tar pit

noun

1. seepage of natural tar or asphalt, especially an accumulation that has acted as a natural trap into which animals have fallen and sunk and had their bones preserved.

1. An accumulation of natural tar or asphalt at the Earth’s surface, especially one that traps animals and preserves their hard parts. Tar pits form when petroleum in subterranean petroleum-bearing rocks oozes up to the surface. As it rises, the petroleum loses its volatile components, forming a thick tar or asphalt deposit.