Great circle analysis of South American VGP-distributions suggests widespread Cretaceous remagnetizations: case study of the Itararé Group Rocks from Brazil

2021 ◽  
Author(s):  
Dario Bilardello ◽  
William Callebert ◽  
Joshua Davis
Keyword(s):  
Sedimentary Rocks ◽  
Careful Analysis ◽  
Pole Position ◽  
Magnetic Data ◽  
South American ◽  
The South ◽  
Virtual Geomagnetic Pole ◽  
Cretaceous Rock ◽  
Mafic Intrusions ◽  
Rock Formations

<p>South American Jurassic/Cretaceous rocks has been troubled by elongated virtual geomagnetic pole (VGP) distributions, while many discordant poles from the Carboniferous to the Triassic have also been recognized, rendering the South American apparent polar wonder path (APWP) problematic. </p><p>We have conducted a paleomagnetic study of the sedimentary Permo-Carboniferous Itararé Group rocks within the state of São Paulo, Brazil, including three intruding mafic sills that are attributed to Early Cretaceus magmatic activity. The site-mean VGP distributions obtained from the sedimentary rocks define elongations that include the VGPs of the mafic intrusions, and are interpreted as remagnetization paths toward the directions characteristic of the sills. These interpretations are supported by extensive rock-magnetic data that provide a viable mechanism for the secondary magnetizations. Careful analysis of the paleomagnetic data of the sedimentary rocks enables isolation of a primary VGP distribution that is consistent with the reference Carboniferous pole position.</p><p>Analysis of other Carboniferous to Triassic South American paleomagnetic VGPs reveals that the majority of these data are also elongated: regardless of the age of the rocks, the elongations dominantly intersect at the location of the Late Cretaceous reference pole, and a second location similar to the intersection of the VGP elongations of some Jurassic/Cretaceous rock formations, and also coincides with the cusp of the debated loop in the Carboniferous-Triassic APWP. Based on multiple lines of evidence, we interpret the elongations and their intersections to reflect remagnetizations that occurred as a result of the widespread magmatism associated with the opening of the South Atlantic. We suggest that the extent of the remagnetizations is formation-specific, and that other rock-formations should be carefully re-evaluated.</p>

A palaeomagnetic survey of South American rock formations - Palaeomagnetic studies on rock formations from Northwest Argentina

1970 ◽  
Vol 267 (1183) ◽  
pp. 481-501 ◽  
Keyword(s):  
Atlantic Ocean ◽  
Geomagnetic Field ◽  
South Atlantic ◽  
South American ◽  
South Pole ◽  
The South ◽  
Remanent Magnetism ◽  
Rock Formations ◽  
Lower Palaeozoic ◽  
La Rioja

Cambrian, Cambro-Ordovician and Ordovician formations of red sandstones and siltstones from the sub-Andean regionso f the Provinces of Salta and Jujuy have been studied. The grouping of n.r.m . directions suggests partial remagnetization after folding in the Tertiary or Quaternary geomagnetic field. Thermal cleaning at 300 °C and higher temperatures destroys this secondary magnetization leaving a magnetization which is accepted as representing the lower Palaeozoic geomagnetic field. Palaeomagnetic south pole positions have been computed and lie in the Atlantic Ocean to the NNE of Brazil. The period between the Carboniferous and Triassic is covered by the Paganzo formation which is exposed in La Rioja Province. The older part (Paganzo II) is reversely magnetized with a south p.m . pole in the South Atlantic, while the upper part (Paganzo III) is normally magnetized with a south palaeomagnetic pole in the vicinity of poles obtained for Triassic rock formations from elsewhere in S. America. Formations of red beds from Salta province regarded as Upper Palaeozoic or Mesozoic yield a south palaeomagnetic pole in the South Atlantic corresponding to a Triassic age. Ore microscope and thermal decay curves suggest that the remanent magnetism is due to haematite.

A palaeomagnetic survey of South American rock formations - Studies on rock formations from Northeast Brazil

1970 ◽  
Vol 267 (1183) ◽  
pp. 463-480 ◽  
Keyword(s):  
Time Interval ◽  
South American ◽  
South Pole ◽  
Present Position ◽  
The South ◽  
Polar Wander ◽  
Rock Formations ◽  
Geomagnetic Fields ◽  
Southeasterly Direction ◽  
Good Agreement

Devonian, Carboniferous and Xriassic formations from Piaui and Maranhao States in the northeast of Brazil have been studied and palaeomagnetic pole positions deduced. During the Devonian and Carboniferous the south pole appears to have moved away from S. America in a southeasterly direction from the vicinity of Rio de Janeiro: in the Triassic it was situated near the present position of the south pole relative to S. America. These results are in good agreement with those from other formations of the same age from other parts of the continent. Thermal cleaning has been carried out. The Devonian formations were almost completely remagnetized by the Mesozoic or Tertiary geomagnetic fields and the primary magnetization is very weak. Polar wander of 40 to 50° appears to have occurred during the time interval under investigation, i.e. M. Devonian to Triassic.

A palaeomagnetic survey of South American rock formations - Palaeomagnetic studies on palaeozoic rocks from Bolivia

1970 ◽  
Vol 267 (1183) ◽  
pp. 502-521 ◽  
Keyword(s):  
Sedimentary Rock ◽  
Buenos Aires ◽  
Cape Town ◽  
South Atlantic ◽  
South American ◽  
The South ◽  
Rock Formations ◽  
The Guianas

The palaeomagnetism of Ordovician and Devonian and Carboniferous sedimentary rock formations exposed in Bolivia has been studied. It is deduced that the south palaeomagnetic pole was situated in the Guianas in the Middle Palaeozoic, and in the south Atlantic, about half way between the present positions of Buenos Aires and Cape Town in the Carboniferous.

Cnidochloa: A New Genus of Grasses from Brazil (Poaceae: Panicoideae: Paniceae)

2020 ◽  
Vol 105 (2) ◽  
pp. 183-194
Author(s):  
Fernando O. Zuloaga ◽  
Sandra S. Aliscioni ◽  
M. Amalia Scataglini
Keyword(s):  
New Genus ◽  
Phylogenetic Position ◽  
South American ◽  
The South ◽  
South American Species ◽  
Molecular Characters

Generic boundaries of the South American species Panicum longipedicellatum Swallen are explored and compared with allied genera of the tribe Paniceae. On the basis of morphological, anatomical, and molecular characters a new genus, Cnidochloa Zuloaga, is proposed. The phylogenetic position of the new genus within the Paniceae is evaluated.

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