stratigraphy, paleontology, petrography, depositional environments, and cycle stratigraphy at Cerro de Cristo Rey, Doña Ana County, New Spencer G. Lucas, New Mexico Museum of Natural History, 1801 Mountain Road NW, Albuquerque, New Mexico 87104, [email protected]; Karl Krainer, Institute of Geology and Paleontology, Innsbruck University, Innrain 52, Innsbruck, A-6020 Austria, [email protected]; Justin A. Spielmann, New Mexico Museum of Natural History, 1801 Mountain Road NW, Albuquerque, New Mexico 87104, justin.spielman[email protected]; Kevin Durney, 11212 Jockey Bluff Drive, Austin, 78748 Abstract

Cretaceous marine and nonmarine strata of late –middle age are exposed around the Cerro de Cristo Rey uplift in southern Doña Ana County, New Mexico. These strata comprise a section approximately 350 m thick and are assigned to the (ascending order) Finlay, Del Norte, Smeltertown, Mule- ros, Mesilla Valley, Mojado (=“Anapra”), Del Rio, Buda, and Mancos (=“Boquillas”) For- mations. Macrofossils and from these strata indicate that the Finlay, Del Norte, Smeltertown, Muleros, and Mesilla Valley Formations are of late Albian age, whereas the Del Rio, Buda, and Mancos Formations are of Cenomanian age. The base of the Cenomanian is most likely at a trangressive surface within the uppermost . The late Albian (Manuaniceras powelli Zone) to early Cenomanian (Neophlycticeras hyatti Zone) sedimentary succession at Cerro de Cristo Rey consists of alternating fossiliferous , with limestone and intercala- tions, and sandstone. Muddy limestone types are commonly wavy to nodular and represent deposits of an open-marine shelf environment below wave base. Intercalated beds rich in mollusc shells are interpreted as storm layers. Shale was deposited in an open-shelf environment below or near wave base during periods of increased siliciclastic influx. Inter- calated thin limestone and sandstone beds are inferred to be storm layers. The siliciclastic Mojado Formation is a regressive-transgres- sive succession formed in depositional envi- ronments ranging from lower shoreface to upper shoreface and even fluvial, again over- lain by shallow-marine siliciclastics. Although the Washita Group section at Cerro de Cristo Figure 1—Location of Cerro de Cristo Rey in southern Doña Ana County, New Mexico (after Lovejoy Rey is much thicker and displays some differ- 1976). ∆ indicates Eocene igneous intrusions—Cerro de Cristo Rey, Cerro de la Mina, Campus Andesite, ences in , the succession shows similar the Three Sisters, and Vado Hill. transgressive and regressive trends compared to the Washita Group of north Texas. Thus, Introduction Cretaceous marine strata, locally strongly we recognize eight -bounded deformed by gravity-glide structures trig- depositional cycles in the Cretaceous sec- Cerro de Cristo Rey is a prominent peak in gered by andesite intrusion” (Lovejoy 1976, tion at Cerro de Cristo Rey, the upper Finlay Doña Ana County, New Mexico, just north p. 24). The Cretaceous strata, a section Formation (youngest cycle of the Freder- of the U.S.–Mexican border and just west of approximately 350 m thick, include rocks icksburg Group), lower Mancos Formation the city of El Paso, Texas (Fig. 1). The moun- of (late Albian) and Late (base of Greenhorn cycle), and six Washita tain was long referred to as the Cerro de Cretaceous (early–middle Cenomanian) Group cycles: WA1 = Del Norte Formation, Muleros, but was renamed Cerro de Cristo age (Figs. 3–4). These rocks have been stud- WA2 = Smeltertown Formation, WA3 = Mule- Rey (“Sierra” de Cristo Rey of Hook 2008 ied for more than a century, most notably ros Formation, WA4 = most of Mesilla Valley and Cobban et al. 2008, also appears on the by Böse (1910) and Strain (1976). Here, we Formation, WA5 = uppermost Mesilla Val- U.S. Geological Survey topographic map of present the first detailed ley Formation and most of Mojado Forma- the area) in recognition of the large statue of tion, and WA6 = uppermost Mojado and Del and sedimentary petrography of the Cre- Rio and Buda Formations. The persistence Christ on the cross at its crest. The mountain taceous strata exposed around the New of cycles from the tectonically passive, open- has an elevation of 1,425 m (4,675 ft) (Love- Mexican periphery of the Cerro de Cristo marine margin of the Gulf of Mexico into the joy 1976; Hook 2008). Rey uplift. We combine these data with tectonically active trough suggests The core of Cerro de Cristo Rey is an paleontology and regional correlations to that regional if not global eustasy, not local andesite laccolith, the Muleros Andes- present the first detailed interpretation of tectonism, drove late Early to early Late Cre- ite of Eocene age (Fig. 2). The laccolith is the depositional environments and cycle taceous at Cerro de Cristo Rey. surrounded by “an annulus of…faulted stratigraphy of the Cretaceous section.

November 2010, Volume 32, Number 4 New Mexico Geology 103 the Cretaceous invertebrate macrofossils he collected at Cerro de Cristo Rey. Adkins (1932) and Imlay (1944) sub- sequently applied Texas stratigraphic names to the section Böse (1910) delin- eated at Cerro de Cristo Rey (Fig. 3). Cór- doba (1968, 1969a,b) proposed a formal lithostratigraphic nomenclature for the Cretaceous section in northeastern Chi- huahua, Mexico. He mapped these units as far north as the international border, so he assigned Cretaceous strata along the southern flank of Cerro de Cristo Rey in Chihuahua to strata of his Ojinaga Group. Del Norte Córdoba (1969a) makes clear the equiva- lence between his stratigraphic names and those introduced at Cerro de Cristo Rey by Strain (1968, 1976). The lithostratigraphic names long applied to Cretaceous strata at Cerro de Cristo Rey were briefly introduced by Strain (1968) and elaborated on by Strain (1976) and Lovejoy (1976). Thus, four strati- graphic names from farther east, in Texas (Finlay, Del Rio, Buda, and Boquillas), are applied, whereas Strain introduced five local lithostratigraphic names—Del Norte, Smeltertown, Muleros, Mesilla Valley, and Anapra (Figs. 3–4). Subsequent workers (e.g., LeMone and Figure 2—Geologic map of part of the New Mexican portion of the Cerro de Cristo Rey uplift (from Simpson 1983; Maudlin 1985; Cornell and Lovejoy 1976) showing locations of measured stratigraphic sections in this study. See Appendix for LeMone 1987; Cornell et al. 1991; Cornell map coordinates of the measured sections. 1997; Lucas and Estep 1998b, 2000; Scott et al. 2001, 2003; Turnšek et al. 2003) have Located on the northern margin of the stratigraphy and paleontology of these employed the lithostratigraphy of Strain Chihuahua trough, the Cretaceous section strata was the monograph of Böse (1910). (1976). The only previously suggested at Cerro de Cristo Rey is between Bisbee He informally divided the Cretaceous modification is that of Lucas and Estep Group sections to the west and Washita section at Cerro de Cristo Rey into 11 Group sections to the east. It thus provides (1998b, 2000), who argued that the Anapra stratigraphic units, many characterized Sandstone is part of the same lithosome as a pivotal reference section for regional cor- by a distinctive assemblage (Fig. 3). relation and testing concepts of Washita the Mojado Formation to the west. They Although Böse (1910) explicitly correlated Group cycle stratigraphy. therefore abandoned the name Anapra these units to formally named units of the Sandstone and replaced it with the term Fredericksburg and Washita Groups and Mojado Formation. Here, we employ the Previous studies overlying Eagle Ford Shale of Texas (as lithostratigraphic nomenclature of Strain had Stanton and Vaughan [1896] and was (1968, 1976) with two modifications, Emory (1857), Stanton and Vaughan (1896), later done by Adkins [1932]), he applied the use of Mojado Formation instead of and Richardson (1909) first reported on no formal lithostratigraphic nomencla- Anapra Sandstone and the use of Mancos the Cretaceous rocks exposed around ture to the Cretaceous section at Cerro de Formation instead of Cerro de Cristo Rey (Fig. 3). However, the Cristo Rey. Most significantly, Böse (1910) (Fig. 4). These modifications are justified real starting point for understanding the provided a monographic description of below.

Figure 3— of Cretaceous lithostratigraphic nomenclature at Cerro de Cristo Rey. Modified from Strain (1976).

104 New Mexico Geology November 2010, Volume 32, Number 4 and serpulids are also present (Böse 1910; Strain 1976; Turnšek et al. 2003; Kollmann et al. 2003). In addition, our thin sections (see below) demonstrate that algae, ostracods, and rare calcisponges are present. Kollmann et al. (2003) recently analyzed the gastropod fossil assem- blage of the Finlay Formation at Cerro de Cristo Rey, identifying the following taxa: Aporrhaidae, Diozoptyxis, Drepanocheilus, Eunerinea aquiline, Naticoidea, Nerinella n. sp., Otostoma elpasensis, Plesioptyxis tex- anus, Rostroptygmatis kervillensis, Turritella, and Tylostoma.

Sedimentary petrography (Figs. 6, 16)

Finlay Formation limestone beds at Cerro de Cristo Rey are mostly bioclastic wacke- stone that is fine-grained and commonly bioturbated. include small mollusc fragments (bivalves, gastropods), ostra- cods, calcareous algae, a few , echinoid spines, and many foraminiferans embedded in a pelmicritic (Fig. 16A– C). Rare calcisponges are present. Locally, the wackestone grades into packstone and rarely into washed grainstone containing (Fig. 16D–F). Many bioclasts are recrystallized. Common foraminiferans are Dictyoconus (particularly in units 2 and 8; Fig. 16D–F) and miliolids, Nummoloculina, Cornuspira, and Ophthalmidium. Most algae Figure 4—Summary of stratigraphic section and age assignments of Cretaceous strata at Cerro de are dasycladacean algae (Permocalculus) and Cristo Rey (modified from Lucas and Estep 1998b, 2000). Only ammonoid zone names in boldface are aciculariaceans (Acicularia or Terquemella). known from ammonoid fossils collected at Cerro de Cristo Rey; presence of other zones is inferred. This facies corresponds to Facies F (bioclas- tic dasycladacean wackestone) of Kollmann Overview Finlay Formation et al. (2003). Below, we present a brief summary of the In the Finlay Formation, beds of inter- Lithostratigraphy lithostratigraphy of the Cretaceous rocks calated nodular limestone are 0.2–5 m thick and composed of limestone nodules exposed at Cerro de Cristo Rey (Fig. 4), The Finlay Formation is the stratigraphi- embedded in shale. The limestone nodules based primarily on the stratigraphic sec- cally lowest unit of the Cretaceous sec- consist of bioturbated contain- tions we measured (Figs. 5–15) and on data tion exposed in the New Mexico outcrops ing a few larger fragments in Strain (1976) and Lovejoy (1976). More at Cerro de Cristo Rey, but its base is not (bivalves, gastropods) and small bioclasts detailed lithologic information on some exposed. Lovejoy (1976) reported a thick- derived from molluscs, ostracods, rare of the units is presented below in ness of 40 m, and total exposed thickness of echinoderms, echinoid spines, and smaller the sections on sedimentary petrography our measured section of the Finlay Forma- foraminiferans. (Figs. 16–24). Note that we refer to all the tion is approximately 41 m (Figs. 5A, 6). The Cretaceous formation rank units exposed only outcrop of the Finlay Formation on the Depositional environments at Cerro de Cristo Rey with the suffix “for- New Mexico flank of the uplift is located at mation,” instead of using the lithic terms our measured section (Fig. 2). The Finlay Formation section exposed at limestone, shale, or sandstone. Finlay Formation strata are a conspicu- Cerro de Cristo Rey is very similar to the Böse (1910) published most of what is ous ledge- and -forming interval of upper part of the Finlay Formation at its stra- known of the Cretaceous paleontology of interbedded light-gray and - totype section in Hudspeth County, Texas Cerro de Cristo Rey. We have extensive stone and nodular limestone in a marly (Steinhoff 2003). Thus, the Finlay Formation macrofossil collections from Cerro de Cris- matrix (Figs. 5A, 6). The succession is strata at Cristo Rey are and nodu- to Rey that we will document elsewhere. thus composed of alternating fossilifer- lar limestones largely devoid of coarse silici- Here, we provide brief summaries of the ous limestone ledges and slope-forming clastic material. Thin-shelled bivalves and paleontology, mostly of relevance to inter- nodular limestone in shale. Limestone spatangoid echinoids dominate the macro- preting the age and depositional environ- ledges are 0.4–5.3 m thick and composed fossil assemblage, and the benthic foraminif- ments of the Cretaceous strata exposed at of bioclastic wackestone to packstone and eran Dictyoconus walnutensis is particularly Cerro de Cristo Rey. We also present a sedi- some rare grainstone. abundant. Deposition clearly took place on mentary petrography of the Cretaceous sec- a shallow-marine platform in a relatively tion at Cerro de Cristo Rey, and we briefly Paleontology restricted circulation shelf environment, and summarize the depositional environments this fits the regional picture of upper Finlay of the Cretaceous formations. The final sec- Bivalves and gastropods are the most deposition (Scott and Kidson 1977; Reaser tion of this article brings these data and common fossils in the Finlay Formation, and Malott 1985; Steinhoff 2003). analyses together to present an interpreta- but foraminiferans (especially Dictyoco- Microfacies and the diverse biota, includ- tion of the cycle stratigraphy of the Creta- nus walnutensis: Figs. 16D–F, 25R–S), cor- ing broken mollusc fragments in the wacke- ceous strata exposed at Cerro de Cristo Rey. als, ammonoids, spatangoid echinoderms, stone to packstone of the massive limestone

November 2010, Volume 32, Number 4 New Mexico Geology 105 Figure 5—Photos of selected Cretaceous outcrops at Cerro de Cristo Rey. of Muleros Formation (Fig. 9). E—Texigryphaea packstone in lower part of A—Overview of Finlay Formation section (Fig. 6). B—Overview of part of Muleros Formation. F—Overview of shale slope formed by Mesilla Valley lower member of Del Norte Formation (Fig. 7). C—Overview of middle part Formation capped by sandstone at base of Mojado Formation (Fig. 10). of Smeltertown Formation (Fig. 8). D—Overview of characteristic outcrop ledges, indicate deposition in an open-shelf of the stratotype section of the Finlay For- upper part regionally (e.g., Steinhoff 2003), setting with moderate energy. The presence mation, although some differences exist. are absent at Cristo Rey. The lower Finlay of dasycladacean algae points to deposition According to Steinhoff (2003), at the strato- Formation of the stratotype is composed of within the photic zone. Intercalated grain- type the lower part of the Finlay Formation deposits formed on a ramp in a stone suggests periodically high-energy is composed of nodular to massive-bedded shallow open-marine shelf environment, conditions. The wavy to nodular bedded limestone (bioclastic wackestone to pack- whereas the upper Finlay Formation repre- limestone, composed mainly of bioturbated stone) interbedded with and . In the sents deposits of a restricted circulation shelf mudstone with a less diverse , sug- upper part of the Finlay Formation massive- environment (Steinhoff 2003). Such a trend gest deposition in a low-energy, shallow- bedded limestone (bioclastic wackestone to from a carbonate ramp in the lower Finlay to marine shelf environment. packstone with a slightly different fauna) a restricted shelf environment in the upper The facies of the massive and wavy to is abundant. , which are common Finlay is not evident at Cristo Rey, although nodular limestone is very similar to that in the stratotype section, particularly in the some shallowing occurred.

106 New Mexico Geology November 2010, Volume 32, Number 4 The cyclic alternation of massive and wavy to nodular limestone evident in the Finlay Formation section at Cerro de Cristo Rey (Fig. 6) is also recognized at the Fin- lay Formation stratotype, where Steinhoff (2003) described nine transgressive-regres- sive high-frequency cycles in the lower high-frequency sequence 1, and 18 cycles in the overlying high-frequency sequence 2. The stratotype section of the Finlay Forma- tion at the Rimrock escarpment, west Texas, is approximately 52 m thick, although the thickness of the Finlay Formation var- ies from less than 15 m to approximately 800 m and more in the deeper parts of its depositional basin, the Chihuahua trough (Steinhoff 2003). Del Norte Formation


At Cerro de Cristo Rey, the Del Norte For- mation of Strain (1968, 1976) rests with sharp contact on the Finlay Formation (Figs. 6–7). It is subdivisions 2 and 3 of Böse (1910), which he estimated to be 20–30 m thick. Our mea- sured section of the Del Norte Formation is the type section of Strain (1976, table 8), where he reported the formation as approxi- mately 17 m thick. However, our section of the Del Norte Formation is 24 m thick and, following Strain (1976), can be divided into a lower (clay) member (approximately 20 m of shale with interbedded sandstone and limestone) and an upper (calcareous) mem- ber (3–4 m of limestone) (Fig. 7). The basal bed of the Del Norte Forma- tion is a prominent, 0.1-m-thick ferruginous sandstone bed that rests with sharp contact on underlying lime mudstone of the Fin- lay Formation (Figs. 6–7). Above this bed, the lower member (“Brick Plant Member” of Strain 1968) of the Del Norte Formation forms a slope above the Finlay Formation (Fig. 5B) and is composed of alternating beds of limestone, siltstone to fine-grained sandstone, and shale. Limestone beds are thin (0.2–0.6 m thick) and form ledges (Fig. 5B). The lower two limestone beds are nodular. Intercalated beds of calcareous silt- stone to fine-grained sandstone in the lower member are 0.3 m thick (Fig. 7, unit 8) and 2.1 m thick (Fig. 7, unit 16). The lower mem- ber is capped by the - and ridge-form- ing upper member (“Refinery Member” of Strain 1968) of the Del Norte Formation, which is 3.5 m thick. A 0.6-m-thick sandy Figure 6—Measured stratigraphic section of Finlay Formation. See Figure 2 and Appendix for loca- and ledge (Fig. 7, unit 19) tion of section. forms its base. Strain (1976, p. 78) stated that the “Lower Kollmann et al. (2003, fig. 9) interpreted the top of the Finlay, so it corresponds to Clay Member [of the Del Norte Formation] the facies succession of the exposed Finlay units 20–24 of our measured section of the is conformable with the Formation at Cerro de Cristo Rey as that of a Finlay Formation (Fig. 6). However, we did below.” However, we agree with Scott et al. shelf lagoon intercalated, near the top of the not observe this “Orbitolina wackestone” (2001, 2003) and Turnšek et al. (2003) that Finlay, with a bioherm fringe facies repre- facies. “Orbitolina” (we take this to refer to the base of the Del Norte Formation at sented by “Orbitolina wackestone.” Accord- Dictyoconus) is present throughout the sec- Cerro de Cristo Rey marks the basal uncon- ing to Kollmann et al. (2003), this bioherm tion and is abundant also in the lower part formity of the Washita Group (see section fringe facies is approximately 8–15 m below (particularly in units 2 and 8). on cycle stratigraphy, page 127).

November 2010, Volume 32, Number 4 New Mexico Geology 107 Sedimentary petrography (Figs. 7, 17) This basal limestone is overlain by two nodular limestone beds (Fig. 7, units 20, 22, The basal sandstone of the Del Norte For- forming recessed notches) alternating with mation (Fig. 7) is fine-grained, mixed silici- limestone ledges. The microfacies is similar clastic and carbonate in composition, con- to that of the basal limestone ledge: poorly taining abundant angular grains, sorted wackestone to packstone and, in a few micas, and (probably) some detrital part, floatstone containing fragmented and feldspars. Carbonate grains are abundant. abraded skeletons. Most abundant are mol- A few fossil fragments such as shell debris, lusc shell fragments derived from bivalves, ostracods, echinoderms, and dasyclad- gastropods, and echinoderms. Echinoid acean algae are present. The sandstone is spines, ostracods, foraminiferans (includ- well sorted and laminated. ing some agglutinated forms), and bryo- Nodular limestone of the Del Norte For- zoans are subordinate. Angular to rounded mation is fine-grained, poorly sorted, bio- detrital quartz grains, mostly 0.2–0.5 mm turbated bioclastic wackestone (Fig. 17A, in diameter and rarely to 1 mm, and a few F) containing abundant fragments of micritic intraclasts are present. The grains calcareous algae (Aciculariacea, Gym- are embedded in micritic matrix. nocodiacea, ?Permocalculus). Mollusc shell fragments (gastropods, bivalves), ostra- cods, foraminiferans, and echinoid spines Depositional environments embedded in gray, micritic, locally pelmic- ritic matrix are subordinate. Algae and Fossils and of the Del Norte For- molluscs are very greatly fragmented and mation indicate deposition in a shallow, recrystallized. Rarely, small voids (?fossils) open-marine environment with periodical- filled with calcite spar are present. ly strong siliciclastic influx. The presence Limestone of the Del Norte Formation of calcareous algae suggests deposition is fine- to coarse-grained, poorly sorted, within the photic zone. Sandstone beds in and commonly bioturbated wackestone to the lower part displaying horizontal lami- packstone (Fig. 17C, E). A few large mol- nation and current ripples are interpreted lusc fragments several cm in size float in the to represent storm layers. Thin sandstone wackestone. Mollusc fragments (bivalves, interbeds displaying horizontal lamina- gastropods) and echinoderms are abundant. tion and ripple intercalated Echinoid spines, ostracods, foraminiferans in shale of a shallow-marine shelf setting (including some large, agglutinated forms), have commonly been attributed to storm and bryozoans(?) are subordinate. Fossils, activity. Thus, Scott et al. (1975) described particularly molluscs, are commonly recrys- similar siltstone to fine-grained sandstone tallized and strongly fragmented. Lithoclasts beds 1–10 cm thick in the Washita Group include small detrital quartz grains that are of Texas, which they interpreted as mostly 0.1–0.5 mm in diameter (rarely to currents formed by storms, tides, rip flow, 1 mm), constituting as much as about 20% or floods. Hobday and Morton (1984) inter- of the rock, and a few peloids and micritic preted similar thin sandstone intercalations intraclasts. Rare grains are pre- in the Lower Cretaceous Grayson Forma- sent. The matrix is micrite. tion (Texas) as deposits of strong bottom Figure 7—Measured stratigraphic section of Siltstone to fine-grained sandstone of the currents below the storm wave base gener- Del Norte Formation. See Figure 2 and Appen- Del Norte Formation is commonly non- ated by large-scale, storm-generated, bot- dix for location of section, and Figure 6 for lithol- laminated and bioturbated, and locally tom-return flow. ogy legend. indistinctly laminated (Fig. 17B, D). The Nodular limestone, which is commonly composition is mixed siliciclastic-carbonate bioturbated and contains micritic to pel- Paleontology with as much as about 40% angular detrital micitic matrix, formed in a low-energy quartz grains that are mostly 0.1–0.2 mm in environment, whereas intercalated lime- The Del Norte Formation has a diverse fossil diameter. Other lithoclasts are peloids, mic- assemblage of bivalves (especially grypha- stone beds containing strongly fragmented, ritic intraclasts, and local fecal pellets with locally densely packed mollusc fragments eids, exogyrids, pectens, and oysters), gas- diameters from 0.3 to 0.5 mm. The most tropods, spatangoid echinoderms, ammo- (coquina) indicate deposition under high- common fossil fragments are derived from energy conditions and may represent storm noids, , , and serpulids (Böse bivalves and gastropods, which are rarely layers. The sharp contact with the under- 1910; Strain 1976; Turnšek et al. 2003). In thin encrusted by bryozoans(?) and annelid lying Finlay Formation is interpreted as a section, we observed dasycladacean algae, worms (serpulid worm tubes). Less abun- transgressive surface, which was followed ostracods, foraminferans, echinoderms, and dant are echinoderms, ostracods, foraminif- serpulid worms (see below). Ammonites erans (including rare agglutinated forms), by deepening upward and a regressive of the upper Albian Adkinsites bravoensis echinoid spines, and bryozoans(?). trend in the upper member of the Del Norte Zone (of Young 1966) are present in the The basal limestone ledge of the upper Formation, which resulted in the deposi- lower member of the Del Norte Forma- member of the Del Norte Formation (Fig. 7, tion of limestone with abundant coquina tion, in units 15–18 of our measured section unit 19) is composed of poorly sorted bio- storm layers. (Fig. 7), which indicates correlation with the clastic wackestone to rudstone containing Kiamichi Formation in north-central Texas. large, broken fragments of bivalves. Other Smeltertown Formation No fossils diagnostic of the Eopachydiscus skeletons are echinoderms, gastropods, marcianus or Craginites serratescens ammo- ostracods, foraminiferans (including agglu- nite zones are present at Cerro de Cristo Rey, tinated forms), echinoid spines, and dasy- Lithostratigraphy so their presence (Fig. 4) can only be inferred cladacean algae. A few intraclasts and many in the upper Del Norte Formation or lower detrital quartz grains are present. Locally, The Smeltertown Formation of Strain (1976) is Smeltertown Formation or missing at an the grains are densely packed, grading into mostly gray shale with limestone nodules that unconformity. packstone. The matrix is micrite. forms a relatively thick slope (approximately

108 New Mexico Geology November 2010, Volume 32, Number 4 60 m) above the upper member of the Del The nodular limestone ledges of unit 5 of Norte Formation (Figs. 5C, 8). Our measured the Smeltertown Formation section (Fig. 8) section of the Smeltertown Formation (Fig. 8) are composed of bioclastic, mixed silici- is the type section of Strain (1976, table 9), clastic-carbonate siltstone, which is partly which he reported to be approximately laminated and partly bioturbated. A few 61 m thick. The Smeltertown Formation large mollusc shell fragments of bivalves is subdivision 4 of Böse (1910), which he and gastropods float in silty matrix. The estimated as 30–50 m thick. siltstone consists of as much as 30% quartz The base of the Smeltertown Formation grains, small carbonate grains, a few is dark-colored shale that sits directly on glauconite grains, and micrite. Bioclasts limestone at the top of the Del Norte For- include abundant ostracods, a few smaller mation (Figs. 7–8). In the lower part of the foraminiferans, rare echinoderms, echinoid Smeltertown Formation (Fig. 8, unit 3), spines, and shell debris. limestone nodules as much as 20 cm in The microfacies of the unit 7 limestone diameter are in a 3-m-thick shale inter- ledge (Fig. 8) is fine-grained, bioturbated val. Sparse limestone nodules are also in mixed siliciclastic-carbonate sandstone shale units 4 and 6. Shale unit 5 contains (Fig. 18B). The sandstone contains abundant thin ledges of limestone nodules and a detrital quartz grains, mostly 0.2–0.5 mm in pebbly zone near the top. This unit diameter, rarely to 1 mm. Most common is also contains many ammonites, especially monocrystalline quartz, and polycrystal- specimens of Mortoniceras equidistans. The line quartz is subordinate. Rare and limestone ledge of unit 7 yields many glauconite grains are present. Quartz grains shells of Texigryphaea. In unit 8, thin lime- are surrounded by thin carbonate cement stone ledges are intercalated in shale. A rims. A few micritic intraclasts are present, 2.3-m-thick interval of sandstone ledges, too. Bioclasts include bivalves, gastropods, mostly full of abundant tests of the large, echinoderms, ostracods, foraminiferans, arenaceous foraminiferan Cribratina texana and rare worm tubes(?). Litho- and bio- and intercalated with shale beds (with clasts float in a micritic matrix. many horizontal grazing traces of Palaeo- Thin limestone beds of the uppermost phycus striatus), forms the top of the Smel- Smeltertown Formation (Fig. 8, unit 8) tertown Formation (Fig. 8). Limestone at consist of bioturbated mudstone (Fig. 18C) the basal Muleros Formation rests with containing a few siliciclastic grains (mostly sharp contact on sandstone at the top of quartz, rare chert, and glauconite grains) the Smeltertown Formation. and bioclasts (mostly ostracods, rare Paleontology bivalve shells, and fragments; probably other skeletons). Siliciclastic The Smeltertown Formation yields fossils grains and bioclasts constitute less than of foraminiferans, bivalves, gastropods, 10% of the rock, and they are locally con- ammonoids, bryozoans, crustaceans, ophi- centrated due to . uroids, echinoids, , and corals The top siltstone to sandstone of the Smel- (Böse 1910; Strain 1976; Nye and LeMone tertown Formation (Fig. 8, unit 9) is fine 1978; Bullock 1985; Bullock and Cornell grained, laminated, and locally bioturbated 1986; Cornell et al. 1991; Turnšek et al. (Fig. 19A–D). Siliciclastic grains constitute 2003). The foraminiferans establish a robust about 50–70% of the rock. Most abundant is correlation of the Smeltertown Formation detrital quartz, and rare are grains of glau- with the Duck Creek Formation of north- conite, opaque , and micas. A few central Texas (Bullock and Cornell 1986). micritic intraclasts are present. Bioclasts, Ammonites of the Mortoniceras equidistans such as shell fragments, echinoderms, and Zone (present in unit 5 of our measured sec- ostracods, are rare. This facies grades into tion; Fig. 8) also correlate the Smeltertown bioclastic wackestone that contains agglu- Formation to the lower part of the Mojado tinated foraminiferans, bivalve fragments, Formation (Fryingpan Member) in and some other bioclasts embedded in silty, the Cooke’s Range of Luna County, New partly peloidal matrix with a few small Mexico (Böse 1910; Cobban 1987; Lucas quartz grains (Fig. 18D–F). et al. 1988; Lucas and Estep 1998b, 2000). Depositional environments Sedimentary petrography (Figs. 8, 18, 19A–D) Dark-colored shale of the Smeltertown For- Unit 3 in our measured section of the mation is indicative of a muddy marine Smeltertown Formation (Fig. 8) is a mixed sea bottom (cf. Scott 1970). From siliciclastic-carbonate siltstone that is of the Smeltertown Formation, Bullock partly laminated and partly bioturbated and Cornell (1986) identified 73 species of (Fig. 18A). The siltstone contains as much foraminiferans that belong to the suborders as 30% detrital quartz grains, abundant car- Texturlariina, Miliolina, and Rotaliina and bonate grains, rare glauconite, and micrite. provided some information on the deposi- Figure 8—Measured stratigraphic section A few large mollusc fragments (bivalves tional environment. Within the formation of Smeltertown Formation. See Figure 2 and and gastropods) float in the siltstone. Other they distinguished three zones character- Appendix for location of section, and Figure 6 fossils present are ostracods, a few smal- ized by distinct assemblages of foraminifer- for legend. Dashed lines identify the ler foraminiferans, rare echinoderms, and ans. Zone 1 (lower 13 m), which correlates three zones of Bullock and Cornell (1986). echinoid spines. with unit 1 of Strain (1976) and with units

November 2010, Volume 32, Number 4 New Mexico Geology 109 planktonic foraminiferans are absent, Paleontology and other rotaliine forms are less abun- The Muleros Formation is very fossilifer- dant than in the underlying strata. Textu- ous, primarily because of the packstones of lariine forms constitute 70% of the tests. the gryphaeid bivalve Texigryphaea washi- Individuals of Cribratina texana comprise 60–99% of the specimens, indicating an taensis it contains (Böse 1910; Kues 1989). It extremely restricted environment, prob- also yields other bivalves, gastropods, rare ably a hypersaline marsh according to ammonoids, common spatangoid echino- Bullock and Cornell (1986), or a shal- derms, foraminiferans (especially the large, low, nearshore shelf with possibly lower arenaceous form Cribratina texana), corals, than normal salinity (R. W. Scott, written borings, bryozoans, ostracods, and comm. 2010). serpulids (Böse 1910; Strain 1976; Kues The foraminiferal assemblages of the 1989; Turnšek et al. 2003). Correlation of shales thus indicate that the Smeltertown the Muleros Formation with the Denton Formation represents an upward-shallow- and Fort Worth Formations of north-central ing succession from a deeper, open shelf Texas is supported by stratigraphic posi- with water depths of approximately 50 m tion but lacks a robust ammonite biostrati- to a shallow restricted shelf environment graphic basis (Scott et al. 2003). with increased salinity. Interbedded silt- stone, sandstone, and limestone beds in the upper part of the succession may represent Sedimentary petrography (Figs. 9, 19E–F, 20, 21) storm layers similar to those of the Del Norte Formation. The uppermost bed of the Smeltertown Formation (Fig. 8, unit 9) is a quartzose siltstone to fine-grained sandstone that is Muleros Formation heavily bioturbated and partly laminated. Most abundant are monocrystalline quartz Lithostratigraphy grains; chert, carbonate grains, opaque minerals, and glauconite are rare. Small Our measured section of the Muleros For- bioclasts including shell debris, ostracods, echinoderms, and a few large bivalve shells mation (Fig. 9) is the type section of the for- float in siltstone to fine-grained sandstone. mation (Strain 1976, table 10). The Muleros The rock is cemented by quartz over- Formation is subdivision 5 of Böse (1910), growths, rarely by calcite cement. which he reported as 30–50 m thick; Strain The limestone beds in the lower part of (1976) reported a thickness of 32 m for the the Muleros Formation (Fig. 9, unit 2) are formation type section. Our measured sec- gray, bioturbated, fine grained, and com- tion of the Muleros Formation is approxi- posed of abundant peloids, a few detrital mately 33 m thick. The formation generally quartz grains, and bioclasts such as echi- forms cliffs and ledgy slopes (Fig. 5D), and noderms, echinoid spines, ostracods, and a many of the limestone beds of the middle few smaller foraminiferans. The matrix is and upper units are Texigryphaea pack- micrite. The limestone in the middle part of stones (Figs. 5E and 9). the Muleros Formation (Fig. 9, units 3–8) is Figure 9—Measured stratigraphic section of Following Strain (1976), the Muleros For- Muleros Formation. See Figure 2 and Appendix mainly composed of bioclastic wackestone for location of section, and Figure 6 for lithology mation can be divided into three members to packstone (Fig. 20D), and subordinately legend. (Fig. 9). The lower 11–12 m is light-colored mudstone and floatstone to rudstone. shale with some thin, intercalated beds of The bioclastic wackestone is fine to coarse 1 and 2 of our section (Fig. 8), is character- bioturbated sandstone and limestone with grained, poorly sorted, commonly biotur- ized by a high abundance of “Hedbergella” abundant Texigryphaea. The limestone is bated, and locally laminated. Abundant planispira and the dominance of rotaliine nodules embedded in brownish silty matrix fossils are large gryphaeid bivalve shells, forms, which constitute 45–90% of the indi- and micrite. The middle part of the Muleros subordinate gastropods, echinoderms, cor- viduals. This assemblage indicates deposi- Formation (from 11.5 to 24.3 m) is composed als, smaller foraminiferans (including large agglutinated forms), ostracods, and echinoid tion in an open, inner-shelf environment of bioturbated micritic limestone interca- spines. A few glauconite grains are present. with water depths of 50 m or less (Bullock lated with thin shale and, in the lower part, and Cornell 1986). Locally, peloids and detrital quartz grains thin bioturbated sandstone. The limestone are present (Fig. 19E, F; Fig. 20A, B, F). Zone 2, including unit 2 and the lower contains Texigryphaea and Cribratina and is 9 m of unit 3 of Strain (1976), which is our The bioclastic mudstone is bioturbated bioturbated. Horizontal, meniscate back- and contains as much as about 5% detrital unit 3 and part of unit 4 (Fig. 8), is char- filled burrows are present in unit 5 (Fig. 9). acterized by textulariine forms, which quartz grains and rare glauconite (Fig. 20E). The upper third of the section (approxi- constitute 55–95% of all individuals, with Fossils such as smaller foraminiferans mately 9 m thick) is composed of alternat- Cribratina texana being the most abundant (including rare, larger agglutinated forms), ing limestone ledges and shale. Limestone species. The presence of Ammobaculites rare ostracods, echinoderms, echinoid and Trochammina is indicative of a shal- intervals are 0.6–1.4 m thick and consist of spines, and other skeletons are floating in low, nearshore environment. Bullock and floatstone/rudstone and packstone contain- micrite. The following foraminiferans are Cornell (1986) concluded that during sedi- ing Texigryphaea. Shale intervals in the upper present in the limestone: Ammobaculites, mentation of this interval some shallowing part are as much as 1.6 m thick. The lower Ataxophragmiidae, and Nodosaria. occurred, causing restriction of circulation. two intercalated shale intervals contain The bioclastic siltstone to mudstone In zone 3, encompassing the upper limestone nodules. The base of the Mesilla (Fig. 9, unit 4) is nonlaminated and biotur- 24 m of the section (upper 22 m of unit Valley Formation is a sharp contact of silty bated (Fig. 20C). Many small and a few larg- 3 and unit 4 of Strain 1976; upper part shale on Texigryphaea packstone at the top of er bioclasts (echinoderms, ostracods, bivalve of our unit 4 and all of units 5–6; Fig. 8), the Muleros Formation (Fig. 9). shell fragments, rare smaller foraminiferans,

110 New Mexico Geology November 2010, Volume 32, Number 4 corals, and bryozoans) float in a silty to mic- ritic matrix. Peloids (fecal pellets?) are local- ly present, as are small quartz grains (< 5%). The floatstone to rudstone (Fig. 9, unit 7) is nonlaminated, poorly sorted, and contains abundant shell fragments of gryphaeids and gastropods (Fig. 21A–B). Many large agglutinated foraminiferans are also present. These foraminiferans include rare agglutinated smaller foraminiferans. Echinoderm fragments, ostracods, smaller foraminiferans, and shell debris are sub- ordinate. A few mollusc shell fragments are encrusted by worm tubes. The matrix is gray peloidal micrite containing a few small quartz grains. The limestone of unit 8 (Fig. 9) is fine- grained, bioturbated wackestone (Fig. 21C) containing abundant small bioclasts such as ostracods, echinoderms, smaller foraminif- erans, mollusc shell debris, and rare larger skeletons of gastropods, echinoderms, and bivalves. The matrix is peloidal micrite containing a few quartz grains and rare glauconite. Unit 10 of our Muleros Formation sec- tion (Fig. 9) is a bioturbated floatstone- rudstone, containing abundant bivalve (Texigryphaea) and gastropod shell frag- ments, many agglutinated foraminiferans, echinoderms, and rare corals (Fig. 21D–E). Smaller foraminiferans, ostracods, and echinoid spines are subordinate. A few skeletons are encrusted by worm tubes. The micritic matrix contains a few angular quartz grains and rare glauconite. The uppermost limestone interval of the Muleros Formation (Fig. 9, units 13–14) is a packstone–rudstone (Fig. 21F) composed of densely packed bivalve shell fragments that are oriented more or less parallel to the bedding plane. Other bioclasts, such as echinoderms, ostracods, and smaller foraminiferans, are rare. The matrix is silt- stone containing abundant angular quartz grains and rare glauconite grains. Locally, some calcite cement is present (“umbrel- la” ). The peloidal wackestone (pelmicrite; Fig. 9, unit 14) is laminated and consists of abundant small peloids, mostly around 0.05 mm in size and a few peloids as large as 0.25 mm in diameter. Bioclasts such as ostracods and foraminiferans are rare. The floatstone–rudstone of the upper part is poorly sorted, nonlaminated, partly bioturbated, and contains abun- dant large gryphaeid and gastropod shell fragments. A few shells display borings and are encrusted by annelid worms (ser- pulid worm tubes). Other bioclasts include echinoderms, echinoid spines, ostracods, foraminiferans (Lenticulina), rare corals, and bryozoans(?). Locally, agglutinated FIGURE 10—Measured stratigraphic section Figure 11—Measured stratigraphic section of foraminiferans are common. The rock con- Mojado Formation (“Anapra Sandstone”). See of Mesilla Valley Formation. See Figure 2 and tains many detrital angular quartz grains Appendix for location of section, and Figure 6 Figure 2 and Appendix for location of section, and for lithology legend. Figure 6 for lithology legend. HCS=hummocky and a few glauconite grains. The matrix is cross-stratification. micrite.

November 2010, Volume 32, Number 4 New Mexico Geology 111 Figure 12—Photos of Cretaceous outcrops at Cerro de Cristo Rey. Formation. Divisions of measuring stick = 0.25 m. D—Base of Del Rio A—Outcrops of Mojado Formation overlying Mesilla Valley Forma- Formation on Mojado Formation (Figs. 11 and 13). E—Overview of Buda tion (Fig. 10). B—Characteristic crossbedded sandstone of Mojado Formation measured section (Fig. 14). F—Contact of Buda and Mancos Formation. C—Dinosaur footprints (ornithopod tracks) in Mojado Formations at measured section (Fig. 15).

Depositional environments shale-dominated strata are relatively deep- limestone of the middle-upper Muleros er marine deposits (though still shallow), (Fig. 9) suggest shallow, carbonate shelf Muleros strata also demonstrate an appar- whereas Texigryphaea packstones and inter- deposition with some coarse clastic influx ent upward-shallowing trend. Thus, lower, calated bioturbated limestones and sandy (cf. Turnšek et al. 2003).

112 New Mexico Geology November 2010, Volume 32, Number 4 transport and deposition as density current forming a thick slope (36.5 m). The black deposits (cf. Scott et al. 1975; Hobday and shale is sharply overlain by coarse clastic Morton 1984). sediments (sandstone) at the base of the The middle part of the Muleros Forma- Mojado Formation (“Anapra Sandstone” of tion (Fig. 9, units 3–8) is dominated by dif- Strain). ferent types of limestone containing a fossil assemblage suggesting a shallow-marine Paleontology setting. Micritic types such as mudstone and wackestone accumulated in shallow, Böse (1910) referred to the Mesilla Valley For- quiet water, where currents were not strong mation as the “capas con [beds with] Ostrea enough to remove the mud. Intercalated quadriplicata [now Peilinia quadriplicata: Kues floatstone to rudstone, commonly devel- 1997],” and most (or all?) fossils of this taxon oped as containing abundant appear to derive from member B of the Mesil- la Valley Formation (Fig. 10). The Mesilla Val- complete and broken gryphaeid bivalve ley Formation yields a profuse assemblage of shells, are interpreted to represent storm gryphaeid bivalves (Texigryphaea) as well as deposits. Such storm layers with abundant other bivalves, gastropods, ammonoids, bra- gryphaeid shells are also present in the chiopods, foraminiferans (particularly Cribra- upper third of the formation, where they tina texana), dinoflagellates, echinoids, serpu- are intercalated with fossiliferous shale lid worms, corals, ostracods, echinoderms, deposited under low-energy conditions. calcareous algae, and some terrestrial plant Deposition of the upper part of the Muleros fragments (Böse 1910; Strain 1976; Cornell thus was also in a shallow-marine setting, 1982; Kues 1989, 1997; Turnšek et al. 2003). but one with more storm deposits than in Correlation of the Mesilla Valley Formation the middle member. with the Weno and Pawpaw Formations The Muleros Formation succession thus (Scott et al. 2003) is based more on strati- indicates an outer-shelf environment with graphic position than on precise biostratig- dominantly shale during deposition of the raphy, although the presence of the bivalve lower part, followed by some shallowing Peilinia quadriplicata in the Mesilla Valley For- and deposition of dominantly limestone mation, also known from the Denton–Main in an inner-shelf environment periodically Street interval in north-central Texas (Scott affected by storms, and again some deep- et al. 2003, p. 315), does support the Weno– ening resulting in increased deposition of Pawpaw correlation. shale with intercalated storm layers in the upper part. Sedimentary petrography (Figs. 10, 22) Mesilla Valley Formation The lower part of the Mesilla Valley Forma- tion (member A) is gray shale with a few thin sandy lenses. The microfacies of the Lithostratigraphy limestone at the base of member B (Fig. 10, unit 3) is bioclastic rudstone–packstone The Mesilla Valley Formation is a slope- (Fig. 22A–B) composed mainly of large, bro- forming, shale-dominated unit approxi- ken bivalve fragments. Subordinate large mately 65 m thick at our measured sec- agglutinated foraminiferans (Fig. 22C), tion (Figs. 5F, 10). This is subdivision 6 of echinoderms, ostracods, and rare smaller Böse (1910), who indicated it is more than foraminiferans are present. The matrix is 20 m thick. Our measured section is the silty and contains abundant small, angular type section of the Mesilla Valley Shale of quartz grains. The large shell fragments are Strain (1976, table 11), who indicated it is randomly oriented parallel to the bedding 64 m thick. plane. Strain (1976) divided the Mesilla Val- The siltstone of unit 4 at the base of ley Formation into two units, a lower shale member B (Fig. 10) is laminated, mixed (59–60 m thick) and an upper sandstone siliciclastic-carbonate and contains rare and shale (4–5 m thick). However, like the bioclasts. The most abundant grain type underlying Muleros Formation, we divide is quartz, and carbonate grains are also the Mesilla Valley Formation into three infor- present. Bioclasts include ostracods, echi- mal members (Fig. 10). The lower member noderms, foraminiferans, and shell debris. (member A) is 13.7 m thick and consists of Glauconite grains are common. Figure 13—Measured stratigraphic section of gray shale with some very thin sandstone In member B, the ripple-laminated silt- Del Rio Formation. See Figure 2 and Appendix lenses. The middle member (member B) is stone of unit 9 (Fig. 10) is partly bioturbated for location of section, and Figure 6 for lithology 14.4 m thick. Its base is a 0.4-m-thick ledge- legend. and contains small and some larger bioclasts forming limestone that contains Texigryphaea. floating in the silty matrix. Larger bioclasts The limestone bed is overlain by shale are bivalve shell fragments, agglutinated The lower part of the Muleros Forma- with thin, fine-grained sandstone ledges and foraminiferans, and rare solitary corals tion is mainly composed of shale that accu- three thicker, siltstone-sandstone intervals (Fig. 22D). Small bioclasts include ostra- mulated on the shelf in areas deeper than (each 0.4 m thick) that display ripple lami- cods, gastropods, small foraminiferans, shell storm-induced currents. Intercalated thin nation. Locally, the sandstone contains shell debris, and rare phosphatic fragments. The sandstone beds probably formed during debris and serpulids, and the thin sandstone silty matrix is composed of 70–80% small storms that resulted in the remobilization beds contain Texigryphaea (upper part). The angular quartz grains, about 2% glauconite, of coarser material and their basinward upper member (member C) is black shale and a few micas in micritic matrix.

November 2010, Volume 32, Number 4 New Mexico Geology 113 member C apparently occurred in a poorly oxygenated environment, which may indi- cate relatively deep water. Mojado Formation


Our measured section of the Mojado Forma- tion (Figs. 11, 12A–D) is the type section of the Anapra Sandstone of Strain (1976, table 12), which he reported as approximately 53 m thick. Here, the Mojado Formation is a - stone-dominated unit as much as 58 m thick (Figs. 5F, 11, 12A–D). It rests with sharp con- tact on shale at the top of the Mesilla Valley Formation (Figs. 5F, 11, 12A) and is sharply overlain by shale and nodular limestone at the base of the Del Rio Formation (Fig. 12D). The topmost bed of the Mesilla Valley Formation at our Mojado Formation sec- tion (Fig. 11) is reddish-brown shale/silt- stone containing abundant quartz, some chert grains, and rare glauconite. The matrix (or cement) is dark brown ( stained). Strain (1976, p. 81) stated that “the base of the Anapra [Mojado] is the lowest sandstone 30 cm thick or more just above the thinly bedded sandstone beds at the top of the Mesilla Valley Shale.” Thus, he included our basal beds of the Mojado Formation (Fig. 10, unit 13; Fig. 11, unit 3) in the Mesilla Valley Formation. Instead, we draw the base of the Mojado Formation at the base of the first traceable sandstone bed of typical Mojado lithology. The Mojado Formation is entirely silici- clastic, being composed of different types of sandstone with intercalated gray and black Figure 14—Measured stratigraphic section of Figure 15—Measured stratigraphic section of Buda Formation. See Figure 2 and Appendix for Mancos Formation (“Boquillas Formation”). See (locally lignitic) shale. A covered interval location of section, and Figure 6 for lithology Figure 2 and Appendix for location of section, (5.4 m) is in the middle of the succession. legend. and Figure 6 for lithology legend. Sandstone intervals are as much as 5.7 m thick, and shale intervals are as much as 3.5 m thick. The following lithofacies are rec- A thin limestone bed intercalated in few thin sandstone lenses, and this appears ognized: (1) thin, fine-grained sandstone beds unit 10 (Fig. 10) is bioturbated bioclastic to represent relatively deep water. The displaying hummocky cross-stratification wackestone containing a few larger and dark shale with intercalated thin sandstone form the lowermost 4.9 m of the succession many small bioclasts floating in micritic lenses of the lower member is interpreted (lower ¾ of unit 3); the sandstone beds are matrix (Fig. 22E). Bioclasts include mol- to record deposition in an outer-shelf envi- interbedded with green shale; (2) iron-mot- lusc shell debris (bivalves, gastropods), ronment, which was only rarely affected tled, hackly sandstone, which is bioturbated calcareous algae, worm tubes (Fig. 22F), by storms. The thin intercalated and has Liesegang banding (units 7, 11); ostracods, echinoderms, smaller foraminif- may represent distal storm layers. Inter- (3) thin, fine-grained sandstone with ripple erans, agglutinated foraminiferans, and calated rudstone to packstone beds (shell lamination (units 16–22); (4) thin, medium- echinoid spines. The matrix is micrite and coquinas) and ripple-laminated sandstone grained sandstone with trough crossbedding pelmicrite. The top of member B (Fig. 10, beds containing fossils such as Texigryphaea (units 4, 6, 8, 10, 17); and (5) thicker, multisto- unit 11) is formed by a fine-grained sand- represent typical storm deposits. ried sandstone beds with larger-scale trough stone interval 0.9 m thick displaying rip- Overlying shale with interbedded Texi- crossbedding (units 13, 15, 25). ple lamination and containing Texigryphaea packstones and ripple-laminated Trough crossbedded sandstone inter- (packstone). Member C is black shale with sandstones (member B) indicate a distinct vals are characterized by erosive lower con- no obvious fossil content. shallowing. Storm layers are more abun- tacts (e.g., Fig. 12B). Several upward-fining dant in member B than in the members and thinning cycles are developed. Each cycle Depositional environments below and above, indicating that some starts with trough crossbedded sandstone, shallowing occurred during deposition of grading into fine-grained, ripple-laminated The shale-dominated Mesilla Valley For- the middle member (Fig. 10). sandstone with shale interbeds, and the tops mation (Fig. 10) mostly represents deposi- The upper part of the formation (mem- of a few cycles are formed by shale. Hum- tion on muddy marine sea bottoms below ber C) is black shale, which we interpret as mocky cross-stratification is only observed wave base. The lower part of the formation relatively offshore marine deposits. Depo- in the lowermost sandstone beds. Neverthe- (member A, Fig. 10) is mostly shale with a sition of the organic-rich black shale of less, marine fossils and marine bioturbation

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Figure 16— photographs of microfacies of the Finlay Formation foraminiferans. Matrix is gray micrite. Sample A26. D—Packstone contain- at Cerro de Cristo Rey (Fig. 6). Sample numbers correspond to unit numbers ing abundant peloids, smaller foraminiferans including dictyoconid forms, in Figure 6. A—Bioclastic wackestone containing abundant broken fragments fragments of dasycladacean algae, and molluscs and some micritic matrix. of recrystallized calcareous algae, molluscs, some echinoderm fragments, Sample A10. E—Packstone–grainstone containing abundant peloids, some and foraminiferans in micritic matrix. Sample A24. B—Bioclastic wackestone orbitolinoid foraminiferans (Dictyoconus), and mollusc shell debris cemented containing abundant fragments of dasycladacean algae, mollusc (bivalve) by calcite. Sample A10. F—Grainstone composed of abundant peloids, some fragments, and some echinoderms floating in micritic matrix. Sample A27. orbitolinoid foraminiferans (Dictyoconus), and other bioclasts including gas- C—Fine-grained bioclastic wackestone–packstone with abundant fragments tropods and echinoderms, cemented by calcite. Sample A10. Width of photo- of recrystallized dasycladacean algae, molluscs, echinoderms, and a few graphs is 6.3 mm. are present in the upper few meters of the Lovejoy (1976) recognized five units. We (Fig. 11, units 12–14); (3) upper interval of Mojado Formation, and we identify a clear believe our measured section can be readily crossbedded sandstones (Fig. 11, units 15–25); break (transgressive surface) approximately divided into at least four intervals: (1) lower and (4) uppermost interval with marine fossils 3 m below its top (base of unit 26, Fig. 11). beds with marine bioturbation and intercalat- and bioturbation (Fig. 11, unit 26). However, Strain (1976) divided the Mojado (his ed shale (Fig. 11, units 3–11), (2) middle, slope- more subdivisions are possible, though they “Anapra”) Formation into four units, and forming interval of mostly siltstone and shale are of little stratigraphic significance.

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Figure 17—Thin section photographs of microfacies of the Del Norte For- D—Mixed siliciclastic-carbonate fossiliferous siltstone containing a few mation at Cerro de Cristo Rey (Fig. 7). Sample numbers correspond to unit mollusc shell fragments and rare echinoderms. Sample B16. E—Bioclastic numbers in Figure 7. A—Bioclastic wackestone containing abundant algal wackestone–packstone containing abundant mollusc (bivalve) shell frag- fragments and mollusc (bivalve) shell debris, a few foraminiferans, and ments (mainly derived from bivalves), subordinate echinoderms, small echinoderms in gray micrite. Sample B2. B—Mixed carbonate-siliciclastic quartz grains, and a few micritic intraclasts in micritic matrix. Sample siltstone containing abundant angular quartz grains and bioclasts such as B22. F—Fine-grained bioclastic wackestone with many mollusc (bivalve) recrystallized bivalve shell fragments (?oysters), some echinoderms, and shell fragments and dasycladacean algae, with subordinate echinoderms micrite. Sample B8. C—Wackestone–packstone composed of echinoderms, in micritic, partly peloidal matrix. Sample B19. Width of photographs is mollusc shell fragments, and quartz grains floating in micrite. Sample B9. 6.3 mm, but for Fig. C is 3.2 mm.

We propose that at Cerro de Cristo Rey et Mountains of County, New Mex- Mojado Formation is divided into three the name Anapra Formation be replaced by ico, the Mojado Formation is approximately members (Lucas and Estep 1998b): (1) Fry- Mojado Formation. To the west and north- 1,500 m of sandstone, shale, and minor lime- ingpan Spring Member, approximately 22 m west of Cerro de Cristo Rey, rocks that strad- stone that overlies the Aptian–Albian U-Bar of sandstone, siltstone, shale, and nodular dle the Albian–Cenomanian boundary are Formation (Zeller 1965). In the Cooke’s limestone that includes fossils of the ammo- assigned to the Mojado Formation of Zeller Range of Luna County, approximately 120 noid Mortoniceras equidistans (Cragin) (Cobban (1965). At the type section, in the Big Hatch- km northwest of Cerro de Cristo Rey, the 1987; Lucas et al. 1988); (2) Sarten Member,

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Figure 18—Thin section photographs of microfacies of the Smeltertown bioclasts (bivalves, gastropods, echinoderms, foraminiferans) floating in Formation at Cerro de Cristo Rey (Fig. 8). Sample numbers correspond micrite. Sample E7. C—Mudstone containing some quartz grains and few to unit numbers in Figure 8. A—Mixed fossiliferous carbonate-siliciclas- bioclasts. Sample E8. D–F—Bioclastic wackestone containing agglutinat- tic siltstone containing some large mollusc (bivalve) fragments, a few ed foraminiferans (Cribratina) and bivalve fragments, and, subordinately, ostracods and foraminiferans, and as much as 30% detrital quartz grains. other bioclasts such as ostracods embedded in silty, partly peloidal matrix Sample E3. B—Fine-grained, mixed siliciclastic-carbonate sandstone containing a few small quartz grains. Sample E9. Width of photograph C composed of detrital quartz grains, a few glauconite grains, and a few is 3.2 mm, and of all other photographs is 6.3 mm. approximately 58 m of sandstone and silt- close correlation (Fryingpan Spring Member the older name of a more regional stratigraph- stone of nonmarine origin; and (3) Rattlesnake correlates to the Smeltertown Formation, and ic unit (Mojado of Zeller 1965). Ridge Member, approximately 6 m of silty Rattlesnake Ridge Member correlates to the sandstone, siltstone, and nodular limestone Del Rio Formation; Lucas et al. 1988). Thus, that yields a bivalve fauna of earliest Ceno- the “Anapra Sandstone” is seen by us as a Paleontology manian age (Lucas et al. 1988). Sandstone and tongue of the (Mojado Forma- siltstone of the Sarten Member are lithologi- tion) present in the Cretaceous section of Cerro The Mojado Formation (“Anapra Sand- cally very similar to the “Anapra Sandstone,” de Cristo Rey. We therefore abandon the local stone”) at Cerro de Cristo Rey contains and the supports a reasonably name Anapra (of Strain 1968, 1976) in favor of dinosaur footprints and plant debris in its

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Figure 19—Thin section photographs of microfacies of the Smeltertown bivalve shell fragments and echinoderms. Sample F1. E—Fine-grained Formation (A–D) and Muleros Formation (E–F) at Cerro de Cristo Rey bioclastic wackestone–packstone overlying gray mudstone. Wackestone– (Figs. 8–9). Sample numbers correspond to unit numbers in Figures 8 and 9. packstone contains bivalve shell fragments, echinoderms, ostracods, a few A—Mixed siliciclastic-carbonate siltstone containing a few glauconite smaller foraminiferans, peloids, and a few small quartz grains. Sample F2. grains and rare bioclasts such as ostracods and echinoderms. Sample E9. F—Coarse-grained bioclastic wackestone, partly floatstone, containing B—Quartzose siltstone with a few carbonate grains, rare glauconite, and abundant bivalve shell fragments (Texigryphaea), subordinate gastropods, few large bivalve fragments. The siltstone is cemented by quartz (authi- echinoderms, foraminiferans, few peloids, and quartz grains in micritic genic overgrowths) and rare calcite cement. Sample E10. C–D—Mixed matrix. Sample F3. Width of photograph D is 3.2 mm, and of all other pho- siliciclastic-carbonate siltstone to fine-grained sandstone containing some tographs is 6.3 mm. lower to middle portions, as well as some conditions during deposition of part of the and agglutinated foraminiferans (Böse 1910; marine fossil fragments and tests of the large Mojado Formation, but are not of precise Strain 1976; Turnšek et al. 2003). We also arenaceous foraminiferan Cribratina texana. biostratigraphic significance. The upper observed dasycladacean algae, foraminifer- The dinosaur tracks are primarily those of 3 m of the Mojado (unit 26) contain fossils ans, echinoderms, and ostracods in thin sec- ornithopods and theropods (Fig. 12C; e.g., of the large exogyrid bivalve Gyrostrea whit- tion (Fig. 23E). Kappus et al. 2003; Kappus 2007) and pro- neyi (known from the Del Rio Formation Strain (1976) placed the base of the vide strong evidence of subaerial, terrestrial in north-central Texas) as well as echinoids Cenomanian at the base of the “Anapra

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Figure 20—Thin section photographs of microfacies of the Muleros Forma- Fine-grained wackestone–packstone with a few large bivalve fragments and tion at Cerro de Cristo Rey (Fig. 9). Sample numbers correspond to unit num- many small bioclasts, peloids, and some detrital angular quartz grains in mic- bers in Figure 9. A–B—Bioclastic wackestone to floatstone containing abundant ritic matrix. Sample D5. E—Mudstone containing quartz grains and smaller bivalve shell fragments (Texigryphaea), subordinate gastropods, echinoderms, textulariid foraminiferans floating in micrite. Sample F5. F—Fine-grained and foraminiferans, including large agglutinated forms in micritic matrix. Sam- wackestone–packstone containing abundant peloids, a few detrital quartz ple F3. C—Bioturbated siltstone–mudstone containing a few bioclasts (bivalve grains, shell debris, echinoderms, smaller foraminiferans, and ostracods. Sam- shell fragments, echinoderms, ostracods) that float in matrix. Sample F3. D— ple F6. Width of photographs A–D is 6.3 mm, and of E–F is 3.2 mm.

Sandstone,” and Lucas and Estep (1998b, the Mojado–Del Rio contact (Turnšek subrounded to rounded, although many 2000) placed it at the base of the Del Rio et al. 2003; Scott et al. 2003) (Fig. 11). grains display authigenic overgrowths Formation. Given that in the regional that are not always easy to recognize. The Washita Group section, the base of the Sedimentary petrography (Figs. 11, 23C–F) most common grain type is monocrystal- Cenomanian is a sequence boundary at line quartz. Subordinate chert grains are the base of the WA6 cycle of deposition, Sandstone of the Mojado Formation is present, perhaps of volcanic origin. Poly- the Albian–Cenomanian boundary is fine- (0.1–0.3 mm) to medium-grained (0.2– crystalline quartz of metamorphic origin most likely at the marine transgressive 0.5 mm) quartz arenite, nonlaminated, and including stretched metamorphic grains surface that is approximately 3 m below well sorted (Fig. 23C–D). Grains are mostly is rare. Detrital feldspars are very rare

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Figure 21—Thin section photographs of microfacies of the Muleros Forma- other bioclasts floating in micritic matrix. Sample F7. C—Fine-grained biotur- tion at Cerro de Cristo Rey (Fig. 9). Sample numbers correspond to unit num- bated wackestone composed of abundant peloidal and small bioclasts (ostraco- bers in Figure 9. A—Floatstone containing gryphaeid shell fragments, some ds, echinoderms, mollusc shell debris, foraminiferans) and a few quartz grains. encrusted by balanids, and agglutinated foraminiferans embedded in micritic, Sample F8. D–F—Floatstone–rudstone with bivalve fragments, agglutinated partly peloidal matrix. Sample F7. B—Wackestone–rudstone with abundant foraminiferans, echinoderms, and corals embedded in micritic matrix. D–E = gryphaeid shell fragments, some gastropods, agglutinated foraminiferans, and sample F10, F = sample F14. Width of photographs is 6.3 mm. and generally altered. Accessory grains Unit 23 (Fig. 11) is a crossbedded, fine- The uppermost Mojado Formation (Fig. 11, are micas (muscovite), tourmaline, zircon, grained, bioturbated bioclastic wacke- units 25–26) is composed of laminated silt- apatite, and opaque grains. The sandstone stone, locally a packstone, containing a few stone to fine-grained sandstone. Grain size is cemented by authigenic quartz over- larger bioclasts (Fig. 23E). Most abundant is mostly < 0.1 mm; however, a few quartz growths, and locally also by microcrystal- are dasycladacean algae and mollusc shell grains as much as 0.5 mm are present. The line quartz and opaque cement (Fe-hydrox- fragments (bivalves, gastropods). Less most abundant grain type is quartz; - ides). Unit 10 (Fig. 11) includes a lens of common are foraminiferans, echinoderms, ate grains are subordinate, and opaques and strongly recrystallized com- echinoid spines, ostracods, and other frag- glauconite are rare. The siltstone to fine- posed of irregularly laminated algal mats. ments. The matrix is micrite to pelmicrite. grained sandstone contains some ostracods,

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Figure 22—Thin section photographs of microfacies of the Mesilla Valley angular quartz grains. Sample G3. D—Bioclastic siltstone composed of Formation at Cerro de Cristo Rey (Fig. 10). Sample numbers correspond to small and larger fossils such as corals, bivalves, and agglutinated foraminif- unit numbers in Figure 10. A–B—Bioclastic packstone–rudstone contain- erans floating in silty matrix. Sample G4. E—Bioclastic wackestone con- ing densely packed bivalve fragments, subordinate echinoderms and other taining bivalve shell fragments, echinoderms, ostracods, and worm tubes bioclasts, a few detrital quartz grains, and rare glauconite. Sample G1. C— embedded in micritic to pelmicritic matrix. Sample G10. F—Worm tubes Bioclastic packstone–rudstone composed of abundant recrystallized shell in a bioclastic wackestone. Sample G10. Width of photographs is 6.3 mm, fragments and agglutinated foraminiferans in silty matrix containing small except for F, which is 3.2 mm. shell fragments, rare foraminiferans, and and shallowing succession, starting with The overlying trough crossbedded intervals echinoderms. Shell fragments are oriented hummocky crossbedded sandstone of the (Fig. 11, units 13 and 15) probably represent parallel to the bedding in unit 26. lower shoreface followed by upper shoreface fluvial channel-fill deposits of a delta plain, deposits represented by alternating, horizon- which are again overlain by shallow-marine Depositional environments tally laminated, ripple-laminated, and trough siliciclastic sediments (units 16–22). The thin, crossbedded sandstone. A shallow-marine intercalated sandstone beds (ripple laminated, The lower part of the Mojado Formation environment is also indicated by a thin stro- horizontally laminated, trough crossbedded) (Fig. 11) represents an upward-coarsening matolite lens within unit 10 (Fig. 11). indicate high-energy conditions and may

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Figure 23—Thin section photographs of microfacies of the Mancos Forma- quartz, cemented by quartz as authigenic overgrowths. Sample H3. D—Quartz tion (A–B) and Mojado Formation (C–F) at Cerro de Cristo Rey (Figs. 11, 15). arenite showing abundant monocrystalline quartz grains with well-displayed Sample numbers correspond to unit numbers in Figures 11 and 15. A—Bio- authigenic quartz overgrowths. Sample H3. E—Bioclastic wackestone contain- clastic wackestone with bivalve shell fragments, calcareous algae, and echi- ing abundant fragments of dasycladacean algae and bivalves, subordinate noderms floating in micrite. Sample I1. B—Bioclastic wackestone–packstone foraminiferans, and echinoderms floating in micritic to pelmicritic matrix. with mostly bivalve fragments, echinoderms, and subordinate other bio- Sample H23. F—Bioturbated peloidal mudstone containing some quartz clasts, micritic matrix, and some calcite cement. Sample I3. C—Fine-grained grains and a few bioclasts. Sample H27. Width of photographs is 6.3 mm, quartz arenite composed mostly of monocrystalline quartz, rare polycrystalline except for D, which is is 3.2 mm. represent storm deposits. A shallow-marine unit 26) is of shallow-marine origin, indi- (1976) reported its thickness as 24–27 m. In our environment is also indicated by a thin lens of cated by the marine fossils. measured section (Fig. 13), the lower 9.7 m (bioclastic wackestone; (most of unit 2) is a nodular limestone inter- Fig. 11, unit 23) that contains abundant dasy- Del Rio Formation val composed of abundant limestone nodules cladacean algae. in a yellow clay slope (Fig. 12D). This inter- The trough crossbedded sandstone of Lithostratigraphy val contains many fossils of Gyrostrea (=Exo- the succeeding 7 m may represent fluvial gyra) whitneyi and gastropods. Above follows or upper shoreface deposits. The overlying, The Del Rio Formation at our measured section a shale slope with some nodular limestone horizontally laminated sandstone (Fig. 11, is approximately 33 m thick (Fig. 13). Lovejoy and three thin limestone beds, each 0.2–0.3 m

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E F Figure 24—Thin section photographs of microfacies of the Del Rio Formation fossil fragments (bivalves, echinoderms) floating in micritic matrix. Sample C9. (A–C) and Buda Formation (D–F) at Cerro de Cristo Rey (Figs. 13–14). Sample D—Peloidal bioclastic mudstone containing a few angular quartz grains, some numbers correspond to unit numbers in Figures 13–14. A—Peloidal wacke- bioclasts (ostracods, shell fragments, foraminiferans, echinoderms), and rare stone with some angular quartz grains and bioclasts such as ostracods, smaller glauconite. Sample D5. E—Bioclastic mudstone composed of gray micrite with foraminiferans, and echinoid spines. Sample C3. B—A few bioclasts (bivalve small and a few larger fossil fragments. Sample D7. F—Fine-grained bioclastic shell fragments, echinoderms, ostracods, foraminiferans) floating in siltstone wackestone containing mostly bivalve fragments, subordinately echinoderms, composed of angular quartz and carbonate grains, rare glauconite. Sample C7. ostracods, and foraminiferans floating in gray micrite. Sample D5. Width of C—Bioclastic mudstone–wackestone containing many small and a few larger photographs A and D is 3.2 mm, and of photographs B, C, E, F is 6.3 mm. thick and forming ledges (units 3–7). Above Formation is composed of nodular limestone and Ilymatogyra arietina), gastropods, spatan- the uppermost limestone ledge, yellowish with thin yellow shale interbeds (unit 9, 4.5 m goids, and ammonoids. In thin section we shale with some nodular limestone is exposed thick), overlain by white limestone of the Buda observed foraminiferans, ostracods, echino- with a thickness of 12.8 m (unit 8). Gyrostrea Formation (Fig. 13). derms, and annelid worm tubes. From the Del whitneyi is also common in the upper part. Rio Formation at Cerro de Cristo Rey, Maul- Turnšek et al. (2003, p. 154) stated that Ilyma- Paleontology din (1985) and Mauldin and Cornell (1986) togyra arietina is the “dominant fossil” in the determined 52 species of foraminiferans. The Del Rio, but our field observations suggest it The Del Rio Formation at Cerro de Cristo Rey foraminiferal assemblage is dominated by is Gyrostrea whitneyi. The top of the Del Rio yields bivalves (especially Gyrostrea whitneyi rotaliine foraminiferans (38 species), which

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Figure 25—Some Cretaceous microfossils of the Cerro de Cristo Rey 27, Fig. 6). M, N—Textulariid foraminiferans (M—Del Norte Formation, unit 14, sections. A, H—Permocalculus sp. (Finlay Formation, A unit 14, H unit 27, Fig. 7; N—Smeltertown Formation, unit 7). O—Pseudonummuloculina heimi (Fin- Fig. 6). B, C—Boulina sp. (Finlay Formation, B unit 12, C unit 20, Fig. 6). lay Formation, unit 10, Fig. 6). P—Lenticulina sp. (Del Rio Formation, unit 3, D, E, G, K—Acicularia or Terquemella sp. (Finlay Formation, D unit 14, E Fig. 13). R, S—Orbitolinoid foraminiferans (Dictyoconus) (Finlay Formation, unit 27, K unit 26, Fig. 6; Del Norte Formation, G unit 9, Fig. 7). F—Neom- unit 8, Fig. 6). T, U, V—Agglutinated foraminiferans (Ammobaculites? and/or eris sp. (Finlay Formation, unit 20, Fig. 6). I, J—Salpingoporella sp. (Finlay Cribratina) (T, U—Smeltertown Formation, unit 9, Fig. 8; V—Buda Formation, Formation, unit 24, Fig. 6). L—Pseudocyclammina sp. (Finlay Formation, unit unit 7, Fig. 14). Scale bar is 0.3 mm, except for K, which is 0.1 mm. constitute 82% of the individuals. Aggluti- Rio Formation (Fig. 11, unit 27) is composed containing abundant quartz. The peloidal nated foraminiferans (suborder Textulariina) of interbedded nodular limestone and shale. wackestone (unit 3) is indistinctly laminated comprise 12 species and 17% of all individu- The limestone beds are bioturbated peloidal and contains as much as about 20% quartz als. Two species belong to milioline foraminif- mudstone containing many peloids, a few (with a grain size as much as approximately erans, constituting 1% of the individuals. quartz grains, rare glauconite, and a few 0.2 mm) and rare glauconite. Most abundant These foraminiferans support correlation of small bioclasts such as ostracods, echino- are small peloids and many small bioclasts the Del Rio outcrops with the Grayson For- derms, and rare foraminiferans (Fig. 23F). such as ostracods, foraminiferans, echinoid mation elsewhere in Texas. Similarly, in our section of the Del Rio spines, and some other small fossils, float- Formation (Fig. 13), the lowermost inter- ing in microspar (cement?). The amount of Sedimentary petrography (Figs. 13, 24A–C) val (unit 2) is nodular limestone and shale quartz grains increases upward to about 30%, capped by a thin limestone bed (unit 3) that and the peloidal wackestone is overlain by At the top of our section of the Mojado For- consists of peloidal wackestone (Fig. 24A), fine-grained sandstone that contains about mation, the basal interval of the overlying Del grading up into fine-grained sandstone 50–60% angular quartz grains, rare glauconite,

124 New Mexico Geology November 2010, Volume 32, Number 4 and a few bioclasts (including ostracods, echi- However, shale with limestone nodules Buda–Mancos contact is poorly exposed and noid spines, echinoderms, shell fragments, and nodular to wavy limestone indicate tectonized (Fig. 12F), so evidence of micro- and rare foraminiferans) in brownish micritic deposition under quiet-water conditions in a features is not clear. The best evidence matrix. deeper, outer-shelf environment. This is also of the Buda–Mancos unconformity at Cerro The limestone bed of unit 5 of the Del Rio indicated by the presence of glauconite, which de Cristo Rey is provided by ammonoid bio- Formation (Fig. 13) is a peloidal wackestone– in modern oceans occurs at depths between stratigraphy (Cobban et al. 2008). The base of grainstone with abundant small peloids and 50 and 500 m (Flügel 2004). Even the wavy the Mancos Formation is in the upper middle foraminiferans. Subordinate are ostracods, to nodular limestone in the uppermost part Cenomanian Acanthoceras amphibolum Zone, echinoderms, echinoid spines, small quartz of the Del Rio Formation formed in a low- whereas the upper Buda is in the lower Ceno- grains (5–10%), a few micritic intraclasts, energy environment. Lithologic evidence of a manian Neophlycticeras (=Budaiceras) hyatti and rare glauconite. The rock is indistinctly drop in sea level to water depths of approxi- Zone—thus, two lower Cenomanian and laminated and calcite cemented. mately 20 m in the upper half suggested by four middle Cenomanian ammonoid zones Unit 7 (Fig. 13) is a bioclastic limestone Mauldin and Cornell (1986) is not observed. are missing at the Buda–Mancos contact, an with some small and larger bioclasts float- Even the uppermost wavy to nodular lime- unconformity of more than one million years stone (bioclastic mudstone) with intercalated ing in silty matrix (Fig. 24B). The silty duration (Cobban et al. 2008, fig. 2). matrix is composed of predominantly shale was deposited in a low-energy environ- ment below wave base. High-energy deposits small angular quartz and carbonate grains, Paleontology subordinate glauconite, and some opaque such as grainstone or packstone are absent. grains. Bioclasts include echinoderms, The Buda Formation yields many gastro- ostracods, shell fragments (bivalves), and Buda Formation pods (mostly turritellids) and bivalves, as rare agglutinated and other foraminiferans. well as some ammonoids, dinoflagellates, The rock is locally bioturbated and calcite serpulids, spatangoid echinoderms, crus- Lithostratigraphy cemented. taceans, corals, and fish teeth (Böse 1910; The nodular limestone of the Del Rio Young 1979; Cornell 1997; Turnšek et al. Formation is a gray, nonlaminated, biotur- At Cerro de Cristo Rey, the best exposed and 2003). Ammonoids we have collected (and bated bioclastic mudstone. The micritic to most complete section of the Buda Forma- will document elsewhere) place it in the pelmicritic matrix contains many small and tion is in Bowen Gulch where it is a promi- early Cenomanian zone of Neophlycticeras a few larger bioclasts. A few small quartz nent, resistant interval of white limestone (=Budaiceras) hyatti (Young 1979). grains and rare glauconite grains are pre- that forms ridges and (Figs. 12E, sent. Bioclasts include ostracods, bivalve 14). Here, the Buda Formation is 15.5 m Sedimentary petrography (Figs. 14, 24D–F) shells, echinoderms, a few foraminiferans, thick (Lovejoy 1976 reported its thickness as rare gastropods, and annelid worm tubes. approximately 12 m) and composed of alter- The basal limestone of the Buda Forma- The uppermost limestone bed of the Del nating limestone and shale with limestone tion (Fig. 14, unit 5) is composed of fine- Rio Formation (unit 9) is composed of bio- nodules. The lowermost limestone of the grained, bioturbated bioclastic wackestone turbated bioclastic mudstone (Fig. 24C). Buda Formation is 0.8 m thick (unit 5) and containing a few larger skeletons (Fig. 24F). Small bioclasts of ostracods, echinoderms, nodular, overlain by a thin nodular lime- Most abundant are mollusc shell frag- foraminiferans, gastropods, bivalves, rare stone with shale and a prominent limestone ments. Less abundant are echinoderms, quartz grains, and very rare glauconite cliff 2.7 m thick (units 6–7). Above the lime- ostracods, echinoid spines, foraminiferans, float in a micritic matrix. stone cliff follows a succession of alternating limestone and shale (units 8–21). Limestone and other recrystallized, indeterminate skeletons. The skeletons float in a micritic Depositional environments beds are 0.3–0.6 m thick and full of gastro- pods. Shale intervals measure 0.3–2.5 m and to pelmicritic matrix. This type grades into bioclastic mudstone containing small and a Del Rio Formation facies (Fig. 13) are contain limestone nodules, which are locally fossiliferous. few larger bioclasts that float in gray mic- similar to those of the lower part of the rite (Fig. 24E). Del Norte Formation (Fig. 7) and indicate The lithology of the Buda Formation sec- tion exposed at Cerro de Cristo Rey most The thick limestone cliff of the Buda shallow-marine deposition. Mauldin and Formation (Fig. 14, unit 7) consists of fine- resembles that of the middle member (Red Cornell (1986) concluded that the forami- grained, bioturbated, bioclastic wackestone Light Member) of the Buda in Trans-Pecos niferans of the Del Rio Formation indicate a with a few larger skeletons. Most abundant Texas (Reaser and Robinson 2003) in being deepening of marine waters (transgression) are mollusc shell fragments (bivalves and a mixture of thin-bedded lime mudstone that culminated in the middle part of the gastropods) and dasycladacean algae; Del Rio, followed by a regression during and nodular, marly limestone. In contrast, ostracods, echinoderms, echinoid spines, deposition of the upper Del Rio. the lower member (Lecheguilla Member) smaller foraminiferans, and rare bryozo- Mauldin and Cornell (1986) indicate that and the upper member (Love Station Mem- ans(?) are subordinate. Many skeletons, the lower half of the Del Rio succession ber) of the Buda Formation in Trans-Pecos particularly molluscs and algae, are recrys- is dominated by rotaliine foraminiferans; Texas are ridge-forming beds of lithograph- tallized. A few micritic intraclasts are pre- the upper half is enriched in agglutinated ic, muddy limestone (Reaser and Robinson sent. The skeletons are embedded in a mic- foraminiferans. The ratio of planktonic 2003). Correlation of the Buda Formation ritic to pelmicritic matrix. to benthic foraminiferans is 0.1–0.6 in the section at Cerro de Cristo Rey to only the The lowermost, gastropod-rich lime- lower half, indicating water depths from Red Light Member to the southeast thus stone bed (Fig. 14, unit 9) is a bioturbated 60 to 100 m. The value drops in the upper has a lithostratigraphic basis, but cannot bioclastic mudstone containing small and half, indicating water depths of 20 m or less be confirmed biostratigraphically because rare larger bioclasts floating in a pelmic- (Mauldin and Cornell 1986). The foraminif- the entire Buda Formation falls within one ritic matrix (Fig. 24D). Most skeletons are eral assemblages indicate that the basal part ammonoid zone, which is the biostrati- derived from bivalves and gastropods, of the Del Rio Formation marks a transgres- graphic means by which Buda sections are and also from dasycladacean algae. Rare sion, and that a deeper shelf environment correlated (Young 1979). ostracods, echinoderms, echinoid spines, (60–100 m) persisted until deposition of the As Hook (2008; also see Cooper et al. 2008) and smaller foraminiferans are present. middle Del Rio Formation, followed by a noted, the top of the Buda Formation usu- The rock also contains a few small, detrital drop in sea level to water depths of approx- ally displays evidence of in the form quartz grains. Another thin section indi- imately 20 m in the upper half (Mauldin of microkarst features at the Buda–Mancos cates a bioturbated bioclastic mudstone and Cornell 1986). contact. However, at Cerro de Cristo Rey the composed of micritic matrix and small

November 2010, Volume 32, Number 4 New Mexico Geology 125 bioclasts such as ostracods, bivalve shell Mancos Formation shell fragments, abundant small bioclasts, fragments, echinoid spines, echinoderms, ("Boquillas Formation") mostly shell debris and foraminiferans and smaller foraminiferans floating in the (globigerinids?), subordinate echinoderms, matrix. Small quartz grains and rare glau- and other bioclasts. A few angular quartz conite are present. Lithostratigraphy grains, , and intraclasts are present. The uppermost limestone bed of the Buda Formation (Fig. 14, unit 21) is composed of At Cerro de Cristo Rey, the exposed thick- Depositional environments bioturbated bioclastic wackestone contain- ness of the Mancos Formation is 18.6 m ing a few larger bivalve and shell fragments (Fig. 15). The total estimated thickness is Deposition of the Mancos Formation took floating in a fine-grained bioclastic matrix. approximately 110 m (Böse 1910; Lovejoy place in normal marine waters. Muddy sea Small recrystallized shell fragments and 1976), but we cannot confirm this estimate bottoms supported characteristic benthic algal debris, ostracods, subordinate small with outcrop data. White, gastropod-rich, organisms such as inoceramid bivalves, gastropods, echinoderms, and smaller nodular limestone of the Buda Formation and nektonic organisms such as ammo- foraminiferans are abundant. The fossils are is sharply and unconformably overlain by noids lived in the water column. embedded in micritic matrix. Similarly, at approximately 5 m of shale intercalated our Mancos Formation section, the topmost with thin sandy limestone and limestone Depositional cycles and Buda Formation (Fig. 15, unit 1) is bioturbat- beds. The uppermost limestone bed of this ed bioclastic wackestone that is poorly sort- interval is 0.2 m thick and forms a ledge. sequence boundaries ed, contains mollusc shell debris (bivalves, Above is a 3.9-m-thick covered interval that gastropods), calcareous algae, echinoderms, conceals a cross fault or fold. Overlying Introduction echinoid spines, ostracods, worm tubes, strata are a 10-m-thick succession of shale and foraminiferans. A few peloids and rare with a few thin sandstone beds. Deposition of the Cretaceous strata exposed glauconite grains are present. The matrix is Böse (1910) and some subsequent work- micrite. at Cerro de Cristo Rey took place just off ers (Fig. 3) referred to these strata as the of the northern margin of the Chihuahua Eagle Ford Formation (Shale). Strain (1976) Depositional environments trough, one of the actively subsiding basins first brought the term Boquillas Formation bordering the late Aptian–early Cenoma- into Cerro de Cristo Rey, although he sug- nian Comanche Shelf, which extended from Regional deposition of the Buda Forma- gested that the names Chispa Summit or eastern across part of southern tion took place in shallow-marine waters Ojinaga might better be applied. We prefer New Mexico and northern Mexico through on a broad, shallow carbonate ramp that to use the name Mancos Formation (Shale), Texas and farther east (Fig. 26). The Creta- extended across much of Texas and parts widely used across New Mexico, for this ceous section at Cerro de Cristo Rey encom- of northern Mexico (Reaser and Robinson shaley interval at the base of the Green- passes the uppermost Fredricksburg Group 2003). Our analysis of Buda microfacies horn cycle of deposition (e.g., Seager 1981; (upper part of Finlay Formation), the entire (most limestones are bioclastic wackestone Molenaar 1983; Lucas and Estep 1998a; Washita Group (Del Norte, Smeltertown, and mudstone) at Cerro de Cristo Rey indi- Lucas et al. 2000). Indeed, Mancos For- Muleros, Mesilla Valley, Mojado, Del Rio, cates they correspond well to the shallow- mation is applied to the same lithosome and Buda Formations), and the basal unit water wackestone–mudstone facies of at nearby outcrops in the southern San (lower Mancos Formation) of the overlying Reaser and Robinson (2003). Andres Mountains, approximately 75 km Greenhorn cycle. It represents a hierarchy of According to Reaser and Robinson (2003), north of Cerro de Cristo Rey, and in the at least three clearly definable depositional the lower member of the Buda Formation was southern Cooke’s Range, approximately cycles (Scott et al. 2003). Here, we identify deposited on a broad open shelf with normal 120 km northwest of Cerro de Cristo Rey. sequence boundaries () and marine water near the basin margin during transgressive-regressive (deepening-shal- the last marine incursion by the Coman- Paleontology lowing) cycles in the Cretaceous section at chean sea. The middle member is interpreted Cerro de Cristo Rey (Fig. 27). as deposits of a shallow, slightly hypersaline Kennedy et al. (1988) described a middle shelf during a drop in sea level. Sediments of Cenomanian molluscan fauna of bivalves First order cycles and sequence boundaries the upper member accumulated in a similar (Ostrea beloiti Logan and Inoceramus arva- environment (on the distal part of an open nus Stephenson) and diverse ammonoids Scott et al. (2000, 2003) consider the entire shelf) as those of the lower member and rep- (including Acanthoceras amphibolum) from Comanchean Series of Texas and adjacent resent the final highstand event. a thin bed of calcarenitic and coquinoidal areas to represent a single, first-order cycle At Cerro de Cristo Rey (Fig. 14) muddy limestone near the base of the Mancos For- of deposition. This cycle includes the Trin- textures, common bioturbation, diverse fos- mation (Fig. 15, bed 3). Turnšek et al. (2003) ity, Frederickburg, and Washita Groups of sil assemblage, and the presence of dasyclad- also state that shark teeth (notably Pty- late Aptian to early Cenomanian age. The acean algae indicate to us that the limestone chodus) are present in the Mancos Forma- lower part of this cycle (Trinity Group and of the lower part of the Buda Formation was tion at Cerro de Cristo Rey. Cornell (1997) most of the Fredericksburg Group) is not deposited in an open, normal marine, low- reported dinoflagellate cysts. We observed exposed at Cerro de Cristo Rey. However, energy shelf environment below the wave dasycladacean algae, foraminiferans, ostra- the upper part of the cycle, and its upper base. Carbonate sedimentation periodically cods, echinoderms, and bryozoans(?) in bounding unconformity (between the Buda was interrupted by deposition of thin shale thin section. and Mancos Formations, see above), is well intercalations. exposed at Cerro de Cristo Rey. Intercalated limestone beds of the upper Sedimentary petrography (Figs. 15, 23A–B) In northern Texas, the entire Comanchean part of the Buda are of the same composi- tion as those of the lower part, indicating section is approximately 250 m thick, whereas a similar . Shale The lowermost thin limestone bed of the at Cerro de Cristo Rey that part of the Coman- is more abundant in the upper part, indi- Mancos Formation (Fig. 15, unit 3) is a chean section exposed is thicker, approxi- cating high rates of fine siliciclastic influx bioclastic wackestone–packstone–rudstone mately 350 m thick. This probably reflects that was periodically interrupted, causing that is poorly sorted and indistinctly lami- greater clastic influx into (and greater subsid- the deposition of limestone beds. A great- nated (Fig. 23A–B). The rock contains a mic- ence of) the Cerro de Cristo Rey Comanchean er amount of shale may be the result of a ritic matrix, and locally some calcite cement section because of its more landward position slight drop in sea level, although deposi- is present. It is strongly recrystallized, and relative to the more offshore sections in north- tion still occurred below wave base. it contains a few centimeter-sized bivalve ern and central Texas (Fig. 26).

126 New Mexico Geology November 2010, Volume 32, Number 4 Formation at Cerro de Cristo Rey, whereas the upper member indicates shallowing. A strong candidate for the next uncon- formity (sequence boundary) is the base of the Smeltertown Formation (Fig. 7, unit 24). The sharp contact of shale on limestone at the base of the Smeltertown Formation indi- cates deepening and marks the next trans- gressive surface. The absence of ammonites indicative of the Craginites serratescens and Eopachydiscus marcianus Zones at Cerro de Cristo Rey may be indicative of a hiatus at the base of the Smeltertown Formation where strata of the Mortoniceras equidistans Zone rest directly on strata of the Adkinsites bravoensis Zone, or it may be that facies restrictions precluded ammonite presence/ preservation in part of the Del Norte–Smel- tertown interval. The shoaling trend from deeper to shallower shelf of cycle WA2, cor- responding to the Smeltertown Formation, is also observed at Cerro de Cristo Rey. Cycle WA3 in north Texas was deposited during a period of general shoreline retreat along the northern basin margin (Scott et al. 2003). An upward-deepening trend is also observed within most of the Muleros Forma- tion with a regressive trend in the uppermost part. Cycle WA3 (Fig. 27) thus encompasses Figure 26—Early Cretaceous depositional basins of the Comanchean Series (uppermost Lower and lowermost Upper Cretaceous) in Texas, northern Mexico, and adjacent areas (after Scott et al. 2003). the entire Muleros Formation, and begins with an upward-deepening trend into off- Second order cycles and sequence boundaries sequence boundaries (and thus stratigraph- shore shale (Fig. 9, unit 2) and then shallow- ic extent) of the lower three cycles. We thus ing into the bioturbated limestones and Texi- In Texas the Fredericksburg and Washita identify six upward-shallowing shale-sand- gryphaea packstones of the middle to upper Groups have long been regarded as sec- stone or shale-limestone cycles bounded by Muleros Formation (Fig. 9, units 3–14). WA3 ond-order cycles of deposition (e.g., Lozo unconformities in the Washita Group sec- is an important regional cycle in New Mexi- and Stricklin 1956; Hendricks 1967; Scott tion at Cerro de Cristo Rey (Fig. 27). co as it is represented by the Tucumcari and Glencairn Formations, which are the first et al. 2003). Across much of Texas, the top The Finlay Formation is the final high- extensive Albian seaway in the northeastern of the Fredricksburg Group is a regional stand of the Fredericksburg second-order part of the state (e.g., Kues and Lucas 1987; hardground with subaerial exposure (uncon- cycle. Steinhoff (2003) identified high-fre- formity) overlain by the Kiamichi Formation Scott et al. 2001). quency cycles in the Finlay Formation that An abrupt deepening of marine waters (base of the Washita Group; Amsbury 2003; begin with nodular, marly layers and grade Scott et al. 2003). Thus, the Fredericksburg at the base of the Mesilla Valley Formation up into massive limestones and are 1–4.5 m and Washita Groups are unconformity- marks the beginning of the next cycle (WA4, thick. The upper part of the Finlay Forma- bounded units with a basal clastic facies that Fig. 27). This cycle begins relatively deep in generally grades up into intercalated shallow- tion exposed at Cerro de Cristo Rey encom- offshore marine muds of member A (Fig. 10, marine and clastics. At Cerro de passes 12 such cycles (Fig. 6). These cycles unit 2) and then shallows through sandstone Cristo Rey, the entire Washita Group second- may correlate to 12 of the 18 high-frequen- and Texigryphaea packstones of member B. In order cycle is exposed (Fig. 27). It is bounded cy cycles that Steinhoff (2003) recognized as north Texas, cycle WA4, which corresponds by distinct unconformities at the base of the part of an upper, high-frequency sequence 2 to most of the Mesilla Valley Formation at Del Norte and Mancos Formations. Only the of the Finlay Formation formed during a Cerro de Cristo Rey (Fig. 27), is a succession uppermost part of the Fredericksburg cycle time of relative sea-level highstand. By this from shallow shelf within the storm wave (upper Finlay Formation) and the lowermost interpretation, the upper Finlay at Cerro de base to a nearshore high-energy setting. A part of the Greenhorn cycle (lower Mancos Cristo Rey represents shoaling up followed shallowing trend is also recorded within the Formation) are exposed at Cerro de Cristo by sea level fall at the end of the last cycle Mesilla Valley Formation from member A to Rey (Fig. 27). of deposition of the Fredericksburg Group member B. The sharp contact between lime- (Amsbury 2003; Scott et al. 2003). stone (Muleros) and shale (Mesilla Valley) is Third order cycles and sequence boundaries As noted above, Scott et al. (2000, 2003) the likely sequence boundary at the base of identified six third-order cycles of deposi- the WA4 cycle. Based on the interpretation of Scott et al. tion in the Washita Group of northern Texas Relatively offshore black shale of mem- (2001, 2003), the Cretaceous section exposed (and at Cerro de Cristo Rey) that they labeled ber C of the Mesilla Valley Formation (Fig. 10, at Cerro de Cristo Rey represents eight WA1 through WA6. Thus, WA1 begins at the unit 12) appears to represent an abrupt deep- smaller-scale (third order?) depositional base of the Del Norte Formation (= base of ening and thus can be interpreted as the base cycles, six of which comprise the Wash- Washita Group), where a ferruginous sand- of the next cycle, WA5. The succession shal- ita Group section (Fig. 27). In the Washita stone rests directly on lime mudstone at the lows upward into interbedded sandstone Group section, Scott et al. (2001, 2003) iden- top of the Finlay Formation (Fig. 27). The con- and shale of the basal Mojado Formation. tify these six cycles (WA1 through WA6) tact reflects an abrupt increase in water depth We thus place the base of WA5 at the base of as shale-sandstone or mudstone-limestone and siliciclastic influx, thus representing a member C of the Mesilla Valley Formation cycles. Our data strongly support this inter- transgressive surface. The transgressional- (Fig. 27). A deepening trend above the first pretation, although we differ from Scott progradational succession of cycle WA1 is thick, crossbedded fluvial sandstone of the et al. (2001, 2003) in our placement of the visible in the lower member of the Del Norte Mojado Formation (Fig. 10, unit 14; Fig. 11,

November 2010, Volume 32, Number 4 New Mexico Geology 127 unit 4) is indicated by bioturbated sand- deposition of shale in the upper part may stones and interbedded siltstones (Fig. 11, indicate a drop in sea level. units 7–14) and is followed by shallowing, The unconformity at the base of the Man- indicated by prograding fluvial sandstones cos Formation (Fig. 27) begins the next cycle (Fig. 11, units 15–25). of deposition (Greenhorn cycle). It repre- In north Texas, WA5 represents a regres- sents a major tectonic reorganization of the sive trend from deep to shallow shelf Cretaceous marine basins of the American conditions (Scott et al. 2003). This trend Southwest (e.g., Mack 1987). At Cerro de is indicated by the facies of the Pawpaw Formation, which northward becomes Cristo Rey, this was the change from dep- very sandy with thin-bedded and trough osition along an extensive carbonate plat- crossbedded sandstone of deltaic origin. form (Comanchean Platform) that bordered The overlying Main Street Formation also a rift basin (Chihuahua trough) to deposi- indicates a northward change from a car- tion in the retroarc foreland basin of the bonate shelf to shoreface environment Western Interior Seaway. with significant input of quartz. A similar The persistence of cycles from the tectoni- shoaling trend is clearly visible within the cally passive, open-marine margin of the Mojado Formation, which approximately Gulf of Mexico into the tectonically active corresponds to cycle WA5: lower shore- Chihuahua trough suggests that regional, face to upper shoreface and finally to flu- if not global eustasy, not local tectonism, viodeltaic sandstone. drove late Early to early Late Cretaceous Cycle WA6 in north Texas is represent- ed by the Grayson and Buda Formations, sedimentation at Cerro de Cristo Rey. which correlate to the uppermost Mojado, Del Rio, and Buda Formations at Cerro Acknowledgments de Cristo Rey (Scott et al. 2001, 2003). The Grayson is characterized by a progressive change from carbonate to clay. The lower We are grateful to George Cudahy for access part is composed of shale with intercalated to land, and assistance in the field from ripple-laminated beds of carbonate silt and Josh Smith. We thank Daniel Vachard, who sand interpreted as storm layers overlain helped us to identify foraminiferans and by clay mainly deposited below the storm algae in thin sections. Comments by Robert wave base. The middle part is represent- W. Scott on an earlier version of this man- ed by nodular wackestone and shale, and uscript greatly improved its content and the uppermost part by shale, interbedded organization. W. R. Dickinson, T. Lawton, marl, and bioturbated limestone. Similar and R. W. Scott provided helpful reviews of are recognized within the Del the submitted manuscript. Rio Formation, although storm layers are absent, and deposition took place in a low- energy outer-shelf environment below the References storm wave base. The uppermost Mojado Formation pre- Adkins, W. C., 1932, The system in Texas; serves a transgressive surface that we iden- in Sellards, E. H., Adkins, W. C., and Plummer, tify as the basal unconformity of the WA6 F. B. (eds.), The : University of cycle (Fig. 11, base of unit 26; Fig. 27). This Texas, Publication 3252, pp. 329–518. Amsbury, D. L., 2003, Stratigraphy of Fredericks- cycle deepens upward through the lower burg Group (middle–upper Albian Cretaceous) Del Rio, then shallows into the platform north-central Texas; in Scott, R. W. (ed.), Creta- carbonates of the Buda Formation. The ceous stratigraphy and paleoecology, Texas and Buda Formation represents the last marine Mexico: Perkins Memorial volume, GCSSEPM transgression of the Comanchean Seaway, Foundation, Special Publications in Geology, v. 1, and Reaser and Robinson (2003) interpreted pp. 227–276. Böse, E., 1910, Monografia geológica y paleontologi- Buda deposition (in Trans-Pecos Texas) as cal del Cerro de Muleros cerca de Ciudad Juárez, representing a transgression across a broad, Estado de Chihuahua, y descripción de la fauna low-relief carbonate ramp (lower Buda = cretácea de La Encanatada, Placer de Guadalupe, Lecheguilla Member), followed by a break Estado de Chihuahua: Instituto Geologico de in transgression and a regression during Mexico, Bulletin 25, 193 pp. Bullock, J. S., 1985, Biostratigraphic study of which terrigenous clays were deposited from the Smeltertown Formation (middle Buda = Red Light Member), cul- (Lower Cretaceous, Albian) of southeastern New minated by a final transgression and high- Mexico: Unpublished M.S. thesis, University of stand (upper Buda = Love Station Member). Texas at El Paso, 155 pp. The Buda outcrop at Cerro de Cristo Rey is Bullock, J. S., and Cornell, W. C., 1986, Biostratigra- the westernmost outcrop of the formation, phy and paleoecology of the Smeltertown Forma- tion, Cerro de Cristo Rey, Doña Ana County, New and is a relatively thin (< 20 m thick) and Mexico; in Hoffer, J. M. (ed.), Geology of south- shaly section of the formation. Given that central New Mexico: El Paso Geological Society, the Del Rio shows an upward-shallowing Guidebook, pp. 73–76. trend, we think it most likely that the Buda Cobban, W. A., 1987, Ammonite of the Sarten was deposited during regression or during Sandstone (Cretaceous), Luna County, New Mexico: U.S. Geological Survey, Bulletin 1641–B, pp. B1–B17. a prograding highstand. Limestone of the Cobban, W. A., Hook, S. C., and McKinney, K. C., Figure 27—Summary of Cretaceous section at Buda Formation at Cristo Rey suggests dep- 2008, Upper Cretaceous molluscan record along Cerro de Cristo Rey showing sequence boundar- osition in an open-marine, low-energy shelf a transect from Virden, New Mexico, to Del Rio, ies and depositional cycles. environment below wave base. Increased Texas: New Mexico Geology, v. 30, pp. 75–92.

128 New Mexico Geology November 2010, Volume 32, Number 4 Cooper, R. W., Cooper, D. A., Stevens, J. B., and Kollmann, H. A., Decker, K., and LeMone, D. V., Molenaar, C. M., 1983, Major depositional cycles and Stevens, M. S., 2008, Geology of the Hot Springs 2003, Facies control of Lower Cretaceous gastro- regional correlations of Upper Cretaceous rocks, Trail area, Ernst and San Vicente Members of the pod assemblages, southwestern ; in southern Colorado Plateau and adjacent areas; in Boquillas Formation; in Cooper, D. A. (ed.), The Scott, R. W. (ed.), Cretaceous stratigraphy and Reynolds, M. W., and Dolly, E. D. (eds.), Mesozoic southern extension of the Western Interior Sea- paleoecology, Texas and Mexico: Perkins Memo- paleogeography of west-central United States: Soci- way: Geology of the and rial volume, GCSSEPM Foundation, Special Pub- ety of Economic Peleontologists and Mineralogists Trans-Pecos, Texas, 2008 Annual Meeting of lications in Geology, v. 1, pp. 101–146. 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November 2010, Volume 32, Number 4 New Mexico Geology 129 Turnšek, D., LeMone, D. V., and Scott, R. W., 2003, Young, K., 1966, Texas Mojsisovicinae () Zeller, R. A., Jr., 1965, Stratigraphy of the Big Hatch- Tethyan Albian corals, Cerro de Cristo Rey uplift, and the zonation of the Fredericksburg: Geological et Mountains area, New Mexico: New Mexico Chihuahua and New Mexico; in Scott, R. W. Society of America, Memoir 100, 225 pp. Bureau of Mines and Mineral Resources, Mem- (ed.), Cretaceous stratigraphy and paleoecology, Young, K., 1979, Lower Cenomanian and late Albian oir 16, 128 pp. Texas and Mexico: Perkins Memorial volume, (Cretaceous) ammonites, especially Lyelliceridae, GCSSEPM Foundation, Special Publications in of Texas and Mexico: Texas Memorial Museum, Geology, v. 1, pp. 147–185. Bulletin 26, 99 pp.

Appendix Location of measured sections

Finlay Formation (Fig. 6)—base at UTM Muleros Formation (Fig. 9)—base at UTM Del Rio Formation (Fig. 13)—base at UTM Zone 13, 355011E 3518134N (NAD 27), Zone 13, 354953E 3517640N, top at Zone 13, 353899E 3118636N, top at top at 355064E 3518629N. 354922E 3517683N. 353871E 3518678N. Del Norte Formation (Fig. 7)—base at top of Mesilla Valley Formation (Fig. 10)—base at Buda Formation (Fig. 14)—base at UTM section A, top at UTM Zone 13, 355084E UTM Zone 13, 354508E 3518122N, top at Zone 13, 353881E 3518823N, top at 3517962N (NAD 27). 354535E 3518200N. 353859E 3518828N. Smeltertown Formation (Fig. 8)—base at Mojado Formation (Fig. 11)—base at Mancos Formation (Fig. 15)—base at UTM UTM Zone 13, 355178E 3517669N, top at UTM Zone 13, 354003E 3518452N, top Zone 13, 353534E 3518775N, top at 355040E 3517595N. at 353967E 3518553N. 353524E 3518792N.

130 New Mexico Geology November 2010, Volume 32, Number 4