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Trends in δ 18 O and δ 13 C values in lacustrine tufa mounds: Palaeohydrology of Searles Lake, California
Author(s) -
Guo Xuan,
Chafetz Henry S.
Publication year - 2014
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/sed.12085
Subject(s) - tufa , facies , geology , paleontology , geochemistry , chemistry , organic chemistry , structural basin , carbonate
Four tufa facies have been identified in abundant tufa mounds that accumulated in Searles Lake, California, USA, during the Pleistocene. Covariance of δ 18 O and δ 13 C values within the tufa facies has been analysed and correlated with palaeo‐lake history. This study demonstrates that characteristics of δ 18 O and δ 13 C 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 δ 18 O and δ 13 C values (δ 18 O = −2·7‰ and δ 13 C = +1·2‰, n = 14). These low values are attributed to rapid increases in the lake volume. This increase was followed by higher average δ 18 O and δ 13 C values of both the nodular (N) facies (δ 18 O = +1·8‰ and δ 13 C = +4·1‰, n = 24) and the columnar (C) facies (δ 18 O = +0·6‰ and δ 13 C = +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 δ 18 O and δ 13 C values for this facies (δ 18 O = +1·4‰ and δ 13 C = +4·4‰, n = 12) are due to evaporation and fast CO 2 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.