From gullies to mountain belts: A review of sediment budgets at various scales

This paper reviews the state of the art in the concept as well as in the application of sediment budgets in sedimentary research. Sediments are a product of mass dispersal at the Earth surface and take part in global cycles. Sediment budgets aim at quantifying this mass transfer based on the principle of mass conservation and are the key to determine ancient fluxes of solid matter at the earth surface. This involves fundamental questions about the interplay of uplift, climate and denudation in mountain belts and transfer of sediments from the continents to the oceans as well as applied issues such as soil and gully erosion, reservoir siltation, and coastal protection. First, after introducing basic concepts, relevant scales and methodologies, the different components of Quaternary routing systems from erosion in headwaters, river systems, glacial and paraglacial systems, lakes, deltas, estuaries, coasts, shelves, epicontinental seas, and deep-sea fans are discussed in terms of their sediment budget. Most suitable are sedimentologically closed or semi-closed depositional environments e.g. alluvial fans, lakes, deltas and deep-sea fans. In a second step, the dynamics of passive, active, and collisional tectonic settings and sediment budgets in related sedimentary basins are explored and new concepts of sediment portioning at large geodynamic scales are introduced. Ancient routing systems are more or less incomplete and may be intensively fragmented or destroyed in active tectonic settings. In terms of sedimentary basin types, rifts, intracontinental and epicontinental settings are preferred objects of sediment budgets, because of their persistence and relatively simple overall sedimentary architecture. However, closing basins, such as foreland, forearc, retroarc, piggy-back and wedge-top basins may provide excellent snapshots of orogenic sediment fluxes. In a third step, the large long-lived routing systems of the Amazon, the Ganges-Brahmaputra, and the Rhine are reviewed. For each system estimates of either sediment volumes (mass) or sediment fluxes of continental and marine subsystems have been compiled in order to receive a complete routing in terms of mass conservation for specific time periods since the Late Glacial Maximum as well as the Cenozoic. Following lessons can be taken from these case studies: (i) depositional centers and fluxes show strong shifts in space and time and call for caution when simply looking at subsystems, (ii) the response times of these large systems are within the Milankovich time interval, thus lower than predicted from diffusion models, (iii) cyclic routing of sediments in continental basins is much more dominated by climate (human) control than by eustacy. and (iv) at long time scales, ultimate sinks win over intermittent storage. It is concluded from this review that the quantitative understanding of global sediment cycling over historic and geologic time and its response to allogenic forcing is still in its infancy and further research is needed towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with global biogeochemical cycles. This includes (i) to better determine response times of large routing systems by linking Quaternary with Cenozoic sediment budgets and continental with marine sub-systems, (ii) to combine advanced provenance techniques with sediment budgets in order to reconstruct ancient systems, (iii) to study sediment partitioning at the basin scale, (iv) to reconcile continental, supply-dominated sequence stratigraphy with the eustatic-dominated marine concept, and (iv) to account for non-actualism of ancient systems with respect to their erosion and transport mode, in particular, during glaciations and pronounced arid intervals. Glacial and eolian sediment routing may cross over hydrologic boundaries of drainage basins, thus challenging the principle of mass conservation. (C) 2012 Elsevier B.V. All rights reserved.