Ankerite

About: Ankerite is a research topic. Over the lifetime, 859 publications have been published within this topic receiving 23960 citations.

On the Frequent Occurrence of Ankerite in Coal

Abstract: There occurs frequently in coal a white carbonate which, when it is referred to at all by scientific writers on coal, is usually described as calcium carbonate. It occurs as a rule in the form of thin layers infilling the joint-cracks which lie normal to the bedding-planes, though at times it may be seen infilling other divisional planes which may cut across the bedding obliquely.

79. diagenetic reactions in deeply buried sediments of the japan sea: a synthesis of interstitial-water chemistry results from legs 127 and 1281

Abstract: Shipboard and shore-based analyses of -230 interstitial-water samples gathered at six sites during ODP Legs 127 and 128 indicate that diagenetic reactions within sediment columns throughout the Japan Sea record the influence of bacterial degradation of organic matter, transformation of amorphous biogenic opaline silica to opal-CT, and formation and alteration of carbonate phases, as well as alteration of crystalline basement and volcanic ash. Organic matter oxidation not only affects the distribution of oxidants (SO4, Mn, and CO2) and dissolved metabolites (alkalinity, NH4, and PO4), but also controls the distribution of many authigenic solid phases. Site 794, located deep in the Yamato Basin, is the only site where sulfate is not completely consumed, whereas Sites 798 and 799 record the total consumption of sulfate at shallow depths and concomitant extreme generation of alkalinity, NH4, and PO4. Authigenic carbonates, phosphates, and barite also record the importance of bacterial activity. The diagenetic opal-A/opal-CT transition is a notable chemical, diagenetic, and stratigraphic horizon that occurs more shallowly in the basinal sites because of their greater geothermal gradient. Due to its effect on the porosity and permeability of the involved lithologies, the siliceous phase transformation effectively restricts diffusion between reactions occurring in the uppermost sediment column from those involved in deep basement alteration. Processes that influence dissolved Ca, Mg, Sr, and alkalinity tend to be preferentially dominant at either basinal (Site 794, 795, and 797) or ridge (all other) sites, due to the distinctly different depths and sedimentation rates of the two depositional regimes. At basinal sites, where sediment accumulation is relatively slow and occurs below the CCD, basement alteration is the dominant influence on dissolved Ca and Mg profiles. At ridge sites, where accumulation is relatively fast and occurs above the CCD, diagenetic reactions such as calcite dissolution, inorganic carbonate precipitation, dolomitization, and siderite/ankerite formation control Ca and Mg behavior. Basement alteration reactions are responsible for large overall decreases in Mg, K, Rb, Li, B, δ l8 0, δD, 87Sr/86Sr, and Na with depth, as well as for increases in Ca and Sr. Alteration of ash in the sediment column also influences these downhole profiles. Site 795, in the Japan Basin, preserves the greatest diagenetic signal of basement alteration. Gradients resulting from basement alteration document the importance of diffusive chemical exchange between the endogenic and exogenic reservoirs.

Mineralogy and geochemistry of Green River Formation Oil Shales, C-A Tract, Colorado

Abstract: Whole-rock chemical data are used to obtain the normative mineralogical composition of 71 samples obtained at 10-ft intervals from a drill core from the C-a Tract in the Piceance Basin, Colorado. The vertical variation of quartz, analcite, albite, orthoclase, illite, pyrite, calcite, dolomite, ankerite, magnesite, Mg-siderite, dawsonite, and nahcolite is discussed. With depth, three mineralogical ''zones'' are distinguished: Mahogany Zone (and stratigraphically higher) oil shale is characterized by dolomite > quartz > calcite, analcite, albite, orthoclase, illite; L-6 to middle of R-5 Zone oil shales are characterized by dolomite > albite, orthoclase > quartz, ankerite; R-5 to R-4 Zone oil shales are characterized by quartz > dolomite > orthoclase, albite, dawsonite, illite. As, Se, and Mo exhibit cyclic trends with depth and are generally more abundant in higher grade zones. No significant correlation exists between organic C and As, Se, or Mo on a core-wide basis. Significant positive correlations between pyrite and As, Se, and Mo suggest that these heavy metals are associated with pyrite, especially with disseminated, fine grained framboidal pyrite. Hg shows a general decrease with depth; no significant correlations exists between Hg and pyrite or organic C. F is most abundant in the feldspar-rich shales and ismore » probably present as fluorite.« less