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Abstract

The Rancho La Brea asphalt seeps of Los Angeles, California is the site of the richest and most diverse assemblage of Pleistocene mammal fossils in the world. The conventional mechanism for the formation of this deposit has herbivorous mammals getting stuck in pools of asphalt one at a time. Carnivores and scavengers were then attracted to the captive herbivore, to become trapped in asphalt themselves in large numbers. This is assumed to have occurred more or less continuously over the last 38,000 years.

Sedimentological and paleontological evidence calls for another interpretation. There is evidence that asphalt did trap some animals - mainly small mammals, small birds, reptiles, and insects in more recent times. Rancho La Brea lacks the evidence expected at a trap site. However, evidence of rapid deposition of the sediments in which the fossils are found argues that most of the animals - especially the larger Pleistocene extinct species - were actually deposited by flash flood events, which in turn attracted scavengers which may have become stuck in the asphalt and buried in subsequent floods on the Los Angeles / Orange County floodplain. Earthquake disruption and liquefaction may also have been factors which accelerated entombment of some of these animals. Evidence further indicates that deposition was not continuous, but a series of rapid catastrophic pulses. Finally, the slow seepage of asphalt through faults in the older underlying marine strata resulted in the remarkable preservation of these fossils.

This deposition is here re-interpreted to be the result of local catastrophism during the waning geologic catastrophism of the post-Flood period. This corresponds with the post Flood climatic cooling which led to what is commonly called the Ice Age.

Keywords

Vertebrate Paleontology, Sedimentology, Catastrophism, Fluvial Deposition - Pleistocene Fossils, La Brea Tar Pits, Asphalt Seeps, Flood Geology, Post Flood Catastrophism

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Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

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