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13-McElwee_VGS (2)
1. THE ORIGIN OF THE COLOR DIFFERENCES IN SANDSTONES OF THE
LOWER CAMBRIAN MONKTON FORMATION
ELISABETH MCELWEE AND CHARLOTTE
MEHRTENS
UVM GEOLOGY DEPT.
2. Samples were taken from four sites:
Pease Mountain
An outcrop along Shelburne Rd
Redstone Quarry
Route 2 in Colchester
L O C A L I T Y M A P
6. P H O T O M I C R O G R A P H O F T H E
W H I T E A N D R E D S A N D S T O N E
7. R E F L E C T E D L I G H T P H O T O G R A P H O F T H E
W H I T E A N D R E D S A N D S T O N E
8. S C A N N I N G E L E C T R O N I M A G E
( S E M )
9. S P E C T R A O F T H E S E M / E D X I M A G E
10. Q U A R T Z , F E L D S P A R A N D L I T H I C
A N A L Y S I S
11. T H E R O L E O F O X I D A T I O N I N
F O R M A T I O N O F T H E R E D S A N D S T O N E
12. E L E M E N T M A P
•Iron, present in
dolomite cement and
clay grains
•Aluminum, present in
feldspar and clay
•Magnesium, present
in dolomite cement
•Sodium, present in
plagioclase feldspar
•Silica, present in
quartz
13. C O N C L U S I O N
• The red coloration of the Monkton strata is due to the presence of ferric iron
oxide (Fe2O3), or hematite.
•Textural differences between the red and white sandstones of the Monkton
explains the color difference. The red sandstone is finer grained and more
poorly sorted so there are grain sizes and pore space for the accumulation of
iron oxide on clays or in cement.
•The textural differences are the result of different energy levels in the tidal
flat environment. Lower energy levels of the tidal flat accumulate the clays
and the pore space between grains where the iron oxide accumulates.
14. Q U E S T I O N S ?
Thanks to: Middlebury Geology for use of their SEM,
Jody Smith for technical expertise, John Hughes for XRD help,
the Hawley and Mudge Foundations, UVM Geology