The measurement of D/H ratio in alkenones and their isotopic heterogeneity

Previous paleoenvironmental studies reported the δD values of a mixture of coeluting alkenones. Here, we present a semi-preparative normal-phase high-performance liquid chromatography–mass spectrometry (NP-HPLC–MS) method for purifying long chain (C₃₇ and C₃₈) unsaturated methyl and ethyl ketones (alkenones) on the basis of chain length and degree of unsaturation.The method was applied to purify alkenones in suspended particles and surface sediments from a site in Chesapeake Bay, eastern USA. The hydrogen isotopic composition of di- and triunsaturated C₃₇ and C₃₈ alkenones differed significantly on the basis of chain length and the degree of unsaturation, demonstrating the importance of gas chromatography–isotope ratio-mass spectrometry (GC–irMS) analysis of individual alkenones for accurate paleoenvironmental reconstruction. Constant fractionation factors between alkenones with different chain length but the same degree of unsaturation (${\alpha }_{{\text{C}}_{37:2}''–''{\text{C}}_{38:2}}\text{and}{\alpha }_{{\text{C}}_{37:3}''–''{\text{C}}_{38:3}}=1.01$) and those with the same chain length but different degree of unsaturation (${\alpha }_{{\text{C}}_{37:2}''–''{\text{C}}_{37:3}}\text{and}{\alpha }_{{\text{C}}_{38:2}''–''{\text{C}}_{38:3}}=0.97$) in all samples suggest that the values may represent hydrogen isotope fractionation associated with elongation and desaturation during alkenone biosynthesis.     

Lithospheric stress in Mongolia,from earthquake source data

Lithospheric stress in Mongolia has been studied using mechanisms of 84 M_(LH)≥ 4 earthquakes that occurred in the 20 th century and instrumental seismic moments of 17,375 M_(LH)≥2.5 events recorded between 1970 and 2000.The M_(LH)≥ 3.5 earthquakes mostly have strike-slip mechanisms in southern and central Mongolia,with frequent reverse-slip motions in the west and normal slip in the north,especially,in the area of Lake Hovsgol.The principal stresses are,respectively,S_HS_vS_h in the center and in the south;high horizontal compression with S_HS_hS_v in the west;and a heterogeneous stress pattern with S_vS_HS_h in the north.According to seismic moments of M_(LH)=2.5 events,oblique slip generally predominates over the territory,at S_v≈S_HS_h,while frequent strike slip motions in the west record high horizontal compression(S_HS_vS_h).Earthquake mechanisms show the principal horizontal compression S_H to be directed W-E in the east,NE-SW in the central and Gobi-Altay regions,and approximately N-S in the west of Mongolia.The patterns of principal lithospheric stresses in the territory of Mongolia have undergone three events of dramatic change for a few recent decades,and these events were synchronous with three similar events in the Baikal rift system(BRS):in the latest 1960 s,latest 1970 s to earliest 1980 s,and in the latest 1980 s to earliest 1990 s.The seismicity of Mongolia has been controlled by superposition of variable stresses associated with rifting activity pulses in the neighbor BRS on the background of quasi-stationary super-regional compression.     

Kinetics of oil group-type generation and expulsion: An integrated application to Dongying Depression,Bohai Bay Basin,China

Pyrolysis of two kerogens isolated from the ${\text{E}}_{2\text{-}3}{\text{s}}_3^3$ and ${\text{E}}_{2\text{-}3}{\text{s}}_4^1$ source rocks in the Niuzhuang sag, Dongying Depression, Bohai Bay Basin, China, was performed in a confined system. The products were extracted with solvent and separated using micro-column chromatography into group-type fractions (saturates, aromatics, resins and asphaltenes) with the kerogen residue in each case undergoing swelling with a variety of solvents. The kinetics for generation and retention of crude oil and its group-type fractions from the kerogens were studied and the kinetic parameters applied to modeling generation and retention of crude oil and its fractions from the ${\text{E}}_{2\text{-}3}{\text{s}}_3^3$ and ${\text{E}}_{2\text{-}3}{\text{s}}_4^1$ source rocks on the basis of burial and thermal history of the Niuzhuang sag. The results show that the “normal oil” was generated at about 4.26 Ma and 24.85 Ma ago, but expelled at about 3.96 Ma and 17.46 Ma ago, respectively, from ${\text{E}}_{2\text{-}3}{\text{s}}_3^3$ and ${\text{E}}_{2\text{-}3}{\text{s}}_4^1$ source rocks. The current proportions of the expelled saturates, aromatics and NSOs are about 60%, 15% and 25%, respectively.     

A simplified method to evaluate the swelling capacity evolution of a bentonite barrier related to geochemical transformations

Bentonites have been proposed as buffer material for barriers in geological disposal facilities for radioactive waste. This material is expected to fill up by swelling the void between the canisters containing the waste and the surrounding ground. However, the bentonite barriers may be submitted to changes of humidity, temperature variation, fluid interaction, mass transport, etc. This could modify the physico-chemical performance of the barrier, mainly on the interface with the steel container and with the geological barrier. The engineered barrier development necessitates thus the study of the physico-chemical stability of its mineral component as a function of time under the conditions of the repository in the long-term. The aim of this paper is to apply a simplified method (volume balance in a saturated medium) to evaluate the swelling capacity evolution of a bentonite barrier because of their geochemical transformations by using a thermo-kinetic hydrochemical code (KIRMAT: Kinetic Reactions and Mass Transport “1D”).The system modelled here consists of 1 m thick zone of water-saturated engineered barrier. This non-equilibrated system is placed in contact with a geological fluid on one side, which is then allowed to diffuse into the barrier, while the other side is kept in contact with iron-charged solution (0.001 mol/kg H₂O). The initial reducing conditions ($P_{{\mathrm{O}}_2}\cong 0$; Eh = −200 mV) and a constant reaction temperature (100 °C) were considered.In the current study the decay of swelling capacity was considered directly proportional on the volume of transformed montmorillonite (cation exchange + geochemical transformation), taking into account that it may be partially compensated by the volume of neo-formed swelling-clays.The results showed that the swelling capacity of the engineered barrier is not drastically affected after about 3000 years of reaction and transport because the volume of neo-formed swelling clays is almost directly proportional on the volume of transformed montmorillonite. In fact, a graphical method predicted that the decay of swelling capacity of the engineered barrier lies between 11% and 14% when the montmorillonite is completely transformed (cation exchange + minimal geochemical transformation) in the system.