Ramah Member of the Crevasse Canyon Formation--A New

RamahMember of theGrevasse GanyonFormation-a newstratigraphic unitin the Zuni Basin, west-central New Mexico

by Orin l. Anderson, New Mexico Bureau of Mines and Mineral Resources, Socorro, NM 87801; and Gary D. Stricker, U.S. Geological Survey, M5972,B,ox25046, DFC, Denver, CO 80225

Abstract important coal-bearing unit that crops out throughout the Zuni Basin (Fig. 1) and is Nonmarine deposition accompanying generally a slope-forming unit. and following a regression of the Cretaceous Changes and reassignments of strati- Interior Seaway during late Turonian time graphic nomenclature should in general left a sedimentary sequence consisting of be avoided exceot in those cases where the fluvial channel sandstones, thin overbank result is a more logical and meaningful sandstones, and paludal shales containing local suc- thin coal beds. This unit is herein designated subdivision of the sedimentary the Ramah Member of the Crevasse Canyon cession. Using this criterion we have pro- Formation. The Ramah Member is locally ceeded not only to recognize the coal- well exposed in the Zuni Basin of west-cen- bearing, upper part of the Gallup Sand- tral New Mexico where it rests on the stone with a formal name-the Ramah Gallup Sandstone (marine) and is overlain Member-but also to reassign it to the by the distinctive, feldspathic Torrivio essentially nonmarine Crevasse Canyon Member of the Crevasse Canyon Formation Formation. This change places a formation (formerly of the Callup Sandstone). Near contact at the top of the light-colored, cliff- Ramah, New Mexico the sequence overlies bedded, the F member of the Gallup but northward forming, persistent and evenly it overlies progressively younger members. fossiliferous sandstones of unequivocal These younger members are discrete sand- marine or marginal-marine origin. The stone units associated with minor oscilla- overlying rocks are mudstone dominated, tions of relative sea level during a major for the most part coal bearing, lacking in regional-scale regression. North and east of marine body fossils, with laterally discon- Puerco Gap, near Gallup, New Mexico, the tinuous sandstone beds of fluvial origin. Ramah Member thins appreciably, and Thus, Iithologies rather than genetic inter- where unmappable it may be included with pretations and subjective considerations the Torrivio Member. Southward from Gallup in the Zuni Basir; the Ramah locally constitute the primary basis for placement FIGURE 1-Index map of Zuni Basin showing approaches 150 ft in thickness and contains of the new Gallup-Crevasse Canyon for- major structurc, lype section of Ramah minable coal beds. The interval was orevi- mational contact, with the genetic contrast Member, and selected localities. ously referred io as the coal-bearing mem- being a secondary factor. The significance ber of the Gallup (Mapel and Yesberger, of this lithogenetic break is that it marks 1985) or the Ramah unit (Anderson and the cessation of marine deposition in the Mesaverde Formation; in ascending order Stricker, 1984). Zuni Basin. With this downward revision thev are the Gallup Sandstone, Dilco Coal In the northem part of the Zuni Basin a of the Crevasse Canyon Formation basal problem may exist locally in determining Member, Bartlett Barren Member, and contact, it is obvious that the Torrivio the top of the Ramah Member. This is due to Gibson Coal Member. Sears recognized Member, as well as the Ramah, become the presence of a fluvial sandstone with the Gallup as the only shore-marginal or part of the Crevasse Canyon Formation. coarse-grained facies that looks much the littoral sand in the entire sequence. No redefinition of the Torrivio per se is same as the Torrivio Member, but underlies However, the upper part of Sears' Gallup it. Two criteria may be to contained herein; it is merely the iubject of employed distin- Sandstone is unequivocally nonmarine, guish the lower sandstone from the Torrivio a passive reassignment, consistent with its coal bearing/ and is the subject of this and properly place it in the stratigraphic physical position-as much as 150 ft paPer. succession: (1) the lower sandstone is gener- stratigraphically above the Gallup Beaumont et al. (1956) elevated the ally not as feldspathic as the Torrivio nor do Sandstone. the coarse-grained facies contain pebble-size Gallun to formation rank and included it material; and (2) the lower sandstone is not as the basal unit of the newly defined Previous studies nearly as widespread as the overlying Mesaverde Group. They also recognized Torrivio, which has a blanket geometry. Most of the geological studies in the and adopted Allen and Balk's (1954) The type section of the Ramah Member is Zuni Basin have focused on the coal Crevasse Canyon Formation as the domi- in the SE% NW% NW% sec. 16 T10N R16W resources in the Upper Cretaceous rocks. nantly nonmarine unit overlying the approximateiy 4 mi southwest of the town Shaler (1907) reported on the coal Gallup Sandstone. The names Dilco, of Ramah. The principal coal lies near the top of the member and was mined during resources of this area following a recon- Bartlett Barren, and Gibson were then uti- the 1920s to supply coal for the Zuni Pueblo naissance survey of the Durango-Gallup lized as member names within the schools. coal field. He assigned all Cretaceous stra- Crevasse Canyon Formation (Fig. 2); this ta above the Mancos Shale to the terminology has been widely accepted Introduction Mesaverde Formation, extending that and is in general use. stratigraphic name southward from the Shomaker el al. (1971) reported in detail This paper describes the stratigraphy, type area near Cortez, Colorado. More on the strippable, low-sulfur coal resources depositional environments, and coal stratigraphic detail and discussion of of the San juan Basin and included a dis- resourcesof the nonmarine, late Turonian structural features was contained in a cussion of the coal resources and reserves (Upper Cretaceous)rocks formerly includ- report by Sears (1925), in a work titled of the Gallup-Zuni Basin. Of specific inter- ed with the Gallup Sandstone,herein reas- "Geology and coal resources of the Gal- est here is their discussion of the School signed to the CrevasseCanyon Formation. lup-Zuni Basin, New Mexico." Sears for- mine coal zone in the central part of the The Crevasse Canyon Formation is an malized the member names of the basin.

February 1996 NewMexico Geology M f i:;"XV 1'-F{lL. i: rjqAlA ?idt; .

FIGURE2-Photograph_of westward-dipping Gallup Sandstone, from Sears (1925) The uppermost sandstone bed of the Gallup was later designated the Torrivio Member by Molenaar (1973). Crevasse Canyon Formation overlies the Torrivio (Photograph by N H. Darton)

An excellent description of the sedimen- was appropriate. However, this inferred Ramah unit informally to refer to the coal- tary facies of the Gallup Sandstone and intertonguing of the Gallup with the bearing strata in the upper Gallup. The associated formations was provided by Crevasse Canyon Formation was not top of the Gallup in those areas was Molenaar (1,973). Molenaar also intro- based on a physical intertonguing of lit- defined as the top of the medium- to duced the name Torrivio Member for the toral sands with coastal plain deposits, but coarse-grained, slightly feldspathic, dis- uppermost/ coarse-grained unit of the rather on an arbitrary definition of the tinctive Torrivio Member, which is present Callup Sandstone. Gallup Sandstone that included a fluvial throughout the Zuni Basin. Hook et al. (1983) presented a redefini- sandstone (the Torrivio) as the uppermost In a review of the usage of the term tion of the Tres Hermanos Formation memoer. Gallup Sandstone, Kirk et aI. (1978, p. I) (middle to late Turonian) and established In a discussion of Cretaceous stratigra- noted that the present usage of Gallup it as being a regressive-transgressive phy and coal resourcesof the Zuni Bisin, Sandstone "results in unnatural and awk- wedge of shoreface- and coastal plain- Anderson and Stricker (1984) used the ward boundaries." They went on to state deposited rocks significantly older than informal term Ramah unit for the coal- that this usage "has forced earlier and cur- the Gallup Sandstone and separated from bearing upper part of the Gallup. This was rent workers alike to obscure and to mis- it by the Pescado Tongue of the Mancos consistent with Sears' stratigraphy of the represent what we think are significant Shale. Previous to this, the Ties Hermanos Gallup Sandstone, except that the Ramah geologic relationships." We concur with sequence had been included as the lower unit is considerably thicker than the Kirk's observations. part of the Gallup. The redefinition equivalent unit at Sears'hogback locality; Millgate (1991) mapped the interval restricted the Gallup Sandstone to late thus, Anderson and Stricker (1984) recog- above the marine Gallup Sandstone as the Turonian and younger rocks. nized the need for a separate stratigraphic Ramah unit but included it with the Molenaar (1983) designated a principal unit but left its nomenclature informal at "lower part" of the Torrivio. His lower reference section for the Gallun Sand- that time. Torrivio represents a locally significant stone, establishing it in the SE7+NE7+sec Following similar logic, Mapel and sandstone, medium to coarse grained, 13 T15N R18W 2 mi east of Gallup, New Yesberger (1985),in their detailed maps of which underlies the more widespread Mexico. (Sears(1925) had not speiified a the Ramah-Navajo Reservation, refrained upper Torrivio that features a blanket type section for his "Gallup member.") from using "Tongue of the Crevasse geometry. Molenaar also presented numerous cross Canyon Formation" for the upper, nonma- When Sears (1925) named the Gallup sections illustrating the stratigraphic rela- rine part of the Gallup and referred to it Sandstone Member of the Mesa Verde tionships of the Gallup to adjacent units. informally as the coal-bearing part of the Formation from exposures in the hogback These data have been widelv used bv sub- Gallup. Thus a proliferation of names was just east of Gallup, New Mexico (Fig. 1), sequent workers in the Zuni Basin and emerging, and no one seemed willing to he included three discrete sandstone units Gallup areas. A nonmarine, coal-bearing accept an intertonguing relationship (Fig. 2). The lower two, which tended to be unit in the upper part of the Gallup was between the Gallup and Crevasse Canyon "Iight gray" (although he noted that the recognized by Molenaar as being a tongue Formations in the Zuni Basin. basal one was locally "red to pink"), were of the Crevasse Canyon Formalion over- Anderson (1987, 1989, 1990), in detailed fine grained, evenly bedded, persistent lain by the Torrivio Member of the Gallup. maps of the Atarque Lake area, Jones units separated by a 30-50-ft-thick shale He advised mappers that usage of the Ranch School quadrangle, and Vander- unit. The uppermost sandstone was term Crevasse Canyon for that interval wagen quadrangle, respectively, used described as pink in most places with lens-

New Mexico Geology February 1996 es of "very coarse material," and "in many are relatively thin and probably in a ward direction. In these areas, the thinned places an arkose." He did not indicate a Iagoonal or bay-fill sequence, versus those Ramah equivalent may be (1) mapped as a thickness for the shale unit that separated of the upper shale which accumulated in a tongue of the Crevasse Canyon Formation the middle sandstonefrom the uppermost floodplain (paludal) environment. (Dilco Coal Member) as Zech (1989) and sandstone, but he did note that it was coal Most later workers accepted Sears others have done, or (2) included with the bearing. The coal was referred to as the (1925)definition of the Callup Sandstone, Torrivio Member of the Crevasse Canyon, Myers coal bed, which was produced and numerous maDS and coal resource especially appropriate where the member locally from the Richards and Myers work have been published using the orig- becomes difficult to map. A third alterna- mines as early as 1886. inal concept of the Gallup. These include tive would be to map it as the Ramah Although Sears (1925) stated that the Shomaker et aI. (7971), Molenaar (1973), ecuivalent in those areas considered to be Gallup Sandstone represented a littoral Hackman and Olson (1977), Molenaar trinsitional between the Zuni and San deposit formed as the Cretaceous sea (1983), Anderson (1987, 1.989, 1990). Juan Basins. As the cross section (Fig. 5) retreated eastward, he did not discuss However, following Molenaar's (1983) illustrates, the Ramah Member is correla- depositional environments in detail. suggestion that the coal-bearing shale unit tive with the lower part of the Dilco Coal Curiously, he did not differentiate the in the upper part of the Gallup (above the Member of Zech(1989), although the basal upper coal-bearing (and obviously non- Iittoral sands of Sears)could be mapped as Ramah, having a more landward (SW) marine) from the lower littoral and marine a tongue of the Crevasse Canyon distribution, is slightly older than the sandstones. Had he recognized that the Formation, Condon (1986), Kirk and Zech basal Dilco. top of the littoral sandstJne represented (1987a,b), and Zech (1989) mapped it as Age constraints on the Ramah consist of the final marine influence in the such in the extreme northern part of the faunal control on the underlying unit and Gallup-Zuni Basin and accordingly Zuni Basin and adjacent San Juan Basin. some lithologic correlation of the overly- placed the top of his "Gallup member" at That stratigraphy left the Torrivio Member ing Torrivio. In the under$ing Gallup that stratigraphic horizon, a much more isolated within the Crevasse Canyon Sandstone a ]uana Lopez-age (early-late natural subdivision of the local succession Formation with no genetic, lithologic, or Turonian) fauna has been found. would have resulted. He did recognize the physical ties to its parent unit-the Gallup Inoceramus dimidius was reported bv overlying Dilco coal member (and in turn, Sandstone-in the Zuni Basin, and point- Anderson (1989) in an upper sandstone of Bartlett and Gibson members) as being ed out the need for some stratigiaphic the Gallup, near Vanderwagen in the cen- "laid down on floodplains of great riverst simplification on behalf of the field geolo- tral part of the Zuni Basin. Molenaar and thus placed a member-rank contact at gist; hence our designation of the Ramah (1983) reported I. dimidius from the basal what he thought was the boundary Member. part of the Gallup in the Horsehead between a littoral sequence and alluvial- Canyon area farther to the south. The floodplain deposits. Hi merely placed this The Ramah Member Torrivio Member, which overlies the boundary too high in the section. Thus, of the Crevasse Canyon Formation Ramah at a scoured contact, is perhaps a the present effort to invoke a more useful "feeder system" for some of the younger, subdivision and lend more utilitv to the The Ramah Member of the Crevasse more seaward tongues of the Gallup, such formation concept cannot be critiiized for Canyon Formation consists of as much as as the C-tongue or member (Molenaar, placing too muih emphasis on lithogene- 150 ft of shale and mudstone, sandstone, personal communication). Nummedal et sis, because the original stratigraphic fine-grained sandstone and siltstone, car- al. (1995) have addressed the relationship nomenclature was based on genetic units; bonaceous shale, and minor coal. The of the Torrivio to the younger tongues of the original work simply had the impor- sequence overlies a marine to dominantly the Gallup, but the area of their discussion tant lithogenetic break placed incorrectly marine Gallup Sandstone and represents lies outside the scope of this paper. These with respect to contemporary views and deposition in paludal and fluvial environ- younger tongues of the Gallup are consid- interpretations. The present work uses ments. The member is named for the vil- ered latest Turonian in age, and thus the lithologies in conjunction with genetic lage of Ramah, New Mexico, an area Ramah Member is accordingly of late interpretations to develop a subdivision where it is well exposed and shows good Turonian age. It is important to note that that should be acceptable to the modern development. The type section is herein these relationships imply that the Torrivio field geologist. designated as being in the NETaNW1/+sec. Member was deoosited as active channel To Sears' credit, it must be noted that he 16 T10N R16W where the unit is 130 ft fill during the ?egressive phase shortly had seen coal not only in the upper shale thick (Fig. 3). A measured section at that after emergence of the coastal plain and unit (above the littoral sands), but also in a locality (Fig. a) illustrates the mudstone- not during a later (transgressive) cycle of lower shale unit separated by the littoral dominated aspect, with only one sand- backfilling the gently incised topography. sandstones. While the present authors stone bed thicker than 10 ft. Three coal Thickness measurements taken along a have not been able to find coal in this zones are present if the very thin one at northwest line more or less parallel to the lower shale at Sears' described locality, the base is included. The other two are depositional strike do not show any sys- elsewhere in the Gallup-Zuni Basin coal considerably thicker at 3.3 ft and 2.0 ft, tematic thinning of the Ramah Member. beds have been documented in a similar and lie 65 and 90 ft above the base, respec- Thicknesses at the southeast end of the shale unit medial to littoral/shoreface tively. basin vary from 100 to 130 ft, whereas in Gallup sandstones. Anderson (1990) Inasmuch as the Ramah Member is the north near Vanderwagen and reported a 3-ft-thick coal bed in a similar lithologically indistinguishable from the Manuelito thickness measurements are in stratigraphic position in the Vanderwagen Crevasse Canyon Formation, it is at most the 105- to 141-ft range. One measured arca 76 mi south of Gallun. Sears clearlv coextensive with the overlying Torrivio section on top of the Torrivio anticline saw the Gallup as a marine sandstoneunit Member. However, it is intended that the near the village of Manuelito revealed a interbedded with coal-bearing sequences usage of the term Ramah Member be thickness of only 95 fU however, the sec- right up through the coarse-grained sand- restricted to the Zuni Basin, even though tion thickens to the west over a very short stone at the top (later designated the as defined it does extend at greatly distance (5-6 mi) to more than 140 ft. A Torrivio Member by Molenaar, 1973) and reduced thickness north and east into the short distance (10 mi) in the other direc- did not recognize the top of the "littoral San Juan Basin. In the more northeast tion (seaward) from this locality, at the deposits" as being significant to local localities the member thins in part because hogback east of Gallup (Fig. 1) where stratigraphic interpretation. If there are of progressivedowncutting ai the base of Sears named the Gallup, the Ramah coal beds present in the lower shale, they the overlying Torrivio Member in a sea- Member has thinned to approximately 40

February 1996 NezuMexico Geology - - Kct Kc-r

FIGURE 3-Photographs of Ramah Member of Crevasse Canyon Formation in Zuni Basin. A, Type locality of Ramah Member at Mower Hill,4 mi southwest of Ramah, New Mexico; B, same area as in A, showing prominent medial sandstone in the Ramah Member; and C, carbonaceous shales of the upper of the Ramah Member overlain by thick-bedded sandstones of the Torrivio Member at ham- mer. Kg, Gallup Sandstone; Kcr, Ramah Member of Crevasse Canyon Formation; Kct, Torrivio Member of Crevasse Canyon Formation.

Scale (ft) Moderate reddish orange to moderate reddish brown, upper medium to lower coarse grained feldspathic sandstone; well developed cross bedding; thickness 1 5 ft

above here Very pale I ano sanoy cotors pinkish and lioht or Yellowsh gray, lower fine sandstone withdark gray carbonaceous clay zones l2 ft and23 ft abova z |itT iJffijt;fl "ale,

c. u- z sanosrone z ft. The rate of seaward thinning of the unit Light olive gray shale in the northern part of the Zuni Basin is zone; thus about 6.7 ft/mi. LlJ Three measured sections of the Ramah a L Very pale orange and yellowish orange, mottled, upper fine grained sandstone; Member were taken throughout the cen- becoming better sorted upward; non:calcareous cemenl (fluvial channel) tral portion of the Zuni Basin (Fig. 6) dur- LU joint e. ing a U.S. Geological Survey-New Light gray silty shale, siltstone, and lower very fine grained sandstone; mottled Mexico Bureau of Mines and Mineral zones with limonite staining; flaser bedding in lowei part suggests lagoonal and/or tidal flats origin for-part of this seqrience; upier partiostly piludal with Resources investigation of coal resources thrn overbank sandstones on the Zuni Reservation. These data show no systematic thinning with the exception that the northeast-thinning trend is appar- -125- ent from the thickness at upper Nutria and very pale orange-moftled, very fine grained sandstone; contains carbonaceous trash zones (splav sand in paralic s along the Nutria monocline; the mono- Gmyish to blackish red silty to sandy shale; fissile; O 5 ft coal bed at base represents cline is the same structure as the hogback beach to marsh or peat swamp transition east of Gallup 20 mi to the north (Fig. 1). Very pale omnge and light gray-mottled, lwer to upper fine grained sandstone; The base of the Ramah Member is gen- burrowed. including Oph iomorph a 3 -150- erally a sharp contact between upper E (base not exposed) o shoreface sandstones of the Galluo and paludal 'i the shale and carbonaceouimud- stones, with overbank deposits, of the Ramah Member. Locally, fine-grained lagoonal or restricted bay-fill sequences FIGURE 4-Measured section at type locality of Ramah Member of Crevasse Canvon Formation form the base, but these grade laterally

NewMexico Geolosu Februarv 1995 SW NE 12 34 E 6 Big Falls E% SW1/a SW% SW% Hunting Torrivio Hogback Big Rock Canyon Sec 34 Sec 9 Canyon Mesa SE1/r NE1/a Hill SW% SE% T14N R2OW T14N R2OW SW% SE% Sec 31 Sec 13 NW% NW% Sec 17 Sec 14 TI 5N R19W T15N R18W Sec 10 T13N R19W T14N R2OW &Sec 5 T16N R17W T14N R19W Dalton Ss Member

Area in whrch Torrivio may be missing; Dilco CrevasseCanyon becomes basal member Formation of Kcc in these areas

Sandstone ====---=-==- - - --

Gallup

EXPLANATION a Burrowed z ,'- Ql3yg6llg I Ophiomorpha burrows ---- Carbonaceous o Bioturbated Shale - @ Calcareousconcretions Siltyor sandyshale Root tubes ."'.'.".. Conglomerate FIGURE S-Regional stratigraphic cross section in northem part of Zuni Basin showing Ramah Member of Crevasse Canyon Formation, stratigraphically adjacent units, and lateral relationship to the lower part of the Dilco Coal Member.

over very short distances into paludal, here. Paleoflow directions in the overlying relate with the coal zone in the middle of coal-bearing sediments. The contrast in Torrivio member have been reported to be the member on the adjacent Manuelito weathering characteristics produces a dominantly east and northeast (Anderson, quadrangle. topographic break that is easy to trace; the 1989). Sears (1925) reported coal production Gallup is a cliff former, the Ramah is a recorded as early as 1886 from the strati- slope former. The top of the Ramah can Coal resources graphic interval now defined as the locally present a problem, however, such Ramah Member. Production was from two as on the TWin Buttes quadrangle where The Ramah Member is not a mator coal- beds, each of which was in the 2.5-3.0-ft Millgate (1991) mapped a lowei Torrivio bearing unit. The coal beds tend to be thin thickness range and occur near the middle with the Ramah Member and also at the and lenticular; however, there are locali- to upper part of the member. Sornetimes boundary between the Vanderwagen and ties where thickness and depth place the referred to as the Myers, or Richards, coal Jones Ranch School quadrangles near Big coals in the resource category, as defined beds from the Myers mine, production Falls Canyon (Fig. 1). At the latter locality by the U.S. Geological Survey (Wood et al., was from secs. 20 and 27 T15N R19W on the Ramah Member is uncharacteristically 1983). the Gallup West quadrangle. dominated by two stacked fluvial-channel In the northem part of the Zuni Basin in Farther south in the basin, Anderson svstems. each about 50 ft thick. A4-ft-thick the Manuelito quadrangle, Anderson (1990) noted coal at several stratigraphic sfialy interval at the top of the two sand- (1991)reported a coal bed as much as 3.5 ft levels in the Ramah Member on the stones is here taken as the top of the thick near the middle of the Ramah Mem- Vanderwagen quadrangle 12 mi south of Ramah Member. The Torrivio Member ber. Outcrop data demonstrate the bed is Gallup. The thickest coal beds are in the overlies with a scoured base of low relief highly lenticular and thins in all direc- upper part of the member near the center and is readily identified by the presence of tions. Proximate analysis indicate the coal of the quadrangle where one S.4-ft-thick very coarse grained facies (generally lack- is high ash. coal zone contains an aggregate of 4.3 ft of ing or very restricted in the lower sand- Immediately to the east on the Twin coal. In at least one locality it appears to stones) and its much greater lateral extent, Buttes quadrangle, Millgate (1991) report- have had very small production, perhaps giving it a blanket geometry. The Torrivio ed coal beds as much as 3.3 ft thick in the for local use in space heating. Several also has a somewhat more feldsoathic middle to upper part of the Ramah Mem- other localities have coal beds in excess of aspectthan the lower sands.Crossbed dip ber. Again lenticularity is suggested by the 3 ft thick at the same stratigraphic level. diiections in the channel systems of thL surrounding measurements, so coal re- Proximate analysis of these coals present- Ramah Member have not been studied in sources are minimal and subeconomic. ed by Anderson (1990) indicate nearly all sufficient detail to permit a discussion The coal zone, however, is thought to cor- the coal beds have high ash (7.0-19.0%)

E^h-,,--,,100A ^r."-ir--;.^a-^l^^, sandstone. Locally the Torrivio Member NWr/4SWr/4 swt/4 Explanation has cut down such that it rests on the coal sec.28 zone. TI 1NR,I 7W Ii:iIJ'Ti-l Crossbedded L'.:.:,r:'.li.':l sandstone Another locality that produced from the School mine coal zone is the Zuni mines lll:ffi Sandstone 7i.:.;;:ii:'; (abandoned) in Coal Mine Canyon near the northeast comer of the Horsehead :-a" i';:-'. Siltstone Canyon quadrangle just south of NM-53. Shale These mines, which produced from two relatively thin beds during 1928-1957, saw CoalBed total production of approximately 46,000 tons and became the most productive of Carbonaceous any coal mines in the Ramah Member. tl Coal-quality and resource data for the tl Tonstein Zuni mines area were presented by tl Shomaker etal. (1971). They reported that NWt/aSWt/+ BurnBreccia (16.4 sec.28 the coal was moderate to high ash to tl Tr 1NRl7W 18.6%) and low sulfur (<0.6%) with BTU zu\2,'' / ClayClasts values of 10,470 to 10,570. Resource esti- iiirili (r? i RootTubes mates at the Zuni mines and for the eastward-adjacent Pescado quadrangle indi- f*jffii ttA Burrowed cate that coal in excess of 7 million tons z :.';1 " :'.::.:;9. underlies the immediate 2 rrrlz area with o CoveredSection maximum overburden of 110 ft. Unfavor- F able stripping conditions exist, however, because much of the overburden thickness e. o is represented by the massive, well- LL indurated sandstones of the Torrivio Member. z o z Summary and conclusions O A more-natural and meaningful break

LU in the late Turonian rocks of the Zuni (t) v) Basin results when the top of the shoreface, lagoonal, and tidally influenced Gal- LU lup Sandstone is adopted as the upper c. contact of the unit and the base of the O Crevasse Canyon Formation. This stratigraphic break is also significant in that it marks the end of marine influence in the sedimentary sequence of the modern Zuni Basin. The overlying strata, formerly included in the Gallup, herein designated as the Ramah Member of the Crevasse Canyon Formation, represent lower coastal plain and fluvial deposition fol- LU lowing a retreat of the Western Interior nz =g Seaway during late-middle and late a6 Turonian time. Age constraints consist of a

Neta Mexico Geology Febrtary 1996 Although all are thin and discontinuous, Resources, Geologic Map 61, scale 1:50,000 New Mexico: U S Geological Survey, Geologic in several areas individual beds attain a Anderson, O L 1989, Geology and mineral resources Quadrangle Map GQ-7592, scale 1:24,000 of the Jones Ranch School quadrangle, McKinley Kirk, A R , md Zech, R S , 1987b, Geologic map of the thickness of 3.5 f! these areas are in the Courty, New Mexico: New Mexico Bureau of Mines Big Rock Hill quadrmgle, McKinley County, New northern part of the basin on the and Mineral Resouces, Geologic Map 65, scale Mexico: U.S Geological Survey, Geologic Vanderwagen and Manuelito quadran- l:24,000 Quadrangle Map GQ-1594, scale 1:24,000 gles. Production has been realized in at Anderson, O. | , 1990, Geology and coal resources of Mapel, W. J., md Yesberger, W L, 1985, Geologic map the Vanderwagen quadrangle, McKinley County, of the Red Lake Mission quadrangle, Cibola County, least three areas; the Myers or Richards New Mexico: New Mexico Bureau of Mines and New Medco: U S Geological Suruey, Miscellaneous mine in sec. 20 T15N R19W the School Mineral Resources, Geologic Map 64, scale 1:24,000. Geologic Investigations Map I-1758, scale 1:24,000 mine in sec. 6 Tl1N R17W, and the Zunr Anderson, O. 1.,7991, Geology and mineral resources Mi-llgate, M. L, 1991, Geologic map of the Twin Buttes mines in sec. 9 T10N R17W. of the Manuelito quadrangle, McKinley Courty, quadrangle, McKinley County, New Mexico: U S. New Mexico: New Mexico Bureau of Mines and Geological Suruey, Geologic Quadrangle Map GQ- AcrrvowrlpcMENrs-The Zuni Trlbal Mineral Resources, Geologic Map 55, scale 1:24,000. 1659. scale 1:24.000 Government extended permission during Arderson, O ]., md Stricker, 1984, Stratigraphy and Molenaar, C M, 1973, Sedimmtary facies and correla- 1983-46 for the purpose of geologic map- coal resources of the Ties Hermanos Formation and tion of the Gallup Sandstone and associated forma- ping and sample collection; for this I am Gallup Sandstone (Upper Cretaceous), Zmi Basin, tions, northwestem New Mexico; in Fassett, J. E. west-central New Mexico; ln Houghton, R L, and (ed.), Cretaceous and Tertiary rocks of the southem grateful. No attempt should be made to Clausen, E. M (eds.), Symposium on the geology of Colorado Plateau: Four Corners Geological Society, visit the sampling localities discussed in Rocky Mountain coal: North Dakota Geological Memoir, pp.85-110. the coal section of this report or to do any Society, Publication 84-1, pp 115-125. Molenaar, C M, 1983, Principal reference section md work on Zuni lands before contacting the Beaumont, E C., Dane, C. H, md Sears,I D , 1956, correlation of Gallup Sandstone, northwestem New Revised nomenclafure of Mesaverde Group in San Mexico: New Mexico Bureau of Mines and Mineral Tiibal Government offices in Zuni, New Juan Basin, New Mexico: American Association of Resources, Circular 1.85,pp 2940. Mexico. Petrolem Geologists, Bulletin, w 40, pp 21.49-2L62 Numedal, D., and Molenaar, C. M, 1995, Sequence The following people either contributed Condon, S M., 1986, Geologic map of the Hunters stratigraphy of ramp-setting, strmd plain succes- data or were helpful with the organization Point quadrangle, Apache County, Arizona, and sion; the Gallup Sandstone, New Mexico; lz Van McKinley Comty, New Mexico: U S Geoiogical Wagoner, j C, and Bertram, G T. (eds ), Sequence and content of this paper: C. M. Molenaar, Survey, Geologic Map GQ-1588, scale stratigraphy of forelmd basin deposits: American 'L:24,000. Quadrangle Marvin Millgate, Frank E. Kottlowski, Association of Petroleum Geologists, Memoir 54. James E. Fassett, and William A. Cobban. Hackmm, R J, and Olson, A B, 1977, Geology,struc- Sears, I D, 1925, Geology and coal resources of the Spencer Lucas and james E. Fassett ture, and uranium deposits of the Gallup 1' x 2" Gallup-Zmi Basin, New Mexico: U S Geological quadrangle, New Mexico and Arizona: U S Suruey, Bulletin 767, 53 pp reviewed an earlier version of this manu- Geological Survey, Miscellaneous Geological Shaler, M. K, 1907, A recomaissance suruey of the script. Llmne Hemenway and Terry Telles Investigations Map I-981, scale 1:125,000 western part of Durango-Gallup coal field of prepared the manuscript, and Rebecca Hook, C S, Molenaar, C M, and Cobbaru W. A, 1983, Colorado and New Mexico: U S Geological Suvey, Titus drafted the illustrations. We are Stratigraphy and revision of nomenclature of upper Bulletin 316,383 pp Cenomanian to Turonim (Upper Cretaceous) rocks Shomaker, W., Beaumont, E. C., and Kottlowski, F all individuals J. grateful to of these for their of west-central New Mexico; lz Hook, S. C. (compil- E , 1971,, Strippable low-sulfur coal resources of the contributions. er), Contributions to mid{retaceous paleontology San fuan Basin in New Mexico and Colorado: New and stratigraphy of New Mexico, part II: New Mexico Bureau of Mines and Mineral Resources, Mexico Bureau of Mines and Mineral Resources, Memoir 25, 189 pp References Circular 185, pp. 7-28 Wood, G H., Kehn, T M., Carter, M D, and Kirk, A R, Huffman, A C, Jr., Zech, R S, Robertson, Culbertson, W. C , 1983, Coal resource classification Allen, J E, and Balk, R, 1954, Mineral resources of J. F., and |ackson, T. J., 1978, Review of the history of system of the U.S Geological Survey: U S. Fort Defiance and Tohatchi quadrangles, Arizona usage of the Gallup Sandstone and related urits, Geological Suruey, Circular 891, 55 pp and New Mexico: New Mexico Bureau of Mines md southem and westem San Juan Basiry New Mexico: Zech, R S, 1989, Geologic map of the TWin Lakes Mineral Resources, Bulletin 36, 192 pp U S Geological Suruey, Open-file Report 78-1055,56 quadrangle, McKinley Comty, New Mexico: U.S. Anderson, O.J,L987, Geology md coal resources of pp Geological Suruey, Geologic Quadrmgle Map GQ- Atarque Lake 1:50,000 quadrangle, New Mexico: Kirk, A R., and Zech, R. S , 1987a, Geologic map of the 1,659,scale 1:24,000 tr New Mexico Bureau of Mines and Mineral Hard Gromd Flats quadrangle, McKinley County,

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