Green River Formation
As talkorigins says, At least one formation contains 20 million varves. That represents more than 50,000 years even if you assume varves were formed at a rate of one per day. And the fineness of the silt precludes the possibility that they could have formed that rapidly.
The problem with this measurement of ages comes when we examine the facts. Fossils are found buried all throughout the layers, well preserved and abundant:
- . . . fossil catfish are distributed in the Green River basin over an area of 16,000 km2 . . . The catfish range in length from 11 to 24 cm, with a mean of 18 cm. Preservation is excellent. In some specimens, even the skin and other soft parts, including the adipose fin, are well preserved (Buchheim and Surdam)
This is a problem because fossils are not preserved under normal circumstances. The varve must lie undisturbed before having another layer deposited on top of it. These layers are often less than a millimeter thick. The fossilized fish would need to not decay for the period between deposits. Research shows, however, that fish will decay within days:
- Experiments by scientists from the Chicago Natural History Museum have shown that fish carcasses lowered on to the muddy bottom of a marsh decay quite rapidly, even in oxygen-poor conditions. In these experiments, fish were placed in wire cages to protect them from scavengers, yet after only six-and-a-half days all the flesh had decayed and even the bones had become disconnected. 
There is no way these layers could have formed annually as suggested, which has led some to consider catastrophic explanations.
- H.P. Buchheim and R.C. Surdam, ‘Fossil catfish and the depositional environment of the Green River Formation, Wyoming’, Geology 5:198, 1977.
- Green River Blues by Paul Garner. Creation 19(3):18–19 June 1997