Objective Taking the typical Luonan profile (LN profile) as the research object, this study analyzes the variations of chromaticity indices and other climatic proxy indices along the profile, and explores the paleoenvironmental significance of the chromaticity indices of the LN profile and the paleoclimatic changes in the Luonan Basin during the mid-to-late Middle Pleistocene.

Methods Comprehensive analysis was conducted on chromaticity parameters, grain size, magnetic susceptibility, and Rb/Sr values at different depths of the LN profile.

Results The results show that:①The chromaticity parameters exhibit regular variations across different stratigraphic units in the profile. Luminance (L^*) and hue angle (h^*) are higher in loess layers than in paleosol layers, with high values indicating relatively dry and cold climatic conditions. In contrast, redness (a^*) and the redness/yellowness ratio (a^*/b^*) are higher in paleosol layers (S1–S6) than in loess layers (L1–L7), with high values indicating relatively warm and humid environments. L^*, a^*, a^*/b^*, and h^* can all serve as good climatic proxy indices to indicate climate changes in this region.② Chromaticity and other climatic proxy indices collectively reveal the climatic changes in the Luonan Basin during the mid-to-late Middle Pleistocene. The accumulation period of loess layers corresponds to cold and humid climatic conditions, while the accumulation period of paleosol layers corresponds to warm and humid conditions.

Conclusions Unlike the dry-cold to warm-wet climate cycles in the Loess Plateau, the Luonan region exhibits a climate cycle of cold-humid to warm-humid. The overall sedimentary environment was humid, with strong weathering and pedogenesis, experiencing a climatic change pattern of cold-wet → warm-wet → cold-wet. The research results provide insights for correctly understanding the living environment and climatic changes of paleohumans in the East Qinling and surrounding areas during the Middle Pleistocene.