Lucas, S.G., DiMichele, W.A. and Krainer, K., eds., 2017, Carboniferous-Permian transition in Socorro County, New Mexico. New Mexico Museum of Natural History and Science Bulletin 77.
MICROFACIES AND SEDIMENTARY PETROGRAPHY OF PENNSYLVANIAN LIMESTONES AND SANDSTONES OF THE CERROS DE AMADO AREA, EAST OF SOCORRO (NEW MEXICO, USA)
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KARL KRAINER1, DANIEL VACHARD2, SPENCER G. LUCAS3 AND ANDREJ ERNST4 1
Institute of Geology, University of Innsbruck, Innrain 52, A-6020 Innsbruck, Austria, email:
[email protected]; Collegial and International Research Centre of Active Seniors (CIRCAS), 1 rue des Tilleuls, 59152 Gruson, France; 3 New Mexico Museum of Natural History, 1801 Mountain Road N.W., Albuquerque, NM 87104; 4 Institute of Geology, University of Hamburg, Bundesstraße 55, D-20146 Hamburg, Germany
2
Abstract—Pennsylvanian strata are well exposed in the Cerros de Amado area, east of Socorro, central New Mexico. The succession is approximately 800 m thick and divided into the Sandia, Gray Mesa and Atrasado formations. Conodonts indicate an Atokan age for the Sandia Formation. The Gray Mesa Formation is divided into Elephant Butte, Whiskey Canyon and Garcia members and dated as early to late Desmoinesian. The Atrasado Formation is divided into eight members (Bartolo, Amado, Tinajas, Council Spring, Burrego, Story, Del Cuerto and Moya members, in ascending order) and ranges in age from late Desmoinesian to middle Virgilian. The Pennsylvanian succession east of Socorro is composed of different types of limestone and intercalated siliciclastic sediments. In the Sandia Formation, the dominant sandstone type is quartz arenite. In the Garcia Member of the Gray Mesa Formation and in the clastic members of the Atrasado Formation, mixed siliciclasticcarbonate sandstone predominates. The most abundant microfacies of limestone are bioclastic wackestone and floatstone. Other microfacies such as mudstone, packstone, grainstone and rudstone are rare, and boundstone is very rare. The most abundant fossils in the limestone facies of all three formations are echinoderms (mostly crinoids), bryozoans and brachiopods. Thus, the dominant grain association type is bryonoderm extended. Subordinately, the chloralgal grain association type is present. Less common are smaller and larger benthic foraminifers, calcareous algae (dominantly phylloid algae), sponges (dominantly spicules), corals, mollusks (bivalves and gastropods), and arthropods (ostracods and trilobites). Common encrusting organisms are cyanobacteria and Palaeonubecularia, and (subordinately) sessile foraminifers, algae, Tubiphytes and bryozoans. The Sandia Formation is characterized by distinct lateral and vertical variations in facies and thickness and represents early synorogenic sediments deposited during the initial phase of the Ancestral Rocky Mountain (ARM) orogeny. The Gray Mesa Formation, particularly the Whiskey Canyon Member, is dominated by limestone with little variation in facies and thickness over a large area, indicating deposition on an extensive, deeper, open marine shelf that extended from Cedro Peak in the Manzanita Mountains of Bernalillo County south to the Caballo Mountains of Sierra County. The Atrasado Formation is a succession of alternating siliciclastic-dominated and limestone-dominated members. Siliciclastic-dominated members display strong lateral variations in thickness and facies, which are indicative of deposition during tectonically active periods, whereas the limestone-dominated members are much more consistent in facies and thickness, pointing to deposition during tectonically stable periods.
INTRODUCTION The Cerros de Amado are rugged hills developed in faulted and folded upper Paleozoic strata exposed along the eastern flank of the Rio Grande rift about 8 km northeast of Socorro, New Mexico (Fig. 1). Much of the bedrock in the Cerros de Amado consists of Pennsylvanian sedimentary rocks, and, indeed, a complete, ~ 800 m thick Pennsylvanian section for this part of central New Mexico can be pieced together across different fault blocks (Lucas et al., 2009a). Conodont biostratigraphy provides most of the published age control of this Pennsylvanian section (Lucas et al., 2009a; Barrick et al., 2013). In this paper, we present new data on the Pennsylvanian section in the Cerros de Amado and: (1) provide a detailed study of the petrography of sandstones and microfacies of limestones; (2) identify the calcareous microfossils; (3) discuss the depositional environments; and (4) provide a paleogeographic reconstruction of the Pennsylvanian succession of central New Mexico based on comparison with other studied sections. METHODS A number of sections through the Pennsylvanian succession in the Cerros de Amado area east of Socorro have been measured that encompass the Sandia Formation, Gray Mesa Formation, Atrasado Formation and Bursum Formation. From the measured sections, samples were collected, from which numerous thin sections were prepared. Thin sections were studied under the microscope, and a microfacies analysis was performed on the carbonate facies. Limestones were classified after the scheme proposed by Dunham (1962), as modified by Embry and Klovan (1971). Petrographic thin sections of sandstones and
limestones were studied to obtain data on the mineralogic composition and diagenesis (total of 320 thin sections). For documentation, thinsection photographs of limestone microfacies, sandstone and fossils were prepared. The first results on the stratigraphy, lithology and petrography have been already published by Lucas et al. (2003, 2009a, b, 2013) and Barrick et al. (2013). STRATIGRAPHY AND LITHOLOGY In the Cerros de Amado region east of Socorro, the Pennsylvanian section is well exposed, approximately 800 m thick and divided into the Sandia, Gray Mesa and Atrasado formations. These are strata of Atokan, Desmoinesian, Missourian and Virgilian age. The overlying Bursum Formation is early Wolfcampian in age as indicated by fusulinids (Lucas et al., 2009a). We studied the Pennsylvanian succession at the following localities: Arroyo de la Presilla (Section A: Sandia Formation, section B: Gray Mesa Formation; Figs. 2-3), Cerros de Amado (section A: Bartolo, Amado, Tinajas members of the Atrasado Formation; section B: Tinajas, Council Spring, Burrego and Strory members of the Atrasado Formation; section C: Garcia Member of the Gray Mesa Formation, Bartolo and Amado members of the Atrasado Formation; section D: part of the Garcia Member; Figs. 4-7), Minas de Chupadera (Bartolo, Amado, Tinajas, Council Spring, Burrego, Story, Del Cuerto and Moya members of the Atrasado Formation; Fig. 8), Bioherm section (Amado, Tinajas, Council Spring, Burrego and Story members of the Atrasado Formation; Fig. 9), Ojo de Amado (Tinajas, Council Spring, Burrego, Story, Del Cuerto and Moya members of the
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FIGURE 1. Map showing the location of the studied sections. APA Arroyo de la Presilla section A; APB Arroyo de la Presilla section B; CAA Cerros de Amado section A; CAB Cerros de Amado section B; CAC Cerros de Amado section C; CAD Cerros de Amado section D; MC Minas de Chupadera; BIO Bioherm section; ODA Ojo de Amado; COY Cerrillos del Coyote. Atrasado Formation; Fig. 10) and Cerrillos del Coyote (Amado, Tinajas and Council Spring members; Fig. 11). The location of the sections is shown on the map (Fig. 1). The Sandia Formation, well exposed at Arroyo de la Presilla, unconformably rests on granite of the Precambrian basement (Fig. 2). Here, the Sandia Formation is 162 m thick, which is one of the thickest Sandia Formation sections in New Mexico (Krainer and Lucas, 2013). The succession is composed of quartz-rich sandstone and conglomerate, siltstone, shale and fossiliferous limestone (Lucas et al., 2009a, b, 2013; Krainer and Lucas, 2013). The overlying Gray Mesa Formation is almost completely exposed at Arroyo de la Presilla, measures 233 m and is divided into Elephant Butte, Whiskey Canyon and Garcia members (Fig. 3). The Elephant Butte Member is 95 m thick and composed of limestone and shale with 10 m of coarse-grained sandstone intercalated near the base. The Whiskey Canyon Member is represented by 35 m of mostly very cherty limestone. The Garcia Member is 103 m thick and composed of limestone with intercalated conglomerate, sandstone and siltstoneshale. The Atrasado Formation is 290 m thick, exposed in the Cerros de Amado at several sections (Figs. 4-7) and divided into eight members: Bartolo (dominantly siliciclastic), Amado (carbonate), Tinajas (dominantly siliciclastic), Council Spring (carbonate), Burrego (mixed siliciclastic-carbonate), Story (carbonate), Del Cuerto (mixed siliciclastic-carbonate) and Moya members (dominantly carbonate) (see Lucas et al., 2009a). The Atrasado Formation or parts of the Atrasado Formation are also exposed at the sections Minas de Chupadera (Fig. 8), Bioherm (Fig. 9), Ojo de Amado (Fig. 10) and Cerrillos del Coyote (Fig. 11). Conodonts from the Sandia Formation from unit 27, which is 47 m above the base, indicate an Atokan age. The Elephant Butte Member, Whiskey Canyon Member and lower part of the Garcia Member are of early Desmoinesian (Cherokee) age. The upper part of the Garcia Member of the Gray Mesa Formation and Bartolo Member of the Atrasado Formation are of late Desmoinesian (Marmaton) age. The Amado Member is of early Missourian, and the Tinajas and Council Spring members are of middle-late Missourian age. The top of the Burrego Member, and the Story, Del Cuerto and Moya members are dated as middle Virgilian (Lucas et al., 2009a; Barrick et al., 2013). The fusulinids collected during this study confirm these conodontdetermined ages. The early Desmoinesian age of the Elephant Butte Member, Whiskey Canyon Member and lower part of the Garcia Member are indicated by assemblages with Beedeina spp. and Wedekindellina spp. The Tinajas Member is middle Missourian due to the presence of relatively primitive Triticites, including T. cf. cameratoides and T. cf. celebroides. The overlying Bursum Formation was studied in detail by Krainer and Lucas (2009) and will not be discussed in this paper.
FIGURE 2. Measured section of the Sandia Formation at Arroyo de la Presilla (section A; location see Fig. 1). For lithologic legend see Figure 7. SANDSTONE AND CONGLOMERATE FACIES Sandstone and conglomerate are common lithologies of the Sandia Formation, particularly in the lower and middle parts of the unit (see Lucas et al., 2009a, b). In the Elephant Butte Member of the Gray Mesa Formation, quartzose sandstone occurs as a prominent, 10-m-thick interval in the lower part and as two thin sandstone beds near the base and in the middle of the member. Sandstone is commonly crossbedded. Two thin limestone conglomerates are also intercalated. Sandstone and conglomerate are absent in the Whiskey Canyon Member. In the Garcia Member, conglomerate and sandstone occur in the upper part of the Arroyo de la Presilla section B and in the lower and middle parts of the Cerros de Amado C section (Lucas et al., 2009a). In the Atrasado Formation, conglomerate and, particularly, sandstone are common lithologies of the Bartolo, Tinajas, Burrego, and Del Cuerto members, whereas the Amado, Council Spring, Story and Moya members are dominated by limestone with minor intercalations of shale and rare sandstone. Siltstone and shale are present in all formations, although mostly covered. CONGLOMERATE AND SANDSTONE PETROGRAPHY Among the sandstones, two types are distinguished: 1. Siliciclastic sandstone is the common sandstone type in the
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FIGURE 3. Measured section of most of the Gray Mesa Formation at Arroyo de la Presilla (section B; location see Fig. 1). For lithologic legend see Figure 7.
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FIGURE 4. Measured section of part of the Atrasado Formation at Cerros de Amado (section A; location see Fig. 1). For lithologic legend see Figure 7. Sandia Formation, also present in the Elephant Butte Member of the Gray Mesa Formation and rare in the Tinajas Member of the Atrasado Formation. 2. Mixed siliciclastic-carbonate sandstone is rare in the Elephant Butte Member, and common in the Garcia Member and all clastic members of the Atrasado Formation (Burrego, Bartolo, Tinajas, Del Cuerto, locally also in the Moya Member). Conglomerate is rare and was observed in the Sandia Formation, Garcia, Amado and Tinajas members. Conglomerate Petrography In the Sandia Formation, conglomerate comprises 2.5% of the section. Conglomerate is poorly sorted at the base, containing mostly angular to subangular quartz clasts. At the base of fining-upward sequences, conglomerates are commonly developed that are trough crossbedded, and moderately to poorly sorted with a maximum grain size of 3 cm. These conglomerate beds are composed of subrounded quartz grains (Lucas et al., 2009a, 2013; Krainer and Lucas, 2013). Several thin conglomerate beds are present within the Garcia Member, which are mostly 0.2-0.6 m thick. Maximum grain size is usually 3-5 cm, rarely 10 cm. Clasts are mostly subrounded. Conglomerate beds are poorly sorted and composed of different types of limestone clasts and subordinately of quartz. Many conglomerate beds also contain fossil fragments, particularly of echinoderms (crinoids), brachiopods and bryozoans, and subordinately of fusulinids, smaller
FIGURE 5. Measured section of part of the Atrasado Formation at Cerros de Amado (section B; location see Fig. 1). For lithologic legend see Figure 7. foraminifers and ostracods. In the Atrasado Formation, thin conglomerate beds are present in the Bartolo, Amado and Tinajas members (Lucas et al., 2009a). Conglomerate in the Bartolo Member is composed of various types of limestone clasts and subordinately of quartz. In the Amado Member, conglomerate is represented by a 0.2-m thick, fine-grained, poorly sorted limestone conglomerate. Maximum grain size is 2 cm. The conglomerate contains different types of limestone clasts (e.g., mudstone, bioclastic wackestone) and silicified limestone clasts. Clasts are subangular to subrounded and embedded
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FIGURE 6. Measured section of parts of the Gray Mesa and Atrasado formations at Cerros de Amado (section C; location see Fig. 1). For lithologic legend see Figure 7.
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FIGURE 7. Measured section of part of the Gray Mesa Formation at Cerros de Amado (section D; location see Fig. 1) and lithologic legend for all measured sections (Figs. 2-11)
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FIGURE 8. Measured section of part of the Atrasado Formation and overlying Bursum Formation at Minas de Chupadera (location see Fig. 1). For lithologic legend see Figure 7.
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FIGURE 9. Measured section of part of the Atrasado Formation at the Bioherm section (location see Fig. 1). For lithologic legend see Figure 7.
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FIGURE 10. Measured section of part of the Atrasado Formation and overlying Bursum Formation at Ojo de Amado (location see Fig. 1). For lithologic legend see Figure 7.
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FIGURE 11. Measured section of part of the Atrasado Formation at Cerrillos del Coyote (location see Fig. 1). For lithologic legend see Figure 7. in micritic matrix that contains skeletons of bryozoans, brachiopods, ostracods and foraminifers. The carbonate conglomerate in the Tinajas Member at Minas de Chupadera is moderately to poorly sorted and contains limestone clasts, including bioclastic wackestone, wackestone-grainstone composed of tubular foraminifers, mudstone and bioclastic mudstone. The clasts are embedded in a sandy matrix of mixed siliciclastic-carbonate composition. The matrix contains mono- and polycrystalline quartz grains, detrital feldspars, a few micas (muscovite, biotite and chlorite), carbonate intraclasts and fossil fragments mainly derived from
echinoderms and brachiopods. Sandstone Petrography Sandstone is common in the Sandia Formation, in the Garcia Member of the Gray Mesa Formation and in the clastic-dominated members of the Atrasado Formation. Two types of sandstones can be distinguished: 1. Siliciclastic sandstone (Sandia Formation, rare in the Elephant Butte Member and the Tinajas Member) 2. Mixed siliciclastic-carbonate sandstone (rare in the Sandia Formation and the Elephant Butte Member, common in the Garcia Member and in the clastic-dominated members of the Atrasado Formation–Bartolo, Tinajas, Burrego and Del Cuerto–and rare in the Moya Member). Siliciclastic sandstone: In the Sandia Formation, coarse-grained sandstone is moderately to poorly sorted, and fine-grained sandstone is moderately to well sorted. Grains are mostly angular to subangular near the base and mostly subangular to subrounded higher in the section. Detrital grains are dominantly quartz. Monocrystalline quartz is more abundant than polycrystalline quartz. Chert grains are very rare (Fig. 18A-C). Detrital feldspars are mostly altered to clay minerals, forming “pseudomatrix” (Fig. 18C, F).The original feldspar content was less than 5%. Very rare are granitic rock fragments composed of quartz and feldspar, fine-grained schistose metamorphic rock fragments composed of quartz and mica and phyllitic metamorphic rock fragments. Detrital muscovite is very rare. Accessory grains are opaques, zircon and tourmaline. Most sandstones do not contain matrix; the detrital grains are cemented by quartz that occurs as authigenic overgrowths on detrital grains (Fig. 18A-B). Locally, fine-crystalline quartz cement is present. A few sandstones contain small amounts of clayey matrix. Locally, coarse, blocky, poikilotopic calcite cement is present that randomly replaces detrital quartz grains. Sandstone in the Elephant Butte Member is similar in texture and composition to the sandstones of the Sandia Formation (Fig. 18D). Sandstone is dominantly coarse grained, moderately to poorly sorted, and the grains are mostly subrounded. Again, mono- and polycrystalline quartz, including rare stretched metamorphic quartz, are the dominant grain types. Chert, altered detrital feldspar grains and micritic carbonate grains are rare. Detrital muscovite is very rare. Small patches of clay minerals most probably represent detrital feldspar grains that have been completely altered and now form “pseudomatrix.” Very rarely, echinoderm fragments are present in the sandstone. The detrital grains are cemented by authigenic quartz overgrowths and coarse blocky calcite cement that randomly replaces quartz. In the Atrasado Formation, siliciclastic sandstone was rarely observed in the Tinajas Member. Sandstone is fine to medium grained and moderately to well sorted. Detrital grains are dominantly subrounded (Fig. 18E, G, H). The sandstone contains abundant mono- and polycrystalline quartz, many detrital feldspar grains that are mainly altered potassium feldspars, including untwinned types, perthitic feldspars and rare microcline. Plagioclase displaying polysynthetic twinings is subordinate. Rock fragments are rare and include granitic and fine-grained schistose metamorphic and micritic sedimentary types. Detrital muscovite is very rare. Detrital grains are cemented by quartz that occurs as overgrowths and by blocky calcite cement that replaces detrital quartz and feldspar grains. Locally, Fe-rich dolomite rhombohedra are observed. Sandstone of the Sandia Formation and Elephant Butte Member is classified as quartz arenite, and sandstone of the Tinajas Member as subarkose (following the classification scheme of Pettijohn et al., 1987). Mixed siliciclastic-carbonate sandstone: In the Sandia Formation, mixed siliciclastic-carbonate sandstone occurs in the upper part of the section. The sandstone is poorly sorted, and detrital grains are subangular to subrounded. Detrital grains include abundant mono- and polycrystalline quartz grains and micritic carbonate grains. Detrital micas (muscovite) are rare. Fossil fragments are common and include shell debris, brachiopods, gastropods, echinoderms (mostly crinoids), bryozoans and ostracods. Mixed siliciclastic-carbonate sandstone in the Elephant Butte Member (Fig. 19F) is moderately sorted and composed of dominantly angular to subangular quartz and carbonate grains. Subordinately, skeletal grains like those in the Sandia Formation are present. The
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FIGURE 12. Thin section photographs of microfacies (mudstone and wackestone) from limestones of the Gray Mesa and Atrasado formations. All photos under plane light. Width of photos A, D, G = 4.6 mm, of photos B, C, E, F, H = 9 mm. A, Bioclastic mudstone containing a few recrystallized skeletons and ostracods. Sample OA 4, Council Spring Member, Ojo de Amado. B, Bioclastic mudstone-wackestone, bioturbated, containing recrystallized skeletons, brachiopod fragments, ostracods and rare smaller foraminifers. Sample OA 22, Council Spring Member, Ojo de Amado. C-D, Nodular mudstone containing dark gray micritic nodules with well-developed circumgranular fissures, which are characteristic of pedogenic carbonate. The mudstone also contains irregular (shrinkage) fissures. Sample MC 27, Story Member, Minas de Chupadera. E, Bioclastic wackestone, bioturbated, containing a diverse fossil assemblage. Sample CAA 18, Amado Member, Cerros de Amado A. F, Lithoclast-wackestone containing abundant peloids, subordinate micritic intraclasts and some ooids and a few ostracods. Sample CAA 26, Tinajas Member, Cerros de Amado. G, Wackestone containing abundant spicules and a few other skeletal grains (“spiculite”). Most of the spicules are oriented parallel to the bedding. Sample AP 46, Elephant Butte Member, Arroyo de la Presilla. H, Bioclastic wackestone containing small skeletons (brachiopod shell fragments and spines, echinoderms, ostracods, and smaller foraminifers) and rare larger brachiopods with both valves preserved. Sample CDA 13, Tinajas Member, Cerros de Amado.
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171 FIGURE 13 (facing page). Thin section photographs of microfacies (various types of wackestone) from limestones of the Gray Mesa and Atrasado formations. All photos under plane light. Width of photos: A, E = 4.6 mm; B, C, D, F, G, H = 9 mm. A, Peloidal wackestone to packstone containing a few skeletal grains (mainly ostracods), micritic intraclasts and rare ooids. Sample CAA 32, Tinajas Member, Cerros de Amado A. B, Bioclastic wackestone containing a diverse fossil assemblage including larger skeletons (brachiopods). Sample AP 61, Whiskey Canyon Member, Arroyo de la Presilla. C, Bioclastic wackestone containing a diverse fossil assemblage including abundant echinoderm, bryozoan and brachiopod fragments. Sample AP 58, Elephant Butte Member, Arroyo de la Presilla. D, Crinoidal wackestone composed of abundant crinoid stem fragments, subordinate brachiopods, some bryozoans and rare other skeletal grains. Sample CDA 16, Tinajas Member, Cerros de Amado. E, Wackestone containing abundant tubular foraminifers, and subordinately ostracods, echinoderms and other bioclasts. The wackestone is poorly washed, grading into grainstone. Sample MC 18, Burrego Member, Minas de Chupadera. F, Bryozoan wackestone containing abundant fragments of bryozoans, subordinately echinoderms, ostracods, and foraminifers. Sample CAC 49, Bartolo Member, Cerros de Amado C. G, Bioclastic wackestone to floatstone containing many bryozoans, brachiopods and echinoderm fragments, Tubiphytes and other bioclasts. Sample MC 30, Moya Member, Minas de Chupadera. H, Fusulinid wackestone, containing subordinately smaller foraminifers, echinoderms, brachiopods and ostracods. Sample ODA 11, Tinajas Member, Ojo de Amado. sandstone contains micritic matrix. In the Garcia Member, mixed siliciclastic-carbonate sandstone is commonly coarse-grained and may grade into rudstone with small amounts of siliciclastic detrital grains (Fig. 19B-E). Sorting is mostly moderate to poor; rarely, well-sorted sandstone occurs. Most of the siliciclastic grains are subangular. Angular grains are present in some of the sandstones. Most abundant are quartz and carbonate grains. The amount of detrital feldspar varies from few to many. Most feldspar grains are altered or partly replaced by calcite. Rare detrital grains include muscovite, siltstone-sandstone grains, glauconite and phosphorite grains. Sandstones are characterized by the presence of a diverse fossil assemblage. Fossils are commonly strongly fragmented and abraded. Common skeletal grains are echinoderms (crinoids), brachiopod shells and spines, and bryozoans. Less common are bivalves, ostracods, smaller foraminifers, fusulinids, palechinid radioles, trilobite fragments and Komia. Sandstone is either poorly washed, containing micritic matrix and some calcite cement, or well-washed with coarse, blocky calcite cement. In well-washed sandstone, crinoid fragments may display syntaxial overgrowths. Rarely, skeletons are partly replaced by chert. Mixed siliciclastic-carbonate sandstones in the Atrasado Formation are fine to coarse grained, moderately to well-sorted and rarely poorly sorted. Siliciclastic grains are mostly subangular (Fig. 19A, G, H). The most abundant grain types are quartz (monocrystalline quartz more abundant than polycrystalline quartz), feldspars (mostly potassium feldspars, less common plagioclase, feldspars are altered and/or partly replaced by calcite) and micritic intraclasts. Rare grain types include granitic and metamorphic rock fragments, micas (muscovite, biotite and chlorite), opaque grains and very rare phosphatic grains. The amount of fossils varies from zero to abundant. The most common skeletal grains are echinoderms, brachiopod shells and bryozoans. Additionally, brachiopod spines, foraminifers, ostracods and shell debris are present. In one sandstone, skeletons, quartz and even feldspar grains are encrusted by cyanobacteria. Most of the sandstones contain micritic matrix (and are poorly washed); some are well washed and cemented by blocky calcite and syntaxial overgrowths on crinoid fragments. LIMESTONE FACIES OF THE SANDIA FORMATION Limestone comprises 7% of the thickness of the Sandia Formation and occurs as one thin limestone bed in the lower part and several, 0.32.2 m thick, bedded, coarse-grained, fossiliferous limestone intervals in the middle and upper parts. Limestone is dominantly wackestone, other microfacies are rare. LIMESTONE FACIES OF THE GRAY MESA FORMATION In the Elephant Butte Member, the following limestone lithotypes occur: (1) thin, wavy bedded limestone (10-20 cm thick beds, dominantly wackestone), (2) medium- to thick-bedded limestone (mostly 20-50 cm thick beds, mainly wackestone), (3) thick-bedded, coarse-grained crinoidal limestone (wackestone, packstone, rudstone), (4) massive to indistinctly bedded algal limestone (0.9-1.8 m thick intervals, algal wackestone to floatstone), and (5) wavy bedded to nodular cherty limestone (bed thickness mostly 10-20 cm, mostly wackestone). Similar lithologies are observed in the Whiskey Canyon Member, which is mainly composed of limestone, particularly cherty limestone, with minor shale intercalations: (1) thin, wavy bedded cherty limestone (wackestone, floatstone; most common lithology), (2) thin, wavy bedded limestone without chert (wackestone, floatstone) , (3) mediumbedded crinoidal limestone (wackestone, rare packestone, grainstone,
rudstone) and (4) medium- to thick-bedded algal limestone (algal wackestone to floatstone). In the Garcia Member of the Arroyo de la Presilla B section, limestone occurs as: (1) thick-bedded crinoidal limestone (wackestone, rare packstone, grainstone, rudstone), (2) thick-bedded fossiliferous limestone (mostly wackestone, floatstone) and (3) thin-bedded, muddy limestone (mudstone, wackestone). At Cerros de Amado D, we observed: (1) thin, wavy bedded cherty limestone (2) thin, wavy to nodular limestone, (3) individual thin limestone beds separated by shale intervals, and (4) thin- to medium-bedded fossiliferous limestone intervals. The most common microfacies is wackestone, locally grading to floatstone. Other microfacies types are rare. LIMESTONE FACIES OF THE ATRASADO FORMATION A more detailed description of the lithology of the Atrasado Formation was presented by Lucas et al. (2009a, 2013). So, only a brief summary is presented here. Limestone is rare in the Bartolo Member, where it occurs as sporadic individual limestone beds and 0.8- and 1.3-m thick limestone intervals, indistinctly bedded, coarse grained and partly crossbedded (rudstone; Cerros de Amado C). The limestone facies is very similar at section Cerros de Amado A (Lucas et al., 2009a). The Amado Member is dominated by limestone with intercalated, mostly covered shale intervals. Most common is wavy bedded, rarely even bedded, cherty and non-cherty limestone. Less common is indistinctly bedded, cherty limestone (Lucas et al., 2009a). Wackestone is the dominant microfacies type. In the Tinajas Member, limestone comprises approximately 7% of the succession. At Cerros de Amado A, individual limestone beds 0.1-0.7 m thick are intercalated in the lower part of the section. Thin limestone beds with intercalated shale and a 0.8-m thick, bedded limestone interval are exposed in the uppermost part of section A. At Cerros de Amado B, three thin, nodular limestone beds are intercalated in the lowermost part of the section. A black shale (unit 6 in Fig. 5) is overlain by a 3-m thick interval composed of wavy- to even-bedded limestone with intercalated, thin shale layers. Limestone beds are 3-40 cm thick. In the upper part of section B, bedded and nodular limestone beds (0.4-3.8 m thick) are intercalated. At Minas de Chupadera, several limestone beds (0.2-0.7 m thick) and thin, indistinctly bedded limestone intervals (0.4-0.8 m thick) and one nodular limestone are intercalated (Lucas et al., 2009a). At the bioherm section, individual limestone beds intercalated in the Tinajas Member are 0.1-0.7 m thick. Nodular limestone is rare, represented by two intervals that are 0.2 and 0.7 m thick. In the lower part of this member a thicker limestone interval occurs that is composed of even-bedded limestone, partly with thin shale intercalations. Limestone is bioclastic wackestone and algal wackestone. Wavy-bedded algal limestone (2.3 m thick) is intercalated in the upper part. The thicker limestone interval (8.6 m) in the upper part that is composed of bedded and massive algal limestone laterally grades into the Ojo de Amado mound complex. One bed of dolomicrite (0.6 m) is intercalated in the middle of the Tinajas Member at the bioherm section. At Cerrillos del Coyote, individual limestone beds measure 0.10.3 m in thickness. Bedded limestone units, partly with thin shale intercalations, are 0.5-0.9 m thick. Dolomicrite beds are 0.3 and 0.4 m thick, and bedded dolomicrite units are 0.5 and 0.8 m thick. The most abundant microfacies type is wackestone; less common are lime mudstone, rudstone and boundstone. The Council Spring Member is one of the most distinctive members of the Atrasado Formation. This member is mostly less than 10 m thick and composed of thin-bedded and indistinctly bedded to massive limestone. In the Ojo de Amado section, the Council Spring
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173 FIGURE 14 (facing page). Thin section photographs of microfacies (various types of grainstones) from limestones of the Gray Mesa and Atrasado formations. All photos under plane light. Width of photos: A, C, E, F, G = 9 mm; B, D, H = 4.6 mm. A, Grainstone composed of dominantly echinoderm (crinoid) fragments, and subordinately of bryozoans, brachiopods and a few foraminifers. Some of the echinoderm fragments display syntaxial overgrowths. Sample AP 66, Whiskey Canyon Member, Arroyo de la Presilla. B, Crinoidal grainstone containing abundant crinoid fragments with well-developed syntaxial overgrowths. Subordinately, bryozoans and other skeletons are present. Sample AP 66, Whiskey Canyon Member, Arroyo de la Presilla. C, Grainstone composed of abundant bryozoan fragments, echinoderms and subordinately of brachiopods, rare other bioclasts and detrital quartz grains. Sample CAC 11, Garcia Member, Cerros de Amado C. D, Crinoidal grainstone with very visible syntaxial overgrowths. Other skeletal grains include bryozoans, brachiopods and ostracods. Sample MC 21, Burrego Member, Minas de Chupadera. E, Grainstone, moderately washed, containing echinoderms and brachiopods, recrystallized skeletons, bryozoan fragments, intraclasts and a few ooids. Sample CAC 48, Bartolo Member, Cerros de Amado C. F, Oolitic grainstone, well-washed. Sample CAC 48, Bartolo Member, Cerros de Amado C. G, Grainstone containing skeletal grains displaying thin micritic envelopes, and some thicker coatings (forming coated grains, oncoids). A few ooids are present. Sample CAC 48A, Bartolo Member, Cerros de Amado C. H, Peloidal grainstone, poorly washed, containing also many micritic intraclasts and a few ooids. Sample CAA 26, Tinajas Member, Cerros de Amado A. Member is 9 m thick and composed of wavy bedded limestone with thin shale intervals, overlain by thicker bedded limestone with shale intervals, thin- and wavy bedded limestone, massive gray limestone containing abundant crinoidal debris and thick-bedded gray limestone containing phylloid algae (Lucas et al., 2013). At Cerrillos del Coyote, the Council Spring Member measures 9.6 m and is composed of thick bedded to massive algal limestone, covered intervals and one intercalated limestone-cobble conglomerate (0.5 m thick). At the bioherm section this member is 6.5 m thick and consists of nodular and bedded limestone with shale intercalations, partly containing phylloid algae. Limestones of the Council Spring Member are mainly composed of wackestone, rarely of grainstone and floatstone. The Burrego Member in the Ojo de Amado section includes: (1) thin, wavy limestone beds intercalated in shale, (2) wavy bedded, cherty limestone, (3) a crinoidal limestone bed, and (4) nodular limestone (Lucas et al., 2013). At Minas de Chupadera, thin bedded, wavy limestone with a few shale intervals forms the upper part of this member (Lucas et al., 2009a). At the Bioherm section, two thin limestone beds (0.1 m) are intercalated in the lower part and a thicker limestone interval (3.9 m) in the middle part, which is composed of nodular sandy limestone, overlain by wavy bedded algal limestone and even bedded limestone. Wackestone is again the most abundant microfacies; subordinately, grainstone, floatstone and rudstone are present. The Story Member at Ojo de Amado is 7 m thick and composed of wavy bedded limestone. At Minas de Chupadera, the lower half of the Story Member is composed of sandstone, and the upper half of thin-bedded limestone (Lucas et al., 2009a, 2013). Limestone is almost entirely composed of wackestone. The Del Cuerto Member is mostly covered at Minas de Chupadera, with only one thin limestone bed exposed near the base (Lucas et al., 2009a). At Ojo de Amado, this member is approximately 5 m thick and composed of alternating limestone and shale. Limestone occurs as nodular and wavy thin beds (0.1-0.3 m thick) and as thicker beds that are indistinctly bedded or massive (Lucas et al., 2013). Wackestone is the dominant microfacies type; rarely, grainstone is present. The Moya Member measures approximately 9 m at Ojo de Amado and is mostly limestone with a few intercalated shale intervals. Limestone includes: (1) nodular limestone, (2) wavy bedded limestone and (3) thicker bedded, partly cherty limestone. At Minas de Chupadera, the Moya Member is approximately 18 m thick, dominantly composed of limestone with covered intervals and rare shale intercalated. Most common is: (1) thin, wavy bedded limestone, and less common are: (2) thicker bedded limestone (near the top), (3) nodular limestone and (4) thin, even-bedded limestone (Lucas et al., 2009a). Wackestone is by far the most abundant microfacies type, subordinately floatstone and rudstone occur. MICROFACIES Mudstone Lime mudstone is rare in the Sandia and Gray Mesa formations. The mudstone that is present contains a few skeletons (bioclastic mudstone). In the Atrasado Formation, mudstone is rare to absent in all members except in the Tinajas Member, where it is quite common. Locally, mudstone grades into wackestone. Approximately 12% of the limestone facies is mudstone. Three types of mudstone are present: bioclastic mudstone (Fig. 12A-B), peloidal mudstone and nodular mudstone (Figs. 12C-D). Bioclastic mudstone contains a few fossils such as spicules, smaller foraminifers, ostracods, echinoderms, bryozoans and recrystallized
skeletons. Locally, small detrital quartz grains are present (Garcia Member). This type may grade into spiculite and bioclastic wackestone. Peloidal mudstone is present in the Tinajas Member. This type is commonly laminated and locally bioturbated. Besides peloids, fecal pellets and intraclasts are locally present . The only fossils are ostracods and rare, larger shell fragments (mollusks). Irregular voids filled with sparry calcite cement may occur. Nodular, inhomogeneous mudstone composed of micritic matrix and dark gray micritic nodules with well-developed circumgranular fissures and an irregular network of fissures filled with calcite cement and a few detrital quartz grains was observed in the Story Member. Mudstone containing subangular to subrounded micritic lithoclasts, some peloids and rare ostracods is present in the Tinajas Member. Wackestone Wackestone is by far the most abundant microfacies type in all three formations, commonly grades into floatstone, and less commonly into grainstone, packstone and rudstone. Wackestone comprises 57% of the limestone facies. The most abundant microfacies throughout the Pennsylvanian succession is bioclastic wackestone containing a diverse fossil assemblage (Figs. 12E, G, H, 13B, C, E). In most samples, echinoderms, bryozoans and brachiopods are the most abundant fossils, and, subordinately, brachiopod spines, ostracods, foraminifers (including fusulinids), gastropods, bivalves, palechinid radioles, sponge spicules, recrystallized calcareous algae and trilobites are present. Individual samples contain Komia (Elephant Butte, Garcia) and fragments of syringoporid corals (Bartolo), microconchids (Amado, Bartolo), Tubiphytes (Tinajas, Moya), and inozoan calcisponges (Amado). Wackestone in the Tinajas Member may contain many fecal pellets. Wackestone of the Bartolo and Burrego members also contains detrital quartz and feldspar grains (mostly 0.1-0.2 mm). The matrix is commonly micrite, partly fine-bioclastic micrite or peloidal micrite. Wackestone is locally bioturbated. Subtypes are crinoidal wackestone to floatstone (Sandia, Garcia, Tinajas; Fig. 13D), bryozoan wackestone to grainstone and floatstone (Garcia, Council Spring; Fig. 13F-G), phylloid algal wackestone to floatstone (Moya), fusulinid wackestone (Fig. 13H) and intraclast wackestone with subordinate fossil fragments (Fig. 12F). In the Tinajas Member, peloidal wackestone, which may grade into packstone and grainstone, is present (Fig. 13A). Besides abundant peloids, this type contains micritic intraclasts, fecal pellets, a few ooids, a few detrital quartz grains and a low diversity fossil assemblage (ostracods, gastropods). Wackestone to floatstone of the Moya Member contains some oncoids formed mainly by tubular foraminifers. Nuclei of the oncoids are mostly micritic intraclasts, and subordinately skeletons and quartz grains. In some of the wackestones, skeletons (shell fragments, phylloid algae, echinoderms, bryozoans) are encrusted by cyanobacteria, calcivertellids, Asphaltina (Sandia), tubular foraminifers and Tubiphytes. Grainstone Grainstone is rare, occurs in the Atrasado Formation (Burrego, Council Spring and Del Cuerto members) and is very rare in the Gray Mesa Formation. Locally, grainstone grades into packstone and rudstone. Grainstone comprises approximately 5% of the limestone. Grainstone in the Elephant Butte Member is poorly washed (wackestone grading into grainstone), is composed of a diverse, fragmented fossil assemblage, and contains a few micritic intraclasts and some peloidal micrite. Well-washed grainstone grades into packstone and rudstone. The most abundant skeletons are echinoderms,
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175 FIGURE 15 (facing page). Thin section photographs of microfacies (various types of packstone) from limestones of the Sandia, Gray Mesa and Atrasado formations. All photos under plane light. Width of photos: A-E = 9 mm; F, G = 4.6 mm; H = 1.8 mm. A, Crinoidal packstone containing a few bryozoan fragments and many detrital quartz grains. Sample AP 13, Sandia Formation, Arroyo de la Presilla. B, Crinoidal packstone composed of densely packed crinoid stem fragments. Locally, sutured grain contacts are developed, indicating pressure solution. A few crinoid fragments are partly replaced by chert (e.g., upper right). Sample AP 68, Whiskey Canyon Member, Arroyo de la Presilla. C, Packstone containing many crinoid fragments, and subordinately brachiopod shell fragments, bryozoans, ostracods and ooids. Sample CAA 7, Bartolo Member, Cerros de Amado A. D, Packstone containing a diverse fossil assemblage, poorly washed. A few skeletal grains are encrusted by cyanobacteria. Sample CAA 7, Bartolo Member, Cerros de Amado A. E, Crinoidal packstone with many bryozoan fragments and some other bioclasts. Sample MC 21, Burrego Member, Minas de Chupadera. F, Packstone composed of abundant fecal pellets, and subordinately of micritic intraclasts and peloids. Sample CAA 31, Tinajas Member, Cerros de Amado A. G, Peloidal packstone, well-sorted, locally containing some micrite patches and rare ostracods. Sample CAA 25, Tinajas Member, Cerros de Amado A. H, Peloidal packstone, detail of G (sample CAA 25). bryozoans and brachiopods, all strongly fragmented (Fig. 14AE). Detrital quartz grains are present in small amounts. Some of the skeletons are encrusted by cyanobacteria. Grainstones in the Whiskey Canyon, Garcia, Burrego and Del Cuerto members contain a diverse fossil assemblage, and are well washed and cemented by coarse, blocky calcite. The most abundant grains are skeletons of echinoderms, bryozoans and brachiopods. A few small detrital quartz grains are locally present. Individual echinoderm fragments display syntaxial overgrowths. Some of the fossils are partly replaced by chert. A few skeletons are encrusted by tubular foraminifers and cyanobacteria. Well to poorly washed oolitic grainstone is present in the Bartolo Member (Fig. 14F). The ooids are 0.25-1 mm in diameter and composed of concentric laminae of tangentially arranged crystals. Subordinately, oncoids are present, composed of a nucleus (shell fragment, echinoderm, bryozoan) encrusted by cyanobacteria (Fig. 14G) and Palaeonubecularia. Skeletons include echinoderms, shell debris, bryozoans, ostracods, rare brachiopod spines, trilobites and calcareous algae. A few detrital quartz grains are present. Locally, the grainstone contains micritic matrix. In the Tinajas Member, a well-sorted, indistinctly laminated lithoclast wackestone to grainstone is intercalated that is composed of abundant peloids, ooids and micritic intraclasts (Fig. 14H). Thin layers of peloidal wackestone to grainstone are also intercalated. Ostracods are the only skeletons. In the Council Spring Member, grainstone is poorly washed (i.e., that is a packstone-grainstone), and either composed of dominantly fragmented bryozoans or of abundant intraclasts and recrystallized skeletons. In the Burrego Member, grainstone grades into packstone and rudstone and is composed of abundant brachiopods and other recrystallized shell fragments, intraclasts, detrital quartz grains and, subordinately, other skeletal grains. Packstone Packstone is present in the Sandia Formation and in most members of the Atrasado Formation, but very rare in the Gray Mesa Formation. Locally, packstone grades into grainstone and rudstone. About 5% of the limestone is composed of packstone. Both wackestone and grainstone locally grade into packstone, and packstone locally grades into rudstone. Like wackestone and grainstone, packstone is characterized by a diverse fossil assemblage (packstone represents the densely packed versions of wackestone and grainstone). The fossils are commonly strongly fragmented and abraded. Many packstones contain small amounts of detrital quartz. Packstone is cemented by coarse, blocky calcite cement, although small amounts of micrite may also be present. In the Sandia Formation, crinoidal packstone is present, which is coarse grained, indistinctly laminated and contains many detrital quartz grains (Fig. 15A). In bioclastic packstone, skeletons of bryozoans, crinoids and brachiopods dominate. In the Elephant Butte Member, bioclastic packstone locally grades into rudstone. Gradations from grainstone to packstone and rudstone were also observed. In the Whiskey Canyon Member, crinoidal packstone to rudstone and bioclastic wackestone to packstone are rarely intercalated in the wackestone-dominated succession (Fig. 15B). Bioclastic wackestone to packstone, mostly composed of echinoderm, bryozoan, brachiopod and fusulinid skeletons, are present in the Garcia Member. In a fine-grained packstone, tubular foraminifers are the most abundant skeletal grains among other fossil fragments. In the Atrasado Formation, crinoidal packstone was observed in the Bartolo, Amado, and Story members (Fig. 15C-E), bioclastic packstone in the Tinajas, Council Spring and Burrego members, and laminated
peloidal packstone in the Tinajas Member (Fig. 15F-H). Peloidal packstone contains a few micritic intraclasts and rare ostracods. Floatstone Floatstone is common in the Gray Mesa and Atrasado formations and commonly grades into rudstone. Approximately 14% of the limestone is composed of floatstone. Floatstone is commonly associated with wackestone (wackestone grading into floatstone) and characterized by some large skeletons (several mm to several cm) and many small skeletons embedded in micrite or peloidal micrite. All floatstones are characterized by a diverse fossil assemblage similar to that of wackestone. Locally, bioturbation is observed. Within the Gray Mesa and Atrasado formations, three types of floatstone can be distinguished: (1) bioclastic floatstone with large skeletons of echinoderms (crinoids), bryozoans, brachiopods and, locally, phylloid algae (Fig. 16A-C); (2) bryozoan floatstone with bryozoans (mostly fenestellids) up to several cm in size embedded in wackestone matrix (common in the Elephant Butte and Garcia members, rare in the Atrasado Formation; Fig. 16D); and (3) phylloid algal floatstone containing large, recrystallized, mostly broken skeletons of phylloid algae embedded in peloidal micrite with a few small skeletons (Fig. 16 E-H). Algal fragments may be encrusted by cyanobacteria, tubular foraminifers, tuberitinids and rarely by bryozoans. Floatstone of the Atrasado Formation (Bartolo, Moya members) also contains small amounts of detrital quartz grains. Phylloid algal floatstone is locally brecciated. In the Moya Member, floatstone containing oncoids embedded in wackestone matrix is present. The nuclei of the oncoids are formed by micritic intraclasts, skeletons and quartz grains and are encrusted by cyanobacteria and abundant tubular foraminifers. Rudstone Rudstone is rare in the Sandia Formation, and occurs in the Gray Mesa Formation (Whiskey Canyon and Garcia members) and in the Atrasado Formation (Burrego, Tinajas and Moya members). Rudstone comprises approximately 5% of the limestone facies. Rudstone is composed of poorly to well-washed, strongly fragmented skeletons, mostly of echinoderms, bryozoans and brachiopods, and subordinately of other skeletal grains (Fig. 17A-H). In the Whiskey Canyon and Garcia members, crinoidal rudstone is present. In the Tinajas, Burrego and Moya members, in some rudstone samples recrystallized shell fragments are the most abundant skeletal grains. Many rudstones also contain small amounts of intraclasts and detrital quartz grains. Locally, grainstone, packstone and floatstone grade into rudstone. Skeletons may be encrusted by cyanobacteria (Fig. 17D, H), tubular foraminifers, including Palaeonubecularia (Fig. 17G), and Tuberitina. Some of the skeletons, particularly echinoderm fragments, are partly replaced by chert. Well-washed rudstone is cemented by calcite, and poorly washed rudstone displays micritic matrix. Boundstone Boundstone is very rare (less than 1%) and was observed in the Gray Mesa Formation (Whiskey Canyon Member) within wackestone and in the Tinajas Member of the Atrasado Formation. Boundstone is very rare in the Pennsylvanian succession of the Cerros de Amado. In the Whiskey Canyon Member, in one sample, tubular foraminifers are abundant, binding the skeletons to form a boundstone. Locally, in the Tinajas Member, abundant binding organisms such as cyanobacteria, Claracrusta, Palaeonubecularia and Tubiphytes are present, forming patches of boundstone. Also, thin layers (up to 1 mm thick) of microbial mats are rarely intercalated in wackestone. Syringoporid (?) Coral Framestone Small colonies of syringoporid tabulate corals occur within the Garcia and Tinajas members, measuring up to about 20 cm in diameter
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177 FIGURE 16 (facing page). Thin section photographs of microfacies (various types of floatstones) from limestones of the Gray Mesa and Atrasado formations. All photos under plane light. Width of photos is 9 mm. A, Floatstone composed of some large and many small fossil fragments. Large fossils are mostly brachiopods, partly with both valves preserved. Sample CAA 28, Tinajas Member, Cerros de Amado A. B, Bioclastic floatstone with large fossil fragments (mostly echinoderms, bryozoans, and brachiopods) floating in micritic matrix. Sample CDA 18, Tinajas Member, Cerros de Amado. C, Bioclastic floatstone composed of large skeletal grains (echinoderms, shell fragments, bryozoans) embedded in wackestone matrix. Sample CAC 1, Garcia Member, Cerros de Amado C. D, Bryozoan floatstone. Large fenestellid bryozoan colonies are embedded in fine bioclastic matrix. Sample MC 20, Burrego Member, Minas de Chupadera. E, Phylloid algal floatstone. Large fragments of recrystallized phylloid algae, subordinately fusulinids, gastropods and rare small skeletal grains embedded in micrite. Sample OA 13, Council Spring Member, Ojo de Amado. F, Phylloid algal floatstone. Broken fragments of recrystallized phylloid algae (?Eugonophyllum) are embedded in micrite. Sample CAC 37, Garcia Member, Cerros de Amado C. G, Phylloid algal floatstone containing recrystallized fragments of phylloid algae that are rarely encrusted by cyanobacteria. Sample AP 42, Elephant Butte Member, Arroyo de la Presilla. H, Phylloid algal floatstone. Large recrystallized fragments of phylloid algae are embedded in micrite that contains a few small bioclastic grains. Sample CAB 14, Council Spring Member, Cerros de Amado B. (Fig. 26D-E). They form a framework of coral branches; the pore space between the coral branches is filled with a wackestone matrix containing a diverse fossil assemblage. Locally, the pore space between the coral branches is filled with coarse calcite cement. FOSSILS OBSERVED IN THIN SECTION In all formations (Sandia, Gray Mesa and Atrasado), the most abundant fossils are echinoderms, bryozoans and brachiopods. In addition, algae, foraminifers, sponges, corals, mollusks, arthropods and problematica are present. No significant change in the biotic composition is observed throughout the Pennsylvanian succession. Bryozoans By far the most abundant fossils observed in thin section are fenestrate bryozoans, which, in wackestone, rudstone and particularly in floatstone (bryozoan floatstone), may be present as colonies up to several cm in size (Figs. 20A, F, 30H). However, because of their fragile colonies, fenestrates are usually present in the form of small fragments, particularly in grainstone, packstone and rudstone, and in mixed siliciclastic-carbonate sandstone. Fenestrates often have attaching discs or root-like holding structures; therefore, they are able to settle on soft substrates. Rarely, they are attached to the skeletal grains. The majority of observed fenestrates are reticulate forms; a few are pinnate (Penniretepora). Less common are trepostome bryozoans (Figs. 20B, E, 30 B, F), which are represented by encrusting (Tabulipora) and branched colonies (e.g., Pseudobatosomella, Dyscritella). Cystoporate bryozoans are relatively rare (Figs. 20G-J, 30A-E), and are represented by three colony shapes: encrusting (Fistulipora), trifoliate prismatic (Prismopora) and bifoliate lenticular (Meekopora, Cystodictyonidae sp. indet.). The two latter forms are erect and need a hard substrate to grow on, whereas Fistulipora can encrust unstable substrates. Indeed, Fistulipora often encrusts skeletal grains, including fragments of other bryozoans. Rhabdomesine cryptostome bryozoans are rare (Figs. 20C, D, K-M, 30G). They are represented by delicate branched colonies. Very rarely, small, dome-shaped cystoporate and trepostome bryozoan colonies were observed encrusting the sediment substrate (Fig. 30A-B). Taylor and James (2013) distinguish nine basic categories of bryozoan colony shapes. In the samples studied here, fenestrate colony shapes are by far the most common type. Most colonies are broken into small fragments, although, particularly in floatstone, many large fenestrate colonies are still intact or toppled in situ. Due to the fact that in most samples, particularly in wackestone, grainstone, packstone, rudstone and mixed siliciclastic-carbonate sandstone, bryozoans are fragmented, the original colony forms are difficult to reconstruct. Other colony forms observed are rare and include encrusting colonies, domal colonies, and delicate and robust branching colonies; the latter two very rare. Encrusting colonies are attached either to the substrate or to a skeleton over their entire underside and are flat. Domal colonies are rare and display a concave underside and some vertical relief. The analysis of bryozoan colony forms shows that the Pennsylvanian paleoenvironments were intermediate between shallow shelf and middle shelf areas. Fenestrate colonies are well adapted to conditions with moderate to low water energy and low rates of sedimentation, and delicate branched and lenticular forms have similar ecological needs (e.g., Amini et al., 2004). Encrusting forms are relatively universal, but they tend to dominate in high energy, shallow environments. They also constitute pioneer communities, being replaced by erect forms in the course of maturation of the community (Boyer et al., 1990). Brachiopods Brachiopods mostly occur as shell fragments, and rarely as single valves and articulated shells, with both valves preserved (Fig. 26A).
The majority of shells and shell fragments are impunctate, rarely pseudopunctate, but some punctate shells are observed. Besides shells, detached brachiopod spines are present in most of the studied thin sections. These spines are easily recognized by their central hollow and concentric, lamellar wall structure. In wackestone and floatstone, large brachiopods with both valves preserved are present. Echinoderms Most common among the echinoderms are crinoid fragments, including transverse sections through columnals showing the characteristic central canal. Connected stem fragments are very rare. Most of the echinoderm skeletons are small (< 2 mm), although in a few samples crinoid fragments with diameters up to several cm are present. Echinoderm skeletons typically occur as single crystals, which in grainstone and rudstone commonly display syntaxial overgrowths. Palechinid radioles are rare but present in many of the studied limestone samples (Fig. 26G-I). Locally, echinoderm fragments are partly replaced by chert. We rarely observed borings on echinoderm fragments. A few echinoderm fragments are encrusted by other organisms such as cyanobacteria, tubular foraminifers and bryozoans. Microbes and Calcareous Algae In the Gray Mesa and Atrasado formations, cyanobacteria occur as encrusting organisms on other skeletons, locally forming coated grains or oncoids. Rarely, in the Tinajas Member thin microbial mats (boundstone) are present. Locally, cyanobacteria and other encrusting organisms form patches of boundstone within wackestones in the Tinajas Member. Calcareous algae are dominantly phylloid algae (Anchicodiaceae), which occur mainly in distinct limestone horizons (phylloid algal limestone) within the Gray Mesa and Atrasado formations. Phylloid algae occur as small fragments, and are less common as up-to-severalcm-long algal blades in phylloid algal floatstone. Commonly, phylloid algae are completely recrystallized. In the Garcia Member, poorly preserved phylloid algal fragments are probably Eugonophyllum. Broken fragments of well-preserved Archaeolithophyllum missouriense are present in a rudstone to fine-grained carbonate conglomerate in the upper part of the Garcia Member (Fig. 21A). Anthracoporella, an aspondyl dasycladacean alga, is present in the Garcia Member as a very rare and poorly preserved skeletal grain (Fig. 21D, F). Epimastopora, another aspondyl dasycladacean alga, was rarely observed in the Atrasado Formation (Amado Member; Fig. 21E, H). Gyroporella was observed in the Council Spring Member (Fig. 21JK). Komia, an ungdarellacean alga, is present in many limestones of all members of the Gray Mesa Formation as a rare skeletal grain type (Fig. 21B-C). Efluegelia, a stacheiacean alga, was rarely observed in the Whiskey Canyon and Garcia members of the Gray Mesa Formation, where it is attached to skeletal grains (Fig. 21I). Claracrusta, a donezellacean encrusting alga, is present in the Bartolo Member. Foraminifers Almost all studied limestone samples contain smaller benthic foraminifers, and many samples contain larger benthic foraminifers (fusulinids). Smaller benthic foraminifers include many sessile forms that lived attached to the muddy substrate or on skeletons (e.g., calcivertellids, Eotuberitina, Tuberitina, Tetrataxis and Palaeonubecularia). Some of the typical smaller foraminifers of the Pennsylvanian succession in the Cerros de Amado region are shown in Figures 22 and 23.
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179 FIGURE 17 (facing page). Thin section photographs of microfacies (various types of rudstones) from limestones of the Gray Mesa and Atrasado formations. All photos under plane light. Width of photos is 9 mm. A, Rudstone composed of abundant bryozoan fragments, and subordinately of echinoderms, brachiopods, smaller foraminifers, ostracods and other bioclastic grains. Sample AP 49, Elephant Butte Member, Arroyo de la Presilla. B, Rudstone, moderately to well washed, containing mainly large skeletons of bryozoans and echinoderms. Sample MC 23, Burrego Member, Minas de Chupadera. C, Rudstone composed of a diverse fossil assemblage including echinoderms, bryozoans, brachiopods, gastropods, fusulinids, and ostracods. Sample CAC 9, Garcia Member, Cerros de Amado C. D, Rudstone containing a diverse fossil assemblage. Many skeletons are encrusted by cyanobacteria. Sample CAA 7, Bartolo Member, Cerros de Amado A. E, Rudstone containing fragmented fossils such as echinoderms, shell debris, bryozoans and brachiopods. Sample AP 60, Elephant Butte Member, Arroyo de la Presilla. F, Bioclastic rudstone containing brachiopod shell fragments, echinoderms, trilobites, bryozoans and small bioclastic grains. Sample CDA 17, Tinajas Member, Cerros de Amado. G, Well-washed rudstone composed of recrystallized skeletons, bryozoans, brachiopods and a few other bioclasts. Many skeletal grains are encrusted by Palaeonubecularia. Sample MC 29, Del Cuerto Member, Minas de Chupadera. H, Rudstone, poorly washed, containing recrystallized shell fragments, gastropods, and a few echinoderms. A few skeletons are encrusted by cyanobacteria. Sample MC 22, Burrego Member, Minas de Chupadera. The assemblage of smaller benthic foraminifers of the Sandia Formation is less diverse than that of the Gray Mesa and Atrasado formations. In the Sandia Formation, we observed species of the following genera: Endothyra, Climacammina, Tetrataxis, Globivalvulina, Calcivertella and Calcitornella. The Gray Mesa and Atrasado formations contain a more diverse assemblage including species of Eotuberitina, Tuberitina, Earlandia, Endothyra, Planoendothyra, Bradyina, Climacammina, Deckerella, Spireitlina, Tetrataxis, Polytaxis, Globivalvulina, Calcivertella, Ammovertella, Palaeonubecularia, Hemigordiellina, Syzrania and Syzranella. The most common smaller benthic foraminifers in the Gray Mesa Formation are species of Tuberitina, Endothyra, Bradyina and Tetrataxis. In the Atrasado Formation, species of Climacammina and Globivalvulina are more abundant than in the Gray Mesa Formation. Most common are, again, species of Tuberitina, Bradyina and Tetrataxis. Smaller benthic foraminifers are present in almost all microfacies except in peloidal wackestone, packstone and grainstone, and in mudstone. Most abundant are benthic smaller foraminifers in wackestone and floatstone. A few benthic foraminifers are even present in mixed siliciclastic-carbonate sandstone. Larger benthic foraminifers (fusulinids) are present in many limestone samples, but only a few limestone beds have abundant fusulinids. In grainstone, rudstone and mixed siliciclastic-carbonate sandstone, many fusulinid tests are fragmented and abraded. Species of Fusulinella are present in the upper part of the Sandia Formation. The Gray Mesa Formation contains species of Beedeina, Wedekindellina and Plectofusulina (Figs. 24A-J, 25A-G), and rare Eoschubertella and Millerella. Fusulinids are rare in the Atrasado Formation (Triticites spp.; Fig. 25H-M). Sponges Fragments of calcisponges (inozoa) are rare in the Gray Mesa and Atrasado formations (Fig. 26F). Spicules are common in many limestone samples of all three formations (Fig. 27M). Locally, spicules are abundant, forming spiculite (Elephant Butte, Story, Burrego). Spicules are calcified and dominantly monaxons, probably derived from siliceous sponges. Corals Fragments of rugose corals are rarely observed in limestones of the Gray Mesa and Atrasado formations (Fig. 26B-C). Small syringoporid(?) coral colonies occur in the Garcia and Tinajas members (Fig. 26D-E). Mollusks (Gastropods, Bivalves) Small gastropods are present in many limestone samples, although rare (Fig. 27A, D). Bivalve shells are rare, mostly fragmented and recrystallized, and therefore difficult to identify. Arthropods (Trilobites, Ostracods) A few fragments of trilobites are present in many limestone samples and also in mixed silicicastic-carbonate sandstone of the Sandia, Gray Mesa and Atrasado formations. They are easily identified when the characteristic shepherd´s crook shape is preserved (Fig. 27B, C, F). Ostracods are present in almost all samples in small amounts. In muddy limestones, some of the ostracods are preserved with both valves. In some peloidal wackestone-packstone-grainstone and mudstone, ostracods are the only fossils.
Problematica (Tubiphytes, etc.) Tubiphytes is present in many limestone samples of the Atrasado Formation (Fig. 27I, J, L), rarely encrusting other skeletons (bryozoans). Microconchids (generally confused with Spirorbis; i.e., coiled shells of polychaete worms) were observed in a few limestone samples of the Atrasado Formation (Amado and Burrego members; Fig. 27G). Asphaltina is very rare in the Sandia Formation and Elephant Butte Member. All samples contain unidentifiable recrystallized skeletons in varying amounts. Many of these recrystallized skeletons are probably derived from mollusks and phylloid algae. Ooids and oncoids are rare. Intraclasts are present in many limestones, although in small amounts. Rarely, fecal pellets were observed. Peloids are a common constituent of many limestones. Coated grains (skeletons displaying thin micritic envelopes) are very rare. Individual samples of the Atrasado Formation contain plant fragments, bones and microscopic fish teeth (ichthyoliths). Encrustations In some of the limestones of all three formations, particularly in wackestone to packstone and floatstone, subordinately in grainstone, and rarely in rudstone, encrusting organisms are present that are attached either to the fine-grained sediment or to various skeletons. Rarely, skeletons or lithoclasts are encrusted to form small oncoids. The most common encrusting organisms are cyanobacteria (Fig. 28A, B, D, E, G, H) and Palaeonubecularia. Cyanobacteria very rarely form thin microbial crusts (stromatolites) or bind sediment (forming boundstone), and they commonly occur as thin encrustations on various skeletal grains. Rarely, Girvanella is present, encrusting skeletal grains and, rarely, detrital quartz and feldspar grains (Fig. 28D-E). In one sample, a calcisponge fragment is encrusted by an assemblage of cyanobacteria, Claracrusta and bryozoans. Very rare are encrustations of Efluegelia on recrystallized skeletons (Fig. 31F) and of Komia (Fig. 31E, H) on recrystallized skeletons and bryozoans. Locally, Tubiphytes is attached to bryozoans (Fig. 31D, J). Palaeonubecularia commonly encrusts skeletal grains (recrystallized skeletons, bryozoans, brachiopods, echinoderms and calcareous algae), and rarely the substrate (Fig. 29B, C, F, I, J, K, L, N, O, P, Q, R). Tuberitina and Eotuberitina are common sessile foraminifers, encrusting the substrate as well as skeletal grains (Fig. 31K). Other sessile foraminifers are Calcivertella (encrusting bryozoans and other skeletons) and Tetrataxis (attached to an echinoderm fragment; Fig. 31G). Bryozoans were observed as encrusting organisms on the substrate and as encrustations on skeletal grains (Figs. 30A-H, 31A-C, I). DISCUSSION In central New Mexico, the sea-floor during the Pennsylvanian (deposition of limestone of the Sandia, Gray Mesa and Atrasado formations) was dominated by sessile benthic suspension feeders: bryozoans, brachiopods and crinoids. Bryozoans are colony-forming, mostly marine, stenohaline suspension feeders producing calcareous skeletons that are commonly well preserved. Most bryozoan communities lived subtidally on the shelf; abundant bryozoans indicate shelf or ramp settings. High-energy environments may also contain cryptic microenvironments such as small caverns in the rock or the undersides of shells where bryozoans that were adapted to quiet water conditions flourished. Bryozoan colonies are a few mm to about 10 cm in size and grow bush-like, fungiform or encrusting. Erect forms cannot survive turbulent water where they are rapidly destroyed. Concentrations
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FIGURE 18. Thin section photographs of sandstone and conglomerate of the Sandia, Gray Mesa and Atrasado formations. All photos under polarized light. Width of photographs: A, B, D, E, F = 4.6 mm; C, G, H = 1.8 mm. A, Sandstone (quartz arenite) composed of mostly monocrystalline, rare polycrystalline quartz and mica (muscovite). Detrital grains are cemented by quartz as authigenic overgrowths. Sample AP 1, Sandia Formation, Arroyo de la Presilla. B, Sandstone (quartz arenite) composed of subangular to subrounded quartz grains, cemented by authigenic quartz overgrowths. Sample AP 2, Sandia Formation, Arroyo de la Presilla. C, Medium-grained sandstone, moderately sorted, composed of detrital quartz grains and “pseudomatrix”. The large “pseudomatrix”-grain in the center of the photograph is probably an altered detrital feldspar grain. The detrital grains are cemented by quartz overgrowths. Sample AP 16, Sandia Formation, Arroyo de la Presilla. D, Moderately sorted sandstone (quartz arenite) composed of abundant detrital quartz grains, and rare echinoderm fragments (center). Detrital grains are cemented by authigenic overgrowths. Sample AP 44, Elephant Butte Member, Arroyo de la Presilla. E, Arkosic sandstone, fine-grained, well sorted, containing detrital quartz grains and many altered feldspar grains. The detrital grains are cemented by quartz overgrowths and mainly by coarse blocky calcite cement. Sample CAA 35, Tinajas Member, Cerros de Amado C. F, Fine-grained sandstone composed of angular to subangular quartz grains and some pseudomatrix (feldspars altered to clay minerals). The sandstone is cemented by coarse, blocky, poikilotopic calcite cement. Sample AP 22, Sandia Formation, Arroyo de la Presilla. G, Fine-grained sandstone composed of detrital quartz, slightly altered feldspars, rare micas (muscovite and biotite) and rare rock fragments. The sandstone is cemented by coarse poikilotopic calcite, which randomly replaced detrital grains. Sample CAB 9, Tinajas Member, Cerros de Amado B. H, Fine-grained sandstone composed of detrital quartz, feldspars, micas, a few rock fragments, including micritic carbonate grains, and calcite cement. Sample CAB 2, Tinajas Member, Cerros de Amado B.
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FIGURE 19. Thin section photographs of mixed siliciclastic-carbonate sandstone and conglomerate of the Gray Mesa and Atrasado formations. A under polarized light, all other photos under plane light. Width of photos: A = 4.6 mm, B-H = 9 mm. A, Mixed siliciclastic-carbonate sandstone, calcite-cemented, composed of mono-and polycrystalline quartz grains, detrital feldspars, carbonate intraclasts and fossil fragments (crinoids, fusulinids). Crinoid fragments display syntaxial overgrowths. Sample CAB 8, Tinajas Member, Cerros de Amado B. B, Mixed siliciclasticcarbonate sandstone composed of abundant monocrystalline, and subordinately polycrystalline quartz grains, detrital feldspars and many carbonate grains (gray). Fossil fragments are rare. Sample CAC 24, Garcia Member, Cerros de Amado C. C, Mixed siliciclastic-carbonate sandstone composed of quartz, detrital feldspars, carbonate intraclasts and large bryozoan fragments. Sample CAD 17, Garcia Member, Cerros de Amado D. D, Mixed siliciclastic-carbonate sandstone composed of quartz, altered feldspars, carbonate grains (intraclasts), echinoderm fragments and a trilobite fragment. Sample CAC 18, Garcia Member, Cerros de Amado C. E, Mixed siliciclastic-carbonate sandstone containing abundant echinoderms (mostly crinoid fragments) and other skeletal grains. Sample CAC 4, Garcia Member, Cerros de Amado C. F, Mixed siliciclasticcarbonate sandstone composed of quartz, carbonate grains and skeletal grains, including echinoderms, shell debris and gastropods. Sample AP 53, Elephant Butte Member, Arroyo de la Presilla. G, Mixed siliciclastic-carbonate sandstone containing small angular quartz grains, detrital feldspars, carbonate intraclasts and skeletal grains, mostly brachiopod shells and echinoderm fragments. Sample MC 1, Bartolo Member, Minas de Chupadera. H, Carbonate conglomerate composed of different types of limestone clasts (mainly mudstone and wackestone) embedded in a fine-grained, mixed siliciclastic-carbonate sandstone matrix. Sample MC 13, Tinajas Member, Minas de Chupadera.
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FIGURE 20. Thin section photographs of bryozoans of the Sandia, Gray Mesa (Whiskey Canyon, Garcia members) and Atrasado formations (Bartolo, Burrego, Moya members). Scale bar = 1 mm. A, Fenestrate bryozoan Penniretepora sp., sample AP 70, Whiskey Canyon Member, Arroyo de la Presilla. B, Trepostome bryozoan Pseudobatostomella sp., sample CAC 14, Garcia Member, Cerros de Amado C. C, Rhabdomesine cryptostome bryozoan Saffordotaxis sp., sample MC 32, Moya Member, Minas de Chupadera. D, Rhabdomesine cryptostome bryozoan Saffordotaxis sp., sample AP 63, Whiskey Canyon Member, Arroyo de la Presilla. E, Trepostome bryozoan Dyscritella sp., sample CAD 8, Garcia Member, Cerros de Amado C. F, Fenestrate bryozoan Rectifenestella sp., sample CAA 7, Bartolo Member, Cerros de Amado A. G, Cystoporate bryozoan Prismopora sp., sample AP 8, Sandia Formation, Arroyo de la Presilla. H, Cystoporate bryozoan Prismopora sp., sample CAC 11, Garcia Member, Cerros de Amado C. I, Cystoporate bryozoan Meekopora cf. prosseri Ulrich in Condra, 1902, sample AP 70, Whiskey Canyon Member, Arroyo de la Presilla. J, Cystoporate bryozoan (Family Cystodictyonidae), sample AP 64, Whiskey Canyon Member, Arroyo de la Presilla. K, M, Rhabdomesine cryptostome bryozoan Saffordotaxis sp., samples CAD 8, CAC 11, Garcia Member, Cerros de Amado C. L, ?Rhabdomesine cryptostome bryozoan, sample ODA 21, Burrego Member, Ojo de Amado.
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FIGURE 21. Thin section photographs of calcareous algae from the Gray Mesa Formation (Whiskey Canyon and Garcia members) and Atrasado Formation (Council Spring Member). Scale bar: A–G, K = 1 mm, H–J = 0.5 mm. A, Archaeolithophyllum missouriense, sample CAC 40, Garcia Member, Cerros de Amado C. B, C, Komia sp., B = sample CAD 6, C = sample CAD 3, all from the Garcia Member, Cerros de Amado. D, Anthracoporella? sp., sample CAC 11, Garcia Member, Cerros de Amado C. E, Epimastoporacean indeterminate, sample OA 23, Council Spring Member, Ojos de Amado. F, Anthracoporella? sp., sample OA 16, Council Spring Member, Ojos de Amado. G, Girvanellacean?, sample CAC 31, Garcia Member, Cerros de Amado C. H, Epimastopora sp., sample OA 23, Council Spring Member, Ojos de Amado. I, Efluegelia sp., sample AP 63, Whiskey Canyon Member, Arroyo de al Presilla. J, Gyroporella? sp., sample OA 21, Council Spring Member, Ojo de Amado. K, Gyroporella sp., sample OA 24, Council Spring Member, Ojo de Amado.
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185 FIGURE 22 (facing page). Thin section photographs of smaller foraminifers of the Sandia Formation, Gray Mesa Formation (Elephant Butte, Whiskey Canyon and Garcia members) and Atrasado Formation (Tinajas, Council Spring, Moya members). Scale bar: A–C = 0.5 mm, all others = 0.1 mm. A, B, C, Bradyina spp. A= sample CAB 17, B = sample CAB 18, Council Spring Member, Cerros de Amado B, C = sample AP 63, Whiskey Canyon Member, Arroyo de la Presilla. D, Calcitornella sp. Sample AP 33, Elephant Butte Member, Arroyo de la Presilla. E, Calcivertella sp. Sample MC 31, Moya Member, Minas de Chupadera. F, Calcivertella sp. Sample AP 67, Whiskey Canyon Member, Arroyo de la Presilla. G, Calcivertella sp. Sample AP 35, Elephant Butte Member, Arroyo de la Presilla. H, ?Calcivertella sp. Sample AP 46, Elephant Butte Member, Arroyo de la Presilla. I, Earlandia sp., Sample CAC 1, Garcia Member, Cerros de Amado C. J, Earlandia sp. Sample AP 35, Elephant Butte Member, Arroyo de la Presilla. K, ?Calcitornella sp. Sample CAD 10, Garcia Member, Cerros de Amado D. L, Climacammina sp. Sample AP 37, Elephant Butte Member, Arroyo de la Presilla. M, Palaeotextularia sp. Sample MC 4, Council Spring Member, Minas de Chupadera. N, Deckerella sp. Sample ODA 11, Tinajas Member, Ojo de Amado. O, Climacammina sp. Sample AP 71, Whiskey Canyon Member, Arroyo de la Presilla. P, Deckerella sp. Sample AP 52, Elephant Butte Member, Arroyo de la Presilla. Q, Palaeotextulariid indet. Sample MC 39, Moya Member, Minas de Chupadera. R, Palaeotextulariid indet. Sample CAB 15, Council Spring Member, Cerros de Amado B. S, Endothyra sp. Sample AP 29, Sandia Formation, Arroyo de la Presilla. T, Endothyra sp. Sample CAD 12, Garcia Member, Cerros de Amado D. U, Endothyra sp. Sample AP 68, Whiskey Canyon Member, Arroyo de la Presilla. V, Endothyranella sp. Sample AP 35, Elephant Butte Member, Arroyo de la Presilla. W, Planoendothyra sp. Sample CAC 27, Garcia Member, Cerros de Amado C. X, Endothyra sp. Sample AP 52, Elephant Butte Member, Arroyo de la Presilla. Y, Endothyra sp. Sample AP 69, Whiskey Canyon Member, Arroyo de la Presilla. Z, ?Endothyranella sp. Sample AP 35, Elephant Butte Member, Arroyo de la Presilla. Aa, ?N. gen. aff. Turrispiroides (= “Monotaxinoides” of the authors). Sample AP 29, Sandia Formation, Arroyo de la Presilla. Bb, Hemigordiellina sp. Sample CAB 10, Tinajas Member, Cerros de Amado B. Cc, Hemigordiellina sp. Sample CAB 18, Council Spring Member, Cerros de Amado B. Dd, Hemigordiellina sp. Sample CDA 20, Tinajas Member, Cerros de Amado D. Ee, Hemigordiellina sp. Sample CDA 21, Tinajas Member, Cerros de Amado D. Ff, Globivalvulina sp. Sample ODA 23, Council Spring, Ojos de Amado. Gg, Globivalvulina sp. Sample ODA 23, Council Spring, Ojo de Amado. Hh, Globivalvulina sp. Sample ODA 23, Council Spring, Ojo de Amado. Ii, Globivalvulina sp. Sample ODA 23, Council Spring, Ojo de Amado. Jj, Globivalvulina sp. Sample ODA 23, Council Spring, Ojo de Amado. Kk, Globivalvulina sp. Sample ODA 23, Council Spring, Ojo de Amado. of massive and encrusting forms suggest high-energy conditions, whereas concentrations of erect, delicate colonies indicate low-energy conditions. In contrast to Mesozoic-modern bryozoans, which are common in cool water, heterozoan carbonates and only minor constituents of modern warm water chlorozoan carbonates, Paleozoic bryozoans were panglobally distributed, and bryozoan-rich deposits during the Paleozoic were formed at all paleolatitudes, including the tropics (Taylor and Allison 1998; Taylor, 2005; Taylor and Sendino, 2010). Erect-growing bryozoans were members of the baffler guild, stabilizing and trapping sediment, although these forms are rarely found in growth position (Fagerstrom, 1987). Brachiopods are solitary marine invertebrate filter feeders with two valves. Almost all brachiopods were attached to the surface by a pedicle. Most brachiopods avoid environments with strong currents or wave action. Some genera have no pedicle and cement the rear of the pedicle valve to the substrate. Spines acted as struts of braces to hold the conical valve in an upright position. In dense clusters, the spines of neighboring brachiopods were entangled to form mutually supporting clusters. Spines of the brachial valve functioned to prevent large, suspended particles from entering the mantle cavity. Brachiopods were members of the constructor guild in brachiopod reefs, or members of the baffler guild or grew parallel to the substrate as binders (Fagerstrom, 1987). The most common echinoderms are crinoids, which are fully marine, sessile filter feeders living in water with normal salinity. Crinoids usually have a root-like attachment, a stem and a calyx with arms. The most common crinoidal skeletons are disarticulated fragments and columnals. Crinoids flourished during the Paleozoic and were abundant in Pennsylvanian carbonates of shallow marine environments. Crinoids lived mainly on the shelf and in shelf-margin settings. Phylloid algae (anchicodiacean algae) are common skeletal grains in many bedded shelf carbonates of the Pennsylvanian and Permian (Wahlman, 2002). Phylloid algae were important mound-building organisms during the Carboniferous and Permian, and they were also present in shelf environments in the photic zone, close to algal mounds (Mamet, 1991). Phylloid algae acted as bafflers, but in most cases in the studied samples, they do not occur in life position. They toppled in-situ or have been transported over short distances and deposited as broken fragments. Almost all samples contain benthic foraminifers that lived either free or attached to the substrate. Most benthic foraminifers were restricted to water with normal salinity, particularly when the diversity of foraminifers was high, as observed in most of our samples. Large benthic foraminifers (fusulinids) are believed to have had symbionts (Ross, 1972; Hallock, 1985) and therefore lived in the photic zone of the shelf. According to Flügel (2004), fusulinids were adapted to shallow, warm and warm-temperate shelf, platform and reef environments. Fusulinids lived in normal marine, well oxygenated settings on the shelf in water depths of a few to a few tens of meters. Sponges are almost exclusively marine benthic suspension feeders. Fragments of calcisponges (inozoa) are very rare, therefore
these sponges are not regarded as good paleoenvironmental indicators. Sponge spicules that are present in many samples and locally abundant, forming spiculites, are probably derived from siliceous sponges. Rugose corals are present, particularly in indistinctly bedded to massive limestone of the Gray Mesa Formation. According to Flügel (2004), rugose corals were widespread in Paleozoic shelf and ramp deposits. Most of the trilobites were benthic organisms that lived in shallow water (Flügel, 2004). Ostracods are common fossils in almost all studied limestone samples. In grainstone and rudstone, thick-shelled ostracods occur that were adapted to high-energy conditions. Summing up, the high diversity and composition of the fossil assemblage of limestone (particularly wackestone, packstone and floatstone) of the Pennsylvanian succession (Sandia, Gray Mesa and Atrasado formations), which was dominated by benthic sessile organisms, clearly indicates depositon in an open-marine shelf environment with normal salinity. The presence of phylloid algae and larger benthic foraminifers indicates deposition within the photic zone. The dominance of muddy textures (wackestone, floatstone) shows that most of the limestone, particularly of the Gray Mesa and Atrasado formations, was deposited in a low-energy setting with water depths of a few tens of meters. Limestone containing a low-diversity fauna indicating deposition in a shallow, restricted marine environment, is rare and occurs only in the Atrasado Formation. Limestone composed of strongly fragmented fossils (grainstone, rudstone) and siliciclastic grains (quartz, feldspar, and rock fragments) is common in the Sandia Formation and in some of the members of the Atrasado Formation, and indicates deposition in a nearshore, high-energy environment. Oolitic grainstone (Bartolo Member) is indicative of deposition in a very shallow, high-energy environment (Flügel, 2004). The most common grain association type in the Pennsylvanian limestones is “bryonoderm extended” (Beauchamp, 1994)–dominated by bryozoans, echinoderms (crinoids) and brachiopods, and additionally corals, benthic smaller and larger foraminifers. This grain association type occurs in non-tropical and tropical environments (Flügel, 2004). Subordinately, in phylloid algal limestone, the “chloralgal association” is present, characterized by the occurrence of calcareous green (phylloid) algae, benthic foraminifers and mollusks. As the “bryonoderm extended” grain association also contains small amounts of photozoan skeletons (corals, algae, large benthic foraminifers), this association may be termed “transitional heterozoan” according to James and Lukasik (2010), which is typical of warm-temperate settings. Heterozoan associations, dominated by bryozoans, brachiopods, echinoderms and mollusks, are typical of cool- and cold-water carbonates (James and Lukasik, 2010). But, heterozoan associations may also occur in warm-water settings below the photic zone. Increased nutrient levels in warm water settings may also cause the development of heterozoan associations (Westphal et al., 2010). According to Cecil (2004, 2015), the occurrence of chert correlates with an arid climate, indicating that quartz-rich dust might be the primary and predominant source of silica for chert, including
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FIGURE 23. Thin section photographs of smaller foraminifers of the Gray Mesa Formation (Elephant Butte, Whiskey Canyon and Garcia members) and Atrasado Formation (Tinajas, Council Spring, Story, Burrego members). Scale bars G, I, J, O, R, P = 1 mm, all others = 0.1 mm. A, Hemigordius sp. Sample CAD 23, Tinajas Member, Cerros de Amado D. B, Hemigordius sp. Sample CAD 22, Tinajas Member, Cerros de Amado D. C, Hemigordius sp. Sample CAC 38, Garcia Member, Cerros de Amado C. D, Palaeonubecularia sp. Sample MC 18, Story Member, Minas de Chupadera. E, Hemigordius sp. Sample CAD 23, Tinajas Member, Cerros de Amado D. F, Planoendothyra sp. 1. Sample CDA 13, Tinajas Member, Cerros de Amado. G, Palaeonubecularia sp. Sample CDA 14, Tinajas Member, Cerros de Amado. H, Hemigordius sp. Sample CAD 23, Tinajas Member, Cerros de Amado D. I, Polytaxis sp. Sample AP 57, Whiskey Canyon Member, Arroyo de la Presilla. J, Polytaxis sp. Sample AP 66, Whiskey Canyon Member, Arroyo de la Presilla. K, Spireitlina sp. Sample CAB 18, Council Spring Member, Cerros de Amado B. L, Spireitlina sp. Sample AP 63, Whiskey Canyon Member, Arroyo de la Presilla. M, Planoendothyra sp. 2. Sample AP 69, Whiskey Canyon Member, Arroyo de la Presilla. N, Syzranella sp. Sample CDA 14, Tinajas Member, Cerros de Amado. O, Polytaxis sp. Sample AP 72, Whiskey Canyon Member, Arroyo de la Presilla. P, Polytaxis sp. Sample AP 61, Whiskey Canyon Member, Arroyo de la Presilla. Q, Syzrania sp. Sample CAB 15, Council Spring Member, Cerros de Amado B. R, Polytaxis sp. (top) and microconchid (bottom). Sample CAD 2, Garcia Member, Cerros de Amado D. S, Tetrataxis sp. Sample CAD 2, Garcia Member, Cerros de Amado D. T, Syzrania sp. Sample MC 16, Burrego Member, Minas de Chupadera. U, Tetrataxis sp. Sample AP 33, Elephant Butte Member, Arroyo de la Presilla. V, Tetrataxis sp. Sample CAC 11, Garcia Member, Cerros de Amado C. W, Tetrataxis sp. Sample AP 63, Whiskey Canyon Member, Arroyo de la Presilla. X, Tuberitina sp., Sample AP 33, Elephant Butte Member, Arroyo de la Presilla. Y, Tuberitina sp. Sample AP 35, Elephant Butte Member, Arroyo de la Presilla. Z, Tuberitina sp. Sample AP 62, Whiskey Canyon Member, Arroyo de la Presilla. Aa, Tuberitina sp. Sample CAA 37, Tinajas Member, Cerros de Amado A. Bb, Syzrania sp. Sample CAC 30, Garcia Member, Cerros de Amado C.
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FIGURE 24. Thin section photographs of fusulinids from limestones of the Gray Mesa Formation (Elephant Butte and Whiskey Canyon members) at Arroyo de la Presilla. Scale bars: B, C, F = 1 mm; all others = 0.5 mm. A, Plectofusulina sp. 1. Sample AP 34, Elephant Butte Member. B, Beedeina sp. Sample AP 34, Elephant Butte Member. C, Beedeina sp. Sample AP 46, Elephant Butte Member. D, Plectofusulina sp. 2. Sample AP 48, Elephant Butte Member. E, Wedekindellina sp. Sample AP 47, Elephant Butte Member. F, Beedeina sp. Sample AP 70, Whiskey Canyon Member. G, Wedekindellina sp. Sample AP 66, Whiskey Canyon Member. H, Beedeina sp. Sample AP 69, Whiskey Canyon Member. I, Wedekindellina sp. Sample AP 64, Whiskey Canyon Member. J, Beedeina sp. Sample AP 64, Whiskey Canyon Member.
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FIGURE 25. Thin section photographs of fusulinids from limestones of the Gray Mesa Formation (Whiskey Canyon and Garcia members) and Atrasado Formation (Tinajas Member). Scale bars: A-F, H = 0.5 mm, G, I-L = 1 mm. A, Beedeina sp. Sample AP 71, Whiskey Canyon Member, Arroyo de la Presilla. B, Beedeina sp. Sample CAD 5, Garcia Member, Cerros de Amado D. C, Wedekindellina sp. Sample CAD 5, Garcia Member, Cerros de Amado D. D, Beedeina sp. Sample CAD 6, Garcia Member, Cerros de Amado D. E, Wedekindellina sp. Sample CAD 6, Garcia Member, Cerros de Amado D. F, Beedeina sp. Sample CAD 11, Garcia Member, Cerros de Amado D. G, Beedeina sp. Sample CAD 15, Garcia Member, Cerros de Amado D. H, Triticites cf. cameratoides Ross, 1965. Sample ODA 10, Tinajas Member, Ojo de Amado. I, Triticites cf. celebroides Ross, 1965. Sample ODA 11, Tinajas Member, Ojo de Amado. J, Triticites cf. cameratoides Ross, 1965. Sample ODA 11, Tinajas Member, Ojo de Amado. K, Triticites cf. cameratoides Ross, 1965. Sample ODA 11, Tinajas Member, Ojo de Amado. L, Triticites cf. celebroides Ross, 1965. Sample ODA 11, Tinajas Member, Ojo de Amado. M, Triticites cf. celebroides Ross, 1965. Sample ODA 11, Tinajas Member, Ojo de Amado.
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FIGURE 26. Thin section photographs of fossils present in limestone of the Gray Mesa Formation (Whiskey Canyon and Garcia members) and Atrasado Formation (Amado Member). Scale bars: A-F = 1 mm, G, H, I = 0.25 mm. A, Brachiopod, both valves preserved, interior displaying a well-developed geopetal structure. Sample CAC 30, Garcia Member, Cerros de Amado C. B, C, Subtransverse sections through solitary rugose corals. Samples AP 51 and AP 57, Whiskey Canyon Member, Arroyo de la Presilla. D, E, Syringoporid corals. Sample CAD 10, Garcia Member, Cerros de Amado. F, Inozoan calcisponge embedded in micrite. Sample CAA 18, Amado Member, Cerros de Amado A. G–I, Transverse sections through palechinid radioles. Samples CAC 8, 11 and 12, Garcia Member, Cerros de Amado C.
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FIGURE 27. Thin section photographs of fossils present in limestone of the Gray Mesa Formation (Garcia Member) and Atrasado Formation (Amado, Tinajas, Story, Moya members). Scale bars: A - D, F, I, J = 1 mm; G, L, M = 0.5 mm; E, H, K = 0.25 mm. A, D, Longitudinal sections through gastropods. A = sample AP 58, Garcia Member, Arroyo de la Presilla; D = sample CAA 18, Amado Member, Cerros de Amado A. B, C, F, Trilobite fragments. B and F are transverse sections through complete trilobite carapaces, C is a curved trilobite fragment showing characteristic shepherd´s crook shape. B = sample CAC 13, C = sample CAC 7, F = sample CAD 12, all Garcia Member, Cerros de Amado C and D. E, Thickshelled ostracod with its two valves in connection. Sample CAD 11, Garcia Member, Cerros de Amado D. G, Microconchid indet (= “Spirorbis“ of the authors). Sample MC 18, Story Member, Minas de Chupadera. H, Nostocites? Sample CAC 26, Garcia Member, Cerros de Amado C. I, J, Tubiphytes sp. I = sample ODA 26, Story Member, Ojo de Amado, J = sample MC 30, Moya Member, Minas de Chupadera. K, ?Salebrid indet. in subtangential section.1. Sample CAC 35, Garcia Member, Cerros de Amado C. L, Tubiphytes sp. Sample MC 31, Moya Member, Minas de Chupadera. M, Polyaxon sponge spicule. Sample CAD 20, Tinajas Member, Cerros de Amado.
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FIGURE 28. Thin section photographs of encrusting organisms of the Gray Mesa Formation (Elephant Butte and Garcia members) and Atrasado Formation (Burrego, Tinajas, Moya members). Scale bars = 1 mm. A, Crust formed by cyanobacteria,?Claracrusta and Palaeonubecularia. Sample MC 32, Moya Member, Minas de Chupadera. B, Inozoan calcisponge encrusted by cyanobacteria, Claracrusta and bryozoans. Sample AP 36, Elephant Butte Member, Arroyo de la Presilla. C, Recrystallized skeleton encrusted by calcivertellids. Sample CDA 22, Tinajas Member, Cerros de Amado. D, Detrital quartz grain encrusted by girvanellacean cyanobacteria, forming an oncoid. Sample MC 36, Moya Member, Minas de Chupadera. E, Bacinella sp. encrusted by girvanellacean cyanobacteria, forming an oncoid. Sample AP 73, Garcia Member, Arroyo de la Presilla. F, ?Claracrusta encrusting a recrystallized phylloid alga. Sample MC 32, Moya Member, Minas de Chupadera. G, Detrital feldspar (left) and quartz (right) encrusted by cyanobacteria. Sample MC 36, Moya Member, Minas de Chupadera. H, Cyanobacteria and Palaeonubecularia sp. encrusting a recrystallized skeleton and substrate. Sample MC 11, Burrego Member, Minas de Chupadera.
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FIGURE 29. Thin section photographs of encrusting organisms of the Sandia Formation, Gray Mesa Formation (Elephant Butte, Whiskey Canyon, Garcia members) and Atrasado Formation (Bartolo, Tinajas, Burrego, Del Cuerto members). Scale bars: A–E = 1 mm, F–R = 0.5 mm. A, Bryozoan colony (? Streblascopora sp.) encrusted by calcivertellids forming an oncoid Osagia sensu stricto. Sample AP 17, Sandia Formation, Arroyo de la Presilla. B, Palaeonubecularia encrusting substrate. Sample CDA 14, Tinajas Member, Cerros de Amado. C, Skeleton encrusted by Palaeonubecularia. Sample MC 29, Del Cuerto Member, Minas de Chupadera. D, Skeleton encrusted by cyanobacteria and calcivertellids. Sample CAA 7, Bartolo Member, Cerros de Amado A. E, Skeleton encrusted by cyanobacteria and calcivertellids forming an oncoid. Sample AP 74, Garcia Member, Arroyo de la Presilla. F, Brachiopod spine encrusted by Palaeonubecularia. Sample MC 29, Del Cuerto Member, Minas de Chupadera. G, Fenestrate bryozoans encrusted by calcivertellids. Sample CAA 7, Bartolo Member, Cerros de Amado A. H, Recrystallized bioclast encrusted by calcivertellids. Sample AP 68, Whiskey Canyon Member, Arroyo de la Presilla. I, Fenestrate bryozoans encrusted by Palaeonubecularia. Sample CAD 10, Garcia Member, Cerros de Amado D. J, Brachiopod spine encrusted by Palaeonubecularia. Sample MC 29, Del Cuerto Member, Minas de Chupadera. K, Skeleton encrusted by Palaeonubecularia. Sample MC 28, Del Cuerto Member, Minas de Chupadera. L, Recrystallized skeleton encrusted by Palaeonubecularia. Sample AP 56, Elephant Butte Member, Arroyo de la Presilla. M, Echinoderm fragment encrusted by Calcivertella sp. Sample AP 38, Elephant Butte Member, Arroyo de la Presilla. N, Recrystallized skeleton encrusted by Palaeonubecularia. Sample MC 29, Del Cuerto Member, Minas de Chupadera. O, Fenestrate bryozoans encrusted by Palaeonubecularia. Sample MC 11, Burrego Member, Minas de Chupadera. P, Q, R, Recrystallized bioclasts encrusted by Palaeonubecularia. Samples CAD 3, Garcia Member, Cerros de Amado D and MC 11, Burrego Member, Minas de Chupadera.
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FIGURE 30. Thin section photographs of encrusting bryozoans from the Gray Mesa Formation (Elephant Butte and Garcia members) and Atrasado Formation (Bartolo and Story members). Scale bars = 1 mm. A, Cystoporate bryozoan Eridopora sp. Sample CAC 30, Garcia Member, Cerros de Amado C. B, Trepostome Tabulipora sp. (top and bottom- “T”) and cystoporate Eridopora sp. (mid part–“E”). Sample CAC 48, Bartolo Member, Cerros de Amado C. C, Cystoporate bryozoan Fistulipora sp. Sample ODA 26, Story Member, Ojos de Amado. D, Cystoporate bryozoan Fistulipora sp. Sample CAC 34, Garcia Member, Cerros de Amado C. E, Cystoporate bryozoan Fistulipora sp. Sample CAC 48, Bartolo Member, Cerros de Amado C. F, Trepostome Tabulipora sp. (bottom–“E”) and cystoporate Eridopora sp. (top–“T”). Fistuliporid bryozoans. Sample CAC 48, Bartolo Member, Cerros de Amado C. G, Rhabdomesine cryptostome bryozoan. Sample AP 55, Elephant Butte Member, Arroyo de la Presilla. H, Fenestrate bryozoan. Sample AP 40, Elephant Butte Member, Arroyo de la Presilla.
194
195 FIGURE 31. Thin section photographs of encrusting organisms from the Gray Mesa Formation (Elephant Butte, Whiskey Canyon and Garcia members) and Atrasado Formation (Story and Moya members). Scale bars: A–D, F = 1 mm, E, G, H, I, J = 0.5 mm, K = 0.25 mm. A, Cystoporate bryozoan Fistulipora sp. encrusting a skeleton. Sample CAD 9, Garcia Member, Cerros de Amado D. B, Cystoporate bryozoan Eridopora sp. encrusting a skeleton and substrate. Sample MC 20, Story Member, Minas de Chupadera. C, Cystoporate bryozoan?Fistulipora sp. encrusting a recrystallized skeleton (?algal fragment). Sample MC 31, Moya Member, Minas de Chupadera. D, Tubiphytes encrusting fenestrate bryozoans. Sample MC 30, Moya Member, Minas des Chupadera. E, Komia encrusting a recrystallized bioclast. Sample AP 34, Elephant Butte Member, Arroyo de la Presilla. F, Efluegelia, encrusting a recrystallized bioclast. Sample AP 68, Whiskey Canyon Member, Arroyo de la Presilla. G, Tetrataxis attached on an echinoderm (crinoid) fragment. Sample CAC 9, Garcia Member, Cerros de Amado C. H, Komia encrusting fenestrate bryozoans. Sample CAD 3, Garcia Member, Cerros de Amado D. I, Fenestrate bryozoan colony encrusting a recrystallized skeleton. Sample CAD 2, Garcia Member, Cerros de Amado D. J, Tubiphytes encrusting a bryozoan colony. Sample MC 30, Moya Member, Minas de Chupadera. K, Eotuberitina encrusting a brachiopod shell fragment. Sample AP 32, Elephant Butte Member, Arroyo de la Presilla. biotic and abiotic precipitates of microquartz and fibrous silica. He argues that during the Morrowan to Desmoinesian, a humid climate with intense chemical weathering prevailed in the eastern and central part of the North American continent, whereas arid climatic conditions and deserts were developed in western Pangea where chert is common in Pennsylvanian marine carbonate successions that also contain finegrained, nonmarine eolian sandstones (eolianites). However, Lucas et al. (2009b) report a lycopsid flora near the base of the Sandia Formation (Atokan), which indicates a wetland swamp flora and perhumid climatic conditions. Falcon-Lang et al. (2016) describe conifer trees from the Late Pennsylvanian Atrasado Formation from a semiarid sabkha environment, although the stumps indicate more sub-humid tropical conditions. The Tinajas shale flora of the Atrasado Formation contains elements of a wetland flora, but also elements indicating seasonality with alternating dry and wet periods (Lerner et al., 2009). Within the Pennsylvanian succession of central New Mexico (Sandia, Gray Mesa and Atrasado formations), eolian sandstones are absent. Most intercalated sandstones are of shallow marine origin, and some (especially in the Sandia Formation) are of fluvio-deltaic origin. Sandstone, particularly of the Sandia Formation, is almost pure quartz arenite, indicating intense chemical weathering of silicate minerals, particularly feldspars. According to Maliva et al. (1989), silica sedimentation on the modern sea floor is virtually entirely biogenic. The primary input of dissolved silica into the ocean is immediately utilized by organisms such as radiolarians or sponges to produce siliceous skeletal elements (Sherwood and Weaver, 1974). The abundance of chert indicates that silica was removed from the seawater by biological processes, mainly by sponges (Maliva et al., 1989). According to Maliva et al. (1989), chert is widely distributed in Paleozoic and Mesozoic carbonate successions. Nodular chert is most abundant in the open-marine shelf and platform facies, which is dominated by muddy lithologies such as mudstone and wackestone deposited below the fair-weather wave base. Silica in most Paleozoic and Mesozoic platform and shelf facies containing nodular chert originated as sponge spicules. This silica was mobilized, redistributed and concentrated locally during diagenesis, forming nodular or bedded chert. The presence of calcified sponge spicules in many of the muddy microfacies (particularly wackestone, rare spiculite), absence of eolian sediments and absence of entirely arid climatic conditions during sedimentation of the Pennsylvanian succession in the Cerros de Amado indicate that a large portion of silica is derived from chemical weathering. Dissolved silica was transported into the sea where it was used mainly by sponges for skeletal secretion. We conclude that the chert nodules within the Pennsylvanian succession, particularly within the Gray Mesa Formation, are derived from silica that was almost entirely biogenic and was redistributed and concentrated during diagenesis. The Sandia Formation exposed at Arroyo de la Presilla is one of the thickest Sandia sections (the only thicker section is in the Los Pinos Mountains to the north) and a cyclic succession of siliciclastic sediments and fossiliferous limestone. The cycles show a transgressive trend from nonmarine (fluvial) to shallow, normal marine settings (Lucas et al., 2009a, b). The Sandia Formation represents early synorogenic sediments deposited during the initial phase of the Ancestral Rocky Mountain orogeny. Thickness and facies of the Sandia Formation display strong lateral variations (Krainer and Lucas, 2013). The thinnest and dominantly siliciclastic sections are exposed in northern New Mexico (Sierra Nacimiento), and the thickest sections are in the Los Pinos Mountains (approximately 170 m) and at Arroyo de la Presilla. The depositional environment of siliciclastic sediments ranges from fluvial to fluvio-deltaic, coastal swamp, brackish, high-energy nearshore to
fine-grained middle-outer shelf settings. Limestones were deposited in restricted, shallow marine shelf settings and open, normal marine shelf settings of low to high turbulence (Krainer and Lucas, 2013). Between the Cerros de Amado and Little San Pascual Mountains to the south, the Sandia Formation grades into the Red House Formation, which, in the Little San Pascual Mountains, Fra Cristobal Mountains and Caballo Mountains is the homotaxial equivalent of the Sandia Formation (Lucas et al., 2012a). The Red House Formation, which is composed of shale and limestone with only minor amounts of sandstone and conglomerate, represents a more distal facies compared to the more proximal facies of the Sandia Formation with higher amounts of coarse siliciclastic sediments that are partly of nonmarine origin (Lucas et al., 2012a). The Gray Mesa Formation is dominantly composed of limestone, including cherty limestone, and interclated mudstone, particularly in the Elephant Butte and Garcia formations. Sandstone is rare (Nelson et al., 2013b). In the area between Cedro Peak (Vachard et al., 2012, 2013; Lucas et al., 2014) and the Cerros de Amado (Lucas et al., 2009a, 2013), the thickness of the Elephant Butte Member ranges from 24 m (Priest Canyon) to 95 m (Cerros de Amado). Sandstone is absent in most sections, but thin sandstone is intercalated at the type section (Gray Mesa) and at Whiskey Canyon (Mud Springs Mountains; Lucas et al., 2012b, 2016). A 10-m-thick sandstone and two thinner sandstone intervals intercalated at Arroyo de la Presilla indicate a local source (?Joyita uplift) that probably was tectonically active during sedimentation of the Elephant Butte Member. Thickness of the Whiskey Canyon Member, which is dominantly composed of cherty limestone with minor mudstone intercalations, is quite uniform over a large area (30-84 m). Limestone is dominantly of muddy textures (wackestone, floatstone), and microfacies and fossil assemblages indicate deposition in a deeper, open marine shelf environment. The Whiskey Canyon Member was deposited on a tectonically stable, wide, unrimmed carbonate platform that extended from Cedro Peak in the Manzanita Mountains of Bernalillo County south to the Caballo Mountains of Sierra County. In the Oscura, Fra Cristobal and Caballo mountains, a subdivision of the Gray Mesa into members is not possible (Lucas and Krainer, 2009; Nelson et al., 2013a). Thickness of the Garcia Member ranges from 42 m (Cedro Peak; Lucas et al., 2014) to more than 200 m at the type section (Gray Mesa; Krainer and Lucas, 2004). Siliciclastic mudstone is more abundant, and locally sandstone and conglomerate are intercalated in the Garcia Member (Cedro Peak, Whiskey Canyon, Arroyo de la Presilla), which we interpret to have resulted from a pulse of ARM tectonic activity. Limestone is dominated by muddy types (wackestone, floatstone) deposited in an open shelf environment below wave base. Periodically, high-energy sediments (grainstone, rudstone) are intercalated, indicating deposition above the wave base. The Atrasado Formation is characterized by the alternation of mostly siliciclastic intervals (Bartolo, Tinajas, Burrego and Del Cuerto members) and mostly carbonate intervals (Amado, Council Spring, Story and Moya members). Dominantly siliciclastic members display much stronger variations in thickness and lateral facies changes compared to the members composed primarily of limestone. For example, the Bartolo Member is very sandy at Priest Canyon but contains little sandstone at Cedro Peak or Cerros de Amado C. The Tinajas Member varies in thickness between 60 m at Cedro Peak and 115 m at Priest Canyon, and contains much more sandstone at Ojo de Amado compared to other sections (Priest Canyon, Cedro Peak, and Cerros de Amado). The Burrego Member is very sandy at Cedro Peak (47 m thick) but has only a few sandstone beds intercalated at Priest Canyon (23 m thick) or at Cerros de Amado (only 13 m thick) (Lucas et al., 2009a, 2013, 2014, 2016). Sandstone is commonly mixed siliciclastic-carbonate in
196 composition, containing abundant skeletal grains, indicating deposition in a high-energy, nearshore environment. Limestone was deposited in a shallow, open to partly restricted marine environment. We interpret these lateral facies variations and differences in thickness to be the result of increased ARM tectonic activity, resulting in increased influx of siliciclastic sediment from reactivated uplifts. The members that are dominantly composed of limestone with some shale and rare sandstone intercalated are generally thinner but more consistent in thickness. For example, the Amado Member ranges in thickness from 9 m (Priest Canyon) to 20 m (Cedro Peak), the Council Spring from 5 to 23 m, and the Moya Member from 5 to 18 m. The thinnest but most consistent member in thickness is the Story Member, which is 6-9 m thick. Microfacies of the limestone indicates deposition in a shallow, low- to high-energy shelf environment. Little variation in thickness and in facies demonstrates that sedimentation of the limestone-dominated members occurred during a period of tectonic inactivity on a wide shelf with little topography. The Bar B Formation, which is exposed in the Fra Cristobal and Caballo Mountains of Sierra County and lacks sandstone, is correlative to the Atrasado Formation, but developed in a more distal facies (Nelson et al., 2013b). CONCLUSIONS The Pennsylvanian succession (Sandia, Gray Mesa and Atrasado formations) in the Cerros de Amado region east of Socorro, central New Mexico, is composed of different lithotypes of limestone and intercalated siliciclastic sediments. The most abundant microfacies of limestone by far are wackestone and floatstone. Mudstone, packstone, grainstone and rudstone are rare, and boundstone is very rare. Almost all microfacies contain a diverse fossil assemblage. Among the sandstones, two types can be distinguished: (1) siliciclastic sandstone (quartz arenite) is the common sandstone type of the Sandia Formation; and (2) mixed siliciclastic-carbonate sandstone is present in the Garcia Member of the Gray Mesa Formation and in the clastic members of the Atrasado Formation. The most abundant fossils in the limestone facies of all three formations are echinoderms (mostly crinoids), bryozoans and brachiopods. Less common are smaller and larger benthic foraminifers, calcareous algae (mostly phylloid algae), and sponges (mostly spicules), corals, mollusks (bivalves and gastropods), and arthropods (ostracods and trilobites). Encrusting organisms are present in many limestone samples, particularly in wackestone, packstone and floatstone. The most common encrusting organisms are cyanobacteria and Palaeonubecularia. There is no significant change in the biotic composition throughout the Pennsylvanian succession. During the Pennsylvanian in central New Mexico, the seafloor was dominated by sessile benthic suspension feeders (bryozoans, brachiopods, and echinoderms). The diversity and composition of the fossil assemblage indicate that limestones of all three formations were deposited in an open-marine shelf environment with normal salinity. Rarely (in the Atrasado Formation), limestone formed in a restricted shallow marine environment, indicated by a low-diversity fossil assemblage. The presence of phylloid algae and larger benthic foraminifers (fusulinids) indicates deposition within the photic zone. The dominance of muddy textures (wackestone, floatstone) demonstrates that most of the limestones, particularly of the Gray Mesa and Atrasado formations, were deposited in a low-energy setting below wave base at water depths of at least a few tens of meters. The dominant grain association type is bryonoderm extended, which occurs in tropical and non-tropical environments. Subordinately, the chloralgal grain association type is present. The presence of small amounts of photozoan skeletons (including the chloralgal association) indicates that the limestones were deposited in at least a warmtemperature setting. The presence of calcified sponge spicules, absence of eolian sandstones (eolianites) and inferred perhumid to seasonal wet climatic conditions during the Pennsylvanian in central New Mexico suggest that silica was produced by intense chemical weathering, transported into the sea and used mainly by sponges for skeletal secretion. The silica in the chert nodules that are very common in the Gray Mesa Formation is interpreted to be almost entirely of biogenic origin. Silica was mobilized, redistributed and concentrated as chert nodules during diagenesis. The Sandia Formation is characterized by strong lateral variations in thickness and facies, ranging from thin, almost entirely siliciclastic successions of a proximal facies to thicker, mixed siliciclastic-carbonate successions of a more distal facies. The Sandia Formation represents
early synorogenic sediments deposited during the initial phase of the ARM orogeny. Southward (south of the Cerros de Amado region), the Sandia Formation grades into the more distal facies of the Red House Formation. The dominance of limestone, particularly cherty limestone, paucity of sandstone and little variations in thickness indicate that the sediments of the Gray Mesa Formation were deposited during a period with little tectonic activity. In particular, the Whiskey Canyon Member, which is very consistent in facies and thickness over a large area, represents deposits of an extensive, deeper, open marine shelf that extended from Cedro Peak south to the Caballo Mountains. Intercalated sandstone and conglomerate in the Garcia Member of the Gray Mesa Formation indicate increasing tectonic activity. The Atrasado Formation is composed of dominantly siliciclastic members that alternate with limestone-dominated members. The siliciclastic-dominated members (including coarse-grained siliciclastic sediments such as sandstone and conglomerate) display strong lateral variations in facies and thickness, whereas the limestone-dominated members are much more consistent in facies and thickness. We interpret the siliciclastic-dominated members to represent deposits of tectonically active periods, whereas the limestone-dominated members document periods that were tectonically stable. ACKNOWLEDGMENTS We are grateful to numerous colleagues for assistance and/or collaboration in the field on this project, particularly J. Barrick, D. Chaney, W. DiMichele, L. Rinehart, J. Schneider, J. Spielmann and T. Suazo. We thank Bruce Allen and James Barrick for providing helpful reviews. REFERENCES Amini, Z. Z., Adabi, M. H., Burrett, C. F. and Quilty, P. G., 2004, Bryozoan distribution and growth form associations as a tool in environmental interpretation, Tasmania, Australia: Sedimentary Geology, v. 167, p. 1-15. Barrick, J.E., Lucas, S.G. and Krainer, K., 2013, Conodonts of the Atrasado Formation (uppermost Middle to Upper Pennsylvanian), Cerros de Amado region, central New Mexico, U.S.A.: New Mexico Museum of Natural History and Science. Bulletin 59, p. 239-252. Beauchamp, B., 1994, Permian climatic cooling in the Canadian Arctic: Geological Society of America, Special Paper 288, p. 229-246. Boyer, M., Matricardo, G., and Pisano, E., 1990, Zoarial forms in the development of a bryozoan community: Anales de Biología (Murcia), v. 16, p. 155-162. Cecil, C.B., 2004, Eolian dust and the origin of sedimentary chert: USGS OpenFile Report 2004-1098, p. 1-13. Cecil, C.B., 2015, Paleoclimate and the origin of Paleozoic chert: Time to reexamine the origins of chert in the rock record: The Sedimentary Record, v. 13, p. 4-10. Dunham, R.J., 1962, Classification of carbonate rocks according to their depositional texture; in Ham, W.E., ed., Classification of Carbonate Rocks – a symposium: American Association of Petroleum Geologists, Memoir 1, p. 108-122. Embry, A.F., and Klovan, J.E., 1971, A Late Devonian reef tract on northeastern Banks Island, N.W.T.: Bulletin of Canadian Petroleum Geology v. 19, p. 730-781. Fagerstrom, J.A., 1987, The Evolution of Reef Communities. Wiley, New York, 600 p. Falcon-Lang, H.J., Kurzawe, F and Lucas, S.G., 2016, A Late Pennslyvanian coniferopsid forest in growth position, near Socorro, New Mexico, U.S.A.: Tree systematics and paleoclimate significance: Review of Palaeobotany and Palynology, v. 225, p. 67-83. Flügel, E., 2004, Microfacies of Carbonate Rocks. Analysis, Interpretation and Application. Springer, Berlin, 976 p. Hallock, P., 1985, Why are larger foraminifera large?: Paleobiology, v. 11, p. 195-208. James, N.P. and Lukasik, J., 2010, Cool- and cold-water neritic carbonates; in James, N.P. and Dalrymple, R.W., eds., Facies Models 4: Ottawa, Geological Association of Canada (GEOtext 6) p. 371-399. Krainer, K. and Lucas, S.G., 2004, Type sections of the Pennsylvanian Gray Mesa and Atrasado formations, Lucero uplift, central New Mexico: New Mexico Museum of Natural History and Science, Bulletin 25, p. 7-30. Krainer, K. and Lucas, S.G., 2009, Cyclic sedimentation of the Upper Pennsylvanian (lower Wolfcampian) Bursum Formation, central New Mexico: Tectonics versus glacioeustasy: New Mexico Geological Society, Guidebook 60, p. 167-182. Krainer, K. and Lucas, S.G., 2013, The Pennsylvanian Sandia Formation in
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Darton’s (1928, pl. 21) cross sections east of Socorro. Units are agg = agglomerate (volcanic); Ca = Abo Sandstone; Cc = Chupadera Formation; Cmg = Magdalena Group; g = granite; i = volcanic flows; K = Upper Cretaceous strata; T = Tertiary conglomerate; Trd = Triassic Dockum(?).
