The general aspects of volcanic ash petrography as they are applicable to the Kansas deposits have been described in an earlier Geological Survey report (Swineford and Frye, 1946). All the volcanic ash deposits studied in Kansas (Table 1) consist predominantly of glassy or vitreous shards rather than rock fragments or crystals. The individual deposits display a wide range in their included contamination of detrital grains, but at all the localities where the ash has been mined or is of commercial grade it contains less than 4 or 5 percent nonvolcanic material. The nonvolcanic material is predominantly quartz and feldspar in sand sizes, and traces of heavy minerals similar to those in the containing clastic sediments. Concretions of calcium carbonate which cements ash shards together into variously shaped bodies in the bed are also common at some localities.
Table 1.--Locations and thicknesses of volcanic ash beds sampled by the State Geological Survey of Kansas. *Samples for which chemical analyses are given in Table 2.
|Chautauqua||CQV-1||NW SE 9-34-12E||4.0|
|Clark||CLV-1||SE SE 23-30-24W||9.0|
|*CLV-1A||SE SE 23-30-24W||4.4||Lower part of CLV-1|
|*CLV-1B||SE SE 23-30-24W||3.0||Above CLV-IA; 1.6 ft. below top|
|CLV-2||NE SW 12-30-23W||6.0|
|Comanche||CMV-1||SE NE 12-31-18W||13.0|
|*CMV-1A||SE NE 12-31-18W||5.5||Lower part of CMV-1|
|*CMV-1B||SE NE 12-31-18W||10.0||Upper part; includes 2.5 ft. CLV-1A|
|CMV-2||NW SW 24-32-17W||6.0|
|CMV-3||NW SE 29-32-16W||2.5|
|CMV-4||Cen. W1/2 7-31-17W||7.0|
|Decatur||DRV-1||SE SW 8-4-29W||5.0|
|DRV-2||NE NE 15-3-30W||3.2|
|Dickinson||DV-1||SW SW 26-14-2E||1.0|
|Ellis||ESV-1||SE SE 17-14-19W||3.5|
|ESV-2||NW SW 5-13-19W||7.0|
|*ESV -3||SW NW 5-13-19W||10.5|
|Ellsworth||ELV-2||CNL SW 22-15-7W||9.0|
|*ELV-2A||CNL SW 22-15-7W||3.0||Lower part of ELV-2 bed|
|ELV-24||SE NW 28-16-7W||13.5|
|*ELV-24A||SE NW 28-16-7W||7.5||Lower part of ELV-24|
|Gove||GV-1||NE SW 21-13-26W||17.0|
|*GV-lA||NE SW 21-13-26W||6.0||Lower part of GV-1|
|*GV -1B||NE SW 21-13-26W||11.0||Upper part of GV-1|
|GV-2||SW SE 25-15-28W||15.0|
|GV-3||SW NW 17-15-27W||13.5|
|GV-4||E1/2 NW 33-15-27W||6.0|
|GV-5||Cen. NE 14-15-28W||6.0|
|GV-6||NW NE 26-15-29W||4.0|
|Graham||GMV-1||NE SW 11-8-25W||6.0|
|Grant||*GTV-1||SE NE 1-30-36W||23.5|
|GVT-2||SE NW 17-30-35W||6.0|
|Gray||GRV-1||NW NW 35-29-27W||4.0|
|GRV-2||SW SW 26-29-27W||11.0|
|Harper||HPV-1||NE NE 29-33-6W||6.0|
|HPV-2||NW SW 18-31-7W||3.5|
|Jewell||*JV-1||N1/2 NE 29-5-9W||6.5|
|JV-2||NW NW 4-2-9W||3.0|
|JV-3||NW SE 32-1-9W||9.0|
|*JV-3A||NW SE 32-1-9W||5.5||Lower part of JV-3|
|*JV-3B||NW SE 32-1-9W||3.5||Upper part of JV-3|
|JV-4||SE SE 33-1-9W||2.0|
|JV-5||NE NE 20-1-6W||10.0|
|*JV-6||NW NE 16-1-6W||17.0|
|*JV-7||SE NE 6-3-8W||2.5|
|JV-8||NE NE 26-1-10W||4.0|
|JV-10||SE NW 5-2-9W||10.0|
|JV-11||SW NE 7-2-9W||8.0|
|*JV-11A||SW NE 7-2-9W||4.0||Lower part of JV-11|
|JV-12||SE 3-2-10W||7.0||Reported thickness|
|Kingman||KMV-1||NW NE 16-25-10W||1.0|
|Kiowa||KV-1||NW NE 5-30-16W||10.0|
|Lincoln||*LV-1||SE SW 27-13-10W||6.0|
|*LV-2||SW SE 27-13-10W||6.5|
|Logan||LOV-1||SW NW 36-12-36W||8.0|
|LOV-2||SE NE 11-13-35W||9.0|
|*LOV-3||SW NW 12-13-35W||14.0|
|LOV-4||Cen. NE 34-14-33W||6.0|
|LOV-5||SE SW 35-13-33W||6.0|
|*LOV-5A||SE SW 35-13-33W||6.0||Selected from LOV-5|
|Lyon||LYV-1||SW SW 10-19-10E||0.5||4 ft. thick in SE SW sec. 10|
|MLV-2||NE cor. 11-4-9E||2.5|
|McPherson||*MPV-1||SE NW 20-18-3W||8.5|
|MPV-2||NW SW 10-18-4W||4.0|
|MPV-3||Cen. E1/2 28-18-5W||3.0|
|MPV-4||W1/2 NW 15-18-4W||3.0|
|MPV-5||NW SW 15-18-4W||4.5|
|MPV-6||SW NW 22-18-4W||6.5|
|*MPV-6A||SW NW 22-18-4W||4.2||Lower part of MPV-6|
|*MPV-6B||SW NW 22-18-4W||2.3||Upper part of MPV-6|
|MPV-7||W1/2 SW 5-18-2W||4.5|
|MPV-8||SE NE 14-18-3W|
|*MEV-1A||SW 34-31-28W||5.0||Lower part of MEV-1|
|*MEV-1B||SW 34-31-28W||4.5||Upper part of MEV-1|
|*MEV-2||SE SE 33-31-28W||4.0|
|MEV-3||SW NE 26-32-28W||18.0|
|*MEV-4A||NE 9-32-28W||8.0||23 ft. below MEV-4B|
|*MEV-4B||NE 9-32-28W||6.0||Upper bed at MEV-4 locality|
|MEV-5||SW 2-31-28W||17.0||(20 ft. with impure ash)|
|MEV-5A||SW 2-31-28W||13.0||Lower part of MEV-5|
|*MEV-5B||SW 2-31-28W||7.0||Upper part of MEV-5|
|MEV-6||E1/2 NE 6-31-26W||20.0|
|MEV-8||SE SE 26-30-28W|
|Ness||*NSV-1||SE NW 30-18-23W||6.0|
|NSV-2||SW SW 6-19-26W||9.0|
|Norton||NNV-1||NW SW 25-2-22W||17.0|
|*NNV-1A||NW SW 25-2-22W||7.5||Lower part of NNV-1|
|*NNV-1B||NW SW 25-2-22W||4.0||Above NNV-1A|
|NNV-2||NW NW 2-4-24W||4.0|
|NNV-3||SE SE 25-3-25W||10.0|
|NNV-4||SW SE 2-3-25W||7.0|
|NNV-5||NE NW 36-2-25W||3.0|
|NNV-7||SE SE 27-4-23W||5.0|
|*NNV-8||Cen. SE 16-1-21 W||4.0|
|Ottawa||OV-1||NE NW 29-10-5W||6.0|
|OV-2||SW SE 3-9-2W||2.0|
|Phillips||*PHV-1||NE NE 19-2-18W||9.0|
|PHV-2||SE NE 33-5-19W||5.5|
|PHV-3||NE NE 33-5-19W||15.0|
|*PHV-3A||NE NE 33-5-19W||7.3||Lower part of PHV-3|
|*PHV-3B||NE NE 33-5-19W||6.0||Above PHV-3A; 1.7 ft. below top|
|PHV-4||Cen. NE 3-2-19W||6.5|
|PHV-5||NW NE 30-1-19W||1.5|
|PHV-6||SW SW 14-1-18W||0.7|
|Pratt||PRV-1||S1/2 SW 21-27-12W||14.0|
|*PRV-1A||S1/2 SW 21-27-12W||7.5||Lower part of PRV-1|
|PRV-2||SW SW 23-27-11W||2.5|
|PRV-3||NE SE 22-28-14W||10.0|
|*PRV-4||NW SE 34-27-12W||4.0|
|Rawlins||*RWV-1||NE NW 14-3-35W||14.0|
|*RWV-1B||NE NW 14-3-35W||6.0||Upper part of RWV-1|
|RWV-2||W1/2 SW 4-4-34W||2.0|
|*RWV-3||NW NW 33-3-34W||6.0|
|*RVVV-3A||NW NW 33-3-34W||3.0||Lower part of RWV-3|
|*RWV-3B||NW NW 33-3-34W||3.0||Upper part of RWV-3|
|*RWV-4||NW SW 22-3-35W||14.0|
|Reno||*ROV-1||NW SE 14-25-8W||10.0|
|*ROV-1B||NW SE 14-25-8W||4.5||Upper part of ROV-1|
|*ROV-2||SE NE 1-25-7W||3.0|
|Rooks||RKV-1||SW SW 18-7-18W||10.0|
|RKV-2||NE NE 7-8-16W||4.5|
|RKV-3||SW SE 31-9-16W||6.0|
|Russell||RV-1||SE SW 19-14-13W||3.0|
|*RV-2||NE NW 2-15-11W||7.0|
|RV-3||SW NW 2-15-11W||10.0|
|Seward||SDV-1||NW NW 35-33-32W||7.0|
|SDV-2||SE SE 35-34-31W||8.0|
|*SDV-3||SW NE 13-33-32W||8.5|
|Sheridan||SNV-1||NW NW 34-8-28W||8.0|
|*SNV-2||NE SW 11-8-28W||6.0|
|SNV-3||SE SW 12-8-27W||3.5|
|Smith||SMV-1||NW NW 31-3-15W||15.0|
|SMV-2||NE SE 32-1-14W||3.0|
|Stafford||SFV-1||NE SW 28-25-11W||2.0|
|Trego||TV-1||NW SE 28-14-21W||7.5|
|TV-3||S. Cen. 26-14-21W||10.0|
|Wallace||WCV-1||SE SE 8-14-38W||3.0|
|Washington||WV-1||NW NW 30-1-4E||1.0|
The volcanic ash, exclusive of contaminants, is almost entirely glass in the form of curved angular fragments of bubble walls. These bubbles occur both singly and as intersecting clusters, and were produced by gases which were released when the molten rock material was discharged from the volcanic vents. A very small amount of crystalline material is present as a volcanic product. Ham (1949, pp. 78-81) has reported that the Oklahoma deposits contain potassium feldspar and quartz of volcanic origin. Volcanic potassium feldspar has been noted in the Pleistocene ash deposits of Kansas.
In chemical composition the fresh glass commonly contains more than 70 percent silica (SiO2), approximately 12 percent alumina (Al2O3), 2 percent ferric oxide (Fe2O3), 7 percent alkalies, and generally less than 3 percent lime (CaO) and magnesia (MgO). Chemical analyses of 54 channel samples of Kansas volcanic ash have been made under supervision of Russell Runnels in the geochemistry laboratories of the Geological Survey and are presented in Table 2.
Table 2.--Chemical composition of 54 volcanic ash samples. (Analyses in State Geological Survey geochemistry laboratory under supervision of Russell Runnels.)
|County||Sample no.||Chemical Analysis|
|aMixed alkalies by difference from 100 percent.|
|bRatio of K2O and Na2O by spectographic determination. Percentage figured from undetermined difference.|
|cK2O and Na2O determined chemically.|
Mechanical analyses were made by a combination of sieving and pipette methods on 12 channel samples from some of the larger deposits. Thirty grams of sample were shaken for 8 hours in a laboratory shaker and dispersed with NH4OH. The size distribution of the material finer than 62 microns was determined by the usual pipetting procedure, assuming a specific gravity for the ash of 2.32. After completion of the pipette analysis, the finer particles were removed by repeated decantation, and the remainder was dried and screened for 10 minutes in a Ro-Tap sieve shaker. The combined results are shown in Table 3. Ro-Tap screen analyses of 96 samples are reported in terms of screen mesh in Table 4. The two sets of analyses differ somewhat in the coarser fractions because large lumps produced by secondary cementation are not included in the data of Table 3.
Table 4.--Screen analyses of 96 volcanic ash samples (analyses by S. K. Chakravorty in Geological Survey laboratories).
|County||Location no.||Percent retained on||Comments|
|20 mesh||60 mesh||100 mesh||200 mesh||Pan|
|DRV-2||8.35||17.35||11.97||17.19||45.13||All contain sand except pan|
|Harper||HPV-1||0.55||2.17||6.44||22.51||68.30||Contains silt and sand|
|NNV-2||7.40||8.21||4.14||11.38||68.84||Altered by weathering|
|NNV-5||10.31||6.17||2.26||9.24||72.00||Contains some sand|
|NNV-6||2.13||4.28||7.90||21.60||64.08||Altered by weathering|
|NNV-7||11.77||6.05||4.68||22.41||55.07||Weathered, contains sand|
|PRV-3B||0.00||0.63||5.38||31.21||62.77||Contains silt and sand|
|PRV-3A||0.19||1.82||12.57||50.44||34.97||Contains silt and sand|
|SNV-3||2.05||3.06||4.74||2.13||69.98||Contains some sand, silt|
The median diameter ranges from 26 to 46 microns in the 12 samples analyzed, and averages 34 microns. The degree of sorting is uniformly high, and the size frequency curves in general are strikingly similar to those reported for wind-blown silt (Fig. 4). This probably is a result of sorting during air transport. Kuenen (1950, p. 345) suggests that volcanic explosions do not produce shards of dimensions smaller than about 5 microns in appreciable quantity. The Kansas size data apparently support his thesis, for all except 4 of the samples show 2 percent or less finer than 5 microns and three of the four exceptions are slightly weathered. However, electron micrographs of the less-than-1-micron fractions show particles having definite shardlike shapes (Pl. 5A) and in a sample from Lincoln County fibrous-type shards were observed in the less than 1 micron fraction. It is possible that sorting is as great a factor as original diameter in determining the size frequency distribution of the ash. Selective weathering may also destroy extremely small particles of glass.
Figure 4--Cumulative size frequency curves for volcanic ash and loess. The ash analyses are typical of unaltered deposits and loess analyses used are of samples of Peoria silt in High Plains upland situations. Note the high degree of similarity among the analyses.
Particle size data on Oklahoma ash reported by Ham (1949) indicate that the Oklahoma material is somewhat coarser than that from Kansas, which is to be expected if Oklahoma is nearer the assumed source area. However, the Kansas samples analyzed show no uniform geographic trends.
The effects of weathering produce alteration both in the chemical composition and physical appearance of the shards. The percentages of silica and alkalies decrease as weathering proceeds. The individual shards of glass take on a cloudy appearance, crystalline calcite develops, a clay coating is formed on the edges, and if the weathering proceeds far enough the particle size significantly decreases. At a few places thin noncommercial bentonite beds associated with Ogallala ash represent an advanced stage of weathering. This bentonite is generally greenish gray in color and one sample from just above the fresh ash in the Calvert pit was shown by x-ray diffraction analysis to be almost pure montmorillonite (personal communication, W. D. Keller) as shown in the electron micrograph in Plate 5B. The Pearlette ash weathers to a lighter color and some deposits are judged on the basis of electron micrographs to yield kaolinite type clay minerals as an alteration product, although x-ray diffraction studies suggest predominance of a montmorillonite mineral.
The distinctive petrographic characters of the several volcanic ash beds in Kansas are described in the following paragraphs.
The Calvert ash is an admixture of two or possibly three closely spaced falls. The glass is characterized by a neutral very light-gray color (approximately N8 of the Munsell classification), although in the field it is usually described as bluish gray. The bluish appearance is thought to be due to reflected light from the sky in the flat platy glass shards, and to the contrast with the more common buff color of adjacent sediments.
The shards of the Calvert ash are characteristically flat and so thin that iridescence is observed in many shards. Bubble junctures are straight or almost straight, and more than one is not commonly present in the same shard (Pl. 4A).
Plate 4--Petrographic features of Kansas volcanic ash. A, Shards from the Calvert mine from the 88-to-125 micron fraction mounted in oil of 1.46 refractive index, magnification 50X. Note thin flat shards with flat bubble junctures typical of the Calvert bed (Swineford, 1951). B, Shards of Pearlette ash from the NE NW sec. 14, T. 3 S., R. 35 W., Rawlins County; mounting same as A. Note thicker glass, curved and fibrous shards typical of Pearlette bed (Swineford, 1951). C, Thin section of cemented (calcium carbonate) Pearlette ash from the SW SW sec. 14, T. 1 S., R. 18 W., Phillips County, magnification 50X (Swineford, 1951). D, Detail of bedding in Pearlette volcanic ash in pit face, in sec. 2, T. 31 S., R. 28 W., Meade County. Ruler is 1 foot long. Note cross bedding (Swineford, 1951). E, Typical bedding of Pearlette volcanic ash exposed in pit face, NW sec. 34, T. 8 S., R. 28 W., Sheridan County.
Plate 5--Electron micrographs of volcanic ash and bentonite. A, Shards from minus-1-micron fraction, Pearlette ash, sec. 2, T. 31 S., R. 28 W., Meade County. Note curvature and angularity of glass. Magnification, 20,000X. B, Bentonite from above fresh ash at Calvert pit of Wyandotte Chemicals Corporation (minus-1-micron fraction). Cottony masses are typical of montmorillonite. Magnification, 20,000X. Elctron micrographs by C.C. McMurtry, Department of Oncology, University of Kansas Medical School. Preparations shadowed with 120 A of chromium at 18°. Scale indicates 1 micron.
The average index of refraction is 1.501 ± 0.001, but there are scattered shards with index slightly greater than 1.503, and the upper part of the bed at the type locality consists predominantly of shards having an index of 1.498 ± 0.001. The Calvert type locality is the only deposit of Kansas volcanic ash in which vertical variation in petrographic character of the fresh glass has been observed. Series samples have been taken from one other deposit provisionally assigned to the Calvert ash bed (location: NE SE sec. 27, T. 4 S., R. 23 W., Norton County) but the degree of weathering precludes differentiation. Many other Ogallala ash deposits have been channel-sampled for this report. Had samples been taken in vertical series they might also have shown nonuniformity of the glass.
The specific gravity of the Calvert glass averages 1.36. Its chemical composition is similar to that of the other Kansas ash deposits, although the percentage of ferric oxide is slightly higher than that of the Pearlette.
The Reager ash fall consists of glass shards which are more strongly curved than those of the Calvert fall, and a larger proportion of the shards show several bubble junctures. The glass is somewhat thicker, and shards having closely spaced parallel junctures are fairly common. The color is gray with a faint suggestion of an orange cast (slightly grayer than Munsell 5YR8/1). The index of refraction of glass from channel samples of this ash has a greater range than that of any other bed described in this report. The average index is 1.503 ± 0.001, but the range is from 1.500 to 1.507. There is some indication that the high-index shards are less stable than the others, and selective destruction of such shards may make positive identification of the Reager bed difficult in some deposits.
A large proportion of the Reager samples contain coarse sand as a contaminant in the coarser fractions.
Two deposits of fresh ash--both in Phillips County--apparently represent a single ash fall. These deposits are similar in appearance to the ash of the Reager bed, but all except a very few of the shards have a restricted refractive index of 1.500 to 1.503. Future detailed study of these deposits may either show them to be modified Reager or differentiate them more positively from other Ogallala falls.
The Pearlette ash is lighter in color than any of the Kansas Ogallala ash deposits and on field inspection appears to be white; however, laboratory comparison with Munsell standards shows that it has a faint pinkish hue. The typical color corresponds closely to Munsell 5YR8/1 (pinkish gray).
The individual shards are very strongly curved, and consequently do not reflect as much light as those of the Calvert or even of the other Ogallala beds. Many of the larger shards include parts of several bubbles, and a few complete bubbles are present in all samples which contain coarse shards. Bubble junctures are commonly sharply curved and intersect at high angles. Fibrous shards are the most distinctive feature of the Pearlette ash, particularly in the finer size fractions. Such shards are shown in Plate 4B. The Pearlette is readily distinguished from Ogallala falls by the presence of numerous vesicles in the glass. These are easily observed in transmitted light and are due to the small radius of curvature of the glass and to the entrapment of air in the capillaries of the fibrous shards. The three-dimensional character of the Pearlette adds to its effectiveness as an abrasive. This angularity is also present in the extremely fine particles. An electron micrograph of ash from the pit in sec. 2, T. 31 S., R, 28 W., Meade County (PL. 5A), shows that particles of 1 micron or less in diameter are strongly curved and angular.
The index of refraction of the fresh glass is uniform from top to bottom of the deposits, nearly all shards having n = 1.499 ± 0.002.
Most deposits of Pearlette ash are soft and unconsolidated. Small concretions cemented with calcium carbonate are present and in Phillips County in the SW SW sec. 14, T. 1 S., R. 18 W., a thin bed solidly cemented with calcite has the appearance of a dense limestone. A photomicrograph from a thin section of this material (PL. 4C) shows some of the large curved shards in cross section.
Kansas Geological Survey, Kansas Volcanic Ash Resources
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Web version Jan. 2005. Original publication date Feb. 15, 1952.