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geoscience crowd sourcing | by subarcticmike
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geoscience crowd sourcing

Geologists on a conference field trip are unraveling a sequence of avalanches in ocean bottom sediments at a mid-continent Precambrian outcrop outside Wawa Ontario, Canada.

 

How were modern-day ocean bottom avalanches found? Much to the surprise of early industrialists, some of the first trans-Atlantic telegraph cables were sequentially snapped by giant deepwater sediment gravity flows. Layered sediments and rock formations resulting from such events falling off the edges of continental shelves around the world were named "turbidites" by scientists. Each layer is an avalanche.

 

Which way is stratigraphic "Up" in these vertically-dipping metasedimentary rocks? Stratigraphic orientation is key. Tough to tell here but features seen elsewhere in the outcrop say that "Up" is to the left in this image which is topographic south.

 

The professor's hand is measuring widths of thin bedding which indicate reduced volumes of gravity-driven material with only fine silt and mud left in motion. Thicker sand-inclusive layers in the same outcrop are stratigraphically lower.

 

from global-scale -

en.wikipedia.org/wiki/Turbidite

 

to scale of individual layer -

en.wikipedia.org/wiki/Bouma_sequence

 

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Taken on May 10, 2017