Detrital remanent magnetization in haematite-bearing Neoproterozoic Puga cap dolostone, Amazon craton: A rock magnetic and SEM study

Abstract

Neoproterozoic cap dolostones of the Araras Group (Mato Grosso, Brazil), deposited on top of glacial diamictites (Puga Formation, ∼630 Ma), yielded a dual polarity component providing a low palaeolatitude for the Amazon craton. Because palaeomagnetic negative directions are very close to the present-day dipolar field, a rock magnetic and SEM study was conducted in order to check the primary nature of the remanent magnetization and to identify the nature and origin of the remanence carriers. Results show that detrital specular haematite (grain size ≥10 μm) is the main magnetic carrier in the Araras dolostones and was likely inherited from the underlying Puga diamictites. In some sites, a mixture of haematite and magnetite carries the remanence of both polarities. The primary nature of the magnetization is supported by the detrital character of the magnetic carriers. In addition, the remanence anisotropy is weak, pointing to the lack of significant shallowing due to compaction. These results reinforce the low palaeolatitude of the Amazon craton at the time of the Marinoan ice age. © 2005 The Authors Journal compilation © 2005 RAS.