Fossil Burial & Preservation

The unusually high quality of fossil preservation at Rancho La Brea occurred because the bones were buried rapidly by the asphalt and sediments. That is not to say that the bones were buried overnight, but they were seldom exposed to elements for an extended length of time. Those that were exposed to natural processes like erosion, for an extended amount of time usually failed to be preserved as fossils.
After the animal remains decayed, the bones became saturated with asphalt and partially or wholly submerged in the seep. After partial burial, winter and spring rains would wash down fresh sediments that mingled with further seepage. It is this cycle, repeated for tens of thousands of years, which contributed to the formation and composition of the fossil deposits.

		Foot Note! Animal tissues and organs such as flesh, hair, cartilage, claws, and feathers have not been recovered from Rancho La Brea. Several types of bacteria helped decompose these materials before complete burial within the asphalt and sediment layers occurred.

Next