As I've written before in this diary, the Calder is what you might call a misfit river sitting in its broad valley near Wakefield doing little more than redistribute the silt on the flood plain. It doesn't seem likely that the present river, even in flood, could have carved out the valley by itself or that it could deposit such vast quantities of sand and gravel across its flood plain.
The Atlantic PeriodMuch of the work of enlarging the valley was probably done by meltwaters during the last ice age when the Calder valley remained ice-free, although their was a glacier in neighbouring Airedale, a little to the north.
As I understand it the gravel deposits are more likely to date from after the ice age, perhaps from a time when it was wetter and warmer than it is today; the Atlantic Period, 7,500 to 5,200 years before the present day (or 5,500 B.C. to 3,200 B.C. if you prefer). The gravels probably contain of material of ice age origin which has been eroded and then redeposited by later rivers.
Large trees buried within the beds also suggest that the gravels may date from this warmer period. During the ice age it's probable that nothing larger than a dwarf willow was able to survive locally.
Carbon DatingThe particular tree that we were looking at today was tall and straight. It might be as old as the gravels or it may have been deposited in a channel cut into existing, and therefore older, gravel bed. It has been dragged out to the edge of the workings so we can't get any precise answer on that. The results of a radio carbon date, or a tree ring analysis would be interesting because, even without a record of exactly where it was found in the gravel pit, the information might help shed some light on the evolution of the valley.