Monterey Formation

Monterey Formation
Stratigraphic range: Miocene
Outcrop of Monterey Formation, Gaviota State Park, California
Typesedimentary
OverliesRincon Formation
Location
Coordinates33°36′N 117°42′W / 33.6°N 117.7°W / 33.6; -117.7
Approximate paleocoordinates33°06′N 114°54′W / 33.1°N 114.9°W / 33.1; -114.9
RegionCalifornia
CountryUnited States
Type section
Named forMonterey, California
Upper Miocene Migeulito member exposed at Hazard Reef, Montana de Oro State Park. This is the first onshore outcrop of the Monterey Formation south of the Monterey Peninsula. Large exposures continue south along the coast, often associated with important oilfields.
Tar "volcano" in the old Carpinteria Asphalt mine. Heavy oil exudes from joint cracks in the upturned Monterey shale forming the floor of mine. 1906 photo, U.S. Geological Survey Bulletin 321
External image
image icon Out-of-phase detachment folds and low-angle faults in the Monterey Formation at “the Boathouse” section, Vandenberg Air Force Base
Fold in Monterey Formation
Fossil crab (Pinnixa galliheri), Monterey Formation, Pacific Grove, California. Carapace is about 3 cm. wide.
Diatomite (diatomaceous earth), Monterey Formation, from a diatomite quarry just south of Lompoc
Heavy oil saturated sandstone from a unit of the Monterey Formation.

The Monterey Formation is an extensive Miocene oil-rich geological sedimentary formation in California, with outcrops of the formation in parts of the California Coast Ranges, Peninsular Ranges, and on some of California's off-shore islands. The type locality is near the city of Monterey, California.[1] The Monterey Formation is the major source-rock for 37 to 38 billion barrels of oil in conventional traps such as sandstones.[2] This is most of California's known oil resources.[3] The Monterey has been extensively investigated and mapped for petroleum potential, and is of major importance for understanding the complex geological history of California. Its rocks are mostly highly siliceous strata that vary greatly in composition, stratigraphy, and tectono-stratigraphic history.

The US Energy Information Administration (EIA) estimated in 2014 that the 1,750 square mile Monterey Formation could, as an unconventional resource, yield about 600 million barrels of oil, from tight oil contained in the formation, down sharply from their 2011 estimate of a potential 15.4 billion barrels.[4][5] An independent review by the California Council on Science and Technology found both of these estimates to be "highly uncertain."[6] Despite intense industry efforts, there has been little success to date (2013) in producing Monterey-hosted tight oil/shale oil, except in places where it is already naturally fractured, and it may be many years, if ever, before the Monterey becomes a significant producer of shale oil.[7]

The Monterey Formation strata vary. Its lower Miocene members show indications of weak coastal upwelling, with fossil assemblages and calcareous-siliceous rocks formed from diatoms and coccolithophorids. Its middle and upper Miocene upwelling-rich assemblages, and its unique highly siliceous rocks from diatom-rich plankton, became diatomites, porcelainites, and banded cherts.[8]

  1. ^ M.N. Bramlette (1946). The Monterey Formation of California and the Origin of its Siliceous Rocks. USGS Professional Paper 212.
  2. ^ Monterey Shale Gets New Look, AAPG Explorer, Nov 2010. Accessed 03/21/2014
  3. ^ The Monterey Formation of California: New Research Directions by Richard J. Behl, California State University, Long Beach, 2012
  4. ^ Sahagun, Louis (May 21, 2014) "U.S. officials cut estimate of recoverable Monterey Shale oil by 96%" Los Angeles Times
  5. ^ Drilling California: A Reality Check on the Monterey Shale J. David Hughes, Post Carbon Institute, 2013.
  6. ^ CCST Releases Report on Well Stimulation Technologies, August 28, 2014. "The 2011 EIA report suggested 15-billion barrels of recoverable oil in these source rocks but a subsequent 2014 correction by EIA reduced the estimate to 0.6 billion barrels. Recovering these resources would certainly require well stimulation. However, Berkeley Lab investigators found no reports of successful production from these deep source rocks and had questions about the EIA estimation methodology. The study's review of the two resource projections from deep source rocks in the Monterey Formation developed by EIA concluded that both these estimates are highly uncertain."
  7. ^ So Much Shale Oil—but So Hard to Get, Wall Street Journal, Updated Sept. 23, 2013
  8. ^ Burnett, William C.; Stanley R. Riggs, eds. (1990-05-25). Phosphate Deposits of the World: Volume 3, Neogene to Modern Phosphorites (Cambridge Earth Science Series). Cambridge University Press. ISBN 0-521-33370-9.