Abstracts

Abstracts Abo Formation and laterally due, in part, to syn-

depositional proximity of remaining highlands,

shelf edge. The lowermost unit averages 0.5 m

thick and compositionally is a silty peloidal wacke-

which were probably tectonically formed during stone. The upper tvvo intervals are subarkosic and

New Mexico Geological Society

the Pennsylvanian Period, andior marine basins. average 4 and 6 m thick (middle and upper units,

The New Mexico Geological Societyannual spring

respectively). All three intervals are in sharp, planar

meeting was held at New Mexico Institute of Min-

SussuRFecs ANALysrsoF THEABo FoRMATToN THE IN contact with the underlying carbonate unit. Locally

ing and Technology (Socorro) on April 3, 7987.

LucERo REGroN.wEsr-cENTRALNuw Maxrco, by the basal contact is planar erosional with obvious

Following are abstracts from the four sessions given

Gregory E. Little, Department of Geoscience, New erosion of the substratum in excess of 1 m of relief

at that meeting. Abstracts from the 1988 meeting

Mefco Institute of Mining and Technology, as evidenced by truncated tepee structures. The

will appear in future issues of Nal Mexico Geology.

Socorro, NM 87801 upper contact of each siliciclastic interval is gra-

dational to locally sharp. Texturally the siliciclas-

Sedimentary geology session Outcropping of the Abo Formation in the Lucero

tics range from subangular silt (<64mm) in the

Inremv REpoRT THEcoNoDoNT BTosTRATIGRApHY region of west-central New Mexico is limited to

oN

silty wackestone to well-rounded, lowet very fine

oF THEKELLv LTMESToNE (MrssrssrrnaN), cENTRAL the Zuni Mountains, Joyita Hills, Sierra Lucere

sand (0.09-0.06( mm) in the subarkose units. Rare,

Nrw Mrxco, by Stanley T. Krukmoski, Depart- Lucero Mesa areas, and east of Socorro. Analysis

isolated, well-rounded, frosted, medium (0.25-0.5

ment of Geoscience, New Mexico Institute of of drill cutting and geophysical logs provides a

mm) quartz sand grains characteristic of the Yates

Mining and Technology, Socorro, NM 8780f stratigraphic framework between surface expo-

in the subsurface are present in the subarkose units

The Kelly Limestone (Mississippian) of central sures. Subsurface data correlate with complete Abo

and are particularlv abundant in the area of the

New Mexico is located in several widespread out- sections near Lucero Mesa and east of Socorro. In

oinchout of each subarkose unit. In contrast a fea-

crops along the western margins of the liio Grande the Lucero region, theAbo Forrnation overlies Pre-

lure unique to the silty wackestone is the presence

Rift. It nonconformably overlies Precambrian cambrian rocks, Pennsylvanian limestones, and

of trace amounts of glauconite. Sorting ranges from

igneous and metamorphic rocks and is uncon- rocks assigned to the Bursum Formation and is

well to very well sorted. The heary-mineral suite

formably overlain bv the Sandia Formation (Penn- overlain by the Meseta Blanca Member of the Yeso

is dominated by a well rounded and abraded zir-

svlvanian). The lower Caloso Member consists of Formation. Thickness of the Abo Formation varies

con-tourmaline-rutile assemblage. Biotics are rare

sindstones. shales, lime mudstones and wacke- from 450 ft over the Zuni uplift to 820 ft near Mesa

within either the silty wackestone facies or the

stones. The upper Ladron Member disconforma- Lucero. The Abo Formation consists of very fine

subarkose facies and are found in greatest con-

bly overlies the Caloso and is composed of crinoidal to medium-grained sandstones, siltstones and

centration and diversity in proxirnity of the Cap-

grainstones and packstones. The basal limestones mudstones with coarser sandstones and conglom-

itan Reef. Biotics range from fusulinids and

of the Caloso Member have produced conodonts erates locally occurring over the Zuni uplift, Joyita

dasycladacean algae to various molluscan and

a s s i g n e d t o t h e s p e c i e s P a t r o g n a t h u sa a r i a b i l i s , Hills, and in exposures east of Socorro. In the

brachiopod fragments. Evidence of burrowing

Polygruthus inonntus, and Pseudopolygnathusfusi- western portion bf the studv area sandstones and

infauna is extremely rare though local, subtle, fab-

indicating a Kinderhookian age. Previously siltstones dominate the Abo stratigraphic section

/ormis ric mottling is apparent in the subarkose facies.

barren strata at the top of the Caloso have yielded by almost 4 to I over mudstones. Mudstones

Sedimentologically the two lithofacies are distinct.

undiagnostic conodont faunas; however, one become more prevalent to the east with sandstone

The silty wackestone is characterized by devel-

specimen, tentatively identified as Gnilhodus typ- plus siltstone to mudstone ratios as low as 1:4.

opment of three facies along a shelfward progres-

bus M7, would suggest a Kinderhookian--earliest High percentages of sandstones and siltstones

sion. Nearest the Capitan is developed a

Osagean time. The Ladron Member has produced suggest alluvial-fan and braided-stream environ-

discontinuous, war1, crypLalgal, laminated facies.

conodonts throughout its thickness. The lowest ments prevailed in the westem oortion of the Lucero

Locally developed within this facies are oscillation

units contain the conodonts Gnathodus texanus and region. To the east, an abundlance of mudstones

ripples containing fusulinids aligned in and par-

Polygtwthus communis communis marking the lower suggests a meandering fluvial environment of

allel to the ripple troughs. Farther shelfward this

texanus Zone (upper Osagean). The top of the Lad- deposition. Initial analysis of wellJog cuwe shapes

facies grades into a waly, laminated, fenesha-l facies.

ron is assigned a latest Osagean-Meramecian age to determine grain-size trends appears compatible

This facies in turn grades farthest shelfward into

because it contains specimens belonging to the with the above interpretations; however this type

a wa\ry, laminated facies containing ostracods and

genus Cazrasgmthus. The Caloso Member was of analysis was found to be more difficult than

calcispheres. The subarkose facies exhibit a shelf-

determined to be Kinderhookian by early workers expected.

ward- diminution of scale, diversity, and abun-

based on brachiopod faunas. It was liter reas- dance of primary sedimentary shuctures from the

signed a middle Oiagean age based on endothyrid MenrNresHEErsANDsToNES THEuppERYATEsFoR-

oF reef proximal area. On the basis of sedimentary-

foraminifers, Latiendothyra, Medioendothyra, and MATroN, sourHERN Guaoelurr Mourrerrus, Nrw structure distribution three facies have been rec-

Tuberendothyra.The Ladron Member was assigned MEXIco, by MageII P. Candelaru, ARCO Oil & ognized in the shelfward progression: 1) small-

to the late Osagean based on brachiopod and blas- Gas Co., P.O. Box 1610, Midland, TX79702 scale cross-laminated facies; 2) ripple cross-lami-

toid assemblages, and the first occurrences of the Middle Permian strata of the Northwest shelf in nated to plane-parallel facies; and 3) nonJami-

foraminifers Prisella, Pseudotaxis, and Tetrataxis. the southern Guadalupe Mountains, New Mexico nated to waw, laminated facies (farthest from the

Results of this study have shown that the Caloso consist of thick shallow marine carbonates inter- shelf edge). ihis facies progression is interpreted

Member is Kinderhookian at its base and possiblv bedded with thinner siliciclastic intervals of uncer- to be the Droduct of shelfward diminution of

earliest Osagean toward the top. The discbnform- tain origin. Most previous studies have categorically hydraulic energy. Moreover, across the area exam-

ity between the two members corresponds to the assigned Capitan-equivalent (Upper Guadalu- ined, none of these sandstones exhibit evidence

Upper typbus and anchoralis-latus Zones (lower- pian) siliciclastic intervals of the Northwest shelf of channeling or down-cutting into the subjacent

middle Osagean). to either of two general depositional environ- carbonate unit. They exhibit no fining or coarsen-

ments, shallow marine or eolian, with few sedi- ing upward sequences, no features interpretable

PelrocunnrNr AND FACTES ANALysrsoF THEABo FoR- mentological observations to support the as evidence of beach or tidal sedimentation, and

MATIoN ALoNc A NW-SE suRrAcE TRANsECToF interpretations. A detailed sedimentologic study no vertical repetitive sedimentation pattems. No

Nsw Mextco, by lohn R. MacMillnn, Geoscience of the three siliciclastic intervals in the upper 15- stratification tvpet *".e identified as unequivocal

Department, New Mexico Institute of Mining 30 m of the Yates Formation, supported by recon- eolian featurei'(i.e. inversely graded translatent

and Technology, Socorro, NM 87801 naissance observations of the underlfng Seven laminae, adhesion ripples, high index ripples,

Paleocurrent analyses in conjunction with width Rivers and overlying Tansi-ll formations, has pro- deflation surfaces or associated interdune pond

to depth ratios of channel sandstones, relative vided strong evidence for a shallow marine dep- facies). All primary sedimentary structurei are

abundance of different lithologies and their con- ositional environment for these shelf siliciclastic interpretable as being of subaqueous origin. Fur-

tact relationships, sedimentary structures and fos- intervals, contrary to prevailing interpretation. The thermore the relative increase in abundance of the

sil content indicate the Abo Formation is composed three siliciclastic units of the upper Yates were medium-sand fraction in the subarkose units near

of various facies (paleoenvironmental deposits) from examined in detail for sedimentologic and petro- the pinchout is thought due to winnowing in the

the Zuni Mountains on the northwest, both sides graphic characteristics within the area extending zone of greater hydraulic energy. Siliciclastic units

of the fuo Grande rift to Socorro, NM, and south- 5 km from the Capitan shelf edge and for 36 km of the Seven Rivers and Tansill Formations are

eastward through Bingham, NM, to the Sacra- parallel to the shelf edge. These upper Yates inter- sedimentologically analogous to these upper Yates

mento Mountains and their transition to Otero vals are continuously traceable across the study intervals. All are herein interpreted as sheet sands

Mesa. These facies include alluvial fans, braided area and well beyond to the west and into the deoosited in a shallow marine shelf environment.

stream channels, meandering stream channels (with subsurface to the east. All three units thicken slightly Th^eshelf hydraulic regime was of moderate to low

their flood plains, natural levees and crevasse basinward prior to pinching out abruptly between energy, which diminished with increasing dis-

splays), and-sandy tidal flats. The occurrence of carbonate Brainstones of the outer shelf within a tance from the shelf edge. The silty wackestone

the facies varies both stratigraphically within the few hundred meters of the Capitan massive at the







Nm Mexico Ceology May 1988

facies represents deposition in a shallow subtidal contact is clearly erosional and the carbonate sub- 2) an upper gypsum member that is as much as

to supratidal (?) environment. The subarkose facies stratum locally exhibits evidence of incipient pedo- 55 m of laminar to massive gypsum--anhydrite.

represents deposition in strictly a shallow subtidal genesis. In marked contrast, the upper contact of Burbank (1930) named the Wanakah Member of

environment of perhaps only a few meters depth. each sandstone with the overlying carbonate unit the Morrison Formation near Ouray, Colorado for

Input of mature likely multicycle siliciclastici to is typically of a more gradational nature. The sand- 20 m of shale, limestone and sandstone underlain

the aqueous shelf environment may well have been stones exhibit no evidence of down-cutting, or by 18 m of gypsum and limestone that he termed

via eolian and/or fluvial processes. However trans- coarsening- or fining-upward sequences. Primary the "Pony Express beds." It has long been clear

port and uniform distribution across the shelf was sedimentary structures are rarely visible; where that Burbank's Pony Express treds : the Todilto

by a variety of shallow marine processes operating present they are small scale (< 20 cm) and discon- Limestone of Gregory and that the remainder of

on various periodicities. These fine-grained sili- tinuous. Their apparent absence is due to high Burbank's Wanakah Member : the unit long (but

ciclastics were winnowed within the outershelf textural maturity (very fine grain size ( 0.1 mm, incorrectly) called Summerville Formation in

hydraulic environment and subsequentlv trans- and high degree of sorting) and/or thorough northwestern New Mexico. The simplest nomen-

ported in suspension across the Capitan massive reworking by infauna. The overall distribution of clatural solution thus is to abandon the term Pony

to be deposited in the deep waters of the Delaware sedimentary structures indicates subaqueous dep- Express, and restrict the name Wanakah to the

Basin. osition within an hydraulic regime of shelfward upper, dominantly clastic portion of Burbank's

diminishing energy. Contrary to most previous original Wanakah Member. This means that the

interpretations, no evidence of eolian stratification Todilto Formation (with two unnamed members)

was found to support an eolian depositional envi- in northwestem New Mexico and southwestem

Omcw or sANDSroNE-{ARBoNATE ALTERNATIoNS oF ronment for the shelf sands. Shelf sandstone Colorado is overlain by the Wanakah Formation.

THE UPPER YATTSFONVENON, NORTHWES'r SHELF. transport processes remain enigmatic but are An altemative solution recentlv advocated bv the

DeLnwenr Basrru, New Mrxtco, by Magelt p. Can- dominantly basinward directed and likely of marine U.S. Geological Survey is to reduce Todilio to

delaria, ARCO Oil & Gas Co., P.O. Box 1610,

origin. Siliciclastic input to the marine shelf envi- member rank as the basal member of Wanakah

Midland, TX 79702

ronment is believed to have been slow but contin- Formation and term the upper, dominantly clastic

The interbedded sandstone and carbonate strata uous along the strandline. The effectiveness of portion of the Wanakah-the Beclabito Member.

of the Permian upper Yates and lower Tansill For- marine transport of siliciclastics across the shelf This solution is less favorab.le because it: 1) unne-

mations on the Northwest shelf of the Delaware was govemei largely by minor episodic relative cessarily introduces a new stratigraphic name

Basin, New Mexico were studied to determine their shelf subsidence, which periodicallv increased or (Beclabito); 2) reduces the two members of the

sedimentologic and temporal relationships. The maintained water depth favorable for subaqueous Todilto to bed status even though they are mapp-

evidence suggests local minor tectonic, as opposed transport of shelf siliciclastics. Apparent unre- able at 1:24,000 scale; and 3) runs contrary to long-

to eustatic, control of carbonate sedimentation and stricted marine transport of quartz sands across standing and extensive published usage, which

of the sandstone-
most basinward 5 km of the Northwest shelf the absence or lack of influence of any hydiographic arate formations.

Yates-Tansill study interval consists of three sand- barrier such as a marginal mound during sand-

stone-carbonate alternations with a composite stone depositional episodes. This condition was

thickness of up to 40 m. The carbonates vary from repeatedly met by a combination of erosional trun-

skeletal grainsiones to nonskeletal wackestones and cation of the shelf crest facies of the marginal mound

range up to 12 m thickness each. The sandstones and subsequent increased shelf wateidepths due Srne.rrcneruy oF THE MoRRrsoN FoRMArroN (LATE

are very well sorted, very fine grained siliciclastic to relative subsidence of a few meters, at which funessrc) N rHE LAMv ,lnla, Savra FE CoulITy,

units from 0.5-8 m thickness and range from silty time siliciclastics were transported basinward by New MExco, AND coRRELATtoN BETwEENTHE

peloidal wackestones to subarkose arenites. The a variety of marine shelf processes. The gradation MonrusoN oN rrc Colonaoo PurEau AND tN EAsr-

Yates-Tansill interval grades laterally basinward of sandstone upward into upward-shoaling, hem- CENTRAL NEw Mrxco, bV Adrian P. Hunt, and

into the Capitan reef facies at the shelf edge. Within iryclic, peritidal carbonates along the crest of the Kenneth K. Kietkt, Department of Geology, Uni-

each of the carbonate intervals a numbir of oeri- shelf marginal mound is interpreted to be a dual versity of New Mexico, Albuquerque, NM 87131

tidal facies have been recognized that collectively lithology depositional couplet. This couplet is The Morrison Formation in the l.amy area (T15N,

exhibit upward-shoaling characteristics. The unique to the area of the shelf crest and consists R10E) consists of 183 m of variegated mudstones,

upward-shoaling sequence is typically 1-2 m thick of a lower sandstone member grading upward to sandstones, siltstones and conglomerate. Based on

each and is hemicyclic. Several of these sequences upward-shoaling peritidal carbonates, which lithologic characteristics and stratigraphic posi-

may exist in vertical succession in each caibonate became episodically emergent locally. In this "all tion, the Recapture, Westwater Canyon, Brushy

unit examined. Commonly a hemicyclic sequence wet" shelf interpretation, the sandstones repre- Basin and Jackpile Sandstone membeis can be rei-

is capped by a ragged erosion surfaie that is over- sent the subtidal sedimentation and the carbon- ognized. The Recapture overlies gypsum or lime-

lain by another similar hemicycle. The stacking of ates represent the intertidal-supratidal stone of the Todilto Formation and consists of 81.3

these truncated upward-shoaling sequencei is sedimentation. The interpretation of minor (1-2 m of pale reddish-brown mudstones and fine-

interpreted to be the product of periiidal sedi- m) episodic relative shelf subsidence controlling grained sandstones. Overlying the Recapture are

mentation to depositional fill level in resoonse to the altemation of shelf carbonate and sandstone 48 m of medium-grained sandstones and minor

episodic relative shelf subsidence of comparable deposition is an alternative to the long-professed mudstones of pale greenish-yellow color. This

magnitude. The upper few centimeters oi many dogma of dominantly eustatic control of North- sandstone sequence, which also includes rare con-

hemicycles evidence peritidal diagenesis intei- west shelf depositional sequences. This interpre- glomerates, is assigned to the Westwater Canyon

pretable in some cases as evidence of emerqence. tation is preferable to previous interpretations in Member. The Brushy Basin consists of 37 m of

In two instances the diagenesis is analog6us to that it is documentable on the scale of an outcrop, variegated grayish-red, purple, and pale olive

incipient pedogenesis implying extendJd sub- it is consistent with the observed sedimentologic mudstones. Overlying the Brushy Basin is 10 m

aerial exposure. In contrast, the contemporaneous and stratigraphic relationships of the Yates-Tansill of white coarse-grained kaolinitic sandstone

shelf carbonate facies farther basinward and far- sequence/ and it may be applicable to comparable assigned to the Jackpile Sandstone Member. Above

ther shelfward do not exhibit upward-shoaling stratigraphic sequences elsewhere in the Permian the Jackpile is a 2--cm-thick femrgenous zone, which

sedimentation, erosion, or comparlble diagenesis. Basin. weathers moderate brown in color. overlain bv 7

The area of upward-shoaling peritidal facies is m of medium-grained white sandstone. This upper

interpreted to represent a paleotopographic high sandstone sequence may be correlated with the

or crest of the geomorphic shelf marginal mound. Encinal Canyon Member of the Dakota Formation.

The relationship of the marginal mound to sand- Toonro As A FoRMATToN,Nor A MEMBER THE oF The stratigraphic section at Lamy represents the

stone deposition has long been enigmatic. The Waruaran FonuerroN, Mroolr Junessrc or easternmost outcrops of the Morrison that can be

interbedded sandstones are seemingly structure- NoRTHERNNew Msxrco, by Spencer G. Lucas, correlated with the sequence on the Colorado Pla-

Iess sheet sands that are continuous across the Department of Geology, University of New teau. Forty miles east at Romeroville Gap (T15N,

study area including the area of shelf crest facies Mexico, Albuquerque, NM 87131 R16E) the members of the Morrison that are pres-

in the subjacent carbonate interval. Within a few Gregory (1971) named the Todilto Limestone for ent at Lamy cannot be recognized. However, in

hundred meters of the shelf edge each sandstone outcrops in Todilto Park, New Mexico, and Darton most of east-central New Mexico, the Morrison

interfingers with and abruptly pinches out into the (1928) and others subsequently extended its dis- section is homotaxial with that on the Colorado

reef-proximal shelf facies-. in general, all three tribution across northern New Mexico. Two infor- Plateau. The evidence from Lamy and Romeroville

sandstone intervals are in sharp but conformable mal members of the Todilto have long been indicates that the homotaxial relationship is not

contact with the underlying ca16onateunits except recognized: 1) a basal limestone member that is as the result of depositional continuity of facies across

across the area of shelf-crest facies where the basal much as 13 m of laminated, kerogenic micrite; and central New Mexico.







May 1988 Nao Mexico Geology

Nsw onsrnvnrtoNs coNcERNtNc rnE Junassrc-CnE-

The Colorado Formation (Upper Cretaceous) in Rio Grande and adiacent areas during a period o{

TAcEous BoUNDARy EAST-cENTnal_

tN Ngw Mexco, southwestern New Mexico consists of approxi- near-maximum municipal pumpage. Based on the

by lohn M. Holbrook and Robyn Wright, Depatt- mately 200 m of interbedded shale and sandstone altitude of screened interval, wells were grouped

ment of Geology, University of New Mexico,

and is exposed at several locations in Grant and into shallow (screened interval above an altitude

Albuquerque, NM 87131

Luna Counties. Three informal members have been of 4,800 ft) or deep (screened interval below an

The "basal white sandstone" of the Cretaceous designated in each of eight stratigraphic sections. altitude of 4,800 ft) zones. Ground water in the

(Albian) Mesa Rica Sandstone in the Tucumcari The lower member is cbmposed- of bioturbated, shallow zone generally moves from north to south

Basin is now recognized as a series of localized fossiliferous siltstone, shale, and very fine grained parallel to flow in the Rio Grande. Ground water

fluvial deposits properly belonging to the under- sandstone and was deposited in a shallow marine in the deep zone generally moves from the north-

lying Jurassic Morrison Formation. Previous mis- or prodelta environment. The rniddle member west to the east and southeast. A poorly developed

interpretation of this relationship has resulted in consists of massive or laminated sandstone, shale, cone of depression within the deep zone was pres-

incorrect placement of the J-K boundary through- and laminated and planar tabular-crossbedded ent in the northeast. Water levels in wells were as

out northern exposures in the Tucumcari Basin. sandstone that were deposited in a delta front much as 18 ft higher in the shallow zone than in

Locally, the kaolinitic and feldspathic "basal white environment. The upper'member is composed of the deep zone in the vicinity of the San jose well

sandstone" can be directly corr-elatedto Monison carbonaceous shale and lenticular, trough-cross- field, indicating a downward gradient.

sandstones and shales that underlie the Albian bedded sandstone. Sedimentarv structures and

Tucumcari Shale. In a landward direction, as the lithologies indicate u .ro.r-urirr" depositional

Tucumcari pinches out and the Mesa Rica becomes environment, perhaps within a lower delta plain. LAND SUBSIDENCE THE sourHERN HuEco Bot_sott,

tN

fluvial, distinction of Jurassic and Cretaceous The Colorado-Formation was deposited in the /. Ni and A. H. Smyth, Department of Physics,

sandstones is more problematic. The storv of the southwesternmost part of the Western Interior Geophysics Program, New Mexico State Uni-

J-K boundary is furiher complicated by tie pres- Seaway. Paleocurrent data from delta plain sand- versity, Las Cruces, NM 88003

ence of a previously unrecognized, genetically dis- stones indicate a northeastward paleosiope. Detri- Ground water, leveling and geological data are

tinct sandstone that occurs locally between the tal modes of 22 sandstones implv derivation from used to study present and future land subsidence

Morrison ("basal white sandstone"j and either the sedimentary and volcanic sourc'e rocks that were in the southern Hueco Bolson. As the result of

Tucumcari or Mesa Rica Formation. This clean. probably part of the arc and back-arc orogenic belt 6;round water withdrawal since 19&1, more than

locally bioturbated, quartz arenite was deposited in southern Arizona and northern Mexico. 46 m of water{evel (piezometric surface) decline

in fluvial and marginal marine (estuarinil envi- has occurred in the study area. Consequently, land

ronments that backfilled topographic lows on the subsidence has occurred within the Hueco Bolson

SaNosroNg pETRoLocy AND pRovENANcE oF THE

post-Morrison surface during base-level rise asso- and has been observed in leveling profiles. Before

Sawre Fr Gnour (Or-rcePlnrsroctrvE) w rHr

ciated with the encroaching Tucumcari sea. As yet 1956, the rate of land subsidence was about 1.7

SOUTHWESTERN ALBUQUERQUE BESN, CPN'T,AI NEW

unnamed, we tentatively place this unit as a baial mm/yr. This rate has increased to 7.4 mmlyr in

Mrxco, by Richard P. Lozinsky, Department of

member of the Tucumcari Shale. A possible strati- recent years, in correspondence with an increased

Geoscience, New Mexico Instihrte of Mining and

graphic equivalent in northeastem New Mexico pumping rate. However, the ratio of land subsi-

Technology, Socorro, NM 87801

and southeastem Colorado is the basal sandstone dence to water-level decline has remained con-

member of the Glencairn Shale. The Santa Fe Group of late Oligocene to middle

stant. This value, about 5 x 10 3, determined

Pleistocene age is the major syn-rift deposit of the

empirically from leveling and water well data, is

Rio Grande rift. Santa Fe Group deposits from the

SaNosrolu MEMBERoF LowER Cnrracnous U-Ban low and is consistent with those values deter-

Gabaldon badlands, Bobo Butte arei, and from the

FoRMATtoN tN EAsr PoTRILLoMouNTAlNs, sourH- mined for regions in which the vertical effective

Humble Santa Fe Pacific #1 and Shell Santa Fe

CENTRAL NEw Mrxco, by Donna Couington, Eanth stress has not yet exceeded the preconsolidation

Pacific #2 oil test wells were analyzed to determine

Sciences Department, New Mexico State Uni- stress. Computer modeling of land subsidence gives

sandstone detrital modes and provenance. Most

versity, Las Cruces, NM 88003 similar ratios of land subsidence to water-level

samples are poorly sorted lithic arenites that were

The sandstone member of the Lower Cretaceous decline. Land subsidence outside the area of lev-

deposited in an alluvial-fan/playa complex. Point

U-Bar Formation in the East Potrillo Mountains, eling surveys can be predicted by our model. Based

counts of 34 stained thin sections show an average

south-central New Mexico, ranges from 25 to 66 on historical water withdrawal rates, preconsoli-

composition of 40qa quartz, MTo feldspar, andT6Vo

m thick, and consists of four intervals of coarse dation stress (equivalent to a hvdrauiic head of

lithics. Plagioclaseand monocrystalline quartz are

sandstone and conglomerate interbedded with very about 60 m) couid be exceeded 6y the year 1998

the dominant detrital grains. Lithic grains average

fine gained sandstone and siltstone. Four litho- when the rate of land subsidence iould iise above

92% volcanic,8% sedimentarv, and (1% meta-

facies have been identified: 1) pebble conglomer- the present rate.

morphic in origin. Conglomerite in the Gabaldon

ate, 2) crossbedded to hummocky stratified coarse badlands and Bobo Butte area contains 50-88qo

sandstone, 3) horizontally laminated sandstone. Oligocene ash-flow tuff. Conglomerate in the Bobo FosstL vrRtpnnetEs FRoM THE MENEFEE FonvaloN

and 4) bioturbated fine sindstone and siltstone. Butte area also contains abottt 257o Cretaceous (Cnrractous), SeNooval Coun-ry, Nrw Msxrco,

Each coarse interval consists of up to three stacked mudstone and sandstone. These data indicate that by L. K. Martini, A. P. Hunt, and S. G. Lucas,

sequences of, inascending order, pebble conglom- the source area for the Santa Fe Group deposits Department of Geology, University of New

erate, crossbedded to hummocky stratified iand- contained ash-flow tuff and Cretaceous sedimen- Mexico, Albuquerque, NM 87131

stone, and horizontally laminated sandstone. The tary rocks. Imbricated clasts show a flow direction

gr-ain-size of each coarse interval increases upward. Abundant, but fragmentary, fossils of verte-

eastward away from the Lucero uplift. This sug- brates are present in the Cleary Coal Member of

The fine sandstone and siltstone lithofaciejis pre-

Eests that the Lucero uplift was the source area the Menefee Formation in the Erlz sec. 19, T14N,

dominantly bioturbated although locally horiion- for these deposits. No ash-flow tuffs or Cretaceous

tal laminations and vertical burrows ire found. RlE, Sandoval County. These fossils occur together

sedimentary rocks are now present in the Lucero with petrified wood and shipworm burrows in

Coarsening-upward sequences are present near the uPlift. Thus, sometime in the past, the Lucero uplift

top of this Jithofacies where it undirlies the coarse channel sandstone. The vertebrate fossils repre-

must have contained at least one ash-flow tuff sheet sent a fish, turtles, dinosaurs (ankylosaurs lnd

intervals. The sandstone member is interDreted as and some Cretaceous sedimentary rocks that have

a stacked sequence of offshore sand ridges depos- hadrosaurids), and a pterosaur and are part of the

subsequently been removed by erosion. University of New Mexico (UNM) collection. They

ited in a shallow marine environment. ihe coirse

intervals were deposited on the up-current side of are: 1) a single, large vertebral centrum (LINM tvIV-

Volcanics and general session 2270) of an amiid; 2) carapace fragments of baenid

the ridges; the fine-grained sandstone and silt- Gnouruo-warnn LEVELs AND DIRECTIoN GRouND-

oF (UNM MF-2261) and trionychid (UNM MV-2262,

stone on the down-current side. The presence of WATER FLow IN THE CENTRAL PARToF Brmtartno

hummocky stratification indicates the importance 2267 and, 2268) turtles;3) scute fragments of an

CouNry, Nsw Mlxrco, SurravtR 1983, bv G. E. ankylosaur (UNM MV-2260); 4) the proximal end

of storms in the evolution of the sand ridges, but Kues,Water Resources Division, U.S. Geological

bipolar paleocurrent data suggest an additio;al tidal of a left femur (UNM MV--2259) and edentulous

Survey, Albuquerque, NM 87102 jaw fragments (UNM MV-2263, 2264) of hadro-

influence.

In 1980, toxic chemicals were detected in water saurids; and 5) the proximal end of the right meta-

samples from wells in and nearAlbuquerque's San carpal IV (UNM MV-2269) of a large pterosaur,

Drrosmrorunt ENvIRoNMEt\trs,sEDTMENT DISpERsAL, Jose well field. At the request of Environmental comparable in size to Pteranodon. Stratigraphic

AND PROVENANCE THE UPPENCNITECTOUS Improvement Dvision of the New Mexico Health

OF relationships of the Cleary Coal Member to better

ColonnDo Fonrvlatror,r, sourHwEsrERN NEw and Environment Department, the U.S. Geologi- dated stratigraphic units indicate that the Cleary

Mrroco, by Edward L. Kaczmarek, Earth Sciences cal Survey conducted a study to determine Found- ranges in age from late Santonian to early Cam-

Department, New Mexico State Universitv. Las water levels and flow direction. Water levels were panian. The vertebrates reported here are the first

Cruces, NM 88003 measured in 44 wells in a 64-mi, area along the







Neu Mexia Geology May 7988

identified from the Menefee Formation and one some of the original textures of these rocks, but it QuerenNnnv RHYoLITE MAGMATIsM THE JEMEz

IN

of the few vertebrate faunas of late Santonian- appears that most metasediments are quartzites, MouNTAINS, I. e. Wolff S. D. Balsley'D. C.

by ,

early Campanian age known from NorthAmerica. quartz-rich arkoses, or quartz-intermediate Kuentz,and S. Sef, Department of Geology,Uni-

The pterosaur from the Cleary Coal Member is the subgraywackes. The metasediments contain low versity of Texas atArlington, Arlington, Tx7ffil9,

first pterosaur fossil discovered in New Mexico. concentrations of Fe, Mg, Ti, and Co, a feature and P R. Kyle, GeoscienceDePartrnent, New

characteristic of clastic sediments deposited on or Mexico Institute of Mining and Technology,

PonpuvnonLast MICRoSTRUCTURESINDIcAToRS

As oF near continental crust. Chemical and petrograPhic Socorro, NM 87801

EARLY STRAINEVENTS METAMORPHIC

IN ROCKg_WTTH studies of the sediments indicate a dominantly fel- Petrographic and geochemicalcharacteristics of

EXAMPLES FROMPRECAMBRIAN ROCKS ftIE PICURIS

OF sic plutonic-volcanic provenance with minor mafic rhvolite; erupted from the femez Mountains dur-

RaNcs, ruonruERN NEw Mrxco. by P. W. Bauer, and andesitic input. Sedimentary structures (e.8. ing the past 3 Ma do not suPPort the notion of a

Geoscience Department, New Mexico Institute crossbedding and imbricated pellets) indicate two single long-lived silicic magma chamberbeneath

of Mining and Technology, Socorro, NM 87801 source directions: one dominant source to the north thJVailesialdera. Pre-caldera andesites and dac-

In multiply deformed, medium- to high-grade

contributing major amounts of felsic igneous ites have trace-elementabundancesindicating

metamolphic rocks, tectonite fabrics (fohations and

detritus, a second, less important source contrib- substantial involvement of uPPer crust in Petro-

lineations) are commonly overprinted or obliter-

uting much finer grained indesitic material from genesis. In contrast, the Bandelier grou-pof rhy-

ated by later generations of structures. However,

a southerly direction. These same sedimentary olites (pre-Bandelierignimbrites, Bandelier Tuffs,

in many rocks these earlier fabrics tend to be pre-

structures suggest that the rocks were deposited and Cerro Toledo rhyolites) may be either lower

served as inclusion trails within and adiacent to

in a series of submarine fans by turbidity currents crustal melts or extreme fractionates of mantle-

porphyroblasts such as gamet, staurolite, anda-

in a prorjrnal environment. Coarse-grained arkoses, derived basalts. While the lower Bandelier Tuff

conglomerates, and quartzites may rePresent appearsto rePresenta single variably fr,actionated

lusite, kyanite, and plagioclase. Petrographic anal-

channel-fill deposits associated with the fans. bitth of higtr-silica rhyolite magma similar in many

ysis of such microstructures in and around

Overall, data suggest that the Hembrillo Canyon respectsto the Bishop Tuff of Califomia, the upper

porphyroblasts and megacrysts in metamorphic

rocks provides a method of reconstructing the

succession was deposited in a continental margin Bandelier displays chaotic intemal chemical vari-

back-arc basin. Cdntinental and arc detritus ias ations indicating a complex origin. It may be derived

occurrence and relative timing of fabric-forming

rapidly fed into a tectonically active basin. lnter- in part from remelted lower Bandelier cumulates.

deformational events. Evidence for these early fab-

rics may be indistinguishable at larger scales of

behaeh with the sediments ire intrusive volcanic Howevet the post-upper Bandeliereruptives (Valles

rocks and felsic tuffs. The mafic rocks in the area Rhyolite) mark a retum toward the earlier upper-

observation. In many rocks these porphyroblasts

are derived from a mantle source with a significant crustal-dominated compositions. The most recent

reveal consistent relationships between mineral

growth and deformation. Eaily Proterozoic meta-

subduction-zone component. unit, the El Caiete Seriesrhyolite (El Cajete pum-

ice, Battleship Rock ignimbrite, the Banco Bonito

sedimentary rocks in the Picuris Range of north- Pernolocv AND cEocHEMIsrRYoF LAvAs FRoM THE

lava) is in intemal petrographic disequilibrium; most

em New Mexico contain a variety of well-preserved NoRTHWEST CERRosDELRIo, by K. E. Duncker and

of the "phenocrvsts" are interpreted as derived

porphyroblasts containing inclusion trails. Although l. A. Wolff, Department of Geoiogy, University from a fre-existing igneous body. The F,l Caiete

unambiguous interpretations of the more complex of Texas it Arlington, Arlington, TX76019' P. T.

microstructures in these minerals are rale, they do

Seriesmagma was erupted in the act of being gen-

Lcat,lmpe/ral C5llege, Lon-don, and P. R. Kyle,

history that is

erated by crustal melting. The Quaternary history

indicate a metamorphidkinematic Geoscience Department, New Mexico Institute

of Jemei Mountains magmatism is thus a succes-

more complicated than is apparent from outcrop- of Mining and Technology, Socono, NM 87801

sion of independently generated silicic magma

scale and map-scale structures. They also suSEest Preliminary analysis of geochemical and pet- bodies, some of which were erupted during or

that mineral growth and deformation are some- rographic data from 40 Cerros del Rio lavas.sug- very soon (10-100 ka) after generation.

how interdependent and that relatively short geits the following: 1) spatial distribution of lava

periods of time separated the major strain events.

['pes may support the existence of a tholeiitic shield EvoLL"noN oF THE Posr-BANDELIER MAGMA TUFF

In the Picuris Range, porphy'roblast microstruc- volcano 1o the northwest of the Cerros field; 2)

tures make it possible to integrate anomalous large- quartz phenocrysts found in the lavas are most

sysrEM,VellEs celosne, Nrw Mexco, by T. L.

scale stmctural and stratigraphic relationships into high- Spell and,P. R. KyIe, GeoscienceDePartment,

frobably xenociystic in nature, rather than New Mexico Institute of Mining and Technol-

a coherent picture of a progressive strain history. pressure phases; and 3) crustal contamination

occurred during the evolution of Cerros del Rio

ogy, Socorro, NM 8780-

GEocnsr'.lIsrnv oF THE HEMBRILLoCANYoN succEs- magma. Cerros del Rio samples were collected on The Valles caldera is located near the center of

sroN, STERRA AND DoNA ANn Couvrtes, Ntw the east side of the Rio Grande from Ortiz moun- the femez Mountains volcanic field in north-cen-

MEXrco, by D. E. Alford, Geoscience Depart- tain and Sagebrush flats, and on the west side of tral New Mexico. The caldera was formed at

ment, New Mexico Institute of Mining and Tech- the river from various locations including Frijoles 1.12+0.03 Ma upon eruPtion of the Tshirege

nology, Socorro, NM 87801 and Alamo Canyons. The dominant lava tyPes Member of the BandelierTuff (upper BandelierTuff)

Proterozoic supracrustal rocks in the central San found on the east side are classified as hawaiites and subsequentemPtying of the upper part of a

Andres Mountains, New Mexico are dominated and andesites with interfingering tholeiites. On zoned rhyolitic magma chamber.Theseevents were

by a large volume of metasediments with lesser the west side of the rivet dominant lava types are followedby resurgence,the formation of a central

amounts of mafic metaigneous rocks and minor classified as tholeiites and andesites with minor structural dome, and eruption within the caldera

amounts of felsic volcanic rocks. These rocks are amounts of interfingering hawaiites. The range of of rhyolitic pyroclastic rocks, lava flows, and domes

collectively referred to as the Hembrillo Canyon chemical variation among all the lavas sampled is of the Vall* Rhyolite Formation. The ValleGrande

succession. Metasediments are an imPortant Part large and may confirm thi suggestion that a shield Member, a BrouP of high-siJicarhyolite domes,

of the succession. Felsic metavolcanic rocks are of ,roLtno, whiih tapped a diffe-r"ent source than that composite domes, and flows erupted on or near

local importance in the Hembrillo Canyon area of the Cerros, is buried under Bandelier Tuff to ring fracture vents encircle the caldera and volu-

only. Th! mafic igneous rocks of the area are com- the northwest. Petrographically, the occurrence of meirically dominate the Valles Rhyolite Forma-

mon throughout the succession and have incom- disequilibrium textures in plagioclase megacrysts, tion. These rocks have I(/Ar ages ranging from

oatible element dishibutions characteristic of basalts in addition to the occurrence of quartz xenocrysts 1.18+ 0.03to 0.45+ 0.02Ma and show progressive

erupted in modem volcanic arcs. Incompatible ele- in all rock types, is consistent with contamination changesin both petrographyand chemistrywith

ment distributions in felsic metavolcanic rocks are by a felsic component. Also, in some andesites, time. Phenocryst assemblages includeQtz + San

similar to rhyolites from continental margin arcs olivine is rimmed by opx reaction halos suggesting + Plag + Bio + Mag-Ilm + Zir + FIbl + All +

and associated back-arc basins. Mafic rocks exhibit that the magma was subiected to mixing with a Ap * CPx. In general, phenocryst Percentages

tholeiitic trends and have undergone olivine plus relatively silica-enriched component. Some quartz range from <2 to ,'35 while plagioclaseand Jer-

or minus clinopyroxene fractionation. Depletion found in the lavas has a stiained metamorphic romagnesian rninerals increasein abundance when

of Ta and Nb relative to REE and Th indicate a texture and small, oriented microlites of ruti]e going from older to younger domes' Changesin

significant subduction-zone comPonent in the indicating that the ultimate source for the quartz ihemistrv include enrichmentsof Na, Si, As, Rb,

source. Felsic volcanics have relatively high con- was a me-tamorphic rock. The existence of Nb and Y, Nb, Mo, Sb, Cs, HREE's, Ta, Pb, Th, and U,

tents of heavy REE and high field strength ele- Ta troughs in cliondrite-normalized incompatible- and depletions of Mg, Al, R K, Ca, Ti, Mn, Fe,

ments, a feature characteristic of felsic volcanics elemeni diagrams for the Cerros del Rio lavas is St, Zr, Ba, LREE's, Eu, and Hf with time. Models

from continental rifts and back-arc basins in or consistent w-ith contamination by crustal material. proposed to account for these changesinclude

near continental cmst. The metasedimentary rocks Incompatible-element ratios (Th/Ta and LalYb) profoessive partial melting of a lower cmstalsource,

of the area are composed of quartzites, feldspathic increase with increasing Fe/(Fe + Mg) suggesting ioof rock contamination, silicate{iquid immisci-

quartzites, arkosites, schists, and phyllites with the importance of AIC Processes in the differen- bility, thermal (Soret) fractionation, and crystal-

minor conglomerates. Metamolphism has obscured tiation of these lavas. liquid fractionation involving side-wall crystalli-







May 1988 Nar MexicoGeology

zation. The latter is the favored model here. Mech- Gila Cliff Dwellings cauldron) and occur in several packstone, and shales. Semi-restricted tidal to

anisms proposed to account for reversals in stratigraphic levels (e.9. Bloodgood Canyon and nearshore environments are reflected in local sec-

differentiation trends at < 0.73 Ma and '- 0.51 Ma Railroad Canvon Tuffs separated bv lerkv Moun- tions bv finelv laminated hematitic dolomites,

are eruption of sufficient volumes of magma to tain Rhyolitej. Ail are younger than the'Bursum nodulai shales, ripple-laminated silty lime mud-

disrupt compositional zonation of magma cham- cauldron assemblages; magmatic evolution was stones-wackestones, pelloidal and oncolitic grain-

ber replenishment. undirectional. Apache Spring, Bloodgood Can- stones, sandy limestone conglomerates, and black

yon, and Railroad Canyon Tuffs have not been carbonaceous shales supporting petrified wood

ConngLatroN oF rcNrMBRrrEs usrNc pALEoMAGNETtsM s e e n i n u n e q u i v o c a l s u p e r p o s i t i o n . C u r r e n t float. Depositional onlap farther to the north

AND {AR/3AR DAnNG, by W. C. Mclntosh, New attempts to solve problems by mapping, geochem- resulted in younger and more terrigenous sequence.

Mexico Bureau of Mines and Mineral Resources, istry, radiometric dating, and magnetostratigra- The cyclic nature of these deposits reflects a prox-

Socorro, NM 87801 phy have revealed additional complications but imity to the shoreline and suggests a raPidly shift-

point toward eventual solutrons. ing base level, possibly controlled by Early

Paleomagnetic studies and {Ar/3eAr dating are

Pennsylvanian glacial eustasy and/or tectonic

powerful, reliable techniques for correlation of Oli-

CovposrrroNal FActES THEBLooDcooD CANyoN

oF loading. The time-stratigraphic position of the val-

gocene ignimbrites (ash-flow tuffs) in the Mogo-

Turr, Mocor-loN-DATTL volcANrc FIELD,sourH- ley-fill depositional unit may be broadly correlated

llon-Dati] volcanic field. Accurate correlation of

these regional ignimbrites has previously been WESTERN Nrw Mexco, by S. I. Seaman, Depart- to other Late Mississippian-Early Pennsylvanian

ment of Geology, University of New Mexico, valley-fill sequences recognized in the Delaware

hampered by lithologic variations within units, by

Albuquerque, NM 87131 Basin and Grand Canyon.

the imprecision of conventional li/Ar dating, and

by the discontinuous pattem of outcrops pro- Up to 300 m of Bloodgood Canyon Tuff fills the

duced by Basin and Range faulting. High-preci- Gila Cliff Dwellings basin. An extensive sheet (to LARAMIDEAND TERTIARY OF

STRUCTURES THESALADO

sion {ArfeAr ages of sanidine separates from 21 MouNrens, Stsnre Couvrv, New Mrxtco, by A.

30 m thick) surrounds the basin in isolated out-

Mogollon-Datil ignimbrites range in age from 35.6 crops. Current research is designed to test whether B. Mayer, Department of Earth Sciences, New

to 24.2 Ma and define four brief eruptive intervals the Gila Cliff Dwellings complex represents a cal- Mexico State University, Las Cruces, NM 88003

(35.6 to 33.5 Ma, 32.0 to 31.6 Ma,29.0 to27.4Ma, dera and whether the Bloodgood Canyon Tuff The Salado Mountains make up the southern

and 24.2 Ma). These ages are sufficiently precise originated within the Gila Cliff Dwellings complex half of an east-tilted late Tertiary fault block located

(relative error +0.15 Ma) to uniquely distinguish or within the neighboring Bursum cauldron. Cor- 12 mi west of Truth or Consequences, New Mex-

between units erupted at least 0.3 m.v. apart. The relation between the Bloodgood Canyon Tuff and ico. The oldest rocks exposed are Precambrian

outflow sheets of Mogollon-DatiI ignimbrites typ- the mineralogically similar Railroad Canyon Tuff, metadiorite, muscovite schist, and granite, which

ically exhibit uniform thermoremanent magnetism which occurs north of the Gila Cliff Dwellings basin, are overlain by approximately 2,000 ft of Paleozoic

(TRM) directions/ many of which are sufficiently is unresolved. Analyses from three traverses sedimentary rocks. During Laramide time, the

rlistinctive to unambiguously identify the unit. Thin, through the Bloodgood Canyon Tuff within the southern half of this area was uplifted as a base-

unwelded distal fringes of some regional ignim- basin and numerous analyses from Bloodgood ment-cored block along an east-trending high-angle

brites have been identified paleomagnetically, Canyon Tuff and Railroad Canyon Tuff outside of fault. Drag folding along the trend of this zone

revealing previously unknown overlapping rela- the basin indicate that: 1) essentially no trace-ele- may suggest a component of left-lateral strike-slip

tionships between units from the Mogollon and ment or major-element zonation exists from the movement. This uplift resulted in the gentle dom-

Socono eruptive centers. Magnetic polarity zone base to the top of the Bloodgood Canyon Tuff within ing of the area and the formation of east-trending

boundaries provide valuable time-stratigraphic the basin; 2) Bloodgood Canyon Tuff and Railroad extensional structures to the north of the fault mar-

marker horizons, some of which can be traced Canyon Tuff outside of the Bursum-Gila Cliff gin. An intermediate-composition dike dated at

throughout much of the volcanic field. Uncer- Dwellings complex are generally enriched in Zr, 43.7+1.7 m.y. intrudes the fault zone providing

tainty of structural correction has been the largest Y Sr, and Ba relative to Bloodgood Canyon Tuff an upper time limit for Laramide deformation in

obstacle to paleomagnetic correlation of Mogo- within the basin; 3) preliminary microprobe results this area. Intermediate-comDosition flows and

llon-Datil ignimbrite outflow sheets because TRM indicate that sanidine crystals in distal Bloodgood laharic breccia, and silicic crystal-lithic and lithic

vectors can be rotated bv tectonic movements. Canyon Tuff are enriched in Ba relative to those ash-flow tuffs buried these structures during mid-

Altematively, where units are identified by inde- in basin-filling Bloodgood Canyon Tuff. These Tertiary time. Late Tertiary extensional block

pendent means, the TRM directions can provide results suggest that there may have been at least faulting raised the Salado Mountains at least 1,500

a sensitive, reliable measure of local tectonic rota- two distinct eruptions of Bloodgood Canyon Tuff, ft along a north-northwest-trending, west-dip-

tions in highly extended terrains. The intracauld- and possiblv three if the Railroad Canvon Tuff is ping fault zone and rotated them approximately

ron facies of Mogollon-Datil ignimbrites commonly a disiinct r.r.rit. I.r addition, the predominant geo- 21" to the east. The trend of faults, as well as maior

show nonuniform magnetizations and cannot be graphic separation of "enriched" tuff outside the tensional fractures, indicate a 6. direction of N70E-

easily correlated with outflow facies using paleo- basin and "depleted" tuff within the basin is dif- S70W. This bounding fault cuts Laramide strucst-

maSnerrsm. ficult to explain with an origin of the tuff in an ures. Uplift and erosion of the late Tertiary block

eruptive center other than the Gila Cliff Dwellings has exoosed a stock of intermediate composition

Pnonlsvs oF BLooDGooD CANyoN Turr (Olr- complex. north of the Salado Mountains in the Garcib peaks.

G O C E N E ,M O C O L L O N _ D A T I LV O L C A N I CF | E L D , Smaller scale north-trendine extensional faulti occur

sou-THwESTERN NEW MEXICO):A REvrEw,by W. E. Tectonics and geophysical session on the east side of these mountains.

Elsfon, Department of Geology, University of New TEcroNIcs AND DEpostrtoNAL ENVIRoNMENTS THE lN

Mexico, Albuquerque, NM 87131 Eanlv PTNNsyLvANTANoF Sor.JTH-cENTRAL NEw Flexunal nosrAsy AND THE upLtFT oF THE SANDTA

Bloodgood Canyon Tuff is a quintessential rnoon- MEXrco, by l. F. Knlesky, Earth Sciences Depart- Moururaws, New MExtco, by T. Wallau and C.

stone tuff, i.e., quenched hypersolvus ignimbrite ment, New Mexico State University, Las Cruces, Chase, Department of Geosciences, University

of quartz and iridescent sanidine cryptoperthite NM 88003 of Arizona, Tucson, AZ 85727

(moonstone). With associated lavas (e.g. rhyolites The Pennsylvanian Magdalena Group uncon- The Sandia Mountains are an eastward-tilted fault

of Diablo Range and Jerky Mountains), it plots at formably overlies Precambrian to Mississippian block of Precambrian rocks situated along the east-

the temary minimum of theAb-Or-SiO5HrO sys- strata throughout south-central New Mexico. ern margin of the Rio Grande rift in central New

tem and is interDreted as the evolved end member Regional southward tilting, warping, and erosion Mexico. They are considered a "classical" example

of high-SiO, magmas of the Oligocene "ignimbrite resulted in progressively older pre-Pennsylvanian of tilt-block mountain building but represent an

flare-up." Certain twofeldspar hrffs and lavas (e.g. subcrop relations from south to north. Normal enigma typical of mountain ranges formed in

Apache Spring Tuff and Fanney Rhyolite of Bur- marine shelf sedimentation was represented bv extensional environments. Most of the uplift of the

sum cauldron, Mogollon Mountains) are inter- upward-shoaling rycles containing mixed silici- Sandias has taken place in the last 15 m.v., coin-

preted as less-evolved members of the same system. clastics and carbonates. Channels cut into Ordo- cident with the opening of the Rio Grande rift.

Differing interpretations of field relations result in vician strata in the southem Caballo Mountain area The present elevation and uplift rate are both much

conflicting petrologic schemes: a) All principal suggest that this area was a relatively deep valley higher than that for surrounding terrain. The San-

moonstone tuffs correlate with Bloodgood Canyon or trough during Late Mississippian-Early Penn- dias are too small to be the result of an upper-

Tuff. Although extensive and voluminous, it is sylvanian erosion. Marine transgression from the mantle driving force, nor has there been signifi-

merely the evolved basal zone of Apache Spring south backfilled the pre-existing stream valleys with cant emplacement of Cenozoic magmatic rocks to

Tuff and is overflow from the Bursum cauldron. sequences of quartz arenite, bioclastic grainstone, build a recent crustal root. We propose that the

Less-evolved Fanney Rhyolite is younger, hence pelloidal-algal wackestone and shales. Topograph- uplift of the Sandia Mountains can be explained

there was a reversal in magmatic evolution. b) ically higher areas were blanketed with thin dis- by flexural isostasy. We propose a three part geo-

Moonstone tuffs erupted from several centers (e.g. continuous beds of bioclastic grainstone, laminated







Nm Mexico Geology May 7988

logic history for the Sandias: a) Precambrian mag- of sediment with P : 2.48 km/sec overlying a layer modeled. The best-fit model consists of a thin (z 70

matism resulted in a locally compensated proto- 20 km thick with an average B : 3.43 km/sec. The m) layer of non-rigid, low-velocity material under-

Sandia mountain range. The batholith cooled at a portion of the crust below 22 km was constrained lain by a second, thin (;60 m) layer of slightly

rate higher than the erosional rate, and eventually to a shear-wave velocity of 3.80 km/sec over a man- higher velocity material. This second layer may be

the underlying lithosphere flexurally suppressed tle with B : 4.40 km/sec. The final model was an earlier, partially solidified intrusion or a crys-

the excess mountain root. b) Late Paleozoic and compared to a surface-wave study for the Albu- talline mush at the base of a single magrna cham-

Mesozoic sediments on the top of the Sandias indi- querque-Belen Basin. The general trends of both ber. The resulting magma body is less than 150 m

cate that the Sandias were a low-relief, regional final models were very similar. However, the pro- in total thickness. A body this thin, even at mid-

topographic high until at least mid-Cenozoic times. nounced velocity minimum seen at approximately crustal depths, would need to be replenished often

The low relief is consistent with a flexural thick- 18 km in the Albuquerque-Belen Basin was not to remain in a nonrigid state.

ness of 15 km (or greater). c) The lithospheric apparent on the final model for the path between

thickness of 15 km was intact until approximately the San Agustin Plains and Carrizozo. EcoNorr,lcs oF coAL pRoDUcnoN cycltcrry, wtrH

15 m.y.a. The onset of extension along the Rio spEcrAL REFERENCE NEw MEXTCO,by orin l.

TO

Grande rift resulted in thinning and finally break- ANALYSE oF THE SEISMOCENIC ZoNE IN THECENTRAL Anderson and Donald L. Wolbug, New Mexico

ing the lithosphere along the Sandia and Rincon Rro Gnallop RrFr NEAR Soconno, NEw Msxtco, Bureau of Mines and Mineral Resources, Socorro,

faults allowing the expression of the Precambrian K. M. King, A. R. Sanford, and L. H. lakshn, Geo- NM 87801

root. The Sandias could have a root as thick as 7 science Deoartment and Geoohvsical Research Production statistics compiled during the last 80

km, but because the mountain range is spatially Center, New Mexico Institufe of Mining and years illustrate the fact that annual coal output

small, it does not have a significant Bouguer grav- Technology, Socorro, NM 87801 varies widely within trends that are periodically

ity signature.

Five hundred thirteen well-located microearth- reversed to lend a cyclical nature to the coal indus-

quakes were used in an analysis of focal depths try in New Mexico. Production trends and the

CANoNcno DE r-A,UvA AxrA, SocoRRo Coul"ry, NEw in the central Rio Grande rift near Socorro, New trend reversals have been related to national eco-

MEXco, by K. B. Brown, Geosciences Depart- Mexico. The seismogenic zone extends from nomic factors and political events, but these events

ment, New Mexico Institute of Mining and Tech- approximately 4 to 12 km in depth with more than and factors are ouite different Drior to and follow-

nology, Socorro, NM 87801 60 percent of the events occurring-number 8 and

between ing 1960. Prior tb 1960, the faftors were: the war-

Cafioncito de la Uva, in central Socorro County 12 km. A sharp decrease in the of focal time economy, the Great Depression, and the

on the edge of the Rio Grande rift, has Paleozoic depths below 12 km is interpreted as the rapid sudden appearance of low-cost convenient natural

rocks and later structural features. Pennsylvanian transition from brittle to ductile crust. This essen- gas. Baseline coal demand was provided by the

Burrego, Story, Del Cuerto, and Moya Formations tially normal depth to the seismogenic zone occurs steel and smelting industries, the electric utility

represent marine deposition. Regression and influx in a region where heat flows as high as 490 mW industrv. and the railroads. Since 1960. wartime

of clastic sediments began with Permian Bursum m'z (11.7 HFU) have been observed and where a have not been a factor, the railroad-

deposition and reached a climax as the fluviatile thin magma body is known to exist at a depth of ".onorrii",

steam locomotive market-has disappeared, the

Abo Formation was deposited. Yeso sandstone, approximately 20 km. Several distributions of focal steel industry has been in recession, and electric

limestone, and gypsum indicate a return of marine depths along a profile within the area are bimodal, utilities have grown to completely dominate the

conditions. The marine and nonmarine sediments possibly indicating a semi-ductile zone from 8 to coal market. Within that market framework, coal

are cut and folded by a suite of features suggestive 10 km lying between layers of more brittle crust must compete with other fuels used in steam elec-

of a wrench regime. North-northwest-trending above and below. Relativelv shallow seismicitv, tric generation. Affecting total coal usage and com-

folds with eastward vergence, north-northwest- with focat depths occurring piedominantly between petitiveness are: 1) the declining U.S. industrial

striking high-angle reverse faults, and northeast- 4 and 8 km, exists approximately 25 km north of base; 2) current low petroleum prices; 3) moder-

striking apparently strike-slip faults indicate a Socorro near the apex of a region of surface uplift. ation in rate of growth of electrical consumption

transpressive regime of north-northeast, right-lat- A previous study of a major swarm in this region in the residential sector; and 4) recent completion

eral displacement, with east-northeast-directed found some rnicroearthouakes whose first motions of nuclear generating stations. In a more extended

comoression. Other fold axes trend northeast- were compressive in allbut 10 to 25 percent of the time frame, Federal coal leasing policy is also of

ward, and suggest a separate period of transpres- focal sphere, implying that these earthquakes may signficance to the coal industry. The dedining U.S.

sion with northeast displacement and southeast- be related to injection of magma, steam, or hot industrial base has not impacted the New Mexico

directed compression. Thrust faults and over- water. coal industry directly although it has had an impact

turned strata ?urther north in the Los Pinos sup- on other mining ventures. Of greater importance

port transpressional hypotheses. Small northweit- INIERNAL STRUCTURE THE SOCORRO

oF MAGMABODY to the state's coal industry have been recent events

trending grabens and extension of the Abo For- D E D U C E DF R O M M I C R O E A R T H Q U A KP . P H E S P

E in the uranium-nuclear fuel cycle industry: 1) the

mation along northerly faults show transtension REFLEcrIoNs, l. P. Ake and A. R. Sanford, Geo'

by disappearance of the uranium mining and milling

has also affected the area. Absolute dating of these science Department and Geophysical Research activities that were large consumers of the state's

events in the Cafroncito de la Uva area has not Center, New Mexico Institute of Mining and coal-generated electric power, and 2) the comple-

been possible because Tertiary volcanics and sed- Technology, Socorro, NM 87801 tion of the Palo Verde nuclear generating station

iments are not present in the area. Similarity to near Phoenix. Moreover, these two events out-

An earlier work comparing the gross character-

Laramide-age compression to the north and south weigh the threats to coal usage posed by low

istics of P- and S-phase reflections indicated that

suggests this deformation is also of Laramide age. petroleum-natural gas prices because electric util-

rapid lateral variations occur in the internal struc-

ities in New Mexico and the mountain states have

ture of the Socorro magma body southwest of

AVERAGE CRUSTAL SHEAR-WAVE VELOCITIES

FROMTHE low fuel-switching capabilities.

Socorro. The present study analyzed the structure

Plaws op Sar AcusrrN To CARRrzozo, NEw of the body ai that location by breaking the prop-

Mrxco urrlrzrNc FUNDAMEN'IAL-MoDE RAYLEICH agation path effects into two parts: upper-crustaU MINERALIZATTON, ALTERATIONAND IGNEOUS ACTIVITY

WAVES, K. K. Hostettler and /. W Schlue, Geo-

by IN THE FLoRIDA MOUNTaTNS,SOTJTHWESTERN NEW

near-surface effects and mid-crustaymagma-body

science Department and Geophysical Research interaction effects. The upper-crustal and near- MEXCo, by Russell E. Clemons, Department of

Centet New Mexico Institute of Mining and surface effects have been approximated by the ini- Earth Sciences, New Mexico State University,

Technology, Socorro, NM 87801 tial portion of the direct P-phase due to the favor- Las Cruces, NM 88003

The shear-wave (B) velocity structure was able geometry of source, reflector, and receiver Manganese, barite, and fluorite have been mined

obtained for a great-cfucle path across the Rio Grande and the small magnitudes of the swarm events and prospected in the Little Florida Mountains.

rift (San Agustin Plains to Carrizozo, New Mexico) used in the analysis. Synthetic seismograms, which Mineral deposits in the Big Florida Mountains

from the linear inversion of phase-velocity data included attenuation and interbed multiples, were include manganese, barite, fluorite, zinc, lead,

acquired from NTSexplosionSERENA. The model calculated and compared to the observed P-phase coppet silvet and gold. Mineralized veins in the

was composed of 12 perfectly elastic, homogene- reflections. The moieling results indicate thlt the Little Florida Mountains are in post-23.6-m.v.-old

ous, isotropic, horizontal layers over an infinite magma body is better approximated by a twoJayer rocks. Veins and oxidized replacement depoiits in

half-space. Initial model parameters, i.e. shear- structure, a thin layer of full-melt underlain by a the Big Florida Mountains are mostly in early

wave velocities, were based upon refraction stud- crystalline mush, than by a singleJayer model. Paleozoic carbonate and alkalic plutonic rocks. A

ies in the region. Due to the limited bandwidth of The layer thicknesses vary by small, but resolvable few veins are in faulted Eocene rocks. Propylitic

the data, velocities below 22 km were not allowed amounts over the '-500 m distance covered by the alteration is pervasive in Tertiary volcanic brec-

to vary significantly during the inversion. Of the reflection points. To determine an "average" struc- cias, and conspicuous epidote coats fractures of

12 initial velocities, only 3 distinct velocity regions ture for the magma body in this area, the stacked these and older rocks in the Florida Mountains.

were obtained. The final model consisted of 2 km spectrum of the observed P-phase reflections was Argillic alteration has significantly changed the







May 1988 Nao MexicoGeology

alkalic syenites throughout the central Florida ico. Gold-bearing quartz veins, found throughout determining mineral distribution, observing tex-

Mountains. Source of Eocene volcaniclastics is the district, are most numerous in the central part. tures and structures, among others. CL studies are

unknown, but andesitic sills and dikes intruded The majority of these veins occur along diabase especially useful in examining carbonatites and

into them indicate post-early Eocene igneous activity dikes that strike N40"W to N, and dip 20'-60'. associated fenitization. Carbonatites are unique

in the Florida Mountains. Fanglomerates shed from Host rocks are upper amphibolite-grade supra- carbonate-rich rocks of apparent magmatic descent

23.6-m.y.-old rhyolites in the Little Florida Moun- crustals of the Bullard Peak Series (minimum age and are characterized by a distinct but variable

tains were lithified and faulted preceding miner- 1550 m.a.), Burro Mountain granite (f450 m.a.), mineralogy, composition, and associated altera-

alizalien. A dacitic volcanic vent in the southeastem and diorite and quartz monzonite of unknown age. tion (fenitization). The Lemitar carbonatites exhibit

Little Florida Mountains is believed to coincide Diabase dikes are not foliated, but some are brighFred CL that is characteristic of carbonatites

with this stage of mineralization. Several small intenselv fractured parallel to strike. Nearlv ver- elsewhere in the world. The bright-red luminesc-

intrusions of finely crystalline adamellite in the Big tical bas'altic and rhyolitic dikes, striking NOO"Eto ence is due to compositional variations in fine-

Florida Mountains, although of unknown age, E, crosscut the diabase dikes. Quartz veins along grained carbonate minerals, predominantly calcite

intrude small Laramide thrust sheets. Litholog- basaltic and rhyolitic dikes are nearly barren of and dolomite. Apatite luminesces blue to green-

ically identical rocks intrude middle Oligocene vol- mineralization. Veins range up to a meter in width, gray to gray and is typically zoned. Magnetite

canic rocks in the Mimbres Basin near Deming. but most are less than quartz, minor pyrite, and occasionally exhibits CL zoning not observed using

An adamellite batholith Drobablv underlies the Fe-Mn oxides. Oxidized vein material, found almost optical microscopy. Examination with the electron

Florida Mountains and nbrtheasiern part of the exclusively on dumps, has a gossan texture and rnicroprobe reveals the zoning is caused by com-

Mimbres Basin. The dacite plug in thesoutheast- consists of Fe-Mn oxides and quartz. Values of plex intergrowths of magnetite, ilmenite, rutile and./

ern Little Florida Mountains represents a surficial unoxidized veins range up to 0.37 oz Auiton and or leucoxene, calcite, and quartz. Fenitization is

venting of this magma during early to middle Mio- up to 0.90 oz Aglton. Nearly all hosFrock Au and the alkalic metasomatic alteration adiacent to car-

cene time. Penecontemporaneously hypabyssal Ag values are below detection limits (10 ppb and bonatites and alkalic rocks. ln the Lemitar Moun-

adamellite intruded the Paleozoic and Cenozoic 5 ppm, respectively). Mineralization has been dated tains, unaltered country rocks exhibit less intense

roof rocks in the Florida Mountain-Deming area. as earlv Cenozoic and mav be related to Laramide luminescence when exposed to CL than carbon-

Associated hydrothermal pneumatolytic fluids intrusive activity in the regron. atites and fenites. K-feldspars are typically blue to

formed the ore deposits and extensive alteration. white or gray, or do not luminesce in unaltered

rocks, whereas they luminesce brown or red in

SceNNnrc ELECTRoN MtcRoscopy oF AUTHIGENTC fenites, probably due to replacement by carbonate

IN

ZEOLITES VOLCANICLASTIC SEDIMENTARY ROCKS and/or activation of ferric iron, rare-earth ele-

Gnolocy AND oRE DEposrrs oF THE sourHERN SAN

FRoMNEw MEXco, by Mark R. Boaie, New Mex- ments, and manganese. Apatites luminesce yel-

MerEo MouNTAlNs, SocoRRo CouNry, NEw

ico Bureau of Mines and Mineral Resources, low to green in unaltered and slightly fenitized

MExtco, by Eugene W. Cox, Consulting Geolo-

Socorro, NM 87801 rocks and luminesce blue to green-gray to gray in

gist, Socorro Engineering, P.O. Box F, Socorro,

NM 87801, Michael L. Hermann, Exploration Authigenic zeolite mineralization in volcaniclas- highly fenitized rocks. Slightly fenitized rocks

Geologist, 5001 Northern Trail NW, Albuquer- tic sedimentary rocks is widespread where rhyo- exhibit veins of red-luminescing carbonate along

que, NM 87720, and Cortney E. Hesse, Explora- litic ash was deposited in basins in the western grain boundaries, within fractures, and replacing

tion Geologist, P.O. Box 571, Socorro, NM 87801 United States. The zeolites are diagenetic altera- chlorite, feldspar, and hornblende. Highly feni-

tion products of the reaction between saline, and tized rocks exhibit bright-red luminescent matrix

The San Mateo Mountains of south-central

usually alkaline, fluids with vitric ash or clay min- with relict feldspars (replaced by carbonate).

Socorro County are located within the Mogollon-

erals. The most common zeolites identified in sed-

Datil volcanic field of southwestern New Mexico.

imentary rocks in New Mexico are clinoptilolite,

A thick sequence of Tertiary-aged tuffs, lavas, and Truessrc srRATrcRApHy, Canruacs AREA, SocoRRo

chabazite, erionite, mordenite, and analcime. Cli-

associated volcaniclastic and sedimentary rocks in Courury, Nsw Mrxco AND THE sourHEAsrERN-

noptilolite is by far the most abundant zeolite and

the southem San Mateo Mountains is exposed in MOSTOUTCROPS THEMOENKOPT

OF FONVATTON. bV

is present in all known zeolite occurrences in the

large tilted fault blocks surrounded by alluvial fans, Adrian P. Hunt and SpencerG. Lucas,Departmeit

state. The others are comparativelv restricted in

low-relief pedimented bedrock surfaces, and scat- of Geology, University of New Mexiio, Albu-

distribution. Authigenic zeolites aie very micro-

tered exposures of pre-Tertiary basement rocks. querque, NM 87f31

crystalline, which makes their examination by

Repeated volcanotectonic activity in the area has

ordinary light microscopy difficult. The scanning Triassic strata in the Carthage area (T5S, R2E)

produced complex stratigraphic and structural

electron microscope is an ideal tool for the study are 163 m of redbeds that rest disconformably on

relationships. Tertiary (Oligocene) rock units of

of these minerals; sample preparation is easy and Permian strata and are disconformablv overlain bv

the southern San Mateo Mountains include the

the instrument provides great depth of field. The a thin sequence of the Upper Jurassic Morrison

Red Rock Ranch Formation (up to 1000 m thick),

form, habit, degree of crystallinity, size, and spa- Formation. Three principal Triassic units can be

Rock Spring Formation (up to 1200 m thick), La

tial and paragenetic relationships of the constit- recognized here: 1) a basal unit that is 15.7 m of

Jencia Tuff (0-25 m thick), Vicks Peak Tuff (300- dorninantly moderate reddish-brown mudstone and

uent minerals can be studied without disrupting

1t100m thick), tuff unit of Turkey Springs (60-120

the sample. Scanning electron microscopy reveals sandstone/conglomerate; 2) a middle unit that is

m thick), tuff unit of Milliken Park (0-60 m thick),

that clinoptilolite occurs as subhedral to euhedral, 6.0 m of moderate reddish-brown conglomeratic

and interbedded lavas including the Springtime

coffin-shaped, monoclinic laths and plates up to sandstone in which clasts are mostly extraforma-

Canyon quartz latite (0-180 m thick). Mafic, inter-

several micrometers in length, either isolated or tional cher! and 3) an upper unit of 141 m dom-

mediate, and felsic intrusive rocks are locally

in clusters. Chabazite crystals are subhedral to inated by moderate reddish-brown and grayish-

exposed along fault systems in the area. Ore

euhedral "cubes" or "rhombs" up to a few microm- red mudstone with thin intraformational conglom-

deposits of the southern San Mateo Mountains

eters on a side. They are typically intergrown, erates and sandstones in its upper half. The basal

occur within distinct host rocks. Gold-silver min-

forming clusters or radial stringers a few microm- unit has been called Santa Rosa Sandstone but is

eralization located in the San Jose mining district

eters long. Erionite and mordenite, often difficult better termed Moenkopi Formation because of its

is hosted by Vicks Peak Tuff within fracture zones,

to differentiate based on morphology alone, occur lithologic similarity to Moenkopi outcrops on the

hydrothermal breccias, and quartz veins. Silver-

as thin fibers or needles tens of micrometers in Sevilleta Grant northeast of Socorro. Furthermore,

gold base-metal deposits in the Diggins prospect

length. Analcime is very distinctive, occurring as typical strata of Santa Rosa in Guadalupe County,

area occur in mineralized tuffs and lavas of the

cubo-octahedral and trapezohedral crystals com- New Mexico, are intensively crossbedded quartz-

Rock Spring Formation and crosscutting intrusive

monly 100 micrometers in diameter. arenites and are quite distinct lithologically from

rocks. Gold mineralization is associated with late-

the basal Triassic unit near Carthage. The Moen-

phase felsic intrusive rocks, fracture systems, and

kopi outcrops in the Carthage area are the south-

alteration zones that are discemible in classified A cernoDclLurrarNEscENcEsruDy oF THE LEMITAR eastemmost outcroDs of this formation. The middle

satellite imagery. CARBONATITES AND ASSOCIATED FENITIZATION, unit near Carthage arguably is homotaxial with the

Soconno CouNrv, New Msxrco, Virginia T. Shinarump Member of the Chinle Formation on

Mckmore, New Mexico Bureau of Mines and the Colorido Plateau, and the upper unit is equiv-

Got-o-sEARtNc euARTz vEINs oF THE CENTRAL IART Mineral Resources, Socorro, NM 87801 alent to the lower Petrified Forest Member of the

OF THEGOLD HILL IrrlvIvc DISTRICT, HIoeIco eNo Cathodoluminescence (CL) is the characteristic Chinle. These stratigraphic assignments are sup-

Gnavr Cour.mns, NEw MEXco, by Robert D. Beard, visible radiation (color) produced in a mineral sub- ported by iithologic resemblances, stratigraphic

Department of Geology, University of New

iected to bombardment of electrons. Many fea- position, regional stratigraphic relationships, and

Mexico, Albuquerque, NM 87131 tures of a sample are observed under CL that are fossils. Fossils from the upper unit near Carthage

The Gold Hill mining district is located approx- not seen using standard optical petrography. pertain to phytosaurs and metoposaurid labyrin-

imately 20 km northeast of Lordsburg, New Mex- Applications of CL include mineral identification, thodonts, indicative of a late Triassic age. tr







Neu Merico Geology May 1988