Foraminiferal record and high-resolution seismic stratigraphy of the Late Holocene succession of the submerged Ombrone River delta (Northern Tyrrhenian Sea, Italy)

摘要

Micropalaeontological data integrated with radiocarbon dates and seismic profiles allow for a recon-struction of the Late Holocene evolution of the Ombrone River delta area during the last 6.0 ka. Seven cores collected in three distinct sectors of the submerged Ombrone delta were studied: the delta front (cores NK7, NK8, BOK5 and BOK10) and prodelta slope (core NK4), which are primarily affected by river input, and the middle shelf (cores NK2 and NK3), which is progressively less influenced by riverine impact. Seismostratigraphic interpretation indicated that the majority of the cores intercepted the most recent deposits of the late Quaternary depositional sequence (unit A), whose base is dated at 2.8 ± 100 ka BP. The deepest and shallowest cores reveal a record of the ancient and the most recent evolution of the succession, respectively, although the most complete palaeoenvironmental evidence comes from the middle shelf (core NK2) and prodelta slope (core NK4). The oldest sedimentary phase is indicated by benthic foraminiferal assemblages and seismic profiles of the middle shelf core and cor-relates with the Late Transgressive Systems Tract (unit B). The following phase is attributed to the Highstand Systems Tract (unit A) and spans the last 3.0 ka. Hierarchical cluster analysis (HCA) (Q-mode) of the benthic foraminifera in the cores resulted in 10 foraminiferal assemblages that correspond to four distinct environments with various degrees of river influence.