Forcing controls on sediment generation and erosion rates in the Earth’s highest coastal range: the Sierra Nevada de Santa Marta (NE Colombia)

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The aim of the project is to study and quantify erosion rates and related controlling mechanisms in the Sierra Nevada de Santa Marta, the highest coastal mountain range on Earth. Sedimentation rates and sediment production are largely determined by external forcing controls as tectonics, climate and lithology which in turn regulate exhumation, water availability and mineralogical response to both mechanical and chemical weathering. 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. River sediments convey a number of information reflecting the provenance signals resulting from detrital contribution of each watershed and are therefore more suitable to constrain erosion rates than other techniques focussing on bedrock. As with any other detrital approach (e.g., sediment gauging, cosmogenic nuclides, and thermochronology), however, the use of mineralogical data to estimate landscape evolution is based on a number of assumptions and limitations. The Sierra Nevada de Santa Marta (SNSM) in the Colombian Caribbean, represent a unique area where to study and quantify the forcing factors regulating sediment generation, production, and transfer in active tectonic settings where chemical weathering prevail. In fact, the combination of high exhumation rates (>1mm/year), the tropical climate, the lithological distribution, the pyramid shape and consequent radial drainage, constitute the ideal conditions for studying the interplay of these factors and their role in determining sediment production, transfer and composition. The research aims at tackling the geological problems using a multidisciplinary approach including analytical tools as cosmogenic nuclides, mineralogy (bulk petrography and Raman heavy mineral analysis), geochemistry and geochronology combined to high-resolution geomorphological and structural analyisis. The suite of analytical techniques also guarantees to avoid (or at least minimise) the potential biasing factors (e.g. mineral fertility) which can alter the correct identification and quantification of contributing lithologies. Fundamental scientific questions focus on (i) the response of each lithology to tectonic and climatic controls and how this controls sediment generation, (ii)the resulting sediment composition delivered by rivers, (iii) the influence of morphological features of drainages eroding and carrying sediments around the SNSM, (iv) the controls regulating erosion and sedimentation patterns for eachdrainage system.