The Kaibab Limestone
(MIDDLE PERMIAN)
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The Kaibab Formation outcrops within the County along the escarpment of the Hurricane Fault. The formation forms cliffs and is well exposed there, particularly near the city of Hurricane. While it is the oldest (lowest) rock outcropping in Zion Park, it is essentially the youngest formation on the Kaibab Plateau to the south where it forms the upper rimrock at the Grand Canyon. The word Kaibab (Kaiba in the Paiute language) purportedly means reclining mountain.
Gregory's (1950) description of the Kaibab is, "White to yellowish massive, more or less dolomitic limestone, in part cherty, fossiliferous, locally gypsiferous." The presence of limestone containing dolomite, gypsum and characteristically marine fossils indicates that the Kaibab was formed near shore under warm and climatic conditions, sometimes under water depths of several meters, sometimes above sea level. Gypsum is a reaction product of anhydrite (calcium sulfate, CaSO) which forms when seawater evaporates in restricted embayments. As the seawater becomes, increasingly saline with continued evaporation, anhydrite (not salt) begins to precipitate and accumulate as a white, muddy deposit. Dolomite (MgCO) is thought to be formed when hypersaline seawater reacts with the limy accumulation of calcium carbonate skeletal remains of marine organisms.
McKee (1952) lists brachiopods, bryozoans, corals, crinoids and sea urchins as major fossils in the Kaibab in this area. Near the top of the formation mollusks become predominant, indicating changing conditions as the sea withdrew and water became shallow. Preservation of fossils in Kaibab outcrops in and near Zion Park unfortunately is quite poor.
It is worthwhile to pause briefly to consider how limy mud becomes limestone. The mud consists of microscopic pieces of crystalline calcium carbonate secreted by marine organisms and parts of their skeletal structure. Because calcium carbonate is relatively soluble in water, the smaller microcrystals tend to dissolve while the larger ones tend to grow. In time the mud is converted to a three-dimensional array of relatively large interlocking calcite crystals held together in the same way as a jigsaw puzzle. Lithification (literally meaning turning to stone) of limy mud is thus similar to the conversion of powder snow into ice on polar glaciers where the temperature never reaches the melting point.
In Kaibab time Washington County was located at the western edge of Pangaea at a latitude of about 10' north of the equator. If Pangaean climatic belts were similar to those of today, then the climate of the Kaibab shore may have been like that of coastal Ghana (West Africa), a moderately dry equatorial land.
There is supporting evidence for this interpretation in the sedimentary structures of nearby strata, McKee and Oriel (1967) show that Permian wind direction in northern Arizona was northerly (from the north) based on analysis of cross-bed directions in windblown sand. This would place Zion in the northern hemisphere belt of tropical northeasterlies at that time, taking into account the counterclockwise rotation of North America since Permian time.
The Kaibab Sea was a marine invasion of the continent, the largest of Permian time, and it was probably due to gentle subsidence of the crust in this area. More than 180 m (550 feet) of sediment were deposited before the sea began to withdraw (meaning that the crust ceased subsiding or was slowly elevated), placing the land increasingly under the influence of terrestrial conditions. An erosional surface of gentle relief marks the top of the Kaibab Formation, closing the Paleozoic Era in southwestern Utah in a very modest fashion. Time boundaries in geological history are seldom heralded by events on a worldwide scale.
SOURCE
-from Geology of Eastern Iron County, Utah by Herbert E. Gregory
Since McKee (1938) split the Toroweap from the Kaibab limestone of Noble (1928), this physical entity has carried the stature of Kaibab Formation, and as such, includes divisions B and A of Noble, or 4 and 5 of Reeside and Bossier (McKee, 1938, p. 12). At the type section of this formation in Kaibab Gulch in southern Utah it consists of 403 ft. of gray, massive, cherty limestone, with the uppermost 77 ft. composed of breccia, conglomerate, shale and sandstone, capped by buff limestone. McKee (1938, p. 28-35) has marshaled an impressive array of factual data bearing upon the Toroweap-Kaibab unconformity. The unconformity is of a widespread, regional nature; it involves a slight deformation of a large area, but not necessarily intense deformation during the post-Toroweap, pre-Kaibab interval. Erosive activity was severe locally only.
The Kaibab Formation is the most widespread carbonate succession of the Permian System within the study area, and adjacent areas as well. As a distinct rock unit it is present in central and northern Arizona, southern Nevada, southern and southwestern Utah, western Utah and eastern Nevada, and is recognized by the writer as far north as the Gold Hill district in Utah, and in northeastern Nevada as far as just north of Ferguson Mountain, about 20 mi. south of Wendover, Utah-Nevada. Where the writer has mapped the formation in the Toana Range, it is seen to thin to a feather edge above the Loray Formation and beneath the Plympton Formation, slightly northwest of Ferguson Mountain. At present it is not certain whether the Kaibab Formation in eastern and northeastern Nevada and western Utah is of the same age as the Kaibab Formation of the study area (Fig. 1). Studies of conodonts now in progress may aid in solving the problem.
The classic paper of McKee (1938) on the Toroweap and Kaibab Formations in northern Arizona and southern Utah clarified many regional relationships of various facies of the Kaibab. That there occurs a westerly transition from a high-clastic facies in the east to predominantly carbonate facies in a westerly and southwesterly direction was demonstrated by McKee. He also identified the members of the Kaibab Formation by Greek letters; these are (in descending order), the alpha, beta, and gamma members (1938, p. 12). The gamma member occurs in central Arizona only. Fortunately, order is emerging from certain stratigraphic ambiguity, because formal names have replaced the semantically-strange terms. Sorauf (1962, p. 117) suggested these changes:
| Kaibab | |
| McKee (1938) | Sorauf (1962, p. 117) |
| alpha member | Harrisburg Member (Reeside and Bassler, 1922, p. 58) |
| beta member | Fossil Mountain Member (new name) |
Fossil Mountain Member-This name was proposed by Sorauf (1962, 117, and 144-152) to replace McKee's beta member of the Kaibab Formation. This suggestion complies with the Code of the, American Commission on Stratigraphic Nomenclature for establishment of formal units (1961, p. 652). Sorauf's dissertation was not published, but perhaps the present paper will in part vindicate his sincere and hard work. The stratigraphic boundaries of the new member remain as defined by McKee (1938, p. 49), who measured it at Fossil Mountain in Grand Canyon National Park (p. 203). This was designated by Sorauf (1962, p. 144) as the type locality and type section for the Fossil Mountain Member. At this locality it consists of 211 ft. of gray to yellow, cherty and non-cherty, limestone and interbedded chert. The cherty, cliff-forming nature of this member identifies it throughout the entire Grand Canyon region. It is the rim-rock of the Grand Canyon, and veritably is the western lithic equivalent of part of the Guadalupe Mountains reef complex. McKee ( 1938 ) , Fisher ( 1961) , and Sorauf ( 1962 ) have provided stratigraphers with a tremendous body of informative objective data relating to the Kaibab Formation of northern Arizona; the interested reader is referred to their work for details.
The Fossil Mountain Member of the Kaibab Formation extends in a westerly and northwesterly direction. This new name replaces Fisher's (1961, p. 126) Member B, which at Parashant and Andrus Canyons ranges in thickness from 270 to 320 ft., consisting of uniformly fine-textured, gray to buff-gray, thick-bedded to massive limestone; chert makes up 50 to 60 percent of the member. Fisher (1961, p. 126139) discusses these cherts at some length. McNair (1961, p. 535-536) measured 330 ft. and 357 ft. for the Kaibab at Pakoon Ridge and South Hurricane Cliffs, respectively. Because his description relates largely to limestones, it appears that this is the Fossil Mountain Member only.
Eastern Nevada surface sections of the member east of the Las Vegas hinge line include the following localities: Tramp Ridge, 430 ft.; western Valley of Fire in the Muddy Mountains, 405 ft.; North Muddy Mountain, south of Glendale Junction, 360 ft.; near Garnet Railroad Siding, 325 ft.; South Muddy Mountains near Bitter Spring Wash, 650 ft.; and at Frenchman' Mountain, 535 ft. The southern part of the Mormon Mountains lies about 15 mi. north of the northern tip of the Muddy Mountains, and is also north of the Las Vegas line; the Fossil Mountain Member of the Kaibab Formation in the Mormon Mountains totals 430 ft. of massive, cherty limestone and dolomitic limestone.
A really-extensive outcrops of this member typify a region west of the Las Vegas line (but east of the Keystone thrust) from Calico Basin (on the north) to just west of State Line Hills of California on the south; possibly, the latter locality should be regarded as the southerly extension of the Las Vegas hinge line, and therefore the section is transitional shelf-basin. The Fossil Mountain Member here, for example, is 142 ft. thick, and consists of fossiliferous, cherty limestone, dolostone, and dolomitic limestone, disconformably overlain by the Moenkopi Formation.
The Fossil Mountain Member of the Kaibab thins in a westerly direction (Fig. 6); it measures 252 ft. at the northern terminus of Blue Mountain Hill (S 18, T 21 S, R 59 E), and in a lone hill three miles to the east, it is 275 ft. thick. This member consists of 254 ft. of thick to massive medium-gray cherty limestone and dolomitic limestone just south of the Flintkote Gypsum plant, adjacent to the road to Blue Diamond Village (S 8, T 22 S, R 58 E). Most of the Toroweap and Kaibab Formations are present in superb outcrops here (see Figs. 7, 10). Fossil Mountain Member of the Kaibab contains productid and spiriferid brachiopods, various large bryozoans, patch reefs of the sponge Actinocoelia maeandrina Finks, algae, and small reef-like masses of bryalgal limestones. Throughout the Bird Spring Range from its northern tip directly south of the Arden-Pahrump road (south of Blue Diamond Hill), to its southern extremity near Goodsprings, this member is characteristically a cliff-forming cherty gray limestone. The thickness varies but little from about 250 ft. in this outcrop band.
As indicated in Figure 6, the Fossil Mountain Member is present west of the leading-edge of the Keystone thrust, and therefore is part of the upper plate. Contrary to most of the Permian sediments here which are marine-basinal, the Toroweap and Kaibab Formations thin rather than thicken. Fossil Mountain Member, for example, is about 200 ft. thick near Lovell Wash, then thins westerly; along with other Middle Permian carbonates, this member was removed by pre-Moenkopi erosion (likely in Late Permian time). The member measures 175 ft. of massive cherty limestone just south of Lovell Wash (S 22, T 22 S, R 57 E), is 132 ft. thick south of Kyle Canyon (SE1/4 T 19 S, R 57 E), and measures 140 ft. north of Kyle Canyon near Grapevine Springs.
Age of the Fossil Mountain Member of the Kaibab Formation probably is upper Leonardian; McKee (1938) gave this age assignment as a result of comparing the brachiopod fauna with that of the standard Permian section of West Texas. Fisher (1961, p. 155-159) discussed the fauna of the Kaibab Formation and seemingly concurred with McKee. Sorauf (1962, p. 168-169) made a brief discussion of the Toroweap and Kaibab faunas, and concluded by stating "It is . . . possible that some of the uppermost beds of the Kaibab Formation in the Grand Canyon region are ... lower Guadalupian." Currently, samples of limestone from the Fossil Mountain Member of the Kaibab Formation are being studied by Dr. David L. Clark of the University of Wisconsin to determine if a conodont assemblage is present; these fossils are proving valuable paleontologic tools for the Permian, particularly where other diagnostic fossils are absent.
McKee (1938) published a detailed discussion of the environment and history of the Toroweap and Kaibab Formations; this classic is well known to all stratigraphers working with Permian rocks. It is obvious from his work, as well as that of Fisher (1961), Sorauf (1962), and many others, that the Fossil Mountain Member accumulated over a large area of the shelf and Cordilleran miogeosyncline farther west during maximum expansion of the Kaibab sea. Figure 12 illustrates some of the facies which characterize this member in the study area.
Harrisburg Member
In their regional study of Permian and related sedimentary rocks in southwestern Utah and northwestern Arizona, Reeside and Bassler (1922, p. 58) pointed out that the uppermost member of the Kaibab Formation consists of shale, gypsum, and limestone. They stated (p. 58): "It may be recognized, in spite of its variability, wherever it occurs, and as it is a definite unit between the upper cliff-forming limestone of the Kaibab and the basal beds of the Moenkopi formation it is here named the Harrisburg gypsiferous member, from its occurrence in the Harrisburg dome, 8 miles east of St. George." Their measured section indicates its thickness in the type section to be 280 ft. McKee (1938, p. 50) made note of the Harrisburg gypsiferous member of Reeside and Bassler, but he rejected the term, not stating his reasons. Seemingly he did not consider it worthy of formal member status, and may have regarded it as a facies variant of his alpha member. Fisher (1961, p. 141-142) also rejected the name Harrisburg, because he believed the sequence of sediments assigned to the Harrisburg to be a facies only of his Member C. It is obvious that neither McKee's alpha member, nor Fisher's Member C can be accepted as a formal member of the Kaibab Formation; Sorauf (1962, p. 153) used the name Harrisburg Member as a formal name for the upper member of the Kaibab Formation in the Whitmore area. The present writer agrees with Sorauf, and has so illustrated it in restored sections from the Grand Canyon west to Blue Diamond Hill west of Las Vegas, Nevada (see Figs. 5, 6).
As interpreted herein, the Harrisburg Member (following Sorauf, the term "gypsiferous" is deleted) is about 300 ft. thick at Hell's Hole, northeast of Whitmore Wash, and consists dominantly of gypsum, with tan limestones and dolostones; a detailed discussion of the various facies of the Harrisburg Member for this locality is given by Sorauf (1952, p. 152-168). McNair (1951, p. 536) did not designate an upper gypsiferous member separate from the main body of limestones of the Kaibab in his measured section at Pakoon Ridge and South Hurricane Cliffs. A thickness of 330 ft. was given for Pakoon Ridge, and 357 ft. for the South Hurricane Cliffs; he mentioned that at both localities upper tan-gray dolomitic limestones of the Kaibab are overlain abruptly by red sandstones and siltstones of the Moenkopi Formation.
Tramp Ridge in southern Nevada, lies about 12 mi. southwest of Pakoon Ridge; outcropping Harrisburg Member measures 180 ft. of gypsum, dolostone, sandstone, and shale. The writer (Fig. 6) believes that a thinner section is present in the Pakoon Ridge-South Hurricane Cliffs area. The South Muddy Mountains (Fig. 6) is located about 24 mi. west of Tramp Ridge, and includes the Bitter Spring Wash area to the south. A recently-constructed blacktop road that traverses the area north of Lake Mead makes much of this area accessible, and many outcrops of Permian and Triassic rocks are immediately adjacent to this road (see Figs. 13, 14). Harrisburg Member of the Kaibab Formation measures from 150 to 190 ft. of gypsum, gypsiferous siltstone and sandstone, and dolomicrite. Excellent outcrops and excavations of the member are present in the Rainbow Gardens-Frenchman Mountain area, about 24 mi. west of the Bitter Spring Wash area; in mapping the Kaibab-Moenkopi contact in this area the writer observed that not only does the Harrisburg Member vary in significant manner in lithology, but also thins and thickens along strike, and locally is absent. Also, in some places it is difficult to distinguish the Lower Red Member of the Moenkopi Formation from the Harrisburg Member of the Kaibab because of similarities in gypsum and gypsiferous sediments. In one measured section (SE 1/4 S 8, T 21 S, R 63 E, and labeled "Gypsum Quarry" on the Henderson topographic sheet), the Harrisburg Member may aggregate as much as 332 feet in thickness; the lower 27 ft. consists of redbeds, overlain in succession by 70 ft. of gypsum, 70 ft. of dolostone, siltstone and shale, 165 ft. of pure to impure gypsum and redbeds, with the uppermost 15 ft. a massive gypsum bed. At another section, in the south-central part of the Rainbow Gardens, the Harrisburg totals 380 ft. in thickness, with pure to impure gypsum comprising most of the lower 165 ft. and interbedded dolomicrite, sandy dolostone, siltstone, shale and thin gypsum above.
The Harrisburg Member of the Kaibab Formation west of the Las Vegas line is not uniformly gypsiferous throughout its outcrop band; rather, by contrast, at many localities the sequence is dominated by aphanitic ash-gray to cream-colored and tan dolomicrite. Three miles east of the Flintkote gypsum plant east of Blue Diamond Hill, gypsum is present only in thin layers and the section (S 2, T 22 S, R 59 E) consists of approximately 150 to 225 ft. of cream-colored very cherty dolomicrite (at the base), overlain by interbedded dolomicrite, claystone, and thin gypsum bands. Longwell et al. ( 1965, p. 38; 152-155, and Fig. 20, p. 153) noted the presence of pure to relatively pure gypsum at Blue Diamond Hill, observing that this passes to anhydrite at depth. Thickness of the gypsum and gypsiferous sediment (the Harrisburg Member), varies from 150 to more than 225 ft. in thickness. The present writer has measured various sections of the Harrisburg Member on top of Blue Diamond Hill, noting that at some localities total thickness of the member is of the order of 240 ft. of dolomicrite at the base, overlain in sequence of redbeds and impure to pure gypsum, more dolomicrite, more exploitable gypsum, with dolomicrite and dolomitic limestone (containing marine fossils) at the top (S 29, T 21 S, R 59 E). About one mile to the south in the main gypsum excavations, more high-quality gypsum is present, fewer redbeds crop out, and dolostones and limestones are thinner (see Figs. 15, 16). From thick, high-quality gypsum beds that make up much of the member in the Blue Diamond mines, the Harrisburg Member undergoes abrupt lateral facies to the northwest where dolostones and gypsiferous claystones comprise the facies (see Fig. 16).
In the Bird Spring Range south of Blue Diamond Hill (east of and adjacent to the Cottonwood Valley-Goodsprings dirt road), west-dipping outcrops of the Moenkopi form a cuesta; the eastern steep-slope contains the Harrisburg Member of the Kaibab near its base (S 2, T 23 S, R 58 E) and consists of about 160 ft. of light gray, tan, to cream-colored cherty and non-cherty aphanic dolomicrite, dolostone, dolomitic limestone, and minor gypsiferous red-beds at the top. Still farther south, and about 3 mi. southeast of Goodsprings, Nevada in the Bird Spring Range (S 1, T 25 S, R 58 E), the Fossil Mountain Member of the Kaibab (which there consists of 175 ft. of cherty to noncherty fossiliferous limestone) is overlain by about 140 ft. of alabaster-like gypsiferous limestone and micrite, herein regarded as representing a southerly facies of the Harrisburg Member. It is not certain if the Harrisburg Member extends into the Clark Mountain Range of eastern California (S 6, T 17 N, R 14 E, San Bernardino County).
In Figure 6, the Harrisburg Member is shown (with query) thinning to a featheredge in the Lovell Wash area of the Spring Mountains. The principal basis for such an assumption lies in the presence of thin tan and ash-gray, aphanitic dolomicrites, dolomitic limestone, and minor red-beds above the Fossil Mountain Member of the Kaibab locally. If true (such as north of Mule Spring south of Lovell Wash, in S 9, 16, T 22 S, R 57 E), then this is the western most occurrence of outcropping Harrisburg in the study area, because the entire Toroweap and Kaibab Formations are absent about 2 to 3 mi. farther west where Moenkopi (Triassic) rests with significant unconformity upon pre-Toroweap unnamed Permian redbeds.
Since the classic work of McKee (1938) with the Toroweap and Kaibab Formations, these Permian carbonates have generally been considered by most workers as of Leonardian age. McKee (1938, p. 170) cited Dictyoclostus bassi (now assigned to the genus Peniculaurus) and other common brachiopod species of the Kaibab Formation as abundant in the Leonard Formation of West Texas (see Sorauf, 1962, p. 168-169). Rugatia parindicus is present in the Leonard and Bone Springs Formations of West Texas, and is also abundant in upper beds of the Kaibab Formation (Sorauf, 1962, p. 169). Baars (1962, p. 209) correlated the Toroweap and Kaibab with the San Andres Formation of New Mexico and stated that the upper San Andres is Guadalupian age in southeastern New Mexico, as shown by diagnostic fusulinaceans. It is therefore possible that some of the upper units of the Fossil Mountain Member, and all the Harrisburg Member, of the Kaibab Formation are of early Guadalupian age.
Deposition of the Fossil Mountain Member of the Kaibab Formation was during the maximum expansion of the Kaibab Sea in the study area; because basal sediments of the Moenkopi Formation (Timpoweap and Lower Red Members) are largely if not wholly nonmarine (fluvial active streams and floodplains), the Harrisburg Member of the Kaibab, therefore, accumulated during regressive phases of the Kaibab sea. The regression, in all likelihood, was not a uniform withdrawal of marine waters, but by contrast may have been punctuated by minor regressions and transgressions with the ultimate in Late Permian regression being accomplished. As herein interpreted, there were areas of evaporite (largely gypsum) accumulation, other places of redbed sedimentation, and localities of restricted environments of the marine realm in which "primary" (i.e., aphanitic dolomicrite) dolomite formation was characteristic. Locally, more normal marine limestone sedimentation proceeded, and various shallow-water marine organisms left a fossil record. Figure 17 is the writer's interpreted lithofacies for the Harrisburg Member.
SOURCE
-from Geology and Natural History of the Grand Canyon Region by The Four Corners Geological Society
