ABSTRACT Analysis of naturally occurring markers of environmental signals, or proxy analysis, in sedimentary records can yield valuable insights into the geologic past. However, these proxies may be altered between sediment source and sink by selective gain, loss, or transformation of individual organic or inorganic components. To aid interpretation of sedimentary proxies, we must understand physical and chemical processes occurring during transit. We track the provenance and transformation of two commonly used proxies, long‐chain n ‐alkanes and heavy minerals, between source and sink along the Río Bermejo, a lowland alluvial river without significant tributaries or distributaries, traversing the east Andean foreland basin. Our sampling strategy allowed determining the sediment input signal and isolating the effects of long‐range transport and transient floodplain storage. Fine‐grained sediments present in the suspended load and deposited in floodplains show heavy n C 29 n‐ alkane δ 2 H values compared to channel bed sediment. Heavy n C 29 n‐ alkane δ 2 H values indicate that organic matter in suspended and deposited sediments was sourced from low elevations, while light n C 29 n‐ alkane δ 2 H values indicate upland sources for the bed sediment. These data suggest that organic matter proxies in finer sediment are overprinted during transient floodplain storage, while organic matter travelling near the river bed is transferred downstream efficiently without significant recycling. Meanwhile, a negative correlation of Zircon‐Tourmaline‐Rutile index and corroded grains of all samples indicates progressive weathering of silicate minerals during transient foreland sediment storage. In particular, sediment deposited on the floodplain is depleted in clinopyroxenes and amphiboles compared to suspended sediment. Combining the physical and chemical characteristics of organic and inorganic proxies can help isolate source area fingerprints and identify the effects of lowland fluvial transit on sedimentary records. This improves our understanding of how source‐to‐sink processes influence the preservation of proxy signals, their transfer into the stratigraphic record, and the potential impacts of flood basin sediment storage on biogeochemical cycles.
Dosch et al. (2026) studied this question.