<Tr> <Th> Start of production </Th> <Td> <! 2007--!> </Td> </Tr> <Tr> <Th_colspan="2"> Production </Th> </Tr> <Tr> <Th> Producing formations </Th> <Td> Michigan Basin </Td> </Tr> <P> The rocks of the Michigan Basin are the source of commercial quantities of petroleum . The most actively drilled - for source of natural gas in recent years has been shale gas from the Devonian Antrim Shale in the northern part of the basin . </P>

How old are the oldest rocks in michigan