Multifactor controls on heterogeneous salinization in lacustrine basins: Insights from quantitative thresholds and triggering conditions

Salinity plays a critical role in lake ecosystems, organic matter enrichment, and source rock formation, and holds significant implications for oil and gas exploration. Therefore, the mechanisms underlying lacustrine salinization have attracted increasing attention. Previous studies of salinization mechanisms have often focused merely on correlations between various factors and salinity. This limited scope has created a gap in the study of quantitative thresholds and triggering conditions, which impedes a comprehensive understanding of heterogeneous salinization mechanisms across temporal and spatial scales. This study investigates the multifactorial controls on heterogeneous salinization of the Paleogene strata of the Bohai Bay Basin, quantitatively elucidating their influence and identifying distinct thresholds or triggering conditions for each factor. The results show that lacustrine salinization heterogeneity is governed by multiple factors, including evaporation, marine transgression, surface runoff and hydrothermal activity: 1) evaporation is the predominant driver of salinization when climatic aridity exceeds a critical threshold (Sr/Cu >25); 2) mantle-derived hydrothermal fluids, not alone but in conjunction with formation brines, can lead to significant salinization; 3) marine transgression can cause substantial dissolved salt influx to lakes during prolonged and extensive transgression, and its salinizing effect is amplified during sustained arid climatic regimes; 4) surface runoff effectively reduces salinity, particularly near river mouths, and the dilution effect becomes significant only when the salinity exceeds 8‰. Collectively, evaporation and large-scale marine transgressions primarily control temporal heterogeneity in lacustrine salinization, whereas hydrothermal activity and surface runoff govern spatial heterogeneity. • Evaporation significantly drives salinization only when climatic aridity (Sr/Cu >25) is high. • Surface runoff reduces coastal salinity, but notable dilution requires salinity >8‰. • Salinization requires mixing of mantle-derived fluids with formation brines, not fluids alone. • Marine transgression in Es 1 /Es 3 caused salinization shifts in Bohai Bay Basin.