Southern Pindos foreland basin : Late Eocene – Early Oligocene stratigraphic evolution and geochemical constraints on the provenance and tectonic setting

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Μποτζιολής, Χρύσανθος
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Pindos foreland basin in western Greece is a tectonic depression that lodges about 2500 meters of Upper Eocene to Lower Oligocene sub-marine fan deposits. This research presents a sedimentological, stratigraphic and paleocurrent analysis of the submarine fan deposits that occur in the central part of Pindos foreland basin, western Greece. Facies analysis suggests that the studied succession includes thirteen sedimentary facies and eleven facies and sub-facies associations. The environments of deposition comprise abyssal plain, outer fan, inner fan, and slope deposits. The stratigraphic analysis documents an upward transition from carbonates to abyssal plain, to outer and eventually to inner fan deposits suggesting progradation of the submarine fan system and progressive infilling of a deep-water sediment depocenter. Sediments suggest deposition close to the onset of Pindos orogen, when sedimentation was unable to exceed the accommodation space created by lithospheric flexure. Paleocurrent data from sole marks reveal two main directional flows. The NE-SW direction suggests that axial flows were dominant during the sediment deposition. The deposition in Pindos Foreland basin is dated to Eocene/Oligocene epoch. However, the exact stratigraphic position of the Eocene-Oligocene boundary is still uncertain. A qualitative analysis has been conducted on calcareous nannofossils and planktonic foraminifera, constraining the depositional age. Pindos Thrust is a crustal-scale structural element that formed Pindos foreland. Thus, Pindos foreland accommodates a syn-orogenic sedimentary succession with thick clastic deposits affected by compressional movements. The present research was based on detailed field campaign mapping and on standard structural techniques and aims to compile the main tectonic elements that shaped the Pindos foreland. The study area is part of the external Hellenides located on the Pindos foreland (SE Aetoloakarnania region). The activation of the NNW Gavrovo Thrust resulted on significant fault-related structures, such as the Varasova, Froxilia and Klokova anticlines. The existence of dextral strike-slip faults like Evinos Fault partitioned the westwards propagating thrusting deformation and acted as a barrier for the emergence of carbonate sediments at the southern part of the study area during the deformation. Based on the registration of bedding orientation, kinematics of meso and large-scale faults at different field outcrops, the relationship between sedimentation and orogenic processes in the area is defined providing new evidence of the evolution of the Pindos foreland basin. Furthermore, this study documents new petrographic and geochemical data for evaluating the composition, weathering condition, provenance, and tectonic setting of the central part of Pindos foreland basin. Conglomerate clast composition analysis suggests that the studied deposits contain mainly limestone clasts, followed by sandstone and chert clasts. It also suggests an additional low-grade metamorphic source, which is confirmed by the Cathodoluminence analysis. Microfacies analysis of the conglomerates clasts further restricts the source rocks that contributed to the basin sedimentation. An upward increase of lithic fragments abundances is documented and ascribed to the progressive unroofing of the Pindos orogenic source regions. This study links for the first time the stratigraphic evolution of the deep-sea fan deposits with the evolutionary stages and the geochemical constrains of the Pindos Foreland system. Multi-dimensional discrimination diagrams suggest a collisional setting and agree with an active continental margin. Geochemical and petrographic analysis suggests that the succession derived from sedimentary, felsic to intermediate igneous and low-grade metamorphic source rocks.
Foreland basin, Sub-marine fans, Progradation, Provenance, Pindos, Paleogene