“…The association of hairy 1 M illite, 1M d I-S and quartz cement (Fig. 4d, f) is usually restricted to elevated temperatures around 70 to 150 °C and is therefore attributed to the advanced stages of sandstone diagenesis and the related burial diagenetic dissolution of feldspar-rich sediments (Nadeau et al 1985; Lynch et al 1997; Haszeldine et al 2000; Baldermann et al 2012). However, the shallow burial of the Valley of Lakes sediments (in the range of few hundred metres) is insufficient to create temperatures suitable for illitization (see discussion below).Fig.…”
The Valley of Lakes is approximately a 500-km elongate depression in Central Mongolia, where Eocene to Miocene continental sediments are long known for their outstanding fossil richness. The palaeontological record of this region is an exceptional witness for the evolution of mammalian communities during the Cenozoic global cooling and regional aridification. In order to precisely elucidate the climatic evolution of the region, we studied the mostly siliciclastic sediments with several levels of paleosols for their sedimentology, mineralogy, major and trace element composition and δ13C and δ18O composition. The obtained results show that temperate hydrothermal fluids induced a strong illitization of the fluvial and lacustrine sediments. This finding contradicts the current conceptual view that the fine fraction of the sediments is of aeolian origin. Moreover, the diagenetic growth of illite resulted in a strong overprinting of the sediments and, subsequently, largely disturbed the pristine mineralogical and geochemical composition of the sediments that could have carried any palaeo-climatic information. An exception is the δ13C (and δ18O) isotope values of authigenic carbonate found in calcrete horizons that still record the ambient climatic conditions prevailing during paleosol formation. Our novel δ13C and δ18O record suggests an early Oligocene aridification in Central Asia at ∼31 Ma, whereas the Oligocene glacial maximum shows no increase in aridification. A second, regional-scale aridification occurs at ~25 Ma and corresponds to a late Oligocene marked mammalian turnover in the Valley of Lakes sediments.
“…The association of hairy 1 M illite, 1M d I-S and quartz cement (Fig. 4d, f) is usually restricted to elevated temperatures around 70 to 150 °C and is therefore attributed to the advanced stages of sandstone diagenesis and the related burial diagenetic dissolution of feldspar-rich sediments (Nadeau et al 1985; Lynch et al 1997; Haszeldine et al 2000; Baldermann et al 2012). However, the shallow burial of the Valley of Lakes sediments (in the range of few hundred metres) is insufficient to create temperatures suitable for illitization (see discussion below).Fig.…”
The Valley of Lakes is approximately a 500-km elongate depression in Central Mongolia, where Eocene to Miocene continental sediments are long known for their outstanding fossil richness. The palaeontological record of this region is an exceptional witness for the evolution of mammalian communities during the Cenozoic global cooling and regional aridification. In order to precisely elucidate the climatic evolution of the region, we studied the mostly siliciclastic sediments with several levels of paleosols for their sedimentology, mineralogy, major and trace element composition and δ13C and δ18O composition. The obtained results show that temperate hydrothermal fluids induced a strong illitization of the fluvial and lacustrine sediments. This finding contradicts the current conceptual view that the fine fraction of the sediments is of aeolian origin. Moreover, the diagenetic growth of illite resulted in a strong overprinting of the sediments and, subsequently, largely disturbed the pristine mineralogical and geochemical composition of the sediments that could have carried any palaeo-climatic information. An exception is the δ13C (and δ18O) isotope values of authigenic carbonate found in calcrete horizons that still record the ambient climatic conditions prevailing during paleosol formation. Our novel δ13C and δ18O record suggests an early Oligocene aridification in Central Asia at ∼31 Ma, whereas the Oligocene glacial maximum shows no increase in aridification. A second, regional-scale aridification occurs at ~25 Ma and corresponds to a late Oligocene marked mammalian turnover in the Valley of Lakes sediments.
“…Diagenetic carbonate isotope geochemistry is widely used for investigating origin and evolution of pore fluids in sandstone lithologies forming major hydrocarbon reservoirs (e.g., Jubril et al, 1998;Haszeldine et al, 2000;Scotchman et al, 2002). In the peculiar context of the sedimentary successions from the continental margin of Antarctica, where pore fluid chemistry appears to be largely influenced by glacial melt processes, we have attempted to interpret results of the isotopic investigations in terms of palaeoclimatic evolution.…”
Section: Evidence For Palaeoclimatic Evolutionmentioning
“…It has been realized that the porosity, permeability and other reservoir properties are the result of both primary depositional facies and diagenetic alterations. Two main goals have driven such studies in the past: 1) the economic motive to predict porosity and permeability in hydrocarbon fields; and 2) the academics motive to understand the motion or stasis of pore fluids and the scale of mass transport to form cements (Haszeldine et al, 2000).…”
Section: Fluids In Sedimentary Basins: Diagenesis To Geosequestrationmentioning
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