ARE AN EARLY BYZANTINE SEISMIC EVENT AND THE END OF THE BEYSEHIR OCCUPATION PHASE LINKED?

Multidisciplinary palaeolimnological studies are used to explore the possible impact of a cluster of earthquakes on the North Anatolian Fault (NAF, Turkey) on the collapse of an arboricultural civilisation (Beysehir Occupation Phase, BOP) stressed by deteriorating climatic conditions at the beginning of the Byzantine Empire.

The end of the BOP at AD c. 200-800 is marked by the collapse of a rich arboriculture in Western Turkey. It is shown to be relatively sudden and dramatic in palaeoenvironmental terms and coincides with changes in the distribution and lifestyles of people. It is still however impossible to establish if this event is synchronous across western Turkey. In Turkey and parts of the Middle-East, the BOP is considered as being a time when the climate is more humid..

A transect of cores across lake Manyas (10 km south of the Sea of Marmara) has revealed a seismite at 4 m depth dated to AD 240-420. Detailed analysis of the sediment structure and biological material contained within the 4-8 cm thick seismite is presented here.

The lake water quality changed suddenly (broken shells, sediment cracks) and briefly (25 years?) with an increased of the biomass and a salt inundation (an expulsion of hydrothermal fluids along the fault?). Our hypothesis is a movement of the Manyas Fault running just south of the lake. This may have diverted briefly the main incoming river, causing a temporary concentration of nutrients.

Events of a similar type/amplitude on the Manyas Fault were rare (1 or 2 in c. 4100 years). The effect of the earthquake was major and more long-lasting than a catastrophic event with a permanent change in terrestrial vegetation on an area that must have extended outside of the drainage basin of lake Manyas.

Attributing the event to a particular known earthquake is difficult, although the historical catalogue for the Sea of Marmara region is one of the longest and most complete in the world. The mid- to –late 4th century AD corresponds to a period of enhanced seismicity. Consequently, several destructive earthquakes fall within our narrow time window. Intriguingly, this period of heightened seismicity appears to affect the wider eastern Mediterranean area during this time, making it is tempting to link this apparent ‘seismic crisis’ with the termination of the BOP.