PREDICTING SAND MINERALOGY WITHIN CORDILLERAN OROGENIC SYSTEMS: MACHINE LEARNING APPLIED TO A GLOBAL DATABASE OF MODERN-PLEISTOCENE SAND SAMPLES (Invited Presentation)

The mineralogy of clastic sand has long been used to decipher the provenance of Cordilleran orogenic systems, with pioneering studies in the 20^th century relating framework grain compositions to end-member geodynamic settings. Application of these tectonically focused models has been widely used to deduce the paleogeographic and paleotectonic context of ancient sedimentary systems, particularly when integrated with radioisotopic dating of detrital minerals and other approaches to provenance analysis. Although multiple studies have corroborated the general linkage between sand mineralogy and geodynamic setting, the actual system of processes that control sand mineralogy is complex, particularly because of interactions and feedbacks between fundamental controlling parameters (e.g., source lithology, climate, relief, slope, etc.) within sediment routing systems.

This presentation explores a new global prediction of sand mineralogy (GloPrSM) with an emphasis on the North and South American cordillera. GloPrSM is based on paired random forest models that predict the total abundance of quartz (Q), feldspar (F), and lithics (L), along with sub-grain types, for level 8 watersheds (~8,000 km² mean area) of the BasinATLAS dataset. The GloPrSM model is calibrated using modal point count data from >3,200 modern-Pleistocene sand samples compiled from over 50 published sources, in conjunction with known values of precipitation, temperature, relief, slope, basin area, and source lithology from upstream watersheds. The GloPrSM model is in broad agreement with expected provenance patterns predicted by Dickinsonian Q-F-L ternary provenance fields. However, pronounced quartz enrichment within low latitudes (30°N to 30°S), likely the result of enhanced weathering of unstable siliciclastic grain types in the tropics, suggests significant climatic overprint on underlying tectonic regimes. Quartz enrichment at the expense of lithic and feldspar content is observed along many river profiles (e.g., the Amazon River), highlighting the complexity of sand’s compositional evolution within some sediment routing systems.