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Stratigraphy of the Carlile Shale (Upper Cretaceous) in Kansas

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Depositional Environment

General Statement

Dacqué (1915, p. 423) has noted that during Cretaceous time the Northern Hemisphere included two climatic provinces, a northern, or boreal, and a southern, or Mediterranean. Sediments of the boreal province are characterized by belemnites, the pelecypod Aucella, and several ammonite genera that are foreign to the Mediterranean region. Large foraminifers, corals, thick-shelled reef-building rudists, and nerineids and actaeonellids (thick-shelled gastropods) are characteristic of the Mediterranean belt and lacking in the boreal region. Dacqué (1915) interpreted the enormous quantity of limestone that extends from Central America eastward to the East Indies as reflecting warm-water conditions, in contrast to cold water of boreal regions. Fossils of the kind restricted to the Mediterranean belt are wholly lacking in the Kansas Carlile, and the only truly boreal elements (belemnites) are not abundant. The sea in Kansas occupied an area between regions where the two climatic provinces were developed typically. Distribution of sediments and fossils is proof that during Carlile deposition the sea in Kansas was connected with waters of both boreal and Mediterranean provinces.

Concerning the Western Interior Cretaceous sea, Reeside (1957, p. 505) wrote, "Two biotic realms contributed to the life in this sea--northern temperate, perhaps cold temperate, and southern warm, perhaps tropical." In addition to nektonic or planktonic forms, such as ammonites and foraminifers, respectively, four invertebrate species found in the Kansas Carlile are known also in the Eagle Ford Group of Texas. On the other hand, four species of Inoceramus in the Carlile are known also in Europe or northern Asia, and only one of these has been reported in Texas. The conclusion may be drawn that elements of the fauna common to Europe and Kansas migrated across an Arctic route.

Explicit data concerning depth, temperature, and salinity are difficult to gather for a sea as ancient as that represented by the Carlile fauna. None of the species is extant, and, except for Foraminifera, most of the genera are extinct, hence conclusions regarding paleoecology can be based only to a slight extent on comparison with ecologic analogues of modern seas.

Depth--The paucity of structural features characteristic of a turbulent environment, the fragility of many well-preserved bottom-dwelling invertebrates, the preservation of paired pelecypod valves (Pl. 27A), the unworn condition of most fossils, and the preservation of thin laminae in some Carlile beds suggest deposition in quiet water, generally below the depth of frequent vigorous wave action. Common features of a shallow-water environment, such as prominent crossbedding, ripple marks, intraformational conglomerates, and tetrapod foot prints, are rare or lacking in the Carlile sediments of Kansas.

Plate 27--Carlile fossils. A, Paired valves of Inoceramus from middle part of Fairport, sec. 22, T. 15 S., R. 20 W., Ellis County (Loc. 17). B, Fish-tooth conglomerate from upper part of Blue Hill, sec. 18, T. 2 S., R. 6 W., Jewell County (Loc. 40).

Two black and white photos; top shows two valves of Inoceramus in place; second shows large number of fish teeth embedded in rock.

In the middle and upper parts of the Fairport Member are numerous thin discontinuous beds of hard limestone composed chiefly of Inoceramus prisms. Most of the limestone beds include fragments of Inoceramus, and some contain an abundance of comminuted shell debris, including fragments of barnacles and oysters, in addition to Inoceramus (Pl. 10B, C). Such lenses are the consequence of bottom disturbance by deep-reaching waves during occasional storms. Imbrication of large shell fragments of I. cuvieri and presence of smaller shell fragments that are oriented both parallel and oblique to bedding can be interpreted as effects of occasional destructive wave action. Oysters attached to the outside of both valves of I. cuvieri prove that the large shells were overturned at times, for these animals lived on the sea floor with both valves parallel to the bottom, as shown below. Layers of marly chalk in the Fairport Member contain, in greater abundance, the same species as intervening chalky shales, and contain also a large quantity of Inoceramus fragments and prisms. The suggestion is made here that waves occasionally stirred the limy mud of the sea floor, setting finer material in suspension, while larger particles, such as fossils and fossil fragments, were concentrated into thin layers that later became marly chalks. Modified, the same interpretation explains the chalky limestone layers in the lower part of the Fairport.

Evidence of wave activity in sediments of the Blue Hill Member is not nearly so abundant, but in a few places the effects of wave or current activity are obvious. At locality 18, valves of the pelecypod Yoldia are concentrated in thin lenses and many of the valves are parallel to one another. In many of the lenses, however, the valves are paired, so it seems that current or wave action was not strong. In a very thin and discontinuous bed of fish-tooth conglomerate at locality 40 (Pl. 27B), many teeth are in parallel alignment and most are fragmentary. A thin sandstone bed in the upper part of the Blue Hill at locality 15 is gently cross laminated; calcareous siltstone in the upper part of the Blue Hill in section 3, T. 10 S., R. 13 W., Osborne County, is gently cross laminated and has small oscillation ripple marks; and calcareous siltstone in the upper part of the Blue Hill at locality 31 is gently cross laminated. At locality 47, Trego County, the Codell contains a few angular clay pellets, which can be interpreted as indication of slight local turbulence. Elsewhere, the Codell Member contains rounded bone and tooth fragments, and the hard brown limestone nodules at the top of the member at locality 22 contain abundant shell fragments that suggest considerable agitation of the sea bottom.

Various authors have summarized the evidence for maximum depth of vigorous wave activity. Weller (1960, p. 356) stated that final deposition of sediment on open coast most likely takes place at depths not much greater than 300 feet. Dunbar and Rodgers (1957, p. 130) gave a similar figure for depth of wave action during heavy storms in the neritic zone. These depths relate to unprotected seas, however, not to nearly landlocked bodies of water. Irregularly distributed shoal areas in the Late Cretaceous sea of the Western Interior, such as those indicated by ripple-marked and cross bedded Codell sandstone of eastern Colorado and by ripple-marked and cross laminated calcareous siltstone in the upper part of the Blue Hill of Osborne County, Kansas, would limit the size of waves and thus would impose a narrower limit on the depth to which wave action could be effective. During Carlile deposition the maximum depth of the sea in Kansas was probably much less than 300 feet.

The absence of remains of other than planktonic algae may signify depths greater than those at which light penetration would have been sufficient to promote algal growth, but the sea in Kansas probably contained enough suspended matter to prohibit a categorical statement as to specific depths that might be indicated by lack of benthonic algae. Bathymetric ranges of extant genera of Carlile invertebrates are much too wide to permit specific depth interpretations.

Temperature--Sverdrup and others (1942, p. 853) have noted that the rate of calcium carbonate precipitation by marine animals is governed chiefly by temperature. Animals that build shells of calcium carbonate are more abundant in warm than in cold water, and the shells of warm-water animals are more strongly constructed than shells of the colder-water animals (Sverdrup and others, 1942, p. 853). The large percentage of carbonate in the Fairport Member and the fact that it is chiefly organic suggest a warm, rather than cool or cold, environment of deposition. This conclusion is borne out by the enormous number of calcium carbonate shells in the Fairport and the large size to which some of the animals grew, especially benthonic forms such as Inoceramus.

Chemistry--The number of benthonic invertebrates in the Kansas Carlile is suggestive of well-oxygenated bottom environments, because such populations could hardly endure long a habitat impoverished of oxygen. Pyrite in sediments of both formations is the product of a reducing environment beneath the sediment-water interface, as explained below, and is not an indication of reducing conditions in the densely populated bottom waters.

In contrast to the Fairport Member, the Blue Hill Member is not generally fossiliferous, but in most places where Blue Hill fossils are preserved, the fauna is diverse. It has been noted that locally a considerable quantity of gypsum has been produced in fossiliferous beds of the Blue Hill Member; the fossils in such places are poorly preserved and are encrusted with gypsum. At localities where large gypsum crystals litter exposed slopes of seemingly unfossiliferous shale, the alteration of CaCO3 to gypsum by the action of weak sulfuric acid may have eradicated all traces of shells. Thus, the absence of fossils in gypsiferous parts of the Blue Hill may be due to post-depositional solution rather than to sparseness of life in a generally hostile environment during deposition.

Any tendency toward extreme environmental factors in the sea results in some kind of faunal restriction. Thus, if waters are too turbid, corals will not survive; if dissolved oxygen becomes sparse, drastic reduction in the fauna results; and if salinity is far from normal, the fauna is likely to include large numbers of individuals of but a few species. I believe that neither the Fairport nor Blue Hill fauna can be regarded as the, product of environmental extremes. The number of benthonic genera in the two units is not large, but probably many other forms of life existed, which have left no record or have not been discovered. Remoteness of the open ocean and dilution by large streams carrying fine detritus to the sea from adjacent land areas may have resulted in water of lower salinity than normal in nearshore areas of the Western Interior sea. During Carlile deposition, however, most of the area that is now Kansas was far from shore, and the water was probably not much diluted by stream discharge. Paleoecological evidence for water of normal, or nearly normal, salinity is discussed below.

Bottom conditions--Both Fairport and Blue Hill environments provided a chiefly soft-mud bottom for the benthonic animals to dwell upon. No indication is found that chalky limestone in the lower part of the Fairport hardened before burial; indeed, sessile species are virtually absent in these beds. The substratum to which most epizoans attached themselves consisted of whole or broken valves of Inoceramus cuvieri. Locally, comminuted shell fragments and Inoceramus-prism sand provided a firm base for attachment of sessile species. Despite occasional wave disturbance of the sea floor, a general quietness is indicated by such features as lack of wear of the fossils (except in the Codell Member), common occurrence of paired pelecypod valves (Pl. 27A), and preservation of stalked barnacles in situ on shells to which they were attached. The entire assemblage of Carlile benthonic invertebrates, except for fragmental fossils in thin local lenses, reflects preservation of individuals at or nearly in their respective places of growth. Fossils preserved on a given bedding plane are thus the remains of a community of organisms.

Rate of sedimentation--That Fairport deposition was considerably slower than Blue Hill deposition is supported by several lines of evidence. (1) Fairport sediments are well bedded and mostly laminated, whereas Blue Hill rocks are poorly bedded. Compaction undoubtedly influenced alignment of fossils, fossil fragments, and pellets in the Fairport, and hence served to emphasize bedding developed during sedimentation (Pl. 6A, C). Lack of well-developed lamination in the Blue Hill could be due to activities of a mobile infauna, but seemingly no vestige remains of such a fauna. The preservation of laminae in chalky shale and shaly chalk of the Fairport, in beds that contain abundant remains of an epifauna, suggests that activities of any infauna that may have existed were negligible. (2) Extensive development of a sessile benthos during Fairport deposition could have occurred only under conditions of slow sedimentation, because Inoceramus cuvieri (the substratum to which the benthos became attached) was itself barely above the sediment-water interface. (3) The concentration of both microfossils and macrofossils vertically through the Fairport is suggestive of far slower rates of sedimentation than for the Blue Hill, where the volumetric concentration of fossils is much smaller.

Differential sedimentation within the Carlile can be demonstrated by comparison, at several localities, of the vertical distance between pairs of marker beds (Pl. 1). Fairport sedimentation, in areas now exposed, consistently was fastest at the south end of the west-central Kansas outcrop and slowest in northeastern Ellis County (Loc. 26). During early Blue Hill deposition, sedimentation was slowest in southeastern Osborne County (Loc. 38). That the thickness differences of parts of the Fairport and parts of the Blue Hill do not indicate the earlier beginning of Blue Hill deposition in some areas than in others is shown by the nearly uniform distance between the base of the Blue Hill and the highest Fairport bentonite marker bed 12 (Pl. 1).

Fairport Chalk Member

Origin of sediments--Most sediment in the Fairport Member is nonterrigenous and was laid down as calcareous mud that contained much clastic material in the form of calcareous fossils and fossil fragments. Five modes of occurrence of calcium carbonate in the Fairport can be discriminated, namely: interstitial spar calcite, recrystallized calcite, microcrystalline-calcite-ooze matrix, pellets, and fossils. Spar calcite is the least common and occurs as interstitial cement, particularly in biofragmental calcarenite beds, and fills the chambers in nearly all foraminifers. Such calcite is formed by precipitation from interstitial fluids. Recrystallized calcite is common in calcarenite beds, where the crystals are comparatively coarse, and in chalky limestone and marly chalk, where most grains are microsparry. Microcrystalline-calcite-ooze matrix, like that dominant in some Fairport rocks, has been interpreted by Folk (1959, p. 8) as the product of chemical or biochemical precipitation. In Fairport rocks, where pellets and foraminiferal tests are essentially intact, the matrix commonly contains microcrystallite calcite ooze that includes some coccoliths. But where pellets have ragged or fuzzy borders and foraminiferal tests have been recrystallized, as in many chalky limestone nodules, much of the ooze matrix has been recrystallized also. The Fairport microsparry calcite has formed by recrystallization of cryptograined calcareous pellets, calcareous foraminifers, and precipitated microcrystalline calcite ooze. Among features that serve to distinguish the finest-grained recrystallized calcite from microcrystalline calcite ooze are greater range in grain size, sparry appearance, and clearly interlocking grains of the former, as well as the usual association of microsparry calcite with partly recrystallized pellets and foraminifers.

Other calcium carbonate in the Fairport Member is biogenic and includes calcareous foraminifers, whole and fragmentary macrofossils, and cryptograined calcareous pellets. The foraminifers are mostly, perhaps wholly, of planktonic origin and, except for those that have been recrystallized, have undergone little post-depositional change. Most abundant among foraminiferal remains are, minute tests of juveniles. Among the macrofossils, Inoceramus is most abundant. Destructive action by waves has so broken many of these fossils that fragments and isolated prisms are commonly the dominant macro-organic element in the chalky strata. The cryptograined calcareous pellets are here interpreted as fecal pellets of unknown organisms, chief in the diet of which were minute algae whose skeletons consisted of coccoliths. Pellets that impart a speckled appearance to most Fairport rocks thus accumulated continuously on the sea floor. Change in marine environment during the closing part of Fairport deposition caused disappearance from the scene of the pellet-producing organisms. This conclusion is based on the gradational upward decrease in number of pellets in the highest Fairport beds and the absence of pellets in the Blue Hill Member.

Fairport strata are most calcareous near the base of the member and least calcareous at the top. Basal strata represent an environment comparable to that of the upper part of the Greenhorn, whereas topmost beds reflect change in environment toward that of Blue Hill deposition. The basal 20 to 25 feet of the Fairport is characterized by very calcareous chalky shale, local shaly chalk, and chalky limestone. In general, these strata contain the largest percentages of calcareous foraminifers, and cryptograined calcareous pellets and the smallest quantity of insoluble residue of any beds in the member. Deposition of these beds at greater distances from shore than higher Fairport strata would account for the virtual lack of terrigenous detritus in the basal Fairport section. Beds and nodular layers of chalky limestone contain a larger total percentage of microsparry calcite, foraminifers, and pellets than adjacent shaly strata. The relatively greater hardness of such beds is due partly to cementation by small quantities of spar calcite but mostly to partial or nearly complete recrystallization of foraminifer tests, calcareous pellets, and especially microcrystalline ooze (Pl. 7). I conclude that accumulating muds were occasionally stirred gently by deep-reaching waves that reworked the fine sediment, destroyed lamination, and produced layers susceptible to the recrystallization process. That recrystallization and lithification occurred during early diagenesis is shown by the uncompressed condition of pellets in chalky limestone, as contrasted to those in adjacent chalky shale. Obviously, laminated chalky shale was not disturbed by wave activity after deposition, hence contains correspondingly small quantities of recrystallized calcite. The nodular character of some chalky limestone layers resulted seemingly from more patchy distribution of reworked sediment, perhaps in hollows on a sea floor made undulatory by very gentle oscillatory movements of the water. The resulting lenses of sediment acted as nuclei for recrystallization that ultimately affected some of the surrounding shaly chalk or chalky shale, as is evident in the concretionary shape of many chalky limestone nodules. More widely scattered nodules in shaly chalk between marker beds 2 and 3 seem to be mainly concretionary (Pl. 5C). Some of the latter at locality 29 are nearly spherical.

Marly chalk layers of the middle and upper parts of the Fairport Member are similar to the chalky limestone in thickness and distribution, and are also the product of wave stirring of bottom sediments. In these rocks, too, matrix recrystallization has been extensive (Pl. 8). Grittiness of most marly chalk is attributable to concentration of fine fossils and fossil debris, including foraminifers and Inoceramus prisms particularly. Furthermore, such beds commonly contain greater concentrations of macrofossils than does adjacent chalky shale. The greater impurity of some marly chalk, contrasted to chalky limestone, is due to the greater quantity of terrigenous detritus deposited in the higher parts of the Fairport section.

Thin biofragmental calcarenite lenses in the member represent short periods of severe wave agitation of the bottom sediments. During such activity, the shell materials scattered through bottom muds were concentrated, while finer materials were temporarily suspended. Some microcrystalline ooze sifted down into the calcarenites as the turbulence subsided. Calcite spar that cements some calcarenite lenses is most likely a precipitate from interstitial water. Locally the calcarenites are tightly cemented because of recrystallization of all constituents.

Quartz, feldspar, and clay minerals in Fairport chalky strata are of terrigenous origin. The quartz, as determined from insoluble-residue and x-ray studies, is nearly all of silt size or finer, except in the uppermost part of the member; the fineness of grain size reflects remoteness of the land source. Clay minerals are present in only small quantity in calcareous rocks of the Fairport Member; therefore the origin of Carlile clay minerals, except in bentonite, is treated below in a discussion of the Blue Hill Shale Member.

Bentonite in the Fairport is seemingly bentonite in the restricted sense, because it is composed chiefly of montmorillonite. The exceedingly widespread distribution of some such layers, having almost uniform thickness, is explained by the uniform fall of volcanic ash on broad areas of the sea floor. Absence of lensing in the bentonite layers and paucity in most adjacent strata of structures or textures resulting from turbulence suggest that the sea into which the ash fell was generally calm. Under such conditions the ash probably underwent little or no sea-bottom transport and thus became devitrified at the original site of deposition. Small quantities of feldspar, quartz, and biotite in the bentonite may be unaltered mineral grains that fell with the ash. Fossils are no more abundant directly beneath the bentonites than elsewhere, indicating that the ash falls had no apparent effect on the benthonic population. Because of known Cretaceous orogenesis in the Cordilleran region and because Upper Cretaceous bentonite layers are generally much thicker in the Rocky Mountain region than in Kansas, a western source is postulated for ash that produced the Fairport bentonite layers. Distribution of bentonite so far to the east of the volcanic area suggests prevailing westerly winds during Late Cretaceous time.

Pyrite in Fairport rocks occurs mostly as minute crystalline aggregates but is found locally as nodules or as replacement of fossils. The richness of the Fairport benthos precludes the possibility of reducing conditions above the sediment-water interface. Thus, the pyrite is probably a product of precipitation from interstitial waters in which reducing conditions prevailed.

Invertebrate paleoecology--Calcareous Foraminifera abound in the Fairport Member in Kansas, and most or all are planktonic species. Miller (1958, p. 102) regarded the small size of Niobrara foraminifers, compared to measurements of the same species from the Gulf Coast Upper Cretaceous, as the consequence of unfavorable sea-water chemistry. Griffith (1947) gave measurements of specimens representing several species of calcareous forms from the Fairport of Kansas and Nebraska, which are known also from the Gulf Coast, Mexico, and Caribbean areas. Except for one species, his measurements fall within the size range of the forms found farther south. A few measurements made by me accord with the observations of Griffith. On this limited basis, seemingly no significant size difference distinguishes foraminifers of the two regions. Genera included for comparison are Gümbelina, Globotruncana, Globigerina, and Gümbelitria; all but the last are usually regarded as planktonic. The wide geographic range of modern globigerinas prohibits any categorical assumptions as to surface temperature of the sea in which the Fairport was laid down. The other genera, with possible exception of Gümbelitria, are extinct.

Several students of Foraminifera have noted the general increase in percentage of planktonic species with increasing distance from shore (Bandy, 1956, p. 186). That such a relationship pertains to fossils in the Carlile Shale of Kansas is manifest in the fact that Fairport sedimentation, as elaborated below, occurred early in a major marine regression. The Blue Hill and Codell, in which agglutinated foraminifers predominate, were deposited later in the same regression and, hence, closer to shore.

Depth of Fairport sedimentation cannot be determined on the basis of comparison of Cretaceous planktonic species with modern forms. Parker (1948, p. 235) has stated that planktonic foraminiferal species are negligible in water less than 50 meters in depth south of Cape Cod, Massachusetts. Phleger (1951, p. 35) found many of the same species to be most abundant in the upper 50 meters in the Gulf of Mexico. Therefore, distribution of these modern species seems to be controlled not by depth or temperature but by some other factor, probably salinity. Both Parker (1948, p. 237) and Bandy (1956, p. 187) indicated that modern planktonic Foraminifera are inhabitants of water of normal salinity. The offshore waters that were inhabited by Fairport planktonic foraminifers most likely were of normal salinity.

Foraminifera are abundant in nearly all Fairport rocks examined in thin section or after crushing. In some samples, spar-filled foraminifers make up as much as 30 percent of the rock. The largest volume of foraminifers is in chalky limestone near the base of the member. Slow sedimentation, in combination with periodic stirring of bottom sediments, could have concentrated such large numbers of these fossils. The only seemingly clear-cut instance of catastrophe is recorded in a sandy chalk layer that lies on a bentonite seam at locality 19. The chalk contains abundant splintery grains of quartz and feldspar, probably of volcanic origin, and numerous foraminifers that may have been killed during the ash fall.

The bryozoans Conopeum and Proboscina are usually found together and commonly occur in abundance in the middle part of the Fairport Member. The bryozoans are attached to the valves of Inoceramus cuvieri or to the other epizoans, including Ostrea, Serpula, and Stramentum?, which, in turn, are attached to large pelecypods. On a few barnacles, Proboscina is restricted to the capitular plates, but the fact that the bryozoan colonies are oriented upward on some barnacles and downward on others seems to preclude any sort of symbiotic relationship. It is probable, however, that the bryozoans oriented with apertures downward were attached after death of the barnacle.

Bryozoans generally inhabit clear water, and their absence from the Blue Hill Member is explained by the greater amount of suspended matter present during deposition of this shale. Bryozoa are abundant in Cretaceous strata of Europe and are more common in the Gulf Coast region of the United States than in the Western Interior. The paucity of these invertebrates in the Western Interior may reflect cooler water than farther south, but the problem of Cretaceous bryozoan distribution needs further study.

Data on modern proboscinas are scattered, but data from several dredging expeditions show that the genus is geographically widespread in modern seas, has a wide bathymetric range, and is probably most common in latitudes within 30° of the equator. Data for Conopeum are even more sparse, but specimens have been dredged from as deep as 1600 feet. Other members of the family Membraniporidae, including the very common genus Membranipora, range from low to high latitudes and are known from waters 100 to 9,000 feet deep. The bryozoans in Fairport rocks have seemingly little depth or temperature significance.

The annelid genus Serpula is represented abundantly throughout the middle part of the Fairport Member. Two species are recognized, of nearly identical structure, habitat, and mode of growth. Where one is numerous, the other is generally absent. Presence of a few specimens of intermediate structure is evidence that the two forms are probably varieties of a single species. Like other epizoans in the Carlile fauna, the serpulas preferred the clearer-water environment that prevailed during Fairport deposition, because no specimens are known from Blue Hill or Codell beds. The chief attachment is to valves of large Inoceramus cuvieri, or to other epizoans, which, in turn, are attached to the big pelecypod. Thus, Serpula may be attached to Ostrea congesta, other serpulas, or even to zoaria of encrusting bryozoans. Orientation of the worm tubes is generally random, the apertures being commonly but not invariably turned toward a perpendicular from the substratum. Parallel orientation of all tubes on a pelecypod valve would be evidence that the pelecypod was standing upright on the sea floor, but all evidence is to the contrary; the substratum for these annelids lay parallel to the sea floor. Attachment to shells of dead I. cuvieri is shown where serpulas are fixed to valve interiors or to valves that had been fragmented by wave activity before the worm tubes were constructed.

Modern serpulas range from tropical to polar latitudes and have been collected in water ranging in depth from a few feet to several thousand feet. Depositional influences such as depth and temperature cannot be determined by simple comparison of ancient and living species of such adaptable invertebrates, but the solid calcite walls of fossil forms may be suitable for oxygen-isotope-ratio studies to measure the ancient temperature.

Barnacles are common in the middle part of the Fairport Member and nearly everywhere are associated with Serpula and bryozoans. Maximum development of the epizoal element during deposition of these strata probably coincides with optimum growth conditions for Inoceramus cuvieri. The pedunculate barnacles are attached generally to valve exteriors of I. cuvieri, but at least one specimen in my collections is attached to Ostrea congesta. A few specimens, each measuring less than 4 mm in height, are attached to the interior of one I. cuvieri. Suggestion is offered that the opened valve of the dead pelecypod was buried too soon to permit growth to maturity of these small barnacles.

The genus Stramentum, to which the Fairport forms are tentatively assigned, is extinct, but modern pedunculate barnacles having an armored stalk are known at depths ranging from the littoral zone to 17,000 feet, from very low to high latitudes, and in water ranging from warm to nearly freezing. The Cretaceous forms cannot be used alone, therefore, as indices of temperature and depth of ancient seas.

Relative depths at which various ammonites lived have been discussed by many authors, and widely differing opinions have been expressed concerning most forms. Perhaps the classic American paper on this subject is that of Scott (1940), who concluded that most ammonites in Cretaceous rocks of Texas were nektobenthonic and that form and sculpture of the shell are of bathymetric significance. He (Scott, 1940, p. 313, 322) noted the association of ammonites having sculptured shells and quadrate whorl sections with uncoiled forms in the Eagle Ford Group of Texas, the same association seen generally in the Carlile Shale of Kansas. For this association, Scott (1940, p. 322) postulated a depth range of 120 to 600 feet, which embraces the probable greatest depth of the Carlile sea.

Modern cephalopods are restricted to marine environments and, as Scott (1940, p. 308) pointed out, inhabit waters of normal salinity. He noted the lack of evidence that ammonites ever lived in fresh or even brackish water. Abundance of ammonites in Fairport strata is strong evidence of deposition in waters of normal salinity.

Large numbers of immature Collignoniceras woollgari on bedding planes in the middle part of the Fairport Member might be explained by some sort of catastrophic event, but the number, geographic extent, and proximity to one another of such bedding planes would require almost continuous "catastrophe". Furthermore, on most of these bedding planes are almost numberless specimens of Inoceramus latus and locally abundant I. cuvieri, barnacles, oysters, bryozoans, and serpulas. The general uniformity of stratigraphic distribution of this faunal association tends to support a nektobenthonic or vagrant-benthonic mode of life for C. woollgari. Such a conclusion is supported by the imprint in chalky limestone, at locality 14, of the ventral impression of a fairly large ammonite, almost certainly C. woollgari.

The greatest numbers of Collignoniceras woollgari are juveniles less than 2 inches in diameter. The cause of death is unknown but may have been overproduction and consequent lack of sufficient food. These animals, like modern Nautilus, were probably carnivorous, and the habitat of C. woollgari, like many modern habitats, could not support large numbers of preying carnivores. The wide distribution of C. woollgari in beds that lack structures indicative of wave or current action seemingly precludes interpretation of the immature forms as a phenomenon of sedimentary sorting.

Scaphites are so sparse in the Fairport Member that the ecology of this group will be treated with that of other species in the Blue Hill Shale Member.

In a very detailed study of Canadian Actinocamax, Jeletzky (1950, p. 21) has pointed out that nearly all Late Cretaceous belemnitids dwelt in boreal seas. Belemnites generally have been regarded as inhabitants of cool waters; thus their abundance in the Favel Formation of Canada and rarity in the coeval Fairport Member may constitute evidence of slightly warmer seas in Kansas than in Manitoba and Saskatchewan. A southward decrease in numbers of Belemnitella along the Atlantic Coastal Plain in the United States (Jeletzky, 1950, p. 22) is analogous to the distribution of Actinocamax in the Western Interior. Paleotemperature studies of Late Cretaceous belemnites by Urey and others (1951) and Lowenstam and Epstein (1954) support the conclusion that the belemnites preferred cool-water habitats. Average temperatures of growth of all belemnite guards range from 16° C, in the Cenomanian, to 20° C, in the Coniacian and Santonian (Lowenstam and Epstein, 1954); Turonian temperatures were 17° to 19° C.

Large specimens of Inoceramus cuvieri everywhere lie parallel to planes of bedding and they undoubtedly assumed this position during life. Had this large species been a burrowing form, perpendicular orientation of at least some specimens could be expected, but no such occurrence has been observed. An upright position, with byssal attachment, is also unlikely, because of the lack of a solid substratum. Epizoans are encrusted heavily on many specimens in the middle and upper parts of the Fairport Member. Oysters are the commonest epizoans, worms next in abundance, then barnacles and bryozoans. The random orientation of the oysters, serpulas, and bryozoans is proof that the valves of I. cuvieri lay horizontal during epizoal growth. Ostrea congesta is commonly attached to both the exterior and interior of the valves and to both exterior surfaces of paired closed valves. Oysters on the interior of I. cuvieri are obviously postmortem epizoans. Where O. congesta is attached to the exterior of both valves, one must conclude that the specimen of I. cuvieri was overturned, perhaps during storms when wave activity reached deeper than usual. I postulate that some epizoal growth occurred during the lifetime of I. cuvieri, because some specimens of the large pelecypod are encrusted with oysters overgrown by worms, which, in turn, are overgrown by bryozoans. It seems unlikely that the valves of a dead I. cuvieri would have remained unburied on the sea bottom long enough for these successive phases of epizoal growth to have been completed.

No specimens of Inoceramus latus bear epizoans. Furthermore, no evidence is found that this species was a burrower. All specimens of I. latus are found lying parallel to planes of stratification. This species must have lain flat on the sea floor, partly or almost wholly covered with mud, and thus did not afford a substratum suitable for epizoal growth.

Ostrea congesta is the most abundant of all pelecypods in the Fairport. Most of these oysters are attached to large flat valves of Inoceramus cuvieri. As noted above, the random orientation of O. congesta proves a position parallel to the sea floor for valves of I. cuvieri, to which the oysters became attached. Like modern oysters, the shape of O. congesta individuals is extremely variable as a result of crowding; upward growth dominated after the specimens could no longer expand laterally. A few of the epizoal oysters not affected by crowding display smoothly rounded outlines, and commonly these reached a length exceeding 1 inch. Paucity of oysters in the lower few feet of the Fairport is related to sparseness of I. cuvieri in these beds. The small number of O. congesta in the topmost part of the member reflects increased turbidity during deposition of this part of the section.

Modern oysters occupy a wide range of habitats. Some live in relatively deep, quiet waters of normal salinity, whereas others inhabit the littoral zone, where they are commonly exposed to the atmosphere for several hours between tides. As Stenzel (1945, p. 37) and many other authors have noted, oysters are regarded generally as brackish-water dwellers. Modern shallow- and brackish-water oysters are mostly large and thick shelled, and locally they construct thick banks or so-called oyster "reefs". Similar thick-shelled oysters are common in near-shore sandy facies of the Western Interior Upper Cretaceous. Obviously, the thin-shelled, small Ostrea congesta of the Fairport Member represents an altogether different sort of environment. Among modern American oysters, the form most similar to O. congesta is O. equestris, distributed from North Carolina to the Gulf Coast and West Indies. According to Abbott (1954, p. 373), O. equestris is an inch or two in length, oval, and has a raised vertical margin on the attached valve. Parker (1955, p. 203) has stated that O. equestris is normally found in waters of high salinity, noting (1956, p. 371) that related forms date back to the Triassic. On the basis of morphological similarity of O. congesta and O. equestris, I suggest that the Fairport Member was deposited in waters of normal or nearly normal salinity.

The habitat of Ostrea congesta is determined best by study of its morphology, faunal associates, and substratum, and the texture, structure, and composition of the enclosing strata. Countless excellently preserved, fragile shells of this oyster, commonly in the life position on large Inoceramus or other firm substratum, such as calcareous sand, clearly indicate a quiet environment, below normal depth of wave activity. In the Weches Formation of the Gulf Coast, Stenzel (1945, p. 45) noted thick-shelled O. lisbonensis in the wave-worked lower part of the formation, but higher in the section a thin-shelled variety is preserved in sediments that lack evidence of wave action and contain other delicate fossils; he concluded similarly that the thin-shelled oysters reflect quiet-water deposition. Other delicate fossils in Fairport strata, such as Bryozoa and pedunculate barnacles attached to O. congesta, support the concept of a generally quiet environment of deposition. The paucity of terrigenous detritus in most Fairport strata suggests that the oysters preferred the far-offshore environment of clear water.

Local lenticular calcarenites contain shell fragments of Ostrea congesta and other fossil debris, all of which indicates the severity of occasional sediment agitation by deep-reaching waves. But these same calcareous sands, after turbulence had ceased, provided support for new generations of O. congesta.

On some shells of Inoceramus cuvieri are enormous numbers of juvenile oysters. Seemingly, these were killed by accumulating sediment before they had a chance to mature. The upper size limit of this species seems to have been less than 2 inches in length and might be a result of premature burial.

Also of interest with respect to Ostrea congesta is the retention of color pattern in one specimen and my discovery of a pearl in another specimen.

In summation, the animal paleoecology of the Fairport Member suggests a well-oxygenated environment far from shore, in waters of normal or near-normal salinity, and below the depth of normal wave activity.

Blue Hill Shale and Codell Sandstone Members

Origin of sediments--Quartz is the dominant mineral in shale samples of the Blue Hill Member. Much of this is very fine silt or even smaller, but the average grain size is considerably larger in the upper part of the member. Such fine quartz detritus is most likely the product of rock abrasion during weathering in, and transport from, the source area. In studied samples kaolinite is second in abundance and next, in nearly equal quantity and locally more abundant than kaolinite, are illite and montmorillonite. Grim (1953, p. 352) pointed out that marine environments are not favorable for the preservation of kaolinite, and later (1958, p. 252) stated that kaolinite persists in ancient rocks but that some is seemingly lost through diagenetic alteration. Weaver (1958) reasoned that most clay minerals in sedimentary rocks are of detrital origin and reflect conditions in the source area, rather than, as generally thought, diagenesis in the place of deposition. Weaver (1958) noted that kaolinite is abundant in all sedimentary environments but is most common in continental and near-shore sediments. Kaolinite can be produced by thorough leaching, probably under humid climatic conditions. That humid, rather than arid, conditions prevailed during the Late Cretaceous in Kansas is indicated by the diverse, well-known flora of the Dakota Formation, leaves and abundant carbonaceous matter in the Graneros Shale, and petrified logs in the Greenhorn Limestone and Fairport Member. In view of the paleogeography of Late Cretaceous time in the United States, the most likely source for large quantities of kaolinite might be the soils of the Wisconsin Highlands or southern Canadian Shield. Because illite forms under conditions of aridity, and because widespread fossil floras tend to rule out an and climate in the eastern part of the Western Interior region during Late Cretaceous time, the Blue Hill illite probably did not originate during Late Cretaceous weathering. Illite is the commonest clay constituent of sedimentary rocks (Weaver, 1958, p. 259) and thus could have been eroded from Paleozoic sediments that in Cretaceous time were exposed around the eastern border of the Western Interior sea. Because kaolinite is not abundant in Paleozoic sediments, such rocks are not likely to have been the chief source of Blue Hill kaolinite. There is general agreement that montmorillonite in ancient rocks results from alteration of volcanic material, and Grim (1953, p. 357) has expressed judgment that much of the montmorillonite in Upper Cretaceous rocks of the central and southern United States had such an origin. Blue Hill bentonite, like that in the Fairport, is dominantly composed of montmorillonite and thus is true bentonite. The small quantity of chlorite found in shale samples of the Blue Hill accords with a statement by Weaver (1958, p. 258) that chlorite is least abundant in marine shales. The Blue Hill chlorite is most likely detrital. Small quantities of feldspar in some Blue Hill samples could be volcanic, but in my opinion a detrital origin is more probable. As Pettijohn (1957, p. 125) has pointed out, feldspar can survive long transport in large streams, although the rate of disintegration is much more rapid in turbulent streams, such as those having steep gradient. The very large quantity of fine to very fine grained terrigenous detritus in the highest beds of the Dakota Formation and in the near-shore deposits of the lower part of the Graneros Shale bespeaks transport by large, low-gradient streams that traversed the land bordering the Late Cretaceous sea of west-central Kansas. Transport by similar streams during the time of Carlile deposition could account for detrital feldspar in the Blue Hill Member.

The flood of coarse silt and fine-grained sand that characterizes uppermost Blue Hill beds and especially the Codell Member reflects approach of the shore of the Late Cretaceous sea to west-central Kansas during a general regression. Siltstone and sandstone of the Codell Member are composed chiefly of quartz but contain smaller quantities of chert, feldspar, and several minor accessories; sorting is fairly good, but most of the grains are subangular; hence, the sediment may be classed as nearly mature. Source areas for the three dominant minerals--quartz, feldspar, and chert--can only be postulated. Each mineral could have been eroded from Paleozoic sediments that bordered the Late Cretaceous sea in the north-central United States, and each could have been derived from Precambrian terrains of the Wisconsin area or southern Canadian Shield. A multiple source is quite possible, in fact, very likely.

Insufficient evidence is available to warrant firm conclusions as to relief in the source region of Blue Hill and Codell detritus. Obviously, this region was not extremely low in relief, because under such conditions any feldspar would have been thoroughly decomposed in the humid climate postulated above. Had the source region been one of high relief, mechanical erosion would have been dominant, and the thorough leaching necessary to produce Blue Hill kaolinites would have been less likely. Furthermore, high relief would result in steep stream gradients, but the grain size of terrigenous detritus is small in most marine and nonmarine Late Cretaceous sandstones of Kansas. Thus, the source area is postulated to have had moderate relief, because in such an environment mechanical erosion and chemical decomposition would achieve the balance capable of producing sediment having the character of Blue Hill and Codell deposits.

Calcareous septarian concretions are seemingly a product of early diagenesis of the Blue Hill shale. Fossils are inferred to be the usual nuclei around which calcareous matter was precipitated, because fragments of fossils are in evidence in nearly all of the larger concretions, and complete fossil specimens are preserved in numerous smaller concretions at certain horizons (Pl. 19A). That the concretions were at least partly lithified before significant compaction occurred is manifest in the uncompressed fossils of the concretions, in contrast to the more or less flattened condition of most fossils preserved in surrounding shale. Bedding in the shale bends beneath and arches over septarian concretions at some localities, thus providing additional evidence of rigidity of the concretions during later stages of shale compaction.

Accumulation of calcium carbonate as concretions in strata otherwise nearly devoid of calcareous rocks needs explanation. The noncalcareous nature of the Blue Hill shale reflects physical and chemical conditions of the sea water during sedimentation, whereas concretion development occurred within the sediments after their deposition. Two different environments are involved. An inverse relationship is indicated between turbidity and carbonate sedimentation in the Carlile sea of Kansas. Virtually no calcium carbonate accumulated on the sea floor during deposition of the clayey Blue Hill shale. Yet, much calcite was precipitated within the sediments to form the septarian concretions. Weeks (1953) concluded that local increase in alkalinity of fluids surrounding decaying organic matter in sediments would cause local precipitation of carbonate and formation of carbonate concretions around the organic nucleus. The lack of concretions around most fossils at some Blue Hill horizons, and the seeming absence of fossil remains in many concretions leaves the problem open for further study. However precipitated, calcareous matter was derived from interstitial fluids that migrated toward centers of precipitation during initial phases of diagenesis, when flow of fluids through the sediments would have been greatest. As pore space in an increasingly greater volume of sediment around the nuclei became charged with mineral matter, clay surrounding the nuclei became incorporated in the concretions. For this reason the concretions have the same color as the surrounding shale. According to Pettijohn (1957, p. 209), the formation of an aluminous gel is involved in the development of septarian concretions. He noted that the manner by which such a gel forms is not understood but that the process involves some expansion, as shown by the marginal cone-in-cone structure. At locality 31 (Pl. i9B) a thin sandstone bed passes through a concretion, arching upward through the center of the mass. This is evidence of the possibility of expansion during growth of septarian concretions. Desiccation, seemingly greatest near the concretion centers, produced the cracks, which later become filled with second- and, still later, third-generation calcite. Greater shrinkage in the larger concretions caused extensive fracturing of the contained fossils.

I cannot agree with the implication of Weeks (1953) that Cretaceous concretion-bearing shales were laid down in stagnant environments. Wherever preserved, the Blue Hill fauna contains numerous benthonic organic remains that do not show signs of transport. The environment was evidently well oxygenated.

Pyrite nodules, common locally in the Blue Hill Member, are products of diagenetic processes, as are the concretions. The character of the bottom fauna of the member precludes possibility of direct iron sulfide precipitation on the sea floor, because such precipitation demands reducing conditions. Preservation of finely divided carbonaceous matter generally throughout the Blue Hill beds suggests that reducing conditions prevailed within unconsolidated mud on the sea floor. Hydrogen sulfide, generated through decomposition of the organic matter by action of anaerobic bacteria, could have combined with iron in interstitial waters to precipitate the pyrite, probably as a colloid. Fluid movements during initial phases of compaction doubtless concentrated the finely divided pyrite, which then formed nodules, usually around buried shells of Scaphites, Inoceramus, or Collignoniceras.

Invertebrate paleoecology--Environmental conditions in the Western Interior sea changed markedly as Blue Hill deposition began. The composition of the benthonic fauna mirrors particularly the change to more turbid waters. Epizoal elements virtually disappeared from the west-central Kansas area, and the total population of bottom-dwelling macroinvertebrates diminished considerably. Many species in the Blue Hill Member are represented sparsely and add little to understanding of the environment of deposition. Owing to the paucity of fossils in the Codell Member, the paleoecology of this unit is poorly known in Kansas.

Many species of calcareous and agglutinated foraminifers have been collected from the Blue Hill shale along the Republican River valley of Kansas and Nebraska (Griffith, 1947). Washed samples of the Blue Hill and Codell Members examined by me contain a preponderance of agglutinated species. In contrast, neither Morrow (1934) nor Griffith (1947) discovered agglutinated forms in the Fairport Member, and I discovered only a few questionable specimens in Fairport insoluble residues. Many Carlile calcareous species are known from both the Blue Hill and Fairport Members. Most of the calcareous foraminifers, perhaps all, were planktonic and thus were not affected by the contrasting bottom conditions that prevailed during deposition of the Blue Hill and Fairport shales. The abrupt appearance of agglutinated, and thus benthonic, Foraminifera in the Blue Hill Shale Member is a direct reflection of environmental change. Although the water was probably shallower during Blue Hill deposition, owing to regressional movement of the sea at that time, change in depth alone would not account for abrupt appearance of the agglutinated species, because such change in depth would be very gradual. On the other hand, during Blue Hill deposition there was an influx of terrigenous silt and very fine sand, of the size used by these species; such material is lacking in most Fairport strata. The availability of material for construction of their tests undoubtedly was one factor in restricting arenaceous foraminifers to the Blue Hill and Codell Members. Stainforth (1952, p. 43) concluded that turbidity was a main factor controlling some faunas consisting solely of arenaceous foraminifers but that turbidity was unimportant in normal marine facies where arenaceous and calcareous foraminifers coexist.

Dominance of arenaceous Foraminifera in the Lower Cretaceous Kiowa Shale of Kansas was interpreted as evidence of a brackish environment by Loeblich and Tappan (1950, p. 4). Lowman (1949, p. 1956) has noted the predominance of Haplophragmoides and Trochammina, both of which are well represented in the Blue Hill, in a brackish-water environment, but Bandy (1956, p. 187) noted that these genera are found in waters ranging from weakly brackish to normally saline. Furthermore, presence of several species of planktonic calcareous foraminifers and the taxonomic diversity of the Blue Hill fauna seemingly is evidence contrary to any major departure from normal salinity.

Unlike the Fairport Member, the Blue Hill contains very few specimens of Ostrea congesta. The greater quantity of fine terrigenous detritus in the Blue Hill Member suggests that waters were too turbid for development of an extensive oyster population. Nearly all of the few oysters collected from the Blue Hill are attached to valves of Inoceramus flaccidus, generally near the hinge, the oyster beak being directed toward the beak of I. flaccidus. The position of the oysters indicates that I. flaccidus must have lain partly buried in sea-floor mud in an upright position, the posteroventral margin of the valves directed downward. The preferred orientation of the oysters is proof that epizoal growth occurred during the lifetime of I. flaccidus.

No observed specimen of Inoceramus cuvieri in the Blue Hill has epizoans attached to the valves, probably because the few oysters that did survive in the turbid environment preferred I. flaccidus as a host, because it projected higher above the sea bottom than did I. cuvieri. Specimens of I. latus in the Blue Hill Member add little to knowledge of their ecology except that the species was tolerant of turbid as well as clear-water environments.

Specimens of Yoldia and Lucina, Bellifusus, Gyrodes, Tessarolax, and Oligoptycha, are elements of a near-shore assemblage of generally thick-shelled mollusks and reflect the regression in progress during deposition of the Blue Hill and Codell Members. That such mollusks are only the vanguard of the near-shore fauna is indicated by the relative sparsity of these fossils. The common preservation of paired valves of such pelecypods as Inoceramus flaccidus, Yoldia, and Lucina and the lack of shells showing signs of wear are evidence that these fossils were not transported far after death and that the species were indigenous to the environment of Blue Hill deposition.

Extant genera of Blue Hill pelecypods provide some evidence of ancient salinity. That Ostrea congesta may be indicative of normal salinity has been noted in discussion of Fairport paleoecology. Modern American species of Lucina are distributed from the intertidal zone to a zone beyond the continental shelf, and, except for one species reported from low-salinity bays by Ladd (1951), most individuals inhabit water of normal or nearly normal salinity. Yoldia is widely distributed in shallow to deep water of the North American shelf, and the genus seemingly favors water of normal salinity.

Except for some specimens of Inoceramus in the limestone nodules at the top of the section at locality 22, pelecypods are almost nonexistent in the Codell Member. As indicated elsewhere in this paper, the most plausible explanation seems to be removal of them by groundwater solution. Near locality 17, however, fragmentary molds of three clams were collected in a sandy shale bed near the top of the Codell. Sculpture preserved in the molds is suggestive of thick-shelled pelecypods of the kind that characterize a near-shore environment. Most pelecypods at locality 22 are fragmentary and are preserved in lenses of "inoceramite". The fossils are part of a lag concentrate produced by considerable agitation of bottom sediments as a result of wave action.

The ammonite Collignoniceras hyatti can be collected at virtually every locality where fossils are preserved in the Blue Hill Member. This fact seemingly supports the concept of a benthonic habitat that is concluded for C. woollgari of the Fairport Member. If these ammonites were surface nekton it would be necessary, in order to account for such distribution, to postulate ubiquitous surface distribution and wide-scale mortality at the precise times when bottom faunas that were destined for preservation were being entombed in the accumulating sediment. More probably, C. hyatti occupied the same habitat as the bottom fauna.

Scaphites was almost certainly a bottom-dwelling ammonite, by reason of the same evidence given for C. hyatti, but the distribution of Scaphites was seemingly controlled more closely by the environment of deposition. Scaphites is very sparse in the Fairport beds and is virtually lacking in the Niobrara Chalk of Kansas (Miller, 1958). So far as I am aware, none have been discovered in the Greenhorn Limestone of Kansas. Thus, Scaphites seems to have preferred the turbid waters that prevailed during Blue Hill deposition to the clearer waters of Fairport sedimentation.

Smooth, discoidal ammonites such as Proplacenticeras have been judged by several authors (see Bergquist and Cobban, 1957, p. 873) to be swimmers or floaters in the open ocean. The sparseness of Proplacenticeras in the Blue Hill Member is in harmony with such a conclusion; indeed, at most fossil localities the genus is sparse and at many others is absent.

The available fossil evidence indicates that Blue Hill and Codell deposition was marked by increased turbidity, shallower water, and introduction of the first elements of a near-shore invertebrate fauna. Such conclusions support the concept of a general regression that began early in Carlile history. Fossils such as planktonic Foraminifera, ammonites, Ostrea congesta, Lucina, and Yoldia suggest that the water during Blue Hill deposition was probably of normal or nearly normal salinity.

Paleogeography and General Sedimentary History

Carlile strata of Kansas represent only a small portion of the sedimentary complex that was laid down in the Rocky Mountain trough during Late Cretaceous time. This trough is conceived as a vast, differentially subsiding area that extended from the Arctic region to the Gulf of Mexico. Locally, as in southwestern Wyoming, Upper Cretaceous sediments nearly 20,000 feet thick were laid down (Reeside, 1944). In the western United States, Late Cretaceous deposits along the western border of the trough are strikingly intertongued strata of marine and nonmarine origin. The oscillatory character of the ancient shoreline in this part of the trough is well documented in several detailed stratigraphic reports, which already have become classics. Westward gradation of nonmarine facies from coastal-plain to piedmont sediments reflects proximity to an extensive range of mountains (Spieker, 1946) that was elevated during the Nevadan Orogeny. Upper Cretaceous marine strata in the Rocky Mountain states generally contain more coarse-grained detritus than equivalent beds in the Great Plains (Reeside, 1957, fig. 7-21), thus providing testimony of the importance of the Nevadan mountains as a source area for Late Cretaceous sediments.

On the eastern edge of the interior sea, one can only speculate as to the position of the shoreline after the beginning of Late Cretaceous marine deposition. Above the lower part of the Graneros Shale of Kansas the section is mostly lacking in sediments, structures, or faunas of obviously near-shore shallow-water origin. In the Carlile, specifically, I have seen no evidence, physical or paleontological, that suggests unequivocally such an environment. The total thickness of Carlile beds in west-central Kansas is greater than in westernmost Kansas or eastern Colorado. The general uniformity of lithology and faunas of the major Carlile divisions throughout Kansas is not characteristic of near-shore sedimentation. Rock textures and structures characteristic of sedimentation in very shallow water are all but lacking in Carlile sediments of Kansas. Thick-shelled mollusks are sparse, and the most conspicuous element of a near-shore Late Cretaceous fauna--thick-shelled oysters--is absent from the Kansas Carlile, except for a single specimen of Exogyra. This evidence is taken collectively to indicate that the Cretaceous shoreline lay scores of miles to the east of the present west-central Kansas outcrop through most of the time of Carlile deposition.

Lower Upper Cretaceous strata in Kansas make up a markedly cyclical succession. The sequence commences with the Dakota Formation, an essentially nonmarine formation comprising chiefly fluviatile and paludal deposits. Dakota sediments grade upward into the Graneros Shale, in which ripple-marked and crossbedded sandstone, fauna, and thin conglomerate layers signify marine deposition in near-shore shallow water. Graneros deposition in Kansas reflects a broadening of the area of Late Cretaceous subsidence and an eastward marine transgression along the border of the Western Interior sea. Uppermost strata of the Graneros are commonly calcareous, contain ammonites and calcareous foraminifers, and contain smaller quantities of sand-size terrigenous detritus than beds below. Overlying beds of the Greenhorn Limestone are dominantly of nonterrigenous origin. Lower Fairport strata represent a cyclical phase nearly identical with that of the upper Greenhorn strata. In both units the calcareous sediment was generated chiefly within the sedimentary basin. The area of carbonate deposition extended across the trough from an area east of the present Kansas outcrop westward to central Colorado, northeastern New Mexico, and the Black Hills region. Farther west the calcareous sediments grade into mainly noncalcareous detrital rocks. The body of carbonate rock represents accumulation during a transgressional maximum, mostly beyond the range of deposition of terrigenous detritus. Increased quantities of land-derived detritus in the middle and upper parts of the Fairport herald regression of the sea in the Kansas area. During Blue Hill deposition, influx of fine-grained terrigenous sediment increased rapidly and brought a halt to carbonate sedimentation in the Kansas part of the Western Interior sea. As the regression neared its maximum, the Kansas area gradually came within range of sand deposition. The Codell Sandstone Member represents maximum influx of land-derived detritus during deposition of the Carlile Shale in Kansas, and also the maximum phase of regression in the first Upper Cretaceous cyclothem.

The source area for most of the terrigenous detritus of the Blue Hill and Codell was probably to the east. The nonmarine Dakota is believed to have had a northerly or northeasterly source in the type area, according to Tester (1929, p. 280), by reason of the direction of fore-set-bed inclination. An easterly source for the Dakota in the Williston Basin has been implied by Gries (1954, p. 447). Westward thinning of the Blue Hill and Codell in Kansas likewise suggests an easterly source for these beds. The sandy nature of the Carlile in southeastern South Dakota, where it lies on the Sioux Quartzite (Bolin and Petsch, 1954, p. 85), testifies to the importance of eastern source areas for Carlile terrigenous detritus.

In many parts of the Western Interior region the cyclic phase represented by the Codell or its equivalent is overlain by dark-gray shale that records renewed transgression. In the Black Hills these sediments are termed the Sage Breaks Member of the Carlile Shale. Reeside (1957, fig. 13) depicted Kansas as an area of erosion during post-Codell-pre-Niobrara time but, as noted above, cited no concrete evidence to indicate that this was subaerial erosion. According to Merriam (personal communication, 1960), dark-gray shale locally occurs between the Codell and Fort Hays in the subsurface of western Kansas. This shale is homotaxial with similar shale in New Mexico and the Black Hills and is proof that the sea remained in Kansas during post-Codell-pre-Niobrara time, in the middle of the area that Reeside (1957, fig. 13) judged to be undergoing erosion. I interpret the lack of equivalents to upper Turner and Sage Breaks strata along the Kansas Carlile outcrop as evidence that the sea floor during this time was above the marine base level, resulting in nondeposition or even sublevation.

Niobrara sediments were deposited during the second Late Cretaceous transgressional maximum, and, like the Greenhorn, mostly beyond the range of terrigenous detrital deposition. The overstep relationship of the Niobrara to the Kansas Codell is the result of rising marine base level. By the time base level had risen to the position at which sediments could again accumulate, the transgression was already at a maximum and thus carbonates were laid down. The resulting hiatus is a regional diastem at which transgressive gray shale is unrepresented.

The marine cyclical succession, of which the Carlile is the regressive part, is here named the Greenhorn cyclothem, because this formation represents the phase of maximum transgression. The asymmetrical cycle comprises seven phases, defined as follows: (1) noncalcareous siltstone or sandstone, commonly clayey, nonmarine or marine, poorly developed macrofauna but much carbonaceous matter, represented by the uppermost Dakota and locally, the lowermost Graneros; (2) dark-gray noncalcareous silty or sandy clay shale and numerous beds of sandstone, poorly developed macrofauna, represented by the lower part of the Graneros Shale; (3) dark-gray noncalcareous silty clayey shale and beds of calcareous sandstone, local septarian concretions, and a normal marine fauna, represented by the upper part of the Graneros Shale; (4) chalky shale and limestone, sparse terrigenous detritus, a normal marine fauna, represented by the Greenhorn and Fairport; local calcareous strata at the top of the Graneros are included in this phase and are analogous to middle and upper Fairport beds; (5) dark-gray noncalcareous silty clayey shale containing septarian concretions, similar to phase 3, represented by most of the Blue Hill Member; (6) dark-gray noncalcareous silty or sandy shale, locally concretionary, similar to phase 2, represented by the upper part of the Blue Hill; (7) siltstone and sandstone, commonly clayey, poorly developed macrofauna, represented by the Codell Member. Carbonaceous matter of sand phase (1) was derived from vegetated lands or swamps over which the sea was transgressing. The lack of plant debris in sand phase (7) in an expectable condition of regression during which incorporation of vegetational litter was at a minimum. The cyclical succession that is outlined here provides a master framework for future interpretive studies of the stratigraphy, paleontology, and sedimentology of Cretaceous strata in Kansas.

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Kansas Geological Survey, Geology
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