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Clays, sediments and landscape history

July 24, 2014

media-20140724 (1)The morning stayed cool, grey and damp, so Ana and I bundled up in waterproofs to hike a couple of kilometres south to the north mouth of the Arolik. We were there to find and sample geological profiles the river had deposited and cut over the last several thousand years. Accompanied by the loyal site dog (Lokys, who soon got tired, started whining, and needed to be carried), we started at the river mouth and collected clay deposits for some experiments — the inhabitants of Nunalleq made considerable amounts of pottery, and Ana is building understanding of the range of variation in clay sources in the immediate area around the ancient village.

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Following that we moved 500 m or so north to some older coastal sections that hadn’t been cut by the river and cleaned back a two-meter-deep section so we could sample and draw the sedimentary sequence and begin making sense of the formation processes that gave rise to the landscape. Our working interpretation is that the deeper grey-blue clays are sediments of the late Pleistocene, and following shoreline transgression are then cut into by braiding streams in the Arolik’s flood plain and filled by low energy organic-rich alluvium during the early Holocene, which are then overlain by the peat sediments.

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Surprisingly this landscape wasn’t under ice even at the maximum extent of the last (Wisconsin) glaciation between about 25 and 20 thousand years ago, so what we’re able to view in these profiles is a near-continuous sequence of landscape evolution under various episodes of climate change. This helps us contextualize human history within the longer term ecological changes that occurred in these dynamic landscapes. We collected soil samples for compositional analysis that will provide some more precise data on formation processes as well as a bucket of good clay for some experimental pottery making later in the week!

The day ended with heavier rain, so by the time we wandered back up to the main excavation the whole crew was muddy, wet and tired — fortunately Cheryl had made a Mexican-inspired feast for us this evening so we were restored and ended the day (very) well fed and content.

JC

One Comment leave one →
  1. Jeff permalink
    August 1, 2014 20:07

    Nice soil profile guys. Interesting to read that this part of the coast may have been unglaciated. I’m aware of refugia south of the Aleutian Islands (and heading down the coast to the panhandle and BC) but not to the north. Some interesting implications for those of you keen on early holocene inhabitation. All the best from sunny Vancouver…

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