NEW YORK (TheStreet) -- Stocks closed out the week with deep losses, capping off a week of plummeting crude oil prices and disappointing earnings reports from industry bellwethers such as Apple  (AAPL) and Caterpillar (CAT).

The S&P 500 was down 1.1%, the Nasdaq slid 1.1%, and the Dow Jones Industrial Average fell 0.9%. For the week, the S&P 500 lost 2.2%, and the Nasdaq slipped 2.3%, their worst weeks since the end of March. The Dow tumbled 2.9% this week.

Oil prices continued to decline as West Texas Intermediate crude closed 0.6% lower to $48.14 a barrel and down 5.4% for the week. Prices dropped after the total number of active U.S. rigs drilling for oil climbed 21 to 659 over the week, according to Baker Hughes. Crude took a dive last week after six world powers agreed to a nuclear deal with Iran that would lead to Iranian oil on global markets.

Amazon (AMZN) was one of the few bright spots on markets Friday after blowing past quarterly estimates. The e-commerce giant earned 19 cents a share while analysts expected a loss of 14 cents. Sales climbed nearly 20% to $23.18 billion, ahead of estimates of $22.39 billion. The better-than-expected quarter was tied to strong sales in North America and growth in Prime subscriptions. Shares surged 10.8%.

Amazon's surge was countered by Biogen (BIIB) which sank 22% after lowering full-year guidance. The biopharmaceutical company anticipates 2015 revenue growth between 6% and 8%, down from previous growth estimates of 14% to 16%.

In other earnings news, Starbucks (SBUX) earned 42 cents a share, a penny above estimates, while revenue climbed nearly 18% to $4.88 billion. Global traffic increased 7% compared to expectations of 6.2%. The stock rose more than 1%.

Visa (V) spiked 4.3% after beating analysts' estimates on the top- and bottom-lines. The credit card company earned 74 cents a share, beating expectations by 15 cents, while sales surged 11.4% to $3.52 billion. Payments volume increased 11% on a constant-dollar basis.

Anthem (ANTM) and Cigna (CI) slipped after announcing a merger deal Friday following a month of reports. Indianapolis-based Anthem will acquire health insurance company Cigna for $54.2 billion, a deal that values Cigna shares at $188 a share. Cigna and Anthem shares fell more than 2%.

AT&T (T) received final regulatory approval for its $48.5 billion acquisition of DirecTV (DTV). The Federal Communications Commission gave approval with conditions including that the combined company doesn't impose higher costs on those who use less data. AT&T and DirecTV shares were up more than 1%.

Sales of single-family new homes in the U.S. fell 6.8% to an annual rate of 482,000 in June, its slowest pace in seven months. Economists had expected a reading of 550,000. New home sales in May were revised down to 517,000 from an original reading of 546,000.

On the economic calendar next week, durable goods orders for June will be released on Monday, the Federal Reserve will convene for a two-day meeting on Tuesday with an announcement due for Wednesday afternoon, and second-quarter GDP estimates will be released on Thursday.