Ordovician and Silurian chitinozoan biozones of

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from the Kirusillas Format ion (Cramer, Diez & Cuerda,. 1974) at Cochabamba (Appendix I). Grahn (2002) described chitinozoans from the Kirusillas and Tar-.
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Geot. Mug. 143 (4). 101M, pp . 509- 529. © 2006 Cumbridg(' University Press dol:10. 101 7/S00 16756R0600207X Printed in Ihe United Kingdom

Ordovician and Silurian chitinozoan biozones of western Gondwana YNGVE G RA H N " UERJ, Faculdade de Geologia, Bloco A - Sala 400 I, Rua Sao Francisco Xavier 524, 20550-013 Rio de Janeiro, RJ " Brazil

(Recei ved 23 November 2004; rev ised \'('1'.\' i OIl received 15 Septembe r 2005; accepted 5 December 2005)

Abstract - A formal Ordovician- Silurian chitinozoan biozonation for western Gondwana is proposed. This palaeogeographic province includes South America, and was located in medium to high latitudes during Ordovician and Silurian times. Ordovician chitinozoans are known from northern Argentina. southern Bolivia. and Brazil. Silurian chitinozoans occur in Brazil. northern Argentina. southern Bolivia and southern Peru. No published information is available about Ordovician-Silurian chitinozoans from Ecuador, Colombia or Venezuela. Altogether more than 150 localities (including wells and outcrops) are included in this study. and 154 species have been encountered. A biozonation based on the first occurrence of critical chitinozoan species is introduced. Five biozones are defined in the Ordovician (zones of Desmochltina sp. gr. minor, Conochitina decipiens, Eremochinna brevis, Lagenochiti na obelig is and Tan uchit ina anticostiensisi , and nine in the Silurian (zones of Beion echitina postrobusta, Spi nachitina ha rringtoni, Pogonochitina dj almuicMu rg achitina margaritana - Salopochitin a monterrosae. Angochitina echina ta, Eisenackitina gra nutato. Fungochitina kosovensis and the subzoncs of Sphaeru chi tina solutidina and Desmochitina cf. D. " elisa). These biozones are compared with known graptolite. conodont, acritarch and spore

zones from the same area. and chitinozoan zones on a global basis. Keywords: Gondwana, Ordovician. Silurian, Chitinozoa. biozonation.

I. Introduction

Gra ptolites and/or shelly fossils from Ordovician and Silurian strata in the intracratonic basins of western Gond wana (Fig. I) are present in north ern Argentina, southern Bolivia and southern Peru. In Brazil and castern Paraguay these fossils arc limited to specific levels in the stratigraphic column, and therefore are only of restricted biostratigraphic value. Recent investigations on chitinozoans, acritarchs and spores have made possible a more detailed dating of the Silurian rocks . It should be noted that such an important microfossil gro up as conodonts is, except for the Ordovician in northern Argentina, Llandovery in southern Peru, early Wenlock in southern Bolivia, and Caradoc strata in eastern Paraguay (Aconttodus sp. reworked with other shelly fossils into Aeronian Vargas Pefia shales: unpub. data), unknown from Ordovician and Silurian rocks of southern Bolivia, Brazil and eastern Paragu ay. Acritarchs and spores have been applied in biostratigraphy only on a limited scale. However, local Silurian chitinozoan biozonations have been suggested for the Parnaiba (Grahn, Melo & Steernans, 2005 ) and Parana (Grahn, Pereira & Bergamaschi, 2000; Grahn, 2005b) basins. The latter scheme has also been applied to lower Siluria n strata in the Tarija Basin (northern Argenti na) by Grahn & Gutierre z (200 I). These local biozones • E-ma il: [email protected]

are not easily applied on a regiona l. and even less so on a global, scale. The purpose of this paper is 10 present an Ordovician-Silurian chitinozoan biozonation applicable for the intracratonic basins of western Gond wana. and to compare this biozonation with other zonations in well-known areas on a global sca le. 2. Previou s chitinozoan studies in th e Ordovician and Silur ian of western Gondwana

Ordovician and Silurian chitinozoans from Brazil and Paraguay have been discussed in a series of internal reports from PETROBRAS and UERJ (Universidade do Estado do Rio de Janeiro) by H. Muller (Internal report, PETROBRA S, Salvador, 1962), R. F. Daemon (Internal report , PETRO BRAS, Salvado r, 1964), Y. Grahn (Internal reports, PETROBRAS , Rio de Janeiro, 1988a-osa

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C. symmetr/ca L. ron/fundus L destombesi

Tremadoc

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e.hirsutaILageno Llanvirn

Baltica

Lagenochitina esthonica Lagenochitina destombesi

Conochitme deciplans

Desmochitina sp.gr. mmor

Figure 3. Correlation between Ordovician chitinozoan biozones in western Gondwana and other areas on a global scale. · 2004 Webby et al. (2004 ).

6.e. Tanuchitino antieostiensis In terval Zone

Zone base definition: FOB of Tanuchitina anticostien sis (Fig. 5c). Characte rization of zone: The co-occurrence of the index species, Armo ricochitina nigerica, Lagenochitina prussica and Rhabdochitin a aff gracilis. Reference section for zone base: PETROBRAS l -AM-l -AM well level 2091 m, Amazonas Basin, northern Brazil. No outcrop sections of the AurasMirim Formation are known. Representative occurrences of zone: Upper part of the Autas-Mirirn Formatio n. Lithostratigraphic distribution: Upper part of the Autas-Mirim Formation in northern Brazil. Age range: Upper Ashgill (Figs 2. 3). Remarks: Tanuchitina anticostiensis is restricted to upper Ashgillian (Rawtheyan) strata. In Quebec , Tanuchitina anticostiensis and Hercochitina crickmayi zones roughly correspond to the T. anticostiensis Zone in western Gondwana.

In this interval, many different Herc ochitina species occurtogether with Con ochitina COllc a va . Conochitina armifera and Ancyro chitina longispina (Appendix 3) (Acha b, 1989). 7. Silurian chitinozoan biozonation of western Gondwana

The Silurian biozonation and its correlation within western Gondwana are shown in Figures 6-8 and 11. A correlation with the global zonation is demonstrated in Figures 9 and 10. 7.a. Belonechitina postrobus ta Range Zone

Zone base definition: FOB of Belon echitina p ostrobusta (Fig. 5d) has not been defined in western Gondwana. The last occurre nce is in the top Rhuddanian strata in eastern Paraguay (Grahn, Pereira & Bergamaschi, 2000).

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Ordovician and Silurian chitinozoan biozones

Section 7.c ). Besides the index spec ies are other

diagnostic species Plectochitina sp. A. Spha erochltina silurica, Spina chitina sp. A. Cono chitinu sp. A !ie/l.m Gra hn i ll Gra hn. Pereira & Bergam asch i. 2000, Plectochitina sp. C se' '''', Grahn ill Gra hn. Pereira & Bergarnaschi, 2000 and Sphaerochuina sp. C .'Ot' /I .\"II Grahn ill Gra hn, Pereira & Bcrgam asch i, 2000 .

Reference section for zone base: Outcrop Minas Cue (G rahn . 2005h ). lower part of the Vargas Pena Formation. Parana Basin. eastern Paraguay, Rep resentative occurrences of zone: Lower part of

the Vargas Pefia Formation in the Parana Basin. eastern Paraguay. Lithostrati graph ic d istribut ion : See rep resent at ive

b Figure a . Ordovic ian chitinozoan index species from western Gondwana. The scale bars represent 100 J.1m. ca) Desmocbitinu sp. gr. minor [Szaniawski ill Chlebowski & Szaniawski. 19 7~) . Dique Sect ion ncar Culpina. base of the Obispo Formation. By courtesy of OrThomas Hcuse (lena. Germany). (b) Ervmocbi tina bsvvis Benoit & Taugourdeau. 1961. Los Colorado Creek. lower partof the Acoite Formation. By courtesy of Or Eduardo Guil lermo Ottonc (Buenos Aires. Argentina).

Characterizat ion o f zone: In the uppermost part , Spinachitina wolfarti. Sphaerochitina palestinaense and Ancyrochiti na llncyn'u appear.

Reference section for zone base: No section known, Representative occurrences of zone: Anschutz Minerals RD-1 16 well. lowermost part of the Vargas Pefia Frn", Parana Basin. eas tern Paraguay, The upper part o f the B. !H,strobustu Zone is also present in the ELET RONO RTE shallow bo reho le SM 10 17, lowermost part of the Pitinga Form at ion . Amazonas Basin. northern Brazil (Gra hn. 2005u ). Lith ostrat igraph ic distribution : Sec repre sent ative occurrences o f zon e above. Age range: Early Llandovery (Rhuddanian) (Figs 6, 8- 11). Remarks: Belonech itina postro bnsta is restricted to lower Lland overy (Rhuddanian) strata. In the g loba l zonalion (Vernie rs et al. 1995 ) the Rhuddan ian includes the Spinachitina frugili... Belonechitina postrobusta. Conochitina electa and lowermost Spin achitina 11I11e1l1rili zones. Other important species in this interval include Ancyrochitina laevaensis, Belonechitina asperu, Plectochitina nodi/era. Angochitina seuratt, Enconochitina iklaensis, Plectochitina paraguayensis and Pterochitina deichaii (A ppendix 3) . 7.h. Sp inQchitinQ hQrrinx toni RanJ,:t' Zone

Zo ne base de finition : FO B of Spinachit ina harringt oni (Fig. 5e). Characterization o f zo ne: In the up pe r part is a subzone with Sphuerochitina solutidina defined (see

occurrcncies of zone. Age range: M iddle Lland overy (Aeronia n) (F igs 6.

8- 11 ). Remarks: Spina chitina harringtoni is restricted to middle Lland overy (Aeronian) strata. In the globa l zonatio n (Verniers et al. 1995) the

Aeronian includes the Spinachitina maennili and Conochitina ulargadu zones. Other important species in this interval include Ancyrochitina com'exa. Conochitina vitrea and in the uppermost part (of the C. alurgada Zone). Plectochitina saharicu and Plectochitina p.\'c!UdOllgg/W;JltllJs (Appendix 3 ). 7.f:.

Spl,"~rtIch itin"

,w /Iltidill" Ran.:,e Su hze ne

Zonebase defi nition: FOB of Spha erochitina solu tidinu (Fig. 5f). Charac terization of zone : Besides the index species are ocherdiagnostic spec ies such as Conochitina sp. A sellSIl Gra hn ill Gra hn, Pereira & Berg amaschi. 2000. Plectochitina sp. C sensu Grah n ill Grahn. Pereira & Bergamasch i, 2000 and Sphuerochitina sp , C ..emil Gra hn i ll Grahn . Pereira & Bcrgamasch i, 2000. Refer ence section for zone base : An schutz Minerals RD-11 6 well. level 300 m, lower part o f the Varg as

Pefia Formation. Parana Basin. eastern Paraguay. Representative occurrences of zone: Lower part of the Vargas Pena Formation in the Parana Basin. castern Paraguay. Lithostra tigraphic distribution : See represent at ive occurrences of zone above. Age ra nge : M iddle Lland ove ry (Aero nia n ) (F igs 6,

8- 11 ). Remarks: Sphaerochitina solutidina is restricted to upper midd le Lland ove ry (upper Aeron ian) strata, In the global zonation (Verniers et ul. 1995 ) this subzone corresponds to the upper Conochitina alargada zone. Ot her importa nt species in this inte rval arc Plectochitina saharica and Plectochitina pseudoagglutinans. ? d. PfJ/:on fJc!litin a dj a/m ai Int erv al Zon e

Zo ne base definition: FO B o f Pogolloclrililla djulmai (Fig. 5g ).

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Y. G RA H N

Figure 5. Ordovic ian and Silurian ch itinozoa n index species from western Gon dwana . The scale bars re present I DO urn. (a l COIlOC!litiJW decipiens Taugo urdcau & Jek hows ky, 19M), PET ROB RAS I-JD- l · Al\t well level 2590 m. Benjamin Constant Fill. (b) t.agenochitina ohdigis Par is. \9 XI. PET RO BRA S I·J D- I· A~1 well. core 18 (l096 m). Benja min Co nstant Fm . (e ) Tanucttitina allticostiellsi.'i(A chab. 1( 77) . PET ROB RAS l -AM- I-At'\'l well. level 209 1 m. Auta s-Miri rn Fm . (d) Belonechitina postrobusta (Nestor. 1( 80 ). Ansch utz Mineral s RD· 116 wel l. level 400.95 111. Vargas Pcf m Fm. (e ) Spinachitina harringtoni Gra hn ill Gra hn. Pereira & Bcrgam aschi. 2000. An sch utz Minera ls RD-115 well. level 14 1.77 m. Varga s Pena Fm. (f) Sphaerochitinu soluti dina Paris. 1988. Anschutz Minerals RD-116 well. level 280 .70 m. Vargas Pcna Fill. (g) Pogonochitina dj ahnoi (Sommer & van Boekcl . 1( 65 ). Outcro p lgarape da Rainha 4-65-68. Pitinga Frn. (lower par t). (h) Dt·smochitina cf D. densu Eisc nnck. 1962 . Ansch utz Minerals RD·11 6 well. level 222 .60 ru, Vargas Pefta Fill. (i ) Marg achitina margaritana tEiscnack. 1( 37). PET ROBRAS I-AM -I -AM wel l. cuttings 1746 -1 749 In. Pitinga

517

Ordovician and Silurian chitinozoan biozones Chitinozoan ranges in the Silurian of western Gondwana

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2'·3 1 Figure 6. Chronostratigraphy and chitinozoan ranges in the Early Silurian of western Gondwana. Chitinozoan Zone 1 - Belonechitina postrabusta , 2 - Spinachitina harringtoni, 3 - Sphaerochitina solutidina, 4 - Desmochitina cf. D. densa, 5 - Pogonochitina djalma i, and 6 - Margachitina margaritana-Saiopochitina monterrosae.

Characterization of zone: In the upper part is a subzone with Desmochitina cf. D. densa defined (see Section 7.e). Besides the index species are other diagnostic species such as Angochitina gurupiense , Cing ulochit ina bouinensis, Eisena ckitina bejui, Plecto chitina pa raguayensis, Ancyrochitina erichseni, Allgochiti lla longicollis, Pogonochitina inornata and Pogonochitina tiunguaense. Reference section for zone base: PETROBRAS l- AM-I -AM well, level 1755 m, Amazonas Basin, northern Brazil. No outcrop section with the base of the P. dj almai Zone is known. Representative occurrences of zone: Several localities within the lower part of the Pitinga Formation in the Amazonas Basin and the Tiangua Formation in the Parnaiba Basin, north ern Brazil.

Lithostratigraphic distribution: See representative occurrences of zone above. Age range: Late middle Llandovery (Acronian) to late Llandovery (Telychian) (Monograptus turriculatus grapto lite Zone in the lower part) (Figs 6, 8- 11). Remarks: Pogonochitina dja lmai range from upper middle Llandovery (uppermost Acronia n) to lower Wenlock (lower Sheinwoodian ) strata. Pogonochitina dja lmai occur together with Tclychian graptolites in the Bove Basin (Guinea) (Paris in Villeneuve et af. 1989). In the globa l zonation (Verniers er al. 1995) this zone can be correlated with the Zone of Eisena ckitina dolioliformis. Other important species in this interval include Pterochitina deichoii. Conochitina vitrea, Plectochit ino pseudoagglutinans,

Fm. (low er part). (j) Salopochltina monterrosae (Cramer, 1969). PETROB RAS t· AM- l -AM we ll, cuttings 1746--1749 m, Pitinga Fm. (lower part). (k) Ango chitin a echinate Eiscnack, 193 1. PETROBRAS I·AM· I-AM well , core 46 (1607.00-16 13 m) , Pitinga Fm. (upper part). (I) Eisenackitina g ranulata (Cramer, 1964 ). PETROBRAS I-AM - I-AM well , core 46 (1607.00- 1613 m) , Pitinga Fm . (upper part). (m) Fungochitina kosovensis Paris, 1981. PETROBRAS I-A M-l ~ A M well, core 46 ( 1607.00--16 13 m). Pitinga Fm. (upp er part) .

5 18

Y. G RA HN Chitinozoan ranges in the Silurian of western Gondwana

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Figure 7. Chronostrat igraphy and chitin ozoan ranges in the Late Silurian of western Gondwana. Chitinozoan Zone 6 - Angochitina ecbinata , 7 - Eisenuckitin a grunulutu, and 8 - Fungochit ina kosovens is. T & J 1960- Taugou rdeau & Jekhowsky (1960).

Plectochitina saharica, Conochitina edje lensis and Conochitina emmastensis (Appendix 3).

7.e. Desmochitina d. D. densa Range Subzo ne

Zone base de finition: FOB of Desmochitina cf. D. densa (Fig. 5h). Characteriza tion o f zone: Besides the index species, other diagnostic spec ies are Pog onochitina inorna ta. Ancyrochitina paranaensis and Linochit ina sp. A sensu Grahn in Grahn, Pereira & Bergamaschi, 2000, have their first appearance in this subzone, and Conoeltitina elongata disap pears in its topmost pan . Reference section for zonc base: Anschu tz Minerals RD-116 well, level 230 m, upper pan of thc Vargas Pena Format ion, Parana Basin , eastern Paraguay, No outcrop section with the base of the Desmochitina ef. D. dens a Subzo ne is known. Repre sentative occurrences of zone: Upper Vargas Pcna Formation in the Parana Basin, eastern Paraguay,

Lithostratigraph ic distribution: See repr esentative occ urrences of zone. Age range: Early late Llandovery (early Telychian ) (Monogmp tus turriculatus graptolite Zone in the lower pan ) (Figs 6, 8- 11). Remarks: Desmochitina cf. D. densa is restricted to lower upper Llandovery (lower Telychian) strata. In the global zonation (Verniers et al. (995) the Desmochitina cf. D. densa subzone is coeva l with the upper Eisena ckitina dolioliformis Zone. See above for characteristic chitinozoan species in this zone (sec Section 7.d).

7.r. .\ /arxachir;na margari/ana-Salopochitina mon terrose e Ran ge Zone

Zone base definition: FO B o f Margachitina margaritana (Fig. 5i) or Salopoelritina monterrosae (Fig . 5j ). Characterization of zone: In addition to the index species, other diagnostic species are Angochit ina sp. A sensu Gra hn & Pari s, 1992, Belonechitino'l

5 19

Ordovicion and Silurian chiti nozoan biozones Lithostratigraphy Chronostrat igra phy

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