ARTÍCULOS ORIGINALES
Middle-Upper Devonian palynoflora from the Tonono x-1 borehole, Salta Province, northwestern Argentina
Sol Noetinger1
1CONICET-UBA. Facultad de Ciencias Exactas y Naturales, Departamento de Geología, Universidad Nacional de Buenos Aires. Intendente Güiraldes 2160, Ciudad Universitaria, 1428 Buenos Aires, Argentina. snoetinger@gl.fcen.uba.ar.
Abstract. The surveyed microflora was recovered from six cores from the Tonono x-1 well in northwestern Argentina. Most of the studied interval corresponds to the Tonono Formation, i.e., the upper part to the Jollín Member and the basal part of the interval may be related to the Michicola Formation. The microflora totals 73 species represented by trilete spores (35 species), microplankton (30 species) including prasinophycean, acritarch and chlorophycean algae and chitinozoans (8 species). The stratigraphic distribution of these species allowed the definition of three associations. The palynoassemblage To1 (3946,5 - 3638,5 m) is characterized by species such as Grandispora douglastownense Mc Gregor, Dibolisporites eifeliensis (Lanninger) McGregor, Verrucosisporites sp. cf. V. loboziakii Marshall and Fletcher, Alpenachitina matogrossensis Burjack and Paris, Alpenachitina sp. cf. A. eisenacki Dunn and Miller and Ancyrochitina simplex Grahn, Bergamaschi and Pereira suggesting a late Eifelian to earliest Givetian age. Based on the presence of Geminospora lemurata Balme, Aneurospora greggsii (McGregor) Streel, Biharisporites parviornatus Richardson, Raistrickia aratra Allen and Leiotriletes balapucencis di Pasquo a Givetian age is proposed for palynoassemblage To2 (3367,35 - 3285 m). Palynoassemblage To3 (3073,2 - 3137,5 m) is predominantly composed of marine elements together with AOM. Few key species are recognized; however the presence of Acinosporites sp. cf. A. eumammillatus Loboziak, Streel and Burjack together with the chitinozoans Angochitina katzeri Grahn and Melo and Angochitina mourai Lange support an early Frasnian age. The distinctive increase of marine elements and AOM between To2 and To3 suggests that a maximum flooding event would have occurred there during this period.
Resumen. Palinoflora del devónico medio-superior del pozo Tonono x-1, Provincia de Salta, Noroeste de Argentina. Se presenta el estudio de seis coronas del pozo Tonono x-1 ubicado en el noroeste Argentino. La mayor parte del intervalo estudiado corresponde a la Formación Tonono; la porción superior al Miembro Jollín y la porción basal podría relacionarse con la Formación Michicola. La microflora recuperada se compone de 73 especies representadas por diversos grupos palinológicos como esporas trilete (35 especies), microplancton incluyendo prasinofitas, acritarcas, algas clorofitas (30 especies) y quitinozoos (8 especies). La distribución estratigráfica de las especies permite distinguir tres asociaciones, la asociación To1 (3946,5 - 3638,5 m), caracterizada por Grandispora douglastownense Mc Gregor, Dibolisporites eifeliensis (Lanninger) McGregor, Verrucosisporites sp. cf. V. loboziakii Marshall y Fletcher, Alpenachitina matogrossensis Burjack y Paris, Alpenachitina sp. cf. A. eisenacki Dunn y Miller y Ancyrochitina simplex Grahn, Bergamaschi y Pereira sugieren una edad eifeliana tardía-givetiana temprana. Debido a la presencia de Geminospora lemurata Balme, Aneurospora greggsii (McGregor) Streel, Biharisporites parviornatus Richardson, Raistrickia aratra Allen y Leiotriletes balapucencis di Pasquo se propone una edad givetiana para la asociación To2 (3367,35 - 3285 m). La asociación To3 (3073,2 - 3137,5 m) comprende predominantemente elementos marinos incluyendo MOA. Se reconocen las siguientes especies clave Acinosporites sp. cf. A. eumammillatus Loboziak, Streel y Burjack junto a los quitinozoos Angochitina katzeri Grahn y Melo y Angochitina mourai Lange las cuales sugieren una edad frasniana temprana. El notable incremento de material de origen marino y MOA entre To2 y To3 sugiere que un evento de máxima inundación podría haber ocurrido allí durante este período.
Key words. Palynostratigraphy; Mid-Late Devonian; Tonono Formation; Salta; Argentina.
Palabras clave. Palinoestratirgrafía; Devónico Medio-Tardío; Formación Tonono; Salta; Argentina.
Introduction
The Tarija basin comprises sedimentary rocks of Silurian to Recent age, which were deposited during several sedimentary cycles. In northwestern Argentina, the Silurian-Devonian unit occurs along an East-West axis and is represented in subsurface mostly by shale and sandstone facies that were mainly deposited in a shallow marine environment. These shales and sandstones increases to over 2000 meters in thickness in the Subandean area and the Chaco- Salteño Plain. Towards the south, these sediments become more continental in character (Disalvo, 2002). Many multidisciplinary works based on subsurface and surface information have been carried out by different oil companies, although, published accounts are less numerous (e.g., Suárez Soruco 2000; Dalenz Farjat et al., 2002; Albariño et al. 2002; Álvarez et al., 2003; Vistalli et al., 2005). The Chaco-Salteño Plain was geophysically surveyed as part of an oil exploration programme. This resulted in the discovery of small, oil/ gas hydrocarbon, fields. The Tonono Field (figure 1A) was discovered in 1969 and holds over 100,000 m3 of condensate (Disalvo, 2002).
Figure 1. A, Distribution of Palaeozoic surface deposits in the Province of Salta, northern Argentina and location of the studied Tonono
x-1 Borehole. B, Comparative stratigraphy of the study area modified from Starck (1999)./ A, Distribución de los depósitos de superficie
Paleozoicos en la provincia de Salta, al norte de Argentina y localización del pozo Tonono x-1. B, Estratigrafía comparada del área de estudio, modificada
de Starck (1999).
This contribution presents a detailed palynological survey of a Devonian palynoflora (microspores, megaspores and microplankton) recovered from six cores of the 3945-3077 m interval in Tonono x-1 borehole. The stratigraphic distribution of the species is analysed and compared with their global ranges to assess the age and correlation of the assemblages defined in this interval. Palynofacies are also considered in order to better understand previous palaeoenvironmental interpretations.
Summary of the stratigraphy and paleontology
The stratigraphic units of the Late Silurian to
Devonian rocks from northern Argentina and southern
Bolivia have been assigned to supersequence
hierarchies by Starck (1995, 1999). This includes a
Silurian-Jurassic tectonic-stratigraphic interval that is
divided into two units separated by a regional unconformity
at the end of the Devonian. In the first
Silurian-Devonian unit, the Cinco Picachos, Las Pavas
and Aguaragüe Supersequences are characterized
by stacked, kilometer scale, coarsening-upward
shale and sandstone facies bounded by first order
flooding surfaces. In this scheme, on the Chaco-Salteño
Plain, the Tonono Formation is part of the Aguaragüe
Supersequence, conformably overlying the
Michicola and Rincón Formations, which in turn are
part of the Las Pavas Supersequence (Starck, 1995)
(figure 1B). Lithologies in the subsurface Rincón Formation
include shales containing macrofossils such
as Metacryphaeus sp., Calmonia subcesiva, Australocoelia
tourtelotti and palaeomicroplankton suggesting a
time range from the Emsian to the Givetian (Cuerda
and Baldis, 1971; Russo et al., 1979, Aceñolaza et al.,
2000, Grahn and Gutierrez, 2001, Grahn, 2003,
Antonelli and Ottone, 2006). The Michicola Formation
comprises a dozen meters of whitish-grey mostly
silicified quartzites (Russo et al., 1979) and is considered,
by some authors a facies variant of the Rincón
Formation (see Aceñolaza et al., 2000). The Michicola
Formation is correlated with the quartzites of
Cerro León in Paraguay, which are supposed to be
Silurian (Padula et al., 1967).
The subsurface Tonono Formation shows a sucession
of dark grey to black, laminated and fissile, very
micaceous, bituminous and carbonaceous shales with
variable sand or silt content. Grey to whitish sandstones
appear in very thin individual layers. Its thickness
varies between 710 and 1960 meters; such variation
is due to erosion during the Chanic orogenic
phase. The uppermost part of this formation is dominated
by quartz sandstones; it is known as the Jollín
Sandstone Member (Padula et al., 1967) and is correlated
with the lower part of the Bolivian Iquiri
Formation dated as Frasnian (Dávila and Rodríguez,
1967). Several unpublished accounts assign an Emsian-
Eifelian to Givetian-Frasnian age for the Tonono
Formation based on its palaeontological content,
which includes the remains of cf. Cyclostigma sp. and
an undescribed trilobite (see Padula et al., 1967;
Böttcher et al., 1984). Azcuy and Laffitte (1981) described
the "association 0" from an unidentified sample
from the Tonono x-1 containing several chitinozoans
and other microplankton such as acritarchs,
chlorophycean algae (e.g., Chomotriletes sp.), prasinophytes
(e.g., Maranhites spp.) and scant scolecodonts.
Within this assemblage there are spores such as Emphanisporites sp. cf. E. rotatus and Grandispora pseudoreticulata among others. This group is recognized as
Upper Devonian. Barreda (1986) studied a complete
Givetian-Frasnian assemblage from the Tonono Formation
on the northeastern Chaco-Salteño Plain -including
microplankton, spores and chitinozoans- but
only published the acritarch association. Volkheimer et al. (1986) also studied the Tonono Formation from
three samples from the Ramos x-1 borehole and one
from the Tonono x-1, where species such as Sphaerochitina sp., Sphaerochitina sp. cf. S. schwalbi and Gotlandochitina sp. occur, assigning a Middle Devonian for
the upper level of the formation. Later on, di Pasquo
(2003) recognized the Macharetí Group unconformably
overlying the Tonono Formation in this borehole
and assigned it an early Pennsylvanian age
based on palynology.
Materials and methods
The Tonono x-1 (To) well (c.a. 63º 38' W, 22º 17' S) is located in the Chaco-Salteño Plain (figure 1.A). It was drilled to a total depth of 4032 meters (13228 feet). Forty-seven core samples were collected from several intervals. One sample from the Upper Devonian section was studied by Azcuy and Laffitte (1981) and Volkheimer et al. (1986). Di Pasquo (2003) studied in detail five core samples (2984 to 2656 m) that yielded diagnostic palynomorphs of the overlying RS and BC Biozones akin to the early Pennsylvanian. An abstract was presented by Noetinger and di Pasquo (2008a) of six core samples between 3073 m and 3945 m depth (figure 2). A detailed survey of these is the subject of this work.
Figure 2. Lithostratigraphic scheme together with the wireline log
of the Tonono x-1 well and the palynological sample depths / esquema
litoestratigráfico junto al perfil eléctrico del pozo Tonono x-1 y las
profundidades de las muestras palinológicas.
Standard palynological methods were performed
to obtain organic residues from the core samples.
These were crushed and then treated first with hydrochloric
and then with hydrofluoric acid to remove
carbonate, silica and silicates, respectively, sieved
with a 25 µm mesh and finally mounted on slides
with glycerine jelly.
Eight types of dispersed organic matter and palynomorph
groups were identified in this study, including
amorphous organic matter (AOM); structured
phytodebris (SP), characterized by identifiable
cuticles and wood; unstructured phytodebris (USP),
known as gelified matter; black phytodebris (BP) or
opaque clasts including charcoal; spores (SPO); phytoplankton
(PHY) comprising acritarchs, prasinophycean
and chlorophycean algae and chitinozoans
(CHI). This is a simplified scheme adapted from
Tyson (1995) for the types of organic components
and palynomorphs found in the analysed assemblages
used to calculate relative percentages allowing
the definition of different palynofacies. Statistical
analyses were also carried out to identify the subtle
differences in the composition of the assemblages. A
palynological marine index (PMI= (Marine Richness
(Rm)/ Terrestrial Richness (Rt) + 1) 100, Helenes et al.
1998) was also calculated in order to support the interpretation
of depositional environments. The values
used are stipulated as in de Araujo Carvalho et al.
(2006), where the marine and terrestrial richness
were expressed as number of genera per sample.
High values of PMI are interpreted as indicative of
normal marine depositional conditions. As the PMI is
based on the palynomorph diversity of terrestrial
and marine palynomorph, it is therefore used as a
substitute for terrestrial/marine ratio.
The identification of palynomorphs was undertaken
using both Leitz Orthoplan and Nikon Eclipse 80i trinocular
transmitted light microscopes, with x1000 maximum
magnification. The photomicrographs were obtained
with Motic (2.0 megapixels) and Pax-it (3.1
megapixels) videocameras and the illustrations are labelled
with BAFC-Pl numbers followed by the England
Finder reference. The studied samples are deposited at
the Department of Geology of the Facultad de Ciencias
Exactas, Físicas y Naturales (University of Buenos
Aires).
Systematic paleontology
List of species
The identified palynomorph taxa are reported by major groups and in alphabetical order. Some specimens not illustrated are grouped at generic level because their poor preservation prevents a more specific assignment. Nevertheless, they are included in the stratigraphic distribution of the assemblages (figure 3), and some of them are figured together with the rest of the species as indicated in brackets (figures 4-8).
Figure 3. Stratigraphic distribution of the species recorded in the
Tonono x-1 well / distribución estratigráfica de las especies en el pozo
Tonono x-1.
Figure 4. 1, Acinosporites acanthomammillatus Richardson BAFC-Pl 1257 (1) L34/2. 2, Acinosporites ledundae Ottone BAFC-Pl 2081 (1)
P43. 3, Acinosporites lindlarensis Riegel BAFC-Pl 1257 (1) V42/3. 4, Acinosporites sp. cf. A. eumammillatus Loboziak, Streel and Burjack
BAFC-Pl 2081 (1) C38/1. 5, Acinosporites sp. cf. A. macrospinosus Richardson BAFC-Pl 1257 (1) M38/4. 6, Aneurospora greggsii (McGregor) Streel BAFC-Pl 1256 (1) Y56. 7, Apiculatasporites microconus (Richardson) McGregor and Camfield BAFC-Pl 1258 (2) S18.
8, Apiculiretusispora plicata (Allen) Streel BAFC-Pl 1257 (1) F28/3. 9, Biharisporites parviornatus Richardson BAFC-Pl 1256 (1) U19.
10, Cymbosporites catillus Allen BAFC-Pl 2080 (1) A46/2. 11, Dibolisporites echinaceus (Eisenack) Richardson BAFC-Pl 1257 (1) Y24/1.
12, Dibolisporites eifeliensis (Lanninger) McGregor BAFC-Pl 1257 (2) D49/3. 13, Dibolisporites quebecensis McGregor BAFC-Pl 1257
(1) H32/2. 14, Dibolisporites uncatus (Naumova) McGregor and Camfield BAFC-Pl 1257 (1) N45/4. 15, Emphanisporites epicautus Richardson and Lister BAFC-Pl 1256 (2) U19. 16, Emphanisporites rotatus McGregor emend. McGregor BAFC-Pl 1255 (1) C46/2. 17, Geminospora lemurata Balme BAFC-Pl 1255 (1) D57/1. Scale bar/ escala gráfica: 1, 2, 3, 5, 6, 7, 9, 11= 15 ?m. 4, 8, 10, 12, 13, 14, 15, 16, 17=
10 µm.
Trilete spores
Acinosporites acanthomammillatus Richardson 1965
(figure 4.1)
Acinosporites ledundae Ottone 1996 (figure 4.2)
Acinosporites lindlarensis Riegel 1968 (figure 4.3)
Acinosporites sp. cf. A. eumammillatus Loboziak, Streel
and Burjack 1988 (figure 4.4)
Acinosporites sp. cf. A. macrospinosus Richardson 1965
(figure 4.5)
Aneurospora greggsii (McGregor) Streel in Becker,
Bless, Streel and Thorez 1974 (figure 4.6)
Apiculatasporites microconus (Richardson) McGregor
and Camfield 1982 (figure 4.7)
Apiculiretusispora plicata (Allen) Streel 1967 (figure
4.8)
Biharisporites parviornatus Richardson 1965 (figure
4.9)
Cymbosporites catillus Allen 1965 (figure 4.10)
Dibolisporites echinaceus (Eisenack) Richardson 1965
(figure 4.11)
Dibolisporites eifeliensis (Lanninger) McGregor 1973
(figure 4.12)
Dibolisporites quebecensis McGregor 1973 (figure 4.13)
Dibolisporites uncatus (Naumova) McGregor and
Camfield 1982 (figure 4.14)
Dibolisporites spp.
Emphanisporites epicautus Richardson and Lister 1969
(figure 4.15)
Emphanisporites rotatus McGregor emend. McGregor
1973 (figure 4.16)
Geminospora lemurata Balme 1962 (figure 4.17)
Grandispora brevizonata (Menéndez and Pöthe de
Baldis) di Pasquo 2007a (figure 5.1)
Grandispora daemonii Loboziak, Streel and Burjack
1988 (figure 5.2)
Grandispora douglastownense McGregor 1973 (figure 5.3)
Grandispora mammillata Owens 1971 (figure 5.4)
Grandispora permulta (Daemon) Loboziak, Streel and
Melo 1999 (figure 5.5)
Grandispora pseudoreticulata (Menéndez and Pöthe de
Baldis) Ottone 1996 (figure 5.6)
Grandispora spp.
Granulatisporites muninensis Allen 1965 (figure 5.7)
Leiotriletes balapucensis di Pasquo 2007a (figure 5.8)
Leiotriletes spp.
Lophotriletes devonicus (Naumova ex Chibrikova)
McGregor and Camfield 1982 (figure 5.9)
Punctatisporites spp. (figure 5.10)
Raistrickia aratra Allen 1965 (figure 5.11)
Retusotriletes spp. (figure 5.12)
Verruciretusispora dubia (Eisenack) Richardson and
Rasul 1978 (figure 5.13)
Verruciretusispora ornata (Menéndez and Pöthe de
Baldis) Pérez Leyton ex di Pasquo 2007a (figure 5.14)
Verrucosisporites premnus (Richardson) Richardson
1965 (figure 5.15)
Verrucosisporites scurrus (Naumova) McGregor and
Camfield 1982 (figure 5.16, 17)
Verrucosisporites sp. cf. V. loboziakii Marshall and
Fletcher 2002 (figure 5.18)
Verrucosisporites tumulentus Clayton and Graham
1974 (figure 5.19)
Verrucosisporites spp.
Figure 5. 1, Grandispora brevizonata (Menéndez and Pöthe de Baldis) di Pasquo BAFC-Pl 1255 (2) G49/4. 2, Grandispora daemonii
Loboziak, Streel and Burjack BAFC-Pl 2081 (2) J19. 3, Grandispora douglastownense McGregor BAFC-Pl 1256 (1) C21/3. 4, Grandispora mammillata Owens BAFC-Pl 1256 (1) H49/2. 5, Grandispora permulta (Daemon) Loboziak, Streel and Melo BAFC-Pl 1255 (1) F44. 6,
Grandispora pseudoreticulata (Menéndez and Pöthe de Baldis) Ottone BAFC-Pl 1256 (1) R33. 7, Granulatisporites muninensis Allen
BAFC-Pl 1256 (1) R31. 8, Leiotriletes balapucensis di Pasquo BAFC-Pl 1255 (1) L61. 9, Lophotriletes devonicus (Naumova ex Chibrikova)
McGregor and Camfield BAFC-Pl 1257 (1) W20/2. 10, Punctatisporites sp. BAFC-Pl 2081 (2) B22/3. 11, Raistrickia aratra Allen BAFCPl
1255 (1) J59. 12, Retusotriletes sp. BAFC-Pl 1258 (1) V43/1. 13, Verruciretusispora dubia (Eisenack) Richardson and Rasul BAFC-Pl
1256 (1) Y22/4. 14, Verruciretusispora ornata (Menéndez and Pöthe de Baldis) Pérez Leyton ex di Pasquo BAFC-Pl 1256 (1) U43/3. 15, Verrucosisporites premnus (Richardson) Richardson BAFC-Pl 2081 (1) W35/1. 16, 17, Verrucosisporites scurrus (Naumova) McGregor
and Camfield BAFC-Pl 1256 (1) Y28/2, BAFC-Pl 2080 (1) G49/3. 18, Verrucosisporites sp. cf. V. loboziakii Marshall and Fletcher BAFCPl
1257 (1) M24. 19, Verrucosisporites tumulentus Clayton and Graham BAFC-Pl 1255 (1) C53/1. Scale bar/ escala gráfica: 1, 3, 4, 6, 8, 10,
11, 13= 20 µm. 2, 5, 7, 12, 15, 18= 15 µm. 9, 14, 16, 17, 19= 10 µm.
Phytoplankton
Ammonidium garrasinoi Ottone 1996 (figure 6.1)
Arkonites bilixus Legault 1973 (figure 6.2)
Crucidia camirense (Lobo Boneta) Ottone 1996 (figure
6.4)
Dactylofusa fastidiona (Cramer) Fensome, Williams,
Barss, Freeman and Hill 1990 (figure 6.5)
Dictyotidium munificum (Wicander and Wood) R.
Amenábar, di Pasquo, Carrizo and Azcuy 2006 (figure
6.6)
Dorsennidium pastoris (Deunff) Sarjeant and Stancliffe
1994 (figure 6.7)
Duvernaysphaera angelae Deunff 1964 (figure 6.8)
Duvernaysphaera tenuicingulata Staplin 1961 (figure 6.9)
Exochoderma arca Wicander and Wood 1981 (figure
6.10)
Exochoderma triangulata Wicander and Wood 1981
(figure 6.11)
Gorgonisphaeridium discissum Playford in Playford
and Dring 1981 (figure 6.12)
Gorgonisphaeridium vesculum Playford in Playford
and Dring 1981 (figure 6.13)
Gorgonisphaeridium spp.
Haspidopalla exornata (Deunff) Playford 1977 (figure
6.14)
Hemiruptia legaultii Ottone 1996 (figure 6.15)
Leiofusa sp. (figure 7.1)
Leiosphaeridia spp. (figure 7.2)
Maranhites mosesii (Sommer) Brito emend. Burjack and
Oliveira emend. González 2009 (figure 7.3)
Maranhites spp.
Micrhystridium? spinoglobosum (Staplin) Sarjeant and
Stancliffe 1994 (figure 7.4)
Multiplicisphaeridium ramispinosum (Staplin) Sarjeant
and Vavrdová 1997 (figure 7.5)
Multiplicisphaeridium sp. (figure 6.3)
Navifusa bacilla (Deunff) Playford 1977 (figure 7.6)
Papulogabata sp. A (figure 7.7)
Polygonium barredae Ottone 1996 (figure 7.8)
Pterospermella capitana Wicander 1974 (figure 7.9)
Pterospermella pernambucensis (Brito) Eisenack,
Cramer and Diez Rodriguez 1973 (figure 7.10)
Quadrisporites granulatus (Cramer) Ströther 1991
(figure 7.11)
Stellinium micropolygonale (Stockmans and Willière)
Playford 1977 (figure 7.12)
Tunisphaeridium caudatum Deunff and Evitt 1968
(figure 7.13)
Veryhachium (Tetraveryhachium) longispinosum (Jardiné et al.) Stancliffe and Sarjeant 1994 (figure 7.14)
Veryhachium (Veryhachium) trispinosum (Deunff)
Stancliffe and Sarjeant 1994 (figure 7.15)
Figure 6. 1, Ammonidium garrasinoi Ottone BAFC-Pl 2080 (1) R39. 2, Arkonites bilixus Legault BAFC-Pl 1255 (2) B20. 3,
Multiplicisphaeridium sp. BAFC-Pl 2080 (1) F40. 4, Crucidia camirense (Lobo Boneta) Ottone BAFC-Pl 1255 (1) D51. 5, Dactylofusa fastidiona (Cramer) Fensome, Williams, Sedley Barss, Freeman, J and Hill BAFC-Pl 1255 (1) V57/3. 6, Dictyotidium munificum (Wicander
and Wood) R. Amenábar, di Pasquo, Carrizo and Azcuy BAFC-Pl 2080 (2) J29/1. 7, Dorsennidium pastoris (Deunff) Sarjeant and
Stancliffe BAFC-Pl 2080 (1) T37. 8, Duvernaysphaera angelae Deunff BAFC-Pl 1256 (2) L43/4. 9, Duvernaysphaera tenuincingulata
Staplin BAFC-Pl 1255 (1) B54. 10, Exochoderma arca Wicander and Wood BAFC-Pl 1255 (1) M45/4. 11, Exochoderma triangulata
Wicander and Wood BAFC-Pl 1255 (2) Y46/2. 12, Gorgonisphaeridium discissum Playford in Playford and Dring BAFC-Pl 1255 (1)
Z40/2. 13, Gorgonisphaeridium vesculum Playford in Playford and Dring BAFC-Pl 2080 (1) T39/2. 14, Haspidopalla exornata (Deunff)
Playford BAFC-Pl 2080 (1) P25/1. 15, Hemiruptia legaultii Ottone BAFC-Pl 2081 (1) L31. Scale bar / escala gráfica: 1, 3, 4, 5, 6, 14, 15= 15
µm. 2, 8, 9, 12, 13= 10 µm. 7, 10, 11= 20 µm.
Figure 7. 1, Leiofusa sp. BAFC-Pl 1255 (1) O41. 2, Leiosphaeridia sp. BAFC-Pl 2080 (1) X37/2. 3, Maranhites mosesii (Sommer) Brito
emend. Burjack and Oliveira BAFC-Pl 1256 (1) U22/4. 4, Micrhystridium? spinoglobosum (Staplin) Sarjeant and Stancliffe BAFC-Pl 2080
(1) L45. 5, Multiplicisphaeridium ramispinosum (Staplin) Sarjeant and Vavrdová BAFC-Pl 1255 (1) M41/4. 6, Navifusa bacilla (Deunff)
Playford BAFC-Pl 2080 (1) P35. 7, Papulogabata sp. A. BAFC-Pl 2081 (3) Y33/1. 8, Polygonium barredae Ottone BAFC-Pl 1255 (2) R46/2.
9, Pterospermella capitana Wicander BAFC-Pl 2080 (1) P37/2. 10, Pterospermella pernambucencis (Brito) Eisenack, Cramer and Diez
Rodriguez BAFC-Pl 1255 (1) U43/3. 11, Quadrisporites granulatus (Cramer) Ströther BAFC-Pl 1255 (1) Y52. 12, Stellinium micropolygonale
(Stockmans and Willière) Playford BAFC-Pl 1255 (1) S47/4. 13, Tunisphaeridium caudatum Deunff and Evitt BAFC-Pl 1255 (2)
F20/3. 14, Veryhachium (Tetraveryhachium) longispinosum (Jardiné et al.) Stancliffe and Sarjeant BAFC-Pl 1255 (2) U49. 15, Veryhachium (Veryhachiurn) trispinosum (Deunff) Stancliffe and Sarjeant BAFC-Pl 2080 (1) T46/1. Scale bar / escala gráfica: 1, 6= 20 µm. 2, 3, 4, 5, 7,
9, 10, 11, 13, 14, 15= 15 µm. 8, 12= 10 µm.
Chitinozoans
Alpenachitina matogrossensis Burjack and Paris 1989
(figure 8.1)
Alpenachitina sp. cf. A. eisenacki Dunn and Miller 1964
(figure 8.2)
Ancyrochitina simplex Grahn, Bergamaschi and
Pereira 2002 (figure 8.3)
Ancyrochitina spp.
Angochitina katzeri Grahn and Melo 2002 (figure
8.4a,b)
Angochitina mourai Lange 1952 (figure 8.5a,b)
Angochitina spp.
Fungochitina pilosa Collinson and Scott 1958 (figure 8.7)
Fungochitina sp. (figure 8.6)
Ramochitina sp. cf. R. ramosi Sommer and Van Boekel
1964 (figure 8.8)
Figure 8. 1, Alpenachitina matogrossensis Burjack and Paris BAFC-Pl 1257 (1) K32, BAFC-Pl 1257 (1) L52/1. 2, Alpenachitina sp. cf. A.
eisenacki Dunn and Miller BAFC-Pl 1258 (2) M36/3. 3, Ancyrochitina simplex Grahn, Bergamaschi and Pereira BAFC-Pl 1257 (2) M54/2.
4a, Angochitina katzeri Grahn and Melo BAFC-Pl 2081 (1) C38/3; b, Detail of ornamentation / detalle de la ornamentación. 5a, Angochitina mourai Lange BAFC-Pl 2081 (1) V38/1; b, Detail of ornamentation / detalle de la ornamentación. 6, Fungochitina sp. BAFC-Pl 2081 (1)
O46/2. 7, Fungochitina pilosa Collinson and Scott BAFC-Pl 2081 (1) E37/2. 8, Ramochitina sp. cf. R. ramosi Sommer and Van Boekel
BAFC-Pl 1257 (1) Q39/2. Scale bar / escala gráfica: 1, 2, 3, 4, 5, 6= 28 µm. 7= 26 µm. 8= 15 µm.
Systematic descriptions
Trilete spores
Anteturma PROXIMEGERMINANTES Potonié
Turma TRILETES Reinsch emend. Dettmann
Suprasubturma ACAVATITRILETES Dettmann
Subturma AZONOTRILETES Lüber emend. Dettmann
Infraturma LAEVIGATI (Bennie and Kidston) PotoniéGenus Leiotriletes (Naumova) Potonié and Kremp 1954
Type species. L. sphaerotriangulus (Loose) Potonié and Kremp 1954.
Leiotriletes balapucensis di Pasquo 2007a Figure 5.8
Remarks. Of all the studied specimens in these samples, the better preserved one is the one illustrated herein. The lack of margin and exinal foldings, recurrent features in this species, offer a wide range of "apparent" ambs from subtriangular (see di Pasquo 2007a, p. 135, fig. 6. F-I) to round (see Amenábar et al. 2006, p. 354, fig. 5 E-J).
Infraturma MURORNATI Potonié and Kremp
Genus Acinosporites Richardson 1965
Type species. A. acanthomammillatus Richardson 1965.
Acinosporites lindlarensis Riegel 1968 Figure 4.3
Dimensions (6 specimens). 46- 64 µm.
Remarks. The mode for the size of the specimens
from Tonono is slightly smaller than the original
population.
Acinosporites sp. cf. A. eumammillatus Loboziak, Streel and Burjack 1988 Figure 4.4
Description. Trilete miospore with a subtriangular
amb. Thickness of the exine 1.5 µm. Laesurae arms elevated,
extending to the equator. Sculptural elements
biform, consisting on a wide base surmonted by a
small element, barely discernible.
Dimensions (1 specimen). 30 µm.
Remarks. The only specimen found, lacks a consistent
thickening of the equatorial region; hence the cf.
assignment.
Acinosporites sp. cf. A. macrospinosus Richardson 1965 Figure 4.5
Remarks. Acinosporites sp. cf. A. macrospinosus is slightly smaller and more rounded. The poor preservation prevents a more reliable identification.
Infraturma APICULATI Bennie and Kidston emend. Potonié
Subinfraturma VERRUCATI Dybová and JachowiczGenus Verrucosisporites Ibrahim emend. Smith 1971
Type species. V. verrucosus Ibrahim 1933.
Verrucosisporites sp. cf. V. loboziakii Marshall and Fletcher 2002 Figure 5.18
Description. Spore radial. Amb circular slighlty oval.
Suturae not visible. Exine sculptured proximally and
distally with verrucae of different sizes, which can be
anastomosed.
Dimensions. 70 µm (one specimen).
Remarks. The poor preservation and the lack of additional
specimens prevent a more precise assignment.
Paleomicroplankton
Group ACRITARCHA Evitt
Genus Multiplicisphaeridium Staplin emend. Sarjeant and Vavrdová 1997.
Type species. M. ramispinosum Staplin emend. Sarjeant and Vavrdová 1997.
Multiplicisphaeridium sp. Figure 6.3
Description. Vesicle spherical, psilate. Numerous
processes, hollow, laevigate as well, homomorphic
to slighltly heteromorphic, with circular bases
proximally contacting the vesicle and acuminated
distal extremities, free communicated with the
vesicle.
Dimensions. Vesicle diameter: 40 µm; processes 9.5
µm long (one specimen).
Remarks. Multiplicisphaeridium sp. resembles Baltisphaerosum sp. in Ottone 1996 even though the former
does not show any basal plug in the processes.
Genus Dorsennidium Wicander emend. Sarjeant and Stancliffe 1994
Type species. D. patulum Wicander 1974.
Dorsennidium pastoris (Deunff) Sarjeant and Stancliffe 1994 Figure 6.7
Remarks. This specimen resembles Villosacapsula semipunctata (Pöthe de Baldis) Sarjeant and Vavrdová 1997 but it has more processes and these are not ornamented. Genus Leiofusa Eisenack emend. Eisenack emend. Combaz et al. emend. Cramer 1970
Type species. Leiofusa fusiformis Eisenack ex Eisenack 1938.
Leiofusa sp. Figure 7.1
Remarks. Leiofusa sp. resembles L. pyrena Wicander and Wood 1981; however, the missing part of this single specimen prevents specific identification. Leiofusa sp. in Ottone (1996, Plate 7, figure 13) has a thiner wall and longer processes.
Genus Papulogabata Playford in Playford and Dring 1981
Type species. P. annulata Playford in Playford and Dring 1981.
Papulogabata sp. A Figure 7.7
Diagnosis. Circular to subcircular vesicle; surface
psilate. Wall presenting three radial thickenings, the
one on the margin is 4 µm in width, the following one
is 8 µm wide and the one closer to the center, surrounding
the cyclopyle (11 µm), is 5 µm.
Comparisons and remarks. Papulogabata annulata Playford in Playford and Dring 1981 is smaller and
has only one thickened ring. P. persica Ghavidel-Syooki
(2003) is much bigger and the vesicle wall can be
scabrated. Because only one specimen of Papulogabata sp. A was found it is placed in open nomenclature.
Chitinozoans
Group CHITINOZOA Eisenack
Order PROSOMATIFERA Eisenack
Family CONOCHITINIDAE Eisenack emend. Paris
Subfamily ANCYROCHITININAE ParisGenus Alpenachitina Dunn and Miller 1964
Type species. A. eisenacki Dunn and Miller 1964.
Alpenachitina sp. cf. A. eisenacki Dunn and Miller 1964 Figure 8.2
Remarks. Despite the poor preservation, the specimen bears processes by the basal margin and by the shoulder, even though the missing collarette and the lack of further specimens prevent a more accurate assignment.
Family LAGENOCHITINIDAE Eisenack emend. Paris
Subfamily ANGOCHITININAE ParisGenus Ramochitina Sommer and van Boekel emend. Paris et al. 1999
Type species. R. ramosi Sommer and van Boekel 1964.
Ramochitina sp. cf. R. ramosi Sommer and Van Boekel 1964 Figure 8.8
Remarks. Because only a fragment of a specimen was found and despite its outstanding ornamentation, a more accurate identification is impossible.
Genus Fungochitina Taugourdeau 1966
Type species. Conochitina fungiformis Eisenack 1931.
Fungochitina sp. Figure 8.6
Remarks. Fungochitina sp. resembles Fungochitina sp. cf. F. pilosa in Grahn and Melo 2002, but the shorter, robust spines, characteristic of this species are difficult to distinguish without a SEM image.
Composition of the assemblages and palaeoenvironmental considerations
The complete microflora recovered along the investigated
interval of the Tonono x-1 Borehole comprises
73 relatively well-preserved species represented
by diverse palynological groups such as trilete
spores (35 species), microplankton including several
prasinophycean and acritarch taxa together with
chlorophycean algae such as Quadrisporites (30
species) and chitinozoans (8 species) (figures 3- 8).
Thermal maturity (TAI) varies between 2 and 3 according
to the scale of Utting et al. (in Utting and
Wielens, 1992). Phytoclasts, such as tracheids and cuticular
fragments, are frequent.
In order to characterize the palynofacies, a matrix
was constructed with the relative percentages of the
palynomorphs and the PMI, as explained previously
(chart 1).
Chart 1. Relative percentage of the phytoclasts and palynomorph
groups and values of Palynologycal Marine Index (PMI) of the assemblages
registered in the Tonono x-1 well / porcentajes relativos
de los fitoclastos y grupos de palinomorfos y valores del Indice Marino
Palinológico (IMP) de las asociaciones registradas en el pozo Tonono x-1.
The palynofacies analysis and quantitative data
displayed reflect paleoenvironmental changes during
the deposition of the succession.
The palynoassemblage of BAFC-Pl 1258 and 1257
is very poorly preserved. There is a high proportion
of structured and unstructured phytodebris and a
very low diversity of palynomorphs. They have similar
PMI values (chart 1) which fall within the lower
values range. The high input of USP together with
the low values of PMI could reflect a nearshore
palaeoenvironment.
The lowest value of PMI is recorded in the palynoassemblage
of BAFC-Pl 1256, in coincidence with
the highest proportion of spores, structured phytodebris
and black phytodebris (chart 1) supporting a
very marginal deposition environment.
Both palynofloras of BAFC-Pl 1255 and 2080
yielded the highest PMI values and phytoplankton
proportion although AOM is absent in the former
and very abundant in the latter. This suggests a closer
affinity with the BAFC-Pl 2081 where AOM proportion
is high as well as the content of phytoplankton
and chitinozoans (chart 1), features that would
reinforce the idea of a marine origin for the amorphous
organic matter (Batten, 1996). AOM is usually
the dominant organic component of sediments accumulated
under anoxic conditions, especially in areas
removed from significant influence of terrestrial input
(e.g., Tyson, 1995). Therefore, a more distal environment
is proposed for the levels BAFC-Pl 2080 and 2081.Even though level BAFC-Pl 1255 has a high
PMI, meaning a high diversity of microplankton, this
value accompanied by a similar proportion of spores
and phytoplankton (see chart 1) suggests a more
marginal setting -an intermediate deposition environment
in between the level BAFC-Pl 1256, representing
the nearest shore one- and the top levels
(BAFC-Pl 2080, 2081).
Age assessment and correlation
Three assemblages are defined based on the
stratigraphic distribution of taxa along the studied
interval, presence/absence of key taxa (see figures 3,
9) as well as abundances of different groups of taxa
(chart 1) and palynofacies analysis. Unfortunately,
the only lithological information available for this
study was the one provided by the interpretation of
the electric log.
The assemblages are characterized by many species
in common with palynofloras from South America and
selected ones from other regions (figure 9).
Figure 9. Stratigraphic ranges of selected taxa occuring in the Tonono x-1 Borehole based on the selected literature / rangos estratigráficos de taxa seleccionados del Pozo Tonono x-1: Marhoumi and Rausscher (1984), McGregor and Playford (1992), Turnau (1996), Quadros
(1999), Vavrdová and Isaacson (1999), Marshall and Fletcher (2002), Grahn (2005 and references therein), Hashemi and Playford (2005),
Grahn et al. (2006), di Pasquo (2007a, and references therein), Al-Ghazi (2007), Amenábar (2007), Amenábar et al. (2006, 2007, and references
therein), di Pasquo and Noetinger (2008), di Pasquo et al. (2009, and references therein), González (2009).
Palynoassemblage To1 (3945-3640,5 m interval)
Although the general preservation of the organic matter is very poor, some stratigraphically important species are recognized. The inception and disapearance of some species with a restricted stratigraphic distribution support a late Eifelian to earliest Givetian age for this interval (see figure 9). The co-occurrence of Acinosporites acanthomammillatus and Acinosporites sp. cf. A. macrospinosus allow its correlation with the lower part of the late Eifelian AD (Acinosporites acanthomammillatus-Densosporites devonicus) Zone of the Ardenne-Rhenish region (Streel et al., 1987), and the Calyptosporites velatus-Rhabdosporites langii and Densosporites devonicus-Grandispora naumovii Assemblage Zones of the Old Red Sandstone Continent (Richardson and McGregor, 1986) and the Grandispora pseudoreticulata Zone (Limachi et al., 1996). Occurrence of Grandispora permulta supports the correlation with the Grandispora permulta Interval Zone (Per), of late early Eifelian through the Eifelian/ Givetian transition, for the Amazon Basin (Melo and Loboziak, 2003). Several common species (e.g., Acinosporites acanthomammillatus, A. lindlarensis, A. macrospinosus, Dibolisporites eifeliensis, D. quebecensis, Grandispora douglastownense) support its correlation with assemblage 1 of the Los Monos Formation at Balapuca (di Pasquo, 2007a,2007b) and the assemblage 2 of the Chigua Formation at Del Chaco Creek (Amenábar, 2007). Moreover, Alpenachitina matogrossensis and Ancyrochitina simplex are recorded in the Alpenachitina eisenacki-Spinachitina biconstricta Concurrent Range Zone of late Eifelian?-early Givetian age in the Paraná basin (Grahn et al., 2002), which is correlated to the Alpenachitina eisenacki Biozone for Western Gondwana (Grahn, 2005). Other taxa disappear around the early Givetian on a world-wide basis (e.g., Dibolisporites eifeliensis, Verrucosisporites sp. cf. V. loboziakii, Alpenachitina sp. cf. A. eisenacki, Ramochitina sp. cf. R. ramosi).
Palynoassemblage To2 (3365,5-3289,5 m Interval)
This assemblage is better preserved than the one
below. The appearance of Geminospora lemurata, in
agreement with the base of the ensensis obliquimarginatus Conodont Zone sensu Weddige (1984; see Loboziak
and Streel, 1995) -together with Biharisporites
parviornatus recognized as a ?late Eifelian - mid-late
Givetian taxon in South America (see di Pasquo,
2007a)- suggests a Givetian age. The appearances
within this interval of Leiotriletes balapucensis, Aneurospora
greggsii, Acinosporites ledundae, Raistrickia aratra,
Arkonites bilixus, Ammonidium garrasinoi, Duvernaysphaera
angelae, Exochoderma triangulata, Maranhites
mosesii, Verrucosisporites tumulentus among others
reinforce this age (see figures 3 and 9).
This assemblage can be correlated with the midlate
Givetian assemblage 2 of Los Monos Formation
at Balapuca (di Pasquo, 2007a, 2007b) from Bolivia,
the assemblage 3 of Chigua Formation at La
Cortadera Creek (Amenábar et al., 2006, 2007), partially
with the palynoflora of the Los Monos
Formation at Galarza Creek (Ottone, 1996) and probably
with the microflora of the Punta Negra
Formation (Rubinstein, 1999, 2000) from Argentina.
In contrast, comparison with the Givetian Verrucosisporites
premnus/V. scurrus Zone of Limachi et al. (1996) of Bolivia and with the Geminospora lemurata- Chelinospora ex gr. ligurata Interval Zone (LLi) for
the Amazon Basin (Melo and Loboziak, 2003) is difficult
because there are few species in common (e.g., Verrucosisporites scurrus, Arkonites bilixus, Geminospora
lemurata).
Assemblage III of Hashemi and Playford (2005),
attributed to the late Givetian-early Frasnian, and the
Frasnian microfloras documented by Balme (1988)
and Playford and Dring (1981) for the Gneudna
Formation in the Carnarvon Basin (Australia) share
with the studied Palynoassemblage To2 only the cosmopolitan
age-diagnostic taxa such as Geminospora
lemurata, Verrucosisporites tumulentus, V. scurrus and Gorgonisphaeridium discissum.
Palynoassemblage To3 (3133- 3077 m Interval)
Preservation of the palynomorphs is fairly good. Only a few key species are recognized at the top of the interval. These are Acinosporites sp. cf. A. eumammillatus together with some key chitinozoans such as Angochitina katzeri, Fungochitina pilosa and Angochitina mourai. The first occurence of A. mourai indicates the base of the Frasnian in all intracratonic basins of Brazil (Gaugris and Grahn, 2006) and its abundance associated to acritarchs and chitinozoans such as Hoegisphaera glabra and Ancyrochitina sp. render an upper Frasnian age in the Bolivian Devonian (Racheboeuf et al., 1993). The occurrence of Cymbosporites catillus -that first appearsing in the highest levels of the LLi Zone (see Melo and Loboziak, 2003)- is recorded here within this interval. This assemblage shares several species with the wide ranging association documented by Ottone (1996) in the Los Monos Formation attributed to the late Givetian-early Frasnian. The association is correlated to the Concurrent Range Zone of Hoegisphaera glabra and Ramochitina derbyi -which defines the Frasnian beds of Brazil (Grahn et al., 2002)- and the Frasnian Hoegisphaera glabra Biozone (Grahn, 2005) on the basis of the presence of the chitinozoans (see figure 3). Hence, a Frasnian age is supported for this assemblage by the significant increase of marine elements and AOM between To2 and To3, which would probably have occurred as a response to a maximum flooding event, possibly related to major global eustatic changes during this time (see Noetinger and di Pasquo, 2008b).
Concluding remarks
This study presents new palynological data on
spores and microplankton for the Tonono x-1 borehole.
The stratigraphic distribution of 73 species of trilete
spores (35 species), microplankton including several
prasinophycean and acritarch taxa together with
chlorophycean algae such Quadrisporites (30 species)
and chitinozoans (8 species) along the studied interval
(between 3945-3077 m) of the Tonono x-1 allow the definition
of three palynoassemblages. Diagnostic markers
present in these assemblages support a late Eifelian
to early Frasnian age to the whole interval. Palynoassemblage
To1 ranges from the late Eifelian to earliest
Givetian. A Givetian age is proposed for association
To2 whilst an early Frasnian is suggested on the
basis of few species for the assemblage To3.
The whole interval corresponds to the Tonono
Formation. The upper part could be attributed to the
Jollín Member and the basal part to the Michicola
Formation according to lithology and age of the assemblages
(see figure 2).
These assemblages contain many cosmpolitan index
species (e.g., Geminospora lemurata, Dibolisporites
eifeliensis, Verrucosisporites scurrus, Grandispora douglastownense
and Acinosporites acanthomammillatus)
that support the correlation mainly with Brazilian
and Euro-American zonations. Other age-diagnostic
taxa are exclusively recorded from South America
(e.g., Grandispora pseudoreticulata, Grandispora brevizonata,
Leiotriletes balapucensis, Acinosporites ledundae),
belonging to the Mid-Devonian to Frasnian Afro-
South American Subrealm (di Pasquo et al., 2009).
Assemblages To1 and To2 are interpreted as reflecting
nearshore, shallow marine depositional conditions,
characterized by a very high terrestrial input,
and variable marine influence. This is in agreement
with a trend towards a sea-level drop proposed by
Albariño et al. (2002), and recorded in this region from
the early Eifelian and apparently maintained through
the Givetian. Assemblage To3 represents a transgressive
period with high diversity and abundance of microplankton
along with high AOM content. It seems
that this change was gradual from continental conditions
during the deposition of To2 (see chart 1) to
shelf marine environments in To3, in agreement with
the record of a new transgressive cycle in the latest
Givetian-early Frasnian according to Albariño et al.
(2002) and Noetinger and di Pasquo (2008b).
Acknowledgements
Thanks are given to Mercedes di Pasquo for her critical comments, invaluable support and constant motivation; to C. Rubinstein, J. Marshall and an anonymous reviewer for their careful and constructive reviews and to Repsol-YPF, for providing the core samples of the Tonono x-1 well in 1998 with permission to publish the results G. Holfeltz is thanked for processing the samples. This study is part of the Ph D. thesis of the author and it was supported with funds from the Agencia Nacional de Promoción Científica y Tecnológica (PICTR 00313/03), the Consejo Nacional de Investigaciones Científicas y Técnicas (PIP 5518 CONICET) and the University of Buenos Aires (UBACYT X 428).
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Recibido: 24 de febrero de 2009.
Adeptado: 6 de octubre de 2009.