Fluvial and alluvial system response to rift basin evolution

The accumulated stratigraphy of alluvial and fluvial successions constitutes a significant proportion of the fill of many continental rift basins. Subsurface studies commonly fail to adequately account for sedimentological complexity, and field-based and remote sensing studies typically focus on a single scale of observation. Detailed analyses of alluvial and fluvial sedimentary successions across multiple scales are required to examine the roles played by extrinsic and intrinsic depositional controls, and to determine response to ongoing basin evolution. Three studies have been undertaken to improve understanding of alluvial fan and fluvial system response to rift evolution. First, three modern-day tilt-block crests from active rifts are analysed through the measurement of their developed catchment and associated fan system morphometrics. Comparisons are made of systems sourced over the footwall slope and those sourced over the hangingwall dipslope. Moreover, comparisons are made of each rift setting and their climatic regimes. The importance of system scale is examined: as catchment size decreases, so fan size decreases, though at a markedly reduced rate. Alluvial fan systems are especially important in smaller rift zones. Second, a 600 m-thick conglomerate-dominated alluvial synrift succession from the Gulf of Corinth, Greece, is analysed through interpretations of facies elements and architectural elements within the context of a spatially and temporally complex framework of rift basin evolution. The system developed as an alluvial fan sourced externally from the rift over the hangingwall dipslope. Rift sedimentation led to overfilled basin conditions, which transitioned rapidly to underfilled conditions following the onset of intrabasinal faulting, which induced rapid subsidence. Results demonstrate the importance of rift evolution as a control on the distribution of depositional environments. Third, 1,531 conglomerate clasts from eight conglomerate lithofacies of a single synrift succession are examined in terms of their qualitative (roundness, composition, shape) and directional (axis lengths, dips, orientations) characteristics. Comparisons between facies enable detailed reconstructions of formative depositional process. The results are integrated to develop a suite of models that improve our understanding of the links between basin-scale dynamics and resultant synrift alluvial stratigraphy, notably allowing for enhanced subsurface prediction of their character.