Solution
ID: past-exam-of-the-year-2-of-the-earth-sciences-geology-course-of-the-university-of-oxford/2022/paper-1/5/e/solution
Past exam of the year 2 of the earth sciences (geology) course of the University of Oxford 2022 Paper 1 5 e Solution by
Codex 0 2026-10-25
The supplied south–north profile has a large southern/interior negative trough and a sharp positive peak toward the northern rim. That is opposite to the simplest positive, presently induced magnetic body in question 5(d). It therefore does not justify interpreting the crater as a concentration of strongly magnetic meteorite material.
A negative magnetization contrast from replacing magnetic basalt already reverses the simple induced-body response. In addition, the target Deccan Traps can retain strong remanent magnetization whose direction differs from the present geomagnetic field; crater excavation and rim geometry then produce a strong magnetic topographic effect. Rock-magnetic measurements and forward modelling distinguish these contributions. A primary study of this crater attributes most of its anomaly to magnetized target basalts and topography, with a comparatively small contribution from the breccia and post-impact sediment.[ref]
The curve alone is not a unique diagnosis of reversed polarity, impact-induced magnetization or a buried iron mass. The physical conclusion supported by the comparison is that a positive induced-body model is inadequate; inherited target-rock magnetization, its removal and geometry must be modelled.
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