Deciphering the relative roles of allogenic versus autogenic controls on fluvial system architecture

Background. The preserved sedimentary architecture of fluvial successions serves as a valuable archive that records factors that govern the form and style of behaviour of fluvial systems. Development of novel and innovative techniques for deciphering the significance of this archive represents an active research avenue that has potential for gaining a better understanding of the complex and inter-dependent relationship between extrinsic (allogenic) and intrinsic (autogenic) controls on fluvial accumulation and long-term preservation. Throughout much of the 1980s and 1990s, allogenic processes such as changes in climate, tectonics and base-level were considered essentially distinct and unrelated to autogenic factors such as style of lateral accretion and avulsion in fluvial systems. However, it is now increasingly recognised that allogenic and autogenic processes operate as interdependent controls on fluvial systems and complex feedback relationships have recently been identified (Colombera et al., 2015). Identifying and quantifying the nature and impact of these interdependent relationships is not straightforward because the preserved geological record of fluvial successions is highly varied. One promising approach to addressing this issue is the quantitative characterization of fluvial successions using a database approach whereby many aspects of fluvial system architecture from many different fluvial system types (both ancient and modern) and from different sedimentary settings (e.g. rift versus foreland basins) are stored in a relational database that can be queried in a sophisticated manner to identify common trends (Colombera et al., 2012, 2013). From an applied standpoint, the development of a database of fluvial architectural styles is significant because it offers the opportunity to develop quantitative models of sedimentary architecture that can be used to make informed predictions regarding likely sand-body distribution, size, lateral extent, connectivity, and overall net-to-gross in a variety of reservoir settings (Colombera et al., 2014). Stratigraphic heterogeneity presents significant challenges for characterizing subsurface reservoirs, including: (i) meso-scale prediction of sand-body architecture and connectivity; (ii) stacking patterns of high-quality channelized facies and elements; and (iii) predicting the effects of macro-scale controls on system-scale spatial variability and stratigraphic evolution at the basin scale.
Aim and objectives. The aim of this project is to develop a series of architectural and sequence stratigraphic models for fluvial successions preserved within a range of rift and foreland sedimentary basin types and to encapsulate these models and the data that underpin them within a database that can be used to predict fluvial system architecture for different basin types and for different climatic settings. A specific research objective is to demonstrate evidence to show that primary allogenic and autogenic controls on preserved fluvial sequence architecture are interdependent and interrelated via a series of complex feedback mechanisms. The research will involve development and employment of the Fluvial Architecture Knowledge Transfer System (FAKTS), a relational database designed and populated by members of FRG-ERG at Leeds. This database will be used to address the following research questions.
1) What is the 3D facies architecture, internal and external heterogeneity, and connectivity of sand-bodies within fluvial systems and their preserved successions in rift and foreland basin settings subject to different climatic settings?
2) How does sand-body connectivity and stacking pattern vary spatially and temporally within such basins as rates of accommodation generation vary?
3) Can generic models be developed to demonstrate a link between sites of channel sand-body amalgamation and sites of sand-body isolation?
4) How do changes to allogenic factors such as climate and tectonic subsidence rate influence autogenic system behaviour such as style of lateral accretion and avulsion of channels and how might is this manifest in the preserved stratigraphic record?
5) How do such controls govern sedimentary heterogeneity at the meso- and macro-scales?
6) What are the implications of the operation of interdependent allogenic and autogenic controls on fluvial system architecture for making predictions regarding reservoir quality in rift and foreland basin settings?