Rising oil prices stirred concerns about inflation, and investors were a bit cautious ahead of corporate earnings this week .... says Peapack Private Wealth Management Senior Portfolio Strategist David Dietze.

"I think a lot of traders wanted just hold back a little bit until they see how bad those numbers are, because the worst thing that could happen to markets is the so-called stagflation where the economy is not revving up, not seeing a lot of growth but you're seeing some severe price increases. That's the kind of the worst of all worlds."

The Dow and S&P 500 shed roughly seven-tenth percent. The Nasdaq slipped six tenths of a percent.

Among the biggest drags on the S&P: Southwest Airlines, down 4%. The low-cost carrier said it expects to resume normal service this week after cancelling more than 2200 flights since Saturday.

And shares of Merck couldn't hold onto their early rally. The drug maker filed for U.S. emergency use authorization for its pill to treat patients with mild-to-moderate COVID-19. That puts it on course to become the first oral antiviral treatment for the disease.