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Lacustrine strata of the Los Rastros Formation (Middle to Upper Triassic) at …


Biology Articles » Paleobiology » Micropaleobiology » Miospores and chlorococcalean algae from the Los Rastros Formation, Middle to Upper Triassic of central-western Argentina » Systematic palynology

Systematic palynology
- Miospores and chlorococcalean algae from the Los Rastros Formation, Middle to Upper Triassic of central-western Argentina

A complete list of palynomorphs recovered at Río Gualo section is given. Spore and pollen grains genera are listed alphabetically. Taxa are only described systematically, in the case of the emendation of the genus Variapollenites Ottone, or when an additional comment was deemed requisite.

Spores

Anapiculatisporites sandrae Ottone in Ottone et al . 1992
Aratrisporites compositus Volkheimer and Zavattieri 1991
Aratrisporites sp. cf. A. parvispinosus Leschik 1955
Baculatisporites comaumensis (Cookson) Potonié 1956
Biretisporites sp.
Cadargasporites baculatus de Jersey and Paten 1964 emend . Reiser and Williams 1969
Cadargasporites cuyanensis Azcuy and Longobucco 1983
Calamospora impexa Playford 1965
Clavatisporites conspicuus Playford in Playford et al. 1982
Clavatisporites sp.
Converrucosisporites cameronii (de Jersey) Playford and Dettmann 1965
Converrucosisporites sp.
Deltoidospora sp.
Leptolepidites volkheimeri Zavattieri 1986
Leptolepidites sp. cf. L. crassibalteus Filatoff 1975
Leptolepidites sp.
Lundbladispora spp.
Osmundacidites senectus Balme 1963
Osmundacidites wellmanii Couper 1958
Neoraistrickia sp.
Playfordiaspora cancellosa (Playford and Dettmann) Maheshwari and Banerji 1975
Polypodiisporites ipsviciensis (de Jersey) Playford and Dettmann 1965
Punctatisporites sp.
Rugulatisporites nelsonensis Raine in de Jersey and Raine 1990
Rugulatisporites sp.
Uvaesporites verrucosus (de Jersey) Helby in de Jersey 1971

Pollen grains

Alisporites australis de Jersey 1962
Alisporites lowoodensis de Jersey 1963
Alisporites parvus de Jersey 1962
Alisporites spp.
Araucariacites australis Cookson 1947
Brachysaccus sp. A
Cedripites tectus Ottone and Rodríguez Amenábar 2001
Cedripites sp. cf. C. pannellai Jain 1968
Cedripites sp. cf. C. priscus Balme 1970
Chordasporites australiensis de Jersey 1962
Cycadopites sp. cf. C. andrewsii Cornet and Traverse 1975
Cycadopites sp. cf. C . follicularis Wilson and Webster 1946
Cycadopites sp. A
Equisetosporites cacheutensis Jain 1968
Inaperturopollenites nebulosus Balme 1970
Inaperturopollenites reidi de Jersey 1959
Lueckisporites spp.
Lunatisporites sp. cf. L. noviaulensis (Leschik) Foster 1979
Lunatisporites spp.
Platysaccus papilionis Potonié and Klaus 1954
Platysaccus queenslandi de Jersey 1962
Protodiploxypinus sp.
Protohaploxypinus sp. cf. P. limpidus (Balme and Hennelly) Balme and Playford 1967
Protohaploxypinus sp. cf. P. microcorpus (Schaarschmidt) Clarke 1965
Protohaploxypinus sp. cf. P. varius (Bharadwaj) Balme 1970
Protohaploxypinus spp.
Pteruchipollenites spp.
Striatopodocarpites pantii (Jansonius) Balme 1970
Variapollenites curviplicatus Ottone in Ottone et al . 1992
Variapollenites rhombicus Ottone in Ottone et al. 1992
Variapollenites trisulcus Ottone in Ottone et al. 1992
Vitreisporites pallidus (Reissinger) Nilsson 1958

Phytoplankton

Botryococcus sp.
Plaesiodictyon mosellanum ssp. perforatum Wille 1970
Plaesiodictyon mosellanum ssp. symmetricum Brenner and Foster 1994

Genus Brachysaccus Mädler 1964

Type species. Brachysaccus ovalis Mädler 1964.

Remarks. Following Potonié (1970) and de Jersey (1972), it is considered that Brachysaccus includes monosulcate pollen grains having an endoreticulate exine. The monosulcate character of the genus is clearly evident in Mädler's (1964) illustration of the type. Amb and sulcus shape are extremely variable in monosulcate pollen grains displaying a homogeneous or granular ektexine. This is extensively discussed below under the genus Cycadopites Wodehouse ex Wilson and Webster 1946. In Brachysaccus , a monosulcate pollen grain with an alveolar ektexine, amb and sulcus shape are relatively uniform, and its structured ektexine probably controls, in different states of pollen hydration, the contraction or stretching of the wall to a significant extent.

Brachysaccus sp. A
Figures 4.J, L

Material estudiado. BAFC-PI 1431 (11) T30/2; BAFC-PI 1431 (11) G41/4.

Description. Monosulcate pollen grain. Amb almost circular. Wall endoreticulate (alveolar ektexine). Exine thickness 3.5-5.5 µm. Ektexine infratectal bacula-like elements forming brochi, 1-2.5 µm in diameter, which are perpendicularly disposed all around the grain. Prothallic pole without apertures, lacking folds or splits. Germinal pole defined by a narrow sulcus, ca. about one tenth of the grain diameter. Sulcus margins occasionally accompanied by folds.
Measurements (25 specimens). Equatorial diameter 55(85)106 µm.
Comparison. Judging from its illustration, Brachysaccus triassicus Tripathi et al . 1990 seems to be comparable to B. sp. A, however, the Indian form was originally described as disaccate. B . sp. A differs from B. ovalis Mädler 1964 and B. eskensis de Jersey 1972 by its almost circular amb. B. indicus Kumaran and Maheshwari 1980, originally also described as disaccate, displays an elliptical to oval amb. The specimen figured by Zavattieri (1991a) as Brachysaccus cf. neomundanus (Leschick) Mädler 1964, from the Triassic Las Cabras Formation, Cuyo Basin, Argentina, is disaccate.

Genus Cycadopites Wodehouse ex Wilson and Webster 1946

Type species. Cycadopites follicularis Wilson and Webster 1946.

Discussion. Following Ottone and García (1991), Cycadopites includes monosulcate pollen grains having a fusiform, oval, subpolygonal to subcircular amb, with a homogeneous wall (homogeneous or granulate ektexine), prothallic pole without apertures; germinal pole defined by a sulcus extending over the full grain length, and absent or minute surficial sculpture. Extant pollen grains of Ginkgophytes, Cycadophytes and some Magnoliaceae, together with fossil pollen grains of Bennettitales, Caytoniales, ?Corystospermales and Pentoxylales are entirely comparable to those here observed (Ottone and García, 1991). Figures 6.A-F are different specimens of extant Ginkgo biloba Linnaeus collected in situ from a microsporangiate organ in Buenos Aires, and mounted, as well as the fossil material, in unstained glycerin jelly. See also the different specimens of G. biloba illustrated by Audran and Masure (1978, plate I). In G . biloba , pollen grain shape (and sulcus shape) reflect differences in orientation within the slide or, most probably, variable states of pollen grain hydration. Furthermore, generic and specific distinctions of fossil pollen grains similar to G. biloba are impossible only using transmitted light microscopy (Ottone and García, 1991). In the Triassic of Argentina, Jain (1968), Herbst (1970), Zavattieri (1987, 1991b, 1992) and Zavattieri and Batten (1996) used different genera for monosulcate pollen grains; e.g ., Bharadwajapollenites Jain 1968, Cycadopites Wodehouse ex Wilson and Webster 1946, Monosulcites Cookson ex Couper 1953, Megamonoporites Jain 1968, Pilasporites Balme and Hennelly emend . Jain 1968, Punctamonocolpites Pierce 1961, and Sulcatopites Jain 1968. These forms should be Cycadopites in view of the above discussion.

Cycadopites sp. cf. C. follicularis Wilson and Webster 1946
Figures 5.B-C

Material estudiado. BAFC-PI 1432 (2) T41/4; BAFC-PI 1432 (2) K53/4.

Description. Monosulcate pollen grain, wall smooth, ca. 0.8-1 µm thick.
Measurements (3 specimens). Equatorial diameter 45(46)48 µm.
Comparison. The Argentine specimens are comparable, except for their thinner exine, with the miospores described by Wilson and Webster (1946). Balme (1970) also included in the species Cycadopites follicularis specimens with an exine about 1 µm thick.

Cycadopites sp. A
Figures 5.A, D

Material estudiado. BAFC-PI 1432 (2) Q50/0; BAFC-PI 1433 (1) J39/3.

Description. Monosulcate pollen grain, wall smooth to chagrinate, ca. 1.2 µm thick. In fusiform specimens, sulcus margin occasionally folded.
Measurements (8 specimens). Equatorial diameter 62(77)101 µm.
Comparison. Specific differences within the genus are often subtle and hard to observe; hence, Cycadopites sp. A superficially resembles many species referred to Cycadopites or related genera. Cycadopites sp. A essentially differs from the type of Cycadopites by its larger size. It resembles specimens referred by Jain (1968) to Pilasporites calculus Balme and Hennelly 1956 and P. crateriformis Jain 1968. Cycadopites linae Herbst 1965 and C. magnus Herbst 1965, cited later by Herbst (1970), Jain (1968) and Zavattieri (1987, 1991b), are also similar to Cycadopites sp. A.

Genus Equisetosporites Daugherty emend . Pocock and Jansonius in Pocock, 1964

Type species. Equisetosporites chinleana (Daugherty) Pocock and Jansonius in Pocock, 1964.

Equisetosporites cacheutensis Jain 1968
Figure 4.K

Material estudiado. BAFC-PI 1431 (11) Z26/2.

Discussion. Following Jain (1968), this species is retained in Equisetosporites . Generic re-attribution is not justified for E. cacheutensis because, in acceptance of its probable ephedroid affinity, pollen grains that display a clear separation between the nexine (endexine?) and the sexine (ektexine?) also characterize extant Ephedra americana Humboldt and Bonpland ex Willdenow (Steeves and Barghoorn,1959), and the Triassic Masculostrobus clathratus Ash 1972 (a probable gnetalean). The type species of Equisetosporites , E. chinleana Daugherty 1941, also displays a central endexinal core detached from its banded outer wall. However, attribution of E. cacheutensis to Equitetosporites , implies a slightly expansion of Pocock and Jansonius' (in Pocock, 1964) circumscription of the genus.

Genus Variapollenites Ottone in Ottone et al ., 1992, emend . Ottone

Type species. Variapollenites curviplicatus Ottone in Ottone et al. , 1992.

Discussion. Variapollenites was first described from the Triassic Rancho de Lata Formation, Main Cordillera, Argentina (Ottone et al ., 1992). The genus encompasses monosaccate pollen grains that display a reticulate pattern on the exine of both the saccus and corpus. Several well-preserved specimens of Variapollenites have been found at Río Gualo section, and also in equivalent horizons at the Hoyada de Ischigualasto. The Los Rastros specimens are better preserved than the ones of the type material, thus providing the basis for an emended generic diagnosis. The Los Rastros specimens show differences in ektexine endoreticulum of opposite faces of the corpus not clearly distinguishable in the (lesser preserved) type material due to preservation.
Emended diagnosis. Radial to bilaterally symmetrical monosaccate pollen grains. Tetrad mark absent. Ektexine endoreticulate, detached from endexine toward the equator. The endoreticulum shows a tendency to radial elongation with larger brochi towards the saccus margin (alveolar ektexine). Endexine forms an almost circular or roundly polygonal, mainly triangular or rhombic, corpus (polar view). Corpus margin exhibits a circumpolar fold system. On one face, the ektexine of the corpus is finely structured (ektexine incipiently alveolar?). On the opposite face, corpus ektexine is finely structured towards the equator, becoming smooth and thinner towards the center. Saccus of almost uniform width, not lobed, or constricted; tri- or quadrilobated.
Comparison. Aberrant extant monosaccate grains of Pinaceae (Vishnu-Mittre, 1957, pl. XX, 10) and Podocarpaceae (Pocknall, 1981, fig. 9, I) are comparable to the type species of Variapollenites , as are specimens figured as cf. Walchia by Reissinger (1950, pl. XVII, fig. 22) from the Lias of Germany, and Monosaccate, undet. by Dybkjaer (1988, pl. 6, fig. 7) from the Lias of Denmark. Walchites gradatus Bolkhovitina 1956, from the Jurassic of Russia, seems to be structurally similar to V. curviplicatus Ottone, but its corpus lacks a circumpolar fold system. Picea sp. from the Miocene of Oregon (Gray, 1964, pl. I, fig. 1) exhibits a morphology closely akin to that of V . rhombicus (for further comparison see Ottone et al ., 1992).

Variapollenites curviplicatus Ottone in Ottone et al. 1992
Figures 4.E-F, H

Material estudiado. BAFC-PI 1431 (11) C22/2; BAFC-PI 1431 (13) T26/1; BAFC-PI 1431 (11) C22/2.

Discussion. The species, as viewed in polar orientation, includes suboval monosaccates displaying a subcircular corpus. The saccus is not lobed. The specimens from Los Rastros often show, conversely to the ones of the type material, a saccus of variable width.

Variapollenites rhombicus Ottone in Ottone et al . 1992
Figures 4.G, I

Material estudiado. BAFC-PI 1431 (8) Q30/4; BAFC-PI 1431 (3) Q36/4.

Discussion. As viewed in polar orientation, the species includes suboval to subrectangular monosaccates with a roundly rhomboidal corpus. The saccus is quadrilobed and constricted at the apices of the corpus. The Los Rastros material include subrectangular forms with a slightly constricted saccus (figure 13), as well as specimens having a highly incised saccus.

Variapollenites trisulcus Ottone in Ottone et al . 1992
Figures 4.A-D

Material estudiado. BAFC-PI 1431 (14) W42/2; BAFC-PI 1431 (10) R37/3; BAFC-PI 1431 (12) Z39/1; BAFC-PI 1431 (11) Y42/0.

Discussion. The species, as viewed in polar orientation, includes subtriangular monosaccates with a roundly triangular corpus. The saccus is trilobate and often constricted at the corpus apices. The saccus of specimens from Los Rastros is, in some cases, less constricted that those of the type specimens.

Acknowledgements

The authors are indebted to C. Marsicano and S. Vigna whose comments and suggestions improved the manuscript; to A. Godeas for helpful advice; to C.L. Azcuy for providing the slides of Ginkgo biloba ; to A. Arcucci for an enjoyable productive field trip to La Rioja province; and to G.D. Holfeltz for laboratory processing and photographic printing. We also gratefully acknowledge the Buenos Aires University (UBA) and the National Research Council (CONICET) for the use of their facilities during this research. This investigation was mostly supported by UBA (TX 179) and CONICET (PIP 02228) grants.


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