Moluscos como proxies de evolución paleoambiental, usos antrópicos y tendencias bromatológicas en contextos históricosel estuario de los ríos Tinto y Odiel (Huelva, España) y el puerto de Portus (Fiumicino, Italia)

Abstract

1. INTRODUCTION The Archaeomalacology is a novel branch of Zooarchaeology whose objective is the study of mollusc remains (shells and plates) in natural accumulations and in shell middens. This discipline has application in paleontological and archaeological research through the taxonomic and taphonomic analysis of shells. Mollusks are a very diverse group that account for 10% of all species in the animal kingdom. In addition, they have been an important source of resources in coastal areas and their shells have a great capacity to stay in the environment. These three qualities ensure a wide representation in archaeological sites and paleontological scenarios. Therefore, they are an important source of information as indirect indicators or Proxies of natural phenomena and the action of man who has used this resource since the Paleolithic, about 300,000 years ago. In recent decades, numerous investigations have focused on the paleoenvironmental reconstruction of coastal areas from the analysis of continuous sediment cores and shell middens. The study of the malacofauna in natural accumulations allows obtaining information on different aspects such as: a) the interpretation of the sedimentary facies and the paleogeographical evolution of the study areas; (b) sea-level fluctuations indicating periods of marine transgressions and regressions; c) differentiation between natural accumulations of native and para-native shells; (d) identification of high-energy events; (e) periods of climate change; and (f) ages of sediments obtained by dating. Regarding the study of shell middens, it allows us to deduce the type of diet of ancient human settlements and their changes, as well as the various uses that were made of the shells. It also allows the establishment of development phases in relevant sites due to their historical importance, conditioned by: coastal dynamics associated with paleogeographical evolution, episodes of overexploitation or climatic and environmental variations. This Doctoral Thesis is carried out by compendium of publications with 4 works: Paleoenvironmental Evolution Holocena del Estero de la Fontanilla (Middle Estuary of the Rio Tinto, S.O. of Spain), Archaeomalacological Analysis of the Conchero de Cañada Honda (Middle Estuary of the Odiel River, SO of Spain), Multidisciplinary and Multivariate Analysis of the Roman Conchero of Isla Saltés (Marine Estuarine of the Tinto and Odiel Rivers, S.O. of Spain) and Paleoenvironmental Evolution of the Canale di Imbocco (Portus, Central Italy) 2. OBJECTIVES • Taxonomic and taphonomic analysis of the malacofauna as a tool for the paleoenvironmental reconstruction of historical sites in Spain and Italy. • Identification of the uses of marine mollusc shells during the Holocene in the estuary of the rivers Tinto and Odiel. 2.1. Sub-objectives • To establish the paleoenvironmental evolution of the cove of La Fontanilla (Palos de la Frontera, S.O. Spain) according to the paleomalacofauna obtained from continuous sediment cores. • Study of the shell midden of Cañada Honda (Aljaraque, S.O. of Spain) and trends in the consumption of molluscs. • Multivariate statistical analysis of the Roman shell midden of Isla Saltés (S.O. Spain), for the differentiation between natural and anthropic concentrations of molluscs. • Inferring the paleoenvironmental evolution of the Roman port of Portus (Central Italy), according to the archaeomalacofauna obtained from continuous sediment cores. 3. AREAS OF STUDY The works included in this Doctoral Thesis correspond to two areas of study: 1) the estuary of the rivers Tinto and Odiel (S.O. of Spain) where the shell midden of Cañada Honda (Aljaraque) and Isla Saltés were analyzed, and four continuous witnesses of sediment in the cove of La Fontanilla (Palos de Moguer); and 2) the ancient Roman port of Portus (S.E. of Rome, Italy), where a witness was obtained in Canale di Imbocco. 3.1.- Estuary of the rivers Tinto and Odiel. Both rivers converge at their mouth to the Atlantic, where they form a wide estuary. Its Holocene evolution starts from an emerged river valley that was flooded during the Flandrian Transgression, and after the regression of the last millennia we differentiate three sections: a) the high estuary characterized by an important process of silting, and where the conchero of Cañada Honda is located; (b) a middle stretch with tidal channels that delimit different islands and host marsh areas, and in which the shell middens of La Cascajera (Isla Saltés) and the cove of La Fontanilla are located; and c) a low plot that coincides with the area of the mouth, with important marine influence and protected by sand bars (Barra de Punta Umbría and Barra de Punta Arenillas). Since the Paleolithic human occupation is detected with important shell middens and Roman factories (cetarias) of the imperial era (centuries I-V AD). In addition, in this same estuary was the medieval port of Palos de la Frontera, from where Christopher Columbus departed for the American continent. 3.2.- Roman port of Portus. During the Roman Republican period, the city of Ostia was Rome's main port for trade in the Mediterranean. At the beginning of the imperial era (27 BCE-476 CE), Rome had one million inhabitants and the needs of supply and communications could not be met with the existing infrastructure in this port. Therefore, in 42 CE, Emperor Claudius ordered the construction of a larger port to compensate for these shortcomings. This new port was later extended by Emperor Trajan, at the beginning of the second century CE, by means of an inner basin. For the next four centuries, Portus was the main imperial port of the Western Mediterranean. The final result of the work of both emperors was one of the great constructions of Roman engineering that included two large docks, several docks for loading and unloading goods and passengers, good´s warehouses, thermal baths and an important network of navigable canals. The set consists of the outer basin or port of Claudio, limited by two large lateral breakwaters and with a central lighthouse that marked the access, and an inner basin or the hexagon of Trajan. Both structures were communicated by an artificial canal or Canale di Imboco, while the inner hexagon also had access to the Tiber River. CONCLUSIONS The four works that make up this thesis have highlighted the potential that archaeomalology has in archaeological and paleontological research, respectively. This type of studies allows to fulfill several objectives: VI. In the samples obtained there are represented current taxa, with well-known distribution and biology, which allow us to infer the paleohabitats of origin. Therefore, in a continuous sample of sediment, we can infer the geological evolution of the study area based on the dating of different stratigraphic profiles. VII. The specificity that some molluscs show towards certain habitats of inland waters or open sea and their presence in stratigraphic profiles, is indicative of changes in sea level. As with the replacement of the gastropod Bittium reticulatum (sandy seabed with presence of phanerogam meadows) by Peringia ulvae (characteristic of muddy plains of medium-high estuaries), indicative of a transgressive episode. VIII. The associations of molluscs and some specific species allow to differentiate high-energy coastal environments (open sea) from other habitats typical of low-energy coasts (inland marsh-type areas), since these environments have different associated biota. IX. The taxonomic and taphonomic study of malacological deposits allows to differentiate between natural accumulations of shells (type cheniers or washover fans) and shell middens. This distinction is based on aspects such as diversity; the proportion of edible species and the size ratio; the presence of signs of handling or cooking; or the absence of microfauna among the samples. X. The species that make up a shells middens in coastal areas come from capture areas more or less far from the "garbage dump". This material serves to delimit the shellfish area and deduce the type of technique used for its capture (manual, use of utensils, etc.). From the shell middens, prorities and evolution of the diet can also be deduced, as well as uses and customs related to the use of shells.