Deciphering tidal signature in a fluvial-dominated delta using digital outcrop models (Roda Sandstone, Eocene, South Pyrenean Basin) - La Rochelle Université
Pré-Publication, Document De Travail (Preprint/Prepublication) Année : 2025

Deciphering tidal signature in a fluvial-dominated delta using digital outcrop models (Roda Sandstone, Eocene, South Pyrenean Basin)

Résumé

Deltaic environments are crucial depositional systems for georesources, often studied for their excellent reservoir quality in both ancient and modern contexts. However, while mixed river tide-influenced deltas are complex and important, they remain underexplored in the ancient sedimentary record. This study focuses on the Roda Sandstone, a Lower Eocene fluvial-dominated, tide-influenced delta system in the Graus-Tremp foreland basin, to address gaps in understanding the interaction between fluvial and tidal processes within these environments. Fieldwork and core analysis were conducted to investigate the Roda Sandstone. Nineteen sedimentological sections were logged, and palaeocurrents were measured in the field. A Digital Outcrop Model (DOM) was created using 11,000 drone-captured images, georeferenced with DGPS data. The Digital Outcrop Model was processed with photogrammetry and analysed using a specialised for detailed stratigraphic and facies interpretation. Additionally, five well cores, totalling 340 m, were described and integrated with the Digital Outcrop Model. The sedimentological and stratigraphic study combined with the Digital Outcrop Model interpretation led to the identification of 10 facies grouped into five facies associations and the recognising of 7 deltaic lobes, representative of fifth-order sequences. The 3D evolution of these lobes reveals variations in progradation directions and the intensity of tidal reworking. This shows a gradual shift to a tidally dominated-deflected delta front as they were prograde. This work enabled the characterization of tidal sedimentary bodies, including the dimensions of tidal dunes and bars, paleo-bathymetries, and their specific locations within both progradational and retrogradational sequences. During regressive periods, the preservation of tidal dunes and bars intercalated in the delta foresets depends on the fluvial sediment supply and autocyclic factors. Whereas the preservation of larger tidal bars on bottomsets is permitted by the lower river sediment supply during transgressive periods of fourth-order cycles. This research advances our understanding of ancient mixed deltas by providing a depositional model that clarifies the preservation of tidal features. Additionally, it underscores the value of DOMs in enhancing correlations, distinguishing different sedimentary structures generated by competing currents, and offering detailed facies mapping for improved paleoenvironmental interpretations.

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Dates et versions

hal-04863300 , version 1 (03-01-2025)

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  • HAL Id : hal-04863300 , version 1

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Perrine Mas, Raphaël Bourillot, Rémy Deschamps, Benjamin Brigaud, Bertrand Saint-Bezar, et al.. Deciphering tidal signature in a fluvial-dominated delta using digital outcrop models (Roda Sandstone, Eocene, South Pyrenean Basin). 2025. ⟨hal-04863300⟩
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