Abstract Alluvial and fluvial fans are the most widespread depositional landforms bordering the margins of long-lived highland regions and actively subsiding continental basins, across a broad spectrum of tectonic and climatic settings. Their significance is relevant not only to the local morphodynamics of mountain regions and proximal basinal sectors, but also to the long-term evolution of sediment-routing systems, affecting the propagation of stratigraphic signals of environmental change and the preservation potential of stratal successions over much larger spatial scales than those they occupy. Subaerial fan systems archive information on the palaeoclimate, local tectonic history and landscape response to various allogenic factors, although our ability to decipher such information is still limited. Early recognition of alluvial fans dates from the late nineteenth century, but a coordinated research community on these systems has been active only over the last few decades and the full relevance of fluvial fan systems to the geomorphology of present day continental basins and to the interpretation of ancient stratigraphic successions has been convincingly demonstrated only over the last decade. This introductory chapter summarizes advances in our knowledge of alluvial and fluvial fans, identifies potential new lines of future inquiry, and presents the contributions to this volume in the context of the current state of research.

Abstract The role of climate change in driving alluvial-fan sedimentation is hard to assess in pre-Quaternary successions, for which detailed chronologies and climate-proxy records cannot be easily established. In the Teruel Basin (Spain), high-resolution (10 4 –10 5 years) chronological and palaeoclimatic information was derived by orbital tuning of Late Miocene mudflat to ephemeral-lake deposits. The semi-arid palaeoclimate made this low-gradient, basinal environment sensitive to thresholds in the local hydrological balance. Basic facies rhythms are attributed to alternating, relatively humid/arid phases controlled by the climatic precession cycle. The lower stratigraphic interval of this reference section interfingers with distal, coarse-clastic beds from a coeval alluvial fan. The consistent interdigitation of debris-flow deposits with distal strata indicative of arid-to-humid climate transitions shows that fan sedimentation was regulated by climate cyclicity. In particular, the largest volumes of terrigenous debris were shed from the fan onto adjacent mudflats during transitions to relatively humid periods with pronounced seasonality, during precession minima. Distal to medial sections within alluvial-fan outcrops also feature prominent, laterally continuous alternations of coarse- and fine-clastic packages. This high degree of architectural organization, uncommon in fan successions, and stratigraphic relationships with the reference section suggest orbitally controlled climate change to have been the forcing mechanism.

Abstract Fans, landforms that record the storage and transport of sediment from uplands to depositional basins, are found on Saturn’s moon Titan, a body of significantly different process rates and material compositions from Earth. Images obtained by the Cassini spacecraft’s synthetic aperture radar reveal morphologies, roughness, textural patterns and other properties consistent with fan analogues on Earth also viewed by synthetic aperture radar. The observed fan characteristics on Titan reveal some regions of high relative relief and others with gentle slopes over hundreds of kilometres, exposing topographic variations and influences on fan formation. There is evidence for a range of particle sizes across proximal to distal fan regions, from c. 2 cm or more to fine-grained, which can provide details on sedimentary processes. Some features are best described as alluvial fans, which implies their proximity to high-relief source areas, while others are more likely to be fluvial fans, drawing from larger catchment areas and frequently characterized by more prolonged runoff events. The presence of fans corroborates the vast liquid storage capacity of the atmosphere and the resultant episodic behaviour. Fans join the growing list of landforms on Titan derived from atmospheric and fluvial processes similar to those on Earth, strengthening comparisons between these two planetary bodies.