Paleomagnetism and magnetic fabrics from the Springdale and Wigwam Redbeds of Newfoundland and their implications for the Silurian paleolatitude controversy

Abstract

In many mobile belts, paleomagnetic directions from elastic sedimentary rocks are typically shallower than directions from associated igneous rocks. This discordance raises questions about the reliability of sedimentary rocks and can lead to controversial paleogeographic reconstructions. In Newfoundland, the controversy over Silurian paleogeography arises from a difference between results from elastic redbeds (with anomalously shallow directions that place Newfoundland at the paleoequator in the Silurian) and coeval epicontinental volcanics (with steeper directions that place Newfoundland at a more southerly paleolatitude). This study tests the possibility that the anomalously shallow redbed directions are the result of internal strain or inclination error related to deposition. We specifically compare coarse-and fine-grained lithologies under the assumption that such remanence-altering effects will be different in rocks with differing mechanical competence.We show that inclinations correlate with lithologic variations, but in a manner opposite to that predicted for the accumulation of internal strain. Based upon a strict set of demagnetization criteria, clearly defined single-component characteristic directions are only observed in the finer grained sandstones. These well-determined directions yield a pre-folding and pre-rotational dual polarity magnetization that places Newfoundland at a paleolatitude of 23"(S) f 9" in the Silurian. This revised paleolatitude is consistent with the volcanic results and with the paleolatitude predicted for Newfoundland from the North American reference path. In contrast, coarse-grained sandstones yield shallower directions that appear to be composites of opposite polarity magnetizations or weakly defined directions with strongly contaminating overprints. Because the shallow magnetizations in the coarser grained samples may have originated as a depositional remanence, we also suspect inclination error related to deposition. The degree of inclination error is consistent with values predicted for redbeds from previously published experimental results. These observations suggest that grain-size considerations are important in assessing the reliability of redbed magnetizations. Recognition of the relationship between grain size and remanence acquisition allows us to resolve the Silurian paieolatitude controversy for Newfoundland.

Inclination variation in the Late Jurassic to Eocene red beds from southeast Asia: lithological to locality scale approach

“…Similar type of behaviour has been reported by Hodych & Hayatsu (1988) on the basis of their palaeomagnetic results from Jurassic red beds. Contrary to these views some of the researchers (Tucker 1979; Stamatakos et al . 1995; Tan et al .…”

“…Similar type of behaviour has been reported by Hodych & Hayatsu (1988) on the basis of their palaeomagnetic results from Jurassic red beds. Contrary to these views some of the researchers (Tucker 1979;Stamatakos et al 1995;Tan et al 2007) have observed that fine-grained magnetic minerals, which carry magnetically hard component and distributed spectra of unblocking temperatures, have accurately recorded magnetic field directions without any inclination error. However, higher degree of inclination shallowing have been observed by them in the coarse-grained sediments, which carry magnetically soft NRM component and discrete unblocking spectra.…”

A successful rock magnetic technique for correctng paleomagnetic inclination shallowing: Case study of the Nacimiento Formation, New Mexico

“…Studies by Anson and Stamatakos et al [1994] have criticized Hodych and Buchan's approach, since they believe that AIR inadequately determines the magnetic fabric in all the remanence-carrying hematite grains. Stamatakos et al [1995] have subsequently provided detailed evidence that the anomalously shallow inclinations in the Silurian redbeds from Newfoundland are due to magnetic overprints dominating the remanence in coarse-grained sandstones.…”

A plate tectonic scenario for the Iapetus and Rheic oceans

“…u Smethurst and McEnroe (2003),. v Stamatakos et al (1995),. w. Johnson and Van der Voo (1985), x Thompson et al (2010),.…”