AB ST R ACT : The relationship between three parameters, the T max given by Rock-Eval pyrolysis, the illite content in illite-smectite mixed layers (I-S) and the Kübler Index (KI) has been investigated in the CretaceousÀNeogene, sedimentary syn-orogenic successions in the Northern Apennines (Italy). A strong relationship was found between maturity stages of kerogen, illite content in I-S and KI. The oil formation zone for continental organic matter (Type III), delimited by T max between 434 and 465ºC, corresponded to rocks with short-range ordering R1, I-S with illite content between 60 and 85% and KI values in the range 0.85À0.65 (ºD2y). Over-mature rocks were characterized by T max >465ºC, a long-range ordered I-S with an illite content >85% and KI in the range 0.65À0.45 (ºD2y). The relationship permits use of both mineralogical parameters and T max to estimate palaeotemperatures in sedimentary successions and it can be exploited in hydrocarbon research to evaluate the petroleum potential.

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The influence of tectonic strain on the diagenetic degree and illitization process of mixed-layers illite-smectite at shallow crustal conditions was studied. For this purpose, the modal composition of clay fraction and illite FWHM parameters of argillites deformed by a regional-scale fault zone were studied in detail by XRD, chemical analyses and by SEM observations. Analyses were performed on deformed samples of the fault rock and compared with the non-deformed rocks off the fault zone. In addition, this paper reports a detailed comparative analysis of deformed (shear surfaces and cleavage domains) and non-deformed domains (lithon cores) of a scaly fabric in the fault rock. A systematic increase in illite concentration, a decrease of Kubler index and FWHM((002)) values, and an enrichment of K(+) ions were observed in cleavage domains with respect to the non-deformed sediments off the fault zone and the lithon cores within the fault rock. Migration of K(+)-rich fluids along scaly cleavage domains causes progressive conversion of smectite-rich I-S to illite-rich I-S and thickening of illite crystallites along the c-direction. Changes in mineralogical and crystallographic parameters, therefore, seem to be strongly controlled by shear plane development in highly sheared rocks