Alluvial development during climate fluctuations depicted with spectral decomposition of the Middle Triassic to Lower Jurassic post-rift succession in the Horda Platform (Norway) and the impact on reservoir properties

For the first time, this study presents interpretations of alluvial fans in spectral decomposition RGB Blends, analysed in seismic time slices from the Middle Triassic to Lower Jurassic stratigraphical interval of the Horda Platform (northern North Sea). The time slices record a shifting alluvial fan front, fluvial variability, uplift and erosion and reveals depositional elements that may set the common conception of the geological development of this area during the Early-Middle Mesozoic up for discussion. Results show that the Upper Triassic Lunde Formation in the eastern margin of the Horda Platform was characterized by the deposition of coalesced alluvial fans. A variable extent of the fan front through the Upper Triassic is linked to interplaying allogenic factors: uplifted source areas in the aftermath of Early-Middle Triassic rifting determined sediment availability; climate transitioning from arid to semi-humid, with increasingly fluctuating precipitation, controlled sedimentation, and run-off; provenance dictated bulk sedimentology and affected prevailing alluvial processes. An overall retreat of the fan system through the Late Triassic coincided with a significant change in landscape characteristics at the transition into the overlying Statfjord Group. Uplift and initial tilting of the Horda Platform caused landscape degradation and the formation of plateaus and incised valleys, contemporaneous with increased humidity and marine transgression, forming estuaries. The shift in depositional style has implications for reservoir properties, creating complexity and heterogeneity in terms of facies distribution and connectivity, which may benefit potential CO2 storage. Upper Triassic alluvial fan development in the Horda Platform (northern North Sea) depicted through spectral decomposition of seismic time slices Enhanced level of seismic stratigraphic interpretation with RGB blending Impact of allogenic factors on alluvial depositional development Implications of alluvial variability on reservoir properties

Automated summary

This study uses spectral decomposition RGB Blends to interpret alluvial fans in seismic time slices from the Middle Triassic to Lower Jurassic stratigraphical interval of the Horda Platform (northern North Sea) for the first time. The analysis reveals shifting alluvial fan fronts, fluvial variability, uplift and erosion, and depositional elements that challenge the common understanding of the geological development of this area during the Early-Middle Mesozoic. The study emphasizes the impact of allogenic factors on alluvial depositional development and the implications of alluvial variability on reservoir properties.