marks a distinct horizon and may be traced Reinterpretation0ftype section 0f over an immense area in New Mexico." How- ever,Rankin (1944,p. 12, 19,20) was the first to formally name the unit and identified it JuanaLopez Member (often incorrectly) in a number of measured sectionsin northern New Mexico and southern Colorado. Rankin (9a4, p. 12, 19, 20) ap- of MancosShale plied the name "Juana Lopez sandstonemem- ber of the " to l0 ft (3 m) of very calcareoussandstone containing Prionocyclus byStephenC. Hook, Paleontologist, NewMexicoBureauof Minesand Mineral Resources, Socorro, NM, and WilliamA. Cobban, Paleontologist, U.S.Geological Survey, Denver, C0 wyomingensis near the top of the Carlile Shale. The type section for this new unit was given as sec.32, T. 15 N., R. 7 8., The Juana Lopez Member (Upper Creta- face (Dane, 1960;Molenaar,1973i Campbell, on the Mesita Juana Lopez Grant, six miles ceous)of the MancosShale (), 1979). Microfossil studiesby Lamb (1968) and northwestof Cerrillos, SantaFe County, New Carlile Shale(Denver and Raton Basins)or Thompson (1972), however, indicate that this Mexico" (Rankin, 1944,p. l9). BentonShale (North Park Basin)is one of the surface may be younger toward the northern Kauffman (in Dane and others, 1966, p. most distinctiveand laterallypersistent litho- edge of the San Juan Basin. Outcrop sections H6, H7, Hl3, H14) examinedthe type section stratigraphicunits in New Mexico,Colorado, we visited indicate that the top of the Juana of the Juana Lopez Member in 1963and con- Utah, and southwesternKansas. The member Lopez Member lies in a lower faunal zone cluded that l) the type section of the member containsan abundantlate (middle along the south side of the San Juan Basin wasactually in sec.33,T. 15N., R.7 E.;2) )invertebrate fauna whose ele- than it does along the east side. ln the the thicknessof the type sectionwas only 3 ft mentshave restrictedvertical ranges and are southernSan Juan Basin near Hosta Butte, 32 l0 inches. the remainder of Rankin's esti- widely distributed in time-equivalentrocks mi (52 km) east of Gallup, the top of the mated l0 ft being composed of baked shale of throughout the Western Interior of North Juana Lopez Member lies in the Prionocyclus Niobrara age; 3) the member at the type sec- America(Dane and others, 1966). macombi Zone. whereas on the east side near tion was composed predominantly of calcare- On the east side of the San Juan Basin. Cuba, the top lies two zones higher in the nite and limestone(hence, the term sandstone where Dane and others (1966)established a Pr ionocyc lus n ovi mexi canus Zone. was dropped from the member name); 4) the 107-ft-thick(32.6 m) well-exposedreference The distinctive lithologic and faunal nature member at the type section was abnormally section (fig. l), the Juana Lopez Member of the Juana Lopez was first noted by New- thin and containedan unusuallysmall percent- rangesin thicknessfrom 90 to 135ft (27.4to berry (1861)near Las Vegas,New Mexico. In age of shale compared with sectionsmore than 4l.l m). Here, and at other localities,the a later publication, Newberry (1876, p. 33) 100 ft (30 m) thick in the San Juan Basin; 5) memberconsists of thin bedsof rusty-brown- presented a detailed measured section of the member at the type section was succeeded weathering,highly fossiliferouscalcarenire in- Cretaceous rocks along the Canadian River disconformably by rocks equivalent to the terbeddedwith dark-graynoncalcareous clay south of Taylor Springs, New Mexico; it in- basal part of the ; and 6) shale. The calcarenitesoccur as both con- cluded the Juana Lopez as a distinct lithology the Juana Lopez at the type section was the tinuous bedsand discontinuouslenses, range characterized as ". . ferruginous, lami- lithologic and time equivalentof only the up- from a fractionof an inch to 2 ft (0.6m) thick, nated, sandy limestone . . [that is] a great per part of the member at the reference sec- are fine to coarsegrained, and are composed store-houseof fossils." Newberry (1876, p. tion. of bioclasticdebris. This debrisgenerally con- 107) also noted that "this ferruginous stratum In connectionwith work on the Juana Lo- sistsof the fragmentedprismatic layer of In- pez Member of the Carlile Shale in the Taylor oceramusshells. Fragmented remains of fish Springsarea of northeastNew Mexico, 109mi teeth,bones, and scalesare commonand led (175 km) northeastof the type section(Hook early workersto describethese beds as "fish- Rro and Cobban, 1980,fig. 6), we visited the type tooth conglomerates"or "fish- bone beds." -l section of the Juana Lopez. After remeasuring Gray septarianlimestone concretions are com- ..-/-\ the type section of the member in a 1965 rail- tLosl- mon in the lower and middle parts of the Alomos road cut of the Atchison, Topeka, and Santa member.Although shaleis the dominant li- saNraFE Fe Railway Company in NW%SE% sec. 33, thology, the hard, platy-weatheringcalcare- f s)o/ sANoovAt\o ; SonroFe T. l5 N., R. 7 E., we suggestmodification of nitesare more conspicuousin outcrop, often z oo,/ l.--.type all but the first of Kauffman's conclusions. littering the slopeswith debris,and generally d ;;xi section This paper presentsour measuredtype section stand in .O/ l; :ocerr,tlos topographicrelief above the softer +/ of the Juana Lopez Member (table l) and shales(Dane and others, 1966). ( t Mesrtode Jlono compares this newly rerheasuredsection with Lopez In the subsurfacethe calcarenitesproduce a _ _ l_ _ _ / | Gtonl | the reference section establishedby Dane and (resistive \ :8ER ALtL Lo ^ ,^ r^h, distinctive "kick" deflection) on NC|A\., | "--1,:____:- others (1966) on the east side of the San Juan (Lilly, \ electriclogs 1952,fig. 2; Bozanic,1955, tQt" to6" Basin. pls.l-3; Lamb,1968, fig. 5; Molenaar,1913, p. 94). The top of this resistivezone (referred FIGURE l-LocnrroNs oF rHE TypEAND REFERENcE Lithology and thickness to by oil-companygeologists sECTtoNSop tHE Junne Lopez MeN4genop rHr as Sanosteeor MnNcos Ssele, Snrrl Fe eNo SnNoovnLCoun. A 1965 railroad cut of the Atchison, SanasteeMember of the )has rrEs, New Mexrco (modified from Dane and Topeka, and Santa Fe Railway Company ex- long beenconsidered a time-synchronoussur- others,1966, fig. l). poses not only the entire type section of the Juana Lopez Member of the Mancos Shale, but also severalhundred feet of Mancos Shale both above and below this member (fig. 2). Two points are readily apparent from a cur- sory examination of this cut. First, the ledge- forming calcarenites in the upper part of the member (fig. 3) are approximately l0 ft (3 m) thick and therefore closely match Rankin's Q9aa, p.20) original estimate.In fact, these upper beds are probably all Rankin intended to include in his definition, although he shows the Juana Lopez to be 50 ft thick on his graphic section no. 6 (Rankin, 1944, fig. 5). Second, the basal calcarenites, although thin and rather inconspicuous on the south side of the cut (fig 2), are well exposed on the north side (fig. 4) and can be traced laterally (to the south) in outcrop. These basal calcarenites also carry the Lopha lugubris-Prionocyclus FIGURE 3-Clost-up vtEw oF Flc 2 sHowtNc upprR LEDGE-FoRMTNGCALCARENITE uNtr oF JueNe Loprz macombi fauna characteristic of the lower MrvsEn Upper contact of Juana Lopez Member shown as dashed line; 5-ft-long (l.5 m) Jacob's staff Juana Lopez in the San Juan Basin and are for scale. separatedfrom the upper, ledge-forming beds The Juana Lopez Member at its type section by approximately 90 ft (27 m) of shale. Hook can be subdivided into three informal units measured the Juana Lopez in this railroad cut similar in lithology and thickness to those at on July 16-18, 1979 (table l) and obtained a the reference section: a lower calcarenite unit ALSOIN THISISSUE: thickness of 106 ft (32.3 m). This measured with approximately l0 ft interbedded shales, ChinleFormation p.22 thickness is almost identical to that obtained (3 with scattered m) thick; a middle shale unit Proterozoictectonic setting p 27 by Dane and others (1966, p. HlO-Hl2) for lenses calcarenite that hosts septarian of Service/News p.30 the referencesection (fig. 5). The Juana Lopez limestone concretions, approximately 8l ft was measured at the type locality by the (24.7 m) thick; and an upper calcarenite unit Jacob's staff method (Kottlowski, 1965, p. with interbedded shales, approximately l5 ft COMINGSOON: 6l-75). The thickness obtained is thought to (4.5 m) thick. These same informal subdivi- . Red Rocktalc deposits be accurate to within l0 percent of true sions at the reference section are approxi- . Geologyand paleontology,Tortugas Mtn. thickness. Several factors other than those mately ll ft (3.3 m), 83 ft (25.3 m), and 12 ft . Kirtlandcrocodile listed by Kottlowski (1965, p. 122) may con- (3.7 m) thick (fie. 5). . Dakota-Mancos,Zuni Basin tribute some error. First, a reliable dip and The calcarenites are hard, brittle, thin- strike measurementcould be obtained only on bedded, platy-weathering rocks that range the uppermost calcarenites (fig. 3); this mea- from a fraction of an inch to 9 inches (0.2 m) surement was then used to measure the thick- thick. Bedding surfaces are generally irregular ness of the entire member. Second, several and highly burrowed and bioturbated. The minor faults with displacementsof lessthan 5 calcarenites are generally fine grained, with ft (1.5 m) cut the member; in unit 19 (table 1) most grains being bioclastic debris derived it was impossible to offset on a key bed to from Inoceramus and Lopha shells; com- New AAexfic@ avoid one of these faults. Third. at least two minuted fish remains are common. These cal- igneous dikes, which weather to small chips carenitesrange in color from medium to dark GEOLOGY and are covered by shale talus, cut unit 3l to brownish gray on fresh surface and weather . Scienceand Seruice (table l). from slightly darker gray to dark yellowish Volume 2, Number 2, MaY 198O

Acting Editor: JoanC Pendleton publishcd quarterly bY Ncw Mexico Bureau of Mines & Mineral Resources a division of New M€xico Institute ofMining & Technology BOARD OF REGENTS Ex Officio Bruce KinE, Governor of New Mexico Leonud De|-ayo, Srperintendent of Publ ic l6truclion Appointed William G Abbott, Srcty/Treas , 196l-1985, Hobbs Judy Floyd, Pres, 1917-1981,Las Cruces Owen Lopez, 191'7-1983, Sanla Fe Dave Rice. 19'12-1983. Corlsbad Steve Torres, 1961-1985, Socorto

New Mexico Institute of Mining & Technology Prcsident Kenneth w. Ford New M€xico Bureau of Mines & Mineral Resources Direclor...,,. FrankE.Kottlowski DepulyDiector... .Ceorges.Austin BureouEditoFGeologist....., .Robertw.Kelley Subsciptiorc: lssued quarterly, Febru{y, May, August, November; subscription price $3.00/yr. Editorial matter: Contributions of possible material for con- sideration in future issucs of NMG ue welcome Materials cannot be returned unless accompanied by return postage Addrss inquiries to the Editor, Nw Mexico Ceology, New Mexico Bureau of Mines & Mineral Resources, Socorro, NM 87801 FICURE 2-Rarlnono cur opArcsrsou. Toprxn. nNoSaNrn Fp Rerluv Coupnrv nr rvpEsEcrtoN oF Ciculalion: l,2N Plant rHt Juela LopEzMEvgEn oF rnp MlNcos SHer-E.View is southeasttoward south side of cut; upper Prirler.'University of New Mexico Printitrg andlower contacts of JuanaLopez Member shown as dashed lines.

May 1980 New Mexico Geology orange where iron content is higher. Most ranges and occurrencesof these speciescom- 90). The Mesita de Juana Lopez has simply have a petroliferous odor, especiallyin the up- pare very favorably with those in the reference beena placename since at least1746, but there per calcareniteunit. section (fig. 5). is no documentaryevidence concerning Juana Dark-gray fissile noncalcareous shale is the The fauna collected at the railroad cut in- Lopezor why the areabears her name(Myra dominant lithology at the type section. These dicates that the type section of the Juana Ellen Jenkins, oral communication, 1979). shalesare conspicuously darker than those of Lopez Member lies entirely within the upper The Mesitade JuanaLopez Grant wasgranted the overlying calcareous shale member of the Turonian (middle Cretaceous) zones of Prio- to Domingo Romero, Miguel Ortiz, and Mancos (fig. 3). Limestone concretions, com- nocyclus macombi, Prionocyclus wyomingen- Manuel Ortiz in January 1782(Pearce, 1965, mon throughout the shales, occur both as sis, and Prionocyclus novimexicanus. These p. 100). isolated bodies and in zones a few feet thick three prionocyclid species serve as name (fig. 6) and are usually septarian. Scattered bearers for the basal three faunal zones of the Conclusions thin lenses of more resistant calcarenite are upper Turonian in the Western Interior (Obra- l) The JuanaLopez Member of theMancos also common. Bentonite beds occur through- dovich and Cobban, 1975;Hook and Cobban, Shaleat its type sectionin a 1965railroad cut out the upper two informal divisions of the 1979; and,Cobban and Hook, 1979).The zone of the Atchison,Topeka, and SantaFe Rail- type section of the Juana Lopez and range of Prionocyclus macombi probably extends at wayCompany in theNW%SEVI sec. 33, T. l5 from a fraction of an inch to 6 inches thick least l0 ft (3 m) below the base of the Juana N., R. 7 E., SantaFe County,New Mexico is (0.15 m). The bentonites are white (fig. 6), Lopez into the underlying shale (USGS Meso- 106ft (32.3m) thick and composedprimarily weather dark yellowish orange, and are often zoic locafity D10810), and the zone of Priono- of dark-graynoncalcareous fissile shale with secondarily gypsiferous. The thickest ben- cyclus novimexicanus extends a few feet into interbeddedcalcarenite beds and lenses;the tonites occur in the upper part of the Juana the overlying shale (USGS Mesozoic locality thickestcalcarenites occur at the top of the Lopez, D10820; fig. 5; and Kauffman ln Dane and member; thin beds of laterally persistent The contact between the Juana Lopez others, 1966, p. Hl3, as Prionocyclus wyom- calcarenitemark the baseof the member.2) Member and the underlying shale member of ingensis elegans Haas). Thus, faunally, it is The memberis succeededconformably by cal- the Mancos is conformable at the type section; not possible to recognize an unconformity at careousshales of lateTuronian (middle Creta- Dane and others (1966, p. Hl0) established either the top or the base of the Juana Lopez ceous)age and conformablysucceeds noncal- that there was a lateral gradation between the Member at its type locality. careousshales of early late Turonian age. 3) basal Juana Lopez and the underlying shale in Descriptions and illustrations of Lopha The Juana Lopez is the lithologic and time the San Juan Basin. The upper contact of the Iugubris, Inoceramus dimidius, Prionocyclus equivalent of the entire member at the Juana Lopez at its type section is conformable macombi, Prionocyclus novimexicanus, and referencesection establishedby Dane and and gradational. Not only are the shales in- Scaphites whitfieldi can be found in Hook and others(1966) on the eastside of the SanJuan terbedded in the upper calcarenite unit cal- Cobban (1979, 1980).Illustrations of most of Basin. 4) The Juana Lopez Member lies en- careous(table I, units 43, 45,47,50), but also the fauna appear in Kauffman (1977). tirely within the late Turonian (middleCreta- the base of the overlying shale unit is silty, ceous) ammonite zones of Prionocyclus with the silt content decreasing upward. No macombi, Prionocyclus wyomingensis, and physical evidence of an unconformity was Historical note Prionocyc lus novi mexicanus. observed at either the lower or upper contacts Although the name Juana Lopez is geolog- In addition,it appearsthat Rankin's(1944) of the Juana Lopez at its type section. How- ically well known, little is known about the original definition of the Juana Lopez was ever, we have recorded an unconformity at the historical person. She was apparently Juana restrictedto the upper calcareniteunit (ap- baseof the Juana Lopez Member in the Taylor Lopez del Castillo (Myra Ellen Jenkins, oral proximately the upper 10 ft-3m-of the Springs area of northeast New Mexico (Hook communication, 1979), whose family is JuanaLopez Member as presentlyrecognized and Cobban, 1980,fig. 4). thought to have come from Bernalillo in 1706 and mapped). The expandedscope of the to help found Albuquerque (Pearce, 1965, p. Juana Lopez apparently originated with Fauna and age Fossils were collected throughout the Juana Lopez Member at the type section (fig. 5). With the exception of the Dl08l4 collection and one concretion from the Dl08l I level. all fossils shown on fig. 5 were collected in place from the railroad cut (fig. 2). Although all lithologies in the Juana Lopez are fossilif- erous, fossils are generally more abundant and better preservedin the calcarenites. The invertebrate fauna at the type section, like that at the reference section (fig. 5; Dane and others, 1966, p. H7-Hl0), is dominated by a few speciesof mollusks. The lower cal- carenite unit is dominated by the oysterLopha lugubris (Conrad), the bivalve Inoceramus dimidius White, and the ammonite. priono- cyclus macombi Meek; the middle shale by Lopha lugubrl's; and the upper calcarenite by the bivalves Inoceramus dimidius and L perplexus Whitfield, and the ammonites Sca- phites warrenl Meek and Hayden, S. whitfieldi Cobban, Prionocyclus wyomingensis Meek, and P. novimexicanus (Marcou). A concretion in unit l0 (Dl08l I level)also containeda new species of the ammonite Coilopoceras and a rare occurrence of the ammonite Hourcquia, FIGURE 4-Bnsnl cALCARENTTEuNrr oF JuaNa Lopez MeMaen ExposEDoN NoRTHsrDE oF RAILRoAD previously reported only from Madagascar, cur Contact of Juana Lopez Member with underlying lower shalemember of Mancos Shale shown as Japan, Russia, and possibly France. The dashedline; 5-ftJong (1.5 m) Jacob's staff for scale.

New Mexico Geology May 1980 Bozanic(1955) and was carriedto its logical kins,Chief, HistoricalServices Division, State TABLE l-Tvpp sEcrtoN oF ruB JunNe LopEz sectionsby Dane and RecordsCenter and Archives,and StateHis- MEunrn op tne Malcos Snale NW%SE% sec. conclusionin surface Mex- (1966). torian, SantaFe, New Mexico, for historical 33. T. 15 N., R. 7 8., Santa Fe County, New others railroad cut of Atchison, Topeka, At- informationon JuanaLopez. C. M. Molenaar ico, exposed in AcrNowr-socMENTS-We thank the Fe Railway Company. Measured by S. C' U.S. Geological and Santa chison,Topeka, and SantaFe RailwayCom- and E. R. Landis,both of the Hook on July 16-18, 1979, using a Jacob's staff, pany for permissionto measurethe type sec- Survey,Denver, Colorado, critically reviewed Abney hand level, and tape. Fossil collections made tion of the JuanaLopez and Myra Ellen Jen- thismanuscript. on June 28, 1979, by W. A. Cobban and S. C. Hook, and by Hook on July l6-18, 1979.

Thickness Unit Description ft in. NW -48 miles (77.2km)- SE Mancos Shale Upper shale member (Part): Referenceseclion Typesection r/. Top of measured section SEr/4sw sec l4,T lgN,R lw Nwr/4SE7osec33,T. 15N,R 7E 54 Bentonite, white

!I )J Shale, calcareous, olive-gray; !I !-I- .'...... _Dl0834 lnoceromus vallarsdorfensis weathersslightly lighter !I I e x u st dE !I /Dlo92o n occ I o mu 5 ta, P USGS Mesozoic locality D10834: -l ,/-P/ t o nocvc lu s nov i h€ x ic o nu t II Inoceramus waltersdorJensis Andert 52 Bentonite, white; weathers dark yellowish orange 51 Shale, olive-gray, calcareous, silty; silt content decreases uP- ward; weathersslightly lighter USGS Mesozoic locality D10820: I nocera m us perplexrs Whitfield Baculi tes y o k oya ma i Tokunaga

--,>\- -,4 and Shimizu

_v_ _\< Prionocyclus novimexicanus (Marcou) Total measured thickness, uqqer shale member l0 ---

colcoreous 3hole lowish orange; fine-grained, wavY bedded, in beds % to 2 inches L:J thick (1.3 to 5 cm); Petroliferous E -D44| r odor: hard resistant unit, basal 6 o Lucino sp @-

-044O9 Lqhd tugubris ..._(DlO8l4) and dark yellow- -o--u- Prionocyc lus mocombi light olive brown ish orange; fine-grained, in beds as much as 3 inches thick (3.7 cm); petroliferous odor; hard resistant unit; contains abundant frag- mented fossils USGS Mesozoiclocality Dl08l8:

OO I noceramus dimidlus White Prionocyclus sp. 46 Shale, dark-gray, calcareous 45 Calcarenite, olive-gray; weathers O-- o- light olive brown to dark yellow- O367t Lopho lugubrisl ish orange; fine-grained, thin- I noceramus d imidius , Prionoctclus mocombi bedded; petroliferous odor; hard, 9@e resistant unit; contains abundant fragmented Inoceramus shells and comminuted fish remains Inoceramus sp. Prionocyclus sp. Shale, dark-gray, calcareous, hard, platy-weathering

1J Calcarenite, olive-gray; weathers FICURE S-Ourcnop sEcrroNs or tHr JunNe Loprz Mrvspn AT rrs REFERENcEAND TypE sEcrtoNs light olive brown to dark yellow- sHowrNc occuRRENCESoF FossrLSReference section from Dane and others (1966, p. Hl0-H12) with ish orange; fine-grained, thin- faunal namesundated; upper member of Mancos Shalenot measuredor described. bedded. hard resistantunit

20 May 1980 New Mexico Geolog! USGS Mesozoic locality Dl08l7: base. and also several calcarenite weathers brownish gray; fine- Inoceramus dimidizs White lensesas much as I inch (2.5 cm) grained, in irregular thin bur- Scaphites warreni Meek and thick in middle of unit l0 0 rowed beds; hard resistantunit Hayden 28 Bentonite. white 0 lV2 USGS Mesozoic locality Dl08l2: Prionocyclus sp. 21 Shale, dark-gray, noncalcareous 8 0 Lopha lugubris (Conrad) 42 Shale, dark-gray calcareous,silty, 26 Bentonite, white 0 Y2 ll Shale, dark-gray, noncalcareous, hard, platy-weathering 25 Shale, dark-gray, noncalcareous; with scattered lensesof calcarenite 4l Bentonite; weathers dark calcarenite lens I ft (0.3 m) from l0 Calcarenite, light-brownish-gray; yellowish orange; gypsiferous top 0 weathers brownish gray; fine- 40 Calcarenite, olive-gray; weathers USGS Mesozoiclocality Dl08l5: grained, with minor interbedded to light olive brown to dark yel- Lopha lugubris (Conrad) noncalcareous shale, in irregular lowish orange; fine-grained, thin- Lq Bentonite, orange-weathering I beds as much as 2 inches (5 cm) bedded; petroliferous odor; hard 23 Shale, dark-gray, noncalcareous, thick; gray limestone concretions resistantunit with zone of poorly fossiliferous as much as l0 inches (25 cm) long USGS Mesozoic locality Dl08l6: concretionsas much as 2 ft (0.6 m) and 4 inches (10 cm) thick occa- I n oceramus dimidltts White ' long and 6 inches (15 cm) high de- sionally developed at top of unit; Scaphites sp. veloped at base, and scattered resistantunit Prionocyclus wyomingensis concretionsin upper half 36 USGS Mesozoic locality Dl08l l: Meek 22 Bentonite, orange-weathering 02 Lop ha lugubris (Conrad) 39 Shale, dark-gray, calcareous,silty 2l Shale, dark-gray, noncalcareous 20 Coilopoceras n. sp. 38 Calcarenite, olive-gray; weathers 20 Bentonite, orange-weathering 0l P r io noc y c lus mo c o m b i Meek to light olive brown and dark yel- l9 Shale, olive-black, noncalcareous, Hourcquia sp. lowish orange; fine-grained, wavy with minor thin calcarenitesin up- 9 Shale, dark-gray, noncalcareous l0 bedded,in beds% to 2 inches(1.3 per half; one limestone concretion 8 Calcarenite, medium-gray; cm to 5 cm) thick; petroliferous I ft (0.3 m) long, 2 inches (5 cm) weathers grayish red to dark yel- odor; hard resistant unit; only thick observed20 ft 6.1 m) above lowish brown; very fine grained, scraps of /noceramzs observed 0 6 base: crossed minor fault of un- burrowed, irregular top and bot- 37 Shale,dark-gray,noncalcareous 0 ll known displacement (probably tom: hard resistantunit. 36 Siltstone, olive-gray; weathers (1.5 (6.7 fess than 5 ft m\) at 22 ft Base of member dark yellowish brown; slightly cal- 1t m) Total thickness,Juana Lopez Mernber 106 % careous,micaceous, very thin bed- USGS Mesozoiclocality Dl08l4 ded, resistantunit 0 lv, (float): Lower shale member (part): 35 Shale, dark-gray, noncalcareous ll0 Prionocyclus macombi Meek 7 Shale, medium-dark-gray; 34 Bentonite. white 06 l8 Bentonite?, orange-weathering; weathers olive gray, noncalcar- JJ Shale, dark-gray, noncalcareous 26 gypsiferouszone '/4 eous, slightly silty; contains scat- 32 Calcarenite, olive-gray; weathers t7 Shale, olive-black, noncalcareous, tered septarian concretions slightly darker; fine-grained, bur- with zone of gray-weathering sep- throughout as much as I ft (0.3 m) rowed, in wavy, irregular beds as tarian limestone concretions as in diameter and zone of concre- much as I inch (2.5 cm) rhick; much as I ft (0.3 m) in diameter tions as much as lVz ft (46 cm) in hard, resistant unit; contains and 6 inches (15 cm) thick that lie diameter in basal 5 ft (1.5 m) 60 0 abundant fragmented 1xoce rd mus 2-3 ft (0.6- I m) above baseof unit l5 6 USGS Mesozoic localitv Dl08l0 3l Shale, dark-gray, noncalcareous; t6 Bentonite. white: weathers vivid l0 ft (3 m) below top: contains zone of flat limestone dark yellowish orange 0 1V, Prionocyclus sp. concretions I ft (0.3 m) in dia- 15 Shaledark-gray, noncalcareous 6 USGS Mesozoic locality D10809 meter and 2 inches (5 cm) thick, 14 Bentonite, white; weathers vivid 20 ft (6 m) below top: (Stanton)? that are I ft (0.3 m) above base; dark yellowish orange J Prionocy clus hydlti also has two basaltic dikes I ft l3 Shale, dark-gray, noncalcareous, l-6 Shale. with thin interbeds of thick 13 0 with minor calcarenite lenses as sandstone(not described) 70 2V, 30 Bentonite, white 0l much as 2 inches(5 cm) thick 8 Total measuredthickness, 29 Shale, dark-gray, noncalcareous; USGS Mesozoiclocality Dl08l3: lower shalemember 130 2V, contains a zone of gray septarian Lopha lugubris (Conrad) limestone concretions as much as Inoceramus dimidius White 3 ft (1 m) in diameter and I fr (0.3 Prionocyclus sp. References m) in thickness, 2 fr (0.6 m) above l2 Calcarenite, light-brownish-gray; Bozanic, Dan, 1955, A brief discussionon the sub- surface Cretaceous rocks of the San Juan Basin: Four Corners Geological Society, Guidebook lst field conference,p. 89-107, I fig., 4 pls., 2 charts, 4 maps Campbell,C.V., 1979,Model for beachshoreline in Callup Sandstone (Upper Cretaceous) of north- western New Mexico: New Mexico Bureau of Mines and Mineral Resources,Circ. 164,32 p.,32 figs., I table Cobban, W. A., and Hook, S. C., 1979, Collig- non iceras wool lgori wo o I Igori (Mantell) ammonite fauna from Upper Cretaceous of Western In- terior, United States: New Mexico Bureau of Mines and Mineral Resources;Mem. 37, 52p.,l2 figs., l2 plates Dane, C. H., 1960, The boundary between rocks of Carlile and Niobrara age in San Juan Basin, New Mexico and Colorado: American Journal of Sci- ence(Bradley volume), v. 258-4, p. 46-56, 3 figs. Dane, C. H., Cobban, W. A., and Kauffman, E. C., 1966, Stratigraphy and regional relationships of a reference section for the Juana Lopez FIGURE 6-Mtoole sHALEuNIT on Junue Lopnz MBnasenoN sourH srDEoF RATLRoADcur showing in- Member, Mancos Shale, in the San Juan Basin, terbeddedlenses of calcarenite,zones of limestone concretions, and two prominent bentonite beds that New Mexico: U.S. Ceological Survey, Bull. (3 are approximately l0 ft m) apart. Note small fault offset of lower bentonite. 1224-H, 15p., 3 figs. rtF

New Mexico Ceolog! May 1980 2l Hook, S. C., and Cobban, W. A., 1979,Priono- teau, J. E. Fassett,ed.: Four CornersGeological fectssamples from the lowestunit, whereonly cyclusnovimexicanas (Marcou)-Common Upper Society,Mem., p. 85-110,l9 figs., I table fine-grained beds have a calcareouscement, Cretaceousguide fossil in New Mexico: New Mex- Newberry, J. S., lE6l, Geotogicalreport' in lves, and from the uppermostmernber, where sand- ico Bureauof Mines and Mineral Resources,An- J. C., Repon upon the Colorado River of the stone beds contain varying amounts of silt- p. west: 36th Congress,lst session,Senate Ex- nual Repon 1977-78, 3,f42, 5 figs. U.S. sizedmaterial. Interpretationsconcerning the 1980, Some guide fossils to the Upper ecutive Document and House Executive Docu- of the formation, however, and CretaceousJuana Lopez Member of the Mancos ment90,pt.3,154p. remainder and Carlile Shales, New Mexico: New Mexico 1876,Geological report, in Macomb' J. N.' thoseregarding overall textural trendsare not Bureauof Mines and Mineral Resources,Annual Reportof the exploringexpedition from SantaFe' significantlyaf fected. Report1978-79, p. 38-49,7 figs. New Mexico, to the junction of the Grand and Kauffman, E. c., 1977, Illustrated guide to bio- GreenRivers of the Great Coloradoof the West in stratigraphically important Cretaceous macro- 1859:U.S. Army EngineerDepartment, p. 9-l18, Unit descriPtlons fossils, Western Interior Basin, U.S.A.: The I I pls. Wood and Northrop (1946)correlated Tri- p. 32 w. A., lts, A Mountain Geologist,v. 3 and 4, 225-274' obradovich,J. D., and Cobban, assicstrata in the Nacimiento Mountains with for Late Cretaceousof the Western pls. time-scale the (Upper )in Ari- F. E., 1965, Measuring stratigraphic Interior of North America: Ceological Associa- the Kottlowski, (1917). sections: New York, Holt, Rinehart, and tion ofCanada,Spec. Paper 13, p. 3l-54, 3 figs. zona,named by Gregory The Chinleis Winston,253p. Pebrce,T. M., ed., 1965,New Mexicoplace names: the only representativeof the Triassic in Lamb, G. M., 1968,Stratigraphy of the lower Man- Albuquerque, University of New Mexico Press, nortl-central New Mexico. Vertebrate re- cos Shalein the San Juan Basin: GeologicalSo- 187p. mains (Reesideand others, 1957) and plant cietyof America,Bull., v. 79,p. 827-854,5 figs. Rankin, C. H., lg4/, Stratigraphyof the Colorado fossils (Daugherty, l94l) found in Chinle Lilly, O. J., 1952,The Doswelloil field, Rio Arriba Group, Upper Cretaceous,in northern New Mex- $trata of the Nacimiento Mountains provide County, New Mexico, rz GeologicalSymposium ico: New Mexico Bureau of Mines and Mineral paleontologicevidence for Upper Triassicage. p., of the Four Corners Region: Four CornersGeo- Resources,Bull. 20, 27 6 frgs. The Chinle Formation in the eastern San p. figs. Thompson, G. G., 1972, Palynologic correlation logicalSociety, 99-103,4 Basin has been divided into four litho- C. M., 1973,Sedimentary facies and cor- and environmental analysis within the marine Juan Molenaar, (Wood and Northrop, relation of the Gallup Sandstoneand associated MancosShale of southwesternColorado: Journal stratigraphic units formations, northwestern New Mexico, in of SedimentaryPetrology, v. 42,p.281-3N tr 1946),listed in ascendingorder: Agua Zarca Cretaceousrocks of the southern Colorado Pla- Sandstone Member, Salitral Shale Tongue, Poleo SandstoneLentil, and tlle upper shale member. In the presentstudy the Poleo Sand- stone Lentil is further divided into upper and lower portions. Depositionalenvironments and The Agua Zarca Sandstone Member, ftrst describedby Wood and Northrop (1946)' crops out in a northeast-southwest-trending paleocurrents0l Chinle Formation belt, thickest (approximately 30 m) near San Miguel Canyon(fi5,2, sectionl). Wherepre- sent,it is a prominentridge former. The Agua (Triassic),eastern San Juan Basin, Z,arcais thin or absent on the French Mesa- Archuleta arch and in the southeasternChama Basin(fig. 3, sections6, 7, 8). Erosionalrem- NewMexico nants of thick channels are present in the south-centralChama Basin. byDennis D. Kurtz and John B. Andorson, Departmsnt ot Geology, Rice Univorsity, Houston, TX The Salitrol Shole Tongue, also first describedby Wood and Northrop (1946),oc- Strata of the Chinle Formation (Upper Tri- depositionalenergy form the basis for a dis- assic)crop out in the Nacimiento Mountains cussionof the tectonicsignificance of the unit. of Rio Arriba and SandovalCounties on the easternside of the San Juan Basin. The strata Methods are exposed in the San Pedro-Nacimiento Paleocurrent measurements were taken uplift, on the French Mesa-Archuleta arch, from small fless than 4 cm), medium (4-15 and in the ChamaBasin (fig. l). As elsewhere cm), and large(more than 15 cm) crossbeds. in the Southwest,the Chinle in north-central Data weregrouped according to the sizeof the New Mexico was depositedunder terrestrial crossbeddingand were statistically analyzed conditionsconsisting of two cyclesof fluvial- using the von Misesdistribution (Till, 1974). to-marshlandor lacustrinesedimentation (Ste- Though relatively few measurementswere wart and others,1972). These cycles reflect the analyzed, each of these directions represents uplift and erosionof nearbyhighlands and can an average for a set of several tens of in- be usedto decipherthe effectsof theseuplifts dividual crossbeds.The mean vector direc- on sedimentation. tions are thus reasonableestimates of paleo- Although the Chinle Formation has been transport direction and paleoslope. voLcANtcs mapped and studied principally to locate and Sediment texture was analyzed by settling assesssedimentary copper deposits near its tube. Thirty rock sampleswere disaggregated UPLIFT base,relatively little work hasbeen done con- by dissolution of carbonatecement in hydro- cerning the details of its depositionalhistory. chloric acid or by pounding. This techniqueis Y#r In describing the lithostratigraphic sequence suitable only for an approximation of mean and the possibledepositional history of the grain size and particle-sizedistribution but is Chinle in north-central New Mexico, this adequate for examining general textural report analyzes changesin sediment paleo- trendswithin a given unit or grosschanges be- transport directionsbetween fluvial cyclesand tween units. A sampling bias is present FIGURE l-LocertoN oF EAsTERN Sen JunN pebble lithologies to document changes in becauseonly rocks with a calcareouscement Bnsln-Cgeva BastN, sgowttrlc MAJoR TEcroNIc sedimentsource areas and dispersalpatterns. wereanalyzed and becauseonly the sand-sized FEATURES,outcrops of Chinle Formation are These changesand concomitant changesin fraction (0.0d to 4.0d) was used.This bias af- delineated and stippled.

May 1980 NewMexico Geology