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Last year Prof Jan Boelhouwers, a geomorphologist with expertise in the weathering of rock, conducted the first survey of degradation of the fossil bed at the West Coast Fossil Park (WCFP), Langebaanweg. Retired from the University of Uppsala, Sweden, he volunteered to spend time and private funds to gain insights into the processes affecting the degradation of the fossils exposed for display. His report enables the WCFP to implement effective measures to improve the durability of these fossils that sustain the park’s education programmes.
Weathering entails processes that break down rocks and minerals on the surface of the Earth. One such process is the variable expansion of fossils and their surrounding sediments when heated by day and contraction when cooling by night. These thermal stresses loosen the grains of sediment adhering to the fossils and cause surface flaking and conchoidal fractures that penetrate the sediment to some depth. Furthermore, the effects of thermal stresses are exacerbated by salt in pore spaces expanding and contracting more than the surrounding material. Variable moisture levels cause salts to expand or contract even more with hydration and dehydration, adding further stress. There may also be chemical weathering of the fossils by sedimentary salts and salts deposited by bird and termite droppings.
Several kinds of weathering are in evidence in the WCFP fossil beds. Although the surface was carefully treated a year ago with a special consolidant designed to bind the material, within months, signs of salt efflorescence, subflorescence and lifting of the surface crust appeared, as did granular disaggregation and surface pitting, producing flakes, granules and fine dust. Some underlying processes, such as the sources of soil moisture and dissolved salts, are inevitable, but are not the first management priorities.
More immediate measures should concern the air temperature and humidity fluctuations in the protective enclosure over the fossil bed, with temperature the main driving factor.
Many fossils are perched on pedestals that are elevated 10-20 cm above the floor. Data loggers recorded that the top of the pedestals experienced daily temperature ranges of over 30º C. By comparison, the daily range on the floor is 20º C. By day, the pedestals were up to 9º C hotter than the floor and 5º C cooler by night.
Boelhouwers used a thermal camera to examine the spatial pattern of temperature across the fossil bed, which revealed even more extreme ranges of temperature fluctuations and differences between the pedestals and floor, as seen in the depicted examples. The conditions under the WCFP enclosure approach the extremes otherwise experienced in hot deserts. Climate controls that reduce the micro-climatic fluctuations are imperative in protecting the fossils from ongoing degradation processes.
Thanks to Boelhouwers, there are guidelines on what to prioritise in terms of fossil conservation measures and research by future students of geomorphology.
