Correlation of fluvial strata in the subsurface–a review

Correlation of ancient fluvial strata in the subsurface is challenging due to complex facies architectures and the lateral discontinuity of facies over short distances (>10 km). The complexity of the strata is due to the interplay of allogenic factors that determine the rate of creation of accommodation, sediment supply and ultimately fluvial architectures on regional scales. The application of commonly used stratigraphic techniques in such successions has allowed for improved regional correlations and an enhanced understanding of the evolution of basin fills. Lithostratigraphy, biostratigraphy, chemostratigraphy, magnetostratigraphy, event stratigraphy, sequence stratigraphy, pedostratigraphy, chronostratigraphy (in particular geochronology), cyclostratigraphy, and provenance stratigraphy are assessed, outlining their benefits, drawbacks and application using several case studies. Lithostratigraphy is highly discouraged as facies boundaries are often time-transgressive. On the contrary, chemostratigraphy, event stratigraphy and provenance stratigraphy show excellent potential for correlating ancient fluvial strata as key signatures can be recognized between different localities over distances greater than 25 km. The character and thickness of paleosols can also greatly enhance both sequence stratigraphic and pedostratigraphic correlations. The most promising correlation technique involves the use of chronostratigraphy (in particular geochronology). The high-precision radiometric dating of tuffs, or precisely dating the youngest zircon population in a sandstone sample using U–Pb CA-TIMS (when available) provides a precise and independent way to correlate fluvially-dominated strata unambiguously over large distances (>100 km). The integration of several techniques, such as sequence stratigraphy in conjunction with pedostratigraphy, is also recommended to construct a comprehensive stratigraphic framework for fluvially-dominated successions. The most appropriate correlation technique is dependent on several factors including budget, the purpose and scope of the study and whether the data come from outcrops or the subsurface. Improved correlations will enhance our understanding of ancient fluvial systems and their resource potential.