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Upper Silurian and Devonian Chitinozoa from central and southern Bolivia, central Andes
Journal of South American Earth Sciences 15 (2002) 315–326 www.elsevier.com/locate/jsames
Upper Silurian and Devonian Chitinozoa from central and southern Bolivia, central Andes Yngve Grahn* Faculdade de Geologia, Universidade do Estado do Rio de Janeiro, Bloco A Sala.13, Rua Sa˜o Francisco Xavier 524, 20559-4001 Rio de Janeiro, Brazil Received 2 January 2002; accepted 2 January 2002
Abstract A study of chitinozoans from Upper Silurian and Devonian strata from south central Bolivia has provided new stratigraphic information and improved correlations with adjacent basins in Argentina, Paraguay, Uruguay, and Brazil. The investigated succession extends from late Ludlow (upper Kirusillas Formation) to late Frasnian (upper Iquiri Formation). Unconformities in the section or condensed intervals occur in latest Pragian to early Emsian and for most of the Eifelian. Two early Givetian chitinozoan species, Ancyrochitina postdesmea and Ramochitina boliviensis, are newly described. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: Chitinozoans; Lithologies; Biostratigraphy; Bolivia
Resumen El estudio de los quitinozoos del Silu´rico superior y Devo´nico de la zona centro-sur de Bolivia ha facilitado nueva informacio´n estratigra´fica y mejorado las correlaciones con cuencas adyacentes en Argentina, Paraguay, Uruguay y Brasil. La sucesio´n estudiada abarca del Ludlow tardı´o (superior de la Formacio´n Kirusillas) al Frasniano tardı´o (superior de la Formacio´n Iquiri). Existen discontinuidades en la seccio´n, o intervalos condensados, en el Pragiano ma´s terminal al Emsiano temprano, y para la mayor parte del Eifeliano. Se describen dos nuevas especies de quitinozoos del Givetiano temprano, Ancyrochitina postdesmea y Ramochitina boliviensis. q 2002 Elsevier Science Ltd. All rights reserved. Palabras clave: Quitinozoos; Lithologies; Biostratigrafia; Bolivia
1. Introduction Chitinozoans from Bolivia have been described or mentioned by Cousminer (1964), Cramer et al. (1974), Sua´rez-Riglos (1975), Rollano-Barrero (1975), Gagnier et al. (1989), Wood and Isaacson (1992), Racheboeuf et al. (1993), Liachenko (1994), Wood (1994), Ottone and Rossello (1996), Limachi et al. (1996), Vavrdova´ et al. (1996), Heuse et al. (1999), and Melo (2000). According to these studies, Bolivian chitinozoan faunas are virtually the same as those from the intracratonic basins of Brazil, Paraguay, Uruguay, and northwest Argentina (Grahn, 1992; Ottone, 1996; Grahn et al., 2000; Grahn and Gutie´rrez, 2001; Grahn and Melo, 2002). The purpose of this paper is to document the chitinozoans and chitinozoan bio* Corresponding author. Fax: þ 55-21-587-7704. E-mail address: [email protected] (Y. Grahn).
stratigraphy from 11 outcrops and two boreholes from Upper Silurian and Devonian strata of south central Bolivia.
2. Material and methods For this study, 103 samples from 11 outcrop localities in the Andes and two boreholes in the lowland plains, south central Bolivia, were examined for Chitinozoa. The locations of investigated outcrop sections are shown in Fig. 1. Geological data from the selected outcrops in south central Bolivia and other references can be found in Lo´pez-Pugliessi and Lo´pez-Murillo (1972), Arispe and Dı´az-Martinez (1996), Limachi et al. (1996), and Miranda (2000). In general, the chitinozoans are poorly preserved. Because of preservational difficulties and irregular, widely spaced sampling, it is not meaningful to plot the chitinozoan ranges in logs. The chitinozoan faunas are therefore
0895-9811/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 8 9 5 - 9 8 1 1 ( 0 2 ) 0 0 0 4 5 - 7
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Fig. 1. Location map of outcrops and wells in south central Bolivia investigated in this study.
discussed as discrete assemblages occurring at different levels within each investigated formation, and their overall stratigraphic ranges are given in Fig. 2. The stratigraphic position of samples is given in Tables 1 –4. The residues were studied for chitinozoans under a binocular stereoscopic microscope, and representative specimens were picked and mounted for scanning electron microscope (SEM) studies performed in cooperation with SEBIPE (CENPES, Petrobras) in Rio de Janeiro. Sample processing and SEM preparation were carried out at the Geological Laboratory (LGPA) of the Geological Faculty at Universidade do Estado do Rio de Janeiro using techniques described by Laufeld (1974). SEM preparations are stored at the Department of Stratigraphy and Paleontology at Universidade do Estado do Rio de Janeiro. Specimens photographed with transmitted light are stored in the collections of SEBIPE, Petrobras, Rio de Janeiro.
3. Geologic setting and biostratigraphy The Peru –Bolivia Basin includes parts of northwest
Argentina, western Paraguay, most of Bolivia and Peru, and Ecuador to westernmost Brazil. The outcrops of its sedimentary infill form an elongate, almost continuous belt of sedimentary rocks paralleling the present-day Andes. During the Early and Middle Paleozoic, a seaway connected the Peru – Bolivia Basin to the Chaco – Parana´ Basin in northeast Argentina and the Parana´ Basin in eastern Paraguay and southern Brazil (Fu´lfaro, 1996; Grahn and Gutie´rrez, 2001). The basement in the Bolivian part of the Basin consists of Upper Proterozoic and Cambrian rocks exposed in a few areas (Sempere, 1995). Deformed Early Paleozoic epimetamorphic rocks are known from the Tarija area, around Cochabamba, and Cerro Chilla, south of Lake Titicaca. In central Bolivia, Lower and Middle Cambrian rocks occur in an east – northeast-trending fold and thrust belt (Sempere, 1995). The maximum thickness of the Silurian and Devonian succession easily exceeds 6000 m (Gonza´lez et al., 1996). In south central Bolivia, the Cancan˜iri Formation represents the basal Silurian. It consists of diamictites with clasts from the igneous, metamorphic, and sedimentary basement. This formation correlates with the Zapla Formation, of middle to late
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Fig. 2. Distribution chart of Late Silurian and Devonian chitinozoan species of south central Bolivia.
Llandovery age, in northwest Argentina (Grahn and Gutie´rrez, 2001). In central Bolivia, the overlying Sacta limestone has been dated as earliest Wenlock (for a discussion of this limestone, see Merino, 1991; Beccar, 1994; Goitia, 1994; Dı´az-Martı´nez, 1997, 1998). However, the Kirusillas Formation is the oldest formation considered in this study. A correlation chart showing the evolution of stratigraphic nomenclature and age interpretations for the Upper Silurian – Devonian formations of south central Bolivia is presented in Fig. 3. 3.1. Kirusillas Formation
Fig. 3. Late Silurian and Devonian correlation chart of south central Bolivia.
The Kirusillas Formation (Ahlfeld and Branisa, 1960) correlates to the Uncı´a Formation of Vargas-Cordova (1970). It unconformably overlies the middle to late Llandovery Cancan˜iri Formation and is transitional to the overlying Tarabuco Formation. Kirusillas Formation lithologies consist of black micaceous shales and mudstones with interbedded fine-grained sandstones. Limonitic horizons, associated with the sandstones, are present in the upper part. The total thickness is estimated to be 2000 m (Gonza´lez et al., 1996). Samples from the upper Kirusillas Formation were investigated from the Sella and Tarabuco sections (Tables 2 and 3). All were barren of Chitinozoa. A Kirusillas Formation bulk sample from near Cochabamba was studied for chitinozoans and acritarchs by Cramer et al. (1974).
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Table 1 Investigated samples in the Angosto de Huacareta and Balapuca sections
They found a chitinozoan fauna representing upper Ludlow to lower Pridoli strata, with species such as a Bolivian variant of Ancyrochitina ancyrea sensu Cramer et al. 1974 (a characteristic late Ludlow species known from the Amazonas and Peru –Bolivia basins), Pterochitina perivelata (Eisenack, 1937), Urnochitina urna (Eisenack, 1934), and others. The same age was confirmed for the upper Cachipunco Formation, Santa Barba´ra Range, northwest Argentina (Grahn and Gutie´rrez, 2001). A Wenlock – Ludlow age was suggested (Lobo-Boneta et al., 1976; Limachi et al., 1996), but the chitinozoans reported by Cramer et al. (1974) indicate the age of the Kirusillas Formation as late Ludlow at the base and early Pridoli at the top. Recently, Toro et al. (1998) found early Ludlow graptolites from the lower Kirusillas Formation. According to Gonza´lez et al. (1996) and Dı´az-Martı´nez (1998), the base of the formation probably is diachronous. 3.2. Tarabuco Formation The Tarabuco Formation (Steinmann in Ulrich, 1892) correlates to the Catavi Formation of Turneaure (1960). It conformably and in transition overlies the Ludlow – early Pridoli-age Kirusillas Formation and is transitional with the overlying Santa Rosa Formation. The lithologies consist of interbedded micaceous dark-gray shales and fine-grained sandstones. The shales occur in 5 – 30 cm thick layers and the sandstones in beds 10 – 100 cm thick. Sandstone
Table 2 Investigated samples in the Rio Pilaya and Sella sections
conglomerates, 5 – 15 cm thick, are present at some levels. The total thickness is estimated to be 1200 m (Gonza´lez et al., 1996). Samples from the Tarabuco Formation were investigated from the Sobo– Sobo, Rio Pilaya, Sella, and Tarabuco localities (Fig. 1, Tables 2 and 3). Determinable species from the Sobo– Sobo section include questionable representatives of Fungochitina kosovensis Paris and Kriz, 1984, Lagenochitina sp. (Fig. 4E), Sphaerochitina patula Jaglin, 1986, Ancyrochitina aff. A. libyensis (Fig. 4F), and Angochitina echinata Eisenack, 1931 (Fig. 6A). This assemblage suggests an early Pridoli age, which is also true for the Tarabuco Formation in the Rio Pilaya section, where the shales yield Angochitina echinata (Fig. 6A) and Cingulochitina serrata Taugourdeau and Jekhowsky, 1960. The uppermost part of the formation, in the Sella section, yields a diversified and abundant chitinozoan fauna of late Lochkovian age, with species such as Eisenackitina cf. E. bohemica (Fig. 6B), Cingulochitina serrata (Fig. 6C), Pterochitina sp., Hoegisphaera sp. (Fig. 4A), Urochitina loboi Volkheimer et al., 1986 and a similar species (Fig. 4B), Angochitina ex. gr. filosa (Fig. 4C), Lagenochitina cf. L. navicula (Fig. 4D), and Sphaerochitina densibaculata Volkheimer et al., 1986; (Fig. 6D). A similar chitinozoan assemblage was described by Vavrdova´ et al. (1996) in the Tequeje Formation in the Madre de Dı´os Basin, north Bolivia. The sequence from the Tarabuco section was barren of chitinozoa. A Ludlow and/or Pridoli age has been suggested for the Tarabuco Formation in the literature (see Fig. 3). Racheboeuf et al. (1993) also include the lowermost part of the Lochkovian. The chitinozoan assemblages in this study suggest an early Pridoli to late Lochkovian age.
Y. Grahn / Journal of South American Earth Sciences 15 (2002) 315–326 Table 3 Investigated samples in the Sobo–Sobo and Tarabuco sections
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ful Margachitina catenaria tenuipes (Paris, 1981; Fig. 4G) were recovered from the first locality. The Rio Pilaya section only yielded Ancyrochitina spp. The presence of Ramochitina magnifica (Lange, 1967a) in the Tarabuco section indicates that the Santa Rosa Formation ranges into the lower Pragian. A Pridoli to early Emsian age has been suggested in the literature (see Fig. 3). The chitinozoan assemblages recovered in this study suggest a late Lochkovian to early Pragian age. Racheboeuf et al. (1993) reported Eisenackitina cf. E. bohemica approximately 43 m above the base of the Santa Rosa Formation, and Gagnier et al. (1989) illustrated Sphaerochitina densibaculata from the basal part, thus confirming a late Lochkovian age for the lower part of the formation. Margachitina catenaria tenuipes is known from late Lochkovian to early Pragian, and Ramochitina magnifica is an index species for Pragian strata in the Parana´ Basin of Brazil, Paraguay, and Uruguay (Grahn et al., 2000). 3.4. Icla Formation
The cooccurrence of Urochitina loboi, Cingulochitina serrata (Cingulochitina striata and Cingulochitina sp. A of Volkheimer et al. 1986), and Sphaerochitina densibaculata is a characteristic late Lochkovian association in the lower part of the Puesto el Tigre Formation, Tarija Basin, northwest Argentina (Volkheimer et al., 1986). At this horizon, a species similar to Urochitina loboi but lacking a spiny peduncle and with a dense spiny ornamentation on the apex (see Fig. 4B) also occurs. This ornamentation is similar to that illustrated by Volkheimer et al. (1986, Fig. 4 therein) for Urochitina loboi, except for the absence of a peduncle. It is possible that this form without a peduncle is an evolutionary predecessor to Urochitina loboi. 3.3. Santa Rosa Formation The Santa Rosa Formation (Ahlfeld and Branisa, 1960) correlates to the Vila Vila Formation of Fricke et al. (1964). It conformably overlies the early Pridoli– late Lochkovian age Tarabuco Formation and is transitional to the overlying Icla Formation. The lithologies consist of micaceous sandstones with beds of silty mudstones. The total thickness is estimated at 1800 m (Gonza´lez et al., 1996). Samples from the Santa Rosa Formation were investigated from the La Yesera, Sobo –Sobo, Rio Pilaya, Tarabuco, and Sella sections (Fig. 1, Tables 2 –4). Only samples from the Sobo – Sobo, Rio Pilaya, and Tarabuco sections yielded sparse chitinozoan faunas. Urochitina loboi? (Fig. 4H) and doubt-
The Icla Formation (Steinmann in Ulrich, 1892) conformably overlies the late Lochkovian – early Pragian Santa Rosa Formation. In this study, distinct lower and upper divisions of the Icla Formation were recognized, which agrees with Racheboeuf et al. (1993). The lithologies consist of silty mudstones with intercalated sandstone beds, approximately 20 – 80 cm thick. The total thickness is estimated to be 1800 m (Gonza´lez et al., 1996). Samples from the Icla Formation were studied from the La Yesera, Sobo– Sobo, Rio Pilaya, Angosto de Huacareta, Tarabuco, and Sella sections (Fig. 1, Tables 1– 4). The Icla sequences in the Rio Pilaya and Angosto de Huacareta sections were barren of chitinozoa. Except for the Angosto de Huacareta section, the lower unit of the Icla Formation is present in all sections, yielding Chitinozoa that include species such as Pterochitina sp. (Fig. 4K), Ramochitina sp., Ramochitina magnifica, and Ancyrochitina sp. A (Cladochitina biconstricta Lange, 1967a pars; Fig. 4J), a species ranging from Pragian to late Emsian). The upper unit of the Icla Formation is characterized by the presence of some Ancyrochitina species (Fig. 6E,F) and Ancyrochitina parisi Volkheimer et al., 1986; (Fig. 4I), which is an index species for the late Emsian (possibly including latest early Emsian and earliest Eifelian) of the Parana´ and Peru – Bolivia basins (Volkheimer et al., 1986; Grahn et al., 2000). North of Tarabuco, the lower Icla Formation, 20 and 75 m above the Scaphiocoelia beds, yields Angochitina aff. A. comosa, an early Pragian species in Europe (Racheboeuf et al., 1993). Scaphiocoelia beds occur at the top of the Santa Rosa Formation and contain a characteristic Pragian chitinozoan fauna. However, Scaphiocoelia beds in the Bele´n Formation (Altiplano Andean Zone) yield Cingulochitina striata (Cingulochitina serrata ) and Sphaerochitina densibaculata, which constitute a late Lochkovian assemblage. A
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Table 4 Investigated samples in the La Yesera, Quebrada Botellas, Quebrada Agua Blanca, Rio Bermejo, Taputa´, MCT-X2, and MCT-X4 sections
Pragian to early Givetian age has been suggested for the Icla Formation (see Fig. 3). Tiella et al. (1998) and Tourneur et al. (2000) recently suggested that dating of the Icla and Bele´n Formations should be reassessed. The chitinozoan assemblages in this study suggest an early to late Pragian age for the lower Icla Formation and a late (possibly including latest early) Emsian –earliest Eifelian age for the upper Icla Formation. 3.5. Huamampampa formation The Huamampampa Formation (Steinmann in Ulrich, 1892) conformably overlies the late Emsian – earliest Eifelian upper portion of the Icla Formation and is transitional to the overlying Los Monos Formation. The lithologies include sandstones in 10 –50 cm thick layers with interbedded silty mudstone. The total thickness is estimated as 300 –700 m (Limachi et al., 1996). Samples from the Huamampampa Formation were investigated from the Sobo –Sobo, Rio Pilaya, Tarabuco, La Yesera, Balapuco, and Angosto de Huacareta sections (Tables 1 –4). All sections yielded early Givetian chitinozoans, though a latest Eifelian age cannot be excluded for the lower part of the formation. From the Sobo – Sobo section, Ramochitina
ramosi Sommer and van Boekel, 1964, Eisenackitina sp., and questionable specimens of Alpenachitina eisenacki Dunn and Miller, 1964 were recovered. The Rio Pilaya section produced Eisenackitina aranea Urban, 1972, Ramochitina sp., Ancyrochitina sp., and Ancyrochitina 121b Lange, 1967b. In the Tarabuco section is an abundant and diverse chitinozoan fauna with Hoegisphaera sp., Ancyrochitina postdesmea n.sp. (Fig. 6G), Ramochitina sp., Ramochitina boliviensis n.sp. (Fig. 4L), Eisenackitina aranea (Figs. 6H, 7B), Alpenachitina eisenacki, Ancyrochitina cf. A. langei (Fig. 7A), and Ancyrochitina 121b Lange, 1967b. The basal part of the Huamampampa Formation is present in the Balapuca section. Characteristic chitinozoans are Lagenochitina sp., Ancyrochitina langei Sommer and van Boekel, 1964, Ramochitina sp., Ancyrochitina sp., and Ancyrochitina 123 Lange, 1967b. The upper part of the formation is present in the La Yesera and Angosto de Huacareta sections. The La Yesera section presents Ancyrochitina sp., Ramochitina sp., Eisenackitina aranea, Ancyrochitina postdesmea n.sp., and Ancyrochitina cf. A. tumida Legault, 1973 (Fig. 5A) and the Angosto de Huacareta section Ancyrochitina 121b Lange, 1967b (Fig. 5C), Ancyrochitina 123 Lange, 1967b, Ancyrochitina cf. A. langei, Eisenackitina aranea, and Ramochitina sp. B (Angochitina devonica of Lange, 1967a; Gotlandochitina sp. B of Paris et al., 1985; Fig. 5B). A late Emsian to early Givetian age has been suggested in the literature (see Fig. 3). Approximately 25 m above the base of the Huamampampa Formation, Racheboeuf et al. (1993) reported Alpenachitina eisenacki and Ancyrochitina langei. The chitinozoans indicate an early Givetian age for these beds. Alpenachitina eisenacki has an Eifelian – early Givetian distribution on a worldwide basis, but it is a common species in the early Givetian of Brazil, and only rare fragments of this species have been found in Eifelian beds. Eisenackitina aranea is another Eifelian – early Givetian species. According to Paris et al. (1985), specimens of Eisenackitina castor (E. aranea ) that are restricted to the Eifelian are smooth, whereas those from the Givetian have spinose surface ornamentation. The specimens present in the Huamampampa Formation are deeply corroded, and it is often not possible to determine if they are spinose. Ramochitina boliviensis n.sp. appears to be restricted to the early Givetian in this collection. Ancyrochitina cf. A. tumida sensu Legault, 1973 is a species from the early Givetian Hungry Hollow, Arkona, Rockport Quarry, and Bell members of the Hamilton Formation and the Dundee Formation, SW Ontario, Canada (Legault, 1973). Ancyrochitina 121b and 123 are similar to species illustrated by Lange (1967b) from the Ereˆre Formation in the Amazonas Basin. Ancyrochitina langei is a species ranging from earliest to latest Givetian in the Parana´ Basin (Grahn, own observations), and Ramochitina sp. B is known from early Givetian strata in the Parana´ Basin and Libya (Paris et al., 1985).
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Fig. 4. Scale bar in the upper left corner is 100 mm. A. Hoegisphaera sp. Sella section, Tarabuco Formation. B. Potential evolutionary precursor to Urochitina loboi. Note the spiny ornamentation at the base. Sella section, Tarabuco Formation. C. Angochitina ex. gr. filosa. Sella section, Tarabuco Formation. D. Lagenochitina cf. L. navicula. Sella section, Tarabuco Formation. E. Lagenochitina sp. Sobo–Sobo section, Tarabuco Fm. F. Ancyrochitina aff. A. libyensis. Sobo–Sobo section, Tarabuco Formation. G. Margachitina catenaria tenuipes. Basal part. Note the thin peduncle. Sobo–Sobo section, Santa Rosa Formation. H. Urochitina loboi? The peduncle is missing. Sobo –Sobo section, Santa Rosa Formation. I. Ancyrochitina parisi. La Yesera section, Upper Icla Formation. J. Ancyrochitina sp. A. Sobo–Sobo section, Lower Icla Formation. K. Pterochitina sp. Tarabuco section, Lower Icla Formation. L. Ramochitina boliviensis n.sp. Tarabuco section, Huamampampa Formation.
3.6. Los Monos Formation The Los Monos Formation (White, 1925) conformably overlies the uppermost Eifelian –lower Givetian Huamampampa Formation. The transition to the overlying Iquiri Formation is not contemporaneous everywhere. The lithologies consist of shales with intercalating sandstones. The estimated total thickness is 100 – 200 m (Limachi et al., 1996). Samples from the Los Monos Formation were investigated from the La Yesera, Balapuca, Sobo –Sobo, Rio Pilaya, and Angosto de Huacareta sections (Tables 1, 2 and 4). All sections except those from La Yesera and Sobo – Sobo, which were barren of Chitinozoa, produced chitinozoans from the early to middle Givetian transition. The
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Fig. 5. Scale bar in the upper left corner is 100 mm. A. Ancyrochitina cf. A. tumida. La Yesera section, Huamampampa Formation. B. Ramochitina sp. B. Angosto de Huacareta section, Huamampampa Formation. C. Ancyrochitina 121b. Angosto de Huacareta section, Huamampampa Formation. D. Ancyrochitina cf. 124. Balapuca section, Los Monos Fm. E. Ramochitina boliviensis n.sp. Balapuca section, Los Monos Formation. F. Ramochitina boliviensis n.sp. Holotype. Balapuca section, Los Monos Formation. G. Ancyrochitina 24. Balapuca section, Los Monos Formation. H. Ancyrochitina sp. Balapuca section, Los Monos Formation. I. Ancyrochitina langei. Angosto de Huacareta section, Los Monos Formation. J. Ancyrochitina taouratinensis. Angosto de Huacareta section, Los Monos Formation.
top of the Los Monos Formation is Frasnian. The Balapuca section yielded Ancyrochitina langei, Ancyrochitina cf. 124 Lange, 1967b (Fig. 5D), Ramochitina sp., Ancyrochitina 24 Lange, 1967b (Fig. 5G), Ancyrochitina 123 (Lange, 1967b), Ramochitina 122 Lange, 1967b, Ramochitina ramosi, Ramochitina boliviensis n.sp. (Fig. 5E,F), Ancyrochitina sp. (Fig. 5H), and Hoegisphaera sp. The section from Rio Pilaya produced Ancyrochitina sp. and Ancyrochitina langei. The lower part of the Los Monos Formation is present at Angosto de Huacareta with species such as Ancyrochitina 24 Lange, 1967b, Ramochitina ramosi, Ancyrochitina langei (Fig. 5I), Ancyrochitina postdesmea n.sp., Ancyrochitina sp. (Fig. 7C), Ramochitina sp., Ramochitina boliviensis n.sp., Ancyrochitina cf. A. morzadeci, Ramochitina cf. R. ramosi, and Ancyrochitina
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Fig. 6. A. Angochitina echinata. Rio Pilaya section, Tarabuco Formation. B. Eisenackitina cf. E. bohemica. Sella section, Tarabuco Formation. C. Cingulochitina serrata. Sella section, Tarabuco Formation. D. Sphaerochitina densibaculata. Sella section, Tarabuco Formation. E. Ancyrochitina sp. La Yesera section, Upper Icla Formation. F. Ancyrochitina sp. Tarabuco section, Upper Icla Formation. G. Ancyrochitina postdesmea n.sp. Tarabuco section, Huamampampa Formation. H. Eisenackitina aranea. Tarabuco section, Huamampampa Formation.
taouratinensis (Fig. 5J). In the literature, the formation has been considered late Eifelian to early Frasnian (see Fig. 3). Ancyrochitina postdesmea n.sp. and Ancyrochitina 24 Lange, 1967b are two common early Givetian species. Ancyrochitina cf. A. morzadeci is an early to middle Givetian species, and Ancyrochitina taouratinensis ranges from the latest early to late Givetian age strata in the Parana´ Basin (Grahn, own observations). 3.7. Iquiri Formation The Iquiri Formation (White, 1925) overlies the early to middle Givetian to Frasnian Los Monos Formation and is unconformably overlain by the glaciogenic beds of the Saipuru Formation. The lithologies consist of sandstones in approximately 20– 80 cm thick beds and 3 –15 cm thick intercalated shale beds. The estimated total thickness is
Fig. 7. A. Ancyrochitina langei. Tarabuco section, Huamampampa Formation. B. Eisenackitina aranea. Tarabuco section, Huamampampa Formation. C. Ancyrochitina sp. Angosto de Huacareta section, Los Monos Formation. D. Ancyrochitina cf. A. morzadeci. MCT-X2, Iquiri Formation. E. Angochitina cf. A. katzeri MCT-X2, Iquiri Formation. F. Spinachitina biconstricta. MCT-X2, Iquiri Formation. G. Ramochitina ramosi. Quebrada Botellas section, Iquiri Formation. H. Ramochitina sp. 1. Rio Bernejo section, Iquiri Formation.
100– 600 m (Limachi et al., 1996). Samples from the Iquiri Formation were investigated from the Quebrada Botellas, Quebrada Agua Blanca, Rio Bernejo, and Taputa´ sections (Fig. 1, Table 4). It is also present in the MCT-X2 and MCTX4 boreholes. All sections yielded chitinozoans. The boreholes contained Spinachitina biconstricta (Cladochitina biconstricta sensu Lange, 1967a pars; Fig. 7F), Ramochitina ramosi, Angochitina cf. A. katzeri (Fig. 7E), and Ancyrochitina cf. A. morzadeci (Fig. 7D), which suggest an early to middle Givetian age. A. katzeri is defined from early Frasnian age strata of the Amazonas Basin by Grahn and Melo (2002). An early to middle Givetian age is recorded in the Quebrada Botellas section with species such as Ancyrochitina langei, Ramochitina ramosi (Fig. 7G), Angochitina cf. A. katzeri, and Ancyrochitina sp. A younger, probably Frasnian age occurs at
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Quebrada Agua Blanca with Lagenochitina avelinoi? Lange, 1952 and Angochitina spp. The sections at Rio Bermejo and Taputa´ yield early late Frasnian age assemblages, including Lagenochitina avelinoi Lange, 1952 (Fig. 8B,E) and a similar species (Fig. 8C,D), Fungochitina pilosa Collinson and Scott, 1958 (Fig. 8A), and Ramochitina sp. 1 (Figs. 7H, 8F). In the literature, the Iquiri Formation is considered Givetian to Frasnian (Fig. 3). The upper part of the formation in central and northern Bolivia is locally eroded and/or resedimented (Lobo-Boneta, 1989; Sempere, 1995). According to Dı´az-Martinez et al. (1996), the Colpacucho Formation, equivalent to Iquiri Formation in the Altiplano, contains early Famennian fossil toward its top. The chitinozoans in this study suggests an early to middle Givetian to early late Frasnian age for the investigated part of the Iquiri Formation. Togachitina (Pellichitina ) eamesi Wood, 1994 was described from the Iquiri Formation at the Lajas locality, but this species was not recovered in this study. In the present collection, most of the Lagenochitina avelinoi specimens display bodies covered with tubercles and flaring apertures. Some specimens display simple, long spines at the margin. This may indicate an evolutionary trend from Lagenochitina to Sommerochitina (Fig. 8C,D). The later genus is known from the latest Frasnian and early Famennian of the Parnaı´ba Basin, northeast Brazil (Costa Cruz and Quadros, 1985).
4. Systematic paleontology Because poor preservation prevails for most of the chitinozoan assemblages, open nomenclature was extensively used to name chitinozoans, including some that are probably new. However, two species were recovered in sufficiently well preserved populations to be described confidently as new species. A correction factor of 0.7 or 0.8, depending on the degree of flattening, was used in the manner of Paris (1981) and Jaglin (1986) to correct for compression. References for all taxonomic names are cited for clarity. Terminology and taxonomic concepts proposed by Paris et al. (1999) follow: Group Chitinozoa—Eisenack (1931) Order Prosomatifera—Eisenack (1972) Family Lagenochitinidae—Eisenack (1931) Subfamily Angochitininae—Paris (1981) Genus Ramochitina—Sommer and van Boekel (1964), emend. Paris et al. (1999) Ramochitina boliviensis n.sp.—Figs. 4L, 5E,F. Derivation of name: Latin, boliviensis, referring to its discovery in Bolivia. Diagnosis: A Ramochitina species with an ovoid body and short cylindrical neck that slightly widens at the aperture. The vesicle is provided with six rows of long simple spines or spines branching distally of their midpoint
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and occasionally near their tips. Vesicle wall between the spines is smooth. Holotype: Fig. 5F, Slide no. 9805087 of PETROBRAS/ CENPES/PDEP/BPA palynological collection, E.F. coordinate P60-4. Type locality: Balapuca section, 102 m above the base of the Los Monos Formation (sample at 229 m, see Table 1), southern Subandean zone, south Bolivia. Description: The long variable spongy spines characterize Ramochitina boliviensis. These are sparsely distributed on the vesicle in six rows. The spines may be simple, branching distally from their midpoints, sometimes near their terminations, or form massive tapering simple spines. The width of spine bases varies between 1 and 30 mm. The cylindrical neck is short, about one-third of the total length, and slightly widened at the aperture. The body is ovoid. The vesicle wall between the spines is smooth. Dimensions (five specimens measured): Total length 160 – 220 mm (Holotype: 220 mm); maximum width 52– 60 mm (Holotype 60 mm), width of aperture 24– 35 mm (Holotype: 35 mm), length of spines 35 –85 mm. The neck is approximately one-third of the total length. Occurrence: Representatives of Ramochitina boliviensis occur in early Givetian (AD Lem spore zone) to middle Givetian (TA spore zone) beds of the Huamampampa, Los Monos, and Iquiri formations, south central Bolivia (see Melo, 2000). Comparison: Ramochitina boliviensis differs from Ramochitina ramosi Sommer and van Boekel, 1964, Ramochitina milanensis Collinson and Scott, 1958, and Ramochitina viridarium Winchester-Seeto and Paris, 1995 because of its much longer and more sparsely distributed spines. Ancyrochitina cf. A. ramusculosa Legault, 1973 (Plate 5, Fig. 8; Plate 6, Figs. 7 and 9 therein) is similar. However, from the description by Legault (1973), the spines should be randomly distributed, and furthermore, Ancyrochitina cf. A. ramusculosa has smaller spines on the neck. Subfamily Ancyrochitininae—Paris (1981) Genus Ancyrochitina—Eisenack (1955) Ancyrochitina postdesmea n.sp. Fig. 6G Ancyrochitina cf. A. desmea Lange 1967a, p. 69– 70, Pl. 1, Figs. 4 – 6. Ancyrochitina cf. A. desmea Legault 1973, p. 18 –19, Pl. 2, Figs. 1 – 3. Derivation of name: Latin, postdesmea, because of its similarity to the late Silurian species Ancyrochitina desmea Eisenack, 1964 and its much younger occurrence than that species in the stratigraphic record. Diagnosis: An Ancyrochitina species with a conical body and cylindrical neck of one-third to one-half of the total length. Margin provided with 8 – 10 thick branching appendices, which often are bent apertureward. Each branch may be further divided into 3—5 smaller branches. Similar spines are present on the neck, though these often are bent
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Domingos Formation, Parana´ Basin, Brazil (Grahn, own observations) and the early Givetian Widder, Hungry Hollow, and Arkona members of the Hamilton Formation, southwestern Ontario, Canada (Legault, 1973). Comparison: Ancyrochitina postdesmea differs from Ancyrochitina desmea Eisenack, 1964 in having a shorter appearance and a smooth vesicle surface between the spines (A. desmea has a finely verrucate surface).
Acknowledgments
Fig. 8. A. Fungochitina pilosa. Rio Bernejo section, Iquiri Formation. B. Lagenochitina avelinoi. Taputa´ section, Iquiri Formation. C. Possible evolutionary predecessor of the genus Sommerochitina. Taputa´ section, Iquiri Formation. D. The same species as C. Detail of the base. Note the basal position of the appendix. E. Lagenochitina avelinoi. Taputa´ section, Iquiri Formation. F. Ramochitina sp. 1. Taputa´ section, Iquiri Formation.
antiapertureward. The vesicle wall between the spines is smooth, and the aperture is straight. Holotype: Lange (1967a), Pl. 1, Fig. 4. M.N. 4296-1. Museu Nacional, Rio de Janeiro. Type locality: The 2-RP-1-MT borehole, core 18, Sa˜o Domingos Formation, Parana´ Basin, Brazil (Lange, 1967a). Description: Ancyrochitina postdesmea specimens are characterized by thick spines and appendices. Margin provided with 8 –10 appendices branching at their tips and then further branching 3– 5 times. Similar spines are present on the neck, often bent antiapertureward, in contrast with the appendices, which often are bent apertureward. Dimensions (six specimens measured): Total length 180 –219 mm (Holotype: 206 mm), maximum width 65– 79 mm (Holotype: 65 mm), width of aperture 27– 40 mm (Holotype 31 mm), length of spines and appendices 24– 65 mm. The neck is between one-third and one-half of the total length. Occurrence: Representatives of Ancyrochitina postdesmea occur in the early Givetian (AD Lem spore zone) to middle Givetian (TA spore zone) beds of the Huamampampa and Los Monos Formations, south central Bolivia. It is also present in contemporaneous beds of the Sa˜o
Thanks are due to the Faculty of Geology at Universidade do Estado do Rio de Janeiro (UERJ) and Prof. Maria Antonieta Rodrigues, director of the postgraduate program at the Faculty of Geology at UERJ, for her enthusiastic encouragement and providing access to the facilities. Dr Souza Cruz (Braspetro, Rio de Janeiro) provided me with the samples for this study. Through the courtesy of Dr Eduardo A.M. Kousoukos, head of SEBIPE at CENPES (Petrobra´s, Rio de Janeiro), I had access to an SEM, and geologist Jose´ Henrique G. de Melo at the same department discussed the geology and reviewed the manuscript. Merrell A. Miller (Saudi Aramco, Dhahran) is acknowledged for a linguistic check of the manuscript. Enrique Dı´az-Martinez (INTA-CSIC, Madrid) translated the Spanish abstract and reviewed the manuscript, and Eduardo G. Ottone (UBA, Buenos Aires) is acknowledged for reviewing the manuscript. All technical assistance from Jorge Louiz dos Santos and Maria Rosalva Campos Coelho at UERJ and Roge´rio da Silva Martins da Costa at CENPES is acknowledged. My sincere thanks to all.
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Upper Silurian and Devonian Chitinozoa from central and southern Bolivia, central Andes Yngve Grahn* Faculdade de Geologia, Universidade do Estado do Rio de Janeiro, Bloco A Sala.13, Rua Sa˜o Francisco Xavier 524, 20559-4001 Rio de Janeiro, Brazil Received 2 January 2002; accepted 2 January 2002
Abstract A study of chitinozoans from Upper Silurian and Devonian strata from south central Bolivia has provided new stratigraphic information and improved correlations with adjacent basins in Argentina, Paraguay, Uruguay, and Brazil. The investigated succession extends from late Ludlow (upper Kirusillas Formation) to late Frasnian (upper Iquiri Formation). Unconformities in the section or condensed intervals occur in latest Pragian to early Emsian and for most of the Eifelian. Two early Givetian chitinozoan species, Ancyrochitina postdesmea and Ramochitina boliviensis, are newly described. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: Chitinozoans; Lithologies; Biostratigraphy; Bolivia
Resumen El estudio de los quitinozoos del Silu´rico superior y Devo´nico de la zona centro-sur de Bolivia ha facilitado nueva informacio´n estratigra´fica y mejorado las correlaciones con cuencas adyacentes en Argentina, Paraguay, Uruguay y Brasil. La sucesio´n estudiada abarca del Ludlow tardı´o (superior de la Formacio´n Kirusillas) al Frasniano tardı´o (superior de la Formacio´n Iquiri). Existen discontinuidades en la seccio´n, o intervalos condensados, en el Pragiano ma´s terminal al Emsiano temprano, y para la mayor parte del Eifeliano. Se describen dos nuevas especies de quitinozoos del Givetiano temprano, Ancyrochitina postdesmea y Ramochitina boliviensis. q 2002 Elsevier Science Ltd. All rights reserved. Palabras clave: Quitinozoos; Lithologies; Biostratigrafia; Bolivia
1. Introduction Chitinozoans from Bolivia have been described or mentioned by Cousminer (1964), Cramer et al. (1974), Sua´rez-Riglos (1975), Rollano-Barrero (1975), Gagnier et al. (1989), Wood and Isaacson (1992), Racheboeuf et al. (1993), Liachenko (1994), Wood (1994), Ottone and Rossello (1996), Limachi et al. (1996), Vavrdova´ et al. (1996), Heuse et al. (1999), and Melo (2000). According to these studies, Bolivian chitinozoan faunas are virtually the same as those from the intracratonic basins of Brazil, Paraguay, Uruguay, and northwest Argentina (Grahn, 1992; Ottone, 1996; Grahn et al., 2000; Grahn and Gutie´rrez, 2001; Grahn and Melo, 2002). The purpose of this paper is to document the chitinozoans and chitinozoan bio* Corresponding author. Fax: þ 55-21-587-7704. E-mail address: [email protected] (Y. Grahn).
stratigraphy from 11 outcrops and two boreholes from Upper Silurian and Devonian strata of south central Bolivia.
2. Material and methods For this study, 103 samples from 11 outcrop localities in the Andes and two boreholes in the lowland plains, south central Bolivia, were examined for Chitinozoa. The locations of investigated outcrop sections are shown in Fig. 1. Geological data from the selected outcrops in south central Bolivia and other references can be found in Lo´pez-Pugliessi and Lo´pez-Murillo (1972), Arispe and Dı´az-Martinez (1996), Limachi et al. (1996), and Miranda (2000). In general, the chitinozoans are poorly preserved. Because of preservational difficulties and irregular, widely spaced sampling, it is not meaningful to plot the chitinozoan ranges in logs. The chitinozoan faunas are therefore
0895-9811/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 8 9 5 - 9 8 1 1 ( 0 2 ) 0 0 0 4 5 - 7
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Fig. 1. Location map of outcrops and wells in south central Bolivia investigated in this study.
discussed as discrete assemblages occurring at different levels within each investigated formation, and their overall stratigraphic ranges are given in Fig. 2. The stratigraphic position of samples is given in Tables 1 –4. The residues were studied for chitinozoans under a binocular stereoscopic microscope, and representative specimens were picked and mounted for scanning electron microscope (SEM) studies performed in cooperation with SEBIPE (CENPES, Petrobras) in Rio de Janeiro. Sample processing and SEM preparation were carried out at the Geological Laboratory (LGPA) of the Geological Faculty at Universidade do Estado do Rio de Janeiro using techniques described by Laufeld (1974). SEM preparations are stored at the Department of Stratigraphy and Paleontology at Universidade do Estado do Rio de Janeiro. Specimens photographed with transmitted light are stored in the collections of SEBIPE, Petrobras, Rio de Janeiro.
3. Geologic setting and biostratigraphy The Peru –Bolivia Basin includes parts of northwest
Argentina, western Paraguay, most of Bolivia and Peru, and Ecuador to westernmost Brazil. The outcrops of its sedimentary infill form an elongate, almost continuous belt of sedimentary rocks paralleling the present-day Andes. During the Early and Middle Paleozoic, a seaway connected the Peru – Bolivia Basin to the Chaco – Parana´ Basin in northeast Argentina and the Parana´ Basin in eastern Paraguay and southern Brazil (Fu´lfaro, 1996; Grahn and Gutie´rrez, 2001). The basement in the Bolivian part of the Basin consists of Upper Proterozoic and Cambrian rocks exposed in a few areas (Sempere, 1995). Deformed Early Paleozoic epimetamorphic rocks are known from the Tarija area, around Cochabamba, and Cerro Chilla, south of Lake Titicaca. In central Bolivia, Lower and Middle Cambrian rocks occur in an east – northeast-trending fold and thrust belt (Sempere, 1995). The maximum thickness of the Silurian and Devonian succession easily exceeds 6000 m (Gonza´lez et al., 1996). In south central Bolivia, the Cancan˜iri Formation represents the basal Silurian. It consists of diamictites with clasts from the igneous, metamorphic, and sedimentary basement. This formation correlates with the Zapla Formation, of middle to late
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317
Fig. 2. Distribution chart of Late Silurian and Devonian chitinozoan species of south central Bolivia.
Llandovery age, in northwest Argentina (Grahn and Gutie´rrez, 2001). In central Bolivia, the overlying Sacta limestone has been dated as earliest Wenlock (for a discussion of this limestone, see Merino, 1991; Beccar, 1994; Goitia, 1994; Dı´az-Martı´nez, 1997, 1998). However, the Kirusillas Formation is the oldest formation considered in this study. A correlation chart showing the evolution of stratigraphic nomenclature and age interpretations for the Upper Silurian – Devonian formations of south central Bolivia is presented in Fig. 3. 3.1. Kirusillas Formation
Fig. 3. Late Silurian and Devonian correlation chart of south central Bolivia.
The Kirusillas Formation (Ahlfeld and Branisa, 1960) correlates to the Uncı´a Formation of Vargas-Cordova (1970). It unconformably overlies the middle to late Llandovery Cancan˜iri Formation and is transitional to the overlying Tarabuco Formation. Kirusillas Formation lithologies consist of black micaceous shales and mudstones with interbedded fine-grained sandstones. Limonitic horizons, associated with the sandstones, are present in the upper part. The total thickness is estimated to be 2000 m (Gonza´lez et al., 1996). Samples from the upper Kirusillas Formation were investigated from the Sella and Tarabuco sections (Tables 2 and 3). All were barren of Chitinozoa. A Kirusillas Formation bulk sample from near Cochabamba was studied for chitinozoans and acritarchs by Cramer et al. (1974).
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Table 1 Investigated samples in the Angosto de Huacareta and Balapuca sections
They found a chitinozoan fauna representing upper Ludlow to lower Pridoli strata, with species such as a Bolivian variant of Ancyrochitina ancyrea sensu Cramer et al. 1974 (a characteristic late Ludlow species known from the Amazonas and Peru –Bolivia basins), Pterochitina perivelata (Eisenack, 1937), Urnochitina urna (Eisenack, 1934), and others. The same age was confirmed for the upper Cachipunco Formation, Santa Barba´ra Range, northwest Argentina (Grahn and Gutie´rrez, 2001). A Wenlock – Ludlow age was suggested (Lobo-Boneta et al., 1976; Limachi et al., 1996), but the chitinozoans reported by Cramer et al. (1974) indicate the age of the Kirusillas Formation as late Ludlow at the base and early Pridoli at the top. Recently, Toro et al. (1998) found early Ludlow graptolites from the lower Kirusillas Formation. According to Gonza´lez et al. (1996) and Dı´az-Martı´nez (1998), the base of the formation probably is diachronous. 3.2. Tarabuco Formation The Tarabuco Formation (Steinmann in Ulrich, 1892) correlates to the Catavi Formation of Turneaure (1960). It conformably and in transition overlies the Ludlow – early Pridoli-age Kirusillas Formation and is transitional with the overlying Santa Rosa Formation. The lithologies consist of interbedded micaceous dark-gray shales and fine-grained sandstones. The shales occur in 5 – 30 cm thick layers and the sandstones in beds 10 – 100 cm thick. Sandstone
Table 2 Investigated samples in the Rio Pilaya and Sella sections
conglomerates, 5 – 15 cm thick, are present at some levels. The total thickness is estimated to be 1200 m (Gonza´lez et al., 1996). Samples from the Tarabuco Formation were investigated from the Sobo– Sobo, Rio Pilaya, Sella, and Tarabuco localities (Fig. 1, Tables 2 and 3). Determinable species from the Sobo– Sobo section include questionable representatives of Fungochitina kosovensis Paris and Kriz, 1984, Lagenochitina sp. (Fig. 4E), Sphaerochitina patula Jaglin, 1986, Ancyrochitina aff. A. libyensis (Fig. 4F), and Angochitina echinata Eisenack, 1931 (Fig. 6A). This assemblage suggests an early Pridoli age, which is also true for the Tarabuco Formation in the Rio Pilaya section, where the shales yield Angochitina echinata (Fig. 6A) and Cingulochitina serrata Taugourdeau and Jekhowsky, 1960. The uppermost part of the formation, in the Sella section, yields a diversified and abundant chitinozoan fauna of late Lochkovian age, with species such as Eisenackitina cf. E. bohemica (Fig. 6B), Cingulochitina serrata (Fig. 6C), Pterochitina sp., Hoegisphaera sp. (Fig. 4A), Urochitina loboi Volkheimer et al., 1986 and a similar species (Fig. 4B), Angochitina ex. gr. filosa (Fig. 4C), Lagenochitina cf. L. navicula (Fig. 4D), and Sphaerochitina densibaculata Volkheimer et al., 1986; (Fig. 6D). A similar chitinozoan assemblage was described by Vavrdova´ et al. (1996) in the Tequeje Formation in the Madre de Dı´os Basin, north Bolivia. The sequence from the Tarabuco section was barren of chitinozoa. A Ludlow and/or Pridoli age has been suggested for the Tarabuco Formation in the literature (see Fig. 3). Racheboeuf et al. (1993) also include the lowermost part of the Lochkovian. The chitinozoan assemblages in this study suggest an early Pridoli to late Lochkovian age.
Y. Grahn / Journal of South American Earth Sciences 15 (2002) 315–326 Table 3 Investigated samples in the Sobo–Sobo and Tarabuco sections
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ful Margachitina catenaria tenuipes (Paris, 1981; Fig. 4G) were recovered from the first locality. The Rio Pilaya section only yielded Ancyrochitina spp. The presence of Ramochitina magnifica (Lange, 1967a) in the Tarabuco section indicates that the Santa Rosa Formation ranges into the lower Pragian. A Pridoli to early Emsian age has been suggested in the literature (see Fig. 3). The chitinozoan assemblages recovered in this study suggest a late Lochkovian to early Pragian age. Racheboeuf et al. (1993) reported Eisenackitina cf. E. bohemica approximately 43 m above the base of the Santa Rosa Formation, and Gagnier et al. (1989) illustrated Sphaerochitina densibaculata from the basal part, thus confirming a late Lochkovian age for the lower part of the formation. Margachitina catenaria tenuipes is known from late Lochkovian to early Pragian, and Ramochitina magnifica is an index species for Pragian strata in the Parana´ Basin of Brazil, Paraguay, and Uruguay (Grahn et al., 2000). 3.4. Icla Formation
The cooccurrence of Urochitina loboi, Cingulochitina serrata (Cingulochitina striata and Cingulochitina sp. A of Volkheimer et al. 1986), and Sphaerochitina densibaculata is a characteristic late Lochkovian association in the lower part of the Puesto el Tigre Formation, Tarija Basin, northwest Argentina (Volkheimer et al., 1986). At this horizon, a species similar to Urochitina loboi but lacking a spiny peduncle and with a dense spiny ornamentation on the apex (see Fig. 4B) also occurs. This ornamentation is similar to that illustrated by Volkheimer et al. (1986, Fig. 4 therein) for Urochitina loboi, except for the absence of a peduncle. It is possible that this form without a peduncle is an evolutionary predecessor to Urochitina loboi. 3.3. Santa Rosa Formation The Santa Rosa Formation (Ahlfeld and Branisa, 1960) correlates to the Vila Vila Formation of Fricke et al. (1964). It conformably overlies the early Pridoli– late Lochkovian age Tarabuco Formation and is transitional to the overlying Icla Formation. The lithologies consist of micaceous sandstones with beds of silty mudstones. The total thickness is estimated at 1800 m (Gonza´lez et al., 1996). Samples from the Santa Rosa Formation were investigated from the La Yesera, Sobo –Sobo, Rio Pilaya, Tarabuco, and Sella sections (Fig. 1, Tables 2 –4). Only samples from the Sobo – Sobo, Rio Pilaya, and Tarabuco sections yielded sparse chitinozoan faunas. Urochitina loboi? (Fig. 4H) and doubt-
The Icla Formation (Steinmann in Ulrich, 1892) conformably overlies the late Lochkovian – early Pragian Santa Rosa Formation. In this study, distinct lower and upper divisions of the Icla Formation were recognized, which agrees with Racheboeuf et al. (1993). The lithologies consist of silty mudstones with intercalated sandstone beds, approximately 20 – 80 cm thick. The total thickness is estimated to be 1800 m (Gonza´lez et al., 1996). Samples from the Icla Formation were studied from the La Yesera, Sobo– Sobo, Rio Pilaya, Angosto de Huacareta, Tarabuco, and Sella sections (Fig. 1, Tables 1– 4). The Icla sequences in the Rio Pilaya and Angosto de Huacareta sections were barren of chitinozoa. Except for the Angosto de Huacareta section, the lower unit of the Icla Formation is present in all sections, yielding Chitinozoa that include species such as Pterochitina sp. (Fig. 4K), Ramochitina sp., Ramochitina magnifica, and Ancyrochitina sp. A (Cladochitina biconstricta Lange, 1967a pars; Fig. 4J), a species ranging from Pragian to late Emsian). The upper unit of the Icla Formation is characterized by the presence of some Ancyrochitina species (Fig. 6E,F) and Ancyrochitina parisi Volkheimer et al., 1986; (Fig. 4I), which is an index species for the late Emsian (possibly including latest early Emsian and earliest Eifelian) of the Parana´ and Peru – Bolivia basins (Volkheimer et al., 1986; Grahn et al., 2000). North of Tarabuco, the lower Icla Formation, 20 and 75 m above the Scaphiocoelia beds, yields Angochitina aff. A. comosa, an early Pragian species in Europe (Racheboeuf et al., 1993). Scaphiocoelia beds occur at the top of the Santa Rosa Formation and contain a characteristic Pragian chitinozoan fauna. However, Scaphiocoelia beds in the Bele´n Formation (Altiplano Andean Zone) yield Cingulochitina striata (Cingulochitina serrata ) and Sphaerochitina densibaculata, which constitute a late Lochkovian assemblage. A
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Table 4 Investigated samples in the La Yesera, Quebrada Botellas, Quebrada Agua Blanca, Rio Bermejo, Taputa´, MCT-X2, and MCT-X4 sections
Pragian to early Givetian age has been suggested for the Icla Formation (see Fig. 3). Tiella et al. (1998) and Tourneur et al. (2000) recently suggested that dating of the Icla and Bele´n Formations should be reassessed. The chitinozoan assemblages in this study suggest an early to late Pragian age for the lower Icla Formation and a late (possibly including latest early) Emsian –earliest Eifelian age for the upper Icla Formation. 3.5. Huamampampa formation The Huamampampa Formation (Steinmann in Ulrich, 1892) conformably overlies the late Emsian – earliest Eifelian upper portion of the Icla Formation and is transitional to the overlying Los Monos Formation. The lithologies include sandstones in 10 –50 cm thick layers with interbedded silty mudstone. The total thickness is estimated as 300 –700 m (Limachi et al., 1996). Samples from the Huamampampa Formation were investigated from the Sobo –Sobo, Rio Pilaya, Tarabuco, La Yesera, Balapuco, and Angosto de Huacareta sections (Tables 1 –4). All sections yielded early Givetian chitinozoans, though a latest Eifelian age cannot be excluded for the lower part of the formation. From the Sobo – Sobo section, Ramochitina
ramosi Sommer and van Boekel, 1964, Eisenackitina sp., and questionable specimens of Alpenachitina eisenacki Dunn and Miller, 1964 were recovered. The Rio Pilaya section produced Eisenackitina aranea Urban, 1972, Ramochitina sp., Ancyrochitina sp., and Ancyrochitina 121b Lange, 1967b. In the Tarabuco section is an abundant and diverse chitinozoan fauna with Hoegisphaera sp., Ancyrochitina postdesmea n.sp. (Fig. 6G), Ramochitina sp., Ramochitina boliviensis n.sp. (Fig. 4L), Eisenackitina aranea (Figs. 6H, 7B), Alpenachitina eisenacki, Ancyrochitina cf. A. langei (Fig. 7A), and Ancyrochitina 121b Lange, 1967b. The basal part of the Huamampampa Formation is present in the Balapuca section. Characteristic chitinozoans are Lagenochitina sp., Ancyrochitina langei Sommer and van Boekel, 1964, Ramochitina sp., Ancyrochitina sp., and Ancyrochitina 123 Lange, 1967b. The upper part of the formation is present in the La Yesera and Angosto de Huacareta sections. The La Yesera section presents Ancyrochitina sp., Ramochitina sp., Eisenackitina aranea, Ancyrochitina postdesmea n.sp., and Ancyrochitina cf. A. tumida Legault, 1973 (Fig. 5A) and the Angosto de Huacareta section Ancyrochitina 121b Lange, 1967b (Fig. 5C), Ancyrochitina 123 Lange, 1967b, Ancyrochitina cf. A. langei, Eisenackitina aranea, and Ramochitina sp. B (Angochitina devonica of Lange, 1967a; Gotlandochitina sp. B of Paris et al., 1985; Fig. 5B). A late Emsian to early Givetian age has been suggested in the literature (see Fig. 3). Approximately 25 m above the base of the Huamampampa Formation, Racheboeuf et al. (1993) reported Alpenachitina eisenacki and Ancyrochitina langei. The chitinozoans indicate an early Givetian age for these beds. Alpenachitina eisenacki has an Eifelian – early Givetian distribution on a worldwide basis, but it is a common species in the early Givetian of Brazil, and only rare fragments of this species have been found in Eifelian beds. Eisenackitina aranea is another Eifelian – early Givetian species. According to Paris et al. (1985), specimens of Eisenackitina castor (E. aranea ) that are restricted to the Eifelian are smooth, whereas those from the Givetian have spinose surface ornamentation. The specimens present in the Huamampampa Formation are deeply corroded, and it is often not possible to determine if they are spinose. Ramochitina boliviensis n.sp. appears to be restricted to the early Givetian in this collection. Ancyrochitina cf. A. tumida sensu Legault, 1973 is a species from the early Givetian Hungry Hollow, Arkona, Rockport Quarry, and Bell members of the Hamilton Formation and the Dundee Formation, SW Ontario, Canada (Legault, 1973). Ancyrochitina 121b and 123 are similar to species illustrated by Lange (1967b) from the Ereˆre Formation in the Amazonas Basin. Ancyrochitina langei is a species ranging from earliest to latest Givetian in the Parana´ Basin (Grahn, own observations), and Ramochitina sp. B is known from early Givetian strata in the Parana´ Basin and Libya (Paris et al., 1985).
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Fig. 4. Scale bar in the upper left corner is 100 mm. A. Hoegisphaera sp. Sella section, Tarabuco Formation. B. Potential evolutionary precursor to Urochitina loboi. Note the spiny ornamentation at the base. Sella section, Tarabuco Formation. C. Angochitina ex. gr. filosa. Sella section, Tarabuco Formation. D. Lagenochitina cf. L. navicula. Sella section, Tarabuco Formation. E. Lagenochitina sp. Sobo–Sobo section, Tarabuco Fm. F. Ancyrochitina aff. A. libyensis. Sobo–Sobo section, Tarabuco Formation. G. Margachitina catenaria tenuipes. Basal part. Note the thin peduncle. Sobo–Sobo section, Santa Rosa Formation. H. Urochitina loboi? The peduncle is missing. Sobo –Sobo section, Santa Rosa Formation. I. Ancyrochitina parisi. La Yesera section, Upper Icla Formation. J. Ancyrochitina sp. A. Sobo–Sobo section, Lower Icla Formation. K. Pterochitina sp. Tarabuco section, Lower Icla Formation. L. Ramochitina boliviensis n.sp. Tarabuco section, Huamampampa Formation.
3.6. Los Monos Formation The Los Monos Formation (White, 1925) conformably overlies the uppermost Eifelian –lower Givetian Huamampampa Formation. The transition to the overlying Iquiri Formation is not contemporaneous everywhere. The lithologies consist of shales with intercalating sandstones. The estimated total thickness is 100 – 200 m (Limachi et al., 1996). Samples from the Los Monos Formation were investigated from the La Yesera, Balapuca, Sobo –Sobo, Rio Pilaya, and Angosto de Huacareta sections (Tables 1, 2 and 4). All sections except those from La Yesera and Sobo – Sobo, which were barren of Chitinozoa, produced chitinozoans from the early to middle Givetian transition. The
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Fig. 5. Scale bar in the upper left corner is 100 mm. A. Ancyrochitina cf. A. tumida. La Yesera section, Huamampampa Formation. B. Ramochitina sp. B. Angosto de Huacareta section, Huamampampa Formation. C. Ancyrochitina 121b. Angosto de Huacareta section, Huamampampa Formation. D. Ancyrochitina cf. 124. Balapuca section, Los Monos Fm. E. Ramochitina boliviensis n.sp. Balapuca section, Los Monos Formation. F. Ramochitina boliviensis n.sp. Holotype. Balapuca section, Los Monos Formation. G. Ancyrochitina 24. Balapuca section, Los Monos Formation. H. Ancyrochitina sp. Balapuca section, Los Monos Formation. I. Ancyrochitina langei. Angosto de Huacareta section, Los Monos Formation. J. Ancyrochitina taouratinensis. Angosto de Huacareta section, Los Monos Formation.
top of the Los Monos Formation is Frasnian. The Balapuca section yielded Ancyrochitina langei, Ancyrochitina cf. 124 Lange, 1967b (Fig. 5D), Ramochitina sp., Ancyrochitina 24 Lange, 1967b (Fig. 5G), Ancyrochitina 123 (Lange, 1967b), Ramochitina 122 Lange, 1967b, Ramochitina ramosi, Ramochitina boliviensis n.sp. (Fig. 5E,F), Ancyrochitina sp. (Fig. 5H), and Hoegisphaera sp. The section from Rio Pilaya produced Ancyrochitina sp. and Ancyrochitina langei. The lower part of the Los Monos Formation is present at Angosto de Huacareta with species such as Ancyrochitina 24 Lange, 1967b, Ramochitina ramosi, Ancyrochitina langei (Fig. 5I), Ancyrochitina postdesmea n.sp., Ancyrochitina sp. (Fig. 7C), Ramochitina sp., Ramochitina boliviensis n.sp., Ancyrochitina cf. A. morzadeci, Ramochitina cf. R. ramosi, and Ancyrochitina
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Fig. 6. A. Angochitina echinata. Rio Pilaya section, Tarabuco Formation. B. Eisenackitina cf. E. bohemica. Sella section, Tarabuco Formation. C. Cingulochitina serrata. Sella section, Tarabuco Formation. D. Sphaerochitina densibaculata. Sella section, Tarabuco Formation. E. Ancyrochitina sp. La Yesera section, Upper Icla Formation. F. Ancyrochitina sp. Tarabuco section, Upper Icla Formation. G. Ancyrochitina postdesmea n.sp. Tarabuco section, Huamampampa Formation. H. Eisenackitina aranea. Tarabuco section, Huamampampa Formation.
taouratinensis (Fig. 5J). In the literature, the formation has been considered late Eifelian to early Frasnian (see Fig. 3). Ancyrochitina postdesmea n.sp. and Ancyrochitina 24 Lange, 1967b are two common early Givetian species. Ancyrochitina cf. A. morzadeci is an early to middle Givetian species, and Ancyrochitina taouratinensis ranges from the latest early to late Givetian age strata in the Parana´ Basin (Grahn, own observations). 3.7. Iquiri Formation The Iquiri Formation (White, 1925) overlies the early to middle Givetian to Frasnian Los Monos Formation and is unconformably overlain by the glaciogenic beds of the Saipuru Formation. The lithologies consist of sandstones in approximately 20– 80 cm thick beds and 3 –15 cm thick intercalated shale beds. The estimated total thickness is
Fig. 7. A. Ancyrochitina langei. Tarabuco section, Huamampampa Formation. B. Eisenackitina aranea. Tarabuco section, Huamampampa Formation. C. Ancyrochitina sp. Angosto de Huacareta section, Los Monos Formation. D. Ancyrochitina cf. A. morzadeci. MCT-X2, Iquiri Formation. E. Angochitina cf. A. katzeri MCT-X2, Iquiri Formation. F. Spinachitina biconstricta. MCT-X2, Iquiri Formation. G. Ramochitina ramosi. Quebrada Botellas section, Iquiri Formation. H. Ramochitina sp. 1. Rio Bernejo section, Iquiri Formation.
100– 600 m (Limachi et al., 1996). Samples from the Iquiri Formation were investigated from the Quebrada Botellas, Quebrada Agua Blanca, Rio Bernejo, and Taputa´ sections (Fig. 1, Table 4). It is also present in the MCT-X2 and MCTX4 boreholes. All sections yielded chitinozoans. The boreholes contained Spinachitina biconstricta (Cladochitina biconstricta sensu Lange, 1967a pars; Fig. 7F), Ramochitina ramosi, Angochitina cf. A. katzeri (Fig. 7E), and Ancyrochitina cf. A. morzadeci (Fig. 7D), which suggest an early to middle Givetian age. A. katzeri is defined from early Frasnian age strata of the Amazonas Basin by Grahn and Melo (2002). An early to middle Givetian age is recorded in the Quebrada Botellas section with species such as Ancyrochitina langei, Ramochitina ramosi (Fig. 7G), Angochitina cf. A. katzeri, and Ancyrochitina sp. A younger, probably Frasnian age occurs at
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Quebrada Agua Blanca with Lagenochitina avelinoi? Lange, 1952 and Angochitina spp. The sections at Rio Bermejo and Taputa´ yield early late Frasnian age assemblages, including Lagenochitina avelinoi Lange, 1952 (Fig. 8B,E) and a similar species (Fig. 8C,D), Fungochitina pilosa Collinson and Scott, 1958 (Fig. 8A), and Ramochitina sp. 1 (Figs. 7H, 8F). In the literature, the Iquiri Formation is considered Givetian to Frasnian (Fig. 3). The upper part of the formation in central and northern Bolivia is locally eroded and/or resedimented (Lobo-Boneta, 1989; Sempere, 1995). According to Dı´az-Martinez et al. (1996), the Colpacucho Formation, equivalent to Iquiri Formation in the Altiplano, contains early Famennian fossil toward its top. The chitinozoans in this study suggests an early to middle Givetian to early late Frasnian age for the investigated part of the Iquiri Formation. Togachitina (Pellichitina ) eamesi Wood, 1994 was described from the Iquiri Formation at the Lajas locality, but this species was not recovered in this study. In the present collection, most of the Lagenochitina avelinoi specimens display bodies covered with tubercles and flaring apertures. Some specimens display simple, long spines at the margin. This may indicate an evolutionary trend from Lagenochitina to Sommerochitina (Fig. 8C,D). The later genus is known from the latest Frasnian and early Famennian of the Parnaı´ba Basin, northeast Brazil (Costa Cruz and Quadros, 1985).
4. Systematic paleontology Because poor preservation prevails for most of the chitinozoan assemblages, open nomenclature was extensively used to name chitinozoans, including some that are probably new. However, two species were recovered in sufficiently well preserved populations to be described confidently as new species. A correction factor of 0.7 or 0.8, depending on the degree of flattening, was used in the manner of Paris (1981) and Jaglin (1986) to correct for compression. References for all taxonomic names are cited for clarity. Terminology and taxonomic concepts proposed by Paris et al. (1999) follow: Group Chitinozoa—Eisenack (1931) Order Prosomatifera—Eisenack (1972) Family Lagenochitinidae—Eisenack (1931) Subfamily Angochitininae—Paris (1981) Genus Ramochitina—Sommer and van Boekel (1964), emend. Paris et al. (1999) Ramochitina boliviensis n.sp.—Figs. 4L, 5E,F. Derivation of name: Latin, boliviensis, referring to its discovery in Bolivia. Diagnosis: A Ramochitina species with an ovoid body and short cylindrical neck that slightly widens at the aperture. The vesicle is provided with six rows of long simple spines or spines branching distally of their midpoint
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and occasionally near their tips. Vesicle wall between the spines is smooth. Holotype: Fig. 5F, Slide no. 9805087 of PETROBRAS/ CENPES/PDEP/BPA palynological collection, E.F. coordinate P60-4. Type locality: Balapuca section, 102 m above the base of the Los Monos Formation (sample at 229 m, see Table 1), southern Subandean zone, south Bolivia. Description: The long variable spongy spines characterize Ramochitina boliviensis. These are sparsely distributed on the vesicle in six rows. The spines may be simple, branching distally from their midpoints, sometimes near their terminations, or form massive tapering simple spines. The width of spine bases varies between 1 and 30 mm. The cylindrical neck is short, about one-third of the total length, and slightly widened at the aperture. The body is ovoid. The vesicle wall between the spines is smooth. Dimensions (five specimens measured): Total length 160 – 220 mm (Holotype: 220 mm); maximum width 52– 60 mm (Holotype 60 mm), width of aperture 24– 35 mm (Holotype: 35 mm), length of spines 35 –85 mm. The neck is approximately one-third of the total length. Occurrence: Representatives of Ramochitina boliviensis occur in early Givetian (AD Lem spore zone) to middle Givetian (TA spore zone) beds of the Huamampampa, Los Monos, and Iquiri formations, south central Bolivia (see Melo, 2000). Comparison: Ramochitina boliviensis differs from Ramochitina ramosi Sommer and van Boekel, 1964, Ramochitina milanensis Collinson and Scott, 1958, and Ramochitina viridarium Winchester-Seeto and Paris, 1995 because of its much longer and more sparsely distributed spines. Ancyrochitina cf. A. ramusculosa Legault, 1973 (Plate 5, Fig. 8; Plate 6, Figs. 7 and 9 therein) is similar. However, from the description by Legault (1973), the spines should be randomly distributed, and furthermore, Ancyrochitina cf. A. ramusculosa has smaller spines on the neck. Subfamily Ancyrochitininae—Paris (1981) Genus Ancyrochitina—Eisenack (1955) Ancyrochitina postdesmea n.sp. Fig. 6G Ancyrochitina cf. A. desmea Lange 1967a, p. 69– 70, Pl. 1, Figs. 4 – 6. Ancyrochitina cf. A. desmea Legault 1973, p. 18 –19, Pl. 2, Figs. 1 – 3. Derivation of name: Latin, postdesmea, because of its similarity to the late Silurian species Ancyrochitina desmea Eisenack, 1964 and its much younger occurrence than that species in the stratigraphic record. Diagnosis: An Ancyrochitina species with a conical body and cylindrical neck of one-third to one-half of the total length. Margin provided with 8 – 10 thick branching appendices, which often are bent apertureward. Each branch may be further divided into 3—5 smaller branches. Similar spines are present on the neck, though these often are bent
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Domingos Formation, Parana´ Basin, Brazil (Grahn, own observations) and the early Givetian Widder, Hungry Hollow, and Arkona members of the Hamilton Formation, southwestern Ontario, Canada (Legault, 1973). Comparison: Ancyrochitina postdesmea differs from Ancyrochitina desmea Eisenack, 1964 in having a shorter appearance and a smooth vesicle surface between the spines (A. desmea has a finely verrucate surface).
Acknowledgments
Fig. 8. A. Fungochitina pilosa. Rio Bernejo section, Iquiri Formation. B. Lagenochitina avelinoi. Taputa´ section, Iquiri Formation. C. Possible evolutionary predecessor of the genus Sommerochitina. Taputa´ section, Iquiri Formation. D. The same species as C. Detail of the base. Note the basal position of the appendix. E. Lagenochitina avelinoi. Taputa´ section, Iquiri Formation. F. Ramochitina sp. 1. Taputa´ section, Iquiri Formation.
antiapertureward. The vesicle wall between the spines is smooth, and the aperture is straight. Holotype: Lange (1967a), Pl. 1, Fig. 4. M.N. 4296-1. Museu Nacional, Rio de Janeiro. Type locality: The 2-RP-1-MT borehole, core 18, Sa˜o Domingos Formation, Parana´ Basin, Brazil (Lange, 1967a). Description: Ancyrochitina postdesmea specimens are characterized by thick spines and appendices. Margin provided with 8 –10 appendices branching at their tips and then further branching 3– 5 times. Similar spines are present on the neck, often bent antiapertureward, in contrast with the appendices, which often are bent apertureward. Dimensions (six specimens measured): Total length 180 –219 mm (Holotype: 206 mm), maximum width 65– 79 mm (Holotype: 65 mm), width of aperture 27– 40 mm (Holotype 31 mm), length of spines and appendices 24– 65 mm. The neck is between one-third and one-half of the total length. Occurrence: Representatives of Ancyrochitina postdesmea occur in the early Givetian (AD Lem spore zone) to middle Givetian (TA spore zone) beds of the Huamampampa and Los Monos Formations, south central Bolivia. It is also present in contemporaneous beds of the Sa˜o
Thanks are due to the Faculty of Geology at Universidade do Estado do Rio de Janeiro (UERJ) and Prof. Maria Antonieta Rodrigues, director of the postgraduate program at the Faculty of Geology at UERJ, for her enthusiastic encouragement and providing access to the facilities. Dr Souza Cruz (Braspetro, Rio de Janeiro) provided me with the samples for this study. Through the courtesy of Dr Eduardo A.M. Kousoukos, head of SEBIPE at CENPES (Petrobra´s, Rio de Janeiro), I had access to an SEM, and geologist Jose´ Henrique G. de Melo at the same department discussed the geology and reviewed the manuscript. Merrell A. Miller (Saudi Aramco, Dhahran) is acknowledged for a linguistic check of the manuscript. Enrique Dı´az-Martinez (INTA-CSIC, Madrid) translated the Spanish abstract and reviewed the manuscript, and Eduardo G. Ottone (UBA, Buenos Aires) is acknowledged for reviewing the manuscript. All technical assistance from Jorge Louiz dos Santos and Maria Rosalva Campos Coelho at UERJ and Roge´rio da Silva Martins da Costa at CENPES is acknowledged. My sincere thanks to all.
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