Triassicstratigraphy andchronology inNew Mexico bySpencer G. Lucas, Museum of NaturalHistorv and Science. 1801Mountain Road NW, Albuquerque, NewMexico 87104

Abstract focused on particular regions of the state formably on Middle (Guadalu- and thus did not produce a unified syn- pian) strata of the Artesia , Glorieta Tiiassic rocks in New Mexico are nonma- thesis of the and , and San Andres Formation. rine strata of Middle and Late Tiiassic age. chronology in New Mexico. During the They () strata belong to are disconformably overlain by the Anton Chico Member of the Moenfooi past 12 , I have studied the Triassic Upper Triassic Chinle Group strata or Formation, an -bounded tec- strata in New Mexico and their correla- younger rocks. Moenkopi strata are pre- tonosequence of fluvial as thick as tives throughout the western United sent at the base of the Triassic across most 41 m Moenkopi strata are present across States. This work, done in collaboration of north and south-central New Mexico most of north and central New Mexico, and with several workers, notably O. Ander- (Lucas and Hunt,1987,1989b; Lucas and in southeast New Mexico thev crop out in son, S. Hayden, A. Heckert, P. Huber, A. Hayden, 1989a,b,1991; Lucas et aL,1990), Lincoln County. Hunt, and K. Kietzke, has produced a and in southeast New Mexico they extend Upper Triassic (late -) stratigraphic and chronological frame- to Bull Gap south of Carcizozo in Lincokr strata in New Mexico belong to the Chinle work for the Triassic strata in New Mex- (Lucas, Croup, an unconformity-bounded tectono- County 7991c). ico, sequence of fluvial, lacustrine, and rare which is reviewed here. Moenkopi strata in New Mexico are eolian red beds as thick as 650 m Chinle readily diJferentiated from underlying strata crop out across north, central, and Moenkopi tectonosequence Permian red beds ( Artesia southeast New Mexico. , The oldest Triassic strata in New Mexico Group) with which they were long con- and biostratigraphy based primarily on belong to the and fused by lithologic characteristics of tex- , allow precise correla- are ture, mineralogy, bedform, and color as tion of Chinle of Middle Triassic (early Anisian) age. Group strata that comprise well as by content (Fig. 2): three depositional sequences separated by Recognition of the Moenkopi Formation 1. Texture-Artesia Group basinwide . These deoosi- in New Mexico was long hindered by tional sequences resulted from base-level McKee (1,954), who concluded that no are very fine to fine grained, relatively changes driven by eustasy. Moenkopi strata are present in the state, well sorted, and rounded. Most of the and by a variety of geologists who resistant Artesia Group beds are either included siltstonesor silty sandstones.In contrast, Introduction Moenkopi strata in the Permian "Betnal" (=Artesia) Formation (Lucas and Moenkopi sandstones are fine to coarse Triassic rocks in New Mexico (Fig. 1) are Hayden, 1991). Some previous workers grained, poorly to moderately sorted, and nonmarine strata of Middle and Late Tri- (e.g., Cooley, 1957; Stewart et al., 1972b), subangular to subrounded. Intraforma- assic age. They belong to two tectonose- however, did recognize "Moenkopi(?) For- tional conglomerates of mudstone and quences with bounding pebbles unconformities mation" strata along the south edge of the siltstone are common in the that correspond to significant tectonic Plateau and as far east as the Moenkopi but virtually absent in the Arte- reorganizations of the depositional sys- Sevilleta Grant in Socorro County. sra. tem. Since their first recognition by Mir- Moenkopi strata in New Mexico belong 2. Mineralogy-Artesia sandstones are cou (1858), Triassic strata in New Mexico to the Anton Chico Member of Lucas and quartzarenites or slightly micaceous have received extensive study by stratig- Hunt (1987). They are fluvial red beds as quartzarenites and are frequently gypsif- raphers, sedimentologists, paleontolo- thick as 41 m dominated by trough-cross- erous. Moenkopi sandstones are mica- gists, geological field mappers, and eco- bedded micaceous litharenites and lithic ceous litharenites and lithic graywackes nomic geologists. Most of these studies graywackes. These strata rest discon- devoid of gypsum. 3. Bedforms-Artesia Group sandstones typically are laminated, rippie laminated, or massive and form laterally persistent, v repetitive (cyclic) beds. Moenkopi sand- ,l stones are typically trough crossbedded and have lenticular beds. tr:3 4. Color-Artesia Group red beds are characteristically moderate reddish brown (I0 R 4/6), commonly called "brick red" or "orange red," with some grayish- Sreen/yellowish-gray reduction mottles or thin bands. Moenkopi strata, in con- ( trast, are characteristically grayish red (5 R 4/2 or I0 R 4/2). 5. Fossil content-Artesia Group strata Iack body , whereas Moenkopi strata (especially conglomerates) have bones and bone fragments, , ?OOKM charophytes, and tetrapod footprints. NEWMEXICO These Moenkopi fossils from New Mex- ico (Lucas and Morales, 1985; Kiet- ,$/ rnrnssrcRocKS 2ke,1.989a,b; Lucas and Hayden, 1989a; Hunt and Lucas, 1993c) indicate correla- tion of the Anton Chico Member with the FIGURE l-Outcrop distribution of Tiiassic strata in New Mexico (after Dane and Bachman, 1965) Holbrook Member of the Moenkopi For- and inset showing the two tectonosequences of riiassic strata present in the state. mation in north and assignment

February 1995 NewMexico Ceology of an early Anisian age to the Anton Chico rocks are mostly red beds of fluvial, lacus- formity above older rocks (Tr-3 unconfor- Member (Morales,1987). Magnetostratig- trine, and rare eolian origin deposited in a mity of Pipiringos and O'Sullivan, 1978), raphy supports this correlation (Steiner single vast basin that extended at least and the top of the Chinle Group also is an and Lucas, 1992;Steiner et aL.,1993). from Wyoming to and from east unconformity of basinwide scope (J-0 to west (Lrcas, 1993; unconformity of Pipiringos and O'Sulli- Chinle tectonosequence Lucas and Marzolf , 1993; Marzolf , 7993). van,1978). Lucas(1993) assigned all Upper Triassic All Upper Triassic strata in New Mexico nonmarine strata in the west-central belong to the Chinle Croup. The base of Chinle Group chronology United Statesto the Chinle Group. These the Chinle Group is everywhere an uncon- Chinle Group biostratigraphy and bio- chronology is based on palynomorphs, megafossil , ostracods, nonmarine molluscs (unionid bivalves and gas- SANTAROSA FORMATION tropods), , and tetra- TecolotitoMember pod vertebrates (Fig. 3). Articles in Lucas and Hunt (1989a) and Lucas and Morales unconformity (1993) present much of this biostratigra- phy and , and Lucas (1995) mottledstrata provides unconformity an extensive review Hunt and Lucas (1993a) summarized tetrapod bios- tratigraphy and biochronology of the Upper Triassic strata of New Mexico. No syndepositional radiometric ages are available for Chinle Group strata in the state, but magnetostratigraphy has been published for several New Mexico sections (reviewed by Molina-Garza et al., 7993). A few salient points are: MOENKOPI 1. The base of the Chinle Group is FORMATION everywhere of late Carnian (Tuvalian) age (Hunt and Lucas, 1991a). Chinle strata below the medial sandstone-conglomerate Anton Chico complex termed Sonsela, Poleo, or Trujillo Member are also of late Carnian age; the Carn- ian- boundary is approximated by the base of the medial sandstone-con- + '"t"r. glomerate complex. Strata of this complex | and the overlying mudrock-dominated units ( Member of Petrified Forest Formation and Rock Forma- tion and their correlatives) are of earlv- middle Norian age. The youngest Chinie Groun strata ( and correiatives) are here regarded as of Rhaetian age, though they could be rSrAssrc slightly older, of late Norian age. No unconformity Chinle Group strata are of age. PERMIAN ]urassic 2. Using the Harland et al. (1990) numerical timescale, the base of the Chinle Group is about 225 Ma, and the top is 208 c onglomerate Ma or slightly older (Fig.3). Chinle Group deposition thus took place during about ss - trough crossbedded 17 million years. 3. Tetrapod biochronology of the Chinle "BERNAL ss - planar crossbedded Group provides the most precise correla- tions because tetrapod fossils allow four ss - laminar intervals of time to be characterized bios- FORMATION' tratigraphically. Palynomorphs and ss - massive megafossil plants allow only three time intervals to be discriminated, whereas siltston€ other fossil groups allow recognition of only two intervals (Fig. 3). Nevertheless, limes t one/dolomite correlations based on different kinds of Chinle Group fossils are consistent with gypsum eacn otner (i19.rnl J,. 4. Correlation of the Chinle Group to the SCCS (standard global chronbstrati- graphic scale) for the (Carn- unconformity ian, Norian, and Rhaetian stages and their SAN ANDRESFORMATION subdivisions: Tozer, 1984, 1994; Visscher, 1992) is based on palynomorphs and FIGURE 2-Measured stratigraphic section at Bemal Butte (from Lucas and Hayden, 1991)to show contrast between "Bernal" (=Artesia) Formation and Moenkopi Formation rs-

New Mexico Ceology February 1995 . Palynomorphs allow cross-cor- relation to marine Alpine strata that con- tain ammonoids (Dunay and Fisher, 1979; Litwin et al., 1991). Tetrapods from most Chinle Group horizons can be correlated directly to the classic of the Ger- manic basin (Lucas and Hunt, 1993).

West-central New Mexico Lucas and Hayden (1989a), Lucas (1993), Anderson and Lucas (1993), and Lucas and Heckert (1994)provide the cur- rent basis for the stratigraphy and chronology of Chinle Group rocks in McKinley and Cibola Counties (Fig. a). This is the thickest Chinle Group section with a total of 650 m. The unit of the Chinle Group here is the Shinarump Formation and mottled strata with a maximu- thickness of 24 m, the thickest sections of mottled strata in New Mexico. Mottled strata are color-mot- tled, extensively bioturbated sandstone, siltstone, and conglomerate that represent a FIGURE (from in LVFS, land-vertebrate fau- weathering profile developed on pre- 3-Summary of Chinle Group chronology Lucas, press). nachrons; SGCS, standard g1oba1chronostratigraphic scale. Chinle (commonly Moenkopi) strata (Stew- art et al., 1972a).For mapping ptrrposes, the informal unit mottled strata is included in the Chinle Group. The Shinarump strata are mostly trough-crossbedded siliceous conglomerates and quartzose sandstones. The overlying Bluewater Creek Forma- tion is as thick as 60 m and is dominated by red-bed mudstones and ripple-lami- nated sandstones. A distinctive 6-12-m- thick rippleJaminated sandstone near the top of the formation is the McGaffey Member of Anderson and Lucas (1993). The Petrified Forest Formation overlies the Bluewater Creek Formation through- out west-central New Mexico and consists of three members (ascending order): Blue Mesa, Sonsela, and Painted Desert. The is mostly bluish and purple smectitic mudstones as thick as 46 m. The Sonsela Member disconformablv overlies the Blue Mesa Member, has a mai- imum thickness of 6L m, and is dominantly trough-crossbedded quartzose sandstones and conglomerates of extra- and intrafor- mational origin with numerous fossil logs. Overlying Painted Desert Member strata FIGURE 4-Correlation of the Chinle Group in New Mexico. BHF, Baldy Hill Formation; LEM, Los are mostly red-bed mudstones with a max- Esteros Member; TLM, Tres Lasunas Member. imum thickness of 335 m. The Formation overlies the paleoflora as well as some tetrapod and nomenclature that is used here. This Painted Desert Member in much of west- invertebrate fossils that establish its age nomenclature is used as far east as the central New Mexico (O'Sullivan, 1974; (Ash, 1978; Lucas and Hayden, 1,989a). Hagan Basin of Sandoval County and the Lucas and Hunt, 1990).It is as thick as 35 Correlation of other Chinle Grouo units in Placitas-Cedar Crest area of Bernalillo m and consists of pedogenically modified west-central New Mexico is 6ased on County (Lucas, 1991a). siltstones, sandstones, and carbonates. It is lithostratigraphic correlation to more fos- Above very limited outcrops of mottled disconformably overlain by the Rock siliferous sections in north Arizona (Lucas, strata developed in Lower Permian strata, Point Formation, as thick as 69 m of 19e3). the base of the Chinle Group is the Agua mostly reddish-brown sandstones and Zarca F ormation, mostly trough-crossbed- siltstones. In McKinley-Cibola Counties North-central New Mexico ded quartzose sandstone and silica-pebble from Thoreau to Mesa Gigante, the Owl Chinle Group stratigraphy in Rio Arriba conglomerate as thick as 61 m. Rock and Rock Point Formations are and Sandoval Counties ( Basin and The overlying Salitral Formation is absent, and the Middle Entrada flanks of the Nacimiento and Jemez dominated by purple smectitic mudstones Sandstone rests directlv on the Painted Mountains) follows Lucas and Hunt and has a maximum thickness of 102 m. Desert Member. (1992) and Hunt and Lucas (1993b). The Poleo Formation disconformably In west-central New Mexico, the Blue- Huene (1911) and Wood and Northrop overlies the Salitral and is grayish-yellow water Creek Formation has an extensive (1946) introduced most of the local trough-crossbedded litharenite and con-

February 1995 Neu MexicoCeology glomerate of both intra- and extraforma- thickness of 38.5 m. South of La Cueva blue smectitic mudstones; and Tres Lagu- tional (silica pebbles) origin as thick as 41 (Mora County), the three Santa Rosa For- nas, mostly trough-crossbedded quartz- m. Red-bed mudstones above the Poleo mation members present in east-central arenites as thick as 45 m. are as thick as 200 m and belong to the Pet- New Mexico (Tecolotito, Los Esteros, and The Garita Creek Formation overlies the by red-bed rified Forest Formation. Tres Lagunas) can be recognized, but to Santa Rosa and is dominated (San Rafael Croup) strata overlie the Petri- the north only the Tecolotito Member is mudstones; its maximum thickness is 152 fied Forest Formation throughout north- presenr. m. Overlying strata of the kujillo Forma- central New Mexico except in the Ghost A similar, north-south distinction can be tion are mostly trough-crossbedded mica- Ranch area of the Chama Basin where the made in immediately overlying Upper Tri- ceous litharenites and intraformational Rock Point Formation is present. Rock assic strata. At Ricardo Creek in Colfax conglomerates with thin interbeds of red- Point strata here are reddiih-brown and Countv. a 13-m-thick section of mottled bed mudstone. The Truiillo is as thick as 68 grayish-red siltstones and ripple-lami- siltstone belongs to the Baldy Hill Forma- m and is overlain by as much as 110 m of nated sandstones as thick as 70 m. tion, whereas to the south strata immedi- Bull Canyon Formation, a dominantly In north-central New Mexico, the Sali- ately above the Santa Rosa Formation are red-bed mudstone unit. The Chinle Group tral. Petrified Forest. and Rock Point For- as much as 26 m thick and are dominantly section in east-central New Mexico is mations produce age-diagnostic verte- red-bed mudstones assigned to the Garita capped by the (maxi- brate fossils. Palynomorphs place the Creek Formation. mum thickness of 140 m), cyclic beds of Carnian-Norian boundarv at about the The overlying is the reddish-brown siltstone and sandstone. base of the Poleo Formation (Litwir et al., most pervasive Chinle Group unit along Age control for the Chinle Group sec- 1991). The Rock Point Formation has the Sangre de Cristo . It is , tion in east-central New Mexico is based yielded all known fossils of the yellow, and gray trough-crossbedded and on tetrapods (Los Esteros, Garita Creek, Rioarribasaurus,formerly known as Coelo- laminated ouartzose sandstone with Trujillo, Bull Canyon, and Redonda) and physis (though the name change is still dis- interbeds of iimestone- and siltstone-peb- megafossil plants (Los Esteros, Bull puted), New Mexico's state fossil (Hunt ble conglomerate. From Naranjos (Mora Canyon, Redonda) (Lucas and Hunt, and Lucas, 1991b). County) south, red-bed mudstones of the 1989b). These fossils establish the Chinle Bull Canyon Formation overlie the Trujillo Grouo section in east-central New Mexico most biostratigraphically sig- South-central New Mexico and are as thick as 140 m. North of Naran- as one of the jos, the Redonda Formation (=Naranjos nificant sections of the Chinle Group. Lucas (1991c) and Lucas and Heckert Formation of Bachman, 1953; =Johnson (1994) reviewed Chinle Group stratigra- Gap Formation of Johnson andBaltz,1960) Northeast New Mexico phy in Valencia, Socorro, and Lincoln overlies the Tiujillo Formation. South of Lucas et al. 0987) reviewed Chinle Counties. Here, the basal Chinle is the Naranjos the Redonda overlies the Bull Group stratigraphy and chronology in the Shinarump Formation (Valencia-Socorro Canvon Formation. The Redonda is Dry Cimarron Valley of east Colfax and Counties) and Santa Rosa Formation (Lin- -osily reddish-brown laminated and rip- Union Counties. These strata extend into coln Countv) above a S-m-thick interval of olelaminated siltstones and sandstones northwest Oklahoma (Cimarron County) color-mottied siltstone, sandstone, and with a maximum thickness of 65 m. and southeast Colorado (Baca County) conglomerate referred to as the mottled No fossils are known from Chinle where an identical local stratigraphic strata. Maximum thickness of the Shi- Group strata along the Sangre de Cristo nomenclature introduced by Baldwin and narump-Santa Rosa is 26 m, and litho- front range. Therefore, correlation of these Muehlberger (1959) is applied (Lucas, logies are mostly trough-crossbedded sil- strata is based solely on lithology and 1993). ica-pebble conglomerate and micaceous stratigraphic position. The oldest Chinle Group strata that crop subarkosic sandstone. out in northeast New Mexico belong to the Overlying blue and purple mudstone- East-central New Mexico Baldv Hill Formation, color-mottled sand- dominated strata belong to the San Pedro and chronol- stone and siltstone at least 37 m thick. The Arrovo Formation, which is as thick as 55 Chinle Group stratigraphy Guadalupe, Torrance, base of the Baldy Hill Formation is not m. A distinctive in the San ogy in San Miguel, and Harding Counties was exposed, but subsurface data indicate it is Pedro , the Ojo Huelos DeBaca, Quay, by Lucas et al. (1985) and Lucas underlain by the Santa Rosa Formation Member, contains Adamanian vertebrates reviewed (1987, 1989b). The same strati- (Foster, 1957). The uppermost 3 m of the and late Carnian ostracods. The Petrified and Hunt nomenclature is used as far west Baldy Hill Formation, the Cobert Canyon Forest Formation overlies the San Pedro graphic Fe County (Lucas, Sandstone Member, disconformably over- Arroyo and consists of Sonsela (up to 10- as Lamy in Santa of the Triassic lies underlying strata and is lithic and m thickness of sandstone and intraforma- 1991a). Continuitv (osa area to Lamy dis- limestone-cobble conglomerate. The over- tional conglomerate) and Painted Desert from the Santa a Late Triassic Ped- lying Tiavesser Formation is as thick as (red-bed mudstones and sandstones up to Droves earlier ideas of New Mexico. 168 m and consists of reddish-brown lam- 58 m thick) members. The Lower-Upper ernal uplift in east-central (1994) recently suggested an inated and ripple-laminated quartzose Dakota Grouo overlies Chinle Lehman nomenclature that sandstone, siltstone, and rare lithic con- Croup strata in south-centralNew Mexico alternative stratigraphic units in their glomerate. It disconformably overlies the locallv where thin outliers of the brings the Texas Dockum "*."oi entirety into east-central New Mexico, but Baldy Hill Formation and is conformably Juraisic are present presented a detailed overlain by yellowish-green and greenish- (Hunt and Lrcas, 1987; Hayden et al., Lucas et al. Q99\ The Chinle gray siltstone, sandstone, and limestone of 1990; Lucas, 1997b). refutation of this proposal. Group section in east-central New Mexico the Sloan Canyon Formation (maximum is very thick (up to 593 m), and its paleon- thickness of 41 m). The youngest Chinle Sangre de Cristo front range tology has been intensively studied. Group strata here are the Sheep Pen Sand- Lucas et al. (1990) reviewed Chinle The Chinle Croun sectionin east-central stone, yellowish-orange laminated quart- Croup stratigraphy and correlation along New Mexico begins with the Santa Rosa zose sandstone as thick as 33 m. the front range of the Sangre de Cristo Formation, which consists of three mem- The Cobert Canyon Sandstone Member Mountains in San Miguel, Mora, and Col- bers (in ascending order): Tecolotito, as and Sloan Canyon Formation produce fax Counties. Here, the Chinle Group sec- thick as 34 m and mostly trough-crossbed- age-diagnostic tetrapod fossils (Lucas et tion begins with the Santa Rosa Forma- ded quartzarenites and extraformational a1.,1987). The Sloan Canyon and Sheep tion, mostly gray and yellow trough- conglomerate; Los Esteros, as thick as 44 Pen Formations have extensive tetrapod crosbedded litharenite with a maximum m and dominantly variegated green and

NezuMexico February 1995 ichnofaunas as well (e.g., Lockley and Hunt, 1993). These fossils establish the correlation of the Chinle Group in north- east New Mexico presentedhere (Fig. 4).

Southeast New Mexico Lucas and Anderson (1992, 1993a, b\ reviewed Chinle Group stratigraphy in Chaves, Eddy, and Lea Counties. Here, the base of the Chinle Group overlies middle Permian (Cuadalupian) Artesia Croup strataor Upper Permian ("Ochoan") strata of the . The basal unit of the Chinle Group is the Santa Rosa Formation (equivalent to the Tecolotito Member to the north), which is as thick as 25 m and consists of trough-crossbedded extraformational conglom6rate and sand- stone with rare beds of mudstone and silt- stone. Above the Santa Rosa Formation are smectitic mudstone and rare sand- stones and conglomerates assigned to the San Pedro Arroyo Formation. A lack of FIGURE S-Sequence stratigraphy of the Chinle Group and postulated base-level changes. age-diagnostic fossils requires that corre- lation of Chinle Group strata in southeast significant reorganization of the biota. Paleozoic , reflecting New Mexico be wholly dependent on primary Few genera of tetrapods Iithology and stratigraphic position. cross an uncon- source areas in low-grade-metamorphic- formity, so that many tetrapod taxa are and sedimentary-rock-clad uplifts outside unique to each of the three depositional of the Chinle depositional basin. In con- Chinle Group sequence stratigraphy sequences. This is also generally true of trast, basal conglomerates of the The stratigraphic correlation and bio- palynomorphs, megafossil plants, ostra- Back-Owl Rock sequence (Fig. 4, interval chronology of the Chinle Group advo, cods, and . A temporal hiatus associ- C') mostly contain intraformational clasts cated here (Fig. a) and elsewhere lLucas, ated with each unconformitv best explains of calcrete and siltstone that are rip-ups 1993) identify two intra-Chinle Group this oattern. from underlying Chinle floodplain unconformities and thus delineate three Base-level-driven sedimentation ex- deposits. depositional sequences (Fig. 5). I have plains well the unconformities associated The youngest Chinle sequence (Rock labelled these two unconformities Tr-4 with and the fluvial architecture of the Point sequence) has a different facies and Ti-5, following the scheme of Pipirin- Chinle Group (Fig. 5). Deposition of the architecture than the underlying se- gos and O'Sullivan (1978).The Chinle Chinle Group began during the late Carn- quences. No basal sandsheet/conglomer- Group sequences take their names from ian with the regional onset of rising base ate is present, and the entire sequence is included stratigraphic units of the Four Ievel. Between the early Anisian (age of dominated by cyclically bedded siltstones, Corners area (Fig. 5). Evidence for the the youngest sediments beneath the mudstones, and fine sandstones deposited widespread intra-Chinle Group unconfor- Chinle) and the late Carnian (about 15 Ma in lakes,by sheetfloods,or in smail dune mities is fourfolcl: on the Harland et a1.,1990 timescale), low fields. After a relatively minor base-level 1. Correlative rocks immediately above base level throughout what was to become fall that produced negtigible incision, a each unconformity overlie rocks of differ- the Chinle depositional basin produced an rapid rise to peak base level could have ent ages in different areas. This probably incised topography caused by differential produced this sequence (Fig. 5). reflects differential erosion associated erosion and sediment bypassing. Rising Lucas (1993), Lucas and Marzolf (1993), with each unconformity. base level that produced the Shi- and Marzolf (1993)advocated eustatic sea- 2. There is a major lithologic change narump-Blue Mesa sequence halted this level changes as the mechanism that drove associated with each unconformity. Rocks incision and bypassing so that coarse- Chinle Croup base-level changes. A of the upper part of the Shinarump-Blue grained basal Chinle sediments (Fig. a, wealth of paleocurrent data indicates that Mesa sequence are smectitic mudstones, stratigraphic interval A) filled in and the paleoslope of the Chinle basin was siltstones, and pedogenic silcretes/cal- buried the pre-Chinle topography. Contin- down to the northwest. Large, Missis- cretes overlain by sandstones and con- ued rise in base level produced aggrada- sippi-scale rivers that flowed across the glomerates at the base of the Moss tion of extensive floodplains around chan- Four Corners to the northwest captured Back-Owl Rock sequence. Smectitic mud, nel meanderbelts (Fig. 4, lower part of smaller Chinle rivers to the south and stones. and pisolitic calcretes of the upper interval B). This culminated in a stable southeast. These large rivers flowed to the part of the Moss Back-Owl Rock sequ-ence Iandscape of fine-grained floodplain Late Tiiassic Pangean shoreline that has are directly overlain by nonsmectitic silt- deposits undergoing extensive pedogene- been palinspastically restored to approxi- stones and mudstones and fine-grained, sis (Fig. 4, upper part of interval B) at peak mate the current Nevada- border laterally persistentsandstones of the Rock base level. (Marzolf, 1993). Marine shelfal Late Trias- Point sequence. Identical base-level changes produced sic strata deposited near this shoreline in 3. At the Tr-4 unconformity, channeling the overlying Moss Back-O*l Rock Nevada (upper Star Peak and Auld Lang into and reworking of underlying sedi, sequence (Fig. 5). The main difference S1'ne groups) have correlative sequence ment is evident in many areas. At the Tr-5 between the two sequences is the clast boundaries and similar sequence geome- unconformity there is evidence of exten- composition of their basal conglomerate try to the lower two Chinle Group sive subaerial weathering (pedogenesis) facies. Basal conglomerates of the Shi- sequences (shelfal marine correlatives of of sediments immediately benelth the narump-Blue Mesa sequence(Fig. 4, inter- the Rock Point sequence are not pre- unconformity val A) mostlv contain extraformational served) (Lucas and Huber, 1994). This 4. Each unconformity corresponds to a clasts of silica (quartzite, chert, jasper) and strongly supports eustasy as the mecha,

February 1995 New Mexico Geology nism that drove Chinle baselevel changes. and biochronology of New Mexico: Lucas, S. G., and Hayden, S. N., 1989a, Triasslc stratiS- raphv of west-central New Mexico; ln Anderson, O. Alternative mechanisms are changes in New Mexico Museum of Natural History and Sci- ence, Bulletin 2, pp.49-60. J., Lucas, S. G., Love, D. W., and Cather, S. M. (eds.), tectonism or climate. Tectonic control of Hunt, A. P., and Lucas, S. G., L993b, Stratigraphy and Southeastern : New Mexico Geo- Chinle base-level changes necessitates of the Chinle Group (Upper logical Society, Guidebook 40, pp. 191-211. uplifts rising and the basin subsiding syn- Triassic), Chama basin, north-central New Mexico: Lucas, S. G., and Hayden, S. N., 1989b, Middle Triassic Moenkopi Formation, Nacimiento Mountains, chronously over a large area (the Chinle New Mexico Museum of Natural History and Sci- ence, Bulletin 2, pp. 67-69 . north-central New Mexico; in Lorenz, i. C., and basin is at least 2.3 million km2 in extent), Hunt, A. P, and Lucas, S. C.,1993c, Tetrapod foot- Lucas, S. G. (eds.), Energy frontiers in the Rockies: an unlikely possibility. No known Late prints from the Middle Triassic Moenkopi Forma- Albuquerque Geological Society, pp. 1.6-77. Triassic climate cycles match Chinle depo- tion, west-central New Mexico: New Mexico Lucas, S. G., and Hayden, S. N., 1991, Type section of the Permian Bernal Formation and the Permian-Tri- sitional cycles, so climate change driving Museum of Natural History and Science, Bulletin 3, o. C20. assic boundary in north-central New Mexico: New the base-level changes also seems improb- Johnson, R. B., and Baltz,E. H., Jr.,1960,Probable Tri- Mexico Geology, v 13, pp. 9-15. able. Base-levelchange due to eustasy was assic rocks along eastern front of Sangre de Cristo Lucas, S. G., and Heckert, A. P., 1994, Tiiassic stratig- the most likely driving mechanism of Mountains, south-central Colorado: American Asso- raphy in the Lucero uplift, Cibola, Valencia and New Mexico; ln Chamberlin, R. Chinle Group sedimentation. ciation of Petroleum Geologists, Bulletin, v. 44, pp. Socorro Comties, 1.895-L902. M., Kues, B. S., Cather, S. M., Barker, J. M., and AcxNowt-EpcMENTS-O. Anderson, S. Kietzke, K. K., 1989a, Calcareous from the Mclntosh, W C. (eds.), Mogollon slope, west-central Hayden, A. Heckert, P. Huber, A. Hunt, Moenkopi Formation (Tiiassic, Scythian or Anisian) New Mexico and east-central Arizona: New Mexico and K. Kietzke collaborated on much of of central New Mexico; ln Anderson, O. J., Lucas, S. Geological Society, Cuidebook 45, pp. 241)54. Lucas, S. G., and Huber, P., L994, Sequence strati- the fieldwork and paleontology upon G., Love, D. W, and Cather, S. M. (eds.), Southeast- ern Colorado Plateau: New Mexico Ceological Soci- graphic correlation of Upper Triassic marine and which this article is based. The National ety, Guidebook 40, pp. 181-190. nonmarine strata, western United States and Geographic Society, New Mexico Museum Kietzke, K. K., 1989b, Calcareous microfossils from the Europe: Canadian Society of Petroleum Geologists, of Natural History and Science, and the Triassic of the southwestern United States; ln Lucas, Memoir 17, pp. 241-254. Lucas, S. G., and Hunt, A. P., 1.987 Stratigraphy of the New Mexico Bureau of Mines and Mineral S. G., and Hunt, A. P (eds.), Dawn of the age of , in the American Southwest: New Mexico Anton Chico and Santa Rosa Formations, Triassic of Resources supported this research. O. Museum of Natural History, Albuquerque, pP. east-central New Mexico: Journal of the Anderson, F. Kottlowski, and C. T. Smith 223)32. Arizona-Nevada Academy of Science, v. 22, pp. reviewed the manuscri.pt. Lehman, T. M., L994, The saga of the 2L-33. and the case of the Texas/New Mexico boundary Lucas, S. G., and Hunt, A. P, editors, 1989a, Dawn of fault: New Mexico Bureau of Mines and Mineral the age of dinosaurs in the American Southwest: References Resources, Bulletin 150, pp. 37-51. New Mexico Museum of Natural History, Albu- Anderson, O. J., and Lucas, S. G., 1993, McGaffey Litwin, R. J., Traverse, A., and Ash, S. R., 1991, Prelim- querque, 414 pp. Member of Upper Tr:iassic Bluewater Creek Forma- inary palynological zonation of the Chinle Forma- Lucas, S. G., and Hunt, A. P., 1989b, Revised Triassic tion, west-central New Mexico: New Mexico tion. southwestern U.S.A., and its correlation to the stratigraphy in the Tucumcari basin, east-central Museum of Natural History and Science, Bulletin 3, (eastern U.S.A.): Review of New Mexico; ln Lrcas, S. G., and Hunt, A. P (eds.), o. G30. Palaeobotany and Palynology, w 68, pp. 269-287. Dam of the ase of dinosaurs in the American Ash, S. R., editor, 1978, Geology, paleontology, and Lockley, M. G., and Hunt, A. P, 1993, A new Late Tri- Southwest: New Mexico Museum of Natural His- paleoecology of a Late Triassic lake, western New assic tracksite from the Sloan Canyon Formation, tory, Albuquerque, pp. 150-170. Mexico: Brigham Young University, Ceology Stud- type section, Cimarron Valley, New Mexico: New Lucas, S. G., and Hunt, A. P, 1990, Upper Triassic Owl ies, w 25, no. 2,95 pp. Mexico Museum of Natural History and Science, Rock and Rock Point Members, , Bachman, G. O., 1953, Geology of a part of northwest- Bulletin 3, pp. 279183. Petaca Pinta, Cibola County, New Mexico: New ern Mora County, New Mexico: U.S. Geological Sur- Lucas, S. G.,1991a, Correlation of Tiiassic strata of the Mexico Geology, v. L2, P.92. vey, Oil and Gas Investigations Map OM 132. Colorado Plateau and southern High Plains, New Lucas, S. G., and Hunt, A. P.,1992, Triassic stratigra- Baldwin, B., and Muehlberger, W. R., 1959, Geologic Mexico: New Mexico Bureau of Mines and Mineral phy and paleontology, Chama Basin and adjacent studies of Union County, New Mexico: New Mexico Resources, Bulletin 137, pp. 47-56. areas, north-central New Mexico; ln Lucas, S. G., Bureau of Mines and Mineral Resources, Bulletin 63, Lucas, S. G.,1.991b, Southeasternmost outcroPs of the Kues, B. S., Williamson, T. E., and Hunt, A. P (eds.), 777 op. Morrison Formation, Capitan, Lincoln County, New IV: New Mexico Geological Society, Cooley, tr,l. E., 1957, Geology of the Chinle Formation Mexico; ln Barker, J. M., Kues, B. S., Austin, C. S., Cuidebook +3, pp. l5l-172. in the upper Little Colorado River drainage area, and Lucas, S. G. (eds.), Geology of the Sierra Blanca, Lucas, S. G., and Hunt, A. P., 1.993, Tetrapod Arizona and New Mexico: Unpublished MS thesis, Sacramento and Capitan Ranges, New Mexico: New biochronology of the Chinle Croup (Upper Triassic), University of Arizona, Tucson, 317 pp. Mexico Geological Society, Guidebook 42, p. 41. western United States: New Mexico Museum of Dane, C. H., and Bachman, G. O., L965, Geologic map Lucas, S. G., 1991,c,Triassic stratigraphy, paleontology Natural History and Science, Bulletin 3, pp. 327-329. of New Mexico: U. S. Ceological Survey, scale and correlation, south-central New Mexico; ln Lucas, S. G., and Marzolf, J.E.,'1993, Stratigraphy and 1:500,000. Barker, I. M., Kues, B. S., Austin, G. S., and Lucas, S. sequence stratigraphic interpretation of Upper Tri- Dunay, R. E., and Fisher, M.1.,1979, Palynology of the G. (eds.), Geology of the Sierra Blanca, Sacramento assic strata in Nevada; ln Dunn, C., and McDougall, Upper Triassic Dockum Croup (Upper Triassic), and Capitan Ranges, New Mexico: New Mexico K. (eds.), paleogeography of the western Texas, U.S.A.: Review of Palaeobotany and Palynol- Geological Society, Cuidebook 47, pp. 243 259. United States-Il: Pacific Section SEPM, Book 71, ogy, v.78, pp. 61-92. Lucas, S. G.,1993, The Chinle Group: revised stratig- oo. 375-388. Foster, R. W., 7957, Subsurface shatigraphy o{ north- raphy and biochronology of Upper Triassic nonma- Lums, S. G., and Morales, M., 1985, Middle Triassic ern Union County: Oklahoma City Geological Soci- rine strata in the western United States: Museum of from the basal Santa Rosa Formation, ety,35th Guidebook, pp. 136-141. Northern Arizona, Bulletin 59, pp.27 50. east-centralNew Vexico; ln Lucas,S. C., and Zidek, Harland, W 8., Armstrong, R. L., Cox, A. V, Cra:ig, L. Lucas, S. C., in press, The Chinle Group, western J. (eds.), Santa Rosa-Tucumcari region: New Mexico E., Smith, A. C., and Smith, D. G., 1990, A geologic United States: a nonmarine standard for Late Trias- Geological Society, Cuidebook 36, pp. 56-58. time scale 1989: Cambridge University Press, Cam- sic time; ln Dickins, T. M., Yin, H., and Lucas, S. G. Lucas, S. G., and Morales, M., editors, 1993, The non- bridge,263 pp. (eds.), Permo Triassic of the Circum-Pacific: Cam- marine Triassic: New Mexico Museum of Natural Hayden, S. N., Lucas, S. G., Hunt, A. P, and Beck, W bridge University Press, Cambridge. History and Science, Bulletin 3, 517 pp. C., 1990, Triassic-Jurassic stratigraphy, Palo Duro Lucas, S. G., and Anderson,O.J.,L992,Tlassic stratig- Lucas, S. G., Anderson, O. J., and Hunt, A. P, 1994, Tri- Canyon, Sevilleta Crant, Socorro County, New Mex- raphy and correlation, west Texas and eastern New assic stratigraphy and correlations, southern High ico: New Mexico Geology, v.72,pp.65,75. Mexico; m Cromll'ell, D. W, Moussa, M. T., and Plains of New MexiceTexas: New Mexico Bureau Huene, F. von, 1911, Kurze Mltteilung iiber Perm, Trias Mazzullo, L. l. (eds.), Transactions Southwest Sec- of Mines and Mineral Resources, Bulletin 150, pp. und Jura in New Mexico: Neues Jahrbuch frir Geolo- tion AAPG, Midland, Texas, 1992: West Texas Geo- 105 126. gie, Paldontologie und Mineralogie, v. 32, pp. logical Society, Midland, pp. 201-207. Lucas, S. G., Hunt, A. P, and Hayden, S. N., 1987, The 730-739. Lucas, S. G., and Anderson, O. 1., 1993a, Stratigraphy Tiiassic in the Dry Cimarron Valley, New Hunt, A. P, and Lucas, S. G., 1987, Southernmost out- of the Permian-Triassic boundary in southeastern Mexico, Colorado and Oklahoma; ln Lucas, S. G., crops of the Morrison Formation in the Carthage New Mexico and west Texas; ln Love, D. W, Haw- and Hunt, A. P (eds.), Northeastern New Mexico: area, Socorro Countv New Mexico: New Mexico ley, J. W., Kues, B. S., Adams, J. W, Austin, G. S., and New Mexico Geological Society, Guidebook 38, pp. Geology, v. 9, pp. 58-62. Barker, J. M. (eds.), Carlsbad region, New Mexico 97-777. Hunt, A. P, and Lucas, S. C.,1,997a, The and west Texas: New Mexico Ceological Society, Lucas, S. G., Hunt, A. P, and Huber, P, 1990, Triassic biochron and the correlation of the nonmarine Guidebook 44, pp. 219-230. stratigraphy in the Sangre de Cristo Momtains, Upper Triassic of : Palaeontology, v 34, pp. Lucas, S. G., and Anderson, O. J., 1993b, Triassic New Mexico; ln Bauer, P W, Lucas, S. G., Mawer, C. 467-50't. stratigraphy in southeastern New Mexico and K., and Mclntosh, W. C. (eds.), Tectonic develop- Hmt, A. P, and Lucas, S. C., 1991b, Rioarribasnurus, a southwestern Texas; ln Love, D. W, Hawley, J. W, ment of the southern Sangre de Cristo Mountains, new name for a Late Tiiassic dinosaur from New Kues, B. S., Adams, J. W., Austin, C. S., and Barker, J. New Mexico: New Mexico Geological Society, Mexico: Paliiontologische Zeitschrift, v. 65, pp. M. (eds.), Carlsbad region, New Mexico and west Guidebook 41, pp. 305-316. 191 198. Texas: New Mexico Geological Society, Guidebook Hunt, A. P, and Lucas, S. C., 1993a, Triassic vertebrate 44,pp.231- 235. (Continuedon p. 17)

NewMexico Geology February 1995 13 biochronology thus indicates a short hiatus in Barroll and Reiter Lucas the U-Bar Formation at the Aotian- (Continued p. boundary. I his hiatus is equivllent to one (Continued trom p. 7) trom 13) ammonite zone, the earliest Albian Hypacantho- and potential: Transactions of the Geothermal Lucas, S. G., Hunt, A. P, and Morales, M., 1985, Strati- plites cragini zone. A marked lithologic change Resource Council, v 4, pp. 61-64. graphic nomenclature and correlation of Triassic New Mexlco: a preliminary from packstones of the uppermost oys- Keller, C. R., and Corde1l, L., 1.983, Bouguer gravity rocks of east-central anomaly map of New Mexico: New Mexico Energy report; in Lucas, S. G., and Zidek, (eds.), Santa ter-limestone member to calcareous and J. Institute. Las Cruces. Rosa-Tucumcari region: New Mexico Geological ledgy, nodular limestones of the overlying lirne- Reiter, M., Eggleston, R. E., Broadwell, B. R., and Society, Guidebook 36, pp. 171.-1.84. phvsical stone- member is evidence of the Minier, J., 1986, Estimates of terrestrial heat flow Marcou, J., 1858, Geology of , with two disconformitv eouivaleni to this hiatus. In from deep petroleum tests along the reports on the prairies of Arkansas and Texas, the southeastern Aiizona, the -Albian in central and southern New Mexico: Joumal of Rocky Mountains of New Mexico and the Sierra boundary is approximately at the lower Geophysical Research, v 891, pp. 6225-4245. Nevada of Califomia: Zwich,144 pp. Mural-upper Mural contact, and in central Weir, J. E., 1965. Geology and availability of ground Mar zolf , J. E., 1993, Palinspastic reconstruction of early the latitude Texas it is at the contact of the water in the northern part of the White Sands Mis- Mesozoic sedimentary basins near of sile Range and vicinity, New Mexico: U.S. Geologi- Las Vegas: implications for the early Mesozoic with the overlying Clen Rose Limestone, but at cal Survey, Water-supply Paper 1801, 78 pp. Cordilleran cratonal margin; in Dunn, G., and present. these sections earliest Albian strata are McDougall, K. (eds.), Mesozoic paleogeography of This suggeststhat tectonismlocaI to southwest- the westem United States-Il: Pacific Section SEPM, ern New Mexico affected marine deposition Appendix A Book 71, pp. 433462. during the Aptian-Albian transition. n Present status of "8" wells McKee, E. D., 1954, Stratigraphy and history of the Tiiassic age: in area Moenkopi Formation of Geological the study Society of America, Memoir 61, 133 pp. We attempted to locate the "B" series of Molina-Garza, R., Geissman, J. W, and Lucas, S. G., wells drilled on the Bosque 1993, Late Carnim-early Norian magnetostratigra- by the USGS phy from nonmarine strata, Chinle Group, New del and described by Cooper Mexico: Contributions to the Triassic masnetic (1968). It was found that none of these Dolaritv time scale and the correlation of nonmarine wells are accessible to a deoth sufficient to and mirine Triassic faunas: New Mexico Museum of allow temperature logging. (Subsurface Natural History and Science, Bulletin 3, pp.345-352. Morales, M., 7987, Terrestrial fauna and flora from the temperature data shallower than about 90 Triassic Moenkopi Formation of the southwestern ft isiikely to be influenced by temperature United States: Joumal of the Arizona-Nevada Acad- fluctuations at the surface, and so such emy of Science, v. 22, pp. 7-79. tiassic Chinle For- data is of little usefulness.) O'Sullivm, R. B.,1974,TheUpper mation in north-central New Mexico; ln Siemers, C. B1-Apparently converted into a wind- T., Woodward, L. A., and Callender, J. F. (eds.), mill well. named Armv well. We located ; New Mexico Geological Society, the well; it's an old bioken-down wind- Guidebook 25, pp. 1.77-1.74. R. B., 1978, Principal mill, no longer operational. Now open to Pipiringos, C. N., and O'Sullivan, unconformities in Triassic and Jurassic rocks, West- about 40 ft (12.2 m), it stil has the wind- 'sucker ern Interior United States-a preliminary survey: U. mill rods' in it, making access to S. Geological Survey, Professional Paper L035-4,29 the wellbore difficult. DD. B2-{ooper (1968) states this well was Steiner, tr,l. B., and Lucas, S. G., 1992, A Middle Triassic paleomagnetic pole for North America: Geological plugged and abandoned. Society of Amer:ica, Bulletin, w 104, pp. 993-998. NewMexico Museum ol B3-{ooper (1968) states this well was Steiner, M. B., Morales, M., and Shoemaker, E. M., plugged and abandoned. 1993, Magnetostratigraphic, biostratigraphic, and NaturalHistory and Science B4-Cooper (1968) states this well was litholoeic correlations in Tiiassic strata of the west- ern U.S.: SEPM, Special Publication 49, pp. L07-11.9. exhibit plugged and abandoned. Stewart, J. H., Poole, F. G., and Wilson, R. F.,7972a, B5-This well is described as being Stratigraphy and origin of the Chinle Formation and june On 3, 1995 the New Mexico drilled "on a topographical high in the old related Upper Triassic strata in the Colorado Plateau Museum of Natural History and Science channel of the Rio Grande". We located region: U. S. Geological Suruey, Professional Paper (Albuquerque) will open its new exhibit 690,336 pp. the well in 1990 in the present channel of H., Poole, F G., and Wilson, R. F., 1972b, featuring Early Permian footprints found Stewart, J. the Rio Grande, about 50 ft (15 m) from the Stratigraphy and origin of the Triassic Moenkopi in the Robledo Mountains near Las east shore in shallow water. There is a con- Formation and related strata in the Colorado "Ancient Plateau region: U. S. Geological Suruey, Professional Cruces. The exhibit, Evidence: crete platform, which presumably was Life Before the Dinosaurs," focuses on the Paper 691, 195 pp. installed at about land surface, now about Tozer, E. T., 1984, The Trias and its ammonoids: the phenomenal fossil record of invertebrate 3 ft (-1 m) above the surface of the water, evolution of a time scale: Geological Survey of preserved ind vertebrate tracks in Lower attached to the well casing. The casing had , Miscellaneous Report 35, 169 pp. Permian strata of the^Abo-Hueco transi- a cover with a rusted-out hinge. When we Tozer, E. T., 1994, Canadian Tiiassic ammonoid faunas: tional zone in Dofla Ana Countv. In ouan- Geological Survey of Canada, Bulletin 467,663 pp. opened the cover, the hinge broke. Inside Visscher, H., 1.992,The new STS nomenclature: tity, quality of preservation,and diversity the casing we found a 7" pipe that led to a Albertiana, no. 10, p. 1. of trackmakers, the Dofla Ana County serrated metal collar, below which the Wood, G. H., and Northrop, S. A., 1946, Geology of the tracks are the best record on , one pipe seemed to widen, but which is Nacimiento Mountains, San Pedro Mountain, and that provides a unique glimpse of terres- adjacent plateaus in parts of Sandoval and Rio blocked by a packer. Everything was Arriba counties, New Mexico: U.S. Geological Sur- trial life and locomotion some 280 million rusted and couldn't be budged. vey, Oil and Gas Investigatlons Map OM-57. n years ago. The exhibit, which occupies B6-Cooper (1968)reports this well was about 2,000 square feet, reconstructs the plugged and abandoned. environment in which the tracks were B7-We located this well iust west of the formed; Hueco Formation invertebrates road along a low-flow channel. The well and fossil driftwood are displaved with was blocked just below the water level (no numerous tracks.The visitor ii also taught more than 10 ft [3.05 m] deep). n how fossil tracks are studied and identi- fied. The New Mexico Museum of Natural History and Science is open 9am-Spm seven days a week; for more information, call (505)841-8837. I

New Meico Geology February 1995