Trends in δ18O and δ13C values in lacustrine tufa mounds: Palaeohydrology of Searles Lake, California

Abstract Four tufa facies have been identified in abundant tufa mounds that accumulated in Searles Lake, California, USA, during the Pleistocene. Covariance of δ18O and δ13C values within the tufa facies has been analysed and correlated with palaeo‐lake history. This study demonstrates that characteristics of δ18O and δ13C values are different in each of the tufa facies and can be related to palaeo‐lake stages. The first facies of tufa formation (P) has relatively low average δ18O and δ13C values (δ18O = −2·7‰ and δ13C = +1·2‰, n = 14). These low values are attributed to rapid increases in the lake volume. This increase was followed by higher average δ18O and δ13C values of both the nodular (N) facies (δ18O = +1·8‰ and δ13C = +4·1‰, n = 24) and the columnar (C) facies (δ18O = +0·6‰ and δ13C = +4·0‰, n = 7). These higher values are interpreted to record a decrease in lake volume due to high evaporation and increased biogenic productivity. Following formation of facies C, the lake was essentially dry during formation of the finely laminated (LC) facies. Facies LC formed subaerially as spring water flowed up through the central conduit of the mounds and cascaded down their periphery. The relatively high δ18O and δ13C values for this facies (δ18O = +1·4‰ and δ13C = +4·4‰, n = 12) are due to evaporation and fast CO2 degassing. Although covariant trends are well‐displayed, variations in lake chemistry alter some of these trends due to periods of hyper‐alkalinity. This study confirms the utility of stable isotopic analyses of lacustrine tufa facies to determine palaeo‐lake history.