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Rivers and early rifting: study of ancient rock record and implications for normal fault systems evolution in the Corinth rift (Greece)


IPGP - Îlot Cuvier


Séminaires Dynamique des fluides géologiques

Salle 310

Romain Hemelsdael

CPRG Nancy

The ancient rock record of fluvial syn-rift successions is used to reconstruct subsidence history in normal fault blocks. Facies analysis of syn-rift infill and stratigraphic correlations across the normal fault blocks enable the regional reconstruction of rift basins. Accepted models for early rifting show that hangingwall depocentres are small and isolated initially. These depocentres enlarge and merge due to lateral fault propagation and linkage. Footwall-derived drainage systems supply fluvial to lacustrine sediments into the hangingwall depocentres. The presence of an antecedent river system is often considered but its impact on facies distribution in time and space is minimal. However, it implies high sediment supply from the onset of rifting (Figure 1). What are the interactions between antecedent rivers and a growing normal fault system? This question is investigated by studying a Plio-Pleistocene fluvial succession in the southern margin of the Corinth rift (Greece). In the northern Peloponnese, early syn-rift deposits are preserved in a series of uplifted E-W normal fault blocks (10–15 km long, 3–7 km wide) that are incised by present-day north-flowing rivers. Stratigraphic and sedimentological analysis are used to decipher the architecture of early rift alluvial systems from source to sink. Lithostratigraphic correlations reveal the complexity of the syn-rift stratigraphy across the different normal fault blocks. Magnetostratigraphy and biostratigraphic markers are used to constraint the tectono-sedimentary evolution of the fluvial system from about 4.0 to 1.8 Ma. We show that coherent grain size and downstream facies variations are observed at the scale of several fault blocks (over 50 km long). Alluvial architecture is not documented in this context. As depocentres enlarged through time, sediments progressively filled palaeorelief, and overfilled both hangingwall depocentres and footwall areas. No significant footwall relief was created and thus no consequent drainage system developed. Facies analysis and palaeocurrent data indicate that sediments were deposited by a NE-flowing low sinuosity gravel braided river system. The main fluvial axis flowed above the active buried faults and remained constant during early rifting. We conclude that sediment supply was dominated by a large-scale antecedent drainage system inherited from the Hellenide mountain belt. These observations from the Corinth rift demonstrate that antecedent drainage systems can be important in the tectono-stratigraphic evolution of rift basins. This has significant implications for the predictions and analysis of fluvial petroleum reservoirs.