ALBERT

Description: Spatial and temporal relationships between climate, tectonics, and sea level have a primary control on sediment transport, storage, and deposition in onshore and offshore depositional environments. Although many simplistic models have tried to predict onshore system behavior and sediment partitioning between onshore and offshore depositional environments in response to changes in these boundary conditions, the alluvial response to changes in external forcings coupled with autogenic processes can be highly complex and unpredictable. The Golo source-to-sink system, on the eastern margin of the island of Corsica in the Mediterranean Sea, provides an ideal laboratory to study sediment partitioning in both onshore and offshore realms. The terrestrial part of the system consists of the Golo River, which debouches onto a narrow shelf (~ 10 km), which in turn passes into a narrow (~ 45 km) confined basin known as the Corsica Trough, dominated by submarine fan deposits. Estimates on timing of late Quaternary fluvial aggradation are compared with timing of sediment storage on the shelf and on the basin-floor fan. The results indicate that onshore deposition and storage of sediment in the fluvial system may occur both during sea-level highstand, transgression, and lowstand. Volume calculations from the alluvial record show that onshore storage is relatively low (~ 13%) relative to the overall sediment budget. Comparing estimated deposition rates with a sediment prediction model further suggests that deep-sea fan sedimentation rates at times may be up to 50% higher or 25% lower than what is being supplied by the river, indicating temporary storage and release of sediment on the shelf. On average, however, there is good agreement between predicted and calculated sediment volumes in the Golo system. The study demonstrates the value of investigating the entire source-to-sink system in order to obtain a comprehensive understanding of sediment dispersal between onshore and offshore depositional environments over 104 year timescales. Observations suggest that alternating periods of aggradation and degradation of the Golo River are controlled by system thresholds controlled from within the catchment. Comparison with climate proxy data and timing of major alluviation events elsewhere in the Mediterranean region supports the notion that each source-to-sink system has a unique threshold that must be exceeded to induce regional aggradation and subsequent terrace formation. The same is also inferred for timing of sediment dispersal to the deep-sea environment. In addition, preservation of onshore sediment is controlled by local factors such as uplift rate and its impact on the aggradational response. It is, therefore, expected that the onshore record may be diachronous on local, regional, and global scales, making detailed correlation difficult except for the most extreme events. Finally, stream incision rates appear to be one to two orders of magnitude higher than regional hinterland denudation rates, indicating that the Golo system is characterized by increasing landscape relief.

Description: Shelves have previously been classified according to a wide range of criteria, such as tectonic, morphological, climatic, and process-based classifications. Here, the formation of shelves is discussed in the context of conditioning from sedimentary and tectonic processes. A three-fold division of shelves is proposed: sedimentary shelves, combined structural–sedimentary shelves, and structural shelves. With a definition of a shelf as a shallow-marine surface of large areal extent located around the margin of a deeper basin (relief hundreds to thousands of meters), most cases of shelf formation can be explained by means of sedimentation, with the only contribution from tectonics being long-term accommodation provided by basinal subsidence. These sedimentary shelves are formed by virtue of differential sediment deposition basinwards in combination with nucleation and propagation of a break in slope around or close to the shoreline. Additional conditions for the formation of sedimentary shelves include (1) deep frontal waters; (2) a hinterland that can deliver a sediment budget large enough to prograde the margin; and (3) transgressions that periodically flood back across the low-gradient coastal and alluvial plains.A structural shelf is a shelf where the shelf edge is a subaqueous structural feature (e.g., a fault escarpment), not propagated by sedimentation, usually sediment starved. Commonly, sediment has draped and infilled smaller-scale topography. Combined structural–sedimentary shelves have a direct structural nucleation of the shelf–slope break. This initial break is then blanketed and propagated by sediments retaining a shelf–slope-break topography which is displaced relative to its structural heritage.

Description: Production, transport, and deposition of siliciclastic sediments takes place across changing altitudes, physical processes, environments, and controls en route from source to sink commonly through a downstream narrowing and then broadening fairway of sediment grains, constituting giant “hourglasses” of nature, a fundamental unit of both geomorphology and sedimentology. Here we review the status of the rapidly evolving multidisciplinary source-to-sink approach, and compare it with the more mature sequence stratigraphic approach. The latter uses outcrop, well, and seismic data to gain information about elements of basin fills with less data coverage and is thus mainly a “sink-to-sink” approach. Source-to-sink on the other hand aims to understand the dynamics and budgets of the complete onshore–offshore sediment fairway, including elements of the transect that are no longer preserved. Furthermore, we summarize the spatial and temporal variability of source-to-sink systems, and discuss qualitative and semiquantitative methods for reconstruction of area, relief, and sediment supply from source terrains. The variability of source-to-sink systems is viewed in the framework of three end-member types, “steep, short, and deep,” “wide and deep,” and “wide and shallow,” where each is characterized by typical patterns of sediment partitioning and long-term preservation. Modern and sub-modern systems are keys to enhance our understanding of their ancient counterparts. Three different time-framework categories for source-to-sink analysis are presented: modern systems, pre-modern Quaternary systems, and pre-Quaternary systems, all of which have large differences when it comes to amount and type of data, controlling factors, accuracy in interpretation, and societal applications. Importantly, systems are evolving through time with the effect that estimations of source-area parameters for one period of time may change significantly into another when boundary conditions are different. Sink reconstruction can, with variable confidence, be established through the use of seismic-reflection, well, and outcrop data, whereas reconstruction of source relief, drainage, and sediment production is a more challenging task. Methods like landscape interpolation, sediment volume backfilling, geomorphological scaling relationships, sediment-load estimations from river data and from stratigraphy as well as geochemical data can, preferably in combination, be used to unravel past source terrains. These methods are presented along with a discussion on how they can improve models for basin fill. Sink and source reconstruction is a two-way process. Source reconstruction sheds light on sink understanding and vice versa. This integrated approach is a prerequisite for further advance in source-to-sink studies. The prognosis of source-area parameters may give additional insight into the complete erosional–depositional system in general and sediment supply in particular and hence enables us to arrive at more robust models and predictions for the sink where resources commonly are contained.