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This contribution examines the climate variations reflected by a mainly lacustrine succession spanning from 17.73 to 14.0 Ma in north‐east Iberia, thus encompassing the Miocene Climatic Optimum (MCO). The study is based on the δ13C and δ18O composition of an array of carbonate facies and marl samples, complemented with sedimentological analysis, illite crystallinity index and magnetic susceptibility data. The onset and ending of the MCO have been detected at ca 17.10‐17.06 Ma and 14.56 Ma, roughly equivalent to the boundaries in the marine record, although with relatively short lags. The variability of the data series evidenced changes in humidity and air temperature through the MCO, some of which coincided with similar variations in other records. Specifically, an evolving positive shift in δ13C values, from 16.5 to 14.5 Ma, seems to fit the Monterey excursion observed in marine records. Likewise, increases in δ18O values between 16.8 and 16.5 Ma and between 14.85 and 14.56 Ma in the study succession concurred with warming intervals recorded in palaeosols of Central Europe, emphasising the coincidence with the temperature maximum at ca 16.6 Ma. A general decline in temperature and an increase in humidity are detected from 14.56 Ma, both with steeper trends until 14.41 Ma then more gradual onwards, indicating the beginning of the Middle Miocene Climatic Transition. These results shed light upon the tightly coincidental features between terrestrial and marine records over those time intervals and, more importantly, highlight the earlier warming and the faster cooling experienced by the lake system as compared with the marine record. These findings provide further evidence to help infer palaeoclimate conditions on a much broader reach than the regional context.
This contribution examines the climate variations reflected by a mainly lacustrine succession spanning from 17.73 to 14.0 Ma in north‐east Iberia, thus encompassing the Miocene Climatic Optimum (MCO). The study is based on the δ13C and δ18O composition of an array of carbonate facies and marl samples, complemented with sedimentological analysis, illite crystallinity index and magnetic susceptibility data. The onset and ending of the MCO have been detected at ca 17.10‐17.06 Ma and 14.56 Ma, roughly equivalent to the boundaries in the marine record, although with relatively short lags. The variability of the data series evidenced changes in humidity and air temperature through the MCO, some of which coincided with similar variations in other records. Specifically, an evolving positive shift in δ13C values, from 16.5 to 14.5 Ma, seems to fit the Monterey excursion observed in marine records. Likewise, increases in δ18O values between 16.8 and 16.5 Ma and between 14.85 and 14.56 Ma in the study succession concurred with warming intervals recorded in palaeosols of Central Europe, emphasising the coincidence with the temperature maximum at ca 16.6 Ma. A general decline in temperature and an increase in humidity are detected from 14.56 Ma, both with steeper trends until 14.41 Ma then more gradual onwards, indicating the beginning of the Middle Miocene Climatic Transition. These results shed light upon the tightly coincidental features between terrestrial and marine records over those time intervals and, more importantly, highlight the earlier warming and the faster cooling experienced by the lake system as compared with the marine record. These findings provide further evidence to help infer palaeoclimate conditions on a much broader reach than the regional context.
An experimental study of the main factors affecting the accuracy of oxygen and carbon isotopic analysis in carbonates dispersed in silicate matrix is carried out. Artificial 1, 2, 5, and 10% mixtures of quartz with carbonates with different isotopic parameters (KH-2, Ko, MCA-8) were analyzed by continuous flow isotope ratio mass spectrometry (CF IRMS). It is established that, in addition to the influence of the instrumental nonlinearity, the results are affected by two factors: trace amounts of CO2, constantly present in the system (the blank effect) and the presence of chemically neutral silicate particles (the matrix effect). The blank effect depends on the isotopic parameters of the sample and has very little influence on the estimated carbonate content in the rock. The matrix effect, on the contrary, strongly affects the estimated carbonate content, and produces the isotopic shift towards underestimated contents of heavy 13C and 18O isotopes. It is shown that this effect is related to the processes occurring near the CO2–acid–quartz interface, which are accompanied by kinetic fractionation of carbon and oxygen isotopes. Both effects are dependent on the amount of silicate matrix in the system and most clearly manifested during analysis of carbonate-poor rocks. When the carbonate content in the rock is about 1–2%, deviations from the true δ13C and δ18O values can reach the first ppm, while carbonate content obtained by chromatographic peak calibration can be underestimated by 20–40%.
An experimental study of the main factors affecting the accuracy of oxygen and carbon isotopic analysis in carbonates dispersed in silicate matrix is carried out. Artificial 1, 2, 5, and 10% mixtures of quartz with carbonates with different isotopic parameters (KH-2, Ko, MCA-8) were analyzed by continuous flow isotope ratio mass spectrometry (CF IRMS). It is established that, in addition to the influence of the instrumental nonlinearity, the results are affected by two factors: trace amounts of CO2, constantly present in the system (the blank effect) and the presence of chemically neutral silicate particles (the matrix effect). The blank effect depends on the isotopic parameters of the sample and has very little influence on the estimated carbonate content in the rock. The matrix effect, on the contrary, strongly affects the estimated carbonate content, and produces the isotopic shift towards underestimated contents of heavy 13C and 18O isotopes. It is shown that this effect is related to the processes occurring near the CO2–acid–quartz interface, which are accompanied by kinetic fractionation of carbon and oxygen isotopes. Both effects are dependent on the amount of silicate matrix in the system and most clearly manifested during analysis of carbonate-poor rocks. When the carbonate content in the rock is about 1–2%, deviations from the true δ13C and δ18O values can reach the first ppm, while carbonate content obtained by chromatographic peak calibration can be underestimated by 20–40%.
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