Los Angeles Basin

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The Los Angeles Basin is the coastal sediment-filled plain located at the north end of the Peninsular Ranges province.[1] in southern California, United States, and contains the central part of the city of Los Angeles as well as its southern and southeastern suburbs (both in Los Angeles and Orange counties). It is approximately 50 miles (80 km) long and 25 miles (40 km) wide, bounded on the north by the Santa Monica Mountains and San Gabriel Mountains, on the east by the Santa Ana Mountains and on the south by the Pacific Ocean and the Palos Verdes Hills, along the coast.[1] The confluence of the Los Angeles and Rio Hondo rivers is the center of the basin.[2]'

LA Basin Oil Fields, USGS
Los Angeles City oil field, 1905

Geology[edit]

Dominant structures in the basin are northwest-southeast trending fault zones causing parallel block faults causing topographic highs and deeper aniclinal structures in which oil fields are located.[3] The principal subsidence and deposition occurred in the Upper Miocene until the Lower Pleistocene.[4] The sediment in the basin is up to 6 miles (10 km) deep. The basin began to form during the Neogene approximately 15 million years ago (mya), when the terrain was underwater, during a crustal upheaval caused by a clockwise shift in the surrounding mountains. The underlying crustal weakening resulted in the formation of the large bowl of the basin. Sediment from the sea and rivers accumulated in the undersea bowl, building up in thick layers. Approximately 5 million years ago, the crustal stretching subsided and the ocean floor of the basin was forced to the surface. Additional sediment accumulated during the upswell resulting in the floor of the basin as it exists today.

Petroleum[edit]

The accumulation of fine-grained sediments with high organic content, interlayered with coarser grained sands, contributed to the formation of large deposits of oil, including the Wilmington Oil Field.[5] Other large active oil fields include the Long Beach Oil Field, the Salt Lake Oil Field and South Salt Lake Oil Field, the Huntington Beach Oil Field, which underlies much of the city of Huntington Beach; and the Torrance Oil Field, adjacent to the Wilmington field on the northwest. Most of the numerous fields in the basin have either been abandoned or greatly scaled back in production since the early part of the 20th century. In the 1890s the oil field directly north of downtown Los Angeles, the Los Angeles City Oil Field, led the state of California in oil production.[6] Some of the oil fields in the dense urban core remain productive, including the Beverly Hills Oil Field.[7]

In 2013, the USGS estimated that the ten giant oilfields in the LA Basin have future potential to produce an additional 1.4 to 5.6 billion barrels of oil, with their best estimate being 3.2 billion barrels. The report acknowledges that only a fraction of this oil is likely to be produced, given the highly urbanized area surrounding the oilfields.[8]

Iodine[edit]

In former years iodine was recovered commercially from brine co-produced with oil. Dow Chemical Company operated a number of plants at oil fields in the Los Angeles Basin, and recovered iodine from brines that averaged 50 parts per million iodine. Production started in 1932 and lasted into the 1960s.[9]

Earthquakes[edit]

Major faults include the Newport-Inglewood Fault, the Whittier Fault, the Santa Monica Fault, the Elsinore Fault Zone and the San Gabriel Fault.[10] For a list of major events:

Subsidence[edit]

Small-scale subsidence has occurred due to ground water withdrawal while large-scale subsidence has been the result of petroleum extraction, the most spectacular examples being the Baldwin Hills dam collapse of 1963 and the sinking of the Long Beach Harbor by several meters, since alleviated through water injection.[11]

See also[edit]

References[edit]

  1. ^ a b Mayuga, M.N., Geology and Development of California's Giant-Wilmington Oil Field, in Geology of Giant Petroleum Fields, Tulsa: American Association of Petroleum Geologists, Memoir 14, pp. 160, 1970.
  2. ^ "The Los Angeles Basin - A Huge Bowl of Sand". LAalmanac.com. Retrieved 2010-11-27. "The point where the Los Angeles and Rio Hondo Rivers merge in the City of South Gate is the geologic center for the Los Angeles Basin.'" 
  3. ^ Mayuga, M.N., Geology and Development of California's Giant-Wilmington Oil Field, in Geology of Giant Petroleum Fields, Tulsa: American Association of Petroleum Geologists, Memoir 14, pp. 160-161, 1970.
  4. ^ Mayuga, M.N., Geology and Development of California's Giant-Wilmington Oil Field, in Geology of Giant Petroleum Fields, Tulsa: American Association of Petroleum Geologists, Memoir 14, pp. 161, 1970.
  5. ^ Mayuga, M.N., Geology and Development of California's Giant-Wilmington Oil Field, in Geology of Giant Petroleum Fields, Tulsa: American Association of Petroleum Geologists, Memoir 14, pp. 162, 1970.
  6. ^ History of Oil Production in California: California Department of Conservation, Department of Oil and Gas
  7. ^ "Oil and Gas Statistics: 2007 Annual Report" (PDF). California Department of Conservation. December 31, 2007. Retrieved August 25, 2009. 
  8. ^ Remaining Recoverable Petroleum in Ten Giant Oil Fields of the Los Angeles Basin, Southern California, USGS, revised 2-2013
  9. ^ G.I. Smith (1966) "Iodine" in Mineral Resources of California, California Division of Mines and Geology, Bulletin 191, p.198-199.
  10. ^ Yerkes, R.F., McCulloh, T.H., Schoellhammer, J.E., and Vedder, J.G.,Geology of the Los Angeles Basin, Southern California, Washington: USGS Paper 420-A, p. A5 and A12, 1965.
  11. ^ Mayuga, M.N., Geology and Development of California's Giant-Wilmington Oil Field, in Geology of Giant Petroleum Fields, Tulsa: American Association of Petroleum Geologists, Memoir 14, pp. 176-180, 1970.