Piero Bellotti

Sequence Stratigraphy and Depositional Setting of the Tiber Delta: Integration of High-resolution Seismics, Well Logs, and Archeological Data

ABSTRACT Using archeological evidence, radiocarbon data, well logs, and high-resolution seismic profiles, we applied sequence-stratigraphic analysis to sediments deposited during the last glacio-eustatic cycle on the Tyrrhenian continental margin embracing the Tiber River months. These sediments form a high-frequency sequence of fifth order that has developed over the last 20,000 yr since the last lowstand, hereafter referred to as the Tiber Depositional Sequence (TDS). The TDS is still evolving and lies on a Type 1 sequence boundary that has been identified both on the shelf and below the present delta plain. This sequence consists of lowstand, transgressive, and highstand systems tracts. The lowstand deposits are not present on the shelf but are found on the continental slope, where they constitute the last progradation set of the continental margin. A network of gullies, active when the river mouth was at the shelf break, is present within the lowstand deposits. The transgressive-systems-tract (TST) deposits lie directly on the basal unconformity. Landwards the TST is represented by a retrogradational parasequence set of fluvial, coastal barrier-lagoon, and lagoonal delta facies. Seaward, on the shelf, these parasequences merge into a seismically transparent deposit that forms a condensed section. The flooding surfaces that bound the parasequences are marked by peat layers that were dated by 14C. The radiometric ages were used to draw a carve of sea-level rise for the last 11,000 yr. The top of the transgressive systems tract (maximum flooding surface) is represented by the last peat layer, which was formed about 4700-5000 yr BP and buried 4-5 m below the present upper delta plain. The highstand systems tract is made up of deposits of the present Tiber wave-dominated delta, i.e., upper and lower delta plain, delta front, and prodelta slope. The aligned beach ridges mark the position of the prograding coastline, which for the last 2500 yr can be dated by archeological and historical data. The recent very fast progradation of the Tiber delta, during the last 500 years, is consistent with historical data on floods of the city of Rome and the suspended load of the Tiber River.

The Tiber river delta plain (central Italy): Coastal evolution and implications for the ancient Ostia Roman settlement

Geomorphologic, stratigraphic, faunistic, palynological and carbon isotope analyses were carried out in the area of the Tiber river mouth. The results depict a complex palaeoenvironmental evolution in the area of the Roman town of Ostia, ascertain the changes of the Tiber river delta over the last 6000 years and support a re-interpretation of some archaeologic issues. The wave-dominated Tiber delta evolved through three distinct phases. In the first step (5000–2700 yr BP) a delta cusp was built at the river mouth, which was located north of the present outlet. Subsequently (2700–1900 BP), an abrupt southward migration of the river mouth determined the abandonment of the previous cusp and the progradation of a new one. The third step, which is still in progress, is marked by the appearance of a complex cusp made up of two distributary channels. The transition from the first to the second evolution phase occurred in the seventh century bc and was contemporary to the foundation of Ostia, as suggested by historical accounts. However, the oldest archaeological evidence of the town of Ostia dates to the fourth century bc, when human activity is clearly recorded also by pollen data. We suggest that the first human settlement (seventh century bc) consisted of ephemeral military posts, with the aim of controlling the strategic river mouth and establishing the Ostia saltworks. Only after the fourth century bc the coastal environment was stable enough for the foundation and development of the town of Ostia.

Benthic foraminiferal assemblages of the imperial harbor of Claudius (Rome): Further paleoenvironmental and geoarcheological evidences

This paper presents a paleoenvironmental reconstruction of historical development in the area of the ancient harbor of Claudius based on micropaleontological and sedimentological data. Benthic foraminifera are reliable tools for this kind of research because they are sensitive to short-time environmental changes induced by both natural and anthropogenic events. By studying eight sediment cores collected from different sections of the harbor, it was possible to reconstruct a comprehensive picture of the harbor complex. Qualitative and quantitative analysis of foraminiferal associations and sedimentological data, along with radiocarbon dating, were useful to identify three key intervals in the history of the coastal area where the harbor developed. The first interval, located at the bottom of all cores, is characterized by a brackish water environment, corresponding to the formation of the first deltaic cusp of the Tiber River. The second interval is characterized by the harbor activities that developed after a general increase in water depth due to a diversion of the Tiber River mouth. The third interval marks the final phase of harbor activities and the subsequent filling of Claudius’ basin. However, a link with the inner Trajanus’ basin was maintained via the central part of the basin, which remained submerged longer, until the early Middle Ages.

Late-Pleistocene and Holocene deposition along the coasts and continental shelves of the Italian peninsula

The aim of this chapter is to outline the depositional and erosional processes that occurred on the coasts and shelves at the margins of the Italian mainland during the late Quaternary sea-level fluctuation. This fluctuation dramatically controlled sedimentary processes through the rapid shift of shoreline position, changes in palaeotopography, and in the size and amounts of sediment derived from the continent. The sea-level fluctuation described occurred during the last 23–25,000 years, and it has been subdivided into three main phases: (1) the final part of the last sea-level fall, the low-stand, and the beginning of the sea-level rise; (2) the sea-level rise; (3) the present highstand. Each phase will be discussed in its general aspects and with reference to some case histories. The marine data mainly derive from high-resolution seismic surveys and from grab, core, and vibracorer samples. The land data consist of stratigraphic, morphological and archaeological records. Analyses carried out on the collected sediments are mostly mineralogical, grain size, microfauna and 14C analyses.

Middle-to late-Holocene environmental changes in the Garigliano delta plain (Central Italy): which landscape witnessed the development of the Minturnae Roman colony?

Geomorphologic, stratigraphic, faunistic, palynological and 14C analyses were carried out in the area of the mouth of the Garigliano River characterized by two strand plains that are referred to the Eutyrrhenian and the Holocene, rimming two depressed zones separated by the Garigliano River channel. This study depicts the palaeoenvironmental evolution over the last 8200 years and the landscape context at the time of Minturnae Roman colony. Between 8200 and 7500 yr BP, a wet zone occurred in the northern zone, whereas in the southern part, a lagoon developed. During the final transgression stage and the beginning of the sea level still stand (7500–5500 yr BP), a freshwater marsh formed in the northern zone, and the width of the southern lagoon decreased. Between 5500 and 3000 yr BP, the coastal barrier changed into a delta cusp, a freshwater marsh also appeared in the southern part and the river wandered between the twin marshes. Because of local uplift, previously unknown in this area, part of the floor of the southern marsh emerged, and after 4000 yr BP, both marshes became coastal ponds with prevailing clastic sedimentation. A progressive increment in anthropic forcing on the land took place after 3000 yr BP. The Marica sanctuary was built (7th century BC), and the Roman colony of Minturnae was developed beginning the 3rd century BC. The shallow depth of the ponds prevented their use as harbours, and saltwork plants can be ruled out based on the faunal and palynological data. The ongoing infilling of both ponds was never completed, and their reclamation is still in progress.

Coastal Morphodynamics AIGeo-WG: new geomorphological legend of the Italian coast.

Abstract from 88th Congress of the Italian Geological Society, 2016-09-07 - 2016-09-09, NaplesAbstract from 88th Congress of the Italian Geological Society, 2016-09-07, 2016-09-09, Naplesbook Edited by D. Calcaterra, S. Mazzoli, F.M. Petti, B. Carmina & A. Zuccari doi: 10.3301/ROL.2016.79