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Chambers Tuff

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Chambers Tuff
Stratigraphic range: mid-late Eocene (late Duchesnean - early Chadronian, 38.29 - 37.14 Ma)
TypeFormation
Unit ofVieja Group
UnderliesBracks Rhyolite
OverliesBuckshot Ignimbrite
Lithology
Primarysandstone, siltstone, conglomerate, tuff
Location
RegionTexas
CountryUnited States
Type section
Named byDeFord (1958)

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.[1] 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.[2]

Geology

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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.[2]

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.[3][4][1][5] The overlying Bracks Rhyolite is dated to 37.14 ± 0.08 Ma.[5]

Paleobiota

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Mammal fossils are found at two particular local faunas in the Chambers Tuff, both found in Presidio County:[2][6]

  • 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.[2] It corresponds to the late Duchesnean NALMA and an early part of magnetostratigraphic chron C17n.[3]
  • 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.[2] It corresponds to the earliest Chadronian NALMA and magnetostratigraphic chron C17n.1n.[3][1] The Rancho Gaitan local fauna, in Chihuahua, Mexico, is very close to the Little Egypt local fauna in age and environment.[2][6] Natural endocasts (brain molds) are abundant in the Reeves bonebed.[7]

Mammals

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Artiodactyla

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Artiodactyls of the Chambers Tuff
Genus / Taxon Species Local fauna Notes Images
Aclistomycter[8] A.? dunagani[8] Little Egypt An early aclistomycterine merycoidodontid (oreodont). Previously considered a species of Merycoidodon.[8]
A. middletoni[8] Porvenir An early aclistomycterine merycoidodontid (oreodont).
Agriochoerus A. antiquus Porvenir,

Little Egypt

 An agriochoerid (claw-bearing oreodont relative).
Archaeotherium A. cf. A. mortoni Porvenir,

Little Egypt

 An entelodont (boar-like relative of hippos).
Bathygenys B. reevesi[8] Little Egypt An early oreonetine merycoidodontid (oreodont).
Brachyhyops B. wyomingensis Porvenir An entelodont (boar-like relative of hippos).
Eotylopus E. cf. reedi Little Egypt An oromerycid (early camel).
Hendryomeryx H. defordi Porvenir A leptomerycid. Previously considered a species of Leptomeryx.[9]
Heteromeryx H. dispar Porvenir An early protoceratid.
Hidrosotherium H. transpecoensis[9] Porvenir A leptomerycid.
Oromeryx O. sp. Porvenir An oromerycid (early camel).
Poabromylus P. kayi Porvenir An early protoceratid.
Protoreodon P. pumilus Porvenir An agriochoerid (claw-bearing oreodont relative).
Pseudoprotoceras P. minor Porvenir An early protoceratid. Previously considered a species of Poabromylus.

Carnivora

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Carnivorans of the Chambers Tuff
Genus / Taxon Species Local fauna Notes Images
Angelarctocyon[1] A. australis Porvenir An indeterminate amphicyonid ("bear-dog").[1] Previously considered a species of Miacis.[10]
Brachyrhynchocyon B. dodgei Little Egypt A daphoenine amphicyonid ("bear-dog"). Formerly known as Daphoenocyon dodgei.[10]
Daphoenictis D. sp. Porvenir[11] A daphoenine amphicyonid ("bear-dog").
Daphoenus D. lambei Porvenir[10][11] A daphoenine amphicyonid ("bear-dog").
Feliformia indet. Little Egypt An 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").[10]
Gustafsonia[1] G. cognita Little Egypt An indeterminate amphicyonid ("bear-dog").[1] Previously considered a species of Miacis.[10]

Eulipotyphla

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Eulipotyphlans of the Chambers Tuff
Genus / Taxon Species Local fauna Notes Images
Centetodon C. chadronensis Porvenir A geolabidid.
Apternodus A. iliffensis Porvenir An apternodontid.

Hyaenodonta

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Hyaenodonts of the Chambers Tuff
Genus / Taxon Species Local fauna Notes Images
Hemipsalodon H. viejaensis[10] Porvenir A hyainailourid.
Hyaenodon H. crucians Porvenir[10] A hyaenodontid.
H. cf. horridus Little Egypt[10]
H. montanus Porvenir[10]
Ischnognathus I. savagei Porvenir[10] A hyainailourid.

Leptictida

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Leptictids of the Chambers Tuff
Genus / Taxon Species Local fauna Notes Images
Leptictis L. douglasi Porvenir A leptictid.
L. wilsoni Little Egypt

Perissodactyla

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Perissodactyls of the Chambers Tuff
Genus / Taxon Species Local fauna Notes Images
Colodon C. stovalli[12] Porvenir,

Little Egypt

 A helaletid (early tapir).
Duchesneodus D. uintensis Porvenir A large horned brontothere.
Haplohippus H. texanus Porvenir An early horse.
Hyracodon H. primus Porvenir,[12]

Little Egypt[12]

 A hyracodontid (lightly-built, pony-like rhino).
Metamynodon M. chadronensis Porvenir[13] An amynodontid (hippo-like rhino).
Mesohippus M. texanus[14] Porvenir,

Little Egypt

 An early three-toed horse.
Penetrigonias P. dakotensis Porvenir An early hornless rhinocerotid (rhino). Reports of Trigonias-like fossils probably represent this species.[12][15]
Protitanops P. curryi Porvenir,

Little Egypt

 A large horned brontothere. Texan fossils of this species were previously described under the dubious name "Menodus bakeri".[16]
Schizotheroides S. jackwilsoni[17] Porvenir,

Little Egypt

 An enigmatic perissodactyl with teeth similar to hyracodontids.
Subhyracodon? S.? sp. Porvenir[12] An early hornless rhinocerotid (rhino). Formerly known as Caenopus.[12]
Toxotherium T. hunteri Porvenir,[12]

Little Egypt[12]

 An enigmatic perissodactyl with a short, broad skull and rhino-like teeth.

Primates

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Primates of the Chambers Tuff
Genus / Taxon Species Local fauna Notes Images
Rooneyia R. viejaensis Porvenir An omomyid (early tarsier relative)

Rodentia

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Rodents of the Chambers Tuff
Genus / Taxon Species Local fauna Notes Images
Adjidaumo A. cf. A. minutus Porvenir An eomyid.
Ardynomys A. occidentalis Porvenir,

Little Egypt

 A cylindrodontid.
Aulolithomys A. bounites Porvenir An eomyid.
A. cf. A. bounites Little Egypt
Cylindrodon C. fontis Little Egypt A cylindrodontid.
Dolocylindrodon D. texanus[18] Porvenir,

Little Egypt

 A cylindrodontid. Previously considered a species of Pseudocylindrodon.[18]
Eutypomys E. inexpectatus[18] Porvenir,

Little Egypt

 A eutypomyid.
Ischyromys I. blacki[18] Porvenir An ischyromyine ischyromyid.
Litoyoderimys L. lustrorum[18] Porvenir An eomyid. Previously considered a species of Yoderimys.[18]
Microparamys M. perfossus[18] Porvenir A paramyine ischyromyid.
Pseudocylindrodon P. neglectus Porvenir,

Little Egypt

 A cylindrodontid.
Pseudotomus P. cf. P. petersoni Porvenir A paramyine ischyromyid. Previously considered a species of Ischyrotomus.[18]
P. johanniculi[18] Porvenir,

Little Egypt

 A paramyine ischyromyid. Previously considered a species of Manitsha.[18]
Quadratomus Q. gigans[18] Porvenir A paramyine ischyromyid. Previously considered a species of Leptotomus.[18]
cf. Simimys cf. Simimys sp. indet. Porvenir A simimyid.
Viejadjidaumo[18] V. magniscopuli[18] Porvenir An eomyid.

See also

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References

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  1. 1 2 3 4 5 6 7 Tomiya, Susumu; Tseng, Zhijie Jack (2016). "Whence the beardogs? Reappraisal of the Middle to Late Eocene ' Miacis ' from Texas, USA, and the origin of Amphicyonidae (Mammalia, Carnivora)". Royal Society Open Science. 3 (10) 160518. Bibcode:2016RSOS....360518T. doi:10.1098/rsos.160518. ISSN 2054-5703. PMC 5098994. PMID 27853569.
  2. 1 2 3 4 5 6 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
  3. 1 2 3 Prothero, Donald R. (1996-06-13), "Magnetostratigraphy of the Eocene-Oligocene transition in Trans-Pecos Texas", in Prothero, Donald R.; Emry, Robert J. (eds.), The Terrestrial Eocene-Oligocene Transition in North America (1 ed.), Cambridge University Press, pp. 189–198, doi:10.1017/cbo9780511665431.010, ISBN 978-0-521-43387-7, retrieved 2026-08-01
  4. ↑ 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.
  5. 1 2 Nyborg, Torrey; Lander, E. Bruce (2022-03-14), "Vertebrate paleontology and Cenozoic depositional environments of Death Valley National Park, California, USA", Field Excursions from Las Vegas, Nevada: Guides to the 2022 GSA Cordilleran and Rocky Mountain Joint Section Meeting, Geological Society of America, pp. 1–22, doi:10.1130/2022.0063(01), ISBN 978-0-8137-0063-2, retrieved 2026-08-02
  6. 1 2 Wilson, John Andrew (1986-12-24). "Stratigraphic Occurrence and Correlation of Early Tertiary Vertebrate Faunas, Trans-Pecos Texas: Agua Fria–Green Valley Areas". Journal of Vertebrate Paleontology. 6 (4): 350–373. Bibcode:1986JVPal...6..350W. doi:10.1080/02724634.1986.10011630. ISSN 0272-4634. JSTOR 4523112.
  7. ↑ Macrini, Thomas E. (2009-12-12). "Description of a digital cranial endocast of Bathygenys reevesi (Merycoidodontidae; Oreodontoidea) and implications for apomorphy-based diagnosis of isolated, natural endocasts". Journal of Vertebrate Paleontology. 29 (4): 1199–1211. Bibcode:2009JVPal..29.1199M. doi:10.1671/039.029.0413. ISSN 0272-4634.
  8. 1 2 3 4 5 Wilson, 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.
  9. 1 2 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.
  10. 1 2 3 4 5 6 7 8 9 10 E. P. Gustafson (1986). "Carnivorous mammals of the Late Eocene and Early Oligocene of Trans-Pecos Texas." Texas Memorial Museum Bulletin 33:1-66
  11. 1 2 Hunt, Robert M. (1996-06-13), "Amphicyonidae", in Prothero, Donald R.; Emry, Robert J. (eds.), The Terrestrial Eocene-Oligocene Transition in North America (1 ed.), Cambridge University Press, pp. 476–485, doi:10.1017/cbo9780511665431.024, ISBN 978-0-521-43387-7, retrieved 2026-08-01
  12. 1 2 3 4 5 6 7 8 Wilson, 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.
  13. ↑ Wilson, J.A.; Schiebout, J.A. (1981). "Early Tertiary Vertebrate Faunas Trans-Pecos Texas: Amynodontidae." The Pearce-Sellards Series, Texas Memorial Museum 33:1-62.
  14. ↑ Forsten, 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.
  15. ↑ Prothero, Donald R. (2005). The evolution of North American rhinoceroses. Cambridge: Cambridge university press. ISBN 978-0-521-83240-3.
  16. ↑ Mihlbachler, Matthew; Prothero, Donald (2021). "Eocene (Duchesnean and earliest Chadronian) brontotheres (Brontotheriidae), Protitanops curryi and cf. Parvicornus occidentalis, from west Texas and Mexico". Palaeontologia Electronica. doi:10.26879/944.
  17. ↑ Schiebout, Judith A. (1977). "Schizotheroides (Mammalia: Perissodactyla) from the Oligocene of Trans-Pecos Texas". Journal of Paleontology. 51 (3): 455–458. ISSN 0022-3360. JSTOR 1303676.
  18. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 A. E. Wood. (1974). "Early Tertiary vertebrate faunas, Vieja Group Trans-Pecos Texas: Rodentia". Texas Memorial Museum Bulletin 21:1-112
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