Digital Varves

What is the NAVC?

Major valley segments of the North American Varve Chronology (NAVC) showing the AM varve year number spans in different drainage basins in the northeastern United States. Click to view full size.

“NAVC” is the abbreviation for the North American Varve Chronology, a revision of Ernst Antevs’ (1922, 1928) original New England Varve Chronology (NEVC). The NAVC is compiled with a new numbering system we refer to as ‘AM’ (short for American) varve years.  Antevs’ original NEVC was compiled in New England ('NE') varve years. The NAVC is now a continuous chronology of 5659 varves (AM 2700-8358) composed of varve sequences in the Connecticut (Lake Hitchcock), Hudson (Lake Albany), Merrimack, Ashuelot, and Winooski valleys. The naming of this new chronology seems appropriate since some varve sequences in the NAVC (and also the old NEVC) occur in places outside New England. Also, in the future it seems likely that the chronology will extend further into New York and into New Jersey and Quebec. It is important to note that Antevs never referred to his chronology as the New England varve chronology but instead this appears to be an informal name invented by others that has stuck over the years.

Revisions of Antevs’ original NEVC were needed to correct errors and the old chronology was actually two chronologies, the lower and upper Connecticut varve sequences that had separate numbering systems (NE-LC and NE-UC numbering systems). This was a major inconvenience when plotting sequences, performing serial analysis, or calibrating the sequences. In 2008 an overlap of the two NEVC’s lower and upper Connecticut sequences was established in varve records from cores in the Connecticut Valley of southern New Hampshire. The NAVC now has a unified numbering system for all the old NEVC sequences and also incorporates corrections based on new core data. New varves were added to the chronology and a few couplets in the old chronology were reinterpreted where two years were collapsed to one year. Flood events in 5 varves in the old NEVC of the Hudson Valley were also reinterpreted, when compared to new overlapping core records in the Connecticut Valley, and now occur in one thick varve of the new NAVC.