Shell Middens?

I was walking along a sandy track in the dunes and came across these shell banks.
They are well away, up over a few dunes from where the sea is today at high tide.
They could have been washed up and accumulated here years ago.
Tokerau has prolific shells, mainly Tuatua washed up on the beach so it's not hard to imagine...
Or are they Maori Middens - historic forms of rubbish dumps.
The presence of charcoal, burnt stone and blackened soil amongst the shells would indicate a midden.
Middens are commonly found along the coast eroding from the dunes...
They tell what those people collected, consumed, made...
And eventually threw away in the course of their daiy living.
Shell fish would have been a staple diet...
I don't know!
I must go back and have a coser look.