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

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Description

The magnetic properties of the Carboniferous-Permian red beds of the Patquía Formation at Punta del Viento, Sierra de Umango and some previously reported localities, all in the Paganzo Basin (Argentina), have been studied. Whereas all sites are characterized by hematite as the main magnetic carrier and a reversed-polarity magnetic remanence, we found a pattern of variation in magnetic properties along the integrated column for Patquía Formation. The Lower Member (Late Carboniferous) showed higher intensity of natural and saturation isothermal remanent magnetisation (NRM and SIRM, respectively) than the Permian Upper Member. The fall in NRM intensity from the Lower to Upper Member of the Patquía Formation may be related to a change in quantity and/or grain-size of the hematite pigment, which may reflect the change in environmental and/or depositional setting. As for directional values of NRM, paleomagnetic poles reported for both sections are clearly different. The lower section provided a pole position coincident with Late Carboniferous poles for Gondwana, while the upper section poles are departed from 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 ~30o counter clockwise rotation of the region, after deposition of the Late Carboniferous lower section, and in coincidence with the San Rafael Orogenic Phase.

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Publié le 01 janvier 2010
Nombre de lectures 9
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REFERENCES
Geologica Acta, Vol.8, Nº 4, December 2010, 373-397
DOI: 10.1344/105.000001578
Available online at www.geologica-acta.com
Paleomagnetism of the Carboniferous-Permian Patquía Formation,
Paganzo basin, Argentina: implications for the apparent polar wander
path for South America and Gondwana during the Late Palaeozoic
1 2 1
S.E. GEUNA L.D. ESCOSTEGUY C.O. LIMARINO
1 Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires / CONICET
Ciudad Universitaria Pab. 2, C1428EHA, Ciudad de Buenos Aires, Argentina. Geuna E-mail: geuna@gl.fcen.uba.ar. Phone
number: 54-11-47883439
2 Instituto de Geología y Recursos Minerales, Servicio Geológico Minero Argentino
ABSTRACT
The magnetic properties of the Carboniferous-Permian red beds of the Patquía Formation at Punta del Viento,
Sierra de Umango and some previously reported localities, all in the Paganzo Basin (Argentina), have been stud-
ied. Whereas all sites are characterized by hematite as the main magnetic carrier and a reversed-polarity magnetic
remanence, we found a pattern of variation in magnetic properties along the integrated column for Patquía For-
mation. The Lower Member (Late Carboniferous) showed higher intensity of natural and saturation isothermal
remanent magnetisation (NRM and SIRM, respectively) than the Permian Upper Member. The fall in NRM in-
tensity from the Lower to Upper Member of the Patquía Formation may be related to a change in quantity and/
or grain-size of the hematite pigment, which may refect the change in environmental and/or depositional setting.
As for directional values of NRM, paleomagnetic poles reported for both sections are clearly different. The lower
section provided a pole position coincident with Late Carboniferous poles for Gondwana, while the upper section
poles are departed from 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
opole 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.
KEYWORDS Red beds. Paleomagnetism. Magnetic remanence. Apparent polar wander.
INTRODUCTION also owing to red beds have demonstrated to be particu-
larly suitable for paleomagnetic studies. Red beds share in
Continental red beds are of special significance in pale- common the red colour given by finely disseminated ferric
omagnetism, not only because they were the first sedimen- oxides, usually in the form of haematite. They comprise a
tary rocks to be studied in any detail (Turner, 1980) but wide range of sedimentary facies mainly deposited in con-
373S.E. GEUNA et al. Paleomagnetism of the Carboniferous-Permian Paganzo basin, Argentina
tinental environments, though some examples of marine haematite crystallisation and changes in the depositional
red beds have been also quoted (McBride, 1974; Franke setting.
and Paul, 1980; Limarino et al., 1987; Hu et al., 2005).
Haematite is usually the main carrier of magnetic re- GEOLOGICAL SETTING
manence in red beds, and hence the age of the remanence
2is given by the time of haematite crystallization. Haematite The Paganzo basin covers an area of 140.000 km
in red beds may form by the oxidation of magnetite, the where mainly continental sedimentation took place from
inversion of maghemite, or the dehydration of goethite, the latest Early Carboniferous to the Late Permian (Lima-
the latter formed by breakdown of hydrous clay minerals rino et al., 1996; Tedesco et al., 2010; Fig. 1). The sedimen-
and ferromagnesian silicates (McBride, 1974; McPherson, tary cover is thinner to the east, where it was deposited on
1980; Dunlop and Özdemir, 1997). All the reactions typi- Proterozoic igneous-metamorphic basement of the Sierras
cally occur during burial in a sedimentary pile, through Pampeanas; in the western part, a narrow belt developed
the diagenetic stage (early diagenesis, mesodiagenesis, te- on more mobile areas, where thicker deposits lie upon
lodiagenesis) in a process that strongly depends on basin metamorphic basement and Lower Palaeozoic sediments
conditions. of the Precordillera (Azcuy et al., 1999). There is evidence
of oblique convergence in the Late Palaeozoic subduction
Continental red beds are extremely sensitive indicators zone to the west (Mpodozis and Kay, 1992; Kay, 1993);
of the nature and extent or red bed diagenesis. The paleo- strike-slip faults have controlled the development of the
magnetic study shows that diagenesis must be a rate proc- forearc basins (Fernández Seveso and Tankard, 1995). A
ess in which the rate, including the rate of acquisition of N-S trending structural high, the Proto Precordillera, par-
magnetization, is determined by a) the original mineralogy tially separated the Paganzo basin from its marine exten-
of sediment, where immature sediments are susceptible to sions to the west: the Río Blanco and Calingasta-Uspallata
more extensive alteration and prolonged magnetization; b) basins (Limarino et al., 1996; Fig. 1).
the depositional conditions, finer grained sediments be-
ing less susceptible to alteration; c) the prevailing climate, Terrigenous clastic fill of the Paganzo basin was origi-
warm arid climates being favourable for the long-contin- nally subdivided into three “stages” referred to as Car-
ued alteration (Turner, 1980). The age of the magnetization boniferous, Permian and Triassic by Bodenbenber (1911).
in red beds is a direct result of the rate of acquisition of Azcuy and Morelli (1970) restricted the name Paganzo
remanence, which is variable because it represents the sum Group to the Carboniferous-Permian sections, separating
of several discrete diagenetic processes.
The Paganzo Basin in western Argentina has been the
+
o +site of deposition for Carboniferous-Permian red beds 28
+
SOUTHwhich provided several paleomagnetic poles, some of them + Western
AMERICA+controversial. Most of them were published before recent domain
+ +methodological advances in the paleomagnetic routine, and DLC+ PVup till now no study has considered the characterization of
the magnetic mineralogy of these red beds. ME+ LaRioja
?HU LC ?+In this paper we present a preliminary study on a section PZO CC
in the Sierra de Umango in Paganzo Basin, where Carbon- Paganzo+
iferous-Permian red beds can be compared with overlying Basin+
red Cretaceous units. The comparison is extended to other +
CHlocalities studied before by Embleton (1970b), Valencio et + SanJuan Easternal. (1977) and Sinito et al. (1979a). The magnetic proper- +
o domain32ties were distinctive for the two members recognized in the +
Late Palaeozoic red beds: haematite is more abundant in the +
+lower fluviatile facies than in the upper desert association, + Mendoza
and both sections provided different paleomagnetic poles.
o o+ 69 W 67 W 0 200km100
We compared the Paganzo basin paleomagnetic poles
FIGURE 1 Sketch of Paganzo Basin, with localities referred in the to the paleomagnetic record from other Gondwana plates
text (modified from Azcuy et al., 1999). Locality codes as in table 3;
during the Late Palaeozoic. We inferred the timing for re- PV is the location of the present study in Punta del Viento, Sierra de
Umango.manence acquisition and analysed it in terms of diagenesis,
374Geologica Acta, 8(4), 373-397 (2010)
DOI: 10.1344/105.000001578
RíoBlancoSub-basin
Famatina
System
Sierras
Pampeanas
Precordillera
V O L C A N I C A R C
Calingasta-Uspallata Sub-basin
C H I L ES.E. GEUNA et al. Paleomagnetism of the Carboniferous-Permian Paganzo basin, Argentina
the Triassic sequence (usually referred to as the Upper Pa- western basin, linked with active subduction during the
ganzo Section or “Paganzo III” in former paleomagnetic Late Palaeozoic. Convergence culminates in the San Ra-
contributions) as an independent cycle. The Triassic ex- fael Orogenic Phase (SROP) during the Early Permian
tensional basins developed following a tectonic inversion (Kleiman and Japas, 2009), whose effects in the western
marked by a major unconformity that truncates Permian margin of Gondwana are reflected in a major erosion sur-
sequences, identified with the Amanaica Orogenic Phase face on which Choiyoi Magmatic Province (280-240 Ma)
(Aceñolaza and Toselli, 1981; Limarino et al., 1988). developed. Lower Choiyoi magmatism is calc-alkaline
with typical continental-subduction signatures, coeval with
The infill of the Carboniferous-Permian basin com- transpression, followed by shoshonitic magmatism related
prises the Paganzo Group, consisting of three stratigraphic to crustal thickening; it was followed by extension and ig-
units: the Guandacol, Tupe and Patquía Fm. (Fig. 2). The nimbrite “flare-up” (Upper Choiyoi), evidence of a change
first stage (Guandacol Fm.) began with deposition of from transpressional to transtensional regimes during the
diamictites or dropstone-bearing mudstones, followed by Permian (Kleiman and Japas, 2009). The SROP might be
marine or deltaic sediments, deposited responsible for the inversion observed in the ea

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