Field investigation, Microfacies analysis, and biostratigraphy have been carried out in the central parts of the Ionian Basin (Aetoloakarnania area, Western Greece) in order to decipher the depositional environments that developed during the accumulation of the Upper Cretaceous to Eocene carbonate succession. Three different Standard Microfacies types (SMF) have been observed, corresponding to two different depositional environments (Facies Zones or FZ) of a platform progradation. The three SMF types which occur in the study area during the Upper Cretaceous to Eocene are: 1. SMF 3 that includes mudstone/wackestone with planktic foraminifera and radiolaria, corresponding to toe-of-slope (FZ: 3), 2. SMF 4, which can be classified as polymict clast-supported microbreccia, indicating a toe-of-slope-slope environment (FZ: 4) and 3. SMF 5 which is characterized by allochthonous bioclastic breccia and components deriving from adjacent platforms and which reflects a slope environment. Microfacies analysis provided evidence of a change in the origin of sedimentary components and biota showing the transition from toe-of-slope to slope, as well as a change in organism distribution.
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 Mediterranean Ridge, the largest physiographic feature in the Eastern Mediterranean Sea, is thought to be an accretionary complex, resulting from the convergence of the African and Eurasian plates. The presence of a salt layer in the upper deforming sequence (Late Miocene evaporites) and the unusually great thickness of the incoming sediment column differentiate the Mediterranean Ridge from most other accretionary complexes. Mud volcanoes are present in this region while various lithotypes from Carboniferous to Pleistocene can act as potential source, reservoir, and seal rocks resulting to the recognition of several potential hydrocarbon plays.
On the island of Kefallinia, which lies at the external edge of the Hellenides fold and thrust system, appear the Paxi and the Ionian Zones. In this study, an Upper Cretaceous carbonate succession, which is a part of the Paxi Zone, cropping out near the area of Sami (central area of Kefallinia), is discussed in detail with regard to its depositional facies, microfacies, biostratigraphy and palaeoenviroments. Detailed sedimentological and palaeontological investigations have been carried out on seven sections and petrographic analysis of thin-sections that led to the recognition of a number of microfacies types grouped into four facies zones. There was recorded a supratidal- intertidal (restricted)-intertidal (open lagoon)- subtidal (or shallow subtidal) vertical transition. Supratidal facies are characterized by fenestral and peloidal wackestone / packstone, intertidal (restricted) facies are represented by bioclastic wackestone and bindstone, whereas intertidal (open lagoon) facies are indicated by bioclastic packstone. Finally subtidal facies are dominated by bioclastic floatstone and grainstone. Benthic foraminifera are especially abundant and along with calcareous algae are the most important fossils used for age determination. The benthic foraminiferal genera that were identified (Cuneolina sp., Quinqueloculina sp., Nezzazata sp., Pseudonummoloculina sp., Dicyclina sp.), in addition with the observed calcareous algae, rudist and gastropods provide significant data for the depositional environments and the paleoecology of the Paxi Zone during the Upper Cretaceous.
In this study, siliceous nodules from the world-famous Myrtos beach, as well as from Avithos beach, in the western flanks of Kefalonia Island in Greece are examined by means of petrographical, mineralogical, geochemical and micropaleontological methods. The objectives of this study are to characterize the textural and compositional features of the nodules, with the aim to provide an initial interpretation of their origin and their diagenetic evolution. The studied siliceous nodules are hosted within Lower Cretaceous thin-bedded limestones at Myrtos and Upper Eocene limestones at Avithos. Nodules from both areas display a characteristic concentric texture at a macroscopic and microscopic scale. They both have a dense fine-grained siliceous sedimentary fabric, composed mainly of microcrystalline or cryptocrystalline quartz and moganite with common residual calcite in the case of Avithos. These results, and in particular the shape of the nodules, along the textural and compositional characteristics, indicate different conditions of formation in the two localities, both during the early epigenetic stages, as well as later during the diagenetic processes. Myrtos nodules originated from Si-precursors deposited in a pelagic environment, going through intense Si-replacement. Avithos nodules were deposited in a more proximal environment, being influenced by a less intense silicification. Nevertheless, the higher degree of recrystallization of Avithos samples indicates a syn- or post-diagenetic tectonic activity that resulted in the circulation of geothermal fluids. The conclusions drawn from this work demonstrate the usefulness of thorough studies of siliceous nodules in order to get a more comprehensive understanding of the initial depositional conditions, as well as diagenetic pathways and processes.
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