Fieldwork Picture of the Day 8

black bog abbey road

John, Walrus, George and the Sandhill Crane

In which we do our best impression of the Beatles Abbey Road cover on Porcher Island (map).  Lining up like this was necessary because the surface of this bog was so mucky we had to dismantle an old grow-op to make a trail across the surface (yes, we then dismantled our trail).  This bog is a few metres  above sea level, but quite quickly down in the core sample there was a clear break to marine sediments, showing sea level had once been higher than today and then dropped to or past modern.  Carbon dating a piece of sediment from the interface showed sea level had fallen past this point by  10,000 years ago.

Terrestrial (left) overlay marine (right) sediments.

Terrestrial (left) overlay marine (right) sediments.

The picture to the right shows the core sample, with the clear distinction made between the brown, terrestrial, pond deposits to the left (upper) side of the core) while in the right (lower, older) part of the core you can see the sediments turn to a greenish marine clay, which contained small shell fragments and salt-water diatoms.  Taking a number of these core samples from different elevations (and therefore of preumptively different dates of sea level change) allows us to stitch together a curve or graph of sea-level history.  Using this curve, we can then identify ancient coastlines (both underwater and above high tide) with greater certainty and accuracy, allowing for more efficient and productive archaeological survey on these ancient landforms.  On the map linked above, you can see the long linear lakes and ponds paralleling the modern shoreline.  These lakes highlight the former  eastern shores of  Oval Bay at higher sea levels.

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