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Grenola Limestone Environment of Deposition

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Cyclic Significance of Grenola Limestone

Definition of the Cycle

Jewett (1933) published the first paper indicating the cyclic nature of Lower Permian rocks in Kansas. He called attention to the repetition of regular sorts of limestone and shale successions but made very little mention of the cyclic significance of faunal assemblages in the deposits.

After field work in the early 30's, Elias (1937) published a much more detailed analysis of the Lower Permian rocks (called "Big Blue Series" by Elias). The cycles were divided into parts termed phases, which he distinguished mainly by the kinds of fossils in the beds. Table 9 illustrates Elias' conception of the phases and depth distribution of various groups of fossils in the Lower Permian rocks.

Table 9--Idealized Big Blue transgressive hemicycle in north-central Kansas. The regressive hemicycle is the same succession, in reverse order. (Modified from Elias, 1937.)

No.PhaseCorresponding typical lithologyDepth
7.Fusulinid phaseLimestone, flint, calcareous shale.160-180'
6p.Brachiopod phase 110-160'
5p.Mixed phaseMassive mudstone, shaly limestone.90-110'
4p.Molluscan phaseClayey shale, mudstone to bedded limestone.60-90'
3p.Lingula phaseSandy, varved (?), rarely clayey shale.30-60'
2p.Green shaleClayey to fine sandy shale, rarely consolidated.0-30'
1.Red shale 0

Although these Lower Permian cycles may be regarded as a continuation of the Pennsylvanian cyclothems, they differ in several respects. Sandstone and coal are absent from most of the Lower Permian cycles, but red shale and green shale commonly are present.

Grenola Cyclothem

The Grenola cyclothem may arbitrarily be defined as beginning at the base of unfossiliferous red and green shale in the Roca formation, next below the Grenola. Elias regarded the red shale as subaereal in origin and the green shale as deposited in shallowest marine water (depths ranging to 30 feet). Krynine (1949), on information provided by Swineford, stated that red beds of the Kansas Permian are primary detrital marine deposits. The fine-grained even texture of these shales and their relatively constant thickness and lateral persistence point to marine origin. Whether these shales were deposited in a submarine or subaereal environment, field evidence proves that known marine nonred sediments in Kansas interfinger southward with coarser red deposits in Oklahoma.

Green shale in the Roca formation, which is next above the red shale, may owe its color to reduction of ferric to ferrous iron, or the color may be due to large quantities of the green chlorite group of minerals (Swineford, Ada, personal communication).

Next below red shale in the Roca is brown shale containing a microfauna represented by Cavellina, Tetrataxis, Hollinella, and ?productids (spines). This assemblage is found also in the Legion Shale member, associated with a molluscan (phase 4) fauna, and it probably indicates that nearshore marine conditions prevailed during deposition of both the Legion member and this shale of the Roca.

An upper brown shale, next above red and green shale, contains very sparse charophytes and a few pistachio-green glauconite pellets, which indicate that marine conditions obtained. Charophytes live today in fresh or brackish water, but during the Permian they may have been washed into shallow marine waters and preserved thus, or they may have been true marine forms. The charophytes may be diagnostic of Elias' Lingula (3) phase, because the brown shale in which they occur is in the correct stratigraphic position for phase 3. No inarticulate brachiopods were found in the charophyte-bearing shale, however.

The Sallyards Limestone contains a predominantly molluscan fauna, consisting mostly of pectinoid pelecypods, which denote the molluscan (4) phase. The Sallyards member may be divided into two distince parts, based on the contained organic fragments. In the lower, shaly limestones of the member, whole pelecypod valves may be found, especially on bedding surfaces, whereas the upper strata consist of osagite limestone containing no megafossils. In the upper beds, small shell particles, which are nuclei for ?algae and Ammovertella, could be derived from pelecypods, gastropods, brachiopods, or ostracodes, and are evidence for a megafauna. Because pectinoid pelecypods are the fossils most commonly found in beds next above and below the upper Sallyards, these shell particles probably are pelecypod fragments. Further evidence that the osagite limestone should represent the molluscan phase (4) is the fact that several fragmentary shells observed have a ribbed surface, resembling a pectinoid fragment, and the fact that small gastropods are common. Therefore, the upper Sallyards is regarded as denoting the molluscan phase of the cyclothem.

As mentioned above, the narrow range in size of the fine organic debris in the osagite limestones seems to indicate sorting by currents or waves. Above the red shale in the Roca, green shale (phase 2), the Lingula (3), and molluscan (4) phases have been noted in that order, and denote part of a transgressive hemicycle. Because there is no apparent break between the lower pectinoid and upper osagite limestones of the Sallyards, it seems logical to assume that the osagite is a continuation of this transgressive condition and was deposited in an environment slightly farther off shore, or in deeper water, than were the lower pectinoid limestones.

Certain requirements must be fulfilled by any explanation of the origin of an osagite limestone, such as the upper Sallyards; (1) a mechanism must be available to produce small shell fragments 1 to 3 mm in length, (2) this or some other mechanism must sort these small particles from larger material and deposit them separately, (3) environmental conditions must be such that algae will flourish and precipitate calcium carbonate around these small shell fragments, and (4) the algae must be able to grow on all sides of the particles. Assuming that wave or current action, or both, is the mechanism that fulfills requirements 1 and 2, it is necessary to distinguish the significant elements of present wave and current action.

Powers and Kinsman (1954), working with cores from the Atlantic continental shelf, have distinguished two zones in the sediments of their cores. An upper (traction) zone is characterized by abundant small organic particles, more than 95 percent of which are 2.0 mm or less in size. This traction zone, providing that algal incrustations developed around the shell particles, could closely resemble an osagite upon lithification. A lower (accumulation) zone contains ". . . a coarser, more abundant, and larger macrofauna, and scarcer microfauna. . . ." Although size ranges of the Recent organic remains closely resemble the size ranges of fossils in the upper and lower Sallyards, Powers and Kinsman's core sediments were gravel and coarse to fine sand, rather than a fine calcium carbonate mud. They postulate that "swell can easily account for the vertical sorting of the sediments. . . ." If vertical sorting is postulated as the mode of occurrence of the osagite limestone, then shell material forming an osagite is broken up, sorted, and then incrusted with algae without appreciable transportation of the shell fragments. If vertical sorting did not take place, the shells must have been broken up in one area, and the small particles suspended or rolled along the botton, accumulating on another part of the sea floor.

In present oceans, maximum breakage of large shells into small fragments takes place where maximum agitation of bottom sediments occurs. According to Garrels (1951), maximum quantities of sediment are stirred up at the plunge point (point where the wave crests begin to break over), as shown in Figure 5.

Fig. 5--Relationship between wave energy and amount of bottom material stirred up. Dashed line, amount of stirred up material; solid line, wave energy. (Garrels, 1951).

Amount of stirred up energy is a narrow peak, closer to shore than the maximum wave energy, which grows slowly and levels as distance from shore increases.

Assuming that shell material is broken up at or near the plunge point, then small shell particles would be transported and gradually carried out to slightly deeper water where the fragments could accumulate under quieter conditions. Algae probably grew on the small shell fragments after sorting, and their presence indicates that conditions were favorable for plant growth. This means that the osagite probably formed at a depth to which light rays could penetrate and that carbon dioxide concentration, pH, salinity, temperature, and amounts of dissolved phosphates and nitrates must have been favorable for plant life (Rankama and Sahama, 1950).

Illing (1954) has shown that calcareous incrusting algae in the Bahamas are most abundant at depths of about 60 feet, for on the Banks, which are less than 60 feet deep, incrusting algae average only 1 percent of the contents of bottom samples, but at the outer edges of the Banks, approximately 60 feet deep, calcareous algae make up 39 and 27 percent of bottom samples in two different areas. If the same order of depth can be assumed for the growth of algal incrustations in osagite, the small shell particles that serve as nuclei may have accumulated at depths approximating 60 feet. Gentle wave or current action, easily developed at a depth of 60 feet, is necessary in that the shell particles must have been turned over from time to time to allow algal growth on all sides. The depth of disturbance of sand on present sea beaches is rarely more than 20 cm (King, 1951). King says:

Assuming a maximum wave height of 20 feet, which is rare close inshore, the corresponding depth of disturbance would be about 20 centimeters or about 8 inches. A more likely depth of disturbance is probably of the order of 6 inches and the average under normal calm conditions is very much less, being about 1 or 2 inches or less. In deep water the depth of disturbance is probably very much reduced, because of the decrease in turbulence of the water as the depth increases.

Heavy wave currents produced by storms would agitate particles down to a depth of 6 inches or less, according to King. Osagite limestone is 2 to 3 feet thick in the Sallyards member, and because algal incrustations are evenly distributed throughout the osagite from top to bottom, the shell fragments must have accumulated slowly, for once an incrusted particle was buried under 6 inches of material, it probably could not be brought back to the surface by wave agitation, and the algae would die. Therefore, the entire 2 to 3 feet of small shell fragments could not have been deposited at or nearly at the same time, but must have accumulated slowly.

From these considerations the following tentative conclusions can be drawn with relation to the origin of osagite beds:

  1. Fragments constituting osagite beds were broken by wave or current action, possibly at the plunge point, and either vertically or laterally sorted.
  2. Light penetration and other environmental conditions must have been favorable for plant growth at the depth of accumulation of the osagite material.
  3. By comparison with the Bahama Banks, the osagite beds probably formed at depths approximating 60 feet.
  4. Algal incrustations throughout the osagite denote slow accumulation of the fragmental shell nuclei.

The Legion Shale member is next above the Sallyards Limestone. Shale beds in the Legion have no megafossils but contain an abundant ostracode assemblage of Cavellina, Hollinella, and Knoxina, and interbedded thin limestone strata contain Aviculopecten, Septimyalina, and Juresania, which denote a molluscan (4) phase. Hence, microfossils in the shale probably represent a micro-equivalent of the molluscan phase indicated by the limestones.

The Burr Limestone member, next above the Legion Shale, contains almost a duplication of limestone groups and fossil assemblages found in the Sallyards. The lower Burr is a pectinoid limestone, like the lower part of the Sallyards member, and the upper Burr strata are osagite limestone, generally thicker than the osagite portion of the Sallyards.

Because shale occurs next below the Sallyards and Burr members, and the limestone groups in both members are similar and in the same relative stratigraphic position, the Burr limestones probably denote a return to environmental conditions like those that affected deposition of the Sallyards. The Legion Shale between these limestones indicates an influx of fine argillaceous material into the area, perhaps due to slight shallowing of the sea. Several thin pectinoid limestones interbedded with the shale indicate that environmental conditions surely were not much modified.

The Salem Point Shale member contains a microassemblage of sparse Cavellina and charophytes and a megafauna of pectinoid mollusks, in thin intercalated limestones, which represent phase 4 of the cycle. In the Legion Shale, Cavellina, Hollinella, and Knoxina were deduced to be a microequivalent of the molluscan phase, and charophytes in the upper part of the Roca Shale were regarded as a microequivalent of the Lingula phase; therefore, the Salem Point member should represent both phases "3 and 4. Charophytes present in the Salem Point perhaps indicate a slight regression or shallowing.

Fusulinid limestone is next above the Salem Point member, hence, the first beds of the Neva member denote Elias' fusulinid (7) phase; phases 5 and 6 seem to be missing. The lowermost limestone of the Neva also contains ramose bryozoans, echinoid spines, and small brachiopod fragments, however, indicating an apparent mixing of fossils diagnostic of phase 6 and phase 7.

The Neva member contains numerous brachiopods, bryozoans, and fusulinids, but pelecypods, common in lower members, are rare or absent. Neva limestone and shale beds are not constant in thickness or lithology from exposure to exposure, denoting that at times deposition of limestone and of shale proceeded simultaneously in different parts of the area. Seemingly some rapid alternation of phases 6 and 7 took place, because thin molluscoid- and fusulinid-bearing rocks are intercalated with molluscoid-bearing beds, and all fusulinid limestones contain other fossil remains.

Total thickness of Neva limestone beds increases southward, possibly indicating that more calcium carbonate sediments were being deposited there, but an increase in amount of argillaceous material northward might mask disseminated carbonate deposition that could be uniform over the area studied.

Every chert-bearing limestone in the Neva also contains fusulinids, and the thickness of chert- and fusulinid-bearing limestone increases southward, which seems to indicate that chert is characteristic of phase 7. The validity of this statement depends on proof that the chert is primary. A similar lateral increase in thickness of chert is found in the Foraker Limestone, two limestone formations below the Grenola (Moore and others, 1951), where both the Hughes Creek Shale member and the Americus Limestone member become cherty in the southern part of Kansas, and contain abundant robust fusulinids both in chert nodules and in limestone. This close stratigraphic recurrence of the same lateral change is an argument for primary, or perhaps penecontemporaneous, deposition of the chert. No evidence for primary or secondary deposition of the chert could be deduced from study of bedding planes in and around chert nodules, nor from examination of arrangement and composition of siliceous and carbonate fossils in the chert.

The upper limestone bed of the Neva member at locality 1 exhibits the mixed (5) phase of the cycle; the bed contains Allorisma, Aviculopinna, and calcareous brachiopods. Recurrence of small Osagia-like forms and gastropods at locality 2 in the upper Neva also indicates a slightly regressive phase, just before the beginning of Eskridge Shale deposition.

Microfossils in the Neva differ from those in lower members; the predominant forms are Climacammina, Bairdia, Tetrataxis, and Glyphostomella, rather than an ostracodal assemblage of Cavellina, Hollinella, and Knoxina. The Neva foraminifers are found in shales characterized by a molluscoid-fusulinid fauna, and this microassemblage is peculiar to phases 6 and 7 in the Grenola in the area studied. Lateral and stratigraphic studies of wider extent are necessary to determine whether this group of fossils is generally associated with deeper water phases of the cycle.

In summary, the Grenola Limestone in the type area exhibits a generally transgressive trend, dominated by a lower molluscan phase and an upper molluscoid-fusulinid phase. The molluscan (4) phase is represented by osagite and pectinoid limestone in the Sallyards and Burr members, and by pectinoid limestone and shale containing Cavellina, Hollinella, and Knoxina in the Legion member. The Neva Limestone contains predominantly molluscoid and fusulinid limestones, phase 6 or phases 6 and 7 being represented in most of the limestone and shale beds. A microassemblage of Climacammina, Bairdia, and Glyphostomella is also judged to represent phases 6 and 7.

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Kansas Geological Survey, Geology
Placed on web June 5, 2007; originally published June 1958.
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