General Character of the Rocks
The Leonardian and Guadalupian? sediments in south-central Kansas are but a small fraction of the deposits of that age in the northern part of the Permian basin. Thhey overlie relatively undisturbed, predominantly normal marine shales and limestones of Wolfcampian age and consist in general of thin-bedded units which display some lateral change in texture (and therefore in overall composition). In general, the lithologic units may be described as blanket deposits, because their lateral extent is at least 11,000 times as great as their thickness (Krynine, 1948, p. 146).
In the Kansas outcropping rocks the lateral variation is not particularly evident except in certain formations, but subsurface data must be taken into account when the regional picture is evaluated.
The source rocks which supplied the outcropping Kansas sediments are several hundred miles from the site of their deposition, but presumably consisted predominantly of acid igneous rocks, older sediments, and minor metamorphic rocks, in decreasing order of abundance. Transport over long distances at low energy levels produced sediments of fine grain and rather uniform mineralogy, so far as clastic particles are concerned. Tracing of the lithologic units in the subsurface shows coarsening to the west and points to the Front Range region and possibly to the Sierra Grande uplift area as source regions (Maher, 1953), and also areas west of the Front Range (Kay, 1951). These positive areas are approximately 150 to 400 miles or more from the area of outcropping red Permian rocks in Kansas. Other local sources are minor uplifts to the south in Oklahoma and Texas.
Distribution of Rock Types
The sediments of the Kansas Permian redbeds consist predominantly of feldspathic siltstones, shales and silty shales, and very fine-grained feldspathic sandstones, with numerous thin beds of dolomite, gypsum, anhydrite, halite, and some limestone. In general, the finer grained clastics are in the lower part of the section, and the fine-grained sandstones in the middle and upper part. The average particle size is also fine (that is, there are fewer sandstones) in the uppermost beds. In geographic distribution the grain size is coarser toward the west and southwest (and also south, in the Whitehorse). Areas of evaporite deposition shift upward stratigraphically toward the west.
The generalized lithology of the outcropping rocks is summarized in Table 2 and presented graphically in Figures 6 and 7.
Table 2--Generalized lithology of the outcropping Leonardian and Guadalupian? sediments in Kansas (Values in percent of total thickness of formation).
|1Coarser clastics predominate in lower two-fifths of formation. Marlow contains 90 percent
sandstone, Relay Creek? 70 percent sandstone, even-bedded member 40 percent sandstone,
and upper shale member 10 percent sandstone.
|2Exclusive of Wellington formation, the sediments are about 87 percent red.|
Figure 7--Stratigraphic distribution of lithologic types and of redbeds.
Character of End Members
As stressed by Krynine (1948, p. 137), sedimentary rocks may be regarded as mixtures of three textural elements: grairis, matrix, and cement.
The end members of the Kansas Permian redbeds are (1) feldspathic sands and silts; (2) clayey matrix which is at least in part authigenic and chiefly red; (3) carbonates and sulfates (predominantly dolomite and gypsum); and (4) salt.
The grains in the redbeds are characteristically of silt or very fine sand size with the following average mineral composition.
|Quartz||75 to 80|
|Micas and detrital chlorites||<2|
The matrix is generally illite clay with significant quantities of chlorite, fine-grained quartz and feldspar, and hematite stain. A few sandstones contain a silt matrix. The clay in some specimens is predominantly montmorillonite, but this is not typical except in the upper part of the section. Some matrix contains no hematite. The typical clayey matrix has approximately the following mineral composition.
|Illite and sericite||50|
|Kaolinite and montmorillonite||<10|
|Quartz and feldspar||>20|
The characteristic cement is dolomite or calcite, or both; some gypsum cement also occurs.
The type of mixture of these three textural elements (and the depositional environment) depends upon degree of activity in the source areas, or, more probably, degree of warping between the source and the site of deposition, character of water from which the sediments were deposited, depending on such factors as effectiveness of barrier to open sea, and degree of rainfall, and possibly diagenesis. The controlling genetic factor seems to be gentle warping in broad shallow basins, plus possible uplift in the source areas.
The principal lithologic types (exclusive of salt) are red and greenish-gray (commonly dolomitic or calcareous) silty shales; red and greenish-gray to white (commonly dolomitic or calcareous) siltstones; red and white very fine-grained feldspathic sandstones; dolomites and limestones; and gypsum and anhydrite.
The overall composition of some typical samples is shown on a trilinear diagram in Figure 8. As shown by the diagram, the siltstones are characteristically calcareous (or dolomitic) and heterogeneous in character. The sandstones are rather well sorted and range from very calcareous (or dolomitic or gypsiferous) to entirely uncemented. The shales are mostly silty, and some have appreciable quantities of carbonates (or sulfates). The evaporites are remarkably free of detrital clastic material.
Figure 8--Over-all composition of some typical sandstones, siltstones, shales, and evaporites from the post-Wolfcampian Permian deposits of Kansas. (t, Taloga; whrc, Relay Creek; whm, Marlow; dc, Dog Creek; b, Blaine; fp, Flowerpot; ch, Cedar Hills; sp, Salt Plain; sc, Stone Corral, n, Ninnescah; w, Wellington.)
Summary of Texture
Particle Size and Sorting
Definition of terms--The clastic deposits of the Leonardian and Guadalupian Series in Kansas include fine-grained sandstones, siltstones, and clay shales. Some of the geologists who have described these rocks in the literature have not used "siltstone" as a descriptive term. This practice has led to a certain degree of confusion concerning the actual texture of these Permian deposits.
In the present report the following terms are used.
Sandstone: A rock consisting of at least 50 percent of grains between 1,000 microns and 62.5 microns (0 to 4Ø) in diameter. Most of the sandstones under consideration are fine grained (250 to 125 microns) or very fine grained (125 to 62.5 microns, or 3 to 4Ø).
Siltstone: A rock consisting of at least 50 percent of grains between 62.5 microns and 3.9 microns (4 to 8Ø) in diameter, or gritty but finer than sand size.
Shale or clay shale: A rock consisting of at least 50 percent of grains finer than 3.9 microns (8Ø), or nongritty.
The adjectives silty, argillaceous, sandy, indicate at least 20 percent of the modifying component.
Grain-size distribution--In general, the rocks in the section are very fine grained. No sandstone sample examined by me has a median grain size coarser than 3Ø (125 microns). No individual detrital grains (other than fragments in intraformational conglomerates) larger than 1,500 microns were observed.
The outcropping rocks include about 15 percent very fine sandstones, 25 percent siltstones, and 50 percent silty shales and shales. The data from mechanical analysis of 41 samples are shown in Table 3. Representative cumulative size-frequency curves are shown in Figures 9 and 10.
Table 3--Mechanical analyses of Leonardian and Guadalupian rocks, arranged in stratigraphic sequence from youngest to oldest formation.
|No.||Formation||Location||Size distribution (percent by weight) in phi units||Mdb||PDO|
upper shale m.
Woods Co., Okla.
Woods Co., Okla.
Woods Co., Okla.
lower 10' Marlow
lower 10' Marlow
lower 10' Marlow
(near Bed 4)
(near Bed 3)
(below Bed 3)
Figure 9--Representative cumulative size-frequency curves for some post-Wolfcampian sandstones and siltstones.
Figure 10--Representative cumulative size-frequency curves for some post-Wolfcampian siltstones and shales.
Sorting--The degree of sorting, expressed as phi percentile deviation (PDØ) ranges from 0.4 to 3.6. In general the sands are well sorted and the shales poorly sorted. This correspondence between size and sorting in sediments is noted by Krynine (1950, p. 80) and Griffiths (1951).
PDØ is plotted against MdØ in Figure 11, and the correlation is evident. The correlation coefficient, r, for 40 pairs is .840. According to Fisher's (1948, p. 209) table this value is statistically significant (P < 0.001). Griffiths (personal communication, April 21, 1954) points out that r2=70.56 percent, or 70 percent of variation in size is common to sorting, and 30 percent is not.
Figure 11--Graph showng relation between particle size and degree of sorting in some post-Wolfcampian Permian sediments.
The relationship between the two variables was computed by the method of least squares, and the line of best fit is superimposed on the chart (Fig. 11). The spread as measured by the standard error of estimate is also indicated. The data can thus be compared directly with those of Griffiths for his Caribbean sediments.
The equation for the line of best fit is PDØ = 0.5769 MdØ - 1.0344. The standard error of estimate, Sy, is 0.51.
Griffiths (1951) indicates that the position of a sample with respect to the band of "average trend" in the coarser grained sediments may have geological significance. It should be noted that the siltstones of the Salt Plain formation are better sorted than the average, whereas those of the Taloga are more poorly sorted. A sample from the Verden "channel" sandstone of the lower Whitehorse of Oklahoma is also plotted, although this point was not used in the other computations. It is interesting to note that the "channel" sandstone sample differs markedly from the normal facies in the size-sorting relationship. This may indicate more rapid "dumping" of sediments in the Verden member, and less reworking of the material. The data suggest that the Salt Plain sediments were subjected to long reworking in comparison with the other samples. This is also the case for the Runnymede siltstone (MdØ = 5.20; PDØ = 1.16) which apparently has broad lateral extent, and for a sample (MdØ = 3.70; PDØ = 0.56) from the "Peace Treaty" bed in the Cedar Hills sandstone which according to Norton (1939, p. 1789) can be correlated "over considerable distances."
It is of interest to note that the value of Sy is lower than most of those of Griffiths (1951) for single formations. This may indicate rather uniform conditions of transport and deposition over a long period of time.
Particle Shape (Sphericity and Roundedness)
Most of the sand and silt grains are subangular to subrounded; this is in large part, but not entirely, a function of the fine average particle size. The apparent roundness is also modified in some samples by incipient overgrowths and in other samples by etching or replacement by carbonate.
The roundness of the 105 to 88-micron fraction was measured on six samples according to the method of Wadell (1935). Fifty quartz grains from each sample were measured. The mean roundness of the 105 to 88-micron fraction ran-,es from 0.395 in a sample from the Marlow to 0.506 in one from the Relay Creek member, Whitehorse formation.
Roundness was measured for 8 size grades in a sample from the Verden sandstone of Oklahoma and the results are included in Table 4. The Verden was chosen because of its wide range in grain size in the sand sizes. Figure 12 shows the diameter in phi units plotted against log mean roundness; except for the larger sizes the points fall on a straight line. This straight-line function is the usual relationship between size and roundness, according to Pettijohn (1949, pp. 404-405). The deviation of the larger grains suggests that they have a different abrasional history. Their petrographic character (strain shadows, abundant chert, no feldspars) also shows that their history differs from that of the smaller grains. The well-rounded character of the large grains in the Verden sandstone is shown in Plate 18C.
Figure 12--Graph showing relation between log size and log roundness in sample from Verden sandstone.
Table 4--Wadell roundness; values for quartz grains from six Permian sandstones
|1135||Relay Creek? dolomite member, Whitehorse||105-88||.506|
|1108||Marlow member, Whitehorse||105-88||.395|
|1104||Verden sandstone member, Whitehorse||310-250||.734|
|Verden sandstone member, Whitehorse||250-210||.606|
|Verden sandstone member, Whitehorse||210-177||.549|
|Verden sandstone member, Whitehorse||177-149||.521|
|Verden sandstone member, Whitehorse||149-125||.507|
|Verden sandstone member, Whitehorse||125-105||.475|
|Verden sandstone member, Whitehorse||105-88||.469|
|Verden sandstone member, Whitehorse||88-62||.445|
|1164||Verden sandstone member, Whitehorse Creek||105-88||.478|
|1147||Basal Cedar Hills||105-88||.503|
In general the feldspar grains (particularly the weathered ones) are slightly better rounded than the quartz, although some feldspars still retain a prismatic shape and are scarcely rounded at all. A few of the zircon and tourmaline grains are very well rounded. Micas are very well rounded at some horizons, particularly in the Salt Plain formation.
No quantitative measurements of sphericity were made. In general the sphericity of the quartz grains seems to be rather low in the finer sizes; that of the large well-rounded grains is high.
Surface textures are varied. A few grains are frosted, but the type of frosting is not everywhere clear. Some is due to minute incipient overgrowths. Some grains, particularly in the upper part of the section, have a bright polished appearance; many of these grains are light orange in color. Surface textures of some of the heavy minerals are discussed in the section on mineralogy.
Summary of Composition
Major constituents--Detrital minerals in the typical sandstone consist of approximately 80 percent quartz, 20 percent feldspar (at least three-fourths of which is without multiple lamellar twinning), and less than 2 percent mica (predominantly muscovite, but some chlorite and traces of biotite). The typical siltstone contains a somewhat larger proportion of mica; in some argillaceous siltstones the mica content may reach more than 5 percent, but such a large proportion is not common. Most of the sandstones contain less than 5 percent of clay minerals (many are nearly free from clay), and the normal siltstones contain 10 to 30 percent. The clay minerals as such are not regarded as 100 percent detrital constituents.
The typical clay shale is silty, with approximately 20 percent quartz, 4 percent feldspar, and 3 percent micas in the silt fraction. The clay fraction (as shown by x-ray diffraction data) also contains quartz, feldspar, and micas, with a somewhat lower proportion of feldspar. It also contains a few percent of hematite which is responsible for the common red color. Most of the clay shales also contain dolomite or calcite or both.
The major constituents of the clay fraction are (besides quartz, feldspar, and hematite) illite, chlorite, montmorillonite, and kaolinite. Of these minerals the typical clay shale contains essentially only illite and chlorite, in the proportion of about 4:1. Some noncalcareous clays contain small quantities of kaolinite, and some clays near the top of the section are chiefly montmorillonite.
The predominant chemical minerals among the major constituents include dolomite, calcite, anhydrite, gypsum, and halite. Each of these occurs in thin essentially monomineralic beds or lenses. Calcite, dolomite, anhydrite, and gypsum are also common cementing materials in sandstones and siltstones, in some sandstones constituting about 50 percent of the rock. Calcite, dolomite, and gypsum occur as veins in some sandstones and silty shales, and as disseminated particles and crystals in many shales.
Sandstones in some zones are characterized by the presence of small unworn overgrowths on some of the quartz and orthoclase grains. One of the dolomite units--the Day Creek--commonly contains nodules and stringers of secondary chert. The time of origin of this chert is not clear; it has been postulated to be Tertiary or younger in age (Norton, 1939, p. 1811) but the presence of greenish-gray Permian montmorillonite clay immediately above it suggests that the silica may have been leached from the overlying bed. A primary origin is of course possible.
Accessory minerals--Accessory heavy minerals are neither abundant nor varied in the upper Permian sandstones. The quantity is everywhere less than 1 percent (not including the micas) and commonly less than 0.4 percent of the total sample. A sample from the base of the Cedar Hills formation was found to contain 0.38 percent heavy minerals, most of which were finer than sand size (less than 62 microns). A sample from the Relay Creek member of the Whitehorse sandstone contains only 0.15 percent heavy minerals, most of which are in the very fine sand sizes.
Except for the micas, there are no obvious stratigraphic variations in mineral suites. The only variations observed by me can be attributed to differences in particle size of the deposit, and perhaps to selective destruction of certain minerals, notably staurolite, after deposition.
The opaque minerals (ilmenite, "leucoxene," magnetite) make up from 40 to 65 percent of the heavy residues (micas excluded). The nonopaque minerals apatite, epidote, garnet, rutile, staurolite, titanite, tourmaline, and zircon form the remainder. Tourmaline, garnet, and staurolite are particularly abundant in the coarser fractions, whereas zircon and the opaque minerals predominate in the finer.
The nonopaque heavy minerals seem to be essentially unaltered, but all the staurolite is corroded. Much of the garnet is pitted; these pits may be vacuoles exposed on surface planes by fracturing (Krynine, personal communication dated April 4, 1954). Many staurolite grains are so delicately etched that they seem to have been corroded after deposition. However, it is conceivable that such grains could have survived transport in a suspension load.
Authigenic nonopaque heavy minerals (G > 2.87) are not common. A few irregularly shaped grains of barite are noted in a few samples from the Whitehorse sandstone.
Chemical analyses of 19 samples from the Leonardian and Guadalupian? Series, two Wolfcampian carbonate rocks, and one upper Pennsylvanian shale are shown in Table 5. Ten of the analyses (1802, 1801, 1794, 1138, 1128, 1146, 1147, 1156, 1137, 1139) were made specifically for this study in the chemical laboratories of the State Geological Survey of Kansas, under the supervision of Russell T. Runnels. The remaining analyses are taken from published reports and from data on file at the State Geological Survey of Kansas. Some of the samples have been studied in thin section or by x-ray diffraction, or both, so that somewhat detailed interpretation of the chemical data is possible.
Table 5--Chemical analyses of selected Permian sediments and a Pennsylvanian shale, arranged in stratigraphic sequence from youngest to oldest rocks.
|Leonardian and Guadalupian|
|1802||Taloga||Red silty shale||60.86||10.421||3.35||0.97||0.81||12.88||0.12||nil||0.02||3.57||0.24||6.524||99.74|
|1801||Basal Taloga||Green shale||50.50||12.741||3.84||0.94||0.77||19.54||0.06||0.17||0.05||2.13||0.20||9.284||100.17|
|Day Creek||Dolomite (Jewett and Schoewe, 1942, p. 111)||1.64||1.28||1.98||31.54||18.02||46.34||100.80|
|Light-red cross-bedded sandstone||85.74||6.841||0.79||0.38||0.49||1.11||0.01||nil||N.D.||2.19||1.16||1.124||99.83|
|Medicine Lodge||Gypsum (Grimsley and Bailey, 1899, p. 147)||0.19||0.105||32.53||0.16||45.73||21.276||99.98|
|1138||Flowerpot||Red silty shale||61.47||14.101||5.76||0.64||0.62||6.95||0.14||0.35||0.06||2.96||1.38||5.484||99.85|
|1128||Cedar Hills||Red sandy siltstone||73.02||7.151||2.01||1.04||4.85||2.54||0.09||nil||trace||1.70||1.38||5.764||99.54|
|1146||Cedar Hills||Red sandy siltstone||75.98||7.921||2.02||0.45||3.16||2.20||0.07||nil||nil||1.87||1.54||4.284||99.49|
|1147||Basal Cedar Hills||White sandstone||83.29||8.191||0.68||0.62||0.72||0.89||0.05||nil||nil||1.75||1.90||1.514||99.60|
|1156||Salt Plain||Red argillaceous siltsione||65.02||11.031||3.93||1.03||4.40||3.28||0.12||nil||0.03||2.57||1.42||6.874||99.67|
|1137||Salt Plain||Red sandy siltstone||77.54||7.691||1.77||0.79||2.61||1.77||0.09||nil||nil||1.66||1.70||3.674||99.29|
|Stone Corral||Dolomite. Av. of 5 analyses (Jewett and Schoewe, 1942, p. 111)||3.00||2.98||0.55||34.41||14.74||42.48||98.16|
|1139||Runnymede||Gray dolomitic siltstone||63.35||8.631||1.70||1.05||6.46||4.95||0.11||trace||0.03||1.62||1.30||10.564||100.337|
|Ninnescah||Red blocky shale (Lab. no. 48275)||52.89||15.831||5.87||1.39||3.97||6.39||0.14||trace||N.D.||3.23||0.72||9.114||99.54|
|Ninnescah||Red blocky shale (49438-42). Av. of 5||56.17||14.021||5.10||1.04||4.52||6.05||0.15||N.D.||2.95||0.69||8.484||99.17|
|Wellington||Gray shale (49414)||44.33||13.68||5.05||1.10||7.86||9.66||0.18||trace||N.D.||2.51||0.67||14.094||99.13|
|Wellington||Gray (and yellow) shale (49417) 34.84||9.92||4.09||0.94||11.90||13.64||0.18||trace||N.D.||1.68||0.36||21.564||99.11|
|Herington||Dolomite (5124, partial analysis)||6.21||1.305||0.79||30.52||18.04||0.04||0.07||43.408||100.30|
|Fort Riley||Limestone (5128, partial analysis)||7.45||1.945||0.84||47.41||2.08||0.05||0.37||38.848||98.61|
|Pennsylvanian (Wabaunsee group)|
|Langdon||Gray shale (Plummer and Hladik, 1951, p. 20)||55.74||21.00||7.49||1.02||0.70||2.57||0.17||nil||3.77||1.54||5.97||99.97|
|"Average" Sediments (Clarke, 1924)|
|Av. of 78 shales (Clarke, 1924, p. 631)||58.38||15.47||6.49||0.65||3.12||2.45||0.17||0.65||3.25||1.31||8.479|
|Av. of 153 sandstones (Clarke, 1924, p. 547)||78.66||4.78||1.38||0.25||5.52||1.17||0.08||0.07||1.32||0.45||6.689|
|1. Contains MnO2.|
|2. Total iron expressed as Fe2O3.|
|3. Contains ZrO2 and V2O5.|
|4. 140°C. to 1006°C.|
|5. Contains MnO2 and TiO2.|
|6. Water at 200°C., plus carbon dioxide (calc.).|
|7. Includes 0.6 percent CuO (determined spectrographically) .|
|6. 105°C. to 1000°C.|
|9. Reported as H2O, CO2, C.|
Fairbairn and others (1951) have shown that there is great variation betwen analyses made in different laboratories. Comparison of the analyses with Clarke's (1921) "average" sandstone and "average" shale may therefore not be of great significance, but in general the greatest differences are in the percentages of MgO and Fe2O3. Analyses of 29 Pennsylvanian shales (Plummer and Hladik, 1951, p. 20), incidentally, are very similar to Clarke's average shale. The nine Permian shales, however, are marked by their extremely high content of MgO (ranging from 6.05 to 19.54 percent, as opposed to 2.45 in the "average" shale and 1.98 ± 0.09 percent in the 29 analyses of Pennsylvanian shales). In comparing the mean values for the Pennsylvanian and Permian analyses (all of which were made in the same laboratory), the value of Student's t is 10.883 for 36 degrees of freedom. For 36 degrees of freedom, t must be not less than 3.59 to be significant at the 0.1 percent level. Thus the obtained difference of 9.94 is statistically significant well beyond the 0.1 percent level of confidence. The magnesium is of course found chiefly in the large quantities of chlorite, and also in dolomite, in most of the Permian shales.
A somewhat unexpected character of the Permian sediments is their rather low percentage of Fe2O3 despite their common bright-red coloration. The iron oxide content of the Permian sediments analyzed (exclusive of the evaporites and rare white sandstones) ranges from 0.79 percent, in a light-red sandstone, to 5.87 percent in a sample of red Ninnescah shale; whereas the average iron oxide content of the 29 Kansas Pennsylvanian shales (most of which are gray) is 6.56 percent, and of Clarke's 78 shales is 6.49 percent.
Student's t test for comparison of mean Fe2O3 content (4.63 percent) of 6 Permian red shales with the 29 Pennsylvanian shales indicates that t is 3.429 for 33 degrees of freedom. For 33 degrees of freedom, t must be not less than 2.7 at the 1 percent level. Thus we may take it with that degree of assurance that the populations are different.
Data for comparison of Fe2O3 content of Permian red shales with Permian green or gray shales are limited. The t test on six red shales and three green or gray shales (mean Fe2O3 = 4.33 percent) indicates that t is 0.424 for 7 degrees of freedom. For 7 degrees of freedom t must be not less than 1.90 to be significant at the 10 percent level. Accordingly, there is no evidence here that the populations are different.
The lower values for Fe2O3 in the Permian shales seemingly cannot be attributed to dilution with free SiO2. Clarke's average sandstone contains 1.38 percent Fe2O3 which is somewhat less than the average iron oxide content of 1.84 percent in seven Permian sandstones and siltstones.
The content of P2O5 in the Leonardian and Guadalupian? rocks is also low (average P2O5 in 9 shale samples is 0.13 percent as opposed to 0.17 percent in Clarke's average shale and 0.19 percent in 29 Pennsylvanian shales). Only two samples exceed Clarke's average; they are both gray shales from the Wellington formation (P2O5 = 0.18 percent). The paucity of P2O5 may perhaps be attributed to adverse living conditions in Kansas during most of Leonardian and Guadalupian? time, for according to Rankama and Sahama (1950, p. 588) phosphorus has distinctly biophile character.
The Na2O: K2O ratios in the Permian sediments are also of interest (Table 6). According to Rankama and Sahama (1950, p. 432) the Na2O: K2O ratio in argillaceous sediments has an average value of 0.36, and that in igneous rocks is 1.09. The average Na2O: K2O ratio in 28 Kansas Pennsylvanian shales is 0.31; that in the 9 Permian shales analyzed is 0.24.
Table 6--Sodium-potassium ratios in some Permian sediments.
|No.||Formation and lithology||Na2O: K2O|
|1802||Taloga red silty shale||0.07|
|1801||Basal Taloga green shale||0.09|
|1794||Whitehorse red dolomite-shale||0.41.|
|1779||Whitehorse dark-red shale||0.18|
|1138||Flowerpot red shale||0.47|
|48275||Ninnescah red shale||0.22|
|49438-42||Ninnescah red shale (average of 5)||0.23|
|49414||Wellington gray shale||0.27|
|49417||Wellington gray and yellow shale||0.21|
|Average of above||0.24|
|Average of 28 Kansas Pennsylvanian shales|
(Plummer and Hladik, 1951, p. 20)
|Average argillaceous sediment|
(Rankama and Sahama, 1950, p. 432)
|Sandstones and Siltstones|
|1816||Lower Whitehorse light-red sandstone||0.53|
|1128||Cedar Hills red sandy siltstone||0.81|
|1146||Cedar Hills red sandy siltstone||0.82|
|1147||Basal Cedar Hills white sandstone||1.09|
|1156||Salt Plain red argillaceous siltstone||0.55|
|1137||Salt Plain red sandy siltstone||1.02|
|1139||Runnymede gray siltstone||0.80|
|Average of above||0.80|
(Clarke, 1924, p. 547)
|[Average igneous rock|
(Rankama and Sahama, 1950, p. 432)]
Seven Permian sandstones and siltstones, on the other hand, have an average ratio of 0.80. This seems to indicate a high proportion of sodic plagioclase feldspar in the sands although large quantities of this mineral are not observed in thin section. Some sodium doubtless occurs in the orthoclase grains, and it is possible that a large proportion of the mineral aggregate grains so common in many of the sandstones are plagioclase feldspars which have been altered and recrystallized without loss of sodium ion (under conditions of high pH).
The medium-grained clastics of the Kansas Permian redbeds consist entirely of very fine-grained sandstones and form approximately 15 percent of the Leonardian-Guadalupian? section. The sandstones are all feldspathic; most of them are stained red by red iron oxide-stained clay minerals or by hematite. Some are highly calcareous, dolomitic, or gypsiferous; other contain no carbonates or sulfate. Degree of size-sorting ranges from very good to moderate; roundness and sphericity of the grains are variable, but the mean values are neither extremely high nor low.
Detailed descriptions of selected specimens will serve to illustrate the various types, their color, texture, composition, and structure.
Light-Red Nonealeareous Sandstone
Light-red (2.5YR6 6), noncalcareous very fine-grained feldspathic sandstone from the lower part of the Marlow member of the Whitehorse sandstone is judged to be typical of the "orange-red" essentially noncalcareous sandstones of the Marlow, and was collected from 10 feet above the base of the Whitehorse, in sec. 4, T. 32 S., R. 13 W., Barber County (Pl. 18D).
Mechanical analysis shows that the sample has a median diameter of 3.47 phi (about 92 microns), and a phi percentile deviation of 0.90. Thus it is a very fine-grained well-sorted sandstone with a relationship between size and sorting which is about average for the Kansas Permian sediments under consideration. In thin section a very few large grains having an average diameter of about 600 microns and a maximum of about 800 microns are scattered throughout the finer sand. Grains of silt size are rare, arid clay coats the sand grains.
The sphericity of the small grains is variable. These grains are angular to subrounded; most are subrounded. The large grains are very well rounded and have fairly high sphericity (about 0.85 projection sphericity according to the chart of Rittenhouse, 1943).
The matrix consists of reddish-brown argillaceous material, much of it with high birefringence, most of which is found by x-ray diffraction to consist of illite and chlorite. The clay coats the sand grains, commonly showing orientation of the flakes normal to the surfaces of the grains. It also fills some small interstices. The clay constitutes less than 10 percent of the rock.
Chemical cement is absent, except for occasional shreds of fibrous gypsum. The bonding effect is due almost entirely to clay. Quartz overgrowths are absent except for a few well-worn ones on occasional large grains. Most of the small grains have normal extinction, but all the large ones show moderate strain shadows. Inclusions in the small grains are of various types. Nonoriented crystalline inclusions (particularly rutile and apatite) are common. Bubble planes are also common, some vacuoles are present, and a few grains contain chlorite inclusions. The quartz is judged to be at least 60 percent of igneous (plutonic) origin and less than 40 percent metamorphic, based on the criteria of Krynine (1946). The large grains have been subjected to some pressure metamorphism.
All degrees of alteration are shown in the feldspars, which range from clear and colorless to nearly opaque from fine-grained alteration products. A few feldspars are saussuritized. Some have red clay along the cleavage planes. The feldspars are composed of about 75 percent orthoclase, 15 percent plagioclase (almost entirely oligoclase-albite), and less than 10 percent microcline. A few large unworn overgrowths occur on orthoclase grains, and many of them have small overgrowths which are scarcely visible in thin section. One of the two large orthoclase grains (neither of which shows normal straight extinction) has a well-developed unworn overgrowth which is not in optical continuity with the grain (Pl. 15A).
Chert occurs as a few small grains only, and includes particles having various crystallite sizes. This occurrence is not typical, for the chert is commonly more prevalent in the larger grains.
Chlorite of sand size occurs as rounded flakes with aggregate polarization. Some grains are slightly brownish-green.
A few fairly well-rounded black opaque grains are noted. These are identified as ilmenite because some of them have a white alteration product. Other white opaque grains are small with irregular "fluffy" shapes, and seemingly were not produced by alteration of ilmenite. Red opaque grains have the same general appearance as the white.
Garnet is the most common of the nonopaque accessory minerals; it occurs as small, colorless, angular to subrounded grains. Most of the tourmaline observed is of igneous varieties (Krynine, 1946a): chiefly rounded and subrounded brown grains with fluid and acicular crystalline inclusions. Zircon occurs as small subrounded grains. One flake of biotite is noted, and one rounded yellow-brown dusky grain having high relief and high birefringence is tentatively identified as titanite.
Heavy mineral separates also include staurolite in the coarser fractions, and prismatic tourmaline (metamorphic?), pink and yellow rounded zircons, and foxy-red rutile in the finer.
In thin section the structure of the sandstone is seemingly massive, with random distribution of the large rounded grains. In some outcrops of the Marlow, however, cross-bedding is faintly evident, and in occasional specimens the large rounded sand grains are concentrated in micro-lentils.
White Noncalcareous Sandstone
There is no clear relationship between carbonate content and color of the sediment. Very pale red sandstones commonly contain more carbonate cement than those which are bright red. White sandstones, however, do not necessarily contain carbonates, although many of them are associated stratigraphically with limestone or dolomite beds.
The following description is of white, friable, cross-bedded, essentially noncalcareous very fine-grained sandstone from one foot below a thin dolomite bed in the Relay Creek? member of the Whitehorse formation (NW sec. 18, T. 33 S., R. 16 W., Comanche County).
Mechanical analysis shows that it is one of the coarsest grained sandstones in the entire section, having a phi median diameter of 3.10 (about 117 microns). The degree of sorting (PDØ = 0.53) is slightly better than average for a sandstone of its grain size, but good sorting seems to be typical of Relay Creek? white sandstones.
A thin section made from this sandstone shows that the sorting is much better than that of the Marlow sandstone previously described. The largest grain observed has a maximum diameter (in the plane of the section) of about 0.4 mm, and the extremely large well-rounded grains are absent. A similarly well-sorted Relay Creek sandstone, but with calcite cement, is shown in Plate 19A. Some samples from the Relay Creek member, however, contain the large rounded grains. Sphericity and roundness of the quartz and feldspar grains range from moderately low to high. Most quartz grains are fairly well rounded and have moderately high sphericity. The higher-than-average roundness (and sphericity) may be attributed to the relatively large size of the grains.
Plate 19--Photomicrographs of thin sections from Whitehorse, Cedar Hills, Salt Plain, and Taloga formations. A, White calcareous feldspathic sandstone, Relay Creek? member, Whitehorse sandstone; NW sec. 18, T. 33 S., R. 16 W., Comanche County. x8.5. B, Red feldspathic sandy siltstone, Cedar Hills formation; NW sec. 9, T. 32 S., R. 10 W., Barber County. x8.5. C, Gray and red calcareous feldspathic siltstone, Salt Plain formation; sec. 3, T. 32 S., R. 9 W., Harper County. x8.5. D, Gray and red feldspathic sandy siltstone, Taloga formation; sec. 3, T. 34 S., R. 26 W., Meade County. x8.5. [Note: web versions are enlarged to show more detail.]
The rock consists of about 96 percent grains, 2 percent matrix, and less than 2 percent cement. The matrix is made up of palegreen clay (illite, chlorite) coating the grains and partly penetrating some grain surfaces. Not all grains are coated with clay; some show definite orientation of the flakes normal to the surface of the grain.
Chemical cement is absent except for a few isolated areas of gypsum cement and a spot of coarsely crystalline calcite cement. One irregularly shaped particle of striated pyrite is observed, and there is also a small area of shrinkage-cracked glauconite associated with brown organic matter. The pyrite and glauconite are not typical of the sandstones in the section, but are thought to have genetic significance in connection with the absence of red coloration.
The sandstone is very friable, and evidently is held together only by the small quantity of clay.
The mineral composition of the grains observed in thin section is about as follows: Quartz, >65 percent; feldspars, <25 percent; chert, <5 percent; rock fragments, 1 percent; white opaques, 1 percent; and zircon, garnet, tourmaline, apatite, chlorite, staurolite, titanite, trace.
The quartz grains contain several types of inclusions, of which small vacuoles, bubble planes, and microlites are the most common. Seventy-five percent of the quartz is judged to have an igneous origin. Several rounded quartz overgrowths are observed. A few grains have red opaque iron oxide coatings, but most of the remainder are coated with green clay.
The feldspars consist of about 85 percent orthoclase, <10 percent plagioclase (chiefly sodic), and less than 5 percent microcline. A large proportion of the feldspar grains are clouded with alteration products; a few are saussuritized. Most of the grains are subrounded to rounded. Rounded feldspar (orthoclase on orthoclase) overgrowths are even more common than rounded quartz overgrowths, although they may be xenomorphic rather than worn. They are illustrated in Plate 15B. Two zoned plagioclases are noted.
Chert is more common than in most thin sections studied. Most of the chert grains are well rounded, and several varieties are present; some contains chlorite and sericite. One subrounded rock fragment consists of a subrounded slightly altered orthoclase grain surrounded on three sides (in the plane of the section) by a substance which seems to be chert, although it may possibly be glassy aphanitic groundmass of a volcanic rock.
Rock fragments include several grains of metaquartzite, one elongate mica-schist, one or more orthoquartzites, one quartz-sericite fragment, one granitic fragment (quartz, orthoclase, sodic plagioclase). The greater-than-average abundance of rock fragments is attributed to the relatively coarse particle size of the sandstone.
The white opaque grains are nearly all fairly well rounded with smooth surfaces. They seem to have formed by alteration of black opaque (ilmenite) grains which have the same general appearance. Their color ranges from nearly white to pale brown. Zircon and garnet are the most common of the nonopaque accessory minerals. The zircon grains are subrounded; the garnet is chiefly subrounded to rounded except where it is somewhat pitted. Tourmaline is chiefly of the subrounded brown igneous variety. Some blue pegmatitic tourmaline is noted in the heavy-mineral separates. Small prismatic grains of this mineral are rare, probably because of selective transport.
Apatite occurs as small rounded grains. One rounded flake of chlorite is observed. Staurolite is relatively scarce and those grains present are strongly etched. Its scarcity may possibly be due to post-depositional removal.
The structure of the sandstone in thin section seems to be massive, although cross-bedding is observed in the field. In summary, the following deductions are made: the quartz and perhaps the orthoclase overgrowths grew in a previous deposit, and became well rounded before their final deposition. The red clay coating so prevalent in most of the section was probably reduced by organic matter in waters which were less alkaline than usual. The presence of organic matter and perhaps temporary approach to more normal marine conditions are suggested by the brown semiopaque material, pyrite, and glauconite. The time of introduction of the gypsum and calcite is not known, but it may have been later.
Red Calcareous Sandstone
For comparison with the foregoing uncemented white sandstone, a brief description of a red, cemented rock is included. This sandstone is also from the Relay Creek member of the Whitehorse formation, and was collected from the same outcrop in sec. 18, T. 33 S., R. 16 W., Comanche County. The sample was taken from a 3-foot bed of red silty sandstone 7 feet below the thin dolomitic limestone layer. This rock is atypical in that it is poorly sorted for its grain size, and in that it has three different cementing materials as well as considerable red clay matrix.
Mechanical analysis gives the value of 3.62 for the phi median diameter (about 82 microns). The phi percentile deviation is 1.59. The thin section shows a few scattered larger quartz grains having an average diameter of 0.4 mm and a maximum observed diameter of 0.7 mm. These grains, however, are so few that their presence is not discernible in the mechanical analysis.
The smaller grains are sharply angular (particularly some feldspar) to subrounded. Some are etched ragged by calcium carbonate. The large grains are very well rounded. The sphericity is low to high in the small grains, and only moderately high in the large ones.
The thin section consists of about 60 percent grains, 35 percent cement, and 5 percent matrix.
The matrix is irregularly distributed and seems to occur as long stringers. In some areas it is a plexus of reddish birefringent material containing randomly oriented muscovite, biotite, chlorite, and small dolomite rhombs. Nearly all the grains are coated with red clay; some grains are particularly heavily coated with red iron oxide and clay, and were probably transported in that condition.
The chemical cement fills about 70 percent of the remaining pore space. It consists chiefly of large areas of calcite up to 2 mm in diameter, the individual crystalline units being larger than the sand grains which they enclose. In the more argillaceous parts of the slide very fine-sand-size dolomite rhombs are common. These rhombs, many of which have hollow centers, do not penetrate any of the sand grains and may be chemical-clastic in origin. Some must be at least in part post-depositional, however, because their crystal form is interrupted by sand grains. Approximately 25 percent of the cement is gypsum, which is commonly associated with the carbonate but occurs in smaller areas. The average size of the individual gypsum crystals is only slightly larger than the average grain size of the sandstone. The sequence in cementation is not clear, except that the carbonate and sulfate cements seem to be post-iron-oxide, for no iron oxide coating cement is observed adjacent to a pore.
The mineralogy is similar to that in the thin section previously described, with the following exceptions. Muscovite and biotite make up almost 1 percent of the grains. They occur as relatively large flakes, some of which are strongly bent between the quartz and feldspar grains. Although black opaques (chiefly ilmenite) are fairly common, white opaque grains of corresponding size and shape are extremely rare.
No structure is visible in the thin section. The rock is massive and texturally nearly homogeneous except for the scattered large grains.
A thin section of Cedar Hills sandy siltstone which shows a similar distribution of red clay and carbonates is shown in Plate 19B.
One other fairly common type of fine-grained sandstone is a mixed detrital chemical clastic material. An example of this is collected from the lower part of the Marlow member of the Whitehorse formation in the SW sec. 4, T. 32 S., R. 14 W., Barber County, Kansas. The rock is a salmon-colored highly calcareous very fine-grained feldspathic sandstone. The phi median diameter is shown by mechanical analysis to be 3.42 (95 microns), and the phi percentile deviation is 0.75. The sorting is about typical for that particle size.
Although the rock consists of about 65 percent calcite (in which the quartz and feldspar grains float), it is very friable and the calcite behaves as discrete sand grains rather than as cement (Pl. 15C). Examination of the sediment in the field leads to its classification as a feldspathic calcite-quartz sandstone. However, it is actually a sandy clastic limestone.
The calcite grains are angular to well rounded, chiefly subangular to subrounded. They show a greater range in grade size than do the quartz or feldspar grains. The grain boundaries are distinct, and some of them are obviously coated with thin films of clay or oxides; this is probably responsible for the friability of the rock. Each grain is a crystallographic unit. In a few areas the space between the calcite grains is filled with calcite which has different optical orientation, but in general the grains seem to fit against each other as if they were in a somewhat plastic or gelatinous condition when deposited; or else the iron oxides and clay materials were expelled as crystallization proceeded from individual centers simultaneously. The nearly uniform particle size distribution in the very fine sand size, however, seems to favor the first explanation. Much of the calcite contains minute inclusions of a green flaky mineral which may be chlorite, and some contains common fluid inclusions.
Clay matrix is essentially restricted to coatings on grains, particularly on detrital grains. The coating ranges from red opaque iron oxide to red clay to buff-colored clay.
The grains are thought to have been deposited with the clay already coating them. Calcite was deposited rapidly as gel along with the grains, from water which also contained ferric iron, magnesium ion, and some silica in solution (colloidal or ionic). Chlorite is considered to have crystallized shortly after deposition. Evidence of reworking of carbonate grains is shown in several thin sections.
Many of the siltstones in the section are very coarse grained; a large proportion of them are just at the sand-silt boundary (average diameter is about 4.50), and these have many of the characteristics of the very fine-grained sandstones described in the foregoing section.
White and Red Calcareous and Dolomitic Argillaceous Siltstones
The following paragraphs describe one of the finer grained siltstones which are common in the Salt Plain formation. It is not typical of the section as a whole, because it is too well sorted for its size; however, it seems to be typical of the Salt Plain except for its color.
The sample was collected from the middle part of the Salt Plain formation in the bluffs northwest of Attica, Harper County (S2 sec. 3, T. 32 S., R. 9 W.). The bed from which the sample was collected is 1.0 foot thick and consists of gray and red mottled slabby calcareous siltstone. Mechanical analysis of a 30-gram sample shows the phi median diameter to be 4.91 (about 40 microns), and the phi percentile deviation to be 1.21. The size and sorting are similar to those of Peoria loess in Kansas (Swineford and Frye, 1951). Some quartz grains in thin section are as large as 60 microns, and some mica flakes are of course much larger.
The thin section consists of about 55 percent grains (quartz, micas, feldspars), 20 percent matrix (chiefly micas and green clay), and 25 percent cement. Elongate and flaky grains show good preferred orientation locally, but the trend varies throughout the slide. The sorting within any one micro-layer seems to be very good.
The quartz grains are angular to subrounded (predominantly angular) and their average sphericity is rather low. The low roundness and sphericity are doubtless correlated with the fine particle size. The flakes of muscovite are markedly well rounded. One slightly worn hexagonal biotite flake was observed.
The matrix, which is not evenly distributed throughout the slide, consists of green micaceous clay (illite and chlorite) and shreds of mica, many of which are bent. There are a few areas of bright-red highly birefringent clay material showing rough optical orientation. Very thin, green, birefringent clay coats most of the grains.
The chemical cement consists of silt-sized blobs of calcite and rarer dolomite rhombs distributed throughout the thin section but particularly abundant in the coarser grained laminae. About one-fifth of the carbonate cement may be dolomite. Some of the cement encloses small spots of black opaque material, and some small areas of brownish-black opaque matter surround a few grains; this seems to be organic material. The bonding effect is probably due primarily to calcite because the rock splits along the micaceous shaly laminae.
The grains in the thin section consist of approximately 70 percent quartz, 15 percent feldspar, 8 percent muscovite, 3 percent biotite, 2 percent chlorite, 1 percent white opaques, and traces of red and black opaques, tourmaline, chert, and possibly metaquartzite.
The quartz grains seem to be at least 60 percent of igneous varieties, but they are so small that their determination is difficult. Nearly all are very angular, and most have greenish-yellow clay coatings. The feldspars are predominantly orthoclase, most of which is very fresh and angular. A few slightly altered plagioclase grains were observed.
Muscovite, biotite, and chlorite occur as large to small flakes. Many are bent around the other grains. Most of the biotite is green, but its high birefringence distinguishes it from the chlorite. Some of the chlorite has aggregate polarization; some flakes are yellowish green.
The white opaque grains are angular to subrounded. Some may be leucoxene. The black opaque grains are small and are more angular than the white particles. The red opaques are similar to the white ones in general appearance.
One tiny green prismatic tourmaline grain with irregular black inclusions is observed. One grain of chert is noted, and one grain is identified as either metaquartzite or coarse chert.
Structurally, the rock is thinly laminated, with thickness of laminae generally less than 3 mm and commonly about 0.3 mm. Clay and fine mica flakes are somewhat segregated into laminae. Cut-and-fill features are present on a microscopic scale, and the laminae are curved (Pl. 19C).
Finer grained siltstones of the Salt Plain are similar to the above, except that preferred orientation of the micas is less pronounced, and the sorting is less perfect.
A red dolomitic feldspathic siltstone from the upper shale member of the Whitehorse formation is also somewhat similar to the siltstones of the Salt Plain, except for its structure (Pl. 15D). The rock is banded, mottled, and sworled, almost as if stirred with a spoon, and the flow structures resemble those in viscous material. Consequently the rock is not slabby. A micro-bedding feature of another red siltstone is shown in Plate 20A. Here the micas are concentrated in the shale lentils.
Another type of siltstone which is particularly common in the upper part of the section (especially in the Taloga formation) is a "micro-puddingstone" containing scattered large round sand grains. The following description is based on study of a thin section from a 0.2-foot bed of gray and red, fairly hard, calcareous massive sandy siltstone of the Taloga formation in the SE sec. 3, T. 34 S., R. 26 W., Meade County (Pl. 19D). The rock, which is exposed in a stream bank, is a common type of sandy siltstone, except for the large quantity of carbonate cement.
Mechanical analysis indicates that the phi median particle size is 4.10 (about 59 microns)--just within the coarse silt range. The phi percentile deviation is 2.19; the rock is therefore much more poorly sorted than average for its grain-size. Poor sorting is not uncommon, however, in samples from the Taloga formation. Examination of the thin section suggests that the size distribution curve is trimodal, with rather large sand grains, coarse silt grains, and mica-like clay. The average diameter of the large grains in thin section is about 80 microns; that of the silt grains is about 40 microns.
The rock consists of about 50 percent grains, 45 percent cement, and 5 percent matrix. The silt grains are very angular to subrounded (especially weathered feldspar). Their sphericity is fairly low to high; most is moderately high. The "large" sand grains are all well rounded (except where replaced with carbonate) and have moderately high sphericity.
The matrix consists of red micaceous "clay" in localized blobs and stringers. The crystallite size is unusually coarse and the micaceous character of the material is obvious. The individual flakes seem to have random orientation. The clay also occurs as red coating on silt and sand grains.
About 90 percent of the cement is calcite, which occurs as intergrown allotriomorphic crystals slightly larger than the average clastic grain size. Dolomite (about 4 percent of the cement) consists of scattered rhombs of coarse silt size. Six percent of the cement is gypsum, also in allotriomorphic crystalline units of approximately coarse silt size to very fine sand size. The gypsum is associated particularly with the red micaceous clay. Gypsum seemingly replaces a few detrital grains. One orthoclase grain is nearly all replaced by gypsum and is surrounded by calcite; calcite replaces part of the gypsum.
The bonding effect is due chiefly to calcite. Much of the gypsum is bent, suggesting that it may have been formed first and later deformed by the growing calcite crystals,
This is one of the most feldspathic rocks examined. The grains consist of about 70 percent quartz; more than 25 percent feldspars; 2 percent chert; 1 percent muscovite; somewhat less than 1 percent chlorite, biotite, ilmenite; and traces of rock fragments, zircon, rutile, and red and white opaque grains. The large grains are 95 percent quartz and 5 percent chert.
Most of the quartz (more than 60 percent) of silt size is characterized by straight extinction, bubble chains, acicular and other igneous-type inclusions. A few grains of vein quartz are observed. All the grains are coated with red clay (except where shattered or replaced by calcite or gypsum). One or two silt grains have been separated and pushed apart by coarsely crystalline calcite. One silt grain with a white opaque clay coating has a worn quartz overgrowth; in general, quartz overgrowths on the silt grains are rare.
Among the large rounded quartz grains, at least 80 percent show pronounced strain shadows; some have many criss-crossing bubble chains. At least two large quartz grains have worn quartz overgrowths, which are separated from the original grains by red clay coatings.
The feldspars are about 70 percent orthoclase, 20 percent plagioclase (chiefly oligoclase), and 10 percent microcline. The grains show various degrees of alteration, and several are partly replaced by calcite or gypsum.
Chert is found in both the sand and silt sizes, and at least four varieties are observed. About 5 percent of the large grains are chert; a large proportion of them are partly replaced by calcite. The calcite has attacked chert more readily than it has quartz (Pl. 20B).
Muscovite occurs as sparsely scattered flakes throughout, but much fine muscovite is concentrated in the clayey laminae (see also Pl. 20A). Chlorite is found as flakes with unit extinction, as green to brownish-green aggregate grains, and as replacement of some orthoclase. Biotite occurs as greenish-brown pleochroic flakes; a few are bent.
Ilmenite is by far the most common opaque mineral. It occurs as subrounded to subangular grains without white spots. The red and white opaque grains are seen on close examination to be, as a rule, heavy coatings on nonopaque grains.
Plate 20--Photomicrographs of thin sections from Taloga, Wellington, and Dog Creek formations. A, Red shale lentil in red feldspathic sandy siltstone, Taloga formation; sec. 3, T. 34 S., R. 26 W., Meade County. x76. B, Large chert grain partly replaced by calcite; Taloga formation; sec. 3, T. 34 S., R. 26 W., Meade County. x76. C, Gray shale from Wellington formation; SW sec. 4, T. 33 S., R. 1 E., Sumner County. x8.5. D, Red silty shale with large dolomite rhombs; Dog Creek shale; sec. 4, T. 32 S., R. 14 W., Barber County. x8.5. [Note: web versions are enlarged to show more detail.]
A few metaquartzite fragments are present, particularly in the large sizes where they constitute almost 3 percent of the large rounded grains. One green foliated metamorphic rock fragment is noted (small suite).
A few small subangular to subrounded grains of zircon are noted, as well as dusky golden-brown grains of rutile.
In thin section the structure is indicated by very irregular or wavy bedding on a small scale, shown by differences in grain size.
Clay Shale and Silty Clay Shale
The shales and silty shales show much variation from one thin section to the next, so that one or two descriptions are not adequate to show their character. Descriptions of a single red and a single gray shale are here followed by brief comments oii thin sections of other specimens.
The first shale thin section described is from typical blocky reddish-brown Ninnescah shale collected in a stream bank along the Cen. S. line sec. 33, T. 26 S., R. 4 W., Reno County. The shale at this locality shows pronounced conchoidal fracture and contains scattered spherical greenish-gray spots with average diameters of about 9 mm, but only a small part of one spot is included in the thin section. In stratigraphic position this shale is close to Norton's Bed 3, or about 170 feet below the top of the formation.
Mechanical analysis indicates that the phi median diameter is 6.87 (about 8.5 microns). Strictly speaking, this is within the silt range, but the rock is classified as clay shale because it is not gritty and because it contains more clay minerals than other constituents. The largest quartz grain observed in thin section is nearly 60 microns in long diameter; most of the silt grains, however, are much smaller (average 20 microns, or less). The phi percentile deviation determined by mechanical analysis is 3.49. This is not so good as the expected degree of sorting, and it is not typical of mechanical analyses from other Ninnescah samples.
The rock consists of about 15 percent grains, 80 percent matrix, and 5 percent cement (or carbonates). The noncarbonate grains are all allotriomorphic, and are predominantly angular to subangular. Their sphericity is moderately low, and they show no preferred orientation.
The matrix is red clay; the slide shows several rounded elongate areas with aggregate extinction in one direction. These do not seem to be mud balls or areas of intraformational conglomerate, but are judged to be postdepositional "growth units" of the clay minerals. Two spherulitic areas are noted. The matrix contains numerous tiny flakes of white mica ("sericite"?), and small areas (up to 0.1 mm in diameter) which are not stained red with iron oxide. Aside from the color, there is no obvious difference between the greenish-gray spots and the red portion.
The chemical "cement," or carbonate fraction, consists of scattered rhombohedra of dolomite, all of silt size, many of which have growth zones or rhombohedral centers of red clay. The dolomite perhaps should not be referred to as cement, because its bonding effect is probably negligible.
The clay (or colloid) and silt grains were doubtless deposited together from water rich in Ca and Mg ions. The dolomite probably grew during deposition, and it may be partly responsible for the blockiness and conchoidal fracture of the rock. The iron oxide in the gray areas may have been reduced by minute quantities of organic matter deposited with the clay and silt.
The composition of the grains is difficult to determine because of their small size and extremely thick clay coating. Study of cleavage, alteration, and refractive indices of grains at thin edges of the section suggests that quartz probably constitutes about 75 percent of the grains; feldspars, 10 percent; and mica, 15 percent. The mica consists chiefly of small shreds of sericite-like material and perhaps should be considered part of the matrix.
Only about 15 percent of the quartz shows undulatory extinction, and most of this mineral is probably igneous in origin. Inclusions are difficult to determine because of the thick section and prevalence of red clay.
The feldspar seems to be chiefly orthoclase; almost no twinned plagioclase or microcline is observed. No chert is noted. The very small grain size may account for the absence of some of these features.
The matrix consists of about 97 percent red clay and 3 percent greenish-gray clay. X-ray diffraction data show that the clay minerals are predominantly illite and chlorite (Table 7). An electron micrograph of particles from the fraction finer than 1 micron is shown in Plate 17.
The rock has a massive structure; some areas are coarser grained than others, but there is no clear bedding or lamination. Some very fine-grained bright red-brown lenses without silt or dolomite seem to be flattened clay galls. The rock, and similar blocky clay shales, may perhaps best be called reddish-brown dolomitic silty claystone.
Table 7--X-ray diffraction data for some shales and silty shales
|1Does not shift after treatment with glycerol.|
|2Slight asymmetry, lost on glycerated sample, suggests small quantity of
mixed-layer mineral or degraded illite.
A greenish-gray, blocky to splintery, silty clay shale, described in the following paragraphs, was collected from a road cut and stream bank exposing beds in the upper part of the Wellington formation 6 miles south of Mayfield, NE SE sec. 17, T. 33 S., R. 2 W., Sumner County. The sediments at this locality consist of thin beds (2 inches to almost 4 feet thick) of variously colored splintery, blocky clay shales. The greenish-gray bed from which the sample for the thin section was collected is 1.7 feet thick and grades upward into brownish-red, green-mottled clay shale. The greenish-gray shale has a general appearance which is typical of most of the Wellington shales.
Mechanical analysis shows the average particle size of the material to be 7.80 phi (about 4 microns). The phi percentile deviation, 3.3, indicates that the relation between size and sorting is about average.
Comparatively few grains of silt size are observed in thin section; only 4 quartz grains with maximum projection diameter greater than 15 microns were noted. Some mica of that size is present. The rock consists of about 75 percent matrix (clay minerals) and 25 percent grains (mica, chlorite, and very small quartz and feldspar grains). No chemical cement is observed.
Parallel alignment of mica and clay is pronounced; this may be related to the absence of chemical cement. The largest silt grains are subangular to angular and somewhat elongate.
X-ray diffraction data indicate that the rock contains detectable quantities of illite, montmorillonite or expanding mixed-layer mineral, chlorite, and quartz, and a suggestion of feldspar. Chlorite is less common than in most of the shales and siltstones. Illite is by far the predominant clay mineral, but the character of the reflections in the diffractometer patterns suggests that it is much more poorly crystallized than are illites in most Pennsylvanian shales of Kansas.
In structure, the rock shows parallel bedding chiefly by the orientation effect, but it appears to be practically massive because of the uniform particle-size distribution throughout the slide.
Carbonates and Sulfates in Shales
Most of the silty shales and shales, both red and gray, contain significant quantities of carbonates or sulfates, or both. Dolomite and calcite are the most common. One greenish-gray (streaked with red) clay shale contains about 5 percent barite and gypsum. The barite occurs as scattered grains of coarse silt size; the gypsum is in slightly smaller units. Orientation of the clay minerals is less perfect than that in the noncalcareous, nonsulfate rock previously described. A clay shale (from the Wellington formation) which contains minute grains of anhydrite (or gypsum) and calcite is shown in Plate 20C.
A greenish-gray silty clay shale (claystone) from the Ninnescah formation contains at least 35 percent carbonate minerals (chiefly dolomite) as disseminated grains. No preferred orientation of the clay minerals is observed.
A very pale greenish-gray silty clay shale (claystone) from the approximate horizon of Ninnescah bed 4, contains not only calcite, dolomite, and barite, but also a trace of green copper carbonate. One area of malachite (?) in a thin section of this material consists of two bright-green grains with green highly birefringent streamers curving out from them. They may have developed from postdepositional alteration of an opaque copper mineral.
Large dolomite rhombs (up to 0.3 mm in diameter) characterize a sample of red silty shale from the Dog Creek formation (Pl. 20D). The silt and clay are somewhat segregated into separate areas, and there are some short streaks of seemingly nearly pure, opaque hematite. The structure is that of an intraformational conglomerate. The dolomite crystals may have been deposited with the clay and shortly after the silt; the whole was later reworked into an intraformational conglomerate.
A mottled red and greenish-gray dolomitic clay shale from the lower Ninnescah (near Bed 2) contains almost 50 percent dolomite. The dolomite rhombs occur as a complex irregular network throughout the clay, much of which shows good aggregate polarization. The network structure may have been formed following shrinkage of the mud. Irregular particles of black opaque material (apparently organic matter) are associated with the clay and also occur as inclusions in some of the larger dolomite rhombs. The presence of organic matter may account for the greenish-gray color of part of the clay, because it seems to have been bleached after deposition. Organic matter is much more common in the green clay than in the red.
A purple shale from the Wellington formation also seemingly owes its color to partial reduction of Fe3+ by organic matter. The organic matter occurs as fine-silt-size particles disseminated throughout the thin section, which also contains much carbonate. Chlorite is no more prevalent than in the common brownish-red dolomitic shales of the Ninnescah.
Mineral Composition of Wellington Shale Sample from Drill Core
A small shale sample from the Morton Salt Company hole No. 4, in sec. 35, T. 23 S., R. 6 W., Reno County, southwest of Hutchinson was analyzed qualitatively by x-ray diffraction for mineral composition. Shales from the Wellington were the only subsurface samples available for comparison with surface material. The specimen was taken from a layer of gray shale interbedded with halite.
The raw sample (-250 mesh) produced reflections for anhydrite and for layer lattice minerals having basal spacings of 14.2, 10.1, and (faint) 7.14 A; and a very small quantity of quartz. Treatment with glycerol did not cause any measurable displacement of the 10 A or 14.2 A lines. A sample boiled in ammonium chloride did not destroy the 14.2 A reflection but produced a faint suggestion of an increase and shift in the 10 A peak. Treatment with warm dilute hydrochloric acid (Brindley and Robinson, 1951, p. 188) removed the anhydrite, and also eliminated the reflections at 14.2. 7.1, 4.84, 2.11, 2.00, and 1.70 A. As a result, the following layer lattice minerals are judged to be present, in order of decreasing quantity: illite, chlorite, and probably a small percentage of muscovite. Halite is not observed.
Formal names of some of the carbonate stratigraphic units are somewhat misleading; thus, those samples of the Milan limestone examined for the present study are mixtures of dolomite and barite, and samples from the Relay Creek dolomite are shown (by x-ray diffraction) to contain at least 50 percent calcite. The basal dolomite from the Medicine Lodge gypsum contains a large proportion of gypsum, and the Carlton limestone of the Wellington formation seems to be dolomite. A few of the dolomites and socalled dolomites are here described in detail.
The first thin section described here is from the Stone Corral dolomite in the NE NE sec. 22, T. 20 S., R. 6 W., Rice County. The dolomite is porous and contains many vugs (about 0.4 to 5 mm in diameter), most of which are filled with clear, coarsely crystalline calcite. Some of the vugs are connected by calcite-filled veins. The main mass of the rock consists of minute rhombs of dolomite having an average diameter of about 10 microns and a maximum diameter of about 20 microns; the sizing is therefore very good.
In composition, the rock consists of about 90 percent dolomite, less than 4 percent quartz and feldspar, and less than 5 percent calcite, most of which occurs as vug fillings. No clay is observed in thin section or detected in x-ray diffraction patterns. Some brown opaque specks of organic matter are present, particularly around the edges of some vugs and as irregular subparallel bands from a fraction of a millimeter to 1 mm thick.
The quartz and feldspar occur as subrounded to very angular grains having an average diameter of about 30 microns and ranging up to 70 microns. Some of the grains have been partly replaced by carbonate. Much of the quartz shows undulatory extinction; perhaps 40 percent of it is of metamorphic origin. The quartz and feldspar are scattered throughout the slide, but seem to be more concentrated in the areas of organic matter (perhaps in part because they are not replaced by carbonate there).
Traces of detrital muscovite, green tourmaline (one grain), and white and black opaque minerals were observed.
The structure is massive and uniform except for branching irregular veins containing calcite and dolomite rhombs, and lenses of organic matter.
The thin dolomite bed at the base of the Medicine Lodge gypsum grades upward from carbonate into massive gypsum. Much of this bed is characteristically oolitic. The description which follows is based on examination of a thin section of oolitic dolomite-gypsum from a road cut south of Sun City in sec. 11, T. 31 S., R. 15 W., Barber County (Pl. 21A).
Plate 21--Photomicrographs of dolomite and halite. A, Oolitic dolomite-gypsum from base of Medicine Lodge member, Blaine formation; SE sec. 11, T. 31 S., R. 15 W., Barber County. x8.5. B, Upper dolomite, Relay Creek? member, Whitehouse sandstone; sec. 18, T. 33 S., R. 16 W., Comanche County. x8.5. C, Day Creek dolomite; sec. 33, T. 32 S., R. 22 W., Clark County. x8.5. D, Halite from Carey Salt Mine, Hutchinson, Kansas. x8.5. [Note: web versions are enlarged to show more detail.]
The texture is chemical-clastic. In general, the fabric pattern is one of odd-shaped oolites (mostly fine-grained dolomite) in a matrix of coarsely crystalline gypsum with dolomite rhombs. Gypsum clearly replaces some of the oolites. The rock is heterogeneous, but the sorting is good with respect to any one constituent. The average size of the oolites is 0.2 mm; the largest is 0.75 mm. Dolomite rhombs range in size from 0.01 mm to 0.08 mm. Some of the gypsum crystals are coarser than 1.5 mm.
Most of the oolites are elongate; some are crescent-shaped. Concentric structure is not well developed. A very few contain small quartz grains as nuclei but most do not; and most of the few scattered quartz grains are not within the oolites at all. There is no visible clay matrix. The cement consists of coarsely crystalline gypsum in some areas, minute dolomite rhombs in others, and mixtures of the two (dolomite rhombs in gypsum) elsewhere. The bonding effect is due chiefly to gypsum.
Seemingly the oolites are the oldest, but gypsum accompanied their deposition and replaced parts of the oolites. Some of the dolomite rhombs are probably post-gypsum, because they are found inside occasional oolites where there has been replacement by gypsum.
In composition, gypsum constitutes about 50 percent of the thin section, and most of the remainder is dolomite. There is less than 1 percent of quartz, and a trace of a grass-green mineral having aggregate polarization (tentatively identified as glauconite).
The small dolomite grains which make up the oolites are not idiomorphic. X-ray diffraction patterns, however, show no indication of calcite. The dolomite rhombs which occur in the matrix are more or less allotriomorphic against the oolites. The quartz grains have nearly all been strongly etched and are partly replaced by gypsum.
Bedding is suggested by differences in character of the cement and in shapes of the oolites. The crescent-shaped oolites are difficult to explain; they may possibly be fragments of older oolites which have been broken up, worn, and redeposited.
The Milan "limestone" is similar to the Medicine Lodge basal dolomite in that it is a mixture of carbonate and sulfate. The following description is based on study of a thin section from the type locality in Sumner County and on x-ray diffraction data on samples from several localities.
The rock is very fine-grained, earthy, porous material which has the general appearance of an argillaceous limestone. Diffraction data indicate that its composition is about 70 percent dolomite, 20 percent barite, 5 to 10 percent illite, less than 3 percent quartz, and a trace of malachite (segregated in green spots).
Texturally, the rock consists of a fine mosaic of dolomite and scattered barite crystals, with scattered small vugs and a faintly spotty appearance. The dolomite and barite particles are about the same size--i.e., 5 to 10 microns in diameter. A few larger crystals (principally barite) partly fill some vugs. Some of the vug fillings are a bright-green fine-grained (some fibrous) copper carbonate mineral which has been identified by x-ray diffraction as malachite. Some of the malachite is associated with or surrounded by a pink mineral which is probably celestite. Norton (1939) found chalcopyrite in the Milan member, but none was visible in the thin section examined by me.
The rock is massive except for the vugs and a vague mottling.
Samples of dolomite from the Relay Creek? member of the Whitehorse formation are shown by x-ray diffraction to contain at least as much calcite as dolomite; there are no reflections from quartz, feldspar, or clay minerals.
A thin section was made from material from a 3-inch bed of Relay Creek? dolomite from sec. 18, T. 33 S., R. 16 W., Comanche County, Kansas. The thin section (Pl. 21B) shows irregular bands of coarse crystals set in a finer matrix. The rock is essentially all carbonate, but the grains are poorly sorted with respect to size, which ranges from coarse silt size to 0.4 mm. The calcite grains, which are the largest, are irregular, straight-sided polyhedra in the plane of the thin section. Most of the dolomite grains are imperfect rhombs. The bonding effect is due to interlocking of crystals. The peculiar moth-eaten appearances of some of the dolomite suggests that it has been replaced by calcite, but this order of succession is not proved. Some of the dolomite appears as skeleton crystals inside calcite. Some dolomite crystals contain dark-brown to black, unidentified inclusions (organic matter?). Some dolomite crystals intersect boundaries between calcite crystals. The dolomite seems to be concentrated in bands in some parts of the slide.
The thin section shows a complex, irregular, wavy structure consisiting of alternating fine and coarse bands, some of which are as thick as 2 mm.
A thin section of pale pink, chert-free Day Creek dolomite was made from rock collected in sec. 33, T. 32 S., R. 22 W., Clark County, Kansas. The section consists of a mass of fine-grained dolomite rhombs with small, coarser grained areas (Pl. 21C). The average grain size is about 80 microns, and the range is from less than 40 microns to 350 microns. The dolomite particles are nearly all idiomorphic or hypidiomorphic; they show no preferred orientation. Some rhombs have black opaque inclusions (organic matter) at their centers. The bonding of the rock is due to intergrowth of dolomite crystals.
The pink color is attributed to a trace of ferric oxide, or iron oxide-stained clay, which fills a few interstices between dolomite rhombs and also coats some rhombs. Irregular elongate areas of coarser dolomite give the rock a mottled appearance. Nothing seen in the thin section corresponds to the wavy-ridged effect observed in weathered exposures.
The Carlton "limestone" of the Wellington formation was not studied in thin section, but x-ray diffraction data from several samples from Marion County indicate that it is composed principally of dolomite, with minor quantities of quartz and feldspars, and a faint suggestion of chlorite and illite. Calcite is not present in quantities detectable by x-ray diffraction.
Megascopically the Carlton is soft, earthy, porous, fine-grained, pale cream-colored rock; some zones are distinctly oolitic.
A thin section from a sample from the Medicine Lodge gypsum (NE NW sec. 8, T. 32 S., R. 14 W., Barber County) is herein described. Megascopically the rock consists of white, coarsely "sugary" gypsum (crystals up to 1 mm diameter) with very pale-gray angular mottled areas. The thin section shows that the rock is homogeneous in composition but that the size sorting of the gypsum crystals is poor; the crystals range in size from less than 60 microns to more than 1,000 microns with an average diameter of about 200 microns. In shape, most of the crystals are prismatic with ragged ends. The bonding effect is due to intergrowth of gypsum crystals.
The only constituents other than gypsum seen in thin section are one idiomorphic crystal of barite, 50 microns in long diameter and containing carbonaceous inclusions, and one allotriomorphic area of unit-crystalline calcite about 80 microns in diameter.
The Medicine Lodge gypsum contains lenses of anhydrite (up to 2 feet thick) about 10 feet above the base of the member. According to McGregor (1948), both the gypsum and anhydrite were original precipitates, with only partial subsequent hydration of anhydrite to gypsum. McGregor reports gradation of anhydrite to gypsum, fracture fillings of gypsum in the anhydrite, absence of anhydrite in the upper and lower part of the gypsum, and no evidence of distortion resulting from hypothetical hydration of anhydrite.
One thin section of salt was examined. The specimen was collected from the Carey Salt Mine at Hutchinson, Kansas. The thin section consists essentially of large allotriomorphic halite crystals, more than 2 inm in diameter, with a few very small mineral and fluid inclusions (Pl. 21D). The impurities are chiefly calcite, anhydrite, and shale.
Growth zones in the halite are marked by negative cubic crystals containing liquid or gas or both. Other fluid inclusions are elongate and are lined up en echelon. Minute grains of allotriomorphic calcite also occur along the growth zones.
Idiomorphic crystals of anhydrite range from fine silt size to larger than 500 microns in long diameter. They occur as microlites and inclusions in the salt, commonly in clusters associated with clay or along growth zones. Anhydrite constitutes less than 1 percent of the thin section.
Very fine-grained gray clay with high birefringence (probably illite) occurs as thin short sinuous streaks which seem to follow boundaries between some of the salt crystals.
A sample of mine-run salt from the Carey mine was found to have a water-insoluble residue of about 1.5 percent.
Kansas Geological Survey, Geology
Placed on web Aug. 25, 2006; originally published May. 1955.
Comments to firstname.lastname@example.org
The URL for this page is http://www.kgs.ku.edu/Publications/Bulletins/111/05_petro.html