The Honggang Member of the Buxin Formation (Early Eocene) is the main source rock in the Sanshui Basin. This work aims at assessing the sedimentary environments of these source rocks based on elemental geochemical data. The distributions of elements (Al, Fe, Mg, Ca, K, Na, P, V, Ni, Co, Cr, Cu, Zn, Sr, Ba, Cd, Li, Mn, Pb and Ti) and elemental ratios (Al/Ti, Fe/Mn, Sr/Ba, Mg/Ca, Sr/Ca, Na/Ca, V/Cr, Ni/Co and Ni/V) serve as proxies for palaeoenvironmental conditions. Elemental concentration and ratios in Lithozone A indicate higher terrigenous fluxes with relatively constant chemical composition and low-O₂-H₂Sbottom waters with higher salinity than the other lithozones. Highly saline bottom waters were probably the consequence of intermittent sea water incursions. Lithozones B and C are characterized by large variations in geochemical features, which reflect rapid fluctuations in palaeoclimate and sedimentary conditions. During humid intervals, elements that are usually enriched in terrestrial detrital minerals, such as Al and Ti, and Al/Ti ratios show high values, while endogenic elements, represented by Mg and Ca, have low concentrations. Palaeo-oxygenation indices suggest anoxic conditions developed in bottom waters, which were favourable for organic matter preservation. Consequently, higher contents of organic carbon are observed. During intervals of dry climatic conditions, characterized by reduced terrestrial input, concentration of terrigenous elements and Al/Ti ratios decreased. Increasing evaporation and salinity resulted in high values of endogenic elements and high Mg/Ca and Sr/Ba ratios. Palaeoredox proxies indicate prevailing oxic environments developed in bottom waters. Salinity indices for the uppermost part of the Honggang Member show lower values, suggesting that an increasing input of fresh waters caused freshening of the lake waters.