Tar pit
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Tar pits, sometimes referred to as asphalt pits, are large asphalt deposits. They form in the presence of petroleum, which is created when decayed organic matter is subjected to pressure underground. 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.[1] Tar pits are often excavated because they contain large fossil collections.[1]
Tar pits form above oil reserves, and these deposits are often found in
Chemistry
Tar pits are pools of asphalt. However, at the beginning of their formation, they were not always sticky and dense. The pools were composed of
Evaporation is an important process in the formation of tar pits. 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. For medium crude oils, the volume may be reduced by 40%.[7] Crude oils will evaporate differently depending on their chemical composition.[4] The average composition of a bitumen sample by weight is 80.2% carbon, 7.5% hydrogen, 7.6% oxygen, 1.7% nitrogen, and 3.0% sulfur.[2]
Notable tar pits
La Brea Tar Pits
The La Brea Tar Pits are located in Los Angeles. The petroleum that is seen on the surface is sourced from the Salt Lake Oil Field reservoir and the oil sands in the Repetto and Pico formations.[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. This process turned the organic matter into oil. 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.[9]
Carpinteria Tar Pits
The Carpinteria Tar Pits are located in Tar Pits Park in Carpinteria, California. These tar pits were predicted to have formed during the Pleistocene. During an excavation project, 25 plant species were recovered along with 55 species of birds and 26 species of mammals.[10] Springs of tar still ooze to the surface through fractures in the underlying stratigraphic layers of marine shale.[10]
Binagadi Asphalt Lake
The Binagadi Asphalt Lake is located in Azerbaijan, or in the Caucasus, a region between the Black Sea and the Caspian Sea. This tar pit is known for preserving the heads and bodies of multiple cave lions, a mammal that flourished in the Pleistocene.[11] A well-preserved horse skull was also found in the Binagadi asphalt lake. It is estimated to be 96-120 thousand years old. It is on display at the Natural-Historical Museum of Azerbaijan in Baku, Azerbaijan.[12]
Pitch Lake
Pitch Lake in Trinidad and Tobago is a large, bowl-like depression filled with bitumen. 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.[13] The lake is cold and dense near the shores, and it has a top layer that can be walked on. Underneath this skin, the asphalt is continuously churning. The lake gets gradually softer and hotter near the center where the bitumen begins to bubble. The gas being released in the middle of the lake is largely methane and an ample amount of carbon dioxide.[14]
Pitch Lake formed thousands of years ago in the presence of tectonic activity. 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. Due to this constant replenishment of the oil and gas, the lake has a slight current. The current is largely unnoticed because the top layer of Pitch Lake is mostly solid.[13]
Fossils
Tar pits are characteristic of their many fossils. This is the case because the thick, sticky asphalt traps animals.[15] Once animals step into the tar, they become immobilized and begin sinking immediately if the asphalt is warm and sticky enough. Predators that see these helpless animals usually would advance into the tar pits with the hope of catching their next meal. As a result, prey are usually found beneath the predator during excavation projects.[15]
The bones and hard parts of the animals are well preserved because they are buried rapidly after the organism's death. 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
In the La Brea Tar Pits, more than one million bones have been recovered since 1906. 231 vertebrate species, 234 invertebrate species, and 159 plant species have been identified.
Living organisms
Life was found in a ca. 28,000-year-old sample of natural asphalt in the La Brea Tar Pits.[17] Hundreds of new species of bacteria were discovered that have the ability to thrive in environments with little to no water or air. They contain special enzymes that can break down hydrocarbons and other petroleum products.[17] The origin of the bacteria in these natural asphalt pits is unknown, but it is believed that they evolved from preexisting soil microorganisms that survived an asphalt seepage event thousands of years ago. 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]
In one study, the predominant bacteria found in the La Brea Tar Pits were of the
Contributions to greenhouse gases
Tar pits are formed by the
The natural geologic sources of methane and other hydrocarbons should be considered when modeling atmospheric greenhouse gases. Not all sources of hydrocarbons in the atmosphere are a result of anthropogenic emissions.[20]
Dangers of tar pits
Hydrocarbon seepage in urban or industrialized areas present a geologic hazard due to the explosive nature of hydrocarbons. On March 24, 1985, a pocket of
Key to paleoplant behavior
Tar pits are excellent preserving agents, and they also have the ability to provide
History of tar pits and humans
A woman's body was recovered from the La Brea Tar Pits in 1914. Only the skull and parts of the skeleton were preserved, and she was determined to have died about 9,000 years ago.[24] She was between the ages 18–24 at death, and she was 4 feet and 8-10 inches tall.[24] This is the only reported instance of human remains found within tar pits.[25]
For thousands of years, Native Americans used tar from the La Brea Tar Pits as an adhesive and binding agent.[1] They would use it as waterproof caulking to line their boats and baskets. When Westerners arrived at the tar pits, they began mining and extracting the tar for roofing material in nearby towns.[1]
References
- ^ a b c d e "La Brea Tar Pits". University of California Museum of Paleontology. Retrieved April 26, 2021.
- ^ a b c "Earth's physical resources: Petroleum: View as single page". www.open.edu. Retrieved April 26, 2021.
- ISSN 1571-9960.
- ^ a b c "Chemical Constitution of Crude Oil | FSC 432: Petroleum Refining". www.e-education.psu.edu. Retrieved April 26, 2021.
- ^ a b c "Chemicals from Oil | S-cool, the revision website". www.s-cool.co.uk. Retrieved April 26, 2021.
- ^ a b "2.5: Hydrocarbon Types | PNG 301: Introduction to Petroleum and Natural Gas Engineering". www.e-education.psu.edu. Retrieved April 26, 2021.
- ^ Fingas, Merv (1995). "The Evaporation of Oil Spills" (PDF). Proceedings of the Eighteenth Arctic Marine Oilspill Program Technical Seminar – via McGill University.
- ^ S2CID 101426941.
- ^ a b c d e "La Brea Tar Pits and Hancock Park | La Brea Tar Pits". tarpits.org. Retrieved April 26, 2021.
- ^ a b Griggs, David (2014). "NEWSLETTER of the Carpinteria Valley Historical Society" (PDF). The Grapevine.
- S2CID 213287530.
- ^ Alakbarli, Farid (2016). "Horses of Azerbaijan: A Historical Survey" (PDF). Azerbaijan Association of Medical Historians.
- ^ a b "Pitch Lake, Trinidad - a geological wonder that is mined for asphalt". National Museums Liverpool. Retrieved April 26, 2021.
- ^ "La Brea Pitch Lake". UNESCO World Heritage Centre. Retrieved April 26, 2021.
- ^ a b "Fossils - Window to the past". ucmp.berkeley.edu. Retrieved April 26, 2021.
- ^ "Dire Wolf". igws.indiana.edu. Retrieved April 26, 2021.
- ^ PMID 17416692.
- ^ Madhusoodanan, Jyoti (August 8, 2014). "Microbes in a Tar Pit". The Scientist. Retrieved August 14, 2014.
- ^ S2CID 22078593.
- ^ ISSN 2169-8996.
- ^ a b Clayton, Janet (1985). "Concern for Methane Hangs Over Fairfax Area". Los Angeles Times.
- ^ PMID 22187970.
- ^ "Climate Change: Atmospheric Carbon Dioxide | NOAA Climate.gov". www.climate.gov. Retrieved April 26, 2021.
- ^ PMID 17800300.
- ^ "La Brea Woman - Los Angeles". www.laalmanac.com. Retrieved April 26, 2021.