Hello Victoria. Varves are layers of slightly different material deposited in lacustrine environments. Varves can be seasonal. yes, spring time may have a bit coarser suspended material that deposits. Sometimes it can be primary particles coated with humic organic materials that deposits in a particular season. Sometimes varves can be annual changes in size and colour of material deposited. Example it could be a very wet year on whole bringing slightly coarser material into the lake.