Abstract

Levels of organic maturity of Mesozoic and Tertiary sequences outcropping in the Central Apennines have been established, using the techniques of vitrinite reflectance, Thermal Alteration Index and fluorescence colours of organic matter to evaluate how these techniques may provide new constraints to the Meso-Cenozoic evolution of this crustal sector. Generally, in exploration geology, the vitrinite reflectance is used to indicate the organic matter maturity to provide data on hydrocarbon maturation. In sedimentary basin modelling, it is adopted to define the paleothermal regime. In fact, vitrinite reflectance (Ro) provides pieces of information on the burial history of sedimentary basins and may be employed to estimate tectonic uplift and erosion rates. Thermal Alteration Index (T.A.I.) and fluorescence colours values can be correlated with Ro and may be used to estimate the degree of maturation when vitrinite is absent. Samples derive from the Sabini and Tiburtini Mts., in slope facies between the Latium-Abruzzi carbonate Platform and the Umbria-Marche pelagic Basin; from the Simbruini and Ernici Mts., in carbonate Platform facies and from Upper Miocene syn-orogenic siliciclastic deposits outcropping between the Olevano-Antrodoco line, towards the West, and the Marsica slope facies, towards the East. Both the pre-terrigenous Meso-Cenozoic sequences show a low grade of organic maturity: Ro values are less than 0.4% in the Sabini and Tiburtini Mts.; Ro <sub>eq</sub> values in the Simbruini and Ernici Mts. range from 0.5% to 0.65%. The main cause for low maturity is indicated by field studies: on both areas, the deposition of huge thicknesses of siliciclastic syn-orogenic deposits never occurred, during the Neogene evolution of this sector of the Apenninic thrust belt. Moreover, the Upper Miocene flysch units show, as well, low levels of maturity: Ro values are less than 0.5%. The results are in agreement with the present tectonic position of these deposits in the Apenninic thrust belt and indicate that during the Neogene evolution they have not been overthrusted by huge volumes of rocks. Slightly higher levels of organic maturity are recorded at the footwall of the Olevano-Antrodoco line and in the Marsica area, where a local increase in temperature probably occurred in shear zones of thrust ramps and in areas of strike-slip tectonics.

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