Study of the fractal characteristics of sediment element geochemistry in the Qiongdongnan Basin and its implications for gas hydrates

• First multifractal evidence for staged sediment provenance in Qiongdongnan hydrate zone. • Low-α CaO–Sr anomalies tightly couple with hydrate sample sites. • Spectrum width quantifies fluid-induced geochemical heterogeneity. • Fractal parameters proposed as new geochemical proxies for locating hydrate-rich zones in the northern South China Sea. The offshore slope of Qiongdongnan Basin represent a highly prospective zone for gas-hydrate prospecting in the northern South China Sea. The geochemical characteristics of sediment elements in this area provide significant insights into deep methane migration and hydrate formation. Traditional methods for hydrate identification, such as bottom simulating reflectors and gas geochemistry, often suffer from limited accuracy and non-unique responses. This study introduces multifractal theory and local singularity analysis to systematically investigate the fractal characteristics of sediment element distribution from an element geochemical perspective, as well as their implications for in the exploration of gas hydrates. Based on data from major, trace, and rare earth elements in surface sediment samples in an area for gas hydrate investigation in the Qiongdongnan Basin, and considering the regional geological context, we find that the distribution of sediment elements exhibits pronounced multifractal characteristics. The multifractal spectrum ( f (α)) parameters effectively characterize the complexity of element spatial distribution, revealing the evolution of sediment sources and depositional environments. Specifically, the upper layer is dominated by authigenic marine sediments, reflecting a stable depositional environment; the middle layer represents a transition from authigenic marine sediments to terrigenous clastic deposits; while the lower layer indicates a mixture of both, suggesting the influence of multi-phase sedimentation and fluid activity. Local singularity analysis further identified regions with low singularity indices (α) that are highly coupled with enrichment zones of elements such as Ca and Sr. These regions may be associated with redox interfaces related to methane leakage and exhibit a high spatial overlap with known hydrate sampling locations, indicating that fractal parameters can serve as effective geochemical indicators for identifying hydrate accumulation zones. This research combines fractal theory with element geochemistry of sediments, providing a new quantitative approach and methodological support for gas hydrate exploration in the Qiongdongnan Basin, and significantly enhances our understanding of the mechanisms of hydrate formation in the northern South China Sea.