If it had not been for LinkedIn, I might never have been aware of the existence of the 2024 Bouguer gravity map of Brazil, and that would have been a pity. Some things jump out almost at first sight, and one of these is the narrow and almost linear gravity high that roughly coincides with the main course of the middle Amazon.
Free-air gravity maps suggest that, rather than having been a rectilinear feature, the subducted portion of the D’Entrecasteaux ridge, which impacts the Vanuatu Trench at a high angle, was curvilinear. The entire region is reminiscent, in size and the disposition of subduction -related volcanics and collision orogens, to the Banda Sea region of eastern Indonesia.
Modern airborne gravity relies largely on measurements of gravity gradients. Given how very small the signal will inevitably be, it is clear that measuring it is bound to be very, very difficult. Nevertheless, it was being done in Australia in the late 1920s with some success.
In the Preface to the report in the Imperial Geophysical Experimental Survey in Australia in the late 1920s and early 1930s, a few unforgettable names were listed. Attached to the survey was ‘J. M. Rayner, of the New South Wales Department of Mines’, and moving to the lower echelons, the Electrical Section had a field assistant called R. F. Thyer, while designated as a Temporary Assistant was one N.H Fisher.
It is not given to many people to be recognised as the most important figure in the geological history of an entire country, but Hugh Davies, who died on April 26 this year, had that distinction.
In late 2022, Bill Hinze published, through the Minnesota Geological Survey, a book entitled From Compass to Drone: The Evolving Role of Magnetics in Mapping the Geology and Ore Deposits of the Lake Superior Region: 1830-2022.