Sand Dunes Rolling Across the South

Ice Age environmental conditions influenced the present day landscapes of many geographical localities, including the Carolina Sandhills.  A recent study determined Ice Age winds shaped the topography of this region.  The sand originated from loose sediment and eroded sandstone within a Cretaceous-age formation located near the surface.  Arid climatic conditions caused by glacial expansion exposed part of this formation.  Frequent droughts reduced vegetative cover, so there were bare patches of soil without tree and grass roots holding the sand in place.  I think overgrazing by megafauna during droughts played a role in denuding the landscape as well.  Cold winds blew the exposed sand into massive eolian dunes that rolled across the land.

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The Sand Hill Region is encircled in red on this map.  At least parts of it originated during Ice Ages when cold winds blew exposed sand across the landscape here.

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Vegetation stabilizes sand dunes in the region today.  Local sand dunes have been inactive for at least 6,000 years.  They were most active during the coldest driest phases of Ice Ages.

The authors of the below referenced study took core samples of sand hill sediment in Chesterfield County, South Carolina.  They found an unconsolidated layer of sand measuring from ~1 foot to about 30 feet deep.  Optically stimulated luminescence dates (See: http://www.usu.edu/geo/luminlab/whatis.html ) suggest dunes were active from 75,000 years BP-37,000 years BP when glaciers were expanding and from 28,000 years BP-18,000 years BP during the Last Glacial Maximum and again from 12,000 years BP-6,000 years BP.  The beginning of the final period of dune activity corresponds with the Younger Dryas cold reversal when average global temperatures suddenly plummeted following a warm climate cycle.  Scientists found no evidence of dune activity between 37,000 years BP-28,000 years BP and 18,000 years BP-12,000 years BP.  These dates correspond with warmer wetter interstadials when plant growth stabilized sand sheets and dunes, holding them in place.  There has been no dune activity in the Carolina Sandhills for at least 6,000 years because higher precipitation levels foster thicker vegetative growth.

great-kobuk-sand-dunes-5

The Great Kobuk sand dune in Alaska.  During the Ice Age landscapes in the sand hill region may have resembled this, though short leaf pines, grass, and scrub oak as well as spruce were the characteristic vegetation between the dunes instead of just spruce.

Sand dunes probably advanced the most on cold windy Ice Age nights.  Experiments show air temperature is a factor in sand particle transport.  Decreasing temperatures increase air density and lower water vapor thus reducing drag on the sand particles.  Larger particles can get picked up and transported by wind more easily when temperatures drop.  The region may have experienced brutally low temperatures compared to present day averages.

Sand dune origin in the Carolina Sandhill region differed a little from sand dune formation in Georgia.  The source of sand in the Carolina Sandhills is a geological formation near the surface, but many dunes in Georgia originated from dry river beds where sand was exposed because water tables dropped.  (See: https://markgelbart.wordpress.com/2012/04/09/the-ohoopee-sand-dunes/ ).

Pollen evidence indicates the dominant flora growing between the sand dunes during the Ice Age consisted of pine, spruce, scrub oak, grass, and asters (sunflowers, daisies, etc.).  It was probably an open woodland type of environment, though scrub oaks may have formed denser thickets.  I believe shortleaf pine (Pinus echinata) and possibly Virginia pine (P. virginiana) were the dominant species of pine here then.  It was too cold and windy for longleaf pine (P. palustris), commonly found here today.  I’m no longer convinced jack pine (P. banksiana) occurred this far south.  Some pollen studies list jack pine as a species present in this region during the Ice Age.  However:

1)The present day range of jack pine is too far away from the Carolina Sandhills. It seems unlikely its range would have retracted so drastically without leaving a relic population anywhere in the south.

2)  There are no definitive macrofossils of jack pine in the south.

3) Evidence jack pine was present in the south is based on identification of pine pollen, but 1 researcher makes the compelling case that jack pine pollen is indistinguishable from shortleaf pine pollen.  (See: https://www.osti.gov/scitech/biblio/564104 ).  Jack pine pollen is distinguished from other species of pine pollen based on the size of its grains but they overlap in size with shorleaf pine pollen grains.  Because shortleaf pine occurs in the region today, it seems more likely pollen evidence represents this species, not jack pine.

The species of spruce tree present in the Carolina Sandhills during Ice Ages was probably the extinct Critchfield’s spruce.  Macrofossils of this species have been found associated with temperate species of hardwoods.  The average annual temperatures of the Carolina Sandhills during Ice Ages was probably similar to present day southern Ohio or Kentucky, not like southern Canada as some researchers estimate based on their mistaken assumptions of tree species composition.  The Carolina Sandhills are located in what was a sharp transition zone of climate during the Ice Age.  A thermal refuge existed to the southeast where warm waters off the Atlantic coast pooled because thermohaline circulation (the tropically heated water that presently flows off the coast of New England) shut down.  But temperatures sharply dropped to the north and west of this thermal refuge, not unlike conditions experienced by mountain climbers rapidly ascending a mountain.

The Carolina Sandhills likely supported significant populations of megafauna, despite the vast expanses of bare sand.  Open grassy land fed mammoths, caribou, horses, bison, llamas, and Harlan’s ground sloth.  Scrub oak thickets attracted herds of flat-headed peccaries.  Giant lions and dire wolves roamed the interdunes, seeking out megaherbivores.

Reference:

Swezey, Christopher; et. al.

“The Carolina Sandhills: Quaternary Eolian Sand Sheets and Dunes along the Updip Margin of the Atlantic Coastal Plain Province, Southeastern United States”

Quaternary Research 86 (2016)

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2 Responses to “Sand Dunes Rolling Across the South”

  1. ina puustinen-westerholm Says:

    Were I loaded with funds..I can imagine a ..fly over..in a private plane..and then..depth imaging machines..from the curr. ‘edges’..of the ancient dunes..to..back about 200 ft. Then..just the insane..digging, sifting and looking..at what could be found..remnant..from 6000ish..years ago.

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