www.geopolar.uni-bremen.de/varves/images/varve_model.png

There are both particle size and organic aspects to varving as shown above. Finer and less organic rich are the winter layers.

North American Glacial Varve Chronology--Tufts

Varved Lake Sediments, by B Zolitschka

The New North American Varve Chronology--J Ridge Tufts

USGS Study of Upper Miss Basin Lake Sediments

Varves wikipedia

Varves are seasonal sediment alternations which appear to represent annual cycles.  They are widely studied and correlated, because seasons cause sedimentary variations that repeat. Like tree rings, they allow us to see year by year change, they record climate and lake level change events and allow reconstruction of evolving landscapes.  We are very rich in varved deposits, and can visit them readily in many nearby places where fine sands silts and clays are exposed such as at Coles Creek near Houghton on the Houghton Canal Road.