PUBLIC TALK: Using the Land-Ocean Transition to Understand Past Coastal Landscapes
|Using the Land-Ocean Transition to Understand Past Coastal Landscapes
A public lecture by Mark Bateman, Director Sheffield Luminescence Dating Laboratory, University of Sheffield and Institute of Advanced Studies Visiting Fellow.
Coastal dunes can contain lengthy, but complex, records of long-term environmental, climatic and sea-level fluctuations particularly where the dune sand has become lithified into aeolianite or calcarenite. Both Australia and South Africa have fairly widespread occurrence of on-shore coastal aeolianites. Aeolianites can form shore-parallel barrier reaching up to 200 m above modern sea level and up to a few km inland.
This talk will focus on Professor Batemanís research on the South African aeolianites which occur in association with world renown Middle Stone Age archaeological sites. The aeolianites provided the caves and at times dune sand inundated or blocked caves aiding archaeological preservation. But why did our early ancestors choose to live in dunefields? What was the environment and coastline like then and how has it changed through time? This talk will show how integrating off-shore and on-shore topography with an extensive luminescence dating programme allows for a better understanding of the evolution of coastlines through time. The sediments themselves can also be used to gives hints of the humans, animals and plants occupying past dunes.
We now know the preserved terrestrial dunes have been constructed over at least the last two glacial-interglacial cycles (back to ~270,000 years) with multiple phases of deposition during sea-level high-stands. Tectonic stability of the region allowed shorelines to reoccupy similar positions on multiple occasions with sediment deflated from beaches building large stacked dunes. Local variation in the off-shore topography controlled when and where these stacked dunes formed. As global sea-levels rose during non-glacial times so pre-existing dunes were eroded and recycled into new on-shore dunes. As global sea-levels fell during glacial times so dune construction moved out onto what is currently the off-shore platform. Thus whilst the preserved on-shore dune and archaeological record looks fragmented this reflects the big changes in coastline position which have occurred in the past. When sea-levels were high, people occupied caves in the aeolianite and utilised both marine resources and the diverse flora and fauna found on the shifting dunes. When sea-levels were lower they followed the coast-line and dunefields onto the newly exposed coastal plain.
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