Paleomagnetic constraints on the age of the Botucatu Formation in Rio Grande do Sul, southern Brazil

Abstract

Paleomagnetic and rockmagnetic data are reported for the aeolian Botucatu Formation, in the southern Brazilian State of Rio Grande do Sul. Oriented samples were taken from a section located between the cities of Jaguari and Santiago. After thermal and alternating field demagnetization, both normal and reversed characteristic remanent magnetizations were found. These results yielded 13 reversed and 5 normal polarity sites, composing a magnetostratigraphic column displaying a sequence of reversed-normal-reversed polarity events. The paleomagnetic pole calculated for 18 sites is located at 114.7 • E, 78.5 • S (dp=8.1 • ; dm=1.2 • ), after restoring the strata to the paleohorizontal. This paleomagnetic pole indicates a Late Jurassic-Early Cretaceous age to the Botucatu Formation in the investigated area, and places the sampling sites at paleolatitudes as low as 21 • S.

A Late Jurassic fossil assemblage in Gondwana: Biostratigraphy and correlations of the Tacuarembó Formation, Parana Basin, Uruguay

“…Because of this, and its stratigraphic relationships with the Arapey Formation, an earliest Cretaceous (Berriasian-Hauterivian) age is proposed for the Rivera Member. The paleomagnetic data recently published by Tamrat and Ernesto (2006) for the correlative Botucatu Formation are consistent with this chronological proposal.…”

Palaeomagnetic confirmation of Palaeozoic clockwise rotation of the Famatina Ranges (NW Argentina): implications for the evolution of the SW margin of Gondwana

“…with Early Cretaceous poles (160-130 Ma) from South America (Fig. 7, Tamrat & Ernesto 2006). Since the IRM inclination experiments described above indicated that no significant inclination shallowing affects these rocks, two possible interpretations are suggested.…”

“…There is no difference in both directions of each pole. (C) LC2 (pole from De La Cuesta Formation, Los Colorados Anticline outcrop) and Cretaceous palaeomangetic poles of South America (Besse & Courtillot 2002; Tamrat & Ernesto 2006).…”

The Early Triassic magmatism of the Alto ParaguayProvince, Central South America: Paleomagneticand ASM data

“…The mean of the minimum axes k 3 (the pole to the foliation plane) directions suggest a dip of 24 ∘ to N205 ∘ , and such a bedding correction would displace the APP paleomagnetic pole to a position (157 ∘ E 80 ∘ S), if taken as representative of the entire igneous province. This pole position is close to the Late Jurassic segment of the apparent polar wander path for South America [29], and would imply in a remagnetization of the entire province, for which there isare no evidences from the paleomagnetic and the rockmagnetic data described above. Therefore, if the maximum axes k 1 are re-ally parallel to the flow direction it is possible that the foliation plane refers only to the Pão de Açúcar complex or it means that the emplacement surface was not horizontal.…”