Chambers Tuff

The Chambers Tuff (or Chambers Tuff Formation) is a geological formation in the Trans-Pecos area of Texas. It preserves fossils dating back to the Eocene epoch, across the boundary between the Duchesnean and Chadronian North American land mammal ages. The Chambers Tuff is the middle of three fossil-bearing sedimentary formations in the Vieja Group, alongside the older Colmena Tuff and younger Capote Mountain Tuff.J. A. Wilson. (1977). "Stratigraphic Occurrence and Correlation of Early Tertiary Vertebrate Faunas Trans-Pecos Texas. Part I: Vieja Area." Texas Memorial Museum Bulletin 25:1-42

Geology Though named as a tuff (airborne ash deposit), most of the Chambers Tuff actually represents water-carried sediments. Most of it comprises multicolored fine-grained sediments, alongside coarse gray conglomerates and a few marker beds with legitimate ash content. The lower marker bed is a soft pale-colored tuff about 100–175 feet above the base of the Chambers Tuff as a whole. The upper marker bed is a tough layer of sanidine-based dark red sandstone higher in the section. A third marker bed, another red sandstone layer, is occasionally found near the top of the Chambers Tuff.

Radiometric (40Ar/39Ar) dating has not been attempted for the Chambers Tuff itself, but it is possible for the volcanic layers which bracket it. Depending on the study, the underlying Buckshot Ignimbrite has been dated to anywhere between 38.29 ± 0.16 Ma and 37.68 ± 0.06 Ma.Kelly, T.S.; Murphey, P.C.; Walsh, S.L. (2012). "New records of small mammals from the middle Eocene Duchesne River Formation, Utah, and their implications for the Uintan–Duchesnean North American Land Mammal Age transition." Paludicola 8: 208–251. The overlying Bracks Rhyolite is dated to anywhere between 37.14 ± 0.08 Ma and 36.67 ± 0.04 Ma.

Paleobiota Mammal fossils are found at two particular local faunas in the Chambers Tuff, both found in Presidio County:

The Porvenir local fauna occurs in the lower layers of the Chambers Tuff, below the lower marker bed and up to 100 feet above it. It corresponds to the late Duchesnean NALMA and an early part of magnetostratigraphic chron C17n. The Little Egypt local fauna occurs in the higher layers of the Chambers Tuff, exposed at sites such as Reeves Bonebed and Chalk Gap Draw. It corresponds to the earliest Chadronian NALMA and magnetostratigraphic chron C17n.1n. The Rancho Gaitan local fauna, in Chihuahua, Mexico, is very close to the Little Egypt local fauna in age and environment. Natural endocasts (brain molds) are abundant in the Reeves bonebed.

Mammals

Artiodactyla Artiodactyls of the Chambers TuffGenus / TaxonSpeciesLocal faunaNotesImagesAclistomycterWilson, John A. (1971). "Early Tertiary Vertebrate Faunas, Vieja Group, Trans-Pecos Texas, Agriochoeridae and Merycoidodontidae". Bulletin of the Texas Memorial Museum, University of Texas at Austin. 18: 1–83.A.? dunaganiLittle EgyptAn early aclistomycterine merycoidodontid (oreodont). Previously considered a species of Merycoidodon.A. middletoniPorvenirAn early aclistomycterine merycoidodontid (oreodont).AgriochoerusA. antiquusPorvenir, Little EgyptAn agriochoerid (claw-bearing oreodont relative).ArchaeotheriumA. cf. A. mortoniPorvenir, Little EgyptAn entelodont (boar-like relative of hippos).BathygenysB. reevesiLittle EgyptAn early oreonetine merycoidodontid (oreodont).BrachyhyopsB. wyomingensisPorvenirAn entelodont (boar-like relative of hippos).EotylopusE. cf. reediLittle EgyptAn oromerycid (early camel).HendryomeryxH. defordiPorvenirA leptomerycid. Previously considered a species of Leptomeryx.Wilson, J.A. (1974). "Early Tertiary vertebrate faunas, Vieja Group and Buck Hill Group, Trans-Pecos Texas: Protoceratidae, Camelidae, Hypertragulidae." Texas Memorial Museum Bulletin 23:1-34.HeteromeryxH. disparPorvenirAn early protoceratid.HidrosotheriumH. transpecoensisPorvenirA leptomerycid.OromeryxO. sp.PorvenirAn oromerycid (early camel).PoabromylusP. kayiPorvenirAn early protoceratid.ProtoreodonP. pumilusPorvenirAn agriochoerid (claw-bearing oreodont relative).PseudoprotocerasP. minorPorvenirAn early protoceratid. Previously considered a species of Poabromylus.

Carnivora Carnivorans of the Chambers TuffGenus / TaxonSpeciesLocal faunaNotesImagesAngelarctocyonA. australisPorvenirAn indeterminate amphicyonid ("bear-dog"). Previously considered a species of Miacis.E. P. Gustafson (1986). "Carnivorous mammals of the Late Eocene and Early Oligocene of Trans-Pecos Texas." Texas Memorial Museum Bulletin 33:1-66BrachyrhynchocyonB. dodgeiLittle EgyptA daphoenine amphicyonid ("bear-dog"). Formerly known as Daphoenocyon dodgei.DaphoenictisD. sp.PorvenirA daphoenine amphicyonid ("bear-dog").DaphoenusD. lambeiPorvenirA daphoenine amphicyonid ("bear-dog").Feliformiaindet.Little EgyptAn unusual snout fragment with a deep premaxilla, broad incisors, and large canines. Potentially a new species of felid (cat) or nimravid ("false saber-toothed cat").GustafsoniaG. cognitaLittle EgyptAn indeterminate amphicyonid ("bear-dog"). Previously considered a species of Miacis.

Eulipotyphla Eulipotyphlans of the Chambers TuffGenus / TaxonSpeciesLocal faunaNotesImagesCentetodonC. chadronensisPorvenirA geolabidid.ApternodusA. iliffensisPorvenirAn apternodontid.

Hyaenodonta Hyaenodonts of the Chambers TuffGenus / TaxonSpeciesLocal faunaNotesImagesHemipsalodonH. viejaensisPorvenirA hyainailourid.HyaenodonH. cruciansPorvenirA hyaenodontid.H. cf. horridusLittle EgyptH. montanusPorvenirIschnognathusI. savageiPorvenirA hyainailourid.

Leptictida Leptictids of the Chambers TuffGenus / TaxonSpeciesLocal faunaNotesImagesLeptictisL. douglasiPorvenirA leptictid.L. wilsoniLittle Egypt

Perissodactyla Perissodactyls of the Chambers TuffGenus / TaxonSpeciesLocal faunaNotesImagesColodonC. stovalliWilson, J.A.; Schiebout, J.A. (1984). "Early Tertiary Vertebrate Faunas, Trans-Pecos Texas: Ceratomorpha Less Amynodontidae." The Pearce-Sellards Series, Texas Memorial Museum 39:1-47.Porvenir, Little EgyptA helaletid (early tapir).DuchesneodusD. uintensisPorvenirA large horned brontothere.HaplohippusH. texanusPorvenirAn early horse.HyracodonH. primusPorvenir, Little EgyptA hyracodontid (lightly-built, pony-like rhino).MetamynodonM. chadronensisPorvenirWilson, J.A.; Schiebout, J.A. (1981). "Early Tertiary Vertebrate Faunas Trans-Pecos Texas: Amynodontidae." The Pearce-Sellards Series, Texas Memorial Museum 33:1-62.An amynodontid (hippo-like rhino).MesohippusM. texanusForsten, A.; McGrew, P.O. (1971). "Early Tertiary Vertebrate Faunas, Vieja Group, Trans-Pecos Texas: Equidae." The Pearce-Sellards Series, Texas Memorial Museum 18:1-16.Porvenir, Little EgyptAn early three-toed horse.PenetrigoniasP. dakotensisPorvenirAn early hornless rhinocerotid (rhino). Reports of Trigonias-like fossils probably represent this species.ProtitanopsP. curryiPorvenir, Little EgyptA large horned brontothere. Texan fossils of this species were previously described under the dubious name "Menodus bakeri".SchizotheroidesS. jackwilsoniPorvenir, Little EgyptAn enigmatic perissodactyl with teeth similar to hyracodontids.Subhyracodon?S.? sp.PorvenirAn early hornless rhinocerotid (rhino). Formerly known as Caenopus.ToxotheriumT. hunteriPorvenir, Little EgyptAn enigmatic perissodactyl with a short, broad skull and rhino-like teeth.

Primates Primates of the Chambers TuffGenus / TaxonSpeciesLocal faunaNotesImagesRooneyiaR. viejaensisPorvenirAn omomyid (early tarsier relative)

Rodentia Rodents of the Chambers TuffGenus / TaxonSpeciesLocal faunaNotesImagesAdjidaumoA. cf. A. minutusPorvenirAn eomyid.ArdynomysA. occidentalisPorvenir, Little EgyptA cylindrodontid.AulolithomysA. bounitesPorvenirAn eomyid.A. cf. A. bounitesLittle EgyptCylindrodonC. fontisLittle EgyptA cylindrodontid.DolocylindrodonD. texanusA. E. Wood. (1974). "Early Tertiary vertebrate faunas, Vieja Group Trans-Pecos Texas: Rodentia". Texas Memorial Museum Bulletin 21:1-112Porvenir, Little EgyptA cylindrodontid. Previously considered a species of Pseudocylindrodon.EutypomysE. inexpectatusPorvenir, Little EgyptA eutypomyid.IschyromysI. blackiPorvenirAn ischyromyine ischyromyid.LitoyoderimysL. lustrorumPorvenirAn eomyid. Previously considered a species of Yoderimys.MicroparamysM. perfossusPorvenirA paramyine ischyromyid.PseudocylindrodonP. neglectusPorvenir, Little EgyptA cylindrodontid.PseudotomusP. cf. P. petersoniPorvenirA paramyine ischyromyid. Previously considered a species of Ischyrotomus.P. johanniculiPorvenir, Little EgyptA paramyine ischyromyid. Previously considered a species of Manitsha.QuadratomusQ. gigansPorvenirA paramyine ischyromyid. Previously considered a species of Leptotomus.cf. Simimyscf. Simimys sp. indet.PorvenirA simimyid.ViejadjidaumoV. magniscopuliPorvenirAn eomyid.

Chambers Tuff

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