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Biostratigraphy
Western Interior Standard Zones
Cobban and Reeside (1952) published a Western Interior zonal scheme that has wide application for Upper Cretaceous rocks in this huge area. Major revisions to that sequence of zones were made by Cobban (1961) and by Cobban and Scott (1972, p. 33) so that the published standard sequence of zones for the section including Graneros Shale, Greenhorn Limestone, and Fairport Member of Carlile Shale, and for equivalent strata, stands presently, as follows:
| European Stages |
Zones | Kansas Section |
|---|---|---|
| Turonian | Collignoniceras woollgari (Mantell) | Fairport Member, Carlile Shale |
| Inoceramus (Mytiloides) labiatus (Schlotheim) | ||
| Greenhorn Limestone | ||
| Cenomanian | Sciponoceras gracile (Shumard) | |
| Dunveganoceras albertense (Warren)* | ||
| Dunveganoceras conditum Haas* | ||
| Dunveganoceras pondi Haas | ||
| Acanthoceras wyomingense (Reagan)1 | ||
| Acanthoceras amphibolum Morrow | Graneros Shale | |
| Acanthoceras muldoonense Cobban & Scott* | ||
| Acanthoceras granerosense Cobban & Scott* | ||
| Calycoceras (Conlinoceras) gilberti Cobban & Scott* | ||
| 1The genus Plesiacanthoceras was erected for this species by Haas 1964, p. 610), and the writer (Hattin, 1968) has used that generic designation for Kansas specimens. However, Matsumoto and Obata (1966, p. 46) and Kennedy and Hancock (1970, p. 465) regarded Plesiacanthoceras as a synonym of Acanthoceras. | ||
Scott and Cobban (1972, p. 33) recognized that the zone of Mytiloides labiatus embraces zones of the ammonites Watinoceras coloradoense and Mammites nodosoides and overlaps the lower part of the C. woollgari range zone. Zones marked by an asterisk have not yet been recognized in Kansas. The A. muldoonense Zone may be represented by part or all of the Callistina lamarensis Assemblage Zone (Hattin, 1965a, p. 40). Fragmentary molds of large, sharply ribbed, horned ammonites have been collected from the interval separating Kansas beds with the D. pondi fauna from those with the S. gracile fauna, and may represent species of Dunveganoceras. The remaining zones are recognized in Kansas, but modification of these zonal concepts is necessary to account for the entire section, and to make best stratigraphic use of the many distinctive species occurring in these rocks. It seems useful to discuss the range zones of the ubiquitous inoceramid bivalves, as well as the assemblage zones of Greenhorn rocks; therefore, a scheme of range zones and assemblage zones is presented in the succeeding pages. The ranges of all taxa assignable at least to the generic level are shown diagrammatically in Figure 15.
Figure 15--Stratigraphic distribution of Greenhorn macroinvertebrate fossils in Kansas. The graphic column of the Greenhorn Limestone is a composite of central and western Kansas sections, with average thicknesses for members and for position of widely traceable bentonite seams and chalky limestone beds. Because the Lincoln Member lacks uniformity from one exposure to the next the lithologic and stratigraphic features are schematic. 1) In Mitchell County (Loc. 1) transitional beds near the top of the Graneros Shale, containing the Acanthoceras wyomingense Assemblage Zone, include both Borissjakoceras orbiculatum and B. reesidei. B. cf. B. orbiculatum has been recorded in this assemblage zone in the lower Lincoln at Locality 12, and B. sp. has been recorded from the lower Lincoln at Locality 23. 2) Across much of central Kansas specimens of Exogyra columbella and Ostrea beloiti in basal Lincoln skeletal limestones may have been reworked from the upper part of the Graneros Shale. 3) The range of Inoceramus cf. I. tenuistriatus is based on specimens from the middle Lincoln at Locality 12 and Hartland marker bed HL-2 at Locality 4 that were identified by E. G. Kauffman. 4) The range of Inoceramus flavus is based on specimens from the middle Hartland at Locality 13 and Hartland marker bed HL-2 at Locality 3 that were identified by E. G. Kauffman. The Hartland specimens are distorted by compaction and may be I. prefragilis. 5) In the lowest part of its range Syncyclonema? sp. has been collected from the Hartland Member at Locality 13 but has not been recorded from equivalent beds in central Kansas. 6) Calycoceras cf. C. naviculare is known in central Kansas from a single specimen collected as float at the Glen Elder dam excavation (Loc. 1) and probably also by fragments from the Sciponoceras gracile Assemblage Zone at a few other localities. 7) The level at which Tragodesmoceras bassi grades upward to T. carlilense has not been established in the Kansas section. 8) In the uppermost part of its range, Mytiloides labiatus is represented by a broad form that is transitional to Inoceramus latus. [An Acrobat PDF version of this figure is available (524 kB).]
Range Zones of Inoceramid Bivalves
At least three readily identifiable species of inoceramids are represented in the Kansas Greenhorn. These are, in order of ascending stratigraphic position, Inoceramus prefragilis Stephenson, Mytiloides labiatus (Schlotheim) and I. cuvieri Sowerby. In central Kansas, except for Ford and southern Hodgeman counties, Inoceramus prefragilis ranges from the base of the Lincoln Member to a position between HL-4 and the top of the Hartland Member. Because of poor preservation (flattened molds; jointing in shaly chalk) in the part of the section where I. prefragilis terminates upward, and where Mytiloides labiatus commences, the exact upper limit of the former is difficult to determine. The difficulty is compounded by the fact that earliest forms of Mytiloides labiatus are commonly more rounded and less oblique than typical specimens occurring higher in the section. The figures below show the approximate limits of these two species at three widely separated localities.
| Uppermost undoubted I. prefragilis (feet above HL-4) |
Lowermost undoubted Mytiloides labiatus (feet above HL-4) |
|
|---|---|---|
| Loc. 1 | 2.7 | 4.6 |
| Loc. 28 | 6.0 | 4.5 |
| Loc. 14 | 3.4 | 3.4 |
At Localities 28 and 14 the two species overlap, but the stratigraphic thickness of this overlap is not great.
Mytiloides labiatus ranges from a position shortly above Hartland bentonite HL-4 to approximately one foot above the first widespread chalky limestone marker bed in the Fairport Member of the Carlile Shale. The most typical forms of this species characterize the upper part of the Jetmore Member and lower part of the Pfeifer Member. In this report the name M. labiatus is used in the broad sense and embraces forms manifesting wide morphologic variation, even within a single bed. The species is most abundant in the three hard beds and Shellrock limestone bed of the Jetmore. In the upper part of the Pfeifer, above the sugar sand, and especially in the lower part of the Fairport, the species is represented by a broad form referred to by Kaufman (1966, p. 36) as I. labiatus aff. hercynicus. This form is transitional with Inoceramus latus J. de C. Sowerby, a species that is characteristic of the Fairport Member, Carlile Shale (Hattin, 1962, p. 55).
The Inoceramus cuvieri Range Zone begins shortly above Pfeifer marker PF-1, at about the level where broad forms of Mytiloides labiatus first appear, and extends upward at least into the lower part of the Blue Hill Member of the Carlile Shale. Most specimens observed in the Pfeifer Member are small and, in the juvenile stages of growth, high inflated. One incomplete specimen 38.5 cm in height was collected from a concretion of chalky-limestone lying beneath the sugar sand marker bed at Locality 28, Russell County (Fig. 14,D). Larger specimens are abundant in the Fairport Member of the Carlile (see Hattin, 1962, Pl. 11, C).
At Locality 23, Hodgeman County, the lower part of the Lincoln contains rare Inoceramus prefragilis and a few specimens of Inoceramus resembling I. rutherfordi Warren; however, better-preserved material is needed to prove the apparent overlap of these two species. At Locality 12, Kearny County, where the Graneros is gradational with the Greenhorn, undoubted Inoceramus rutherfordi occur within 5 feet of the formational contact, and Inoceramus prefragilis occurs directly above the contact, but ranges of the two species have not been demonstrated to overlap.
Assemblage Zones
Acanthoceras wyomingense Assemblage Zone
The oldest assemblage zone recognized in Greenhorn rocks of Kansas is that characterized by Acanthoceras wyomingense. This zone is well developed in the basal part of the Lincoln Member at Locality 23 where the assemblage is preserved in skeletal and chalky limestone of the lowest 2 feet of the formation. At this locality the assemblage includes the following species.
| Ammonites: | |
| *Acanthoceras wyomingense (Reagan) | |
| Borissjakoceras sp. | |
| Eucalyoceras sp. A. | |
| Pseudocalycoceras sp. | |
| Stomohamites cf. S. simplex (d'Orbigny) | |
| Pelecypods: | |
| *Exogyra columbella Meek | |
| Inoceramus prefragilis Stephenson | |
| Inoceramus cf. I. rutherfordi Warren | |
Common forms are preceded by an asterisk; the remaining forms each are represented in my collection by only a few specimens. At this locality Graneros beds containing the Ostrea beloiti Assemblage Zone of Hattin (1965, p. 40), are missing, and the Lincoln rests unconformably on Graneros beds containing the Callistina lamarensis Assemblage Zone (Hattin, 1965a, p. 44; 1968). At several nearby localities in Hodgeman and Ford counties noncalcareous shale of the Graneros contains only fossils of the C. lamarensis Assemblage Zone and is overlain sharply by skeletal limestones of the basal Greenhorn. For example, at Locality 8, Ford County, the basal bed of the Lincoln is an Ostrea beloiti shell hash and this rests sharply on Graneros beds containing the C. lamarensis assemblage. The oysters probably represent a lag concentrate derived from the O. beloiti zone by sublevation that preceded the main phase of Lincoln deposition. The only other macroinvertebrate fossil recorded in this O. beloiti bed is an abraded gastropod identified as Lispodesthes? sp. Inoceramus prefragilis occurs in shaly chalk lying 6 feet above the base and well-preserved non-crusbed specimens are preserved in a discontinuous bed of chalky limestone having ball-and-pillow structure that lies 7 feet above the base of the Lincoln. The species is common in strata above the limestone bed. At the same locality, poorly preserved molds of Eucalycoceras sp. A occur in a chalky limestone bed lying 10 feet above the base of the member. Proximity of Locality 8 to Locality 23, and similarity of stratigraphic relations at both, suggests that the lower part of the Lincoln Member at Locality 8 probably represents the A. wyomingense Assemblage Zone. At Locality 12, Kearny County, much of the Lincoln Member apparently lies in the A. wyomingense Assemblage Zone. Small, imperfect molds possibly belonging to this species have been collected from the lower part of the member and a single, large, flattened mold was recorded from 5.7 feet above the base of the member. At this locality Inoceramus prefragilis ranges throughout the member, but is not known from the I. rutherfordi-bearing beds that comprise a Graneros-Greenhorn transitional sequence at the top of the Graneros Shale. The lower few feet of the zone also contains Ostrea beloiti, Desmoceras sp., Borissjakoceras cf. B. orbiculatum, and Eucalycoceras sp. A. The last form compares well with some of the Eucalycoceras from Localities 8 and 23, but none are identifiable specifically. Graneros beds lying about 4 feet beneath the base of the Lincoln here contain excellent specimens of Inoceramus rutherfordi, Ostrea beloiti, molds of Borissjakoceras sp. and Stomohamites? sp., and the mold fragment of a large, horned ammonite. These upper Graneros fossils seemingly represent the uppermost part of the O. beloiti Assemblage Zone.
Northward from southern Hodgeman County (Loc. 23), the unconformity separating the Graneros and Greenhorn climbs in the section so that in the area between northern Pawnee and Lincoln counties basal Greenhorn beds assigned to the Calycoceras? canitaurinum-Exogyra aff. E. boveyensis Assemblage Zone rest unconformably on Graneros beds containing the Ostrea beloiti Assemblage Zone (Hattin, 1968). In this area the contact lies on or as much as 3.2 feet above a regionally persistent bentonite seam ("X" bentonite of authors).
At some localities north of Lincoln County the Graneros-Greenhorn contact is apparently conformable, e.g. Localities 6 and 46, but fossil evidence is insufficient to document the biostratigraphic zonation. However, at Locality 1, Mitchell County, Graneros beds above the "X" bentonite are far thicker than usual (17.6 feet) and evidence is lacking for unconformity at the Graneros-Greenhorn contact (Hattin, 1968). These upper Graneros beds are silty and weakly calcareous at the base, grading upward to silty chalky shale at the top. This interval contains a layer of calcareous septarian concretions which is apparently the source of a few specimens of Acanthoceras wyomingense collected by local residents. The concretions also contain rare Stomohamites sp. Adjacent underlying calcareous and chalky shales contain the following forms.
| Ammonites: | |
| Borissjakoceras reesidei Morrow | |
| Borissjakoceras orbiculatum Stephenson | |
| Eucalycoceras sp. | |
| Stomohamites cf. S. simplex d'Orbigny | |
| Bivalves: | |
| corbulid (1 mold) | |
| Inoceramus cf. I. rutherfordi | |
This assemblage resembles those of the lower Lincoln at Localities 12 and 23 but occurs here in the Graneros Shale. Typical skeletal limestones of the basal Lincoln, with faunal elements of a succeeding assemblage zone, lie above the shale section just described.
Thus the Acanthoceras wyomingense Assemblage Zone is recognized with certainty only at three Kansas localities (12, 23, and 1). Stratigraphic considerations and limited paleontological data suggest that equivalent strata are present also in the lower part of the Lincoln at Locality 8. The assemblage zone is equivalent to the Acanthoceras? wyomingense zone of Cobban (1961) and according to Jeletzky (1968, p. 24) is approximately equivalent to the Acanthoceras athabascense zone of Canada.
Calycoceras? canitaurinum-Exogyra aff. E. boveyensis Assemblage Zone
The second Greenhorn assemblage zone is known mostly from skeletal limestones (chiefly calcarenites) lying at the base of the Lincoln Member in the middle part of the central Kansas outcrop, from east-central Hodgeman County to Mitchell County. The zone probably is represented also by basal Lincoln beds farther to the northeast, but diagnostic species of the zone have not yet been recorded from that area. This assemblage is characterized by Calycoceras? canitaurinum Haas, Exogyra aff. E. boveyensis Bergquist and Eucalycoceras sp. B. These species represent the D. pondi zone of Cobban and Reeside (1952, p. 1017) and of Cobban (1961, p. 740), and the zone of Calycoceras? canitaurinum of the Pueblo, Colorado area (Cobban and Scott, 1972, p. 33). Specimens assigned to D. cf. D. pondi are known from two or three central Kansas localities, but are too rare to be considered as zonal indices. The C.? canitaurinum assemblage includes the following species.
| Ammonites: | |
| Calycoceras? canitaurinum (Haas) | |
| †Dunveganoceras cf. D. pondi Haas | |
| *Eucalycoceras sp. B | |
| *Stomohamites cf. S. simplex d'Orbigny | |
| Bivalves: | |
| †Exogyra columbella Meek | |
| *Exogyra aff. E. boveyensis Bergquist | |
| *Inoceramus prefragilis Stephenson | |
| Ostrea beloiti Logan | |
| Cirripeds: | |
| †Calantica? sp., isolated plates | |
Names preceded by an asterisk are most common, those preceded by a dagger are rare, all others are of intermediate abundance. No single locality has yielded all species in this assemblage; the best collections are from Localities 3 and 26 in Russell County.
At Locality 30, east-central Hodgeman County, the basal Lincoln contains Ostrea beloiti, Inoceramus prefragilis, and Eucalycoceras sp. B. This small assemblage is assigned to the Calycoceras? canitaurinum-Exogyra aff. E. boveyensis Assemblage Zone. just 10 miles farther south, at Locality 23, the basal Lincoln contains the Acanthoceras wyomingense Assemblage Zone. This seemingly anomalous biostratigraphy has been explained by the writer (Hattin, 1965, p. 44) who showed that the unconformity separating the Graneros and Greenhorn climbs stratigraphically northward from Locality 23 so that at Locality 30 the basal Lincoln is younger than at Locality 23.
At Locality 55, southeastern Hodgeman County, Exogyra aff. E. boveyensis is common in beds lying 9 to 10 feet above the base of the Lincoln. Shortly, to the west, at Locality 8, Ford County, this species is common in the upper 4.3 feet of the Lincoln where it occurs with abundant Inoceramus prefragilis, isolated cirriped plates, and fragmentary ammonite molds that compare well with Calycoceras? canitaurinum. Still farther west, at Locality 12, Kearny County, E. aff. E. boveyensis occurs sparingly in the upper 6 feet of the Lincoln Member where it is associated with Inoceramus prefragilis and Eucalycoceras sp. B. At Locality 13, Kearny County, I. prefragilis, Eucalycoceras sp. B., and Stomohamites cf. S. simplex occur in the topmost bed of the Lincoln. At these five localities (30, 55, 8, 12 and 13) the stratigraphic position of elements of the Calycoceras? canitaurinum Assemblage Zone lends force to the argument that the Lincoln Member is diachronous, climbing the section from west to east, and that lower Lincoln beds in the middle part of the central Kansas outcrop pass southwestward into the middle and upper parts of the member in southern Hodgeman, Ford, and Kearny counties.
In sections containing elements of the Acanthoceras wyomingense and Calycoceras? canitaurinum assemblages, the two zones are separated by a few feet of strata having Inoceramus prefragilis as the only common species. For example at Locality 12 approximately 5 feet of strata lying in the middle of the Lincoln Member are at present not assigned to either assemblage zone. At Locality 8, approximately 5 feet of strata, lying 4.3 to 9.3 feet below the top of the member, are unassigned. At Locality 1, the two assemblages occur within 1.5 feet of each other in Graneros-Greenhorn transition beds near the top of the Graneros Shale.
Undesignated Assemblage Zone
The third well-defined Greenhorn assemblage zone is that of Sciponoceras gracile, discussed later, which lies in the midst of the Hartland section of central Kansas, and in the basal 6.7 feet of the Bridge Creek Member in Hamilton County. Between the Calycoceras? canitaurinum and Sciponoceras gracile Assemblage Zones are many feet of Lincoln and/or Hartland beds in which the only common macroinvertebrate fossil is Inoceramus prefragilis. Invertebrate fossils from this interval in central Kansas are listed below.
| Ammonites: | |
| ammonite mold, possibly Dunveganoceras (Loc. 3, near middle of Lincoln) | |
| Desmoceras (s.l.) sp. (Loc. 26, in lower half of Lincoln) | |
| Eucalycoceras sp. B (Locs. 2, 3, 26, 27, 38, lower half of Lincoln) | |
| Stomohamites? sp. (Loc. 26) | |
| Bivalves: | |
| Exogyra aff. E. boveyensis Bergquist (Locs. 6, 47) | |
| Inoceramus prefragilis Stephenson (throughout the interval) | |
| ostreid fragments (Locs. 3, 26, 27, lower half of Lincoln) | |
| Cirripeds: | |
| Stramentum sp. A (Locs. 3, 4, 28) | |
In westernmost Kansas, beds containing the Sciponoceras gracile fauna lie in the lower part of the Bridge Creek Member rather than in the Hartland as in central Kansas. In this area apparently the entire Hartland lies between beds containing elements of the Calycoceras? canitaurinum assemblage and the base of the Sciponoceras zone. The Hartland Member contains the following forms at Locality 13, Kearny County.
| Ammonites: | |
| ammonite mold, possibly Dunveganoceras, upper part of Hartland | |
| Desmoceras (s.l.) sp. (bed 19 feet above base of Hartland) | |
| Eucalycoceras sp. B (lower half of Hartland) | |
| Stomohamites? sp. (bed 19 feet above base of Hartland) | |
| Bivalves: | |
| Inoceramus flavus Somay (distorted specimen, maybe I. prefragilis) | |
| Inoceramus prefragilis Stephenson (throughout the Hartland) | |
| Syncyclonema? sp. (lower part of Hartland) | |
Gross similarity is evident in the assemblage of fossils that appear in the two lists given above, but preservation of fossils recovered from the interval is mostly too poor for the collection to be of much biostratigraphic value at this time. At Locality 12, Kearny County, Exogyra aff. E. boveyensis ranges into the basal foot or two of the Hartland, and at Locality 13 Eucalycoceras sp. B ranges stratigraphically upward to a chalky limestone bed lying 19 feet above the top of the Lincoln. This suggests that the Calycoceras? canitaurinum assemblage may embrace part of the Hartland in that area. In central Kansas Eucalycoceras sp. B. occurs well above beds containing C? canitaurinum or Dunveganoceras cf. D. pondi. Until better-preserved ammonite specimens are recovered from the middle and upper parts of the Lincoln of central Kansas, and from the Hartland of western Kansas, the upper limit of the C? canitaurinum-Exogyra aff. E. boveyensis Assemblage Zone must remain undefined. For the present, most of the Lincoln and the lowermost Hartland of central Kansas, and possibly all of the type Hartland are considered simply as an undesignated assemblage zone. Apparently these beds correspond in large part to the Dunveganoceras conditum and D. albertense zones of Cobban (1961, p. 740) and of Cobban and Scott (1972, p. 33).
Sciponoceras gracile Assemblage Zone
The most highly diversified faunal assemblage in Greenhorn rocks of Kansas is that belonging to the zone of Sciponoceras gracile (Shumard) of Cobban and Reeside (1952, p. 1017). In Kansas this assemblage consists of the following species:
| Ammonites: | |
| Allocrioceras annulatum (Shumard) | |
| *Baculites sp. (smooth form) | |
| †Calycoceras cf. C. naviculare (Mantell) | |
| †Hemiptychoceras reesidei Cobban & Scott (2 specimens, from Locs. 2 and 3) | |
| *Kanabiceras septemseriatum (Shumard) | |
| Metoicoceras whitei Hyatt | |
| †Pseudocalycoceras dentonense (Moreman) | |
| †Scaphites brittonensis Moreman | |
| Sciponoceras gracile (Shumard) | |
| Worthoceras gibbosum Moreman | |
| *Worthoceras vermiculum (Shumard) | |
| Pelecypods: | |
| Inoceramus flavus Sornay | |
| *Inoceramus prefragilis Stephenson | |
| Inoceramus cf. I. tenuistriatus Nagao & Matsumoto | |
| †Martesia? sp. ( 1 specimen) | |
| †Plicatula? sp. (2 specimens) | |
| Phelopteria sp. A. | |
| †Teredolithus sp. | |
| Gastropods: | |
| *Cerithiella sp. A. | |
| Brachiopods: | |
| †Discinisca sp. | |
| Cirripeds: | |
| acrothoracian barnacle borings | |
In this list, the more common forms are preceded by an asterisk; rare forms are preceded by a dagger. The most abundant and characteristic species is a much inflated form of Inoceramus prefragilis.
This assemblage characterizes Hartland strata in the interval extending from the base of marker bed HL-1 to the first continuous bed of chalky limestone lying above marker bed HL-2. Plicatula? sp., Discinisca sp. and Teredolithus sp. occur in marker bed HL-1, although one specimen of Plicatula? sp. was recorded also from 0.5 foot beneath that bed. The greatest diversity of species occurs in marker bed HL-2 from which 12 forms have been recorded. Kanabiceras septeniseriatum, Sciponoceras gracile, Phelopteria sp. A, and Cerithiella sp. A first appear in bed HL-1 and, terminate at a discontinuous chalky limestone bed lying shortly above HL-2. Several species in this assemblage have been recorded only in marker bed HL-2 (Fig. 15). Worthoceras vermiculum, Baculites sp. and Allocrioceras annulatum first appear in bed HL-2 and range slightly higher in the section than S. gracile. Only Inoceramus prefragilis and Phelopteria sp. A range throughout the interval regarded as comprising this zone.
Elements of this faunal assemblage have been reported from localities scattered widely through the Gulf Coast and Western Interior region from Texas (esp. Moreman, 1942), where the fauna occurs in the Britton Formation, to Utah (Gregory, 1950; 1951), where the fauna occurs in the Tropic Shale, and north to Montana (Cobban, 1951, p. 2184) where this fauna occurs in the Greenhorn of the, northwestern flank of the Black Hills. Sciponoceras gracile, the index species of this assemblage, occurs also as far to the northwest as the Sweetgrass Arch (Cobban, 1955, p. 202), where it occurs in the Colorado Shale. The fauna is well known in the lower part of the Bridge Creek Limestone Member of the Greenhorn in central Colorado (e.g. Scott, 1962, p. 13) and southeastern Colorado (Cobban and Scott, 1972, p. 31). Although S. gracile has not yet been reported from Canada, Stelck and Wall (1955, p. 16) reported S. cf. S. gracile from the Peace River area of Alberta and Jeletzky (1968, Fig. 2) recognizes a Baculites (Sciponoceras) cf. gracile and Prionocyclus (Collignoniceras) n. sp. subzone within the Watinoceras and Inoceramus labiatus zone of the Canadian Western Interior. This distinctive and extraordinarily widespread assemblage of organisms occurs in Kansas in a stratigraphic thickness of only 3.6 to 6.7 feet, thus making it one of the most distinctive and valuable biostratigraphic units in the Kansas Cretaceous.
Undesignated Assemblage Zone
Above the Sciponoceras gracile Assemblage Zone are several feet of strata from which little else than Inoceramus prefragilis has been collected. This interval includes all beds from the uppermost occurrences of the S. gracile assemblage, i.e. the widespread chalky limestone bed lying anywhere from 1.3 feet (Loc. 1) to 2.7 feet (Loc. 14) above Hartland marker bed HL-2, to the apparent lowest occurrences of Mytiloides labiatus (Schlotheim), Tragodesmoceras bassi Morrow, and Watinoceras reesidei Warren. [Note: Where this bed is missing, or poorly developed, as at Localities 4 and 6, the highest occurrence of the S. gracile assemblage is in HL-2.] This interval reaches maximum known thickness at Locality 14 where it is 6.9 feet, and in central Kansas diminishes gradually and uniformly northeastward from Localities 8 and 51 where it is 4.7 feet thick.
Mytiloides labiatus-Watinoceras reesidei Assemblage Zone
This assemblage zone is characterized generally by the two zonal indices and extends from the lowest occurrence of M. labiatus, in the upper part of the Hartland Member, upward approximately to and including Jetmore marker bed JT-6. The lowest observed occurrence of Mytiloides labiatus is in a 1.1-foot-thick shaly chalk unit lying 3.65 feet above marker bed HL-3 in the Bridge Creek Member at Locality 14. The species occurs also in the superjacent chalky limestone bed where M. labiatus is accompanied by Tragodesmoceras bassi?, Puebloites, and Watinoceras reesidei?; this limestone is the second one above marker bed HL-3. A mold of T. bassi (Pl. 6,H) was collected in the fourth chalky limestone bed above HL-3 at Locality 51 where the species occurs with Watinoceras sp. (probably a coarsely ribbed variant of W. reesidei). Watinoceras reesidei is abundant and well preserved in Jetmore markers JT-1 and JT-6. The upper limit of this zone is defined arbitrarily, because W. reesidei is known sparingly in the Jetmore to as high as marker bed JT-8, but other species are more characteristic of the interval above JT-6. Poorly preserved specimens of Baculites cf. B. yokoyamai are known in the interval extending from JT-1 to JT-5 but are more characteristic of the overlying assemblage zone. Species occurring in this assemblage zone are as follows:
| Bivalves: | |
| Anomia sp. A. | |
| †Inoceramus prefragilis Stephenson (basal part of zone only) | |
| *Mytiloides labiatus (Schlotheim) | |
| ostreid sp. | |
| Cephalopods: | |
| Baculites cf. B. yokoyamai Tokunaga & Shimizu (sparse poorly preserved specimens) | |
| †Mammites nodosoides subsp. wingi Morrow? (JT-2 at Loc. 38) | |
| †Tragodesmoceras bassi Morrow | |
| †Puebloites sp. (Loc. 14 only, at base of zone) | |
| *Watinoceras reesidei Warren | |
| †Vasoceras birchbyi Cobban & Scott (JT-1 only, Loc. 14) | |
| Brachiopods: | |
| †Discinisca sp. | |
Common species are prefixed with an asterisk; rare species are prefixed with a dagger. This assemblage zone corresponds to the zone of Watinoceras coloradoense (Henderson) of Cobban and Scott (1972, p. 33).
Mytiloides labiatus-Mammites nodosoides Wingi Assemblage Zone
This assemblage zone overlaps that of the preceding zone in a single bed, JT-6, where Mammites nodosoides wingi is first an important species. The upper limit of this assemblage zone is the Shellrock limestone bed (JT-13) which is the known upper limit of occurrence of M. nodosoides wingi. The best preserved specimens of Baculites cf. B. yokoyamai occur within this assemblage zone, in beds JT-6 through JT-11. This assemblage is also characterized by Tragodesmoceras bassi most Kansas specimens of which were collected from the interval JT-8 to JT-12.
Fossils in the Mytiloides labiatus-Mammites nodosoides wingi Assemblage Zone include the following:
| Ammonites: | |
| *Baculites cf. B. yokoyamai Tokunaga & Shimizu | |
| *Mammites nodosoides subsp. wingi Morrow | |
| Stomohamites cf. S. simplex (d'Orbigny) (mold in JT-13 at Loc. 46) | |
| Tragodesmoceras bassi Morrow | |
| *Watinoceras reesidei Warren (common only in JT-6) | |
| Pelecypods: | |
| *Anomia sp. A. | |
| *Mytiloides labiatus (Schlotheim) | |
| †Pseudoperna bentonensis Logan | |
| *Pycnodonte sp. A. | |
| Teredolithus sp. | |
| Brachiopods: | |
| †Discinisca sp. | |
| Cirripeds: | |
| †scalpellid | |
Common forms are preceded by an asterisk; rare forms are preceded by a dagger. This assemblage corresponds to the Mammites nodosoides zone of Cobban and Scott (1972, p. 33).
Undesignated Assemblage Zone
The stratigraphic interval from the top of the Shellrock limestone bed (JT-13) to the base of marker bed PF-1 contains no unique species that is common, and is therefore considered as an undesignated assemblage zone. Species recorded in this interval include the following:
| Bivalves: | |
| Anomia sp. A | |
| *Mytiloides labiatus (Schlotheim) | |
| *Pseudoperna bentonensis Logan | |
| Cephalopods: | |
| Baculites cf. B. yokoyamai Tokunaga & Shimizu | |
| hamitids, juveniles | |
| †Watinoceras reesidei Warren | |
| †Tragodesmoceras bassi Morrow? | |
| Cirripeds: | |
| Stramentum canadensis (Whiteaves) | |
| scalpellid, sp. | |
Common species are prefixed by an asterisk, rare species are prefixed by a dagger. The top of this zone marks the apparent upper limit of Watinoceras reesidei but the available material is of poor quality and specimens are very rare in this interval.
In this interval Tragodesmoceras bassi is known from poorly preserved material at a single locality.
Mytiloides labiatus-Collignoniceras woollgari-Inoceramus cuvieri Assemblage Zone
The uppermost part of the Greenhorn in Kansas is characterized by late, usually broad forms of Mytiloides labiatus, together with Inoceramus cuvieri Sowerby and Collignoniceras woollgari (Mantell). The base of this assemblage zone is Pfeifer marked bed PF-1. Collignoniceras woollgari apparently first appears in the section at this level, based on poor material, and is known definitely from about 2 feet above this marker bed. Inoceramus cuvieri first appears 2.3 feet above PF-1 at Locality 19 (Rush County), 3 feet above PF-1 at Locality 5 (Ellis County), and in the first concretionary bed of chalky limestone below the sugar sand (PF-2) at a number of other localities. Molds of juvenile ammonites probably assignable to Tragodesmoceras bassi occur shortly below the sugar sand at Locality 49, Mitchell County and a single fragmentary mold suggesting this species was collected from the first chalky limestone marker bed of the Fairport Member in northeastern Ellis County, but the species, if indeed it is T. bassi, is rare in all beds above JT-12. At Locality 14, Hamilton County, I. cuvieri has not been identified positively in the Bridge Creek Member and C. woollgari was not recorded there below the Fencepost limestone bed. Collignoniceras woollgari and I. cuvieri range upward throughout the Fairport Member, Carlile Shale, and the latter apparently continues into the lower part of the Blue Hill Member, Carlile Shale, in central Kansas (Hattin, 1962, p. 82).
The top of the Mytiloides labiatus-Collignoniceras woollgari-Inoceramus cuvieri Assemblage Zone lies about 1 foot above the first chalky limestone bed in the Fairport Member, Carlile Shale, at the level where the broad form of Mytiloides labiatus gives way, by evolutionary gradation, to Inoceramus latus J. de C. Sowerby. This broad form of M. labiatus was referred to as I. labiatus aff. hercynicus by Kauffman (1966, p. 36). The assemblage zone contains the following species:
| Bivalves: | |
| Anomia sp. A | |
| *Inoceramus cuvieri Sowerby | |
| *Mytiloides labiatus (Schlotheim) | |
| Pseudoperna bentonensis (Logan) | |
| Cephalopods: | |
| *Baculites cf. B. yokoyamai Tokunaga & Shimizu | |
| Collignoniceras woollgari (Mantell) (most abundant in Fencepost bed) | |
| †Stomohamites cf. S. simplex (d'Orbigny) (PF-1 at Loc. 14) | |
| Tragodesinoceras bassi Morrow? | |
| †T. carlilense Cobban | |
| hamitids (minute crystalline casts) | |
| Cirripeds: | |
| scalpellid, sp. | |
| †stramentid, sp. | |
Common forms are preceded by an asterisk; rare forms are preceded by a dagger. juvenile forms of Tragodesmoceras from the lower part of the zone are assigned questionably to T. bassi Morrow. A single specimen of T. carlilense Cobban, from the Fencepost limestone bed, was recorded from a block of stone that forms part of the east wall of Albertson Hall at Fort Hays Kansas State College in Hays. The assemblage zone corresponds roughly with the zone of overlap of C. woollgari and Inoceramus labiatus as shown by Cobban and Scott (1972, p. 33) but embraces also the lower few feet of the Fairport Member, Carlile Shale.
Correlation
The Acanthoceras wyomingense Assemblage Zone corresponds to the Western Interior zone of Acanthoceras? sp. A of Cobban and Reeside (1952, p. 1017), a species later identified as Acanthoceras? wyomingense by Cobban (1961, p. 739), and with the zone of Plesiacanthoceras wyomingense of Cobban and Scott (1972, p. 33). According to Jeletzky (1968, p. 24), the Canadian zone of A. athabascense Warren and Stelck is approximately equivalent to the zone of A? wyomingense. American occurrences of the zonal index species have been documented by Cobban (1951), Cobban and Reeside (1952a), and by Haas (1963, p. 13). In addition to Kansas occurrences, the species has been recorded in the uppermost part of the Belle Fourche Shale in the Black Hills (Cobban, 1951, p. 2182), near the middle of the Frontier Formation in central and south-central Wyoming (Cobban and Reeside, 1952a), in the upper half of the Frontier Formation in north-central Wyoming (Cobban and Reeside, 1952a, p. 1955), and from near the base of the Cody Shale in south-central Montana (Cobban and Reeside, 1952a, p. 1960). Acanthoceras athabascense, regarded as a synonym of A. wyomingense by Haas (1963, p. 3), has been recorded in the lower part of the Labiche Shale of Alberta.
In Kansas and elsewhere in the Western Interior region, beds containing Acanthoceras wyomingense are underlain by strata containing Acanthoceras amphibolum and Inoceramus rutherfordi. In a discussion of the Acanthoceras rhotomagense group of ammonites Kennedy and Hancock (1970, p. 488) noted that this nearly worldwide Middle Cenomanian group is apparently absent from the Western Interior and that its place "is possibly occupied by A. amphibolum Morrow." Kauffman (1966, p. 36) regarded the late forms of Inoceramus rutherfordi, which occur with A. amphibolum, as Middle Cenomanian in age, but Cobban and Scott (1972, p. 31) assigned this species to the Late Cenomanian. Haas (1963, p. 13) believed A. wyomingense indicated a Late Cenomanian age, as did Scott and Cobban (1972, p. 31, 33). Jeletzky (1968, p. 24) suggested that in Canada A. athabascense (=A. wyomingense) is of early Late Cenomanian age. The earliest occurrences of Inoceramus prefragilis, which in Kansas are with A. wyomingense, were regarded as Late Cenomanian in age by Kauffman (1966, p. 36). This form was recorded in the Greenhorn of Colorado and westernmost Kansas as Inoceramus pictus J. de C. Sowerby by Cobban and Scott (1972) and was regarded as synonymous with I. pictus by Seitz (1959, p. 117). Apparently the two forms are biostratigraphically analogous, if not conspecific. Porthault and others (1966, p. 436) indicate that in France the earliest occurrences of I. pictus are early Late Cenomanian, and Seitz (1959, p. 120) showed the earliest occurrences in Germany also are of Late Cenomanian age.
The Calycoceras? canitaurinum-Exogyra aff. E. boveyensis Assemblage Zone corresponds to the zone of Dunveganoceras pondi of Cobban and Reeside (1952, p. 1017) and to the Calycoceras? canitaurinum zone of Cobban and Scott (1972, p. 33). Molds resembling D. pondi have been recorded in basal Lincoln strata at a few central Kansas localities. Haas (1949) described these two species on the basis of specimens from near the base of the Cody Shale close to Greybull, Wyoming. The two species occur also in the uppermost part of the Frontier Formation 16 miles south of Greybull, Wyoming (Cobban and Reeside, 1952a, p. 1957). In south-central Montana both species occur in the lower part of the Cody Shale in the Crow Indian Reservation (Cobban and Reeside, 1952a, p. 1961). In the Black Hills area these species occur in the basal part of the Greenhorn (Cobban and Reeside, 1952a, p. 1945). Calycoceras? canitaurinum has been reported from the upper part of the Lincoln Member in the Littleton area, Colorado (Scott, 1962, p. 13) and from the upper part of the Lincoln Member near Pueblo, Colorado (Cobban and Scott, 1972, p. 15). These last occurrences correspond in stratigraphic position with the upper Lincoln position of the C? canitaurinum-E. aff. E. boveyensis Assemblage Zone in Ford and Kearny counties, Kansas. This zone is of Late Cenomanian age (Cobban, 1961, p. 740; Jeletzky, 1968, p. 27; Cobban and Scott 1972, p. 31).
The first of the three undesignated assemblage zones described above, representing the middle and upper parts of the Lincoln Member and lowermost Hartland of central Kansas, and virtually all of the type Hartland of Kearny County, corresponds to the Late zones of Dunveganoceras conditum and D. Albertense of Cobban (1961, p. 740) and of Cobban and Scott (1972, p. 33).
The Sciponoceras gracile Assemblage Zone has wide distribution in the Western Interior and Gulf Coast regions of the U.S., as outlined in an earlier section. In central Kansas it occurs in the middle part of the Hartland Member; in western Kansas it occurs in the lower few feet of the Bridge Creek Member. The assemblage occurs also in the lower part of the Bridge Creek Member of the Greenhorn in central and southern Colorado (Scott, 1962, p. 13; Kauffman, 1961, p. 329-330; Cobban and Scott, 1972, p. 31). In Utah the assemblage occurs in the Tropic Shale (Gregory, 1950, p. 104; 1951, p. 36). In central Texas the assemblage has been recorded in the Britton Formation (Moreman, 1942, p. 194) and in West Texas in the Chispa Summit Formation (Adkins, 1931, p. 38). Jicha (1954, p. 27) reported the assemblage from the lower part of the Colorado Shale (=Mancos Shale?, query mine) in southwestern New Mexico and Page and Repenning (1958, p. 118) noted occurrence of the assemblage in the lower part of the Mancos Shale in the Black Mesa Basin of Arizona. Farther north, elements of the S. gracile assemblage occur in the upper part of the Greenhorn Limestone in the Black Hills region (Cobban, 1951, p. 2185) and in the lower part of the Cody Shale along the east flank of the Bighorn Mountains of north-central Wyoming (Cobban and Reeside, 1952a, p. 1955). The zonal index, S. gracile has been recorded from as far to the northwest as the Sweetgrass arch of northwestern Montana where it occurs in the Colorado Shale (Cobban, 1951, p. 2186). Finally, S. cf. S. gracile has been reported from the Kaskapau Formation of Alberta (Stelck and Wall, 1955, p. 16) where, together with an undescribed species of Prionocyclus, it is the basis for a subzone that Jeletzky (1968, fig. 2) correlated with that of S. gracile in the U.S.
The Sciponoceras gracile Assemblage Zone was interpreted as lying at the base of the Turonian Stage by Cobban and Reeside (1952), but this zone and the equivalent Canadian zone were regarded by Jeletzky (1968, fig. 2) as lying shortly above the base of that stage. However, Cobban (1971, p. 18) has recently interpreted the zone as being of very late Cenomanian age and Cobban and Scott (1972, p. 31) regard this zone as being of latest Cenomanian age on the basis of occurrence in it of "Pseudocalycoceras, Calycoceras of the naviculare group, and Inoceramus pictus" (= I. prefragilis of the present report). The problem of the Cenomanian-Turonian boundary has been debated by numerous authors and will not be dealt with here. It is sufficient to note that the S. gracile assemblage contains elements that have been traditionally assigned to the Late Cenomanian as well as a few forms, such as Worthoceras vermiculum (Portbault and others, 1966, p. 436), that occur in the Early Turonian of Europe. In this report I am considering the S. gracile assemblage as latest Cenomanian in age on the basis of occurrence in it of Calycoceras cf. naviculare and Pseudocalycoceras.
The second undesignated assemblage zone apparently marks the base of the Turonian because none of the forms diagnostic of the Cenomanian have been recorded in it. This zone is characterized by the upper part of the range of Inoceramus prefragilis. In Europe, the equivalent species, I. pictus, crosses the Cenomanian-Turonian boundary (see Seitz, 1959, p. 120; Porthault and others, 1966, p. 436).
Mytiloides labiatus is universally accepted as an Early Turonian index fossil (Jeletzky, 1968, p. 28). The three Greenhorn assemblage zones containing this species are therefore all regarded as of Early Turonian age. The Mytiloides labiatus-Watinoceras reesidei Assemblage Zone corresponds with the zone of Watinoceras coloradoense (Henderson) of the Bridge Creek Member in Colorado (Cobban and Scott, 1972, p. 33) and represents the lower part of the zone of Inoceramus labiatus and W. reesidei of Cobban (1951, p. 2197). Less than a dozen specimens in my large Watinoceras collection seem to fit the description of Watinoceras coloradoense, but none of these specimens is complete and most are fragments of adult whorls. The vast majority of my specimens, more than 95%, are clearly assignable to W. reesidei. The adult stage of W. reesidei has not been described, so the questionable specimens may be W. reesidei rather than W. coloradoense. In my collection the larger specimens of W. reesidei include two varieties, one having dense ribbing and weak tuberculation (Pl. 8, J; 9, F) and another having less dense, very strong ribbing with strong tuberculation (Pl. 9,G). The latter form has dense ribbing in the earlier stages of growth and shows neither the thinning and increase in density of ribs nor decrease in size of tubercles in the adult stage as in W. coloradoense (Cobban and Scott, 1972, p. 76). The form shown in Plate 9,G is regarded as a coarse variant of W. reesidei and may be expression of sexual difference from the more densely ribbed variety. Cobban and Scott (1972, p. 21) reported W. coloradoense from the basal bed of the Jetmore equivalent of the Bridge Creek at my Locality 14 (Hamilton County). Poor material in my collection from the same bed is identified equivocally as W. reesidei.
Watinoceras reesidei is widely distributed in North America. This species occurs with Mytiloides labiatus in the lower part of the Colorado Shale in northwestern Montana (Cobban, 1956, p. 1003), and in the Greenhorn Member of the Cody Shale of southern Montana (Richards, 1955, p. 52). In Canada these two species occur together in many areas along the foothills of the Canadian Rockies and adjacent plains, including the lower part of the Alberta Group and equivalent strata. For example, cooccurrence of W. reesidei and M. labiatus has been reported in the Vimy Formation in southern Alberta (Stott, 1963, p. 45), from the Kaskapau Formation of northern Alberta (Warren, 1930, p. 58), and from equivalent rocks in the District of Mackenzie (Warren, 1947, p. 119). Cobban and Gryc (1961, p. 178) have recorded the cooccurrence of these two species in the Seabee Formation of the Arctic slope of Alaska.
The Mytiloides labiatus-Mammites nodosoides wingi Assemblage Zone corresponds to the Mammites nodosoides zone of Cobban and Scott (1972, p. 31) and spans an almost identical interval within the Jetmore Member of central Kansas as in the Bridge Creek Member near Pueblo, Colorado. Mammites nodosoides is a well-known Early Turonian species and is widely distributed in Europe, southern Asia, Africa, and South America (see Lawrence and others, 1966, p. 293; Cobban and Scott, 1972, p. 79). In the American West and Southwest forms referable to W. nodosoides have been reported from widely scattered localities in Texas (Powell, 1963, p. 310), New Mexico (Lawrence and others, 1965, p. 293), Colorado (Scott and Cobban, 1972, p. 81) and Kansas (Morrow, 1935, p. 467, 468), and Mammites aff. nodosoides has been reported from as far north as northern Wyoming where it occurs with Inoceramus labiatus and Watinoceras cf. coloradoense (Hose, 1955, p. 98). Specimens are sparse in all Kansas sections and the paucity of references to M. nodosoides in literature on the Western Interior suggests that the form was common only locally. Morrow (1935, p. 464) recorded M. wingi (=M. nodosoides wingi of this report) in the Pfeifer Member of the Kansas Greenhorn but to date I have found no specimens above the Shellrock limestone bed (JT-13) of the Jetmore Member.
The third undesignated Greenhorn assemblage zone occupies the lower few feet of the Pfeifer Member and lies within the range zone of Mytiloides labiatus. Its age is therefore early Turonian. This interval apparently corresponds to beds 121 through 129 in the Rock Canyon section described by Cobban and Scott (1972, p. 22).
The uppermost biostratigraphic unit in the Kansas Greenhorn is defined on the basis of overlap in the range of Mytiloides labiatus with the ranges of Collignoniceras woollgari and Inoceramus cuvieri. On the basis of overlapping range zones, this unit can be considered a concurrent range zone (American Commission on Stratigraphic Nomenclature, 1970, p. 12). The overlapping range of M. labiatus and C. woollgari is now widely recognized as evident in the work of Reeside (in Bass, 1926, p. 66), Matsumoto and Miller (1958, p. 354), Hattin (1962, p. 54) Cobban and Scott (1972, p. 33), and Jeletzky (1968, p. 30).
Collignoniceras woollgari has wide distribution in the U.S. Western Interior, including an area extending on the east from central Kansas and southern Colorado to western Iowa, northeastern Nebraska and the Black Hills and on the west from northeastern Arizona to northwestern Montana. Although additional references could be cited, the principal ones are summarized by Cobban and others (1956, p. 1271-1272). Occurrences of this species in the Upper Cretaceous of Canada have been summarized briefly by Jeletzky 1968, p. 30). Matsumoto (1959, p. 106) stated that the species occurs in the Gulf Coast region (apparently in the Arcadia Park Formation of the Eagle Ford Group) and also in the Chispa Summit Formation of West Texas (1959, p. 92). Specimens are known also from the Upper Cretaceous of California and Oregon (Matsumoto, 1959, p. 108). In the British Chalk C. woollgari occurs in the zone of Terebratulina lata (Wright and Wright, 1951, p. 30) which also contains broad forms of Mytiloides labiatus (Woods, 1912, p. 13) and the earliest forms of I. cuvieri (Woods, 1912, p. 7). The T. lata zone therefore is at least in part correlative with the Mytiloides labiatus-C. woollgari-I. cuvieri Assemblage Zone of Kansas. Basse (1959, p. 15, 16) has indicated a Middle Turonian age for strata in northern France that contain C. woollgari, and Matsumoto (1959, p. 108, also noted the Middle Turonian age of this form. However, the small part of the C. woollgari Range Zone that overlaps the upper part of the M. labiatus Range Zone is here considered to be of latest Early Turonian age. Refinements in inoceramid taxonomy, involving broad forms of M. labiatus s.l., may eventually justify assignment of this assemblage zone to the early Middle Turonian.
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Kansas Geological Survey, Geology
Placed on web June 5, 2010; originally published May 1975.
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