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Microprobe Analysis of the Iron-bearing Sediment
- Texas A&M University Press
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Microprobe Analysis, Iron-bearing Sediment 21 Microprobe Analysis of the Iron-bearing Sediment ✦ T hree samples of burial fill taken in the area of dense red pigment between and below the distal left humerus and left ribs were studied using a petrographic microscope and a JEOL 8900 electron microprobe under the following conditions: (1) an acceleration voltage of 15 kv; (2) a beam current of 10 nA; and (3) a beam diameter of 10 µm. The purpose was to identify the composition of the reddish stained sands. The following standards were used: (1) USnM 143965 for na, K, and MG; (2) USnM R-2912 for Si, Al, and Ca; (3) USnM 157872 for Mn; and (4) USnM 10421 for P. The results were normalized to the nominal compositions of the standards and adjusted to represent 100% of the sample. Samples designated AL-11 and AL-20 consisted of unlithified and very poorly sorted quartz grains ranging in size from coarse sand (1–0.5 mm) to silt (63–30 µm). All of these samples have a chalky, reddish brown, ferruginous calcareous coating. Sample AL-12 differed only in that there was enough calcareous material to consolidate the quartz grains into a weakly cemented sandstone (fig. 14, color section). The microprobe analyses of this coating on the grains and the matrix in sample A-12 (table 2) indicate high quantities of calcium, silica, and iron. These concentrations would be expected from calcareous ferruginous quartz sand. This iron-rich, calcareous, silty sandstone with its reddish brown coloration could be considered to be a type of sediment-rich ocher. 21 TABLe 2. eLeCTrON MiCrOprOBe ANALySiS OF ArCH LAke SOiL SAMpLeS (wT.%). Sample n SiO2 Al2 O3 FeO MgO MnO CaO K2 O Na2 O P2 O5 Total Sample AL-11 7 Mean 34.6 10.6 5.7 2.7 0.5 43.5 1.2 0.9 0.2 100 s. d. 8.1 4.4 0.7 0.3 0.9 12.1 0.3 1.0 0.1 Sample AL-20 18 Mean 20.2 6.4 4.1 2.8 0.1 64.7 0.8 0.6 0.4 100 s. d. 12.1 3.9 2.1 1.4 0.2 20.5 0.4 1.9 0.3 Sample AL-12 9 Mean 36.1 8.9 5.8 2.8 0.5 43.6 1.6 0.6 0.2 100 s. d. 11.1 2.2 1.7 0.7 1.4 13.5 0.5 0.3 0.1 ...