Geological map of the Pliocene succession of the Northern Siena Basin (Tuscany, Italy)

Abstract

The late Miocene-Pliocene sedimentary fill of the Siena Basin (Tuscany, Italy) consists dominantly of clastics and has internal architecture that reflects the interplay of tectonics, relative sea-level changes and climate variations. Pliocene sediments are extensively exposed and overlay both late Miocene deposits and pre-Neogene bedrock. Specifically, Pliocene basin margin sediments consist largely of sand with gravel and mud intercalations, deposited mainly in nearshore settings with minor fluvial depositional episodes. They grade basinward to dominantly offshore fines with intervening turbiditic sand bodies. New fieldwork revealed that basin margin deposits, notwithstanding lithologically rather homogeneous, are made of a variety of sedimentary facies and bear several unconformities. They have been traditionally described and mapped using lithostratigraphic criteria, that have proven to be unfit to represent such complex stratigraphic architectures. The aim of this paper is to describe the allostratigraphic architecture of the Pliocene deposits exposed in a marginal key-area (45 km 2 ) of the northern Siena Basin by means of a 1:10,000 scale geological map. The recognized succession of allostratigraphic units and their bounding discontinuities, along with new biostratigraphic data from calcareous plankton, provides new insights into the geological history of the Siena Basin and represents valuable constraints for long-distance correlation.

Provenance and geological significance of red mud and other clastic sediments of the Mugnano cave (Montagnola Senese, Italy)

“…The sedimentary infill of this cavity is one of its most striking features (Fig. 3) and it was recently investigated by Martini (2011). The same author, on the basis of sedimentological and stratigraphic evidences, interpreted the origin of this cave in the framework of the rock-ghost weathering theory (Quinif, 2010 and references therein).…”

Geological map of Pliocene-Pleistocene deposits of the Ambra and Ombrone valleys (Northern Siena Basin, Tuscany, Italy)

“…facies associations) that were subdivided into allounits, namely stratigraphic units bounded by both unconformities and correlative-conformity surfaces (North American Commission on Stratigraphic Nomenclature, 1983). Facies association mapping was adopted since it is a powerful tool to define depositional history and basin-scale geometry of sedimentary successions (Arragoni et al, 2012;Ghinassi, Libsekal, Papini, & Rook, 2009;Martini et al, 2011Martini et al, , 2013. Allounits are preferred to depositional sequences (Vail, Mitchum, & Thompson, 1977), UBSU (Salvador, 1987) or synthems (Chang, 1975;International Subcommission on Stratigraphic Classification, 1987;Salvador, 1994) because of their wide applicability in narrow confined basins characterized by erosional, non -depositional and correlative-conformity surfaces, either in marginal or depocentral areas.…”

“…The stratigraphic architecture of Pliocene deposits is relatively poorly known, except for some areas, recently investigated according to allostratigraphic and sequence-stratigraphic principles (Arragoni, Martini, & Sandrelli, 2012;Martini et al, 2011Martini et al, , 2013. Specifically, according to Martini et al (2011) the Pliocene deposits of the northern basin margin (alluvial-to-inner shelf marine sediments) are organized in four allostratigraphic units. Marine sedimentation ended in the latest Piacenzian, when an overall uplift of southern Tuscany resulted in subaerial exposure and sedimentation of Pleistocene alluvial deposits (Costantini et al, 1982;Martini & Sagri, 1993).…”

“…The Pliocene succession consists of alluvial deposits (De Castro & Pilotti, 1933;Manganelli, Aldinucci, Capezzuoli, & Benocci, 2007;Manganelli, Martini, & Benocci, 2011;Martini et al, 2011), passing upward into nearshore (deltaic-non deltaic) deposits often rich in molluscan assemblages (Manganelli, Spadini, & Martini, 2010).…”

“…The Siena Basin ('central' basin) (Brogi, 2011) was filled with about 1000 m of Miocene continental deposits unconformably overlain by about 600 m of Pliocene alluvial to shallow marine deposits (Costantini et al, 1982;Martini, Aldinucci, Foresi, Mazzei, & Sandrelli, 2011;Martini et al, 2013). The stratigraphic architecture of Pliocene deposits is relatively poorly known, except for some areas, recently investigated according to allostratigraphic and sequence-stratigraphic principles (Arragoni, Martini, & Sandrelli, 2012;Martini et al, 2011Martini et al, , 2013. Specifically, according to Martini et al (2011) the Pliocene deposits of the northern basin margin (alluvial-to-inner shelf marine sediments) are organized in four allostratigraphic units.…”