Flavia Botti

Sedimentary and tectonic burial evolution of the Northern Apennines in the Modena-Bologna area: constraints from combined stratigraphic, structural, organic matter and clay mineral data of Neogene thrust-top basins

Vitrinite reflectance and mineralogical data from 55 samples collected from the Mt. Cervarola Sandstones and the Granaglione Sandstones (thrust-top basin Cervarola Successions) testify the severe thermal maturity of the present-day outcropping successions. This is due to the deep tectonic burial the successions underwent during Miocene chain building. Lower levels of thermal maturity are recorded in the Mt. Cervarola Sandstones. They form a thick upper thrust sheet (Ro% ranging between 1.0 and 1.2%; I% in I/S mixed layers ranging between 80 and 85%). Higher levels of thermal maturity characterise the structurally lower thrust sheets, made up mainly of Granaglione Sandstones (Ro% ranging between 1.2 and 1.5%; and I% in I/S mixed layers between 85 and 90%). Maturity generally decreases from hinterland to foreland. Integration of Ro% and I% in I/S data with published low-temperature indicators allowed to reconstruct a maximum tectonic burial ranging between ~3.5 on the upper thrust sheet and ~5 km on the lower ones. Burial was mainly due to the early emplacement of the Ligurian Unit and the Modino Unit on top of the studied units and to later piggy-back thrusting of the Mt. Cervarola Sandstones onto the Granaglione Sandstones.

Clay mineral assemblages and vitrinite reflectance in the laga basin (Central Apennines, Italy) : What do they record?

Temperature-dependent clay mineral assemblages and vitrinite reflectance data have been used to investigate levels of diagenesis from the Messinian Laga Basin in the Central Apennines developed at the footwall of the Sibillini Mts. and the Gran Sasso Massif. Data are from stratigraphic units forming the main siliciclastic basin fill up to Middle Messinian gypsum-arenites and its pre-orogenic substratum. Specifically, the largest Rom% values and percentages of illite layers in illite-smectie (I-S) are found in the basin depocenter and at the footwall of the main carbonate thrust sheets. Smaller Rom% values, and percentage of illite layers in I-S characterize less subsided sectors surrounding the depocenter.The X-ray diffraction data were treated using decomposition methods and the peaks identified were rationalized in terms of discrete and/or mixed-layer phases. Complex clay mineral assemblages were found in the Laga Fm. including three sub-populations of illitic material corresponding to authigenic and detrital components. I-S mixed layers record the maximum paleotemperature the Laga Fm. experienced, which is directly related to its burial history. Kübler index (KI) data, however, suggest higher temperatures related to detrital K-micas inherited from the uplift of the Alpine-Apennines chain.A tentative calculation of paleotemperatures from selected data of organic and inorganic parameters is also proposed and compared with recent sedimentological, stratigraphic and structural data. We conclude that the Laga Basin fill never experienced temperatures of >100–110°C, generally due to variable sedimentary loading, whereas localized anomalous heating is due to the effect of the tectonic emplacement and subsequent local erosion of the Sibillini and Gran Sasso thrust sheets.

Oligocene-Miocene foredeep deposits in the Lake Trasimeno area (Central Italy): insights into the evolution of the Northern Apennines

In the Trasimeno Lake area (Umbria Region), several thrust sheets belonging to the Sansepolcro-Monte Filoncio and Rentella Units, are interposed between the Tuscan Nappe (in the hanging-wall) and the Umbria-Romagna Unit (in the footwall). The thrust sheets succession of the Sansepolcro-Monte Filoncio Unit is made up of Rupelian-Chattian Scaglia toscana Fm. and Chattian-Aquitanian foredeep deposits of Macigno Fm.; the base of the siliciclastic succession becomes gradually younger eastward. The compositional mode of the fine-grained rock fragments in the arenaceous turbidites is comparable with that of the upper part of the Macigno Fm. in the Tuscan Nappe. The succession of the Rentella Unit includes Rupelian-Aquitanian Monte Rentella Fm. and Aquitanian-Burdigalian foredeep siliciclastic turbidites of the Montagnaccia Fm.. In the lower portion of the Montagnaccia Fm. a level of black cherty horizons is present, as detected in all Aquitanian-Burdigalian successions of the Northern Apennines. The compositional mode of the fine-grained rock fragments in the turbidites is comparable with that of Marnoso-Arenacea Fm.. All these data allow an Oligocene-Miocene paleogeographic reconstruction of the Northern Apennines foredeep. Based on the age, the compositional mode and structural position, the Rentella and Sansepolcro-Monte Filoncio Units can be compared to the Carigiola and Acquerino Units cropping out in the Tuscan-Emilian Apennines.

Surface-subsurface structural architecture and groundwater flow of the Equi Terme hydrothermal area, northern Tuscany Italy

A multidisciplinary integrated approach was used to study the structural architecture influencing the circulation pattern of geother -mal fluids in the Equi Terme area (NW Alpi Apuane, Tuscany). Geological-structural surveys were carried out to define the structural setting of the area and to characterize geometries and kinematics of fault systems. Chemical (major components) and isotopic analyses (δ18O‰, δ2H‰, 3H, δ13C‰[DIC], δ34S‰[SO4]) were performed on thermal water and cold springs. A geophysical survey was also conducted by means of both Magnetotelluric and Electrical Resistivity Tomography methodologies, in order to gain insight into the resistivity distribution at depth and to indirectly image the subsurface structure. This multidisciplinary approach proved to be a powerful tool, since it unravels the complexity of this natural geothermal system and provides useful suggestion for reconstructing the fluid circulation outflowing at the Equi Terme thermal spring. Results pointed out how the E-W oriented fault system (the Equi Terme Fault) play a key role in controlling the thermal groundwater outflow, and the chemical-physical features of this resource. This structural lineament separates high permeability carbonate complexes (footwall), in which both shallow and deep flow paths develop, from a medium-low permeability succession (hangingwall) that contains evaporitic formations from which thermal water acquires a high salinity and a composition of the Na-Cl (Ca-SO4) type. During the uprising along the fault system, the thermal water is also affected by a mixing with shallow fresh-cold waters that lead to a strong seasonal variation in the chemical-physical properties of the thermal springs.

Structural and Thermal Constraints to the Tectonic Evolution of Foredeep Successions in the Northern Apennines, Italy

A multi-method investigation (structural analysis, organic matter thermal maturity and clay mineralogy) was carried out on highly deformed foredeep successions in the Northern Apennine with special regard to shear zones in the Lago Trasimeno area (Rentella Unit) to unravel the main structural mechanisms and the thermal condition of the Miocene accretionary processes of the Northern Apennines belt. The Rentella Unit consists of a foredeep succession deposited in a paleogeographic domain between the Tuscan and the Umbria-Marche Domains. Meso- and microstructural data indicate shear planes compatible with C-planes (N160°, 45°SW). C-planes veins show dilational jogs and a staircase shape coherent to a top-to-the-NE sense of shear. Type II calcite twins in the shear zone associated veins suggest temperatures of 150-200°C. Temperature-dependent clay minerals and vitrinite reflectance indicate lower maximum paleo-temperatures (<100-110°C) in the early diagenesis and in the immature to early-mature stages of hydrocarbon generation. Thermal parameters suggest the development of the shear zone in the foredeep deposits at shallow depths (<3 km). Hot fluids coming from deeper structural levels within the collisional prism caused higher temperatures recorded in calcite twins of the shear zone veins.