Investment guru Marc Faber says Thursday’s selloff in commodities showed sector bulls had finally "thrown in the towel."

“This weakness is a clear indication of a global economic contraction,’’ Faber, editor and publisher of the 'Gloom, Boom and Doom' report, told CNBC.

"Fundamentals have been deteriorating for some time but now the eternal bulls have thrown in the towel.’’

The Thomson Reuters-Jefferies CRB commodities index lost more than 2 percent on Thursday, its biggest decline this year, as disappointing economic data from the U.S., China and Europe pointed to a weak global economy.

West Texas Intermediate crude plunged 3.5 percent to close at $78.20 per barrel, the first close below $80 since October.

Faber said he expects more weakness in industrial commodities, though he said agricultural commodities "look better."

Andrew Su, CEO of Compass Markets, a Sydney-based commodity broker, told CNBC he expects selling to continue.

“Fundamentals haven’t changed but investor sentiment certainly has,” Su said. "All our September-quarter targets have either been reached or are very close to being achieved.’’

Daryl Guppy, a technical analyst and trader, told CNBC that if oil falls below $78 a barrel, then it may fall further to around $68.

Brent crude traded in London rebounded above $90 a barrel Friday from an 18-month low, Reuters reported. Down about 30 percent from its 2012 high reached in March, Brent remained on track for its biggest weekly loss in nearly a year.

"It has been a long fall, driven by global economic slowdown and oil fundamentals such as weaker demand from China," said Tony Machacek, an oil futures broker at Jefferies Bache, according to Reuters.