Processes and typology in Gilbert-type delta bottomset deposits based on outcrop examples in the Corinth Rift

Abstract

Middle Pleistocene Gilbert-type delta in the Gulf of Corinth, Greece, has been investigated combining field methods and photo acquisition by drone to generate a high-resolution 3D model. This study case can be used to document four different dynamics in Gilbert-type bottomset deposits, each one of which is characterized by a specific range of facies, facies associations and geometries: (1) the sandy-gravelly bottomset, (2) the erosionalbypass stage, (3) the fine-grained bottomset and (4) the massive-sandy bottomset. By comparing the typologies of the bottomset, we propose a conceptual model that predicts the occurrence of these four different bottomset stage dynamics depending on the stratigraphic context. During highstand normal regression, the gravelly bottomset develops under subcritical flow. The supercritical flow undergoes a stationary hydraulic jump in the toeset due to the slope break. As a result, a low-relief channellevees system is formed in the bottomset. The channels are filled/reworked by backstepping conglomeratic lenses interbedded with silty concave-up and concave-down levees. During normal regression, the foreset beds are steeper than during previous stage and scoured in the upper part. In the bottomset, significant erosion recording sediment bypass downstream toward the pro-delta can be observed. During lowstand normal regression, a starved fine silt to shale bottomset onlaps onto the major erosional surface. The bulk of the coarsegrained sediments is stored in the delta topset and foreset. During the transgressive to highstand stage, the former topset and foreset are eroded by high-density turbidity currents and massive-sandy turbidites are deposited in the bottomset, which onlap onto the foreset beds and form a slope apron geometry in the delta toe. The stratigraphic model improves the prediction for the sand distribution within the various parts of the bottomset. This approach is particularly relevant for clastic depositional systems with high sediment discharge and a high accommodation rate.

Sedimentology and U-Pb dating of Carboniferous to Permian continental series of the northern Massif Central (France): Local palaeogeographic evolution and larger scale correlations

“…Foreset of delta (Postma and Roep, 1985;Rubi et al, 2018) Dbo GFd, GSm, GSh, Smm, Sl, F, Fl, Fc, rare C, Gmm2…”

“…Bottom set of delta (Postma and Roep, 1985;Rubi et al, 2018) L1 F, Fl, Fc, thin layers of Sl, GSh, GSm, ( Fig. 3d), GFd Lake with sediment supply deposited laterally to the delta L2 F, Fl, Cs, C, GFd Lake environment with rare stromatolites or carbonate layers or more frequently few sediment supply with soft-sediment deformation Tab.…”

“…3a) or locally by horizontal laminations (GSh facies, Table 2). The GSt, GSh and GSm facies are stacked together ( with some hydraulic jump (IGSt) and slump occurrences, typical of delta deposits (Postma and Roep, 1985;Rubi et al, 2018). The facies association marked by the development of siltstone and coal layers (F and C facies, Table 2) is named FP (Fig.…”

“…From 446 to 400 m (Fig. 2), a new facies association appears, characterised by the predominance of gravel to fine facies affected by SSD (GFd facies, interbedded with foreset delta (Dfo) and delta-front (Dfr) facies associations, and is therefore attributed to the bottomset deposits of the delta system (Postma and Roep, 1985;Rubi et al, 2018). In consequence, this core interval records an evolution from delta deposits with foreset and bottomset deposits (Dfo and Dbo, Fig.…”

Axial and transverse deep‐water sediment supply to syn‐rift fault terraces: Insights from the West Xylokastro Fault Block, Gulf of Corinth, Greece

“…Here, we summarize stratigraphic mapping and mesoscale architectural observations within the West Xylokastro Fault Block (WXFB), Gulf of Corinth, Greece, to develop a new conceptual model for deep‐water syn‐rift depositional systems fed by coeval transverse and axially input systems. The syn‐rift infill of the WXFB was principally fed by the Evrostini and Ilias Gilbert‐type deltas at the western tip of a structural high, the Xylokastro Horst (Figures and ) (Gobo, Ghinassi, & Nemec, , ; Gobo, Ghinassi, Nemec, & Sjursen, ; Rohais, Eschard, et al, ; Rohais, Joannin, et al, ; Rohais, Eschard, & Guillocheau, ; Rubi, Rohais, Bourquin, Moretti, & Desaubliaux, ; Zhong, Escalona, Sverdrup, & Bukta, ). The related deep‐water sediments, the Rethi‐Dendro Formation, are exposed ~10 km basinward from these fan deltas (Gawthorpe et al, ; Koutsouveli, Mettos, Tsapralis, Tsala‐Monopoli, & Iokim, ; Leeder et al, ; Tsoflias, Fleury, & Iokim, ).…”