The Ordovician magnetostratigraphic time scale: reliability and correlation potential

A compilation of global Ordovician palaeomagnetic results for magnetostratigraphic purposes reveals data of varying quality. Data were classified as either "fundamental', "supplemental' or "unconstrained' depending on available biostratigraphic and palaeomagnetic constraints on the rock-age and magnetisation-age respectively. An Ordovician magnetostratigraphic polarity time scale (OMTS) is presented using the above analysis. The reversal frequency during the c.70Ma of the Ordovician period (approximately 1 polarity change per 5Ma) is an order of magnitude less than that observed during Late Cretaceous-Cenozoic time (approximately 1 change per 0.5Ma). This observation implies two important consequences: (1) the proposed scale will only be useful for high precision correlation of strata deposited close to reversal boundaries; and (2) the apparent simplicity of the scale should allow intercontinental correlation of strata "to within a polarity zone' with relative ease. -from Authors