How much methane clathrates are buried in continental deposits? Methane clathrates are


  solid clathrate compound (more specifically, a clathrate hydrate) in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice.


They mostly are on the bottom of the world's oceans; however, the overly brief wikipedia section for continental deposits suggests that it also occurs in Siberia, northern Canada and Alaska.

How much methane clathrates are believed to be buried in these continental deposits?
According to Role of methane clathrates in past and future climates, 


  Methane occurrences and the organic carbon content of sediments are
  the bases used to estimate the amount of carbon currently stored as
  clathrates. The estimate of about 11,000 Gt of carbon for ocean
  sediments, and about 400 Gt for sediments under permafrost
  regions...


So 400 billion tons.