DEPARTMENT OF THE INTERIOR MISCELLANEOUS FIELD STUDIES U.S. GEOLOGICAL SURVEY MAPMF-2067 PAMPHLET
CORRELATION CHART OF LOWER CRETACEOUS ROCKS, MADISON RANGE TO LIMA PEAKS AREA, SOUTHWESTERN MONTANA
By R.G. Tysdal, T.S. Dyman, and DJ. Nichols
Abstract change in nomenclature is arbitrary, but is pbced along the axis of the Ruby River valley, which Lower Cretaceous strata in southwestern Montana separates the Snowcrest Range from the Greenhorn were deposited in a nonmarine facies of the and Gravelly Ranges. Cordilleran foreland in the west and in a marine shelf facies of the foreland in the east. Some of the strata represent time-equivalent sediments deposited in INTRODUCTION different environments, and different names have been applied previously to the same strata even within the Lower Cretaceous rocks in southwestern Morgana same area. The four measured sections presented here represent strata that were deposited in the forehand are in sequences of strata that have been telescoped by basin of the Cordilleran thrust belt in the west and in thrust faults of Late Cretaceous to early Tertiary age, a shelf facies of the foreland in the east The f firata and facies represented in the measured sections record cyclic sedimentation during a succession of originally were deposited farther apart than they are marine transgressions and regressions, which were now. Strata described herein are underlain by the caused by an interaction of source-area tectorism, Aptian to Albian(?) Kootenai Formation and are basin subsidence, and varied rates of sedimentation. overlain by the Cenomanian to Turonian lower part The four measured sections are in sequences of r*rata of the Frontier Formation. that have been telescoped by thrust faults of Lara^de In the Snowcrest Range and Lima Peaks area, age, thus facies represented in the measured sequences strata represented by the two westernmost measured were originally deposited farther apart than the^ are sections are assigned to the Albian Blackleaf now. Some of the strata represent time-equivalent Formation, which contains the Flood Member and the sediments deposited in very different environments, overlying volcaniclastic-rich Vaughn Member. The and several names have been applied to the same Taft Hill and Bootlegger Members of the Blackleaf strata within the same area. Hence, nomenclature! Formation, in their type sections near Great Falls, are problems of the region represented by the section0 are not recognized by us in southwestern Montana. The addressed in this report. two easternmost measured sections represent strata in Strata equivalent to several formations present on the Madison, Gravelly, and Greenhorn Ranges, where the shelf also can be recognized in the ba^inal Albian rocks are assigned to the Thermopolis Shale, sequences to the west. Facies changes occur from Muddy Sandstone, and Mowry Shale. In east to west, but the rock units are recognized as southwestern Montana the Thermopolis Shale and broadly similar. The purpose of this report is to overlying Muddy Sandstone are lithically equivalent review stratigraphic relationships and nomenclature in to the Hood Member of the Blackleaf Formation, the region, and to present a revision of the whereas the Mowry Shale is equivalent to the Vaughn correlations for the units. These goals are Member. Strata in the Snowcrest Range have accomplished through the presentation of new data, characteristics in common with both the eastern and including measured sections, and reinterpretation of western facies. The geographic location for the existing data. MEASURED SECTIONS Formation. Several different names had been used previously for strata that here are called Blackleaf The locations of the four measured sections are Formation, but no consistent pattern of nomenclature shown on figure 1. The two westernmost measured had been established, in part because of local sections, Lima Peaks and Antone Peak, and the lower lithologic and facies changes and the great distance part (Warm Springs Creek) of the Greenhorn between outcrops and type localities. The decision by composite section in the valley between the Dyman and others (1984) and Dyman (1985a, b, c) to Greenhorn and Gravelly Ranges, were selected from apply the names Blackleaf and Frontier to Cretaceous twelve original descriptive sections released in Open- strata in Beaverhead County and the southwestern part File reports by Dyman and others (1984), Dyman of Madison County, Mont, was made after reviewing (1985a, b), and additional data of Dyman. The upper the literature and carefully examining the area near part (Cow Camp) of the Greenhorn composite Blackleaf Creek, Mont., the type area of the Frontier section, and the Lincoln Mountain section in the at Cumberland Gap, Wyo., and additional outcrops Madison Range, are previously unpublished sections (Dyman and Nichols, 1988). of Tysdal. These four sections record the most The measured sections bridge areas where different diverse strata that we know of in the region. The shelf and foreland basin terminology are used Lincoln Mountain section is nearly completely currently. The lithic character of the Lower exposed, but the Antone Peak section in the southern Cretaceous stratigraphic units is very much the same part of the Snowcrest Range is poorly exposed. The in the Madison, Greenhorn, and Gravelly Ranges. In lower and upper parts of the Greenhorn composite the Lima Peaks area, however, the lithic equivalents section lie within 1.5 mi (2.5 km) of one another. of the eastern units are different and use of the The four measured sections and their stratigraphic Blackleaf name is appropriate. Strata of the correlations are presented here using the SRG Snowcrest Range, represented by the poorly exposed (Stratigraphic Report Graphic). The SRG is a Antone Peak section, seem to have characteristics stratigraphic applications computer program more like those of the Lima Peaks section than those developed by the U.S. Geological Survey and of the Greenhorn composite section. Reconnaissance Petroleum Information Corporation of Denver, Colo. data suggest that the Lower Cretaceous rocks of the The SRG accepts sedimentologic, paleon to logic, Snowcrest Range may change character gradually lithologic, paleoecologic, and nomenclature data for along the length of the range. Hence, the geographic outcrop sections and cores, and displays these data in location for the change in nomenclature is somewhat a scale-variant format (see "Explanation of measured arbitrary, but is here placed along the axis of the sections") (Petroleum Information Corporation, 1984; Ruby River valley, which separates the Snowcrest Dyman and others, 1985). The SRG is proprietary to Range from the Greenhorn and Gravelly Ranges (fig. Petroleum Information Corporation, but is available 1). This placement is respectful of historical usage of by contract to the U.S. Geological Survey for a nomenclature in the Greenhorn and Lima Peaks areas, variety of research applications. as well as the differing lithic character of the Lower Cretaceous units in different parts of the region. Lower Cretaceous strata of the eastern part of the STRATIGRAPHY Centennial Mountains are judged to have characteristics more in common with the eastern The eastern two measured sections represent strata strata than with the Blackleaf rocks. Post-Kootenai of the Madison, Gravelly, and Greenhorn Ranges (fig. Lower Cretaceous strata present in the Exxon and 1). The Lower Cretaceous rocks in these areas are American Quasar boreholes near the western part of assigned to the Aptian to Albian(?) Kootenai the Centennial Mountains (fig. 1) were assigned to Formation and the Albian Thermopolis Shale, Muddy the Blackleaf Formation by Perry (1986), but Perry Sandstone, and Mowry Shale; lowermost Upper (oral commun., 1987) now believes that strata of the Cretaceous rocks are assigned to the Cenomanian to American Quasar borehole (the eastern of the two Turonian lower part of the Frontier Formation. In boreholes) are more representative of facies recognized the Snowcrest Range and Lima Peaks area, within the eastern part of the region considered in this represented by the western two measured sections, report. strata correlative with those formations previously Stratigraphic relationships and regional named are assigned to the Aptian to Albian(?) correlations are illustrated in figure 2. In discussing Kootenai Formation, the Albian Blackleaf Formation, stratigraphic relationships, we generally proceed from and the Cenomanian lower part of the Frontier east to west, from shelf to foreland basin. All megafossils reported here, including those in (cited, where appropriate, in following section- of cited references, were identified by W.A. Cobban this report) who were specifically concerned ^'ith except where otherwise noted. Palynomorphs were Lower Cretaceous rocks, and who also examined identified by D J. Nichols and are shown in tables 1 rocks in part of the region of the four measured and 2. sections presented in this report Many studies divided strata above the Kootenai into lithofacies, members, or formations. Becruse PREVIOUS WORK the names and the strata that workers included differed from one area to the next, other studies are cited and Early works concerned with the Lower and Upper discussed where applicable in the following sections. Cretaceous rocks in southwestern Montana We have attempted to cite all relevant university commonly were mapping studies, and they generally theses, but others of which we were unaware may left the sequence separated into the Kootenai exist. Formation and an undivided unit of overlying strata. In the general area of the measured sections, strata above the Kootenai were assigned to the "Colorado KOOTENAI FORMATION and Montana formations" (Peale, 1896), "Colorado formation" (Mann, 1954, 1960), "Colorado Shale" The Kootenai Formation is discussed briefl;' in (Lowell, 1965), Colorado Group (Klepper, 1950; this report because it underlies all of our measured Christie, 1961; Becraft and others, 1970; Garihan and sections, and contact relationships with overlying others, 1983), Blackleaf and Frontier Formations rocks require an understanding of the upper part of the undivided (McBride, 1988), or were neither divided nor Kootenai. The basal part of each of the measured named (Swanson, 1950; Brasher, 1950; Sheedlo, sections shown represents strata of the uppermost part 1984). In the Lima area, the Aspen Formation of the Kootenai Formation. In southwes*^rn (Scholten and others, 1955; Ryder, 1968; Ryder and Montana the Kootenai has been divided into as ir<*ny Ames, 1970; Skipp and others, 1979), and "Colorado as six units (for example, DeCelles, 1986). It Shale" (Sadler, 1980) also have been used for these typically contains a basal conglomeratic sandstorm, a strata. The term Colorado Group is not used here. variety of medial sandstone and mudstone strata, and The stratigraphy of the Upper Cretaceous Frontier carbonate strata in the upper part. Two unit" of Formation and correlative strata has not been worked carbonate strata have been recognized regionally, the out in the western part of southwestern Montana; upper of which contains an abundance of gastropods hence, facies relationships between the Frontier and (Holm and others, 1977). The gastropod limestone is Upper Cretaceous rocks of the Colorado Group in commonly considered to mark the top of the northwestern Montana are unknown. The Aspen formation in southwestern Montana and is usel in Formation (Veatch, 1907) is geographically restricted this report. to eastern Idaho and western Wyoming, where it is In the shelf area of southwestern Montana, used in conjunction with the underlying Bear River gastropods are absent locally from the uppemost Formation. Strata described here resemble the carbonate strata, as shown by our studies and the Blackleaf Formation in northwestern Montana more graphic sections of Vuke (1984) in the Madron than they resemble the Bear River Formation. Range. The overlying lower sandstone membe^ of The post-Kootenai Lower Cretaceous strata on the the Thermopolis Shale, or equivalent lithofacies, eastern side of the Pioneer Mountains, northwest of lacks carbonate beds in the sections examined b" us the area of our sections, were assigned to the in the Madison, Greenhorn, and Gravelly Ranges. "Colorado formation" (Richards and Pardee, 1925; Klepper (1950) previously had used the gastrcr>od Karlstrom, 1948), left unnamed (Myers, 1952), and limestone to mark the top of the Kootenai in the later placed in the Colorado Group (Ruppel and Snowcrest Range. The contact is sharp, marks an others, 1983; Pearson and Zen, 1985; Zen, 1988). upward change from nonmarine to marine strata, and We cite these studies because they include some of is disconformable. In the Lima Peaks frea, the earliest work undertaken on Lower Cretaceous non-gastropod-bearing limestone occurs upsectin of strata in southwestern Montana, and indicate that the the gastropod limestone. Discontinuous lenses of strata do not readily lend themselves to subdivision. nodular micritic limestone and calcareous mudstr»ne In addition, the Pioneer Mountains area contains are interbedded with sandstone and siltstone tha* are strata that were studied in detail by other workers typical of the lower sandstone member of the Thermopolis. These strata were assigned to the lower Vaughn Member consists predominantly of part of the Blackleaf Formation by Dyman and nonresistant beds of nonmarine bentonitic mudstc^e Nichols (1988) because (1) the gastropod limestone is in pastel shades of gray, green, pink, orange, 2 id a widespread marker unit that is readily identifiable, brown in the area of our measured sections, although (2) the gastropod limestone is readily mappable, and nonbentonitic mudstone is present in the Madison (3) the carbonate beds above the uppermost gastropod Range. Porcellanitic mudstone, volcaniclassic limestone are discontinuous and thus do not represent sandstone and siltstone, and tuff are also present in a reliable marker unit the study area but are more abundant and form part of A late Albian palynomorph assemblage was a much thicker Vaughn sequence west and northwest identified in the uppermost part of the Kootenai of the area of this study. Formation in the Lima Peaks section, providing a Lithic units of the Blackleaf Formation of tvrs maximum age for the Blackleaf Formation at this report are similar to the four lithofacies intervals locality (table 1). The assemblage was obtained from (designated A, B, C, D) of Schwartz (1972, 1983). dark-gray shale below the uppermost gastropod But, because Schwartz did not publish his measured limestone bed. sections or present them in his dissertation, prec;«e correlation with his lithofacies intervals is difficult On the other hand, some major differences erist BLACKLEAF FORMATION between his descriptions of the four intervals and our observations. For example, descriptive material in The Blackleaf name previously had been used for Schwartz (1972) makes clear that, as defined by hrm, Lower Cretaceous rocks in southwestern Montana the upper part of the Blackleaf Formation in so^e (including the area of the four sections presented here) areas in the Greenhorn Range includes Upper by Schwartz (1972,1983), James (1977), and Suttner Cretaceous strata that we consider part of the Frontier and others (1981); and in the Lima Peaks area by Formation. Perry and others (1983) and Perry (1986). In addition, The Blackleaf Formation in the area of the western Dyman and others (1984), Dyman (1985a, b, c), and two sections varies in thickness from a maximum of Dyman and Nichols (1988) used Blackleaf for the 1,500 ft (457 m) at the Antone Peak section in the western three of the measured sections presented in Snowcrest Range to a minimum of 1,394 ft (425 m) this report. at the Lima Peaks section. Similar thicknesses have In northwestern Montana, Cobban and others been reported in the subsurface near the Lima Peaks (1959) named four members of the Blackleaf section (Perry and others, 1983). Corrected dip-me*er Formation, from bottom to top: Flood, Taft Hill, data (W.J. Perry, Jr., oral commun., 1985) for the Vaughn, and Bootlegger (fig. 2). Detailed measured American Quasar Peet Creek Federal 29-1 borehole sections of these members were presented in Cobban (fig. 1) suggest a thickness of 1,525 ft (465 m), a and others (1976). The Flood(?) name has been used value comparable to the thickness exposed near Li*na in southwestern Montana by Perry and others (1983). Peaks. Dyman (1985a, b, c), Dyman and Nichols (1988), and The lithology, thickness, and other geologic Schwartz (1972,1983) used informal names for lithic properties of the members and (or) lithic units of the intervals or units of the Blackleaf Formation. We Blackleaf Formation are discussed below with follow Perry and others (1983) in using the name correlative strata of the Thermopolis Shale, Mu(My Flood Member to encompass the lowermost strata of Sandstone, and Mowry Shale. the Blackleaf Formation, consisting of two sandstone units separated by a unit of black shale (the lithic equivalent of the shale member of the Thermopolis THERMOPOLIS SHALE Shale). We recognize that the sandstone units of this tripartite member differ in character from those in the The name Thermopolis Shale is used in the type section near Flood Siding in Cascade County, Livingston area of southwestern Montana (figs. 1,2) Mont. Preliminary study of correlative sandstone for a sequence of strata that is composed of th-ee units between Lima Peaks and the Drummond area of informal members: a lower sandstone, a mid^e central western Montana indicate that their character shale, and an upper sandstone (Roberts, 1965,1972). differs areally, although the tripartite nature still Roberts recognized these members as litsic exists. We have not recognized the Taft Hill and equivalents of the Fall River Sandstone, the SI ull Bootlegger Members in southwestern Montana. The Creek Shale, and the Muddy Sandstone, respectively. The lower sandstone also is the lithic equivalent of member is 50 ft (15 m) thick, and its lithic equivr *ent the "rusty beds" that make up the upper part of the in the lower part of the Flood Member of the Cleverly Formation in Wyoming; and the middle Blackleaf Formation at the Lima Peaks section shale is the lithic equivalent of the Thermopolis increases to a thickness of 220 ft (67 m). Shale. For the southern part of the Madison Range, In the Madison Range, the lower sandsrone Witkind (1969) had tentatively made correlations with member of the Thermopolis Shale was assigned to the rocks of the Livingston area and used the the lower part of the Bear River(?) Formatior by Thermopolis name. In this report, and in Tysdal (in Austin and Stoever (1950); Hall (1961) used the n^me press), we follow the usage for contiguous strata in "upper sandstone member" of the Kootenai northwestern Wyoming and use the name Muddy Formation; Hadley (1969a, 1980) used "shale unir" of Sandstone for the upper sandstone in the Madison, the Kootenai Formation; Lauer (1967), Ray (19^7), Greenhorn, and Gravelly Ranges. We follow Roberts Rose (1967), and Bolm (1969) also placed the (1972) in using the informal name lower sandstone sandstone in the upper part of the Kootenai; Wi'-on member of the Thermopolis Shale for the lithic (1970) subdivided the unit into a silly sandsrone equivalent of the Fall River Sandstone and the rusty member and an overlying rusty beds member and beds, and shale member of the Thermopolis Shale for placed both in the Kootenai; Witkind (19*9) the correlative of the Thermopolis Shale in designated the rocks the "sandstone member of the Wyoming. Using either the Fall River or Skull Thermopolis(?) Shale"; Kehew (1971) and Walsh Creek names would entail transposing names across (1971) mapped it with the Thermopolis Shale; Vuke areas of southern Montana for which the Wyoming- (1984) used the named "rusty beds member of the derived nomenclature now is widely used. lower Thermopolis Formation"; and Tysdal and Simons (1985) referred to the unit as the lower ha1f of the Thermopolis Shale. Lower sandstone member of the In the Greenhorn Range and the northernmost part of the contiguous Gravelly and Snowcrest Ran"*?.s, Thermopolis Shale, and Flood Mann (1954,1960) included sandstone here assigned Member of the Blackleaf Formation to the lower sandstone member in the "up*>er sandstone member" of the Kootenai Formation, and The lower sandstone member of the Thermopolis Hadley (1960, 1969b, 1980) used the term "sf*ale Shale in the Madison Range is composed of pale- unit" of the Kootenai Formation. In the central part brown to rusty colored, fine-grained, crossbedded of the Snowcrest Range, Gealy (1953) and ZeMer quartz arenite, and characteristically displays abundant (1954) recognized these clastic rocks as equivalents of oscillatory ripple marks. The upper few feet of the the rusty beds and mapped them as part of the unit at Lincoln Mountain is composed of maroon to Thermopolis Shale. In the southern part of the dark-brown siltstone, separated by mudstone layers. Snowcrest Range, Keenmon (1950) assigned the The lower contact is sharp and probably is sandstone unit to the basal sandstone member of the unconformable. Vuke (1984) reported the unit to be Bear River(?) Formation. In the southern part of the almost entirely quartz arenite at some localities. Gravelly Range, Christie (1961) and Sonderegger and According to Vuke (1984) for the Madison Range, others (1982) mapped the sandstone as the top un:* of and Schwartz (1972) for the entire region, the the Kootenai. In the Centennial Mountains and the sandstone member is marine and was deposited in a southern part of the Gravelly Range, Honkala (1^9) shoreface environment. In the Flood Member of the apparently placed the lower sandstone member in the Blackleaf Formation in the two western sections, the "Colorado shale." Also in the Centennial Mount ;ns, lithic equivalent of the lower sandstone member of Kennedy (1947) assigned the sandstone immedia^-ly the Thermopolis consists of green to gray and red above the gastropod limestone of the Kootenai to the calcareous mudstone, quartz- and chert-rich sandstone, Bear River Formation; Witkind (1975, 1982) and and micritic and nodular limestone; these strata were Witkind and Prostka (1980) placed this sandstone unit deposited in fluvial, lacustrine, and near-shore marine in the Thermopolis(?) Shale. In the Lima a~ea, environments (Dyman and Nichols, 1988). Dillon (1949) included this sandstone in the F«Nar The lower sandstone member is 121 ft (37 m) River Formation. thick at the Lincoln Mountain measured section, and Three molds oflnoceramus comancheanus Cra^in, ranges from 55 to 120 ft (17 to 37 m) thick within a species of late Albian age, were found in the upner the Madison Range (Vuke, 1984; Witkind, 1969). At part of the lower sandstone member of the the composite Greenhorn section the lower sandstone Thermopolis near Monument Hill in the Gravelly Range, about 10 mi (16 km) south of the Greenhorn Formation by Austin and Stoever (1950); the nrme composite section (Dyman and Nichols, 1988). Thermopolis(?) Shale was used by Hall (1961) and Three species of lacustrine ostracods (identified by the "dark-shale member" by Hadley (1969a, 19PO), I.G. Sohn) were reported by Hadley (1980, p. 71-72) both of whom equated it with the black shale unit of from the lower part of the lower sandstone member the Thermopolis Shale of Wyoming. Lauer (19^7), near the Greenhorn composite section. They are Ray (1967), Rose (1967), Bolm (1969), KeHw Cypridea wyomingensis Jones sensu Peck 1941, (1971), and Walsh (1971) placed the shale unit in the Cvpridea anomala Peck 1941, and Eupera onestae Thermopolis Shale; and Wilson (1970) used the name (McLeam). Thermopolis Shale for the black shale unit o^ly. Other workers recognized its equivalence to the S ull Creek Shale of Montana, but applied different naires: Shale member of the Thermopolis basal strata of the upper part of the ThermopolH?) Shale, and shale unit of the Flood Shale (Witkind, 1969); upper member of the Member of the Blackleaf Formation Thermopolis Formation (Vuke, 1984); and upper part of the Thermopolis Shale (Tysdal and Simons, 19^5). In the Madison, Gravelly, and Greenhorn Ranges In the Greenhorn Range and the northernmost and the Centennial Mountains, the shale member of parts of the contiguous Gravelly and Snowc^est the Thermopolis Shale is a marine unit that is Ranges, Mann (1954,1960) described the black shale composed mainly of black fissile shale, but contains unit and assigned it questionably to the "Colorado thin beds of sandstone in the uppermost part. The Formation." Hadley placed the same unit in the equivalent lithofacies of the Flood Member of the Thermopolis Shale, variously calling it the "middle Blackleaf Formation in the Snowcrest Range and shale member" (Hadley, 1960) and later the "dvk- Lima Peaks area consists predominantly of mudstone, shale member" (Hadley, 1980), and recognize*? its shale, siltstone, and subordinate fine-grained lithic correlation with the Skull Creek Shale. In the sandstone and limestone; these strata were deposited central part of the Snowcrest Range, Gealy (1953) and in lagoonal to shallow-marine environments (Dyman Zeigler (1954) mapped these strata as the and Nichols, 1988). The shale member is 39 ft (12 Thermopolis Shale. In the southern part of the m) thick at the Lincoln Mountain section, and ranges Snowcrest Range, Keenmon (1950) included U"-so from about 30 to 300 ft (10 to 90 m) thick in the strata within the Bear River(?) Formation. In the Madison Range (Vuke, 1984; Witkind, 1969). In the southern part of the Gravelly Range, this lithofa'ies area from the Greenhorn and Snowcrest Range was called "Cretaceous Shale, unnamed" (Sonderepger sections to the Lima Peaks section, the shale and others, 1982), and "Colorado shale" (Honkala, lithofacies ranges from 56 to 240 ft (17 to 73 m) 1949). In the Centennial Mountains, Kennedy (11H7) thick. At the Lima Peaks section, the shale interval mapped the shale as part of the Bear River Formation; of the Blackleaf is poorly exposed. Dyman and others Witkind (1975, 1976) mapped it as the BearRive*h (0.3-m) thick volcaniclastic sandstone unit, which she assemblages from the pastel beds at the Lima Peaks placed in the uppermost part of the Muddy Sandstone. section yielded forms indicative of Cretaceous age We agree that the two volcaniclastic sequences are (table 1). Although no further age refinement was correlative, but consider the light-colored sandstone in possible, these assemblages are consistent r-ith assemblages in the Madison Range that are Albian in shale, and were deposited in fluvial and shallow- age. marine^) environments. The lower strata contain palynomorphs of Cenomanian to Turonian age (trble 1). Upper part of Mowry Shale The base of the Frontier Formation was placed at the base of the first sandstone unit above the dfk- At Lincoln Mountain in the Madison Range, the gray mudstone of the Mowry Shale in the Madron Vaughn Member is overlain by 274 ft (84 m) of dark- Range, and at the base of the first sandstone or gray mudstone and silty mudstone that contain a few conglomeratic bed above the Vaughn Member in the minor interbeds of sandstone, bentonite, and coal. area of the other sections. At the Lima Pe^ks These strata represent marine and marginal-marine section, about 30 ft (9 m) of dark-gray nonvolcnic deposits; marsh, stream channels, and overbank shale of Cenomanian age occurs above the Vaughn deposits are present according to Vuke (1984). No Member of the Blackleaf Formation and below time-equivalent dark-gray mudstone strata are known sandstone of the Frontier. Because lower Frontier in the area of the western three sections, although sandstone and conglomerate beds are laterrUy such strata may have been deposited and subsequently discontinuous in the Lima Peaks area, it is eroded prior to deposition of the Frontier Formation. appropriate to place the base of the Frontier at the The top of the Mowry in the Madison Range was base of the shale, which also is a regional chosen at the base of a sequence of chert-rich unconformity (Dyman and Nichols, 1988). """he sandstone beds that aggregate about 50 ft (15 m) thick contact is probably diachronous, and correlation was and which are placed in the Frontier Formation best made where palynomorph data were available. (Tysdal and Simons, 1985). The long-ranging marine brachiopod Lingula Strata of the upper part of the Mowry Shale, or subspatulata Hall and Meek was found in the brsal Mowry undivided where pastel beds are absent in the sandstone of the Frontier Formation at the Line oln Madison Range, were assigned to the Aspen(?) Mountain section in the Madison Range and was Formation by Austin and Stoever (1950). Hall associated with an unidentifiable juvenile ammoirite. (1961), Lauer (1967), Ray (1967), Kehew (1971), and Basal strata of the Frontier in the Greenhorn Walsh (1971) mapped these rocks as Upper composite section yielded the marine bivalve Cretaceous strata undivided. Bolm (1969) assigned Pleurocardia pauperculum (Meek) (Dyman and the post-Vaughn strata to a unit of undifferentiated Nichols, 1988). Cretaceous rocks, and Rose (1967) used "Albino" for them. Wilson (1970) assigned them to the Mowry Shale. Hadley (1969a, 1980) assigned strata of the upper member to the Frontier Formation. Schwartz REFERENCES CITED (1972) considered them as part of his lithofacies interval D. Vuke (1984), Tysdal and Simons (1985), Austin, W.H., and Stoever, E.G., Jr., 1950, and Tysdal (in press) assigned the strata to the upper Reconnaissance geology of the south flank of part of the Mowry Shale. Cinnamon Mountain, Gallatin Courty, At Lincoln Mountain in the Madison Range, we Montana: Ann Arbor, University of Michigan obtained Albian palynomorphs from lower and upper M.S. thesis, 102 p. beds of the upper member of the Mowry Shale, and Becraft, G.E., Kiilsgaard, T.H., and van Noy, R.M., Albian dinoflagellates from the upper beds (table 1). 1970, Mineral resources of the Jack Creek Ba^in, Wilson (1970, p. 50) reported dinoflagellates from the Madison County, Montana: U.S. Geologfcal basal strata of the upper member, immediately above Survey Bulletin 1319-B, 24 p. the pastel beds. Bolm, J.G., 1969, Geology of the Lone Mountain area, southwestern Montana: Moscow, University of Idaho M.S. thesis, 38 p. FRONTIER FORMATION Brasher, O.K., 1950, The geology of part of the Snowcrest Range, Beaverhead County, Montrna: Strata assigned to the Frontier Formation differ in Ann Arbor, University of Michigan M.S. the^s, lithology and thickness from one section to the next. 58 p. Lower strata of the Frontier are composed of lithic Christie, H.H., 1961, Geology of the southern par* of sandstone, conglomerate, ben ton i tic mudstone, and the Gravelly Range, southwestern Montana: Corvallis, Oregon State University M.S. thesis, Dyman, T.S., and Nichols, D.J., 1988, Stratigraphy 159 p. of mid-Cretaceous Blackleaf and lower part of the Cobban, W.A., Erdmann, C.E., Lemke, R.W., and Frontier Formations in parts of Beaverhead and Maughan, E.K., 1959, Revision of Colorado Madison Counties, Montana: U.S. Geological Group on Sweetgrass arch, Montana: American Survey Bulletin 1773, 31 p. Association of Petroleum Geologists Bulletin, v. Garihan, J.M., Schmidt, C.J., Young, S.W., jmd 43, p. 2786-2796. Williams, M.A., 1983, Geology and recurrent ___1976, Type sections and stratigraphy of the movement history of the Bismark-Span;sh members of the Blackleaf and Marias River Peaks-Gardiner fault system, southwest Montana, Formations (Cretaceous) of the Sweetgrass arch, IQ Lowell, J.D., Rocky Mountain foreland barms Montana: U.S. Geological Survey Professional and uplifts: Rocky Mountain Association of Paper 974,66 p. Geologists, p. 295-314. Crabtree, D.R., 1988, Mid-Cretaceous ferns in situ Gealy, W.J., 1953, Geology of the Antone Peak from the Albino Member of the Mowry Shale, quadrangle, southwestern Montana: Cambridge, southwestern Montana: Palaeontographica, Mass., Harvard University Ph. D. dissertation, Abteilung B, v. 209, 27 p. 143 p. DeCelles, P.G., 1986, Sedimentation in a Hadley, J.B., 1960, Geology of the northern parr of tectonically partitioned, nonmarine foreland the Gravelly Range, Madison County, Montana, basin The Lower Cretaceous Kootenai in. Campau, D.E., and Anisgard, H.W., eds., Formation, southwestern Montana: Geological West Yellowstone-Earthquake area: Billings Society of America Bulletin, v. 97, p. 911-931. Geological Society llth Annual Field Dillon, E.L., 1949, Stratigraphy of an area near Conference Guidebook, p. 149-153. Lima, Beaverhead County, Montana: Urbana, ___1969a, Geologic map of the Cameron University of Illinois M.S. thesis, 103 p. quadrangle, Madison County, Montana: U.S. Dyman, T.S., 1985a, Preliminary chart showing Geological Survey Geologic Quadrangle Map stratigraphic correlation and lithofacies GQ-813, scale 1:62,500. description for the Lower Cretaceous Blackleaf __1969b, Geologic map of the Varney quadrangle, Formation and lower Upper Cretaceous Frontier Madison County, Montana: U.S. Geological Formation (lower part) in Beaverhead and Survey Geologic Quadrangle Map GQ-814, scale Madison Counties, Montana: U.S. Geological 1:62,500. Survey Open-File Report 85-729,9 p., 1 pi. __1980, Geology of the Varney and Came-on __1985b, Measured stratigraphic sections of quadrangles, Madison County, Montana: U.S. Lower Cretaceous Blackleaf Formation and lower Geological Survey Bulletin 1459,108 p. Upper Cretaceous Frontier Formation (lower Hall, W.B., 1961, Geology of part of the upoer part) in Beaverhead and Madison Counties, Gallatin Valley of southwestern Montana: Montana: U.S. Geological Survey Open-File Laramie, University of Wyoming Ph. D. Report 85-431,72 p. dissertation, 239 p. .1985c, Stratigraphic and petrologic analysis of Holm, M.R., James, W.C., and Suttner, LJ., 1977, the Lower Cretaceous Blackleaf Formation and Comparison of the Peterson and Drar«y the Upper Cretaceous Frontier Formation (Lower Limestones, Idaho and Wyoming, and the part), Beaverhead and Madison Counties, calcareous members of the Kootenai Formation, Montana: Pullman, Washington State western Montana, ia Heisey, E.L., and others, University Ph. D. dissertation, 230 p. eds., Rocky Mountain thrust belt, geology and Dyman, T.S., Materna, W.L., and Wilcox, L.A., resources: Wyoming Geological Association, 1985, Stratigraphic applications of the Geologic 29th Annual Field Conference Guidebook, p. Analysis System (GAS) [abs.]: American 259-270. Association of Petroleum Geologists Bulletin, v. Honkala, F.S., 1949, Geology of the CentenHal 69, p. 251. region, Beaverhead County, Montana: / nn Dyman, T.S., Niblack, Robert, and Platt, I.E., 1984, Arbor, University of Michigan Ph. D. Measured stratigraphic section of Lower dissertation, 145 p. Cretaceous Blackleaf Formation and lower Upper James, W.C., 1977, Origin of nonmarine-marine Cretaceous Frontier Formation (lower part) near transitional strata at the top of the Kootenai Lima, in southwest Montana: U.S. Geological Formation (Lower Cretaceous), south west ^ Survey Open-File Report 84-838,25 p.
10 Montana: Bloomington, University of Indiana County, Montana: U.S. Geological Survey Ph. D. dissertation, 281 p. Miscellaneous Field Studies Map MF-180^A, Karlstrom, R.N.V., 1948, Geology and ore deposits scale 1:50,000. of the Hecla mining district, Beaverhead County, Perry, WJ., Jr., 1986, Critical deep drillholes and Montana: Montana Bureau of Mines and indicated Paleozoic paleotectonic features nor*h of Geology Memoir 25, 87 p. the Snake River down warp in soutVrn Keenmon, K.A., 1950, The geology of the Blacktail- Beaverhead County, Montana, and adjacent k'^ho: Snowcrest region, Beaverhead County, Montana: U.S. Geological Survey Open-File Report 86- Ann Arbor, University of Michigan Ph. D. 413, 16 p. dissertation, 207 p. Perry, W.J., Jr., Wardlaw, B.R., Bostick, N.H., and Kehew, A.E., 1971, Environmental geology of part Maughan, E.K., 1983, Structure, burial his*Try, of the West Fork basin, Gallatin County, and petroleum potential of frontal thrust belt and Montana: Bozeman, Montana State University adjacent foreland, southwest Montana: American M.S. thesis. Association of Petroleum Geologists Bulletin, v. Kennedy, G.C., 1947, Preliminary report on the 67, p. 725-743. geology of a portion of the SE 1/4 Lyon Petroleum Information Corporation, 1984, Geologic quadrangle, Montana-Idaho: U.S. Geological Analysis System (GAS): Denver, Colo., Survey Open-File Report, 1 p., 1 pi., map scale Petroleum Information Corporation, Technical 1:21,000. Services Training Manual, 195 p. Klepper, M.R., 1950, A geologic reconnaissance of Ray, J.D., 1967, Structure and stratigraphy of the pans of Beaverhead and Madison Counties, Cinnamon Mountain area, Gallatin Cor^ty, Montana: U.S. Geological Survey Bulletin 969- Montana: Corvallis, Oregon State University C, p. 55-85. M.S. thesis, 148 p. Lauer, J.C., 1967, The stratigraphy and structure of Reeside, J.B., Jr., and Cobban, W.A., 1960, Sti-ties the Snowflake Ridge area, Gallatin County, of the Mo wry Shale (Cretaceous) and Montana: Corvallis, Oregon State University contemporary formations in the United Stater and M.S. thesis, 165 p. Canada: U.S. Geological Survey Professional Lowell, W.R., 1965, Geologic map of the Bannack- Paper 355,126 p. Grayling area, Beaverhead County, Montana: Richards, R.W., and Pardee, J.T., 1925, The Me'iose U.S. Geological Survey Miscellaneous Geologic phosphate field, Montana: U.S. Geological Investigations Map 1-433, scale 1:31,680. Survey Bulletin 780-A, 32 p. Mann, J.A., 1954, Geology of part of the Gravelly Roberts, A.E., 1965, Correlation of Cretaceous and Range, Montana: Yellowstone-Bighorn Research lower Tertiary rocks near Livingston, Montana, Association, Contribution 190,92 p. with those in other areas in Montana and __1960, Geology of part of the Gravelly Range Wyoming, in Geological Survey research, 1965: area, Montana, in Campau, D.E., and Anisgard, U.S. Geological Survey Professional Paper 525- H.W., eds., West Yellowstone-Earthquake area: B, p. 54-63. Billings Geological Society 11th Annual Field ___1972, Cretaceous and Early Tertiary Conference Guidebook, p. 114-127. depositional and tectonic history of the McBride, B.C., 1988, Geometry and kinematics of Livingston area, southwestern Montana: U.S. the central Snowcrest Range; a Rocky Mountain Geological Survey Professional Paper 52^-C, foreland uplift in southwestern Montana: 120 p. Kalamazoo, Western Michigan University M.S. Rose, R.R., 1967, Stratigraphy and structure of part thesis, 213 p. of the southern Madison Range, Madison and Myers, W.B., 1952, Geology and mineral deposits of Gallatin Counties, Montana: Corvallis, Omgon the northwest quarter of the Willis quadrangle and State University M.S. thesis, 172 p. adjacent Browns Lake area, Beaverhead County, Ruppel, E.T., OTCeill, J.M., and Lopez, D.A., 1983, Montana: U.S. Geological Survey Open-File Preliminary geologic map of the Dillon 1 x 2 Report 52-105,46 p. quadrangle, Montana: U.S. Geological Sunrey Peale, A.C., 1896, Description of the Three Forks Open-File Report 83-168, scale 1:250,000. sheet (Montana): U.S. Geological Survey Atlas, Ryder, R.T., 1968, The Beaverhead Formatio^-A Folio 24, 10 p. Late Cretaceous-Paleocene syntectonic deport in Pearson R.C., and Zen, E-An, 1985, Geologic map southwestern Montana and east-central Idaho: of the eastern Pioneer Mountains, Beaverhead
11 University Park, Pennsylvania State University Swanson, R.W., 1950, Geology of a part of the Ph. D. dissertation. 153 p. Virginia City and Eldridge quadrangles, Montana: Ryder, R.T., and Ames, H.T., 1970, Palynology and U.S. Geological Survey Open-File Report, 12 p. age of Beaverhead Formation and their Tysdal, R.G., in press, Geologic map of the Sphinx paleotectonic implications in Lima region, Mountain quadrangle and adjacent parts of the Montana-Idaho: American Association of Cameron and Hebgen Dam quadrangles, Petroleum Geologists Bulletin, v. 54, p. 1155- Montana: U.S. Geological Survey 1171. Miscellaneous Investigations Series Map 1-1815, Sadler, R.K., 1980, Structure and stratigraphy of the scale 1:62,500. Little Sheep Creek area, Beaverhead County, Tysdal R.G., Dyman, T.S., and Nichols, DJ., in Montana: Corvallis, Oregon State University press, Lower Cretaceous bentonitic strata in M.S. thesis, 289 p. southwestern Montana assigned to Va^tfin Scholten, Robert, Keenmon, K.S., and Kupsch, Member of Mowry Shale (east) and of BlacHeaf W.O., 1955, Geology of the Lima region, Formation (west): The Mountain Geologist, southwestern Montana and adjacent Idaho: Tysdal, R.G., and Simons, F.S., 1985, Geo'igic Geological Society of America Bulletin, v. 66, map of the Madison Roadless Area, Gallatm and p. 345-404. Madison Counties, Montana: U.S. Geological Schwartz, R.K., 1972, Stratigraphic and petrographic Survey Miscellaneous Field Studies Map MF- analysis of the Lower Cretaceous Blackleaf 1605-B, scale 1:96,000. Formation, southwestern Montana: Veatch, A.C., 1907, Geography and geology of a Bloomington, Indiana University Ph. D. portion of southwest Wyoming: U.S. dissertation, 268 p. Geological Survey Professional Paper 56,178 p. __1983, Broken Early Cretaceous foreland basin Vuke, S.M., 1982, Depositional environments cf the in S.W. Montana Sedimentation related to Cretaceous Thermopolis, Muddy and Mowry tectonism, ia Powers, R.B., ed., Geologic Formations, southern Madison and Ga^atin studies of the Cordilleran thrust belt: Denver, Ranges, Montana: Missoula, University of Colo., Rocky Mountain Association of Montana M.S. thesis, 141 p. Geologists, p. 159-183. __1984, Depositional environments of the Early Sheedlo, M.K., 1984, Structural geology of the Cretaceous western interior seaway in northern Snowcrest Range, Beaverhead and southwestern Montana and the northern U^ted Madison Counties, Montana: Kalamazoo, States, in Stott, D.F., and Glass, DJ., eds.. The Western Michigan University M.S. thesis, 132 Mesozoic of middle North America: Canadian P. Society of Petroleum Geologists Memoir 9, p. Skipp, Betty, Prostka, H.J., and Schleicher, D.L., 127-144. 1979, Preliminary geologic map of the Edie Walsh, T.H., 1971, Quaternary geology of the east Ranch quadrangle, Clark County, Idaho, and portion of West Fork basin, Gallatin County, Beaverhead County, Montana: U.S. Geological Montana: Bozeman, Montana State University Survey Open-File Report 79-845, scale M.S. thesis. 1:62,500. Wilson, M.D., 1970, Cretaceous stratigraphy e* the Sonderegger, J.L., Berg, R.B., and Mannick, M.L., southern Gallatin and Madison Ranges: 1982, Geologic map of the northern part of the Moscow, University of Idaho Ph. D. dissertation, Upper and Lower Red Rock Lake quadrangles, 86 p. Beaverhead and Madison Counties, Montana, la Witkind, IJ., 1969, Geology of the Tepee Creek Sonderegger, J.L., Schofield, J.D., Berg, R.B., quadrangle, Montana-Wyoming: U.S. and Mannick, M.L., 1982, The upper Centennial Geological Survey Professional Paper 609, 101 Valley, Beaverhead and Madison Counties, P- Montana: Montana Bureau of Mines and __1975, Geology of a strip along the Centennial Geology Memoir 50, 53 p. fault, southwestern Montana and adjacent I^aho: Suttner, L.J., Schwartz, R.K., and James, W.C., U.S. Geological Survey Miscellaneous 1981, Mesozoic to early Cenozoic foreland Investigations Series Map 1-890, scale 1:62 500. sedimentation in southwest Montana, ia Tucker, __1976, Geologic map of the southern part of the T.E., ed., Field conference and symposium Upper Red Rock Lake quadrangle, southwestern guidebook to southwest Montana: Montana Montana and adjacent Idaho: U.S. Geological Geological Society Guidebook, p. 93-103.
12 Survey Miscellaneous Investigations Series Map Geological Survey Miscellaneous Investigations 1-943, scale 1:62,500. Series Map 1-1216, scale 1:62,500. ___1982, Geologic map of the Centennial Zeigler, J.M., 1954, Geology of the Blacktail area, Mountains Wilderness Study Area and Beaverhead County, Montana: CambrMge, contiguous areas, Idaho and Montana: U.S. Mass., Harvard University Ph. D. dissertation, Geological Survey Miscellaneous Field Studies 147 p. Map MF-1342-A, scale 1:50,000. Zen, E-an, 1988, Bedrock geology of the Vipond Park Witkind, IJ., and Prostka, H.J., 1980, Geologic map 15-minute, Stine Mountain 7 1/2-minute, and of the southern part of the Lower Red Rock Lake Maurice Mountain 7 1/2-minute quadrangles, quadrangle, Beaverhead and Madison Counties, Pioneer Mountains, Beaverhead County, Montana, and Clark County, Idaho: U.S. Montana: U.S. Geological Survey Bulletin 1625, 49 p.
114' 113' 112' 111'
BOZEMAN o LIVIN6STOJ' ^ i »^ O
_ t ^ Gallatin Greenhorn ^Madison \ Ran°e ' Range Ran9e '
10 20 30 MILES I i I i I) i i 0 10 20 30 40 "" ~ 44*
Figure 1.-Index map of southwestern Montana showing mountain ranges, locations of measured sections, and line (bold) marking geographic position of change in nomenclature of Lower Cretaceous rocks. Bold line is dotted where no Cretaceous rocks are preserved. Abbreviations for measured sections are as follows: AN, Antone Peak; O"!, Cow Camp; LM, Lincoln Mountain; LP, Lima Peaks; WS, Warm Springs Creek.
13 SOUTHWESTERN MONTANA NORTHWESTERN ASE (THIS REPORT) NORTHWESTERN MONTANA Western area Eastern area WYOMING
Cretaceous Cenomanian andTuronian Late Marias River Frontier Frontier Frontier Shale Formation Formation Formation (part) (part) (part) (part)
/^Bootlegger Upper a *"?. Member ""* i Vaughn >»c. 0)-« part * Mowry 1FormationBlackleafj Z (0 Vaughn FormationBlackleaf 0 JC Member Z CD Vaughrfx. "° Shale Member Member *^? EarlyCretaceous c T:r~~~T r ' ' I' _i ' ID Taft Hill Muddy Muddy 1-1 Member Sandstone Sandstone r-«J3 Flood < Member jolisShale Shale Thermopolis Flood iThermop- member Shale Member Sandstone ?- mi .fan ' i. _. i OM "i member Cloverly T o T r T--» >^-r^_^*. Aptianl Kootenai Kootenai Kootenai Formation Formation Formation Formation
Figure 2.~Correlation chart of Lower Cretaceous rocks in western Montana and northwestern Wyoming.
14 Table I.-Species list ofpalynomorphs identified (by DJ. Nichols) in collections from the measured sections presented here
[Sampled horizons are indicated by arrows at left margin of graphic sections. Species 1-10 are marine taxa; all others are nonmarine. Symbols are as follows: , present; , not present]
D65B6D Frontier Formation D6774 do. D6735 ... do.
D6777 Mowry Shale D6456A do . D64568 do. D6776 do. D6586C Vaughn Member D6586B do.
D6586A Kootenai Formation Table 1. Alphabetized list of species. Index number corresponds to row number in table 1
Number Species 28 Acanthotriletes sp. D 38 Aequitriradites spinulosus 11 Append!cisporites jansonii 23 Append!cisporites spp. 19 Araucariacites austral is 3 Baltisphaeridium? sp. 21 Cal1ialasporites sp. 29 Camarozonsporites insignis 4 Chichaouadinium vestiturn 12 Cicatricosisporites spp. 7 Cleistosphaeridium multispinosum 13 Concavissimisporites variverrucatus 30 Corollina sp. 31 Costatoper-f orospori tes -foveolatus 8 Cribroperidinium edwardsii 35 Cupul i-feroi daepol lent tes spp. 41 Cupul i-feroipol leni tes sp. 14 Cyathidites minor 24 Cycadopites sp. 9 Cyclonephelium sp. 32 Deltoidospora sp. 42 Densoisporites sp. 1 Dino-f lagel late cysts, unidentified 39 Echinatisporis varispinosus 22 Eucommiidites minor 34 Foraminisporis wonthaggiensis 36 Foveotriletes sp. 16 Gleicheniidites senonicus 17 Laevigatosporites sp. 25 Leptolepidites sp. 33 Lycopodiumsporites sp. 43 Microreticulatisporites sp. 5 Nyktericysta sp. 1O 01igosphaeridium pulcherrimum 2, 01 igosphaer idium sp. 4O Phyllociadidites inchoatus 15 Pityosporites sp. 44 Podocarpidites sp. 45 Pseusdoschizaea sp. 6 Pterospermella sp. 26 Retimonocolpites peroreticulatus 37 Rugubivesiculites sp. 18 Taxodiaceaepollenites hiatus 20 Tricolpites sp. 46 Triporoletes reticulatus 27 Vitreisporites pallidus 47 isoetalean microspores
16