Subdivision of the Precambrian

Abstract

AbstractThe Precambrian record is so fragmentary and from such widely contrasting terrains that attempts to erect any formal subdivisions would appear to be premature. The methods that have been used in the Phanerozoic rocks cannot be used for subdividing the Precambrian as they are peculiarly suitable for fossiliferous largely undeformed sedimentary units in which the sedimentary record is relatively full. Isotopic dating methods also become so imprecise over the major portion of Precambrian time that it is only rarely possible to use them to define particular events with the same precision as those dated in the Phanerozoic record, although this is changing with increasing analytical accuracy.The use of biological criteria for the erection of a chronostratigraphic scale is seen as a future possibility, but the methods of defining the units that are used in the Phanerozoic are thought inappropriate, and the characterization of a particular chronostratigraphic unit (e.g. by the presence of metazoan trace fossils) is seen as more appropriate.International agreement on the time for particular boundaries in the Precambrian is regarded as an attempt merely to define the terms already in use rather than having any scientific basis. It is possible that future research may reveal global events which are recognized to be unique and these may provide more reliable datum planes to use. If they are also related to changes in the way the earth behaved through time it would be logical to use these as markers for any major subdivisions of Precambrian time. None have