The stock market opened in positive territory Thursday but was burning off the gains in afternoon trade as investors digested the potential impact on the economy of the fiscal cliff deal and proposed spending cuts on the U.S. economy and as the Federal Reserve considers ending its massive monthly bond purchases this year. In afternoon trade, the SPDR S&P 500 (SPY) shed 0.16% to 145.83. PowerShares QQQ (QQQ), tracking the 100 largest nonfinancial