Tar pit
If this crude oil seeps upward via fractures, conduits, or porous sedimentary rock layers, it may pool up at the surface.
[1] The lighter components of the crude oil evaporate into the atmosphere, leaving behind a black, sticky asphalt.
If the structure above the concave-down fold (arch) is a non-porous rock or aquitard, such as shale, it is considered an anticlinal trap.
A reservoir of light crude oil on Earth's surface can be reduced by up to 75% of the initial volume just after a few days, forming asphalt as the resulting product.
[8] These oil deposits were formed during the Miocene Epoch when marine plankton organisms accumulated in an ocean basin.
[9] Over time, sediments buried the organisms 300 to 1000 meters below Earth's surface, subjecting them to high pressures.
The 6th Street Fault that cuts through the Salt Lake Oil Field is the conduit that feeds the La Brea Tar Pits.
[8] Petroleum migrated to the surface over time, trapping and preserving animals and plants for the past 50,000 years.
This tar pit is known for preserving the heads and bodies of multiple cave lions, a mammal that flourished in the Pleistocene.
The lake has a maximum depth of 250 feet with an area of 100 acres, making it the largest deposit of solid bitumen on Earth.
The gas being released in the middle of the lake is largely methane and an ample amount of carbon dioxide.
Movement along a fault created a fracture that tapped into an oil and gas reservoir deep within the crust.
The oil and gas seeped upward to Earth's surface through the fracture over time, creating Pitch Lake.
Beneath the surface, the hard parts are engulfed with asphalt, and they are protected from climate variations like rain, wind, or snow that may accelerate weathering processes.
Asphalt also lacks oxygen and water, so major decomposing organisms like aerobic fungi and bacteria are absent.
[9] The most frequent large mammal found in the La Brea Tar Pits is the dire wolf, one of the most famous prehistoric carnivores that lived during the Pleistocene.
The soil microorganisms had to adapt and undergo genetic changes to help tolerate the harsh, new environment, which ultimately gave rise to new bacterial species.
[17] Pitch Lake, another asphalt pit in Trinidad and Tobago, is also a habitat for microbial communities of archaea and bacteria.
Bacterial microorganisms from the orders Burkholderiales and Enterobacteriales have been found living in microliter-sized droplets of water recovered from the lake.
[19] Ongoing research is being conducted in Pitch Lake because it mimics the environment found on the surface of Saturn’s largest moon, Titan.
[20] The emissions are the highest along the 6th Street Fault, which is the conduit that feeds the tar pits with crude oil from the sediments underneath Earth's surface.
The La Brea Tar Pits have the highest natural gas flux measured for any onshore seepage zone in the United States.
On March 24, 1985, a pocket of methane gas passed through a small opening between the floor slab and foundation walls of a Ross clothing department store in Los Angeles, only about a mile north of the La Brea Tar Pits.
[21] Tar pits are excellent preserving agents, and they also have the ability to provide carbon isotope data for trees that have fallen into the asphalt.
