A Hydrochemical Method for Identifying Orbital Imprints of Dust in Paleofluvial Sequences

Mineral dust plays an important role in Earth's climate system, yet it is difficult to identify dust imprints in paleofluvial sediments, especially on orbital timescales. Here, we present high‐resolution authigenic carbonate Ca–Mg–Sr compositions in a fluvial sequence under the transport pathway of Asian dust. The Mg/Ca, Sr/Ca, and Mg/Sr ratios exhibit distinct transitions in both secular trends and orbital cycles at ∼8 Ma. Before ∼8 Ma, given similar Mg and Sr partitioning behaviors during carbonate formation, hydroclimate changes yielded strong orbital signals in the Sr/Ca and Mg/Ca ratios but no detectable signals in the Mg/Sr ratios. After ∼8 Ma, given the strengthened input of Mg‐rich dust during cold‒dry periods, the Mg/Sr and Mg/Ca ratios clearly exhibited orbital signals, but the Sr/Ca ratio did not. Such transitions in carbonate composition corroborate the dust‐induced changes in fluvial hydrochemistry, offering an innovative methodology for detecting orbital dust cycles in paleofluvial systems. Plain Language Summary A set of criteria, that is, transport and sedimentation dynamics, the surface morphology of quartz grains and provenance indices, were employed to recognize eolian deposits in past fluvial sediments. However, distinguishing eolian dust at orbital scales poses a challenge, as high‐resolution records that meet these criteria are difficult to reconstruct. Here, we present high‐resolution records of authigenic carbonate compositions from Neogene fluvial sediments in the Linxia Basin, a key downwind catchment area for Asian dust. The carbonate elemental compositions, in conjunction with sedimentary Sr‒Nd isotopes, exhibit a long‐term two‐stage evolution marked by a pivotal shift at ∼8 Ma. This transition is most likely attributed to an increase in Asian dust deposition since that time. On orbital timescales, the periodic fluctuations in extrabasinal dust flux, characterized by Mg‐rich but Sr‐poor components (mostly dolomite), have led to pronounced alterations in the orbital patterns of carbonate Ca‐Mg‐Sr compositions since ∼8 Ma. Our findings indicate that carbonate Ca‐Mg‐Sr compositions can offer a straightforward and innovative approach for pinpointing eolian dust activity on orbital timescales when extrabasinal dust can be appropriately distinguished. Key Points A close examination of carbonate compositions offers a new method for identifying orbital dust cycles within continental fluvial systems The authigenic carbonate composition i