I have always found this image to be very useful in showing the difference between flood deposits and varves:
From here:
http://www4.uwsp.edu/...icipants/dutch/vtrips/scablands0.htm
These varves are found in the Channeled Scablands where there were numerous, catastrophic floods from outflow of glacial Lake Missoula. In the middle of the photo you see fine grained sediments consistent with slow deposition of clay particles. Above and below the varves are flood sediments which are coarser. As anyone can see, varves and flood deposits are easily differentiated.