Floodbasin deposits as indicators of sandbody geometry and reservoir architecture
Palaeosol development is controlled by topography, drainage, substrate, climate and time. The types and maturities of soil developing within fluvial systems are also controlled by avulsion and terracing. Soil forming models relate variations in pedogenic maturity and morphology to these processes. The pedofacies model and pedofacies sequences apply to lateral and vertical packages deposited under aggradational conditions while the chronosequence model applies across floodplain terraces. The Upper Triassic, Upper Petrified Forest Member, Arizona contains fluvial channel sandstones encased in thick mudstones. Differences in palaeosol development were produced by variations in sedimentation rate, terracing and drainage conditions. The pedofacies and chronosequence models apply to these palaeosols. The Owl Rock member was deposited in lacustrine and lacustrine margin environments. Soil forming models were not recognised here because pedogenic horizons were subject to intense burrowing and reworking by advancing lacustrine margins. Continued basin subsidence and decreasing sediment supply caused the change in depositional environments between the two Members. The Upper Silurian, Old Red Sandstone, Dyfed comprises thick fluvial deposits and numerous stacked palaeosols. Fluvial architecture and palaeosol development was controlled by avulsion, phases of erosion and influxes of volcanic ash. Channel morphologies were broad and sheet-like. Soil morphology and structure reveals complex cycles of varying aggradation and erosion within the sediments. Palaeosols contain variations in maturity consistent with the pedofacies relationship and pedofacies sequences. Upper Triassic to Lower Jurassic Lunde and Statfjord Formations, Snorre Field, North Sea comprise fluvial channels which change from isolated ribbons encased in thick mudstones to laterally extensive channels and palaeosol development decreases from moderate to poor. Regional changes in climate and basin configuration controlled the evolution of the fluvial regime and patterns of pedogenic maturity were not apparent.