.AJ-INER), Chilingote (loosely found block near section Fig. 5b), Upper Hettangian, silicified ?phragmocone (TUB 900925/8/1). Bloc sdpard trouvd pros de la coupe 5b, phragmocSne silicifid.

Fig. 3 - C u r v i c e r a s sp., Chilingote (section Fig. 3), Middle Hettangian (Reissi Zone), two specimens. Small specimen : Phragmocone (with shell) and half last whorl body chamber (internal mold) (TUB 901001/1/1). Large specimen : Phragmocone (with shell) and last whorl body chamber (internal mold, in part crushed, with shell remains) (TUB 901001/1/2). Petit specimen : phragmoc6ne (avec test) et dernier demi-tour loge d'habitation (moule interne). Grand specimen : phragmoc6ne (avec test) et dernier tour, loge d'habitation (moule interne, partiellement dcras~, avec des restes du test). Fig. 4a,b - B a d o u x i a c a n a d e n s i s (FREBOLD), S of Suta, Upper Hettangian, half last whorl body chamber (internal mold), calcitic phragmocone mostly with shell (TUB 900924/6/1). Dernier demi-tour loge d'habitation (moule interne), phragmoc6ne calcitique, presque enti~rement pourvu du test. Fig. 5, 8 - S t o r t h o c e r a s sp., Chilingote (hill W of farmhouse at bridge), uppermost Middle or lowermost Upper

Hettangian. 5a,b. Silicified phragmocone with shell (TUB 900928/4/1). 8a,b. Last whorl body chamber (internal mold), phragmecone with shell (TUB 900928/4/2). Colline ouest de la ferme au pont. 5a, b. Phragmoc6ne silicifid avec test. 8a, b. Dernier tour loge d'habitation (moule interne), phragmoc6ne avec test.

Fig. 6, 7 - S c h l o t h e i m i a ? sp., Chilingote (hill W of farmhouse at bridge), uppermost Middle or lowermost Upper Hettangian. 6a,b. Fragment with part of body chamber (internal mold) (TUB 900928/4/3). 7. Half last whorl body chamber (internal mold), phragmocone with shell (TUB 900928/4/4). Colline ouest de la ferme au pont. 6a, b. Fragment avec partie de loge d'habitation (moule interne). 7. Dernier semi-tour, loge d'habitation Onoule interne), phragmoc6ne avec test. Fig. 9 - S c h l o t h e i m i a cf. m a r m o r e a (OPPEL), S of Suta, Upper Hettangian, partially crushed phragmocone, in part with shell (TUB 900924/5/1). Phragmoc6ne partiellement dcrasd, en partie avec test. Fig. 10, 11 - S u n r i s i t e s ? cf. p e r u v i a n u m (LANGE), S of Suta, Upper Hettangian. 10. Phragmocone (in part with

shell) with beginning of body chamber (TUB 900924/4/1). l l a , b . 2/3 of last whorl body chamber (internal mold), phragmocone with shell (TUB 900924/4/2). 10. Phragmoc6ne (en partie avec test) avec commencement de loge d'habitation. 11a, b. Deux tiers du dernier toul, loge d'habitation (moule interne), phragmoc6ne avec test.

Fig. 12 - D i s c a m p h i c e r a s cf. reissi (TILMANN), Chilingote (section Fig. 3), Middle Hettangian (ReissiZone), two specimens. Small specimen : Phragmocone (with shell) with part of body chamber (internal mold) (TUB 901001/1/3). Large specimen : At least 2/3 of last whorl body chamber (internal mold), phragmocone with shell (TUB 901001/1/4). Petit specimen : phragmoc6ne (avec test) avec partie de loge d'habitation (rnoule interne). Grand specimen : deux tiers du dernier tour : loge d'habitation (moule interne), phragmoc6ne avec test.

Fig. 13 - D i s c a m p h i c e r a s reissi (TILMANN),Chilingote (section Fig. 3), Middle Hettangian (Reissi Zone), half last whorl body chamber (crushed internal mold), phragmocone in part with shell (TUB 901001/2/1). Dernier demi-tour : loge d'habitation (moule interne dcrasd), phragmocdne en partie avec test.

Fig. 14 - P s i l o c e r a s cf. p r i m o c o s t a t u m HILLEBRANDT, Chilingote (section Fig. 5a) , Lower Hettangian, phragmocone, in part with shell (TUB 900925/4/1). Phragmoc6ne, en partie avec test. Fig. 15, 16 - P s i l o c e r a s t i l m a n n i LANGE 15. Chilingote (section Fig. 4, lowermost horizon), Lower Hettangian (Tilmanni Zone), involute variety, phragmecone (mostly with shell) with ?beginning of body chamber (TUB 900928/1/1). 16a,b. 3,5 km south of Tingo, Lower Hettangian (Tilmanni Zone), evolute variety, phragmocone, in part with shell (TUB 900921/3). 15. Variet~ involute, phragmoc6ne (preque enti~rement pourvu du test) avec ?commencement de la loge d'habitation. 16a, b. Varidtd dvolute, phragmocdne, en partie avec test.

Fig. 17 - R h a b d o c e r a s sp., section E of Levanto, Lower Rhaetian, mostly external molds (partially crushed) (TUB 900922/7). Le plus souvent, moules externes (en partie ecrasds). Fig. 18 - C h o r i s t o c e r a s sp., section 3,5 km S of Chillo, Rhaetian, crushed internal mold (TUB 900923/1/1). Moule interne dcrasd.

Fig. 19a,b - C h o r i s t o c e r a s sp., road Maino to Magdalena (first hairpin bend), ?Upper Rhaetian, 2/3 of last whorl body chamber (in part with shell), phragmocone mostly with shell (TUB 900922/7). Deux tiers du dernier tour : loge d'habitation (en partie avec test), phragmoc6ne presque enti~rement pourvu du test.

Fig. 20a,b - C h o r i s t o e e r a s sp., Chilingote (section Fig. 4, lowermost horizon), Lower Hettangian (Tilmanni Zone), fragment of phragmocone, with shell remains (TUB 900928/1/2), x 2. Fragment de phragmoc6ne, avec restes du test.

Fig. 21, 22 - C h o r i s t o c e r a s cf. m a r s h i (HAuER), crushed specimens. 21. Section 3,5 km S of Chillo, Upper Rhaetian, internal mold (TUB 900923/4). 22. Section E of Levanto, Upper Rhaetian, external mold (TUB 900926/3). 21. Moule interne.22. Moule externe. Nat. size unless otherwise indicated.

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::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: Chambara : i : i : i : ~ ~ - i i ! l • ;-

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Figure 6 - Facies interfingering rdgion gtudige.

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

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of formations

- ":-:" - ":':':':':'

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found in the investigated

slope 50 to 100 m north of the first section. The Triassic Jurassic boundary is not exposed. Horizons with loosely and closely coiled P. tilmanni are found. Above these beds a limestone bed yielded a new species of Psiloceras (P1. 1, fig. 14) which is transitional between P. tilmanni and P. primocostatum. This species was also found in a loose block together with P. tilmanni. This block probably derived from the uppermost part of beds with P. tilmanni. Above the horizons of P. cf. primocostatum the strata are not exposed. Stratigraphically about 20 m higher the section continues (Fig. 5b). The lower part yielded silicified Discamphiceras cf. reissi and Storthoceras. D. cf. reissi is also found in higher beds. Above beds with silicified small gastropods, a characteristic bed with Sunrisites cf. peruvianum occurs. The uppermost bed yielded Schlotheimia cf. marmorea. A loosely found block yielded specimens of Schlotheimia cf. montana (P1. 1, fig. 2a,b) . This block probably derived from strata below the horizon with S. cf. peruvianum. At the uppermost part of the slope west of the farmhouse a limestone bed containing Discamphiceras, Storthoceras (P1. 1, fig. 5, 8) and specimens transitional between Storthoceras and Schlotheimia (P1. 1, fig. 6, 7) was found. A third section was m e a s u r e d about 500 m south of the farmhouse (Fig.2e, 3). At this section the complete sequence from uppermost Triassic beds up to Upper H e t t a n g i a n beds is exposed. P. tilmanni was found in three horizons. The middle part of the section yielded horizons with Discamphiceras cf. reissi (P1. 1, fig. 12) and Curviceras (P1. 1, fig. 3) and Discamphiceras reissi (P1. 1, fig. 13) which

:::::::::::::::::::::::::::::::::::::::::::::::::::

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area. Indentation des facies dans les formations de la

are well preserved and in part large. Silicified and mostly small Storthoceras and perhaps transitional forms to Schlotheimia were found in the following beds. Ammonites again are more frequent in the uppermost part of the section, but most specimens are small, in part silicified and badly to isolate. Horizons with small Sunrisites are characteristic. Above the section follows a series of siltstones (finebedded itself) and siltic limestones with layers of shales and horizons of limestone concretions. This series yielded Arietitidae (Vermiceras or Metoyhioceras) and Angulaticeras of E a r l y Sinemur i n age. Chilingote is the type locality of t h e Chilingote formation (Weaver 1942) and was said to be of Hettangian age, but the facies of the Chilingote formation at Chilingote encloses also the uppermost Triassic. C h a n g e s of facies and paleogeography (Fig. 1, 2, 6) - Characteristic changes of facies occur from north to south within strata of the same age. This fact was not known up to now. Boundaries of facies are passing obliquely in time through different types of facies (Fig. 6). The northern part of the investigated area (loc. 1) is dominated by finebedded siltstones and marly argillites (mostly decalcified) and encloses at least the complete Rhaetian, Hettangian and Lower Sinemurian. The lithostratigraphic n a m e Aramachay formation was introduced for this facies. In southwestern direction (loc. 2) this facies

305 passes to equally finebedded siltstones and argillites but containing additionally some silty limestone beds of low thickness and rare horizons with limestone concretions which increase in southwestern direction (Tingo). South of Tingo the calcareous siltstones and silty limestones are getting thicker. They alternate with finebedded siltstones and argillites. Some horizons with limestone concretions also occur. The Rhaetian to Sinemurian sequence near Suta (Fig. 2) is composed of a series of well bedded, calcareous siltstones (finebedded itself), some limestone beds and rare horizons with calcareous concretions. This facies is typical for the Suta formation (Weaver 1942). The Triassic part of the sequence in the southernmost part of the area (Chilingote) is composed of more or less thickbedded limestones without horizons of ammonites. The Hettangian of this area is characterized by well bedded limestones with thin layers of shales and some silty limestones of small thickness. Horizons with ammonites are frequent and at least some of these horizons are tempestites. The Triassic part of this facies could be included in the Chambara formation. This name was proposed for Triassic strata of this facies. The lithostratographic name of the Chilingote formation (Weaver 1942) was introduced for the Hettangian part of this facies. Both facies do not differ essentially from each other. Especially in the lower part of the Chambara formation at other localities, additionally siliceous limestones, siliceous horizons and siliceous concretions are found. But there are also localities (e.g. Quebrada Tingo, Rin Suta) with Rhaetian limestone beds which yie:~ed silicified ammonites. These beds are said to belong to the Chambara formation. The Lower Sinemurian beds of Chilingote are developed in the facies of the Suta formation. Thicknesses of series of the same age are lowest in the area of the Chilingote formation respectively the Chambara formation and highest in the area of the Aramachay formation, although the compaction rate of the latter formation must have been much higher. The Hettangian is about 120 m thick near Levanto and only about 30 m at Chilingote. B i o s t r a t i g r a p h y (Tab. 1) - This chapter also includes remarks to the nomenclature of some ammonites. At the TriassicJurassic boundary, no facies change is found in the Aramachay and Suta formations of the investigated area. Also the Hettangian and Sinemurian are passing facially into each other. On the contrary, in the area of the Chambara and the Chilingote formation respectively the first bed of Hettangian age lies with an

unconformity upon Rhaetian beds. The basal Hettangian bed also yielded a fragment of Choristoceras which probably was reworked from Triassic beds. A significant change of facies in the area of Chilingote took place at the boundary between strata of Hettangian age (Chilingote formation) and strata of Sinemurian age (Suta formation). Rhabdoceras of Early Rhaetian age was found additionally t o Triassic genera which were previously described. In Upper Rhaetian beds only Choristoceras occurs. Different species m a y be distinguished according to coiling, whorl height and density of ribbing. The youngest forms belong to the group of Choristoceras marshi (HAUER). Well preserved and uncrushed specimens of Choristoceras are very rare. Basal Hettangian sediments are characterized by horizons with Psiloceras tilmanni Lange. Coiling of this species is very variable (P1. 1, fig. 15, 16). Up to now only specimens were described and figured which are closely coiled. Loosely coiled specimens are rare and often larger. These specimens are identical to P. pacificum (GUEX) which was described from North America (Nevada). The involute specimens have an umbilical width as found in P. planorbis (Sow.) from England. The evolute specimens are nearly as evolute as P. psilonotum (QUEN.) from the Swabian Jurassic. An exact comparison with P. planorbis is not possible because the specimens from England are crushed. The whorl width of P. psilonotum is smaller t h a n found in P. tilmanni and the suture of the latter species is less simplified but not as complicated as found in P. calliphyllum (NEUMAYR) from the Northern Calcareous Alps. This species is also more evolute. The Tilmanni Zone was proposed by Hillebrandt (1988). This zone yields the oldest Jurassic ammonites of South America and probably this zone is also found in North America. The Tilmanni Zone probably is the time equivalent of the Planorbis Zone in Europe. The Tilmanni Zone is best developed in the area of the Utcubamba valley. At most Chilean sections this zone could not be proved. Together with P. tilmanni and above beds with this species a new species of Psiloceras (P1. 1, fig. 14) with plicated ribs on the inner whorls was found. This species is transitional between P. tilmanni and P. primocostatum HILLEBRANDT. The new species has a more rounded cross section of whorls t h a n P. primocostatum. In Northern Chile this species characterizes the first Hettangian ammonite horizons, together with other species of Psiloceras.

306

NW

Europe

Northern Calcareous Atps

South America

South America Peru

Chlte

Zones

Zones

HILLEBRAHDT1990 Zones

Subzones

S.depressa o.

S .angulata

S.complanata

Zones

Subzones

S. marmorea

Zones

S. cf. merrnorea

S.cf. m a r m o r e a

S.cf. m o n t a n a

S.cf. rnontana

D. reissi

D.reissi

"S.angulata"

S.extrcmodosa

2

-5 .#

A.liosicus

A. lequeus

D. reissi

K. megastomcl

C. portlocki

"1R planorbis 0

P. pllc,,tulum

r, r.~

Ch. m a r s h i

R primocostatum P. t i l m a n n i

P. primocostetum R tiimanni

P. plonorbls

Rh.suessi o

R rectocostatum

P. rectocostotum P.colliphyl[u m

Ch. morshi o

.--

'Curviceras ssp.'

C. peruvianum

C.johnstoni

Ch.cf.marshi

~/stuerzenboumi

Ch.cf. cr ickmcyi

S.reticu[at us

Ch.cf. nobile

S, q u i n q u e punctatus

R ex.gr, roemeriperuv~anum

Ch. cf. marshi I,

i

: P. p n m o c o s t a t u m R tilmonni Ch.cf. marshi

Chonstoceras ssp." Ch.cf. crickmayl Rhabdoceras, Peripleur ires, Metasibirites

Ch. cf. nobile P.e x g r..roeme r i peruwanum

Tableau 1 - Correlation c h a r t of E u r o p e a n and South American a m m o n i t e zones of R h a e t i a n and H e t t a n g i a n age. Tableau de

corrdlation pour les zones d'ammonites de l'Europe et de l'Amdrique du Sud d'dge Rhgtien et Hettangien.

Above the Primocostatum Zone of Northern Chile two f u r t h e r ammonite zones are following which were not found in the area of the Utcubamba valley. The upper one of these zones was named after "Caloceras" (= ?Sunrisites) peruvianum LANGE (HILLEBRANDT, 1988). This species was described as Psiloceras johnstoni SOW. from Chilingote (Tilm a n n 1917) but cannot be classified as Psiloceras or Caloceras because it is found in Upper Hettangian beds. The type material of Tilmann was studied, and on the same rock yielding a fragment of "C". peruviannum, the external impression of a large Alsatites s.1. (?Alpinoceras) was found, similar to specimens which occur in the Upper Hett a n g i a n of Peru, Chile and Argentine. Together with specimens very similar to "C". peruvianum in Northern Chile ammonites are found (e.g. Curviceras a r m a n e n s e (REPIN), C. cf. subangulare ( O P P E L ) ) which are of uppermost Early or lowermost Middle Hettangian age. This zone m u s t be named after a new species not yet described. Very similar species to "C". peruvianum also occur in the Upper Hettangian of Northern Chile and they are included in the genus Sunrisites. This g e n u s was described from North America and the Northern Calcareous Alps. The Middle H e t t a n g i a n of the Utcubamba valley is characterized by Discamphiceras. Besides of D. r e i s s i (TILMANN) similar forms are found which

are within the variability of this species or which are separate species or subspecies of D. reissi. Together with Discamphiceras Curviceras are found in the lower part and Storthoceras in the upper part. Similar species of these genera also occur in Northern Chile and they are typical for the Reissi Zone (Hillebrandt 1988). A horizon containing Storthoceras and a transitional form between Storthoceras and Schlotheimia, is of uppermost Middle or lowermost Late Hettangian age. The Upper Hettangian is characterized by Sunrisites, Badouxia, Alsatites s.1. and Schlotheimia. Besides Sunrisites? peruvianum probably additional species of this genus occur which are also found in Northern Chile. Badouxia is represented by a species which at least is closely related with Badouxia canadenis (FREBOLD) (P1. 1, fig. 4a,b) described from North America. In the lower part of the Upper Hettangian a species of Schlotheimia (P1. 1, fig. 2a,b) is found which is closely related with Sch. montana (W.~INER) from the Northern Calcareous Alps. In the upper part occurs a species similar to Sch. m a r m o r e a (OPPEL) (P1. 1, fig. 9) which in Europe characterizes the uppermost Hettangian. A similar subdivision is possible in Northern Chile. Above beds of Uppermost Hettangian age strata characterized by Arietitidae (Vermiceras or Metophioceras) with a wide umbilicus are following. Similar forms are found in the lowermost Sinemurian of Europe and North America.

307 A c k n o w l e d g e m e n t s - The field work was financed by the G e r m a n Research F o u n d a t i o n (DFG). For import a n t information for the fieldwork I am indebted to Ing. Geol. A. Wilfredo S~nchez Fern~indez (Ingemmet, Lima) and Dr. P. Prinz (University of Marburg).

REFERENCES GEYER O.F. 1979 - A m m o n i t e n aus dem tieferen Unt e r j u r a von Nord-Peru. Pal~iont. Z., 53 : 3/4, 198213. HILLEBRANDT A.v. 1988 - A m m o n i t e Biostratigraphy of the South A m e r i c a n H e t t a n g i a n . Description of two new species of Psiloceras. 2nd Int. Symp. Jurassic Strat., 1 : 55-70. HILLEBRANDT A.v. 1990 - The Triassic/Jurassic Boundary in N o r t h e r n Chile. Cahiers Univ. Cath. Lyon, s~r. Sci., 3 : 27-53.

JAWORSKI E. 1922 - Die m a r i n e Trias in S~idamerika. N. Jahrb. Min. Geol. Paliiont. B.B., 47 : 93-200. PRINZ P. 1985 - Stratigraphie u n d A m m o n i t e n f a u n a der Pucara Gruppe (Obertrias U n t e r j u r a ) von NordPeru. Palaeontogr., Abt. A, 188 : 153-197. TILMANN N. 1917 - Die F a u n a des U n t e r e n Lias in Nord- u n d Mittelperu. N. Jahrb. Min. Geol. Pal~iont., B.B., 41 : 628-712 WEAVER CH.E. 1942 - A general s u m m a r y of the Mesozoic of South America and C e n t r a l America. Proc. 8th Amer. Sci. Congr., 4 (Geol. Sci.) : 149-193.

A.v. H I L L E B R A N D T Institut ffir Pal~ontologie und Geologie Technische Universit~it Berlin Ernst-Reuter Platz 1 10587 Berlin, Allemagne