** Shares of railroad operators Union Pacific UNP.N and Norfolk Southern NSC.N down 4.5% and 5.3%, respectively, in morning trading

** The U.S. Surface Transportation Board says it has paused the review of UNP and NSC's $85 billion merger application, while it seeks more information from the companies

** "Several aspects of the revised application... are unclear or underdeveloped and require supplementation at this stage," it added

** Including session's moves, UNP up 15.4% and NSC gained 6.5% YTD