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Andean geology

versión On-line ISSN 0718-7106

AndGeo vol.42 no.2 Santiago mayo 2015

http://dx.doi.org/10.5027/andgeoV42n2-a04 

 

The Valanginian Olcostephaninae Haug, 1910 (Ammonoidea) from the Andean Lower Cretaceous Chanarcillo Basin, Northern Chile

Los Olcostephaninae Haug, 1910 (Ammonoidea) valanginianos de la cuenca andina de Chañarcillo del Cretácico Inferior del Norte de Chile

 

* Francisco Amaro Mourgues1, 2, Luc G. Bulot3, Camille Frau4

1 IRD-LMTG Observatoire Midi-Pyrénées, 14 Avenue Edouard Belin, 31400 Toulouse, France.
2 Servicio Nacional de Geología y Mineraía, Sección Paleontología y Estratigrafía, Tiltil 1993, Ñuñoa, Santiago, Chile.
3 UMR CNRS 7730 CEREGE, Aix-Marseille Université, Case 67, 3 Place V. Hugo, 13331 Marseille Cédex 03, France. bulot@cerege.fr
4 9bis Chemin des Poissoniers, 13600 La Ciotat, France. camille_frau@hotmail.fr
* Permanent adress: TERRA IGNOTA. Heritage & Geosciences Consulting, Dr. Cádiz 726, Ñuñoa, Santiago, Chile. amourgues@terraignota.cl


ABSTRACT. Ammonites of the genus Santafecites Etayo-Sema and subgenus Olcostephanus (Viluceras) Aguirre-Urreta and Rawson are described for the first time from Chile. The succession of Olcostephaninae from the Chanarcillo Basin of northern Chile is described in the light of new collections and revision of historical material. The occurrence of mixed Andean and Mediterranean faunas supports the correlations proposed with the ammonite scales of the Neuquen Basin and the Mediterranean Province.

Keywords: Olcostephaninae, Lower Cretaceous, Northern Chile, Systematic Paleontology, Biostratigraphy.


RESUMEN. Los Olcostephaninae Haug, 1910 (Ammonoidea) valanginianos de la cuenca andina de Chañarcillo del Cretácico Inferior del Norte de Chile. Son descritos amonites del género Santafecites Etayo-Serna y del subgénero Olcostephanus (Viluceras) Aguirre-Urreta y Rawson, por primera vez en Chile. Se describe la sucesión de Olcostephaninae de la Cuenca de Chañarcillo en el Norte de Chile sobre la base de nuevas colecciones y revisión de material histórico. La ocurrencia de una mezcla de faunas andinas y mediterráneas sustenta las correlaciones propuestas con las escalas de amonites en la cuenca de Neuquén y la provincia Mediterránea.

Palabras clave: Olcostephaninae, Cretácico Inferior, Norte de Chile, Paleontología Sistemática, Bioestratigrafia.


 

1. Introduction

Olcostephanids are an important component of the Valanginian ammonite faunas of the Chanarcillo Basin (northern Chile), where they occur at two discrete intervals in the lower part of succession. The first one is characterized by the conspicuous occurrence of the cosmopolitan Olcostephanus (Olcostephanus) atherstoni (Sharpe, 1856) whereas the other is a level with Olcostephanus (Viluceraspermolestus (Leanza, 1957).

The first Olcostephaninae species mentioned in the Chilean literature is Olcostephanus (O.) curacoensis (Weaver, 1931) but the ammonites were not described and/or illustrated (Tavera, 1956; Corvalan, 1974; Corvalan in Segerstrom et al., 1963). These authors assigned the Argentinean species to different genera, all of which are now regarded as junior objective synonyms of Olcostephanus Neumayr, 1875. It was reported from several localities of the Punta del Cobre and Abundancia formations south and north of Copiapo. O. (O.) curacoensis is herein considered, in agreement with Riccardi et al. (1971) and Aguirre-Urreta and Rawson (1997), a synonym of O. (O. ) atherstoni.

The second level is characterized by a very distinctive fauna of evolute olcostephanids. This was recorded by Corvalan in Segerstrom et al. (1963) and Corvalan (1974) with a new species, ‘Holcostephanus copiapoensis nov. sp.’, but neither a description nor an illustration was given; this is therefore a nomen nudum according to the International Code of Zoological Nomenclature. Examination of the specimen labeled ‘Holcostephanus copiapoensis nov. sp.’ in the Corvalan collection by one of us (FAM), allows us to regard this taxon as an invalid synonym of Olcostephanus (Viluceras) permolestus.

The insights issued from this paleontological study permits to discuss and precise the former ammonite biostratigraphic long distance correlations between the European and South Central Andean regions. In this way, the stratigraphic record of the Andean Chanarcillo Basin, represent a link between the Neuquen Basin and Tethys ammonite biostratigraphic record.

2. Stratigraphy and fossil localities

The oldest sequences recorded until now from the marine Chanarcillo Basin are the Punta del Cobre and Abundancia formations, which are respectively assigned to an Early and Late Valanginian age (Mourgues, 2004; Aguirre-Urreta et al, 2007). These outcrops are located southeast of the city of Copiapo, in the northernmost part of the Chanarcillo Basin (Fig. 1). Nevertheless, (?) Middle to Upper Berriasian ammonites (Malbosiceras gr. malbosi in Aguirre-Urreta et al., 2007, fig. 6A) were collected 80 km north of Copiapo and are currently under study.

 

FIG. 1. Geographic distribution of the olcostephanid faunas of the Chañarcillo
Basin (simplified after SERNAGEOMIN, 2002).

 

The Abundancia Formation (‘Capas de Abundancia’, Biese in Hoffstetter et al., 1957) is the oldest lithological unit of the Chanarcillo Group (Segerstrom and Parker, 1959). It is characterized by well bedded grey mudstones interbedded with arkoses, which pass vertically and laterally into the Nantoco Formation limestones, and lies on the Punta del Cobre Formation (Segerstrom and Ruiz, 1962; Marschik and Fontbote, 2001, p. 413). This latter unit is composed of a pile of andesitic to basaltic andesitic lava flows, conglomerates, sandstones, tuffs and dacitic dome complexes, including sedimentary layers in its upper levels. The contact between this unit and the overlying Abundancia Formation is transitional, and has been defined by the first occurrence of a continuous bed of massive limestone or its metamorphosed equivalent. The following localities have been investigated.

2.1. Cerro La Vinchuca

Discontinuous outcrops of the Chanarcillo Group were observed southwest of Inca del Oro, which were previously investigated by Moraga (1977). Two different levels have yielded ammonites, where two distinctive faunas were identified. From bottom to top these are: Lissonia Gerth, 1925 (to which Raimondiceras Spath, 1924 is likely to be a synonym) and O. (O.) atherstoni. The historical collection of SERNAGEOMIN contains a single specimen herein identified as Santafecites santafecinus (d’Orbigny, 1842) from the same locality (Chong collection, SNGM 07) and described below.

2.2. Puquios area

The Puquios area is characterized by complex tectonics that affects the whole Mesozoic sequence. It is known in the literature as the ‘Caos de Puquios’ and was studied by Sepulveda and Naranjo (1982) and Mpodozis and Allmendinger (1992). These authors describe a series of 200 m of bioclastic and oolithic limestones that yielded ammonites of Late Valanginian to Barremian age. The material is kept in the collection of SERNAGEOMIN and contains a single specimen of Santafecites santafecinus (Sepúlveda collection, SNGM 1536) described below.

2.3. Quebrada Melendez

The Quebrada Melendez is one of the reference sections for the Lower Cretaceous of the Chañarcillo Basin. The succession crops out in a tributary creek, east of the Copiapó valley (Fig. 2). It shows the most complete series of the Upper Valanginian to Lower Aptian strata. From this locality O. (O.) curacoensis and Lissonia riveroi (Lissón, 1907) were reported (Corvalán, 1974). We have observed that near the top of the Abundancia Formation, an ‘Ammonitico rosso’ bed contains abundant O. (Viluceras) permolestus associated with numerous neocomitids, such as juvenile N. (Neocomites) peregrinus (Rawson and Kemper, 1978), Neocomites (Sabbaiceras) beaumugnensis (Sayn, 1907) and Rodighieroites cardulus Company, 1987. These neocomitids are under study with associated material from others localities.

 

FIG. 2. Lithologic sections of the upper part of the Abundancia Formation (Quebrada Meléndez)
and upper part of the Punta del Cobre Formation (Quebradas Nantoco-Los Algarrobos).

 

2.4. Quebradas Nantoco-Los Algarrobos

A volcanoclastic succession in the upper part of the Punta del Cobre Formation crops out at Quebrada Los Algarrobos. Two fossiliferous siltstone levels were recognized; a lower one with Lissonia sp., and an upper one containing O. (O.) atherstoni (Fig. 2). From the same locality, previous investigators have mentioned L. riveroi and O. (O.) curacoensis and other neocomitids such as ‘Acanthodiscus’, ‘Thurmanniceras’ by Corvalán in Segerstrom et al. (1963) and ‘Cuyaniceras’ by Marschik and Fontboté (2001).

The upper fossiliferous level with O. (O.) atherstoni was also identified at Quebrada Nantoco. We collected three specimens from that locality (SNGM 1021 [7-9]), which are associated with a specimen of Bochianites sensu lato, several meters above a bed with Lissonia.

3. Systematic Paleontology

The material described herein is stored in the Paleontological Collections of the Servicio Nacioal de Geología y Minería (SERNAGEOMIN) Museum, Santiago, with the prefix SNGM. Most of the material belongs to the collection of one of us (F.A.M.). Specimens from the Corvalán, Chong and Sepúlveda collections have also been included in this study.

Dimensions of specimens are indicated as follow: d: diameter; wh: whorl height; wt: whorl thickness; wu: width of umbilicus. M: macroconch; m: microconch. In the synonymy list, v indicates that we have seen the specimen(s).

Superfamily Perisphinctaceae Steinmann, 1890
Family Olcostephanidae Haug, 1910 
Subfamily Olcostephaninae Haug, 1910

(=Taraisitinae Cantú-Chapa, 1966; Capeloitinae Cantú-Chapa, 2009; =Garcitinae Cantú-Chapa, 2012; =Saynoceratinae Cantú-Chapa, 2012)

The subfamily Taraisitinae is herein as a junior subjective synonym of Olcostephaninae since its type genus Taraisites Cantú-Chapa, 1966 is a junior subjective synonym of Olcostephanus (Olcostephanus) (see discussion in González Arreola et al., 2014, p. 59). The type genus of Garcitinae is Garcites Cantú-Chapa, 2001, a taxon based on pyritized internal moulds ofjuveniles olcostephanids. In our opinion the diagnostic features retained by Cantú-Chapa (2001) are diagenetic artifacts due to the alteration of pyrite on the ventral area of the moulds. As a consequence Garcitinae is a nomen dubium based on olcostephanids that cannot be identified at the genus level. Bulot et al. (1990a) showed that the Valanginites-Saynoceras lineage directly derives from the subgenus Olcostephanus by complex heterochronies. Placing Valanginites Kilian, 1910 and Saynoceras Munier-Chalmas, 1894 in different subfamilies is artificial and do not reflects the iterative evolution of the Olcostephaninae. We therefore regard Saynoceratinae as an artificial grouping of micromorphic genera that derivates from Olcostephanus sensu stricto at different moments (Bulot et al., 1990a). The same is true for the Capeloitinae, whose type genus Capeloites Lissón, 1937a, derivates from the Olcostephanus rootstock in the late Lower Hauterivian (Kemper et al., 1981; Bulot, 1990a; Rawson, 2007).

Genus Santafecites Etayo-Serna, 1985

Type-species: Ammonites santafecinus d’Orbigny, 1842, by original designation of Etayo-Serna (1985, p. xxiv-22).

Remarks: In Colombia, Santafecites was reported from the base of the Upper Valanginian together with Saynoceras verrucosum (d’Orbigny, 1841), above the Valanginites, Raimondiceras, Lissonia and Acantholissonia Leanza, 1972 assemblage that characterize the Lower Valanginian (Etayo-Serna, 1985 and personal communication, 1999). It should be noted that there is striking similarities between S. santafecinus and Sphaeroceras broggianus Lissón, 1937b from the Valanginian of Peru. This later species that has been differently interpreted in the literature (Benavides-Cáceres, 1956; Nikolov, 1965; Riccardi and Westermann, 1970; Klein, 2005) and recently designated as the type species of Peruvites by Cantú-Chapa (2012). Unfortunately the exact stratigraphic position of the Peruvian taxon is poorly constrained even if it seems closely allied to Valanginites argentinicus Leanza and Wiedmann, 1980 from the early Lower Valanginian of the Neuquén Basin. Santafecites is therefore likely to derivate from an endemic Valanginites-like form (=Peruvites), but pending a thoroughful description of the Colombian representative of the latter this hypothesis remains speculative.

Occurrence. Early Upper Valanginian of Colombia (Etayo-Serna, 1985). The genus is herein reported from Chile for the first time (?Upper Valanginian). Ammonites santafecinus was also mentioned from Perú by Steinmann (1930) and Lissón and Boit (1942) but this occurrence was never confirmed.

Santafecites santafecinus (d’Orbigny, 1842)
Figs. 3, 4A-J

v 1842 Ammonites santafecinus d’Orbigny, p. 34, Pl. 1, Figs. 3, 4.

1985 Santafecites santafecinus (d’Orbigny), Etayo-Serna, p. xxxiv-22.

Holotype: By monotypy, the specimen figured by d’Orbigny, 1842, p. 34, Pl. 1, Figs. 3, 4, from Santa Fe (de Bogotá), Colombia, kept in the Museum National d’Histoire Naturelle de Paris (d’Orbigny collection, R-3148).

Material: Two specimens (table 1). One large and crushed adult from the Puquios area (SNGM 1536, Sepúlveda collection) and a fragmentary specimen from Cerro La Vinchuca (SNGM 07, Chong collection). 

Description: Umbilicus small with poorly defined umbilical region. Ribs organized in bundles with branching at, and above, the umbilical shoulder. The ornamentation seems to be smoother on the outer part of the whorl (? body chamber). No clear bullae or tubercles are visible. The ribs are interrupted on the venter and form a weak groove. They are alternate on both sides of the groove. Suture line is too poorly preserved for description.

Remarks: Since the original figure and description by d’Orbigny (1842), the species was never figured nor described again. The holotype is illustrated here as well as some Colombian specimens (Figs. 4A, B, E, F, H, and I) from the Breistroffer collection (Grenoble University). The larger crushed specimen matches well the holotype (Fig. 3) and the reference material from these collection (compare Figs. 4A, B, E, F, H, and I). It shows all typical features of the genus and species, e.g., ribs originating from periumbilical bullae interrupted on the ventral area and not opposite. The smaller specimen (Dmax ca. 40 mm), represented by half a whorl still septate at D. ca. 36 mm, is slightly different. It is also a typical sphaerocone with rounded venter and whorl section broader than wide, with the maximum width on the umbilical wall. The smaller specimen (SNGM 07) differs from the Colombian material in its smaller size, lack of bullae and weaker ornamentation. Nevertheless, there is no doubt that it belongs to the genus Santafecites (general morphology, ventral groove and alternate ribs that are interrupted on the venter). It may represent the microconch form of S. santafecinus.

Occurrence: As for genus.

 

FIG. 3. Santafecites santafecinus (d’Orbigny, 1842).
Holotype, MHNP R-3148, d’Orbigny (specimen figured by
d’Orbigny, 1842, p. 34, Pl. 1, Figs. 3, 4, from Santa Fe (de Bogotá).

 

FIG. 4. Santafecites santafecinus (d’Orbigny, 1842). A-B, E-F, H-I. side and
ventral view of BF-28d to f from Colombia (Breistroffer collection, University
of Grenoble); C-D. side and ventral view of SNGM 07 (Chong collection, Cerro
La Vinchuca, Chile); G, J. side and ventral view of SNGM 1536 (Sepúlveda
collection, Puquios, Chile).

 

TABLE 1. DIMENSIONS SANTAFECITES SANTAFECINUS (D’ORBIGNY) SPECIMENS.

 

Genus Olcostephanus Neumayr, 1875

Remarks: As herein understood, the genus Olcostephanus is subdivided into three subgenera: Olcostephanus, Jeannoticeras Thieuloy, 1965 and Viluceras Aguirre-Urreta and Rawson, 1999. Para-stieria Spath, 1923a and Mexicanoceras Imlay, 1938 are considered as separate genera. Holcostephanus Sayn, 1889 and Astieria Pavlow, 1892 are junior objective synonyms of Olcostephanus. Subastieria Spath, 1923b; Rogersites Spath, 1924; Maderia Imlay, 1938; Taraisites, Satoites Cantú-Chapa, 1966 and Lemurostephanus Thieuloy, 1977 are junior subjective synonyms of Olcostephanus.

Subgenus Olcostephanus Neumayr, 1875

Type-species: Ammonites asterianus d’Orbigny, 1840, p. 115, Pl. 28, Figs. 1, 2 (only), by subsequent designation of Baumberger (1910, p. 3). As already pointed out by Bulot (1990a, p. 5), the specimen from the d’Orbigny collection figured and considered as lectotype by Baumberger (1910, Pl. 32, Figs. 1, 2) does not match the original description or figure of d’Orbigny. The revision of the type material (Bulot, 1990a) suggests that the original drawing is reconstructed from different specimens, some of which belongs to O. (O.) guebhardi (Kilian, 1902), a taxon closely allied to O. (O.) atherstoni (see below); the others to the O. (O.) densicostatus (Wegner, 1909)-sayni (Kilian, 1895) lineage. This view was supported by Busnardo et al. (2003, p. 48-49) and Gauthier et al. (2006, p. 29-30).

Diagnosis: Compressed to strongly inflated cadicones, with strongly arched to well rounded venter. Primary ribs usually present on umbilical wall, commonly terminating in tubercles at umbilical shoulder, from which arise straight or slightly curved secondary ribs, usually in fasciculate bundles. Commonly 3-4 secondaries per bundle, although there may be as many as 6-9 or as few as 2. Secondary ribs may bifurcate on the flanks, while intercalated ribs between bundles are the rule. Ribbing always passes uninterrupted across venter; also it may weaken in some species. Parabolae or constrictions may or may not be present, but are absent on the outer whorls of macroconchs. The genus is dimorphic; microconchs are small and bear lappets on the aperture; macroconchs are larger, with a simple peristome (modified after Cooper, 1981, p. 161). 

Occurrence: Olcostephanus (Olcostephanus) is widely distributed in the Mediterran-Caucasian and Indo-Pacific subrealms of the Tethyan Realm and adjacent areas of the Boreal Realm sensu Westermann (2000). In the western Tethys, the subgenus is known to range from the highest Upper Berriasian (F. boissieri Zone, T. otopeta Subzone) to the high Lower Hauterivian, L. nodosoplicatum Zone, O. (O.) variegatus biohorizon (Bulot, 1990a; Bulot, 1992; Bulot et al., 1993; Bulot and Thieuloy, 1995). In South America, Olcostephanus (Olcostephanus) is known from Colombia, Perú, Chile and Argentina. The oldest occurrence was reported from the early Valanginian of the Neuquén Basin (Aguirre-Urreta and Rawson, 1999) and possibly Colombia (Etayo Serna, written communication 1999). ‘Middle’ Valanginian Olcostephanus of the atherstoni group occur in all countries listed above except Perú (Riedel, 1938; Haas, 1960; Riccardi et al., 1971; this paper). Late early Hauterivian Olcostephanus of the sayni-variegatus (Paquier, 1900) plexus are known from all those countries except Chile (Riedel, 1938; Haas, 1960; Robert et al, 1998; Aguirre-Urreta and Rawson, 2001).

Olcostephanus (Olcostephanus) atherstoni (Sharpe, 1856)
Figs. 5, 6

v 1856 Ammonites Atherstoni Sharpe, p. 196, Pl. 23, Figs. 1a, b.
v 1856 Ammonites baini Sharpe, p. 197, Pl. 23, Figs. 2a-b.
v 1860 Ammonites asterianus (d’Orbigny), Pictet and Campiche, p. 298, Pl. 43, Figs. 1, 2.
1863 Ammonites Schenki Oppel, p. 286, Pl. 81, Figs. 4a-c.
v 1878 Ammonites asterianus (d’Orbigny), Bayle, Pl. 55, Fig. 1 (only). 
v 1902 Holcostephanus (Astieria) guebhardi Kilian, p. 866, Pl. 57, Fig. 2.
1902 Astieria cf. atherstoni (Sharpe), Karakasch, p. 11, Pl. 1, Fig. 3.
1903 Holcostephanus (Astieria) schencki (Oppel), Uhlig, p. 130, Pl. 18, Figs. 2a-c.
v 1907 Astieria atherstoni (Sharpe), Baumberger, p. 39-47, Pl. 21, Fig. 3, Pl. 23, Fig. 1, Pl. 24, Figs. 2, 5, Text-figs. 114-117. 
v 1907 Astieria cf. atherstoni (Sharpe), Baumberger, Pl. 25, Fig. 4. 
v 1908 Astieria leptoplana, Baumberger, p. 9-12, Pl. 26, Fig. 4, Pl. 28, Fig. 2.
v 1908 Astieria imbricata Baumberger, p. 14-18, Pl. 26, Figs. 2-3, Text-figs. 123-126. 
v 1908 Astieria actinota Baumberger, p. 18-20, Pl. 26, Fig. 1. v 1908 Holcostephanus wilmanae Kitchin, p. 195, Pl. 9, Figs. 1,1a. 
v 1908 Holcostephanus rogersi Kitchin, p. 201, Pl. 9, Fig. 3, Pl.10, Fig. 2. 
v 1908 Holcostephanus modderensis Kitchin, p. 202, Pl.10, Fig. 3. 
v 1919 Astieria catulloi Rodighiero, p. 83, Pl. 9, Fig. 9. 
v 1930 Rogersites sphaeroidalis Spath, p. 144, Pl. 13, Fig. 5, Pl. 15, Fig. 1. 
v 1930 Rogersites otoitoides Spath, p. 149, Pl. 14, Fig. 1. 
v 1930 Astieriapsilostoma var. lateumibilicata Roch, p. 314, Pl. 16, Figs. 3a, b 
1931 Astieria curacoensis Weaver, p. 427, Pl. 49, Figs. 326-327, Pl. 50, Fig. 328.
1931 Astieria sudandina Windhausen, Pl. 33, Fig. 1 (nomen nudum).
v 1932 Rogersites douvillei Besairie, p. 44, Pl. 5, Figs. 9, 9a, Text-fig. 2.
1933 Astieria atherstoni (Sharpe), Roman, p. 21-22, Pl. 4, Fig. 1 (only)
v 1936 Rogersites curvicostatus Besairie, p. 141, Pl. 12, Figs. 7, 10, Pl. 13, Fig. 8. 
v 1936 Rogersites douvillei Besairie, p. 138, Text-fig. 9, n° 2. 
v 1936 Rogersites baini var. ambikyi Besairie, p. 138, Pl. 13, Fig. 5, Text-fig. 9, n° 3. 
v 1939 Olcostephanus (Rogersites) schencki (Oppel), Spath, p. 30, Pl. 2, Fig. 6, Pl. 18, Figs. 9-10.
1944 Holcostephanus midas Leanza, 1944, p. 16, Pl. 1, Figs. 1a-c.
1944 Holcostephanus auritus Leanza, 1944, p. 18, Pl. 2, Figs. 1a-c
1958 Olcostephanus curacoensis (Weaver), Corvalán and Pérez, 1958, p. 38, Pl. 12, Fig. 27.
1970 Olcostephanus cf. O. atherstoni Baumberger (non Sharpe), Imlay and Jones, p. B38-B39, Pl. 8, Fig. 15, Pl. 9, Figs. 1-3, 6-10. 
v 1962 Holcostephanus schencki Uhlig (non Oppel), Collignon, p. 36, Fig. 859. 
v 1962 Holcostephanus atherstoni (Sharpe), Collignon, p. 38, Fig. 860. 
v 1962 Holcostephanus douvillei (Besairie), Collignon, p. 43, Fig. 869.
v 1971 Olcostephanus atherstoni (Sharpe), Riccardi et al., p. 91, Pl. 12, Figs. 3-4, Pl. 13, Figs. 1-5, Text-figs. 3-10.
1980 Olcostephanus (Olcostephanus) atherstoni (Sharpe), Leanza and Wiedmann, p. 945, Pl. 1, Fig. 1.
1980 Olcostephanus (Olcostephanus) sakalavensis (Besairie), Leanza and Wiedmann, p. 946, Pl. 1, Fig. 3.
v 1977 Olcostephanus (Olcostephanus) salinarius Spath, Fatmi, Pl. 3, Figs. 1a, b (only).
v 1981 Olcostephanus (Olcostephanus) sp. (= ‘Proastieria’ Stolley), Kemper et al., p. 268-269, Pl. 35, Fig. 2.
v 1981 Olcostephanus (Olcostephanus) atherstoni (Sharpe). Cooper, 1981, p. 182, Figs. 19, 24-26, 27A-D, 28-33, 38, 40-43, 55, 118, 143C-D, 151A. 
v 1981 Olcostephanus (Olcostephanus) rogersi (Sharpe), Cooper, 1981, p. 221, Figs. 70-73, 74A-B, 75A-B, 76, 131A-B, 150E-G. 
v 1981 Olcostephanus (Olcostephanus) baini baini (Sharpe), Cooper, 1981, p. 263, Figs. 114-129,130A-B, 131C-J, 132-135, 143A-B, 144A-D, 150C-D, 151B-D. 
v 1981 Olcostephanus (Olcostephanus) baini var. sphaeroidalis (Spath), Cooper, 1981, p. 263, Figs.
144E-G, 145-146, 149, 150A-B, F.
v 1981 Olcostephanus (Olcostephanus) ventricosus (von Koenen), Cooper, p. 300, Fig. 154 (only). 
v 1981 Olcostephanus atherstoni (Sharpe), Leanza, p. 169-170, Pl. 15, Figs. 1-8, Pl. 19, Figs. 16-17. 
v 1985 Olcostephanus astierianus (d’Orbigny), Cecca, p. 157, Pl. 6, Figs. 1a, b.
v 1985 Olcostephanus densicostatus (Wegner), Company, p. 118, Pl. 1, Figs. 3-7.
v 1986 Olcostephanus psilostomus psilostomus (Neumayr and Uhlig), Kvantaliani and Sakharov, p. 56, Pl. 1, Figs. 1, 2.
v 1986 Olcostephanus convolutus (von Koenen), Kvantaliani and Sakharov, p. 57, Pl. 1, Figs. 3.
1986 Olcostephanus cf. guebhardi (Kilian), Howlett, p. 71, Figs. 2a, b.
v 1987 Olcostephanus densicostatus (Wegner), Company, p. 594, Pl. 6, Figs. 5-6. 
v 1988 Olcostephanus atherstoni (Sharpe), Riccardi, Pl. 5, Figs. 1-2.
v 1990a Olcostephanus (Olcostephanus) guebhardi (Kilian), Bulot, p. 87, Pl. 6, Figs. 1-10, Pl. 7, Figs. 1-3, Pl. 8, Figs. 1-7, Pl. 11, Figs. 1-2.
v 1990b Olcostephanus (Olcostephanus) guebhardi (Kilian), Bulot, p. 8, Pl. 1, Figs. 4, 5. 
v 1991 Olcostephanus (Olcostephanus) guebhardi morphotype querolensis (Kilian), Ettachfini, p. 113, Pl. 11, Figs. 1, 3, 7, 8.
v 1991 Olcostephanus (Olcostephanus) guebhardi aff. morphotype querolensis (Kilian), Ettachfini, p. 113, Pl. 11, Fig. 2.
v 1991 Olcostephanus (Olcostephanus) guebhardi lateumbilicatus (Roch), Ettachfini, Pl. 11, Figs. 4, 6.
v 1991 Olcostephanus (Olcostephanus) cf. psilostomus lateumbilicatus (Roch), Ettachfini, Pl. 11, Figs. 10, 11.
v 1992 Olcostephanus (Olcostephanus) guebhardi morphotype querolensis Bulot, Pl. 1, Fig. 1.
v 1992 Olcostephanus (Olcostephanus) guebhardi (Kilian), p. 151, Bulot, Pl. 1, Figs. 2a, b.
1992 Olcostephanus aff. guebhardi (Kilian), Kemper, Pl. 35, Figs. 1a, b.
v 1993 Olcostephanus (Olcostephanus) atherstoni (Sharpe), Aguirre-Urreta, Pl. 2, Figs. 6, 7. 
v 1995 Olcostephanus atherstoni (Sharpe), Aguirre-Urreta and Rawson, p. 453, Figs. 6h-i. 
v 1997 Olcostephanus atherstoni (Sharpe), Aguirre-Urreta and Rawson, Pl. 1, Figs. c-e.
1997 Olcostephanus (O.) catulloi (Rodighiero), Faraoni et al., Pl. 5, Fig. 17.
2001 Olcostephanus (Olcostephanus) guebhardi (Kilian), Wippich, Pl. 10, Figs. 2-11, Pl. 11, Figs. 1-2.
2003 Olcostephanus (Olcostephanus) guebhardi (Kilian), Wippich, Fig. 8d, Fig. 9e.
2003 Olcostephanus (Olcostephanus) guebhardi (Kilian), Lukeneder and Harzhauser, Fig. 3a.
2004 Olcostephanus (Olcostephanus) guebhardi (Kilian), Lukeneder, Fig. 6.
2004 Olcostephanus (Olcostephanus) atherstoni (Sharpe), Mourgues, Fig. 5a, g.
2004 Olcostephanus (Olcostephanus) guebhardi lateumbilicatus (Roch), Ettachfini, Pl. 23, Fig. 2-6.
2004 Olcostephanus (Olcostephanus) guebhardi morphotype querolensis Bulot, Ettachfini, Pl. 23, Fig. 7-10.
2005 Olcostephanus (Olcostephanus) atherstoni (Sharpe), Aguirre-Urreta et al., Fig. 5a.
2007 Olcostephanus (Olcostephanus) guebhardi morph. type querolensis Bulot, Lukeneder, Fig. 4F-I.
2007 Olcostephanus (Olcostephanus) atherstoni (Sharpe), Aguirre-Urreta et al., Fig. 6C, G, Fig. 10F. 
2010 Olcostephanus guebhardi (Kilian), Vašiček, p. 399, Pl. 1, Fig. 2, Pl. 2, Fig. 2.
? 2010 Olcostephanus guebhardi (Kilian), Fözy et al., Fig. 3R.

 

FIG. 5. Olcostephanus (O.) atherstoni (Sharpe, 1856). A-B. SNGM 1021-17;
C-D. SNGM 1021-14; E-F. SNGM 1021-8; G-H. SNGM 1021-26; I. SNGM 1021-23;
J-K. SNGM 1021-19; L-M. SNGM 1021-18; N. SNGM 1021-15; O. SNGM 1021-20;
P, T. SNGM 1022-3; Q, U. SNGM 1021-10/11; R. SNGM 1021-29; S. SNGM 1021-16;
V. SNGM 1022-15; W. SNGM 1022-4. All specimens from bed PC2 at Quebrada Los
Algarrobos (Mourgues collection) except E and F from Quebrada Nantoco.

 

FIG. 6. Olcostephanus (O.) atherstoni (Sharpe, 1856). A. SNGM 1022-7; B. SNGM 1022-15;
C-D. SNGM 1022-13; E-F. SNGM 1022-14; G. SNGM 1022-16; H. SNGM 1022-4;
I. SNGM 1022-3; J-K. SNGM 1022-2; L-M. SNGM 1022-10; N-O. SNGM 1022-5 from bed PC2
at Quebrada Los Algarrobos (Mourgues collection). All specimens natural size except H (x 0.7).

 

Holotype: By monotypy, the specimen figured by Sharpe (1856, p. 196, Pl. 23, figs. 1a, b), from the Sundays River, South Africa (British Museum, BM-C32202), refigured by Cooper (1981, p. 183-184, figs. 24, 25).

Material: 41 specimens (tables 2 and 3): 3 from Quebrada Nantoco (SNGM 1021 [7-9]), 36 from Quebrada Los Algarrobos (SNGM 1021 [10-28], SNGM 1022 [2-18]) and 2 from 3 km to northwestern of Cerro La Vinchuca (SNGM 1537 [1-2]).

 

TABLE 2. DIMENSIONS OLCOSTEPHANUS (O.) ATHERSTONI (SHARPE)
MICROCONCH SPECIMENS.

 

TABLE 3. DIMENSIONS OLCOSTEPHANUS (O.) ATHERSTONI (SHARPE)
MACROCONCH SPECIMENS.

 

Description: Microconch [m]: the microconch consists of immature examples of 25-30 mm diameter, with at least some part of the body chamber preserved. Septation ceases at diameters of about 20-25 mm. The shell is slightly involute, cadicone with moderately depressed to semicircular whorls. The umbilical slope is moderately steep with a rounded margin. The umbilicus is moderately deep and narrow where its diameter (wu) is approximately 28% of the shell diameter (d). The venter and flanks are rounded. Maximum width of whorl at umbilical bullae. Rursiradiate primary ribs arise near the umbilical seam, progressively becoming prominent on the umbilical slope, and forming bullae-like tubercles on the upper part of the umbilical margin.  There are 9-12 primary ribs per half-whorl. Bundles of three to four (exceptionally 5) secondary ribs associated with each bulla, but an additional one or two may be intercalated between two bundles. There are 40-45 secondary ribs per half-whorl. No constrictions were observed our examples.

Macroconch [M]: the shell of the macroconch is moderately small with diameters between 70-85 mm. Some specimens are septate to at least 40-50 mm. The body chamber occupies at least % of the last whorl. These forms are more involute than the microconchs, with the umbilicus (wu) reaching approximately a fifth of the shell diameter (d). The umbilical slope is steep with a rounded margin. Ribbing is finer and denser than in microconchs, and slightly rursiradiate. There are 13-15 primary ribs per half-whorl. Bundles of four to six secondary ribs are associated with each bulla, but an additional rib may be intercalated between two bundles. There are 55-70 secondary ribs per half-whorl. Neither constrictions nor parabolae was observed in our material.

Discussion: As already mentioned by Riccardi et al. (1971), Cooper (1981), Company (1987) and Bulot (1990a, 1992), the Olcostephanus of the atherstoni plexus are characterized by a marked dimorphism. The Chilean material also illustrates this feature (Fig. 7). The dimorphism clearly affects size, coiling and ribbing. The microconchs are more evolute, smaller and with coarser ribs than the macroconchs.

 

FIG. 7. Plot of umbilical width (wu) against shell diameter (d) for Olcostephanus (O.) atherstoni
(Sharpe, 1856) and O. (Viluceras) permolestus (Leanza, 1957).

 

It should also be noted that the material from Atacama is closer to the population from the Mediterranean Tethys than to the one from South Africa and Argentina (Neuquen Basin). As a whole, our population is very similar to O. (O.) guebhardi and its morphotypes as defined by Bulot (1990a, 1992). This includes not only O. (O.) guebhardi s. str. but also O. (O.) guebhardi morphotype querolensis Bulot, the O. (O.) densicostatus (Wegner) in Company (1987, Pl. 15, Figs. 1-8, Pl. 19, Figs. 16, 17).

On the other hand, some of the South African microconchs figured by Cooper (1981, p. 265, Fig. 115, Fig. 129B) under O. (O.) baini baini, considered herein as a junior subjective synonym of O. (O.) atherstoni, hardly differ from the microconchs of O. (O.) guebhardi. Similarly, the larger macroconchs of O. (O.) guebhardi (morphotypes querolensis and hollwedensis) fall within the adult size of the smaller South African and Argentinean O. (O.) atherstoni. As a consequence, we cannot see any reason to keep O. (O.) guebhardi separate from O. (O.) atherstoni. Because of priority rules, O. (O.) guebhardi is a junior subjective synonym of O. (O.) atherstoni.

Nevertheless, it should be noted that in Southeastern France the oldest representatives of O. (O.) atherstoni, O. (O.) guebhardi ‘forme primitive’ in Bulot (1990a, 1992), first occur in the middle part of the B. campylotoxus Subzone (B. subcampylotoxus biohorizon sensu Bulot and Thieuloy, 1995). The acme of the species ranges from the upper part of the B. campylotoxus Subzone to the uppermost part of the K. biassalense Subzone (B. campylotoxus biohorizon to K. inostranzewi Zone sensu Bulot and Thieuloy, 1995). These forms, always cadicones, lose at the adult stage the sphaerocone morphology of the precursors. It is among those populations that the morphology is closer to the typical O. (O.) atherstoni from South Africa. They also include large numbers of typical O. (O.) guebhardi.

At the top of the K. biassalense Subzone, the populations are affected by a new morphological change that affects mainly the density of ribbing, while the general form of the shell remains unchanged. Bulot (1990a, 1992) introduced the name querolensis for this morphotype that shows its acme in the S. verrucosum Subzone and disappears at the top of the K. pronecostatum Subzone. Most of the Chilean macroconchs described herein clearly belong to this morphotype.

Similarly, Ettachfini (1991) showed that the morphotype succession identified in south-east of France is also represented in the Valanginian of the Essaouira basin (Morocco). In South-eastern Spain, O. (O.) atherstoni is represented only by the morphotype querolensis, which shows the same distribution as in France. The German morphotype hollwedensis Bulot (=‘Proastieria’ sensu Stolley, 1937) is known only from the lower part of the P. hollwedensis Zone of the Lower Saxony and Yorkshire basins of Northern Europe (Kemper et al., 1981). Similar forms also occur in the ‘Marnes à Astieria’ of the Jura platform in Switzerland (Bulot, 1992). This morphology is by far the closest to the typical O. (O.) atherstoni from South Africa. The time span of the hollwedensis morphotypes merely represents an equivalent of the uppermost B. campylotoxus and lower K. biassalense Subzones of the Mediterranean standard ammonite scale.

From the Neuquen basin, the species described by Leanza (1944), O. (O.) auritus and O. (O.) midas, correspond respectively to the macroconchs and microconchs of our O. (O.) atherstoni.

Subgenus Viluceras Aguirre-Urreta and Rawson, 1999

Type-species: Simbirskites permolestus Leanza, 1957, by original designation of Aguirre-Urreta and Rawson (1999, p. 351).

Diagnosis: An evolute to serpenticone subgenus of Olcostephanus characteristically with well-developed constrictions and flares, particularly in the adult growth stage.

Discussion: The relationships between Viluceras, Simbirskites, Lemurostephanus and Olcostephanus have been discussed at length by Aguirre-Urreta and Rawson (1999, p. 343 and 351-352) and we fully agree with those authors on the systematic position of Viluceras as a subgenus of Olcostephanus. As already mentioned above and for the reasons given by Aguirre-Urreta and Rawson (1999, p. 351-352), we also regard Lemurostephanus as a junior subjective synonym of Olcostephanus s. str.

Occurrence: Until the recognition of its occurrence in Chile (Mourgues, 2004), the subgenus was known only from the middle part of the Upper Valanginian of the Neuquen Basin in Argentina (Aguirre-Urreta and Rawson, 1999). The reported occurrence of O. (V.) permolestus from south-east France (Autran, 1993) is erroneous and will be discussed below.

Olcostephanus (Viluceras) permolestus (Leanza, 1957)
Fig. 8

v 1957 Simbirskites permolestus Leanza, p. 16, Pl. 3, Fig. 1.
v 1963 ‘Holcostephanus copiapoensis nov. sp.’: Corvalan in Segerstrom et al., p. 10.
v 1974 ‘Holcostephanus copiapoensis nov. sp.’: Corvalan, p. 19.
v 1974 Olcostephanus (Lemurostephanus) permolestus (Leanza): Leanza and Wiedmann, p. 949, Pl. 1, Fig. 2, Pl. 2, Fig. 1.
v 1980 Olcostephanus (Lemurostephanus)permolestus (Leanza): Aguirre-Urreta, Pl. 2, Fig. 4 (holotype refigured from opposite flank).
non 1993 Olcostephanus (Lemurostephanus) permolestus (Leanza): Autran, Pl. 4, Fig. 2.
v 1995 Olcostephanus (Lemurostephanus) permolestus (Leanza): Aguirre-Urreta and Rawson, Pl. 1g (re-illustration of Aguirre-Urreta, 1993, Pl. 2, Fig. 4).
v 1997 Olcostephanus (Lemurostephanus) permolestus (Leanza): Aguirre-Urreta and Rawson, Figs. 6a, b.
v 1999 Olcostephanus (Lemurostephanus) permolestus (Leanza): Aguirre-Urreta and Rawson, p. 352353, Figs. 4e, f, I, j; Figs. 5a-n; Fig. 6; Figs. 7a-f, i, j.
v 2002 Olcostephanus (V.) permolestus (Leanza): Mourgues, p. 75.
v 2004 Olcostephanus (Viluceras) permolestus (Leanza): Mourgues, Fig. 5f.
2005 Olcostephanus (Lemurostephanus) permolestus (Leanza): Aguirre-Urreta et al., Fig. 5b.
2007 Olcostephanus (Viluceras) permolestus (Leanza): Aguirre-Urreta et al, Figs. 6D-E, Fig. 10I.

 

FIG. 8. O. (Viluceras) permolestus (Leanza, 1957). A, G. SNGM 1538-1; B. SNGM 1023-2;
C. SNGM 1023-12; D, J. SNGM 1538-2; E. SNGM 1023-9; F. SNGM 1023-5;
H-I. SNGM 1023-8; K-L. SNGM 1023-3. All specimens from bed G3-3
at Quebrada de Melendez (Mourgues collection), except A, G, D and J (Corvalan collection).

 

Holotype: By original designation, the specimen figured by Leanza (1957, p. 16, Pl. 3, Fig. 1), from El Durazno hill, Central West Argentina. Universidad de Buenos Aires, CPBA 7018. Refigured by Aguirre-Urreta (1993, Pl. 2, Fig. 4) and Aguirre-Urreta and Rawson (1995, Pl. 1, Fig. g; 1999, p. 350, Fig. 5a). 

Material: 19 specimens (table 4 and 5), from Quebrada de Meléndez (SNGM 1023 [1-17]; SNGM 1538 [1, 2], Corvalán collection).

 

TABLE 4. DIMENSIONS O. (VILUCERAS) PERMOLESTUS (LEANZA)
MICROCONCH SPECIMENS

 

TABLE 5. DIMENSIONS O. (VILUCERAS) PERMOLESTUS (LEANZA)
MACROCONCH SPECIMENS

 

Description: The examples are dimorphic in size. Small microconch of 35-45 mm diametre, serpenti-cone with a large umbilicus (wu=35-48% of d). The subcircular whorl section overlaps approximately a third of the preceding whorl. The umbilical slope is quite shallow and rounded and becomes moderately steep in the adult macroconch. The rectiradiate primary ribs are coarse, slightly concave, and form bullae-like tubercles on the upper part of the umbilical margin. From each bulla arise associated bundles of two to three (frequently two) secondary ribs, gently rursiradiate on the upper third of the whorl. An additional one may be intercalated between two bundles. Constrictions are frequent.

Remarks: Both our macroconchs and microconchs fall in the range of intraspecific variation accepted by Aguirre-Urreta and Rawson (1999) for this species (compare our Figs. 8B, E and K with their Figs. 5h, i and n). As in the Argentinean material, microconchs show a significant variation in rib density, degree of inflation, as well as in strength and frequency of constrictions and flares.

Outside southern South America, a single specimen was reported from south-east France by Autran (1993) as O. (Lemurotephanus) permolestus. As already noted by Bulot (1990a) and Aguirre-Urreta and Rawson (1999), this record is based on the misidentification of macroconch forms of O. (O.) nicklesi.

4. Biostratigraphic implications

As in the Neuquen Basin, the genus Olcostephanus occurs at two main distinct levels. The lower one is characterized by a monospecific assemblage of O. (O.) atherstoni, while the upper one is marked by the co-occurrence of O. (V) permolestus with various Neocomitidae such as N. (Neocomites) peregrinus, Neocomites (Sabbaiceras) beaumugnensis and Rodighieroites cardulus.

Both O. (O.) atherstoni and O. (V) permolestus were retained by Aguirre-Urreta and Rawson (1997, 1999) as index species for zones and subzones of the Valanginian of the Neuquen Basin (Fig. 9). As already pointed out by those authors, the lower and middle part of the O. (O.) atherstoni Zone, O. (O.) atherstoni and Karakaschiceras attenuatum subzones, span the Lower/Upper Valanginian boundary on evidence of ammonites common to Argentina and the Mediterranean Tethys.

Until now, O. (O.) atherstoni was considered by one of us (L.G.B.) as the southern hemisphere counterpart of the North Tethyan species O. (O.) guebhardi. As discussed above in the light of the Chilean material, we are now convinced that the two taxa should be considered as synonyms. For the reasons given in our discussion of the intraspecific variability of O. (O.) atherstoni, we therefore consider that the base of the Argentinean O. (O.) atherstoni Zone correlates with the middle part of the B. campylotoxus Zone of the Mediterranean zonal scheme (Fig. 9).

Even if the First Apparition Data (FAD) of Karakaschiceras sensu Bulot and Thieuloy (1995) and Neohoploceras Spath, 1939 occur at the base of the K. biassalense Subzone of the Mediterranean zonal scheme, we herein consider that the Argentinean K. attenuatum Subzone better correlates with the K. pronecostatum Subzone of the Mediterranean zonal scheme. This view is supported by the fact that Neohoploceras arnoldi sensu Aguirre-Urreta (1998) is closely allied, if not identical, to Neohoploceras gr. depereti/schardti sensu Bulot and Thieuloy (1995). Similarly, the general morphology of K. attenuatum (Behrensen, 1892) and K. neumayri (Behrensen, 1892) is closer to that of the group of K. pronecostatum Felix, 1891, including K. quadristrangulatum (Sayn, 1907), than to the late Lower Valanginian forms of the K. biasselense/inostranzewi plexus. As a consequence, the correlation proposed herein is slightly different from that formerly published by Rawson (1999, 2007) and Aguirre-Urreta et al. (2007).

 

FIG. 9. Ammonite zonal scheme for the Chanarcillo Basin and proposed correlation
with the Neuquen Basin (Aguirre-Urreta and Rawson, 1999; Rawson, 1999) and the
West Mediterranean Province (Reboulet et al., 2011).

 

So far, the Argentinean O. (V.) permolestus Subzone has been correlated with the O. (O.) nicklesi Subzone of the Mediterranean ammonite scale (Aguirre-Urreta and Rawson, 1999, p. 356; Aguirre-Urreta et al., 2007; Rawson, 2007). As Viluceras is unknown outside southern South America, this view was mainly based on the co-occurrence O. (O.) mingrammi (Leanza), an evolute Olcostephanus, that shows some morphological affinities with the plexus of O. (O.) nicklesi Wiedmann and Dieni, 1968. Nevertheless, those authors also noted, that in south western Europe, the range of evolute Olcostephanus s. str. started in the N. peregrinus Subzone and carried on in the C. furcillata Subzone with such species as O. (O.) detonii (Rodighiero, 1919) and O. (O.) mittreanus (d’Orbigny, 1850). Our new material shows clearly that O. (V) permolestus is associated with Neocomites (N.) peregrinus in Chile. We therefore suggest that the O. (O.) permolestus Subzone correlates with the N. peregrinus Subzone of the Mediterranean standard scale of Reboulet et al. (2011) (Fig. 9).

The stratigraphic record of the Chanarcillo Basin represents a bridge between the Neuquen Basin and the Tethys region, where the typical Andean faunas were documented in association with Tethysian ammonites which allows us to precise the former biostratigraphic long distance correlations, for the Valanginian ammonite biozones.

Acknowledgements

This research was supported by the following projects:

'Levantamiento Hoja Vallenar' (SERNAGEOMIN) and 'Bilans et processus des systèmes carbonatés' (FRE CNRS 2761, University of Marseille I). Additional financial support was provided by UMR CNRS 5563-IRD (University of Toulouse III).

Access to collections in Chile was made possible by courtesy of Prof. E. Pérez d’A. and Dr. A. Rubilar (SERNAGEOMIN). Prof. M.B. Aguirre-Urreta (Universidad de Buenos Aires) and Prof. P.F. Rawson (Scarborough) are gratefully acknowledged for access to collections in their care and fruitful discussions on the systematics and biostratigraphy of the olcostephanids of the Neuquén Basin. Personal communications by Prof. Fernando Etayo-Serna (Bogotá) and Dr. C. Arévalo (SERNAGEOMIN) have improved an original draft of this manuscript.

The photographic work was carried out by Mrs. A. Fontana (Santiago) and A. Arnoux (University of Marseille). For their help in the field, we are also very grateful to Mr. P Herrera (SERNAGEOMIN, Copiapó) and Prof. E. Jaillard (University of Grenoble).

 

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Manuscript received: July 16, 2014; revised/accepted: January 27, 2015; available online: February 05, 2015.

 

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