The cyclic repetition of rock units similar in lithology, sequence, and thickness, one above the other, in the Lower Permian of Kansas has been well known since Elias' (1937) unique publication. These cyclothemic rocks are thought to have been deposited in shallow epicontinental seas covering a vast flat shelf area of the Nebraska-Kansas-Oklahoma region. Moore (1959) summarized current cyclothem interpretations involving matters such as the "significance of knife-sharp lithologic boundaries."
Without attempting to remark at length on the ultimate causes of cyclothemic sedimentation, several matters including the one quoted above from Moore should be introduced here in the light of what is observable in the Red Eagle cyclothem. This will set the stage for interpretation given in the following pages.
The sharp Glenrock-Bennett contact is, for all practical purposes, a time plane within the Red Eagle cyclothem. Although this contact is chosen for special mention, the Howe-Roca contact is almost as sharp. This does not imply that gradational lithologic boundaries are not common in the Red Eagle cyclothem. It is merely a reminder that boundaries between the members and formations are relatively sharp and that they reflect more sudden widespread changes in depositional conditions; whereas, within the formations and members sedimentary conditions must have changed more gradually, because most lithologic boundaries therein are gradational through an inch or two of column.
Another subject for comment is the proportion of noncalcareous clastic material to calcium carbonate in these rocks. Few clastic rocks in the Red Eagle cyclothem are free of calcareous matter, and so indicate a measure of continuous carbonate deposition. Clastic carbonates complicate the situation. Insoluble residues and stratigraphic data indicate that Red Eagle clastic silicates seem to have come from sources north, east, and south of the outcrop belt.
Paleoecological evidence indicates that the aforementioned sharp lithologic changes could result from abrupt changes of water depth. Current opinion acknowledges that the cause of the cyclothems generally embraces such depth changes over the entire Midcontinent shelf-basin. Whether the changing depths record epeirogenic or eustatic movements is a current problem. Changes in relative supply rates of clastic detritus are presumably allied to the depth changes, which affected other factors and helped to produce the different lithologies.
Because no cyclothem is complete or symmetrical, in the ideal sense of Elias (1937), it is obvious that depth changes were neither uniform in rate nor continuous. Within any cycle, and subservient to the overall deepening or shallowing of the seas and general subsidence of the shelf-basin, there were temporary reversals of direction (or local lags in the rate) of depth change.
The assembled evidence indicates that all sediments of the Red Eagle cyclothem in Kansas were deposited in shallow, flat-bottomed, epicontinental seas far from land. Sedimentary conditions during deposition of the Roca Formation were somewhat similar to those that earlier produced the Johnson Formation. Sedimentary conditions that yielded the Red Eagle Formation were unique within the Red Eagle cyclothem.
Paleoecological interpretations developed in the preceding pages are used in the following attempts to reconstruct the paleosedimentation of the Red Eagle cyclothem.
Deposition of the Johnson Shale
The several aforementioned types of shale and mudstone which make up most of the Johnson Shale show no regularity of habit or stratigraphic position except in the upper few feet of the formation.
The few red shale beds in the middle part of the Johnson Formation at opposite ends of the Red Eagle outcrop belt are difficult to explain. They contain the same clay minerals and structures as the other clearly marine Johnson shale. It seems reasonable to believe that the redbeds are very shallow marine deposits probably derived from red soil. Their position at the northernmost and southernmost ends of the outcrop belt, hence probably closer to the Wolfcampian land, supports the possibility of terrestrial derivation. Conceivably the constituents of the green shale in areas between the redbeds might have lost an original red color by chemical reduction of iron during long transportation toward the central part of the basin. Had they been deposited in the red condition, they would probably still be red, because, as Grim (1951) pointed out, red sediments once deposited tend to stay red.
The origin of red terrestrial source materials requires comment. It is not likely that the red materials were derived from previously existing redbeds because few such beds are known to exist in older Paleozoic rocks to the north, east, and south of the Red Eagle belt of outcrop. The idea of red soil as the source material is favored. This implies the possibility of a warm, moist (Krynine, 1949) regional climate (periodically dry) at least for a short duration near the middle of Johnson time.
Many of the Johnson shale and mudstone units are greenish gray, and almost all are calcareous. The carbonate distribution is not systematic. Many beds contain 10 to 50 percent of calcium carbonate and a few contain less than 10 percent. These proportions vary abruptly from bed to bed. Most of the carbonate material is extremely fine grained. A small amount in the uppermost shale is attributable to calcareous ostracode shells.
Interpretation of the origin of these calcareous shale and mudstone beds requires an estimation of the method of precipitation of the calcium carbonate and of its relation to the preponderant muddy clastics that obscure it. Interpretations of the mechanics of precipitation of calcium carbonate have been reviewed at length by many authors (e.g., Cloud and Barnes, 1948; Emmons, 1928; Revelle and Fairbridge, 1957; Rodgers, 1957; Zeller and Wray, 1956). Two plausible explanations of the origin of the aphanitic calcium carbonate in the Johnson Shale are available: (1) inorganic precipitation resulting from liberation of CO2 from sea water saturated with carbonate, by agitation or rise in temperature (Emmons, 1928; Zeller and Wray, 1956), and (2) organic precipitation as the familiar algal "dust" particles. In either circumstance, precipitation probably would have occurred mainly in the upper levels of the Johnson waters, and the precipitates would have mingled with the silicate clastic materials while descending to the depositional interface.
The preponderance of clay clastic material in the Johnson sediments suggests moderately turbid waters. The paucity of silt probably indicates deposition far from the source, although source rocks may have been sediments containing few coarse clastics. Sedimentary structures in a few of the laminated shale beds suggest accumulation in very shallow water. Some of the lamination and fissility may be ascribed to periodic thin accumulations of organic material (Ingram, 1948, 1953) or to laminar deposits of clay floccules (Keller, 1936). Difficulties of thin-sectioning such shale prevent certification of the textural nature of the laminae. However, in the laminated argillaceous limestone (platestone) of the upper part of the Johnson Shale, the laminae can be studied. Microscopic graded bedding above some platestone laminae (observable in magnified peel prints) seems to be diastemic, and, with traces of brecciation, may record turbulence which occasionally stirred up the accumulated sediments.
Faint scour effects and ripples are present in the platestone near the top of the Johnson Shale. A few indistinct low ripples are also evident in some of the laminated gray shale at the top of the formation. Such features could be caused by wave-induced turbulence.
The carbonized gymnosperm wood and spore assemblage in the upper few feet of Johnson Shale seems to indicate that the climate on land marginal to the sedimentary basin was temperate to cool (Cousminer, 1960, personal communication) as Johnson time drew to a close. Accordingly, it is suggested that the shallow waters of late Johnson time also might have been comparatively cool.
A few thin laminae in upper shale consist of accumulations of marly calcium carbonate. Presumably these reflect brief but rapid falls of algal or inorganically precipitated calcium carbonate particles. Variations of water temperature (an abnormally warm period) or clearing might have caused such vigorous carbonate production. It has been suggested above that the thin accumulations of ostracode shells along some calcareous laminae may be the result of mass mortalities caused by sudden changes of temperature or salinity. If salinity or temperature change was the cause of mortality, it might have been by way of control over inorganic and organic nutrients in the water rather than by direct effects on the perished ostracodes. If the laminae are of particulate algal calcium carbonate, the same sorts of indirect controls over nutrients might have stimulated algal activity temporarily. In any event, the chemistry of the water must have influenced the precipitation of calcium carbonate (organically or inorganically) and the settling of organic colloidal detritus in order to produce laminae in the Johnson mud.
Some of the smooth, delicate ostracodes in the upper Johnson may well be brackish-water forms. If so, they and the few charophytes that are also present would give support to the idea that waters of later Johnson time were less saline (brackish?) than those of the medial part of the Johnson when the redbeds were deposited.
In southern Kansas the uppermost Johnson Shale, which elsewhere has almost no fossils other than ostracodes and plant remains, is more calcareous than usual and has interbedded thin, nodular, aphanitic, argillaceous limestone. The shale beds contain common productid brachiopods and other fossils similar to the Bennett Shale fauna. Thus, in late Johnson time, while conditions hospitable to few animals other than ostracodes seemingly prevailed from central Kansas to Nebraska, southern Kansas seems to have undergone conditions favorable to establishment of a mixed fauna associated with periodic deposition of limy argillaceous, and calcareous, mud. Apparently limestone was deposited in temporarily clear water when the omnipresent calcium carbonate deposition outweighed the silicate clastics. That is, most of the clay clastics seem to have settled out before reaching Cowley County in southern Kansas. Perhaps this reflects temporarily dry climates in, and less erosion of, source areas. Stratigraphic data suggest that the source areas of upper Johnson clastics were located at some distance to the north, east, and south of Kansas.
Altogether, the Johnson facies pattern suggests that the Bourbon Arch area may have been weakly active in late Johnson time, so that it interfered with free passage of silicate clastics from the northeast into possibly deeper water (indicated by the mixed shelly fauna) of the Cowley County area. Silicate clastics from the south were not always sufficient to maintain an excess over carbonates. Thus, the Grand Summit area in Cowley County seems to have been an area in the Cherokee Basin which was sometimes beyond the reach of clastics from low source areas far to the north or northeast, but usually accessible to clastics from the south. This concept is not new. Jewett (1951, p. 127) suggested that during Late Pennsylvanian time sediments from areas to the north and south mingled in the Cherokee Basin. Such conditions seem to have persisted during the late Johnson part of the Early Permian. It may be assumed that much of the Johnson clastic material of Cowley County must have been transported from a landmass to the south and east of Kansas. The fact that the Highway 38 section (closer to the postulated southern source) has more Johnson clastics than the Grand Summit section lends support to this hypothesis.
Plant remains and ostracodes characteristic of the upper Johnson Shale in northern and central Kansas are mingled with the mixed fauna of the Cowley County area. Here the ostracodes are not confined mainly to laminae, as in the north. Perhaps this was the breeding area for the northern ostracodes. In order to attain their present distribution, the plant remains must have drifted all over the late Johnson sea. Landmasses generally to the north, east, and south of the present outcrop could have been the sources of such materials. Presumably their dispersal was assisted by winds.
In summary, Red Eagle cyclothem sedimentation is interpreted to have begun with the accumulation of redbeds in very shallow, turbid, warm, slightly hyperhaline water during the medial part of Johnson time. Deposition continued while the regional climate became cooler and more moist than when the redbeds were deposited. Clastics came from probably low landmasses to the north, east, and south. Tectonically active localities in the Ozark and Ouachita regions may have contributed clastics. The composition and fine texture of the clastic sediments both suggest distant source areas and reworking of earlier Paleozoic beds containing fine clastics. Calcium carbonate was deposited with the clastics. Late in Johnson time, faint upwarps in the area of the Bourbon Arch interfered with movement of clastics from northern and northeastern source areas to the Cherokee Basin. At the same time, waters were slightly deeper in the Cherokee Basin than farther north and a mixed fauna (see Table 5) developed. Land plant fragments, and possibly seaweed, drifted over the entire area during late Johnson time.
Deposition of the Red Eagle Limestone
Glenrock Limestone Member
The sharp basal contact of the Glenrock Limestone marks an abrupt change in depositional conditions. The muddy, sparsely populated Johnson waters cleared suddenly, and so provided the habitat for the prolific benthonic fauna of the Glenrock Limestone. This is inferred from insoluble residues, which showed a decrease of silicate clastics from nearly 90 to less than 10 percent across the Johnson-Glenrock contact.
It has been noted that in some places the lower part of the Glenrock Limestone is nearly void of fusulinids. Their numbers increase upward. In these few places fusulinids may have been late arrivals which slowly multiplied with the passage of time. The Glenrock sediments wherein fusulinids are sparse contain slightly larger amounts of insoluble residue in their matrices than where fusulinids abound. Moreover, the areas of such fusulinid scarcity are in Nebraska and northern Kansas. A suggested explanation is that in early Glenrock time sources of clastics were nearer to the sites of deposition than later in Glenrock time. That is, waters were deepest and shorelines most remote at the end of Glenrock time.
This explanation does not overlook the fact that percentages of insoluble residue may be controlled by relative rates of carbonate versus silicate-clastic deposition. However, upon consideration of the generally uniform character of the Glenrock, there is no evidence of marked change in rate of carbonate deposition during Glenrock time. That is, the slight variations in percentage of insoluble content are thought to be the result of changed rates of silicate clastic supply, and indicate a remote source of clastics.
The Glenrock Limestone is remarkably uniform in thickness (0.2 to 2 feet) and lithology through some 150 miles of outcrop between Bennet, Nebraska, and Allen, Kansas. Unique facies occur locally in the Manhattan and Paxico areas. Although its basal contact is gently undulatory (Pl. 1A), the top is remarkably flat and clearly defined. Thus, at the close of Glenrock deposition the floor of the sea must have been even flatter than at the beginning. During Glenrock time, sediments must have accumulated evenly over this shelf area or the unit would not be so uniform. Similarly, south of Allen, Kansas, where the average thickness of the Glenrock is less, accumulation must have been slower or of shorter duration. Uniform accumulation is easier to explain for lime materials than for silicate clastics. The silicate clastic materials in the Glenrock Limestone are mainly clays, which, because of their slow rate of settling, may well have drifted far from their source in only mildly agitated water. If it is granted that the bulk of the Glenrock Limestone was organically precipitated, and that it was probably derived locally, it seems evident that in order to deposit such a widespread uniform unit the same strikingly uniform depth and limy conditions must have prevailed over a great area of the Midcontinent shelf-basin.
It is clear that a sudden eustatic change of water depth would be effective almost simultaneously over all parts of such a flat area. This would be followed instantaneously by changes in animal growth and sedimentation across the shelf, which would explain the ubiquitous sharp (0.1-inch) contact between the Glenrock Limestone and the overlying Bennett black shale. These phenomena establish the Glenrock-Bennett contact as a distinct time plane. If not, the contact must be a plane which crosses time planes at an incalculably "small oblique angle" (Moore, 1959, p. 51).
The paleoecological evidence, derived principally from the fusulinids and traces of Osagia, suggests that the Glenrock Limestone was deposited in water less than 50 feet deep. Sedimentological evidence seems to support this estimate, because the Glenrock shows no internal traces of scour nor any breaks in depositional continuity. That is, the Glenrock was deposited below effective wave base, which is usually much shallower than 50 feet. In fact, Dietz and Menard (1951 ) have implied that the depth of vigorous abrasion of bottom sediments by wave turbulence is commonly less than 30 feet. This does not suggest that other currents did not influence the Glenrock bottom sediments, because it is likely that weak tidal currents were active.
In many places the shell components of the Glenrock Limestone are randomly oriented. However, the faint orientation of some fossil fragments roughly parallel to bedding is common enough to suggest that they were so aligned by gentle currents sweeping the Glenrock sea bottom. That some brachiopod shells were thus aligned, concave upward, seems a good indication that only gentle currents prevailed. Significantly, a number of delicate unbroken and articulated brachiopod shells are preserved, the fusulinids are essentially undamaged, and there is no internal evidence of scour. Slight textural variations of Glenrock matrix indicate that the currents, although always gentle, varied sporadically in their intensity.
Nevertheless, there is a considerable quantity of broken shell material in the Glenrock Limestone. In view of probabilities indicated by studies of present-day sediments, the breakage and comminution of these materials may be the result of their passage through the masticatory mechanisms or alimentary tracts of burrowing and mud-feeding organisms. Perhaps fish and other suprabenthonic organisms were similarly effective in breaking shells. Another possibility is that the shells were weakened by boring organisms to the point where the gentlest currents were sufficient to shatter them.
Upward of 60 percent of the Glenrock calcium carbonate is of clearly visible shell detritus (especially fusulinids and brachiopods). The remainder, the matrix, consists of aphanitic calcium carbonate. Some of the matrix is undoubtedly fine shell detritus, but much of it is suspected to be recrystallized algal particles and algal needles, affected by intrastratal solutions during diagenesis. [Note: Such aphanitic calcium carbonates have been attributed by some authors to purely physiochemical precipitation. Doubtless, some of it was thus derived, but as Lowenstam (1955) and others have pointed out, in Recent sediments algae are known to deposit aragonitic calcium carbonate needles which formerly would have been considered inorganic.] Whether such algal particles fell from near-surface waters or whether some of them formed in lesser amounts at greater depth is unknown. The latter possibility is mentioned because of the implied clarity of the water, which could have permitted photosynthesis, however slight, at the bottom of the Glenrock sea.
As stated above in the discussion of paleoecology, the traces of Osagia in parts of the Glenrock Limestone do not occur on the fusulinids. The same is true for tiny gastropods. From this it is inferred either that these organisms did not accumulate algal coatings because of their mobile habit, or that the chemistry of their shells or individual microenvironments was unfavorable to algae. The Glenrock fauna suggests nearly normal salinity and pH in clear water.
At the Manhattan and Paxico sections the Glenrock Limestone contains numerous Osagia and conglomeratic fragments of material similar to upper Johnson muddy limestone in the Alma area, where the Glenrock is absent (probably because of nondeposition). The numerous Osagia and the scarcity of fusulinids at Manhattan and Paxico indicate that Glenrock waters in these localities were slightly shallower than to the north or south. The combined lithologic and stratigraphic evidence is best explained by postulating a local rise of the Nemaha Anticline in the Alma area. Thus, the pebbly materials at Manhattan and Paxico could have been eroded from upwarped Johnson deposits (shoals?) near Alma. This suggests that the Alma area was a shoal in Glenrock time, but it does not rule out the possibility that the area was actually elevated slightly above sea level. Neither is the possibility of partial deposition and removal of Glenrock at Alma entirely ruled out, despite the fact that Bennett sediments in adjacent areas contain no recognizable evidence of reworked Glenrock deposits.
The Glenrock Limestone is also absent at the Elmdale and Saffordville sections and in Greenwood County. This is also taken as evidence that gentle uplift (or lag in subsidence rate) of the Nemaha Anticline area at the western end of the Bourbon Arch and of the northern part of the Otto-Beaumont Anticline (Fig. 1) may have controlled the depositional pattern during Glenrock time.
Where the Glenrock Limestone reappears to the south of these structural features, just east of the Otto-Beaumont Anticline (Grand Summit and Highway 38 sections), it is comparatively thin, full of fusulinids, and somewhat similar to its local development at Coffman Ranch in central Kansas. These areas may have subsided slightly less rapidly during Glenrock time than did contiguous areas of Nebraska and northern Kansas; that is, the rate of accumulation of Glenrock sediments was slower in the south than in the north. Whereas the sedimentary pattern of Glenrock Limestone reflects positive tectonic activity in central Kansas, there is no corresponding evidence in Nebraska and northern Kansas, where the uniform physical properties and thickness of the Glenrock Limestone are independent of anticlinal structural trends.
Because the sea bottom was so nearly flat, it can be assumed that when Glenrock waters deepened, shorelines expanded far beyond their Johnson position, so that terrestrial silicate clastics could have settled long before they reached the area of study. This would account for the comparative purity of the Glenrock Limestone. The slightly greater than average amount of Glenrock clastics in southern Kansas (Highway 38 section) indicate comparative closeness of source areas in Oklahoma or uplifts in the source areas, or both. It is believed that, southward in Oklahoma, the GIenrock Limestone must grade to a facies indistinguishable from Johnson Shale or undifferentiated Red Eagle Limestone.
Bennett Shale Member
The basal black shale of the Bennett Member is attributed to a strong reducing (euxinic) environment of deposition, where oxygen was used up by decaying organic matter more rapidly than it could be replaced by diffusion. Lingula and Orbiculoidea in the Bennett basal shale suggest deposition at nearly intertidal depths. Thus, it is evident that the change from Glenrock carbonates to Bennett dark mud attended a very rapid shallowing of the Red Eagle sea from depths of perhaps 40 to 10 feet or less.
The basal Bennett is black because it is charged with finely divided carbonaceous organic residues and traces of pyrite. Hydrofluoric acid residues from the black shale contain small amounts of dark-brown, waxy plant material together with spores. This brown substance also contributes to the dark color. Conditions at, or soon after, the deposition of the organically rich mud must have been such that the organic material (plant and animal) was only partially decomposed because of insufficient oxygen. Therefore it seems likely that this decomposition was effected principally by aerobic bacteria, but anaerobic bacteria, and enzymatic reactions (which can continue even after the death of enzyme-producing organisms), also might have been involved. Sulfides of hydrogen produced during this decay must have added to the toxicity of the environment and contributed, during diagenesis, to the traces of pyrite now present in the shale. Toxicity probably prevented scavenging and mud-eating organisms from dwelling in and working-over the bottom sediments. Thus, the original sedimentary lamination is preserved intact, and much carbonaceous organic material still remains. Some of the organic material is the waxy dark-brown substance mentioned above.
Conodonts and spores, with Orbiculoidea and a few Lingula at the base, are the principal fossils found in the black shale at the base of the Bennett Member. These mainly phosphatic remains were probably preserved because of, rather than in spite of, the toxic conditions, much in the same way that formaldehyde preserves flesh from decay by arresting bacterial activity. Arenaceous foraminifers and ostracodes are very scarce in the black shale.
The abundance of Orbiculoidea (with Lingula) at the base of the Bennett black shale and the relative paucity of these specimens above the base suggest that these animals were able to tolerate the initial Bennett toxicity but perished during a period of mass mortality, after which only a few hardy individuals and their descendants survived. These may have been the only animals actually able to live on the black muddy bottom of the earliest Bennett sea. The numerous conodonts and scarce foraminifers and ostracodes seem to have developed elsewhere than on the toxic bottom. Perhaps the conodont-bearing animals ventured too close to the toxic bottom water and perished. The scarce arenaceous foraminifers and ostracodes were possibly washed into the black mud area by very gentle currents. The organic material contributing to the black color was probably from soft-bodied pelagic, nektonic, or benthonic animals and some plant drifters which fell to the bottom.
It must be noted that even the blackest Bennett shale contains up to 30 percent of calcium carbonate. Certainly the calcareous material did not originate at the muddy bottom; because very little of it is shell material, it must have fallen from near-surface water where algae or agitation could have caused precipitation of calcareous particles.
The bulk of the black shale, and in fact all Bennett shale, is composed of illite and traces of calcium montmorillonite. Such mineralogy seems typical of black shale rich in organic matter (Weaver, 1958). The presence of montmorillonite with illite suggests that the pH of the water was somewhat greater than 7, because montmorillonite is unstable under acid conditions (Carroll, 1959). Perhaps the illite also is favored by such an alkaline environment (Grim, 1951 ).
A number of the black beds are claystone rather than shale. This might indicate essentially uniform conditions of deposition during comparatively lengthy periods in early Bennett time.
The laminations of the shale are ascribed to slight variations in particle size. Temporary diminution of near-surface turbulence may have allowed more coarse particles than normal to fall and to form laminae. On the other hand, slight variations in the amount of organic fall also seem to have contributed to the lamination, for some laminae appear darker. Ingram (1953) also noted that extremely thin organic films contribute to the lamination of shale. Some laminae seem to be concentrations of abnormally fine clay. Various factors might explain the sudden flocculation of fine clay in upper water levels; these include changes of ion concentration, concentration of colloids, and temperature.
The preservation of many of the primary black shale laminae indicates not only the absence of mud-working organisms but also the probable absence of turbulence capable of significant scouring, because no traces of scour or disrupted bedding are present. At first glance this might seem somewhat anomalous, because Orbiculoidea and Lingula indicate water shallow enough to be above normal wave base; that is, they lived within reach of wave-induced turbulence. However, it must be recognized that in shallow water much wave motion becomes translatory in direction and tends to smooth sediments, rather than scour them deeply. Moreover, the soft and sticky black mud may have been sufficient to protect the shells from breakage. [Note: Numerous small, delicate pelecypods seen by the author in sticky black mud beneath only 25 feet of water in Long Island Sound, New York, are mostly unbroken.]
Although the black shale reflects euxinic conditions of deposition, there is no ready explanation of the means by which the Bennett waters could have been restricted. Shallowing could have left shoals between the area of study and the open sea to the south and west. Coincidentally, the Glenrock Limestone is everywhere covered by black or dark gray Bennett Shale, and the two sedimentary units maintain an approximately proportional thickness. This could indicate that the same basin pattern persisted in the region during the accumulation of the two, despite their different lithologies, and that the changes of conditions across the Glenrock-Bennett contact were uniformly widespread.
The fusulinids at the top of the accumulated Glenrock deposits might have been suffocated by the Bennett black mud or poisoned by the increasingly toxic water. Death of the fusulinids was followed immediately by an influx of numerous Orbiculoidea and a few Lingula. It is scarcely possible that the fragmentation of the orbiculoids at the very base of the Bennett could be due to wave action. However, in the overlying black shale fewer orbiculoids are broken, so that wave action, if responsible for breakage, might not have been severe. Lingula in the basal Bennett black shale suggests that these beds probably were deposited at, or not far below, intertidal depths.
In view of the prevailing flatness of the underlying beds, the shallowed sea of earliest Bennett time must have exposed extensive mud flats at times of low tide, especially after prolonged periods of strong winds from one general direction. Exposure would have been most complete in nearshore areas of loosely consolidated deposits, which could have been eroded easily (e.g., by rainfall at low tide) and dispersed by waves. Much of the argillaceous material of the lower Bennett may have been thus derived. As the nearshore material was removed, erosion would become slower and less detritus would be available for transport. If the sea deepened again, the shoreline would move farther away and the supply of detritus to the area of study would diminish even more. Although these remarks emphasize the role of changing depth in governing the proportion of detrital material in the Bennett Shale, uplift or climatic change in distant source areas may have been the major control. However, the sedimentary record seems to indicate increasing depth with the passage of Bennett time, because Bennett black basal shale grades upward into gray shale of the middle part of the Bennett, which contains a variety of shelly fossil remains but very few conodonts. [Note: Gray color is the result of lesser amounts of carbonaceous organic material.] This profuse medial Bennett fauna indicates that waters circulated more freely and had deepened slightly. Although freer circulation could have resulted from tectonic removal of a restrictive barrier, the breaching of a barrier by a eustatic rise of water is preferred because it better explains the deeper water fauna and sediment composition.
Some of the gray shale contains 10 to 20 percent more carbonate and is more coarsely laminated than the black shale. Some of the gray shale laminations seem to be tiny diastems. In central Kansas, the shale gives way to very pure medial Bennett limestone. Apparently the sea shallowed and the rate of clastic supply dwindled, so that the water cleared and carbonate deposition (largely by algae) overwhelmed the few clastics that did arrive.
Where the Glenrock Limestone is missing (e.g., Saffordville and Elmdale), Bennett gray calcareous shale rests on upper Johnson. This demonstrates a local paraconformity representing Glenrock and earliest Bennett time, and suggests uplift (shoals?) in the contiguous Nemaha Anticline and Bourbon Arch areas. Perhaps such elevations restricted the circulation of the early Bennett sea, and so led to the aforementioned euxinic bottom conditions.
Some Bennett gray shale contains traces of glauconite. Although much has been written about the origin of glauconite, few conclusions are definite. Glauconite in the Bennett suggests conditions such as those outlined by Lochman (1957), that is, slow sedimentation, much putrefying organic material, and a large and varied fauna. Lochman also noted that glauconite forms in marine water away from the freshening influence of large rivers, free of coarse detritus originating in crystalline source areas, and under somewhat anaerobic conditions. Cloud (1955) affirmed Lochman's basic requisites and also suggested that glauconite usually forms at depths less than 200 feet and at temperatures greater than 15° C (60° F). Faunal evidence places the deposition of Bennett Shale in water up to 50 feet deep and above 20° C (68° F).
The minor accumulation of medium-bedded limestone in the lower half of the Bennett Member in Nebraska has been described above with the stratigraphy of the Bennett. Limestone constitutes almost all of the Bennett Member, indeed, almost all of the Red Eagle Limestone formation, in southern Kansas and northern Oklahoma. Stratigraphic evidence shows that the carbonate deposition that predominated in the southern regions throughout Bennett time periodically advanced into the clay (shale) regions to the north--that is, the supply of clastics from the north diminished during these times so that tongues of pure limestone were deposited in central Kansas. At the same time, the relatively greater deposition of carbonates was sufficient to make mud in Nebraska extremely calcareous. Because much of the Bennett carbonate is believed to be algal, it might be expected that in clearer water during times of less suspended clay the absolute rate (unit thickness per unit time) of such carbonate deposition would have accelerated considerably. Conversely, comparatively less algal carbonate would accumulate from muddy water. Indeed, the thickness of limestone facies of the Bennett Member is greater than contemporaneous shale facies, perhaps giving a false impression that, on the average, rates of sedimentary accumulation of carbonates were markedly greater than for mud. However, when the differential diagenetic compaction of the two types of sediment is considered, it must be concluded that their rates and original amounts of sediment accumulation were not greatly different over broad areas. The absolute thickness and accumulation rate of all marine sediments are, of course, ultimately controlled by the rate and total amount of regional subsidence of the basin floor, as modified by local upwarpings or lags in rate of subsidence. Southern Kansas, where the Bennett section is slightly thickened and where calcareous facies predominate, appears to have experienced slightly greater total regional subsidence than Nebraska and northern Kansas. This coincides with the generally greater regional thickness of the Council Grove Group in Oklahoma than in Nebraska.
The major physical, chemical, and biological controls of carbonate deposition are well known. Cloud and Barnes (1948), Emmons (1928), and Revelle and Fairbridge (1957) have provided thorough summaries.
Most sea water is saturated with calcium carbonate (Twenhofel, 1932, p. 320). Rodgers (1957) suggested that large-scale carbonate deposition from sea water may require a small degree of oversaturation, and he noted that, with a few special exceptions, marine organisms acquire most of the available calcium carbonate before chemical precipitation can occur. This concept, with the field and laboratory evidence, lends weight to the interpretation that little of the Red Eagle Limestone was precipitated inorganically.
Trask (1937) noted that the percentage of calcium carbonate in shallow-water marine sediments increases with increase of surface-water temperature. He also observed a direct correlation between the calcium carbonate content of bottom sediments and the salinity of overlying surface water. Where salinity is below 34‰ (normal marine salinity is about 36‰), the sediments generally contain less than 10 percent of calcium carbonate. The sediments generally contain more than 50 percent of calcium carbonate where salinity slightly exceeds 36‰. Because nearly all Bennett sediments contain more than 10 percent of calcium carbonate, it seems likely that the salinity of normal marine Bennett water exceeded 35‰. Bennett limestone may have been deposited at slightly higher salinities than the shale, during climatic periods when salinity was higher, and when less detritus was washing into the basin. Faunal and other evidence implies that Bennett waters were warm. Lowenstam's (1959) O18/O16 data might suggest that the upper Bennett shale beds (with Neospirifer) were deposited at temperatures commonly above 22° C (72° F).
The paucity of clay in limestone of the Bennett Member implies clear water. Although fossil shells are not abundant in these limestone beds, the faunal assemblages indicate deposition at generally shallow depths, some less than 10 feet. The bulk of the rock is aphanitic calcareous matrix. At a few localities the matrix displays traces of linear algal calcium carbonate ribbons, a few of which are broken. Some are clear, sparry, recrystallized replacements. It is believed that algae precipitated most of the nondescript aphanitic calcitic matrix material in very fine particulate form. Probably some of this material was brought down primarily as aragonite needles (Lowenstam, 1955). Where aphanitic calcite coincides with crustose or linear algae, the latter may have acted as filter traps for the finer material. It seems that such trapping of sediment might have given rise to calcilutaceous mud banks or shoals resembling those described by Ginsburg and Lowenstam (1958) and Harbaugh (1959, 1960).
The irregular bedding planes of the Bennett limestone are seams having slightly greater than average clay content. Such deposition of clay could have resulted from slight increase of noncarbonate clastic influx from the distant sources, or, as Keller (1936) suggested, it could result from sudden flocculation and settling of clay normally kept in suspension.
Within each limestone bed much of the matrix material contains extremely small fossil fragments, many randomly oriented but many showing moderate alignment parallel to bedding. Rare traces of scour and sorting are noticeable but developed on a very small scale. Some large delicate brachiopods are preserved intact with concave sides up. Other brachiopods, still articulated, are filled with aphanitic calcareous mud.
Johnson (1957) showed that such shells can be buried by scouring at velocities below those necessary to take the shells into suspension. The assembled evidence points toward gentle current activity during deposition of most of the Bennett limestone. Hence, in the absence of shell-shattering turbulence or currents, the finely fragmental condition of most fossil shells is attributed to scavengers, including both mud eaters and borers.
The fossils in the Bennett calcareous shale, although Including the same genera is those in the southern limestone, seem larger, less finely comminuted, and scarcely abraded. They are scattered randomly throughout the shale. They seem to have been broken and transported short distances by currents somewhat stronger than those indicated by the limestone record. This interpretation is supported by the presence in the shale of a greater number of robust shells which supposedly reflect turbulent water. Some of the shells show evidence of boring by other organisms. Perhaps this facilitated their fragmentation. However, interpretation of apparent faunal differences may be slightly prejudiced, because fossils are easier to remove from shale than from limestone.
The regional pattern of Bennett deposition, after the initial black shale, was limestone in the south and shale in the north. Clastics seem to have come mainly from the north and east. Southern Kansas appears to have been beyond the reach of some of the clastic material. However, at the Burbank section the Bennett limestone beds contain considerable amounts of clay detritus, showing the additional effect in Oklahoma of a southern source area. The relative thinness of the Bennett part of the column, together with the interbedding of thin Bennett limestone and shale in Lyon and Greenwood Counties, seems to indicate slightly less subsidence in the Bourbon Arch and Otto-Beaumont Anticline areas and shows that the Bourbon Arch was (as in the Pennsylvanian) an area of "meeting and overlap of sediments from southerly and northerly directions" (Jewett, 1951). In fact, the Bourbon Arch might have been a barrier to free movement of clastics to southern Kansas from source areas to the north and east, thereby permitting the accumulation of the very pure Bennett limestone in Elk and Cowley Counties.
In these counties and in the Eskridge-Coffman Ranch area, the predominant carbonate deposition, once established, continued until the end of Bennett time. However, between these limestone areas the faunal-lithologic record reveals that after accumulation of 1 or 2 feet of Bennett limestone, clay drifted in and muddied the water so that calcareous mud (argillaceous limestone and very calcareous shale) deposition resumed and continued in slightly deeper water through late Bennett time.
At the Eskridge-Coffman Ranch area the lower Bennett limestone facies is not easily explained, for it begins suddenly amid shale on three sides. Nevertheless, it is markedly similar to the widespread platform limestone of southern Kansas. The limestone facies seem to represent a low-relief, shallow, marine bank development whereon upright algae may have trapped finer algal carbonates and other calcareous remains. Such a shoal condition may have been caused by local crustal upwarp. This idea is admittedly conjectural, but the available data permit no acceptable alternative hypotheses. In any event, the arriving clay clastics settled nearby so that clear water prevailed across the shoal. Deposition of algal calcium carbonate seems to have proceeded rapidly under such conditions and thus accounts for the somewhat thicker and nearly pure Bennett limestone accumulation in the Eskridge-Coffman Ranch area.
In this area the upper part of the Bennett consists of about 12 feet of rubbly, indistinctly thin-bedded, richly fossiliferous limestone. Profuse brachiopods, bryozoans, foraminifers, and especially crinoid columnals make up much of the rock. The purity of the limestone is evidence that late Bennett waters in this area must have been nearly clear. Moreover, it is known that crinoids enjoy clear, warm, gently agitated water, and bryozoans good oxygenation; so these conditions must have prevailed in the Eskridge-Coffman Ranch area during late Bennett time.
The crinoidal upper Bennett sediments seem to have been agitated by gentle currents, because many crinoid columnals and brachiopod shells are preserved undamaged and articulated. Severe currents would have shattered, disjointed, and abraded them.
It also should be noted that this crinoidal upper Bennett facies is developed only where the lower part of the Bennett limestone is thick. At the close of Bennett time the Eskridge-Coffman Ranch area was probably under 5 or 10 feet of water, while surrounding waters might have been slightly deeper. That is, the thick lower and middle Bennett limestone may have supported a broad platform perhaps a fathom higher than the neighboring sea floor, and the crinoids grew on the platform.
The crinoidal part of the Bennett contains about 2 or 3 percent more insoluble clay residue than either the osagitic Howe or the underlying Bennett limestone. This is attributed to the fact that the depositional environment had many stalked crinoids and fenestellate and ramose bryozoans which probably served as filter-traps for clay and calcareous algal particles that otherwise would have remained in suspension. The combination of ideal living conditions for calcareous shelled animals and the trapping of extra amounts of clay sediment might explain the thicker-than-normal Bennett limestone accumulation at Eskridge and Coffman Ranch.
All along the present outcrop belt the Bennett sequence above the black shale could have been deposited at water depths between low tide and 10 fathoms. It is postulated that the sea generally deepened after deposition of the basal Bennett black shale (Fig. 5C). During this deepening, the shores of the terrestrial source areas must have retreated considerable distances landward, if due recognition is given to the prevailing flatness of the depositional shelf. The relatively greater number of bryozoan genera, with many genera of brachiopods, in most of the medial shale, combined with stratigraphic evidence, suggests that the shale represents water possibly 50 feet or more in depth; that is, the sea was undoubtedly deeper than that of earliest Bennett time wherein the Orbiculoidea fauna thrived.
In central Kansas, shallower water seems to have produced the sparsely fossiliferous medial limestone beds of the Bennett Member. The uppermost Bennett shale and limestone units record the reestablishment of a mixed fauna (Elias, 1937, p. 410), indicating that toward the close of Bennett time the sea was somewhat deeper again (see Fig. 5). This set the stage for deposition of the Howe Limestone. The percentage of insoluble clastics in the upper part of the Bennett Shale decreases upward, and the Bennett-Howe transition is commonly gradational through less than a foot of column. The indication is that waters shallowed in latest Bennett time while the supply of clastics diminished. Although the relative decrease of clastics could mean lower source areas, it could have resulted from a drier climate in the source area (perhaps attended by increased salinity) or from the development of a submarine barrier. In any event, the change from Bennett to Howe sedimentation was marked by a rapid and great reduction of the supply of clastics. That is, clear shallow water attended the beginning of Howe deposition.
Howe Limestone Member
The Howe Limestone in Nebraska and northern Kansas has been described above as a fairly uniform, aphanitic, sparsely fossiliferous unit. The pelecypods Allorisma and Aviculopinna were found in this limestone in Nebraska. Tiny gastropods and traces of fenestellate bryozoans are randomly present. One coiled and several straight nautiloid cephalopods were found with the osagite at the top of the Howe Limestone in central Kansas.
From Manhattan, Kansas, to the vicinity of the Oklahoma-Kansas border, the Howe is an osagite containing much algal calcium carbonate. The paleontological record indicates that the Howe Limestone corresponds to the molluscan phase of Elias (1937). Lane (1958) presented evidence that similar osagite in the Grenola cyclothem also represents the molluscan phase of Elias' ideal cycle (1937, p. 411). According to Elias, the Howe Limestone would therefore record deposition in sea water 60 to 90 feet deep. However, Lane (1958) concluded that Grenola osagite beds probably formed at depths approximating 60 feet. The paleoecological evidence assembled in this study supports the postulate that the osagitic Howe Limestone accumulated in water much less than 60 (perhaps less than 10) feet deep. Imbrie and others (1959) interpreted Osagia facies as shallow nearshore deposits.
Lane (1958) indicated that algal incrustations throughout the Grenola osagite denote slow accumulation of the fragmental shell nuclei. Lane's (p. 153) reasoning is also valid for Howe osagite. The only significant difference in the occurrences is that the Howe Limestone contains sparse osagitic pellets near the base and these increase in number upward so as to dominate the texture at the top. Obviously, conditions favoring these algae improved with the passage of time. This might mean that the water shallowed from 2 or 3 fathoms to lesser depths wherein the algae flourished. The fact that algae did thrive implies, of course, that ecological factors other than depth and light were also favorable.
In central Kansas the algal coatings on the individual Howe osagite pellets are thicker near the top of the Howe Limestone than below. This is interpreted as additional evidence that water shallowed with the passage of Howe time. The osagitic facies of the Howe Limestone in southern Kansas is relatively thinner than that of the Howe in central Kansas, while the osagite pellets are very similar to those in the middle of the Howe in central Kansas. This suggests that Howe waters were slightly deeper in southern Kansas.
O'Connor and Jewett (1952) referred to the osagitic Howe texture as a "spergenite." Although this term is not used in this report, it is significant to note that Wolfenden (1958)--with reference to Carboniferous limestone in England--postulated a pH of about 8 for precipitation of spergenitic limestone. For this and other reasons it seems that a pH value of 8 might also be applied to the Howe osagitic limestone.
The evidence which shows that Howe waters were probably shallower than Bennett waters also implies, as a corollary, that Howe shorelines were nearer to the area of study than were Bennett shorelines. Yet the Howe Limestone rarely contains more than 10 percent of insoluble clastics (clay), whereas between central Kansas and Bennet, Nebraska, the upper Bennett deposits are quite argillaceous. The scarcity of Howe silicate clastics is therefore taken to indicate that Howe source areas must have worn to low relief by the end of Bennett time, or that the climate might have become warmer and drier so that relatively few clastics were washed to the sea, or both. if the Howe climate was comparatively warm and dry, salinity would have been slightly raised and precipitation of algal calcium carbonate doubtless would have been sufficient to account for the profuse Howe Osagia.
Neither the aphanitic nor osagitic facies of the Howe Limestone is distinctly bedded. The limestone is essentially a massive unit without diastems. This, as well as uniform texture, points to more or less continuous deposition in comparatively quiet water. Conditions of Howe Limestone deposition were probably similar to those on the present Bahama Bank. Cloud and Barnes (1948) stated that conditions similar to present-day limestone deposition on the Bahama Bank "probably existed in epeirogenic seas not receiving quantities of terrigenous sediments such as might be found far from shore, adjacent to land approaching sea level." It has already been pointed out that the Red Eagle sediments, particularly limestone, were deposited upon a great shelf under conditions much like those described in the above quotation. [Note: The Glenrock and Howe Limestones also correspond to the "platform limestones" of Sloss (1947, p. 109); that is, they accumulated in areas "adjacent to positive areas either peneplained, submerged, or too far distant to supply significant quantities of clastics."] However, because deep oceanic depressions surround the Bahama Bank, an exact comparison is not implied. Nonetheless, the great areal extent, flatness, warmth, sediments, shallowness, and subdued but free water circulation of the Bahama Bank correspond to some of the environmental conditions suggested by the faunal assemblage, stratigraphic pattern, and lithology of the Howe Limestone.
Whereas the Glenrock and Bennett regional depositional patterns seem to have been faintly governed by tectonic activity along structures such as the Nemaha Anticline and Bourbon Arch, the distribution and thickness of the Howe Limestone gives no evidence of similar control. In fact, the Howe Limestone seems to reflect a time of tectonic quiescence. It passes unchanged across all known major structural features in eastern Kansas.
The gentle currents mentioned for upper Bennett sedimentation in the Eskridge-Coffman Ranch area can be applied also to the unbedded Howe osagitic facies, wherein individual pellets are unabraded and only vaguely oriented parallel to bedding; so they apparently suffered only mild agitation. An occasional gentle rolling would permit algal calcium carbonate to surround the nuclei. Thus, the moderate sorting, the lack of bedding, and the implicit slow steady accumulation (Lane, 1958) suggest that gentle currents washed about the osagite pellets in Howe time.
A crude idea of the current velocity necessary to move the osagite pellets can be derived from Hjulstrom's (1939, p. 10) diagram. Most pellets are 0.2 to 1.0 millimeter in diameter and hence are of the size range of particles most easily moved by flowing water. According to Hjulstrom, particles in this size range could be moved by current velocities not significantly less than 10 centimeters per second. Obviously, the pellets began as small nuclei which would have required velocities periodically greater than 10 centimeters per second to move them enough to turn them over. Toward the top of the Howe the pellets increase in size and have thicker Osagia coatings. This distribution may signify that current velocity decreased during Howe time, while the water shallowed. Although the origin of the implied currents cannot be determined, the estimated velocities are nevertheless of the order of current velocities known to develop at or near wave base. [Note: Dietz and Menard (1951) pointed out that maximum current velocities at wave base are about 15 or 20 cm/sec.] Moreover, it is almost certain that the Howe bottom was within reach of wave base. It is probable that mild tidal currents in Howe time were available to augment or counteract wave-induced currents and turbulence.
The regional pattern of Howe aphanitic limestone in the north and osagite to the south also requires consideration. The aphanitic facies commonly contains nearly 10 percent of insoluble clay, whereas the osagite contains less than 6 percent and is slightly thinner than the northern counterpart. Greater thickness and greater clastic content in Nebraska suggest that the principal source area of the scarce Howe clay was somewhere to the north and east of Nebraska.
The reason for the facies change from aphanitic to osagitic limestone is not certain. All that can be deduced is that in central and southern Kansas osagitic algal pellets developed on the floor of the Howe sea, indicating that the water was clear enough to transmit the sunlight necessary for benthonic algal photosynthesis. Small amounts of the calcareous material of the osagite pellets and their matrix may have originated as algal "dust" particles, but most of it seems to have been benthonically secreted by calcareous algae. Perhaps Howe waters were shallowest in central Kansas.
Although much of the Howe aphanitic limestone is thought to be consolidated algal particles, this does not exclude the presence of significant calcareous particles produced by near-surface warming or agitation (Emmons, 1928). The particles could have been in the form of aragonite needles (Revelle and Fairbridge, 1957, p. 258) later altered to calcite. Consistent with present-day requirements for carbonate deposition, this interpretation assumes that northern Howe waters were warm, normally saline or slightly hyperhaline, and saturated or slightly oversaturated with calcium carbonate (Pearse and Gunter, 1957, p. 133; Rogers, 1957). If planktonic lime-secreting algae were numerous enough, it is possible that the water could have been turned milky by fine algal carbonate particles (Revelle and Fairbridge, 1957, p. 258). This would interfere with passage of sunlight to the sea bottom, thereby directly or indirectly disfavoring benthonic organisms. This could explain the fact that the calcaphanitic Howe facies contains relatively few fossils and lacks benthonic Osagia.
The preceding comments about algal precipitation of calcareous particles also would imply diurnal production (Revelle and Fairbridge, 1957, p. 258). Consequently, if most of the calcareous material is algal, Howe time probably saw periods of water clear enough for sunlight to reach the bottom of the sea. It seems reasonable, therefore, to assume that a moderate number of benthonic animals and plants did thrive on the Howe sea floor. This is an obvious conclusion for the osagitic Howe facies wherein great numbers of foraminifers and tiny shell materials are nuclei for the algally coated pellets. However, the light color and insoluble residues of the Howe Limestone (and other Red Eagle limestone units) show it to be low in nonshelly organic residue content.
Why, then, is the Howe light colored and why are fossils and organic residue so scarce in the aphanitic Howe facies? A simple explanation is that organic detritus, had it existed, could have been destroyed or particle size reduced by soft-bodied scavengers and mud eaters and by decay in an oxidizing environment. This could also account for the Howe aphanitic texture and lack of bedding. Dapples (1938) and Ginsburg (1957) have drawn attention to the fact that a variety of scavengers, mud eaters, and shell borers are collectively capable of working over prodigious quantities of sediment in short periods of time. They destroy organic residues in sediments, reduce particle size, and efface stratification. Furthermore, Sloss (1947) noted that "light color reflects thorough decay and removal of organic material under shallow circulating waters," and Ginsburg (1957, p. 89) stated that "light color and low organic content suggest an oxidizing environment with pH's near 7.5."
Deposition of the Roca Shale
Rocks within the lower part of the Roca Shale record a pattern of changing environments similar to those of the upper part of the Johnson Shale but in reverse order. However, the Roca lacks the plant remains of the upper Johnson. After Howe deposition calcareous mud was deposited in progressively shallowing water until the redbeds of the medial Roca ended the Red Eagle cyclothem. Thereafter, the sea deepened again during the progressive (transgressive) half of the succeeding Grenola cyclothem (Lane, 1958). Preceding interpretations imply that all Roca (and analogous Johnson) waters were probably much less than 10 feet deep, and shallowest when the redbeds were deposited (see Fig. 5). All Roca sediments, including the redbeds, are judged to be marine, but they contain few fossils.
Roca deposition began with the sudden introduction of a large volume of muddy clastics. The bulk of the lower Roca shale and mudstone is composed of clay, with variable small amounts of silt. The silt particles are subangular to subrounded quartz grains and silt-size, buff-colored clay aggregates. The silt content is slightly greater than in upper Johnson.
Most of the lower Roca is light, faintly greenish-gray, and moderately calcareous shale. Few shale beds are noncalcareous. The Roca Shale contains the same clay minerals as the marine Red Eagle Limestone formation.
The few fossils in the Roca Shale have little diagnostic value. The high clay content of the shale implies turbid water. It is believed that the small amounts of calcium carbonate common in these sediments fell from near-surface water as algal particles or were precipitated because of water agitation or rise in water temperature (Zeller and Wray, 1956). This suggests fairly warm waters saturated with calcium carbonate.
As previously mentioned, Trask (1937) found that commonly less than 5 percent of bottom sediment is carbonate beneath water wherein salinity at the time of deposition is less than 34‰. Although carbonate percentage is known to depend upon relative volumes of supplied silicate clastic and carbonate components, Trask's figure and the other evidence suggest that during much of early Roca time the moderately calcareous (more than 5 percent CaCO3) mud of the lower Roca must have been deposited from water wherein salinity was probably near the modern ocean average of 35 to 36‰. In the same way it may be inferred that the few noncalcareous or slightly calcareous Roca shale beds indicate temporarily freshened water of less than 34‰ salinity.
A few ostracodes and fewer gastropods are almost the only fossils preserved in the Roca Shale. Therefore, Roca waters must have been inhospitable to most shelled animals. Had other fossils been present, at least a few of their hard structures should have survived diagenesis with the ostracodes, and the laminations of the Roca Shale would not be so well preserved.
Some of the lower shale contains up to 40 percent of carbonate, much of which is concentrated in secondary limestone nodules. In Nebraska and northern Kansas, aphanitic limestone is developed in the lower shale. Traces of ostracodes and arenaceous foraminifers have been found in some of these limestone beds. Their purity is evidence that the supply of clastics to the Roca sea occasionally dwindled until the water was clear. Explanations offered for the Howe aphanitic limestone and calcareous algal particles also may apply to the Roca limestone.
An overturned slump block of Roca limestone (Pawnee section) revealed short partition-like prominences on its base (Pl. 6C) which appear to have filled cracks in the top of underlying greenish-gray shale. [Note: The marine origin of the slumped limestone is revealed by traces of arenaceous foraminifers, ostracodes, gastropods, and faint traces of brachiopods at the top. The underlying shale is similar to other known marine shale.] The cracks may be subaerial and provide evidence that the shale accumulated at approximately intertidal depths. Desiccation could have occurred during an unusually prolonged exposure to the air (due to persistent unidirectional winds with exceptionally low tides?). The topmost mud beneath the limestone is only slightly calcareous and could have been deposited under abnormally low salinity conditions such as in extensive intertidal areas directly affected by rainwater.
The limestone records a temporary incursion of the sea and salinity possibly near 36 or 37‰. Accumulation probably took place below, but not far below, normal low-tide level.
The thin red shale of the Roca Shale in Nebraska and Kansas is taken to mark the terminal depositional event of the Red Eagle cyclothem. It is believed to be a very shallow marine deposit accumulated at intertidal depths at a time of maximum regression of the sea, when the shoreline was relatively close to the study area and the climate was moist and warm with periodic dry seasons. The only fossils in the red shale are scarce, tiny gastropod fragments similar to those in the Red Eagle Limestone and in the lower part of the Roca Shale. The possibility that they may be allochthonous pulmonate forms should not be dismissed. In one measured section near Burbank, Oklahoma, the lower Roca is nearly all red. This leads to the interpretation that southern source areas were near the study area during the first half of Roca deposition. That is, a major part of Oklahoma possibly was upwarped at the end of Howe deposition and was the principal source of southern Roca red sediments. The thin redbeds which reach into Nebraska are believed to reflect suddenly increased supply of red clastics from the southern, eastern, and northern sources during times of shallowest water; and they also reflect oxidizing conditions sufficient to maintain the original red color. Whether this would be due to tectonism or marked climatic change in the source areas is unknown. At other times, of cooler drier climate, the rate of supply of red clastics was slower, and they were reduced to a greenish-gray color on their way into and across Kansas.
The red color of these sediments is believed to have come from red soil. Although most of the red material probably washed into the area of study it is likely that some of it blew in. Krumbein (1947) stated that red color is an indicator of the absence of organic material. Insoluble residue studies confirm this for Roca red shale. Some authors have implied that because of their common association with evaporites, redbeds generally reflect highly saline water. In the outcropping Red Eagle cyclothem, there is no such direct evidence that Johnson and Roca redbeds were deposited in highly saline water, but it is possible that weathering could have removed the evidence from the rock record.
Cyclothemic Nature of the Sedimentary Facies
The preceding discussion has shown that deposition of redbeds in very shallow water, with appropriate climatic conditions, in Johnson and Roca time, respectively, began and ended the Red Eagle cyclothem. Some beds between these markers show evidence of deposition in somewhat deeper water. However, presumed depositional depths considerably shallower than Elias' are applied herein to the principal lithofacies and biofacies recognizable in the Red Eagle cyclothem (see Tables 6 and 7). To explain the ecologic conditions suggested by the Red Eagle cyclothem record, maximum depths of deposition need not exceed 60 feet, whereas Elias suggested a maximum of 180 feet. Such a 60-foot figure is admittedly disputable. Perhaps a range between 50 and 100 would be preferred by many paleoecologists. Selection of such a figure is intended only to suggest a reasonable order of magnitude significantly different from Elias' figure and presumably more in harmony with current knowledge of modern sedimentary environments.
Table 6.--Depths of deposition postulated for facies types represented in the Red Eagle cyclothem.
|Red shale facies||high intertidal|
|Green shale facies||low intertidal|
|Black shale facies||0 to 10 feet|
|Osagite limestone facies||0 to 10 feet|
|Aphanitic limestone facies||0 to 10 feet|
|Algal limestone facies||0 to 20 feet|
|Bioclastic limestone facies||10 to 20 feet|
|Conglomeratic bioclastic facies||10 to 20 feet|
|Fusuline limestone facies||10 to 40+ feet|
|Shelly shale-limestone facies||10 to 50+ feet|
Figure 5A duplicates part of a figure shown by Elias (1937, p. 406) to illustrate his interpretation of depths of deposition of rocks now known as the Red Eagle cyclothem. Figure 5B is similar in form and purpose, but the depth curve was derived by applying Elias' interpreted depths of phase deposition (Table 4) to the sequence of his phases recognized by me and listed in Table 5. Figure 5C illustrates the depths of deposition of the Red Eagle cyclothem solely as interpreted in this report.
Figure 5.--Composite section of Red Eagle cyclothem in east-central Kansas and interpreted depths of deposition. A, Depths as diagrammed by Elias (1937, p. 407, fig. c). B, Depths adjusted according to Elias. Depth curve is based on Elias' phases now recognized in the Red Eagle cyclothem and interpreted using Elias' postulated depths of phase deposition. C, Postulated depths of deposition as interpreted in this study.
Summary of Major Facies Types in the Red Eagle Cyclothem
Imbrie and others (1959) and Laporte (1962) recognized and interpreted a number of distinct facies that reoccur vertically and laterally in several parts of the Beattie cyclothem, which is stratigraphically about 100 feet above the Red Eagle cyclothem in the Kansas Permian. Some of these facies types are also present in the Red Eagle and other Wolfcampian cyclothems. The system of facies interpretation introduced by Imbrie and others (1959) differs markedly from, and is in some respects superior to, the system employed by Elias (1937).
Table 7.--Summary of interpreted ecologic conditions during deposition of definitive faunal-lithologic phases in the Red Eagle cyclothem.
|Units of the
Red Eagle cyclothem
|medial red shale||high
|lower greenish-gray shale||low
|Red Eagle Limestone|
|Howe Limestone Member||0-10||4r||>7.5||>70||?>37||oxidizing
|Bennett Shale Member|
|upper gray shale||10-50+||5r||8.0-8.2||>72||35-37||turbid||free|
|lower gray shale||10-50+||5p||8.0-8.2||>70||35-37||turbid||free|
|basal black shale||0-10+||3p||low oxygen||turbid||restricted|
|Glenrock Limestone Member||10-40+||7||8.0-8.2||>70||35-37||oxidizing
|upper greenish-gray shale||low
|medial red shale||high
Figure 6 attempts to portray the major Red Eagle cyclothem facies after the fashion of Imbrie and others (1959, p. 73) and Laporte (1962, p. 526) but incorporates the green shale and red shale facies (phases) of Elias (1937) and the black shale and three other facies types recognized in this study.
Figure 6.--Diagrammatic cross section showing arrangement of Red eagle cyclothem facies along line from Bennet, Nebraska, to Burbank, Oklahoma. Diagram corresponds to correlated columnar sections in Figure 2. A large PDF version of this figure is available.
Red Shale Facies
These rocks are the almost barren red shale defined by Elias (1937) as marking upper and lower boundaries of Kansas Permian cyclothems. Elias postulated that they were deposited above the littoral zone, but it is proposed here that although climatic influences causing red soil on land were most responsible for their red color, they were deposited at shallow, possibly intertidal, depths in slightly hyperhaline water resulting from warm, periodically dry climate. In the Red Eagle cyclothem these facies occur near the middle of the Johnson and Roca Shales.
Green Shale Facies
These facies are the sorts of greenish-gray and gray calcareous shale that, in the upper part of the Johnson Formation, contain ostracodes, plant remains, and a few charophytes. Similar shale in the lower Roca is nearly barren. A few random argillaceous limestone layers, some platy, others nodular, occur in these facies. The green shale facies are interpreted as the records of mainly intertidal (rarely deeper) deposition in slightly brackish water, possibly under moist climate. Elias (1937) viewed this "phase" as representing deposition at depths between 0 and 30 feet.
Black Shale Facies
Fresh exposures of this facies are characteristically dark gray to nearly black, and they almost invariably contain numerous Orbiculoidea and conodonts and rare Lingula. The black shale facies is interpreted as the record of deposition just below mean low-tide level within a poorly oxygenated basin having restricted internal circulation and lacking free communication with the open sea. Commonly the black shale facies grades vertically to lighter gray shale belonging to shelly facies. The black shale weathers to light brownish gray. In the Red Eagle cyclothem it occurs at the base of the Bennett Shale.
Fusuline Limestone Facies
These are essentially the same as the fusuline facies recognized by Imbrie and others (1959) and Laporte (1962), but they do not contain chert. They are equivalent to rocks of Elias' (1937) fusulinid phase, which he believed were deposited at depths between 160 and 180 feet. The upper part of the Glenrock Limestone typifies this facies in the Red Eagle cyclothem. At some localities the fusuline limestone facies grade downward to bioclastic limestone facies (containing few or no fusulinids) in the lower part of the Glenrock. Although numerous fusulinid foraminifers dominate the fusuline limestone facies, Osagia remains are also present in significant quantities. Laporte's (1962, p. 541) view that these facies were deposited at depths probably not greater than 50 feet is supported in this study.
Bioclastic Limestone Facies
In the Red Eagle cyclothem the lower part of the Glenrock Limestone, especially in Nebraska and northern Kansas, is bioclastic limestone facies. Finely broken carbonate shell materials and Osagia remains, much as described by Imbrie and others (1959, p. 72) and Laporte (1962), dominate the facies. In the Glenrock Limestone the bioclastic facies in the lower part grades upward to fusuline limestone facies, as in the Cottonwood Limestone (Laporte, 1962, p. 527). The bioclastic facies appears to have accumulated in freely circulating, normally saline warm water at depths slightly shallower than for fusuline limestone facies deposition.
Conglomeratic-Bioclastic Limestone Facies
Rocks of this facies have matrices similar to bioclastic limestone facies (with numerous Osagia), but the matrices are hidden amid numerous pebbles and granules of aphanitic, slightly argillaceous, soft limestone or highly calcareous mudstone. The conglomeratic-bioclastic facies in the Glenrock Limestone is best developed at Manhattan, Kansas, where the pebbles are interpreted as reworked upper Johnson deposits eroded from shoals near Alma, Kansas.
Shelly Shale-Limestone Facies
The thinly interbedded, shelly, fossiliferous calcareous shale and nodular limestone of the upper part of the Johnson Shale in southern Kansas is the best example of shelly facies in the Red Eagle cyclothem. Much of Imbrie and others' (1959) description of Beattie shelly facies could be applied equally well to Johnson shelly facies.
The shaly parts of the Bennett Shale Member lack thinly interbedded limestone but contain a shelly fauna of fewer unbroken shells than the Johnson shelly facies. Like the shelly facies of the Cottonwood Limestone (Laporte, 1962, p. 540), the Bennett shelly facies correspond to Elias' mixed phase and contain some fossils of his brachiopod and molluscan phases. Bennett shelly facies also contain sparse fragments of Orbiculoidea, which are numerous in, and characteristic of, the black shale facies.
Deposition of some shelly facies might have occurred in water slightly deeper than for fusuline limestone or bioclastic facies. This viewpoint resembles that of Laporte (1962, p. 540).
Algal Limestone Facies
Rocks of this facies commonly contain less than 5 percent of insoluble residue and they make up the major part of Bennett limestone. The common aphanitic calcareous matrices contain comparatively few fossil genera, most of which (including rare Orbiculoidea fragments and fusulinids) are represented in shelly facies. The few horn corals in the Red Eagle cyclothem are mostly confined to the algal limestone facies. Sparse Osagia beans and fragments are also present. Much of the aphanitic carbonate is judged to be of algal origin. In some parts of this facies, crustose algal remains (Anchodium?) contribute up to 15 percent of the rock. Imbrie and others (1959) chose to identify the latter rocks separately as "Anchodium? facies." The algal limestone facies probably accumulated in warm water slightly shallower than that in which fusuline or shelly facies came to rest.
Osagite Limestone Facies
Pelletoid, oolitic, or pseudo-oolitic limestone characterizes this facies. The pellets or ooliths consist of calcareous nuclei such as tiny foraminifers, mollusks, and fragments thereof, surrounded by concentrically layered coatings of algal calcium carbonate (Osagia). Most pellets are subspherical, but many are bean or sausage shaped, depending mainly on the shape of the nucleus. The upper parts of some limestone beds of the osagite limestone facies contain up to 70 percent of pellets in a microcrystalline matrix. These textures have been called osagites. They grade downward to rock that contains fewer irregularly shaped Osagia bodies than the osagites proper. Bun-shaped, concentrically laminated, calcareous algal mounds (Pl. 6A) are associated with osagite at one locality. South of Manhattan, Kansas, the Howe Limestone is typical of the osagite limestone facies in the Red Eagle cyclothem. This is similar to the Type a Osagia facies defined by Imbrie and others (1959, p. 72). The facies is judged to represent warm, almost hyperhaline water and deposition at depths only a few feet below low-tide level, under turbulence and circulation conditions as suggested by Imbrie and others (1959).
Aphanitic Limestone Facies
Howe Limestone from Manhattan, Kansas, northward typifies the aphanitic limestone facies. The Howe is light-gray, uniform, aphanitic limestone commonly containing from 5 to 15 percent of insoluble residue (mostly clay) and few fossils. The limestone weathers to shades of rusty and yellowish light brown and is commonly vuggy. Much of the aphanitic calcium carbonate is thought to be of algal origin. The facies is believed to be the record of deposition in slightly hyperhaline warm water that was somewhat restricted from free interchange with open sea water. Depths of deposition were about the same as for osagite limestone facies.
Kansas Geological Survey, Geology
Placed on web Jan. 4, 2007; originally published Dec. 1963.
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