Laramide Stratigraphy of the Little Hatchet Mountains, Southwestern

Home , Chamita Formation, Little Hatchet Mountains, Mojado Formation, Palomas Formation, Ringbone Formation, Rubio Peak Formation

Laramidestratigraphy ofthe Little Hatchet Mountains, southwesternNew Mexico by TimothyF. Lawtonl;George T. Basabitvao2;Scott A. Hodgson';Dee A. Wilsons;Greg H. Mack';Wittian C. Mclntosh{;Spencer G. Lucass;and Kenneth K. Kietkes lDepartment Mexico LasCruces, NM 88003; 2U. S. Geological Survey, P.0. Box 6544, Las Cruces, NM 88003; 3ledsette'BrashearsofGeological a Granam'utnc- Sciences, New State University, socorro'NM87801; fl?liJll,,1iiil';ii?Ll,1lfil,3i#iJJi'ilHilyil:sfiilJ:fi,:,1,ffiil'f#[}"'3!^*"'ces' Abstract Cretaceous-Paleogenerocks of the Little Hatchet Mountains in southwestern New Mexico include the Ringbone, Hidalgo, and Skunk Ranch Formations. The Ringbone Formation is up to 1,600 m (5,250ft) thick and rangesin age from late Campanian through early Maas- trichtian. It was deposited in alluvial- fan, fluvial, and lacustrine environments. The Hidalgo Formation, which overlies the Ringbone, comprises 1,700 m (5,500 ft) of volcanic breccia, flows, and tuff. Radiometric age control on rocks collectedin the Little HatchetMountains indicatesan agerange ot77.4to6L.7 Ma for the Hidalgo Formation. The Skunk Ranch Formation is up to 490 m (1,605 f0 thick and Paleocen'e-Eocenein age, basedon ostracodesand gastropods.It overlies volcanic flows in the uppermost part of Ringbone and contains an andesite brecciain its middle membet defined here. These volcanic rocks are interpreted as flows associatedwith the Hidalgo Formation; thus, the Skunk Ranch is inferred to be correlative, at least in part, with the Hidalgo Forma- tion. The Skunk Ranch Formation accumulated in alluvial-fan and lacustrine settings. Cretaceous-Paleogenestrata of the Little Hatchet Mountains record the in- timate association of volcanism with Laramide deformation in southwestern New Mexico. In addition, the stratigraphy lends support to proposed mod- els of two periods of crustal deformation during the Laramide orogeny of the southwestern United States.These two periods include latest Cretaceousbase- ment-block uplift associated with development of lntermontane (Ringbone) basins and a Paleocene-Eocene(Skunk Ranch) phase of shortening that deformed the earlier basins and modified patterns of sedimentation. Late-phase deformation was accompanied bv formation of both reuerseand normal iaults.

Introduction The sedimentologic record of the Lar- amide orogeny in the southwestem United States consists of widely scattered exposures, diverse lithologies, and scant diagnostic fossil material. These charac- teristics impede correlation of mappable units and obscure the tectonic origin of some units. Uppermost Cretaceous strata FIGURE l-Geologic map of northern part of Little Hatchet Mountains, modified from Zeller in- inferred to represent Laramide deposits (7970), Rosaz (1989),and-Hodgson (1991).Generalized traces of measured sections in Fig. 3 A, B, C, and D. Kh, Hell-to-Finish Formation; Ku, U-Bar Formation; are widely distributed in southeastern Ar- dicated by line segments Km, Mojido Formation; Ringbone Formation, divided into lower (Krl), middle (Krm), and upp-er izona and northern Sonora (Dickinson et (Kru) members;TKh, Hidalgo Formation; Skunk RanchFormation, divided into lower (Tsl), middle al.,1989); Paleogene deposits of probable (Tsm), and upper (Tsu) members; Tv, Eoceneand Oligocene volcanic rocks; Q, Quaternary de- Laramide origin are likewise present in posits. ContaitJ between members of Ringbone located very approximately in northeast corner southwestern and south-central New of rnap. Tertiary intrusive rocks in the Hidalgo Formation northeast of the Hidalgo fault are not Mexico (Seager and Mack, 1986). rG shown. Western and eastern map boundaries are edges of R16W

New Mexico Geology February 1993 With the exception of the Cabullona Ba- sin in northern Sonora (Lucasand Gon- Lasky (1947) Zeller (1970) This Repon Age zliez-Le5n, 1990), the most complete, known Laramide successionoccurs in the C) Little Hatchet Mountains of southwestern SkunkRanch Ringbone SkunkRanch (Zeller, Although the !l c.r New Mexico 1970). Conglomerate Formation Formation YO g9 range is structurally complex, the Upper €v Cretaceousand Paleogenestratigraphy is Hidalgo Hidalgo Hidalgo -?- complete and well exposed. reasonably Volcanics Volcanics Formation The Little Hatchet Mountains contain an excellent record of the Laramide history of the southwesternUnited States.Lar- PlayasPeak amide rocks are exposed in four blocks Formation separated by faults (Fig. 1), but correlation of stratigraphic sectionspermits a re- o construction of the original stratigraphic Howells Ridge relationships. Formation Ringbone Ringbone Q In this paper, we summarize our recent Formation Formation g work on the Laramide stratigraphy of the J Little Hatchet Mountains. The data in- Ringbone clude measured and correlated strati- Shale graphic sections (Basabilvazo, 1991.; Wilson, 1991),geologic mapping (Hodg- son, 1991),bioshatigraphic control (Law- BrokenJug ton et al., 1990;Lucas et al., 1990),and a Limestone new 4Ar/3eArdate. The new age and rec- ognition of key correlative intervals re- FIGURE 2-Comparison of stratigraphic terminology of this report.with Previous stratigraphic quire revision of the stratigraphicsequence nomenclature of the Little HatcheiM6untains. Age iiierpretation applies to this-report only: Lasky in the range. In addition, the depositional (1947)considered the illustrated formations to 6e Early Cretaceousage based on fossils in the record supports the hypothesis that Lar- ifo*"ttt Ridge Formation, part of which is now consideredU-Bar Formation (Zellet, 1970),and PlayasPeak amide deformation occurredin two stages: in the CorbeitSandstone, not ,ho*n but placedby Laskybetween Howells Ridge and Neither of the previous strati 1) a late Campanian-early Maastrichtian Formations and now consideredMojado^Formati,on (Zeller, 1970). sequencebecause each contains correlation errors. episodeof transpressionalblock uplift and graphic successionsis depicted in its original basin formation (Seager,1983);2) a Pale- ocene-early Eocene episode of thrusting stone, in the Ringbone Formation, al- Mountains, volcanic rocks assignedto the or convergentwrenching (Hodgson, 1991). though he retained the name Hidalgo Hidalgo Formation have yielded zircon The volcanism appears to have begun Volcanics. fissioi-track ages of 67-3t7.1' Ma, during the first episode of deformation Neither of the previous stratigraphic 57.9+2.7Ma, and 54.9-r2.7Ma (Marvin and continued into the second. studiescorrectly depicts the proper ageor et al., 1978). The younger ages may be sequenceof lithologic units in the Little reset and probably record thermal effects Previous stratigraphic nomenclature Hatchet Mountains. Lasky believed all the from intrusion of the Lordsburg stock Although only a small body of previ- stratigraphic units to be Early Cretaceous (Loring and Loring, 1980). ously publishedwork existsfrom the Lit- age oh the basis of marine fossils in the tle Hatchet Mountains, the stratigraphic Howells Ridge Formation and Corbett Stratigraphy and age of Laramide strata nomenclatureis diverse(Fig. 2), partly as Sandstone.These strata have been reas- a result of the complex structural geology signed, in part, to the Lower Cretaceous Uppermost Cretaceousand ?aleogene of the range. Strataconsidered by us as U-Bar and Mojado Formations, respec- rocks^of this report are included in the Ringbone Formation were originally as- tively, by Zeller (1970).Zeller considered Rinebone, Hidalgo, and Skunk Ranch order (Fig. 2). signed by Lasky (1947)to the Broken Jug the Ringboneto be Late Cretaceousor early ForXrations,in aicending a Limestone, the Ringbone Shale,the How- Tertiary ageon the basisof the fossil palm, These units do not occur together in ells Ridge Formation, the PlayasPeak For- Sabal,now re fenedto Sabalites(Zelle1, 1970; singlestratigraphic sequence anywhere in mation, and the Skunk Ranch Lucaset al., 1990).The overlyingHidalgo thJrange, in part becausethe Hidalgo Conglomerate(lower part), in ascending Volcanicswere regardedby Zeller as early and Skrink Ranch are lateral equivalents order.The CorbettSandstone, considered Tertiary based on the presenceof fossil and in part becauseshifting loci of dep- by Lasky to lie between the Howells Ridge dicotyledonouswood. osition iocallv resulted in erosion of the and PlayasPeak Formations, is actuallya Radiometricdating of the Hidalgo For- Ringbone prior to Skunk Ranch deposi- about the mu- Lower Cretaceous formation and is not mation in the northern Part of the Little tion. Uncertainty remains included in our Ringbone Formation. Hatchets and inferred equivalents in the tual relationshipsof the Hidalgo and Skunk Lasky assigned a thick sequence of an- Pyramid Mountains to the northwest sup- Ranch Formations; however, we believe desitic breccia, tuff, and flows to the Hi- ports a Cretaceous-Tertiary age for the the correlationspresented here are correct dalgo Volcanics. He applied the name volcanic pile. An andesite flow in the up- in general. The Laramide units are de- Skunk RanchConglomerate to the young- per part of the Ringbone Formation, sam- scribed briefly in the following sections est sedimentarybedrock unit in the range. pled by Lasky and studied later by Marvin and new data pertaining to their ages The Skunk RanchFormation of this report et al. (1978),yielded a zircon fission-track summarized. is svnonvmouswith Laskv'sSkunk Ranch, age of 69.6+3.2 Ma. Porphyritic basalt excLpt near Playaslea( 1), where from the Hidalgo Formation in an area 1flg. Ringbone Formation our upper member of the Ringbone cor- east of that studied by us yielded whole- responds to the lower part of his Skunk rock K-Ar agesof 63.0+2.0 Ma and The Ringbone Formation consists of Ranch Conglomerate. Zeller (1970) in- 6'1..7+2.2Ma (Loring and Loring, 1980). conglomerate,sandstone, siltstone, and cluded all of the above formations named In the Pyramid Mountains, about 35 km mudstone with a maximum measured by Lasky (1947),except the Corbett Sand- (21 mi) northwest of the Little Hatchet thicknessof L,600m (5,250ft; Basabilvazo,

February 1993 Nr"u Mexico Geology South D North Fault

ffi"m a"| rufr;qConglomerate $ 7it o o o o) Sandston e b olo dQd ffi (u o) G o:a A o .D Mudstone, 4O Unconlormity q) I l-l siltston e Uppermbr De Volcanic Rocks: I Q. l-,-" 0l v0 breccia Mlddlembr lo""l flow, Skunk Ranch Qa Frl Formation '4' lv'l flow breccia Unconlormitv- \ o^ \ Lower Q"z 71.44 ArlAl Airfall tuff zVolcanic cla sts E

Olistostrome uppermbr E F autt 1000 Bingbone Dinosaurbone Formatlon Rlngbone a cf Albertosaurus Formatlon Incompfete o A/---'-' Ostracode o ./ -----' E- o Middle mbr /- E Correlation Lower mbr

-'-Cnconl v or mit Y ts

mbr Lower 4km

FIGURE 3-stratigraphic relationships of Upper Cretaceousand Paleogenerocks, northern part of Little Hatchet Mountains, New Mexico. Locations of sections are in Fig. 1. Lithologiesihown'are generalizedand repreient dominant rock type of a given interval. Faults indicated are reverse faults that separate each rieasured seclion (Fig. 1; Hoigson, 1991).Fission-track age indicated beiide cofumtt D was reported by Marvin et al. (1978)for an andesite flow in the upper member of the Ringbone Formation sampled by Lasky (7947).

1991).Three informal membersare mapp- to 2 m (5 ft) thick are present in the mud- in northwestern New Mexico (Lucas et able in the northern part of the Little stone. A single interval in the mudstone al., 1990).A pollen assemblagecollected Hatchet Mountains (Basabilvazo,199L; contains deformed sandstone beds and from the Ringbone somewhat uPsection Hodgson, 1991).Descriptions below are boulders of conglomerate and fossilifer- of the dinosaur fossils includes the form taken largely from Basabilvazo(1991). ous calcareoussiltstone. This interval of Aequitriraditesspinulosus (Rosaz, 1989), The lower member is about 100m (330 soft-sediment deformation and slumping which occurs only in upper Campanian ft) thick and rests unconformablyon the is about 10 m (33 ft) thick. Sandstonein- strataof centralUtah (Fouchet al., 1983). Lower Cretaceous Mojado Formation in terbeds are lithic arkosescontaining com- The upper member of the Ringbone the study area (Zelle1, 1970; Hodgson, mon volcanic-lithic fragments (Basabilvazo, consists of cobble and pebble conglom- 1991).It consistsof sedimentary-clastcon- 1991). The middle member records con- erate and sandstone. Basal beds of the glomerate and sublithic sandstonein beds ditions characteristicof lacustrine and la- member abruptly overlie the middle 1-15 m (3-50 ft) thick. Pebblesand cobbles custrine-deltaic settings. The interval of member in southem parts of the study were derived from Paleozoicand Lower soft-sediment deformation probably rep- area and comprise conglomeratecontain- Cretaceoussedimentary formations. Large resents an olistostrome in a lake of con- ing boulder-sized clasts. As in the lower clasts, which reach a maximum dimen- siderabledepth (Basabllvazo,1991). Air- member,the conglomeratecontains mainly sion of 1 m (3 ft), are composed exclu- fall tuff beds in the member are important clasts of sedimentary rock types. Con- sively of Lower Cretaceouslimestone and markers that may be correlated between glomeratedecreases in abundanceand clast limestone-clastconglomerate. This obser- the southern and northern exposures of Jize to the north and is replacedby in- vation suggeststhat most of the Paleozoic the unit (Fig. 3; Basabllvazo, l99l). terbedded sandstoneand shale. The mid- limestone clasts are recycled from Lower Dinosaur fossils and pollen constrain dle part of the member near Playas?eak Cretaceousconglomerate. Associated the age of the middle member of the Ring- (Fig. 3, section B) contains thin andesite sandstonebeds include both sedimentary bone Formation. Fossil dinosaur remains, flows (Hodgson, 1991) that provide a sublitharenites and lithic arkoses (Basa- including bones and teeth, are widely dis- means of correlating the unit in the study bllvazo, 1991). tributed, both geographically and strati- area. Andesite clasts that occur in upper- The middle member is dominated by graphically, in the middle member. most conglomeratebeds of the Ringbone dark-gray mudstone with subordinate in- Vertebraeand a tooth assignableto cf. AI- (Basabilvazo,1991) resemble lithologies in terbedded sandstone. Dramatic thicken- bertosaurusfrom the middle part of the the Hidalgo Formation and are inferred ing occurs southward in the middle member (Fig. 3, section B) indicate a late to have been derived from early Hidalgo member near Playas Peak (Fig. L; Basa- Campanian-Maastrichtian age by com- deposits, which are time equivalents of bilvazo, 1991).Silicic air-fall tuff beds up parison with faunas of the SanJuan Basin the Ringbone.

New Mexico Geology February 1993 Hidalgo Formation The Hidalgo Formation consists of ba- saltic and andesiticflows, flow brecciaand tuff of intermediate composition approximately L,700 m (5,500 ft) thick (Zeller, 1970). This thickness is a minimum be- cause the upper part of the unit is trun- cated by the Hidalgo fault (ZeIley 1970; Hodgson, 1991).Basal beds of the Hidalgo rest with sharp contact on the Ringbone in northern outcrops. As noted above, flows in the upper part of the Ringbone suggestcomplex interfingering of epiclas- tic and volcanigenic units, the latter per- haps representing precursorsof the Hidalgo volcanic sequence. Our under- standing of the Hidalgo is preliminary, but it appears to be broadly dMsible into three units of subequalthickness. The lower unit is a complex of dominant tuff brecciaand flow brecciawith subordinate air-fall tuff. The middle unit is poorly exposed, ap- parently dominated by fine-grained ail- fall or ash-flow tuff. The upper unit consists of flows, flow breccia,and tuff breccia similar to the lower unit. The Hidalgo Formation is interpreted to represent the margin of a stratovolcano complex. The D tuff brecciasrepresent lahar deposits, which dominate the section. FIGURE 4-Ostracodes and gastropods from the Ranch Formation in {Ar/3eAr Skunk the Little Hatchet We have obtained a age of Mountains. A,B,Pseudoeocyprispagei,leftvalves C,Bisulcocyprideaaruadensis,leftvalve D,Gon- 71.44+0.79Ma on a hornblendeandesite iobasis(G) and Lioplacodes(L) packstone. Bar scalesare 500 pm for A and B, 100 pm for C, and I from the baseof the Hidalgo section (Fig. cm for D. 3, section D). This age accordswell with the biostratigraphic data from the under- lying Ringbone and indicates that the siltstone. Clast size in conglomerate de- abruptly overlain by mudstone. The up- lowermost Hidalgo Formation is some- creasesupsection. Basalboulder con- per part of the middle member consists glomeratebeds contain clastsderived only of gray, monomict andesitic breccia cap- from Lower Cretaceousunits, the Hell-to- ped by stromatoliticlimestone about 10m Finish, U-Bar, and Moiado Formations. (30 ft) thick. The brecciais approximately Uppermost conglomeratebeds contain 70 m (210 ft) thick in measured section A oncolites and clasts coated with thin mi- (Fig. 1) and thins southward and north- agesmay be resetand need to be re-eval- crite rims. The member is approximately westward. It resemblesflow brecciaof the uated. 110 m (350ft) thick in the south; north- Hidalgo Formation, but we have not yet ward, acrossthe Mojado fault (Hodgson, satisfactorilyconfirmed its Hidalgo source. 199L), it thickens abruptly to nearly 450 The middle member was depositedin Skunk Ranch Formation m (1,475ft). Both the iower and middle a varietv of lacustrine,lacushine-delta. and The Skunk Ranch Formation overlies the membersare offsetacross the Moiado fault, lacustrine-marginenvironments (Wilson, Ringbone Formation in the vicinity of Pla- with offset measuring tens of meters. In 1991).An ostracodefauna (Fig. 4A-C) col- yas Peak but overlies the Lower Creta- contrast,hundreds of metersof offsetare lected low in the unit includesthe forms ceousU-Bar Formation in its southemmost requiredto juxtaposeRingbone and U-Bar Pseudoeocyprispagei and Cyprideaantaden- exposures (Fig. 1). Identification of the beds acrossthe samefault (Fig. 1; Hodg- sis (Lawton et al., 1990),now termed Bl- base of the formation has been made by son, 1991).The lower member was de- sulcocyprideaaruadensis (Wilson, 1991).This walking along beds from south to north posited in alluvial-fanand braided-fluvial assemblageindicates a Paleoceneto Eo- and providesjustification for moving the environments(Wilson, 1991).The upper cene age for the middle member of the base of the Skunk Ranchupsection rela- part probably representslake-margin de- Skunk Ranch Formation. Fossil beds in tive to its original baseas defined by Lasky posits, possibly fan deltas. the samestratigraphic interval include the (1947).The base of Lasky's Skunk Ranch The middle member is approximately freshwater gastropods,Goniobasis and Lio- corresponds to the base of the upper 250 m (820ft) thick. In its lower part, it placodes(Fig. aD), forms found in the up- member of the Ringbone described here. consistsof dominant dark-gray to olive- per Paleocene-lowerEocene Flagstaff The Skunk Ranch is divided into three gray laminated mudstone with subordi- Limestone of central Utah (La Rocque, informal members. All three membersare nate sandstone.In the middle part of the 1e60). presentin the southernmeasured section member, millimeter-scalesiliceous lami- The upper memberof the Skunk Ranch (Fig. 3, sectionA), but the upper member nae in the mudstone resemble varves. Formation,present only in sectionA (Fig. is missing in the vicinity of Playas Peak Sandstonebeds are thin (5-30 cm; 2-I2 L), where it is 136m (446ft) thick, consists asa result of omissionby normal faulting. inches) and commonlv contain svmmet- of limestone- and chert-pebble conglom- Descriptions of the members are taken rical ripples. Soft-sediment defoimation erateinterbedded with medium- to coarse- from Wilson (1991). is present in some sandstoneintervals. grained litharenite. It was deposited by The lower member consistsof boulder Sandstonebeds are arranged in succes- braided rivers (Wilson, 7991).The upper and cobble conglomerate interbedded sions to 2 m (6 ft) thick that thicken and member is gradational on the middle with red sandy siltstone and olive-gray coarsen upward. Each successionis member.It is truncatedbeneath a flat{ying

February 7993 Nm Mexico Geology successionof andesiticbreccias and vol- s Dlck fault zone caniclasticsthat are probably broadly Copper Howells Ridge laull equivalent to the Rubio Peak Formation pC I of middle Eoceneage (Hodgson, 1991). Sandstone beds of the Skunk Ranch Formation are sedimentary litharenites. Grain types include chert and carbonate lithic fragments derived from a sedimentary sourceterrane (Wilson, 1991).

Discussion Laramide sedimentary and volcanic strata describedabove record crustalde- formation in southwestern New Mefco during a period extending from the late Campanian through the late Paleocene- early Eocene.Overlap of folded strata by LittleHatchet Mountains a flat{ying volcanic successionthat may circa 63 Ma be equivalent to the Rubio Peak Forma- tion indicatesthat deformationat leastpre- dated the middle to late Eocene,but may haveceased earlier in the Eocene.The history of deformation recorded by sedimentary basin development accordswell with observed crosscutting relationships and constrains more precisely the time during which Laramide events occurred than do structuralrelationships alone. The revised stratigraphy presented here in- FIGURES-schematic north-south crosssection through areaof Fig. 1 during deposition of middle dicatesthat basin evolution was complex member of Skunk Ranch Formation, showing partitioning of both Ringbone and Skunk Ranch Howells_Ridgefault had and followed a two-stasehistory. The first depocenters during late Laramide deformation. Prior to this time, the the transpott of volcanic material south into the Skunk Ranch stage is marked by the northward-thin- served as an effeciive barrier to Formation. p4, Precambrianrocks; Pz, Paleozoicstrata, undifferentiated; Kh, Hell-to-Finish For- the ning clasticwedge of the Ringbone, mation; Ku, u-Bar Formation; Km, Mojado Formation; Kr, Ringbone Formation; TKh, Hidalgo secondstage by the developmentof sep- Formation; Ts, Skunk Ranch Formation. No vertical exaggeration. arate,roughly contemporaneous,epiclas- tic and volcanicdepocenters recorded by the Skunk Ranch and Hidalgo Forma- tions, respectively. an intermontane basin yoked to the Hi- sin partitioning subsequently separated The Ringbone is interpreted to have ac- dalgo uplift, with a thick proximal section the Hidalgo and Skunk Ranch depocen- cumulated during shortening accompa- that thinned toward the northeast. ters, preventing influx of volcaniclastics nied by basement-blockuplift, perhapsof The Ringbone Basin itself was de- into the southern depocenterprior to dep- transpressionalorigin (Seager,1983; Seager formed in the Maastrichtian. Uplift that osition of the middle member of the Skunk and Mack, 1986).A basement-coredup- accompaniedthe deformationpartitioned Ranch. Skunk Ranch deposition stepped lift, the Hidalgo uplift, lay southwestof the once-broadbasin into two depocen- southward onto the hanging wall of the the Ringbone depocenter(Seager and ters, one in which the Skunk Ranch was Mojado fault, which had been previously Mack, 1986).The sedimentary-clastcon- deposited and another, lying north of the marked by major uplift as all members of glomerateof the lower and upper mem- Howells Ridge fault, in which the Hidalgo the Ringbone were deformed. Some bers was shed northeastward from the accumulated(Fig. 5). That deformationhad movement on the fault neverthelesscon- uplift as erosion began to strip its Pha- begun to affect the Ringbone is suggested trolled thickness variation in the Skunk nerozoiccover. It is alsopossible that some by eastward stepping of the Hidalgo onto Ranch, resulting in a thick lower member conglomerate of the lower member was pre-Ringbone rocks in the northern part on the footwall and a thin lower member shed from the north and northwest (Bas- of the study area (Fig. 1). Ringbone strata on the hanging wall. We believe that the abilvazo, 1991).Sandstone in the lower in that transition appear to thin beneath southward shift in the locus of Skunk and middle members was depositedby the sharp contact with the Hidalgo, in- Ranch deposition resulted from activa- axial-fluvial systemstransporting vol- dicative of at least local angular discor- tion of a north-trending normal fault sys- canic detritus from the west and north- dance. tem that forms the eastern boundary of west. The ultimate sourceof the volcanic- Although the lateral relationshipsof the most Ringbone exposures and all Skunk lithic grains was probably the |urassic and Skunk Ranchand Hidalgo Formations are Ranch exposures(Fig. 1). It thus aPPears Cretaceousarc assemblageof south-cen- imperfect\ understood, structural and that normal and reversefaulting were co- tral Arizona (e.9., Lipman and Sawyer, topographic separation of the two units eval on different structural trends. 1985;Lipman and Hagstrum,1992). must have existed to preserve the striking Detritus in the Skunk Ranch was shed The southern edge of Ringbone expo- compositional contrast of those units. northward from a source terrane more sure coincideswith the Moiado fault sys- North of the Moiado fault, the Skunk proximal or more elevated than the ter- tem (Hodgson, 1991),but the baiin Ranch section is largely concordantabove rane that served as the sourceof the Ring- probably extended farther south in the the Ringbone, indicating that the absence bone conglomeratebeds. This is indicated Campanian. This is inferred from the of Hidalgo there is not due to uplift after by the large size of the boulders, their presenceof deformed,fine-grained lacus- Ringbone deposition. Moreover, the thin exclusive Lower Cretaceous derivation, trine strata of the middle member adia- andesite flows and andesite clasts in the and imbrication in the conglomerate(Wil- cent to the fault (Fig.1), indicating that it upper member of the Ringbone indicate son, 1991).Lower Cretaceousstrata, in- did not always form the basin margin. We probable geographic continuity with the duding Hell-to-Finish, U-Bar, and Mojado tentatively regard the Ringbone Basin as Hidalgo depocenter. We suggest that ba-

Nm Mexico Geology February 7993 nism suggeststhat the changewas gradual. The Laramide stratigraphy of the Little HatchetMountains, if correlatedwith units in southeasternArizona and south-central New Mexico, provides a unique link between sedimentarybasins formed to the southwest in Arizona and northern So- nora and basinsformed on the craton (Fig. 6). The basinsof southeastemArizona and northern Sonora contain Upper Creta- ceousrocks correlative with the Ringbone Formation. The correlative strata are similar in appearance and depositional en- vironment to the Rinebone and overlie Lower Cretaceousrock"s of the BisbeeBa- sin. In contrast, with the exception of the depocenter occupied by the McRae For- mation (Fig. 6), Laramide basins to the Rhyolite Tuff northeast of the Little Hatchet Mountains u contain strata equivalent to the upper part of the Skunk RanchFormation. These Cabullona units Group typically overlie Paleozoicstrata or basement and are overlain by andesitic units correlative with the Rubio Peak. They ac- cumulatedin sedimentarybasins forhed adjacentto basement-corbduplifts in the craton (e.9., Seageret al., 1986).Thus, Laramide basins in the geographic area encompassedby the Early CretaceousBis- FIGURE 6-Correlation of Upper Cretaceous-Paleogenesedimentary and volcanic units in the bee Basin formed during a brief period in Little Hatchet Mountains with units of southeasternlrizona, northein Sonora, and south-central the late Campanian and early Maastrich- New Mexico. Late Cretaceo-usage of Amole Arkose based on interfingering relationships with tian. Thesebasins appear to be older than Confidence PgakTuff (P.W. Lip1na1,pers.comm. 1990).Age of HidalgoFormltion depictei taken cratonic Laramide basins immediately to from range of published agesin Little Hatchet Mountains d'lscussedin"text. Modified fiom Lawton the north, which formed in the Paleoiene and C-lemons(1992). Time scale from Harland et at. (7990).Volcanic symbols: v silicic volcanic and early Eocene. unit; inverted v, intermediate volcanic unit. Ac

February 1993 New Mexico Geology Gillette,D. D., Wolberg,D. L., andHunt, 4.P.,1986, the Cordilleran volcanic arc in southeastern Ari- Mineral Resources,Open-file Report 385 [in French, Tyrannosaurus rex from the McRae Formation zona: implications for regional tectonics and ore with English summary and captionsl. (Lancian, Upper Cretaceous),Elephant Butte Res- deposits: Geological Socie$ of America, Bulletin, Seager,W. R., 1983, Laramide wrench faults, base- eruoir, Siena County, New Mexico: New Mexico v. TM, pp.32-i9. ment-cored uplifts, and complimentary basins in Geological Society, Guidebook to the 37th Field Lipman, P W., and Sawyer, D. A., 1985:Mesozoic southern New Mexico: New Mexico Geology, v. 5, Conference,pp. 235-238. ash-flow calderafragments in southeasternArizona pp.69-76. Harland,W. 8., Armshong, R. L., Cox, A. V, Craig, and their relation to porphlry coPPerdePosits: Ge- Seager,W. R., and Mack, G. H.,7986, Laramidepa- L.E., Smith,A. G., and Smith,D. G., 1990,A geo- ology, v. 13, pp. 652-656. leotectonicsof southern New Mexico; in Peterson, and sedimentationin the logic time scale1989: Cambridge University Press, Loring, A. K., and Loring, R. B., 1980,ICAr agesof l. A., (ed.), Paleotectonics States:American New York, 253 pp. middle Tertiary igneous rocks from southern New Rocky Mountain region, United Memoir 41, Hodgson, S. A., 1991,,The geology and tectonicsof Mexico: IsochronAy'y'est,no. 28, pp.1,7-19. Association of Petroleum Geologists, and pp. 669-685. the northem Little Hatchet Mountains, Grant Lucas, S. G., Basabilvazo,G. T., and Lawton, T. F., Seager,W. R., Mack, G. H., Raimonde,M. S., and Hidalgo Counties, southwesternNew Mexico: Un- 1990,Late dinosaursfrom the Ringbone Cretaceous Ryan, R. G., 1985,Laramide basement-coreduplift published MS thesis, New Mexico StateUniversity, Formation, New Mexico, U.S.A.: southwestern and basinsin south-centralNew Mexico:New Mex- Las Cruces,117 pp. CretaceousResearch, v. 11, pp. 343-i49. La Rocque,A., 1950,Molluscan faunas of the Flagstaff ico GeologicalSociety, Guidebook to the 37th Field C.,1990, Reporte Formation of central Utah: Geological Socie$ of Lucas,S. G., and Gonz6lez-Le6n, Conference, pp. 123-130. preliminar del CretdcicoTardio de America, Memoir 78, 100 pp. sobre dinosarios Thorman, C. H., and Drewes, H., 1980,Geologic map la de Cabullona, Sonora: Universidad de Lasky, S. G., 1947,Geology and ore deposits of the cuenca of the Victorio Mountains, Luna County, south- Geologia Boletin, v. 7 no. Little Hatchet Mountains, Hidalgo and Grant Sonora, Departemento , western New Mexico: U.S. Geologic Suruey, Mis- 1.,pp. l-5. Counties, New Mexico: U.S. Geological Suruey, cellaneousField Shrdies Map MF-1175,scale 1,:24,W. ProfessionalPaper 208, 101pp. Maruin, R. G., Naeser, C. W., and Mehnert, H.H., Wilcox,R. E., Harding, T. P., and Seely,D. R.,1973, Lawton, T. F., and Clemons, R. E., 1992, Klondike 1978, Tabulation and radiometric ages-including Basic wrench tectonics: American Association of Basin-late Laramide denocenterin southern New unpublished K-Ar and fission-trackages-for rocks Petroleum Geologists, Bulletin, v. 57, pp. 74-96. Meico: New Mexico Giology, v. 14, no. 1, pp. in southeastern Arizona and southwestern New Wilson, D. A., 1991,,Depositional environments, lJ. Mexico: New Mexico Geological Society, Guide- provenance, and age determination of the Skunk Lawton, T. F., Mack, G. H., Basabilvazo,G. T., Wil- book to the 29th Field Conference, pp.243-252. RanchFormation, Little Hatchet Mountains, south- son, D. A., Lucas,S. G., and Kietzke,K. K., 1990, Rosaz, T., 1989, Le passage des Cordilldres nord- western New Mexico:Unpublished MS thesis,New Uppermost Cretaceousand Paleocenestrata in the am6ricains aux Sierras Madres mexicainesle long Mexico State University, Las Cruces, 87 pp. Little Hatchet Mountains, southwesternNew Mex- du Texas Lineament- G6ologie de SW du Nou- Zeller, R. A., Jr.,1970, Geology of the Little Hatchet ico (abs.):New Medco Geology,v. 12, no. 1, p. 16. veau-Mexique (USA): Bulletin Centres de Re- Mountains, Hidalgo and Grant Counties, New Lipman, P. W., and Hagstrum, J. T., 1992, Jurassic cherces-Exploration-Production Elf Aquitaine, v. Mexico: New Mexico Bureau of Mines and Mineral ash-flow sheets.calderas. and related intrusions of 73, pp. 247-275;New Mexico Bureau of Mines and Resources,Bulletin 96, 22 pp. !

t-Xl€-tt-tt-tl-ttl:tt-xl-)lt:lt:ll-Xl--ll-Xl-xl-'l

Lucas et al. (Cont;nuedfrom p. 8) Kurten, B., and Anderson, E., 1980,Pleistocene mam- continental deposits of New Mexico: an overview: O'Neill, F M., and Rigby,J. K.,Jr.,1982,A rare-fossil mals of North America: Columbia Universitv Press. Geological Society of America Bulletin, v. 92, pp. skeleton of Ccmelopsfrom PleistocenedePosits near New York, zt42pp. 917-932. Albuquerque: New Mexico Geological Society, Lambert, P. W.,7968, Quaternary stuatigraphyof the Lucas,S. G., and Logan, T. R., 1984,Pleistocene horse Guidebook to 33rd Field Conference,pp.82-84. Albuquerque area,New Mexico: Unpublished PhD from the Albuquerque area, New Mexico: New Osborn, H. F., 1918, Equidae of the Oligocene, Mi- dissertation, University of New Mexico, 329 pp. MexicoJournal of Science,v.24, pp.2932. ocene, and Pliocene of North America, icono- Lambert, P. W., 1.978,Upper Santa Fe stratigraphy Lucas, S. G., and Oakes,W.,1986, Pliocene(Blancan) graphic type revision: Memoir of the American and geomorphic features of the Llano de Albu- vertebrates from the Palomas Formation, south- Museum of Natural History, new series, v 2, pp. querque:New Mexico Bureauof Mines and Mineral central New Mexico: New Mexico Geological So- 1-330. Resources,Circular 153, p. 151. ciety,Guidebook to 37th Field Confercnce,pp.249- Smith, R. L., Bailey,R. As., and Ross,C. 5., 7970, Logan, T. R., 19U, Early Iruingtonian (early Pleisto- 255. Geologic map of the femez Mountains, New Mex- cene) mammals from the upper part of the Santa Lucas,S. G., Williamson,T., and Sobus,J., 1988,Late ico: U.S. Geological Suroey, Miscellaneous Geo- Fe Group, AlbuquerqueBelen Basin, central New Pleistocene(Rancholabrean) mmals from the Edith logic Investigations Map I-571. Mexico: Geological Society of America, Rocky Formation, Albuquerque, New Mexico: New Mex- Tedford, R. H., 1981, Mammalian biochronology of Mountain Section, Abstractswith Programs,v. 16, ico fournal of Science,v 28, pp. 51-58. the late Cenozoicbasins of New Mexico:Geological no. 4, p.245. MacFadden, B. 1., 79n, Magnetic polarity stratigra- Society of America Bulletin, v.92, pp. 1008-1022. Logan, T. R., Lucas, S. G., and Sobus,J. C., 1984, phy of the Chamita Formation stmtotyPe (Mio- Tedford, R. H., 1982, Neogene stratiSraPhy of the Blancan-Irvingtonian boundary in the Ceja Mem- Pliocene) of north-central New Mexico: American northwestem Albuquerque Basin:New Mexico Ge- ber of the Santa Fe Formation, Tijeras Anoyo, Al- Journal of Science,v. 277, pp. 769-800. ological Society, Guidebook to 33rd Field Confer- buquerque area, New Mexico: New Mexico Geology, Machette, M. N., 1978a,Geologic map of the San ence, pp. 273278. v. 5, no. 1, p. 14. Acacia quadrangle, Socorro County, New Mexico: Voorhies, M., 1969,Taphonomy and population dy- Lozinsky, R. P., Hawley, J. W., and Love, D.W.,1991,, U. S. GeologicalSurvey, Geologic Quadrangle Map namics of an early Pliocenevertebrate fauna, Knox Geologic overuiew and Pliocene-Quaternary his- GQ-141s. County, Nebraska:University of Wyoming Contri- tory of the Albuquerque Basin,central New Mexico: Machette, M. N., 1978b,Preliminary geologicmap of butions to Geology, SpecialPaper 2,59 pp. New Mexico Bureau of Mines and Mineral Re- the Socono 1" x 2" quadrangle, central New Mex- Webb, S. D.,1965, The osteologyof Camelops:Science sources,Bulletin 1.37,p. 1,57-162. ico: U.S. Geological Suruey, Open-file Report 78- Bulletin of the Los Angeles Coun$ Museum, v. 1, Lozinsky, R. P, and Tedford, R. H., 1991, Geology 607. 54 PP and paleontology of the Santa Fe Group, south- Machette, M. N., 1978c, Quaternary faults in the White, J. A., 1987,The Archaeolaginae(Mamrnalia, western Albuquerque Basin,Valencia County, New southwestern United Statesby using buried calcic Lagomorpha) of North America, exchding Archneo- Mexico: New Mexico Bureau of Mines and Mineral paleosols:fournal of Research,U.S. GeologicalSur- lagus and Palolax: lownal of Vertebrate Paleontol- Resources,Bulletin 132, 35 pp. vey, v. 6, pp. 359J81. ogy,v.7, pp. 425-450. Lucas,S. G., 1987,American mastodontfrom the San- Madden, C., 7987,Mammoths of North America: Un- Williams,G. 8., and Rust,B. R., 1977,Thesedimen- dia Mountains, New Mexico: New Mexico Journal published PhD dissertation, University of Colo- tology of a braided river: Joumal of Sedimentary of Science,v. 27, pp. 29-j2. ndo,247 pp. Petrology, v. 39, pp. 649-679. Lucas, S. G., and Efiinger, I. A., 1997,Mammuthus Manley, K., 1978, Geologic map of Bernalillo NW Wright, H. E., Jr.,1946, Tertiary and Quaternary ge- from Lincoln County and a review of the mam- quadrangle, Sandoval Counry New Mexico: U. S. ology of the lower Puerco area, New Mexico: Ge- moths from the Pleistoceneo{ New Mexico: New GeologicalSuruey, Geologic Quadrangle Map GQ- ological Societyof America Bulletin, v. 57, pp. 383- Mexico GeologicalSociety, Guidebook to 42nd Field tMs. 456. Conference, pp. 2n -282. Olsen, S. 1., 1979, Osteology for the archaeologist: Lucas, S. G., and Ingersoll, R. V, 1981, Cenozoic PeabodyMuseum, Cambridge, 186pp.

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