Reflections on Coastal Aeolian Research

Cronulla dunes with the city of Sydney in view.

A recent issue of the journal Aeolian Research (2015, vol. 17) contained an article entitled Synthesis on Quaternary aeolian research in the unglaciated eastern United States. It is a multi-authored paper by a team from the United States Geological Survey (USGS) led by Helaine Markewich. This paper is one of the most comprehensive and well documented  Quaternary regional syntheses that I have read in recent years and raises questions about the origin of landforms and processes at work in coastal areas affected by climate change during the late Quaternary.

You may ask why am I interested in this work. Two main reasons: first, part of their study involved particular areas that I had the pleasure of visiting and studying during my period as a postgraduate at Louisiana State University in the 60s; and second, there are interesting parallels with aeolian activity over the same period in eastern Australia. There is a third more academic reason: it is a joy to read the outcomes of good science!

The paper by Markewich et al. examines aeolian deposits in two quite different regions , the lower Mississippi Valley (LMV) and the Atlantic Coastal Plain (ACP). These are non-glaciated areas on North America but were affected in part by river incision and fluvial deposition as well as extensive aeolian deposition during glacial periods. In the LMV silt sized particles were blown eastwards off the valley floor to cover adjacent slopes as loess. Over the years there had been debates about the origin of these deposits.  There is no activity today that even approximates what was going on during the glacial period when glaciers were growing and decaying further up the Mississippi Valley into the Laurentide Ice Sheet. But there is no doubt now where these deposits came from and their age. Along the coastal plain of the Atlantic, and eastern part of the Gulf of Mexico, sand dunes were forming during this period. Their paper brings together information and the extensive literature from both regions and assesses the extent and complexity of climate changes during the last glacial interval.

I did not publish any of my observations from the LMV although while serving as an instructor at LSU I took students into gullies to inspect sections in bluffs leading to the Mississippi Valley. I also examined electron microscope images of the highly angular silt grains. My main work, however, was in Horry County and Marion County , South Carolina, an area that also interested the USGS team. I published several papers on Quaternary features of this area including the enigmatic “Carolina Bays” (see Geol. Soc. America Bull., 1970,vol.81). The term Bay here does not refer to an arm of the sea but a shrub that now grows in a depression carved by wind during glacial times and now vegetated. My work helped define aeolian processes at work on late Quaternary fluvial sand deposits in valleys of the ACP and on older Quaternary coastal sand barriers. Winds reworked these coastal and fluvial materials to  form source-bordering dune landforms. Markewich et al. illustrate many of these features and use them to interpret  palaeo-wind fields. Different dating techniques are used to document the age of deposits including thermoluminescence (TL) and optically stimulated luminescence (OSL), and the ages are related to oxygen isotope stage (OIS) boundaries.

Over the past three decades there have been several significant studies of aeolian deposits in Australia. The 2012 book edited by Bishop and Pillans (Australian Landscapes) contains several synthesis papers (e.g. by Fujioka and Chappell; and one by Hesse). The focus is mostly on inland and desert dune systems. However, a story is gradually emerging on east coast dunes from Cape York to Tasmania . David Price from University of Wollongong has been a major contributor to determining the age of these dunes using TL and OSL techniques. In 1994 he helped Pat Hesp, Ted Bryant and me with a set of dates on some of the Pleistocene dunes, and is currently working with me on a cliff-top dune site near my home in Vaucluse. More work is to be done by others in places such as the southern Queensland dune islands and the vegetated dunes of northeast Tasmania. A synthesis should soon emerge. I encourage those working in this field today to look at the work of Markewich et al. as see how they handled such a geographically dispersed data set and used that data to draw conclusions on Quaternary climate change.

– words by Prof. Bruce Thom