Sunday, April 26, 2009

Formation of Rodinia

"For every tectonic event there is a sedimentary response" Dr. Ebert

Greetings all, this is mt first post and I'd like to start by taking you on a journey that I recently travelled with my Historical Geology at SUNY Oneonta. This journey, guided by Dr. Ebert, took as back 1.2 billion years into the past and forward in time to look at glacial features.

Our first stop is in the Mohawk River Valley 1.2 billion years in the past. The rocks are a highly metamorphosed gneiss. There are two distinct features present in the gneiss. The first is the pink and purple crystals that can be found all over the rocks. These crystals are in fact garnets! The other predominate feature is extensive foliation, or banding, seen with in the rocks. The foliation is both on small scale

Our second stop brings us to Canajoharie where a large grouping of sedimentary rocks begins to show us some indicators that an orogeny, mountain building event, is eminent. The first two lays of rock are carbonates. The first layer is dolostone, a chemically altered limestone, and the second layer is a limestone. The first layer is bare of fossils except for stromatolites, a feature formed by mats of algae. This, combined with the present of carbonates indicates that the environment was very warm. The second layer was rich in bryozoans, brachiopods and crinoids. The third and final layer was an extremely black shale. The black shale indicates that the water extremely deep and very anoxic. The only life that can be found in these shales are graptolites, a floating organism. The two limestones are part of what is called The Great American Bank, a large deposit of carbonate rocks that indicate the subsidence of the continent. The shale is part of what is called the Starved Basins which is a time when the crust has subsided a lot and has a very small sediment source.

The third stop brought us to a sequence of alternating sandstone and shales. These rocks were filled with burrows and flute casts, a sedimentary structure that indicates the flow of water and sediment. This sequence is known as flysch. This is a sequence that indicates that an approaching landmass is now close enough to dump sediment on the area.

Our final stop was in Schoharie and was simply a fossil prospecting run. These fossils were everywhere at this site, among them were bryozoans, cephalopods, brachiopods, crinoids and tentaculids.

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