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Graneros Shale in Central Kansas

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Paleogeography and General Depositional History

Graneros sediments were deposited near the eastern margin of the vast, shallow Western Interior Sea which occupied a differentially subsiding depression known as the Rocky Mountain trough. High lands on the west side of the trough were created during the Nevadan Orogeny and furnished much of the detritus that comprises the existing thick sections of Cretaceous rocks in the western part of the trough (Spieker, 1946; Reeside, 1957). A land area of low relief bordered on the eastern side of the trough and furnished a much smaller volume of sediment to the eastern shelf region of the sea.

Immediately prior to deposition of the Dakota Formation, the: central Kansas area and much of the surrounding Great Plains and southern Rocky Mountains region was undergoing erosion (Reeside, 1957, fig. 6). Marine deposition was. occurring in the northern part of the trough and in Texas. Early late Cretaceous subsidence initiated regional marine transgression across the formerly eroding region. The spreading sea ultimately inundated the entire trough in a great seaway extending, as indicated by fossils common to the two regions and to areas between, from Texas to the Arctic Region.

The earliest marine influence in central Kansas came from the south as indicated by late Cretaceous marine macroinvertebrates in the upper part of the Dakota Formation. Most of these fossils have not been reported elsewhere in the Western Interior but are known in the upper part of the Woodbine Formation of Texas (Hattin, 1965, p. 87). Indeed, the earliest Late Cretaceous marine lithologic succession in Kansas bears a close resemblance to the Woodbine-Eagle Ford beds of northeastern Texas. Mollusk-bearing ferruginous sandstone in the upper part of the Dakota of Kansas is indistinguishable from similar rock in the Lewisville Member of the Texas Woodbine. Silty shale is identical in outward appearance to that which I have seen in the Templeton Member of the Woodbine. The lower part of the Eagle Ford is calcareous, rests with sharp contact on non calcareous beds of the Woodbine, and at many localities, like the Greenhorn, it consists at the base of skeletal limestone containing Inoceramus fragments and fish remains. Many fossils in the three Kansas formations are known also in the lithologic counterparts in Texas, but exact age equivalence is not implied because the faunas may be facies controlled. The late Cretaceous shoreline moved northward from Texas, and eastward from Colorado, where fossils near the top of the Dakota are of Comanchean age, and fossils collected by Erie G. Kauffman (written communication, 1964) in the lower part of the Graneros apparently represent a zone that is older than any part of the Graneros in central Kansas. Conformability of the Graneros on the Dakota in Colorado indicates inception of Graneros deposition earlier in that state than in Kansas. The shoreline lay in the central Kansas area during the time the uppermost Dakota beds were laid down in that part of the State, and the shoreline continued to migrate progressively eastward or northeastward as Graneros sediments were deposited.

The Graneros macroinvertebrate fauna is dominated by southern species, some of which have not been reported north of Kansas and among which only Inoceramus rutherfordi, Exogyro columbella, and specimens questionably identified as I. dunveganensis have been reported farther north than Montana. A few species of Graneros foraminifers that were first reported in Texas are also known from the Cretaceous of northern Alaska, but all of these are long-ranging forms.

The fluviatile nature of much of the Dakota Formation in Kansas is generally agreed upon (Rubey and Bass, 1925; Plummer and Romary, 1942; Franks, et al., 1959). Conspicuously crossbedded, lenticular bodies of generally ferruginous sandstone are regarded as channel deposits, thin-bedded sandstone and varicolored clays and silts are floodplain and possibly lacustrine sediments, and some of the lignites are the product of river-created paludal conditions. This nonmarine part of the Dakota locally contains a rich fossil flora. The uppermost few feet of the Dakota exhibit a wide range of variation in lithology and stratigraphy, as described above, and contain marine fossils at a number of localities. These marine beds are transitional with the nonmarine part of the Dakota both vertically and laterally. In this part of the section, stratigraphically equivalent positions are occupied at various localities within a few miles of one another by carbonaceous shale with lignite, carbonaceous sandstone and siltstone, sandstone with abundant marine invertebrate remains, sandy shale with arenaceous foraminifers, or by shale that can scarcely be distinguished: from that of the Graneros. I believe that these relationships are best interpreted as the result of environmental differences on the topset plain of a major deltaic complex.

The wide distribution of channel deposits throughout the Dakota sediments in Kansas (Plummer and Romary, 1942, p. 328) can be attributed to the main channel and distributary system of the major stream( s) that deposited the formation. The complicated transition from nonmarine to marine strata near the top of the formation is the result of deposition along a coastline made irregular by seaward extension of the deltas, concomitant landward embayments of the sea between distributaries, and development of swamps and marshes virtually at sea level adjacent to the stream courses. In this sedimentary setting the Graneros-like shales near the top of the Dakota are envisioned as deposits of local coastal embayments; foraminifer-bearing carbonaceous clays in the same stratigraphic position elsewhere as deposits of coastal lagoons; lignites and underlying siltstone with upright reed molds as deposits of marshes that developed around the margins or on top of lagoonal deposits; and thick locally carbonaceous sandstone units at the top of the Dakota as deposits laid down at or just off the mouths of streams.

The inception of marine deposition in the upper part of the Dakota was brought about by continuation of subsidence that caused gradual but progressive eastward migration of the shoreline throughout the time of deposition of the Graneros in Colorado and Kansas. Graneros rocks do not exhibit complex facies relationships like those of the Dakota and represent near- and offshore marine deposition associated with the deltaic environment. The implication of a transgressional succession upward from fluviatile and marginal marine deposits in the Dakota to entirely marine conditions in the Graneros cannot be mistaken; however, the sections that I have examined lack unequivocal evidence of beach deposits. Such beach sediments as may have developed wherever waves attacked the deltaic shoreline were apparently reworked during the transgression and may now be represented by the more or less evenly bedded sandstone that lies at the top of the Dakota in most places and that locally contains invertebrate fossils and/or fragments of carbonized wood.

Although there is an obvious danger in making a direct comparison between the preserved record of an ancient delta and sediments of a modern one, qualitative similarities are manifest between marine sediments of the Dakota-Graneros stratigraphic sequence and the seaward sequence of Mississippi Delta sediments as described by Scruton (1956, 1960). Deltaic frontal deposits of the Cretaceous submarine-topset plain are represented by bodies of very fine-grained sandstone and by sand and silt layers and lenses, which were concentrated by wave and current reworking, and that are interlaminated with silty shale. Beds of this kind, occurring especially in the uppermost part of the Dakota and locally in the lowest part of the Graneros, are characterized by paucity of fossils and abundance of carbonaceous matter. Beds analogous to Mississippi pro-delta silty clays or foreset beds are represented in the Graneros by silty shale in the lower and middle parts of the formation. Lenses and laminae of sand and very fine silt show an irregular but progressive decrease upward in this part of the formation. Beds in the Graneros analogous to Mississippi Delta offshore clays or bottom set beds lie near the top of the formation where laminae and lenses of silt are sparse and very fine calcareous sand is locally concentrated in thin beds of skeletal limestone. Laminations are very rare in offshore clays in the Mississippi Delta at depths of 120 feet or more, apparently because waves capable of performing the necessary winnowing did not reach these depths (Scruton, 1955, p. 39). In the Western Interior Sea, waves the size of those on an exposed continental shelf probably could not form, but the presence of silt laminae and lenses near the top of the Graneros, even though sparse, would seemingly indicate depths of water considerably less than 120 feet as a maximum in which Graneros deposition took place.

The seaward changes in character of deltaic sediments are not peculiar to the Mississippi Delta. For example, in the pro-delta slope of the Rhone Delta van Straaten (1959) found a seaward gradation from more sandy and silty deposits near distributary mouths to purer clays in the distal reaches of deltaic deposition. He likewise observed a seaward decrease in degree of sediment lamination. Similar observations have been recorded recently for the Niger Delta by Allen (1964).

According to Shepard (1956, 1960) woody material is common in all Mississippi Delta sediments but is decreasingly abundant in a seaward direction. In the Graneros Shale, carbonaceous matter is progressively less abundant upward in the section, but is more abundant and of larger particle size in some sandstone beds than in the surrounding shale. As I have stated above, this is because the sandstone beds reflect, at least in part, temporary increases in river discharge.

Sandstone beds are most prominent in the Saline and Smoky Hill River valley areas, and denote nearness to the ancient river mouth( s). Subaqueous plastic flow structures were observed only in sandstone beds lying near the middle of the Graneros in this same area, attesting to slightly greater seaward inclination of the sea bottom at that time, perhaps on a deltaic foreset slope. Some of the most spectacularly crossbedded channel sandstone bodies in the Dakota lie near the top of that Formation in the Saline River area. These sandstones were interpreted as deposits of a major channel in Russell County by Rubey and Bass (1925, p. 61). The available evidence indicates that a major center of deltaic sedimentation existed in this area during a part of late Cenomanian time.

In the Dakota-Graneros strata the preserved sedimentary sequence is the reverse of that accumulating in the modern Mississippi Delta because the latter is a prograding deposit and the Dakota-Graneros complex accumulated during marine advance. As noted by Scruton (1960, p. 82) the constructional and destructional phases of development in rapidly built deltas are clearly differentiated, but this is not true in slowly built deltas. Except for possible beach destruction, the uppermost Dakota-Graneros sequence is well preserved, owing perhaps to a rate of subsidence sufficient to prevent extensive reworking of the entire complex during transgression rather than to slow deposition.

Migration of the late Comanchean--early Gulfian shoreline in the Great Plains states was not in a continuously eastward direction. The "D" and "J" sandstones of the subsurface in western Kansas and adjacent states to the west and northwest are tongues of the Dakota Formation and reflect westwardly prograding phases of deltaic deposition each of which was followed by renewed eastward transgression (for discussion see Haun, 1963).

Deposition of Graneros sediments occurred during the transgressive half of a clearly defined cycle of marine sedimentation that culminated with deposition of the Greenhorn Limestone and has been named the Greenhorn cyclothem (Hattin, 1962b, p. 124). The cyclothem is asymmetrical stratigraphically but nearly symmetrical lithologically and comprises seven phases including: (1) ferruginous marine sandstone and silty, carbonaceous, or sandy shale in the upper part of the Dakota Formation; (2) silty or sandy shale and thin sandstone beds of the lower part of the Graneros Shale; (3) silty shale with calcareous sandstone, skeletal limestone, and local septarian concretions of the upper part of the Graneros; ( 4) shaly chalk and chalky limestone of the Greenhorn and the Fairport Chalk Member of the Carlile Shale; (5) silty concretionary shale comprising most of the Blue Hill Shale Member of the Carlile; (6) silty or sandy, locally concretionary, shale of the upper part of the Blue Hill; and (7) siltstone, sandstone, and silty or sandy shale of the Cadell Sandstone Member of the Carlile. Details of the cyclothem are discussed more fully elsewhere (Hartin, 1964 fl966]).


1. The Graneros Shale of central Kansas is a distinctive, mappable lithostratigraphic unit that is transitional vertically and laterally with the underlying Dakota Formation and which underlies, along a sharp contact, the Greenhorn Limestone.

2. Graneros rocks are chiefly of polygenetic terrigenous origin and were derived from source areas lying to the east or northeast of the present outcrop. Kaolinite, angular quartz, and rock fragments are believed to be first-cycle sediments and probably came from the southern part of the Canadian Shield. Illite, chert, rounded quartz and heavy minerals, and possibly much of the glauconite were reworked from a Paleozoic sedimentary terrain. Montmorillonite was derived largely from a volcanic source lying beyond the western edge of the Western Interior Sea. Shell and bone debris in limestone and bone beds is of local origin.

3. The bentonite marker bed is the same as the "X" bentonite of Colorado and Wyoming and possibly also the Soap Creek bentonite of Montana. Northwestward thickening of the bentonite suggests an eruptive source in the Nevadan orogenic belt, probably in Idaho.

4. Marine macro invertebrate fossils in the Graneros of central Kansas are more numerous and widely distributed than heretofore supposed. These fossils comprise two assemblages, the strata characterized by each constituting an assemblage zone. The lower assemblage zone is characterized by Callistina lamarensis, the upper by Ostrea beloiti.

5. Faunal evidence substantiates temporal correlation of the Graneros of Kansas with part of the Graneros of the southern Rockies, part of the Mancos Shale of Utah and New Mexico, part of the Belle Fourche Shale of Wyoming and Montana, part of the Dunvegan Formation of Alberta, and with some part of the Lewisville and Templeton members of the Woodbine Formation in Texas. The Callistina lamarensis Assemblage Zone lacks index species of Inoceramus or ammonites presumably because of adverse environmental conditions. It cannot, therefore, be correlated precisely with the standard zonal sequence elsewhere in the Western Interior. This Zone may be equivalent to part or all of the Borissiakoceras compressum Zone, or may be merely a part of the Plesiacanthoceras amphibolum Zone, but for paleoecologic reasons, lacks species indicative of that zone. Strata containing the Ostrea beloiti assemblage embrace part or all of the Zone of P. amphibolum plus a few feet of younger strata.

6. Absence of Plesiacanthoceras wyomingense in the upper part of the Graneros in the central part of the Graneros outcrop supports lithostratigraphic evidence for an unconformity at the Graneros-Greenhorn contact. The same unconformity is recognized in the southern part of the outcrop belt, the C. lamarensis assemblage occupies all of the Graneros, and the Ostrea beloiti assemblage is not represented in the formation. Although P. wyomingense occurs near the base of the Greenhorn at one locality in the latter area the Graneros-Greenhorn contact there apparently represents a larger hiatus than it does farther to the north in Kansas.

7. Stratigraphic, lithologic and faunal evidence indicates that deposition of the Graneros began in shallow, turbid, nearshore marine water of less than normal salinity. Later deposition occurred in progressively deeper, less turbid, offshore water of normal salinity. As a consequence of unstable bottom conditions during deposition, most benthonic macro invertebrates in the C. lamarensis assemblage were endobenthonic forms whereas those in the O. beloiti assemblage were epifaunal and nektonic forms. Increasing salinity during deposition is indicated by the combined evidence of distribution of kaolinite, inarticulate brachiopods, limestone beds, foraminifers, and ammonites. Sedimentary structures and planktonic foraminifers suggest that water depth probably ranged from less than 30 feet during deposition of the lower part of the formation, to perhaps 70 feet for the middle part, with a maximum not exceeding 100 feet for the upper part of the formation. Coquinoidal limestone and bone beds are a consequence of storms which stirred bottom sediments to greater depths than usual and concentrated coarse organic debris while finer material was carried temporarily in suspension.

8. Deposition of Graneros sediments in central Kansas was influenced largely by discharge of a major stream system or systems which created a deltaic complex along the eastern margin of the Western Interior Sea. Nonmarine channel, floodplain, and swamp deposits in the Dakota formed on the surface of the delta. Overlying or laterally gradational marine sandstone and silty, carbonaceous, or sandy shale in the uppermost few feet of the formation are interpreted as deposits of a deltaic submarine topset plain, and sedimentation in local coastal embayrnents is represented by silty shale like that of the Graneros. Silty shale and thin sandstone beds in the lower part of the Graneros accumulated in a relatively nearshore environment and may be largely the deposits of a deltaic foreset slope, especially in areas where plastic flow structures indicate a submarine slope that was greater than that for adjacent beds. The purer, less silty shale beds near the top of the Graneros were deposited farthest from shore and are interpreted as bottom set beds of the deltaic complex.

9. The Graneros Shale represents part of the transgressive hemicycle of the Greenhorn cyclethem which was laid down during the first late Cretaceous cycle of marine deposition in Kansas. The cyclothem is asymmetrical stratigraphically and nearly symmetrical lithologically and comprises seven phases. Maximum transgression, and greatest distance from the eastern shoreline, is represented by the Greenhorn Limestone (phase 4); the Graneros Shale constitutes phases 2 and 3.

10. In central Kansas erosion of the Graneros Shale occurred before the inception of deposition of the Greenhorn Limestone. Evidence for subaerial erosion is lacking; accordingly, I believe that removal of parts of the Graneros resulted from the process known as sublevation. Because basal Greenhorn strata contain less terrigenous detritus than adjacent parts of the Graneros, sublevation apparently did not result from regressional phenomena. I conclude, therefore, that positive crustal movement in the central Kansas region was the primary factor responsible for the hiatus at the Graneros-Greenhorn contact.

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Kansas Geological Survey, Geology
Placed on web Dec, 15, 2014; originally published December 1965.
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