Stable isotope composition of bulk and secondary carbonates from the Quaternary loess-paleosol sequence in Süttő, Hungary

Stable carbon and oxygen isotope composition of pedogenic carbonates were studied from the Quaternary loess-paleosol sequence of Süttő in Hungary to investigate genetic processes in a paleoenvironmental context and to distinguish subtypes. Bulk carbonate samples taken at 2 cm vertical resolution, and microscale secondary (authigenic) carbonates (calcified root cells, carbonate coatings, hypocoatings, and earthworm biospheroids) and concretions at 10 cm resolution were analysed to interpret stable isotope variations. Isotope values of bulk samples were in the range of 2.6‰ to −13.9‰ and −2.3‰ to −17.0‰ (vs. VPDB) for δ13C and δ18O, respectively. The isotope compositions of secondary carbonates clearly distinguished between the organically related and inorganic (direct) precipitation of the different subtypes. In general, secondary carbonates showed more depleted values than bulk samples. Calcified root cells have the most depleted isotope composition with mean values of −16.0‰ and −11.8‰ for δ13C and δ18O, respectively. Results indicate that loess and paleosol secondary carbonates reveal pedogenetic information during the different climatic phases. Carbon and oxygen isotope analyses are valuable to classify secondary carbonates and to serve as proxies for the interpretation of paleoenvironmental conditions, e.g. moisture conditions, leaching, the role of organic matter or vegetation. Secondary carbonates are more reliable than bulk samples because of their direct connection to the host strata.