The Miocene successions of the Fiora Hills

43-CORNAMUSINI 404-424_GEOLOGIA 28/11/11 12.57 Pagina 404

43-R2 – CORNAMUSINI

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Ital.J.Geosci. (Boll.Soc.Geol.It.), Vol. 130, No. 3 (2011), pp. 404-424, 14 figs., 1 tab. (DOI: 10.3301/IJG.2011.17) © Società Geologica Italiana, Roma 2011

The Miocene successions of the Fiora Hills: considerations about the development of the minor basins of Southern Tuscany GIANLUCA CORNAMUSINI (*), (**), LUCA MARIA FORESI (*), GIOVANNI MASSA (**), FILIPPO BONCIANI (**), IVAN CALLEGARI (**), SIMONE DA PRATO (***) & ALESSANDRO IELPI (*)

ABSTRACT The Miocene sequences of Southern Tuscany represent the first post-nappe sedimentary record of the Northern Apennines, and are linked with the opening of the Tyrrhenian Sea. The sequences are located in several basins, characterizing the hinterland of the orogen. They are settled on a stack that is composed of deformed tectonic units and are capped by Plio-Pleistocene deposits. The respective basins have been strongly controlled by tectonics, which have remarkably forced the sedimentation. The Fiora Hills represent the southernmost area of Tuscany, where there are some minor but significant examples of these basins. In particular, they are the Fiora and the Tafone basins, the infillings of which are characterized by Miocene successions subdivided into several depositional units separated by unconformity or correlative conformity surfaces. This study deals with the stratigraphic features of such Miocene basinal infillings, with the aim being to define the depositional architecture and the tectonic-sedimentation interplays. Moreover, the collected data also enables there to be a discussion of some of the aspects of the basins’ structuring that are linked with the Miocene evolution of the hinterland of the Northern Apennines. The entire Miocene succession of the Fiora Hills spans from the Langhian up to the late Messinian, with there being minor differences between the Fiora-Tafone basins and with the nearby Albegna Basin. In general, we recognize: the basal Ponsano P Unit (middle Miocene), which is referable to coastal-shallow marine environment; the Lignitiferous T Unit (late Tortonian-early Messinian), which is referable to fan-delta and lacustrine systems; the Acquabona-Spicchiaiola M1 Unit (early Messinian), which is referable to lagoonal fan-deltaic environment; the Castelnuovo M2 Unit (early Messinian), which is referable to shallow marine environment; and the “LagoMare” M3 Unit (late Messinian), which is referable to fan-deltaic lacustrine systems. The Miocene succession is overlaid by PlioPleistocene marine to continental succession. The Miocene basins have settled on deformed Ligurian allochthonous units, which are markedly structured in tectonic depressions and highs and coherently so with the “crustal lateral segmentation” model. The development of the Miocene sedimentation in this sector of the chain appears to be strictly connected to the tectonic evolution of the Tyrrhenian Sea rifting. The middle Miocene deposits may in fact be related to the first syn-rift shallow-marine basins, marking the beginning of the post-nappe phase. During late Tortonian-early Messinian, important lacustrine-fan-delta systems dominated in the basins and represented the development of the middle Miocene stages. They evolved during the early Messinian in lagoonal fandeltaic systems and then in shallow-marine systems. The transition to the upper Messinian deposits is marked by a significant unconformity, which is marked locally by angularity, thus noting an intramessinian deformative episode. This characterizes the lacu-

(*) Dipartimento di Scienze della Terra, Università degli Studi di Siena, Via Laterina, 8 - 53100 Siena. Corresponding author: Gianluca Cornamusini, e-mail: [email protected] (**) Centro di Geotecnologie, Università degli Studi di Siena, Via Vetri Vecchi, 34 - 52027 San Giovanni V.no (AR). (***) CNR-IGG Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse di Pisa, Via G. Moruzzi, 1 - 56124 Pisa (Italia).

strine fan-deltaic systems that are linked to the Messinian salinity crisis for the paleo-Mediterranean Sea. The stratigraphic differences between the Fiora Hills’ basins are therefore linked to the somewhat different basinal sedimentary evolution, which is connected to the development of morphological/tectonic ridges.

KEY WORDS: Stratigraphy, basin evolution, Fiora Hills, Southern Tuscany, Miocene.

INTRODUCTION

In the Northern Apennines hinterland framework, the post-nappe deposition began between the early Miocene (inner sectors, Marina del Marchese Fm., Pianosa Island) and the middle Miocene (Southern Tuscany), and then developed between the late Miocene and the Pleistocene (BOSSIO et alii, 1993; CARMIGNANI et alii, 1995). Nowadays, the middle to the upper Miocene sequences crop out in the hinterland sector in some areas of Central and Southern Tuscany, such as the Fiora Hills (which are the subject of this paper). The Fiora Hills’ Miocene deposits (southernmost Tuscany) are organized in small basins which are filled by somewhat different successions, like in the Tafone and Fiora basins (fig. 1). Such successions are composed of several depositional units that lie unconformably above deformed units of the apenninic orogenic stack; they are in turn unconformably covered by Plio-Pleistocene deposits. This study outlines the main stratigraphic and architectural features of these successions, with particular focus on the relationships between Miocene deposits and both the pre-Neogene bedrock and the overlying PlioPleistocene sequences. The aim is to define the stratigraphic architecture and tectonic-sedimentation interplays of the Fiora and Tafone basins. The age constraints of the mapped units are inferred from the literature, regional context, neighbouring basins and original data. Meanwhile, acquired data further enables a brief discussion of some of the aspects of: the “serie ridotta” Auctt. (DECANDIA et alii, 1993) development; the occurrence of folding structures in the Miocene deposits; and, more generally, the geodynamic significance of the middle Miocene deposits in the Neogene depositional evolution of the Northern Apennines hinterland. Finally, the revision of the Fiora Hills Miocene and the comparison with the successions of the nearby Albegna Basin (BOSSIO et alii, 2003-2004) will improve the knowledge of the Miocene basins of the Northern Apennines’ southern hinterland.


THE MIOCENE SUCCESSIONS OF THE FIORA HILLS

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Fig. 1 - a) Location sketch of the study area (square), with on evidence the Middle Tuscan Ridge and the Lower-Middle Miocene outcrops, which are Pianosa Island, Ponsano, Rencine and Fiora Hills; b) Simplified geological sketch of the southern Tuscany ranging from Grosseto to Montalto di Castro; the study area is represented inside the black line.

GEOLOGICAL OUTLINES

The hinterland Miocene sequences of the Northern Apennines are characterized by different stratigraphies that are strongly influenced by the tectonic evolution of the basins. Such basins have been regarded as originating and developing in an extensional tectonic regime that is attributed to the eastwards shifting of the orogenic compressional and Tyrrhenian rift systems (MARTINI & SAGRI, 1993; CARMIGNANI et alii, 1995; JOLIVET et alii, 1998; BRUNET et alii, 2000). In contrast, some authors (BOCCALETTI & SANI, 1998; BOCCALETTI et alii, 1999; BONINI et alii, 2001; SANI et alii, 2009) hypothesized the basin development as the expression of a compressive regime, characterized by thrust-top systems with very few minor extensional episodes (BERNINI et alii, 1990). Moreover, the character of the middle Miocene successions is still debatable, since they have been regarded as syncollisional thrust-top deposits (described as epiligurian in BALDACCI et alii, 1967; MARTINI et alii, 1995), or alternatively as the basal portion of the post-collisional depositional cycle (CARMIGNANI et alii, 1995; BROGI, 2004a; BONCIANI et alii, 2005) and named as “Neoautochthonous cycle” (BOSSIO et alii, 1993 cum. bib.). These

successions mark the start of the post-nappe/syn-rift deposition (PASCUCCI et alii, 1999), which began during the early-middle Miocene for the Tyrrhenian area (CARMIGNANI et alii, 1994, 1995; JOLIVET et alii, 1998; PASCUCCI et alii, 1999). The Fiora Hills are characterized by NNW-SSE orientated ridges, which separate small sedimentary basins (fig. 1) where pre-Miocene deformed units crop out (see also BETTELLI, 1985). These units are stacked in a tectonic-orogenic pile which goes upwards from the bottom as follows: the Monticiano-Roccastrada Unit; the Tuscan Nappe; and the S. Fiora-Morello Unit. The Monticiano-Roccastrada Unit represents the basal tectonic element and consists of metamorphic upper Permianmiddle Triassic formations of the Tuscan Domain (LAZZAROTTO et alii, 2003). The Tuscan Nappe is a deformed, non-metamorphic Tuscan Domain tectonic unit which, in the study area, is represented only by its youngest (Macigno or Scaglia Toscana fms, Eocene to Late Oligocene in age) and its oldest formations (Cavernoso Limestone Fm., Late Triassic in age). The uppermost S. Fiora-Morello Unit is a strongly allochthonous nappe derived from the deformation of the oceanic External Ligurian Domain. It is represented in the area by the Santa Fiora and Pietraforte formations (Cretaceous),


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Fig. 2 - Stratigraphic panel showing the organization of the Miocene-Pleistocene successions in the entire Southern Tuscany, Albegna Basin, Fiora Basin and Tafone Basin.

which characterize the substratum of the Miocene postcollisional succession. This orogenic stack was successively dissected by different generations of extensional structures. Firstly, it was strongly forced by ramp-flat-ramp low-angle detachments (LANF sensu COLLETTINI et alii, 2006), which involved a strong crustal delamination (“serie ridotta” Auctt.), and then by the direct imposition of higher terms of the orogenic stack directly onto the lowermost terms (LAVECCHIA et alii, 1984; BERTINI et alii, 1991; DECANDIA et alii, 1993), thus forming a megaboudinage-style crustal structuring (GIANNINI et alii, 1971; BROGI, 2004a,b) or a generalized lateral segmentation (BROGI & LIOTTA, 2008 cum. bib.). Such a typical setting consists of isolated Tuscan Nappe cores (megaboudins or extensional horses in BROGI, 2008) which are interposed between markedly thinned sectors where the Ligurian units have been carried onto the lower terms by tectonic ramps (extensional duplex of BROGI, et alii, 2003; BONCIANI et alii, 2005; BROGI, 2008). The tectonic event responsible for such a setting has been identified by BROGI et alli (2005) as the early-middle Miocene D2 event, and has been linked with the beginning of the post-nappe orogenic collapse (CARMIGNANI et alii, 1994, 1995) through the development of large east-dipping detachments (DALLMEYER & LIOTTA, 1998; BROGI & LIOTTA, 2008). Furthermore, according to BROGI (2004a), BONCIANI et alii (2005), and BROGI et alii (2005),

the structural and morphological deeps set by the LANFs corresponded with the middle Miocene basins, which would have begun their development as bowl-shaped structures (BROGI, 2011) settled onto the hanging wall of extensional detachments (hanging wall basin of MCCLAY, 1990, see also in BROGI & LIOTTA, 2008). Furthermore, the low-angle extension developed diachronously from west to east, as demonstrated by the age of the deposits (middle-late Burdigalian up to Serravallian-early Tortonian). Alternatively, FINETTI et alii (2001) and PERTUSATI et alii (2004) proposed a different model, dominated by out-of-sequence cover thrusting and pinch-and-swells in a compressive context. Following on from this, from the late Miocene up to the Pleistocene (DECANDIA et alii, 1993; BONCIANI et alii, 2005), middle to high-angle normal faults dissected all of the earlier setting. BOSSIO et alii (1998) and LAZZAROTTO et alii (2002) subdivided the entire post-nappe sequence of Southern Tuscany into several stratigraphic-depositional units (fig. 2) bounded by unconformities and correlative-conformities. The middle-upper Miocene basal succession (Ponsano Unit) crops out in Central to Southern Tuscany in only a few restricted areas (fig. 1). This unit consists of shallow marine sandstones, which lie unconformably on the Ligurian units. It has been referred to the middle-late Burdigalian in the western offshore Pianosa Island (COLANTONI



& BORSETTI, 1973; BOSSIO et alii, 2000; FORESI et alii, 2000) and to the Serravallian-early Tortonian in its onshore easternmost outcrops (MAZZEI et alii, 1981; FORESI et alii, 1997; BOSSIO et alii, 2000-2001; FORESI et alii, 2003; COSTANTINI et alii, 2009), thus emphasizing a diachronous transgression. In the regional framework (LAZZAROTTO et alii, 2002; COSTANTINI et alii, 2009), the Ponsano Unit is unconformably covered by the Lignitiferous T Unit (alluvial fandeltas and lacustrine environment deposits, late Tortonian-earliest Messinian in age), passing upwards to the Acquabona-Spicchiaiola M1 and Castelnuovo M2 units (these are lacking eastwards to the Middle Tuscan Ridge, BOSSIO et alii, 1993, 1998), which are referred respectively to lagoonal and shallow marine environment deposits that are early Messinian in age. Moving upwards, the “Lago-Mare” M3 Unit, which lies on the M2 unit due to an unconformity, consists of evaporite-lacustrine deposits which refer to the late Messinian Mediterranean salinity crisis. The Miocene succession is then unconformably covered by the marine Pliocene I Unit and the alluvial Pleistocene Q2 Unit.

MAIN STRUCTURAL FEATURES OF THE NEOGENE BASINS OF THE FIORA HILLS

The post-collisional sedimentary basins that formed during post-collisional phases in the Fiora Hills are (fig. 1): the Albegna, the Fiora, the San Martino sul Fiora and the southern Tafone. These basins are structured to form a NNW-SSE basin-and-ridge complex, which is bounded to the north by the transversal (WSW-ENE) Pliocene Albegna Basin. This is characterized by a set of tectonic lines which, according to PASQUARÈ et alii (1983), ZANCHI & TOZZI (1987) and TOZZI & ZANCHI (1991), outlines a transtensive system linked with the main transversal lines of the Northern Apennines orogen (GHELARDONI, 1965; PASCUCCI et alii, 2007). The Fiora and Tafone basins are separated by the “transversal” WSW-ENE orientated Argentario-MancianoPoggio al Corno Ridge (fig. 1) and represent good examples to explain the post-collisional evolution of the Fiora Hills area. This ridge corresponds to an important lowangle detachment which, with the exposure of the lowermost terms of the orogenic stack (Monticiano-Roccastrada Unit, fig. 3), emphasizes the uplift of the southern section at the footwall. The Fiora Basin (12 km long, 5 km wide) is bounded to the north, through a NE-SW normal fault, by the Pliocene Albegna Basin. Eastwards it is delimited by the Quaternary Vulsini Mts. Volcanites, southwards from the Palaeozoic-Triassic bedrock forming the Argentario-Manciano-Poggio al Corno Ridge, and westwards from the Manciano Ridge. In this latter case, the Miocene deposits lie unconformably on Ligurian formations, representing the hanging-wall of an east-dipping LANF (close to Poggio dei Prati) which has Tuscan Nappe formations at the footwall (fig. 3). The respective basinal infilling is structured in two gentle NNW-SSE synformal folds, separated by NNW-SSE normal faults (fig. 4). The Tafone Basin is located south of the ArgentarioManciano-Poggio al Corno Ridge and now constitutes a narrow (10 km long, 2 km wide) depression that is linked southwards with the wider Tarquinia Basin. The basin is

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bounded by normal faults on both the eastern and western sides (figs. 3 and 4). Meanwhile, the Mt. Maggiore and Mt. Bellino ridges are characterized by outcrops of the Monticiano-Roccastrada Unit and the Cavernoso Limestone Fm., and are capped by the Ligurian S. Fiora-Morello Unit, which represents the stratigraphic substratum of the Miocene Tafone succession. This has also been confirmed by several unpublished industrial mining drilling reports (obtained between the 1950s and 1970s). These documents reveal that some tens of metres of Miocene deposits in the central part of the Tafone Valley are lying on 20-200 metres of Ligurian Unit, which is in turn lying on 5-35 metres of the Cavernoso Limestone Fm. or, less frequently, directly on the metamorphic formations. The low-angle detachment at the base of the Ligurian Unit dips towards the east, close to the western border of the basin, and is cut by high-angle normal faults (figs. 3 and 4). The Miocene basinal infilling, which lies at the hanging-wall of the LANF, is gently deformed to form a NNW-SSE orientated syncline (fig. 4), while the Pliocene-Pleistocene succession is not folded. Moreover, minor folding structures involving the T-M1-M2 deposits occur locally on the eastern flank of the main basinal syncline, near the Roccaccia normal fault (Acqua Bianca Creek of fig. 3). These metre-scale overturned asymmetrical folds outline a SW-dipping cascade-fold envelope with SW vergence (towards the basinal centre). The Pleistocene deposits seal the Tafone and Roccaccia high-angle normal faults bounding the structural depression, which thus confines the same deposits.

STRATIGRAPHY OF THE NEOGENE SUCCESSION

The Fiora Hills Neogene succession has been subdivided into unconformity bounded units (depositional units in BOSSIO et alii, 1998, 2003-2004), with slightly stratigraphic differences between the two Tafone and Fiora basins. These are reported in figs. 2 and 5, and are compared with the nearby Albegna Basin. The Fiora Basin is characterized by (from the bottom, fig. 5): Manciano Sandstones Fm. (Ponsano P Unit); Fosso Bianco Clays and Poggio Piazza dei Tori Conglomerates (Lignitiferous T and Acquabona-Spicchiaiola M1 units); Monte Nero Conglomerates and Sandstones (“Lago Mare” M3 Unit); “Argille Azzurre” Fm. (Pliocene I Unit); Pleistocene Q2 Unit. The Tafone Basin is instead filled with (from the bottom, fig. 5): Torretta sul Fiora Conglomerates and Botro dell’Acqua Bianca Clays (Lignitiferous T, AcquabonaSpicchiaiola M1, Castelnuovo M2 units); Monte Nero Conglomerates and Sandstones (“Lago Mare” M3 Unit); “Argille Azzurre” Fm. (Pliocene I Unit); Valle del Tafone Conglomerates (Pleistocene Q2 Unit). PONSANO P UNIT Manciano Sandstones Fm. The Ponsano Unit occurs as Manciano Sandstones Fm. at the base of the Miocene infilling in the southern part of the Fiora Basin (fig. 3). It is not present in the Tafone Basin. It lies through a sharp, angular unconformity on the Santa Fiora Fm. (S. Fiora-Morello Unit), while it is


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Fig. 3 - Geological sketch map of the study area representing the lithostratigraphic units. h – mine anthropogenic deposits; b – Holocene alluvial-colluvial deposits; bn – Upper Pleistocene terraced alluvial-colluvial deposits; tr – Quaternary travertines; vul – Pleistocene volcanoclastic deposits; CVT – Tafone Valley Conglomerates (middle Pleistocene); FAA – “Argille Azzurre” Clays Fm. (early Pliocene); CMN – Monte Nero Conglomerates and Sandstones Fm. (late Messinian); ABA – Botro dell’Acqua Bianca Clays Fm. (early Messinian); ABAc – conglomerate-sandstone lithofacies of the Botro dell’Acqua Bianca Clays Fm.; CPT – Poggio Piazza dei Tori Conglomerates Fm. (late Tortonian-early Messinian); FOS – Fosso Bianco Clays Fm. (late Tortonian-early Messinian); CTF – Torretta sul Fiora Conglomerates (late Tortonian-early Messinian); AMN – Manciano Sandstones Fm. (Langhian-Serravallian); AMNa – conglomerate lithofacies of the Manciano Sandstones Fm.; FIA –Santa Fiora Fm. (late Cretaceous); PTF – Pietraforte (Cretaceous); MAC – Macigno (late Oligocene-basal Miocene); SCA – “Scaglia Toscana” Fm. (Cretaceous-Oligocene); CCA – Cavernoso Limestone Fm. (late Triassic); TOC – Tocchi Fm. (late Triassic); VER – Verruca Fm. (early-middle Triassic); CRP – Poggio al Carpino Sandstones Fm. (late Permian-?early Triassic). Fig. 3 is also available in the Digital Supplementary Material.


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Fig. 4 - Cross-sections for the Fiora Basin (A-A’ and B-B’) and for the Tafone Basin (C-C’ and D-D’).



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BOSSIO et alii (1998) have indicated a Langhian-Serravallian age for this formation, even though the age has been a matter of debate in the literature (GIANNINI, 1957; DESSAU et alii, 1972; MARTINI et alii, 1995; BARBIERI et alii, 2003). LIGNITIFEROUS T UNIT-ACQUABONA-SPICCHIAIOLA M1 UNITCASTELNUOVO M2 UNIT Herein, the T, M1 and M2 units are treated altogether as a complete succession; indeed, it is objectively difficult to separate these depositional units in the study area, since they are characterized by correlative conformities and smooth transitions (BOSSIO et alii, 1998), which is analogous to what was documented by BOSSIO et alii (2003-2004) for the Albegna Basin and by BOSSIO et alii (1998) for the Volterra Basin in Central Tuscany. Such a succession is lacking in the M2 Unit in the Fiora Basin, whereas it is complete in the Tafone Basin (fig. 2). In more detail: in the Fiora Basin, the T/M1 succession is comprised of Fosso Bianco Clays and Poggio Piazza dei Tori Conglomerates, ca. 200-300 metres thick; meanwhile, in the Tafone Basin, the base of the succession is represented by the Torretta sul Fiora Conglomerates, which lie above the Ligurian Unit. It also belongs to the T Unit and passes upwards to the Botro dell’Acqua Bianca Clays (M1/M2 units). The succession there is about 100-150 metres thick. Fosso Bianco Clays Fig. 5 - Schematic stratigraphy for the Fiora and Tafone basins. LIG – Ligurian units; AMN – Manciano Sandstones; FOS – Fosso Bianco Clays Fm.; CTF – Torretta sul Fiora Conglomerates Fm.; CPT – Poggio Piazza dei Tori Conglomerates Fm.; ABA – Botro dell’Acqua Bianca Clays Fm.; CMN – Monte Nero Conglomerates and Sandstones Fm.; FAA – “Argille Azzurre” Clays Fm; CVT – Tafone Valley Conglomerates.

unconformably covered by the Fosso Bianco Clays Fm. (Lignitiferous T Unit). It is composed of thick to very thick, strongly bioturbated strata of hybrid/mixed sandstones of medium to coarse grain-size. The strata are massive or have low to high-angle cross-laminated portions (both planar and trough crossed). They are also often amalgamated or have little-expressed stratification. Pebbles, with a good roundness and a mainly sphaerical shape, may occur as floating elements in the sandstone strata or as discrete polygenic beds. The latter are particularly common in the lower portion of the formation, framing typical matrix-supported basal lithofacies (AMNa of fig. 3). They are mainly derived from limestones (which often show lithofagus boring) and less from sandstones or ophiolites belonging to the Ligurian formations. The sandstones are mainly lithic arkose in composition (FONTANA, 1980), and made of fragments of igneous (granitoids), volcanic, metamorphic, ophiolitic and Ligurian-like calcareous parent-rocks, as well as relevant carbonate fragments. The fossil remains of echinoids (Scutella in particular, fig. 6a), lamellibranches (ostreids, pectinids), bryozoans, algal fragments and benthic foraminifers are diffused in the sandstones, whereas thin, sporadic sandy levels rich in complete ostreids and with various ichnofacies, such as Glossifungites, also occur (MARTINI et alii, 1995).

The Fosso Bianco Clays crop out widely in the Fiora Basin, but are not present in the Tafone Basin. They rest unconformably on the S. Fiora-Morello and Ponsano units (fig. 3). The Fosso Bianco Clays are composed of greybrownish, massive or laminated clays, with thin dark grey organic matter-rich levels and lens-shaped polygenic strata of conglomerates and fine to coarse sandstones. The frequency and thickness of the conglomerate strata increase upwards and also occur locally at the bottom. Decimetre-thick levels of brown-reddish siltstones and heavily laminated calcareous marls containing Bithynia opercula are also present. Samples FIO 1-4 (Manciano-Pitigliano road, NNE to P.gio Piazza dei Tori) were collected from the Fosso Bianco Clays (fig. 7), and highlighted the presence (tab. 1) of carbonized vegetal debris, abundant Bithynia opercula, Characeae oogonia, and immature ostracod valves of Candona sp. Samples FIO 6 and 8 (Manciano-Montenero road, W to P.gio Caprareccia) exclusively contain small reworked foraminifera (both benthic and planktic), which probably belonged to the Manciano Sandstones Fm. Meanwhile, samples FIO 12-19 were collected from the Mt. Nero and Bitorto Creek areas, where the Fosso Bianco Clays Fm. is characterized by a thin layer of alternate clays, silty clays and conglomerate strata. They contain rare Bithynia opercula, abundant Characeae oogonia and common ostracods (Cyprideis sp., Amnicythere sp. and Loxoconcha sp.); reworked benthic and planktic foraminifera are also common. Finally, samples FIO 20-22 (collected in the southernmost outcrops of P.gio Ornelleta) contain only ostracod remains, with Cyprideis sp. and Loxoconcha sp. identified therein.



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Fig. 6 - Features of the Miocene deposits of the Fiora Basin: a) massive sandstone facies of the Manciano Sandstones Fm. containing some rests of the echinoid Scutella; b) conglomerate, sandstone and mudstone beds of the Poggio Piazza dei Tori Conglomerates exposed along the Pitigliano-Manciano road; c) particular of the picture b, with on evidence conglomerate beds interlayered with very coarse sandstone, siltstone and clay beds; d) poorly organized conglomerates of the Monte Nero Conglomerates and Sandstones lying unconformably onto grey clays (on the right); e) particular of picture d, showing a poor pebble and cobble organization due to a light orientation and imbrication of these latter, arrows indicate clasts of the Manciano Sandstones; f) markedly disorganized lithofacies of the Monte Nero Conglomerates and Sandstones, with very poor sorting and very crude clast alignments.


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Fig. 7 - Synthetic stratigraphy of the Fiora Basin, relative to the Unit T-Unit M1, represented by the Fosso Bianco Clays and the Poggio Piazza dei Tori Conglomerates.

Fig. 8 - Synthetic stratigraphy of the Miocene succession of the Tafone Valley; the placement of the detailed stratigraphic logs of the fig. 11 is showed.

Poggio Piazza dei Tori Conglomerates

of fine limestones (prevailing), both carbonatic and quartz-rich sandstones, and cherts, all derived from Ligurian units and the Manciano Sandstones Fm. The upper part of the formation reveals a gradual increase in the rubefaction of both pebbles and matrix. The biostratigraphic samples collected from the thin interlaid siltstone-clay layers of the uppermost part were barren.

These conglomerates crop out extensively in the middle and southern Fiora Basin (fig. 3). With alternations from the underlying Fosso Bianco Clays, they gradually pass into thick conglomerate bodies, with a typical thickening-coarsening upwards trend (fig. 7). The formation is composed of heterometric and polygenic conglomerates (figs. 6b, c), and are well stratified and generally fairly cemented, with textures ranging from matrix-supported to clast-supported. The conglomerate strata are massive or reveal clinostratification and faint imbrications of elongated pebbles and inverse grading. Cut and fill structures and strata amalgamation also occur. The conglomerate strata sometimes grade upwards to sandstone and pebbly-sandstone, with trough-cross laminations and imbrications. The pebbles have a subsphaerical to a sub-flattened shape, a medium to high roundness and an average size of some cms. They consist

Torretta sul Fiora Conglomerates These conglomerates occur in the Tafone Basin as coarse-grained bodies lying at the base of the Miocene succession (fig. 8). They represent the Lignitiferous T Unit, moving upwards to the Botro dell’Acqua Bianca Clays (M1-M2 units of fig. 8). They are organized in 1-2 metres-thick, frequently amalgamated strata (fig. 9a), since the stratification is poorly expressed, especially in the lower portion. The strata thickness decreases



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TABLE 1 Taxa distribution (Ostracoda, benthic foraminifera and others) for the samples collected in the Miocene depositional units.

upwards, while the organization and the occurrence of finer granulometries (thin gravels and sands) increase. Strata with abundant sandy matrix have plane-parallel pebbly alignments. The thinner strata are tabular, while the thicker strata have a general lens-geometry. The latter are generally disorganized at the bottom and more structured in the upper parts, where they reveal imbrication, both planar parallel and crossed faint lamination, traction marks, both inverse and normal grading, and frequent erosional cuttings. Clast sizes range from a few mm to tens of cm and the texture is moderately matrix-supported and sometimes clast-supported. The roundness is generally high and the shape ranges from sphaerical to flattened. Both the clasts and the matrix have a reddish colouring, due to hematite coating. The pebbles are polygenic, with calcareous, arenaceous and carbonatic-arenaceous lithologies that are derived from Ligurian units and the Manciano Sandstones Fm. (fig. 10). This formation passes upwards into the Botro del l’Acqua Bianca Clays (fig. 8), with gradual contact through alternation and a fining upwards trend. Its thickness is about 15-20 metres. The matrix and the clay interlayers do not contain any fossils. Botro dell’Acqua Bianca Clays The Botro dell’Acqua Bianca Clays do not occur in the Fiora Basin (fig. 5), although they constitute most of the Tafone Miocene infilling, cropping out mainly in the cen-

tral Tafone Valley (fig. 3). They overlie (fig. 8) the Torretta sul Fiora Conglomerates conformably through a thinning-fining upwards trend, whereas they are overlaid unconformably by the upper Messinian Monte Nero Conglomerates and Sandstones and by the lower Pliocene “Argille Azzurre” Fm. This formation is characterized by massive or faintly laminated grey-blue, slightly marly clays and silty clays, with cm-thick dark bands. Centimetre-thick levels of brownish siltstone and sandstone also occur. Sometimes, particularly in the lower part of the formation, lens-shaped bodies of conglomerates and sandstones, up to 5-10 metres thick, are interlaid and have been mapped as conglomerate-arenaceous lithofacies (ABAc of fig. 3). The conglomerate strata range from 5-10 up to 80 cms thick, and are generally matrix-supported and well-cemented, with well-rounded and subsphaerical to discoidal shaped pebbles up to some centimetres in size. They also reveal both normal grading, with a sandstone or pebbly sandstone partition at the top (fig. 9b), and inverse grading (generally organized in some cm-thick traction bed sets). A faint plane-parallel to low-angle cross-lamination is also present and associated with the imbrication and alignment of the disc-shaped pebbles. The sandstone and pebbly sandstone (figs. 9c, d, e) beds may be either massive or structure-rich, with coarse cross-lamination revealing a similarity with sigmoidal or hummocky-type lamination. Strata are characterized by small and gentle ripples, with a SE to NW palaeoflow. Sometimes, faint bottom current structures (flute/groove casts) and load casts are also present.


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Fig. 9 - Features of the Miocene deposits of the Tafone Basin: a) polygenic conglomerates in lenticular amalgamated beds, belonging to the Torretta sul Fiora Conglomerates; in the upper bed a crude orientation of the pebbles is evident; b) overturned decimetre thick-bed, with graded conglomerate base and sandstone upper part, where prevailing Ligurian limestone pebbles can be observed; c) amalgamated multiple-beds level of pebbly sandstones with sub vertical overturned attitude (the arrow indicates the stratigraphic polarity) interlayered to gray clays and silts, belonging to the Botro dell’Acqua Bianca Clays; d) detail of the previous photo, the bed is subdivided in two part: the upper part (of the photo) is characterized by pebbles and granules and the lower part is arenaceous with coarse plane-parallel lamination (stratigraphic high, the arrow shows the stratigraphic polarity); e) 45° south-west dipping cross-laminated sandstone bed interlayered with clays of the upper part of the Botro dell’Acqua Bianca Clays, the arrow shows the polarity; f) massive gray clays with a level characterized by ostreid concentration, belonging to the Botro dell’Acqua Bianca Clays (the black line shows the boundary between the fossiliferous level and the clays; moreover the sub vertical attitude is shown).



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Fig. 10 - Conglomerate and sandstone petrofacies of the upper Miocene deposits (for the placement of some samples on the stratigraphic log, see fig. 11): 1) Microconglomerate (sample TAF 1) interlayered in the lower portion of the Botro dell’Acqua Bianca Clays Fm.: Lc carbonate lithoclasts, Ls siltstone fragment, Ar siliciclastic sandstone fragment with calcite cement; 2) Mixed/hybrid sandstone (sample TAF 10) belonging to the Botro dell’Acqua Bianca Clays Fm., with quartz-feldspar clasts and intrabasinal carbonate granules with abundant carbonate cement; 3) Very coarse sandstone-microrudite, with hybrid/mixed composition, containing siliciclasts, carbonate lithics and bioclasts (sample TAF 14 of Botro dell’Acqua Bianca Clays Fm.): La shale lithic, Ls siltstone fragment, Lc carbonate lithic; 4) Algae in mixed/hybrid microrudite (sample TAF 14 Botro dell’Acqua Bianca Clays Fm.); 5) Mixed/hybrid microrudite (sample TAF 14 Botro dell’Acqua Bianca Clays Fm.): Q quartz, Lc carbonate lithic, Lm carbonate micrite lithic, Lb basalt lithic (ophiolite); 6) Coarse sandstone with mixed/hybrid composition (sample TAF 19 Botro dell’Acqua Bianca Clays Fm.): Lm carbonate micrite lithic, Ls siltstone fragment.


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The sandstone and conglomerate compositions are quite similar. Furthermore, they are also more or less the same as the Torretta sul Fiora Conglomerates, with prevailing clasts of fine and marly limestone, siltstone and siliciclastic and mixed/hybrid sandstone (fig. 10), indicating that the Ligurian and Ponsano units are the major sources. The maximum thickness of the Botro dell’Acqua Bianca Clays Fm. is about 150 m; this estimate derives also by the industrial boreholes located to south of the Mt. Maggiore Ridge. The lower part of the formation (Unit M1 in fig. 8) contains (samples BC1 and BC3) rare foraminifers (figs. 8 and 11, tab. 1), such as Ammonia beccarii tepida and Cribroelphidium decipiens, and more common ostracods like Candona sp., Cyprideis cf. agrigentina., Loxoconchissa (Loxocaspia) cf. cosentinoi, Mediocytherideis (Sylvestra) posterobursa, Loxoconchissa (Loxocaspia) tuberosa, Amnicythere spp., and Loxoconcha sp., which characterize a lagoonal brackish environment. The middle part of the formation (Unit M2) contains plant debris and macrofossils, which sometimes lie in discrete horizons; Ostrea, which are also in nests (fig. 9f), Chlamys and other pectinids are common. Some of the samples collected from the clay levels of the middle part, reveal a rather rich and diversified microfossil content. More precisely, samples TAF 2, 4, 5 (fig. 11) and 25 contain assemblages (tab. 1) composed of: benthic Foraminifera (Ammonia beccarii beccarii, Ammonia beccarii tepida, Cribrononion punctatum, Cribroelphidium decipiens, Elphidium advenum, Nonion depressolum, and Protelphi dium granosum and not determined small miliolids); Ostracoda (Aurila albicans, A. cf. cicatricosa, Occlusacythereis simulans, Keijella lucida, Leptocythere sanmarinensis., Loxoconcha cf. punctatella, Neomonoceratina laskarevi Xestoleberis cf. communis, and X. reymenti); and abundant fragments of echinoids (TAF 4 and TAF 5) which are typical of a coastal marine environment. The upper part of the formation (Unit M2) (samples TAF 7 and TAF 9 of fig. 11) contains oligotypic assemblages composed of Ammonia beccarii tepida, Cyprideis cf. agrigentina and Candona sp., which are typical of a brackish environment. “LAGO-MARE” M3 UNIT Monte Nero Conglomerates and Sandstones The Monte Nero Conglomerates and Sandstones crop out in the northern area of the Fiora Basin (Mt. Cavallo, Poggio Caprareccia, Mt. Nerino and Mt. Nero of fig. 3) and in the southernmost part of the Tafone Basin (Cretoni). Their bottom is erosional and lies unconformably above the T-M1-M2 sequence (on the Fosso Bianco Clays in the northern sector; on the Poggio Piazza dei Tori Conglomerates in the central-southern sector of the Fiora Basin; and on the Botro dell’Acqua Bianca Clays in the southern sector of the Tafone Basin). The conglomerates are slightly cemented, with interlayered levels of sandstone and subordinate siltstone and clay. They are polygenic, disorganized and matrix-supported, with well developed hematite coatings on the clasts and matrix (fig. 6d).

Fig. 11 - Detailed stratigraphic logs of portion of the Botro dell’Acqua Bianca Clays, with sample levels. The stratigraphic location is shown in fig. 8.



The pebbles are mainly derived from Ligurian formations such as: limestones and sandstones (Palombini Shale Fm.); carbonate/hybrid sandstones (Pietraforte Fm.); greygreenish cherty limestones; cherts; carbonate/siliciclastic micro-rudites (“Cicerchina” Auctt., coarsest lithofacies of the Pietraforte Fm.); and bioclastic/siliciclastic calcarenites (Manciano Sandstones Fm.) (fig. 6e). The rare conglomerate/breccia pebbles seem to be derived from upper Miocene formations. The conglomerate amalgamated strata and strata-set (each some metres thick) show an upwards increase in textural organization and a decrease in grain-size up to the sandstone or pebbly sandstone portions (fig. 12). The lower part of each stratum is characterized by the occurrence of heterometric pebbles and cobbles with abundant sandy matrix. The clasts range from 10 cm up to a maximum of 50 cm (very rare). They are also well rounded and the large examples have a sphaerical-subsphaerical shape, whereas the smaller pebbles have both a sphaerical and sub-flattened shape, with a clear imbricate fabric. The upper part of each stratum is instead marked by finer granulometries and prevailing sub-flattened pebbles, creating an overall, major textural maturity (primarily expressed by a clear imbrication fabric). Lens-shaped, coarse sandy and fine gravelly interlays are more frequent, and are well-cemented and coated in a reddish hematite film. These interlays are associated with darkreddish, sandy-clayey paleo-soils. Such strata-sets, occurring in the lower and upper parts of the column of fig. 11, are interlaid with several metres-thick horizons of conglomerates which are characterized by an even higher chaoticity (fig. 12), with up to one metre large boulders, a higher content of clayeysandy matrix, higher chaoticity and a very marked oxidation coating (intermediate part of the column of fig. 12). The stratification is not expressed and the pebbles are generally well-rounded (with sporadic sub-angular elements) but moderately sphaerical (fig. 6f). Erosional surfaces, bounding different bodies, are commonplace. The composition is very similar to the other deposits of the formation, even if they tend to be monogenic, with a prevalence of Palombini Shales Fm.-like arenaceous pebbles and cobbles. All of the micropaleontological samples collected from the rare, fine sediments are barren. PLIOCENE I UNIT The Pliocene I Unit is represented in the study area by the “Argille Azzurre” Fm., which crops out into the southern Tafone Valley, where it rests unconformably on the Botro dell’Acqua Bianca Clays Fm. It also crops out into the northern margin of the Fiora Basin, and constitutes the major depositional unit of the Pliocene Albegna Basin (BOSSIO et alii, 2003-2004). The “Argille Azzurre” Fm. is composed of massive grey-bluish clays and slightly marly clays, with common gastropods and lamellibranches (ostreids and pectinids). Rarely, thin clayey-silty and clayey-sandy beds may also

Fig. 12 - Stratigraphic column of the Monte Nero Conglomerates and Sandstones, close to the Mt. Nero. The succession is subdivided in three portions, the lower and upper parts are related to moderately organized conglomerate lithofacies, whereas the intermediate one is referable to an highly disorganized paraconglomerate lithofacies.

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Fig. 13 - Tectonic scheme showing the “serie ridotta” Auctt. or lateral segmentation setting for the Fiora Hills, as detectable through geological map (fig. 3) and cross-sections (fig. 4). Thicker lines indicate ramp-flat-ramp east-dipping detachments, while the Tuscan Nappe cores are like extensional horses (after BROGI 2004b, 2008; BONCIANI et alii, 2005).

occur. The few biostratigraphic samples collected from the unit are characterized by the high content of both the planktic and benthic specimens (with plankton > benthos), thus confirming the Early Pliocene age, as reported by FREGNI et alii (1985) and DESSAU et alii (1972), who recognized the G. margaritae and the G. puncticulata-G. margaritae foraminiferal biozones of IACCARINO & SALVATORINI (1982) and IACCARINO (1985). In terms of our data, the assemblages from sample TAF 23 seem to refer to the G. puncticulata Biozone, as indicated by the occurrence of abundant specimens of the nominal marker and the absence of Globorotalia margaritae.

faults bounding the Tafone Valley (both the eastern and western sides), and are always proximal to strong mi neralization areas (stibine mines). To take in consideration the stratigraphic framework and the quotes of the outcrops, the eastern travertines (close to the Fattoria di Montauto, ranging from 110 to 160 metres asl) may be referred to the middle-late Pleistocene (analougously to the northernmore travertines of Poggio al Corno Ridge and Stellata Creek, 250-300 metres asl of elevation) and the western outcrops (close to the Tafone Creek, 90-95 metres asl) to the Holocene (analougously to those of the Fiora River, close to the Bianco Creek confluence, 130 metres asl of elevation).

PLEISTOCENE Q2 UNIT The Pleistocene deposits mark the entire Tafone Valley, and are composed of a 10-20 metre thick succession lying unconformably above the older successions and matching the Valle del Tafone Conglomerate Fm. DESSAU et alii (1972) described them as “Alluvioni antiche terrazzate” (old terraced alluvial deposits) and generically dated them to the Quaternary. This Q2 Unit is formed by polygenic conglomerates with sandy and pebbly-sandy interlays. The conglomerates are matrix-supported, poorly cemented and very heterometric, commonly without an organized structure. The clasts have a maximum size of some decimetres, medium to poor rounding, and are of variable shapes (sub-equant/disc-shaped/stick). They also have a different composition, which varies from abundant quartzites and phyllites to minor limestones and sandstones, indicating a prevailing provenance from the Monticiano-Roccastrada Unit and less from non-metamorphic units. Both the clasts and the matrix have a dark reddish oxidation coating. Stratification is very poorly expressed and masked by frequent erosive structures and amalgamation surfaces, whereas volcano-clastic layers, derived from the Latera Volcanic Complex (320-240 ka in BARBERI et alii, 1994), occur in some outcrops. Accor dingly, an ?early-middle Pleistocene age can be extended to the entire unit. Their elevation ranges from about 240 m asl close to the Roccaccia fault to about 150 m asl close to the Tafone Creek, respectively on the eastern and western sides of the Tafone Valley; southward their elevation is about 100 metres asl. Furthermore, more recent deposits also occur (fig. 3), such as alluvial sequences, travertines and volcaniclastites. The travertines are located near to the master

DISCUSSION

CONSIDERATIONS

ABOUT THE TECTONIC LATERAL SEGMEN-

TATION AND SIGNIFICANCE OF THE MIDDLE

MIOCENE

DEPOSITS

A number of insights about the “serie ridotta” Auctt. structure, which is best expressed in the Fiora Hills, come to light when considering the amount of data collected during this study (fig. 13). Indeed, how the stratigraphic and structural settings of the Fiora Hills have been strongly forced by crustal delamination, thus developing the Miocene basins, has been verified. In the particular context of the Fiora Basin, the entire Miocene succession lies above Ligurian units which, by way of low-angle detachments, rest on Triassic evaporites and Monticiano-Roccastrada Unit. According to the BROGI & LIOTTA (2008) model, the Poggio dei Prati LANF (southwestern side of the Fiora Basin, fig. 3), which bounds the Ligurian units, Miocene deposits (roof-wall), and Tuscan Nappe (foot-wall), may correspond to an eastdipping ramp of the Fiora Basin. The southern sector of the study area (Tafone Basin) is delimited to the north (Fiora Basin) by a large, lowangle detachment ramp (south of Pelagone creek, fig. 3) which, more or less, corresponds with the ArgentarioManciano-Poggio al Corno Ridge (figs. 1, 3). This detachment separates two areas with differential crustal delamination: a northern area at the hanging-wall, corresponding to the Fiora Basin where Ligurian units lie on Tuscan Nappe and Cavernoso Limestone formations



(fig. 4); and a southern area at the footwall, corresponding with the Tafone Basin, where Ligurian units lie also on older and lower terms of the Monticiano-Roccastrada Unit (figs. 3, 4). The substratum of the Miocene Tafone Basin is cha racterized by a strong stratigraphic omission, with very well expressed “serie ridotta” from the direct overlying of the Ligurian units onto the Cavernoso Limestone Fm. or the metamorphic formations of the Monticiano-Roccastrada Unit. The LANFs responsible for this setting (a LANF crops out close to the Tafone Creek) have been later dissected by high-angle normal faults. As already pointed out by a number of authors (BROGI, 2004a, 2011; BONCIANI et alii, 2005; BROGI & LIOTTA, 2008) for other areas of Southern Tuscany, this evidence emphasizes the close connection between the structuration of the “serie ridotta” (extensional-lateral segmentation phenomena) and the Miocene basins, with their relative sedimentary infilling. This is particularly clear for the Ponsano Unit deposits, which were previously described as “epiligurian”, because of their attitude and stratigraphic setting. These aspects are well-expressed in the southern Fiora Basin, where the Manciano Sandstones Fm. lies unconformably on the S. Fiora-Morello Unit along the flat surface of maximum delamination of the P.gio dei Prati LANF, thus determining its superimposition onto the Cavernoso Limestone Fm. and the Monticiano-Roccastrada Unit. On the basis of these premises, the geodynamical context suggested herein for the Ponsano Unit in the study area is relative to a shallow extensional basin developed in the first rifting phases of the orogenic hinterland and linked with the lateral tectonics segmentation (BONCIANI et alii, 2005; BROGI et alii, 2005). In such a context, the Manciano Sandstones may have been laid in a structural depression corresponding with a flat surface of maximum delamination (see in BONCIANI et alii, 2005). LATE MIOCENE FOLDING STRUCTURES Folding structures involving Miocene sediments are not very common for the hinterland of the Northern Apennines. Their limited occurrence has been used by different authors to demonstrate two opposing geodynamic models (see chapter on Geological Outlines). A wide discussion of the structural style of the entire Tuscan post-nappe sequence is beyond the scope of this paper, even if some comments can be made about the folding structures detected in the study area. The other Miocene basins of Tuscany in which folding structures are better expressed are: the Casino Basin (north of Siena, LAZZAROTTO & SANDRELLI, 1977; BOSSIO et alii, 2000-2001); the Radicondoli Basin (west of Siena, BONINI et alii, 1994; BONINI & MORATTI, 1995; MORATTI & BONINI, 1998; BROGI & LIOTTA, 2008); and the Velona Basin (north of Mt. Amiata, BONINI et alii, 1999). In the Fiora Hills, both the infilling successions of the Fiora and Tafone basins are structured in gentle synclines, while meso-scale folds also occur in the latter. So: (a) the Miocene deposits stand over strongly delaminated crustal sectors and then probably recorded lateral segmentation and extensional tectonics before and during the late Miocene; (b) the Miocene P, T-M1 and M2 depositional units are involved in broad and gentle synformal

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NNW-SSE orientated folds. The latter are parallel to and superimposed above deep lateral segmentation structures. The development of such synforms may be related to: (i) passive extensional processes where the hanging wall block moves over a ramp-flat geometry fault (TWISS & MOORES, 1992); (ii) a late Messinian compressional pulse (in agreement with PASQUARÈ et alii, 1983), since the M3 Unit shows little or no folding evidence (as for the Radicondoli Basin, BONINI et alii, 1994); (iii) a Messinian transpression linked with the development of major transversal tectonic lines (Albegna Line, PASCUCCI et alii, 2007) and the Pliocene Albegna Basin. In a similar way, the Miocene of both the Radicondoli and Casino basins, which are located between two major transversal lines (Piombino-Faenza to the north and Arbia-Marecchia to the south; PASCUCCI et alii, 2007 cum. bib.), contains remarkable folding structures; and (c) the west-verging cascade meso-scale folds of the Tafone Basin are located on the eastern border and dip towards the depocentre, involving the T-M1-M2 succession. They are very similar to the folding structures of the Miocene Radicondoli (BONINI et alii, 1994; BROGI & LIOTTA, 2008) and Casino deposits (LAZZAROTTO & SANDRELLI, 1977; BOSSIO et alii, 2000-2001). This latter folding style is related in this study to gravity-driven phenomena (LAZZAROTTO & SANDRELLI, 1977; BROGI & LIOTTA, 2008), which were probably triggered by the major synformal structuring that may have easily deformed the soft upper Tortonian-lower Messinian deposits. PALEOENVIRONMENTAL AND BASIN EVOLUTION During the middle Miocene, the lateral segmentation (BROGI & LIOTTA, 2008 cum. bib.), the activity of the eastdipping LANFs (BROGI et alii, 2003; BROGI 2008) and the consequent crustal delamination caused the development of morphological-structural depressions occupied by narrow, shallow marine basins (fig. 14a). Such basins, lying above Ligurian units, are probably linked to the late Burdigalian-Langhian transgression, which involved the entire northern-apenninic hinterland (BOSSIO et alii, 2000). According to PASCUCCI et alii (1999), these bowlshaped basins are a typical expression of the Tyrrhenian pre-syn-rift phase; thick shallow water successions (Manciano Sandstones Fm.) settled down with the development of wave-dominated tidally-influenced barred shorefaces (MARTINI et alii, 1995), while close, coarse fan-delta systems were sourced from Ligurian rocks. Following on from this, the Serravallian-Tortonian boundary records a regression (and emersion) in both the study area and all of Western Tuscany, with the consequent partial erosion of the Manciano Sandstones. The regression was mainly driven by the tectonic evolution of the area, but climatic eustasy may also have contributed. In fact, HAQ et alii (1987) record a sea level fall in the late Serravallian, with a sharp shift just at the SerravallianTortonian boundary, while a cold-climate phase is also recorded in the early Tortonian (BARRON et alii, 1991; MILLER & SUGARMAN, 1995). The further development of the lateral segmentation processes caused a general basinal deepening in the late Tortonian-early Messinian. According to some authors (BALDI et alii, 1994; DECANDIA et alii, 2001; BONCIANI et alii, 2005), a series of middle- to high-angle normal faults may have dissected the earlier LANFs’ framework. The


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Fig. 14 - Hypothesized palaeogeographic cartoons for the Fiora Hills during Miocene-Early Pliocene.

sedimentary expression is, in any event, the establishment of the late Tortonian freshwater basinal system, with the deposition of the Lignitiferous T Unit (fig. 14b), which may have partially occupied the former middle Miocene depressions. Accordingly, the T-M1-M2 units’ succession represents the sedimentary infilling that is relative to the development of the basins during the late Tortonian-early Messinian (LAZZAROTTO et alii, 2002). The older formation of such a succession for the Fiora Basin is represented by the Fosso Bianco Clays. On the basis of the lithology and microfossil content, these clays are referred to a freshwater-mesohaline environment that both characterizes the regional Lignitiferous Unit (BOSSIO et alii, 1998) and is correlatable with the Torrente Fosci Clays of the Volterra Basin (LAZZAROTTO et alii, 2002), late Tortonian-early Messinian in age (BOSSIO et alii, 1978). The major upwards occurrence of coarser deposits (Poggio Piazza dei Tori Conglomerates) for the Fiora Basin is linked with the development of fan-delta systems (NEMEC & STEEL, 1988; WESCOTT & ETHRIDGE, 1990; GAWTHORPE & LEEDER, 2000) fed by the Ligurian/Ponsano unit rocks. The environmental context is similar to that of the coeval deposits of the western-most Miocene Albegna Basin (BOSSIO et alii, 2003-2004), where a freshwater to brackish shift is recorded (even if the develop-

ment of fan-deltas in the latter is not significant). Accordingly, a first transgression (fig. 14c) has been recorded (freshwater to brackish shift), followed by an increase of clastic input, which involves a normal regression (fandelta progradation and alluvial fan establishment). In the particular context of the Tafone Basin, the T-M1-M2 succession has a clear thinning-fining upwards trend (fig. 8). A basal conglomeratic portion with sandstone interlays (Torretta sul Fiora Conglomerates) passes upwards into a mainly clayey succession (Botro dell’Acqua Bianca Clays), with interlaid conglomerates and sandstones. Considering the very scarce fossiliferous content of the Torretta sul Fiora Conglomerates, this may be due to continental freshwater conditions. The sedimentological features relate to massive processes, such as debris flows or hyper-concentrated flows (POSTMA & ROEP, 1985; MULDER & ALEXANDER, 2001), representing coarse fandelta facies associations (sensu WESCOTT & ETHRIDGE, 1990) within a small and narrow lacustrine basin (fig. 14b). In view of the paleo-flow indicators (pebbles imbrication), the main source area was probably located to the east of the basin, corresponding with Ligurian and Ponsano unit rocks. The lack of Tuscan-like clasts possibly indicates that the Tuscan Nappe was still un-exposed (or



outcropping far from the basinal area), and then confirms how the basins developed in morpho-structural depressions belonging to the lateral segmentation structuring. The micropaleontological content of the Botro dell’Acqua Bianca Clays records some changes in water salinity. The lower part of the unit (corresponding to the M1 Unit of BOSSIO et alii, 1998) is characterized by brackish water. Differently, the middle section is related to a very shallow marine environment and the upper part “returns” to brackish again. The middle and upper parts correspond to the M2 Unit. Unfortunately, the complete lack of marker planktic taxa prevents precise dating. Nonetheless, the Botro dell’Acqua Bianca Clays are the only pre Zanclean-post late Tortonian unit to contain fossils of marine environment. In the Tuscan hinterland, this condition is typical of the pre-evaporitic early Messinian age (BOSSIO et alii, 1996, 1998; RIFORGIATO et alii, 2008). This attribution is also confirmed by FREGNI et alii (1985), through the occurrence of typical ostracod assemblages, and by DESSAU et alii (1972) through benthic foraminiferal assemblages, including Bolivina dentellata and Bulimina echinata. We consider that the upper portion of the unit, which “returns” to a brackish environment during a period of continuous sedimentation, is the same age. It is interesting to note that the M2 Unit of the Tafone Basin, which represents the unique outcrop of such a unit on the outer part of the Middle Tuscan Ridge (fig. 1), has until now only been recognized on the inner sectors (BOSSIO et alii, 1998). The T-M1-M2 Tafone succession thus highlights a deepening upwards trend that is relatable to the Messinian transgression, namely a fan-deltas lacustrine system shifted into a brackish-lagoon and then shallow marine environments (figs. 14b, c). The salinity fluctuations for the Tafone Basin (from lagoonal to marine and back), may be related both to sea-level oscillations, the setting of littoral barriers linked with the deltaic activity, and then to the development of protected lagoons (see GALLOWAY, 1975; WESCOTT & ETHRIDGE, 1990). Already in this phase, the successions of the Albegna, Fiora and Tafone basins begin to be distinguished from each other, indicating the complexity of the basinal sy stem. In fact, the Albegna Basin also records a quite similar trend, since a lacustrine system interested by retrogradational fan-deltas turned into a restricted lagoonal environment, but without a proper marine transgression (BOSSIO et alii, 2003-2004). It is thus clear how the three basins of the Fiora Hills evolved differently during the late Tortonian-early Messinian (figs. 14b,c). Such differences may be related to (i) differential lateral segmentation developments (BROGI & LIOTTA, 2008) and/or (ii) the individuation of WSW-ENE ridges, such as the Argentario-Manciano Ridge separating the northern Fiora and Albegna basins from the southern Tafone and Tarquinia basins. During the late Messinian, the M3 Unit deposition began in conjunction with the Messinian salinity crisis. According to BROGI & LIOTTA (2008, cum. bib.), an extensional tectonic event marks this stage, while other authors (PASQUARÈ et alii, 1983; ZANCHI & TOZZI, 1987; BONINI & SANI, 2002 cum. bib.) assert that it instead corresponds to a compressional event. Meanwhile, the Monte Nero Conglomerates and Sandstones of the M3 Unit correspond to the Poggio Campana Conglomerates of BOSSIO et alii (2003-2004) for the Albegna Basin.

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The barren nature of the respective finer portions may suggest a continental freshwater environment. Taking into account the sedimentological characteristics, the depositional elements are typical of the coarse clastic systems (alluvial fan and lacustrine fan-deltas) that are fed mainly by Ligurian terms (fig. 14d), less by the Ponsano Units and barely by the T-M1 Unit (Poggio Piazza dei Tori Conglomerates). The depositional sequences, which reveal a gradual textural maturity and fining upward trends, may indicate subsequent switches from proximal to distal alluvial facies and the development of braided streams above the alluvial fan. The presence of paleo-soils and the significant oxidation probably recorded long periods of subaerial exposure. The strong chaotic setting of a notable fraction of the entire M3 Unit succession may in fact indicate the common occurrence of cohesive debris flows (BLAIR & MCPHERSON, 1994; LEEDER, 1999). Furthermore, the presence of interlayered proximal less organized and almost monogenic conglomerates, probably references the interplay of two different alluvial fans (GAWTHORPE & LEEDER, 2000; BRIDGE, 2006) connected with an alluvial plain: a wider and medium-distal fan draining Ligurian and fewer Miocene outcrops; and a minor, very proximal local system characterized by a scarce load, draining a restricted Palombini Shales Fm. outcropping area. The quite similar late Messinian depositional evolution of the Fiora and Albegna basins differs from that of the Tafone Basin. It is probable that the two northern basins were communicating (at least partially), while the southern Tafone Basin was isolated due to the uplifting Argentario-Manciano-Poggio al Corno Ridge. The next Pliocene I Unit marks a significant transgression in the entire Mediterranean (BOSSIO et alii, 1993, 1998), which in the study area is represented by an external shelf marine environment, as demonstrated by the good differentiation of the foraminiferal assemblages. Furthermore, another tectonic crisis generated highangle normal fault systems, thereby developing deep structural depressions (DECANDIA et alii, 1993) in the entire southern Tuscany sector. The stratigraphic architecture of the Pliocene I Unit differs completely from the setting of the Miocene units (PASQUARÈ et alii, 1983; ZANCHI & TOZZI, 1987; BOSSIO et alii, 2003-2004). In this study, this characteristic has been attributed, especially for the Albegna Basin, to the individuation of WSW-ENE orientated (ZANCHI & TOZZI, 1987; TOZZI & ZANCHI, 1991) transversal tectonic lines, such as the Albegna Line (PASCUCCI et alii, 2007). Moreover, these lines may have determined the development of transtensive basins (Albegna Basin in fig. 14e) and the coeval propagation of both transtensive and transpressional structures. From the early Pliocene, the entire study area experienced a generalized regression and then a final emersion (AMBROSETTI et alii, 1978; BARBERI et alii, 1994; BOSSIO et alii, 1998) that is linked with the activity of the high-angle normal faults which uplifted the Mt. Bellino Ridge. This was followed by (middle-upper Pliocene/early Pleistocene) the exhumation of the lower metamorphic terms of the Monticiano-Roccastrada Unit (on the basis of the regional thermo-chronological data from BALESTRIERI et alii, 2003). Such a strong uplift in the Tafone Valley involved the development of a clastic-dominated alluvial pattern, which drained the metamorphic terms of


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the Mt. Bellino Ridge preferentially. The respective alluvial braided system, with close, small alluvial fans near to the major eastern bounding fault, characterizes the Valle del Tafone Conglomerates, which unconformably cover all of the underlying units and are confined to the lower sectors of the morpho-structural depression. Moreover, both the occurrence of a lot of metamorphic clasts in the Valle del Tafone Conglomerates, which are totally lacking in the Miocene conglomeratic formations below, and their sealing of the high-angle Tafone Valley faults (Roccaccia and Tafone faults), permit further considerations to be made. Indeed, the age constraints for the exhumation of the metamorphic Mt. Bellino Ridge and the highangle normal fault main activity can be stated as being between the early-middle Pliocene (age subsequent to the herein “Argille Azzurre” Clays) and the early-middle Pleistocene (age prior to the sedimentation of the Valle del Tafone Conglomerates).

CONCLUDING REMARKS

The Miocene tectono-sedimentary evolution of the Fiora Hills is forced by the post-nappe interplays between the depositional patterns and tectonic events which characterize the inner Northern Apennines. The basin development is due to the effect of crustal thinning, which is linked to the lateral segmentation process (serie ridotta Auctt.), affecting the hinterland of the chain. This process started from the early-middle Miocene. The basins developed as bowl-shaped structural depressions, which were NNW-SSE orientated, and then settled onto Ligurian units and became deformed to set gentle synclines. Following on from this, and starting from the early Pliocene up to the Pleistocene, NNW-SSE orientated high-angle normal faults, along with WSW-ENE orientated transtensive faults, dissected the Miocene basins to develop PlioPleistocene basins. The Miocene successions infilling the Fiora and Tafone basins are similar, but with differences due to differential tectonic-morphological frameworks and the uplift of the transversal Argentario-Manciano-Poggio al Corno Ridge. In particular, the middle Miocene Manciano Sandstones of Unit P represent the first shallow-marine syn-rift deposits of the post-nappe basin system of the Northern Apennines hinterland. The sedimentation took again du ring the late Miocene, with the development of lacustrine settings with fan-delta systems sourced mainly by Ligurian units, then interested by the early Messinian marine transgression, which led to a brackish water paleoenvironment with huge fan-deltas for the Fiora Basin, and to a brackish-shallow marine paleoenvironment for the Tafone Basin. During the late Messinian, lacustrine and alluvial plains with alluvial fans developed, which was linked to the Mediterranean salinity crisis. The early Pliocene marks a new wide transgression, leading to shallowmarine conditions.

ELECTRONIC SUPPLEMENTARY MATERIAL This article contains supplementary material, which is available online to authorized users (DOI: 10.3301/IJG.2011.17).

ACKNOWLEDGMENTS Dr. Rudy Rossetto, who preliminarly approached to the geological mapping of part of the area is thanked. We are also grateful to Prof. Alessandro Bossio and Dr. Anna Maria Bambini for their support in the ostracods analysis. Moreover, we are indebted with the editor Prof. Sandro Conticelli and with Prof. Vincenzo Pascucci and an anonymous reviewer, for their critical reading of the manuscript. Sally-Ann Ross is thanked for language editing. Research funded by PAR 2006 - Università degli Studi di Siena, Resp. G. Cornamusini.

REFERENCES AMBROSETTI P., CARBONI M.G., CONTI M.A., COSTANTINI A., ESU D., GANDIN A., GIROTTI O., LAZZAROTTO A., MAZZANTI R., NICOSIA U., PARISI G. & SANDRELLI F. (1978) - Evoluzione paleogeografica e tettonica nei bacini tosco-umbro-laziali nel Pliocene e nel Pleistocene inferiore. Mem. Soc. Geol. It., 19, 573-580. BALDACCI F., ELTER P., GIANNINI E., GIGLIA G., LAZZAROTTO A., NARDI R. & TONGIORGI M. (1967) - Nuove osservazioni sul problema della Falda Toscana e sulla interpretazione dei Flysch arenacei tipo “Macigno” dell’Appennino settentrionale. Mem. Soc. Geol. It., 6 (2), 213-242. BALDI P., BERTINI G., CAMELI G.M., DECANDIA F.A., DINI I., LAZZAROTTO A. & LIOTTA D. (1994) - La tettonica distensiva post-collisionale nell’area geotermica di Larderello (Toscana meridionale). Studi Geol. Camerti, Vol. spec., 1, 183-193. BALESTRIERI M.L., BERNET M., BRANDON M.T., PICOTTI V., REINERS P. & Z ATTIN M. (2003) - Pliocene and Pleistocene exhumation and uplift of two key areas of the Northern Apennines. Quat. Int., 101-102, 67-73. BARBERI F., BUONASORTE G., CIONI R., FIORDELISI A., FORESI L., IACCARINO S., LAURENZI M.A., SBRANA A., VERNIA L. & VILLA I.M. (1994) - Plio-Pleistocene geological evolution of the geothermal area of Tuscany and Latium. Mem. Desc. Carta Geol. d’It., 49, 77-134. BARBIERI M., CHIOCCHINI U. & MADONNA S. (2003) - Nuovi dati sull’età dell’Arenaria di Manciano (Miocene) sulla base dei valori di rapporto isotopico 87Sr/86Sr (Italia centrale). Boll. Soc. Geol. It., 122, 351-354. BARRON J.A., LARSEN B. & BALDAUF J.G. (1991) - Evidence for late Eocene to early Oligocene Antarctic glaciation and observations on Neogene glacial history of Antarctica. Results of Leg, 119. Proc. ODP, Sci. Results. College Station, Texas, 869-891. BERNINI M., BOCCALETTI M., MORATTI G., PAPANI G., SANI F. & TORELLI L. (1990) - Episodi compressivi neogenici-quaternari nell’area estensionale tirrenica nord-orientale. Dati in mare e a terra. Mem. Soc. Geol. It., 45, 577-589. BERTINI G., CAMELI G.M., COSTANTINI A., DECANDIA F.A., DI FILIPPO M., DINI I., ELTER F.M., LAZZAROTTO A., LIOTTA D., PANDELI E., SANDRELLI F. & TORO B. (1991) - Struttura geologica fra i monti di Campiglia e Rapolano Terme (Toscana meridionale): stato attuale delle conoscenze e problematiche. Studi Geologici Camerti, 1, 155-178. BETTELLI G. (1985) - Geologia delle alte valli dei fiumi Albegna e Fiora (Toscana meridionale). Geol. Rom., 24, 147-188. BLAIR T.C. & MCPHERSON J.G. (1994) - Alluvial fans and their distinction from rivers based on morphology, hydraulic processes, sedimentary processes, and facies assemblages. Journ. Sed. Res., A64 (3), 450-489. BOCCALETTI M. & SANI F. (1998) - Cover thrust reactivations related to internal basement involvement during Neogene-Quaternary evolution of the northern Apennines. Tectonics, 17, 112-130. BOCCALETTI M., BONINI M., MORATTI G. & SANI F. (1999) - Compressive Neogene-Quaternary tectonics in the hinterland area of the Northern Apennines. Journ. Petr. Geology, 22, 37-60. BONCIANI F., CALLEGARI I., CONTI P., CORNAMUSINI G. & CARMIGNANI L. (2005) - Neogene post-collisional evolution of the internal Apennines: insights from the upper Fiora and Albegna valleys (Mt. Amiata geothermal area, southern Tuscany). Boll. Soc. Geol. It., Vol. Spec., 3, 103-118.



BONINI M. & MORATTI G. (1995) - Evoluzione tettonica del bacino neogenico di Radicondoli-Volterra (Toscana meridionale). Boll. Soc. Geol. Ital., 114, 549-573. BONINI M. & SANI F. (2002) - Extension and compression in the Northern Apennines (Italy) hinterland: evidence from the Late Miocene-Pliocene Siena-Radicofani Basin and relation with the basement structures. Tectonics, 21 (3), 1-35. BONINI M., BOCCALETTI M., MORATTI G. & SANI F. (2001) - Neogene crustal shortening and basin evolution in Tuscany (northern Apennines). Ofioliti, 26, 275-286. BONINI M., CERRINA FERONI A., MARTINELLI P., MORATTI G., VALLERI G. & CERTINI L. (1994) - The intramessinian angular unconformity within the Radicondoli syncline (Siena, Tuscany, Italy): structural and biostratigraphical preliminary data. Mem. Soc. Geol. Ital., 48, 501-507. BONINI M., MORATTI G. & SANI F. (1999) - Evolution and depocentre migration in thrust-top basins: inferences from the Messinian Velona Basin (northern Apennines, Italy). Tectonophysics, 304, 95-108. BOSSIO A., CORNAMUSINI G., FERRANDINI J., FERRANDINI M., FORESI L.M., MAZZANTI R., MAZZEI R. & SALVATORINI G. (2000) L’evoluzione sedimentaria neogenica dell’area tirrenica settentrionale (Toscana marittima, Isola di Pianosa, Bacino di Aléria in Corsica orientale). Actes du Congrès Environnement et Identité en Méditerranée, Université de Corse, Juin 2000, Interreg II, 72-79. BOSSIO A., COSTANTINI A., FORESI L.M., LAZZAROTTO A., MAZZANTI R., MAZZEI R., PASCUCCI V., SALVATORINI G., SANDRELLI F. & TERZUOLI A. (1998) - Neogene-Quaternary evolution in the western side of the Northern Apennines (Italy). Mem. Soc. Geol. It., 52, 513-525. BOSSIO A., COSTANTINI A., LAZZAROTTO A., LIOTTA D., MAZZANTI R., MAZZEI R., SALVATORINI G. & SANDRELLI F. (1993) - Rassegna delle conoscenze sulla stratigrafia del Neoautoctono toscano. Mem. Soc. Geol. It., 49, 17-98. BOSSIO A., ESTEBAN M., GIANNELLI L., LONGINELLI A., MAZZANTI R., MAZZEI R., RICCI LUCCHI F. & SALVATORINI G. (1978) - Some aspects of the upper Miocene in Tuscany. Messinian Seminar, 4, Roma 9-14 settembre 1978, 25-45. BOSSIO A., ESTEBAN M., MAZZANTI R., MAZZEI R. & SALVATORINI G. (1996) - Rosignano reef complex (Messinian), Livornesi Mountains, Tuscany, Central Italy. In: Models for carbonate stratigraphy from Miocene reef complex of mediterranean Region (Franseen E.K., Esteban M. & Rouchy J.M., eds). SEPM, Concepts in Sediment and Paleont., 5, 277-294. BOSSIO A., FORESI L.M., MAZZEI R., SALVATORINI G., SANDRELLI F., BILOTTI M., COLLI A. & ROSSETTO R. (2003-2004) - Geology and stratigraphy of the southern sector of the Neogene Albegna River Basin (Grosseto, Tuscany, Italy). Geol. Rom., 37, 165-173. BOSSIO A., MAZZEI R., SALVATORINI G. & SANDRELLI F. (2000-2001) Geologia dell’area compresa tra Siena e Poggibonsi (“Bacino del Casino”). Atti Soc. Tosc. Sc. Nat., Mem., Serie A, 107, 69-86. BRIDGE J.S. (2006) - Fluvial facies models: recent developments. In: Facies Models Revisited (Posamentier H.W. & Walker R.G., eds.). SEPM Spec. Publ., 84, 85-170. BROGI A. (2004a) - Miocene extension in the inner Northern Apennines: the Tuscan Nappe megaboudins in the Mt. Amiata geothermal area and their influence on Neogene sedimentation. Boll. Soc. Geol. It., 123, 513-529. BROGI A. (2004b) - Miocene low-angle detachments and upper crust megaboudinage in the Mt. Amiata geothermal area (Northern Apennines, Italy). Geodin. Acta, 17 (6), 375-387. BROGI A. (2008) - The structure of the Monte Amiata volcano-geothermal area (Northern Apennines, Italy): Neogene-Quaternary compression versus extension. Int. Journ. Earth Sci., 97, 677-703. BROGI A. (2011) - Bowl-shaped basin related to low-angle detachment during continental extension: The case of the controversial Neo gene Siena Basin (central Italy, Northern Apennines). Tectono physics, 499, 54-76. BROGI A. & LIOTTA D. (2008) - Highly extended terrains, lateral segmentation of the substratum, and basin development: the middlelate Miocene Radicondoli Basin (inner northern Apennines). Tectonics, 27, 1-20.

423

BROGI A., LAZZAROTTO A., LIOTTA D. & CROP 18 WORKING GROUP (2005) - Structural features of the southern Tuscany and geological interpretation of the CROP 18 Seismic Reflection Survey (Italy). Boll. Soc. Geol. It., Vol. Spec., 3, 213-236. BROGI A., LAZZAROTTO A., LIOTTA D. & RANALLI G. (2003) - Extensional shear zones as imaged by reflection seismic lines: the Larderello geothermal field (Central Italy). Tectonophysics, 363, 127-139. BRUNET C., MONIE P., JOLIVET L. & CADET J.P. (2000) - Migration of compression and extension in the Tyrrhenian sea, insights from 40 Ar/39Ar ages on micas along a transect from Corsica to Tuscany. Tectonophysics, 321, 127-155. CARMIGNANI L., DECANDIA F.A., DISPERATI L., FANTOZZI P.L., LAZZAROTTO A., LIOTTA D. & OGGIANO G. (1995) - Relationships between the Tertiary structural evolution of the Sardinia-CorsicaProvencal Domain and the Northern Apennines. Terra Nova, 7, 128-137. CARMIGNANI L., DECANDIA F.A., FANTOZZI P.L., LAZZAROTTO A., LIOTTA D. & MECCHERI M. (1994) - Tertiary extensional tectonics in Tuscany (Northern Apennines, Italy). Tectonophysics, 238, 295-315. COLANTONI P. & BORSETTI A.M. (1973) - Geologia e stratigrafia dell’Isola di Pianosa (Arcipelago Toscano, Mar Tirreno). Giorn. Geol., 39 (1), 287-302. COLLETTINI C., DE PAOLA N., HOLDSWORTH R.E. & BARCHI M.R. (2006) - The development and behaviour of low-angle normal faults during Cenozoic asymmetric extension in the Northern Apennines, Italy. Journ. Struc. Geol., 28, 333-352. COSTANTINI A., DECANDIA F.A., LAZZAROTTO A., LIOTTA D., MAZZEI R., PASCUCCI V., SALVATORINI G. & SANDRELLI F. (2009) - Note Illustrative della Carta Geologica d’Italia alla scala 1:50.000, Foglio 296-Siena. ISPRA - Servizio Geologico d’Italia, 129 pp. DALLMEYER R.D. & LIOTTA D. (1998) - Extension, uplift of rocks and cooling ages in thinned crustal provinces: The Larderello geothermal area (inner northern Apennines, Italy). Geol. Mag., 135, 193-202. DECANDIA F.A., LAZZAROTTO A. & LIOTTA D. (1993) - La “Serie ridotta” nel quadro dell’evoluzione geologica della Toscana meridionale. Mem. Soc. Geol. It., 49, 181-190. DECANDIA F.A., LAZZAROTTO A. & LIOTTA D. (2001) - Structural features of southern Tuscany, Italy. Ofioliti, 26 (2a), 287-300. DESSAU G., DUCHI G. & STEA B. (1972) - Geologia e depositi minerari della zona Monti Romani-Monteti (Comuni di Manciano e Capalbio, Grosseto) e Ischia di Castro (Viterbo). Mem. Soc. Geol. It., 11, 217-260. FINETTI I., BOCCALETTI M., BONINI M., DEL BEN A., GELETTI R., PIPAN M. & SANI F. (2001) - Crustal section based on CROP seismic data across the North Tyrrhenian-northern Apennines-Adriatic Sea. Tectonophysics, 343, 135-163. FONTANA D. (1980) - Caratteri petrografici e sedimentologici delle Arenarie di Manciano nella Toscana meridionale. Miner. Petrog. Acta, 24, 77-94. FORESI L.M., BAMBINI A.M., MAZZEI R., PICCINELLI B. & SANDRELLI F. (2003) - La base dell’arenaria di Ponsano nella sua area tipo e nella zona di Casole d’Elsa (Toscana). Atti Soc. Toscana Sci. Nat. Mem., Ser. A, 108, 1-6. FORESI L.M., CORNAMUSINI G., BOSSIO A., FERRANDINI M., MAZZEI R., SALVATORINI G. & ARGENTI P. (2000) - The Miocene sedimentary succession of the Pianosa Island, Northern Tyrrhenian Sea. Abstract del Convegno della Società Geologica Italiana “Evoluzione geologica e geodinamica dell’Appennino”, Perugia, febbraio 2000, 155-157. FORESI L.M., PASCUCCI V. & SANDRELLI F. (1997) - Sedimentary and ichnofacies analysis of the Epiligurian Ponsano Sandstone (Northern Apennines, Tuscany, Italy). Giorn. Geol., 59, 301-314. FREGNI P., GASPERI G. & GELMINI R. (1985) - Il Messiniano tra la Toscana meridionale e il Lazio settentrionale. Mem. Soc. Geol. It., 25, 141-144. GALLOWAY W.E. (1975) - Process framework for describing the morphologic and stratigraphic evolution of deltaic depositional system. In: Deltas (Broussard M.L., Ed.), Houston Geological Society, 87-98.


424


GAWTHORPE R.L. & LEEDER M.R. (2000) - Tectono-sedimentary evolution of active extensional basins. Basin Research, 12, 195-218. GHELARDONI R. (1965) - Osservazioni sulla tettonica trasversale dell’Appennino settentrionale. Boll. Soc. Geol. It., 84 (3), 277-290. GIANNINI E. (1957) - I fossili dell’Arenaria di Manciano (Grosseto). Paleontol. Ital., 51, 97-103. GIANNINI E., LAZZAROTTO A. & SIGNORINI R. (1971) - Lineamenti di stratigrafia e di tettonica, Toscana meridionale. Rend. Soc. It. Min. Pet., 27. HAQ B.U., HARDENBOL J. & VAIL P.R. (1987) - Chronology of fluctuating sea level since the Triassic. Science, 235, 1156-1167. IACCARINO S. (1985) - Mediterranean Miocene and Pliocene planktic foraminifera. In: Plankton Stratigraphy (Bolli H.M., Saunders J.B. & Perch-Nielsen, Eds.), Cambridge Earth Science Series, Cambridge Unipress, 281-314. IACCARINO S. & SALVATORINI G. (1982) - A framework of planktonic foraminiferal biostratigraphy for Early Miocene to Late Pliocene Mediterranean area. Paleontologia Stratigrafica ed Evoluzione, 2, 115-125. JOLIVET L., FACCENNA C., GOFFÉ B., MATTEI M., ROSSETTI F., BRUNET C., STORTI F., FUNICIELLO R., CADET J.P., D’AGOSTINO N. & PARRA T. (1998) - Midcrustal shear zones in postorogenic extension: example from the northern Tyrrhenian Sea. J. Geoph. Res., 103, 12123-12160. LAVECCHIA G., MINELLI G. & PIALLI G. (1984) - L’Appennino Umbromarchigiano: tettonica distensiva ed ipotesi di sismogenesi. Boll. Soc. Geol. It., 103, 467-476. LAZZAROTTO A. & SANDRELLI F. (1977) - Stratigrafia e assetto tetto nico delle formazioni neogeniche nel Bacino del Casino (Siena). Boll. Soc. Geol. It., 96 (5-6), 747-762. LAZZAROTTO A., ALDINUCCI M., CIRILLI S., COSTANTINI A., DECANDIA F.A., PANDELI E., SANDRELLI F. & SPINA A. (2003) - Stratigraphic correlation of the Upper Palaeozoic-Triassic successions in Southern Tuscany, Italy. Boll. Soc. Geol. It., Vol. spec., 2, 25-35. LAZZAROTTO A., SANDRELLI F., FORESI L.M., MAZZEI R., SALVATORINI G., CORNAMUSINI G. & PASCUCCI V. (2002) - Note Illustrative della Carta Geologica d’Italia alla scala 1:50.000, Foglio 295 Pomarance. Servizio Geologico d’Italia, L.A.C. Firenze, 2002, 140 pp. LEEDER M. (1999) - Sedimentology and Sedimentary Basins. From Turbolence to Tectonics. Blackwell Science, 592 pp. MARTINI I.P. & SAGRI M. (1993) - Tectono-sedimentary characteristics of Late Miocene-Quaternary extensional basins of the Northern Apennines, Italy. Earth Sci. Rev., 34, 197-233. MARTINI I.P., CASCELLA A. & RAU A. (1995) - The Manciano Sandstone: a shoreface deposit of Miocene basin of the Northern Apennines, Italy. Sedimentary Geology, 99, 37-59. MARTINI I.P., SAGRI M. & COLELLA A. (2001) - Neogene-Quaternary basins of the inner Apennines and Calabrian arc. In: Anatomy of an Orogen. The Apennines and Adjacent Mediterranean Basins (Vai G.B. & Martini I.P., eds.). Kluwer Ac. Pubs., 375-400. MAZZEI R., PASINI M., SALVATORINI G. & SANDRELLI F. (1981) - L’età dell’“Arenaria di Ponsano” della zona di Castellina Scalo (Siena). Mem. Soc. Geol. It., 21, 63-72.

MCCLAY K.R. (1990) - Extensional fault systems in sedimentary basins: a review of analogue model studies. Mar. Pet. Geol., 7, 206-233. MILLER K.G. & SUGARMAN P.J. (1995) - Correlating Miocene sequences onshore New Jersey boreholes with global O-18 and Maryland outcrops. Geology, 23, 747-750. MORATTI G. & BONINI A. (1998) - Structural development of the Neogene Radicondoli-Volterra and adjoining hinterland basins in Western Tuscany (Northern Apennines, Italy). Geol. J., 33, 223-241. MULDER T. & ALEXANDER J. (2001) - The physical character of subaqueous sedimentary density currents and their deposits. Sedimentology, 48, 269-299. NEMEC W. & STEEL R.J. (1988) - Fan Deltas: Sedimentology and Tectonic Settings. Blackie, London. PASCUCCI V., MARTINI I.P., SAGRI M. & SANDRELLI F. (2007) - Effects of transverse structural lineaments on the Neogene-Quaternary basins of Tuscany (inner Northern Apennines, Italy). In: Sedimentary Processes, Environments and Basins: a Tribute to Peter Friend (Nichols G., Williams E. & Paola C., Eds.). Special Publication, 38, I.A.S., 155-182. PASCUCCI V., MERLINI S. & MARTINI I.P. (1999) - Seismic stratigraphy of the Miocene-Pleistocene sedimentary basins of the Northern Tyrrhenian Sea and western Tuscany (Italy). Basin Res., 11, 337-356. PASQUARÈ G., CHIESA S., VEZZOLI L. & ZANCHI A. (1983) - Evoluzione paleogeografica e strutturale di parte della Toscana meridionale a partire dal Miocene superiore. Boll. Soc. Geol. It., 25, 145-157. PERTUSATI P.C., MUSUMECI G., BONINI L. & FRANCESCHI M. (2004) The Serie Ridotta in southern Tuscany: a cartographic example and consideration on the origin. In: The “Regione Toscana” Project of Geological Mapping, 183-186. POSTMA G. & ROEP T.B. (1985) - Resedimented conglomerates in the bottomsets of Gilbert-type gravel deltas. Journ. Sed. Petr., 55, 874-885. RIFORGIATO F., FORESI L., ALDINUCCI M., MAZZEI R., DONIA F., GENNARI R., SALVATORINI G. & SANDRELLI F. (2008) - Forami niferal record and astronomical cycles: An example from the Messinian pre-evaporitic Gello Composite Section (Tuscany, Italy). Stratigraphy, 5 (3, 4), 267-282. SANI F., BONINI M., CERRINA FERONI A., MAZZARINI F., MORATTI G., MUSUMECI G., CORTI G., IATTA F. & ELLERO A. (2009) - Messinian-Early Pliocene crustal shortening along the Tyrrhenian margin of Tuscany, Italy. Ital. J. Geosci. (Boll. Soc. Geol. It.), 128 (2), 593-604. TOZZI M. & ZANCHI A. (1991) - Il caso dell’Albegna nel quadro dei lineamenti antiappenninici lungo il margine tirrenico della Toscana. Studi Geol. Cam., Vol. Spec., 1991 (1), 193-198. TWISS R.J. & MOORES E.M. (1992) - Structural Geology. W.H. Freeman and Company, New York, 532 pp. WESCOTT W.A. & ETHRIDGE F.G. (1990) - Fan deltas: alluvial fans in coastal settings. In: Rachocki A.H. & Church M. (Eds.), Alluvial fans: a field approach. John Wiley & Sons, 195-211. ZANCHI A. & TOZZI M. (1987) - Evoluzione paleogeografica e strutturale recente del Bacino del Fiume Albegna (Toscana meridionale). Geologica Romana, 26, 305-325.

Manuscript received 3 February 2011; accepted 10 July 2011; editorial responsability and handling by S. Mazzoli.

The Miocene successions of the Fiora Hills

The Miocene successions of the Fiora Hills

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