Weathering Intensity in Lowland River Basins: From the Andes to the Amazon Mouth

Actively eroding mountains supply un-weathered material into large river basins. It is still not known whether these un-weathered minerals undergo significant chemical weathering during storage in continental alluvial deposits within the surrounding lowland areas. Here we use previously reported weathering and erosion fluxes of rivers from the Amazon Basin to assess this effect. We show that the fraction of total denudation (weathering plus erosion) occurring as dissolved export experiences only a slight increase during transfer through the lowlands. The overall low weathering intensity of Andean sediments throughout the Amazon basin is attributed to the fact that source rocks are recycled meta-sedimentary rocks.