Nature of magnetic grains and their effect on the remanent magnetization of basalts

The Magnetic Mineralogy of the Precambrian Banded Haematite Jasper Formation, Orissa, India.

“…The first is similar to the group 3 behaviour described from basalts by SENANAYAKE and MCELHINNY (1981) and attributed by them and other workers (e.g. RADHAKRISHNAMURTY et al, 1977) to multidomain (MD) magnetite-the peak corresponding to the isotropic point of magnetite. This peak is suppressed in single domain magnetite (SENANAYAKE and MCELHINNY, 1981).…”

The Strength of the Geomagnetic Field at the Cretaceous-Tertiary Boundary: Palaeointensity Results from the Deccan Traps(India)and the Disko Lavas(Greenland).

“…It is becoming increasing clear that at present we do not understand the changes in magnetic mineralogy and the rock magnetic processes which occur in lavas. RADHAKRISHNAMURTY et al (1977) presented palaeointensity estimates from ten Deccan lavas. Using a continuous heating process where the magnetisation was monitored during heating in zero-field and cooling in a known laboratory field, they obtain a mean geomagnetic field which is 55%® of its present strength.…”

“…Expressed as a VDM, this would be about 4.2x 1022 Amt which is identical to the value obtained here. Commenting on their earlier work, RADHAKRISHNAMURTY et al (1991) note that thermal alteration commonly occurred during such experiments so uncorrected results should be regarded as unreliable.…”

The Correlation of Long-Term Trends in the Palaeointensity and Reversal Frequency Variations.

“…2 is that (a) the results based either on a large population or on the comparison of the two sets of methods are taken to be more reliable (shown by closed circles) compared to (b) those based on a single method used on a small number of samples (shown by open circles). This reduces the reliability of several VDM estimates, e.g., for the late Permian Canadian dacites (SCHWARZ and SYMONs,1969) and middle Cretaceous Rajmahal traps (RADHAKRISHNAMURTY et al, 1977), and of older palaeointensity data on Deccan basalts (SMITH, 1967a;KONG, 1974), even though they are based either on the Thellier method or on its variants.…”