Filippo Bonciani

The Miocene successions of the Fiora Hills: considerations about the development of the minor basins of Southern Tuscany

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 “Lago-Mare” M3 Unit (late Messinian), which is referable to fan-deltaic lacustrine systems. The Miocene succession is overlaid by Plio-Pleistocene 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 fan-deltaic 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 lacustrine 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.

Geological map of the Chianti Mts (Northern Apennines, Italy)

A detailed stratigraphical-structural survey combined with classical geological mapping has been performed in the northern Chianti Mts, part of the Northern Apennines Orogen (central Italy). The study area can be subdivided in different tectonic and depositional units: (i) the widely outcropping Tuscan Nappe (middle/late Lias–earliest Miocene), thrusted to the west by (ii) Ligurian units (Cretaceous–Eocene) and unconformably covered by (iii) post-nappe deposits (Pliocene–Pleistocene). The Chianti Mts are structured as a mega-antiformal fold, dissected by WSW-ENE transversal lines and by NNW-SSE normal faults linked with the exhumation of the Northern Apennines Range, developing a basin/ridge structure. As results, (i) a new improved stratigraphic frame is here proposed; (ii) several tectonic and stratigraphic domains have been newly recognised; (iii) a large area characterised by severe internal deformation has been recognised and mapped as an imbricate fan thrust system, linked with transversal lines.

Did the Nile River flow to the Gulf of Sirt during the late Miocene

Satellite imageries from Landsat ETM+ and ERS (European Remote Sensing) Radar sensors, together with elevation data collected by the Shuttle Radar Topography Mission (SRTM) in addition to recent and older bibliography, have led to the hypothesis that, before the Late Messinian drawdown of the Mediterranean Sea, the River Nile flowed into the Libyan palaeo-Sirt. The study is still in progress; in this paper data are presented from three areas, showing evidence of palaeo-drainage of Tortonian-Late Messinian age, that could be considered sufficient to delineate the course of the Nile River up to the Gulf of Sirt (fig. 1).

Sensitivity Analysis for Shallow Landsliding Susceptibility Assessment in Northern Tuscany

In two areas located in the north-western part of Tuscany, central Italy, Lunigiana and Garfagnana, noticeable heavy rainfall events occurred in the last years. During these events, the rainfall amounts and intensities triggered a great number of shallow landslides, causing damages, injuries and human losses. Steep slopes and deep valleys induced a persistently high relief of energy and high shallow landsliding susceptibility. In the present paper, the authors considered 4 heavy rainfall events that affected the area in 2009–2011. They carried out an analysis including a statistical modelling of spatial landslide occurrence by using Random Forest classifiers (RFc) after model selection by means of a stepwise AIC (Akaike Information Criterion) procedure. Event landslides occurrences permitted to build four event-specific RFc training sets, considering a large number of predictors reliable to characterize landslide susceptibility. Furthermore, the analysis took into account some relevant meteorological variables directly linked to the events themselves. An exploratory evaluation of the skills of a numerical weather prediction (NWP) model was conducted, to give a reliable supply to the RFc framework by using its weather forecast. For one selected event, a shallow landslide hazard model with meteorological inputs was validated. The preliminary results are shown and discussed.

Stratigraphic architecture of an outer ramp/basinal turbidite fan carbonate system in a foreland basin ("Scaglia Toscana" Fm., Chianti Mts, Northern Apennines, Italy)

The Chianti Mts, part of the Northern Apennines orogen, represent an ideal case study to depict the relationships between outer carbonate ramps and basin plain carbonate turbidite systemsin foreland basins. The main object of this research is the Scaglia Toscana Fm., a ca. 200 metres thick Eocene-Oligocene succession of polychromous shales, marls, pelagic limestones and turbidite calcarenites, with marked lateral/vertical complexity, having its type-section in the Chianti Mts. During fi eldwork, the fm. has been subdivided in four partially interfingered members (from the bottom and northernmost): Sugame Marls; Cintoia Shales; Montegrossi Calcarenites; Dudda Shales and Limestones. The formation relates to three depositional systems: a middle to outer carbonate ramp dominated by hemipelagic deposition; a basinal plain whose sediments distribution was mainly forced by redox/oxic conditions and calcite-lysocline fluctuations; a thinning- and fining-upward, coarse- to fine-grained carbonate turbidite system. The Scaglia Toscana basin was located on the Adria continental micro-plate, foreland of the developing Northern Apennines orogen, whose facies distribution was mainly controlled by block faulting and differential subsidence. The Chianti Mts. represent then a crucial sector, since they expose the junction between a northern SSE-dipping ramp and a southern basinal plain with turbidite fl oor fans. A general southwardand upward-shift from ramp, basinal plain and turbidite fan facies has been recognized and remarked since the pioneering studies of the 1960s. Nonetheless, an exhaustive facies and architectural analysis is still lacking in literature. To fill this gap, the partial and preliminary results of a field logging, integrated with sedimentary facies analysis are reported here.

Geology of the ‘Coltre della Val Marecchia’ (Romagna-Marche Northern Apennines, Italy)

ABSTRACT A detailed geological map at 1:50,000 scale of the Marecchia Valley and adjoining areas (Northern Apennines, NA, Italy) is presented here. The Marecchia Valley represents a geological ‘unicum’ for the NA and it has been the focus of scientific debate for a long time, due to the occurrence in the area of the ‘Coltre della Val Marecchia (CVM)’, a complex stack of allochthonous and semi-allochthonous units emplaced in a foredeep basin during the Late Miocene to Early Pliocene. In order to clarify the geological evolution for this area, the lithostratigraphic relationships and the tectonic framework have been studied, allowing better understanding of the complex relationships between tectonics and sedimentation. The main result has been a new evolutionary framework for this sector of the orogen during the Late Miocene-Early Pliocene. Several new findings about the geological-structural setting and stratigraphy, result from the geological map presented here. These are overall supported by stratigraphic and tectonic evidence, which suggest time and modes of the CVM allochthonous emplacement within the Messinian-early Pliocene foredeep successions. Relationships between the allochthonous and autochthonous formations allowed recognition of two different bodies in the CVM, gravitationally emplaced following different trajectories and timing.