The Wreford limestone and adjacent shales include beds that are traceable laterally for great distances and that consist of lithologic types that are repeated two, three, or more times within the stratigraphic span of the formations studied. Moreover, these recurrent types have a definite stratigraphic relation to one another. The adherence of the Wreford limestone to the general pattern of sedimentary cycles in the "Big Blue" series of Kansas has been noted above. The individual rock types represent phases of rhythmic sedimentation during successive advances and retreats of the early Permian sea. The sediments deposited during a single sedimentary cycle of the type that occurred during Pennsylvanian time have been called cyclothems by Wanless and Weller (1932, p. 1003). Hemicycle is a name that can be applied to either the transgressive or regressive portion of a cyclothem. Megacyclothem is the name applied to a cycle of cyclothems (Moore, 1936a, p. 29).
Some rock types are encountered at only one or very few places. These include a coal seam 1.0 mm thick in the Speiser shale at one exposure and a fine-grained channel conglomerate at another. Certain limestones observed locally in various stratigraphic positions contain no diagnostic fossils and are very argillaceous. They have no easily interpretable relationship to other parts of the cyclothem. Based on the past observations by the writer, they are judged to be deviant rock types still within the limits of variation of adjacent types.
Rocks that have characteristic lithology, fauna, and cyclic position and that are common in the Speiser shale, Wreford limestone, and Wymore shale are each described in detail below. Reference is made first to the physical characteristics, then to the environment of deposition, including consideration of position in the sedimentary cycles.
At four localities in southern Kansas lenticular bodies of unfossiliferous sandstone exist in the midst of the red shale sequence. At two places the sandstone is massive to thick bedded, friable to well cemented, cross-bedded, and light-grayish yellow-orange. The grain size of the sandstones is coarsest at locality 121, where the maximum thickness of 20 feet was observed. The edge of a channel is well exposed at locality 125. Three and four bodies of sandstone are present at localities 119 and 120, respectively (Pl. 7A). At both these exposures the several sands are thin to medium bedded, well cemented, very fine grained, locally cross-bedded, and yellowish gray but exhibiting some reddish staining. An exception is a thick-bedded, light-yellowish-gray, lenticular sandstone bed, the uppermost of four at locality 120 (Pl. 7A), which resembles more closely the sands at localities 121 and 125. Wherever observable, the sandstone bodies are level on the upper surface and convex downward on the lower.
|Grain sizes of sandstone in the
Speiser shale at locality 120, Cowley County.
|1/2 to 1/4 mm||1.12 percent|
|1/4 to 1/8 mm||80.05 percent|
|1/8 to 1/16 mm||12.10 percent|
|<1/16 mm||6.72 percent|
The sand grains of this sample are predominantly quartz and are angular owing to crystal growth by secondary addition of silica. Most of the grains of all sizes show some well-developed crystal surfaces, and many euhedral crystals can be observed. Granular reddish-brown limonite is sparsely present in the fine-sand fraction. Limonite cubes pseudomorphous after pyrite, as well as flakes of muscovite, are common in the very fine sand. Other minerals are virtually absent. Other sands examined are composed of quartz grains except for a very small amount (less than 1 percent) of muscovite and minor amounts of limonite. In a few specimens calcite cement is observed, but most samples are only slightly calcareous.
Petrographic examination of some of the more compact sands, which could not be disaggregated readily, showed uniform grains dominantly of fine and very fine sand size. Most of the grains show angularity, perhaps due to secondary addition like that described above. The reddish color observed is probably a limonitic stain. Quartz grains are dominant; minor amounts of limonite and muscovite are present.
Red shales are characteristic features of the middle parts of the Speiser and Wymore shales. The color ranges from pale red to very dusky red and includes grayish and purplish hues. Shaly bedding and a tendency to weather blocky are characteristic of the red shales. In most places red shale is in abrupt contact above and below with shale of greenish hue, or thinly interstratified with several beds of greenish shale, or grades through transitional beds mottled with greenish shale.
Almost all of the red shales are silty, locally enough so as to be classed as mudstones. Fine sand is present in the red mudstones, although in most it is only a small percentage of the whole. Sand/shale ratios for most red shales are less than 1/10, though ratios of 1/2 have been observed. As much as 84 percent of calcareous material has been noted in one of the red-shale units, and all the red shales are calcareous to some degree; 30 percent soluble material is not unusual for this type of rock. Mineral grains found in washed residues include quartz sand and silt grains and granular reddish-brown limonite.
Fossils are exceedingly rare in the red shales. A few charophyte oogonia were found at a single locality.
Green shale is commonly observed in the lower part of the Speiser shale and is almost invariably present in the middle Speiser and lower and middle parts of the Wymore shale. It is uncommon in the Havensville shale. The green strata cyclically precede and follow red shales where the latter are present. The color ranges from grayish-yellow green to grayish green and includes some shades of olive green. Bedding and weathering characteristics are much the same as in red shale.
Most of the green shales are silty and are as sandy as the red, and many are true mudstones. Sand, where present, is very fine grained. Sand/shale ratios ranging from 1/2 to 1/25 are observed. As much as 50 percent soluble material has been detected in green shale but 30 percent is more usual. The washed residues contain grains of clear detrital quartz, aggregates of granular limonite, sparse crystalline pyrite, crystalline calcite pellets, and sparse hematitic material.
These fossils, with exception of Paraparchites, Bairdia, Cavellina, and fragmentary vertebrate remains, were noted in samples from only one or two localities. The fauna as a whole is very sparse, and some seemingly unfossiliferous green shales were encountered.
|Fossils Observed in Green Shales of the Speiser,
Havensville, and Wymore Shales.
The contact of green shale with red has been discussed above. At many exposures a grayish-yellow, dusky-yellow, or light olive-gray shale overlies the upper green shale of the Wymore and Speiser shales. The contact between the two is transitional, and the fauna in the yellowish shale shows a change to marine conditions.
Between the green-shale phase and the molluscan-limestone phase of the Wreford megacycle lies dusky-yellow, yellowish-brown, grayish-yellow, or olive-gray silty shale, mudstone, or argillaceous limestone. This seemingly heterogeneous assemblage of rocks has a constant position in relation to cycles of sedimentation. The phase is so named because grayish-yellow mudstone is more common in this part of the cycles than any of the other variants. At some exposures green shale is in direct contact with molluscan limestone, the yellowish phase being absent altogether. In most exposures contact of mudstone with overlying molluscan limestone is sharp, but that with underlying green shale is gradational, the transition beds being mottled. Usually, units of this lithology are sparsely fossiliferous. Faunas, where present, are intermediate in composition between those of the green shale and the molluscan limestone. As much as 84 percent of calcareous material has been observed in samples from these beds. The sand/shale ratio ranges from about 1/2 to 1/100. In most places a large percentage of silt and sand is observed. Shaly or laminated bedding is characteristic of strata having this lithology. This phase is represented in the upper Wymore shale at some localities (24, 30, 93) by a medium-hard, very calcareous mudstone or very silty limestone that is thin bedded or laminated.
Minerals in the grayish-yellow mudstones include subangular to well-rounded clear or amethystine quartz grains of granule, sand, and silt size; jaspery silica; milky-white replacement silica; hematite; limonite as granular pellets, tiny botryoidal masses, and as an alteration product of hematite and pyrite; finely divided muscovite; and calcite in granular pellets, small crystals, and crystalline masses.
This phase of sedimentation contains a much more diversified fauna than the green shale. The following fossils have been observed, sparse forms being indicated by (s) and common forms by (c).
|Fossils of the Grayish-Yellow Mudstones of the
Speiser, Havensville, and Wymore Shales.
|Charophyte oogonia (s)|
|Ammovertella sp. (s)|
|Cornuspira sp. (s)|
|Globivalvulina sp. (c)|
|Orthovertella sp. (s)|
|Worm tubes (s)|
|Septopora sp. (s)|
|Productid spines (c)|
|Aviculopecten sp. (s)|
|Bairdia sp. (c)|
|Bythocypris sp. (s)|
|Cavellina sp. (c)|
|Hollinella sp. (s)|
|Kirkbya sp. (s)|
|Knoxina sp. (s)|
|Macrocypris sp. (s)|
|Paraparchites sp. (s)|
|Crinoid stems (s)|
|Echinoid spines (s)|
|Holothurian hooks (s)|
|Fragmentary remains (s)|
Beds of argillaceous to very shaly limestone typically lie between the grayish-yellow mudstone (or green shale) phase and the calcareous-shale phase in the Speiser shale and Wreford limestone. Most deposits representing this phase of sedimentation are 0.1 to nearly 1 foot thick. Individually, the units consist of a single thick bed, several thin beds, or shaly strata. The limestones range from yellowish gray to dark gray. At all exposures where the limestones are well developed, Aviculopecten (Pl. 18A) and, commonly, Septimyalina are the diagnostic megafossils. It is for this reason that the name "molluscan limestone" has been applied.
Plate 18--Molluscan limestone. A, Slab containing abundant Aviculopecten from limestone bed in lower Havensville shale, x1. NW sec. 21, T. 11 S., R. 8 E., Riley County (Loc. 36). B, Peel photograph, x4, of molluscan limestone from Speiser shale. Note rough alignment of structures. NW sec. 10, T. 7 S., R. 9 E., Pottawatomie County (Loc. 1). C, Peel photograph, x4, of molluscan limestone from Havensville shale. Note abundant Ammodiscus (white rod-shaped structures) SW sec. 3, T. 7. S., R. 9 E., Pottawatomie County (Loc. 2). D, Peel photograph, x4, of limestone from the upper Speiser shale. Note abundant organic structures. SW sec. 19, T. 32 S., R. 8 E., Cowley County (Loc. 117).
A remarkable development of molluscan limestone is found in the Havensville shale at many exposures in northern Kansas, especially in Marshall and Pottawatomie counties. At localities 8, 10, 12, and 21 the middle of the member includes a fairly thick sequence of thin-bedded, very argillaceous limestone, which contains a sparse molluscan assemblage. Above this lies a thick molluscan-limestone bed, which bears abundant algal remains as well as Aviculopecten and various other small pelecypods. The thick bed is profusely fossiliferous at locality 13, but the mollusks are small. Adjacent sections likewise include a greater-than-usual thickness of molluscan limestone, although not so much as in the named exposures. The mudstone phase of sedimentation, which is ordinarily found between two molluscan limestone beds in the Havensville in northern Kansas, is absent in these sections.
At several localities in northern Kansas rounded granules and pebbles of clay and limestone are found in the molluscan-limestone phase of the upper Speiser shale. Bedded and nodular chert is not observed to be present.
A finely granular texture is prevalent among the molluscan limestones (Pl. 18B). Much of the matrix consists of silt and clay, especially in the more shaly varieties. Etched surfaces exhibit numerous fossil fragments and entire shells, the latter aligned parallel to the bedding. Aligned fossil fragments are found in one sample. Many of the fossils are silicified. Algal structures resembling Osagia are present in several of the specimens studied, but they are not abundant.
Insoluble residues contain much the same sort of material seen in other limestones of the Speiser shale and Wreford limestone. All molluscan-limestone residues contain moderate to profuse numbers of foraminifers of the genus Ammovertella, which is found commonly with Ammodiscus. The latter is present in great abundance in a few places (Pl. 18C). The types of insoluble materials present in selected rock specimens are listed below in order of their relative abundance in the samples. An average residue of about 4 percent is observed, although one specimen yielded 20 percent.
|Insoluble Residues of Molluscan Limestones
of the Speiser Shale and Wreford Limestone.
|Granular and chalcedonic chert, mostly as fossil-replacing minerals|
|Quartz silt and sand grains and loosely aggregated silt (in part? foraminiferal debris)|
|Limonite, reddish-brown to yellowish-orange, granular|
Petrographic examination of a thin section of the more thick-bedded variety of molluscan limestone (Loc. 1) shows a rock of uniform texture composed of minute grains of calcite. Small fossil fragments aligned parallel to the bedding are common, many of them being affected by recrystallization. Crystalline calcite fills the interior of some of the fossils. Scattered oölites exhibit concentric lamination of thin calcite layers. A faint cross formed in the planes of polarization and radial appearance in the laminae suggest orientation of calcite crystals perpendicular to the surface of the oölites. Nubecularia, a calcareous foraminifer, is abundant in the thin section and it is commonly contained within oölites. A selected sample of the more argillaceous shaly bedded type of molluscan limestone also shows, in thin section, a fine-grained calcite matrix but appears "dirty" because of an abundance of clay. Numerous fossils, mostly fragmentary, are oriented quite diversely, and nearly all consist of recrystallized calcite.
Crystalline calcite is found as internal fillings and drusy calcite as internal incrustations of fossils. Numerous specimens of Ammodiscus are conspicuous, these likewise showing random orientation.
Although only one or two fossils seem to be ubiquitous in the molluscan limestones, many are believed by the writer to maintain a fairly constant association. In the following tabulation of fossils an asterisk denotes the diagnostic forms.
|Fossils Observed in the
Molluscan Limestones of the
Speiser and Havensville Shales.
|*Gastropods, tiny internal molds|
Ordinarily, the molluscan fauna is found in a limestone phase of sedimentation that contains few, if any, forms typical of other units. Probably no ideally complete cycle of sedimentation exists, however, and in the sequence of the Wreford megacyclothem there are definite exceptions to every generalization. The most symmetrically disposed molluscan beds, with relation to the Wreford limestone, are found in northern Kansas. Fairly persistent and faunally distinctive molluscan beds lie below and above the Threemile limestone in the first cycle of deposition and below the Schroyer limestone in the second cycle. In the upper Schroyer member, there are beds equivalent to the molluscan limestone, although the organic content of these, to be described below, differs markedly. Locally, as in Pottawatomie County, the molluscan beds of the Havensville shale are decidedly more algal than elsewhere.
Maximum divergence from ideal cyclic conditions is observed in Cowley County. The molluscan beds of the upper Speiser shale contain admixtures of the fauna typical of the calcareous-shale unit above. Locally, Aviculopecten and other diagnostic fossils seemingly are lacking in the limestone near the top of the Speiser shale. Instead, elements of the calcareous shale fauna are found in the first limestone above the red-shale-green-shale-mudstone sequence. Furthermore, mollusks are very commonly found stratigraphically above Derbyia-bearing limestone, which also contains other fossils characteristic of calcareous-shale units. In southern Butler County and in Cowley County the entire upper portion of the Speiser shale consists of interbedded thin limestones and shales. Derbyia, Juresania, Aviculopecten, and Aviculopinna are the dominant fossils in these rocks. The two phases of sedimentation, which are so distinct to the north, are here intermingled lithologically and paleontologically.
Local variations in the position of the molluscan phase are known. At a few exposures the Aviculopecten assemblage of the upper Havensville shale lies in the upper part of limestone that contains a calcareous-shale fauna. This is unusual because the phenomenon is observed in the transgressive stage of sedimentation and the normal succession of faunas is reversed. At these localities, however, mollusks are found also in the shale below the limestone.
Thin sections of limestone containing fossils characteristic of both the molluscan-limestone phase and the calcareous-shale phase were made and studied petrographically. These sections are described as follows:
- Upper Speiser shale (Loc. 117). The very fine granular matrix is composed of calcite grains. The rock is medium gray. Numerous large fossil fragments are aligned parallel to the bedding and are composed of coarsely crystalline secondary calcite. The internal filling of most of the larger fossils clearly shows a finer grain than the surrounding rock. Innumerable foraminifers, which resemble Ammodiscus, and small fossil fragments are present in the rock (Pl. 18D).
- Upper Speiser shale (Loc. 117). The finely granular, medium-gray matrix contains numerous crystallized fossils and abundant Ammodiscus. A few structures show thinly laminated concentric layers of calcite. Under crossed nicols, a black cross appears, which is centered over the structure. This indicates a radial arrangement of calcite crystals perpendicular to the laminae. Undoubted oölites show this petrographic feature, and it may be that the structures are true oölites.
- Upper Havensville shale (Loc. 72). The matrix is composed of irregular fine grains of calcite and extremely abundant fossil fragments. Fossils are aligned parallel to the bedding. The shell fragments have not been recrystallized to any marked degree; original structure is preserved in many. Incrustations of thin laminae of calcite around many fossil fragments seem to be oölites. A black cross under crossed nicols indicates radially arranged crystals in the laminae. The rock is mottled yellowish brown and medium gray.
The limestones that contain fossils characteristic of both the molluscan phase and the calcareous-shale phase of sedimentation are yellowish gray to medium-dark gray, including yellowish-brown and olive-gray hues. Finely granular texture and alignment of fossils parallel to the bedding are typical. Residues contain the same insoluble materials as those from the molluscan limestone, arenaceous foraminifers being conspicuous. The following list of organic remains shows the mingling of molluscan-limestone fauna and calcareous-shale fauna in these beds.
|Fossils Observed in Certain
Unusual Molluscan Limestones of the
Speiser Shale and Wreford Limestone
|Fenestrate and ramose types|
The preceding discussion of variations in the phases of sedimentation indicates that (1) the calcareous-shale type of mixed fauna is not wholly restricted to rocks of that lithology; (2) the molluscan-limestone type of fauna may be found in shale, although not typically so; and (3) the two assemblages may be found intermingled in both limestone and shale units. None of these variations is in serious disharmony with the cyclic pattern of sedimentation. The paleoecological implications are discussed below.
Very fossiliferous calcareous shales lie stratigraphically between chert-bearing limestone and argillaceous limestone bearing near-shore mollusks or are situated between two chert-bearing limestones. Calcareous shale typically ranges from grayish yellow and yellowish gray to medium and dark gray. The colors are commonly mottled. Thin limestone nodules or lenses are common in northern and central Kansas, and toward the south this type of lithologic unit becomes progressively more calcareous. In the latter region shaly limestones or thin-bedded, gray, argillaceous limestones are a conspicuous feature of the calcareous-shale units. Bedding in the calcareous shales is typically shaly even where the shale locally grades into an argillaceous limestone. The contact with underlying or overlying limestones is somewhat gradational.
Shale of this type may contain as much as 75 percent soluble material, although about 60 percent is average. The sand/shale ratio ranges from 1/2 to 1/25, but the larger ratios are due to the presence of silicified fossil fragments retained in the sand fraction. Except for fossils, the sand grains are very fine and consist chiefly of quartz. Of the other minerals found in these shales, most common are small aggregates of reddish-brown granular limonite, but common also are botryoidal limonite, hematite, drusy pyrite, plates and small granular pellets of secondary crystalline calcite, chert as fossil-replacing material, quartz sand and silt grains, small clusters of euhedral quartz crystals, and asphaltic residue. Not all of these are present in any one sample, but some are found in each sample examined.
The fauna of the calcareous-shale units is the most abundant and most varied taxonomically of any in the Wreford megacyclothem. Certain forms are nearly everywhere found in the assemblage. The fossils are tabulated below by phyla. Asterisks precede the forms that are diagnostic, and forms that are sparse, or known only locally, are indicated by (s). All other fossils listed have a moderate distribution in the calcareous-shale units.
|Fossils Observed in
Calcareous-Shale units of the
Speiser Shale and Wreford Limestone
|Osagia sp. (s)|
|Climacammina sp. (s)|
|Fusulinids, juveniles (s)|
|Geinitzina sp. (s)|
|?Orthovertella sp. (s)|
|Aulopora sp. (s)|
|Stereostylus sp. (s)|
|Cyclostome, encrusting (s)|
|Streblotrypa sp. (s)|
|Trepostome, encrusting (s)|
|?Batostomella sp. (s)|
|Aviculopecten sp. (s)|
|Pseudomonotis sp. (s)|
|Septimyalina sp. (s)|
|Cornigella sp. (s)|
|Ellipsella sp. (s)|
|Healdia sp. (s)|
|?Haworthina sp. (s)|
|*Crinoid plates and stems|
|Holothurian spicules, wheels (s) and hooks|
|*Fragmentary remains, plates, teeth, bones|
Although typically characterized by brachiopods, bryozoans, and echinoderms, these beds do contain mollusks. The assemblage has been called the mixed phase by Elias (1937, p. 411) and is number 5 of his ideal "Big Blue" cycle.
Chert-bearing limestone is the most persistent and prominent type of rock in the Threemile and Schroyer members of the Wreford formation. Such beds invariably lie at the base of each of these members, in the upper Threemile limestone at most exposures, and commonly within the shale sequence below the algal limestone of the Schroyer member (Pl. 5B, 9A, 16C, 17C, etc.).
Chert, which is the most diagnostic feature of the Wreford limestone, comprises both discontinuous-nodular and continuous pinching-and-swelling beds. Two general types are common: (1) hard, gray, noncalcareous, compact to slightly porous chert, which commonly exhibits a lighter-colored weathered shell; and (2) hard, bluish-gray, porous, calcareous chert, which exhibits concentric layering throughout.
Limestones in which chert is a persistent feature exist in distinguishable units 0.5 to more than 6 feet thick. Strata of this type are dominantly medium to thick bedded and generally hard. The color most commonly observed is yellowish gray or grayish yellow, dusky-yellow, light-gray and light-olive-gray hues being seen more rarely. Weathered, the rocks take on a grayish-yellow hue. These beds are topographically expressed as chert-covered slopes. The completely fractured nature of the chert beds causes rapid collapse during stream undercutting, and there is little resistance to slumping and creep on hill slopes. The most characteristic fossils to be found in this phase of sedimentation are fragments of fenestrate and ramose bryozoans, crinoid stems, echinoid plates and spines, productid spines, and shells of Dictyoclostus, Composita, and Wellerella.
Texturally, finely-granular and subgranular matrixes are the most common (Pl. 19A,B,C,D). Subcrystalline textures are observed in only a few samples. Structures in the limestone consist mainly of shell fragments, many of which are replaced by chert. Fossil debris is at best fragmentary and only moderately abundant in most places; however, locally there are great quantities of whole fossils and broken fragments. Alignment parallel to bedding planes is the usual arrangement of these constituents (Pl. 20A,B,C).
Plate 19--Chert-bearing limestone. A, Peel photograph, x2, of cherty limestone from lower Threemile member. SW sec. 3, T. 7 S., R. 9 E., Pottawatomie County (Loc. 2). B, Peel photograph, x4, of cherty limestone from upper Threemile member. Center sec. 35, T. 22 S., R. 9 E., Chase County (Loc. 93). C, Peel photograph, x2, of cherty limestone from lower Schroyer member. SE sec. 16, T. 15 S., R. 7 E., Morris County (Loc. 67). D, Peel photograph, x4, of cherty limestone from upper Schroyer member. NE sec. 34, T. 11 S., R. 6 E., Geary County (Loc. 30).
Plate 20--Silicified fossils in cherty limestone. A, Enteletes from lower Threemile limestone, x 1/2. Center sec. 35, T. 22 S., R. 9 E., Chase County (Loc. 93). B, Composita from lower Threemile limestone, x 1/2. SW sec. 36, T. 32 S., R. 8 E., Cowley County. C, Chonetes from upper Threemile limestone, x1. SW sec. 22, T. 16 S., R. 10 E., Lyon County (Loc. 69).
Insoluble residues of the cherty limestones are diagnostic. Quartz-silt aggregates are abundant in most of the samples studied. Limonite is common, but it is seen in residues of all phases of deposition. Granular and chalcedonic chert, existing as fossil-replacing materials, are found in all the residues, but they are likewise observed in nearly every type of limestone studied. The insoluble substances found in residues of chert-bearing limestone are listed below. An asterisk indicates the most abundant types and an (s) follows those that are uncommon.
|Insoluble Residues of Cherty Limestones of the Wreford Formation|
|*Fossils replaced by granular and chalcedonic chert|
|*Quartz silt, loose and aggregated|
|*Quartz sand, very fine grains|
|Chalky tripolitic chert|
|Chalky chert (s)|
|Limonite pseudomorphs of pyrite (s)|
|Granulated chert (s)|
|Drusy chert (s)|
|Drusy quartz (s)|
|Lacy granular chert (s)|
The arenaceous foraminifers are of the same types as occur in molluscan limestone and in algal beds. Aggregates of quartz silt grains are probably in part the fragments of these protozoans or may belong to some problematic foraminiferal species. Most of the limestones produced 1 percent or less of residue, although as much as 70 percent was observed. All large percentages of insoluble materials are due to abundant tripolitic chert, which, though large in volume, comprises a relatively small proportion of the total sample weight.
Thin sections of chert-bearing limestone from several localities were studied petrographically. Brief descriptions of these follow.
- Lower Threemile limestone (Loc. 102). Matrix of very fine granular calcite. Few fossils, small, and aligned parallel to the bedding. Some areas filled by crystalline calcite.
- Lower Threemile limestone (Loc. 115). Matrix of very fine granular calcite. Fossils very abundant, rudely oriented parallel to the bedding, commonly recrystallized, some filled internally or replaced by chert. Bryozoan and brachiopod debris especially abundant. A few structures show concentric lamination around crystalline nuclei and exhibit a black cross under crossed nicols. These are possibly algal in origin but may be oölites.
- Lower Threemile limestone (Loc. 115). Matrix of fine granular calcite. Fossils abundant, fragmentary, commonly replaced by crystalline calcite or chert, but many show original structure. Bryozoan and brachiopod fragments are recognizable. Small chert nodules are irregular in shape and are in gradational contact with the limestone. Rosettes of fibrous chalcedony and other cryptocrystalline features are abundant in the chert.
- Lower Schroyer limestone (Loc. 30). Matrix of extremely fine granular calcite. No structures other than sparse tiny ?fossil fragments. A single grain of crystalline quartz noted. This is a very dense limestone.
- Lower Schroyer limestone (Loc. 67). Matrix of fine granular and crystalline calcite. Fossil fragments very abundant; most show original structure, commonly filled internally with crystalline calcite, and very roughly oriented parallel to the bedding. Crinoid, bryozoan, and brachiopod fragments abundant. Concentrically laminated calcite structures resemble those of (2) above.
- Middle Schroyer limestone (Loc. 3). Matrix of very fine granular calcite. Fossil fragments very abundant, aligned parallel to the bedding, many recrystallized, but most exhibit original structure. Large areas of coarsely crystalline calcite. Some replacement of fossils by crystalline quartz. Most recognizable organic fragments are bryozoan and brachiopod remains.
It is clear, upon reviewing these descriptions, that the dominant type of matrix is finely granular. Crystalline calcite is common. Abundant, very small fossil fragments are in evidence and are either unmodified, recrystallized, or replaced by chert. All three types generally exist in each chert-bearing limestone.
The fossils of the cherty limestone are similar to those found in the calcareous shale but are generally less abundant and far less diversified. Of course, many fossils in the shale are microscopic and are easily detected in washed samples, whereas in limestone only insoluble microfossils can be identified, easily. In the following list of fossils seen in the cherty limestone an asterisk precedes the most common forms and an (s) follows those that are uncommon.
|Fossils Observed in the Cherty
Limestones of the Wreford Formation
|Osagia sp. (s)|
|Ammodiscus sp. (s)|
|Schwagerina sp. (s)|
|*Fenestrate and ramose types|
|Orbiculoidea sp. (s)|
|Aulopora sp. (s)|
|Aviculopecten sp. (s)|
|Aviculopinna sp. (s)|
|Gastropods, small molds (s)|
|Septimyalina sp. (s)|
In northern and central Kansas the upper Threemile limestone contains persistent beds of light-colored, thick-bedded to massive, porous, sparsely fossiliferous chalky limestone that bears little chert. In most exposures the chalky limestones are light yellowish gray to light grayish yellow. The weathered rock is grayish yellow and commonly is cavernous. The surface of freshly broken rock is powdery. Chert-bearing limestone generally lies above, as well as below, these beds. Limestones of this lithology are traceable from Marshall County to Chase County. There the rock aspect changes; chert is more abundant, and the color of the rock darkens. In Marshall, Pottawatomie, Riley, and Geary counties this part of the Threemile limestone, with a single observed exception, is 2 to 5 feet thick. The small amount of chert contained within these beds comprises one to five layers of small spheroidal nodules, or at a few exposures, continuous beds of chert. The sparse fossils in these beds consist mainly of echinoderm, bryozoan, and brachiopod remains.
Beds representing this phase of sedimentation exhibit remarkable thickening within very short distances in Wabaunsee, Morris, Lyon, and Chase counties, and at two exposures (including Loc. 27) in Geary County. The chalky limestone is about 25 feet thick at locality 135, and at locality 90 it is about 22 feet thick. The thick chalky limestones contain a few discontinuous "beds" of small, spheroidal nodules of compact chert, most of which lie at the base or in the uppermost portion. Huge spheres and irregular nodules of layered calcareous chert as much as 3 feet in diameter are seen at localities 27 and 90 (Pl. 11C, 12A). The main body of limestone at these places is thick-bedded to massive, virtually structureless, and only sparsely fossiliferous.
Fossils, where abundant in these unusual limestones, consist mainly of fenestrate bryozoans. These are present in quantity sufficient to contribute significantly to the large thickness encountered. At many places, notably localities 67 and 90, corals are moderately abundant in the top foot of the massive limestone. Stereostylus and Dibunophyllum are represented, the latter commonly crowded together to form an almost colonial mass (Pl. 21A). Specimens of the brachiopod genus Composita, although nowhere abundant in the chalky limestone, are found at most exposures.
Where the Threemile limestone is abnormally thick, the Havensville shale is very thin. There is only 1.5 feet of shale between the Threemile and Schroyer members at locality 90 (Pl. 12A). Similarly, at locality 67, only 5 feet of shale is present. Although most of the upper part of the section is covered at locality 135, there seems to be only 3 or 4 feet of Havensville shale. Because there is an almost unbroken geographical succession of localities where the thickening is observed, it is concluded that the chalky limestones constitute a virtually continuous body of fairly homogeneous character. Because of uniformity in lithology, fossils, geographic pattern, and lateral stratigraphic relationships, the sections that exhibit an abnormal thickness of chalky limestone are judged to be exposed parts of a large reef. When plotted on a map, the localities form a broadly arcuate belt convex toward the northwest (Fig. 5). Local, coarse, conglomeratic to coquinoidal limestones in the upper Threemile limestone and lower Havensville shale are known in exposures adjacent to reef sections. These deposits, none of which is very thick, may be talus that accumulated along the reef flank before burial by younger sediments.
Figure 5--Location of sections exposing reef-like thickening of Threemile limestone.
Texturally, finely granular matrix is dominant in the chalky beds. The individual grains of loosely cemented calcite are dull and lusterless. The chalky limestones are nearly all very porous. Irregularly rounded or elongate solution pits abound in the rock. Some beds containing abundant randomly oriented, subequal, elongate openings are traceable for many miles. Some crystalline calcite is present in openings in the rock, and the surfaces exposed to weathering commonly are recrystallized to a depth of as much as 0.5 inch.
Structures in the rock consist of fossils, which are generally fragmentary and aligned roughly parallel to the bedding. There is little replacement of organic structures by silica.
Insoluble residues of the chalky limestones amount to less than 1 percent. Although many types of residue material are common, none is diagnostic. The list of residues below is arranged in order of relative abundance.
|Insoluble Residues Observed in Chalky
Limestone of the Threemile Member
|Fossils replaced by granular and chalcedonic chert|
|Quartz silt aggregates|
|Quartz sand, very fine|
|Drusy granular chert|
|Limonite pseudomorphous after pyrite|
Several thin sections of chalky limestone were studied. Brief petrographic descriptions of these follow.
- Upper Threemile limestone (Loc. 49). Matrix of very fine granular calcite and a minor quantity of finely crystalline calcite. Structures include extremely abundant small fossil fragments, oriented quite randomly. Bryozoans are most numerous. Little recrystallization of organic fragments. Some replacement by cryptocrystalline silica.
- Upper Threemile limestone (Loc. 58). Matrix of very fine granular calcite. Abundant minute fossil fragments aligned roughly parallel to the bedding, mostly bryozoan. Numerous tubular and threadlike structures, probably Girvanella. Many fossils are recrystallized; few are replaced by cryptocrystalline silica.
- Upper Threemile limestone (Loc. 67). Matrix of very fine granular calcite. Fairly abundant fossils, randomly oriented, consist mostly of small bryozoan fragments. Some fossils are recrystallized or internally filled with crystalline calcite, or both. Cryptocrystalline silica is common as replacement material in fossils.
- Upper Threemile limestone (Loc. 90). Matrix of very fine granular calcite. Abundant, small, randomly oriented fossil fragments, mostly bryozoan. Sparse tubular, threadlike structures may be Girvanella. One large bryozoan fragment is encrusted by laminated calcite, which contains discontinuous radiating tubules. This structure is probably algal. Some fossils recrystallized.
- Upper Threemile limestone (Loc. 135). Matrix of very fine granular calcite. Sparse. crystalline calcite partly as internal fillings of fossils. Structures include numerous small fragmentary fossils, dominantly bryozoan. Many fossils encrusted by dense laminated calcite of ?algal origin. Very abundant tubular threadlike structures, probably Girvanella.
All the slides examined have a very fine granular matrix and a minor amount of crystalline calcite. Cryptocrystalline silica is sparse. Bryozoan and algal remains constitute the dominant structures.
The fossils seen in the chalky limestones, with the exception of Dibunophyllum and Streblotrypa, are all abundant in the calcareous-shale phase and the cherty-limestone phase. Although not abundant, Dibunophyllum seems to be diagnostic, because it was observed in other kinds of rocks in only one or two places. The relative abundance of other organisms is more significant than mere presence of any one genus or a particular assemblage of genera. Fenestrate bryozoans, echinoderm remains, and corals are proportionately much more common than in other phases of sedimentation. Shells of Composita, although nowhere numerous, are seen at almost every exposure of chalky limestone. Listed below, by phyla, are the fossils that are observed. An asterisk precedes the more abundant forms, and rare kinds are followed by and (s).
|Fossils Observed in Chalky
Limestone of the Threemile Member
|Tetrataxis sp. (s)|
|Sponge spicules (s)|
|Bryozoans, encrusting types|
|Gastropods, tiny molds (s)|
|*Echinoid plates and spines|
Across the entire state a very prominent algal limestone lies at the top of the Schroyer member. Algal beds are also seen at the top of the Threemile limestone southward from northern Butler County and in the Havensville shale in Chase, Cowley, and Pottawatomie counties. The thickness of these beds is variable, ranging from 0.8 foot to more than 6 feet. In general, the thickest algal limestones are seen in southern Kansas. Grayish yellow, yellowish brown, and yellowish gray are dominant colors. The algal beds are massive to thick-bedded and very hard. There is a common tendency toward (1) cavernous weathering and (2) the formation of well-rounded exposed surfaces. Topographically, the algal beds form benches that may be traced for many miles, the limestone cropping out as a resistant rimrock.
Algae constitute a large proportion of the rock, hence the name. In many samples, as much as 95 percent of the limestone is made up of calcareous structures probably formed by lime-secreting algae. The most common, indeed almost ubiquitous, form is that called Osagia. An individual colony consists of a small, somewhat disc-shaped calcareous mass, which, when sectioned, exhibits roughly concentric calcite laminae around a curved shell fragment in the central portion. Thickening of the laminae on top and around ends of the shell fragment causes a concavity on the lower side of the colony. The resulting colony appears bean-shaped in vertical section. Some forms that are referred to Osagia have a straight central bar and in section appear elliptical. In no other way do they differ from the typical Osagia. The calcareous foraminifer Nubecularia is commonly intergrown with Osagia, although it can also be free in the limestone matrix. Associated with Osagia, and at one or two places almost wholly making up beds that elsewhere contain abundant Osagia, are small (1 to 3 mm) concentrically laminated calcareous structures that exhibit radial crystal arrangement. These closely resemble radial-type oölites in every detail. Elongate or irregular shapes are most commonly observed. It is possible that these structures are algal in origin. Mollusks and arenaceous foraminifers are almost invariably associated with the algae, and a small proportion of the fauna consists of brachiopods, bryozoans, and echinoderms.
The algal limestones are not uniform in texture. Subgranular to subcrystalline matrixes are characteristic, and the matrix is ordinarily subordinate to the more abundant algal portion of the rock.
Structures in the algal beds seemingly are due mainly to the activity of lime-secreting algae. So abundant are the individual colonies (and oölites in some beds) that they are commonly packed tightly one against the other, generally with completely random orientation (Pl. 21B,C). Fragments of mollusks, brachiopods, and other invertebrate fossils can be seen in most of these beds. Complete or partial replacement of shell fragments by milky-white chalcedonic silica is a common feature.
Plate 21--Features of chalky and algal limestones. A, Chalky limestone containing abundant corals (Dibunophyllum), x 1/2. SE sec. 16, T. 15 S., R. 7 E., Morris County (Loc. 67). B, Peel photograph, x4, of algal limestone from the upper Schroyer member. SW sec. 16, T. 11 S., R. 8 E., Riley County (Loc. 36). C, Peel photograph, x2.5, of algal limestone from the upper part of the Threemile member. NE sec. 19, T. 25 S., R. 8 E., Butler County (Loc. 103).
Of unusual interest are vertical cylindrical openings an inch or two in diameter and as much as 3 feet in length, which are abundant in the algal limestones of the Threemile limestone and Havensville shale in Cowley County. Large boring clams of the genera Aviculopinna and Allorisma are found associated with these holes, and for this reason the openings are regarded as the borings of these organisms. The abundance of mollusks in these beds and a smaller number of algae than are observed in the Schroyer algal beds have led the writer to refer to these boring-filled strata as algal-molluscan limestones. The walls of most borings are studded with Osagia. In many places along the outcrop of the limestone the borings have been enlarged by solution. Within the borings are fragmentary fossils, mostly bryozoan, brachiopod, and echinoderm remains. In Cowley County, borings of the type described were observed in each of the three members of the Wreford limestone.
The algal-molluscan beds in the middle Havensville shale and upper Threemile limestone of Cowley County contain sparse small, light-gray nodules of compact chert at a few localities. A bed of bluish-gray layered calcareous chert lies near the base of the upper Threemile algal-molluscan bed. The petrography of these rocks is discussed in the part of the paper devoted to chert.
The insoluble residues of the algal limestones are listed below in order of decreasing importance.
|Insoluble Residues of Algal
Limestones from the Wreford Formation
|Quartz silt aggregates|
|Fossils replaced by granular and chalcedonic chert|
|Quartz sand grains|
The most characteristic portion of the residue consists of arenaceous foraminifers; an abundance of quartz silt aggregates and limonite is observed in nearly every limestone residue, and the other materials are not found everywhere in the algal beds. Abundant quartz sand grains are present in the uppermost Threemile limestone bed in Cowley County.
Several thin sections of algal limestone from each of the three members of the Wreford formation were examined petrographically. Brief descriptions of these follow.
- Top of Threemile limestone (Loc. 103). Matrix of coarsely crystalline calcite. Structures include randomly oriented fossil fragments (crinoid remains, bryozoans, gastropods, and ostracodes are recognizable) all coated with a thin layer of finely crystalline or laminated calcite, seemingly algal. Many of the algal incrustations are truly Osagia. The central nucleus of each algal colony is a recrystallized shell fragment.
- Top of Threemile limestone (Loc. 115). Matrix of finely crystalline and finely granular calcite is dominant over enclosed structures. Numerous fossil fragments, most of which are encrusted by a thin calcareous layer probably of algal origin. Relatively few structures resemble Osagia. Nubecularia sparsely represented.
- Upper Havensville shale (Loc. 13). Matrix of coarsely crystalline calcite. Structures include abundant, mostly recrystallized fossil fragments encrusted with thinly laminated calcite. All incrustations are probably algal in origin. Many Osagia-like algae are present, some clearly showing the slender tubular structure of Girvanella. Supposed oölitic structures are possibly algal incrustations around nontabular nuclei.
- Middle of Havensville shale (Loc. 115). Matrix finely granular; sparse crystalline calcite. Fossils moderately abundant; crinoid remains, Nubecularia, ostracodes, and numerous small Osagia. Osagia have nuclei of recrystallized fossil fragments; Nubecularia inclusions in the encrusting laminae. Threadlike structure of Girvanella visible in some Osagia colonies.
- Top of Schroyer limestone (Loc. 36). Matrix of coarsely crystalline calcite. Oölitic structures very abundant, exhibiting concentric laminae of calcite in which individual calcite crystals are radially arranged. Nubecularia, also very abundant, commonly encrusted by algae. Osagia present but not abundant. Nuclei of all algal structures are recrystallized shell fragments, molds of gastropods, or foraminifers.
- Top of Schroyer limestone (Loc. 104). Matrix finely subcrystalline. Structures are mainly oölitic incrustations around recrystallized fossil fragments. Ostracodes, Nubecularia, and crinoid fragments are recognizable. Oölites exhibit laminated calcite with radially arranged crystals in each layer. Osagia present but not abundant.
- Top of Schroyer limestone (Loc. 108). Matrix subgranular. Structures consist of fossils and fossil fragments encrusted by laminated calcite, individual crystals of laminae radially arranged. Nubecularia very common, some not encrusted. Crinoid remains are recognizable. Osagia present but not abundant; central nuclei consist of calcite, which is probably recrystallized fossil fragments.
The fossils that have been found in algal beds are listed below. The diagnostic forms are preceded by an asterisk. Sparse non-typical forms are followed by (s).
|Fossils Observed in Algal
Limestones of the Wreford Limestone
|Epimastopora sp. (s)|
|Tetrataxis sp. (s)|
|Fenestrate and ramose types|
|Chonetes sp. (s)|
|Composita sp. (s)|
|Derbyia sp. (s)|
|Dictyoclostus sp. (s)|
|*Gastropods, tiny molds|
|Septimyalina sp. (s)|
|?Astartella sp. (s|
|Fragmentary remains (s)|
Two types of chert are known in the Threemile and Schroyer members of the Wreford limestone. The most common is compact to slightly porous, noncalcareous, nodular to bedded, and fossiliferous, and is abundant at every Kansas exposure. The color ranges from very light grayish yellow to almost black, and mottling is observed in many specimens. The name flint has been applied to the dark-gray and black varieties; however, in order to avoid confusion, the writer will use the term chert for all colors, with the understanding that darker varieties commonly are referred to as flint. Weathering of the chert produces a light-colored shell ("patina" of some geologists), which is of variable depth. Small nodules are commonly weathered all the way to the center. Continuous beds of the chert are 0.1 foot to 1 foot thick. All the chert beds exhibit conchoidal fracture and are vertically jointed at close intervals.
The configuration of the chert beds presents one of the most interesting and characteristic features of the two limestone members (Pl. 8B,C; 9A,C; 11B; 16B,C, etc.). The average thickness of continuous beds of chert is about 0.2 to 0.3 foot. The upper and lower surfaces are nodular, at many exposures exhibiting elongate vertical projections (Pl. 22A). At several places a higher bed or flattened ellipsoidal nodule may be connected to a lower bed by vertical projections, which thus join the two. Vertical openings or "holes" through the chert layers are observable in most of the beds, and vertical sections through the openings give the appearance of discontinuity in otherwise continuous beds. Circular to elliptical bodies of limestone are commonly seen within the chert in vertical exposures of the latter. These are not isolated nodules but normally deposited limestone lying between two layers of chert that have more than the ordinary number of vertical protuberances, or limestone within very nodular chert beds (Pl. 9B). Some beds are composed of very irregular nodules with knobby surfaces, but nevertheless are persistent laterally (Pl. 22B).
Plate 22--Unusual features of chert beds. A, Upward projection of chert bed in Threemile limestone. Center sec. 13, T. 16 S., R. 10 E., Lyon County (Loc. 54). B, Very nodular bed of chert in upper Threemile limestone. NE sec. 21, T. 4 S., R. 7 E., Marshall County (Loc. 7). C, Calcareous chert lens below chert bed in Threemile limestone. SE sec. 3, T. 17 S., R. 8 E., Morris County (Loc. 68).
The contact of chert beds with the surrounding limestone is sharp in almost all places. The outer edges of chert beds and the surfaces surrounding limestone inclusions are smoothly rounded, broken only by the slight projection of some of the numerous fossils concentrated at the outer edges of the beds.
Laterally, the chert in many beds is observed to be interrupted by limestone, the bed in such places appearing as a layer of large flattened nodules. Where the horizontal extent of limestone masses equals or exceeds the length of the stratigraphically equivalent chert masses, a truly nodular bed of chert exists. Many of the so-called "beds" of chert consist of isolated nodules, which are elliptical (rarely almost circular) in vertical section. Nodular layers of chert generally lie not along bedding planes but completely surrounded by unbroken beds of limestone. At many localities elliptical nodules spaced many feet apart lie at the same stratigraphic level. Almost without exception the nodules are aligned parallel to the bedding. At a very few exposures in Cowley County, cylindrical bodies of chert are found oriented oblique to the bedding. The origin of these nodules is explained below.
Shaly bedded argillaceous limestones of the chert-bearing type ordinarily contain no bedded chert but do bear numerous small spheroidal to irregular nodules throughout. These are generally completely weathered, and invariably they are oriented parallel to the bedding.
Polished surfaces of chert samples show two main types of matrix, (1) a yellowish-brown fairly clear portion and (2) a translucent to nearly opaque whitish portion. Either type may be dominant. Where the first is dominant, the second exists as cloudy inclusions of whitish silica grains. Where the second type dominates, the first exists as minute clear globules enmeshed in what seems to be a lacy or skeletal meshwork of whitish silica. The skeletal meshwork may be smoothly continuous or composed of innumerable minute grains.
Fossils within the chert are almost invariably silicified, although unreplaced crinoidal fragments can be seen here and there. Secondary calcite is observed sparingly as an internal filling in fossil fragments. Large fossils are generally concentrated at the borders and minute ones scattered within the chert. Bryozoan, echinoderm, and brachiopod remains are the most abundant. Numerous rodlike structures, which resemble small productid or echinoid spines, are found in many samples and may be sponge spicules, but this is questionable because few undoubted sponge remains were observed during the investigation.
The fossils are oriented randomly. Only rarely are bedding planes noted in the chert. Almost all the chert exhibits a homogeneous interior without evidence of stratification or uniform orientation of constituent structures. Shrinkage cracks are almost entirely absent in the chert.
Several thin sections were examined with a petrographic microscope. Brief descriptions of these are presented below:
- Upper Threemile limestone (Loc. 2). Matrix of minutely crystalline chalcedony. Fossils sparse, some filled with finely crystalline quartz, some replaced by fibrous chalcedony, which shows a brushlike structure. Small circular areas filled with fibrous chalcedony that has radial structure.
- Upper Threemile limestone (Loc. 68). Matrix of minutely crystalline chalcedony. Fossils common, replaced by chalcedony. Some fossils filled internally by fine crystalline quartz, others by fibrous chalcedony. Numerous circular areas of fibrous chalcedony that shows radial structure.
- Upper Threemile limestone (Loc. 69). Matrix of minutely crystalline chalcedony. Structures include numerous fossil fragments, all replaced by chalcedony, some of which is fibrous. Circular areas of fibrous chalcedony that has radial structure. Some crystalline quartz grains. Dark concentric layering visible on fresh rock parallel to border of nodule. The color pattern has no relationship to texture and was probably caused by weathering.
- Middle Threemile limestone (Loc. 115). Matrix of minutely crystalline and fibrous chalcedony. Fossils replaced by fibrous chalcedony. Crystalline quartz grains and circular areas of radially arranged fibrous chalcedony. Nodules gradational with limestone.
Most fossils in the chert are excellently preserved. Forms are the same as those contained in the surrounding limestone. Bryozoans, brachiopods, echinoderm remains, and trilobite fragments are most common. A few foraminifers were generically identified by examination of polished surfaces. It is unnecessary to tabulate the fauna because of its similarity to that of the limestone. Presumably, all forms to be found in the limestone should be in the chert also.
The second type of chert contains disseminated calcite and is calcareous, brownish gray to dark bluish gray or dark gray, concentrically layered, and sparsely fossiliferous (Pl. 10A,B,C; 11A). Although this kind of chert can be seen in both limestone members of the Wreford formation across the entire state, in the Schroyer limestone member it is most abundant in northern Kansas, whereas in the Threemile limestone member there is a much greater quantity in southern Kansas. In northern Kansas, calcareous chert forms incomplete rims around or nuclei within the more abundant ordinary chert. Hemispherical masses of calcareous chert lie below and above the smaller, elliptical, ordinary chert nodules at localities 68 and 82 (Pl. 22C). Southward from central Chase County the calcareous chert occupies a more and more prominent place in some beds of chert. In northern Butler County both the Threemile and Schroyer limestone include beds that contain nearly equal amounts of both types of chert. In southern Butler County, a 1-foot bed of the calcareous chert lies in the lower Threemile limestone. Two such beds are found over most of Cowley County, a 1-foot bed in the middle Threemile, and a 0.3-foot bed at the base of the algal-molluscan phase in the uppermost part of the member. Locally, irregular nodules of noncalcareous chert are enclosed within the calcareous cherts (Pl. 10C). At some exposures both of these beds are nodular rather than continuously bedded (Pl. 10A, 11A). Calcareous cherts are not generally in as sharp contact with the limestones as are the noncalcareous cherts.
Samples of calcareous chert were sectioned and studied with a petrographic microscope. Typical descriptions are given below.
- Lower Schroyer limestone (Loc. 30). Matrix of mottled finely granular calcite and minutely crystalline chalcedony, some areas of nearly equal admixture of calcite grains and chalcedony. Fossils in calcareous part mostly unreplaced, some of those in chert replaced by fibrous chalcedony. Some radially fibrous chalcedony in the chert.
- Lower Schroyer limestone (Loc. 108). Limestone, calcareous chert, and ordinary chert. Chert matrix of minutely crystalline chalcedony, fossils replaced by crystalline quartz and fibrous chalcedony. Calcareous chert dominantly finely granular calcite and unreplaced fossil fragments, subordinate cryptocrystalline chalcedony and crystalline quartz. Chert-limestone contact sharp, chert-calcareous-chert contact fairly sharp, calcareous-chert-limestone contact gradational.
- Middle Threemile limestone (Loc. 115). Matrix banded, light-colored broad bands dominantly finely granular calcite and some cryptocrystalline chalcedony, dark narrow bands of cryptocrystalline chalcedony and finely granular calcite. Light-colored bands contain abundant fossil fragments, some unreplaced, others replaced by fibrous chalcedony or internally filled by crystalline quartz. Circular areas of fibrous chalcedony in both types of bands. Light-colored bands grade outward to darker ones, which contrast sharply with the next light-colored band. A limonite film is concentrated at the sharp contact, and limonite grains are disseminated in the dark bands.
Fossils in the calcareous chert are the same kinds as those of the adjacent limestone. Crinoid stems and productid spines dominate the sparse assemblage.
Kansas Geological Survey, Geology
Placed on web Feb. 16, 2009; originally published April 1967.
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