LOS ANGELES (Reuters) - The U.S. Coast Guard has determined that natural petroleum seepage from beneath the Pacific seabed was the source of a large oil slick that appeared last week off the Southern California coast west of Santa Barbara.
The slick, which spanned several square miles of the ocean about 1,000 yards (meters) from shore, was first spotted last Wednesday off Goleta State Beach, not far from the site of an oil pipeline rupture in May, raising concerns of another spill in the area.
Three energy companies that own and operate offshore platforms in the region all denied that any of their operations were the source of the mysterious oil sheen.
The Coast Guard dispatched a team to collect samples from the slick that were sent to a government laboratory in Connecticut for comparison with tar balls previously found on area beaches and material taken from nearby drilling platforms and vessels.
The tests concluded that oil found in the water last week originated from natural seepage, the Coast Guard reported on Monday. The agency said the sheen, which was too thin to be recovered, would continue to dissipate on its own.
The welling up of petroleum through fissures in the seabed, especially in an area known as Coal Oil Point, occurs on a regular basis in the oil-rich but ecologically sensitive Santa Barbara Channel.
As much as 2,400 barrels of crude oil gushed onto a pristine beach and into the Pacific about 15 miles (25 km) west of Goleta in May when an onshore pipeline weakened by corrosion burst near shore.
The accident marked the largest oil spill to hit the Santa Barbara coast northwest of Los Angeles since a massive 1969 blowout dumped up to 100,000 barrels of petroleum into the channel.
(Reporting by Steve Gorman; Editing by Sandra Maler)