Tar pit

A tar pit, or more accurately known as an asphalt pit or asphalt lake, is a geological occurrence where subterranean bitumen leaks to the surface, creating a large area of natural asphalt.[1][2] This happens because after the material reaches the surface its lighter components vaporize, leaving only the thick asphalt.

Known Tar Pits
There are other fossil-bearing asphalt deposits in Oklahoma, Texas, Peru, Trinidad, Iran, Russia and Poland.
 * La Brea Tar Pits Los Angeles, California, US
 * La Brea Tar Pits Los Angeles, California, US
 * La Brea Tar Pits Los Angeles, California, US

For other rich deposits, fossilized where they occurred, see Lagerstätten. Tar pits are the resting places of many fossils.

Paleontological significance
Animals are usually unable to escape from the asphalt when they fall in, making these pits excellent locations to excavate bones of prehistoric animals. The tar pits can trap animals because the asphalt that seeps up from underground forms a bitumen pit so thick that even mammoths find it impossible to free themselves before they die of starvation, exhaustion from trying to escape or from the heat that would come from the sun. Over one million fossils have been found in tar pits around the globe.