From the Editor | June 2021

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Assessing the Effect of Mineral Alteration on Palaeointensities Derived from Volcanic Rocks of Cretaceous Age

The appearance of superchrons within the palaeomagnetic record has aroused considerable interest amongst those seeking to understand the processes driving the geomagnetic field. Efforts to understand dynamo processes underlying superchrons require a fuller understanding of the magnitude of the Earth’s magnetic field during these periods. This has drawn focus on the Cretaceous Normal Superchron, 83 – 121 Ma, a period of almost 40 million years when the Earth’s magnetic field remained in a fixed, normal polarity aligned close to the Earth’s rotation axis, as it is today.

Difficulties arise when using the magnetisation of rocks as a proxy for the ancient magnetic field; non ideal behaviour of a material combined with in situ and laboratory alteration and oxidation can result in unreliable estimates of both field strength and direction. This study primarily focuses on the effect of mineral alteration on rocks of Cretaceous age, the resulting changes in magnetic characteristics and their effects on palaeointensities.

For palaeointensity investigations, it is paramount the sample retains an original thermal magnetic remanence, a TRM, but it can be difficult to assess whether this is the case. By applying palaeointensity methods to Cretaceous basalt, whilst simultaneously carrying out rock magnetic and microscopy analysis, I assess the effect of mineral alteration on palaeointensities derived from volcanic rocks of Cretaceous age.

For anyone interested in the outcomes of this work or a discussion on the Earth’s magnetic field – please feel to get in touch, it is a subject I hold close to my heart.

The Houston Geological Society is a great organization and I appreciate your company this year with the Bulletin. I wish Scott Sechrist the best with taking over as Editor and I’m sure he’ll have many a story to share with us.

Keep well, see you soon,
Ceri