Paleoenvironmental reconstruction of the southern extension of the Tiber delta with the Ostia palaeo lagoon: interplay between human activity and landscape change

As today, in antiquity the importance of coastal and deltaic environments lay in the sea’s integrating role in the subsistence, resources, and trade opportunities of its people. For the first large towns of the late Bronze/early Iron Age in Central Italy, salt was an indispensable commodity being the only means available to preserve food, both for consumption and trade. It was produced in the coastal areas but the early production sites, techniques employed, and trade are still uncertain/poorly understood.

            In the southern part of the Tiber delta palaeo-lagoon of Ostia, at the archeological site of Piscina Torta, heaps made of hundreds of thousands of potsherds were found, possibly related to the salt production technique known as briquetage and pointing at the existence of a major early salt production and trading industry. This coastal area likely holds an outstanding record of the Late Holocene paleoenvironmental changes and of the interaction between climatic variations and coastal processes in an area actively modified and adapted by human activity.

            An intensive coring campaign at the site and subsequent analyses led to the identification of three stages in the development of the lagoon and its palaeo-inlet towards the sea. During the first phase, the lagoon was well connected to the sea and filled with marine sands. Later on, the inlet was blocked by a newly formed beach ridge, and peat accumulation started. During this second stage, the margins of both the lagoon and inlet were characterized by a highly evaporative environment with carbonate precipitation. Most probably, these sediments were used and leached for producing the brine needed for the salt production by briquetage, a method which consists in boiling such brine in typical reddish jars to obtain a salt cake. Furthermore, heaps composed of both inlet fill, and pottery found around the archeological site suggest how the channel connecting the sea with the lagoon may have been modified by anthropic activities. In a last (third) phase, presumably of medieval age, a marine transgression led to inundation of the lagoon and deposition of highly fossiliferous fine textured sediments.

In this contribution, we show the results of a detailed geochemical and micropaleontological analysis (benthic foraminifers) of a continuous section sampled in the ancient lagoon of Ostia, in the form of a paleoenvironmental reconstruction of the area before, during and after its human occupation. Radiocarbon dates provide a firm time frame for the palaeo-lagoon evolutionary phases, while grain size analyses performed both on the inlet fill and the sediment heaps found at the site, revealed new details regarding the human modification of the landscape.