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Konnarock Formation rhythmites by Callan Bentley

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About This Gigapan

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Taken by
Callan Bentley Callan Bentley
Explore score
1
Size
1.22 Gigapixels
Views
3749
Date added
Nov 29, 2010
Date taken
Nov 23, 2010
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Description

Rhythmites are rhythmically-bedding sedimentary deposits, deposited in a sedimentary basin with some regularly-shifting condition like tidal cycles or day/night changes. The gigapan shows an outcrop of the Konnarock Formation, a bit east of Konnarock, Virginia, in the Blue Ridge province. They are Proterozoic in age. These rocks are interpreted as lake sediments that show rhythm in their seasonality: summer and winter alternating between fine clay (winter) and coarser silt and sand (during the summer, when the ice has thawed and the water feeding into the lake is flowing faster). Bright pink, grainy samples are arkose, a comositionally immature sandstone that corresponds to times when the turbulence/energy of the depositional water went up temporarily. You can find a few cobbles of arkose in this debris pile. While most of these sediments are reddish (indicative of relatively oxidizing conditions during deposition), there are also a few greenish layers, which indicate periods of lower oxygenation in the lake. Another thing to notice is the pronounced foliation that has been imparted to the clay-rich layers (but not so much to the silt-rich layers), causing the cobbles to break off in a "rounded stairstep" pattern.

Higher up in the stratigraphic sequence, these rhythmites begin to show dropstones, iceberg-rafted clasts that drop out into the calm waters mid-lake where these much finer sediments were being deposited. Dropstones impinge on the pre-existing muddy layers they drop into, and subsequent muddy layers are draped over top of them. Above the dropstone-bearing rhythmites, the Konnarock Formation transitions to a full-on diamictite, interpreted as glacial till that has been lithified. In other words, the sediments record the advance of ancient glaciers into a Mesoproterozoic lake basin. These glacial deposits have been correlated with the widespread "Snowball Earth" episode(s) of glaciation during the Proterozoic Eon.

Two cm-scale pencils are positioned in the image to provide a sense of scale. Also, see if you can find the small "Jack O Lantern" eraser that is hidden somewhere in the gigapan.


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Stitcher Notes

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GigaPan Stitch version 1.1.1241 (Windows)
Panorama size: 1218 megapixels (52060 x 23404 pixels)
Input images: 350 (25 columns by 14 rows)
Field of view: 85.6 degrees wide by 38.5 degrees high (top=25.2, bottom=-13.2)
Settings:
Vignette correction on: c1=-0.00425 c2=-0.0362
All default settings
Original image properties:
Camera make: Canon
Camera model: Canon PowerShot SX120 IS
Image size: 3648x2736 (10.0 megapixels)
Capture time: 2010-11-24 02:46:21 - 2010-11-24 03:23:44
Aperture: f/5
Exposure time: 0.01
ISO: 80
Focal length (35mm equiv.): 361.4 mm
Digital zoom: off
White balance: Fixed
Exposure mode: Manual
Horizontal overlap: 43.5 to 50.2 percent
Vertical overlap: 39.7 to 45.1 percent
Computer stats: 8175.03 MB RAM, 4 CPUs
Total time 37:02 (6.3 seconds per picture)
Alignment: 19:51, Projection: 5:16, Blending: 11:55
(Preview finished in 27:39)

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