Combined facies analysis and quantitative characterisation of fluvial stratigraphic architecture at outcrop and in subsurface well data

Abstract

Integrated analysis of channelised fluvial sandbodies and their relationship to surrounding fine-grained floodplain fines enables interpretation of avulsion style and its links to allogenic and autogenic controls on stratigraphic architecture. A fundamental gap in our knowledge still lies in predicting the distribution and connectivity of channelised sandbodies generated via avulsion in the stratigraphic record. This thesis presents a study of two comparable high-quality fluvial successions; the upper Cretaceous Blackhawk Formation of the Wasatch Plateau, Utah, U.S.A, and the middle Jurassic Ness Formation of the Brent Field, North Sea, U.K.

The aim of this research is to combine the use of aerial photographs, spatial statistical analysis (Besag’s L function, lacunarity), fieldwork, and core to investigate the spatial distribution, geometry, stratigraphic architecture, and connectivity of channelised fluvial sandbodies. The data attained from this study will enhance understanding into the way in which fluvial environments operate through time, and build upon existing models of fluvial stratigraphic architecture. Analysis of measured section data from both case studies identified environments associated with wave-dominated delta plain deposition. Localised stratigraphic architecture reveals three styles of channel avulsion: avulsion by incision, avulsion by progradation and avulsion by annexation. Spatial statistical analysis reveals three styles of stratigraphic channel distribution: channel clustering, compensational stacking, and spatial randomness. Sandbody size and distribution, and the character, vertical stacking and abundance of lithofacies and palaeosols (entisols, inceptisols, histosols) differs locally within the two formations, however such variations are not consistent over basin-wide scales. These findings do not conform to existing models of alluvial architecture which typically relate such stratigraphic patterns to allogenic controls. These results suggest that deposition took place in the absence of or independent from any variation in external basin boundary conditions (e.g. sea level, tectonics and climate) and thus may be primarily controlled via autogenic responses such as avulsion.