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L45 Turbidity flow structures on rock. Cornwall, UK
Position:
N50° 46'
W04° 34' approx.
Elevation:
at sea level
Image format:
LF MF 35mm
TURBIDITY FLOW STRUCTURES ON ROCK
You are looking at a rock that once formed on the sea bed about
300 million years ago. Imagine an ocean floor at the edge of the
CONTINENTAL SHELF. Huge volumes of SEDIMENT are TRANSPORTED into
the ocean by rivers draining the nearby land - maybe similar to
the sediment brought to the waters of the Gulf of Mexico by the
Mississippi River in modern day America. Every so often, banks
of accumulated sediment collapse when they grow too large and
unstable. Clouds of sediment flow across the sloping sea bed towards
the ABYSSAL PLAINS. These TURBIDITY FLOWS finally run out of energy
and settle on the sea bed. Larger particles settle first forming
sand deposits while smaller, clay particles settle on top gradually.
Then along comes another turbidity flow (TURBID means the same
as CLOUDY). The first deposit is ERODED by the new flow. Larger
stones in the base of the flow cut deep grooves in the older surface.
Then more sand and mud settle, preserving what was left of the
first flow. Preserving, in fact, even the grooves that were cut.
This view shows two such grooves and a host of other flow marks
(looking just like tongues) and marks the passage of a turbidity
flow on an ancient sea bed. The hammer provides an idea of scale.
Images L44 & L46 show other views of some TURBIDITY DEPOSITS.
Less detail
Image Trail:
L44 Folded rock. Cornwall, UK
L46 Fossilized ripple marks on titled rock beds. Cornwall, UK
Links:
www.elnino.usgs.gov/landslides-sfbay/photos.html
www.wwwdwatcm.wr.usgs.gov/fs_landslide.html
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