- © 2000 by AASP Foundation
Lower Carboniferous to Permian palynological zones are described from sections in central–western Argentina. In ascending stratigraphic order these zones are: (1) the Cordylosporites–Verrucosisporites (CV) Assemblage Biozone (spanning the Malimán and Cortaderas formations); (2) the Raistrickia densa–Convolutispora muriornata (DM) Assemblage Biozone (which is subdivided into: Sub-biozone A in the Guandacol and equivalent formations, Sub-biozone B in the Tupe Formation and equivalents, and Sub-biozone C in the upper part of the Santa Máxima and El Imperial formations); (3) the Fusacolpites fusus–Vittatina subsaccata (FS) Interval Biozone in the Bajo de Véliz and Tasa Cuna formations and equivalents, and (4) the Lueckisporites–Weylandites (LW) Assemblage Biozone in the De La Cuesta and Yacimiento Los Reyunos formations. The oldest biozone (CV) is assigned to the Early Carboniferous and the overlying DM Biozone to the Late Carboniferous. The uppermost FS and LW bio zones are Permian in age. Palynological records show the impact of the Early-to-Late Carboniferous glacial event, which caused significant changes in the composition of the assemblages from this interval. Further studies are necessary to calibrate a regional geological time scale in Gondwana, which is essential for precise correlation.
The present study is based on palynological data from Upper Palaeozoic sediments in the west-central part of Argentina, principally from the litho stratigraphic units of the Angualasto (Limarino and Césari, 1993) and Paganzo groups (Azcuy and Morelli, 1970). These sequences comprise the Lower Carboniferous–Upper Permian interval and contain fossiliferous assemblages that are comparable with other Gondwana palynofloras. They constitute some of the best-known fossil associations in the western Gondwana. Considering recent studies, a revised biostratigraphic characterization of the local assemblages is now possible. The distribution of miospores and acritarchs in sequences from localities within the Paganzo, Calingasta-Uspallata, Río Blanco and San Rafael basins are described in this paper. The most important localities described are shown in Text-Figure 1⇓; additional information can be obtained from the published sources cited herein.
New qualitative and quantitative bio stratigraphic information is presented. The zoning of the sequences involves a detailed systematic revision of palynomorphs from many assemblages. Palynological data obtained from these gondwanic strata have permitted the recognition of a succession of palynological assemblages of Carboniferous and Permian age. However, precise correlation of these successions to other bio stratigraphic frameworks previously proposed for the Gondwana is still the topic of discussion.
Figured specimens have designations from the Palynological Collection of the Geology Department, Buenos Aires University (BAFC-Pl), and the Palynological Collection of the B. Rivadavia Museum (BAPm). Provenance of the specimen is given as a number (in parentheses) that corresponds to to the collection site shown on the location map (Text-Figure 1⇑).
PREVIOUS ARGENTINIAN PERMIAN–CARBONIFEROUS PALYNOSTRATIGRAPHY
Earlier palynological biostratigraphic studies from non-marine Upper Carboniferous and Lower Permian sediments in Argentina are summarized in Text-Figure 2⇓. Azcuy (1979) developed a biostratigraphic framework for Argentina and Brazil based on the first appearance of form taxa that defined discrete intervals, termed “stages.” Later, Azcuy and Jelín (1980) named the lowest subdivision the Ancistrospora Palynozone, which is overlain by the Potonieisporites Palynozone and Palynozone III. Based on the first appearance of monosaccate pollen grains in the second palynozone, and the first appearance of striate pollen in the higher assemblage, the proposed succession appears to be valid. However, the biozones were established on data collected from only a few localities. The increased knowledge derived from more diversified assemblages from different geographic areas (and at different stratigraphic levels within a single sequence) indicated some potentially erroneous interpretations (Azcuy, 1986; Césari, 1986c). For example, monosaccate pollen grains, which were identified in both the Ancistrospora Palynozone (Azcuy and Gutiérrez, 1984) and the Potonieisporites Palynozone (defined on the basis of a single core sample from the Salinas de Mascasín well), are herein correlated with other described palynofloras previously assigned to the Ancistrospora Palynozone. Azcuy (1986) assigned the Salinas de Mascas in palynoflora to the uppermost Carboniferous because the overlying red beds appear to be be lower Permian based on correlation with outcrop sections. This correlation, however, has not been sufficiently documented to date.
Another biostratigraphic approach was proposed by Césari (1986c), who analyzed previously published (Césari, 1986a, b) quantitative and qualitative data in a Paleozoic sequence from the Paganzo. The discovery of monosaccate pollen grains as well as rare bisaccate striate grains in the Tupe Formation (bearing the classical NBG flora) in association with spores originally assigned to the Ancistrospora Palynozone, allowed this author to suggest a revision of the zonation. The Potonieisporites–Lundbladispora Biozone was therefore proposed and this was further subdivided into a lower Raistrickia–Plicatipollenites (RP) Sub-biozone and an upper Interval Sub-biozone. In the R-P Sub-biozone, all of the known palynofloras from the Tupe, Lagares, Malanzán and Jejenes formations that contain plant remains belonging to the NBG Assemblage Biozone were included. The Interval Sub-biozone was recognized in the Chacoparanense Basin, but not in the Paganzo Basin. Finally, the Cristatisporites Biozone in the Chacoparanense Basin (Russo et al., 1980) was considered equivalent to the Palynozone III of Azcuy and Jelín (1980), and is represented by the palynofloras from the Bajo de Véliz Formation. Later, Césari and Vázquez-Nístico, (1988) recorded monosaccate pollen grains from the Guandacol Formation, which underlies the Tupe Formation. In addition, palynofloras of the Interval stage were recognized in the central–western basins by Ottone (1987, 1989) and García (1995, 1996). The new information available from the Upper Carboniferous sequences suggests a possible subdivision of the R-P Sub-biozone and provides critical new data regarding the Interval stage. Furthermore, new findings on Lower Carboniferous palynofloras (Césari and Limarino, 1992, 1995) have expanded the scope of our palynofloristic knowledge in Argentina.
A biostratigraphic framework for the Chacoparaná Basin was proposed by Russo et al. (1980) based on assemblages that were considered to be Late Carboniferous to Middle Permian in age. The authors defined three biozones: the Potonieisporites–Lundbladispora, Cristatisporites, and Striatites zones. Later, Vergel (1993) subdivided the Cristatisporites Biozone into three stages, simply labeled as “lower,” “middle,” and “upper.” The Potonieisporites–Lundbladispora palynoflora is characterized by rare taeniate pollen and abundant trilete spores. Césari (1986c) considered this biozone to be equivalent to the “Interval Sub zone” in the Paganzo Basin (see Text-Figure 2⇑). This hypothesis was supported by Vergel (1993) who identified several species in common with the assemblages of the Paganzo Basin. The Cristatisporites Biozone is recognized by an increase in striate pollen grains and the first appearance of Granulatisporites micronodosus and G. confluens, among others.
According to Vergel (1993), the lower sub-biozone is characterized by the occurrence of Vittatina saccata, Protohaploxypinus perfectus and Mar supipollenites striatus. The middle sub zone is distinguished by the increase in striate and bisaccate pollen and by the absence of Convolutispora muriornata and Pseudoreticulati-sporites pseudoreticulata. The upper sub zone is defined based on an increase in the global abundance of striated and bisaccate pollen, which includes the first records of Striomonosaccites crucistriatus and Lunatisporites variesectus, among others. Finally, the Striatites Assemblage Biozone is characterized by the dominance (80%) of striate pollen grains.
Carboniferous and Permian sedimentation took place in a large area in western and northwestern Argentina (Archangelsky and Andreis, 1996). To the east, the pericratonic Paganzo Basin was a large (140,000 km2) depositional area located to the west of the cratonic area of Sierras Pampeanas (Azcuy et al., 1987a; Limarino et al., 1996a). Mainly continental sedimentation started during the early Late Carboniferous and the basin was filled by the Late Permian. In contrast, to the west both the Río Blanco and Calingasta-Uspallata basins are characterized predominantly by marine sedimentation (Lopez-Gamundí et al., 1987; Limarino et al., 1996b). In the Río Blanco Basin, Neopaleozoic sequences overlie Devonian strata and contain marine invertebrates that suggest an Early Carboniferous age. The San Rafael Basin is located to the south, in Mendoza Province (Azcuy et al., 1987b; Espejo et al., 1996), and during the Late Paleozoic it was probably a shallow bay.
In this basin thick sequences of glacial, marine, alluvial, lacustrine, fluvial and eolian deposits of Carboniferous and Permian age, referred to the Paganzo Group, were deposited. In this section, we have analyzed the Guandacol, Tupe, Bajo de Véliz and De La Cuesta formations and their stratigraphic equivalents.
This formation has a wide geographic distribution in the Precordillera and Sierras Pampeanas areas. The base of the formation consists of sandstones and diamictites (tillites and resedimented paraconglomerates) which are overlain by transgressive marine mudstones (probably during a postglacial transgression). The sequence is in turn overlain by deltaic sediments, including sandstone–mudstone couplets that were deposited by turbidity currents. Sandstones, mudstones and some conglomerates were deposited in delta-plain environments near the top of the formation. The mudstones from the lower levels of the unit contain palynofloras at the Agua Hedionda locality (San Juan Province; Text-Figure 1⇑, loc. 1). Césari and Vázquez-Nístico (1988) described assemblages containing dominant spores (Lundbladispora, 63%) and sub-dominant monosaccate grains (30%). Nearby, at the La Delfina mine (Text-Figure 1⇑, loc. 2), samples from the middle and upper part of the unit also contain palynofloras; quantitative data suggest an inverse relationship between spores and pollen at this locality (Ottone and Azcuy, 1986, 1990). Also, from the Agua Hedionda area (Text-Figure 1⇑, loc. 1), the uppermost mudstones of the Guandacol Formation contain assemblages composed of spores (55%) and subordinate monosaccate grains (Césari and Vázquez Nístico, 1988).
The sequence at the La Esperanza mine (San Juan Province; Text-Figure 1⇑, loc. 3) provides additional information regarding the vertical distribution of palynomorphs through the Guandacol Formation (Ottone, 1991). The assemblages from this formation are important because of the occurrence of marine forms that are related to green algae.
Furthermore, deposits equivalent to the Guandacol Formation have been identified in different areas of the basin (Text-Figure 3⇓); as a result, the lower member of the Agua Colorada Formation, the Malanzán Formation and lower parts of the Lagares and Jejenes formations, are all correlative with the Guandacol Formation.
The Lower Member of the Agua Colorada Formation is composed of lacustrine and glaciolacustrine sediments and has yielded palynofloras from outcrops at Casa Blanca, Las Gredas and Las Trancas creeks in the Los Berros-Portezuelo Blanco area, in Puesto El Vallecito, and at the La Estrella mine (La Rioja Province; Text-Figure 1⇑, loc. 4; Azcuy et al., 1982; Azcuy and Gutiérrez, 1984; Gutiérrez, 1987, 1988, 1993, 1995; Limarino and Gutiérrez, 1990; this paper) as well as from Paiman Creek and the La Laja quarry in Catamarca Province (Text-Figure 1⇑, loc. 5; Vergel and Luna, 1992, Vergel et al., 1993).
In the Sierra de Los Llanos (La Rioja Province; Text-Figure 1⇑, loc. 6), the lacustrine sequence of the Malanzán Formation has yielded an abundant palynoflora (“Asociación A” of Azcuy, 1975b). The lower part of the Lagares Formation at the Paganzo locality (Text-Figure 1⇑, loc. 7) bears rich palynological assemblages (Menéndez and Azcuy, 1969, 1971, 1973) in which Azcuy and Gutiérrez (1984) reported the presence of monosaccate pollen grains for the first time in this area.
The paleoenvironmental interpretation of the Jejenes Formation exposed at Las Lajas Creek (San Juan Province, Text-Figure 1⇑, loc. 16), which is based on acritarch–leiosphere/spore ratios, suggests a nearshore marine environment for the basal and middle parts of the sequence; the interpretation is reinforced by dominant woody organic matter in certain samples (Césari and Bercowski, 1998).
Palynological study of the Tupe Formation began with the work of Césari (1984, 1986a, b) at the type locality in Sierra de Maz (La Rioja Province; Text-Figure 1⇑, loc. 8). The sequence is principally composed of sandstones and conglomerates deposited in fluvial environments. Eighteen samples distributed through 70 m of sediments from the La Negra and La Victoria coal mines yielded rich assemblages, and these were analyzed both quantitatively and qualitatively. Also, Césari and Limarino (1987) analyzed palynological data from another locality at Sierra de Maz-La Cortadera Creek (Text-Figure 1⇑, loc. 9). Three samples from different levels yielded several new species from the Tupe Formation. This formation also crops out in the anticline in the Huaco area (San Juan Province). In this sequence, the sediments bear palynofloras equivalent in composition to others within Sierra de Maz (Ottone, 1991). Ottone and Azcuy (1991) described in detail the palynofloras from Agua Hedionda in the Huaco area (Text-Figure 1⇑, loc. 1).
Sediments belonging to the Upper Member of Agua Colorada Formation, Loma Larga Formation, and the middle and upper parts of the Lagares Formation, are considered equivalents of the Tupe Formation.
The Upper Member of the Agua Colorada Formation (La Rioja Province, Casa de Lata, Agua Colorada and Primera Agua localities, Santa Rosa and Río Tambillos–Las Pircas mines; Text-Figure 1⇑, loc. 10) contains palynological as-semblages that were studied by Menéndez (1965), Menéndez and González-Amicón, (1979), Gutiérrez (1988, 1993), and revised in this paper.
Palynofloras from carbonaceous mudstones in the upper part of the Lagares Formation (fluvial facies) were described from various localities. At the Alberto and Antonio mine (Text-Figure 1⇑, loc. 11) the palynoflora is dominated by trilete spores (96.5%) that are principally represented by Apiculiretusispora (Césari and Gutiérrez, 1985). Morelli et al. (1984) and Gutiérrez and Césari (1989) described a palynoflora from the La Margarita mine (Text-Figure 1⇑, loc. 12) dominated by Lundbladispora (78.4%), and which also contained freshwater algae (Portalites, 3%). At the La Petisa mine (Text-Figure 1⇑, loc. 13), the palynological association (Gutiérrez and Césari, 1989) is dominated by trilete spores, principally Horriditriletes (55.2%).
González-Amicón (1973) and Gutiérrez and Césari (1987) recognized four palynological associations from the fluvial mudstones that form the middle–upper part of the Jejenes Formation at the Las Crucecitas locality (= Retamito), San Juan Province (Text-Figure 1⇑, loc. 16). In the La Mina Creek locality (San Juan Province; Text-Figure 1⇑, loc. 16), a palynoflora dominated by monosaccate pollen grains (63%) including Plicatipollenites malabarensis, Potonieisporites novicus, Caheniasaccites ovatus and Crucisaccites sp., with subordinate Lundbladispora braziliensis, was described by Gutiérrez and Césari (1987).
The only palynoflora recorded from the “Estratos de Mascasín” was obtained from black carbonaceous shales in the YPF LR SM.es-1 well, Salinas de Mascasin, between 3423 and 3429 mbpp (Text-Figure 1⇑, loc. 14; Azcuy and Jelin, 1980; Azcuy, 1986; this paper). Our analysis shows the following composition in the samples: trilete spores (73%), monosaccate pollen grains (26%), bisaccate grains (0.5%), striate pollen (0.5%). A revised analysis of the original sample material allowed us to recognize the presence of Apiculatasporites caperatus, Apiculiretusispora ralla, A. sparsa, Calamospora smileyana, Plicatipollenites malabarensis, Potonieisporites magnus, Limitisporites hexagonalis, Caheniasaccites verrucosus, Cannanoropollis densus, Protohaploxypinus sp., Dibolisporites lictor and Cyclogranisporites micro granulatus.
The Loma Larga Formation at Sierra de los Llanos (La Rioja Province; Text-Figure 1⇑, loc. 6) is composed of braided and meandering fluvial deposits. Azcuy (1975a, b) described rich palynofloras in the formation and recognized two populations (B and C) which were dominated by zonate spores and subordinate monosaccate pollen grains.
The Trampeadero Formation, exposed at La Cébila Creek (La Rioja Province; Text-Figure 1⇑, loc. 15), is composed of fossiliferous lacustrine sediments (probably related to glacial conditions) overlain by fluvial deposits. The lacustrine mudstones yielded rich palynofloras (Barreda, 1986) with abundant spores and monosaccate pollen grains.
Bajo de Véliz Formation.
Studies describing the palynofloras from lacustrine sediments in the Pallero Member at Bajo de Véliz (San Luis Province; Text-Figure 1⇑, loc. 17) were carried out by Menéndez (1971), Azcuy and Jelín (1980), and Hünicken et al. (1981). For this paper the original material studied by Menéndez (1971) was examined and some of the species identifications were rejected, while other taxa were recorded in the section for the first time. The revised list of species is shown in the Appendix⇓. The most significant taxa include Protohaploxypinus amplus, P. limpidus, Vittatina subsaccata, Marsupipollenites striatus, Fusacolpites fusus, Hamiapollenites fusiformis, Latusipollenites quadrisaccatus, Barakarites rotatus, Apiculatisporis cornutus, Granulatisporites sp. cf. G. trisinus, Kraeuselisporites sanluisensis and Cristatisporites longispinosus. Our revision recognizes an assemblage composed of spores (69.1%; principally Kraeuselisporites [37.2%], Cristatisporites [5.3%] and Punctatisporites [2.9%]), monosaccate pollen grains (27.3%), bisaccate pollen grains (1.7%), striate grains (1.1% ), and plicate grains (0.9%).
Recent studies of the Tasa Cuna Formation (Córdoba Province; Text-Figure 1⇑, loc. 27) described palynofloras characterized by the presence of Vittatina subsaccata, Vittatina sp. cf. V. ovalis, V. fasciolata, Weylandites magmus, Marsupipollenites striatus, Fusacolpites fusus, Protohaploxypinus amplus, Cristatisporites longispinosus, Kraeuselisporites sanluisensis, Granulatisporites sp. cf. G. trisinus, among others (Césari et al., 1999).
De La Cuesta Formation.
Aceñolaza and Vergel (1987) illustrated a palynoflora from the green marls from the middle part of the formation, which crops out at the Los Jumes locality (Sierra de Famatina, Catamarca Province; Text-Figure 1⇑, loc. 18). The assemblage is characterized by the presence of bisaccate and striate pollen grains (80–85%) as well as monosaccate grains and spores. Although this assemblage was not described in detail, it is clearly different from the association described in the preceeding section and resembles the late Permian associations in the Chacoparanense Basin (Russo et al., 1980).
This basin is located in the western parts of the San Juan and Mendoza provinces and is characterized by sediments deposited in coastal to fluvial environments. The Del Ratón, El Retamo, Santa Máxima, Cerro Agua Negra and La Puerta formations are analyzed in this paper.
Del Ratón Formation.
The strato type of this Lower Carboniferous formation is located at km 117 of National Route No. 20, San Juan Province (Text-Figure 1⇑, loc. 19). The sequence is principally continental, and only one palynological assemblage has been described from it. The association is characterized by scarce cingulizonate, apiculate and camerate spores that suggest a Vise anage(Sessarego and Césari, 1989).
El Retamo Formation.
A poorly-preserved and monotonous palynoflora was reported by Carrizo (1992) from outcrops at El Retamo and De Un Salto Creek in Sierra de Barreal (San Juan Province; Text-Figure 1⇑, loc. 24). The assemblages comes from the upper part of the unit, which is continental in origin.
Santa Máxima Formation.
Ottone (1987, 1988, 1989) studied palynofloras recovered from outcrops at Cerros Bayos and Los Mananatiales (Mendoza Province; Text-Figure 1⇑, loc. 20). He recognized three associations, which were simply labeled as “lower,” “middle,” and “upper” (see Appendix⇑). The “lower” association is present in the basal strata of the unit and is composed of trilete spores, monosaccate and bisaccate pollen grains, and it contains marine species (acritarchs) in some stratigraphic intervals (Los Manantiales Creek-V locality, BAFCPl 518 and 507). The “middle” assemblage (represented by the marine deposits of the middle part of the unit) contains spores, monosaccate and bisaccate pollen, scolecodonts and scarce acritarchs. Finally, the “upper” association is restricted to the continental deposits of the upper part of the unit. It is composed of spores (principally apiculate and cingulizonate forms), and by striate, monosaccate, bisaccate and plicate pollen grains. A revision of the stratigraphic data of Ottone (1987) allows us to propose the restriction of the striate pollen grains (viz. Lueckisporites) to the top of the sequence (Los Manantiales Creek-V locality, BAFCPl 505–481 and 503).
Cerro Agua Negra Formation.
Outcrops at the intersection of Las Leñas and San Francisquito creeks (San Juan Province; Text-Figure 1⇑, loc. 21) contain the only known palynoflora from this formation. These poorly-preserved assemblages were described and illustrated by Gutiérrez (1992), who suggested a Late Carboniferous–Early Permian age for the assemblage based on the presence of Granulatisporites austroamericanus, G. varigranifer, Apiculiretusispora variornata, A. tuberculata, Cristatisporites spinosus, C. scabiosus and Vallatisporites ciliaris.
La Puerta Formation.
Ottone and Rosello (1996) reported a palynological association from the La Puerta Formation in the east-central region of the Cordillera Frontal, 40 km northwest of Calingasta (San Juan Province; Text-Figure 1⇑, loc. 22). The association is composed of bisaccate and striate pollen grains, along with scarce acritarchs. The presence of Fusacolpite ssp., Lueckisporites sp., Lunatisporites sp., and Vittatina sp. suggests a Permian age for the sequence.
Río Blanco Basin
This basin, located in western parts of the La Rioja and San Juan provinces, is characterized predominantly by marine sediments. We have included the Malimán and Cortaderas formations (which constitute the Early Carboniferous Angualasto Group) in our analysis
Outcrops in the type locality of the formation (La Cortadera Creek, San Juan Province; Text-Figure 1⇑, loc. 23) contain rich assemblages deposited on a low energy marine platform (Limarino and Césari, 1993). The palynofloras are characterized by the presence of smooth, verrucate and cingulizonate spores, along with scarce acritarchs (Césari and Limarino, 1995). The associated fauna suggests an Early Carboniferous age for the sequence.
This formation overlies the Malimán Formation. Palynofloras from the lower and middle sections of the unit were reported by Césari and Limarino (1992). The assemblages are composed of trilete spores (99.5%) and acritarchs (0.5%) that suggest an Early Carboniferous age for this part of the sequence. The possibility of reworked of Devonian species in these assemblages is quite possible and this phenomenon will be analyzed in detail in a planned systematic revision.
San Rafael Basin
The El Imperial Formation is the only Neopaleozoic unit in the basin that contains documented palynofloras. Fossiliferous localities (Text-Figure 1⇑, loc. 25) are located in the southern part of the Mendoza Province at Arroyo El Imperial, Zitro mine, Puestos Pantanito Agua de las Yeguas and Río Atuel Canyon (Azcuy and Gutiérrez, 1984, 1985; García and Azcuy, 1987; García, 1991, 1995, 1996). García (1991, 1996) recognized two palynological associations, assigned to the middle Late Carboniferous and the Early Permian, respectively. The lower assemblage is present in the basal and middle parts of the formation and is subdivided into two sub-associations: association “A” which is characterized by continental species, and association “B” which includes rare (up to 6.3%) acritarchs and scolecodonts in the middle to upper levels of the sequence. The upper association (only identified at Puestos Pantanito and Agua de las Yeguas, BAFCPl 427) is dominated by bisaccate (52.5%) and monosaccate, striate grains in association with cingulizonate and smooth spores.
Permian Oriental Basin
Recently, Césari et al. (1996) described two palynological assemblages from the Yacimiento Los Reyunos Formation in the Mendoza Province (Text-Figure 1⇑, loc. 26). The material was obtained from cuttings samples from the E-49 exploratory well and was recovered from a dark siltstone and mudstone interval in the Psefític Member. The palynofloras are characterized by the presence of 48–53% striate pollen. The presence of Staurosaccites cordubensis, Lueckisporites latisaccus, L. stenotaeniatus, L. virkkiae, Weylandites magmus, Fusacolpites fusus, Marsupipollenites striatus, Striatoabieites mulsitriatus, Vittatina fasciolata and Lunatisporites variesectus, among other species, permits comparison with the Striatites Biozone of the Chacoparanense Basin. Geologic and geochronologic analyses suggested ages of no older than late Artinskian–Kungurian for this assemblage (Césari et al. 1996). Recently, Melchor (1999) indicated that new 40Ar/39Ar dating suggests a maximum age of 266.3 Ma for the palynological assemblage, which is Artinskian according to Haq and Eysinga (1998).
The distribution of species described from northwestern Argentina is documented in the Appendix⇑ (extremely rare forms, with poorly-defined morphology or questionable identifications are not included). Based on a combination of criteria, including major quantitative changes in assemblage composition and the appearance or disappearance of characteristic species, a sequence of palynological zones extending from the Tournaissian–Visean to Early Permian ages is proposed. The following four biozones have been recognized, in descending stratigraphical order:
Lueckisporites–Weylandites Assemblage Biozone Fusacolpites fusus–Vitattina subsaccata Interval Biozone Raistrickia densa–Convolutispora muriornata Assemblage Biozone
C assemblage Sub-biozone
B interval Sub-biozone
A interval Sub-biozone
Cordylosporites–Verrucosisporites Assemblage Biozone
Cordylosporites–Verrucosisporites (CV) Assemblage Biozone
This is the oldest of the proposed Neopaleozoic miospore zones in northwestern Argentina. The miospore assemblages assigned to the CV Biozone are from the Malimán Cortaderas and El Ratón formations. The biozone is characterized by the presence of Cordylosporites marciae, Verrucosisporites congestus, Verrucosisporites sp. cf. V. papulosus, Crassispora scrupulosa, Dibolisporites microspicatus, Grandispora saurota, Knoxisporites literatus, Retusotriletes avonensis, and acritarchs. The reference section is located at La Cortadera Creek, in San Juan Province (Text-Figure 1⇑, loc. 23).
Raistrickia densa–Convolutispora muriornata (DM) Assemblage Biozone
We propose the sequence that crops out in the Huaco area (Text-Figure 1⇑, loc. 2 and 3) as the type locality for this biozone. Assemblages from the biozone are characterized by the presence of monosaccate pollen such as Plicatipollenites spp., Potonieisporites spp., Cannanoropollis spp. and Crucisaccites spp., and by bisaccate pollen (Platysaccus spp., Limitisporites spp., etc.) associated with the miospore taxa, Apiculiretusispora variornata, A. alonsoi, A. tuberculata, Foveosporites hortonensis, Convolutispora muriornata, Anapiculatisporites argentinensis, Cristatisporites inconstans, Granulatisporites varigranifer, Raistrickia rotunda, R. densa, Vallatisporites ciliaris and the megaspore Sublagenicula brasiliensis. This biozone is subdivided in three subzones.
Interval Sub-biozone A.
This subzone occurs in the Guandacol and Malanzan formations, in the lower member of the Agua Colorada Formation and in the basal part of Lagares and Jejenes formations. Lithologically, the base of the zone is characterized by sandstones and mudstones that contain paleofloristic remains of the NBG Biozone of Argentina. Subzone A is characterized by the first appearance of Plicatipollenites spp. and it is separated from Subzone B by the first appearance of Protohaploxypinus spp. Sub-biozone A differs from the underlying CV Biozone by the consistent presence of monosaccate pollen grains, the occurrence of bisaccate pollen, and the presence of other taxa of trilete spores. The reference section for this biozone is the Guandacol Formation at the La Esperanza mine (Text-Figure 1⇑, loc. 3).
Interval Sub-biozone B.
This sub-biozone occurs in the Tupe, Loma Larga and Trampeadero formations, in the upper member of the Agua Colorada Formation, in the “Estratos de Mascasín”, in the middle and upper levels of the Lagares and Jejenes formations, and in the lower parts of the Imperial and Santa Máxima formations. The abundance and diversity of miospores in this sub-biozone are similar to the underlying sub-biozone. Cingulizonate spores such as Cristatisporites, Kraeuselisporites and Vallatisporites are common. The presence of Proto-haploxypinus spp. in this biozone defines its base. Outcrops of the Agua Colorada Formation at the Casa de Lata locality (Text-Figure 1⇑, loc. 10) yielded palynofloras with Protohaploxypinus; this is one of the oldest known reported occurrences of the genus in Argentina. Assemblages from the Tupe Formation at the La Victoria and La Negra mines (Text-Figure 1⇑, loc. 8) are the most diversified and best known for this zone.
Assemblage Sub-biozone C.
This sub-biozone is identified by the introduction of Quadrisporites spp., scolecodonts, and by acritarchs such as Michrystridium sp. and Verhyachium sp. Species from the underlying and overlying biozones are also present. The reference sections are the Santa Máxima Formation (more precisely, the upper parts of the sequence which crop out in El Chiquerito Creek [BAFCPl 376], Los Piedrines Creek-II [BAFCPl 436], and Los Manantiales Creek-III [BAFCPl 520 and 521′; see Ottone, 1987] [Text-Figure1⇑, loc. 20]), the Cerro Agua Negra Formation (Gutiérrez, 1992), and some intervals in the El Imperial Formation (outcrops along El Imperial stream, BAFCPl 409 and 720 to 723; lower part of the Zitro mine sequence, BAFCPl 553; and outcrops of Puestos Agua de las Yeguas and Pantanito, BAFCPl 405; see García, 1991, 1996) (Text-Figure 1⇑, loc. 25). All of these rocks represent marine–littoral deposits.
Fusacolpites fusus–Vittatina subsaccata (FS) Interval Biozone
This biozone is recognized in the Bajo de Véliz and Tasa Cuna formations and in the upper sections of the Santa Máxima (Los Manantiales Creek-V locality, BAFCPl 473) and El Imperial (Puestos Agua de las Yeguas and Pantanito sequence, BAFCPl 427) formations. At Los Manantiales Creek-V, considered here as a reference section, the boundary with the underlying biozone and the transition to the overlying biozone (LW) occurs within the sample interval BAFCPl 473 to 505. The base of the FS Biozone coincides with the base of the Gangamopteris mega floristic biozone (Early Permian). A basaltic horizon is inter bedded with the lower part of the equivalent sedimentary sequence (Patquia = La Colina Formation) and geochronological dating suggests a maximal age of 302 ± 6 and 288 ± 7 Ma (Thompson and Mitchell, 1972) for the palynofloras. The first appearance of Fusacolpites fusus and an increase in striate pollen grains mark the base of the biozone. Other taxa typical of this biozone include Distriatitesinsolitus, Vittatinasubsaccata, Hamiapollenites fusiformis, Striatoabieites multi striatus, Marsupipollenites striatus, Latusipollenites quadrisaccatus, Barakarites rotatus, Granulatisporites sp. cf. G. trisinus, Kraeuselisporites sanluisensis, Lophotriletes rarus, L. cursus and Apiculatisporis cornutus.
Lueckisporites–Weylandites (LW) Assemblage Biozone
The base of this biozone is defined by the first appearance of Lueckisporites spp. This zone is identified in the Yacimiento Los Reyunos, De La Cuesta and La Puerta formations, and in the uppermost parts of the El Imperial Formation (samples BAFCPl 505–481 and 503 from the Los Manantiales Creek-V section of Ottone, 1987). Reference sections are Yacimiento Los Reyunos Formation in the E-49 well (characterized by the dominance of striate pollen grains with Lueckisporites spp., Lunatisporites spp., Weylandites spp., Vittatina spp., Marsupipollenites spp.) (Text-Figure 1⇑, loc. 26) and the sequence at Los Manantiales Creek-V (Text-Figure 1⇑, loc. 20).
AGE OF THE BIOZONES
The palynological biozones discussed above could not be related to an international timescale using invertebrate assemblages, or by direct correlation of Southern Hemisphere palynological species to forms found in the Northern Hemisphere. Only two volcanic horizons for which there are available radiometric dates are intercalated in the succession and can therefore be correlated with northern stages. In addition, only one ammonoid fauna provides independent bio stratigraphic control for the sequence(Text-Figure 3⇑); only sediments in the Malimán area contain Protocanites scalabrinii Antelo (=Michiganites), an ammonoid of late Tournaisian–early Visean age. The majority of the Carboniferous and Permian plant macrofossils, palynomorphs and invertebrates found in northwestern Argentina are endemic to Gondwana, principally from South America.
CV Assemblage Biozone
The main taxa identified in this biozone suggest an Early Carbon ifero usage. These include Cordylosporites marciae, Verrucosisporites papulosus, V. congestus, Dibolisporites microspicatus, D. distinctus, Crassispora scrupulosa, Anapiculatisporites semisentus, A. amplus, Dyctiotriletes connatus, Grandisporadebilis, Pustutalisporites giberosus, and Knoxisporites literatus (see Playford, 1985, 1991, 1993; Utting et al., 1989; Clayton and Turnau, 1990; Playford and McGregor, 1993; Mahdi and Butterworth, 1994; Turner and Owens, 1993; Zhu, 1993; Clayton, 1995).
DM Assemblage Biozone
Although some palynofloras from this biozone come from deposits influenced by glaciation, we do not see evidence of reworking in the sections. Some of the more long-ranging species have preservational and color characteristics which are very similar to the other specimens, and are therefore interpreted not to have been recycled from older sediments.
Three events can be used as time indicators: (1) the abundance of radial and bilateral monosaccate pollen, (2) the introduction of taeniate saccate pollen at the base of the biozone, and (3) the presence of striatitid bisaccate pollen in Subzone B. In Argentina, monosaccate pollen first appears in Subzone A, which in accordance with stratigraphic data is found close to the base of the Namurian. Monosaccate pollen also seems to appear synchronously in the Namurian A of Australia, Libya, northern Africa, and China (Brugman etal., 1985; Loboziak and Clayton, 1988; Jones and Truswell, 1992; Clayton, 1995; Zhu, 1993), although some Visean records of Potonieisporites are reported from eastern Europe (Clayton, 1985), the Donetz Basin (Teteriuk in Owen et al., 1978), England (Turner et al., 1995), Poland and Artic Canada (Clayton, 1985). The probable relationship between the rise of cordaitalean plants and monosaccate pollen grains is recognized in Argentina as well as in Australia (see Jones and Truswell, 1992). Balme (1980) proposed that the transition to assemblages with abundant radial and bilaterally symmetrical monosaccate pollen grains coincided with the cessation of coal-swamp development in Laurasia, suggesting a global climatic change corresponding with cooling in Gondwana. Hardy plants such as the cordaitales (which produce monosaccate pollen) dominated the floras under these conditions of decreasing global precipitation. This event is recognized in Argentina within Subzone A. Balme (1980) also suggested that the introduction of taeniate disaccate pollen was effectively globally synchronous and was induced by rapid global climatic amelioration following the glaciation of Gondwana. This event occurs in Subzone B of Argentina.
In addition, bissacate pollen grains appear for the first time in the Namurian of China (Zhu, 1995) and in the West phalian A in Western Europe (Clayton et al., 1977) and northern Africa. Although bissacate striate pollen grains (Protohaploxyinus) appear for the first time in the middle Namurian of China (Zhu, 1993, 1995) and Brazil (Piccarelli et al., 1993), they first occur in upper Namurian sediments in Australia (Jones and Truswell, 1992; Roberts et al., 1995).
Playford and Helby (1968) described an assemblage from the Australian Italia Road Formation that has many species of spores in common with the DM Biozone, including Punctatisporites lucidulus, Raistrickia accincta, R. radiosa, Rattiganispora apiculata, Reticulatisporites asperdictyus, R. magnidictyus, Foveosporites pellucidus, Grandispora maculosa and Psomospora detecta. According to Roberts et al. (1995), this palynoflora is late Visean in age. Nevertheless, the known ranges of species such as Psomospora detecta, Rattiganispora apiculata and Punctatisporites lucidulus are extended in to the Namurian–Asselian in Australia.
Therefore, an early Namurian age for the base of the DM Biozone seems concordant with the oldest known records of monosaccate, bisaccate and taeniate pollen grains. More-over, previous records of some spore species (Text-Figure 4⇓) allow us to assume a Late Carboniferous (Namurian–Stephanian) age for this biozone.
FV Assemblage Biozone
Although Vittatina species are common in Permian sequences, they are also known from the West phalian D in Arabia (Owens and Turner, 1995), and from the Stephanian B of western Europe (Clayton et al., 1977). Fusacolpites fusus and F. ovatus have been recorded from the Early Permian (Bose and Kar, 1966; Kar and Bose, 1967; Ghavidel-Syoki, 1993), and Distriatites insolitus is recorded from the Asselian of Libya (Loboziak and Clayton, 1988). An earliest Permian age is proposed for this biozone, which is equivalent to the mega floral Gangamopteris Biozone.
LW Assemblage Biozone
Polyplicate pollen grains such as Weylandites appear for the first time in the Stephanian B–C of Canada (Utting, 1989), and they are typically recorded in the Permian Gondwanic strata (Lidstrom, 1995). Lueckisporites virkiae and Marsupipollenites spp., which are abundant in Permian assemblages, have been recorded in the West phalian D of the Donetz Basin (Teteriuk in Owen et al., 1978). Scheuringipollenites ovatus and Weylandites lucifer appear for the first time in Assemblage Zone V in India (Tiwari and Tripathi, 1992), which is Artinskian in age. In agreement with the radiometric data (Césari et al. 1996; Melchor, 1999), we propose an age no older than Artinskian for the LW Biozone.
COMPARISON WITH OTHER GONDWANIC ZONES
The eastern Australia palynostratigraphic framework, which is based primarily on the work of Evans (1967, 1969), Kemp et al. (1977) and Price (1983), divides the Carboniferous–Lower Permian into seven stages and sub-stages, each of which is marked by the first occurrence of specific index taxa. Jones and Truswell (1992) and Roberts et al. (1995, 1996) summarize the following Australian Carboniferous to Lower Permian palynozones:
Anapiculatisporites largus Assemblage (Kemp et al., 1977) – early Visean;
Grandispora maculosa Assemblage(Kemp etal., 1977) – late Visean;
Spelaeotriletes ybertii Assemblage (Kemp et al., 1977) – Namurian;
Granulatisporites (=Pseudoreticulatispora) confluens Zone (Foster and Waterhouse, 1988 and Backhouse, 1991) – Asselian–early Sakmarian;
Stage 3a (Price, 1976; Kemp et al., 1977) – Sakmarian age. (In the Western Australian palynostratigraphic zonation established by Backhouse (1991, 1993), the Pseudoreticulatispora pseudoreticulata and Striatopodocarpidites fusus zone correspond to Stage 3a, while the Microbaculispora trisina Zone is equivalent to a major part of Stage 3b (latest Sakmarian–early Artinskian).
Jones and Truswell (1992) defined five local palynological Oppelzones for the Galilee Basin (western Australia). They recognized a superzone equivalent to Spelaeotriletes Assemblage, which can be divided into three zones: labeled A, B and C. Zone C of Jones and Truswell (1992) is constrained to be older than 323 Ma using zircon dates from material in the overlying unit (Roberts et al., 1995); palynologically the zone is characterized by the first appearance of Protohaploxypinus. Foster and Waterhouse (1988) correlated the Cristatisporites Biozone in Argentina with the Granulatisporites confluens Zone in Australia.
The Argentinian CV Biozone is probably correlative with the Anapiculatisporites largus Assemblage in Australia. Australian palynofloras contain some miospores typical of the CV Biozone, including Cordylosporites marciae, Crassispora scrupulosa, Anapiculatisporites semisentus, and Dibolisporites microspicatus.
The best intercontinental correlation can be established between the Spelaeotriletes ybertii Assemblage–Diatomozonotriletes birkiadensis Assemblage and the DM Biozone (Text-Figure 5⇓). These associations show the first appearence of monosaccate pollen grains and rare occurrences of taeniate pollen. The presence of Striatopodocarpidites spp., abundant bisaccate pollen, Weylandites spp., Vittatina fasciolata, Marsupipollenites striatus and Scheuringipollenites, together suggest correlation between the Australian Stage 3 and the Argentinian LW Biozone. However, radiometric data suggest an older age (Sakmarian) for the Australian biozone.
Assemblages equivalent to the Argentinian DM Biozone have been recognized in Brazil (Lima et al., 1983; Souza et al., 1993; Rocha Campos and Anelli, 1996). These comprise the oldest Carboniferous palynofloras in the Paraná Basin of Brazil. Species in common between Australia and Argentina include Anapiculatisporites concinnus (=A. argentinensis), Apiculiretusispora tuberculata, Granulatisporites varigranifer, Raistrickia paganziana, R. rotunda, Secarisporites irregularis, Foveosporites hortonensis, Cristatisporites spinosus, C. inordinatus, C. menendezii, Arhensisporites cristatus and Protohaploxypinus sp.
Marques-Toigo (1991) described palynological assemblages from Permian sediments in the Paraná Basin of Brazil. Oneintervalzone—the Cannanoropollis korbaensis Zone — was proposed for the Lower Permian. It was defined by the stratigraphic ranges of Cannanoropollis korbaensis and Potonieisporites simplex and correlated with the Cristatisporites and “III” palynozones of Argentina. The lower part of the Cannanoropollis korbaensis Zone is dominated by monosaccate pollen; in the middle part there is an increase in trilete spores, and the upper part is characterized by abundant taeniate bisaccates. Correlation of this biozone with Chacoparanense assemblages is reliable, however correlation with the palynofloras from northwestern Argentina is more difficult (Text-Figure 5⇑).
From the northern Gondwana margins in northeast Libya, the palynofloras of the Plicatipollenites malabarensis–Cannanoropollis janaki (MJ) Biozone (Loboziak and Clayton 1988) are similar to the Argentinian DM Biozone (Text-Figure 5⇑). These assemblages are characterized by the first appearance of monosaccate pollen.
Assemblages from the Al Khlata Formation reported by Besems and Schuurman (1987) and Love (1994) may be represented in Argentina. The DM Biozone is probably a correlative of the Potonieisporites Assemblage and Microbaculispora Assemblage, and the FS Biozone is probably equivalent to the Cycadopites cymbatus Assemblage (Text-Figure 5⇑). Stephenson (1998) recognized the presence of the Granulatisporites confluens Oppel Zone in glaciogene sediments from the Al Khlata Formation and suggested correlation with the Cristatisporites Zone in Argentina
Indian assemblages are dominated by monosaccate pollen grains. Tiwari and Tripathi (1992) divided the glacial to fluvioglacial sedimentary rocks of the Talchir Formation into three assemblage zones. The oldest and least diversified of these is the Potonieisporites neglectus Assemblage Zone, which is dominated by radial and bilateral monosaccate pollen. This is followed by the Plicatipollenites gondwanensis Assemblage Zone and the Parasaccites korbaensis Assemblage Zone (in the latter zone, monocolpate and bisaccate pollen grains first appear). In the Karharbari Formatio, Tiwari and Tripathi (1992) recognized the Crucisaccites monoletus Assemblage Zone characterized by the first appearance of taeniate non-saccate and bisaccate pollen grains, and the Scheuringipollenites barakarensis Assemblage Zone dominated by non-taeniate bisaccates. Correlation of the Indian and Argentinian biozones is difficult; nevertheless we propose that the Scheuringipollenites barakarensis Assemblage Zone (V) is equivalent with the Argentinian LW Biozone using the first appearance of Weylandites (Text-Figure 5⇑).
Antarctic Paleozoic palynological studies principally focus on Upper Carboniferous–Permian strata. The presence of rocks of unequivocal Carboniferous age has not been documented, although non-illustrated listings of Early and Middle Carboniferous miospores from Hope Bay and Alexander Island have been published (see Playford 1990). Nevertheless, Playford (1990) expressed doubt concerning the reliability of these data. Permian assemblages recently studied by Lindström (1995) and Farabee et al. (1990, 1991) have the best potential correlation with palynofloras from the Argentinian Chacoparanense Basin.
MEGAFLORISTIC AND PALEOCLIMATIC RELATIONSHIPS
The following paleofloristic zones, in order from oldest to youngest, are recognized in the Upper Paleozoic continental facies of north western Argentina :Archaeosigillaria–Frenguellia (AF), Nothorhacopteris argentinica–Botrychiopsis weissiana–Ginkgophyllum diazii (NBG) Interval Biozone and Gangamopteris Biozone (characterized by the first appearance of Glossopteridales) (see Archangelsky, 1996; Archangelsky et al., 1996a, b). Detailed comparison of the paleofloristic composition of the biozones follows; inferred botanical affinity of the miospores follows Balme (1995).
The AF Biozone is composed of abundant but monotonous associations containing herbaceous lycophytes (Protolepidodendrales), pteridophytes (Cladoxylales) and pteridosperms. These fossiliferous strata contain palynofloras referred herein to the CV Biozone. The palynofloras are more diverse, containing species related to different groups of pteridophytes (Zygopteridales, Botryopteridales, Cladoxylales, Marattiales and Filicales), lycophyte-elements of the Isoetales, Chaloneriaceae and Sigillariaceae. Species related to the barinophytopsids and rhyniophytes are also present. The palynological assemblage indicated that many species are not preserved as foliage macrofossils in this stratigraphic interval.
The AF Biozone is referred to paleoclimatic Phase I (López-Gamundí et al., 1992), and is characterized by temperate and humid preglacial conditions. Limarino et al. (1996b) included in Phase I carbonaceous shales and some coal-bearing strata belonging to Del Ratón Formation, together with the major part of the Malimán Formation and the Lower Member of the Cortaderas Formation.
Paleoclimatic Phase II (López-Gamundí et al., 1992) represents a glacial event that resulted in the widespread development of diamictites and other glacially-related features. Evidence of this phase is present in the lowest stratigraphic levels of the Guandacol and Agua Colorada formations, and in the uppermost part of the Cortaderas Formation (Limarino et al., 1996). Paleofloristic associations belonging to NBG Biozone are recognized inmediately above these strata.
Paleoclimatic Phase III is divided into two sub-phases. Sub-phase IIIa is related to deglaciation conditions and is represented by a marine postglacial transgression that consists of fine sediments which were deposited in lacustrine and fiord environments. These deposits are exposed in the lower parts of the Agua Colorada, Guandacol, Jejenes and Lagares formations. Palynofloras from the Guandacol and Jejenes formations (Sub-biozone A) contain some acritarchs, which corroborate the marine influence. Assemblages from the Guandacol Formation (NBG) are composed of herbaceous lycophytes, pteridosperms, cordaites, early pteridophytes, and probable ginkgophytes. The equivalent palynofloras are dominated by species related to ferns (principally Zygopteridales, Marattiales, Filicales, Cladoxylales, and Botryopteridales), lycophytes (Chaloneriaceae and Selaginellales)and the interval contains the first appeareance of conifers. This latter group is represented by species related to the families Emporiaceae, Utrechtiaceae, Ulmaniaceae and Ferugliocladaceae, and to the Order Cordaitales. A subdominant group is composed of species related to the sphenophytes, Barinophytopsida, and freshwater algae.
The NBG paleofloristic associations are different from the underlying preglacial AF Assemblage and this dissimilarity is also registered in the palynofloras. One of the most significant changes is the incoming of cordaitalean and monosaccate pollen grains in the postglacial strata.
Sub-phase IIIb is characteristic of temperate (or cold temperate) and humid climates, which resulted in the accumulation of the coal beds and carbonaceous mud-stones present in the Tupe, Lagares and Agua Colorada formations. Palynofloras from this paleoclimatic phase are referred to Sub-biozone B. Floras from the lower and middle parts of the Tupe Formation and equivalent strata have the same basic components as the underlying associations, but in addition are characterized by the first appeareance of arborescent lycophytes and sphenophytes. The same groups persisted in the palynofloras, however some differences are apparent, including:
the dominance of trilete spores related to pteridophytes;
significant quantitative changes in the pollen assemblages through the sequence. These variations probably reflect a warming trend which followed the end of glacial conditions and the increasing diversity of plant communities;
the first appearance of the Glossopteridales–Peltaspermales group with Protohaploxypinus, Pteruchipollenites and Striatoabieites pollen.
The upper parts of the Tupense sequences contain paleofloristic assemblages characterized by true ferns (Filicales), Cordaitales, Equisetales and abundant conifers. However, the equivalent palynofloras are dominated by species referred to lycophytes together with the coniferophytes, pteridophytes and sphenophytes. Marine and brackish species also occur in these strata.
Paleoclimatic Phase IV represents a paleoclimatic period that is transitional between humid–temperate (Phase IIIb) and arid (Phase V) conditions. Sediments from the Bajo de Véliz and Tasa Cuna formations are included in this phase and contain palynofloras referred to the FS Biozone. Bajo de Véliz is one of the best Permian fossiliferous deposits in Argentina; this flora and its equivalents are characterized by the incoming of Glossopteridales, as well as new groups among the sphenophytes. Cordaitales are represented by very large leaves and lycophytes are similar to the Chaloneriaceae. Conifers are abundant, and the pteridophytes are probably represented by sterile fronds of Alloiopteris and Sphenopteris in the Tasa Cuna Formation. Palynofloras in these strata are dominated by lycophyte and conifer groups, with relatively scarce pteridophytes and sphenophytes. The Glossopteridales–Peltaspermales are represented by specimens of Vittatina, Alisporites, and Fusacolpites.
Paleoclimatic Phase V corresponds to an important arid episode that produced the formation of eolianites and lacustrine deposits, for example, in the Upper Member of De La Cuesta Formation and the Yacimiento Los Reyunos Formation. These two units contain palynofloras here referred to the LW Biozone. These associations are characterized by the dominance of species related to the Glossopteridales and Peltaspermales, as well as subordinate Coniferophyta. The bisaccates are common among the pollen flora, and representatives of the Podocarpaceae (Lunatisporites),Majoniaceae(Lueckisporites), Voltziales (Illinites); the incoming of Weylandites (Peltaspermales) first appear in this interval.
We propose the following palynological biozones for the Carboniferous–Permian sequences of the west-central part of Argentina (in order from oldest to youngest):
Cordylosporites–Verrucosisporites (CV) Assemblage Biozone.
This is the oldest (Lower Carboniferous) of the biozones and it is identified in strata bearing paleofloristic remains of the Archaeosigillaria–Frenguellia Biozone and invertebrate fossils which suggest a Late Tournasian–Early Visean age.
Raistrickia densa–Convolutispora muriornata (DM) Assemblage Biozone.
This interval is characterized by the presence of monosaccate pollen, and by bisaccate pollen associated with trilete spores. This biozone is considered to be Late Carboniferous in age and is subdivided in three sub-biozones.
Interval Sub-biozone A.
The sub-biozone is marked by the first appearance of Plicatipollenites spp.. Sub-biozone A differs from the underlying CV Biozone by the constant presence of monosaccate pollen, the bisaccate pollen occurrence, as well as a suite of new trilete spore taxa. These compositional differences between the CV Biozone and Subzone A reflect the appearance of a new flora due to the influence of glaciation (including Cordaitales).
Interval Sub-biozone B.
This sub-biozone is defined by the appearance of Protohaploxypinus spp. It typically occurs in the coal beds belonging to paleoclimatic Sub phase IIIb, which is characteristic of temperate and humid climates, and which contains abundant paleofloristic remains of the NBG Biozone.
Assemblage Sub-biozone C.
This sub-biozone is identified by the first appearance of scolecodonts, Quadrisporites spp. and acritarchs, and by the presence of a number of species shared with the underlying and overlying biozones. The sub-biozone is indicative of marine-littoral deposits. Equivalent sequences bear paleofloristic assemblages of the “Interval Biozone.”
Fusacolpites fusus–Vittatina subsaccata (FS) Interval Biozone.
The base of this zone coincides with the base of the Gangamopteris mega floristic biozone (lowest Permian). An intercalated basaltic horizon in the lower part of the sedimentary sequence (with apparent dates of 302 ± 6 Ma and 288 ± 7 Ma) indicates a maximum possible age for the palynofloras. The first appearance of Fusacolpites fusus and an increase in striate pollen mark the base of the zone. This biozone is separated from the overlying zone by the first appearance of Lueckisporites spp.
Lueckisporites–Weylandites (LW) Assemblage Biozone.
The biozone is characterized by the dominance of striate pollen grains including Lueckisporites, Weylandites, Vittatina and Marsupipollenites. An age no older than Artinskian is proposed for the biozone, using radiometric data.
The distribution of the miospore groups has significant biostratigraphic implications. These data provide more precision concerning first appearance datums of selected species and genera, which in turn have important implications for intercontinental correlation. The first appearances of some groups of spores and pollen appears to be controlled by climatic conditions. The best example of this relationship is the appearance of monosaccate pollen in close association with the Early-to-Late Carboniferous glacial event.
This research was funded by grants from the National Agency for the Promotion of Science and Technology of Argentina (PICT 04821) and the CONICET (PIP 0455). Thanks are due to Dr. S. Archangelsky for reading and commenting on an early version of this manuscript, to Elizabeth Rovere for the assistance in the translation, and to the editors of Palynology for suggested improvements. We would like to thank Dr. Guillermo E. Ottone who allowed us to use invaluable information. S. Césari extends her thanks to the Yacimientos Petrolíferos Fiscales staff for providing samples from the Salinas de Mascasín well.