4 -. T e r t i a r y and Quaternary - .. Baca Formation , . The Datil Formation (Winchester, 1920), a name now abandoned (Elston, 1 9 7 6 , p. 1 3 4 ) , has been . s e p a r a t e d i n t o t h e Baca Formation,SpearsFormation, A-L .. . PeakTuffand Hells Mesa Tuff, . . La J a r a ' P e a k B a s a l t i c A n d e s i t e . k i l p o l t . , . . . .. . . . . . . . . m)-:of' -:. . .. and o t h e r s ( 1 9 4 6 ) . d e s i g n a t e d . t h e b a s a l '684 f t ( 2 0 8 . 5 . . ... . . . .. ..: Winchester's (1920)-measured s e c t i o n of t h e D a t i l F o r m a t i o n , . . . as '&e type sec%ion f o r . t h e Eaca Formation.This. . . ~~~ ~ 1 N. , R. -. .measured section bf'the 4 I?. , and sec.tion . . i , . EacaFormation exposed". Palae'osyops,, a smaLl rhinocekas-type . . , .. . . anima1'of.Bridger' . . from t h e Baca Formati'on. .. North of . . . D a t i l , t e e t h and borie fragments of Protoreodon bjumilus~a.. . . . l a t e Eocene x e l a t i v e of t h e modern-day sheep, were 'found i n , . I Baca s t r a t a (Snyder, '1970). Fossil wood from t h e Baca has b e e n ' i d e n t i f i e d as' Palmoxyl'on sp.. - and Leguminoxylon sp. which supports t h e Eocene ageassignment(Snyder,, .. . . , .. . and o t h e r s ais0 i n d i c a t e t h e Baca t o be a t l e a s t a s young a s Eocene (Chaiffetz , i n p r e p a r a t i o n ) . 1971) .. I .. . . '.I " .%. . . . . . . Tilia-type pollen, Jugladaceous forms, , . . . . . . a t t h e type .locality. .. At.Carthage , Gardner (1910) recovered a t o o t h of . . ! . .. (Middle Eocene)age ' i s t h e only published ~ . . .. . . _.r. 365 f t (111.3 m) was "covered" or "not . .. O f t h a ts e c t i o n , ' Baca Canyon, secs. 4 , was measured in t h e upper portion of 5,. 8 , and 9 , T. ... . . . . . .. . , 9 89 . . Potter (19701, in an unpublished thesis, reported, making several partial measurements which he.compiled, in . . words, by "somewhai questionable correlations" into his o& a complete section. Potter (1970) found the Baca to be 697 ft (212.5 m) thick at Baca' Canyon, secs. 4,. 5 and 8, , R. T. 1 nf., 4 W.. The thickness of the'Baca . '(762.0 .. . m) as not exceed indicatedby driliing, .. . but 1150ft (350.5 m) .. ;' in .. , is2500, ft . typical'iy.' . outcrop . . . .. .. . the . it . Carihage and Joyita: 0ther.formations to time I . . Hills'areas . that . equivalent , . are . to . . of . ', . similar . .. . those in' Baca lithologies and . , include the Eagar, . Canyon. close . . - Baca . .is.' . . the . . with ,.. 'th%ckness about 6 0 0 ft.'(182.9 rn) ' (Snyder,. 1971). . . . . ... . Wilpolt and others( 1 9 4 6 ) correlated rocks' of the .. does .. McRae, , Cub Moun't;lin, ..and Galisteo. The age of the Eagar Formation, . . . . . a westward continuation 'the of Baca in Arizona (Snyder, .. 19711, and is' coal uncertain.. in Formation, the basal Elephant and is therefore but .it contains portion Butte dam . (Sirrine, area, . .a , . post-Laramide Galisteo age fauna .1956) The McRae ' contains Triceratops Cretaceous in part (Lee and Knowltori, 1917). The Cub Mountain'Formation,Capitan-Ruidosoarea, . . .I Cretaceous . .. is . . . , I.. topre-Oligocene in age .(Keiley, 197i).The Formation, withina range south' of Santa . . from Pe, Paleocene is to' of uncertain Eocene onbased limited plant remains (Lee and Knowlion, 1917)'. ' Sedimentation in the Sari Juan and Raton basins continued throughout the lqte Cretaceous and ea'rly !Pert$&, Fqunql . . . . . . . evidence . indicatesa Eocene age for the San Jose Formation (Lucas; 1977). Because early Tertiary rocks are similar lithologically, . separated geographically,, and differing ages, it is " . . . reasonable.. to conclude. that sedimentation . and western Arizona occurred in New Mexico . from the Cretaceous through . . the Eocene in isolated but somewhat geneticaily'. related .. .. ' . . , . . . . .. .. . . :. ,. . . .. . . . .basins,.,(Tonking,L1957)... . . . -.-.: . . .- . . . . . .. .. .. . . . . . . . . . *... ." - . " _ . T.he..times~.-and,.ratesi,of.~:.s,ubsldence .-. . . . . . . . . . ... . . . . . ... 1 .. I . and . ~ .- , . . . . " sediment .. accumulation .., . undoubtedly . . . . . to.basin. The stratigraphic . fluctuated . position and sediment of sparse record are basin duration of 'gaps . . .. in <he from , . difficult .to establish. because paieontological Contrbl. The .base of the Baca rests' ... . Mesaverde, a relationship ,. . that . unconformably on the . can be 'demonstrated . . difficult to ascertain at a single but' is ', . . location. The boundary 'between the formations changes regionally . . character' laterally . . In general, the occurrence . colored . lower of . . .. . . and shale red . o r . . . . . stones of the' and, this .. color sandstone that" .shales change is useful in contact of ,Formationsis marked .. lithologies . pink- sand- distinguishing hue . . the . . .. . . and Mesaverde t a k e on a greenish . formations. The contains .. . . uppermost . . bounhary'.is. at placed the f'irst the feldspar. . ,.Often potassium . . . places is difficult''to delineate. in Baca . the by Baca . and alternating overlying beds of Spears Baca and Spears andwas mapped at the lowest bed containing.,;. * 91 volcanic detritus. Beds of the Baca are arkosic and of the Spears, on rich in granitic rock fragments. Beds the other hand, contain abundant volcanic material.a At distance the Baca and Spears can generally be differentiated on the basis of color and weathering. The Baca strata'are various hues of red, generally forming low plains with ' isolated light-gray conglomerate or sandstone ledges, . . . . . . . . .. ... . . ,:th.e-Spears a.s. . . . . rounded, ... l;ight-p.u,~~~e,,.,...,.i . .. . ... . ... . :.. . . . . .. ouf: .. ... - crops . . , . . . .. . whereas . . . . . .. .. . . . . . . .. . . . . . . .. . . : . . . . . . . . I_ rough-textured sandstone hiils. . . . . . . . . . . Potter (1970) divided the Baca 'into three informal . . members. These'members are, in ascending order: a lower red mudstone-sandstone member, an arkosic sandstone member, . . .. and an upper red mudstone-sandstone member. In the study I aiea three . informal members. of the Baca are easily . distinguished. 'Potter'.& (1970) terminology of' these'.members'# . . .. . . . - however, lacks descriptive viability and therefore a .. . . . ' ' . . : slightly 'modified version of terminology is proposed;. The ... . . lower .red mudstone could more accurately be called .the . , conglomeratic .~ . memberas conglomerates in the restricted to . . . khis. out the Baca: be the A the rest more gray of portion; The arkosic .sandstone' . . member is 'misleadingas .arkosic . from are . . . largely would' Baca ' ' sandstones descriptive sandstone the Baca ncme for member' by its are found this as . through- subdivision this Dortion characteristic of Potter's color. The upper red,mudstone-sandstone member is sufficiently descriptive. Therefore] the terminology differs .gray-yelIow and quartzite fragments are Precambrian rocks. 'Rounded considered limestone' to be-derived fragments are from . . commonly fossiliferous, containing crinoid stems, brachiopods, bryzoans and other fossils of Mississippian to Permian age. .. Two types of fossilized wood,occur .unrounded and genetically related in to the the Baca; isone Baca, a and ... second type is darker in colo~,rounded, and presumed to; . . .. . . . . . Conglomeratic .. . . strata are . . . . . . . .. ... . . . .. . . . . .. . . . ............ -:... ..:~ . . ..: . ..:...... ~ fiave.been reworked-. from the.Triassic, :(Potter.,' 1970):z: . . . . . . . . . . . . . . X..' generally, a grayish type color . . . . .. . . in. contrast to 'the reddish hue of the mudstone. The sand. .. . . . . .. stones . . . and . .. . . . . . . conglomerates are mudstone and more . . . . . .. : . . . . . . 'stepped'ledges nature. and .I form .. . . ' than . . . _. . in thickness that 'vary . . . the I. , resistant to .erosion ~ ..... due to ' their lenticular Trough very-low-angle ... :. cross-stratification is common . . . . . thickest' sandstone.or in . the conglomerate The sandstones. ' unit measured, 27, unit .. is 35 ft (10.7 thick.' Siltstones and claystones are m) . burxowed in many places. The burrows are non-branching, . vertical and horizontal, about inch( 6 mm) in diameter, :' . . . . , ' . . , . . . 'and several inches long. . . :~ . The gray sandskone .. . member, . units . 29 through 3 2 , is . . . . composed almost entirely of interbedded, light-greenish. " , ,. . . . . . . gray (S GY 8/1) and . thin-bedded . yellowish-gray ( 5 Y 8/1) , clayey, sandstones and siltstones (fig.2 5 shales occur in this .. interval.. The & 26). gray No red sandstone '' member is 176'ft (53.6 m) thick, loosely consolidated, and forms . . slopes or level plains. The rock is composed predominately , : -700' . . -600' .. Figure 26. .. Upper'253 ft (77.3 m) of the Baca Formation e 0 of-silt-to coarse-sand-sized quartz and 97 gray-colored potassium feldspar. The grains are moderately sorted and - subrounded to subhedral. Yellow limonite halos commonly encircle organic debr.is and fossilized tree , trunks in this . member (fig. 27). Conglomeratic cross-bedded sand lenses, as well ,as limestone beds are present localiy,9 and secs 11, T. 1 N., . . ... .~ :. . . The . R. 4 W.. . .. r8d mudstone . . . . . .member, 'Tuniks'33:'through ... . .. . . . . .. . . . .-5X. .'i. s 244 . . ; '. . -. . , ft. (74.5 m) thick and composed mostly of grayish-red .. . . . '(10 R 4/2) to . . .. . reddish-brown' (1.0 R 4/4) silty mudstone. . . . . 3 inches (8 cm) thick, are interThin sandstones:, about . . . bedded in the lower portion of this segment. The sandstones .. . . are very light'gray '(N 8) .. rounded,' well sorted, very-fine-sand-to silt-tsized grains.In the . . .. . portion of the member pale-red (10 as25 Et (8..6 m) thick .. . . 6/2) sandstones . .asmuch . upper ' . . .. . . - , composed'of are . . .. . interbedded' with , mud- stones.. The sandstones consist of moderately sorted,' ! '' . . , . . . loosely consolidated coarse arkosic sand. Numerous veins . . . . . of satin spar gypsum and one thin vein of light blue Telestite. w a s observed . . . . . .. . the type locality. in the . 'upper of portion the' ' . , I ,. . . . 1 . Baca .at . . ' ~ . 'The sand-and silt-sized constituents of the Baca . are about30 percent quartz,20 percent percent quartzite,10 percent percent dividedamo:lg plagioclase, .. . ' . chert, microcline,20 . . and the potassium remaining 20 feldspar , . . carbonate, muscovite, and mudstone grains. The cement 'of . .. the sandstones is partly an early generation of silicia ' but is largely a later genGration carbonate. The grains are conkonly layerof hematite. coated abythin .:,. '. Fine-' . grained 'hematite "and carbonate occurs in shales'of Baca Formation. . ' . the' . The Baca accumulated in one of many basins produced by the Laramide orogeny. The .dimensions and shape &e of .. . . Baca basin belt. are the unknown .basin . ' but .judging from the . probably present oukcrop .. was elongate east. to west and . slightly sinuous between highland masses. Highlands . . . . . . bordering the basin during Baca depositon include: Zuni, . DefiJ.nce on the and Lucero east, . . 'uplifts on the . . Magdalena north, . Joyita Hills uplift . uplift to the south, and'Mogollon highlands to the southwest.' Undoubtedly, smaller, local .. . . . .. uplifts also influenced Baca ., sedimentation. .. . . Snyder (1971) interpreted the ciimate during Baca deposition to'be arid to semiarid, and g'ave the following .. as evidence: entrenched ij ., .. coarse-grained sediments in deeply channels;2).reddish . . . coloro f the finer grained . rocks; 3) lack of abundant organic trash (believed by Snyder . to be . dueto the.'paucityof vegetation); and 4) 'presence . . of continental limestones thoughf to be ca'liche. Johnson (1978) .advocatesa wetter climate, in .the range, of 'semiarid to subhumid. As evidence he cites the following: 1) lack of obvious' .. indicators.or aridity, . . such as primary evaporites, 2) the fact that caliche, wind reworked sand, and carbonates; ........................ ....... ........ ,,~ .... (L. .. .i.-X':.I.I.'.:..........?.~'...~. .??.& ~, ...?.. 100 described by Potter (1970), develops best in. semiarid rather climates; 3 ) abundance of.root even than arid if actual organic tropical floras and Although the . that .. the debris faunas writer mottling 4) humid scarce; and is of i 3 neighboring .concurs with Eocene basins. ' , Johnson% .. conclusion, ' . climate was wet and hot during Baca deposition, . . certain points should be made. First, limestones found in ....... gray shales. . .and have . yielded Lacustrine. algae (Chaiffetz, in . . . . . . . . preparation). A lacustrine .. origin, not soil-profile caliche, ,' . . . . .... .. ' is postulated for. these beds. Mudcracks in the Baca (Tonking, 1957), suggests alternate "wetting and' drying. I Second, the MacRae'.,, . basin that Johnson (1978) advances ? as proof of a wet climate for the'middle Eocene is in part , ' . . . late . . Cretaceous Formation middle of In the Eocene ' age, San. as in the older Juan Baca than Basin in the The Baca.San is New Jose ' unquestipnably Mexico from the (Bridger) limited faunal evidence available. The fauna of' San the Jose Formation are.typical (LucaS, 1977). Thirdly, of savanna-like upland . 'assemblages , ~ 'only 'the .clay . constituents . of the Baca sediments are characteristically red. 'Siltand sand clasts .. are shadesof gray.withonly a few grains with coatings of iron oxides. Magnetite and other iron-bearing minerals 'in . . .... the Baca are mainly unaltered, pigment is not a product of in situ indicating tha.t the rea alteration: of iron-bgaring detrital grains,a process described by Walker (1967). Because the red pigment is almost exclusively in the clay ' fraction . of . due to the rocks'the-origin the.weathering aofsoil of the red rich in color brown is probably' ferric material. . . The . . sediment is transported in the brown'hydrated form, and .. converted ,toa bright red by dehydration and oxidation after " , deposition (Van' Houten, 1968). The oxidation probably was . . . .. . . . . _ .. * . _ . . -. .. .~I ciose.-to the deposifionai interface lsecause"after-deepel:' . . . i: ,' '. ' buria.1 clayey-sediments could not.oxidize easily. A .. .. . . . . seasonallyrainy,hot,savanna-1,ikeclimateisanideal . . ,. . . setting for. drying ferric hydroxide to hematite (Schmalz, .. -1968). . . , . . . . , ' I . Baca clasts are varied and Snyder (1971) concluded tha.t . . the Baca The clasts granitic, sediments in the . were . derived from ,area studied were metamorphic and fron the source .rock must source derived primarily The sources. limestone . . . multiple .. ' . areas. . from distance . have. . been short for the following reasons.: 1) large size of 'granitic boulders in the Bacat 2) angularity ,. euhedral of some of the constituent.:; and unaltered. . feldspars, and 4) presence.of clasts. Potter of the Baca 3 ) occurrence of ' , . '~ limestone (1970) concluded that."some of the constituents were transported no morea few 'thanmiles. 'I Blatt and others (1972) state:thatfeldspar grains are fairly durable and can be transported great distances without,significant Feductiori in total. volume percentage, but are greatly .~ " .. reduced insize,whentransported distances of only.20 to 25 . e 102 "_ Alluvium BacaFormati:on, m i d d i eu n i t i n d i c a t e d by s t i p p l i n g . . -. . Current d i r e c , t i o n , p e b b l e imbrication . Bimodal c u r r e n t i n d i c a t o r , l o g a1 ign'ment 0 . 1 mile I F i g u r e . .28, , . 'mi (32.2 to 40.2 km). Judging from the granite boulders in the lower Baca, a nearby source for at least this of boulder size, material is.-indicated. Other constituents principally limestone could come and quartzite, are more rounded and . have from more distant . ..' , sources. .Pebble imbrications, cross-bedding,. ripples, and long . . , axis'of tree trunks members of the in Baca the conglomera.tic . .. and gray sandstone .. . .. . . . .. . . . . . . flowing current .. ... indicate southeastward 'a (fig. 28). Therefore, the' source area probably was 'to .the ., .. . . . . . .:. northwest. Potter (1970) and Johnson (1978) proposed the . . Lucero uplift and Snyder (1971) .,theZuni ' uplift as the source of the Baca sediments in the area studied. Although . . .. . the. Lucero. .. uplift is closer and . . Paleozoic . could' limestone to 'have provided .. , . or'quartzites .granites the Baca, no area during the oEocene r at present. . . were exposed The'Ladron in that Mountains, with .a Precambrian .granitic and . . guartzite core,is a Miocene uplift (Bruning, 1973) and ' could . not .. . have The, Zuni is could have contributed the been closest . .. the source . . . but as the area Zuni studied, to. Eocene Baca sedimentation. " . known. to.uplift, the northwest of granitic.and quartzitic seems unlikely that boulders of the of granite . and large angular material; . is 60 mi (96.6,km). northwest Tplift it that feldspars could, have came . . from a . such distant source., Yet, no alternate source area to the'nortihwest can .. be . . suggested. 104 e Until 1978, most workers have considered the Baca as . a fluvial 'channel and floodplain sequence (Potter, 1970; - and Snyder, 1971) However, Johnson (1978) interpreted the Baca, from 'west to east, to a progression of generally be facies from humid alluvial fan, fluvial-meander belt, to lacustrine d.elta. In the area studied Johnson.(l978) ,calls . 'the . .. . . lower conglomeratic. . .the . .. '. . . . . .. member, a lacustrine . .. . . . . . , fan' .. ... . delta; . . .. middle . gray sandstone member, a distai h&id . . .. .alluvial , . ; . . .. . fa.n; and the upper red .mudstone-sandstone member, a . . . . .. .. lacuskine fine-grained fan delta. . . , The writer believes the Baca to .. . . . , be a.fluvia1 largely . . sequence. The .disagreement with Johnson is based on the . ... gollowing reasons.. First, evidence for a large lake in .. < I 3 .this. area is lacking. There are ..no sLoreline deposits or . . . . . . .. . . ... . supportive faunal evidence. Second, the red colorof the . . .. .. sediments is more:suggestive of subaerial.than . subaqueous ' . I exposure. Johnson' (1978) defends this point by suggesting .. . . .. , lake o r lakes: a shallow; polymictic (frequent overturn) . . . ' the frequent overturn would allow . . . . dxidation. . -and cause red.coloration. However, because the thicknesses of deltaic . . . , , .... . . sand. bodies describeh by Johnson" a s .are much as, 30 .ft . the, . . . . . . 1 . (9.1 m) thick they therefore require similar water depths. Thirdly; the fan delta complex is, composed of many.small . . deltaic sand bodies that would require an extensive fluvial . . ' system to supply the material. However,.the fluvial facies tract .is . only a small segment of Johnson's (1978) . ....<.:. . . example, on t h e west side ofthe interpretation.For MountainsJohnson(1978) Bear shows t h e e n t i r e Baca s e c t i o n , . . about 500 f t (152.3 m) of l a c u s t r i n e d e l t a i c f a c i e s , , w i t h o u t a s s o c i a t e df a c i e s .F o u r t h l y ,a c c o r d i n g to Johnson(1978) a deltaic origin for parts evidence for of the Baca are t h e upward coarsening of g r a i n s i z e per sedimentary package; .. , I . mud t o sand r a t i o ; extensiveburrowing;convolutebedding;high . . afld 'vertical',sequence .: of . sedimentary . .. . . . .. .. " structures.. . : . t . ., .. .. . , , .I.n. .o p p o s i t i o n , :, . . . . _. _~ - : t h e writer points out that convolute bedding, burrowing and . root mottling . Singh, 1975) are common i n ' f l u v i a l s e q u e n c e s ( R e h e c k .. . . ' I n t h e B,ada' t h e sand:mud estimated .to be about 1:l. realm o ff l u v i a ls y s t e m s . .:. . . . . upward. . . . may n o t . . Bluck . (1971) has shown ' t h a t t h e head p o r t i o n o f p o i n t b a r s i n coarse-grained meanderbelt can coarsen . '. upward . . r e p r e s e n t a t r u ed e p o s i t i o n a lc y c l e .A d d i t i o n a l l y . . . .. This r a t. i. o i s n o t o u t s i d e , t h e d e p o s i t i o n a l package t h a t Johnson(1978)promotes .. I. ... . . Also; t h ec o a r s e n i n g . r and . ratio is . ._ . .. . . a Also, t h e . . . writer has found the sandstone bodies variable i n b o t h g r a i n s i z e . . throughout and document. ' i n t h e Bacll t o be and sedimentary structures . . a t y p i c a l v e r t i c a l sequence d i f f i c u l t t o ,. . . . ., .. . Baseh on' t h e d a t a above t h e 'writer concludes t h a t t h e . . . . Baca i n t h e a r e a ' s t u d i e d w a s deposited by streams c a r r y i n g coarse-grained.seaiment and t h e climate .subhumid. . .. ' The f l o o d p l a i n w a s savanna-like I n t h e s t u d i e d az& the south- . . . . . .