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Temperature-dependent clay mineral assemblages and vitrinite reflectance data have been used to investigate levels of diagenesis from the Apenninic-Maghrebian fold-and-thrust belt in eastern Sicily at the footwall of the Peloritani-Calabride Arc. Data are from units sampled along a regional transect between the Nebrodi Mountains to the north and Mount Judica to the south. These units developed in very different tectonic settings from those of oceanic to passive continental margin domains deformed during the Cenozoic mountain building and related active margin deposits. The integration of organic and inorganic thermal indicators allowed us to distinguish among different tectonic settings, with thermal maturity generally decreasing from hinterland to foreland as a result of progressively less severe thermal evolution and/or tectonic loading during the mountain building. Specifically, the highest vitrinite reflectance (VRo%) values (ca. 0.60%-0.75%) and percentages of illite layers in illite-smectite (I-S; 60%-80%) are found in trench-involved and accreted passive margin units. Lower VRo% values (0.20%-0.47%) and percentages of illite layers in IS (30%-60%) are found in thrust-top and foredeep basin deposits and far-traveled Sicilide units that have escaped involvement in trench evolution. Furthermore, either sedimentary or long-lived tectonic burial (at least more than 5 m.yr.) seem to have affected levels of diagenesis of the studied successions. The correlation between organic and inorganic thermal indicators is satisfactory for most of the samples derived from hemipelagic and siliciclastic deposits, whereas it is poor for some proximal siliciclastics. A tentative calculation of paleotemperatures is also proposed for the studied tectonostratigraphic units. [ABSTRACT FROM AUTHOR]