hey joe, congratulations on yer endeavor, and yer very wise to consult the vast resources here as you start yer journey.

sounds indeed like yer upper horizon soils are clay rich (perhaps clay loams or clay with silt/ silty clay loams which are great pond soils). silt soils will settle very fast in the mason jar test.

useful info is that depending on size of area and thickness of clay soil horizon, you may have a great on-site source for clay soils if'n when you dig yer pond and find coarser soils below, you can "borrow" to pack areas of pond bottom.

IMO, you still need to dig some test pits though and find out what is present at the depth you want yer pond to be.

GSF are people too!