Thermal maturation as revealed by micro-Raman spectroscopy of mineral-organic aggregation (MOA) in marine shales with high and over maturities

Laser Raman spectroscopy of organic matter in coals and sedimentary rocks has been increasingly investigated to assess thermal maturity.Pure organic matter such as vitrinite and solid bitumen,as well as isolated kerogen are definitely selected for this purpose,but there has been no systematic report on the Raman spectral parameters directly based on mineral-organic aggregations(MOA)in shales.In this paper,the Raman spectral characteristics and parameters of MOA in two sets of marine shale samples from southern China with either different TOC contents(TOC=0.10–4.59%)or different maturities(BRo=1.71–4.57%)were investigated.It was found that the Raman technique is very sensitive to the organic matter in MOA.As the TOC content of the shales reaches about 0.60%,perfect Raman spectra with D and G bands derived from organic matter in MOAwere obtained,and the Raman parameters of MOA are in good agreement with those of its associated solid bitumen,and can indicate the thermal maturity just like those of solid bitumen.Using the Raman parameters of MOA is a potential alternative way to estimate maturity levels of high and over mature shales,especially those lower Paleozoic and Precambrian shales that lack macerals suitable for reflectance or Raman measurements.

Spatial Variation in Soil Chemistry on a Sub-Antarctic Island

On both west and east sides of sub-Antarctic Marion Island (47oS, 38oE), total Na and exchangeable Na, Mg and K concentrations in the soil decline with increasing distance inland and altitude, related to a decrease in the intensity of seaspray deposition. On the east side, the coastal plain is wide and slopes gently up to the mountainous interior and total C, total N and soil moisture content all decrease significantly, whereas bulk density increases significantly, as one moves away from the sea, reflecting a gradual change from organic, wet, low bulk density peats characteristic of low-land coastal regions to mineral, dry, high bulk density volcanic soils characteristic of inland areas. On the west side, the narrow coastal plain is bounded by an escarpment that rises up very steeply to the highland interior. There, sampling was largely restricted to the coastal plain (soils are rare on the escarpment and interior) and did not cover the same transition from organic to mineral soils as on the east side. Hence, total C, total N and bulk density did not change significantly with increasing distance inland on the west side. Most total Mg is in the mineral fraction of the soil, with a lesser contribution by organic, exchangeable and soil solution forms of Mg. On the east side the gradual transition from highly organic peats to very mineral soils results in an increase in total Mg going inland, but on the west, where there was not this change in soil minerality, total Mg decreased with increasing distance inland, reflecting the decreasing intensity of seaspray. Once the between-side differences in the influence of altitude and distance from the sea are accounted for, there are significant differences in soil chemical composition between the two sides of the island. Overall, west side soils are more influenced by both seaspray and the parent volcanic basalts than are east side soils.

Surface Force Analysis of Pyrite (FeS2): Its Reactivity to Amino Acid Adsorption

It is well known that mineral surfaces play an important role as catalysts for abiotic polymerization of amino acids to form peptides, which are the main components of the first self-replicating system. Understanding the mechanism behind the adsorption of simple amino acids on mineral surfaces is a topic of great interest not only in field of prebiotic evolution and but also in many other branches of material sciences. Various clay minerals have been suggested for studying how organic molecules were first synthesized in a prebiotic “inorganic” environment. Among them, pyrite (FeS2) is one of the most potential minerals as it possesses a highly reactive surface to drive molecular adsorption in prebiotic chemistry reactions. Recent theoretical experiments suggest that amino acids are adsorbed on the pyrite surface depending on its surface structures. However, these results have not been tested experimentally, and the exact mechanism of the specific interactions on this mineral has not been fully resolved yet at the molecular level. In this work, through quantitative force analysis with atomic force microscope (AFM) in which a single amino acid residue was mounted on the tip apex of AFM probe, we were able to find the reaction sites and study the interaction forces between the amino acid and the pyrite surface. Our results of Raman spectroscopic studies and force measurements with a well-designed AFM probe demonstrated for the first time that pyrite provided higher adsorption probabilities of amino acid residues for the chemical reactions at surfaces.