کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
9535670 1356890 2005 10 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Elemental composition of calcites in late Quaternary pedogenic calcretes from Gujarat, western India
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات زمین شناسی
پیش نمایش صفحه اول مقاله
Elemental composition of calcites in late Quaternary pedogenic calcretes from Gujarat, western India
چکیده انگلیسی
Pedogenic calcretes commonly exhibit clotted micrite, circum-granular calcite (grain coats) and microspar/spar veins. The three calcite-types with different dimensions were analyzed for their magnesium content to determine the relationship between crystal elongation and magnesium incorporation. The results show a very low MgO content for grain coats and microspars and high values for clotted micrite indicating that the ideal kinetic model does not hold true and several variables govern the end composition of calcites. The magnesium concentrations of meteoric calcites are genetically linked to the evolutionary history of the soil and climate. Grain coats, which are elongated calcites, contain the least amount of Mg and is related to the initial stages of pedogenesis wherein the limiting factor is the Mg/Ca ratio of the parent fluid. Lower magnesium contents arise due to smaller quantities of Mg being released during incipient weathering. Micrite morphology and composition is controlled by the greater availability of Mg ions through weathering, higher pCO2 in soil due to increased time-dependent soil respiration, which causes a rise in calcite precipitation rates and clay authigenesis. This in turn exerts a physical control on morphology by occluding pore space and providing numerous nuclei for calcite precipitation. The wide variability in spar cements is inherently controlled by inhomogeneties in parent fluid compositions with lower-than-micrite values on account of slower precipitation rates.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Asian Earth Sciences - Volume 25, Issue 6, November 2005, Pages 893-902
نویسندگان
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