Deep Sea Debris Flow

2014

 
 
This remarkable boulder came from Covington, Michigan, about 40 miles south of Houghton. It is a sample of the Michigamme Formation, about 1.8 billion years old. The green color of the rock reflects the reduced iron of the rock which equilibrated with Earth’s ocean before it was oxidized completely. This boulder is similar in age to the impactite boulder that you can visit only 200 yards SE of here, just east of Fisher Hall. It represents a mixture of metamorphosed sedimentary and volcanic rock, which formed in the deep ocean from massive debris flows falling off of volcanic source areas within the ocean. The rock is foliated as a result of metamorphic recrystallization of micaceous minerals. The formation contains iron formation and slaty horizons as well as immature sediments, and represents the deep ocean environment of Proterozoic Earth during ocean oxidation.
Michigamme Formation: Metagraywacke

How would the rock’s color change if the ocean was oxidized?

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