Paleomagnetism of Caacupé and Itacurubí groups, western border of Paraná Basin, Paraguai

PALEOMAGNETISM OF CAACUPÉ AND ITACURUBÍ GROUPS, WESTERN BORDER OF PARANÁ BASIN, PARAGUAI

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HELMA S. BERQUÓ, MARCIA ERNESTO and ROBERTO SIQUEIRA

Instituto Astronômico e Geofísico, USP, São Paulo, SP.

Presented by ANTONIO C. ROCHA-CAMPOS

The Silurian-Ordovician sequence, west of Paraná Basin is represented by the Caacupé Group (Paraguari, Cerro Jhú and Tobatí formations) and the Itacurubí Group (Eusébio Ayala, Vargas Penã and Cariy formations). This sequence is composed of basal conglomerate followed by continental/ marine sandstones, glacial diamictites, transgressive marine shales and regressive marine sandstones. The succession corresponds to a great transgressive-regressive cycle.

Two main components of magnetization, A (Dec = 348, 9^o Inc = - 42.9^o N= 19, = 11.5^o k= 7) and B (Dec = 163, 2^o Inc = 48.6^o N= 7, = 9.9^o k= 22) were identified by means of paleomagnetic analyses and rock magnetic studies. These two components seem to characterize a dipolar geomagnetic field. The paleomagnetic pole based on both directions is located at 79^oS 22^oE (N= 26, = 4.9^o). This pole is close to the geographic pole and to South American Mesozoic paleomagnetic poles suggesting a possible remagnetization during Permo-Triassic or Cretaceous times. This remagnetization could be due to the thermal effects imparted by the Mesozoic magmatic events.

On the other hand, the two directions of magnetization are similar to those found for the Lipeón formation (Subandean Silurian sediments, NW Argentina) and the Serra Grande, Pimenteiras and Cabeças formations (Parnaíba Basin, Brasil), suggesting that the magnetization of the Caacupé Group was acquired during the Lower Paleozoic at latitudes as low as the present ones. (December 10, 1999)

Publication Dates

• Publication in this collection
  05 Jan 2001
• Date of issue
  Dec 2000