Uplifted Turbidites EarthCache
Hidden : 3/8/2013
Difficulty:
2 out of 5
Terrain:
2 out of 5

Size: Size: other (other)

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Geocache Description:


Turbidites are underwater landslides of sediment that cover vast areas of the deep ocean floor. Turbidites form in the deep ocean near the continental shelf. Classic turbidite sequences are made up of graded beds of sediment. This means that the grains at the bottom of the sequence are larger than the grains at the top of the sequence. In a complete sequence the bottom sediments are pebble sized conglomerates, followed by coarse then fine-grained cross-bedded sandstone, then shale, and finally silt. This series is called the Bouma cycle. The beginning of a new turbidite sequence can be seen by a distinct transition between a finer grained layer to a larger grained layer. It is unusual to see all of a complete Bouma cycle, as successive turbidity currents may erode the unconsolidated upper sequences.

Formation of Turbidites

Turbidites are sediments which are transported and deposited by density flow.

Density flow differs from tractional flow (frictional flow), which is the type of flow found in a normal river or stream. Tractional flow works by carrying particles of rock along by frictional drag of water on the particle. In order for the particles to be transported, the water must be travelling at a high enough velocity in order to suspend the particle in the water and move it along. The greater the size or density of the particle, the greater the water velocity needed to suspend the particle and transport it.

Density flow, however, occurs when liquefaction of sediment during transport results in a change to the density of the fluid. This can happen with very turbulent liquids which have suspended loads of fine grained particles forming a slurry (a watery mixture of insoluble matter). The change in density of the water can result in larger fragments of rock being transported at water velocities too low to otherwise do so because the water plus sediment has a higher density than just the water by itself and is therefore closer to the density of the rock.

Classic, low-density turbidites are characterized by graded bedding, current ripple marks, thick sediment sequences, and regular bedding (regular bedding results in densest particles settling first).

Tectonic Uplift

Tectonic uplift is a geological process most often caused by plate tectonics which increases elevation. Along the westcoast of Canada there are several fault lines which could have resulted in the uplift seen at this location.

Logging requirements:
Send an email through my geocaching profile with answers to the following questions:
1. In a 1 metre section, how many density flows occurred (count the layers) (choose any section you like)?
2. How did you determine the start and end of each flow (answer can be found in cache page).
3. Based on the thickness of each of the layers was each sedimentation event the same size? Include how you came to that conclusion.
4. What processes could have resulted in the normally horizontal turbidites to uplift?
5. Post a photo of yourself or your GPS at the location.

Sources:
http://en.wikipedia.org/wiki/Turbidite

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