This study concerns the Holocene evolution of the Ostia palaeolagoon on the Tyrrhenian coast of Italy, integrating sedimentary, biological, and geochronological proxies from sediment cores. Three sedimentary phases are distinguished, beginning with Phase I (~ 12,000 BCE to 5045–4801 cal BCE). It corresponds to the transgressive systems tract, during which rapid sea level rise created dynamic coastal conditions, including lagoonal environments and barrier systems that migrated landward. The stabilization of sea level around 5000 cal BCE marked the highstand systems tract, initiating a river-dominated Tiber delta system and driving coastal progradation. This Phase II (5045–4801 to 1900 cal BCE) is marked by peat accumulation as the lagoon became increasingly isolated due to the growth of barriers and the progradation of the delta. Toward the top of the sequence, a mm-thick tephra layer has been recognized as being the Avellino tephra (~ 1900 cal BCE). Consistent with data from the Tiber River in Rome ( Marra et al., 2025 ), a strong decrease in peat accumulation rate between 3652 and 3520 BCE and ~ 1900 BCE seems to be related with the 4.2 ka BP Event, a climatic anomaly associated with cooler, arid conditions and a sea level stillstand or slight fall. This period marks significant shifts in the hydrological regime, reflected in both the sedimentary record and associated biological proxies. However, a marked depositional hiatus (~ 1900 to 890–770 cal BCE) characterizes the subsequent interval, before sedimentation resumes with phase III (890–770 cal BCE to Medieval times) and the establishment of an enclosed lagoon, with limited connection to the sea. Due to the accretion and expansion of coastal barriers, the lagoon fully evolved into a freshwater environment, which was reclaimed for agricultural and urban use in modern times. The stability of the marine sediments of the palaeolagoon, deposited on top of Late Pleistocene beach ridge sands, provides robust markers for reconstructing Holocene sea level altitudes that are not biased by compaction. During early lagoon phases, sea levels were approximately 1.5 m below the present. The sedimentary hiatus possibly linked with temporary sea level lowering was followed by a gradual rise during the Late Holocene. These findings, reflecting the interplay of sedimentary processes, climatic events, and human activity, underscore the value of multi-proxy analyses for reconstructing coastal palaeoenvironments and understanding long-term dynamics in Mediterranean settings. • Multi-proxy reconstruction of Holocene evolution of the Ostia palaeolagoon. • Three phases linked to sea-level change, delta growth, and barrier accretion. • Stable sandy substrate provides robust, compaction-free sea-level markers. • Mid-Holocene hiatus suggests sea-level stillstand. • New sea-level estimates refine Tyrrhenian trends and regional curves.
Bulian et al. (Fri,) studied this question.