| Abstrakt: |
This study investigates the upper Magdalena river basin (Colombia), which is characterized by tectonic activity, tropical climate, heterogeneous lithological assemblages, and anthropic influence. It aims to comprehend factors controlling sediment generation, flux, and composition by incorporating petrographic data from 27 recent fluvial samples along with geochemistry, geomorphological parameters, historical precipitation, land cover, landsliding and suspended sediment load data. The analysis shows mismatches between sand composition and drainage lithology distribution. A new set of endmember mixing models is presented, quantifying the impacts of erodibility, sand generation potential (related to lithology), and sediment connectivity between hillslopes and river outlets (related to geomorphology). Results show enhanced sediment generation from sedimentary rocks (up to 40%) due to high erodibility, and decreased sediment flux from low‐ to medium‐grade metamorphic rocks (up to 60%) due to controlling morphometric parameters. Overrepresentation of plutonic and high‐grade metamorphic rocks and underrepresentation of volcanic rocks (up to 100%) are controlled by mineralogical and textural parameters. Enhanced landsliding activity in areas with volcanic activity occasionally overshadows basin‐wide compositional trends driven by morphological and lithological characteristics, as it controls rare overrepresentation of volcanic and low‐grade metamorphic detritus in the sand fraction. Sediment retention by hydroelectric dams significantly decreases suspended sediment flux by 30%, while deforestation plays a minor role in sediment flux. This study underscores the importance of coupling sediment generation, geomorphology and the distribution of stochastic events related to seismic activity in any sediment production‐focused study and for developing numerical models in Quantitative Provenance Analysis (QPA). Plain Language Summary: This study examines what controls the production of sand and its transport in rivers in a region with a tropical climate, earthquakes, different rock types and human interventions in nature: the upper reaches of the Magdalena River in Colombia. Compositional data of river sediment along with various spatial data sets have been used. The analysis shows that rock types do not occur in the same proportions in the sand as they do in the catchment areas. A new mathematical model is presented showing how different rock types and characteristics of the mountain slopes affect sand production and transport. Mobilization of sediment by landslides can significantly alter sand compositions, particularly in areas with active volcanism. Sediment transport in suspension decreased by 30% due to the operation of the hydroelectric Betania dam. This study underscores the importance of carefully considering rock type and geomorphology in any study on sediment production and transport as well as in creating mathematical models in this field. Key Points: Lithological characteristics and hillslope morphometry are the dominant controls on sand generation and flux in the Upper Magdalena ValleyThe distribution of landsliding events locally overshadows lithological and morphometric basin‐wide controls on sand compositionsThe construction of hydroelectric reservoirs decreased suspended sediment flux by 30% [ABSTRACT FROM AUTHOR] |
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