Onaga Shale (strat. sections 9, 10, 12, 14)--The Onaga Shale (Moore and Mudge, 1956, p. 2273), the lowermost formation of Permian age, is composed, in ascending order, of the Towle Shale, Aspinwall Limestone, and Hawxby Shale Members. The formation is rather poorly exposed in the western half of the area. Along Massasoit Creek southwest of Dover and along the north edge of the area east of Delia, the Onaga is 27-31 feet thick. South of Dover, where it contains channel deposits, the Onaga may be as much as 155 feet thick. It rests conformably on the Brownville Limestone Member of the Wood Siding Formation, and, except where the channels are present, its members are conformable.
Towle Shale Member--The Towle Shale Member (see chart by R. C. Moore and G. E. Condra, in Moore, 1932, p. 95-97) is 6.5-11.5 feet thick south of the Kansas River and about 15-17 feet thick north of the river. Near Dover, where the member contains channel deposits that are entirely of Towle age, it is as much as 62 feet thick. Along the Wakarusa River the channel deposits are estimated to be about 140 feet thick. South of Dover the Towle could not be differentiated from the channel deposits of the Plumb Shale Member of the Wood Siding Formation; together, the units are probably as much as 125 feet thick.
The Towle is mainly light-olive-gray to olive-gray and light-greenish-gray (and some grayish-red) slightly to very silty laminated to platy partly micaceous claystone. Grayish-red claystone occurs mainly in the upper part, and conspicuous grayish-red to dusky-red siltstone commonly occurs in the lower part, especially north of the Kansas River; at places the two rock types are interbedded. The claystone generally weathers light olive gray, yellowish gray, and olive brown. The siltstone is clayey to finely sandy, generally platy to very thin bedded, and micaceous. Argillaceous limestone nodules, most of which are very light to light gray but some of which are light grayish red, are common in the upper part of the Towle.
Several limestone beds that are generally less than 1 foot thick are present in the member north of the Kansas River. They are light olive gray to light greenish gray, medium light gray, or light brownish gray; they weather light olive gray to light olive brown or yellowish gray and commonly have a banded and granular appearance. The limestone is very fine grained, moderately to very argillaceous, partly nodular, and sparsely to moderately fossiliferous.
Large channel deposits are common in the Towle Shale Member and are well exposed near Dover. Smaller deposits occur near the north edge of the area east of Delia. A broad channel trends northeastward for about 6.5 miles from Lomis Creek and the upper reaches of Ross Creek southwest of Dover (Mudge, 1956, fig. 3, p. 670-671). The northwest side of this channel is now concealed by the alluvial fill of Mission Creek. Near the head of Ross Creek, the channel apparently intersected a northwest-trending channel that was generally alined along the present Wakarusa River; both channels were part of the same drainage system during Early Permian time.
The channel along Mission Creek is well exposed at "Echo Cliff," in the NW SW sec. 3, T. 13 S., R. 13 E., and nearby, along Lomis Creek in the SW SE sec. 4 (strat. section 9), Moore (1936b, fig. 30) assigned all deposits at "Echo Cliff" to the Towle channel and correlated them with the Indian Cave Sandstone (the lower, major part of the Towle Shale Member) of southeastern Nebraska. Mudge (1956, p. 665) recognized deposits of two channels at "Echo Cliff" and along Lomis Creek; the lower deposits, probably in the Plumb Shale Member of the Wood Siding Formation, are overlain disconformably by limestone conglomerate marking the base of a channel of Towle age.
The conglomerate, 2.4-3.4 feet thick, is composed of medium-light-gray to light-olive-gray very finely crystalline hard sandy limestone that weathers dark yellowish orange and yellowish brown with a red hue. It contains abundant subangular to subrounded granules and pebbles as much as 0.15 foot long and 0.05 foot wide of dense argillaceous limestone, dark-reddish-brown ironstone, and claystone. The limestone pebbles, some of which are fossiliferous, weather pale yellowish brown to dark grayish red. Fragments of carbonized wood, nodules of pyrite, and reworked fossil remains are also abundant. Many of the limestone fragments are from the Brownville and Grayhorse Limestone Members of the Wood Siding Formation (Mudge, 1956, p. 671). Locally along Lomis Creek the conglomerate is split into two beds by a wedge as much as 0.5 foot thick of olive-gray sandy micaceous siltstone and light-yellowish-brown sandstone. The conglomerate commonly forms a prominent ledge and breaks into large slabs that split into irregular layers and chips. Along Lomis Creek this conglomerate overlies parts of several fornrations, including channel deposits of the Plumb Shale Member of the Wood Siding Formation, beds in the lower few feet of the Friedrich Shale Member of the Root Shale, and, locally, the Grandhaven Limestone Member of the Stotler Limestone.
The conglomerate was traced southeastward from "Echo Cliff" for about 1 mile to Ross Creek. The lower part of the thick sequence of channel deposits east of Ross Creek and east of Dover (pl. 3) probrubly inoludes beds of the channel facies of the Plumb Shale Member of the Wood Siding Formation; however, because the conglomerate between the Plumb and the Towle was recognized in only a small area southeast of Dover, the beds in the Plumb could be differentiated only in that area.
Conglomeratic limestone, probably deposited near the edge of the Towle channel, marks the base of the channel in a small area in the N2 sec. 1, T. 13 S., R, 13 E., in the SE sec. 36, T. 12 S., R. 13 E., in ,the SW sec. 31, T. 12 S., R, 14 E. (strat. section 10), and also in an area to the north in the NW SW sec. 29 and the E2 sec. 30, T. 12 S., R. 14 E. The limestone is medium light gray to medium gray, silty to sandy, pyritic, and hard. Most of the granules and pebbles are subrounded and less than 0.05 foot long, but some are as much as 0.1 foot long. These pebbles and granules are composed of dark claystone, yellowish-brown-weathering limestone, and ironstone. Fragments of crinoid stems, brachiopods, gastropods, and plants are abundant. The uppermost part of the bed is very sandy and at several places is ripple marked. The limestone forms a conspicuous ledge throughout much of its outcrop area. At some places this conglomeratic limestone bed overlies channel deposits tentatively assigned to the Plumb Shale Member of the Wood Siding Formation; at others the limestone rests on beds that occur in the normal sequence of the Plumb. The conglomeratic limestone is at the approximate stratigrruphic position of the Grayhorse Limestone Member of the Wood Siding.
At "Echo Cliff" and along Lomis Creek, the basal conglomerate is overlain by as much as 23 feet of light-yellowish-gray to light-olive-gray very fine grained laminated micaceous carbonaceous sandstone that is interbedded in part with sandy siltstone. Locally, fragments of the basal conglomerate are incorporated in the lower few feet of the sandstone. The upper part of the channel fill is composed of light-olive-gray silty claystone containing thin beds of light-olive-gray and brownish-gray generally argillaceous unfossiliferous limestone. Because the rocks in the upper part of the channel fill and those in the regular sequence of the Towle are similar, it is difficult to determine the top of the channel.
The channel exposed along Mission Creek is filled mainly with sandstone and siltstone, but in places, particularly where the channel was shallow, it is filled mostly with greenish-gray silty claystone (see strat. section 10). East of Dover, along the road is sec. 36, T. 12 S., 13 E., lenses of hard very calcareous partly crossbedded sandstone, some of which show oscillation-type ripple marks, are common in the channel. Some sandstone closely resembles sandy limestone. Limestone beds in the shallower parts of the channel are commonly fossiliferous; locally the claystones also contain Lingula and ostracodes.
The channel along Mission Creek ranges in depth from about 10 feet to possibly as much as 125 feet. Where it is shallow, only beds as low as the upper part of the Plumb Shale Member of the Wood Siding Formation have been removed; but in its deepest part the channel apparently eroded into the lower part of the Pillsbury Shale. South of Dover, where channel deposits of Plumb and Towle ages are undifferentiated, limestone conglomerate 1.8 feet thick that may mark the base of the channel crops out in a cut bank in the SE NE NW sec. 2, T. 13 S., R.13 E., about 10 feet stratigraphically above a nearby outcrop of the Maple Hill Limestone Member of the Zeandale Limestone.
The channel along the Wakarusa River (pl. 3) is more than 4 miles long, about 1-2.5 miles wide, and about 140 foot deep. The sides of the channel are difficult to delineate accurately, except where channeling has removed limestone units; consequently, the boundaries are inferred in many places. The channel fill is well exposed in only a few places, but it appears to he dominantly laminated to platy sandstone and sandy siltstone, particularly in its lower part. In the NW sec. 29, T. 13 S., R. 14 E., the lower part of the channel is interbedded micaceous siltstone and dark-yellowish-orange very fine grained subangular to subrounded platy micaceous sandstone cemented by iron oxide. The upper part of the channel, exposed along a creek in the SE NW sec. 26, T. 13 S., R. 13 E., is mainly yellowish-gray partly sandy finely micaceous siltstone but includes some medium-dark-gray platy claystone. The siltstone contains beds of light-gray to olive-gray limestone concretions, some of which are 0.6 foot thick and almost 2 feet long and contain fresh-water pelecypods. Several very thin beds of medium-light-gray unWssiliferous limestone also occur in this part of the channel.
The channel along the Wakarusa River originated in the Towle Shale Member, truncated the Wood Siding Formation (as in the center of the SE sec. 14 and SE NW sec. 26, T. 13 S., R.13 E.), and cut down almost to the top of the Tarkio Limestone Member of the Zeandale Limestone.
A large block of Stotler Limestone and strata in the uppermost part of the Pillsbury Shale occurs in the SE SE sec. 24, T. 13 S., R. 13 E., and in the SW SW sec. 19, T. 13 S., R. 14 E., in a position much lower topographically than nearby outcrops of Stotler Limestone. This block is apparently enclosed on three sides by channel deposits of Towle age; terrace material in the Wakarusa River valley conceals the other side. The block apparently slumped into the Towle channel, possibly owing to undercutting of the channel side (pl. 3, cross section A-A'). A similar but smaller slump block of SootIer Limestone along a creek in the SW SW NE sec. 19, T. 13 S., R, 14 E., is surrounded by channel deposits of Towle age; this block is too small to show on the geologic map. The beds in the block dip about 30° N. Mudge (1956, p. 669) also observed slump blocks in channel deposits, in Pottawatomie County.
Two or more channels occur in the TowIe Shale Member east of Delia, and a small intraformational channel, previously recognized by Mudge (1956, p. 671), is well exposed in a roadcut in the NW NW sec. 27, T. 9 S., R. 13 E. The latter channel is filled with very fine grained micaceous sandstone and sandy siltstone and is truncated by a thin limestone conglomerate. Mudge (1956, p. 671) staked that the channel is not more than 300 feet wide and probably not more than 10 feet deep. A larger channel is present in the SE sec. 23, the W2 sec. 25, and much of sec. 26, T. 9 S., R. 13 E.; but because of poor exposures, its boundaries are poorly defined. In a small exposure in a streambank in the center of the NW SW sec. 25, T. 9 S., R. 13 E., the channel fill is light-olive-gray thin-bedded partly clayey sandstone and grayish-black to black slightly sandy very carbonaceous siltstone containing some sandstone concretions. The sandstone has some carbonaceous material, and the siltstone has carbonized wood and coaly streaks at the channel base. A bed 0.3 foot thick of soft coal that may be at the top of the channel is exposed in a road ditch in the NE SW sec. 26, T. 9 S., R. 13 E. This channel originates in the Towle Shale Member about 9 feet below the Aspinwall Limestone Member of the Onaga Shale and seems to have cut down into the French Creek Shale Member of the Root Shale. The lowest observed position of the channel base, however, is about 5 feet above the top of the Nebraska City Limestone Member of the Wood Siding Formation.
Fossils are sparse to moderately abundant in the limestone beds of the Towle Shale Member, and locally a few occur in the claystone and the siltstone. Pelecypods are abundant; foraminifers, crinoid stems, ramose and fenestrate bryozoans, brachiopods, and ostracodes are less abundant. Carbonized plant fragments are abundant in the channel deposits; crinoid stems, brachiopods, pelecypods, gastropods, ostracodes, and possible Osagia are present locally in the upper part of the deposits, especially in limestone beds.
Aspinwall Limestone Member--The Aspinwall Limestone Member (Condra and Bengston, 1915, p. 17) south of the Kansas River generally consists of two limestones separated by claystone; these beds correspond to the two lower limestones and the intervening shale of the Aspinwall of Mudge and Burton (1959, p. 44-45). North of the river the member is composed of one or, in a few places, two beds of limestone having a total thickness of 2-3 feet. The limestone beds vary widely in number and thickness and, to some extent, in lithology; consequently the upper and lower contacts of the Aspinwall are difficult to identify and map consistently, Near the middle of the overlying Hawxby Shale Member are one or more limestone beds that closely resemble beds in the Aspinwall; locally, where the Hawxby is thin and exposures are poor, part of the Hawxby may have inadvertently been included in the Aspinwall.
The upper limestone commonly forms a relatively inconspicuous hillside bench over much of the area; locally the basal limestone also forms a bench. On grassy slopes, the smooth plates and cobbles and the brecciated appearance of the weathered upper limestone aid in locating the member. The Aspinwall ranges in thickness from 1.5-11.5 feet.
The basal limestone of the Aspinwall south of the Kansas River is commonly very light gray to medium light gray and light olive gray, very finely crystalline, very thin to thin bedded, hard, and compact and at most localities contains abundant pelecypods. Locally the bed contains Osagia or foraminifers or is unfossiliferous. At many places the weathered limestone contains many dark-brown or yellowish-brown pyritic specks and shows indistinct banding owing to very small areas of dense limestone dispersed in the granular matrix. A few small nodules of light-red celestite are present locally.
The middle part of the Aspinwall is mainly claystone but contains several lenticular limestones generally less than 0.4 foot thick. The claystone is light olive gray to yellowish gray and light greenish gray and in places is silty, Some grayish-red claystone is present locally in the area northwest of Dover. The individual claystone units are generally 2-3 feet thick but locally are as much as 6 feet thick. The limestone in the middle of the Aspinwall is light gray and yellowish gray, in part argillaceous, hard and generally unfossiliferous. Yellowish-brown iron oxide specks are abundant in some beds, Small nodules and very thin lenses of limestone are common in the claystone.
A distinctive limestone occurs at the top of the Aspinwall Limestone Member throughout most of the area south of the Kansas River. This limestone is commonly light to medium gray, very fine grained, argillaceous, hard, and compact, Characteristically it contains many subangular to subrounded fragments of dense limestone that are generally darker than the matrix; these fragments are all less than 0.1 foot in diameter and most are much smaller. The fragments weather very light gray and stand in relief on weathered surfaces. In places the upper limestone contains minute shell fragments and yellowish-brown limonitic specks, Questionable ostracodes were seen in a few angular fragments at one locality.
North of the Kansas River the Aspinwall is generally a single bed of medium-gray very fine to fine-grained argillaceous thin-bedded fossiliferous limestone that weathers to smooth plates and cobbles, which are commonly porous and contain abundant yellowish-brown limonitic specks. This bed seems to be equivalent to the upper limestone of the Aspinwall south of the river, and thin limestone beds designated as being in the upper part of the underlying Towle Shale Member may actually correlate with beds in the lower part of the Aspinwall to the south, Mudge and Yochelson (1962, p. 22) thought that the lowermost bed of the Aspinwall in Wabaunsee County is probably correlative with the single bed of Aspinwall at the type locality in southeastern Nebraska.
Pelecypods and gastropods occur in most of the limestone beds of the Aspinwall; pelecypods are particularly abundant in the lower limestone. Ostracodes are common in the upper limestone, and Osagia is locally present in the lower limestone. A few crinoid stems, fenestrate bryozoans, brachiopods, and foraminifers were noted in places.
Hawxby Shale Member--The Hawxby Shale Member (see chart by R. C. Moore and G. E. Condra, in Moore, 1932, p. 95-97) is poorly exposed in its outcrop area north and south of the Kansas River, Mudge and Burton (1959, p. 183) measured a complete section in the SE SE sec. 10, T. 13 S., R. 13 E. The Hawxby is 12-26 feet thick, averaging about 17 feet in thickness, and is dominantly light-olive-gray and light-olive-brown partly silty claystone. The claystone is laminated to platy and commonly calcareous and in many places contains small nodules or lenses of argillaceous limestone. The member includes some yellowish-gray and medium-dark-gray to dark-gray platy to very thin bedded siltstone and one or more beds of limestone.
South of the Kansas River a limestone 1.5-3 feet thick occurs in the middle or upper part of the Hawxby. The limestone is light gray to light olive gray, very fine grained, thin bedded, hard, and compact. It weathers to smooth light gray, pale yellowish brown, or yellowish orange cobbles. The limestone contains many pale-brown iron oxide specks, and at a few places angular limestone fragments show in relief on its weathered surfaces (strat. section 9). The weathered bed is commonly porous and locally forms a minor bench. At most places this bed is unfossiliferous, but locally it contains a few minute shell fragments. This bed closely resembles the lower limestone of the Aspinwall Limestone Member; but where it contains angular limestone fragments, it resembles the upper limestone of the Aspinwall. North of the Kansas River thin beds of light-olive-gray very finely crystalline moderately fossiliferous limestone occur in the lower part of the member. A coal bed about 0.2 foot thick is present in the upper 3 feet of the Hawxby along the stream in the SW SW sec. 26, T. 13 S., R. 13 E.
In the southern part of the area, shell fragments, probably of pelecypods, and some possible specimens of Osagia occur in the limestone beds. To the north these beds contain abundant myalinid pelecypods and gastropods and some crinoid stems and possible brachiopods. E. L. Yochelson (written commun., 1960) identified Permophorus, Glabrocingulum?, and high-spired gastropods from the Hawxby in the NW NW SE sec. 1, T. 10 S., R. 12 N. At places in the northern part of the area, claystone in the Hawxby contains carbonaceous material.
Falls City Limestone (strat. sections 12, 14)--The Falls City Limestone (Condra and Bengston, 1915, p. 17) is poorly exposed in the southwestern part of western Shawnee County and vicinity; in places in the northwestern part the formation forms a minor hillside bench; On the geologic map (pl. 3) the Falls City is combined with the overlying Janesville Shale, Several thin limestone beds of similar lithologic and paleontologic character compose the Falls City Limestone (Mudge and Burton, 1959, p. 47). Some of these beds may not correlate with the type section of the formation in Richardson County, Nebr, (Condra, 1927, p. 82; Mudge and Yochelson, 1962, fig. 9, p. 23). The Falls City ranges in thickness from 6 to 17 feet (Mudge and Burton, 1959, p. 182) in the vicinity of Dover and is 3.2 feet thick in the northwest corner of the area. The top of the formation is very difficult to determine, which thus accounts for the differences in the reported thickness. The Falls City rests conformably on the Onaga Shale.
South of the Kansas River two or more limestone beds 0.2-1 foot thick are separately by relatively thick units of claystone. The limestone is generally light to medium gray and light olive gray, very fine grained, very thin to medium bedded, hard, compact, and partly coquinoidal. Some beds are slightly to moderately argillaceous and contain small fragments of greenish-gray, grayish-yellow, and light-olive-gray claystone, On weathering the limestone is light olive gray, orange, and brown and forms thin resistant vertically jointed beds, the surfaces of which are covered with fossil debris.
Claystone of the Falls City Limestone is light olive gray and partly silty and in places contains many very small nodules or very thin lenses of light-yellowish-gray argillaceous limestone. South of the Kansas River claystone constitutes most of the formation. North of the river the Falls City is much thinner, has more conspicuous topographic expression, and is composed chiefly of limestone that has the same lithology as that to the south, but it weathers pale yellowish brown and light olive brown. The upper part commonly has very thin light-colored dense argillaceous limestone streaks that give the weathered outcrop a banded appearance. The upper surface of the weathered rock is commonly rough, irregular, and deeply pitted.
Pelecypods are characteristically abundant in most of the limestone beds. Gastropods are abundant in many beds, and crinoid columnals, ramose and fenestrate bryozoans, and brachiopods are present locally.
Janesville Shale (strat. sections 11, 12)--The Janesville Shale (Moore and Mudge, 1956, p. 2273) is composed, in ascending order, of the West Branch Shale, Five Point Limestone, and Hamlin Shale Members. It underlies grass-covered slopes south and west of Dover and in the northwestern part of the mapped area. The Five Point Limestone Member forms a prominent bench near the middle of the Janesville along much of the outcrop. The Janesville is 70-75 feet thick near Dover and about 55 feet thick north of the Kansas River. On plate 3 the outcrop of the Janesville is combined with that of the underlying Falls City Limestone, but the Five Point Limestone Member is mapped separately. The contact between the Janesville Shale and the Falls City Limestone is conformable, and the contacts between the members of the Janesville are also conformable.
West Branch Shale Member--The West Branch Shale Member (Condra, 1927, p. 82) is generally 26-33 feet thick, but locally in the SW sec. 26, T. 13 S., R. 13 E., it is 42-47 feet thick. It is mainly claystone but contains some sandstone and thin beds of limestone, siltstone, and coal. The claystone is light olive gray, laminated to platy, in part silty, and, in the upper few feet, locally calcareous. It weathers light olive gray, yellowish gray, and light olive brown. Very thin layers of ironstone concretions occur locally.
Thin beds of sandstone form hard, resistant layers locally in the upper and middle parts of the West Branch Shale Member; but in the SW sec. 26, T. 13 S., R. 13 E., a sandstone unit 33-38 feet thick apparently fills a channel. The sandstone is generally light olive gray and light gray, but in the channel it is grayish orange. Weathering modifies the color to light olive gray or light olive brown. The sandstone is very fine grained, laminated to platy, and micaceous. Carbonaceous material is abundant on bedding planes.
Siltstone of the West Branch is light olive gray and medium to medium dark gray, weathers to shades of olive gray mottled with brown, and generally is clayey to finely sandy, laminated, and micaceous. A bed 1-3 feet thick of very argillaceous limestone that weathers to yellowish-orange box work occurs about 5-10 feet above the base of the member. Another bed of limestone 1-3 feet thick occurs 3.5-9.5 feet below the top of the West Branch in most of the southern outcrop area. This bed is medium gray to olive gray, very fine grained, argillaceous, platy to thick bedded, hard, and compact. These limestones were described by Mudge and Burton (1959, p. 48) and by Mudge and Yochelson (1962, p. 25). Very thin lenses of limestone were also noted locally in the claystone and siltstone units.
One or more coal beds 0.1-0.2 foot thick occur in the West Branch in most exposures. The most continuous one is 0.5-5 feet below the top of the member and in places is associated with dark-olive-gray and black very carbonaceous claystone. A coal bed is present locally near the middle of the member and one occurs in places in the lower 1 foot.
Fossils are common in many of the limestone beds and in the upper few feet of the claystone. Crinoid columnals and brachiopod shells and spines are abundant; pelecypods, gastropods, bryozoans, and questionable ostracodes are less abundant. A few fusulinids were noted at the top of the member at one locality. Very small carbonized plant fragments occur in many of the sandstones and siltstones.
Five Point Limestone Member--The Five Point Limestone Member (see chart by R. C. Moore and G. E. Condra, in Moore, 1932, p. 95-97) forms a prominent hillside bench southwest of Dover. Large rectangular blocks break from the ledge and slide onto the grassy slope below. In the northwestern part of the area the member is generally covered, but locally it forms a narrow bench. The Five Point ranges in thickness from about 4 to 8 feet. Changes in thickness are commonly rather abrupt. The Five Point apparently is absent from a small area in the S2 sec. 27, NE sec. 34, and NW sec. 35, T. 13 S., R, 13 E., probably owing to erosion of a channel from the Hamlin Shale Member.
Near Dover the Five Point consists of two limestones separated by claystone or very argillaceous limestone. The lower limestone is 0.32-2 feet thick, and where thickest, it crops out as a vertically jointed ledge. The limestone is medium gray and light olive gray, very fine grained, thin to medium bedded, hard, and compact. In places it is slightly to moderately argillaceous and very fossiliferous. The member weathers light olive gray and yellowish orange. The lower limestone has several claystone partings 0.2-0.4 foot thick near the south edge of the area.
The intervening claystone is generally about 0.3-1 foot thick but is as much as 3 feet thick locally. It is light olive gray to yellowish gray, laminated, and caloareous and grades laterally into very argillaceous limestone.
The upper limestone, about 0.5-4 feet thick, is light gray to light olive gray, and yellowish gray, very fine grained, argillaceous, and very thin to thin bedded. It generally weathers light olive gray to light yellowish gray, but in some outcrops it weathers a conspicuous white to very light gray. It commonly breaks into small angular fragments but locally weathers to porous dark-yellowish-orange rubble. The upper limestone is commonly unfossiliferous but in a few places contains many fossils.
North of the Kansas River the Five Point Limestone Member, exposed along the road in the NW SW SW sec. 5, T. 10 S., R. 13 E., consists of a 1.4-foot-thick yellowish-gray to light-olive-gray silty very fossiliferous lower limestone overlain by a 0.9-foot-thick unit of interbedded light-olive-gray silty fossiliferous limestone and platy calcareous siltstone. The upper limestone, 3.5 feet thick, is olive-gray, hard, dense, and coquinoidal; it locally weathers to large blocks and has an "oatmeal" texture.
The lower limestone of the Five Point is very fossiliferous throughout the area. In many outcrops in the southern part, fossils in the upper limestone are either sparse or absent; at other outcrops they are abundant. North of the Kansas River the upper bed contains abundant brachiopods, crinoid stems, and ramose and fenestrate bryozoans. Fusulinids are commonly abundant in the lower bed but are locally sparse or absent, and they are apparently absent from the upper bed. Trilobites are present in the lower limestone, and horn corals locally occur in claystone partings. A few pelecypods, gastropods, and what may be Osagia were noted in the upper limestone. The claystone is commonly unfossiliferous, but, where it grades to argillaceous limestone, it generally contains fossils similar to those in the adjacent limestone, E. L. Yochelson (written commun., 1960) identified the following forms from this member:
USGS fossil locality 19463-PC. In the SE cor. SW sec. 33, 13 S., R. 13 E., immediately south of the mapped area.
Crinoid calyx (cf. Delocrinus)
Trilobite pygidium (cf. Ditomopyge)
Hamlin Shale Member--The Hamlin Shale Member (Moore, Elias, and Newell, 1934) is about 40 feet thick near Dover and is estimated to be about 30 feet thick north of the Kansas River. The Hamlin is primarily light-olive-gray and light-greenish-gray laminated to platy claystone that is commonly very silty. In the southern outcrop area the lower few feet of the member is very calcareous and commonly contains many very small round very argillaceous unfossiliferous limestone nodules, some of which are pyritic and weather moderate yellowish brown. This part of the Hamlin weathers to conspicuous barren light-colored outcrops.
In the northern outcrop area a zone about 8 feet thick of grayish-red and light-greenish-gray claystone occurs locally about 15 feet below the top of the member. The upper part of the zone contains a slightly resistant bed about 3 feet thick of laminated very micaceous siltstone that weathers moderate brown. Locally this bed is very ferruginous and weathers to hard moderate-yellowish-brown fragments. In the northern part of the area the claystone overlying the resistant siltstone bed contains many limestone nodules that weather yellowish gray to very light gray. The claystone at the top of the member is slightly micaceous, contains a few moderate-yellowish-brown calcareous siltstone pellets, and weathers to pale-yellowish-brown blocky fragments. A bed about 2.4 feet thick of hard platy calcareous sandstone is present at the base of the member locally in the northern part of the area.
Thin limestones occur at random throughout the Hamlin Shale Member and are apparently more abundant north of the Kansas River. Several beds, each about 1 foot thick, of light-olive-gray hard silty fossiliferous limestone occurring in the lower 10 feet of the Hamlin are exposed locally north of the river. A thin continuous algal limestone, the Houchen Creek Limestone Bed, occurs near the middle of the Hamlin in Jackson and Pottawatomie Counties (Mudge and Yochelson, 1962, p. 27); because of limited exposures of the Hamlin, the Houchen Creek was not recognized in western Shawnee County and vicinity. A 0.2- to 0.9-foot-thick sandy micaceous limestone, in places containing a breccia of ironstone fragments at the base, is present near the middle of the Hamlin about 4 miles southwest of Dover. A moderately resistant bed about 3 feet thick of light-olive-gray very argillaceous unfossiliferous limestone occurs about 3 feet below the top in both the northern and southern outcrop areas. The bed weathers to a grayish-yellow or pale-yellowish-orange cellular rubble. A few other thin beds of cellular-weathering limestone, as well as several beds of limestone concretions as much as 0.3 foot thick and 0.6 foot long, occur in the upper part of the member near Dover. The concretions are medium gray to olive gray, hard, and dense and break with subconchoidal fracture.
The narrow channel that apparently eroded the underlying Five Point Limestone Member in the S2 sec. 27, NE sec. 34, and NW sec. 35, T. 13 S., R. 13 E., is filled with sandstone and sandy siltstone, possibly of Hamlin age.
Crinoid columnals, bryozoans, brachiopods, pelecypods, and plant fragments occur locally in limestone beds of the Hamlin Shale Member, and plant fragments are abundant in claystone of its uppermost part in outcrops in the northern part of the area.
Foraker Limestone (strat. sections 13, 14)--The Foraker Limestone (Heald, 1916, p. 21, 25) is composed, in ascending order, of the Americus Limestone, Hughes Creek Shale, and Long Creek Limestone Members. It crops out in the southwest corner of the western Shawnee County and vicinity study area and in very small areas in the northwest corner (pl. 3). The Foraker is about 45 feet thick southwest of Dover and appears to be 30-35 feet thick in the northwest corner. The Foraker rests conformably on the Janesville Shale, and the contacts between Foraker members are also conformable.
Americus Limestone Member--The Americus Limestone Member (Kirk, 1896, p. 80) is about 2.5 feet thick in the northern outcrop area, and 5.7 feet thick in the southern outcrop area; it consists of two limestones separated by claystone. The usage of the Americus in this report follows that of Mudge and Burton (1959, p. 53-54). Their report and the one by Mudge and Yochelson (1962, p. 30-33) discuss in detail the correlation of the Americus in Kansas.
The upper limestone of the Americus, particularly in the southern outcrop area, forms a prominent and very conspicuous hillside bench marked by large limestone blocks that break from the ledge and slump onto the upper part of the steep slope below. The lower limestone forms a minor ledge in stream cuts but is covered elsewhere. As pointed out by Mudge and Burton (1959, p. 54), the sequence in the Americus of two limestones separated by claystone can be mistaken, on casual examination, for a similar sequence of limestone beds in the middle of the overlying Hughes Creek Shale Member. Characteristics, however, such as the distinctive outcrop pattern and the different color, hardness, and fossil content of the Americus Limestone Member make it easily distinguishable from the limestone beds of the Hughes Creek that form only an inconspicuous hillside bench.
In the southern outcrop area the lower limestone is 1.8-2.3 feet thick and consists of one or two beds of light-gray to medium-dark-gray limestone that weathers light gray to light olive gray partly mottled dark yellowish orange. This lower limestone is thin to medium bedded and fine grained and contains abundant foraminifers(?) and many well-preserved pelecypods. Its basal 0.2 foot contains lobate or lens-shaped algal deposits (stromatolites) that are darker, harder and denser than the limestone matrix. When viewed through a microscope the stromatolites appear granular and finely laminated. The stromatolites were described in detail by Mudge and Yochelson (1962, fig. 13, p. 31). The lower limestone is generally moderately argillaceous, but the upper part of the algal zone is very argillaceous. At places the lower limestone occurs as two equally thick beds separated by a 0.1-foot-thick parting of interbedded olive-brown very calcareous claystone and very argillaceous limestone. The lower of the two limestone beds commonly forms a thin ledge, whereas the upper bed weathers to irregular platy fragments.
In the northern outcrop area the lithology of the lower limestone of the Americus is similar to that in the southern outcrop area, but the bed is only about 0.5 foot thick. The stromatolite zone occurs at the base, but the upper part apparently does not contain pelecypods. A quarter of a mile west of the mapped area, in the SW cor. SE NE sec. 2, T. 10 S., R. 12 E., nodules about 0.3 foot long and 0.05 foot thick of pale-yellowish-brown to medium-gray dense fossiliferous chert are present at the base of the lower limestone; the chert may also be present but not recognized in this bed within the western Shawnee County area. Along the road on the west line of the NW NW sec. 6, T. 10 S., R. 13 E., a 0.1-foot-thick conglomeratic limestone occurs at the top of the lower bed. This conglomerate is composed of subrounded to rounded granules and pebbles of medium-gray dense limestone, very argillaceous limestone, and calcareous claystone in a matrix of light-gray finely crystalline limestone. The fragments are generally less than 0.02 foot in diameter, but a few are as much as 0.05 foot in diameter. The pebbles of argillaceous limestone and calcareous claystone weather dark yellowish orange. The layer weathers with many small pIts and is partly stained by iron oxide.
The claystone of the Americus Limestone Member is 2.2-2.5 feet thick in the southern outcrop area but thins to 0.3 foot in the northern area. In both areas the claystone is poorly exposed, but where observed it is slightly silty, calcareous, and finely laminated and weathers yellowish gray or pale yellowish brown. In the northern area it contains many pellets 0.01 foot thick and as much as 0.03 foot long of very argillaceous limestone that weathers white to very light gray. The claystone seems to be unfossiliferous.
The upper limestone of the Americus is 0.9-1.2 feet thick in the southern part of the area and 1.8 feet thick in the northern part. The limestone is medium light gray to medium gray, very fine grained and finely crystalline, and very hard. It weathers light olive gray to medium light gray and breaks into large tabular blocks along strong vertical joints. Some blocks are as much as 6 feet wide and 20 feet long, Locally in the southern part the limestone is sparsely pyritic, and at places in the northern part it contains small nodules of light-red barite. Fossil fragments, especially crinoid stems, weather in relief on the bed.
The fossils of the Americus Limestone Member aid in its identification. The lower limestone is characterized by masses of the stromatolite Collenia (Mudge and Yochelson, 1962, p. 29) in the basal part and by a very fine debris of foraminifers (?) and ostracodes in the upper part. Myalinid pelecypods are abundant in the upper part in the southern outcrop area. Less common fossils in the lower limestone include fusulinids, crinoid columnals, bryozoans, and brachiopods. The upper limestone generally contains many fusulinids and white crinoid columnals and less abundant brachiopods and ramose bryozoans. Fusulinids, however, are sparse or absent north of the Kansas River.
Hughes Creek Shale Member--The Hughes Creek Shale Member (Condra, 1927, p. 85) is 35-40 feet thick southwest of Dover and about 25 feet thick north of the Kansas River. The member consists of claystone and several thin limestone beds. The claystone is generally light olive gray to olive gray, but some is grayish yellow, almost white, or black. It is calcareous to very calcareous and partly silty; it weathers light olive gray and light yellowish gray.
Limestone of the Hughes Creek is commonly light olive gray to olive gray but some is medium light gray and medium dark gray. It is very fine grained and generally argillaceous and weathers light olive gray mottled in places with medium dark gray on the upper surfaces. The beds weather either to small tabular blocks with rounded edges or to thin irregular plates. Two fairly resistant limestone beds separated by a 0.6-foot-thick claystone bed occur near the middle of the Hughes Creek southwest of Dover. The limestone are moderately hard, are vertically jointed, and crop out as ledges in streambanks. The resemblance of these beds to the Americus Limestone Member is discussed on p. 188.
The profusion of fossils, particularly fusulinids, is an aid in identification of the Hughes Creek Shale Member. Even where the member is covered, the soil generally contains many fossils. Fusulinids are very abundant in the upper part and are common, particularly in claystone, in the lower part. In the southern part of the area, most limestones also contain abundant fusulinids, which are sparse in these beds north of the Kansas River. Brachiopods, especially Ohonete8 and productoids, are abundant; and crinoid stems, ramose and fenestrate bryozoans, echinoid spines and plates, and foraminifers are common, 08agia, gastropods, and ostracodes are sparse to moderately abundant locally. E. L. Yochelson (written commun., 1960) identified the following fossils from the Hughes Creek in a roadcut in the SW cor. NW sec. 6, T. 10 S., R.13 E,:
Fusulinids, undet. (USGS colln. f12956)
Chonetes granulifer Owen
Neospirifer cf. N. kansasensis (Swallow)
Long Creek Limestone Member--The Long Creek Limestone Member (Condra, 1927, p. 85) crops out only in interstream divides, and its outcrop is marked by abundant limestone cobbles. The member seems to be about 5 feet thick in the southern outcrop area. In the northern outcrop area about 2 feet of the Long Creek is exposed along the road on the west line of the SW sec. 5, T. 10 S., R. 13 E.
The Long Creek is composed of light-olive-gray very fine grained moderately argillaceous very thin to medium-bedded limestone that weathers mainly grayish orange and moderate yellowish brown. The weathered limestone forms rounded cobbles and platy fragments that are deeply pitted and on which fossil fragments commonly weather in relief. Crystals of white and moderate-reddish-orange calcite and celestite partly fill small geodes and partially replace fossils. Chert nodules as much as 0.2 foot long, but generally less than 0.1 foot long, also occur in the Long Creek. The chert is white, moderate reddish orange, or brownish gray to moderate yellowish brown, and in part fossiliferous. Fragments of chert, calcite, and celestite generally mantle the outcrop and aid in identification of this member.
Pelecypods are locally abundant in part of the Long Creek, but most of the member appears to be virtually unfossiliferous. A few brachiopods and gastropods were noted, and in places the chert is fossiliferous.
Johnson Shale--The Johnson Shale (Condra, 1927, p. 86) is the stratigraphically highest bedrock unit in the area. It is poorly exposed near the southwest and northwest corners of the area (pl. 3). The Johnson apparently consists of light-olive-gray claystone containing a few very thin beds of yellowish-gray cryptocrystalline unfossiliferous limestone concretions. Only about 20 feet of the Johnson is exposed in western Shawnee County and vicinity, but the formation averages 25 feet in thickness in Wabaunsee County (Mudge and Burton, 1959, p. 58). The Johnson Shale rests conformably on the Foraker Limestone.
Kansas Geological Survey, Geology
Placed on web October 2005; originally published 1967.
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