Stratigraphy of the Tanos and Blackshare Formations (Lower Santa Fe Group), Hagan Embayment, Rio Grande Rift, New Mexico

Home , Abiquiu Formation, Amalia Tuff, Cochiti Formation, Espinaso Formation, Zia Formation

Stratigraphy of the Tanos and Blackshare Formations (lower Santa Fe Group), Hagan embayment, Rio Grande rift, New Mexico

Sean D. Connell, New Mexico Bureau of Geology and Mineral Resources–Albuquerque Office, New Mexico Institute of Mining and Technology, 2808 Central Ave. SE, Albuquerque, New Mexico 87106, [email protected], Steven M. Cather, Nelia W. Dunbar, William C. McIntosh, and Lisa Peters, New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, New Mexico 87801

Abstract Introduction by the Budaghers fault. The Hagan embayment lies just east of the Santo Domingo Over a kilometer of sedimentary and vol- The Santa Fe Group (upper Oligo- sub-basin, a deep structural sub-basin canic rocks of the Santa Fe Group are cene–Pleistocene) comprises the sedimen- within the northern part of the Albu- exposed in the Hagan embayment, a struc- tary and volcanic fill of the Rio Grande rift querque Basin (Grauch et al., 1999). This tural re-entrant between the Albuquerque (Chapin and Cather, 1994). Geologic map- and Española Basins. We identify two new tilted and fault-bounded embayment ping and stratigraphic studies of the Santa lithostratigraphic units, the Tanos and Black- exposes one of the most complete Phanero- share Formations, that resulted from late Fe Group exposed along Arroyo de la Vega zoic stratigraphic sections in central New Oligocene to late Miocene sedimentation de los Tanos in the Hagan embayment, Mexico (Pazzaglia et al., 1999). Paleogene along the northeastern margin of the Albu- northeast of Espinaso Ridge (Fig. 1), con- nonvolcanic deposits exposed in the querque Basin and Hagan embayment. We strain the initial development of the Rio Hagan embayment include arkosic sand- designate exposures in Arroyo de la Vega de Grande rift in north-central New Mexico. stone, conglomerate, and mudstone of the los Tanos as the type section and the San According to a K–Ar age reported for a Diamond Tail and Galisteo Formations Felipe Pueblo NE quadrangle as the type basalt flow near the base of the Santa Fe (Fig. 2; Stearns, 1953b; Gorham and Inger- area for these two formations. The Tanos Group (Kautz et al., 1981), these deposits Formation is 279 m (915 ft) thick at the type soll, 1979; Lucas et al., 1997). Conglomerate represent some of the oldest exposed rocks locality where it disconformably overlies the beds of the Diamond Tail and Galisteo For- Espinaso Formation. The Tanos Formation of the Albuquerque Basin area (cf. Bach- mations contain rounded metaquartzite, consists of a basal conglomerate overlain by man and Mehnert, 1978). These exposures chert, and petrified wood clasts (Stearns, mudstone and sandstone, representing dep- provide an opportunity to study early rift 1953b; Gorham and Ingersoll, 1979). Con- osition in a closed basin. The overlying sedimentation and to characterize lower glomerate of the upper Eocene–Oligocene Blackshare Formation is over 1,000 m (3,281 Santa Fe Group deposits that are buried by Espinaso Formation containing volcanic ft) thick and contains dominantly sandstone younger rift-basin fill in the Santo Domin- rocks and sandstone conformably overlies with interbeds of lenticular conglomerate, go sub-basin. The presence of upper the Galisteo Formation (Stearns, 1953a, b; conglomeratic sandstone, and minor mud- Oligocene deposits supports conclusions stone, commonly arranged in fining-upward Erskine and Smith, 1993). from other studies of rift-related extension sequences. Paleocurrent measurements, Volcanic products of the Espinaso For- gravel composition, and field relationships elsewhere in New Mexico (e.g., Chapin mation, which have been studied exten- indicate derivation from the neighboring and Cather, 1994; Smith, 2000; Mack et al., sively (Kautz et al., 1981; Erskine and Ortiz Mountains. The Blackshare Formation 1994; Smith et al., in press). Smith, 1993), are associated with the conformably overlies and interfingers with This paper summarizes results of geo- emplacement of the Ortiz porphyry belt in the Tanos Formation and represents a gener- logic mapping and stratigraphic studies of the Ortiz Mountains and Cerrillos Hills al westward progradation of the Ortiz the San Felipe Pueblo NE quadrangle (Stearns, 1953a; Kautz et al., 1981; Erskine Mountains piedmont during Miocene time. (Cather et al., 2000) and defines two new and Smith, 1993). The Ortiz Mountains are Stratal tilts of the Tanos–Blackshare succes- formation-rank lithostratigraphic units of sion decrease upsection, indicating that sub- a 26–36 Ma belt of Eocene–Oligocene por- sidence and deposition occurred concurrent- upper Oligocene and Miocene deposits of phyritic, hypabyssal-intrusive (subvol- ly. Subhorizontally bedded conglomerate the lower Santa Fe Group. In accordance canic) rocks exposed on the footwall of the and sandstone of the Pliocene–Pleistocene with the North American Commission on La Bajada fault, just east of the study area Tuerto formation* overlie the Blackshare For- Stratigraphic Nomenclature (NACSN, (Kelley, 1977; Kautz et al., 1981; Maynard mation in angular unconformity. A basaltic 1983), we describe three informal members et al., 1990). The Espinaso Formation is flow near the base of the Tanos Formation of the Tanos Formation and four informal divided into a lower calc-alkaline assem- yielded an 40Ar/39Ar age of 25.41 ± 0 .32 Ma. members of the Blackshare Formation. We blage and an upper alkaline assemblage A volcanic ash within the Blackshare Forma- conclude with some implications that this 40 39 (Erskine and Smith, 1993). Rocks of the tion yielded an Ar/ Ar age of 11.65 ± 0.38 study has on models of the tectonic devel- lower assemblage were erupted between Ma and geochemically resembles one of the opment of the Española and northern middle Miocene Trapper Creek ashes from 36 and 34 Ma, followed by eruption of the the northeastern Basin and Range province. Albuquerque Basins (e.g., Ingersoll, 2001). upper assemblage between 30 and 26 Ma The base of the Tanos Formation is older (Maynard et al., 1990). than the basal Zia Formation, which is The stratigraphic nomenclature of rift- exposed along the northwestern margin of Geologic setting and basin fill (i.e., Santa Fe Group) in the study the Albuquerque Basin, indicating that dep- previous studies area has undergone a number of changes osition of the Santa Fe Group began earlier to over the years (Fig. 2). Stearns (1953a, b) the east. The Hagan embayment is a northeast-tilt- first described the study area in detail and ed structural re-entrant between the La defined the subjacent Eocene Galisteo and *Editor’s note: It is the lead author’s belief Bajada and San Francisco fault zones. Eocene–Oligocene Espinaso Formations. that the Tuerto gravels of Stearns (1953b) is a These fault zones define the eastern mar- Lucas et al. (1997) replaced the lower part mappable and lithologically well devined unit gin of the Rio Grande rift along different of Galisteo Formation with the Diamond that should be given formation-rank status. Ele- parts of their traces (Kelley, 1977). The Tail Formation. Stearns (1953b) tentatively vation of the Tuerto gravels to formation rank Hagan embayment is bounded to the north assigned deposits overlying the Espinaso will be proposed in a future publication.

November 2002, Volume 24, Number 4 NEW MEXICO GEOLOGY 107 o 106 o 30' 105 45' 35 o Jemez t 55' l e u d a n volcanic f Los a r o t s i Alamos field t r G a j o i M a Pajarito R P o Plateau Española t s iisto Mts Basin r C

Cerros n a del Rio Santa Fe SSangre de Cr volcanic r Tent ive e R Rocks field ta F L an a S

Santo B a

j a Domingo d Fe a ta an nt sub-basin e S me s ay c b

SDP a m Ga e liste r o Ck. p Santa m Cerrillos

e Fig. 3 e Ana d n Hills

n t a Mesa r Bf G AVT SFP T on HE G qu EER a e list A R eo y C o re io . ek R AdT

f Ortiz f B F L S Mts. New Placitas

o Sandia Mexico 35 15' Mts. San Pedro Mts.

SFP = San Felipe Pueblo LBf = La Bajada fault 0 10 20 km SDP = Santo Domingo Pueblo ER = Espinaso Ridge HE = Hagan embayment AVT = Arroyo de la Vega de los Tanos SFf = San Francisco fault AdT = Arroyo del Tuerto 0 10 mi Bf = Budaghers fault

FIGURE 1—Location of the Santo Domingo sub-basin (Albuquerque Basin), Hagan embayment, Ortiz Mountains, San Felipe Pueblo 7.5-minute quadrangle study area (Fig. 3), and other major features of the northern Albuquerque and southern Española Basins. The Hagan embayment is bounded by the San Francisco, Budaghers, and La Bajada faults. The Tijeras fault (not shown) trends to the northeast through the Ortiz Mountains. Drainages of Arroyo de la Vega de los Tanos and Arroyo del Tuerto, San Felipe Pueblo, Santo Domingo Pueblo, Santa Fe, and Los Alamos are shown for reference.

Formation to the Abiquiu(?) Formation, southern Española Basin. This group usage perennial streams and rivers associated primarily on stratigraphic position and the was extended throughout the rift (e.g., with the ancestral Rio Grande flowed presence of tuffaceous rocks exposed on Hawley, 1978; Chapin and Cather, 1994). toward southern New Mexico (Hawley, the footwall of the La Bajada escarpment The lower Santa Fe Group represents dep- 1978). Deposition of the upper Santa Fe (Fig. 1). Overlying deposits were assigned osition within internally drained basins Group ceased during Pleistocene time, to the Santa Fe Formation and Tuerto grav- (bolsons) that contain broad alluvial plains when the Rio Grande began to incise into els by Stearns (1953b). Kelley (1977) and ephemeral or intermittent playa lakes the earlier aggradational phase of the assigned the Abiquiu(?) Formation (sensu fed by streams draining emerging basin- Santa Fe Group basin fill (Spiegel and Stearns, 1953b) to the Zia Formation. margin uplifts (Chapin and Cather, 1994). Baldwin, 1963; Hawley, 1978). Spiegel and Baldwin (1963) elevated the Upper Santa Fe Group strata record depo- Petrographic criteria (using only sand- Santa Fe Formation to group rank in the sition in externally drained basins where stone) define formal and informal units

108 NEW MEXICO GEOLOGY November 2002, Volume 24, Number 4 Tanos and Arroyo del Tuerto (Fig. 4; Stearns Kelley Epoch This study Appendix). Data from the Merrion Oil (1953b) (1977) Blackshare Federal #1 (sec. 34 T14N R6E, 0 Holo. New Mexico Bureau of Geology and Min- 0.01 undivided Quaternary deposits eral Resources, NMBGMMR Subsurface Library #47490) and the Pelto Oil Black- share Federal #1 (sec. 25 T14N R6E, - E T N S

I NMBGMMR Subsurface Library #26091)

1 E E C L O P 1.59 Ma oil-test wells were also examined. Colors Tuerto Tuerto Tuerto were documented using the Munsell 2 E N gravels gravels fm.

E (1992) method. Texture and bedding were C Sierra O

I described according to Dutro et al. (1989) L P Ladrones and Ehlers and Blatt (1982). Fm. Radioisotopic ages of volcanic material ? ? were measured using the 40Ar/39Ar tech- 5 ? ? nique at the New Mexico Geochronologi- E cal Research Laboratory (NMGRL), New N

E ? ? ? ? C Mexico Institute of Mining and Technolo- O I 10 M gy in Socorro, New Mexico. Groundmass 11.65 Ma concentrates from basaltic units were analyzed by the furnace incremental heating Blackshare Fm. e Santa Fe Santa Fe age spectrum method (Peters, 2001a, 2002). t a l 15 Fm. Fm. Sanidine concentrates from an ash layer were analyzed using the single-crystal e l d ) d a total fusion method (Peters, 2001b). Ana- i M m ( e ? ? ? ? lytical methods and results of dating are in m i

T Peters (2001a, b, 2002). y

20 l Abiquiu(?)

r Zia

a Tanos Fm. The geochemical composition of the e Fm. Fm. glassy component of tephra layers was quantitatively determined using a Cameca e t a

l SX-100 electron microprobe. Tephra sam- 25 25.41 Ma ples were mounted in epoxy disks and pol- y l r a

e ished using pure diamond powder sus- E 26.9 Ma N

E pended in distilled water. Approximately C

O Espinaso Espinaso Espinaso Fm. 20 points on each sample were analyzed G 30 I L

O Fm. Fm. 31.88 Ma for major elements plus fluorine, chlorine, and sulfur. The largest possible beam size E N

E was used for the microprobe analyses in C O 40 E order to minimize volatilization of sodium,

E Galisteo Fm. reaching a maximum size of 25 µm. Stan- N E

C Galisteo Galisteo dard ZAF procedures were used for recal- O

E culation of analyses. Analyses were nor- L

A Fm. Fm. 50 P malized to 100 wt%, and means and stan- Diamond Tail Fm. dard deviations were calculated for each data set, discarding any obvious statistical outliers. Data sets were compared using 60 statistical difference calculations described by Perkins et al. (1995).

FIGURE 2—Comparison of stratigraphic nomenclature of Cenozoic deposits in the study area. Selected geologic time boundaries shown (not to scale). Tanos Formation Radioisotopic age control points from Cather et al. (2000, 2002), Peters (2001a, b, 2002), and Kautz et al. (1981). The Tanos Formation is a new lithostratigraphic unit herein named for Arroyo de la Vega de los Tanos, a tributary to the within the Santa Fe Group and subjacent arkose and feldspathic litharenite with a Rio Grande. The base of the type section is strata in the Albuquerque and Española mean quartz content (QFL%Q) of 35 ± 17% at a spring near the northwestern corner of Basins. The Diamond Tail and Galisteo (Large and Ingersoll, 1997) and is substan- sec. 28 T14N R6E, of the San Felipe Pueblo Formations contain mostly quartz rich tially greater than the lithic arkose of the NE 7.5-min quadrangle (Fig. 3). At the type arkose (Gorham and Ingersoll, 1979). subjacent Espinaso Formation, which has a section (Fig. 4), the Tanos Formation is 279 Sandstones of the Espinaso Formation con- mean quartz content of less than 5% m (915 ft) thick and consists of reddish- tain quartz-poor arkose and lithic arkose (Kautz et al., 1981). brown to reddish-yellow sandstone and (Kautz et al., 1981). Large and Ingersoll reddish-brown and olive-gray mudstone (1997) studied the composition of medi- Methods overlying a very pale brown basal con- um- to very coarse grained sandstone from glomerate (Appendix). Concretionary post-Espinaso Formation deposits in the The study area was mapped at a scale of sandstone intervals and thin rhizoconcre- Hagan embayment to define their vol- 1:24,000 (Fig. 3), and deposits of the Santa tionary beds are locally present. Bedding canic-hypabyssal petrofacies. They con- Fe Group were divided into textural litho- of the Tanos Formation dip 20–32° north- cluded that this petrofacies is composition- facies following the methods of Cather east. The Tanos Formation is exposed in ally related to rocks of the Ortiz Moun- (1997). Two stratigraphic sections were the San Felipe Pueblo NE and Hagan tains. This petrofacies is dominantly lithic measured in Arroyo de la Vega de los

November 2002, Volume 24, Number 4 NEW MEXICO GEOLOGY 109 (Santo Domingo Pueblo quadrangle) G o Qu alisteo 35 Ck 30' Qu QTsp QTsp Qu Qu 2 S d i l e 2 QTsa Qu 68 QTsa fa 2 Qu u lt 2

Qu 22 Qu 5 Qu lt QTsp fau s Tbm gher Qu Buda 15 3 ) 64 e l Tbs g Qu 25 n 7

a c ) r 3

b e d anos l a los T 24 g u de n q ga 3 a Ve Tbcs r o a d l l

e a b d Qu a u e

o q u oy P r d r i

Tbcs r e A 2 Tbcs d

p 23 i a l e M (

F Qu Tg Qu t 3

n QTsp l a u Tbs a S f Qu (

Qu 25 Tbc 2 63 Ku 1 o c s i c n Te Qu a r Qu Ttu QTsp F 28 Diamond MBS Tail fault Tbs 60 Qu n a S Qu 28 76 Ttl PBS

Ku lt u A 33 a y Tg Tbcs f o . 2 Qu JTr 85 o 24 T 35 o Ku Td QTt n 32 Ttu s q 31 o u 24 n 22' e 4 a Qu T 30" JTr QTt o 106 o 22' 30" 0 1 2 km (Hagan quadrangle) 106 15' 0 1 2 mi

Qu . QTsa Tbm Tbcs Ttl Te Td JTr . m m F . F

Quaternary alluvium, s axial-fluvial muddy conglomeratic lower Espinaso Diamond Jurassic– m e e r F n sandstone sandstone conglomerate undivided a Fm. Tail Fm. Triassic, undiv. o s h r o s d n k a

QTt QTsp Tbc Tbs a Ttu Tg Ku c 1 L T a l a r B Tuerto fm. r piedmont conglomerate sandstone sandstone & Galisteo Cretaceous,

e Localities i

S mudstone Fm. undivided 24 PBS fault, bar on bedding oil-test downthrown side measured well section

110 NEW MEXICO GEOLOGY November 2002, Volume 24, Number 4 Arroyo de la Vega 200 de los Tanos Paleosol UNIT continues Poor exposures Q G3, G4

) Rhizoconcretions m (

s Conglomerate 100 s e s

n lenses, schematic c k b c i

T P h Cross-stratification T

N Gravel count site O I T ) A

s O b M T R ( O

s 0 F e i c E a f R

o Pelto Oil A h t H N i l

S Blackshare Federal #1 e

K 3.8 km 3.7 km n C o t A

s south east 020ohmm L d B n el: 1835 m a Arroyo del s M Tuerto no UNIT Tuerto fm. data T I

L G2 I N U K J A

e H n o t

s I N d n O I a s T A r

a H l M u R

G l b l O a a B t m F s r s s t S e l u u p

G o a O r f p e N u m u A n T F

F E

e C n o t E s d u D

m D e l d

d C i C lower m D B conglomerate B 8

basalt flow G1 g o A A l r e t

10-12 e

ESPINASO FM. m fmcpc b fmcpc b - p i

ms gmsg d continues

FIGURE 3—Simplified geologic map of the San Felipe Pueblo NE 7.5-min FIGURE 4—Stratigraphic sections of the Tanos and Blackshare Forma- quadrangle (modified from Cather et al., 2000). Localities discussed in text tions at Arroyo de la Vega de los Tanos and Arroyo del Tuerto (Fig. 3). include Arroyo de la Vega de los Tanos (1) and Arroyo del Tuerto (2) strati- Comparisons to an induction resistivity log of the Pelto Oil Blackshare graphic sections, the Pelto Oil Blackshare Federal #1 (PBS), and Merrion Federal #1 indicate that this well penetrated deposits similar to the type Blackshare Federal #1 (MBS) wells, and gravel count sites in the Tuerto section. An angular unconformity between the projection of the Espina- formation (3) and upper Blackshare Formation (4). Volcanic units include so and Tanos Formations is interpreted from a continuous dip-meter a 25.41 Ma basaltic flow at the type section (1), a 11.65 Ma fallout ash (a), log for this well. Strike and dip symbols indicate the average orienta- three correlative fluvially recycled fallout tephra, including the 11.65 Ma tion of deposits above and below this contact. Horizontal scale indi- ash (a, b, c), and a 1.59 ±0.02 Ma lapilli of the lower Bandelier Tuff (d). cates approximate maximum grade (m = mudstone; s = sandstone; g = Major structural features include the Budaghers, San Francisco, Diamond conglomerate). Diamonds denote locations of gravel counts shown on Tail, and Tanos faults. The La Bajada fault is 2–3 km (1–2 mi) east of the Figure 5. quadrangle.

November 2002, Volume 24, Number 4 NEW MEXICO GEOLOGY 111 Tuerto where it consists of very pale brown to G6 n=86 formation light yellowish-brown tabular sandstone with thinly bedded rhizoconcretionary n=77 intervals with sparse scattered pebbles. G5 This unit is characterized by medium- to thick-bedded, massive to cross-stratified Blackshare G4 n=70 sandstone. The contact with the overlying Formation Blackshare Formation is gradational and placed at the lowest lenticular, pebbly to G3 n=68 cobbly sandstone in the upper tabular sandstone member. The Tanos Formation G2 n=80 may interfinger with the Blackshare For- mation; however, the degree of interfinger- ing is obscured by the Tuerto formation. Tanos G1 n=141 Formation The Tanos–Blackshare contact chosen at the measured sections differs slightly from 0 20 40 60 80 100 the mapped contact, which was placed at the top of the highest, thickly bedded tab- Percent (%) ular sandstone. This boundary can be resolved within a few tens of meters depending upon the criterion used (i.e., highest tabular sandstone vs. lowest lentic- Ortiz porphyry metaquartzite siltstone ular conglomerate). The resistivity log for the Pelto Oil Blackshare Federal #1, drilled nearly 5 km (3 mi) southeast of the Tanos Formation hornfels chert sandstone typesection (Fig. 3), indicates the presence FIGURE 5—Stacked bar graph illustrating upsection variations in gravel composition in the Tanos, of four somewhat distinctive intervals in Blackshare, and Tuerto formations. Gravel of the Ortiz porphyry dominates the basal Tanos Forma- the upper part of this well that roughly tion (G1). Gravel in the Blackshare Formation (G2–G4; G5 at locality 3) becomes more diverse upsec- correspond to the rocks exposed at the tion. The Tuerto formation at locality 4 (G6) is heterolithic and contains a greater abundance of horn- type section (Fig. 4). Resistivity signatures fels gravel (50%) than the underlying Blackshare Formation. in units A and C show greater variability compared to units B and D, suggesting the presence of interbedded coarse-grained quadrangles. The Tanos Formation is sub- The lower Tanos Formation contains a and fine-grained intervals. Units B and D divided into three informal members: a black, 2.5–3.0-m-thick (8–10-ft-thick), lack the major resistivity shifts of A and C, basal conglomerate, a middle mudstone, basaltic lava flow that is discontinuously suggesting that B and D are lithologically and an upper tabular sandstone. exposed along the northeastern flank of similar. Correlation of unit B to the upper The lower conglomerate member is Espinaso Ridge. At the type section, this tabular sandstone member is reasonable approximately 12 m (39 ft) thick at the type flow is approximately 9 m (30 ft) above the because exposures are of relatively uni- section and thickens to approximately 31 base and contains white to olive-yellow, form sandstone. m (102 ft) at Arroyo del Tuerto (Arroyo spheroidal nodules of celadonite(?) and Gravels of the Tanos and Blackshare For- Pinovetito of Stearns, 1953b), approxi- altered olivine crystals. The underlying mations indicate a general increase in com- mately 4 km (2 mi) to the south (Fig. 1). pebbly sandstone is reddened, indicating positional diversity upsection (Fig. 5). The This unit thickens to as much as 100 m (328 thermal alteration of underlying deposits Tanos Formation contains only a few per- ft) based on interpretations of borehole during emplacement of the basalt. The top cent of nonigneous pebbles, such as petri- geophysical logs from the Pelto Oil Black- of the basalt is not reddened, suggesting fied wood and rounded metaquartzite. share Federal #1 well (Fig. 4). At the type emplacement as a subaerial lava flow. The Blackshare Formation contains more section the lower conglomerate is very The middle mudstone member is 144 m diverse gravel types, most notably, vari- pale brown to reddish-yellow, thinly to (472 ft) thick at the type section, where it ably colored, thermally metamorphosed medium-bedded conglomerate and peb- conformably overlies the lower member. sandstone and shale (hornfels), and petri- bly to cobbly sandstone. Gravel contains The base of the middle member is chosen fied wood. The overlying Tuerto formation recycled porphyritic volcanic and at the lowest ripple-laminated sandstone, a contains the most diverse clast assemblage hypabyssal-intrusive detritus, derived common sediment type in the lower part and contains abundant hornfels. from the neighboring Ortiz Mountains, of this member. Most of this member is a The boundary between the Espinaso and and sparse, rounded metaquartzite peb- thick succession of medium- to thick-bed- Tanos Formations is relatively easy to dis- bles that were probably derived from the ded, reddish-brown mudstone and clay- tinguish in the field, where the lower Galisteo Formation (Fig. 5). Sparse paleo- stone with thin- to medium-bedded, olive- Tanos Formation conglomerate rests on the current observations (n = 8) indicate a gray mudstone interbeds. Sandstone beds Espinaso Formation with a sharp and westerly paleoflow direction with mean increase in abundance upsection toward scoured contact (Fig. 7). The upper part of azimuth of 287 ± 19° (Fig. 6). Erskine and the upper tabular sandstone member. the Espinaso Formation is a well-consoli- Smith (1993) report calc-alkaline porphyry Mudstone beds thin southeast of the type dated but poorly cemented succession of gravel in the basal Santa Fe Group in the area. Thin, discontinuous gypsiferous light-gray to white sandstone and con- Hagan embayment that is compositionally mudstone beds are locally present in the glomerate. The Tanos Formation is very related to the lower Espinaso Formation; middle mudstone and upper tabular sand- pale brown to reddish yellow and cement- however, no attempt was made to differ- stone members in Arroyo del Tuerto ed with calcium carbonate. The uppermost entiate volcanic or hypabyssal-intrusive (Appendix). Espinaso Formation is commonly white to gravel in the Tanos or Blackshare Forma- The upper tabular sandstone member is gray and contains alkaline volcanic gravels tions in this study. 123 m (404 ft) thick at the type section, that contain biotite and clinopyroxene

112 NEW MEXICO GEOLOGY November 2002, Volume 24, Number 4 crystals (Erskine and Smith, 1993). The rally based members, two of which are North Tanos Formation contains a wider diversi- represented at the type section. These tex- ty of volcanic gravel types than in the tural lithofacies do not occur in any partic- underlying upper Espinaso Formation. ular stratigraphic order, but the lower part These Tanos Formation gravels range in of the Blackshare Formation exhibits a color from dark gray to reddish brown and crude upward-coarsening trend beginning black, and contain sparse nonvolcanic con- with the sandstone lithofacies (Tbs), and stituents, such as rounded quartzite peb- coarsening upward into conglomeratic bles and petrified wood. sandstone (Tbcs) and conglomerate (Tbc) Additional information on the character units. The muddy sandstone unit (Tbm) of the Tanos–Espinaso Formation contact follows this coarsening-upward trend to comes from an interpretation of borehole the northeast. geophysical data from nearby oil-test The conglomeratic member (Tbc) consists wells. The Pelto Oil Blackshare Federal #1 of well-cemented conglomerate and subor- fully penetrated the Cenozoic section. The dinate sandstone. The conglomeratic sand- scout ticket for this well places the Espin- stone member (Tbcs) contains roughly aso–Santa Fe Group contact at approxi- subequal amounts of sandstone and con- mately 451 m (1,480 ft) below land surface glomerate. Conglomerate is similar to the n=68 (bls). A continuous dip-meter log for this conglomeratic lithofacies and forms beds FIGURE 6—Rose diagram of paleocurrent data well indicates the presence of an angular that are 50–200 cm (20–79 inches) thick. Al- (grouped into 10° intervals) determined from unconformity at approximately 460 m though most of the conglomeratic sand- gravel imbrication, channel orientations, and (1,510 ft) bls. The underlying strata are ori- stone lithofacies is coarse-grained, thick- cross-stratification in the Tanos (n = 8) and ented N25°E, 10–12° northwest; overlying bedded mudstone is locally present. The Blackshare (n = 60) Formations, indicating west- deposits are N60°W, 8° northeast. This con- sandstone member (Tbs) contains sand- ward paleoflow from the Ortiz Mountains. A tact likely corresponds to the discon- stone with subordinate conglomerate and mean paleocurrent azimuth of 284 ± 8° was formable Espinaso–Tanos Formation con- mudstone, commonly arranged in fining- determined for 68 measurements. Paleocurrent tact exposed at the type section (Fig 4). upward sequences. A 10-m-thick (33-ft- data compiled from data on the geologic map of thick) interval of well-sorted sandstone and the San Felipe Pueblo NE quadrangle (Cather et al., 2000) and supplemented by additional meas- Blackshare Formation olive-gray mudstone containing sparse urements taken during stratigraphic descrip- scattered selenite gypsum is recognized in tions. The Blackshare Formation is a new litho- the sandstone mem- stratigraphic unit herein named for the ber approximately Blackshare Ranch site in Arroyo de la Vega 70 m (230 ft) strati- de los Tanos. The Blackshare Formation is graphically below more than 1,000 m (3,281 ft) thick as esti- locality a (Fig. 3). mated from stratigraphic sections and geo- The fine-grained logic mapping. Conglomerate beds are muddy sandstone lenticular, and sandstone intervals com- member (Tbm) is monly fine upward into thinly bedded exposed along the mudstone. Dips in the Blackshare Forma- eastern margin of tion progressively decrease upsection, from the study area and 16° to 1° northeast; stratal tilts are typically contains subequal greater near faults. proportions of The type section of the Blackshare For- sandstone and mation begins north of Arroyo de la Vega weakly cemented, de los Tanos, approximately 280 m (919 ft) commonly reddish- above the base of the type section of the brown mudstone. Tanos Formation (Fig. 3, Appendix). Paleo- Weakly developed current observations (n = 60) on conglom- paleosols are locally eratic beds indicate a westerly paleoflow common in the direction with mean azimuth of 284 ± 8° muddy sandstone (Fig. 6). A complete section of the Black- and sandstone share Formation was not measured because members. exposures are quite poor east of highway The sandstone NM–22. The top is overlain by the Plio- member conform- cene–Pleistocene Tuerto formation in an ably overlies the angular unconformity, and the succession Tanos Formation at is cut by the La Bajada fault. The minimum the type section. thickness for the Blackshare Formation is This lower sand- estimated to be at least 1,260 m (4,134 ft). stone pinches out to Gravel in the Blackshare Formation con- the south, and tains mostly monzanite and latite porphyry south of Arroyo del with sparse rounded metaquartzite, petri- Tuerto the conglom- fied wood, iron-stained sandstone, and eratic sandstone hornfels. The Blackshare Formation is conformably over- exposed in the San Felipe Pueblo NE, lies the Tanos For- Hagan, and Madrid quadrangles. mation. At the type The Blackshare Formation, as mapped in section, the sand- FIGURE 7—Contact between white sandstone and conglomerate of the the study area (Fig. 3), contains four textu- Espinaso Formation (left) and pale-brown conglomerate of the Tanos For- mation (right). Scale is 1.5 m high.

November 2002, Volume 24, Number 4 NEW MEXICO GEOLOGY 113 stone-dominated members are very pale zones in the Tanos Formation and general (NMGRL#51451; Peters, 2001a). The age of brown to reddish-brown sandstone with in- lack of evaporitic beds within the mud- this basaltic flow is similar to the terbedded mudstone and scattered lenti- stone-dominated intervals suggest that the Cieneguilla basanite (Cieneguilla limbur- cular pebble to cobble conglomerate. basin floor may represent deposition in a gite of Stearns, 1953a, b), which was dated Ash beds are recognized in the con- ground-water recharge or through-flow using the K–Ar method at 25.1 ± 0.7 Ma glomeratic sandstone member near the playa-lake system (Rosen, 1994); however, (Baldridge et al., 1980). The Cieneguilla Budaghers fault. These white to light-gray a detailed evaluation of basin-floor deposi- basanite has been recently re-mapped in ashes range from a few centimeters to tional environments and paleohydrology the southwestern Santa Fe embayment and approximately 3 m (10 ft) in thickness and was not attempted. Mudstone and ripple- dated using the 40Ar/39Ar method at 26.08 contain no obvious nonvolcanic detritus. laminated and tabular sandstone are simi- ± 0.62 Ma (Koning and Hallett, 2000). The thickest bed is cross-stratified and lar to descriptions of fluviolacustrine facies Although these two flow units are similar contains scattered lapilli. Faults obscure of the Popotosa Formation (lower Santa Fe in age, the Tanos Formation flow was not physical correlation of these ashes; howev- Group) exposed at the southern end of the petrographically or chemically compared er, geochemical analyses indicate these Albuquerque Basin and in the Socorro to the Cieneguilla basanite. ashes are geochemically indistinguishable Basin (Asher-Bolinder, 1988). The presence The magnitude of the Tanos–Espinaso (Table 1) and are similar when imaged of low-angle ripple laminations in the mid- Formation unconformity is poorly con- with backscattered electrons on the elec- dle mudstone and upper, tabular sand- strained but represents less than 4–5 m.y. tron microprobe. These ashes are com- stone members indicates fluvial deposition of erosion or nondeposition at Espinaso posed mainly of glassy shards, mostly of sandstone interbeds, probably associat- Ridge. Work is currently underway to date between 50 and 200 µm (0.002–0.008 inch- ed with streams along the distal piedmont the top of the Espinaso Formation in the es) in the longest dimension. Many shards and margin of the basin floor. Hagan embayment. Some age constraints are rectangular in backscattered electrons, The Blackshare Formation contains for the Espinaso Formation are known and suggesting a platy morphology in three mostly fluvial sandstone and conglomer- help constrain the magnitude of this 1 dimensions. Many tricuspate shards are ate. Sparse mudstone beds, some of which unconformity. Huerfano Butte (E ⁄2 sec. 22 1 observed. These shards represent rem- are similar to the Tanos Formation mud- and W ⁄2 sec. 23 T13N R6E), a low hill on nants of the intersection of three bubbles, stones, are locally present. The presence of the northern part of the Hagan quadran- and they are formed by explosive erup- abundant Ortiz porphyry detritus in cross- gle, which was informally named by tions driven by vesiculation (Fisher and stratified sandstone beds supports stream- Stearns (1953b), lies within the upper part Schmincke, 1984). The shard shapes and flow-dominated deposition from the Ortiz of the Espinaso Formation (Cather et al., purity and the well-sorted nature of the Mountains. Fining-upward sequences of 2002). Groundmass concentrates from samples suggest derivation from a pri- conglomerate and sandstone, generally Huerfano Butte rock yielded an age of mary ashfall event (Heiken and Wohletz, capped by thin, discontinuous mudstone, 31.88 ± 0.24 Ma (NMGRL#2566, Peters, 1984). The shards in both samples are are common in this unit. The lack of medi- 2002). Work is currently underway to unbraided and contain delicate glass um- to thick-bedded mudstone and pres- radioisotopically date an ash-flow tuff in structures that are unbroken, suggesting ence of fining-upward sequences of con- the upper Espinaso Formation approxi- that little transport occurred after primary glomeratic sandstone, sandstone, and mately 100 m (328 ft) below the deposition; however, the ash at locality b is minor mudstone and paleosols indicate Tanos–Blackshare contact at the type area. approximately 3 m (10 ft) thick and cross- deposition along a stream-flow dominated Preliminary results of 40Ar/39Ar dating of stratified, indicating some fluvial rework- piedmont derived from the Ortiz Moun- this tuff suggest emplacement around 30 ing of this deposit. tains. However, a general upward- and Ma (R. Esser, pers. comm. 2002). Kautz et southeastward-coarsening trend in much al. (1981) report a K–Ar age for a nephelene Depositional environments of the Blackshare Formation suggests that syenite of 26.9 ± 0.6 Ma on Espinaso Ridge. deposition first occurred as a prograding Projections of their locality indicate it is Mudstone in the Tanos Formation is thinly piedmont wedge along the eastern margin approximately 160 m (525 ft) below the top to thickly bedded and comprises about a of the Rio Grande rift. of the Espinaso Formation. This rock lies third of the type section. The abundance of below the ca 30 Ma tuff, suggesting that mudstone suggests deposition in quiet Age and correlation the 27 Ma age reported by Kautz et al. water settings near the basin floor. The (1981) may be in error, and indicating that presence of olive-gray mudstone beds The ages of the Tanos and Blackshare For- additional 40Ar/39Ar dating is required to within a dominantly reddish-brown mud- mations are constrained by 40Ar/39Ar dat- constrain the age of the top of the Espinaso stone succession suggests deposition in an ing and geochemical correlations. Ground- Formation. oxidizing, alluvial- or mud-flat environ- mass concentrates from an olivine-bearing The age of the Blackshare Formation is ment with occasional deposition in shal- basaltic flow near the base of the Tanos constrained by a dated volcanic ash at low lakes or ponds under reducing condi- Formation type section yielded a whole- locality a, which is stratigraphically locat- tions. The presence of rhizoconcretionary rock 40Ar/39Ar age of 25.41 ± 0.32 Ma ed approximatley 1,060 m (3,478 ft) above

TABLE 1—Mean of electron microprobe analysis (n) of tephra in the Black- homogeneous reference materials and counting statistics, in weight per- share Formation at tephra localities illustrated in Figure 3. All analyses nor- cent: P2O5 = ± 0.1, SiO2 = ± 0.5, TiO2 = ± 0 .01, Al2O3 = ± 0 .03, MgO = ± 0.12, malized and reported in weight percent. Major elements, chlorine (Cl), and CaO = ± 0.05; MnO = ± 0.03, FeO = ± 0.07, Na2O = ± 0.09, K2O = ± 0.19, Cl fluorine (F) were analyzed by electron microprobe. Errors (± σ) of deter- = ± 0.01; F = ± 0.1. mination for the electron microprobe are based on replicate analyses of

Sample n P2O5 SiO2 TiO2 Al2O3 MgO CaO MnO FeO Na2OK2OF Cl Mean, locality a 19 0.02 77.37 0.22 12.15 0.04 0.64 0.03 1.86 2.88 4.62 0.12 0.04 ± 1σ 0.02 0.67 0.03 0.28 0.02 0.04 0.02 0.07 0.18 0.75 0.08 0.01 Mean, locality b 20 0.01 76.60 0.20 12.51 0.04 0.62 0.01 1.86 2.97 4.96 0.15 0.05 ±1σ 0.01 0.34 0.03 0.17 0.02 0.05 0.02 0.12 0.10 0.38 0.09 0.01 Mean, locality c 20 0.01 76.97 0.21 12.52 0.04 0.63 0.01 1.86 2.92 4.60 0.16 0.05 ± 1σ 0.02 0.64 0.03 0.18 0.02 0.04 0.02 0.07 0.17 0.63 0.08 0.01

114 NEW MEXICO GEOLOGY November 2002, Volume 24, Number 4 the base of the Tanos Formation. Sanidine tion is not warranted because of these dif- are buried by the (upper Miocene–Pleis- concentrates from this ash yielded a laser ferences in composition, source area, depo- tocene) Sierra Ladrones Formation. fusion 40Ar/39Ar age of 11.65 ± 0.38 Ma sitional environment, and location in the Stratal tilts within the Tanos and Black- (NMGRL#51627, Peters, 2001b). The vol- basin. Deposits of the Tanos Formation are share Formations tend to decrease upsec- canic ashes of localities a, b, and c are also slightly older than the basal Zia For- tion, indicating coeval sedimentation and chemically and morphologically indistin- mation, which is biostratigraphically con- subsidence occurred during Oligocene guishable from ashes in the upper part of strained between 19 and 22 Ma (Tedford through late Miocene times. A period of the Cerro Conejo Member of the Zia For- and Barghoorn, 1999). Extrapolation of tilting and extensive erosion occurred after mation, exposed approximately 30 km (19 Tedford and Barghoorn's magnetostrati- deposition of the Blackshare and before mi) west of the study area and south of graphically determined stratal accumula- aggradation of the Pliocene–Pleistocene Santa Ana Mesa. Koning and Personius (in tion rates to the base of the Zia Formation Tuerto formation. The lack of regional tilt- press) correlated the Cerro Conejo ashes to suggests that deposition of the Zia Forma- ing of the Tuerto formation indicates little three ashes, ranging from ca 10 to 12 Ma, tion began around 19 Ma. deformation occurred since Pliocene time. that were derived from the Trapper Creek The Tanos and Blackshare Formations The timing of late Miocene deformation tephra succession from the northeastern are similar in age to the Popotosa Forma- and erosion of the Hagan embayment is Basin and Range province (Perkins et al., tion, which is exposed at the southern mar- not well constrained, but they may have 1998). The upper age limit of the Black- gin of the Albuquerque Basin and in the happened during a time of increased sub- share Formation is not known, but it is adjacent Socorro Basin. Deposits of the sidence along the western structural mar- older than the overlying Pliocene–Pleis- Popotosa Formation are interpreted to gin of the Santo Domingo sub-basin (Smith tocene Tuerto formation. More than 200 m record deposition within fault-bounded, et al., 2001). (656 ft) of Blackshare Formation lies above internally drained basins (Chapin and A 40Ar/39Ar age on a basalt flow near the the 11.65 Ma ash, indicating that deposi- Cather, 1994). The Blackshare Formation is base of the Tanos Formation demonstrates tion continued into late Miocene time. older than the Cochiti Formation, which is a late Oligocene age and confirms a K–Ar The Tanos Formation was originally associated with deposition of volcaniclas- age from the northern tip of Espinaso assigned to the Abiquiu(?) Formation by tic detritus derived from the Keres Group Ridge (Kautz et al., 1981). These ages make Stearns (1953b), mainly based on strati- along the western margin of the Santo the Tanos Formation the oldest exposed graphic position (age equivalence) and the Domingo sub-basin and southeastern unit of the Santa Fe Group in the Albu- presence of tuffaceous sediment. The Jemez volcanic field (Smith et al., 2001). querque Basin area. Given an estimated Abiquiu Formation was deposited Although the upper age limit of the Black- thickness of approximately 1,060 m (3,478 between 26 and 18 Ma (Tedford and share Formation has not been established, ft) of Tanos and Blackshare deposits pre- Barghoorn, 1993). Deposits of the Abiquiu it is probably older than the ancestral Rio served between dated volcanic units, Formation in its type area, approximately Grande fluvial facies of the Sierra Oligocene–Miocene stratal accumulation 70 km (43 mi) northwest of the Hagan Ladrones Formation (Smith et al., 2001), rates (not corrected for compaction or the embayment, consist largely of volcanic which marks the end of closed-basin depo- presence of intraformational unconformi- sediment derived from the Latir volcanic sition in the Albuquerque Basin. ties or hiatuses) in the Hagan embayment field of northern New Mexico (Lipman were approximately 76 m/m.y. (249 and Reed, 1989; Smith et al., in press). Most Discussion ft/m.y.). The presence of paleosols and notably, the rhyolitic Amalia Tuff, a signif- compaction of the mudstone beds indicate icant constituent in the Abiquiu Formation Results of this stratigraphic study allow a minimum estimate of accumulation. This (Smith, 1995), is not present in the Tanos inferences to be made regarding the geo- rate is similar to estimates of 69–83 m/m.y. and Blackshare Formations. A Latir source logic evolution of the Hagan embayment (226–272 ft/m.y.) for early and middle would require deposition via south-flow- and the eastern margin of the Rio Grande Miocene sediments exposed along the ing streams to reach the Hagan embay- rift. The Tanos–Blackshare succession northwestern margin of the Albuquerque ment. Such a paleoflow trend is not sup- records deposition in an actively subsiding Basin (Tedford and Barghoorn, 1999). ported by west-trending paleocurrent basin, part of which is now exposed in the These late Oligocene–middle Miocene val- observations from the Tanos and Black- Hagan embayment. Deposition of the ues are significantly lower than 600 share Formations. Furthermore, an Tanos Formation began after erosion m/m.y. (1,968 ft/m.y.) estimates for late Abiquiu Formation assignment for Tanos removed part of the Espinaso Formation. Miocene accumulation of fluviolacustrine Formation is not supported by petrograph- The Tanos Formation is interpreted to rep- deposits of the Popotosa Formation in the ic studies of sandstone that indicate deri- resent deposition near the margin of a southern part of the Albuquerque Basin vation from the Ortiz Mountains area basin-floor fluviolacustrine or playa-lake (Lozinsky, 1994). High late Miocene rates (Large and Ingersoll, 1997). system that was fed by streams draining were probably due to increased basin sub- Kelley (1977) assigned these rocks to the the Ortiz Mountains. Although thick evap- sidence or to geographically variable sub- Zia Formation of Galusha (1966), presum- orite beds were not observed, these sidence rates. Pliocene accumulation rates ably because of the low stratigraphic posi- deposits were probably laid down in a slowed to approximately 22–33 m/m.y. tion within the Santa Fe Group, and low-gradient or quiet-water basin-floor (72–108 ft/m.y.; Lozinsky, 1994). because of the light color of the sandstone environment within a closed basin. Mud- The composition of gravels in the Tanos beds. The Zia Formation, exposed 30–45 stone beds within the Blackshare Forma- and Blackshare Formations indicates local km (19–28 mi) to the west, contains thick tion may also indicate continued fluviola- derivation from the adjacent Ortiz Moun- eolianite that was deposited by westerly custrine sedimentation through middle tains. Hornfels gravels are interpreted to winds with sparse, widely spaced, south- Miocene time. Because the mudstone of be sandstone and shale from underlying east-flowing streams (Beckner and Mozley, the Tanos Formation extends to the north upper Paleozoic and Mesozoic strata that 1998; Gawne, 1981). Aside from scattered and northwest, where the San Francisco were thermally metamorphosed during intermediate volcanic pebbles of Oligocene and Budaghers faults truncate it, fluviola- emplacement of the Ortiz porphyry belt. age (Tedford and Barghoorn, 1999; Connell custrine deposits probably once extended Greenish-gray banded and dark-gray et al., 2001b) at the base of the Zia Forma- beyond the present structural limits of the hornfels probably originated from Creta- tion, there are virtually no volcanic gravels Hagan embayment. Correlative deposits ceous rocks (S. Maynard, pers. comm. in this deposit. Assignment of the Hagan are probably preserved on the hanging 2000). The general upsection increase in embayment succession to the Zia Forma- wall of the San Francisco fault, where they compositional diversity of gravel and

November 2002, Volume 24, Number 4 NEW MEXICO GEOLOGY 115 increase in hornfels through the other faults now buried by the Tuerto for- Creek succession of the northeastern Basin Tanos–Blackshare and Tuerto succession mation. Another possibility is that progres- and Range, and tephra in the upper part of reflects a progressive unroofing of the sive exposure of quartz-rich strata the Cerro Conejo Member of the Zia For- Ortiz Mountains. An Ortiz Mountains occurred by erosion of the formerly exten- mation. The ages of these volcanic units provenance interpretation is also support- sive cover of Oligocene volcanic and intru- indicate that stratal accumulation rates, ed by paleocurrent data indicating deposi- sive rocks. In the former case, quartz con- not corrected for compaction, were on the tion from west-flowing streams and sup- tent should increase sharply at the Espina- order of approximately 76 m/m.y. (249 ports the findings of Large and Ingersoll so–Tanos boundary. In the latter case, ft/m.y.) for the late Oligocene and middle (1997). quartz content should gradually increase Miocene interval. Gravity data indicate that the Albu- upsection from the Espinaso Formation. Deposition of the Tanos Formation is querque Basin is greatly segmented by partly coeval with deposition of the faults (Grauch et al., 1999), which hamper Conclusions Abiquiu Formation; however, paleocurrent reconstruction of early rift structure across measurements, field relationships, and the Rio Grande rift at this latitude. The The Tanos and Blackshare Formations are petrographic data indicate derivation from greater antiquity of the Santa Fe Group new lithostratigraphic units proposed for the neighboring Ortiz Mountains. The base within the Hagan embayment compared over a kilometer of upper Oligocene– of the Tanos Formation is older than the with the northwestern Albuquerque Basin upper Miocene deposits exposed in the Zia Formation at the northwestern margin is contrary to expectations of a recently Hagan embayment. Conglomeratic units of the Albuquerque Basin, suggesting that proposed tectonic model of the northern of the Tanos and Blackshare Formations deposition began earlier along the eastern Rio Grande rift (Large and Ingersoll, 1997; contain abundant rocks of the Ortiz por- basin margin, rather than along the west- Ingersoll, 2001). This model proposes that phyry belt, indicating local derivation ern margin of the Albuquerque Basin. the Albuquerque and Española Basins from the adjacent Ortiz Mountains. Paleo- were once part of a single, west-tilted half- current observations indicate deposition to Acknowledgments graben basin called the Tesuque Basin. the west and support petrographic data for According to this model, the development an Ortiz Mountains provenance. This study was funded in part by the New of the east-tilted Albuquerque Basin The Tanos Formation unconformably Mexico Statemap Program of the National occurred during late Miocene time as the overlies the Espinaso Formation. Expo- Cooperative Geologic Mapping Act of 1992 Sandia Mountains rose. Comparison of sures of this contact along the northeastern (P. W. Bauer, Program Manager) and the depositional patterns across the northern flank of Espinaso Ridge are discon- New Mexico Bureau of Geology and Min- Albuquerque Basin and Hagan embay- formable; however, examination of a con- eral Resources (P. A. Scholle, Director). The ment indicate deposition of piedmont and tinuous dip-meter log from a nearby oil- authors thank the Pueblo of San Felipe, basin-floor fluviolacustrine strata began test well suggests that this boundary is an Pueblo of Santo Domingo, Diamond Tail along the eastern margin of the rift. Slight angular unconformity toward the structur- Ranch, and Ball Ranch for facilitating erosion of the Espinaso Formation al margin of the Hagan embayment, south- access to the San Felipe Pueblo NE quad- occurred before deposition of the Tanos east of the type section. The Blackshare rangle and surrounding areas. We thank Formation; however, erosion removed Formation conformably overlies the Tanos Ms. Leanne Duree for allowing access to nearly all of Oligocene volcaniclastic rocks Formation and represents continued sedi- parts of Arroyo de la Vega de los Tanos. along the northwestern margin of the mentation from the Ortiz Mountains. Discussions with Steve Maynard, Gary Albuquerque Basin before deposition of Stratal tilts of the Tanos–Blackshare succes- Smith, John Hawley, and Charles Stearns the Zia Formation at around 19 Ma. Age sion decrease upsection in a continually greatly improved this contribution. David relationships support initial deposition subsiding basin. Subhorizontally bedded Sawyer provided data for the Pelto Oil along the Hagan embayment, rather than conglomerate and sandstone of the Blackshare Federal #1 well. Kathleen along the northwestern margin of the Pliocene–Pleistocene Tuerto formation McLeroy assisted in stratigraphic descrip- Albuquerque Basin, as required by the overlie the Blackshare Formation in an tions. Comments on an earlier draft of this model of Ingersoll (2001). angular unconformity. paper by John Hawley are greatly appreci- Petrographic studies of the Galisteo, The Tanos Formation contains mudstone ated. Leo Gabaldon and Kathryn Glesener Espinaso, and Tanos–Blackshare Forma- and sandstone with minor conglomerate drafted the geologic map. This paper ben- tions yield additional information regard- interbeds that represent deposition in efited from reviews by Gary Smith, ing the tectonic development of the Hagan playa-lake and piedmont settings within a Spencer Lucas, Richard Tedford, and embayment and vicinity. Sandstone of the hydrologically closed basin. The Black- Charles Stearns. Equipment brand-names Espinaso Formation is nearly devoid of share Formation contains sandstone with discussed in this report are for descriptive detrital quartz (Kautz et al., 1981), where- interbeds of lenticular conglomerate, con- purposes only and do not necessarily indi- as, the quartz content of the Tanos and glomeratic sandstone, and minor mud- cate endorsement by the New Mexico Blackshare Formations ranges from stone, commonly forming fining-upward Bureau of Geology and Mineral Resources approximately 20% to 70% (Large and sequences. The Blackshare Formation rep- or the state of New Mexico. Ingersoll, 1997; see discussion in Connell resents deposition of a westward prograd- and Cather, 2001; Connell et al., 2001a). ing piedmont derived from the Ortiz This abrupt increase in quartz content sug- Mountains. Local mudstone beds in the References gests rapid exposure of quartz-rich rocks, Blackshare Formation may indicate contin- Asher-Bolinder, S., 1988, Stratigraphy of reference such as the Galisteo Formation and older ued closed-basin deposition. sections in the Popotosa Formation, Socorro The Tanos and Blackshare Formations County, New Mexico: U.S. Geological Survey, sedimentary rocks. Sparse pebbles of Bulletin 1800, 22 pp., 1 pl. rounded metaquartzite and petrified contain ashes and a basalt flow that con- Bachman, G. O., and Mehnert, H. H., 1978, New wood present in conglomeratic beds of the strain ages of deposition. A basalt flow K–Ar dates and the late Pliocene to Holocene Tanos and Blackshare Formations also near the base of the Tanos Formation yield- geomorphic history of the central Rio Grande support derivation from the Galisteo or ed an 40Ar/39Ar age of 25.41 ± 0.32 Ma. region, New Mexico: Geological Society of Amer- Diamond Tail Formations. This abrupt Sanidine concentrates from one of these ica, Bulletin, v. 89, no. 2, pp. 283–292. 40 39 Baldridge, W. S., Damon, P. E., Shafiqullah, M., and increase in quartz content could originate fallout ashes yielded a Ar/ Ar age of Bridwell, R. J., 1980, Evolution of the central Rio from Oligocene–Miocene uplift of the La 11.65 ± 0.38 Ma. This ash geochemically Grande rift, New Mexico—new potassium–argon Bajada or Tijeras fault zones, or possibly resembles the middle Miocene Trapper ages: Earth and Planetary Science Letters, v. 51,

116 NEW MEXICO GEOLOGY November 2002, Volume 24, Number 4 no. 2, pp. 309–321. Hawley, J. W., ed., 1978, Guidebook to Rio Grande Snake River Plain volcanic province: Geological Beckner, J. R, and Mozley, P. S., 1998, Origin and rift in New Mexico and Colorado: New Mexico Society of America, Bulletin, v. 107, pp. spatial distribution of early vadose and phreatic Bureau of Mines and Mineral Resources, Circular 1484–1506. calcite cements in the Zia Formation, Albu- 163, 241 pp. Perkins, M. E., Brown, F. H., Nash, W. P., McIntosh, querque Basin, New Mexico, USA: Special Publi- Heiken, G., and Wohletz, K. H., 1985, Volcanic ash: W., and Williams, S. K., 1998, Sequence, age, and cations of the International Association of Sedi- University of California Press, 250 pp. source of silicic fallout tuffs in middle to late mentology, v. 26, pp. 27–51. Ingersoll, R. V., 2001, Structural and stratigraphic Miocene basins of the northern Basin and Range Cather, S. M., 1997, Toward a hydrogeologic classi- evolution of the Rio Grande rift, northern New province: Geological Society of America, Bulletin, fication of map units in the Santa Fe Group, Rio Mexico and southern Colorado: International v. 110, no. 3, pp. 344–360. Grande rift, New Mexico: New Mexico Geology, Geology Review, v. 43, no. 10, pp. 867–891. Peters, L., 2001a, 40Ar/39Ar geochronology results v. 19, no. 1, pp. 15–21. Kautz, P. F., Ingersoll, R. V., Baldridge, W. S., from San Felipe, Capilla Peak, and Tome NE Cather, S. M., Connell, S. D., and Black, B. A., 2000, Damon, P. E., and Shafiqullah, M., 1981, Geology quadrangles: New Mexico Geochronological Preliminary geologic map of the San Felipe of the Espinaso Formation (Oligocene), north- Research Laboratory, Internal Report NMGRL- Pueblo NE 7.5-min quadrangle, Sandoval Coun- central New Mexico: Geological Society of Amer- IR-135, 10 pp. ty, New Mexico: New Mexico Bureau of Mines ica, Bulletin, v. 92, no. 12, Part I, pp. 980–983, Part Peters, L., 2001b, 40Ar/39Ar geochronology results and Mineral Resources, Open-file Geologic Map II, pp. 2318–2400. from San Felipe Pueblo ashes: New Mexico OF-GM 37, scale 1:24,000. Kelley, V. C., 1977, Geology of Albuquerque Basin, Geochronological Research Laboratory, Internal Cather, S. M., Connell, S. D., Lucas, S. G., Picha, M. New Mexico: New Mexico Bureau of Mines and Report NMGRL-IR-132, 8 pp. G., and Black, B. A., 2002, Preliminary geologic Mineral Resources, Memoir 33, 60 pp. Peters, L., 2002, 40Ar/39Ar geochronology results map of the Hagan 7.5-min quadrangle, Sandoval Koning, D. J., and Hallett, R. B., 2000, Geology of from Huerfano Butte basalt: New Mexico County, New Mexico: New Mexico Bureau of the Turquoise Hill 7.5-min quadrangle, Santa Fe Geochronological Research Laboratory, Internal Geology and Mineral Resources, Open-file Geo- County, New Mexico: New Mexico Bureau of Report NMGRL-IR-222, 2 pp. logic Map OF-GM 50, scale 1:24,000. Mines and Mineral Resources, Open-file Geolog- Rosen, M. R., 1994, The importance of groundwater Chapin, C. E., and Cather, S. M., 1994, Tectonic set- ic Map OF-GM 41, scale 1:24,000. in playas—a review of playa classifications and ting of the axial basins of the northern and central Koning, D. J., and Personius, S. F., in press, Prelim- the sedimentology and hydrology of playas; in Rio Grande rift: Geological Society of America, inary geologic map of the Bernalillo NW quad- Rosen, M. R. (ed.), Paleoclimate and basin evolu- Special Paper 291, pp. 5–25. rangle, Sandoval County: New Mexico Bureau of tion of playa systems: Geological Society of Connell, S. D., and Cather, S. M., 2001, Stratigraphy Geology and Mineral Resources, Open-file Geo- America, Special Paper 289, pp. 1–18. of the lower Santa Fe Group, Hagan embayment, logic Map, scale 1:24,000. Smith, G. A., 1995, Paleogeographic, volcanologic, north-central New Mexico—preliminary results: Large, E., and Ingersoll, R. V., 1997, Miocene and and tectonic significance of the upper Abiquiu New Mexico Bureau of Geology and Mineral Pliocene sandstone petrofacies of the northern Formation at Arroyo del Cobre, New Mexico; in Resources, Open-file Report 454b, pp. H49–H56. Albuquerque Basin, New Mexico, and implica- Bauer, P. W., Kues, B. S., Dunbar, N. W., Karl- Connell, S. D., Cather, S. M., McIntosh, W. C., Dun- tions for evolution of the Rio Grande rift: Journal strom, K. E., and Harrison, B. (eds.), Geology of bar, N., Koning, D. J., and Tedford, R. H., 2001a, of Sedimentary Research, v. 67, no. 3, pp. 462–468. the Santa Fe region: New Mexico Geological Soci- Stratigraphy of lower Santa Fe Group deposits in Lipman, P. W., and Reed, J. C., Jr., 1989, Geologic ety, Guidebook 46, pp. 261–270. the Hagan embayment and near Zia Pueblo, New map of the Latir volcanic field and adjacent areas, Smith, G. A., 2000, Oligocene onset of Santa Fe Mexico—implications for Oligo-Miocene devel- northern New Mexico: U.S. Geological Survey, Group sedimentation near Santa Fe, New Mexico opment of the Albuquerque Basin (abs.): New Miscellaneous Investigations Series Map I-1907, 2 (abs.): New Mexico Geology, v. 22, no. 2, p. 43. Mexico Geology, v. 23, no. 2, pp. 60–61. sheets, scale 1:48,000. Smith, G. A., McIntosh, W. C., and Kuhle, A. 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A., 1993, Composi- mentation, and evolution of the southern Rio co: U.S. Geological Survey, Water-supply Paper, tional characterization of volcanic products from Grande rift, New Mexico, USA: Sedimentary WRI–1525, 258 pp. a primarily sedimentary record: Geological Soci- Geology, v. 92, no. 1–2, pp. 79–96. Stearns, C. E., 1953a, Early Tertiary volcanism in the ety of America, Bulletin, v. 105, pp. 1214–1222. Maynard, S. R., Martin, K. W., Nelson, C. J., and Galisteo–Tonque area, north-central New Mexi- Fisher, R. V., and Schmincke, H. U., 1984, Pyroclas- Schutz, J. L., 1990, Geology and gold mineraliza- co: American Journal of Science, v. 251, no. 6, pp. tic rocks: Springer-Verlag, 472 pp. tion of the Ortiz Mountains, Santa Fe County, 415–452. Galusha, T., 1966, The Zia Sand Formation, new New Mexico: Mining Engineering, v. 42, no. 8, Stearns, C. E., 1953b, Tertiary geology of the Galis- early to medial Miocene beds in New Mexico: pp. 1007-1011. teo–Tonque area, New Mexico: Geological Soci- American Museum Novitates, v. 2271, 12 pp. Munsell Company, 1992, Soil color chart: Kollmor- ety of America, Bulletin, v. 64, pp. 459–508. Gawne, C., 1981, Sedimentology and stratigraphy gen Instruments Corp, New York, no pagination. Tedford, R. H., and Barghoorn, S., 1993, Neogene of the Miocene Zia Sand of New Mexico, summa- (NACSN) North American Commission on Strati- stratigraphy and mammalian biochronology of ry: Geological Society of America, Bulletin, v. 92, graphic Nomenclature, 1983, North American the Española Basin, northern New Mexico; in no. 12, Part I, pp. 999–1007. stratigraphic code: American Association of Lucas, S. G., and Zidek, J. (eds.), Vertebrate pale- Gorham, T. W., and Ingersoll, R. V., 1979, Evolution Petroleum Geologists, Bulletin, v. 67, no. 5, pp. ontology in New Mexico: New Mexico Museum of the Eocene Galisteo Basin, north-central, New 841–875. of Natural History and Science, Bulletin 2, pp. Mexio; in Ingersoll, R. V., Woodward, L. A., and Pazzaglia, F. J., Woodward, L. A., Lucas, S. G., 159–168. James, H. L. (eds.), Santa Fe country: New Mexi- Anderson, O. J., Wegman, K. W., and Estep, J. W., Tedford, R. H., and Barghoorn, S., 1999, Santa Fe co Geological Society, Guidebook 30, pp. 219–224. 1999, Phanerozoic geologic evolution of the Albu- Group (Neogene), Ceja del Rio Puerco, north- Grauch, V. J. S., Keller, G. R., and Gillespie, C. L., querque area; in Pazzaglia, F. J., and Lucas, S. G. western Albuquerque Basin, Sandoval County, 1999, Discussion of new gravity maps for the (eds.), Albuquerque geology: New Mexico Geo- New Mexico; in Pazzaglia, F. J., and Lucas, S. G. Albuquerque Basin area; in Pazzaglia, F. 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November 2002, Volume 24, Number 4 NEW MEXICO GEOLOGY 117 Appendix A Type section of Tanos and Blackshare Formations in Arroyo de la Vega de Abney level and Jacob staff. Stratigraphic offset across Arroyo de la Vega los Tanos, Hagan embayment, San Felipe Pueblo NE 7.5-min quadrangle. de los Tanos measured using tape and compass. Colors are dry. Textural Base of measured section at N: 3,919,920 m; E: 380,530 m and top of meas- abbreviations include: very fine, vfL, vfU; fine, fL, fU; medium, mL, mU; ured section at N: 3,921,000 m; E: 381,360 m; (UTM zone 13S, NAD 1983). coarse, cL, cU; and very coarse, vcL, vcU. Numerical unit designations Measured upsection from unit 1 by S. D. Connell and K. McLeroy using an established upsection and listed in descending stratigraphic order.

Unit Description Thickness Unit Description Thickness (m) (ft) (m) (ft) Blackshare Formation, conglomeratic sandstone sandstone with reddish-brown (5YR 5/3–7/4), medi- (Tbc, 43 m) um- to thick-bedded, cemented mudstone interbeds Q. Conglomerate and conglomeratic sandstone; massive that comprise 15–20% of unit. Sandstone exhibits nor- to crudely bedded, clast- and matrix-supported, cob- mal grading. Gravelly intervals comprise 5–15% of ble to boulder conglomerate. Matrix is light-brown to unit and consist of matrix-supported pebbly to cobbly pink (7.5YR 6/4–7/4), very coarse grained (vcU), sandstone; gravel ranges from 2 mm to 20 cm in diam- poorly sorted pebbly sandstone. Cobbles and boul- eter. Unit also contains scattered, <4-cm-thick, low- ders are subrounded to subangular and range from 30 angle planar crossbeds and <4-cm-thick, matrix-sup- to 100 cm in diameter (mostly 20–40 cm). Clast count ported, pebbly sandstone and reddish-yellow (7.5YR near middle of unit (n = 68) indicates gravels com- 7/6), lenticular, concretionary sandstone interbeds. posed of Ortiz porphyry (79%), black and brown sub- Top contains thick-bedded, reddish-brown (5YR 5/3) 31.5 103 rounded polished chert (15%), rounded metaquartzite mudstone. (3%), sandstone (2%), and hornfels (1%). Clast count L. Sandstone and conglomeratic sandstone; conglomer- near top of unit (n = 70) indicates gravels composed of ate comprises 70% of unit, mostly clast- and matrix- Ortiz porphyry (73%), black hornfels and rounded supported, thin- to medium-bedded pebble to cobble chert (19%), rounded metaquartzite (3%), and sand- conglomerate and pebbly sandstone. Forms series of stone (5%). Section ends on hill top where deposits are fining-upward sequences. Gravel size ranges from 1 poorly exposed. 43.0 141.0 cm to 8 cm in diameter. Conglomerate is subrounded Blackshare Formation, sandstone (Tbs, 260 m) to subangular, matrix supported with clast-supported P. Sandstone and pebbly sandstone; light-brown to pink lenses predominantly composed of Ortiz porphyry. (7.5YR 6/4–7/3) and very pale brown (10YR 7/3), Gravel (n = 80) composed of Ortiz porphyry (75%), massive to thin-bedded, fine-grained (fL–fU) and hornfels (13%), and sandstone (12%). Interbedded very coarse grained (vcU), well-sorted sandstone with with very pale brown (10YR 7/3), medium-bedded, reddish-yellow (5YR 6/6), medium-bedded, very fine poorly sorted pebbly sandstone. Contains ~15-cm- to fine-grained (vfU–fL) sandstone interbeds and thick, scattered, very coarse grained (vcU), well- medium- to thick-bedded mudstone and poorly sort- cemented sandstone lenses and very pale brown ed pebbly to cobbly sandstone lenses; pebbles are (10YR 7/4) and massive, clast-supported pebbly 2–10 cm in diameter. Measurements of the westward sandstone and conglomerate interbeds. Weakly projection of the Tbc/Tbs (unit Q/P) contact indicate cemented with calcium carbonate. Contains interbed- that the 11.65 Ma ash of locality a is approximately 525 ded, reddish-yellow (5YR 6/6), muddy sandstone m above this unit. 59.2 194 beds as much as 3 m thick. Upper 19 m is pink (7.5YR O. Sandstone and mudstone; very pale brown to pale- 7/4), fine- to medium-grained (fU–mL), moderately 35.2 115 brown (10YR 8/3–6/3) and light yellowish-brown sorted, cemented sandstone that grades into reddish- (10YR 6/4), medium- to thick-bedded, moderately to brown mudstone. well-sorted, very fine to medium-grained (vfU–mU) Tanos Formation, upper tabular sandstone (Ttu, 123 m) sandstone and cemented sandstone (~20–30%) with K. Sandstone; pink (7.5YR 7/4) and very pale brown thick-bedded, coarse pebbly sandstone and <5% red- (10YR 7/4), very fine to medium-grained (vfU–mL), dish-brown (5YR 5/4), medium-bedded mudstone carbonate-cemented sandstone and thin- to medium- interbeds. Pebbles are mostly rounded to subangular bedded, reddish-brown (5YR 5/4) sandstone and and range between 3 and 7 cm in diameter. Contains mudstone interbeds. Grains are well sorted and thick-bedded, well-cemented concretionary sand- rounded to subrounded. Unit grades upward into stone that weathers into 30–40-cm-diameter spher- claystone. Upper contact is scoured by pebbly sand- 63.7 209 9.0 52 oidal concretions. stone of overlying Blackshare Formation. N. Conglomeratic sandstone and mudstone; pink (7.5YR J. Sandstone; pink (7.5YR 7/4–8/3) and very pale 7/3–7/4), fine- to very coarse grained (fL–fU and brown (10YR 7/3), medium- to coarse-grained (mL– vcU), poorly sorted (and medium-grained [mU], cL), poorly sorted, slightly cemented sandstone and moderately sorted) sandstone with medium- to thick- reddish-yellow and reddish-brown (5YR 5/4–7/6), bedded, medium-grained (mU), well-cemented sand- slightly silty sandstone and mudstone with <5-cm- 16.0 52 stone and pebbly sandstone interbeds. Sandstone thick pebbly sandstone interbeds. interbeds are spaced <2 m apart, comprise 15% of I. Sandstone; very pale brown (10YR 7/4–8/2) and gray unit, and contain low-angle crossbeds. Mudstone (10YR 5/1), fine- to medium-grained (fU–mU), thin- (10–15%) is reddish brown (5YR 5/3–5/4) and medi- to medium-bedded, well-cemented sandstone with um to thick bedded. Gravel is generally <5 mm but subhorizontal laminations. Upper part of unit is a reaches a maximum of 6–20 cm in diameter. Pebbly to massive, fine- to coarse-grained (fU–cU), poorly sort- cobbly sandstone contains abundant rounded to sub- ed sandstone with scattered (10%), fine- to coarse- rounded Ortiz porphyry; <5% of clasts are grained (fL–cU), slightly bioturbated concretionary metaquartzite and chert. Approximately 2–5 m below sandstone. Lower part of unit is crudely bedded. the top, the section grades upward to the reddish- Weathers to a brown (7.5YR 4/3) to very dark gray brown claystone that contains scattered (1–2-cm- (7.5 YR 3/1). Contains subhorizontal (5-mm-diame- diameter) calcium carbonate-cemented nodules. 70.7 232 ter), cylindrical concretions and rhizoconcretions. M. Sandstone and mudstone; very pale brown (10YR Moderately to poorly exposed. Locally contains 1–2- 7/3) and pink (7.5YR 7/3–7/4), medium- to thick- cm-diameter spheroidal concretions. Upper part of bedded, very fine to fine-grained (vfL–fU) and coarse- unit contains light-gray (10YR 7/2), fine- to medium- grained (cL–cU), well-sorted sandstone and cemented grained (fL–mL), moderately sorted, calcium carbon-

118 NEW MEXICO GEOLOGY November 2002, Volume 24, Number 4 Appendix A, continued.

Unit Description Thickness Unit Description Thickness (m) (ft) (m) (ft)

ate-cemented concretionary sandstone that weathers 23.5 m above base. Top is 2.4-m-thick, greenish-gray into spheroids and ellipsoids 36.9 121 (5GY 6/1) mudstone. 29.9 98 H. Sandstone; (mostly covered) very pale brown (10YR C. Sandstone; pink (7.5YR 7/3) and very pale brown 7/3), massive to thin-bedded, very fine to medium- (10YR 7/3), fine- to medium-grained (fU–mL), well- grained (vfU–mU) sandstone with faint, 1–5-mm- sorted sandstone with very thin bedded and light- thick, subhorizontal laminations and planar cross- pink (7.5YR 8/2), lenticular, cemented, ledge-forming stratification and 1.5–1.8-cm-thick, lenticular, calcium sandstone interbeds (<5% of unit) and reddish-brown carbonate-cemented concretionary zones. Near the (5YR 5/4) mudstone interbeds. Sandstone exhibits top of the unit is 1–10-cm-thick, fine- to coarse- 5–10-mm-thick ripple laminations. Middle of unit grained (fU–cL) sandstone with low-angle planar contains a 2-m-thick, massive, reddish-brown to yel- crossbeds. Top of unit at floor of Arroyo de la Vega de lowish-red (5YR 4/4–4/6) mudstone; upper 40 cm los Tanos. Projected stratigraphic offset across arroyo contains scattered spheroidal to ellipsoidal calcium may yield ~15-m error in thickness estimate. 28.5 93 carbonate nodules. Contains thin, discontinuous G. Sandstone; (mostly covered) pale-brown to white altered volcanic ash beds. 29.5 97 (7.5YR 6/4–8/1), fine- to medium-grained (fL–mL), B. Sandstone; (mostly covered) pink to light-brown well-sorted sandstone interbedded with medium- to (7.5YR 7/4–6/4), fine- to medium-grained (fU–mU) thick-bedded, yellowish-brown (10YR 6/4–5/4) sand- sandstone and slightly silty sandstone. 19.5 64 stone and medium- to thick-bedded, light reddish- Tanos Formation, lower conglomerate (Ttl, 12 m) brown mudstone. 33.0 108 A2. Basaltic flow; very dark gray (N 3/0) to yellowish- Tanos Formation, middle mudstone (Ttu, 144 m) brown (10YR 5/6) olivine basalt. Olivine crystals are F. Mudstone and sandstone; interbedded light olive- deeply weathered. Lower 1.5 m contains 50–80% gray (5Y 6/2–6/4) and light reddish-brown (5YR 6/4), white (10YR 7/4) and yellow to olive-yellow (2.5Y medium- to thick-bedded mudstone (~60%) and very 7–6/6), 2–5-mm-diameter spheroidal nodules of pale brown (10YR 7/4–8/2), fine- to medium-grained celadonite(?). Weathers to olive yellow (5Y 6/6) and (fU–mL), moderately sorted sandstone (~40%). Mud- weak red (2.5YR 4/2). Rests on reddish-brown to red- stone contains carbonate nodules and 2–3-cm-thick dish-yellow pebbly sandstone, and base appears to be fibrous calcite layer. White (2.5Y 8/1), very fine thermally altered. Upper contact is poorly exposed grained (vfL), thin altered volcanic ash approximately but does not contain reddish-brown baked zone. 2.5–3.0 8–10 18–19 m above base. Contains minor, discontinuous, A1. Conglomeratic sandstone and conglomerate; (mostly yellow (2.5Y 7/6), fine-grained (fL), thick-bedded, covered) very pale brown (10YR 8/3) to reddish-yel- well-sorted sandstone. Upper 12 m is a thin- to medi- low and yellow (7.5–10YR 7/6), massive to crudely um-bedded sandstone with well-cemented sandstone bedded, thin- to medium-bedded, very fine to very lenses near the top. Gradational with overlying unit. 61.4 201 coarse grained (vfL–vcU) sandstone and poorly sort- E. Mudstone and sandstone; basal 2.3 m is light reddish- ed pebbly sandstone and conglomerate with scattered brown (5YR 6/4), thin-bedded mudstone; upper 1.5 m ~30-cm-thick cobble-boulder conglomerate lenses is very pale brown (10YR 7/3), fine-grained (fL) and that comprise ~30% of unit. Gravel locally coated by thin-bedded, tabular sandstone. 3.8 12 red (10R 4/6–4/8) clay films. Pebbles comprise D. Mudstone; light greenish-gray (5GY 7/1), very fine 15–25% of the unit and range from 1 cm to 5 cm and grained (vfL) and well-sorted mudstone. Basal 1 m is 20–60 cm in diameter; mostly ranging from 2 cm to 10 a thin-bedded, greenish-gray (10Y 6/1), silty clay- cm in diameter. Contains pebbles and cobbles of Ortiz stone. Contains yellow (10YR 7/8), fine- to medium- porphyry (98%), rounded metaquartzite and chert grained (fL–mU), well-sorted, thin-bedded sandstone (2%). Overlies Espinaso Formation with sharp, slight- with 1–3-cm-thick, strong-brown (7.5YR 5/6) banded ly scoured, bedding-parallel contact. 9.2 30 stains. White (2.5YR 8/1), thin-bedded, very fine Espinaso Formation (Te, 460 m; Kautz et al., 1981) grained (vfL) altered volcanic ash(?) is approximately White to light-gray volcaniclastic sandstone and conglomerate. Not described.

November 2002, Volume 24, Number 4 NEW MEXICO GEOLOGY 119 Appendix B Reference section of Tanos and Blackshare Formations in Arroyo del Tuer- Measured upsection from unit 1 by S. D. Connell and K. McLeroy using a to, Hagan embayment, San Felipe Pueblo NE 7.5-min quadrangle. Base of Brunton compass and Jacob staff. Colors are dry. See Appendix A for tex- measured section at E: 381,470 m; N: 3,916,240 m (UTM zone 13S, NAD tural abbreviations. Numerical unit designations established upsection, 1927). Top at E: 381,860 m; N: 3,916,960 m (UTM zone 13S, NAD 1983). but listed in descending stratigraphic order.

Unit Description Thickness Unit Description Thickness (m) (ft) (m) (ft)

Tuerto formation Tanos Formation, middle mudstone (Ttu, 93 m) Not described. E. Sandstone and mudstone; (mostly covered) very pale Blackshare Formation, conglomeratic sandstone (Tbc, 104 m) brown (10YR 7/3–4), fine-grained (fL), thin-bedded, I. Pebbly sandstone and sandstone; (poorly exposed) cemented sandstone and light greenish-gray (5GY 40–50% pebbly sandstone and 15% conglomerate con- 7/1) to reddish-brown, thin- to medium-bedded taining Ortiz porphyry (83%), hornfels (7%), quartzite mudstone. Also contains very pale brown (10YR (4%), chert (4%), and sandstone (2%) clasts ranging 8/2–3), coarse-grained (cL–cU), poorly sorted pebbly from 6 cm to 12 cm in diameter. Grades upsection to sandstone and brownish-yellow (10YR 6/6), thin-bed- pink (7.5YR 7/4), medium- to coarse-grained ded concretionary sandstone. 32.5 107 (mU–cL), weakly cemented sandstone with yellow- D. Sandstone and pebbly sandstone; very pale brown ish-red (5YR 5/6), very fine grained (vfL) silty sand (10YR 8/2) to pink (7.5YR 8/2), thin-bedded, fine- to near the top. 39.0 28 coarse-grained (fL–cU), cemented sandstone with H. Pebbly sandstone; (poorly exposed) pinkish-white reddish-brown silty sandstone laminae and brown- (7.5YR 7/4–8/2), medium-grained (mL–mU), thick- ish-yellow (10YR 6/6), 50–100-cm-thick, well-cement- bedded pebbly sandstone (50–70% of unit) interbed- ed, well-sorted, fine-grained (fL–fU) concretionary ded with pink (7.5YR 7/3–4), fine- to medium-grained sandstone. Top contains 1.5-m-thick, reddish-brown (fU–mL), thickly bedded silty sandstone (~20% of (5YR 5/4) mudstone. 38.5 126 unit). Grades up into pink (7.5YR 7/4), medium- to C. Silty sandstone and pebbly sandstone; pink to pink- coarse-grained (mU–cL), weakly cemented sandstone ish-white (7.5YR 8/2–7/4), massive, fine- to coarse- that grades upward into yellowish-red (5YR 5/6), grained (fL–cU) silty sandstone with scattered round- very fine grained (vfL) silty sandstone. 64.5 216 ed pebbles (< 2 cm in diameter). Contains brown Tanos Formation, upper tabular sandstone (Ttu, 84 m) (7.5YR 5/3–4), medium-bedded, fine- to medium- grained (fU–mL) concretionary sandstone and very G. Sandstone and pebbly sandstone; very pale brown pale brown (10YR 7/3), fine- to medium-grained (10YR 8/2), very fine grained (vfU), thin- to medium- (fL–mL) silty sandstone interbeds and brown (7.5YR bedded, tabular to low-angle planar crossbedded and 4/4) clay with scattered carbonate nodules. Pebbles ripple laminated sandstone with lenticular pebbly are predominantly Ortiz porphyry with sparse sandstone interbeds. Approximately 5% of the unit quartzite. Gravelly intervals commonly grade up into contains well-cemented, ledge-forming pebbly sand- sandstone with weakly developed paleosols. 21.8 72 stone beds. Pebbles range from 4 cm to 11 cm in diameter. Lower 16 m is transition between sandstone of Tanos Formation, lower conglomerate (Ttl, 41 m) Tanos Formation and piedmont facies of Blackshare B. Pebbly sandstone; pink and very pale brown (7.5YR Formation. Upper part contains pale-yellow (2.5YR 7/3–4 & 10YR 7/3–4), fine- to coarse-grained (fU–cL), 8/2), thinly bedded, well-sorted sandstone and light poorly sorted, well-cemented, thin- to medium-bed- olive-brown (2.5Y 5/4) claystone and light-gray (2.5Y ded, clast-supported pebbly sandstone. Pebbles com- 7/2), tabular sandstone with nodular carbonate. Top pose 25–70% of unit. Contains interbeds of pink contains very pale brown (10YR 7/3) and pink (7.5YR (7.5YR 7/4), thin, cross-laminated silty sandstone and 7/3), well-sorted, medium-grained (mL), planar slightly silty sandstone and brown (7.5YR 5/4–5/3), crossbedded sandstone with scattered 30-cm-thick laminated mudstone and concretionary sandstone gravel lenses. 36.5 120 lenses. Base of unit is reddish-yellow (7.5YR 6/6) F. Sandstone and mudstone; very pale brown (10YR sandstone. Gravels contain 96% Ortiz porphyry and 7/3) to light reddish-brown (5YR 6/4) and white ~4% subrounded metaquartzite. Fining-upward (7.5YR 8/1), moderately to well-sorted, thin- to medi- sequences of conglomerate and sandstone common. um-bedded, medium- to coarse-grained (mL–cL), tab- Upper contact gradational. 30.7 101 ular sandstone with silty sandstone 2–5-mm-thick A. Pebbly sandstone and conglomerate; pinkish-white to laminae. Interbedded with light greenish-gray (5GY pink (7.5YR 8/2–3) sandstone with very dark gray 7/1) and light reddish-brown (5YR 4/4–6/4), thin- to (7.5YR 3/1) pebbles and small cobbles of Ortiz por- medium-bedded mudstone, brownish-yellow (10YR phyry. Sandstone is poorly sorted, medium to coarse 6/6) concretionary sandstone, and light greenish-gray grained (mL–cU) with subrounded to subangular (8/1 10Y), very fine to fine-grained (vfU–fL) pebbly grains. Lower contact is sharp, poorly exposed, and sandstone lenses. Thinly laminated to thin-bedded, recognized by color change. 10.5 34 light-brown (7.5YR 6/4) gypsiferous mudstone Espinaso Formation (Te) interbeds scattered in tabular sandstones. Contains scattered thin to medium beds of pale-brown (10YR Pebbly to cobbly sandstone and conglomerate; white 6/3) pebbly sandstone. Several sandstone and mud- pebbly to cobbly sandstone with dark-gray specks stone beds are faulted. Upper part of unit contains (10YR 8/1–3/1) and pebble to cobble conglomerate; light greenish-gray (5GY 8/1) mudstone and white well-cemented, medium-bedded, tabular, medium- to (2.5YR 8/1) siltstone. Upper contact is irregular and coarse-grained (mU–cU), moderately sorted sand- scoured by conglomeratic sandstone of overlying stone. unit. 47.8 57

120 NEW MEXICO GEOLOGY November 2002, Volume 24, Number 4