Title: Detrital
remanent magnetization in haematite-bearing Neoproterozoic Puga cap
dolostone, Amazon craton: a rock magnetic and SEM study
Document Type: Article
Language: English
Abstract: Neoproterozoic
cap dolostones of the Araras Group (Mato Grosso, Brazil), deposited on
top of glacial diamictites (Puga Formation, similar to 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 mu m) 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.
Author Keywords: cap
dolostone; DRM; haematite; magnetic mineralogy; Neoproterozoic
KeyWords Plus: LATE
PALEOZOIC REMAGNETIZATION; ACQUISITION CURVES; SNOWBALL EARTH;
BREAK-UP; CARBONATES; MINERALS; LIMESTONES; PALEOMAGNETISM;
FINGERPRINT; COERCIVITY
Addresses: Font
E (reprint author), Univ Sao Paulo, Inst Astron Geofis & Ciencias
Atmosfer, Dept Geofis, Sao Paulo, Brazil
Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, Dept
Geofis, Sao Paulo, Brazil
Observ Midi Pyrenees, UMR 5563, LMTG, Toulouse, F-31400 France
Publisher: BLACKWELL
PUBLISHING, 9600 GARSINGTON RD, OXFORD OX4 2DQ, OXON, ENGLAND
Subject Category: GEOCHEMISTRY
& GEOPHYSICS
IDS Number: 976ZR
ISSN: 0956-540X
