James M. Galloway, Geologist, Pacific OCS Region
As long as humans have recorded their history, the natural occurrence of oil and gas at
the earth's surface has been of great curiosity and considerable economic interest. Oil,
tar, and natural gas seeps are part of the natural environment, and geological and
archeological evidence shows that seepages have occurred throughout California for
thousands of years. Even today, natural hydrocarbon seeps along the California coast
continue to be more than an idle curiosity. Two small underwater containment structures
positioned near Goleta Point, placed to collect natural seepage, have alone captured over
4 billion cubic feet of natural gas since 1982: enough natural gas to supply the needs of
over 25,000 residential natural gas users each year.
HISTORIC IMPORTANCE
The importance of petroleum predates written history, evidenced in many Old World
archaeological sites. It is no surprise that the Native Americans of the coastal areas of
California, like the inhabitants of the Old World, incorporated naturally occurring
hydrocarbons into their cultures. The earliest accounts of oil and gas seepages in
California come to us from the seventeenth century annals of the European explorers.
Native Indians, including the Chumash, Yokuts, Achomawi, and Maidu used oil, tar, bitumen
and other natural substances from the seeps for ceremonial and recreational purposes. Oil
was often used as a base for paints and asphaltum, a brownish-black mixture used in
paving, roofing, and waterproofing, was used as a mastic to inlay colorful stones and
shell fragments.
Pedro Fages, a Spanish explorer and military commander of the Monterey Presidio, in his
report to the Viceroy of New Spain recorded the use of tar and oil by the natives near
Mission San Luis Obispo. Fages' account, written in 1775, mentions natives using tar for
water- proofing baskets and pitchers and for caulking small boats. Fages also noted "
... pools of bitumen bubbling out of the ground" near the mouth of the Santa Clara
River. In 1776, Spanish missionary Pedro Font recorded that "... much tar which the
sea throws up is found on the shores, sticking to the stones and dry, little balls of tar
are also found. Perhaps there are springs of it which flow out into the sea." In
1793, during the travels of English explorer James Cook, his navigator, George Vancouver,
recorded in his journal that they had anchored off of Goleta. Vancouver reported that the
sea was "... covered with a thick, slimy substance, which, when separated or
disturbed by any little agitation, became very luminous, whilst the slightest breeze, that
came principally from onshore, brought with it a very strong scent of burning tar."
He continued that "... the sea had the appearance of dissolved tar floating on its
surface, which covered the ocean in all directions within the limits of our view."
Early California pioneers (c. 1850) used the oil from natural seeps to grease their
wagon wheels and settlers and ranchers, especially in the Santa Barbara, Ventura, Los
Angeles, and Orange county areas, used seeped oil for lubricating farm machinery, for
tarring roofs, and for illumination. Early on seeps were exploited by digging directly
into them. Just as one would sink a shallow water well, diggers shoveled down until oil
and tar began to ooze into the pit, or until the petroleum fumes and gas overcame them. In
Ventura and Kern Counties, mining techniques were used to tunnel into the mountainsides,
with elaborate lighting and ventilation systems. By the 1870's, technological advances
allowed the development and use of specially designed oil drilling tools to sink wells
deeper than any digger could excavate.
From the 1860's to the early 1900's, every oil or gas field discovered in California
was located on the basis of nearby seeps. In California, the earliest oil exploration
efforts began in areas where numerous seeps, such as Ojai and Santa Paula, occurred. The
first commercial oil discoveries in Pennsylvania spurred both commercial and academic
interest in coastal California oil, tar, and gas seeps.
SCIENTISTS INVESTIGATE
In the mid-nineteenth century, little scientific evidence existed concerning the origin
and habitat of oil and natural gas. Geologic science was in its infancy and the branch
known as petroleum geology was not yet conceived. It was during this time that geologists
began to study the nature of oil seeps and how they related to the age, structure,
stratigraphy, and lithology of rocks. It was determined that rocks like sandstone, shale,
and limestone contained oil, gas, and tar, and that rocks like granite, marble, or lava
did not. Indeed, those rocks that had been deposited in ancient oceans or great lakes were
most likely to contain petroleum. It was also noted that coal-bearing rocks were likely
formed in swampy environments.
Early geologists learned that seeps generally occur where bituminous, or oil-bearing
rocks were exposed at the earth's surface by erosion, or where a fault was present. Almost
every major petroleum producing province in the world has been discovered because of
surface seepage. Some famous oil seeps, such as the La Brea Tar Pits or the Pitch Lake of
Trinidad, formed accumulations so large that they trapped the people or animals that
unwittingly stumbled into them. The Perpetual Fires of Baku, in a large gas seep area in
Azerbaijan, were known to the ancients.
Oil, tar, and gas seepages are common along the California coastal areas because of the
geologic history of the area over the last 70 million years. Scientists have studied this
history as it is recorded in the rocks and fossils, and their research indicates that the
paleogeography of the area was significantly different than it is today.
Anywhere from 70 to 30 million years ago the topography of the coastal areas
of North America was similar to that of today's South American west coast. Mountainous
areas flanked the coastline but the mountains were continually worn away by erosion and
the great amounts of sand, silt, and clay sediments that washed down the rivers and dumped
into offshore basins. Over millions of years, these sediments accumulated, lithified, and
formed strata comprised of sandstone, siltstone, and shale. In some shallow water areas
calcium carbonate-rich reefs formed and were preserved as limestone.
Geologists study these rocks, called the Great Valley Sequence, where they are now
exposed. These rock formations are seen in the Santa Ynez, San Raphael, and Santa Susana
Mountains as well as the Channel Islands and are the same rocks that have been observed in
deep wells throughout the San Joaquin and Sacramento basins and much of the Coastal
Ranges.
About 30 million years ago, the tectonic plates collided along the North America-East
Pacific boundary causing dramatic alterations to the shape and form of the coastal areas.
Great fault systems, such as the San Andreas fault, were formed. Massive blocks of land
were rotated, translated, and jostled. Rock formations were folded and faulted to form
mountain ranges. Deep depressions subsided, forming basins which caught eroded sediments.
The oceans off the coast were rich in biological activity and organic detrital matter
filtered down to the ocean floor, mixing with sediments to form the building blocks of
hydrocarbon-rich petroleum source rocks.
According to petroleum geologists, good source rock contains about 1% total organic
carbon (TOC). In the California coastal areas, the source rocks often contain 4-6%, with
some zones measuring almost 20% TOC. It is no wonder then that, where the source rocks are
exposed at the surface, they literally bleed petroleum. It is also no surprise that oil,
tar, and gas seepages occur offshore.
Over the last 20,000 years, relative sea level has risen more than 300 feet. The
erosion that today exposes oil seeps along the beaches and in the local hills did the same
to areas now under water. A significant difference between offshore seeps and onshore
seeps is that underwater seeps are subject to the weight of the seawater column and to
shifting ocean floor sediments. Seeps are affected by tidal changes, and, like onshore
seeps, offshore seeps are stimulated by earthquake activity. Because ocean temperatures
are more constant than air and ground temperatures, underwater seeps do not speed up or
slow down on hot or cold days. They do, however, show seasonality in seepage rates.
Today, especially on a warm summer day, a person driving through Santa Paula will smell
petroleum fumes and notice thick, black crude oil running down the side of the road ...
exactly what the Chumash smelled centuries ago. All over California, from Humboldt to Kern
to San Diego Counties, place-names such as Oil Creek, Petrolia, Oildale, Brea, and Coal
Oil Point testify to the widespread occurrence of petroleum seepages.
References:
Hodgson, Susan F., 1987, Onshore Oil and Gas Seeps in California, California Division
of Oil and Gas
Wilkinson, Elbert R., 1971, "California Offshore Oil and Gas Seeps"
California Summary of Operations Vol.57 No.1
California Offshore Gas, Oil, and Tar Seeps, RH Prepared by the Staff at the State
Lands Commission
Annual Report of the State Oil and Gas Supervisor Publication PR06, for the years
1982-1990
Bibliography:
California Offshore Gas, Oil and Tar Seeps Prepared by the Staff of the State Lands
Commission, D.J. Everitts, C.F. Eaton, R.G. Paul, E.E. Welday, circa 1977, 449 pages
Papers herein include:
Natural Gas and Oil Seeps, Santa Barbara Basin, Calif.; P.J. Fischer
Oil and Tar Seep Studies on the Shelves off Southern California, Santa Monica Bay; T.L.
Henyey, T.R. Nardin, B.A. Nardin
Oil and Tar Seep Studies on the Shelves off Southern California, Seismicity of the
Southern California Coastal Zone; T.L. Henyey and Ta-liang Teng
Oil and Tar Seep Studies on the Shelves off Southern California, Chemical Weathering of
Oil and Tar from Natural Seeps; T.L. Henyey and T.J. O'Neil
Chemistry of Marine Petroleum Seeps and their Relation to Exploration and Pollution;
W.E. Reed and I.R. Kaplan
Relationship of Migration of Natural Seep Material to Oceanography of Santa Barbara
Channel; R.L. Kolpack
Airborne Remote Sensing Applications for the Detection and Monitoring of Oil from
Natural Seeps and Other Sources; J.E. Estes and S.T. Kraus
Oil Seep Survey Over Coal Oil Point and Santa Barbara Channel, California, October 1976
S.T. Kraus and J.E. Estes
Oil and Tar on Santa Barbara Region Beaches; E.E. Welday
Natural Oil and Gas Seeps, Santa Barbara Basin, Calif., P.J. Fischer, Marine Studies
75-4, Department of Geosciences, California State University Northridge, 40 Pages
Natural Oil and Gas Seeps and Geology of the Northern Santa Barbara Basin, Calif. P.J.
Fischer, Department of Geosciences, California State University Northridge, December 1976,
62 pages (This is the preliminary report which became Chapter 1 of the 1977 State Lands
Commission Compendium, cited herein)
Natural Tar Seeps and Asphalt Deposits of Santa Barbara Iris Priestaff, California
Geology, August 1979, p 163-169
Oil and Gas Seeps in California Susan F. Hodgson, California Division of Oil and Gas
Publication, TR 26, 1987, 97 pages
Oil and Gas Seeps in Santa Monica Bay, J.M. Galloway and M.S. Cranswick, Minerals
Management Service, Pacific OCS Region, unpublished internal memorandum, March 1991, 7
pages
Petroliferous Seeps, Historical Perspective, Appendix B in Development of South Ellwood
Offshore Oil Field, Environmental Impact Analysis: Phase 1, for Atlantic Richfield
Company, Volume 1, Draft Environmental Impact Report, State Lands Commission, State Lands
Division, July 1974
Submarine Tar Mounds, Santa Barbara County, California, J.W. Vernon and R.A. Slater,
AAPG Bulletin, Vol 47 No 8, 1963, p 1624-1628
Tar Balls on Southern California Beaches, J. Grant, Mineral Management Service, Pacific
OCS Region, unpublished internal memorandum, April 1990, 4 pages plus misc. press
clippings