geoscience crowd sourcing
Geologists on a conference field trip are unraveling an ancient 2.7 Ga sequence of avalanches in ocean bottom sediments. This site has since become a mid-continent Precambrian outcrop in vicinity of Wawa, Ontario, Canada.
How were modern-day ocean bottom avalanches found? Much to the surprise of early industrialists, 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 in this outcrop 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 facing 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 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
geoscience crowd sourcing
Geologists on a conference field trip are unraveling an ancient 2.7 Ga sequence of avalanches in ocean bottom sediments. This site has since become a mid-continent Precambrian outcrop in vicinity of Wawa, Ontario, Canada.
How were modern-day ocean bottom avalanches found? Much to the surprise of early industrialists, 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 in this outcrop 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 facing 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 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