Discussion of 'Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf'1.

The paper 'Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf' (Romer et al., published in 2011) describes six samples of which four are from the Meguma Supergroup of Nova Scotia. Previous work indicates that these samples are Cambrian and that they were deposited in a deep-water turbidite basin ('Megumia'), not on the Avalonian shelf. The geochemical data support models for Mn concentration, involving oxidation and reduction in a sedimentary environment but do not constrain water depth. Likely correlatives are in the Cambrian of North Wales and not in the European localities sampled by the authors. [ABSTRACT FROM AUTHOR]