Chevron ( CVX) warned Tuesday that third-quarter earnings will fall sharply from second-quarter levels.The San Ramon, Calif., oil company cited a sharp decline in refined-product margins for the downstream business along with the impact of nonrecurring items. The latest quarter is expected to include $700 million in asset impairments, environmental remediation provisions, income tax adjustments, asset retirement obligations and severance provisions. Chevron made $5.4 billion, or $2.52 a share, for the second quarter ended June 30. Analysts surveyed by Thomson Financial were looking for a profit of $2.18 a share for the third quarter ended last month. Chevron said the U.S. West Coast industry refining margin indicator for the full third quarter declined more than 50% from about $30 per barrel in the second quarter. The U.S. Gulf Coast light-heavy-differential marker averaged $31.50 per barrel, down over 15% in the full third quarter. Outside the United States, benchmark refining margins were also considerably lower. During the full third quarter, the Los Angeles mogas marketing margin indicator fell by more than 50% to $2.42 per barrel, while the Houston mogas indicator declined over 30% to $2.63 per barrel. Shares fell $1.60 to $91.20.