Transgressive depositional systems: coastal deltas and incised valley fills

Esther Stouthamer, Steven Darby, Douglas Edmonds

The surface and subsurface of Holocene deltas and incised valley fills are formed under the influence of post-glacial sea-level rise, in interplay with sediment supply, tectonics, and autogenic processes. Upstream sediment supply to a delta or incised valley is mainly controlled by climate and human impact (e.g. river damming). Downstream deposition is controlled by coastal morphology, waves, tides, and rivers debouching into the sea or ocean. Besides these up- and downstream controls, inherited topography and autogenic forcing within a delta system or incised valley determines its depositional development over time.
In this session we focus on post-glacial depositional processes in transgressive systems, their surficial evolution and resulting subsurface architecture over time. We specifically welcome contributions on how changes in upstream (e.g. climate, human intervention) and downstream (e.g. sea-level) boundary conditions, autogenic processes (e.g. avulsion), and fluvial-coastal interaction over time influence the coupled evolution of the surface and subsurface of modern deltas and river plains.

Flood sequences and paleofloods

Rajiv Sinha

Several parts of the world frequently experience large floods and understanding the temporal variability of the flooding events at historic scale and to pinpoint the causal factors have been popular research topics. Several large floods in southeast Asia have occurred during the post-1950 period and a majority of these coincide with the excess monsoon epochs. However, the identification of pre-historic floods (paleofloods) in sedimentary records has always been a challenge. Even though several large rivers in the world are highly susceptible to floods, only some of them are geomorphologically suitable for paleoflood analysis. Paleoflood data are increasingly becoming important for flood risk assessment as the classical flood frequency analysis using historical flood data are often not adequate in several regions. It is equally important to understand the feedbacks of landuse changes, sediment dynamics, and climate change on floods. We welcome abstracts on this important area of research which requires an integration of sedimentology with hydrology and geomorphology for process understanding of flood sequences and paleofloods.

Megafan and fans sedimentology

Anne Mather, Laura Evenstar, Adrian Hartley

Landforms described as alluvial fans/megafans form across a spectrum of spatial (a few km2 to >1000km2 ) and temporal (century to millennial) scales. They are just one part of a system which comprises a catchment area and an associated depositional fan body. Within sedimentary basins it is typically the larger fan systems that are most likely to be preserved over the longest time-scales, and provide the longest, though not necessarily most complete sedimentary record. Often, particularly on large systems, the catchment area may have a very different climate to the associated fan depositional body. The fan depositional processes thus provide a valuable record of the catchment area characteristics such as mountain range climate, whilst the internal stratigraphy of the fan may reflect forcing factors such as significant catchment changes (e.g river capture; climate change) and piedmont tectonics. Alluvial fan systems are consequently powerful records of longer-term landscape change. We encourage papers on any aspect of fans and megafans embracing field, laboratory, theoretical, and numerical approaches intended to advance our knowledge of how to unlock the potential from alluvial fan archives. In particular we encourage contributions addressing sedimentary process and scaling relationships across fan systems and novel quantitative approaches to better understanding fan despositional systems.

Geoarchaeology of alluvial environments: hydroclimate and ancient society

Willem Toonen, Julie Durcan, Kim Cohen

Alluvial environments have always been a focus for human activity, and studies of human-environment interactions are a key theme within geo- and archaeological studies. However integrated studies are relatively rare, despite the dynamic and complex relationships between humans and the fluvial environment. At local and regional scales, there are examples where climatic variability and changing alluvial contexts have represented both opportunities and challenges for humans. We welcome papers considering relationships between ancient societies and environment. The session has no fixed temporal focus; instead contributions spanning a broad time range are encouraged - from early hominids, Mesolithic hunter-gatherers, Old World riverine civilizations, to the historical period. Furthermore, we invite papers on methodological advances; i.e. resolving fluvial archives and palaeohydrologic extremes (floods and droughts), improving chronologies, or incorporating analysis of large datasets that are pivotal to understand human-river-climate interactions.