Stable isotope and mineralogical investigations on clays from the Late Cretaceous sequences, Haţeg Basin, Romania

Abstract

In the Haţeg basin, South Carpathians, a thick continental sequence accumulated during the Maastrichtian. The alluvial sequences are characterized by the formation of paleosol horizons developed on the alluvial plain. In order to investigate the environmental signal stable isotope and mineralogical investigations have been carried out on smectites from paleosol. The RX as well as the FTIR spectra of the fraction < 2 µm indicate that the main clay mineral is smectite. Based on XRF analysis, the smectite is a montmorillonite with the formula {Na 0.67 Ca 0.1}[Al 1.19 Mg 0.62 Fe 3+ 0.19] (Si 3.78 Al 0.22 O 10) (OH) 2. FTIR data show that interlayer water from smectite is liberated after ~ 24 h heating at 200 °C. Stable isotopic composition of precipitations have been monitored in the Hateg basin and in a neighbored area situated in the Apuseni mountains. The results show the same meteoric water line (LMWL) with the equation δD = 7.9 ⁎ δ 18O + 8.14 for both sites. Stable isotope data on clay fraction less than 2 µm show that the structural water from smectites formed under different environmental conditions during the Maastrichtian have re-equilibrated isotopically with the present meteoric water.