Palynology of the Las Curtiembres Formation (Late Cretaceous, Salta Group Basin), Las Conchas Creek area, northwestern Argentina

Paula L. Narváez¹ and Ignacio F. Sabino²

¹Departamento de Geología y Paleontología, Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), Consejo Nacional de Investigaciones Científicas y Técnicas (CCT-CONICET- Mendoza), C.C. 330, 5500 Mendoza, Argentina. pnarvaez@lab.cricyt.edu.ar
²Cátedra de Geología Histórica, Facultad de Ciencias Naturales, Universidad Nacional de Salta, Buenos Aires 177, 4400 Salta, Argentina. ignaciosabino@yahoo.com.ar

Abstract. This study provides the first palynologic record of the Las Curtiembres Formation (Late Cretaceous, Salta Group Basin) in northwestern Argentina. Two palynologically productive samples were obtained from the Morales Member in the area of the Las Conchas creek, Salta Province. Nineteen morphospecies are recorded for the Formation. The samples show poor preservation of the specimens and low diversity. The palynomorph association is characterized by the prevalence of species that belong to the Ephedraceae (6 species with 57% of total abundance), possibly suggesting semiarid conditions and a warm-dry paleoclimate at the time of deposition. Low humidity could also be inferred from the low abundance and diversity of pteridophyte species and the presence of Cheirolepidiaceae (Classopollis sp.) and Proteaceae (Peninsulapollis gillii (Cookson) Dettmann and Jarzen). The pollen grain Peninsulapollis gillii is a chronostratigraphic indicator of an age not older than Campanian-Maastrichtian, which would be coincident with the previous dating (77±5 Ma) of the Las Conchas Basalt effusions.

Resumen. Palinología de la Formación Las Curtiembres (Cretácico Tardío, Cuenca del Grupo Salta), área de la quebrada Las Conchas, noroeste argentino. El presente estudio brinda el primer registro palinológico de la Formación Las Curtiembres (Cretácico Tardío, Cuenca del Grupo Salta) del noroeste argentino. Se obtuvieron dos muestras palinológicamente fértiles del Miembro Morales en el área de la quebrada de Las Conchas, provincia de Salta. Un total de 19 morfoespecies se identificaron para la formación. Las muestras presentan pobre preservación de los ejemplares y baja diversidad. La asociación de palinomorfos se caracteriza por un predominio de especies pertenecientes a las Ephedraceae (6 especies con una abundancia total de 57 %) que posiblemente indicarían condiciones semiáridas y un paleoclima cálido- seco al momento de la depositación. Esta baja humedad se podría inferir también por la baja abundancia y diversidad específica de pteridofitas y la presencia de Cheirolepidiaceae (Classopollis sp.) y Proteaceae (Peninsulapollis gillii (Cookson) Dettmann y Jarzen). El grano de polen Peninsulapollis gillii es un indicador cronoestratigráfico de edad no mayor que Campaniano-Maastrichtiano, lo que coincidiría con dataciones del Basalto Las Conchas (77±5 Ma).

Key words. Palynology; Late Cretaceous; Las Curtiembres Formation; Salta Group Basin.

Palabras clave. Palinología; Cretácico Tardío; Formación Las Curtiembres; Cuenca del Grupo Salta.

Introduction and geologic setting

In this paper, we present the first palynologic record for the Late Cretaceous Las Curtiembres Formation (Pirgua Subgroup, Salta Group) in northwestern Argentina (figure 1). The possible paleoenvironmental conditions at the time of deposition are also inferred.

Figure 1. Location map / mapa de ubicación. 1, Pre-Cretaceous outcrops / afloramientos pre-cretácicos; 2, Pirgua Subgroup / Subgrupo Pirgua; 3, Balbuena and Santa Bárbara Subgroups / Subgrupos Balbuena y Santa Bárbara; 4, Post-incaic outcrops / afloramientos post-incaicos; 5, State boundary / límite provincial; 6, Palo Seco creek (PS) location / sección de la quebrada de Palo Seco (PS).

The Salta Group (Turner, 1959) constitutes the basin fill of the rift developed from the Neocomian to the Middle Eocene in northwestern Argentina (Salfity and Marquillas, 1994). The Pirgua Subgroup (Reyes and Salfity, 1973), which represents the synrift fill of the basin, is composed of red beds and volcanic rocks (Marquillas et al., 2005).
In the Alemanía depocenter, the Pirgua Subgroup comprises, from base to top, the La Yesera, Las Curtiembres and Los Blanquitos formations (figure 2). The lower La Yesera Formation (Yacutuy Member) is composed of conglomerates; the middle part of siltstones and sandstones (Las Chacras Member), and the upper section of conglomerates similar to those of the base (Yacutuy Member) (Sabino, 2004). The overlying Las Curtiembres Formation is composed of fine-grained sediments widely distributed in the basin. During the rift climax, the Las Conchas Basalt (Reyes and Salfity, 1973) was formed by pyroclastic and lava flows (Galliski and Viramonte, 1988). Green siltstones, whitish sandstones and micritic limestones of the lacustrine Morales Member accumulated in this volcanic event (Salfity and Marquillas, 1994; Sabino, 2004) (figure 3). The Morales Member, which belongs to the middle section of the Las Curtiembres Formation, is known for its fossil pipid frogs that appear together with badly preserved plant remains (Reig, 1959) and clupeiform fish (Báez, 1981). During the late synrift, the coarse-grained sandstones and conglomerates of the Los Blanquitos Formation were deposited.

Figure 2. Stratigraphic log of the Salta Group in the southern area of the basin / columna estratigráfíca del Grupo Salta en el área austral de la cuenca.

Figure 3. Stratigraphic log of the Morales Member in the Palo Seco creek (modified from Damiani, 2006) / columna estratigráfica del Miembro Morales en la quebrada de Palo Seco (modificado de Damiani, 2006).

The age of the Pirgua Subgroup is known by scarce radiometric dating of basaltic rocks (Bossi and Wampler, 1969; Valencio et al., 1976; Reyes et al., 1976), which indicate Neocomian to Late Senonian ages, and by Senonian dinosaurs of the upper Los Blanquitos Formation (Powell, 1979). Las Conchas Basalt was dated 80 to 74 Ma (Valencio et al., 1976; Reyes et al., 1976; Galliski and Viramonte, 1988).
The samples were collected from the Palo Seco creek, an affluent of the Las Conchas creek (Alemanía depocenter of the Salta Group Basin) (figure 1), which is the type area of the Morales Member. The Palo Seco creek is located 7 km north of the Morales bridge of the Las Conchas creek, where the type section of the Morales Member is proposed (Damiani et al., 2006). In this section, the thicknesses of the Las Curtiembres Formation and the Morales Member are 500 m and 27.5 m respectively, and the base of the member is located 180 m above the base of the Las Curtiembres Formation (figure 3).
There are few previous palynologic papers dealing with the Cretaceous of the Salta Group Basin. Palynologic studies carried out by Moroni (1982) at the Yacoraite Formation (Maastrichtian-Danian, Balbuena Subgroup) in the Lomas de Olmedo Subbasin cores, revealed forms resembling Aquilapollenites magnus Regali, Uesugui and Santos 1974, Crassitricolporites brasiliensis Herngreen 1972, Zlivisporis blanensis Pacltová 1961, Gabonisporis vigourouxii Boltenhagen 1967, Psilastephanosporites cf. brasiliensis Regali, Uesugui and Santos 1974, and numerous polyplicated grains. Moreover, in the Lomas de Olmedo Subbasin, Late Cretaceous palynomorphs have been found 100 m below the top of the Los Blanquitos Formation (Moroni, 1985 as cited in Carlé et al., 1991), however the identified specimens were not listed. Quattrocchio et al. (2005) report a Late Senonian palynoflora from the passage beds between the Los Blanquitos and Lecho formations in the Vilches locality. They describe an association of typical Mesozoic taxa together with some angiospermous pollen previously observed in younger sediments and at lower latitudes of tropical South America and Africa. Other relevant studies concerning specifically the Alemanía Subbasin were those of the Danian Tunal Formation (Quattrocchio et al., 1988; Quattrocchio and Volkheimer, 1988, 2000a, 2000b; Volkheimer et al., 2006). Most of the species encountered during the present study were previously mentioned in an abstract without further analysis (Narváez et al., 2005).

Materials and methods

Four samples from the outcrops of the Palo Seco creek were processed for palynologic studies, two of them yielded palynomorphs (figure 3). All the species described here belong to the sample PL-20 from the top of the Morales Member that contained the best preserved palynoflora.
The extraction of palynomorphs from the samples was done in the Paleopalynologic Laboratory of the Argentine Institute of Snow Research, Glaciology and Environmental Sciences (IANIGLA, Mendoza), using standard palynologic processing techniques (Volkheimer and Melendi, 1976), which involve crushing the samples with mortar and posterior treatment with hydrochloric and hydrofluoric acids. The palynologic slides are stored at the Paleopalynology Collection of the Department of Geology and Paleontology at IANIGLA as numbers of catalogue: 8361 to 8364 MPLP (Mendoza-Paleopalinoteca-Laboratorio- Paleopalinología).
The material was studied using a Leitz Dialux 20 microscope. Coordinates of specimens are denoted by an England Finder reference. The palynologic analysis includes the systematics, the comparison of the palynomorphs with modern taxa and the statistic study of the assemblage. Full description is given only of those species with open assignation.

Taxonomic list of identified species

Fungi

Diporisporites oblongatus Ke and Shi 1978 (Figure 4.1)

Figure 4. Spores and gymnospermous pollen grains / esporas y polen de gimnospermas. 1, Diporisporites oblongatus Ke and Shi 1978, 8364E: J36/3 MPLP; 2, Baculatisporites sp., 8364F: L39/1 MPLP; 3, Deltoidospora minor (Couper) Pocock 1970, 8364O: C24 MPLP; 4, Inaperturate indet, 8364D: F40/3 MPLP; 5, Classopollis sp., 8364N: S25/3 MPLP; 6, Singhia sp., 8364K: K43/1 MPLP; 7, Cycadopites nitidus (Balme) de Jersey 1964, 8364F: K32 MPLP; 8, Ephedripites caichigüensis (Volkheimer and Quattrocchio 1975) nov. comb., 8364M R22 MPLP; 9, Ephedripites multicostatus Brenner 1963, 8364K: D38/1 MPLP; 10, Ephedripites sp. 1; 8364L: O41 MPLP; 11, Ephedripites sp. 2, 8364L: Z27 MPLP; 12, Gnetaceaepollenites sp., 8364D: D45 MPLP. Scale bar / escala gráfica = 10 mm.

Pteridophytes (trilete spores)

Baculatisporites sp. (Figure 4.2)
Deltoidospora minor (Couper) Pocock 1970 (Figure 4.3)

Gymnosperms

Classopollis sp. (Figure 4.5)
Cycadopites nitidus (Balme) de Jersey 1964 (Figure 4.7)
Ephedripites caichigüensis (Volkheimer and Quattrocchio 1975a) nov. comb. (Figure 4.8)
Ephedripites multicostatus Brenner 1963 (Figure 4.9)
Ephedripites sp. 1 (Figure 4.10)
Ephedripites sp. 2 (Figure 4.11)
Gnetaceaepollenites sp. (Figure 4.12)
Singhia sp. (Figure 4.6)

Angiosperms

Liliacidites vermireticulatus Archangelsky and Zamaloa 1986 (Figure 5.3)
Peninsulapollis gillii (Cookson) Dettmann and Jarzen 1988 (Figure 5.1)
Rhoipites sp. cf. R. sp. B Quattrocchio and Volkheimer, 1988 (Figure 5.4)
Rousea patagonica Archangelsky 1973 (Figure 5.5)
Striatricolporites sp. (Figure 5.2)
Tricolpites sp. (Figure 5.6)
Triporopollenites sp. (Figure 5.7)

Figure 5. Angiospermous pollen grains / polen de angiospermas. 1, Peninsulapollis gillii (Cookson) Dettman and Jarzen 1988, 8364S: F41/2 MPLP; 2, Striatricolporites sp., 8364M: U40/2 MPLP; 3, Liliacidites vermireticulatus Archangelsky and Zamaloa 1986, 8364K: D38 MPLP; 4, Rhoipites sp. cf. R. sp. B (Quattrocchio and Volkheimer 1988), 8364D: X26 MPLP; 5, Rousea patagonica Archangelsky 1973, 8364T: U41/3 MPLP; 6, Tricolpites sp., 8364O: Y22/1 MPLP; 7, Triporopollenites sp., 8364K: F35/4 MPLP. Scale bar / escala gráfica = 10 mm.

Inaperturate indet (Figure 4.4)

Systematic palaeontology

Genus Baculatisporites Pflug and Thompson in Thompson and Pflug 1953

Type species. Baculatisporites primarius (Wolff) Pflug and Thompson in Thompson and Pflug 1953.

Baculatisporites sp.
Figure 4.2

Description. Trilete spore. Amb subtriangular. Straight laesurae almost reaching the equator. Surface ornamented with numerous cylindrical baculae (3 μm length, 1 mm width), many of them fused at the base. Also some verrucae interspersed. Exine 1 μm thick.
Dimensions. 43 μm equatorial diameter (1 specimen).

Studied material. 8364F: L39/1 MPLP.

Comparison. Our specimen resembles B. kachaikensis Llorens and A. Archangelsky 2005 described for the Lower Cretaceous of the Austral Basin, Argentina (Archangelsky and Llorens, 2005). Although the latter presents broader baculae with cones and spinulae but no verrucae.
Botanical affinity. Osmundaceae, Hymenophyllaceae.

Genus Classopollis (Pflug) Pocock and Jansonius 1961

Type species. Classopollis classoides (Pflug) Pocock and Jansonius 1961.

Classopollis sp.
Figure 4.5

Description. Monoporate pollen grain. Ovoid in equatorial view. Equatorial thickening of 3-6 μm with approximately 6 anastomosed endostriae. Scabrate exine of ca. 1 μm width. Pore diameter: 14 mm.
Dimensions. 28 x 21 μm (1 specimen).

Studied material. 8364N: S25/3 MPLP.

Remarks. The presence of only one specimen in equatorial view does not allow an assignation at the species level although must be mentioned its morphologic similarities with C. classoides (Pflug) Pocock and Jansonius 1961.
Botanical affinity. Cheirolepidiaceae.

Genus Ephedripites Bolkhovitina 1953

Type species. Ephedripites mediolobatus Bolkhovitina 1953.

Ephedripites caichigüensis (Volkheimer and Quattrocchio 1975a) Narváez and Sabino nov. comb.
Figure 4.8

Basionym. Equisetosporites caichigüensis Volkheimer and Quattrocchio 1975a. Ameghiniana 12, pp. 236, plate 10, figs. 15-16; plate 11, figs. 1-4; holotype 893j BA Pb 42.8/100.5, plate 10, figs. 15-16.

Dimensions. Polar: 32-66 μm, equatorial: 21-26 μm (10 specimens).

Studied material. 8364K: H45/1, V26/3 MPLP; 8364L: L33/4, L36/3, T28/2, T35, V45/4, W40, Z25/3 MPLP; 8364M R22 MPLP.

Remarks. Volkheimer and Quattrocchio (1975a) originally described the species as Equisetosporites caichigüensis. We make the new combination and use Ephedripites instead, as it is more indicative of the botanical affinity of the genus.
Previous records in Argentina. Jurassic to Lower Cretaceous of the Neuquén Basin (Volkheimer and Quattrocchio, 1975a,b; Quattrocchio, 1980a; Volkheimer, 1980; González-Amicón and Volkheimer, 1982a,b; Prámparo and Volkheimer, 1999, 2002).
Botanical affinity. Ephedraceae.

Ephedripites sp. 1
Figure 4.10

Description. Polyplicate pollen grains, oval to ellipsoidal in outline. The sculpture consists of approximately 14-25 narrow ridges (1-2.5 μm width) that run obliquely along the longitudinal axis and converge at its ends. Fine furrows alternating with ridges (0.1-0.25 μm). The grain shows a cross pattern due to the superposition of both faces. Exine: 0.4-1 μm thick.
Dimensions. Polar: 32-54 μm, equatorial: 15.5-24 μm (21 specimens).

Studied material. 8364K: F45, F45/4, H44/1, L32/2, O40/3 MPLP; 8364L: L43/1, O36/2, O41, P27/1, Q42/4, T28/3, T35/3, U34/2, Y31/1, Y45, X45 MPLP; 8364M: O42/3, S41, U29/1, W27/1, Y31/1 MPLP.

Remarks. Some grains show a wider furrow extending along the grain from pole to pole that could be interpreted as the colpus.
Comparison. The specimens are similar to Ephedripites torosus Mädler 1964 described in Cretaceous associations from Gabon (Azéma and Boltenhagen, 1974).
Botanical affinity. Ephedraceae.

Ephedripites sp. 2
Figure 4.11

Description. Polyplicate pollen grain, ellipsoidal in outline. Exine composed of numerous narrows ridges (0.5-0.7 μm width) running obliquely to the longitudinal axis and merging in areas close to the apices. The furrows alternating with the ridges are of approximately 0.1 μm width. Exine: 0.5 μm thick.
Dimensions. 56 x 29 μm (1 specimen).

Studied material. 8364L: Z27 MPLP.

Comparison. The surface pattern of our specimen is similar to Steevesipollenites multilineatus Stover 1964, found in Brazilian associations (Herngreen, 1973; Regali et al., 1974), although it does not have the clear thickening of the exine in the poles characteristic of Steevesipollenites.
Botanical affinity. Ephedraceae.

Genus Gnetaceaepollenites Thiergart 1938

Type species. Gnetaceaepollenites ellipticus Thiergart 1938.

Gnetaceaepollenites sp.
Figure 4.12

Description. Polyplicate pollen grains, oval to almost rounded in outline with flat ends. Exine with up to 10 parallel ridges (2.5-7.5 μm width) disposed obliquely to the longitudinal axis, reaching the poles but not coalescing. The furrows have almost the same width as the ridges (2.5-9 μm). Exine: 0.5 mm thick.
Dimensions. Polar: 54-56 μm, equatorial: 36-44 μm (3 specimens).

Studied material. 8364D: N27/2, D45 MPLP; 8364K: O33/2 MPLP.

Remarks. After a taxonomic summary of several polyplicated Ephedraceae genera, Lima (1980) includes in Gnetaceaepollenites all the Ephedra type grains with ridges that do not fuse at the ends.
Comparison. The specimens in our samples are similar to some of the grains mentioned by Herngreen (1973) as belonging to the Ephedripites barghoornii/staplinii formgroup, in the Albian-Cenomanian of Brazil.
Botanical affinity. Ephedraceae.

Genus Rhoipites Wodehouse 1933

Type species. Rhoipites bradleyi Wodehouse 1933.

Rhoipites sp. cf. R. sp. B Quattrocchio and Volkheimer 1988
Figure 5.4

Dimensions. 41 x 21 μm (1 specimen).

Studied material. 8364D: X26 MPLP.

Remarks. The presence of only one specimen does not allow a conclusive assignation to the species R. sp. B described by Quattrocchio and Volkheimer (1988).
Previous records in Argentina. Rhoipites sp. B was found in the Late Cretaceous (Maastrichtian) of the Neuquén Basin (Papú, 2002), the Paleogene of the Salta Group Basin (Quattrocchio and Volkheimer, 1988; Quattrocchio et al., 1997; 2000; Ruiz et al., 1999, Volkheimer et al., 2006) and in the Eocene-Miocene Colorado Basin (Guerstein, 1990; Ruiz et al., 1999).

Genus Singhia Srivastava 1968

Type species. Singhia diversus (Stover) Srivastava 1968.

Singhia sp.
Figure 4.6

Description. Polyplicate pollen grain, ellipsoidal to slightly rounded in outline. Exine with 5 ridges on one face of 1.9-2.3 μm width each one. The ridges run parallel to the longitudinal axis and coalesce with each other near their ends.
Dimensions. 32 x 22 μm (1 specimen).

Studied material. 8364K: K43/1 MPLP.

Comparison. It is similar to Gnetaceaepollenites diversus Stover 1964 (Regali et al., 1974) but with less number of ridges.
Botanical affinity. Ephedraceae.

Genus Striatricolporites (Van der Hammen) ex Leidelmeyer 1966

Type species. Striatricolporites pimulis Leidelmeyer 1966.

Striatricolporites sp.
Figure 5.2

Description. Tricolporate, oblate pollen grain. Colpi almost reaching the poles. Pores with diffuse borders (4.5-7 μm equatorial lenght). Thin exine of ca. 1 μm thickness. Striated tectum with lumina of less than 0.5 μm width. Dichotomous and anastomosed striae, uniformly arranged on the surface and mostly running along the polar axis.
Dimensions. 27 μm equatorial diameter (1 specimen).

Studied material. 8364M: U40/2 MPLP.

Comparison. S. gamerroi Archangelsky 1973 presents the same sculpture but with a subprolate to prolate shape (Archangelsky, 1973).
Botanical affinity. Unknown.

Genus Tricolpites Cookson ex Couper 1953

Type species. Tricolpites reticulatus Cookson ex Couper 1953.

Tricolpites sp.
Figure 5.6

Description. Tricolpate, oblate pollen grain. Convex mesocolpia. Colpi incised ¾ distance to pole. Entire surface with uniform reticulum, lumen size 0.5 mm in diameter. Exine 0.8 μm thick.
Dimensions. 45 μm equatorial diameter (1 specimen).

Studied material. 8364O: Y22/1 MPLP.

Comparison. T. reticulatus Cookson ex Couper 1953 has the same surface ornamentation but the equatorial diameter is generally smaller (20 (26) 32 μm, Jarzen and Dettmann, 1989).
Botanical affinity. Gunnera, Haloragaceae.

Genus Triporopollenites Pflug and Thomson in Thomson and Pflug 1953

Type species. Triporopollenites coryloides Pflug in Thomson and Pflug 1953.

Triporopollenites sp.
Figure 5.7

Description. Triporate pollen grain, amb subtriangular with convex sides. Equatorial pores slightly aspidate at the angles. Pore canal diameter ca. 3.5-4.5 μm. Exine around the pores slightly thickened, forming a weak annulus around the aperture of 3-4 μm thick. Exine elsewhere scabrate, approximately 1 μm thick.
Dimensions. 38-41 μm equatorial diameter (2 specimens).

Studied material. 8364K: F35/4 MPLP; 8364L: Z35/1 MPLP.

Comparison. The description given here coincides mostly with T. sp. from the Neogene of Papua New Guinea (Playford, 1982), except from the larger size of the latter (48-56 μm). Our specimen also resembles T. sp. D illustrated in Braman (2001) but no description is given in his paper to corroborate the correspondence.
Botanical affinity. Unknown.

Inaperturate indet.
Figure 4.4

Description. Inaperturate specimens, oval in outline. Finely scabrate surface. Thin walls (0.5 mm thick), with many folds.
Dimensions. 46-51 μm (2 specimens).

Studied material. 8364D: F40/3 MPLP; 8364U: R43/2 MPLP.

Discussion

Both palynologically productive samples show a low abundance, diversity and poor preservation of palynomorphs. Only one could be used to describe this association. Several descriptions were based on single specimens and also there is a relatively high representation of indet. specimens, which are broken, with degraded walls or even colourless ("ghosts"), all conditions that make them impossible to be assigned to any known taxa (figure 6). Therefore, no accurate paleoenvironmental conclusions can be drawn from the samples. Hence, we only make inferences from this first recovered association of the Las Curtiembres Formation.

Figure 6. Circular diagram showing the relative percentages of the taxonomic groups found in the Las Curtiembres Formation, Las Conchas creek / diagrama circular mostrando los porcentajes relativos de los grupos taxonómicos encontrados en la Formación Las Curtiembres, quebrada Las Conchas.

Nineteen palynomorph species have been identified in this study. There is a clear predominance of gymnospermous pollen (79%), while the angiospermous pollen content is relatively low (11%) (figure 6). A high diversity of Ephedraceae is observed in the association, with 3 genera and 6 species (Ephedripites spp., Gnetaceaepollenites sp. and Singhia sp.) with 57 % of the total assemblage. This clear predominance of ephedroid pollen grains could be indicative of semiarid conditions and a warm paleoclimate at the time of deposition of these samples. The low humidity could also be inferred by the poor diversity of pteridophyte species, with only two species (Deltoidospora minor and Baculatisporites sp.) accounting for 3% of the entire spore-pollen assemblage, and the occurrence of the families Cheirolepidiaceae (Classopollis sp.) and Proteaceae (Peninsulapollis gillii).
At the base of the Morales Member more humid conditions are inferred, based on the abundance of green shales and micritic limestones that are interpreted as deposited during the maximum flooding of the synrift stage; however, the palynologic assemblage is interpreted as deposited in more arid conditions which correspond to the upper part of the member that is transitional with the red beds of the upper Las Curtiembres Formation.
The palynologic association described here has typical Middle and Late Mesozoic representatives
such as Classopollis or the ephedroid pollen. It also contains some long-ranging palynomorphs, such as Deltoidospora minor and Cycadopites nitidus, which cannot be used to infer age. Nevertheless, the presence of the species Peninsulapollis gillii is more relevant from the stratigraphic point of view, indicating an age not older than Campanian-Maastrichtian (Baldoni and Askin, 1993; Papú, 2002), which is in accordance with the 77±5 Ma dating of the pyroclastic and lava flows (Valencio et al., 1976).

Acknowledgements

Thanks to W. Volkheimer for the critical reading of the manuscript. We are also very grateful to E. Schrank, V. Barreda and M. Prámparo for their helpful comments to improve the manuscript. And to A. Moschetti for her valuable help in processing the samples. This research was supported by FONCyT-ANPCyT (Fondo para la Inversión Científica y Tecnológica - Agencia Nacional de Promoción Científica y Tecnológica, PICT 12419 and 12492), CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas, PIP 5222) and CIUNSa (Consejo de Investigaciones de la Universidad Nacional de Salta, projects 1220 and 1281). This study is part of the doctoral thesis of P. Narváez (PROBIOL, National University of Cuyo, Mendoza).

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Recibido: 2 de julio de 2007.
Aceptado: 4 de abril de 2008.