Decoupling Distribution of n-Alkanes in Aeolian Sand and Vegetation of the Northern Ulan Buh Desert, China: Insight into Organic Matter Preservation in Arid Regions

Fallen leaves and their decomposition directly deposit leaf wax n-alkanes into sediments, which can be used to identify local flora. These n-alkanes are important for studying past vegetation and climate, but their distribution in sediments must be known. Aeolian sand n-alkanes are particularly important for understanding paleoclimates in arid regions, despite the challenges of extraction due to their extremely low abundance. To investigate the preservation of plant leaf wax n-alkanes in deserts, we analyzed n-alkanes in aeolian sands from the Northern Ulan Buh Desert (UBD), China, and compared them to the surrounding vegetation. We calculated the total n-alkane concentration (ΣALK), average chain length (ACL21–35), and carbon preference index (CPI21–35). In the Northern UBD, aeolian sand n-alkanes have lower ΣALK, indicating microbial degradation. The eastern aeolian sand has lower CPI21–35 and ACL21–35 than the adjacent vegetation, whereas the western sand values are consistent with the plants, likely due to the transport of plant-derived materials by wind and water from the nearby mountains. Our study shows that sedimentary n-alkane signatures are not only determined by local vegetation but also influenced by environmental factors like temperature and precipitation. Additionally, local deposition processes play a significant role in determining the properties of these n-alkanes.