[1] The sculpture of valleys by flowing water is widely recognized, and simplified models of incision by this process (e.g., the stream power law) are the basis for most recent landscape evolution models. Under steady state conditions a stream power law predicts that channel slope varies as an inverse power law of drainage area. Using both contour maps and laser altimetry, we find that this inverse power law rarely extends to slopes greater than ∼0.03 to 0.10, values below which debris flows rarely travel. Instead, with decreasing drainage area the rate of increase in slope declines, leading to a curved relationship on a log-log plot of slope against drainage area. Fieldwork in the western United States and Taiwan indicates that debris flow incision of bedrock valley floors tends to terminate upstream of where strath terraces begin and where area-slope data follow fluvial power laws. These observations lead us to propose that the steeper portions of unglaciated valley networks of landscapes steep enough to produce mass failures are predominately cut by debris flows, whose topographic signature is an area-slope plot that curves in log-log space. This matters greatly as valleys with curved area-slope plots are both extensive by length (>80% of large steepland basins) and comprise large fractions of main stem valley relief (25–100%). As a consequence, valleys carved by debris flows, not rivers, bound most hillslopes in unglaciated steeplands. Debris flow scour of these valleys appears to limit the height of some mountains to substantially lower elevations than river incision laws would predict, an effect absent in current landscape evolution models. We anticipate that an understanding of debris flow incision, for which we currently lack even an empirical expression, would substantially change model results and inferences drawn about linkages between landscape morphology and tectonics, climate, and geology.

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Valley incision by debris flows: Evidence of a topographic signature

The study of source‐to‐sink systems relates long‐term variations in sediment flux to morphogenic evolution of erosional–depositional systems. These variations are caused by an intricate combination of autogenic and allogenic forcing mechanisms that operate on multiple time scales – from individual transport events to large‐scale filling of basins. In order to achieve a better understanding of how these mechanisms influence morphological characteristics on different scales, 29 submodern source‐to‐sink systems have been investigated. The study is based on measurements of morphological parameters from catchments, shelves and slopes derived from a ∼1 km global digital elevation model dataset, in combination with data on basin floor fans, sediment supply, water discharge and deposition rates derived from published literature. By comparing various morphological and sedimentological parameters within and between individual systems, a number of relationships governing system evolution and behaviour are identified. The results suggest that the amount of low‐gradient floodplain area and river channel gradient are good indicators for catchment storage potential. Catchment area and river channel length is also related to shelf area and shelf width, respectively. Similarly to the floodplain area, these parameters are important for long‐term storage of sediment on the shelf platform. Additionally, the basin floor fan area is correlative to the long‐term deposition rate and the slope length. The slope length thus proves to be a useful parameter linking proximal and distal segments in source‐to‐sink systems. The relationships observed in this study provide insight into segment scale development of source‐to‐sink systems, and an understanding of these relationships in modern systems may result in improved knowledge on internal and external development of source‐to‐sink systems over geological time scales. They also allow for the development of a set of semi‐quantitative guidelines that can be used to predict similar relationships in other systems where data from individual system segments are missing or lacking.

Relationships between morphological and sedimentological parameters in source-to-sink systems: a basis for predicting semi-quantitative characteristics in subsurface systems

Melanges represent a significant component of collisional and accretionary orogenic belts and occur widely around the world. Since its first introduction and use, the term has evolved to cover both processes (tectonic, sedimentary, and diapiric) and tectonic settings of melange formation. The meaning and significance of various terms referring to the origin of ‘block-in-matrix chaotic rocks’ are still subject to debate. This study presents a historical overview of the evolving melange concept and investigates the relationships between melange types and their tectonic settings of formation. We investigate the contribution of mass-transport versus contractional deformation processes at the onset of melange formation and throughout the evolution of different melange types, and the nature of the continuum and transition from broken formations to true tectonic melanges. A melange is a mappable chaotic body of mixed rocks with a block-in-matrix fabric whose internal structure and evolution are intimately linked...

Mélanges and mélange-forming processes: a historical overview and new concepts

Oxalate production by fungi: significance in geomycology, biodeterioration and bioremediation

The Schmidt Hammer, originally designed for testing the hardness of concrete in 1948, was first used in a geomorphological context in the 1960s. Since then the advantages and disadvantages of the device for measuring rock characteristics have become apparent, and the Schmidt Hammer has been used for an increasing range of purposes, including the study of various weathering phenomena, the relationships between rock strength and landform, and for relative dating of a range of Holocene features. Readings of rock hardness have often been found to correlate well with other measures of rock character, such as uniaxial compressive strength and Young’s Modulus of Elasticity.

The Schmidt Hammer in geomorphological research

The Cilento Group (Lower-Middle Miocene), the Monte Sacro Conglomerate (Upper Miocene), the Gorgoglione Formation (Upper Miocene), and the Crati submarine fan (Holocene) are four turbidite sequences deposited in northwest-southeast-trending thrust-top basins of the southern Apennines (Italy) foreland region. The Corigliano basin is a part of the modern Taranto Gulf foredeep basin that developed since the late Pleistocene. Sandstone detrital modes of the Miocene turbidite units are quartzofeldspathic (Petrofacies 1, 2a, 4, 5, 8; Q62F25L13), quartzolithic (Petrofacies 2b; Q60F16L24), and arkosic (Petrofacies 7; Q50F45L5, reflecting a collisional orogenic provenance. Volcanolithic sandstones (Petrofacies 3, Q23F11L66) suggest an important contribution also from a volcanic source area related to the convergent-continental-margin volcanism connected with the collisional tectonic regime that affected the western Mediterranean (e.g., Sardinia volcanic arc). Individual carbonatoclastic beds (hybrid arenite, biocalcarenite, and mudstone) are interbedded with sandstone units of the ilento Group. They have siliciclastic content of about 35% and are quartzofeldspathic (Petrofacies 6; Q53F23L24). These beds (0.10-65 m thick) record impulsive gravitational collapses of the carbonate-platform passive margin to the east and southeast. The petrologic parameters show a temporal evolution from metasedimentary to granitic-gneissic provenance ascribed to different tectonostratigraphic units of the Calabrian arc. Nine Miocene petrofacies suggest dynamic evolution of the source terranes from Laughian to Tortonian time. Facies, dispersal patterns, and petrologic parameters of the Miocene sandstones suggest a provenance from the northern and western margins of the basins. Comparison between the Holocene Crati Fan (Petrofacies 9; Q54F24L22) and Miocene detrital modes suggests that the sandstones of the Cilento Group, the Monte Sacro Conglomerate, and the Gorgoglione Formation were derived from unroofing of the thrusted basement block, transported by torrential-type, fluvio-deltaic systems and then funneled into a major turbidite dispersal system, analogous to the modern Crati submarine fan of the Corigliano thrust-top basin.

Detrital modes and provenance of Miocene sandstones and modern sands to the Southern Apennines thrust-top basins (Italy)

Weathering and morphogenesis in a mediterranean climate, Calabria, Italy

Plutonic and gneissic rocks of the Sila Massif in the uppermost portion of the Neto drainage basin (Calabria, Southern Italy) weather and erode under a humid Mediterranean climate. During the development of weathering profiles, a combination of chemical weathering and granular disintegration processes occurred. Chemical weathering involves a loss of both plagioclase (mainly during grus generation) and K-feldspar (mainly during soil formation). This loss is attributed to transformation of plagioclase to clay minerals and to leaching and dissolution of K-feldspar. Sand composition is quartzofeldspathic and nearly homogeneous along the main channel of the Neto River, even where the river cuts across a blanket of sedimentary cover. Thus, fluvial transport does not alter sand composition within the Neto drainage basin. Petrographic indices are effective in (1) discriminating between contributions from similar (granite and gneiss) source rocks (Qm/F); (2) relating the provenance of plutoniclastic and gneissiclastic sand found in the headwaters to grus horizons (Qm/F; Q/Rg); and (3) distinguishing between upstream first-cycle and downstream multicycle sand (Q/Rg). This last distinction is further emphasized by considering both aphanitic and phaneritic varieties of rock fragments (RgRmRs diagram). Chemical weathering is the main sand producer within the regolithic environment in northern Calabria. In addition, rapid erosion resulting from steep slopes removes weathered products, and rapid and short transport leads to minimal sediment maturation. In general, the F/Q index is climate and relief dependent; thus, it should be used in conjunction with palaeoclimatic and palaeophysiographic evidence for provenance interpretations of ancient quartzofeldspathic sandstones.

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The effects of source rocks and chemical weathering on the petrogenesis of siliciclastic sand from the Neto River (Calabria, Italy): implications for provenance studies

The Transverse Ranges of southern California represent an uplifted and variably dissected Mesozoic magmatic arc, and Mesozoic to Holocene sedimentary and volcanic strata deposited in convergent and transform tectonic settings. Modern sand within part of the Western Transverse Ranges represents: first-order sampling scale of the Santa Monica and the San Gabriel Mountains; second-order sampling scale of the Santa Clara River draining both mountain ranges; and third-order sampling scale of the beach system between the mouth of the Santa Clara River and the eastern Santa Monica Mountains, and turbidite sand of the Hueneme-Mugu submarine fan.



Source lithology includes plutonic and metamorphic rocks of the San Gabriel Mountains, and sedimentary and volcanic rocks of the Santa Monica Mountains. First-order sands have large compositional variability. Sand from local coastal drainage of the Santa Monica Mountains ranges from basaltic feldspatholithic to quartzofeldspathic. Sand of the San Gabriel Mountains local drainages has three distinct petrofacies, ranging from metamorphiclastic feldspatholithic to mixed metamorphi/plutoniclastic and plutoniclastic quartzofeldspathic. Second-order sand is represented by the main channel of the Santa Clara River; the sand has an abrupt downstream compositional change, from feldspathic to quartzofeldspathic. Third-order sand (beaches and deep-sea turbidite samples) of the Santa Monica Basin is quartzofeldspathic. Beach sand is more quartz-rich than is Santa Clara river sand, whereas turbidite sand is more feldspar-rich than is beach sand. Deep-sea sand has intermediate composition with respect to second-order samples of the Santa Clara River and third-order samples of the beach system, suggesting that (1) the Santa Clara River is the main source of sediments to the marine environment; and (2) local entry points from canyons located near local drainages may generate turbidity currents during exceptional flood conditions. Petrologic data of modern sand of the study area are highly variable at first- and second-order scale, whereas third-order sand is homogenized. The homogenized composition of deep-marine sand is similar to the composition of most ancient sandstone derived primarily from the Mesozoic dissected magmatic arc of southern California. This study of the Western Transverse Ranges illustrates the effects of source lithology, transport, depositional environment, and sampling scale on sand composition of a complex system, which provides insights regarding actualistic petrofacies models.

The effects of source lithology, transport, deposition and sampling scale on the composition of southern California sand

Weathering and soil features in the upland landscapes developed on granitic terrains of the Sila Grande Massif (Calabria, South Italy) have been studied in this work. The attempt to link field scale and micromorphological observations in order to better understand the main weathering processes and their controlling factors is revealed to be very powerful. Six soil profiles in the area around the Cecita Lake, representative of different geomorphological units, were characterised by field work, optical microscopy and SEM-EDS analysis. A strong influence on weathering and pedogenesis by micro-scale features of primary minerals and parent rock fabrics is shown. Key roles are played also by relief, in the development and preservation or stripping of regolith + soil mantles in relation to natural and man-induced phenomena; by time, controlling rates and degree of development of the main weathering features; by climate, in terms of type and intensity of dominant processes.

Emilia Le Pera

Papers

Detrital modes and provenance of Miocene sandstones and modern sands to the Southern Apennines thrust-top basins (Italy)

Weathering and morphogenesis in a mediterranean climate, Calabria, Italy

The effects of source rocks and chemical weathering on the petrogenesis of siliciclastic sand from the Neto River (Calabria, Italy): implications for provenance studies

The effects of source lithology, transport, deposition and sampling scale on the composition of southern California sand

Weathering and pedogenesis in the Sila Grande Massif (Calabria, South Italy): From field scale to micromorphology