Geoarchaeology of burnt mounds: site formation processes, use patterns, and duration
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Date
02/07/2019Author
Gardner, Tom
Metadata
Abstract
Burnt mounds, accumulations of fire-cracked stone and fuel residues dating largely
from the Bronze Age, are a widespread and numerous site type across Britain and
Ireland. However, the function, duration, and depositional history of this site type
remains unknown. This study examines the formation processes and duration of burnt
mounds using a new multi-proxy geoarchaeological methodology comprising
micromorphology, x-ray fluorescence, loss on ignition, and soil pH assessment
alongside radiocarbon dating and statistical exploration. The sampled material covers
nine sites across northern Britain, spanning Northumberland, Wester Ross, and
Orkney.
This work shows that the burnt mounds assessed are complex and multi-faceted,
consisting primarily of fuel residues; wood and grasses in Northumberland and
Wester Ross, and peat, turf, and seaweed in Orkney. Many sites contain discrete
deposits of bone, unburnt plant tissues, and rubified sediments, and the use of earth-ovens
is suggested at one site by repeated layers of charred grasses and massive
rubified peds. Mounds were deposited in small increments, each representing either
one discrete firing event or the admixing of several firing events. Principal component
analysis of quantitative multi-element and sedimentological data was able to group
burnt mound deposits by fuel type, which was verified by micromorphology.
Micromorphological and sedimentological analyses identified widespread natural
sediment incursion and taphonomic processes across all mounds. These incursions
often represent hiatuses in deposition and indicate the recurrent, cyclical, or even
seasonal use of these sites. Although manifested differently due to local
environmental conditions, natural formation processes show recurrent abandonment
and cyclical patterns of use at sites through the deposition of material of similar types.
Limited seasonal indicators such as desiccation features, soil formation, and rain-splash
crust formation suggest hiatuses in wetter seasons and activity in drier
seasons. Available radiocarbon dates suggest that the depositional duration of most
mounds was around 100 years, although outliers exist.
Together, these data indicate for the first time that burnt mounds were not the product
of single large events such as monumental feasting, but rather represent a more
gradual accumulation of small-scale activities by small communities or groups that
were cyclical in nature. This has implications for wider interpretation, both of burnt
mounds and the socioeconomic systems that they represent, which is discussed.
Equally, this study argues that burnt mounds warrant more direct archaeological
attention as they contain well-stratified deposits that hold palaeoenvironmental and
geoarchaeological records of human-environment interactions over the short to
medium term. Consequently, this study puts forward a best practice excavation and
sampling guide to inform on future work, angled towards the policy and developer-funded
sectors.