Mesozoic Reversal Stratigraphy

Abstract

McElhinny and Burek¹ have attempted to derive a palaeo-magnetic stratigraphy for the Mesozoic from an exhaustive literature search. This expands, and in several important respects differs from, the earlier work of Burek². The method used is basically that used to first establish a magnetic chronology for the most recent segment of geologic time³ without the advantages of fine radiometric age control. There are in addition significant stratigraphic problems, the familiar boundary problems, which make intercontinental comparisons difficult. This leaves the authors at the mercy of the data available, a point clearly brought out in the “News and Views” section of the same issue of Nature. The purpose of this letter is to emphasize these dangers and underline the need, implicit in ref. 1 for studies directed specifically at the problem of reversal chronology. Such studies, the equivalent of palae-ontological inch by inch collecting, are few in number if we exclude the study of oceanic cores. The first was probably that of Khramov⁴, and subsequently Helsley⁵ and his coworkers⁶ have made a number of controlled collections. We would like to refer to some work on Permian rocks⁷ and present day studies of Jurassic rocks⁸.