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Volume 8, NO 4, Decernber 20fO m The Late Palaeozoic of western Gondwana: new contributions from southern South America Edited by LA. Spalletti, C.O. Limarino and S. Geuna UAB . I r- - . . CTJA ida, CSIC U.Ht.*L.Uhh-.-. i

Geologica Acta

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Page 1: Geologica Acta

Volume 8, NO 4, Decernber 2 0 f O m

The Late Palaeozoic of western Gondwana: new contributions

from southern South America

Edited by LA. Spalletti, C.O. Limarino and S. Geuna


r - - . . CTJA ida, CSIC U.Ht.*L.Uhh-.-.


Page 2: Geologica Acta
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ISSN 1695-6133 Online ISSN 1696-5728


1341 1 The Late Palaeozoic of Western Gondwana: New insights from South American records / L.A. SPALLEiTI, C.O. LlMARlNO and S. GEUNA

/ 3491 Did Patagonia collide with Gondwana in the Late Paleozoic? Some insights from a multidisciplinary study of magmatic units of the North Patagonian Massif


1 3731 Paleornagnetism of the Carboniferous-Permian Patquía Formation, Paganzo basin, Argentina: irnplications for the apparent polar wander path for South America and Gondwana during the Late Palaeozoic


1 3991 Glacial events in Carboniferous sequences from Paganzo and Río Blanco Basins (Northwest Argentina): Palynology and depositional setting -- . -- -- -


1 4191 A synthesis of palynological data from the Lower Permian Cerro Pelado Formation (Paraná Basin, Uruguay): A record of warmer climate stages during Gondwana glaciations


1 431 / lnternal anatomy of an erg sequence frorn the aeolian-fluvial system of the De La Cuesta Formation (Paganzo Basin, northwestern Argentina) -


14491 Fluvial and eolian ichnofaunas frorn the Lower Permian of South America (Patquía Formation, Paganzo Basin)


14631 Changes in the architecture of fluvial deposits in the Paganzo Basin (Upper Paleozoic of San Juan province): an exarnple of sea level and climatic controls on the development of coastal fluvial environments


/ 4831 Palynology of the Permian San Miguel Formation (Western Paraná Basin, Paraguay): Gondwanan biostratigraphic correlations


1501 / Bivalves and brachiopods in the Carboniferous - Early Permian of Argentine Precordillera: Diversification and faunal turnover in Southwestern Gondwana


1 5191 The coupled occurrence of Cimmenella-Jakutoproductus (Brachiopoda: Productidina) in Patagonia. implications for Early Permian high to middle paleolatitudinal correlations and paleoclimatic reconstruction


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G e o l o g i c a A c t a , Vo1.8, N o 4 , D e c e m b e r 2 0 1 0 , 3 4 1 - 3 4 7 D O ! : 1 0 . 1 34411 0 5 . 0 0 0 0 0 0 1 5 7 6 Avai lab le o n l i n e a t w w w . g e o l o g i c a - a c t a . c o m

The Late Palaeozoic of Western Gondwana: New insights from South American records


I 1 I Centro de Investigaciones Geológicas (FCNyM, UNLP - CONICET) Calle 1 no 644, B1900TAC La Plata. Argentina. E-mail: spalleQcig.museo.unlp.edu.ar

12 I Facultad de Ciencias Exactas y Naturales (UBA - CONICET) Pabellón 2 Ciudad Universitar'i 1428 Buenos Aires, Argentina. Limarino E-mail: [email protected] Geuna E-mail: [email protected]

Late Palaeozoic basins of southern South America offer an exceUent opportunity to study sequences deposited in contrasting tectonic regimes, shifting climatic conditions and diñerent sea level positions. From the tectonic point of view, these Late Palaeozoic basins developed in three scenarios (Limarino and Spalletti, 2006): arc-related or Proto-Paciíic basins, retroarc or peripheral basins, and large intmmtonic or intraplate basins (Eig. 1). Arc-reW or Proto-Paciíic basins formed aiong the westemmost and highly mobile area of Gondwana, in which volcanism played a fundamental role. In turn, retroarc or peripheral basins which are characterkd by a thickfossiliferous Late Mississippianupto Late Pemiianrecord, re- less magmalic activity and minor deformation. Fmally, large intraaatonic or intraplate basins developed under more stable tectonic regimes and their sedimentary record was mainly controlled by significant climatic and eustatic osciilations (e.g. Paraná Basin).

The effects of dramatic climatic changes andlor eustatic oscillations on Late Palaeozoic basins have been widely studied. Altemating glacial and interglacial periods as well as processes of progressive aridification towards the Middle and Late Permian times have been recognized (Fig. 2). Moreover, a complete record of sea level changes was defined in the intracratonic basins from the Pennsylvanian to the Latest Permian (Fig. 2).

Despite the irnportance of the aforementioned issues, the stratigraphic and sedimentological information

obtained from South American basins has been frequently overlooked in regional or global-scale studies. Although this may be attributed to the lack of knowledge about the Carboniferous and Pennian Systems in southern South America, there is abundant literature on the sedimentary and palaeontological record of these basins. This is clearly documented in specific papers and in comprehensive compilations, such as those of Bigarella et al. (1966), Archangelsky (1987,1996), and Veroslavsky et al. (2006), arnong others.


Severa1 remarkable aspects of the western Gondwana geology can contribute to an improved understanding of the history of the whole Gondwana supercontinent. Four major issues can be highlighted: 1) the Late Palaeozoic orogenic evolution of the western Gondwana margin, 2) the effect of the widespread Perrnian-Tnassic volcanism, 3) the timing of the Late Palaeozoic glacial event, and 4) the Late Palaeozoic bioestratigraphic record.

Late Palaeozoic orogenic evolution of the western Gondwana margin

According to Ramos et al. (1984, 1986) the Chilenia Terrain accreted to the western margin of southern Gondwana dunng the Middle to Late Devonian. Limarino

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L.A. S P A L L E T T I e t a l . Late Palaeozoic of Western Gondwana

proposed by Veevers and Powell (1987) who recognized two major glacial events, the older one (Visean in age) involving local alpine glaciation, and the younger one (Latest Pennsylvanian - Early Permian) characterised by widespread ice sheets. This model was later refined by different contributions, and Isbeli et al. (2003a and b) identified three principal glacial intervals in the Toumasian, Namurian - Early Westphalian and Late Pennsylvanian - Cisuralian.

How can Late Palaeozoic South American basins contribute to these models? Firstly, although the oldest record of the Late Palaeozoic glaciation is well documented in South American basins as demonstrated by Díaz-Martínez et al. (1993), Isaacson et al. (1999) and Caputo et al. (2008), among others, it is not clearly recognized across the rest of Gondwanaland. These authors described Late Devonian - Early Carboniferous glacial diamictites in the Andean Altiplano Belt of Bolivia and in the Paraná, Solimoes and Parnaíba basins of Brazil. Secondly, the chronology of the glacial event is currently being refined from radiometric ages obtained from the Paraná Basin (Brazil). Rocha Campos et al. (2008) reported SHRIMP ages from 295 I 2.6 Ma to 299.1 I 2.6 Ma on zircons found in the Río Bonito Formation, deposited on top of glacial diamictites included in the Itararé Group. These data not only provide a better constraint on the ages of a glacial

--- - - - Narnuria


maximum in western Gondwana, but also suggest that the end of the glaciation in Brazil was older than previously considered. This problem must be examined in detail in the near future, as well as the implications of these ages for the glacial chronology, when the glacial deposits of the Paraná and Karoo basins are considered together and compared.

The biostratigraphic record in western Gondwana

The complete biostratigraphic record found in western Gondwana basins must be highlighted. In fact, there are few places in Gondwana that show a continuous fossiliferous record from the Early Carboniferous to the Late Permian. South American basins provide abundant fossil floras, marine invertebrates and palynological material from the earliest Carboniferous to the latest Permian. By contrast, the fossiliferous record of central Gondwana (South Africa and Antarctica) is mainly restricted to the Permian or the Latest Carboniferous.

The Mississippian time interval, which is not weli represented in Gondwana, is composed of thick sequences with abundant marine and continental fossiliferous assemblages in Bolivia and Argentina. This is the case of the Early Carboniferous Archaeosigillaria-Frenguellia flora (Arrondo et al., 1991; Archangelsky, 1996), and the recently defined Frenguellia eximia - Nothorhacopteris

- 2l6rrn9 -7- -x trans. : -

Para uazú transgressior \+.\=Y \T-

MaJormarine hansgmsskm m Bwb-Wiak pmgmMbaI ~aqwwes m Malnly fluvial aadh&atlar

A Ghdd diamlclilee v ~ ~ I c ~ - Re#caal-

FIGURE 2 l Palaeoenvironmental ewolution of Me Upper Palaemoic basins of South America (modlfied imm Llmarino and Spalletti, 2006).

Geologica Acta, 8 ( 4 ) , 341-347 (20101 DOI: 10.1344/105.000001576 .

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Geologica A c t a , Vo1.8, N o 4 , D e c e m b e r 2 0 1 0 , 3 7 3 - 3 9 7 DOI: 10.1 34411 05.000001 578 Available on l ine a t w w w . g e o l o g i c a - a c t a . c o m

Paleomagnetism of the Carboniferous-Permian Patquía Formation, Paganzo basin, Argentina: implications for the apparent polar wander oath for South America and Gondwana during the Late Palaeozoic


I i I Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires 1 CONICET Ciudad Universitaria Pab. 2, C1428EHA, Ciudad de Buenos Aires, Argentina. Geuna E-mail: [email protected]. Phone

num ber: 54-1 1-47883439

12 1 Instituto de Geología y Recursos Minerales, Servicio Geológico Minero Argentino

1 A B S T R A C T I

The magnetic properties of the Carboniferous-Permian red beds of the Patquía Formation at minta del Viento, Sima de Umango and some previously reported localities, al1 in the Paganzo Basin (Argentina), have been stud- ied. Whereas ail sites are characterized by hematite as the main magnetic carrier and a reversed-polarity magnetic remanente, we found a pattern of variation in magnetic properties along the integrated icolurnn for Patquía For- mation. The h w e r Member (Late Garboniferous) showed higher intensity of natural and saturation isothermal remanent magnetisation (NRM and SIRM tensitv from the Lower to UDW Member

, respectively) t h a n e ~ e r m i a n - ~ ~ p e r Member. The of the Patauía Formation mav be related to a change

fallinNRMin- in auantitv andl

or gr&-size of the hernatite &gnent, which may reflect the change in enviromental andlor depsi~onal &tting. As for directional values of NRM, paleomagnetic poles reported for both sections are clearly different. The lower mtion provided a p l e position coincident with Late Carboniferous poles for Gondwma, whde the upper section poles are departed fmm the Early Permian position. We cannot decide whether the Upper Member pole is due to a primary. magnetisation at 290 Ma or to a remagnetisation at -260-270 Ma; even so, the obtained paleomagnetic pole is robust and indicates a rapid apparent polar wander in a -30" counter clockwise rotation of the region, after deposition of the Late Carboniferous lower section, and in coincidence with the San Rafael Orogenic Phase.

KMYORDS 1 Red bsds. Paleomagnetism. Uagnetic remanonce. Apparent polar wantkr.

Continental red beds are of speciai significance in paie- omagnetism, not only because they were the fmt sedimen- tary rocks to be studied in any detail ( k e r , 1980) but

also owing to red beds have demonstrated to be particu- larly suitable for paieomagnetic studies. Red beds share in comrnon the red colour given by finely disseminated ferric oxides, usually in the form of haematite. They comprise a wide range of sedimentary facies mainly deposited in con-

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S . E . GEUNA et a l Paleomagnetisrn of the Carboniferous-Perrnian Paganzo basin, Argentina

the Triassic sequence (usually referred to as the Upper Pa- ganzo Section or "Paganzo 111" in former paleomagnetic contributions) as an independent cycle. The Triassic ex- tensional basins developed following a tectonic inversion marked by a major unconformity that truncates Permian sequences, identified with the Amanaica Orogenic Phase (Aceñolaza and Toselli, 198 1 ; Limarino et al., 1988).

The infill of the Carboniferous-Permian basin com- prises the Paganzo Group, consisting of three stratigraphic units: the Guandacol, Tupe and Patquía Fm. (Fig. 2). The first stage (Guandacol Fm.) began with deposition of diamictites or dropstone-bearing mudstones, followed by marine or deltaic dropstone-bearing sediments, deposited in the Proto Precordillera and in areas proximal to palae- otopographic highs. The Tupe Fm. represents Carbonifer- ous aggradational and progradational filling dominated by fluvio-deltaic deposits, coal, and some black shales, inter- leaving to the west with shallow marine and deltaic depos- its. The Patquía Fm. marks the final phase of basin fi11 and is characterised by stratigraphic onlap and a change from subaqueous to subaerial dominated sedimentation, com- prising red beds deposited in ephemeral stream and playa- lake environments (Limarino et al., 2006).

The Patquía Fm. red beds lie unconformably on Tupe Fm., though the unconformity is noticeable only in margin- al areas of the Paganzo basin, as it becomes a paraconform- ity basinward (Limarino et al., 2006). Fluvial sedimenta- tion resulted in three major association of facies: 1) alluvial fans and proximal braided alluvial plains, 2) high-sinuosity river systems and 3) sand or gravelly channel belts encap- sulated in floodplain deposits.

Braided or meandenng fluvial deposits were pro,ges- sively replaced by low-energy ephemeral nver successions, and then by aeolian and lacustrine deposits (Limarino et al., 2006). Two different sections in the Patquía red beds have been distinguished based on the change from fluviatile to aeolian environments (Azcuy and Morelli, 1970). The transition from humid to semiarid conditions marked by this facial change in Patquía Fm. (López Gamundí et al., 1992) is accompanied by a change in the palaeocurrents pattems, from W-NW to SE, and in petrofacies, with higher supply of acidic volcanic lithic fragments, all of which can be interpreted as due to a change in regional dip lead by thermal dorning and uplift in the Permot- riassic magmatic arc to the west (Caseiíi and Limarino, 2002; Limarino et al., 2006). Silcretes formed in weathered tephra- rich paleosoils are found near the transition from the Lower to the Upper Member of the Patquía Formation (Lirnarino and Caselli, 1995), indicating that was a period of low depositional rate and a rising supply of volcanic material.

Simultaneous with deposition of red beds in the east- ern basin, magmatic arc-related deposits are found in the

westem basin, linked with active subduction during the Late Palaeozoic. Convergence culminates in the San Ra- fael Orogenic Phase (SROP) during the Early Permian (Kleiman and Japas, 2009), whose effects in the westem margin of Gondwana are reflected in a major erosion sur- face on which Choiyoi Magmatic Province (280-240 Ma) developed. Lower Choiyoi magmatism is calc-alkaline with typical continental-subduction signatures, coeval with transpression, followed by shoshonitic magmatism related to crustal thickening; it was followed by extension and ig- nimbrite "flare-up" (Upper Choiyoi), evidence of a change from transpressional to transtensional regimes during the Permian (Kleiman and Japas, 2009). The SROP might be responsible for the inversion observed in the eastem basins at the end of the Permian (- Amanaica Phase, Aceñolaza and Toselli, 1981), as suggested by Azcuy et al. (1987).

Recent high-resolution U-Pb ages on tuffs allowed refining the timing of the different geological events in Paganzo basin (Gulbranson et al., 2008,2010). An age of 319.6 I 0.08 Ma places the Guandacol Fm. in the latest

Time Stage Period Supersequence (Ma)

. . .., Roadian




Lower Patquía

., Guandacol

Pre-Paganzo Gr

FIGURE 2 1 Stratigraphic framework for the Paganzo Group (from Gul- branson et al., 2008, 20101, referred to the Geomagnetic Polarity Time Scale (GPTS, Ogg and Smith, 2004); Carboniferous chronostratigraphy from Heckel and Clayton (2006). The column to the lefi is the magneto- stratigraphy, white (black) indicating reversed (normal) polarity zones. The lithostratigraphic units recognized at present are accompanied to the right by the original denomination for Paganzo Group (Bodenbender, 191 1; P1, P2 and P3 are Paganzo 1 , 2 , 3 respectively). GPTS generated with program TSCreator PRO (Ogg and Lugowski, 2008).

Geologica Acfa, 8 ( 4 / , 373-397 (20101 DOI: 10.134411 05.000001 5 7 8

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A synthesis of palynological data from the Lower Permian Cerro Pelado Formation (Paraná Basin, Uruguay): A record of warmer

climate stages during Gondwana glaciations

I 1 I Sección Paleontologia, Facultad de Ciencias lguB 4225, 11400, Montevideo, Uruguay. Beri E-mail: b[email protected] Martinez-Blanco E-mail: [email protected]

Mourelle E-mail: domodicaQgmail.com

1 A B S T R A C T 1

h s paper presents a synthesis of the palynological record in the Cerro Pelado Formation deposits (Lower 'ermian, Paraná basin, Cerro Largo Department, north-eastern Uruguay) based on pre-existing data and new indings. The successions studied in this formation consist mainly of non-marine to glacial-marine mudstones and

Zhacoparaná Basin of Brazil, Argentina and Uruguay point to their Early Permian age. The most widespread spore genera in these assemblages are Punctatisporites, Lundbladispora, Vallatisporites and Granulatisporites. Among xillen nrains, Caheniasaccites, Httatina, Potonieisporites, Protohaploxypinus and Plicatipollenites are the most

$acial lobe advanke-retreat phases) alte&ating with warmer clirnatic episodes. Thes&isod& could be recognGed hanks to sub-glacial and melt water related continental deposits that would bear characteristic palynological issemblages, like the recorded in the Cerro Pelado Fm. successions.

YEWORDS 1 Lower Permian. Palynology. Interglacial-postglacial episodes. Gondwana. Uruguay

Iuring the Late Palaeozoic of Gondwana, an Ice Age char- icterized by short, discrete glacial events separated by pe- iods of warmer climate occurred (Fielding et al., 2008).

Late Palaeozoic sedimentary sequences are well repre- sented in the Paraná Basin in Uruguay and, as these strata probably record the moments of massive expansion of ice (Fielding et al., 2008), it is of interest to carry out paly- nological analyses and characterize the plant comrnunities

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A. B E R I e t a l . Palynological data from Lower Permian, Uruguay

that inhabited Western Gondwana by that time. This paper aims to present a synthesis of al1 available palynological data, complemented by new contributions, of the Cerro Pelado Formation (successions previously included in the San Gregorio Formation), which has been attributed to the Lower Permian (Gutiérrez et al., 2006).

The first palaeopalynological study of the Upper Palaeo- zoic in Uruguay was conducted by Martínez Macchiavel- lo (1963), who anaiysed the San Gregorio and Tres Islas Formation. Later, Marques-Toigo (1970, 1972, 1973, and 1974) studied the palynological content of the San Grego- rio Formation from a systematic standpoint, complemented by biostratigraphic observations. Subsequently, several ad- ditional publications have addressed the systematic paly- nology and biostratigraphy of the San Gregorio Formation (Beri and Daners, 1996; Beri and Goso, 1996, 1998; Beri et al., 2006; and GutiCrrez et al., 2006). However, these publications were based on single boreholes.

Three major basin types occurred in the Late Palaeozoic of South America: intracratonic or intraplate, arc-relat- ed, and retroarc. Intraplate basins (i.e., Paraná, Chaco- Paraná, Sauce Grande-Colorado, and La Golondrina) are floored by continental or quasi-continental crust, with low or moderate subsidence rates and limited magmatic and tectonic activity (Limarino and Spalletti, 2006). The Paraná Basin is an intracratonic ramp basin of the South American platform formed in response to the geological stabilization that followed the Brasiliano cycle. This basin is filled by thick and widespread sedimentary sequences that cover approximately 1,700,000 km2 in central-eastern South America, including present-day territories of Uru- guay, Brazil, Paraguay and Argentina, where it is known as Chaco-Paraná Basin (Holtz et al., 2008) (Fig. 1). The south-eastern portion of the Paraná Basin extends into the northern Uruguay occupying an area of approximate- ly 90,000 km2 within the country where it is cailed the Northern Basin (de Santa Ana et al., 2006b). Palaeozoic outcrops are distributed throughout an area of 24,000 km2 in the Cerro Largo, Tacuarembó, Rivera and Durazno Departments of Uruguay; while the rest of the sequence is covered by Lower Cretaceous extrusive rocks and younger sedimentary rocks (Andreis et al., 1996) (Fig. 1). According to de Santa Ana et al. (2006b), the begin- ning of the Neopalaeozoic sedimentation is characterised by extensive glacial, glacial-marine or glacial-influenced sedimentary records. The lithological formations corre- sponding to this time interval in Uruguay are, from bot- tom to top, San Gregorio, Cerro Pelado, Tres Islas, Frayle Muerto, Mangrullo, Yaguarí and Buena Vista (de Santa Ana et al., 2006a) (Fig. 2).

The Cerro Pelado Formation is a sedimentary succession of fine-grained rocks (mudstones, diarnictites and fine- grained sandstones), which are greyish to blackish and brownish in colour. This formation records a transgressive event reported by de Santa Ana et al. (2006b). Previously, the successions of this formation were considered the up- per sequences of the San Gregorio Formation (Caorsi and Goñi, 1958; Ferrando and Andreis, 1986) which in its tum can be correlated with the Itararé Group in Brazil (Petri and Fúlfaro, 1988). Two depositional cycles were identi- fied for the San Gregorio Formation (de Santa Ana, 1989). The lower cycle, geographically restricted to the Río Ne- gro Vailey of Umguay and adjacent areas, consists mainly of diamictites, conglomerates, sandstones and, to a lesser


-a"d lmpJ. R d s

FIGURE 1 1 Map of sample lowtions (modified from Goso, 1995; Soum et al., 2007).

Geologica Acta, 8 ( 4 ) , 4 1 9 - 4 2 9 ( 2 0 1 0 ) DOI : 10 .1344/105.000001580

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Geologica A c t a , Vo1.8, N o 4 , D e c e m b e r 2010, 449 -462 DOI: 10.1 344/105.000001582 Available on l ine a t w w w . g e o l o g i c a - a c t a . c o m

Fluvial and eolian ichnofaunas from the Lower Permian of South America (Patquía Formation, Paganzo Basin)


I 1 I Departamento de Ciencias Geológicas, FCEN, UBA Ciudad Universitaria Pabellón 11, 1428 Buenos Aires, Argentina. Krapovickas E-mail: [email protected]

Caselli E-mail: [email protected]

12 1 IANIGLIA, CCT-CONICET, Mendoza Adrián Ruiz Leal s/n, Parque Gral. San Martín, 5500 Mendoza CC330. Argentina E-mail: [email protected]

13 1 h a de Zoología, Universidad Nacional de San Luis Chacabuco 917,5700 San Luis Argentina. E-mail: [email protected]

lñe Lower Pennian Patquía Forrnation is the youngest unit of the Paganzo Basin, western Argentina. The lower section consists of red mudstones, and fine- and coarse-grained sandstones deposited in fluvial systems with extensive and thick floodplain deposits. These rocks contain a low-diversity and relatively abundant association of trace fossils suggesting the activity of a sub-superficial to superficial fauna. The association is characterized by Rusophycus carbonurius (Cubichnia), Cruziana problematica (Repichnia), and Palaeophycus tubularis (Domichnia) of the Scoyenia ichnofacies. Disarticulated fish remains are also present. The upper section is dominated by red, cross-bedded, medium- to fine-grained sandstones deposited in eolian systems that host a low- diversity and low-abundance association of trace fossils that indicates the activity of a mainly superficial fauna. Tetrapod footprints (Chelichnus duncani, oval digit imprints, short parallel grooves, and sinusoidal grooves), horizontal to vertical burrows (Palaeophycus tubularis and Skolithos isp. respectively), and &opod trackways are the typical components of these deposits. The association shows elements of the three presently proposed eolian ichnofacies (Chelichnus, Octopodichnus and Entradichnus ichnofacies) suggesting the necessity of revision and the possible integration of these separate ichnofacies hto a single model. The record of fossil vertebrate tracks is uncornrnon in Lower Permian strata of South America. Therefore, the ichnologic record of the Patquía Fonnation is a significant contribution to the understanding of Lower Pennian South Arnerican ichnofaunas.

KEYWORDS ( Scoyenia ichnofacies. Eolian ichnofacies. Tetrapod footprints. Early Pennian. Patquia. Formation.


Upper Paleozoic ichnofaunas have been extensively morded in the Northem Hernisphere including both ver-

tebrate and invertebrate trace fossils (e.g. Gilmore, 1926; Hunt et al., 1995; Haubold and Lucas, 2003; Minter, et al., 2007). The records of trace fossils mostly correspond to strata assigned by different authors to the Lower Perm-

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K R A P O V I C K A S e l a l . Fluvio-Eolian ichnofaunas from the Patquía Formation .

The sedimentary facies of the Patquía Formation were studied in detail by Caselli (1998). This author included several Permian redbed successions that occur in the basin at the Patquía Formation (see also Caselli and Lirnarino, 2002). Two intervals within the Patquía Fonnation were recognized in the Paganzo area (Fig. 2). The lower interval is 240111-thick, and is characterized by red mudstones and he-grained sandstones interbedded with light red pebbly and coarse-grained sandstones. The tabular mudstones and fine-grained sandstone beds are either massive or show parallel- or ripple cross-larnination. Individual beds are 0.20-1.5m thick. These deposits contain invertebrate trace fossils (Rusophycus carbonarius, Cruziana problematica, and Palaeophycus tubularis) and disarticulated fish re- mains (Fig.2). The lenticular pebbly and coarse-grained sandstone beds are 0.20- 0.80m thick and display parallel, planar, and trough cross-stratification. The lower interval was interpreted as deposited in fluvial environments, in which floodplain areas dominated over channel subenvi- ronments (Caselli, 1998).

The upper intemal is 160 m-thick and is dorninated by red, high-angle planar cross-bedded, well-sorted, ma-


ture, medium- to fine-grained sandstones. The basal suc- cession is dominated by 0.10-0.20m thick, parallel-lami- nated, ripple cross-larninated, and planar cross-stratified sandstones interpreted as low-angle sand-sheet deposits (Caselli, 1998). This facies records invertebrate trace fos- sils (Palaeophycus tubularis, Skolithos isp., and arthropod trackway), and a variety of tetrapod fossil footprints (Che- lichnus duncani, oval digit imprints, short paraliel grooves, and sinusoidal grooves) (Fig.2). The succession passes up- wards into thick-bedded, high-angle cross-stratified sand- stone beds. This interval has been interpreted as dune and interdune deposits of an extensive eolian system developed under arid conditions (Caselli, 1998).

The age of the Patquía Formation is poorly constrained. The fossil content suggests an Early Permian age (e.g. Frenguelli, 1949; Limarino and Césari, 1985). Paleomagnet- ic information and absolute ages (K-Ar) of basalt interbed- ded near the base of the Patquía Formation in the Paganzo area indicate a Late Carboniferous to Early Permian age (263 +_ 4 a 302 f 6 M.a. ) (Thompson and Mitchell, 1972; Valencio, 1972; Valencio and MitcheU, 1972; Valencio et al., 1977; Sinito et al., 1979).

FIGURE 1 I Geologic map of the Paganzo Group in the Paganzo area.

Geologica Acta, 8(41, 449 -462 (2010) DOI: 10 .1344/105.000001582