Titanium isotopes in detrital sediments: A reliable proxy for the protoliths composition?

Recently, non-traditional stable isotope systems have become new tools to track weathering and sediment transport processes and to obtain information about the lithological and chemical composition of drainage networks. Because the Ti isotope composition (δ⁴⁹Ti) increases with the SiO₂ concentration of rocks, Ti isotopes have received increasing attention to reconstruct the chemical composition of the continental crust through time (Greber et al., 2017). Chemical weathering and hydrodynamic sorting of sediments during transport may however cause fractionation of Ti isotopes and bias the δ⁴⁹Ti of the sediment record (Klaver et al., 2021; Xinyue et al., 2022).

To investigate potential biases and their extent in the sedimentary record, we measured the δ⁴⁹Ti signature of lacustrine sediments and respective catchment bedrock and weathering profiles from two study areas that represent geochemical and weathering endmembers; (i) Lake Grimsel in Switzerland displaying a felsic catchment dominated by physical weathering and (ii) Lake Towuti in equatorial Sulawesi, Indonesia, with an ultramafic to mafic catchment and intense chemical weathering.

Shallow sediments collected at Lake Grimsel composed of different particle sizes ranging from clay to gravel, as well as samples from a sediment core spanning the past 10 kyr, display a constant δ^49/47Tiof +0.32 ± 0.03‰. This value is expected from the granodioritic protolith in the catchment. We also did not find any Ti isotope fractionation associated with chemical weathering based on two soil profiles from the catchment of Lake Towuti in Indonesia. Furthermore, samples from a sediment  core from Lake Towuti spanning the past ~1 Myr display δ⁴⁹Tiin a narrow rangebetween +0.09 to +0.17 ‰ (both ± 0.03‰; 2SD), and this value is between the Ti isotope signature present in soil and bedrock in the catchment that range from +0.07 to +0.26‰ (both ± 0.03‰; 2SD). Due to the heterogeneous δ⁴⁹Ti of the catchment of Lake Towuti further mass balance modeling is required to assess if the Ti isotopic composition of the lake sediments reflects that of the eroded protolith.  

 

REFERENCES

Greber, N. D., Dauphas, N., Bekker, A., Ptáček, M. P., Bindeman, I. N., & Hofmann, A. (2017). Titanium isotopic evidence for felsic crust and plate tectonics 3.5 billion years ago. Science, 357(6357), 1271-1274.

Klaver, M., MacLennan, S. A., Ibañez-Mejia, M., Tissot, F. L., Vroon, P. Z., & Millet, M.-A. (2021). Reliability of detrital marine sediments as proxy for continental crust composition: The effects of hydrodynamic sorting on Ti and Zr isotope systematics. Geochimica et Cosmochimica Acta.

Xinyue, H., Jinlong, M., Gangjian, W., Zhibing, W., Le, Z., Ti, Z., & Zhuoying, Z. (2022). Mass-dependent fractionation of titanium stable isotopes during intensive weathering of basalts. Earth and Planetary Science Letters, Volume 579.