Paleomagnetic And Magnetostratigraphic Data From The Rosário Do Sul Formation Of The Rio Grande Do Sul State, Brasil

The sedimentary Rosário do Sul Formation (southern Brasil), believed to be of Late Triassic age was sampled<br>for paleomagnetic study from the in Rio Grande do Sul State of. In most sites both thermal and alternating field<br>demagnetization in 12-17 steps revealed either a reversed or normal characteristic remanent magnetization<br>(ChRM). Combining results yield 11 reversed (RSF-R) and 4 normal (RSF-N) magnetized sites and the later was<br>interpreted as a secondary magnetization. This secondary magnetization was acquired during Early Cretaceous<br>due to reheating or/and chemical remagnetization by the overlying thick sequences of the Serra Geral flood<br>(SGF) basalt. The mean primary paleomagnetic direction calculated using only 11 reversed polarity sites (RFSR)<br>yields, Dec=166.3°, Inc=35° (α95=5.9° and k=61), implying in a ~14° counter clockwise rotation in the<br>declination and a shallow inclination. The mean inclination is shallow as expected due to compaction of the<br>sediments by the overlying SGF basalt. The associated virtual geomagnetic pole is located at 71°E and 74°S.<br>The rotated virtual geomagnetic pole of the primary magnetization (RSF-R*) do not match other South American<br>poles of Triassic age. However, the rotated paleomagnetic pole (79.9°S, 127.13°E) is close to Middle- Late<br>Jurassic VGP's calculated on volcanic deposits in South America.