A classification of Upper Pennsylvanian and Lower Permian shales has produced nine groups of samples that can be distinguished on mineralogy and geochemistry. As a laboratory exercise this has its merits, but to be of practical benefit it is also necessary to relate this classification to the sedimentary deposits observed in the field. It was with this aim in mind that a number of samples, analyzed by X-ray diffraction, emission spectroscopy, and electron spin resonance, were thin-sectioned and petrologically examined. This section presents a brief description of the facies distinguished and the implications for environments of deposition.
Following the recent work of Gipson (1965), Odom (1967), Gillott (1969, 1970), and O'Brien (1968, 1970) on the environmental significance of shale fabrics, select samples were examined using a scanning electron microscope to aid the interpretation of fine-grained sedimentary rock fabrics and to determine the depositional conditions under which the rocks were developed. A microscopic fabric analysis technique, developed by Brewer (1964, 1972) for the study of soils, was also applied with the general view of elucidating depositional environments.
Two-hundred-fifty thin sections of selected shales were prepared at the Central Petrographic Section Services of Dallas, Texas by a process of vacuum-impregnation in epoxy and cutting in kerosene. Some wedge-shaped sections were prepared for examination of shale fabrics. Photomicrographs of representative slides are included with discussions of specific rock types.
Several scanning electron microscope sample mounts were prepared by breaking roughly square chips off the original shales. Samples (three cubic mm approximately) were cemented onto aluminum stubs leaving a freshly fractured surface face up. A fine platinum coating was then vacuum sprayed over each sample to alleviate conductivity problems. The samples were then examined using a Cambridge scanning electron microscope belonging to the Geology Department at Leicester University. Electron photomicrographs of shale samples are included in the following sections
Four principal facies were recognized in Upper Pennsylvanian and Lower Permian clastic deposits. These include a black shale that is considered the most distinctive of all Kansas deposits; a calcareous, grey shale facies that with the black shale facies constitutes a group of sediments known as inside shales (Davis and Cocke, 1972); and a sandstone and siltstone facies that together with a thick, brown clay-shale facies forms outside shales. Minor facies, such as a red and purple shale and shale partings in limestone beds, are also recognized. Aspects of each facies apparent in hand specimens or thin sections are discussed in the following sections.
Black Shale Facies
Shales belonging to this facies are typically black, carbonaceous, fissile, and thin-bedded, containing numerous phosphorite laminae and scattered elliptic phosphorite nodules (Plate 2A, B). Fossils commonly recognized in black shales include fish spines, conodonts, orbiculoid brachiopods, and thin-shelled pectinid clams, although radiolaria, sponge spines, cephalopods, and sharks' teeth have been found (Plate 2C, D). Macerated plant fragments are also common.
Plate 2--A. Hushpuckney Shale (sample 24) showing small elliptic phosphorite nodules and thin phosphorite laminae in a black, clay mineral matrix. The nodules lie parallel to the laminations of the shale. Scale matches that of the following photomicrograph. B. Stark Shale (sample 31) showing occasional phosphorite nodules in a dense clay matrix. A few quartz grains can be detected on the thinner edge of the slide. Scale = 2 mm. C. Muncie Creek Shale (sample 55) contains large elliptic phosphorite nodules (up to 4 cms in length). Within the nodules a number of radiolaria are preserved. Scale = 0.5 mm. D. Within the same nodules, spicules are concentrated in large numbers. The irregular black patches are thought to be organic material. Scale = 0.5 mm. E. An electron photomicrograph of a Stark Shale (sample 7) fabric, showing flat plate-like clay minerals lying parallel to the planes of fissility. The clay mineral plates occur in groups or domains. Scale = 0.14 mm.
This facies, although normally represented only by a few meters of sediments, is laterally persistent from Iowa to southern Kansas (Moore, 1964). Further south, the black shales grade into thicker sections of light-colored shales that contain normal marine fossils such as brachiopods, gastropods, echinoderms, corals, and bryozoans (Evans, 1967, 1968; Heckel, 1972a). This, in turn, grades into the non-marine deltaic clastics of Oklahoma (Wanless et al., 1970). In Iowa and Nebraska, a facies change to a fully marine section is often suggested by the reappearance of light-colored marine shales below the black shale facies.
Evans (1967) and Heckel (1972a) have established that the undisturbed nature of even stratification manifest in the primary phosphorite laminae precludes the former existence of either a root system of attached vegetation or an unpreserved burrowing or bottom-feeding fauna. The presence of detrital material of only the finest sizes (primarily quartz grains scattered throughout the black shales), combined with the abundance of thin phosphorite laminae indicating long-term cessation of detrital sedimentation (Bromley, 1967; Heckel, 1972), suggests that the areas of black shale development represent nearly currentless, sediment-starved regions where slow deposition occurs. The fully marine extensions of black shales in Iowa and southern Kansas indicate that black shales are probably marine deposits resulting from slow sedimentation.
The conditions responsible for the formation of black shales have been reviewed by Heckel (1972a, 1978), who concluded that in respect to the Heebner black Shale (Shawnee Group) stagnation of the sea was the most likely cause. Evans (1967) has suggested that stagnation could have been caused by a submarine barrier, resulting from sedimentation across the mouth of the Midcontinent sea. Alternatively, the barrier may have developed as a topographical high associated with the continuation of the Ouachita foldbelt.
One view of the Kansas epeiric sea during the deposition of black shales consists of a broad saucer-shaped basin in which circulation ceased over most of the bottom and into which only the finest suspended detritus was spread by currents. The aerated surface waters contained a fauna of nektonic fish and conodont organisms along with epiplanktonic brachiopods and pectinids (Heckel, 1972a). On the edges of the basin, deltaic detrital sediments built the sea bottom up above the level of stagnation into aerated waters where benthonic life could be supported (Wanless et al., 1970).
However, studies by Heckel (1977) now suggest that black shales may be developed below an established thermocline "that was strong enough to prevent local wind-driven cells of vertical circulation from replenishing oxygen to the sea bottom" (Heckel, 1977, p. 1O54). In high sea-level stands, a quasi-estuarine cell may have existed in which upwelling cold phosphate-rich water depleted the epicontinental sea of oxygen, resulting in anoxic water conditions and deposition of black, organic-rich muds.
Berendsen and Zeller (1978) have alternately suggested that some black shales (in the Cherokee) exhibiting a radiolarian-sponge fauna (Plate 2C, D) indicate relatively shallow water conditions of deposition, possibly in anoxic shoreline embayments and lagoons. Similarly, Merrill and Von Bitter (1976) have accepted the presence of two types of black shale in the Midcontinent, reflecting the earlier conclusions of Moore (1964) and Schenk (1967).
Geochemically, the presence of organic matter in black shale environments encourages the development of reducing conditions in which the trace elements Cd, Cr, Mo, Ni, Pb, V, and Zn are enriched. The organic matter also causes the dispersion of clay mineral particles by neutralization of surface changes (Moon, 1972) and gives rise, on compaction, to the fissility of black shales. Scanning electron micrographs of black shales (O'Brien, 1968; Plate 2E) indicate that clay particles occur in parallel "domains" and that planes of fissility correspond to zones of organic material (Odom, 1967). High fissility also indicates an abiotic environment of deposition (Byers, 1974).
In thin section, black shales contain abundant phosphorite bands and nodules in a black, organic-rich matrix. The phosphorite laminae rarely exceed one mm in thickness but may extend up to several centimeters in length. Phosphorite nodules also vary considerably in size and often contain fossils such as radiolaria and spicules (Plate 2C). Both laminae and nodules lie along planes of fissility. In the intervening black matrix, little detail can be distinguished except a few small quartz grains. In Brewer's micromorphological classification of sedimentary facies (Brewer, 1964, 1972; Bullock and Mackney, 1970; Burnham, 1970), the fabric of black shales is generally argillasepic unistrial, i.e., they consist primarily of clay minerals that exhibit preferred parallel orientation, giving specimens as a whole a unidirectional striated extinction pattern.
Although samples of this facies are mineralogically indistinguishable from other fine-grained shale groups, they are geochemically distinct, i.e., they all fall into one cluster. This facies is, therefore, a unique constituent of Kansas sediments supporting the level of importance as marker units currently placed on these shales by the Kansas Geological Survey.
Summarizing: the black shale facies is inferred as a marine deposit resulting from slow deposition in an oxygen-depleted sea. Parts of the Heebner Shale, Muncie Creek Shale, Eudora Shale, Larsh and Burroak Shale, Hushpuckney Shale, and Stark Shale are typical of this facies.
Sandstone and Siltstone Facies
The sandstone and siltstone facies is found irregularly throughout the Upper Pennsylvanian clastic deposits but is almost unknown in the Lower Permian. It consists primarily of yellow to brown, arkosic greywackes and yellow/brown to grey, laminated siltstones that possess all the features of deltaic clastics. In outcrops, the sandstones are generally massively bedded with occasional irregular laminations (outlining particles or organic matter) and cross-bedding (Plate 3A). The physical extent of these sandstone bodies, documented by Sanders (1959) and Wanless et al. (1963, 1970), indicate that they represent basal deltaic channel deposits. The laminated siltstones, on the other hand, show graded bedding and flow structures such as load casts and microslumps, and probably represent delta-front deposits.
Plate 3--A. A section of the Tonganoxie Sandstone (samples 294, 295) showing several beds of massive sandstone with occasional irregular laminations. Beds are approximately 2-3 ft. thick. B. In the same outcrop as A, cross-bedded sandstones are also in evidence. C. In thin section, sample 294 consists of moderately sorted, subangular to angular quartz grains, plagioclase feldspar and zircon grains in a matrix of clay minerals. Scale = 0.1 mm. D. A Doniphan Shale sample (121) typifies many sandstones in the Upper Pennsylvanian, with hematite coating on the subangular quartz grains. Scale = 0.05 mm. E. Frequently, quartz grains in the sandstones (sample 85) contain fluid and solid inclusions. One of the fluid inclusions in the central quartz grain also appears to contain a gas bubble. Scale = 0.05 mm. F. A photomicrograph of a Stull Shale sample (85) showing numerous angular to subangular quartz grains in a matrix of mica and clay minerals. In the center, one relatively fresh albite- twinned plagioclase grain is preserved. Scale = 0.1 mm.
Massive channel sandstones are found in the Noxie Sandstone Member (Horne, 1965) of the Kansas City Group, in the Tonganoxie Sandstone (Plate 3B) and Ireland Sandstone Members of the Douglas Group (Bower, 1961), in the Pillsbury Shale, Root Shale, and Wood Siding Formation of the Wabaunsee Group, and finally in the Towle Shale Member of the Admire Group. Most are sinuous bodies that extend over northeast Kansas, southeast Kansas, or northern Oklahoma and contain sediments derived from the Ozark Dome of Missouri and the Ouachita tectonic belt of Oklahoma and Arkansas respectively. Channel deposits pass laterally into deltaic fine sands and siltstones (Wanless et al., 1970) characterized by uneven cross-lamination and reworking.
In thin section, the sandstones appear to be poorly to moderately sorted with numerous angular and subangular rock fragments, hematite, and clay mineral coated quartz grains (Plate 3D, E, F), and occasional fresh to slightly weathered, albite-twinned plagioclase (Plate 3E), microcline, orthoclase, and zircon grains in a clay mineral matrix (Plate 3C). Samples vary in texture from immature sandstone to arkosic greywackes. Fragments of shale, igneous rocks, quartzite, undulous quartz, chert, and organic material may be seen.
Laminated siltstones are found primarily in the beds separating the limestone formations, designated by Schwarzacher (1967, 1969) as outside shales, e.g., Kanwaka, Tecumseh, and Calhoun Shales of the Wabaunsee Group. In hand specimen and thin section, samples consist of alternating yellow-brown siltstones or silty shales and darker, fine-grained, slightly more carbonaceous shales (Plate 4C). Graded beds and fining upwards cycles are common. Although contacts at the base of each siltstone band are sharp, indicating a brief diastem, boundaries are often quite wavy, load casts are frequently present (Plate 4A, B), and some small slumps are visible. The siltstone bands contain moderately sorted subangular quartz grains with occasional mica flakes, plagioclase feldspars, rock fragments, and carbonaceous material. In contrast, the finer bands are made primarily of mica and clay minerals with irregular amounts of fine silt-size quartz grains. In both layers, however, it is apparent that the mica flakes lie parallel to the laminae (Plate 3C), giving the siltstones an argillasepic, insepic, or silasepic unistrial fabric (Plate 4D, E; Brewer, 1964).
Plate 4--A. A siltstone band in the Heumader Shale (sample 75) shows regular alternations of silty shales (light area) and fine-grained, slightly carbonaceous shales (darker zones). In many cases, load casts are developed, particularly where concentrations of silt grains develop. In this example, the pressure of the overlying silt has forced the softer darker shale up into the silt band. Scale = 0.5 mm, B. A load cast, developed in the Severy Shale (sample 162), shows how silt grains are concentrated at the base of the structure. Note also how the organic matter forms a layer around the base of the cast. Scale = 0.5 mm. C. Alternating carbonaceous and silty shale bands predominate in most siltstone, including the White Cloud Shale (sample 173)). Note the wavy nature of the banding. Scale = 1 mm. D. The fabric of siltstones is typically argillasepic unistrial, i.e., all the clay minerals and mica flakes are aligned, producing a undirection extinction pattern. Sample 16. Scale = 0.2 mm. E. An electron photomicrograph of sample 16 shows the regular plate-like distribution of clay minerals. Occasional quartz grains interrupt this pattern. Scale = 0.015 mm.
The zones of laminated siltstones closely resemble the regular layered structures recognized by Moore and Scrutton (1957) in modern prodelta deposits in bays and along the coast of the Gulf of Mexico. Formation of these deposits apparently results from rapid deposition with little reworking of sediments. Fossil criteria (Heckel, 1972a) also indicate a restricted marine environment undergoing rapid sedimentation and subject to high turbidity and fluctuating salinity for many of these thick, poorly fossiliferous Pennsylvanian shales. A few siltstones and silt shales characterized by uneven lamination, ripple cross-lamination, and extensive reworking are identified by Wanless et al. (1970) as also belonging to a deltaic facies.
This facies, therefore, represents a deltaic sequence consisting of channel sandstones, delta sands and siltstones, and delta-front silts and shales which correspond to the deltaic units described by Wanless et al. (1970) for the Midcontinent.
Calcareous, Grey Shale Facies
Thin beds separating limestones in limestone formations are known as inside shales (Schwarzacher, 1969) and consist primarily of fossiliferous, grey, green, and brown, blocky, calcareous shales. Most samples from this facies are massive or rubbly, but a few are laminated and fineigrained in texture.
This facies is thought to be a fully marine phase of deposition as it contains a characteristic marine fauna. Moore (1964) identified a number of ecosystems in these sediments of which the Derbyia, Rhombopora, Neochonetes, and Derbyia-Neochonetes assemblages are most distinctive. Derbyia and other salinity-tolerant brachiopods and clams characterize the ecosystem found, for example, in the Speiser Shale of the Council Grove Group. Hattin (1957) interpreted the environment of deposition as belonging to an offshore zone of near normal salinity in which weak turbulence resulted from wave activity. Disseminated calcium carbonate was judged to be derived from shell disintegration. The Rhombopora assemblage is identified in the initial parts of several marine sequences, e.g., the Doniphan Shale of the Wabaunsee Group, and is characterized by abundant ramose bryozoans such as Rhombopora and Batostomella. The lowest marine shaley deposits of some limestone formations contain abundant chonetoid brachiopods, particularly Neochonetes. This ecosystem, exemplified by a Neochonetes assemblage in the Snyderville Shale of the Shawnee Group, has a shallow-water habitat where a mud bottom bordered the shore (Moore, 1964). Finally, Moore (1964) and Imbrie, Laporte, and Merriam (1964) distinguished an ecological community, typified in the Florena Shale (Council Grove Group), that corresponds to the Snyderville assemblage in Neochonetes and Derbyia content but also contains abundant fusulinids such as Schwagerina. The assemblage is, therefore, thought to have developed in the middle or regressive part of a cyclothem.
Although four fossil assemblages can be distinguished in this facies, it is most difficult to subdivide the facies on lithological evidence. However, from Moore's ecological survey, we can conclude that this facies generally represents open-marine and shallow-water conditions.
In thin section, samples vary from slightly silty, laminated, brown shales to highly calcareous, fossiliferous, marine, grey shales although the majority are calcareous, fine-grained, light grey or brown, coarsely laminated shales. The presence of laminae in shales reflects the absence of burrowing organisms in the substrate and indicates deposition in an environment free from tidal or current movements. Off-shore marine deposition is inferred by the occurrence of brachiopods such as Derbyia and thin-shelled bivalves. However, in the calcareous shales there is evidence for both near-shore and off-shore environments. In samples that are listed as dolomitic shales in the mineralogical classification, dolomite crystals are developed extensively, suggesting a diagenetic alteration of some sediments. Plate 5A-D illustrates the variety of sediments and textures associated with this facies.
Plate 5--A. A sample of the Oketo Shale (265) contains numerous fossils such as fusulinids (outlined by organic matter), bryozoans, and clam fragments, in a fine-grained calcite matrix. Scale = 0.25 mm. B. A fossiliferous sample of the Queen Hill Shale ( 136). Punctate brachiopods, lamellibranch fragments, and the fusulinids are found in abundance. Apart from an occasional quartz grain, the matrix is a grey micrite. Scale = 0.5 mm. C. A Grant Shale sample (272) illustrates the type of fabric developed in a shale containing few fossils. Numerous small calcite crystals can be seen within matrix of organic matter, clay minerals, and the occasional quartz grain. Scale = 0.1 mm. D. Another fabric developed in a calcareous shale--Galesburg Shale (27)--contains far more organic matter and clay minerals. The beginning of mica alignment can be seen on the right of the sample. Scale = 0.1 mm. E. Red shales have many types of fabrics but the two most commonly recognized are illustrated in this and the following photomicrograph. Numerous well-sorted quartz grains are surrounded by a stained, fine-grained matrix of clay minerals and calcite. Sample 270. Scale = 0.1 mm. F. This fabric contains reworked stained pellets surrounded by a fine-grained calcite matrix. Calcite overgrowths on the pellets are developed. Sample 256. Scale = 0.5. mm.
Red and Purple Shale Facies
This facies is characterized by red, green, and purple mottled, calcareous shales and is only found in Lower Permian beds. Although only a few samples belonged to this facies, their characteristic colors make it a distinctive facies in the field, and a brief description is therefore included here.
In hand specimen, samples are mottled red, green, or purple, hard, blocky, calcareous shales containing no fossils. The facies is found within outside shales (thick grey shales separating limestone formations) and rarely thickens to more than 3 in in any one bed. Furthermore, this facies shows rapid lateral variations.
Thin sections (Plate 5E, F) reveal the presence of many fine, silt-size quartz particles within a matrix of stained, fine-grained calcite and clay minerals. Some samples appear to contain reworked pellets and sediments. Color variation recorded in the shales is a reflection of the iron and/or organic content. Red colors arise from the presence of ferric oxide in the essential absence of organic material whereas green shales are probably deposited with some organic material that reduces the red ferric ion to the ferrous state (Elias, 1937). The stratigraphic association of green shales immediately above and below red shales indicates this to be true. Wells (1950) found small amounts of organic material in Eskridge red shales which he interpreted as an indication of deposition on land or in the tidal zone. Green shales were thought to be of shallow-marine origin. However, red deposits are now known to form in a variety of climates and depositional environments (Broecker, 1974; Walker, 1974) from deep sea clays to moist tropical soils. It can therefore be inferred that, as red beds are not good paleoenvironmental indicators (Berner, 1971), Wells' interpretation is open to doubt. Unfortunately, until some viable alternative is proposed, this hypothesis has to be retained.
Mineralogically, samples from this facies are all carbonates and consequently fall into group E of the mineralogical classification. However, their trace-element geochemistries vary so considerably that samples fall into clusters X, A, and D of the combined mineralogical and geochemical classification. Nevertheless, there is some uniformity in the major oxide content of the shales, for example consistently high Fe oxide and CaO content.
This facies represents, therefore, a locally important field unit, but at the same time is indistinguishable from other calcareous shales in terms of mineralogy and geochemistry. It would seem appropriate to consider this facies as a minor variation of the calcareous shale facies described previously.
Shale Partings in Limestone
A number of limestone units exhibit distinct layering in which the limestone beds are separated by thin shale partings. Although the thin shale studied by Troell (1969) was used as an internal stratigraphic datum, normally on exposure the partings weather back into the outcrop face and thus receive little attention. They frequently contain corals and encrusting bryozoans that require clear water, relatively slow deposition, and a firm substrate (Heckel, 1972a). These ecological considerations and the areal extent of each thin parting indicate that the shales result not from a rapid influx of clastics but rather from a long-term cessation of carbonate deposition with very slow accumulation of suspended detritus.
In thin section, partings from the Winterset Limestone (Kansas City Group) and Beil Limestone are laminated calcareous brown to grey shales with abundant fragments of brachiopods, fusulinids, corals, and organic matter (Plate 6A, B).
Plate 6--A. A shale parting in the Winterset Limestone (sample 35) is calcareous, fine-grained, and laminated with a few fossils. Scale = 0.4 mm. B. A Beil Limestone sample (137) illustrates the fabric of shale partings. They are typically fine-grained, calcareous, grey or brown with occasional quartz grains. Scale = 0.1 mm. C. A sample from the Chanute Shale (48) is representative of the clayey-shale facies. In this thin-section, most are fine-grained, brown to grey, rather silty shales with scattered fossils. Scale = 0.1 mm. D. Another laminated silty shale showing gravitational bands. Scale = 0.05 mm. E. A typical exposure of the clayey-shale facies in a road-cut near Kansas City. Samples (69 to 71) of the Lane Shale were obtained from this site.
Brown, Soft, Clayey Shale Facies
Thick, fine-grained, soft shale bands occur in many outside shales constituting a poorly fossiliferous, near-shore, marine sedimentary deposit. This facies generally displays a monotonous sequence of olive-grey to brown, slightly silty shales with thin zones of laminated siltstones occasionally carrying plant fragments.
Early work recognized both non-marine and marine environments in the outside shales (Moore, 1929). Later, however, identification of the consistent position of outside shale formations between definitely marine limestone sequences, the general barrenness of the shales, and the occurrence (even though local) of non-marine lithologies caused them to be considered as wholly or predominantly non-marine deposits (Moore, 1936), a concept that persists today.
However, recent investigations by Heckel (1972a), and Heckel and Baesemann (1975) have revealed the presence of fossils scattered throughout a number of outside shales, particularly in the Kansas City and Lansing Groups. Most of the fossils recovered are conodonts and small, thin-shelled pelecypods and gastropods, suggesting shallow-water or relatively rapid deposition or both. Shales of this facies are often found in association with deltaic sandstones and siltstones which necessarily place much of the facies in the near-shore shallow marine regime. Wanless et al. (1970) have therefore equated these deposits with prodeltaic marine muds and bottomset deltaic beds.
In thin section, samples from this facies are revealed as fine-grained brown to grey, occasionally silty shales containing a few isolated fossils and organic material (Plate 6C, D, E). Texturally, these shales are generally argillasepic and moderately to weakly unistrial (Brewer, 1964) although an occasional inundulic or insepic fabric was noted, indicating a lack of disruptive influences such as burrowing animals, tides or currents, and confirming the environmental interpretations placed on this facies.
Clastic sedimentary deposits from the Upper Pennsylvanian and Lower Permian of Kansas can be grouped into six facies representing differing environmental conditions.
The most distinctive of these facies is a black, laminated shale that is used as a marker horizon in cyclothems (Moore, 1950). Developed in a shallow-water epeiric sea, it contains a sparse epiplanktonic fauna indicating anoxic bottom waters. Closely associated with this facies (as inside shales) are sediments that fall into the calcareous grey shale facies. These shales are deposited primarily in open-marine, shallow-water conditions and are characterized by abundant brachiopods, bivalves, fusulinids, and bryozoans.
Inside shales separate limestone units within limestone formations whereas outside shales are intercalated between the formations. Two facies can be differentiated in the outside shales, a sandstone and siltstone facies and a brown, soft, clay-shale facies. Both represent environments of deposition characteristic of deltaic sedimentation. First, the sandstone and siltstone facies consists of channel sandstones, laminated prodelta siltstones, and deltaic sands and siltstones (terminology of Wanless et al., 1970). The source of the detrital material is primarily from the Ouachita foldbelt although subsiding deltas are developed on the low-lying land area to the north of the Forest City Basin. A minor source may originate in the Ozark dome of Missouri (Wanless et al., 1970). The brown, clay-shale facies can be equated to delta bottomsets and prodelta marine clays (Wanless et al., 1970).
A number of shale partings occurring in limestones constitute the fifth facies. Although geochemically and mineralogically indistinguishable from other calcareous shales, they form a unique sedimentological facies. From ecological and lithological considerations, it is inferred that each thin parting developed in near-diastemic conditions.
A minor facies recognized in Lower Permian deposits is a red and purple shale lithology. It is interpreted as a product of near-shore or even tidal environments.
Kansas Geological Survey, Geology
Placed on web May 6, 2009; originally published December 1979.
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