578 Location and stratigraphy


Location.—The type section of the Lake Valley Formation is located on the northwestern slope of Apache Hill immediately north of the Lake Valley mining district in the southwestern part of Sierra County, New Mexico (USA) (Figs. 1, 2). We studied bryozoans from the Andrecito Member (samples LVT 15 and 17) and Tierra Blanca Member (samples LVT 29 and 34) of the type section of the Lake Valley Formation (Fig. 2).


Stratigraphy.—The type section of the Mississippian Lake Valley Formation has an exposed thickness of 71 m and is divided into four members, which (in ascending order) are: Andrecito, Alamogordo, Nunn, and Tierra Blanca members (Fig. 2). The Lake Valley Formation is underlain by the Mississippian Caballero Formation, which is 17m thick and rests on greenish shale of the Upper Devonian Percha Formation (see Krainer and Lucas, 2012). The type section of the Lake Valley Formation (Fig. 2) was


recently studied in detail by Krainer and Lucas (2012). Here, we present a brief summary: The Andrecito Member (13.9 m) is composed of cherty,


wavy bedded micritic limestone, alternating with shale; wavy bedded cherty limestone containing abundant crinoid fragments and bryozoans; medium-bedded, very cherty limestone; and coarse-grained, cross-bedded crinoidal limestone with chert nodules (Fig. 2). Limestone is composed of wackestone to packstone; grainstone and floatstone containing a diverse fossil assemblage of echinoderm fragments (crinoids), bryozoans, ostracodes, brachiopods, gastropods, rare algae, and foramini- fers; and a few other skeletal grains (Fig. 3.1, 3.2). The Alamogordo Member (7.2 m) consists of thick-bedded


to massive, light gray micritic limestone containing chert nodules (Fig. 2). The dominant microfacies is bioclastic mudstone, and subordinately wackestone to packstone contain- ing a diverse fossil assemblage, including bryozoans. The Nunn Member (17.6 m) is composed of marl and shale


with intercalated marly limestone and limestone containing abundant crinoidal fragments and bryozoans (Fig. 2). The microfacies is wackestone to packstone containing spicules, ostracodes, echinoderm fragments, bryozoans, brachiopods, and rare trilobites. The Tierra Blanca Member is the thickest member (31.7 m)


and represented by fossiliferous, mostly coarse-grained limestone, locally displaying cross bedding (Fig. 2). These limestones alternate with marly shale and covered (shale) intervals. Limestone is composed of packstone to rudstone, grainstone, and wackestone to floatstone (Fig. 3.3, 3.4). All microfacies contain fragmented fossils, particularly echino- derms (crinoids) and bryozoans. Limestones of the Lake Valley Formation are composed of


a typical ‘bryonoderm’ grain association (sensu Beauchamp 1994, Beauchamp and Desrochers 1997), which is common in upper Paleozoic sedimentary successions. According to Krainer and Lucas (2012), the Caballero and Lake Valley formations represent two transgressive-regressive depositional sequences. The depositional environment ranges from low-energy, deeper shelf to high-energy storm deposits.


Figure 1. Location of type section of Lake Valley Formation in Sierra County, southwestern New Mexico, USA.


Materials and methods


Bryozoans were studied in thin section using a binocular micro- scope with transmitted light. In total, 43 thin sections were pre- pared from rock samples. Morphological character terminology is partly adopted from Hageman (1991) for fenestrates and Hageman (1993) for cryptostomes. The spacing of structures is measured as the distance between their centers. Statistics were summarized using arithmetic mean, sample standard deviation, coefficient of variation, and minimum and maximum values.


Repositories and institutional abbreviations.—The studied mate- rial is deposited at the New Mexico Museum of Natural History and Science (NMMNH), Albuquerque,New Mexico, USA. Other repositories include ISGS (ISM)=Illinois State Geological Survey, Illinois State Museum, Springfield, Illinois, and USNM PAL=National MuseumofNatural History (formerly United States National Museum), Paleobiology Department, Washington, DC.


Systematic paleontology


Phylum Bryozoa Ehrenberg, 1831 Class Stenolaemata Borg, 1926


Superorder Palaeostomata Ma, Buttler, and Taylor, 2014 Order Cystoporata Astrova, 1964 Suborder Fistuliporina Astrova, 1964 Family Fistuliporidae Ulrich, 1882


Genus Cystomeson new genus


urn:lsid:zoobank.org:act:F9FAFAF3-988D-43A2-BA9F- E5568F3C4A5B


Type species.—Cystomeson sierraensis new species, by monotypy.


Journal of Paleontology 92(4):577–595


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