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Abstract: A layered double hydroxide (LDH) hydrotalcite–pyroaurite solid-solution series Mg3(Al x Fe1− x )(CO3)0.5(OH)8 with 1− x =0.0, 0.1……1.0 was prepared by co-precipitation at 23±2°C and pH=11.40±0.03. The compositions of the solids and the reaction solutions were determined using ICP-OES (Mg, Al, Fe, and Na) and TGA techniques (CO3 2−, OH−, and H2O). Powder X-ray diffraction was employed for phase identification and determination of the unit cell parameters a o and c o from peak profile analysis. The parameter a o = b o was found to be a linear function of the composition. This dependency confirms Vegard''s law and indicates the presence of a continuous solid-solution series in the hydrotalcite–pyroaurite system. TGA data show that the temperatures at which interlayer H2O molecules and CO3 2− anions are lost, and at which dehydroxylation of the layers occurs, all decrease with increasing mole fraction of iron within the hydroxide layers. Features of the Raman spectra also depend on the iron content. The absence of Raman bands for Fe-rich members (x Fe >0.5) is attributed to possible fluorescence phenomena. Based on chemical analysis of both the solids and the reaction solutions after synthesis, preliminary Gibbs free energies of formation have been estimated. Values of ΔG°f(hydrotalcite)=−3773.3±51.4kJ/mol and ΔG°f(pyroaurite)=−3294.5±95.8kJ/mol were found at 296.15K. The formal uncertainties of these formations constants are very high. Derivation of more precise values would require carefully designed solubility experiments and improved analytical techniques. [Copyright &y& Elsevier]

• Introduction of a new online pyrolysis carbon isotope analysis method. • Case study of sample material from different locations and depositional environments. • Isotopic fractionation curves are related to depositional environment and maturity. • Maturity is reflected in the carbon isotopic difference of the Rock-Eval S1 and S2. The source material, the mode of photosynthesis, the organic matter (OM) type, the paleoenvironmental conditions and thermal degradation all determine the isotopic composition of OM. This study presents a novel analytical technique and demonstrates its potential to enhance the understanding of the preservation and maturation-related isotopic compositional changes in OM from different paleoenvironments. A new Rock-Eval type pyrolysis coupled to isotope ratio mass spectrometry (py-IRMS) method has been developed to monitor the isotopic changes during Rock-Eval type pyrolysis while simultaneously recording pyrograms to obtain S1 and S2 peaks compatible with standard Rock-Eval pyrolysis. An automated cryotrapping method allows the sequential sampling of product from defined pyrolysis portions. Each subsample is subsequently transferred to the isotopic ratio mass spectrometer for carbon isotopic measurements. In addition, the cryotrap serves to focus sample peaks, enabling robust and reproducible results even at standard Rock-Eval heating rates. In combination with a standard elemental analyser coupled to an isotopic ratio mass spectrometer (EA–IRMS) it was possible to deconvolute the carbon isotope composition of the reactive components, bitumen and inert components of OM. This allowed us to observe depositional control as well as changes imposed by maturation. Our initial results show the potential of the proposed isotopic screening method to deduce a variety of organic geochemical properties of different OM types based on differences in their carbon isotope compositions. Our results suggest that the ability to produce significant isotopic fractionation during the proposed pyrolysis method is highly dependent on the preservation state of the OM and the thermal maturity. [ABSTRACT FROM AUTHOR]

The Eisenhower Range is a N–S trending mountain range in the Transantarctic Mountains (TAM) adjacent to the NW Ross Sea Embayment. New AFT and apatite (U–Th–Sm)/He (AHe) data from vertical basement profiles supplemented by paleotemperature and pressure estimates derived from Beacon sandstones provide new quantitative results on regional burial evolution and first regional constraints on basin inversion and exhumation processes. AFT ages between 32 ± 2 and 259 ± 18 Ma and AHe ages of 37 ± 3–173 ± 16 Ma correlate positively with sample elevations. Thermal history modeling of these data and complementary thermal indications detect heating of the paleosurface on the Eisenhower Range to temperatures ≥ 80 °C subsequent to Ferrar magmatism, and constrain Late Eocene rapid cooling. Regression of modeled paleotemperatures against sample elevations refers to a high Jurassic (~ 45 °C/km) and a moderate Cretaceous–Eocene (28 ± 8 °C/km) geothermal gradient. The texture of Beacon sandstones supports strong mechanical compaction that requires a higher overburden than preserved in the stratigraphic record. Modeled paleotemperatures and pressures suggest basement burial that increases from Late Jurassic (0.7–1.1 km) to Eocene (1.8–2.1 km). The overburden comprises 0.7–1.1 km cumulative Beacon/Ferrar rocks and 0.7–1.4 km of post-Ferrar sediments. Rapid cooling of the whole sample suite between ~ 35 and 30 Ma implies fast erosion of the post-Ferrar sediments and (re-) exposure of underlying magmatic rocks. Subsequent differential sample cooling to present-day surface temperature infers ongoing exhumation by glacial incision enhanced by isostatic response to basin inversion. Decreasing amounts of exhumation from the coast (> 3 km) toward the interior (1.5–2.2 km) point to backstepping incision along the fault controlled Priestley Glacier. Substantial exhumation of the Eisenhower Range since the Late Eocene is hence triggered by both tectonic and climatic factors, superimposed by considerable lithological influence during the initial exhumation stage. [ABSTRACT FROM AUTHOR]