Silurian microplankton from the Cachipunco Formation ( Santa Bárbara Range ; Andina Central Basin ) , Jujuy , Argentina

The palynological content of Cachipunco Formation is described in this contribution. This formation lies in the Santa Barbara Range, Jujuy Province, and outcrops at two localities: Angosto Los Pereyras and Cumbre los Pereyras. The more complete succession is the one from Angosto Los Pereyras, where the formation comprises 273 m of dark siltstones interstratified with thin sandstones and without visible base or top. The microfloristic associations are characterized by the presence of: Ammonidium ludloviense (Lister) Dorning, Barbestiastra barbata (Downie) Sarjeant & Stancliffe, Domasia quadrispinosa Hill, Leiofusa exilata Dorning, L. parvitatis Loeblich, Multiplicisphaeridium arbusculum Dorning, M. eoplancktonicum (Eisenack) Lister, Neoveryhachium carminae Cramer, Proteolobus cylindricus Al-Ruwaili, Tylotopalla maraca Díez & Cramer, T. robustispinosa (Downie) Eisenack et al., Veryhachium trisphaeridium Downie, and Ambitisporites avitus Hoffmeister. According to the stratigraphic distribution of the theses species, the age of the Cachipunco Formation can be constrained to a Wenlockian-Ludlovian range. A new species is proposed Multiplicisphaeridium baldisii sp. nov.

Zapla Formation is composed mainly by argillaceous sandstones, which present disperse quartz clasts; sandstones and diamictits.It may reach up to 100 m in thickness and it was originally referred to the Llandoverian, based on stratigraphic correlation (Antelo, 1973;Cuerda & Antelo, 1973).Notwithstanding, more recent works (Monaldi & Boso, 1987;Astini et al., 2004;Rubinstein, 2005;de La Puente & Rubinstein, 2007;Rubinstein et al., 2007) reassigned it to the Ordovician due to the finding of Dalmatina at the top of the unit.Lipeón Formation comprises a monotonous succession, between 600 and 1,600 metres in thickness, of siltstones and fossiliferous sandstones.According to Andreis et al. (1982), it formed in an extern marine platform, beneath the wave base level.Benedetto et al. (1992) gave this formation a Llandoverian-Pridolian age, but Rubinstein & Toro (2006) assigned it to the Llandovery-Ludlow based on the palynomorphs and graptolites content.
In outline, Cachipunco Formation comprises a succession of laminated black shales, rich in fossils and pyrite, interstratified with quarcitic sandstones.It is partially equivalent to Lipeon Formation, with a greater participation of sandstones.According to Mingramm et al. (1979) it would have been deposited in a sublitoral marine environment.This unit was proposed by Padula et al. (1967) grouping the "piso Z1" of Hagerman (1933) and Bellmann´s "Gotlandico" (1962).
The aim of the present paper is to discuss the palynological content (acritarchs, prasinophyceaes and spores), from the Cachipunco Formation, in the Santa Bárbara range (South-eastern Jujuy Province; Fig. 1.2).Benedetto et al., 1992).2, Geological Map of Santa Barbara Range.

GEOLOGICAL SETTING AND BIOSTRATIGRAPHY
The palynological samples were collected from two different sections both corresponding to the Cachipunco Formation: Angosto Los Pereyras and Cumbre Los Pereyras (Fig. 1.2).The area is located approximately 150 km to the Southeast of San Salvador de Jujuy, Jujuy Province.

Angosto Los Pereyras
Angosto Los Pereyras is located to the North of the Arroyo Colorado and to the East of Santa Clara City.At this location, Cachipunco Formation comprises 273 meters of micaceous, dark-grey to yellow siltstones without visible base or top (Fig. 2.1).These siltstones, which are bioturbated, are intercalated with thin beds of light-grey, micaceous, argillaceous fine sandstones

Cumbre Los Pereyras
This section is located near 8 kilometers to the north of Angosto Los Pereyras.It comprises 135 meters of siltstones and sandstones, of similar characteristics of those from Angosto Los Pereyras, but with a larger proportion of sandstones than in the latter (Fig. 2.2).

Biostratigraphy
Cachipunco Formation was originally referred to the Early Devonian due to the presence of macrofloristic remains (see Padula et al., 1967, Mingramm et al., 1979).Subsequently, was transferred to the Middle-Late Silurian (Baldis, 1972;Antelo, 1978;Vistalli, 1990), and more recently, Grahn & Gutiérrez (2001), assigned it a Late Llandoverian Early Pridolian age, based on the analysis of the chitinozoa content of the unit.

MATERIALS AND METHODS
Forty palynological samples were collected from the Cachipunco Formation, 30 of which were found to be productive.Samples were processed using palynological HCl-HF-HCl acid maceration techniques (see Wood et al., 1996).Slides were examined using light microscopy and scanning electronic microscopy.
Light photomicrographs were taken on an Olympus BX-51 microscope using an Olympus C-5000 digital camera, while the scanning micrographs were taken on Philips XL-30 at 20 kV.All figured material is housed in the collection of the MACN (Museo Argentino de Ciencias Naturales "B.Rivadavia") under the prefixes BA Pal (Buenos Aires, Palynology).The specimen locations are referred using England Finder coordinates.
The preservation state of the material is quite bad, being the majority of specimens fragmented, often impregnated with pyrite and most of them showing signs of corrosion.Such situation made difficult the assignment of same palynomorphs.
For identification purposes, different measures were taken, as referred on the systematic section., where N1 and N3 represent the minimum and the maximum value measured respectively, and N2 the mean for all the specimens evaluated.The number of specimens measured appears between brackets.In the Synonym and Distribution sections it is included primarily the material described for Argentina.For the graphic showing vertical and percentage distributions (Figs. 3 and 4) there where counted between 200 and 300 palynomorphs per slide.
Remarks.These specimens are assigned to Ammonidium cf.waldronense (Tappan & Loeblich) Dorning since the number of processes is not as high as it is in the holotype (more than 40; Tappan & Loebliech, 1971) and no assessment of the vesicle ornamentation can be made due to the bad preservation state of the material.The material illustrated by Pöthe de Baldis (1987) as Caiacorymbifer cf.waldronis (sic) might be considered to be co-specific with the one described here, based on the processes characteristics and the relationship processes length/vesicle diameter (0.37 in Pöthe de Baldis 1987).
Ammonidium sp.A (Fig. 3.3)  Playford (1977) have been considered by several authors (Playford, 1977;Sarjeant & Vavrdova, 1997) to be synonyms.Mullins (2002) maintained them as separated species, hinged on the characteristics of the processes, being broader-based and more robust in D remota, and the ornamentation of the vesicle, which is micropuntuate to foveolate in D. denticulata.Additionally to this, we consider D. remota to have a distinct sub polygonal vesicle, and more processes than D. denticulata.Therefore, we consider them to be different species.
The specimens described as D. cf.remota (Deunff) Playford by Pöthe de Baldis (1997a), clearly presents all the distinct characteristics of D. denticulata, a globular vesicle with few processes arising from it, so we reassign them herein.In the same way, the material illustrated by Pöthe de Baldis (1997b), depict similar characteristics to those of D. denticulata, a spherical vesicle, with 4-5 long processes, and therefore is reassigned to that species.Probably, the material described by Rubinstein (1997) as Evittia denticulata denticulata (Cramer) Le Hérissé, also corresponds to D. denticulata, since both preset similar vesicle and processes characteristics.(Deunff) Playford 1977 (Fig. 3.8) Dimensions.V∅ = 22(28.2)36µm, PL = 20(27.7)37µm, P∅B = 3(3.9)5µm, P∅D = 0.5-1.5 µm; 7-13 processes (20 specimens measured).Remarks.Diexallophasis denticulata (Stockmans & Willière) Loeblich (1970) has lesser processes and a subspherical vesicle.Diexallophasis downtongorgensis Mullins (2004) Wood (1981), as the latter is larger and has most process bifurcated.Diexallophasis sp A is differentiate from D. denticulata due to the vesicle shape (being in the former much more polygonal than in the latter), to the presence of ridges in the base of the processes and the fact that distal ends in this species are acuminated and do not show any type of bifurcation.Diexallophasis remota is separated from D. sp A. based on this species has a quadrangular vesicle, with lesser processes (up to 6) than D. remota.Diexallophasis mucronata (Stockmans & Willière) Priewalder has a smaller vesicle and its processes present a distinct pattern of branching (Stockmans & Willière, 1963;Priewalder, 1987).It differs from D. downtongorgensis Mullins (2004) in having a larger vesicle, more notorious ornamentation and the same wall thickness in both, vesicle and processes.
Remarks.Almost all specimens are incomplete.
According to Fensome et al. (1990) Eupoikilofusa filifera is an invalid combination and it must be referred to Dactylofusa filifera (Downie) Fensome et al. (1990), however Dorning (1994) made a revision of these generas maintaining as a valid genera Eupoikilofusa.The differentiation between E. sriatifera and E. filifera is based on the number and general characteristics of their striaes.In the first one, striaes appear in a large number, being them thin and discontinuous, while in the second one, the striaes are thick, continuous and there are only between 2 to 5 of them in each individual.
In conformity with this, Leiofusa argentina Pöthe de Baldis (1971) is a junior synonym of E. filifera not of E. striatifera as stated by Priewalder (1987).The material described by Rubinstein (1990), and classified as L. cf.striata Britos & Santos, could be reubicated as E. filifera due to the number (2-4) and characteristics of the striations seen on the illustration of that specimen.The material from La Horqueta Formation categorized as Dactylofusa striatifera (Cramer) Fensome et al. (Rubinstein, 1997) seem to be E. filifera (Downie) Dorning, due to the number of the striations (4) that can be seen in the illustration.
Eupoikilofusa striatifera (Cramer) (1965) is considered to be a junior synonym of L. bernesgae by Moreau-Benoit (1974).The differences in size of the material described by Pöthe de Baldis (1975a) and Rubinstein (1990) are not enough criteria to separate these materials from L. bernesgae, as stated also by Rubinstein (1992b).Leiofusa "banderilla" Cramer, described by Pöthe de Baldis (1971), showed all the distinctive characteristics (shape and size of the vesicle, length of the processes) of L. bernesgae, consequently it becomes reassigned here.Leiofusa banderillae Cramer (Pöthe de Baldis, 1987) has the appearance of being a specimen of L. bernesgae, but both processes are broken, making such designation impossible.The original material of L. banderillae Cramer (1964a) has longer processes (between 100-150 µm).Remarks.All specimens are incomplete.Leiofusa fusiformis Eisenack (1934) presents a pilome and a different shape of the processes; L. parvitatis Loeblich (1970) is smaller (the overall length varies from 50 to 93 µm).Eupoikilofusa filifera (Downie) Dorning (1981) and E. striatifera (Cramer) Cramer (1970a) are similar in size, but both present striations (or folds) on their surface.Eupoikilofusa tenuistriata (Pöthe de Baldis) Pöthe de Baldis (1981) presents subtle striations on its wall and has a different vesicle shape.
Remarks.Despite the fact that Leiofusa exilata Dorning (1981) is smaller in width than the specimens described here, we assigned it to this species based on the similarities both share in length, general shape and relation: vesicle width/ total length.Leiofusa exilata is also similar in size to L. estrecha Cramer (1964a), differing from it the overall shape and the width/total length relationship.Remarks.Leiofusa estrecha Cramer (1964a) is larger (overall length varies between 120-400 µm).Eupoikilofusa filifera (Downie) Dorning (1981) is also larger and displays between 3-5 thickenings on its surface.Remarks.Leiofusa cf.tumida Downie as described by Rubinstein (1990) is smaller (total length is 60 µm), but the difference in size is not enough criterions to substantiate its separation.Remarks.In all the observed individuals processes were broken, making a more accurate assignation impossible.The specimens illustrated by Pöthe de Baldis (1975aBaldis ( , 1981Baldis ( , 1997aBaldis ( , 1998) ) as Leiofusa aff.estrecha, L. banderillae, L. tumida, and L. bernesgae respectively, display all the characteristics of the species described here.Leiofusa sp.A differs from L. bernesgae Cramer (1964a) and L. tumida Downie (1959) in the shape of the vesicle (which is cylindrical to rectangular in the former) and the nature of its processes (which are solid).It can be distinguished from L. estrecha based on its size (being the latter much larger, with overall lenghts that varies from 120 to 400 µm) and from L. banderillae Cramer (1964a) contrasting the length (around 100-150 µm) and nature of the processes, as well as the shape of the vesicle.

Leiofusa tumida
Genus    Baldis (1974) display wide variations in the branching pattern.According to the characteristics depict by Fig. 5 -the presence of processes both acuminated and bifurcated and the fact that such bifurcations take place at half of the processes' length-we consider proper to reassign such material to M. arbusculum.Multiplicisphaeridium ramusculosum Lister (1970)  Remarks.This species is characterized by the shape and width of its processes, the variations in the ramification patterns and the lack of conspicuous ornamentation.The characteristics exhibit by the material described as Multiplicisphaeridium ramusculosum Deflandre by Pöthe de Baldis (1974) -wide processes and a conspicuous ramification patternallow their reinterpretation as M. baldisii sp.nov.Multiplicisphaeridium ramusculosum has longer and slender processes than M. baldisii.Pöthe de Baldis (2000) assigned individuals similar to M. baldisii to the specie Evittia escobaides (Cramer 1964b), but the latter has a polygonal vesicle and presents only one order of branching, characteristics that clearly distinguish both species.
Multiplicisphaeridium baldisii is differentiated from M. sp.A, as described on this work, based on the length, shape and number of the processes.It differs from M. sp B in the pattern of ramification of the processes.It is separated of M. sp C due to the shape of the processes, being in the latter mucho wider at the base, and presenting high-angled bifurcations.Also, M. sp.C has distally solid pinnulas.(Eisenack) Lister 1970 (Fig. 5.4)  Sarjeant & Vavrdová (1997).The main characteristic to differentiate both genera is the nature of their processes.In Oppilatala, processes do no communicate freely with the vesicle interior since their bases have a basal plug, while in Multiplicisphaeridium are open to the vesicle cavity.So, if the original holotype of M. eoplanctonicum has their processes in free communication with the vesicle interior, as it is described, the assignment of this specie to the genus Oppilatala would be erroneous.Consequently, the assignment of this specie to the genus Multiplicisphaeridium is based on the fact that the processes are open to the vesicle interior.Multiplicisphaeridium eoplancktonicum differs from M. arbusculum Dorning (1981) in having a distinct branching pattern, in the former is irregular, while in the latter, the processes branch dichotomously several times.Multiplicisphaeridium ramusculosum Lister (1970) has processes that branched distally.(Deflandre) Lister 1970 (Fig. 5.6) Dimensions.VØ = 22(26.3)(5 specimens measured).

Multiplicisphaeridium ramusculosum
Remarks.Multiplicisphaeridium snigirevskaiae (Stockmans & Willèrie, 1963;Fensome et al., 1990) is similar in size and pattern of branching, but it has a hexagonal vesicle.It differs from M. pardaminum Díez & Cramer (1976) in having shorter processes and another branching style.Multiplicisphaeridium fermosum Cramer (1970) has ramifications up to the 3rd order, and present a slightly different ramification pattern.
Multiplicisphaeridium ramusculosum Lister (1970), M. arbusculum Dorning (1981), and M. eoplanctonicum (Eisenack) Lister (1970) have more flexible, longer and slender processes.It is differentiate from all the other species described here due to the characteristics of its processes (base diameter and ramification pattern).A more exact assignation could not be made due to the state in which the material is found.
According to Mullins (2001) N. carminae has also a more complex pattern of folds.Due to a preservation bias, not all the individuals observed here show the pattern of folds.The specimens described by Pöthe de Baldis as N.? sp.(Pöthe de Baldis, 1998) and Veryhachium valiente Cramer (Pöthe de Baldis, 1998) are very similar to the specimens assigned here to N. carminae.It has similar dimension of vesicle and processes.The absence of the characteristic fold of Neoveryhachium may be due to a preservation bias.Genus Onondagaella Cramer emend.Playford 1977 Type species: Veryhachium asymmetricum Deunff 1954 (a nomen nudum until validated by Deunff, 1961).
Onondagaella asymmetrica (Deunff) Cramer 1966 (Figs. 6.1, 7.4) Remarks.Since the small number of specimens present, we uncertainly assigned this species based on the width of its processes, since they are much shorter and broader than in the holotype as described by Mullins (2001).

ACRITARCA INCERTAE SEDIS
Acritarca type A (Fig. 6.9) Description.Vesicle polygonal in outline, formed by the coalescence of 7 to 9 conical processes.The broad-based processes are bifurcated up to three times.The first bifurcation develops at half of the process's length.Vesicle and processes evenly covered with grana and/or spines.No excystment method observed.
Remarks.This species is differentiated from Barbestiastra Downie emend.Sarjeant & Stancliffe (1994) due to the fact that Barbestiastra has acuminate processes while this species present distal ramifications.

MICROPLANKTON CHARACTERISTICS
Angosto de Los Pereyras Section (Fig. 8) The analized associations present a great diversity of species between the 10 and 140 meters, being identified more than 22 species in each level.On the other hand, in the base and the superior section of the stratigraphic column the specific diversity is much lower (between 8-17 species per level) At a generic level, associations are clearly dominated by the Leiospaeridia genera, with minor participation of Onondogaella, Multiplicisphaeridium, Diexallophasis, Verhya chium, Neovarhyachium, and Leiofusa.
A Wenlockian-Ludlovian age is inferred for this association based on the stratigraphic range of the most important species identified for it (Fig. 5).
The age for this section, as stated by Grahn & Gutiérrez (2001) based on the chitinzoarian content, is slightly younger (Wenlokiano-Pridoliano) Figs. 8. Percentage distributions of the taxas identified at Angosto los Pereyras (Fig. 3) and Cumbre Los Pereyras (Fig. 4) according to the following than the age obteneid from the acritarchs (Ludlovoian-Wenlockian).
Cumbre de Los Pereyras Section (Fig. 9) The inferior sector of this section (30 meters) comprises only one palynological association (BA Pal 6003).In that section only Leiosphaeridia and some specimens of Gorgonispaeridium where identified.Between the 40 and 120 meters, the studied associations (7 in total) display a moderate to low diversity (between 3-20 species per level).
Taking into account the previous distribution in other Argentinian formations of the identified taxones from Cachipunco Formation (Fig. 11) it is possible to notice a remarkable afinity with the palynoflore from Los Espejos Formation.
Though the palynological association from that litostratigraphic unit is one of the better known of Argentina (see Rubinstein, 1993Rubinstein, , 1995)), is important to mention the fact that 27 species over a total of 36, have been identified for both formations.

CONCLUSIONS
The palynological content of Cachipunco Formation is described here for the first time.The following species: Domasia quadrispinosa, Leiofusa exilata, L. parvitatis, Proteolobus cylindricus y Tylotopalala maraca, are described for the first time for the Silurian of Argentina.A new species, Multipliscispharidium baldisii, is here proposed.
Finally, based on the palynological content of the Cachipunco Formation, a Wenlock-Ludlow age is assigned to this litostratigraphic unit.Such age, slightly differs from the one obteined by Grahn & Gutiérrez (Wenlock-Pridoli, 2001), from the chitinozoarian content of this formation.

Fig. 1 .
Fig. 1. 1, Map showing the location of the Silurian Central Andean Basin in South America (Modified fromBenedetto et al., 1992).2, Geological Map of Santa Barbara Range.
Abbreviations of such measures are as follows: V∅ = Diameter of the vesicle; VW = Width of the vesicle; VL = Length of the vesicle; VT = Total length of the vesicle (including processes); PL = Length of the processes; PN = Number of processes; PØ = Diameter of the processes; P∅B = Diameter of the bases of the processes; P∅D = Diameter of the distal end of the processes; PL/V∅ = Length of the processes/ vesicle diameter ratio; VW/VL = Vesicle width/ vesicle length ratio; VW/VT = Vesicle width/vesicle total length ratio; ∅ = Diameter (for spores); Cw = Cingule width; Zw = Zone width.Such measures are presented in the format N1 (N2) N3
Silurian microplankton from the Cachipunco Formation concave.A short process arises from each pole of the vesicle.Processes are hollow, open to vesicle cavity and simple.They are preferentially displaced to the straighter side of the vesicle.No excystment method observed.