Geology of the Espinaso Formation (Oligocene), North-Central New Mexico

Geology of the Espinaso Formation (Oligocene), north-central New Mexico

P. F: KAUTZ' Oil Conservation Commission, P.O. Box 4980, Hobbs, New Mexico 88240 R. V. INGERSOLL Department of Geology, University of New Mexico, Altiuquerque, New Mexico 87131 W. S. BALDRIDGE Geosciences Division, MS 978. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 P. 'E. DAMON Laboratory of Isotope Geochemistry, Department of Geosciences, University of Arizona,

, M:SHAFIOULIAH Tucson, Arizona 8572 1 'Prewnt nddress: Oil Conservation Commiss;on. P. 0. Box 1980. Hobbs. New Mexico 88240

The Geological Society of America Bulletin, Part II, v. 92, p. 2318-2400, 22 figs., 8 tables, December, 1981, Doc. no. M11208

central New Mexico (Fig. 1). INTRODUCTION Exposures of the Espinaso occur as

The Espinaso Formation (Oligocene) isolated outcrops near. the Cerrillos

primarily consists of 430 m U€ water- Hills, Galisteo Creek and Santa Fe

laid, immature, volcaniclastic sandstones River, and in the Hagan basin. The

conglomerates, and bounder conglomerates largest and least deformed exposure.

interbedded with matrix-supported pebble of the formation crops out in,the , KO boulder conglomerates that represent type area along Espiriaso Ridge within

debris-flow deposits. Isolated occur- the Hagan basin (Figs. 1,2). -Espinaso . rences of poorly welded, lithic- to Ridge is the principle area of study

crystal-rich deposits with pumic swarms for this investigation.

represent pyroclastic-flow deposits. The The purpose of this investigation -

geographic position, lithologic simi- was: to develop a better understanding

larity with respect to intrusive rocks, of the depositional history of the

'coarseness of sediments, and lithofacies Espinaso and geologic events of the

types suggest that. the Espinaso was Oligocene' in north-central New Mexico.

deposited by alluvial fans which radiated Therefore, this study was designed to

from magmatic centers in the Ortiz Moun- analyze stratigraphic, petrologic,

tains and Cerrillos Hills of north- and paleocurrent .data and to integrate 2318

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Figure 1. Location map of Espinaso Ridge, Hagan basin,

Cerrillos Hills, Ortiz Mountains, and other features in

('s'ludy area.

Figure 1 appears on the following frame.

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3JC

Figure 1.

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Figure 2. View looking north toward end of BsBinaso Ridge, Hagan basili.

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these data into the broader,tectonic PliEVIOUS WORK history.

Stratigraphic work included detailed Early work on what later became

mapping along Espinaso Kidge at a scale known as the Espinaso Formation was

of 1:12,000. U.S. Geological Survey primarily of a reconnaissance nature,

7 7 1/2-minute7 1:24,000 topographic maps with empdasis on the related intrusive

of the Hagan and San Fclipc Pueblo NE rocks and associated ore dcposits of

quadrangles were enlarged and used for the Cerrillos Hi1 1s and Ortizkoun-

base maps. Stratigraphic sections were tains. Johnson (1902, 1903 a,b,c) ' I measured at six locations along Espinaso mapped and described a portion of the

Ridge. Petrographic data were .obtained Espinaso as part of a broader study

from ober 40 thin sections. These data of the Cerrillos Hills.

were supplemented by chcnical analyses &yan and Upson (undated) first

of fou'r flows and clasts and four K-Ar ' described and named what they called

dates. Palcocurrent directions were the "Espinaso Volcanics" in an unpub-

determined by dip azimuths of imbricated lished manuscript (Stearns, 1943). .\ clasts, from azimuths of long axes of The formation name was published for

matrix-supported clasts, from azimuths the firs; time in a description of the

of channel axes, jx6d from dip azimuths of underlying Galisteo Formation and

crossbeds. described in a reconnaissance study

All of the above detailed data-and (Stearns, 1943, 1953a). Stearns (per-

maps may be found in Kautz (1981); from sonal communs., 1979, 1981) summarizes

which most ~f this paper is taken. how the Espinaso Volcanics and thc

Preliminary results have been presented Espinaso Ridge were named:

orally (Kautz and Ingersoll, 1981). "The conspicuous hogback between

the Tonque and Snnto Doming0 valleys .I a

' was named Espinaso de Clotero Montoya

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(also known as Pinovctito Ridge) by Stoll (1957) described the Espinaso

Bryan for Sr. Clotero Montoya who lived Formation and associated intrusive

at the northern end of the ridge. Bryan rocks in their study of the "Geology

named the Espinaso Volcanics for the rela- of the Cerrillos Area." They con-

tively.. resistant rocks of Espinaso de cluded that, during Espinaso time, Clotero Montoya. Ihen I did my areal there were four major periods of

studies in 1939-1941, local residents in igneous activity in the area. Sun

the Hagan basin used the name'Pinovetito and Baldwin (1958) subdivided the

Ridge, and Arroyo Pinovetito For the Espinaso in the Cienega area into an

gulch which cuts through the south end andesite'breccia-unit, a calcic-

(Arroyo del Tuerto on 1954 topographic latite unit, and a glassy-latite

map). It seemed best to retain the name unit. Other geologic mapping includes

Espinaso (de Clotero Plontoya) for the the Madrid 30-minute quadrange, the

ridge and Pinovetito for the arroyo." GaJisteo 7 1/2-minute quadrangle,

Later workers have used the name Albuquerque basin, and Espnnola basin

"Espinaso Volcani cs ,", However, the (Bachman, 1975; Johnson, 1975;

majority of the formation consists OF Kelley, 1977,' 1978). Related studies

sedimentary rocks. Therefore, the term include det-,Led investigations of

"Espinaso Formation" was adopted by * the underlying Galisteo Formation

Bachman (1975) and Baltz (1978); this (Gorham, 1979; Corham and Ingersoll,

terminology is used in the present report. 1979).

Additional references to the Espinaso Several workers have obtained K-Ar

can be. found in regional studies. Anderson dates of the Espinaso and related .C \ (1960) and Harrison (1949) mapped and intrusives. Weber (1971) dated horn-

described portions of Espinaso Ridge in blende from porphyritic-latitc cobbles

regional studies of the Hagan c09l basin from a conglomerate in Arroyo del

and the Santo Domingo basin. Disbrow and Tuerto. Latite intrusives of the

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Cerrillos Hills and Ortiz Mohntains lotcst Cretaceous -to Eocene time

were dated by Bachman and Mehne% (1978). (Woodward, 1974). The Oligocene

Baldridge and others (1980) reported new history of the area is closely related

K-Ar dates in their study of the central to the San Pedro-Ortiz porphyry belt.

Rio Grande rift. The Rio Grande rift and related

provinces of the Hagan basin or embay- TECTONIC SETTING ment, the Jemez volcanic field, and

.For most of New Nexico, three major the Sandia uplift formed during the

stages of structural and rectonic evolu- Neogene (BaYtz, 1978).

tion are recognized for,the Cenozoic. Laramide tectonic activity in north-

These include the Laramide orogeny central Aew Flexico was characterized

(Paleocene-Eocene) , mid-Tertiary inter- by basemmt uplifts associated with

mediate to silicic volcanism (Oligocene), adjacent sedimentary basins (Baltz,

and Neogene (Miocene to Holocene) bimodal 1978 ; Woodward, 1974 ; Woodward and

volcanism and extension (Baltz, 1978; Ingersoll, 1979). These basins filled

Chapin, 1979; Chapjn and Seager, 1975; rapidly with synorogenic fluvial and

Dickinson, 1979; Lucas and Ingersoll, lacustrine sediments. These events

1981; Seager, 1975; Woodward and Ingersoll are recorded in the Hagan basin by

1979). fluvial sediments of the Galisteo for- - The principal tectonic features of mation, which were derived mainly from

north-central New Mexico are the southern the Nacimiento and Sangre de _cr.i.stp

Rocky Mountains, Rio Grande rift, Jemez uplifts (Gorham, 1979; Gorham and Inger-

volcanic field, Sandia uplift, and San soll, 197%.

Pedro-Ortiz porphyry belt (Fig. 3). The'Laramide orogeny has been inter-

The San Juan basin, Nacimiento uplift, preted as the tesult of progressive

and Sangre de Cristo uplift began to flattening of the Subducted Farallon

form during the Laramide drogeny of plate from 80 m.y. B.P. (Lat'e

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106'

35:

Figure 3. Hajor tectonic features of north-central New Mexico

(after Woodward, 1974).

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Cretaceous) until 40 m.y. B.P. (Eocene) grade sweep of arc volcanism (Coney,

(Coney, 1978; Dickinson and Snyder, 1978). 1978; Coney and Reynolds, 1977; Keith,

Laramide deformation can be explained by 1978; Stewart and oxhers, 1977). From

plate descent at abnormally shallow angle 49 m.y. B.P. to PO m.y. B.P., the dip

with subhorizontal interaction beneath the of the subducted slab increased to nor-

overriding plate (Dickinson and Snyder, mal values (Dickinson, 1979). As the

1978(, which failed by deep-seated basement slab dip increased, arc magmatism

shear. A magmatic null (Damon and others, swept westward from central New Elexico

1964) resulted from the flattened slab,. toward the continental margin.

Beginning at approximately the Eocene- By the Eliocene, regional stresses

Oligocene boundary, volcanic activity had changed from compressional to pre- occurred in ..che San Juan Mountains in dominantly tensional as rifting Colorado, the Cerillos-Ortiz-San Pedro began with the formation of broad basins,

centefs, and the Datil-MogoLlon volcanic grabens, and tilted fault blocks

field in Xcw Mexico (Fig. 4). These (Kelley, 1977). The Sandia uplift

eruptions, which formed widespread and Jemez volcanic fields formed con- <. breccia complexes and alluvial aprons, temporaneously with rifting (Baltz,

are generally latite to andesite in com- 1978; Kelley and Northrop, 1975). In

position (Balt?, 1978; Chapin and Seager, the Hagan area, synorogenic rift-related

. .l- 1975). In north-central New Mexico, sediments of the Santa Fe' Group (Oligo-

this activity is represented by the cene through Pliocene-) unconformably

Espinaso Formation and associated in- overlie the Espinaso (Kelley and North-

trusives of the Cienega area, Cerrillos rop, 1975). Extensional tectonics and

Hills, Ortiz Elountains, San Pedro Moun- a growing tendency toward bimodal vol-

tains (Fig. 5). canism began at approximately the same

The mid-Tertiary magmatic episode time in both the Rio Graride rift and the

(Oligocene) can be related to the retro- Basin and Range province, soon after

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Figure 4. Paleotectonic and paleogeographic sketch

map of the cordilleran region 30 m.y. B.P. (Oligqcene)

(after DLckinson, 1979).

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166. C Volcanic contor and * intrusivo bodies.- 0 Lor Alomor

0 ! Modrid

Bmrncdillo

Figure 5. Flap of north-central New Mexico showhg probable area

of deposition of the Espinaso Formatibn and associated mqgktic

centers during the Oligocene (after Baltz, 1978).

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,first interaction between the Pacific and of vertebrate fossils designated the '

North American plates and initiation of Tonque local fauna by Lucas and Kues .

the San Andreas transform at approximatel) (1979). Pterodon, Uintacyon, Teleodus

'39 m.y. B.P. (Atwater, 1970; Dickinson, uintensis, Forstercooperia, and Poabro- \ r 19.79; Woodward add Ingersoll, 1979). mylus have been identified from the

Renewed.extensiona1 deformation of the Tonque local fauna, and their presence

'late Miocene to.Pliocene age resulted in indicates that the uppermost Galisteo

the narrow grabens of the modern Rio. is Duchesnean (late Eocenc) in age

.Grande rift (Baldridge and others, 1980; (Lucas and Kues, 1979). They concluded

Manley and Mehnert, 1981). that there is no fossil evidence to

indicate an Oligocene age for the AGE' OF .THE ESPINASO FORMATION uppermost Galisteo.

There are no previous reports of Latitic and monzonitic intrusive

fossils being found in the. Espinaso For- rocks are exposed in a north-south

. mat-ion. During the ptesent study, minor line of hills including La Cienega,

' amounts of petrified wood (2 to 50 cm in Cerrillos Hills, Ortiz Mountains, San

length) were found throughout the' forma- Pedro Mountains, and South Mountain

tion. No specific identification of the (Fig. 5). Plutons in these magmatic

.wbod has been attempted. centers were intruded contemporaneously

Stearns (1943) found abundant disarticu with deposition of alluvial sediments

lated bones in Arroyo del Tuerto ,(also of the Espinaso (Disbrow, 1953;

known as Arroyo Pinovetito), in a limey Stearns, 1953a). Bachman and Mehnert

mudstone bed within 'the transitional zone (1978) published K-Ar dates of 47 2

between the Galisteo and Espimso forma- 3.2 m.y. for a latithntrusive from

tions. This deposit and stratigraphically the southern part of Cerrillos Hills

equivalent deposits on Sweet's Ranch north. and 34.0 2 2.2 m.y. for a latite sill

eas.t of Cerrillos contain an assemblage on the west side of Ortiz Mountains.

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They imply that the Cerillos Hills sample La Cienega areas (Fig\ 1). An andesite

is probably contaminated by inclusions. flow from Arroyo Hondo dates at 29.3

Also, they suggest that a date of 34 m.y. -+ 0.6 m.y. In the Cienega area, they

is more representative of the age of reported K-Ar dates of 30.2 _+ 0.7 m.y.

intrusions in the Cerrillos Hills and for an augite monzonite intrusive,

Ortiz Mountains. and 25.8 -+ 0.9 and 25.94 0.6 m.y.

.Jaffe and others (1959). reported lead- for the cnlcic-latite unit (Fig. 6).

alpha ages of 32, 35, 46, and 46 m.y. for Their glassy-latite unit originally

a stock in the Cerrillos Hills. These was called part of the Espinaso Fbrma-

ages are similar to those of Bachman and tion by Stearns (1953a). However,

Mchnert (19789 ; contamination [by common this unit (19.6 -+ 0.6 and 19.5 5 0.5

(nonradiogenic) lead] also may be the m.y.) is much younger than the rocks

explanation' for 'the older dates for these in the type area. Therefore, the

samples. glassy-latite unit should be redefined

Weber (1971) reported hornblende dates as a separate formation, possibly part

from cobbles of latite porphyry from a con of the Santa Fe Group.

glomerate ibterbedded with volcaniclastic In this study, four samples were col-

sandstone in Arroyo del Tuerto at 36.9 5 Lfcted for K-Ar dating in order to

1.2 my. This sample is approximately establish the age range of the Espinaso .w 250 m above the base of the Espinaso Formation in its type area (Table 1).

(this section is approximately 430 m A date of 34.6 5 0.7 m.;.. on a block of

'thick) near the top of the middle con- calcic quartz latite within a lahar

glomerate and sandstone member (see- deposit (Sample ESP-4) (359) indicates

be low). a maximum possible age lor deposition

Baldridge and Athers (19%) have of the lahar unit. This sample is

repor.ted K-Ar dates for the Espinbso nsar the base of the U lr,cg member

Foriation in the Arroyo Hondo and and is approximately 200 m above the

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SANTO ESPA~OLA BASIN DOMINGC BASIN SERIES SOUTHEASTERN

TESUOUE FM

20 MY* MIOC E NE SANTA FE ' GROUP

I* C22Z

A ESPINASO 30MYa ESPINASO FM 011 GOC EN€

.---? --

GALISTEO F GALISTEO FM EOCENE 40MY=

A K-Ar dates Baldridge and others (1980) . y New K-Ar dates

Figure 6. Correlation chart and K-Ar dates of upper

Eocene to lower Miocene formations 0.f north-central

NCW Mexico,

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TABLE 1. ANALYTICAL DAT~K-AR DATES, SAMPLE DESCRIPTIONS AND LOCALITIES

Sample Rock type Sample description and location No.

~ ~~ ~~ UAKA Nepheline Flow in Espinaeo Fm. approximately 300 m 81-07 Latite aboveBase.. From northern part of Espinaso (344, Ridge, 35 25,.97'Nr, 106 20.06'W. ESP-1, S-87)

I UAKA 01 ivine Flow just Gbove base of Santa Fe Group,. 81-08 ' Tholeiite northern part of Espinaso Ridge, 35 26.30tN, (357, 106 20.24 '.W. ESP-2, S-117)

UAKA Calcic Clast from coniIom2iatic sandstone 10 m 81-09 Latite above base of Espinaso,Fm.,Arroyo del (358, Tuerto, 35 22-99", 106 18.81'W. ESP-3 S-118)

UAKA Calcic Quartz Block from debris-flow unit, approx. 200 m 81-10 La t i te above base of Espinaso Fm.,35 21.48'N, (359 106 17.66'W. ESP-4, s-119)

-10 -1 -10 -1. Constants X =4.963 x 10 yr ; Xe= 0.581 x 10-lOyt'l; A= 5:544 x 10 yr B *. , 40K/K = 1.167 x 10'4 atom/atom

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TABLE 1. (COn?%Ued)

L- / -_ 40 K-analysis IOGENIC Ar Percent atmospheric Age in Individual Mean ar~on-40 r 10-12rn/g E.Iillion x Individual Mean of %K Individual Mean Analysis Years . Analyses 5.655 5.633 261.8 “264.5 14.7 15.1 . 2 6.95.6 5.672 262.4 15.1 5.614 261.2 15.5 5.593 275.1 25.0 259.3 14.9 267.2 15.1

0.7288 0.7277 31.77 31.86 51.4 51.2 25.15.6 0.7274 31.94 * 51.1 0.7268

0.9444 0.9435 56.84 56.68 15.2 15.5 34.35. a 0.9426 56.70 15.5 0.9414 56.50 15.9 0.9456

1.261 1.248 76.49 75.6; 16.9 17.6 34.6s. 7 1.232 74.91 18.2

1.238 ‘ 75.02 17.9 1.260 76.27 17.5

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base of the Espinaso (see below). (latest Oligocene) (Van Couvering,

A calcic-latite .cobble (SampJc ESP-3) 1978).

(358) from a conglomeratic sandstone in The radiometric data indicate' that

Arroyo del Taerto 10 m above the lower the Espinaa ,formation spans most of

conpact of the Espinaso dates at 34.3 2 the Oligocene and that the base of

0.8 m.y. This indicates a maximum possibl the Santa Fe Group in this area is

age of depositionLfor the conglomeratic lapest .Oligocene in' age.

sandstone bed. The,combined paleontologic LXTE EOCENE TO EARLY MOCENE REGIONAL and radiometric data indicate that the VOLCANISM lower contact of the Espinaso is near

the Eocene-Oligocene 'boundary (38 m.y. From late Eocene and extending through'

B.P.) (Van Couvering, 1978). There is out most of the Oligocene, volcanic

approximately 12 m of Galisteo sandstone activity occurred at discrete centers

and mudstone above the limey-mudstone frop north-central Cobrado to south-

fossil beds discussed by Lucas and Kucs western New blexico (F&. 4). In

(1979).. This allows the possibility north-central Colorado,. the volcanic

Chat the top of the Galisteo may be Oligo- activity included the Specimen Nountain

cene,.although the data are inconclusive. volcanics'of the Specimen-Lulu-Iron

In the uppcr Espinaso, 100 m below Mountain area and the Rabbit Ears vol-

the contact with the Santa Fe Group, a canics of the Middle Park area (Corbett,

/ nephelineLlat ite flow (uv, Sample ESP 1968) (Fig. 7). In south-central Colo-

-1) (344) dates at 26.9 2 0.6 m.y. The rado and ad2acent parts of New Mexico,

Santa Fe includes a small olivine-tholei- a large composite volcanic field

ite flow (Sample ESP-2 (357), 2 m above probably existed which includes the

contact ,with the Espinaso), which dates a San Juan, West Elk, Thirtynine Mile and 25.1 5 0.6 m.y. Therefore, the upper con- Silver Cliff-Rosita Hills volcanic

tact of the Espinaso is 26 to 25 m..y. old fields (Steven and Epis, 1968). In

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Figure 7. Correlation chart pf.upper Eocene to lower /' Miocene formaiions of Colorado and New Mexicd. , Figure 7 appears on the following frames.

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n 3 5 I WGAN 8ASI JEW MEXU NEW MEXICO SERIES \ Elslm and @hem This ~eport (197% I

W* 4

W Gila Conglorneratw Sonlo Fe GIOIJD Santo k Lo1 Pmo1 m Group

W Z Volcanic W and 0 30 Volmniclortlc Eipinoio Fm Eipinaro Fm 0 units (3

Coneior Fm

Bqra tin Gahstco Fm El Rilo Fm

0 W I Loromide Anderilea. 1 .----- I !

Figure 7.

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Figure 7. (Continued)

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the remainder of New Mexico, volcanic magmatic types: olivine nephelinite,

activity primarily is represented by olivine tholeiite, alkali olivine

the Espinaso Formation and associated basalt, and quartz tholeiite.

intrusives of north-central New Mexico b!i d e 1y s c a t t e red int e rme d i a t e to

and, in southwest New Mexico, by vol- silicic volcanism occurred within and

canics and sediments of the Datil-Mogollor peripheral to the Rio Grandc rift fol-.

volchnic field (for example, Elston and lowing the end of major Oligocene

others, 1968, 1976b). activity. This volcanism is repre-

Late Eocene to early Oligocene volcaniz sented by the glassy-latite unit in

of this region was mainly andesite to the Cienega area, quartz latite upper

latite in com$osition, with some rhyolite member in the eastern San Juan mun-

(Elston and others, 1976a; Epis and tains, the Upper Andesite of the I Chapin, 1968; Lipman and others, 1970; Thirtynine Mile volcanic field, and

Siems, 1968). Volcanism during middle the lavas interbedded in the Popotosa \ and late Oligocene ranged from basaltic Formation in the Socorro-Magdalena

andesite to rhyolite. However, the com- area (Fig. 7). This also suggests

position of the Espindso was mainly lthat the klassy-latite unit at La

latitic with some- andesite throughout the Cienega should be redefined as a sepa-

Oligocene. rate formation from the Espinaso.

Widespread intermediate and silicic The oldest volcanic rocks of the

volcanism ended about 26 m.y. B.P. (Fig. Jemez Mountains are the volcanic and

7). In the central 'Rio Grande rift, mafic intrusive rocks of the Bland'district.

and ultramafic volcanism began abruptly These volcanics cohsist of basaltic,

at 25 m.y. B.P. (latest Oligocene) andesitic, and dacitic flows and

.(Baldridge and others, 1980). This mafic stocks of monzonite and grandiorite

and ultramafic volcanism was volumetri- (Kelley, 1978; Smith and others, 1970).

cally minor and included a variety of Smith and others (1970) correlated the

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by Jaffe and others (1959) indicate that zone is thickest (15 m) in Arroyo del

part of the Bland district volcanics Tuerto and consists of red and green

might be the same age as the glassy-latite mudstone at the base and sandstone at

unit at La Cienega. the top. North and south of Arroyo

del Tuerto, the transitional zone STRATIGRAPHY AND SEDIMENTOLOGY varies from 3 to 5 m and consists Regional Relations entirely of sandstone. The sandstone The Espinaso Formation overlies the I of the transitional zone usually Eocene Galisteo Formation (Steams, 1953a) is horizontally stratified, moderately

In the Hagan basin and the Cienega area, to poorly sorted, medium- to coarse-

the Espinaso appears conformable and grained pebbly sandstone. It grades

gradational with the underlying Galisteo. upward into pure volcaniclastic

Near thc associated intrusive rocks of sandstone. The clcsts consist of

the Cerrillos Hills, the Espinaso uncon- well-rounded pebbles of quartzite

formably overlies the Galisteo (Disbrow, and chert with subangular pebbles and

1953). This relationship is angular cobbles of volcanic rocks. The propor- close to the intrusive .and chan f es to a tion of quartzite and chert commonly disconformity Ifarther cast. East of the decreases upward relative to vol-

Cerrillos Hills, near Ortiz and Kennedy canic clasts.

(Fig. l), the Espinaso is locally uncon- The Espinaso is overlain uncomform-

formable with the underlying Galisteo ably by tippermost Oligocene to T4olo-

(Stearns, 1953a). cene stata. In the Hagan basin, the

In the Hagan basin and the Cienega Santa Fe Group (prTmarily Etiocene-

areas, the lower contact is placed at the Pliocene) and the Tuerto Gravels (Plio-

top pf the transitional Jone between the cene or Pleistocene) overlie the I

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Espinaso (Kelley, 1977). The contact the Ingersoll, 1979).

Expinaso and the Santa Fe Group is. The Galisteo consists of inte_rbedded

slightly angular to disconformable. The variegated mudstone, sandstone, and

I Sjmta Fe Group here has been called Zia conglomerate deposited in .floodplains

and Abiquiu by other workers. Additional and fluvial channels within a rapidly

work is needed to resolve this uncertaint) subs'iding basin (Gorham and Ingersoll,

Near La Cienega and east of the Cerrillos 1979). These sediments were derived

Hills, the flat-lying conglomerates of from Laramide uplifts of the Sangre

the Pliocene or Pleistocene Ancha Forma- de Cristo and Nacimiento mountains.

Lion (Johnson, 1975; Sun and Baldwin, Santa Fe Group. In the Hagan area

1958) overlie gently to moderately dipping the Santa Fe Group conformably to dis-

beds .of the Espinaso. conformably overlies the Espinaso

Formation (Kelley and Northrop, 11)75). Stratigraphy of Other Units It is overlain unconformably by the

Galisteo Formation. The Galisteo For-' Tuerto Gravel, Quaternary .pediment

mation (Eocene) unconformably overlies deposits. and valley alluvium.

Cretaceous strata of the Mes9verde Group The Santa Fe Group consists of,tan,

and th&Mancos Formation (Gorham, 1979). pink and orange-buff arkosic sand-

In the Hagan area, it rests on the Mesa- stones interbedded with red and green

verde Group with a slight angular uncon- mudstone. The base contains lenticular

formity. The Galisteo is overlain con- ' conglomeratic sandstones. The con-

formably and gradationally by the Espi- glomeratic sandstones contain pebbles .

naso Formation. However, in other loca- ^of quartzite, chert, and porphyritic '

tions, it is overlain unconfonably by the latite. [See Gawne (1981) for details

Sante Fe Group and younger strata. "In of the Zia Sand Formation at other 4 the Hagan basin, thickness of the Calisteo -locations; the Zia probably is, in

ranges from 261 to 129'; m (Gorham and part, correlative with basal Santa Fe

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strata in the Hagan basin. The Abiquiu with an aphanitic groundmass with

Formation (Vazzana and Ingersol, 1981) phenocrysts of olivine, and prominept

is another correlative unit. ] secondary malachite, azurite, and

Near the northern part of Espinaso calcite filling vesicles and lining

Ridge, an olivine-tholeiite flow is inter- fractures. The flow is up to 4 m

bedded in' the Santa Fe Group, 2 m above thick,

the contact with the Espinaso. This flow Younger Cenozoic Units.. Three

is correlated with the Cieneguilla younger units overlie and/or intrude

Limbprgite of the Cienega area, on the the Galisteo, Espinaso, and Santa / basis of chemistry and K-Ar dates. The Fe in the Hagan area: the Huerfano

Cieneguilla Limburgite consists of Butte Basalt (and associated dikes),

olivine-nephelinite and olivine-tholeiite the Tuerto Gravel (which overlies the

flows. The chemical analysis of sample Ortiz erosion surface of Bryan (1938),

ESP 2 (357) is similar to some units of and pediment gravels. Kautz (1981)

the Limburgite (Table 2). Sample 142 andaearns (1953a,b) discuss these

of Sun and Baldwin (1958) is an olivine units in more detail.

tholeiite, which is somewhat lower in General Description of the Espinaso SiO and higher in normative olivine 2 Format ion than sample ESP.2 (357) (Table 2).

Baldridge and others (1980) 'report a date The lower Espinaso is character-

of 25.1 2 0.7 m.y. for an olivine ized 'by bluish-gray sandstones,

nephelinite from the Limburgite. The showing horiz-ontal stratification

age of the flow interbedded in the basal and rare planar and trough cross-

Santa Fe Group is 25.15 0.6 m.y. bedding, interbedded with thin lensese

(Table 1). of conglomeratic sandstone. The olivine tholeiite is charac2 er- The middle Espinaso primarily con- istically black, dense to vesicular, sists of horizontally s,tratified, gray.

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Sample 357* Sample 142t

sio2 50.06 47.52 Ti02 1.56 1.69 14.35 14.61 A1203 2.07 2.30 Fe203§ FeO 9.40 10.48 8.08 9.121 MgO t CaO 10.50 9.80 MnO 0.08 0.20 Na20 2.92 2.58 '(20 0.77 0.89 0.24 0.29 '2'5 Total 100.03 99.48

Orthoclase 4.56 5.31 Albite 26.27 23.37 Anor thite 23.82 25.82 Nepheline 0.00 0.00 Diopside 21.44 17.02 'L Hypersthene 8.10 3.67 Olivine 10.97 19.40 Magnetite 2.17 2.43 Ilmeni t e 2.18 2.37 Apatite 0.50 0.61

. *This analysis was obtained 'following techniques of Bfldridge (1979).

+Sun and Baldwin (1958). Recalculated on volatile-free basis.

§Fe203 calculated from Fe 0 /FeO = 0.22. 23

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to yellbwish brown conglomerates showing eratic sandstone (L ss,css); a middle

both normal and reverse grading. Channel- conglomerate and sandstone (M cg,ss);

fill deposits of conglomerates are common a middle lahaf: assemblage and con-

fhe conglomerates are overlain by a glomerate (>I lr,cg); an upper lava

sequence .of debris-f tow deposits, pyro- flow (Vv); an upper, lnhar assem-

clastic-flow units, and conglomerates blage,and conglomerate (U lr,cg); and

of the upper Espinaso. Thsmean clast ah upper conglomerate and sandstone

size of, he previously described units (U dg9-1

shows an overall upQ&r&warseniiig mega- Lower Sandstone and Conglomeratic

sequepce .- Sandstsnc (I, ss,css). Theewest

The uppermost Espinaso consists of member of the Espinaso consists'of

boulder conglonperates that grade 'upward bluish-gray volcqnickistic sandstones

to cobble conglomerates interbedded with interbedded with lenses of conglomer-

sandstones. 1n.these units, the mean atic sandstone. It is upcposed in

clast size displays ,an upward-fining- moderate to .steep slopes along the

megasequence. western base of Espinaso Ridge. .. On

many slope:; it is covered by vegcta- .Espinaso Members , tion and debr,i's from the overlying

The members of the Espingso described bl CR,SS. and it. is observe4 bestdn

by Steams (1953a;p. 422) in the the numerous arroyos which dissect

Arroyo del Tuerto (Arroyo Pinovetito,) the western' side .of the ridge. It

area are recognized easily along EsGinaso is 49 'm thick-in Arroyo del Tuerto

Ridge (Figs. 8, 9). ' However, .for' and thins northward to 42 .m and .south-

0 / Y. mapp;ng purposes, in this study, @* ward to 36 rn (Fig. 9). The L ss,css

Fxpihaso is divided into six members; is conformable and gragat,ional with

"he litho'logic 'rnernbeis of the Espinaso the underlyi'ng &list6oi Formation,. The

4 .. include : a loder sandstone -and conglon- lbwer. coqtact is placed ab the dowest

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STEARNS (19530) THIS REPORT

UNIT

UNIT m

M cg,ss

M Ir;cg,

I UNIT H"

I UNIT I' Transitional ' Zone' I . GALISTEO ' FM.

Figure 8. >Stratigraph$ norncnclature of # < ?r Espinaso Format ion along '&.pinas0 Ridge.

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I Montop Secliod

2 ArroyoSecllon dd Tuerlo *22 30' 3 ArroyoSection Tonque

M CQ ss 4 Arroyo Coyole SeCl'On 1 hlOOm SO m 1Om

Figure 9. Schemat'itc .cross section along Espinaso Ridge, showing Espinasomembers.

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occurrence of totally volcanic detritus. beds. The pebbles and cobbles are

The upper contact is characterized by an usually randomly oriented, but

abrupt change to conglomerates o€ the locally, they arc imbricated. Saod-

M cg,ss. stones are composed of subangular to

The L ss,oss is characterized by' subrounded feldspar (60%) and lithic

sheet-like lenticular sandstones and fragments (40%); they are slightly

conglomeratic sandstones. The beds are to moderately cemented by calcium carbo-

lenticG,lar t ransvcrse to paleocurrent nate and clay.

directions and sheet-like parallel. to The.conglomeratic- sandstone lenses

paleoflow directiork. Locally, there are matrix supported with a polymodal

are some isolated conglomerates filling site distribution. Clasts range in

paleochannelq. This ccmber is generally size upward to 0.8 m. They are usually

well bedded; thickness of beds ranges randomly oriented, but in some loca-

from 0.1 to 4 m. Individual Sandstone tions, they are imbricated. The l and cbnglomeratic s'andstlone beds usually clasts are rounded to subangular an4

display upward-fining sequences. The are predominantly andesitic to latitic.

conglomeratic layers in L ss,csS overall Locally, some minbr quartzite pebbles

exhibi t an upward coarsening megasequence (less than 1%) occur near the top of - of mean maximum clast size. L- ss,css.

Sandstone units are dominahtly medium The sandstones and conglomeratic

to coarse grained and locally contain sandstones of the L ss,css are inter-

basal pebbly or cobbly layers that preted as sheet-braided alluvium

grade upward to nedium-grained sandstone deposited by 4 network of braided

at the top. Sandstones are poorly to streams. Poorly sorted, horizontally

moderately sorted and _predominantly stratified coarse sanqstones probably < Horizontally stratif'ied. Locally, there represent deposition i,n longitudinal

are pbnar and trough-cross-stratified bars (for examp:&, Smith, 1970).

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Horizontally stratified sandstones indi- ridge (Fig.' 9). The lower contact ,' cate currents in either lower or upper of the'member i.$ characterized by

flow regimes (Miall, 1978). The t.rough; channeling and scburifi3,into the

and planar-crossbedded sandstones may L ss,css. The upper contact is repre-

represent dunes, transverse bars, or sented by an abrupt change to a

sandwaves formed by currents in the lower sequence of lahar, deposits :, 'The

flow regime. These characteristics, most complete exposures of% c4,ss

along with the sheet-like lenticular are Yound in Arroyo del Tueto and

layers of sandstones and conglomerates, Arroyc) Tonquc.

suggest sheet-flood deposits of alluvial The Ei cg,ss member is character-

fans (Collinson, 1978; Reineck, and Singh, ' ized by abundant conglomerates inter-

1980). The L ss,css is also similar' bedded with' lenticular saridstone beds,

to the "Bijou Creek type" braided-stream finely laminated mudstone; and some I,

deposits of Miall (1978) (Fig. 10). This isolated debris-flow dLposits. Con- t type is characteristic of high-energy flak glomerates filling paleochannels are

conditions and environments dominadcd by common in

flash floods. *Arroyo del Tuerto, thc predominant

Middle Conglomerate and Sandstone facies is clast-suppdrted conglomer- c 01 cg,ss). The overlying member consists at%; howeve.r, north of the Arroyo,

of gray to yellowish b'rown volcaniclastic. the M cg,ss grades from clast-supported

conglomerates and sandstones (Fig.. 11). conglomerates at the base, to sand-.

South of *Arroyo del Tuerto, it is inter- matrix-supported' conglomerates and

bedded with the wedge-shdped Fl lr, cg. , sandstones in the middle, with clast-

The member is 215 m thick in Arroyo del supported conglomerates at the top.

Tuerto and thins to 187 m south of Arioyo Individual beds show upward-fining

Tonque. ' IL attains a maximum thickness sequences. Overall, there are several

of 258 m along the northern part of the upward coarsening-megasequences of

SP minor- superimposed debris-f low channel, . Sh deposits deposits Sr Sh I superimposedflood bar-edge ,cycles sand wedge

debris-f low deposit 'stream- f low i channel deposits ti f 51 super imposed bars 0'i

Figure 10. Vertical-profile models for braided-stream deposits. Arrows show small-scale

cyclic sequences. 'Conglomerate' clasts are not shown to scale. Sr = very fine to coarse .- sand with rippi'es; Gms ,= massive\' matrix-supported gravel (debris-flow deposits) ; "4 Gm = massive, horizontall$ bedded, imbricated gravel; Fm = mud; St = trough-crosssbedded,

medium. to pebbly sand; Sp = planar-cross-bedded, medium to pebbly sa-nd; Sh = horizon.tally

laminated, very fine to pebbly sand; Gt = troygh-cross-bedded, s&atified gravel.. .. 7 [At'ter 'l'able 1 and Figure 1 of Miall (1978).]

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Figure 11. Typical interbedded conglomerates and sandstoncs of I.! cg,cc

member (Arroyo del Tuerto). Largest clast (lower right foreground) is

approximately 30 cm in diameter.

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mean maximum clast size. . (35%). Near the top of the M cg,ss,

Conglomerates of the msare main11 massive sandstones locally are inter-

horizontally bedded, polymodal,. and clast- bedded with'finely laminated sand-

supported. Some appear massive where stones and mudstones..

bedding' has a uniform texture. Conglom- . The depositional environment of

erates showing either normal or reverse M cg,ss is interpreted to have been

grading are common. Horizontally strati- braided streams similar to the "Scott

.fietl conglomerates commonly are imbricatec type" (Miall, 1978) (Fig. 10). The

with the a-axis transverse to flow and "Scott type" braided stream is 0 the b-axis dipping upstream (for example characteristic of proximal braided

Walker., 1975). Clast size ranges' from streams'and alluvial fans where con-

2 nun to 1.6 m in diameter; maximum clast glomerate is the predom'inant facies.

size increases southward from Arroyo del This interpretation is based on the

Tuerto. Clasts consist predominantly of dominance of horizontally stratified,

subrounded to angular porphyritif latite. imbricated conglomerates i nterbedded

Some clasts appear to have been shaped with planar- and trough-crossbedded

by columnar; jointjs in' lava flows in their sandstones and finely laminated mud-

source areas. Locally, some quartzite stone. The horizontally stratified

pebbles occur neGr the base and top of conglome ratys probably represent longi-

Fl. cg ,-ss . tudinal bars. Planar-crossbedded

Sandstone-units comprise fine- to . sandstones may 'represent transverse

coarse-grained, poorly to 'well sorted, bars or sandwaves, and trough-cross-

subangular grains. 'They are usually hori- bedded sandstones may'reprcsent duqes b zontally stratified, but .trough and planar (for example, Yiall, .1978). Laterally

crossbedding is common, Sandstones are continuous mudstone is interpreted to

composed of feldspar (60% to 657$, horn- be overbank flood deposits.

blende (0 to 5X) aqd lithic fragments

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~~ ~

I.liddle Lahar Assemblage and Conglomer- ranging in size from coarse sand to

ate (M lr,cg). The M lr,cg is an assem- mud. Clasts commonly are randomly

blage of yellowish brown, gray, and reddi: oriented. Upper surfaces of these

gray lenticular lahar deposits. with inter- deposits are usually irregular, with

bedded conglomerates, sandstones, and boulders protruding from the top of

some pyroclastic-flow deposits. This each. bed. , In some deposits, the clasts b member has a variable thickness and is a are inversely graded near the bo'ttom

wedge-shaped lens within the M C~,SS. It of the unit and poorly but normally

pinches out 0.5 km north of Arroyo del graded in 'the middle. The clasts pre-

Tuerto (Fig. 9). In Arroyo del Tuerto, dominantly consist of gray to reddish

it is 14.5 in thick. The lower contact is gray porphyritic latite;

placed at the lowest occurrence of a Thf clast-supported boulder -conglomer-

sequence of lahar deposits near the base ates are mainly horizontally bedded and

'I of the M cg,ss. Its-upper contact is polymodal. Clasts are angular to sub-

placed at the highest occurrence of the rounded and rang? from cobbles to

lahar sequence. boulders, 1.0 m in diameter. Boulders

This member is composed of matrix- make up 10% to 50% of the clasts.

supported pebble to boulder conglomerates Locally, the cobbles show imbrication. ,I interbedded with clast-supported boulder The py;oclastic-flow deposits usually

conglomerates, conglomerates and sand- are confined to paleochannels. The

stones -of the M cg,ss, and isolated deposits are pinkish gray, partially

pyroclastic-flow deposits. welded, crystal-rich ash-flow dep.osits.

Matrix-supported conglomerates are Lithic fragments usually are angular

massive and poorly sorted. CLas-ts are and inversely graded near the base and ,. angular to svbrounded and range%p to 3 m normally graded in the center. These

in maximum dimension. They commonly are deposits are characterized by pumice

supported by a poorly sorted mqtrix swarms near the top of .each unit.

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'Ihe matrix-supported conglomerates are related to eruptions may form by

interpreted as lahar deposits. The terin failure of natural dams or by flash

lahar is used in this report as a desig- floods due to increased runoff

nation for mudflows and debris flows associated- with the accumulation of

that originated on the slopes of a volcanc a mantle of ash on the upper slopes

(Bullar, 1976; Crandell, 1971; Harris, of volcanoes. Lahhrs unrela'ted to

1980). This interpretation is based on volcanism occur when the :combination

the following characteristics of debris- of the fo1,lowing conditions ocdurs:

flow deposits: matris supported, lack of (1) a debris source, (2)'adequatd

internal stratification, poor sorting, , moisture, and (3) steep slope. The

and coarseness '(Bull, 1972; Crandell, 1971 association of byroclastic-f low

Hiall, 1978). deposits with the lahar deposits sug- I Crandell (1971) recognized three gests-that the lahars may be directly

general categoties of lahar flows: those or indirectly related to eruptions.

that are (1) directly related to, and The clast-supported conglomerates

immediate results of, eruptions; (2) in- of the M lr,cg member ake in,terpre-

directly related to eruptions; and ted to be p?oximal braided-stream '

(3) not related in any way to specific depo+ts of alluvial fans. This

volcanic activity., Lahars may result interpretation is based on their simi-

directly from eruptions by the emptying larity to the conglomerates of the

of crater lakes, incorporation of water M cg,ss. into- avalanches, or catastrophic mel'ting Upper Lava Flow (u).A reddish of snow or ice by hot ash: In Indonesia,' brown lava flow (0 to 12 m thick)

eiplosive activity on Kelut Volcano crops out at the northern end of Espi-

periodically ejects water. from its -rater naso Ridge at the 'top of the M cg,ss

lake, resulting in the 'formation of mud- member (Fig+?). Stearns (1953a)

flows (Bullard, 1976). Lahars 'indir;ectly interpreted these exposures as two

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~~~ ~ ~ ~~

trachyte flows, 3 to 15 m thick.. Andersoi members. It is 55 m thick in Arroyo

(1960) classified them as basalt flows. del Tuerto and thickens southward to

Detailed mapping reveals that the exposurt 152 m, 1 km south of Arroyo Tonque, I represent one lava flow offset by several (Fig. 9). The lower. contact is charac- \ faults (Kautz, 1981). . terized by an abrupt change fromlcon-

The base of the lava flow fills small glomerates to a sequence of lahar.

channels in the underlying M cg,ss. The deposits. The member's upper contact

top of the flow is re.latively flat. In is placed at the highest occ.urrence of .* handspeqimen , this flow is reddish lahar deposits.

brown and slightly vesicular and, contains This member is characterized by

phenocrysts of hornblende and plagioclase .. bluish-gray, pinkish-gray, and yellowish- inanaphanitic groundmass. Whole-rock brown matrix-supported , cobble- to-boulder'

analysis of this flow indicates that this conglomerates associated with pyroclas-

rock is a nepheline latite (Table 33. tic-flow deposits and interbedded with

The petrology of this flow contrasts clast-supported conglomerates and sand-

with that of the majority of clasts in stones.

the Espinaso. However, two channel-fill The matrix-supported conglomerates

.deposits of conglomerates at the top of occur as an assemblange of two or more

the M cg,ss consist of clasts similar . beds interbedded with clast-supported

to the flow. conglomerates (Fig. 12). The 'lasts

Upper Lahar.Assemblage and Conglom- consist of angular to subrounded

erate (U 1r;cg). Deposits of the U lr,cg porphyritic latite ranging in size'

consist of a'sequence of lahar deposits, from cobbles to boulders, commonly i conglomerates, sandstones, a'nd pyroclastic- up to "2 m,dn diameter. Beds n6ar the

flow deposits. This member occurs along top of the U lr,cg contain angular

the length of Espinaso Ridge and inter- megaclasts that range up to 6 m in

tongues with the M cg,ss and U cg,ss, maximum dimension. Clasts are supported

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TABLE 3. COMPOSITION (WT. Z) AND BARTH-NIGCLI CATION NORMS (CATION 2) OF NEPHELINE LATITE FLOW (U- lv)

Sample 344*

sio2 57.96

Ti02 0 :40

21.41 A1203 Fe 0 -t 0.68 23 FeO 3.ii

MgO 0.78

CaO 2.45

MnO 0.19

Na 0 5.87 2 6.73 K2° 0.08 '2'5 Total 99.66

Corundum 0.22' .Orthoclase 38.81 Albite 31.91 Anorthite 11.36 Nepheline 11.73 Olivine 4.57 Magnetite 0.69 I lmenit e 0.54 Apatite 0.16

*This analysis was obtained following techniques of Baldridge (1979).

tFe203 calculated Fe 0 /FeO 0 0.22. from 23

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Figure 12. Coakc conglomerate (cg) (clast-supported) overlain by lahor

deposit (lr) (matrix-supported) from U h,cg member (Arroyo del Tuerto). The

lahar deposit is approximately 2 m thick.

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by a matrix of poorly sor.,ted sandstone. predominantly horizontally strati-

Flatrix ranges in size from mud to coarse fied. Generally, clasts show no

sand. There are two types of deposits. preferred orientation, although r The first type is characterized by angular ‘locally, they are imbricated. The

blocks with no preferred orientation sup- clasts generally are well sorted in

ported ida%n unstratified matrix’. The the middle part of the member.

second type is characterized by inversely . However, locally, they are vp-y

graded blocks with a high concentration , poofly sorted and have variable size

of boulders at the top, which are sup- . distributions where they are associ-

ported in an unstratified matrix. . ated with lahars. Overall, the

The pyroclastic-flow depositx usually clasts of this member show an upward-

are confined to paleochannels. Most coarsening megasequence.

paleochannels,contain one flow unit; Physical characteristics of the

however, one paleochannel in Arroyo Tonque mat r ix-s up po r ted conglomerates indi-

contains 5 flow units (Fig. 13). The cate that they were deposited as

deposits consist of pinkish gray to brown, lahars. The association of lahar

partially welded, lithic- to crystal-rich . deposits ‘with pyroclastic-flow deposits

latite clasts.. The lithic fragments are suggests that the lahars may be

usually inversely graded near the base directly or indirectly related to

and normally graded in the center of the eruptions in the Cerrillos Hills and

deposit (Fig. 14). Pumice fragments Ortiz Mountains. In the U lr,cg, some

are inversely graded from base to top, lahays fill paleochannels that have

probably due to their low density. Beds been cut into pyroclastic-flow

usually contain pumice swarms aE the top deposits. Where channeling into

of each flow near the center of the paleo- the pyroclastic-flow deposits has not

channel. occurred, flows are overlain by fluvial

Clast-supported conglomerates are conglomerates. Hooke (1967) recognized

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Figure 13. A. Sequence of five pyroclastfc-flow deposits filling a paleochannel in U Zr,cg member (Arroyo Tonque) .

B. Close-up of A. Note white pumice swarm near top of each

flow.

Figure 13 appears on the following frame.

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Figure 13.

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j Figure 14. Pyroclastic-flow deposit (approxgmately 5 m thick) within

U Zr,cg member (Arroyo del Tuerto). Pumice clasts are inversely graded

frs bottom to top, with high concentration at top (ligh colored). Lithi'c

clasts are inversely graded near base and normally graded near center. L. L. - -- thin, white, ash-fall deposits occur at base.

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gravels. Proportions de'plend on the stream deposits, as we11 as primary

availability of readily' weathered detritus braided-stream deposits.

in the source area. The accumulatioh of The above characteristics suggest

ash on the upper flanks of a volcano can that the U lr,cg was deposited in a

result in crcute change-s in the hydrologic braided-stream environment similar

regime of streams (Waldron, 1967). Waldro to the "Trollheiy type" (Miall, 1978)

reports in his study of Irazu Volcano (Fig. 10). The "Trollheim type"

that the mantle of ash not only destroyed braided stream is characteristic of

much of the vegetation, but also that a proximal streams of alluvial fans sub-

chin, impermeab,le crust formed on the ject to debris flows.

surface of the.ash. Runoff produced Upper Conglomerate and Sandstone

torrents of fiash~floods and debris florrs. (U cg,ss). The Ilppt-rmost member in

The scouring and dndercutting of valley the Espinaso consists of gray to yellow-

walls and the removal of debris along ish brown volcaniclastic conglomerates

valley floors by flash floods have been and sandstones. The member is 86 m

shown to form debris flows (for example, thick in Arroyo del Tuerto and thins

Beaty, 1963, 1970; Blissenbach, 1954; northward to 49 m (Fig. 9). South of

Crandell, 1971; Sharp and Nobles, 1953; Arroyo del Tuerto, the top of the

Varnes, 1978; Waldron, 1967). Espinaso is covered by vegetation

The horizontally stratified, well- and detritus. The lower contact of

sorted, clast-supported conglomerates the U cg,ssisinterbedded with the

probably represent longitudinal bars of u Ir,cg member. The upper contact is

proximal braided streams (for example, represented by an abrupt change to a

Hiall, 1978). The poorly sorted, clast- sequence of quartzose arkosic sand-

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stones and conglomeratic sandstones of energy braided streams near the base.

the Santa Fe Group. The introduction of finer-grained

The U cg,ss member is characterized sandstones suggests a lowcr-energy

by abundant boulder conglomerates at the depbsitional environment near the end

base which grade upward into pebble and of Espinaso time. The upward-fining

cobble conglomerates interbedded with megasequence suggests a elecrease of

lenticular sandstones near the top of paleoslopc and lowering of: relie'f in

the member. Individual beds show upward- the source area.

fining sequences. Overall, dhis member PALEOCURFSNTS displays an upward-fining megasequence of Methods mean maximum clast size.

Conglomerates of the U cp,ss are.mainlj Paleocurrent directions were deter-

horizontally bedded, polymodal, and clast- mined at 116 localities along Espinaso

supported. Quite commonly, they are mas- Ridge. At each locality, 3 to 20 atti-

sive, with uniform bedding. Some boulder tudes were measured. Paleocurrent di-

conglomerates are imbricated, with a-axis rections of sediments in the Espinaso

transverse to flow and b-axes dipping were determined by computing vector

upstream. However, most conglomerates in resultants from dip azimuths of imbri-

this member show no preferred orientation cated clasts, azimuths of long axes of

of clasts. matrix-supported clasts, azimuths of

The sandstones consist of fine- to channel axes, and dip azimuths of cross-

coarse-grained, poorly to well-sorted, sub. beds. Most were measured on imbricated

angular grains. They arc ' usually hori- clasts. Paleoflow directions for the

zontally stratified, but locally, they U lv flow were determined by visually

are trough crossbedded. plotting crystal lineations in oriented

The depositional environment of the hand samples with the aid cf,.a protractor 2 U cg,ss is interpreted to have been high- (Bornhorst, 1976; Smith And khodes, 1972).

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All data were corrected for regiohal Orientations of microscopic and

dip, and the vector resultant, vector megascopic phenocrysts in ash and lava I magnitude, standard deviation, and varianc flows have been shown to correspond

were determined using a' computer program with flow directions (Chapin and Lowell,

(see KaUt.2, igsij. 1979; Elston and Smith, 1970; Rhodes

Horizontally stratified conglomerates and Smith, 1972; Smith, 1968; Smith and

and conglomeratic sandstones commonly con- Rhodes, 1972). Smith and Rhodes'

tain disk-shaped imbricated clasts, with studies of lava flows were based on

the a-axes transverse to flow and b-axes over 20,000 measurements of volcanic

dipping upstteam. This fabric is charac- units with known and unknown sources.

teristic of clasts rolling on stream They established the accuracy and relia-

be& (Walker, 1975). bility of this technique with over 11,000

The azimuths of long axes of matrix- measurements of elongate crystals from

supported clasts were recorded by measur- porphyritic basaltic andesite with a

ing within the bedding plane the angle known source on Mount Taylor, New Mexico.

between strike of the bed and the long The directional fabric reflects the lami-

axes of the clasts (pitch). These nar flow in lava.

measurements were made using a level and In the present stbdy, four oriented

protractor. This method allows for the samples were collecteg in the flow

rotation of linear features in the field from the same locality.. Flow lineation

by adding or subracting the measured angle was determined by measuring the long axes

to the direction of strike (Potter and cf elongate phenocrysts; in oriented

Pettijohn, 1977). slabs cut parallel to the plane of

\here the thrce-dimensi,onal shapes of bedding. Approximately 50 measurements

paleochannels were observed, the azimuths were made on each slab wibh a binocular

of the channel axes were measured usjng a microscope and protractor. Two hundred

brunton compass. phenocrysts were measured for the U lv

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flow (Fig. 15). results of north and south regions

divided in10 individual members. Data

Discussion . Kautz (1981) describes locations of

individual outcrops where paleocurrents :Along Espinaso Ridge, there apparently

were measured and vector resultants at are two major dispersal orientations.

each location. Measurements were grouped This is illustrated best by the syste-

in three ways by location and strati- matic contrast between paleo-current

graphic position in order to illustrate directions along the northern and

variations in stream-flow pattern. Vector southern parts of the ridge (Figs. 17,

resultants and rose diagrams then wer.e 18). Outcrops along Espinaso Ridge

plotted for each grouping (Figs. 16, 17, were divided into northern and southern

18). regions by an east-west line tnrough

Figure 16 illustrates the paleocurrent the center of section 4, T. 13Y, R. 6 E.

# directions in each secimentary member For each region, a gradual change in

of the Espinaso Formatidn. No measure- dispersal pattern can be seen in verti- ments were recorded in the -bM 1 ,c cal sequence (Fig. 18). Paleocurrent because of the lack of imbrication.and data tor the northern region suggest

crossbedding. Only a few measurements that the early'Espinaso streams flowed

were 'recorded for the poorly exposed toward the south-southwest (vector

U'.lr;cg and U cp,ss members. The uni- resultant =.222")and that, by late

,4.- formity of paleocurrent direction is Jhpinaso time, streams flowed toward

notable. Figure 17 divides thc.r&ta the southwest (vector resultant = 240"). I along Espinaso'.Ridge into northern and In the southern region, early Espinaso

southern regions. The boundary between .streams appear to have flowed toward

the two &;.'eas is just north of Arroyo del the northwest (vectij-esultant = 326'),

Tuerto (Fig. 9)-. Figure 18 contains the and by late Espinaso time, streams

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Figure 15. Rose diagram for measurements of elongate crystal axes

for U It, member.

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262

iio

I I10

Figure 16. Rose diagrams for paleocurrent measurements from each member.

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-90

Figure 17. Rose diagrams for paleocurrent measurements

for the Espinaso Formation 19 the northern and southern

regions, Espinaso Ridge.

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ESPINASO FORMATION

ESPINASO _. RI DCE L s5cEs -u Iv u cg ss

BASE TOP

Figure 18. Rose diagrams illustrating paleocurrent.. resultants for five Espinaso 1 members in the northern and southern regions, Espinaso Ridge.

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flowed toward the west-northwest (vector over 40 thin sections. Fifty-two

. resultant = 281'). The' &ward decrease samples were obtained from medium- to I in variation in paleocurrenf _directions coarse-grained sandstones along

between the two regions and progressive Espinaso Ridge. Additiohal thin sec-

convergence to a more westerly direction' tions were obtained from clasts' col-

can be attributed to progradation and lected from conglomerates and conglow

coalescing of alluvial-fan systems. eratic sandstones.

The stratigraphy and variation in Sandstone sampl-es were taken from

thickness of the transitional zone between rock that appeared to be least altered *,I the Galisteo and Espinaso Formations sug- by calcite cement and weathering..Slabs

gest the presence of a paleotrough near were cut normal to bedding and imprtg-

Arroyo del Tuerto from late Galisteo nated with epoxy. Thin sections were

time through Espinaso time. The p??eo- not stained for either plagioclase or

current data indicate that, during potassium fledspar in order to avoid

Espinaso time, the paleotrough was an masking lithic-fragment textures. Thin

area of coalescing fans, with a regional sections of igneous clasts were half-

paleoslope towards the WesJ. The streams stained for both pagioclase and potassium

from the two alluvial fans probably flowed feldspar.

toward the paleotrough. As the alluvial Approximately 500 points per section

fans prograded westward and the paleo- were counted on a square grid determined

trough filled with sediments, variation by a mechanical stage. The grid was at

in vector resultants between the two least 1 mm in size. The size of the

regions decreased. grid used was slightly larger than the

largesb grain size. PETROGRAPHY AND CHEMISTRY The methods used to point-c'ount the Petrographic Procedures thin sections were based on the <$hniques

Petrographic data were obtained from of Dickinson (1970), Ingersoll (1978),

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and Ingersoll and Suczek (1979). .The in all samples. Only 6 grains of

parameters used in this study (Table 4) microclj.qe were counted in all sections

are similar to those used by Gorham (1979 studied. The microcline in sqmple

Primary parameters include all mineral KZ-41 has subrounded shapes, sug-

types and' textural variations; secondafy gesting possible derivation from older

?* parameters are calculated percentages or sediments. (Galisteo?). Most plagio-

ratios. Volcahic lithic types were clase is complexly zoned. Although

identified using the criteria described oscillatory and normal zoning is com-

by Dickinson (1970). Crystals wer mon', several grains show albite twin-

(than 0.0625 mm within lithic fragments .ning. These grains are predominantly

were counted as Q, F, M, Amp, Pyx, or Op, angular; some grains, are euhedral.

as appropriate. Many of the plagioclase crystals~are \ surrounded by glass. Data Volcanic lithic fragments constitute

Table 5 contains all point-count data a significant proportion of the frame-

on Espinaso samples. Components of wqrk grains (25% to 35%). Volcanic

Espinaso samples can be divided into fragments can be divided into four

framework grains (56% to 94X.) and inter- classes: lathwork, microlitic, fel-

stitial material (6% to 44%). The sitic, and vitric (Dickinson, 1970).

samples primarily consist of feldspar Lathwork fragments contain plagioclase

and volcanic lithic fragments, However, laths in intergranular and intersertal

amphibole, pyroxepe, and/or interstitial textures. Wicrolitic fragments contain

material are locally significant consti- plagioclase crystals arranged so that

tuents; the fabric is trachytic, felted, or

Feldspars are the most abundant com- hyaloptilitic. The microlites range

ponent of the framework.grains (45% fo in composition from An to An (oligo- 27 40 67%). Plagioclase is the dominant variety clase to andesine), as determin&i by

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TABLE 4. PRkYPOINT-COUNT PARAMETERS (AFTER DICKINSON, 1970; GOREiAM, 1979; INGERSOLL’,. 1978; INGERSOLL AND SUCZEK, 1979)

~ Q Total quartzose grains QP Polycrystalline quartz (inc. chert,) I, Qm Monocrystalline quartz F Total feldspar P Plagioclase feldspar K Potassium feldspar L Total unstable lithic fragments Lv Volcanic lithic fragments (inc.- fine-gn. hypabyssal) OP ’Opaque grains M Total phyllosilicates hP Amphiboles Px Py Foxenes Dm Detr i tal matrix (or t homa t r ix aid prbtoma t r ix) cc Cement (calcite) Ck Cement (clays) CS Cement (silica) cz Cement (zeolites) Rc Replacement product (calcite) Rk Replacement product (clays) V Voids Lvl Volcanic lithic fragments (lathwork) LVn Volcanic lithic fragments (microlitic) Lvf Volcanic lithic fragments (felsitic) Lw Volcanic lithic fragments (vitric)

QP /Qm "P K L Lv OP M Amp Px Dm

BASAL SANTA FE GROUP

Kz-81 - 122 74 7 122 122 20 1 29 15 - KZ-86 - 41 181 4 91 91 27 7 46 5 16 ESPINASO FORMATION -U c- Member Kz-84 - 1 335 - 11 11 11 53 1 12 s ' KZ-88 - - 250 - 61 61 8 45 1 27 KZ-89 - - 298 - 11 11 19 80 5 6 Kz-90 - - 269 - 15 15 10 73 2 6 c U lr,cq Member KZ-61 - - 175 - -78 78 15 27 3 173 Kz-71 - - 229 - 61 61 9 53 6 23 KZ-73 - - 248 - 34 34 13 54 6 39 M cg,ss Member (Northern Region) Kz-95 - 3 247 I- 51 51 16 60 3 55 KZ-96 - 3 240 1 91 91 - 70 1 51 * Kz-100 - '2 233 - . 78 78 15 70 - 22 I Kz-101 - 2 256 - 56 56 6 75 - 39 KZ-107 - - 198 - 82 82 22 - 83 1 73 KZ-110 - 6 249 - 89 89 6 - 62 1 50 KZ-111 - 2 258 - 75 75 13 - 77 1 28 M cg,ss Member (Southern Region) Kz-39 4 8 173 - 133 133 30 3 33 11 25 KZ-18 - 6 174 - 100 100 12 - 67 1 56 Kz-20 - 22 197 - 111 111 19 - 88 - 23 KZ-40 - - 207 - 223 223 34 - 15 8' 9

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cc Ck cs cz Rc Rk V Lvl Lvm Lvf Lw Total Count 8

29 14 116 6 5 10 80 20 91 - 520

76 -. 11 - 500 108 28 61 - 528 81 10 11 - 5 10 113 8 15 - 508

- 71 66 10 s 545 119 - 59 2 500 106 39 34 -. 539

18 3 47 4 503 42 32 65 26 532 40 7 77 1 507 - 14 43 13 514'; 21 3 82 - 484~~. 36 26 50 39 526 46 6 64 11 506,

24 23 123 9 474 42 4 86 14 504 38 9 84 27 509 1 2 218 - 500

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QPQm P K L Lv OP M Amp Px Dm

M cg,ss Member (Southern Region) (cont.) KZ-58 - - 187 - ... 94 . 94 11 1 76 7 86 Kz-59 -2 184 - 109 109 6 - 52 - 87 Kz-60 -1 198 - 108 108 8 - 84 10 36 Kz-76 -2 184 - 109 109 6 - 52 - * 87 Kz-79 -’- - 195 - 141 141 6 - 53 - - M lr,cg Member KZ-41 2 18 187 4 128 14 4 23;’ 10 15 ”:$28 KZ-42 -2 267 1 98 98 33 - 48 2 49 Kz-54 - - 182 - 4 4 21 - 40 23 179 . Kz-55 - - 168 - 31 31 23 - 36 20 209 K2-75 -5 227 - 68 68 ‘47 - 28 1 37 L 86,~s~Member I LEVl4 - - 200 - ,130 130 16 5 23 16 19 Kz-4 - - 178 - 114 114 6 1 38 9 37 Kz- 7 - ,- 214 - i36 136 13 - 71 1 23 Kz-12 - - 204 - 14 0 140 14 1 29 20 27 Kz-37 - - 19 - 138 138 21 1 30 17 24 KzT74 - 36 196 2 142 142 10 - 33 2 3 Kz-104 . - - 238 - 96 96 15 - 86 4 28 Kz-109’ - 4 305 - 84 84 13 - 111 - 32 Transitional Zone (Galisteo)

Kz- 1 4 98 153 6 91 91 11 5 23 4 68 * Kz-3 - 25 163 - 76 76 16 - 39 1 18 IKZ-6 - 43 190 - 114 114 15 - 46 2 3

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TABLE 5. (com5imed)

cc Ck cs cz Rc Rk V Lvl Lvm Lvf Lw Total Counts 14 - - - - 6 18 - 73 19 .. 2 500 - 58 2 - - - 45 - 68 41 - 545 - 6 33 - - 3 13 . - 89 19 - 500 - 52 - 1 - - 5- 99 10 - 498 1 75 - 4 - - 20 - 108 33 - 495

8 21 56 5 - 5 74 - 125 3 - 574 4 15 - 28 - - 47 - 97 1 - 594 - - - - - 51 20 - 4 - - 520 -

- - - 12 - 1 30 - 30 1 - 530 ' 25 51 - 11 - - 4- 64 4 - 504

1 - - 89 56 - 129 1 - 555 13 5 5 2 47 - 105 4 5 457 ,,+ ,,+ - , 41 - 1 '6' - 136 - - 506 1 6 57 - - 1 24 - 140 - - 524

1 23 47 - - 1 22 - 138 ' - - 522 16 53 - 7 25 - 142 - - 525 - 33 - - 9- 96 - - 509 - 17 - - 34 - 84 - - 600 .

6 1 - - 30 - 89 2 - 500 10 24 - 19 - - 19 - 76 - - 410 79 8 ------114 - - 500

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by the "microlite method" (Heinri&, 16% of the total rock. It'is common

1965, p. 362-364). Felsitic fragments for the mudflow samples to have

comprise a microcrysfalline mosaic of detrital matrix as high as 44%. .. feldspar and quartz with some micropheno- Cements constitute a significant pro-

crysts of plagioclase. Vitric fragments portion of some samples,-ranging up

mainly consist of thick-walled glass sharc t'o' 18% of the LQtal, rock. At least ' .. 3 .; and rare puece fragments. four types of cements are recognized:

Hornblende, oxyhornblende (basaltic phyllosilicates, silica, zeolites

hornblende) , and pyroxene constitute 9% .(heulandite), .and calcite.

to 24% of the framework.grains. Biotite Secondary parameters were comphted

is less common and is found in significant to characterize Espinaso petrology

amounts only in the L ss,css member. (Table 6). The uniformity of petrology

Quartz (0 to 3%), which is extremely throughout the members is noteworthy. .C rare as framework grains, can be subdivide Figure 19 illustrates the restricted

into three categories. Single quartz Qmcdompositions of the Espinaso and

crystals commonly are well rounded; some shows how they contrast with those of

have well rounded overgrowths, indicating the Galisteo Formation (Gorham, 1979)

reworking of older sediments. Grains of and the Santa Fe Group '(pre5ent study),

aggregate quartz conposed of crystals A purely volcanic provenace is indi-

coarser than 0.0625 mm commonly are sub- cated for the Espinaso, in contrast

angular and slightly strained. Polycrystal- to the nonvolcanic provenance of the

line quartz composed of grains finer than Galisteo (Gorham, 1979; Gorham and

0.0625,mm usually is subrounded. Ingersoll, 1979) , and the mixed prqve-

Interstitial material is divided into nance of the transitional zone and

two groups: detrital matrix and cements. the Santa Fe (for example, Dickinson,

Detrital matri.x ((0.03 mu) is present in 1970).

most sandstone .samples and averages about Subtle contrasts in petrology occur

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BASAL SANTA FE GROUP /” KZ-81 38 25 38 0.91 1.00 KZ-86 13 58 29 0.98 1.00 Mean 25 42 33 0.95 1.00 -+ -+ -+ -+ -+ -+ Std. dev. 18 23 6 0.05 0.00

ESPINASO FORMATION.

U cg,ss Member

KZ-84 0 97 3 1.00 1.00 Kz-8 8 0 80 20 1.00 1.00 KZ-89 0 96 4 1.00 1.00- Ke-90 0 95 5 1.00 1.00

U lr,cg Member KZ-61 0 69 31 1.00 1.00 KZ-71 0 79 21 1.oo 1.00 Kz-73 0 88 12 ‘ 1.oo 1.00

)I cg,ss Member (northern regibn) KZ-95 82 17. 1.00‘ 1.00 KZ-96 72 27 -. 1.00 1.00 Kz-100 74 25 1.00 1.00

KZ-101 82 17 ’ 1.00 1.00 KZ-107 71 29 1.00 1.00 Kz-110 72 26 1.00 1.00 KZ-111 77 ‘ 22 1.00 1.00

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M c6,ss Member (southern region)

Kz-39 5 4 42 1.00 1.00 Kz-18 62 36 1.00 1.00 Kz-20 60 33 1.00 1.00 Kz-40 48 52 1.00 1.00 Kz-58 65 35 1.00 1.00 Kz-59 62 37 1.00 1.00 Kz-60 64 36 1.00 1.00 Kz-76 62 37 1:oo 1.00 Kz-79 58 42 1.oo 1.00

M lr,cg Member Kz-41 56 38 0.98 1,00 \ Kz-42 73 26 1.00 1.00 Kz-54 77 23 1.00 1.00 Kz-55 84 16 1.00 - 1.00 Kz-75 76 22 1.00 -. 1.00

L ss,css Member LEV14 0 61 39 1.00 1.00 Kz-4 0 61 39 1.00 1.00 Kz- 7 0 61 39 1.00 1.00 Kz-12 0 59 41 1.00 1.00 Kz-37 0 59 41 1.00 1.00 Kz-74 10 53 38 0.99 1.00 KZ-104 0 71 29 1.00 1.00 Kz-109 1 78 21 1.00 1.00 mean 1 71 28 1.00 1.00 -+ -+ -+ -+ -+ -+ std. dev. 2 12 12 0.00 0.00

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Transitional Zone (Galisteo) Kz-1 29 45 '26 0.96 1'. 00 Kz-3 10' 62 28 1.00 1.00 KZ-6 12 55 33 1.00 1.00- mean 17 54 29 0.99 1.00 -+ -+ -+ -+ -+ -+ std. dev. 10 9 4 0.02 0.00

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F c Figure 19. Quartz(Q)$etld'$par(F)-lithic(L) triangle showing means and fields of

variation [see Ingersoll and Suczek (1979) for discussion] for Espinaso Formation (Te),

Galisteo Formation (Tg) (from Gorhan, 1979), and transitional zone (uppermost Galisteo).

Also shown (+) are two samples from the Santa Fe Group, which directly overlies the

Espinaso. See text for discussion.

tlat there is a tendency for the propor- Espinaso (Tables 3 and 8, respectively).

tion of feldspar (plagioclase) to increasc These rocks are nepheline latite, cal-

upsection at the expense of volcanic lithi cic latite, and calcic quartz latite,

fragments. This might represent the respectively. The clasts are typi-

exposure of intrusive bodies, with time, cal of the majority of clasts in the

as overlying volcanics are eroded (for Espinaso; the nepheline-latite flow is

example, Dickinson and Rich, 1972; somewhat atypical, although some clasts

Ingersoll, 1978). Alternatively, it of similar composition occur at approxi-

may reflect increased crystallization mately the same stratigraphic level.

of melt in feeder pipes with time. Compositions of the tdo clasts are

There also is a subtle contrast in similar to those of volcanic rocks of

petrology between the northern and the Cienega area (Table 8). Compar-

southern parts of the M cg,ss member , able data are not available from the

that may reflect different source areas. Ortiz center, although over-all compo-

The northern part has systematically sitions are similar.

higher GFLJ F and lower QFLZ L than da+ Conclusions the southern part (Table 6). It is un-

clear whether this reflects erosion of In the Espinaso formation, high QFL% I' different source areas (Cerrillbs Hills feldspar and QFL% lithic fragmentS,

vs. Ortiz Mountains) or different parts along with high values of P/F (0.98

of the same source (see below). to 1.00) and Lv/L (1.00) (Table 6) .

require a volcanic source terrane. In Chemistry addition, the abundance of rnicrolitic

hole-rock, major-element analyses volcanic fragments indicates sources

(elect ton-microprobe analySis of fused of intermediate composition.

beads: Baldridge, 1979) were obtained The presence of rounded overgrowths

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TABLE 7. MEANS AND STANDARD DEVIATIONS OF QFL PERCENTAGES FOR LOWER (LSS,CSS), MIDDLE (MLR,CG, MCG,SS) AND UPPER (ULR,CG, UCG,SS) PARTS OF THE ESPINASO FORMATION

QFL% Q QJ?L%F QFL% L

Middle 152 6851 0 3OklO I Lower 13 6328 3657

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Sample 358" Sample 359" Sample 72B-t Sample 84-t Sample 162t

sio2 56.75 60.73 56.17 61.03 59.98 Ti02 0.76 0.66 0.86 0.67 0.64 19.23 *l2'3 16.96 17.51 16,.41 17.74 Pe203 5 1.12 0.96 1.49 1.04 1.04 FeO 5.11 4.36 6.75 4.70, 4.69 MgO 2.54 2.14 1.82 1.26 1.86 CaO 7.23 6.20 6.62 5.76' 6.45 MnO 0.04 0.07 0.08 0.16 tr Na20 3.58 4.55 4.15 3.94 4.01 2.92 2.31 3.85 3.92 2.25 K2° '2'5 '2'5 0.46 0.11 0.53 0.28 0.35

TOTAL 99.74 99.05 99.83 99.16 '99.01

Quartz 4.23 8.19 0.00 8.38 9.99 Orthoclase 17.29 13.73 22.86 23.44 13.44 Albite 32.22 41.09 37.40 35L81 36.47 1 Anorthite 27.84 19.15 '17.86 15.71 24.03 Diopside 4.08 8.86 9.34 9.07 4.82 Hypers thene 11.15 6.82 8.36 4.94 8.51 Olivine 0.00 0.00 0.31 0.00 0.00 Magnetite 1.17 , 1.01 1.56 1.10 1.10 Ilmenit e 1.06 0.92 1:20 0.95 0.90 Apatite 0.96 0.23 1.11 0.60 0.74

*These analyses were obtained following techniques of Baldridge (1979). tSun and Baldwin (1958). Recalculated on volatile-free basis. ,§Fe0 calculated from Fe203/Fe0 = 0.22 23 .

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of quartz and subrounded microcline in (also, see Baltz, 1978; Corham and

two samples suggests a very minor contri- Ingersoll, 1979 ; Logsdon , 1981).

bution from sedimentary rocks. A possiblc The synorogenic sediments of the

source for these reworked sediments is by Galisteo Formation were deposited

erosion of sedimentary rocks near the vol- by high-energy rivers flowing into

canic center that were uplifted by intru- a deepening and enlarging basin

sion of igneous stocks. (Fig. 20) (Gorham, 1979). Gorham

The Espinaso Formation contains ande- recognized three periods of fluvial

site, calcic quartz latite, calcic latite, deposition which reflected tectonic .” dacite porphyry, and nepheline latite. events: (1) early Galisteo time

The presence of undersaturated silicic (deposition by low-sinuosity meander-

rocks (nepheline latite) indicates that ing streams; granitic and metamorphic

magmagenesis in source areas was complex. source areas in the Brazos-Sangre de

All of the data are consistent with Cristo geanticline) (Fig. 20A);

derivation of the Espinaso from either or (2) middle Galisteo time (deposition

both the Cerillos and Ortiz centers by ,high-energy braided streams; sedi-

(Fig. 5). mentary, granitic, and metamorphic

source areas in the Nacimiento uplift) BAS IN EVOLUTION (Fig. 20B); (3) late Galisteo time Pre-Espinaso Time (deposition by meandering streams; pre-

A detailed discussion of the predominantly fine-grained detritus derived

Espinaso history of the Hagan area is from distant sources as both Brazos-

outlined by Gorham (1979). Tectonic Sangre de Cristo and Nacimiento uplifts

activity was characterized by rise of the were eroded) (Fig. 2OC).

Brazos-Sangre de Cristo geanticline and The uppermost Galisteo Formation con-

the Nacieento uplift and by the formation tains abundant volcanic material. In

of the associated Galisteo-El Rito basin the Hagan area, paleocurrents indicate

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A B c

Figure 20. Schematic paleotectpnic-paleogeographic maps of north-central New Mexico during

early Galisteo time (A), middle GAlisteo time (B), late Glaisteo time (C), and latest

Galisteo-earliest Espinaso time (D). Stippled pattern shows depositional basin. See text

for discussion. [After Baltz (1978), Gorham (1979), Gorham and Ingersoll (1979) .]

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a reversal of paleoslope as volcanic and totally volcanic material. Thes@fans

tectonic activity began along the San prograded over an area of low physio-

Pedro-Ortiz porphyry belt near the end graphic relief (Fig. 21).

of the Eocene (Figs. 20D, 21). Before McGowen and Groat (1971) have pro-

the magmatic centers became significant posed a model that divides alluvial

sources for volcanic detritus, uplift fans into proximal-fan, midfan, and

along the San Pedro-Ortiz porphyry belt distal-fan components. The proximal

resulted in erosion of the Galisteo (Fig. fan is characterized by matrix-supported-

21). The transitional zone between the and/or clast-supported-conglomerate

Galisteo and Espinaso Formations repre- facies. Midfan areas usually contain

sents sediments that were deposited by conglomerate and planar-crossbedded-

streams flowing away from the incipient sand facies. The distal fan is charac-

magmatic centers (westward in Hagan area). terized by.trough-crossbedded-sand and

These streams carried volcanic material silt facies with thin bands of con-

and reworked detritus from the Galisteo, glomeratic-sand facies.

'and possibly, older formations (Gorham, Along Espinaso Ridge, the L ss,css

1979; Gorham and Ingersoll, 1979). member represents a network of braided

sheet-flow deposits of a distal fan Early Espinaso Time ("Bijou Creek type" of Miall, 1978).

The continuation of volcanic activity In other distal areas, the Espinaso

and uplift at the Ortiz and Cerrillos also is characterized by a basal sand-

centers resulted in a progressive increase stone and conglomeratic sandstone (for

of volcanic material 'in the transitional example, Santa Fe River area, area

zone between the Galisteo and Espinaso northeast of Kennedy, Fig. 1). In

Formations. By early Espinaso time, the the more proximal areas, the contact

magmatic centers became primary source between the Galisteo and Espinaso For-

areas. for alluvial fans consisting of mations is characterized by.an abrupt

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Figure 21. Schematic cross sections of Ortiz Mountains magmatic

center and its western flank, where Espinaso Formation ekosed along

Espinaso Ridge was deposited (after Fig. 5 of Disbrow and Stoll, 1957).

(1) During Galisteo deposition (Eocene). (2) During deposition of

transition between *Calisteo and Espinaso. (3;) 'Early Espinaso time.

(4) Middle Espinaso time. (5) Late Espinaso the'. (6; Latest

Espinaso time, Symbols: Jte = 'Jurassic Todilto and Entrada Format.ions;

Jm = Jurassic Morrison Formation; Kd = Cretaceous Dakota Formation;

Km = Cretaceous Mancos Formation; Kmv = Cretaceous Mesaverde Group;

Tg = Eocene Galisteo Formation; V = Volcanics and volcaniclastik;

G = Gravel (including conglomerates, debris-flow deposits, and some

interbedded sandstones and pyroclastic deposits); S = Sandstone

(including interbedded conglomerates and pyroclastic deposits).

Figure 21 appears on the following frame.

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r c Iw t

Tq Kd, ‘Kmv Km

J 1.4 Jm’ 2

- Tg LMV Kd Km J?/ JId I

FAgure 21.

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~ ~~

(for example, northwest of Ortiz) (Fig. 1 build up of the magmatic center (Fig.

21). As the alluvial fans in the Middle Espinaso Time Hagan area prograded westward, paleo-

Middle Espinaso rocks (M cg,ss and current directions changed to a more . r M cr,cg) are characterized by significant uniformly westward direction (Figs.

amounts of coarse conglomerates.. Facies ' 18, 22).

within middle Espinaso members consist Late Espinaso Time predominantly of horizonatally st ratified, - imbricated conglomerates interbedded with Beginning approximately 27 m.y. B.P.

planar- and trough-crossbedded sandstones. there was a change in volcanic activity

The conglomerates and sandsfones of the in the magmatic centers, as represented

M cg,ss probably were deposilted by braidec by the I flow, ash-flow deposits,

9 streams of the "Scott type" (Miall, 1978). and associated lahar deposits (Figs.

Minor explosive activity in the Ortiz 12, %, 14). Where channeling into

magmatic center is recorded by ash-flow pyroclastic-flow deposits had occurred,

depos-its and associated lahar deposits of lahar deposits commonly filled these

the M lr,cg member. channels. This suggests that the

The "Scott type" braided stream i.s lahars might have formed by flash

characteristic of proxima'l braided streams floods scouring into recent pyroclastic

and alluvial fans where conglomerate is flows.

the predominant facies. Clasts of the The presence of horizontally strati-

conglomerate show an upward-coarsening fied conglomerates and lahar deposits

sequence of mean maximum size. This suggests deposition in proximal

coarsening probably ref lectg progradation braided-stream environments of alluvial

of the alluvial fans and an increase in fans subject to debris flows (the

paleoslope due to tectonic activity "Trollheim type" of Miall, 1978).

resulting from continued magmatism and The base of the U cp,ss member con-

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/’/-- -\ / \ / \

A B

Figure 22. Schematic dispersal directions for Espinaso deposits

along Espinaso Ridge. Paleocurrent data show predominantly northy

west transport along southern half of ridge and predominantly south-

west transport along northern half of r&dge. This probably .reflects

two coalescing alluvial fans with sources in,the Ortiz and Cerrillos

magmatic centers (A). Alternatively, deposition may have occurred

on two separate fans, both of which were derived from the Ortiz

center (B). Available data do not differentiate these alternatives.

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~ ~~ ~~ ~

sists of boulder conglomerates. These variety of magmatic types: olivine

conglomerates indicate deposition in high- nephelinite, olivine tholeiite, alkali

energy braided'streams. The boulder con- olivine basalt, and quartz tholeiite.

glomerates grade upward into cobble con- Basins which existed at 25 m.y.

glomerates interbedded with sandstones, B.P. continued to fill with sediments.

suggesting lower-energy braided-stream .At about 20 to 19 m.y. B.P., there

environments. This upward-fining mega- was minor intermediate to silicic

sequence suggests a decrease of paleoslope volcanism within and peripheraldo

and lowering of relief in the source area the rift (Baldridge and others, 1980).

concurrent with the end of volcanic This is represented by the glassy-

activity (Fig. 21). latite unit of Sun and Baldwin (1958)

near La Cienega. The modern Rio Grande Post-Expinaso Time rift has evolved as regional extension,

Initial tectonic extension in north- bimodal volcanism, basin filling, and

central New Mexico probably occurred dissection have continued to the

. between 27 and 25 m.y. B.P. (Baldridge present.

and others, 1980). In the Hagan basin Acknowledgments area, sediments of the Santa Fe Group

began accumulating in a broad basin by Financial assistance was provided 25 m.)...B.P . [also, see Gawne (1981) and to Kautz by the New Mexico Bureau of

Vazzana and Ingersoll (1981) for discus- , Mines and Mineral Resources and the sion of related strata]. Mafic and ultra- New Mexico Geological Society. Acknow-

mafic volcanism began abmptiy at 25 m.y. ledgment is made by Ingersoll to the

B.P., as intermediate and silicic vol- donors of the Petroleum Research Fund,

canism waned (Baldridge and others, 198b). administered by the American Chemical

This mafic and ultramafic volcanism was Society, for partial support of this

volumetrically minor and included a research. Support for Baldridge was

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provided by the Office of Basic Energy Bachman, G. O., and Mehnert, H. H., 1978,

Sciences of fhe U.S. Department of Energy New K-Ar dates and the late Pliocene

The geochronologic work of Damon and to Holocene geomorphic history of

Shafiqullah was supported by NSF Grant the central Rio Grande region,

EAR-7811535. New Mexico: Geological Society of

The following provided assistance in a America Bulletin, v. 89, p. 283-292.

variety of ways: R. R. Butcher, C. E. Baldridge, W. S., 1979, Petrology and

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Frietze, J. Kautz, W. E. Kautz, A. M. Kudc basaltic rocks from the central Rio

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MANUSCRIPT RECEIVED BY THE SOCIETY ,

OCTOBER 8, 1981

MANUSCRIPT ACCEPTED

OCTOBER 8, 1981

.-C'

Printed in U.S;A.

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