The effects of climate change on eroding landscapes and the terrestrial sedimentary record are poorly understood. Using mountain catchment-alluvial fan systems as simple analogues for larger landscapes, a wide range of theoretical studies, numerical models and physical experiments have hypothesized that a change in precipitation rate could leave a characteristic signal in alluvial fan sediment flux, grain size and down-system fining rate. However, this hypothesis remains largely untested in real landscapes. This study measures grain-size fining rates from apex to toe on two alluvial fan systems in northern Death Valley, California, USA, which each have well-exposed modern and ca 70 ka surfaces, and where the long-term tectonic boundary conditions can be constrained. Between them, these surfaces capture a well-constrained temporal gradient in climate. A grain-size fining model is adapted, based on self-similarity and selective deposition, for application to these alluvial fans. This model is then integrated with cosmogenic nuclide constraints on catchment erosion rates, and observed grain-size fining data from two catchment-fan systems, to estimate the change in sediment flux from canyon to alluvial fan that occurred between mid-glacial and modern interglacial conditions. In a fan system with negligible sediment recycling, a ca 30% decrease in precipitation rate led to a 20% decrease in sediment flux and a clear increase in the down-fan rate of fining, supporting existing landscape evolution models. Consequently, this study shows that small mountain catchments and their alluvial fan stratigraphy can be highly sensitive to orbital climate changes over <10 5 year timescales. However, in the second fan system it is observed that this sensitivity is completely lost when sediment is remobilized and recycled over a time period longer than the duration of the climatic perturbation. These analyses offer a new approach to quantitatively reconstructing the effects of past climate changes on sedimentation, using simple grain-size data measured in the field.

Calabria is one of the fastest-uplifting and most seismically active regions in the Mediterranean, yet the time-averaged (~ 10 6 yrs) rates of normal faulting remain poorly constrained. Here, we use DEM analysis, geologic cross-sections, and a compilation of published data to quantify systematically along strike, the fault throws and timeaveraged throw rates of the Serre, Cittanova, Armo, East Crati and West Crati faults. We show that regional uplift has uplifted both their hangingwall and footwall blocks by ~200-400 m, and the Aspromonte massif by up to ~1150-1300 m. We find that these faults have throws between ~ 640-1430 m, and throw rates between ~ 0.7-1.5 mm/yr. Their footwall ranges have variable proportions of inherited relief, up to ~ 300-800 m. The channels draining these ranges reflect the active normal faulting and relief in their steepness indices, becoming ~5-8 m 0.9 steeper for each in 0.1 mm/yr throw rate increment and each 100 m relief increase. Finally, the presence of knickpoints suggests that these channels are transiently responding to changes in relative base level, which could be due to fault linkage or regional strain rate increases for the southern Calabrian faults; and to regional uplift acceleration in the case of the Crati faults. Supplementary material: 76 topographic profiles of the marine terraces, 146 river long profiles. Calabria is one of the fastest uplifting regions in the Mediterranean (e.g. Ferranti et al., 2006; Antonioli et al., 2006). Here, high relief is generated by the superposition of back-arc normal faulting and long wavelength regional uplift. However, the origin, timing and relative contributions of these two mechanisms are still highly debated (e.g.

The volumes, rates and grain size distributions of sediment supplied from hillslopes represent the initial input of sediment delivered from upland areas and propagated through sediment routing systems. Moreover, hillslope sediment supply has a significant impact on landscape response time to tectonic and climatic perturbations. However, there are very few detailed field studies characterizing hillslope sediment supply as a function of lithology and delivery process. Here, we present new empirical data from tectonically‐active areas in southern Italy that quantifies how lithology and rock strength control the landslide fluxes and grain size distributions supplied from hillslopes. Landslides are the major source of hillslope sediment supply in this area, and our inventory of ~2800 landslides reveals that landslide sediment flux is dominated by small, shallow landslides. We find that lithology and rock strength modulate the abundance of steep slopes and landslides, and the distribution of landslide sizes. Outcrop‐scale rock strength also controls the grain sizes supplied by bedrock weathering, and influences the degree of coarsening of landslide supply with respect to weathering supply. Finally, we show that hillslope sediment supply largely determines the grain sizes of fluvial export, from catchments and that catchments with greater long‐term landslide rates deliver coarser material. Therefore, our results demonstrate a dual control of lithology on hillslope sediment supply, by modulating both the sediment fluxes from landslides and the grain sizes supplied by hillslopes to the fluvial system. Copyright © 2017 John Wiley & Sons, Ltd.

One of the most conspicuous features of a mountain belt is the main drainage divide. Divide location is influenced by a number of parameters, including tectonic uplift and horizontal advection. Thus, the topography of mountain belts can be used as an archive to extract tectonic information. Here we combine numerical landscape evolution modelling and analytical solutions to demonstrate that mountain asymmetry, determined by the location of the main drainage divide, increases with increasing uplift gradient and advection velocity. Then, we provide a conceptual framework to constrain the present or previous tectonic uplift and advection of a mountain belt from the location and migration direction of its main drainage divide. Furthermore, we apply our model to Wula Shan horst, Northeastern Sicily, and Southern Taiwan.

A B S T R A C TA key factor in the downstream dispersal and fractionation of sediment is the grain size distribution of sediment supplied by upstream catchments. Modeling of the grain size distribution of modern bedload in the main trunk channels of tectonically uplifting catchments, including the sediment at their outlets, and the weathering products of a range of bedrock lithologies in southern Italy and Sicily reveals fractal dimensions of 2.3-2.7, similar to the fractal dimension of many natural materials undergoing fragmentation. We examine the impact of changing statistical properties of the grain size distribution of the sediment supply in simulating grain size trends in sedimentary basins. Model simulations show a marked movement of the gravel front and patterns of progradation and retrogradation in basin stratigraphy. These grain size trends and sedimentary architectures are generated simply by variations in the grain size mix of the sediment supply, without variations in base level or sediment discharge. Variation in the grain size distribution of the sediment supply may therefore act as a first-order control on sequence stratigraphic architectures in sedimentary basins.