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Stanton Formation

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Depositional Significance of Stanton Facies in Southeastern Kansas

The following brief consideration of probable environments of deposition of Stanton facies in southeastern Kansas is based mainly on the general lithologic, paleontologic, and stratigraphic observations presented above. A more complete analysis will require more detailed areal study of each facies and its lateral and vertical contacts, particularly in the terrigenous detrital units.

Carbonate Rocks

Carbonate rocks signify voluminous local carbonate production with protection from, or slowdown of, terrigenous detrital influx.

Phylloid-algal mound complexes--Depositional environment of the greatly thickened limestones composed of phylloid-algal-dominated mound facies that characterizes all three limestone members in northern Montgomery County is treated in Heckel and Cocke (1969, p. 1066-1069). To summarize the significant points, these features are subregional buildups of carbonate sediment resulting from relatively rapid accumulation of the remains of a luxuriant growth of phylloid algae, thereby maintaining their optimum, well-illuminated, shallow-water environment in response to subsidence of the sea bottom. That sedimentation did compensate for subsidence and thus maintain shallow depths during deposition of the limestone members is shown not only by continuation of algae-rich facies up to the top of each member, but also by development of channels at the top of the mounds, implying response to need for tidal drainage of the algae-choked sea bottom, which would occur most likely in very shallow water. Thus, the mound facies can be considered to have developed as the response to subsidence of an algae-covered sea bottom just below sea level. Mound growth probably ceased in different cases because of (1) overwhelming by terrigenous clastics, or (2) a drop in sea level, or (3) a temporarily increased rate of sea level rise beyond that which could be compensated by algal sediment production.

Topographic relief of about 80 to 100 feet has been mapped on the northwest edge of the combined Captain Creek-Stoner mound in northern Wilson County (Heckel, 1972a, p. 590). Similar determinations based on elevations are difficult to make across the Elk River Valley, which has eroded out much of the south ends of the mounds in northern Montgomery County. It is not unreasonable to expect, however, that relief of at least the difference in thickness between mound and off-mound facies was developed at the south ends of the buildups in northern Montgomery County. Support for this lies in the lack of intercalated shale in the mound facies, particularly in the upper parts, a situation expected only if the limestone buildups stood substantially above any contemporaneous incoming terrigenous muds, and certainly not expected if muds were being introduced at the same topographic level. Thus the Captain Creek, Stoner, and South Bend mounds probably stood nearly 50, 10 to 30, and 20 feet respectively above off-mound facies to the south. In support, the South Bend mound exhibits about 7 feet of relief in 300 feet across the quarry west of U.S. 160 just south of the Elk River bridge.

Skeletal calcarenites--Three units composed basically of skeletal calcarenite are the Rutland bed, Bolton bed, and the small lens exposed within the Rock Lake Shale on the north side of Timber Hill. Other calcarenites that are directly associated with the algal mounds generally reflect wave and current action in shoal water at the tops of the mound complexes (Heckel and Cocke, 1969, p. 1066-1068), and are not treated further here.

By virtue of its lenticular nature over a small region, conspicuous cross-bedding, and preponderance of abraded grains in a sparry matrix, the Rutland bed represents a well-washed, probably wave-swept accumulation of algal and shell debris, apparently in the form of an offshore bar. The dominance of phylloid algal debris, particularly Archaeolithohyllum and nondescript codiaceans, both of which are rare outside the mounds, suggests a source in the mounds where these types of algae dominate the biota. The substantial abrasion displayed by many of these grains would support transport from as far as the top of the Stoner mound at least 2 miles away. Dasyclad green algae, on the other band, are rare in the mound facies; thus their abundance in the Rutland bed suggests another source, perhaps nearly in place, inasmuch as dasyclads characterize shoals associated with reefy buildups throughout much of their history (Wray, 1971). Although the solenoporid fragment is hardly enough for definite interpretation, this type of red algae is found elsewhere in the Stanton only in a similarly well-washed mound-edge calcarenite to the north in Wilson County. The invertebrates in the Rutland bed also point to a source other than the mounds. Aside from the in-place origin suggested by some nearly whole fenestellid bryozoan fronds and crinoid calyces, the rich invertebrate fauna at the top of the underlying Eudora is a possible source for transported material. The scattered ooids and mud clasts suggest even different sources. Thus the Rutland bed represents a cessation or winnowing of terrigenous influx for a time while skeletal debris from a variety of distant and nearby sources was swept into a windrow-like shoal-water bar.

The high degree of sorting, in particular the absence of grains above a critical size (Fig. 23), and its development as a single thin layer, strongly suggest that the sorted-abraded skeletal calcarenite lying within the Rock Lake Shale above the south end of the Stoner mound on the north prong of Timber Hill is a storm deposit. Although abrasion would support transport for a large distance, it is more likely inherited from a previous environment of long-term water agitation. Unique to this layer is the predominance of foraminifers along with probable fragments of phylloid algae. Whereas origin of the algal fragments could be attributed to erosion of an exposed unlithified part of the top of the Stoner mound, the foraminifers have no other known area of concentration to serve as their source, unless they represent a winnowed concentrate of nearby unstudied shales.

Although the generally spar matrix and lensing nature along outcrop suggests that wave or current action influenced development of the Bolton bed, the greater number of whole shells combined with lesser amounts of grain abrasion indicates less consistent water turbulence than influenced the Rutland bed. A greater abundance of ooids further differentiates the Bolton bed, but the constant water agitation they imply is incongruent with the many larger whole shells present. This, in conjunction with presence of non-oolitic grains of similar size, suggests that the ooids formed in a different area and were subsequently washed into the preserved Bolton environment, where a variety of invertebrates were living. The near lack of phylloid algae undoubtedly reflects greater distance from the mounds. Occurrence of osagia-type encrusting foraminiferal-algal? coatings on many of the larger shells reflects some little understood aspect of biotic succession in many Pennsylvanian marine environments. Presence of such coating on all sides of some shells suggests enough agitation occasionally to overturn the shells, but the generally unequal coatings on most of the shells points to only intermittent agitation of any force. Thus the Bolton bed appears to represent a less strongly wave-washed accumulation of shell debris in a broader, probably deeper area than the Rutland bed, perhaps an open lagoon into which ooids were periodically transported from a more strongly agitated shoal or shoreline.

Oolites--Dominantly oolitic rocks include the lower layer of the Captain Creek in northern T. 33 S., R. 15 E., the Tyro bed, and most of the third and fourth oolitic zones in the Rock Lake.

Captain Creek oolite, where well developed, is generally poorly exposed, but samples show that it is petrographically similar to much of the Tyro. Westward and southwestward gradations of the Captain Creek oolite layer include stromatolitically coated shells, pebbles, and surfaces, all suggesting a shallow restricted lagoon around this side; the environment of the main part of the oolite to the northeast is probably similar to that of the Tyro bed.

The Tyro oolite was considered by Harbaugh (1960, p. 229) to represent a shallow agitated marine shoal environment similar to that of the Great Bahama Bank, although admittedly with a terrigenous detrital sequence. Certainly the pervasive presence of thick coatings on small grains and thin coatings on larger grains, along with sparry matrix, well-developed cross-bedding and particularly the large-scale thickening and thinning of the bed, are compatible more with a continually agitated, broad open shoal environment like the Great Bahama Bank than with the shoreline or less agitated oolite environments described by Rusnak (1960) and Freeman (1962). Portions of the Bahamian oolite shoals are characterized by parallel sets of huge bars, several feet thick, that thin locally to disappearance in the troughs (Ball, 1967, p. 563, 570). This seems compatible with the apparent geometry of the Tyro bed. Although tidal currents are largely responsible for the agitation of the Bahamian shoals, flood tides in places are stronger than ebb tides toward the interior of the platform, and cross-bedding dip directions show movement predominantly in one direction (Ball, 1967, p. 561). Thus, the consistently westward to southwestward-dipping sets of cross-beds (Fig. 18) measured at three Tyro localities are compatible, at the present state of knowledge, with either tidal or unidirectional currents. A southwestward trend of ooid movement is suggested also by spot samples from other localities: the thinnest oolitic coatings are found in the northeasternmost exposure whereas the thickest coatings (thus the largest ooids) are found in the westernmost exposure on Hafer Run. Although a greater quantity of systematic data will be necessary to substantiate this trend, the suggestion at this point is that oolitic coatings formed progressively thicker as the ooids moved southwestward off an open shoal, just as ooids apparently grew in size to pisolites as they moved off the edge of a thick algal buildup in the Plattsburg Limestone in Wilson County (J. M. Cocke assisted by author; see also Kettenbrink and Manger, 1971, p. 435-436). The west side of such a shoal to the northeast during Tyro deposition is suggested by the substantially steeper westerly dips recorded in the northeasternmost Tyro exposures across section 6-34-15. The skeletal material in the Tyro is mostly oolitically coated (Fig. 19), which shows that it too was rolled about and probably largely transported, with perhaps little indigenous to the shoal environment of unstable substrate, another situation that is compatible with the Bahamian model.

Oolites of the third and fourth zones generally involve various combinations of thinner oolitic coatings, mixtures of uncoated with thickly coated grains, and skeletal grains having osagia coatings. These features would be more characteristic of the shoreline oolite environment described by Rusnak (1960), in which agitation may be constant where the ooids are forming, but near which various associated non-oolitic subenvironments provide places where other grains can avoid oolitic coating and where invertebrates can live on different substrates, some eventually becoming covered by algal-foraminiferal crusts. Presence of shale pebbles at places within these oolitic horizons indicates nearby erosion of mud, perhaps in channels that normally occur in a shoreline regime. The fossiliferous quartz sandstones merely represent variants of such a nearshore regime where no oolitic coating was taking place. The number and type of invertebrate groups present, particularly the stenohaline echinoderms, indicate that nearly normal marine salinities were established within portions of the regime. Because these limy horizons signify times of lessening of the terrigenous detrital influx dominating this portion of the Stanton, if they do lie at only two well defined and fairly traceable zones, they signify times of reduction of detrital influx over a substantial area. If most localities represent different horizons, then the limy deposits formed in different places where detrital influx was reduced at different times. Because the zones that can be mapped do not seem continuous over the entire belt, terrigenous clastics were undoubtedly flooding in continuously in some places, while other areas witnessed development of less diluted, thin impure carbonates.

Sponge-rich calcilutites--Presence of calcilutite matrix and several invertebrate groups, including echinoderms, signify a quiet environment with normal marine salinity for this facies in both the Captain Creek and South Bend Members. Dominance of nomally subordinate calcisponges suggests some slight modification of the normal open marine regime, and the later complex algal? and invertebrate encrustations on larger organisms and mud surfaces (Fig. 8) suggest perhaps another type of modification of the environment through time. A lagoonal environment suggested by Wilson (1957a, p. 26) seems reasonable only if freely connected with the open sea. Apparently its initial conditions underwent as yet unspecified changes in circulation or other factors, while remaining within the relatively open marine regime.

A similar calcisponge-rich biota characterizes off-mound calcilutites determined to have been deposited in water several tens of feet deeper than the Stanton mound complex in Wilson County to the north (Heckel, 1972a, p. 590). Sponge-rich calcilutites are considered to represent a deeper-water facies also around Middle Pennsylvanian phylloid-algal buildups in the Paradox Basin (Elias, 1963, p. 196). The probably algal-influenced encrustations evident in the southern Montgomery County sponge-rich calcilutites, however, would place a lower depth limit on their place of formation. These encrustations characteristically involve a number of different kinds of foraminifers, thin layers of badly recrystallized, possibly archaeolithophyllid red algae, micrite laminations that may be attributed to poorly calcified blue-green algae, the problematicum Tubiphytes, and rare fistuliporid bryozoans (Fig. 8). The presence of a greater diversity of organic components in these encrustations imply more favorable conditions than normally attributed to a stromatolite environment (see below). Thus a quiet open marine lagoon, shallow enough for certain types of algal growth but deep enough that waves did not consistently agitate the bottom seems reasonable for the sponge-dominated calcilutites. This slightly deeper position is supported by best development of the South Bend portion of this facies where the unit overlies shale rather than sandstone, which suggests that compactional sag over the shale formed a slightly deeper embayment between the sandstone bodies that are common elsewhere at the top of the underlying Rock Lake Member.

Stromatolites--This facies includes those encrustations on shells and surfaces peripheral to the Captain Creek oolite as well as the untraced lenticular horizons within the Eudora-Rock Lake interval to the south. Although resembling closely in band specimen the familiar stromatolites sensu stricto of Logan, Rezak, and Ginsburg (1964), which contain no skeletal remains and thus are attributed wholly to mats of non-calcified blue-green algae, the Stanton stromatolites contain a large number of small agglutinated encrusting foraminifers with some larger calcareous forms (Fig. 22), and thus resemble osagia coatings in microstructure. They are intermediate in biologic composition between stromatolites in the strict sense, which imply very restricted intertidal to supratidal conditions, and the more biologically diverse invertebrate-rich encrustations in the sponge-rich calcilutite facies which imply more favorable conditions in a more open environment. The Stanton stromatolites with osagia microstructure probably developed in a nearshore semi-restricted subtidal to perhaps low intertidal environment. They seem to reflect a deterioration of the more open environment that is represented by the wide variety of shells they encrust, perhaps through restriction of circulation brought about by nearby sedimentation.

Terrigenous Detrital Rocks

These rocks signify access to a terrigenous detrital provenance.

Shales--Several types of shales are recognized, including fossiliferous and "unfossiliferous" gray to brown varieties, and fissile black shales. Few were delineated in much detail because of poor exposure, and none were studied microscopically.

Many apparently unfossiliferous light-brown shales occur in the Rock Lake Member, where they constitute most of the thin northern end of the unit, and underlie, surround and interbed with the sandstones to the south. Inasmuch as other apparently unfossiliferous Pennsylvanian shales in Kansas have turned out under closer examination to contain a variety of fossils (Heckel, 1972b, p. 259), the shales within the southern Stanton should be subjected to more detailed investigation; specifically they should be washed for microfossils in order to determine at least whether they represent marine or nonmarine environments.

Fossiliferous shales, gray to brown in color, occur more commonly in the Eudora interval and carry two distinct macrofossil assemblages: (1) One is a diverse bryozoan-brachiopod-echinoderm-dominated biota best developed near the top of the Eudora above and south of the Stoner Limestone pinchout. This assemblage is somewhat similar to those occurring in the Bolton bed and in higher fossiliferous sandy horizons in the Rock Lake as well as generally in bedded limestones north of the algal mounds. Thus it probably represents a detrital mud-dominated variant of the normal quiet-water open marine environment.

(2) The other assemblage is a molluscan fauna dominated by snails and clams, and containing, in places, ammonoids, nautiloids, brachiopods, and crinoids. This is similar to the so-called Wann fauna, which Newell (1933, p. 142-144) considered "geosynclinal" because of its extensive development in the thicker sequences of Oklahoma. This molluscan fauna appears in Kansas in the Eudora Member at several localities, as well as in the lower Wann Formation below the Tyro oolite. Presence of echinoderms and cephalopods in this assemblage indicates normal marine salinity, but the remainder of the assemblage points to some sort of restriction. Lack of suspension-feeding bryozoans and reduction in numbers and diversity of crinoids and brachiopods suggest that the water may have been quite turbid. The dominance of snails and clams, many of them burrowers, and the shale lithology also are compatible with a turbid-water, soft-substrate, but otherwise nearly normal marine environment that one might expect in the portion of a sea under substantial, but not overwhelming, fine detrital influx.

Black shales are colored by an abundance of organic matter and are characterized by lack of benthonic fossils, which together signify an environment with oxygen-starved (anoxic) bottom water that rendered the substrate inimical to life. The thin black shale found at the base of the Eudora above thinned Captain Creek (and Tyro) south of the mound complex occupies the same stratigraphic position as the black Eudora of the north, one of several black shales characteristic of this horizon within Missourian and lower Virgilian limestone formations (megacyclothems) in Kansas. Black shale occurs in the Eudora only where the underlying Captain Creek is thin. Because thick Captain Creek consists mainly of the topographically high phylloid-algal facies, the black Eudora is developed only over topographic lows on the Captain Creek. This can be measurably documented where the Eudora is black shale within the major channels in Wilson and Woodson counties. Thus the anoxic environment responsible for this thin horizon of black shale apparently involved slowdown of deposition combined with bottom stagnation below a certain depth, and it affected only the deeper portions of the sea (Heckel, 1972b, p. 264).

Sandstones--In general, sandstones signify an influx of quartz sand which may be distributed through a number of environments. These are as yet largely undetermined in the Stanton. Within the mound region, sandstone in the Rock Lake fills in lows developed in places on top of the Stoner mound. South of the Stoner mound, the Timber Hill siltstone bed, which separates the Rock Lake from the Eudora, is a relatively tabular, though lenticular unit for which the scattered brachiopods and particularly the echinoderm remains indicate the marine regime.

Farther southward the two major sandstone facies recognized in the Rock Lake interval can be related provisionally to the deltaic environmental regime, as Wilson (1957b, p. 433) has suggested previously. The thick, massive, laterally restricted sandstones, typified by much of the Onion Creek body, probably represent channels of continual water movement such as rivers or distributaries in the subaerial to submarine environmental transition. The thin-bedded sandstones, particularly those regularly interbedded with thin shales, probably represent quiet areas of intermittent sand influx such as the flood plain and interdistributary marshes and lagoons where intermittent flooding and levee breaching brought sand periodically into a normally muddy environment. The thin sandstones carrying shale pebbles reflect such an environment where cohesive lumps of eroded mud are commonly incorporated into the moving sand. The same general pattern of two similar major facies in the Chanute Formation below the Iola Limestone has been interpreted in this way (Haggiagi, 1970). In the younger Elgin Sandstone, elongate bodies of thick sandstone have been interpreted as bar-finger sands generated by delta distributaries (Brown, 1967). Other environments of sand deposition are probably also represented in various Stanton sandstones. For example, beaches and offshore bars may have been responsible for the thin even-bedded facies occurring in part of the northwestern extent of the Onion Creek body (Fig. 24). More detailed work on geometry and structures is needed to adequately determine origin of most Stanton sandstones.

Conglomeratic sandstone at base of South Bend--Unlike the Rock Lake sandstone beds that carry only shale pebbles, the conglomeratic sandstone at the base of the South Bend contains pebbles of calcilutite, quartz siltstone and sandstone, wood fragments and chert, as well as shale, along with both whole and fragmented fossils and a concentration of the largest quartz grains (many exceeding 1 mm) in the Stanton (Fig. 11). Furthermore, this basal South Bend horizon can be traced not only over all of southern Montgomery County, but also northward where it maintains its conglomeratic nature, at least locally across the algal-mound facies belt and on into northeasternmost Kansas (Ball, 1964, p. 62). The basal contact is sharp over shales and limestones in Montgomery County, but only locally is sharp over sandstones. The concentration of the coarsest quartz grains in the sequence suggest a well-winnowed lag deposit. The wide variety of sources represented by the pebbles, along with widespread distribution of the deposit and its sharp contact over a variety of rocks that represent environments of different topographic relief, indicate a regional subaerial erosional event of substantial vertical magnitude. The lack of a sharp contact over many sandstones probably reflects mainly the tendency of sand to remain loose and unindurated relative to carbonate or clay-dominated sediment in the subaerial environment. Many fossil fragments may have been eroded out of underlying deposits, or in the case of the wood, derived from trees living on emergent land. Whole marine fossils (and some of those represented by less abraded fragments) may have lived, however, in the earliest marine stages of South Bend deposition.

It is obvious that this erosional event, apparent nearly everywhere between the Rock Lake and South Bend Members, requires regression of the sea during latest stages of Rock Lake deposition, followed by transgression to initiate South Bend deposition. Regression in the Rock Lake is not only suggested locally by the probable deltaic environments developed near the top throughout much of southern Montgomery County, but also is indicated by the assemblage of land plants occurring near Garnett in east central Kansas (Moore et al., 1936), and by a variety of other features reflecting subaerial exposure at a number of places along outcrop in Kansas (Ball, 1959, p. 287) and in Nebraska (Russell, 1972). Furthermore, subaerial exposure at this horizon is compatible with Oakes' (1940a) assertion of a sub-Birch Creek unconformity (although erosion on the scale necessary to explain northward and southward disappearance of the Torpedo Sandstone is unwarranted). Transgression is indicated within the South Bend by the vertical succession of (1) the laterally variable conglomeratic base that represents erosion before, and agitation during, early inundation of an irregular surface, followed upward by (2) the relatively homogeneous marine calcilutite that represents a quiet environment below wave base developed in deeper water relatively uniformly over features of differing topographic relief, including both local thick sandstone lenses in southern Montgomery County and irregularities of the algal-mound complexes father north. The South Bend mound complex occurring locally on the thickest and probably most prominant portion of the Stoner mound represents the main departure from this pattern of uniformity across an area where depths after transgression remained sufficiently shallow for phylloid algae to proliferate.

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Kansas Geological Survey, Geology
Placed on web Jan. 20, 2009; originally published May 1975.
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