Siliceous concretions (nodules), from two different geological settings—the Apulian platform margins in Kefalonia island, and the Ionian Basin in Ithaca, Atokos, and Kastos islands—have been studied both in the field and in the laboratory. Nodule cuttings are mainly characterized by the development of a core, around which a ring (rim) has been formed. Mineralogical study, using X-ray powder diffraction (XRPD) analysis, showed that the rim is usually richer in moganite than the core. Homogeneous concretions, without discernible inner core and outer ring, were observed generally in both settings. Mineralogical analysis of the selected siliceous concretions from Kefalonia island showed the presence mostly of quartz and moganite, while calcite either was absent or participated in a few samples in minor/trace abundances. Moganite was generally abundant in all the samples from Kefalonia island. Concretions from the Ionian Basin showed a variation in the quartz, moganite, and calcite contents. Mineralogical differences were recognized both between the different studied geodynamic settings and internally in the same setting, but with different stages of development. The above-mentioned differential diagenesis on nodules evolution could be related to the presence and/or abundance of stylolites, later fluid flows, restrictions from one area to another due to synchronous fault activity, and the composition of substances dissolved in fluids. Moreover, the development of concretions produced secondary fractures in the surrounding area of the nodule-bearing rocks.

The studied section, up to 10 m thick with 17 different carbonate beds, showed the interaction between a giant slide and the pre-existing normal faults during the upper Cretaceous time. There are three major points of consideration in the studied section: (1). The presence of two slump horizons, up to 1 m thick each, within the stratigraphic column, related to the basin floor instability, due to normal listric faults activity. (2). The presence of many normal, with listric geometry, faults, with an ESE–WNW direction, and mostly west-dipping. These faults acted during the sedimentation processes and produced the basin floor inclination for the slumping when still the sediments were unconsolidated. This tectonic activity seems to terminate in the upper part of the stratigraphic column. (3). After the development of the slumps and the normal faults’ activity, which produced a displacement of up to 30 cm, a new event was characterized in the region. The completely studied block probably rotated to the west and thus the instability of the sediments produced a giant slide, up to 7 m thick and with movement up to 0.9 m, cutting the pre-existing normal faults. The knowledge of the regional evolution, with extensional tectonics during the Jurassic to early Miocene periods, which was inverted to a compressional regime during the middle Miocene, as well as the presence of a major normal fault along the studied section with an NNW–SSE direction, suggested that the studied section was situated on the hanging wall of the above fault during the extensional regime.