Congruent Weathering of Continental Silicates During Warm Periods: Evidence From Lithium Isotopes in Marine Sediments

Dissolution of secondary clay minerals during continental weathering (hereafter clay dissolution) has been proposed as a mechanism to explain some of the low seawater lithium isotopic ratios (δ 7 Li) observed in the geologic past. However, direct evidence for clay dissolution on Earth surface remains limited, and the controlling factors are poorly understood. Here, we suggest that δ 7 Li of fine sediments can serve as a proxy for clay dissolution. We analyzed δ 7 Li of the sediments from the Ocean Drilling Program site 1148, and developed a stoichiometric model to disentangle the respective contributions of source rock fragments and marine authigenic aluminosilicate clays to the sediment Li budget. Our results reveal low δ 7 Li in continentally formed clays during the warm interval of 23–15 Ma, followed by a progressive increase during 15–5 Ma, coinciding with global cooling. We suggest that warm and tectonically stable conditions might have promoted clay dissolution on continents.