The sedimentary response to normal faulting in the Pliocene marine Siena-Radicofani Basin (Tuscany, Italy)

The Siena-Radicofani Basin is part of a broad N-Strending tectonic depression located in the innerNorthern Apennines, filled by Miocene to Pliocenecontinental and marine deposits. The tectonic evolution of the Siena-Radicofani Basin,as well as that of the other Neogene basins of the innerNorthern Apennines, is still under discussion and is theobject of scientific debates. Most authors refer thedevelopment of these basins to the early-middle Miocene-Present extensional tectonics (Carmignani et al. 2001 andreference therein), whilst others consider them as thrust-top basins (Finetti et al., 2001 and references therein)implying a different interpretation of the NorthernApennines Neogene structural evolution. As result ofthese different points of view, the Siena-Radicofani Basinhas been differently interpreted: it has been considered asa thrust-top-basin (Bonini and Sani, 2002) and as ahanging wall basin related to extensional detachments andsuperimposed high-angle normal faults (Brogi, 2011). Inthis latter interpretation, the later evolution of the basin isconsidered to have been influenced by NNW-SSEtrending syn-sedimentary high-angle normal faults whichwere active during the early Pliocene and have slightlymodified the previous architecture of the basin. Thisinterpretation is based on the analysis of seismic reflectionprofiles, whereas detailed sedimentological andstratigraphic information were lacking and couldtherefore not be used to assess the possible tectoniccontrol over the sedimentation processes. In this contribution, we report the results of a detailedstudy carried out on five coeval sedimentary sectionslocated in as many key areas, where some main normalfaults have been identified, with the aim of reconstructingthe possible tectonic control on the sedimentationprocess. These sedimentary sections recorded differentdepositional environments (i.e. alluvial fans, marinemouth bar-type to Gilber-type deltas, deep-waterolistostromes), each one characterized by the occurrenceof coarse-grained sediments. In contrast, coarse-graineddeposits are generally uncommon in the older andyounger stratigraphic records of the Siena-RadicofaniBasin. Each section is discussed in terms offormation/degradation of accommodation space,sediment supply availability and vertical stacking ofdifferent sedimentary environments. Detailed bio-chronostratigraphic data, combined with palaeosoilsinformation, allowed tectonic and climatic signatures tobe distinguished. The main results indicate that sedimentation wasstrongly influenced by the activity of normal faults locatedin the basin margins during the lower Pliocene. Faultingprocesses in these areas activated the uplifting of thefootwall blocks and caused subsidence in the adjacentareas (hanging wall), producing high-relief morphologicalprofiles that fed the depositional environment withcoarse-grained sediments. The subsiding hanging wallallowed the development of different types of depositionalsystems, which required high-sediment supply and acontinuous increase in the available accommodationspace simultaneously.All the evidences strongly support the thesis thatnormal faults were active during the early Pliocene in theSiena-Radicofani Basin, thus supporting for anextensional framework instead of a compressional one. (PDF) The sedimentary response to normal faulting in the Pliocene marine Siena-Radicofani Basin (Tuscany, Italy). Available from: https://www.researchgate.net/publication/289260055_The_sedimentary_response_to_normal_faulting_in_the_Pliocene_marine_Siena-Radicofani_Basin_Tuscany_Italy#fullTextFileContent [accessed Feb 18 2022].