In a major energy sector development, ConocoPhillips (COP) has struck an all-stock deal to buy rival Marathon Oil Corporation (MRO) for $22.5 billion, including debt. This would consolidate Conoco’s position in America’s shale fields.Over the past year, there have been multiple deals where large energy sector companies have been buying out whatever remains of the once vast shale resources. Companies like Exxon Mobil Corporation (XOM) and Chevron Corporation (CVX) kickstarted these acquisitions, and others f ...