Varves in marine sediments: A review

The postulated occurrence of varves in pre-Quaternary rocks is critically discussed in this review with representative examples. In the case of non-evaporitic laminations in fine-grained ancient marine rocks, such as banded iron formations and black shales, laminations may not be varves but instead may have multiple alternative origins such as event beds or formation via bottom currents that transport and sort silt-sized particles, clay floccules, and organic-mineral aggregates in the form of migrating bedload ripples.