# Malone Formation

The Malone Formation is a geologic formation in Texas. It preserves fossils dating back to the Jurassic period.

## Description

One of the few geological formations in Texas dating to the Jurassic period, the Malone Formation unconformably overlies the Permian Briggs Formation, and laterally changes thickness dramatically from 45 meters on the east side to 325 meters in the northwest part of the Malone Mountains. It has been split into two subdivisions: a lower member containing Idoceras suggesting a Kimmeridgian age, and an upper member containing Kossmatia indicating a Tithonian age. Geochronological analysis of detrital zircon suggests an age of 151±2 Ma for the formation, supporting its dating to the late Jurassic.

### Depositional environment

The Malone Formation represents a fan-delta system in a shallow marine to marginal marine environment, deposited along the northern edge of the Chihuahua trough (a sedimentary basin mostly located in northeast Mexico). Many fossils found in the formation represent marine invertebrates.

## Fossil content

| Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon | Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited. |

### Vertebrates

Remains of vertebrates in this formation are rare and mostly poorly-preserved. Two cycloid fish scales, a pycnodont tooth and bone fragments of 'enaliosaurs' (a classification now obsolete) have been reported from the Malone Formation, but are not well-described.
Vertebrates reported from the Malone Formation :
| Genus | Species | Presence | Material | Notes | Images |
| cf. Plesiosauria | | Northwest Malone Mountains (Jackson Ranch area). | Propodial (TMM 47259–1). | A small, possibly juvenile plesiosaur. | |
| cf. Pliosauridae | | Northwest Malone Mountains (Jackson Ranch area). | Vertebra (TMM 44038–1). | A pliosaur. | |

### Invertebrates
#### Annelids

Annelids reported from the Malone Formation :
| Genus | Species | Presence | Material | Notes |
| Serpula | S. gordialis | 1.5 miles east of Malone station. | Numerous specimens. | A tube worm. |
| Serpula | S. sp. | 1.5 miles east of Malone station. | Multiple specimens. | Larger than S. gordialis. |
| Serpula | S. sp. | 1.5 miles east of Malone station. | 1 specimen now lost. | Distinct from the other Serpula of the formation. |

#### Bivalves

Bivalves reported from the Malone Formation :
| Genus | Species | Presence | Material | Notes |
| Anatina | A. obliquiplicata | 1.5 miles east of Malone station. | 8 specimens. | A duck clam. |
| Anatina | A.? pliculifera | 1.5 miles east of Malone station. | 1 specimen. | A duck clam. |
| Arca | A.? dumbli | 1.5 miles east of Malone station. | 5 specimens. | An ark clam. |
| Arca | A. taffii | 1.5 miles east of Malone station. | 1 specimen. | An ark clam. |
| Astarte | A. breviacola | 1.5 miles east of Malone station. | Numerous specimens. | An astartid. |
| Astarte | A.? craticula | 1.5 miles east of Malone station. | 1 specimen. | An astartid. |
| Astarte | A.? isodontoides | 1.5 miles east of Malone station. | 1 specimen. | An astartid. |
| Astarte | A. malonensis | Various localities in & around Malone Mountain. | Numerous specimens. | An astartid. |
| Astarte | A. posticalva | 1.5 miles east of Malone station. | 21 specimens. | An astartid. |
| Corbula | C.? maloniana | West base of Malone Mountain. | Cast of a right valve. | A corbulid. |
| Cucullaea | C. castilloi | Northwest end of Malone Mountain. | 2 specimens. | A false ark shell. |
| Cucullaea | C. catorcensis | East of Malone Mountain. | 4 casts. | A false ark shell. |
| Cucullaea | C.? texticostata | 1.5 miles east of Malone station. | 1 specimen & a fragment. | A false ark shell. |
| Cucullaea | C. transpecosensis | 1 mile northeast of Malone, El Paso County, Texas. | 1 specimen. | A false ark shell. |
| Craginella | C. goodellii | 2.4 km east for Malone station. | 18 specimens. | A megatrigoniid, originally reported as Trigonia goodelli. |
| Cyprina | C. coteroi | 1.5 miles east of Malone station. | 4 (& 2 doubtful) specimens. | |
| Cyprina | C.? streeruvitzii | 1.5 miles east of Malone station. | 11 incomplete specimens. | |
| Exogyra | E. potosina | West of Malone Mountain. | 6 specimens. | A gryphaeid. |
| Exogyra | E. subplicifera | 1.5 miles east of Malone station. | 19 specimens. | A gryphaeid. |
| Gervillia | G. cinderella | West base of Malone Mountain. | 1 specimen. | A bakevelliid. |
| Gervillia | G. corrugata | 1.5 miles east of Malone station. | 23 imperfect specimens & fragments. | A bakevelliid. |
| Gervillia | G.? riograndensis | West base of Malone Mountain. | 1 specimen. | A bakevelliid. |
| Gryphaea | G. mexicana | Various localities in & around Malone Mountain. | Numerous specimens. | A gryphaeid. |
| Leda | L.? navicula | East slope of Malone Mountain. | Cast of a left valve. | |
| Lima | L. interlineata | 1.5 miles east of Malone station. | Valves & fragments. | A file shell. |
| Lima | L. (Ctenostreon) riograndensis | 1.5 miles east of Malone station. | 1 specimen. | A file shell. |
| Lucina | L.? emarginata | 1.5 miles east of Malone station. | 3 specimens. | A lucinid. |
| Lucina | L. planiuscula | Northwest end of Malone Mountain. | 4 shells & about a dozen casts. | A lucinid. |
| Lucina | L. potosina | 1.5 miles east of Malone station. | 5 specimens. | A lucinid. |
| Lucina | L. potosina var. metrica | Various localities in & around Malone Mountain. | Over 200 specimens. | A lucinid. |
| Martesia | M. maloniana | Various localities in & around Malone Mountain. | Casts. | A piddock. |
| Modiola | M. geniculata | 1 mile east of Finlay station. | A left valve. | A mussel. |
| Modiola | M. maloniana | Various localities in & around Malone Mountain. | 4 specimens. | A mussel. |
| Mytilus | M. nuntius | 1.5 miles east of Malone station. | A well-preserved cast. | A mussel. |
| Ostrea | O. sp. | 1.5 miles east of Malone station. | 3 imperfect valves. | A true oyster. |
| Pecten | P. (Camptonectes) insutus | Various localities in & around Malone Mountain. | About 50 specimens. | A scallop. |
| Pholadomya | P. marcoui | 1.5 miles east of Malone station. | 10 specimens. | A pholadomyid. |
| Pholadomya | P. paucicosta | 1.5 miles east of Malone station, & 2 miles east-southeast from Finlay station. | 27 specimens. | A pholadomyid. |
| Pholadomya | P. praeposita | 1.5 miles east of Malone station. | 4 specimens. | A pholadomyid. |
| Pholadomya | P. tosta | 1.5 miles east of Malone station. | 25 specimens. | A pholadomyid. |
| Pinna | P. quadrifrons | Various localities in & around Malone Mountain. | Numerous specimens. | A pen shell. |
| Pleuromya | P. inconstans | Various localities in & around Malone Mountain. | Numerous specimens. | |
| Pleuromya | P. inconstans var. curta | Southern part of Malone Mountain & 1.5 miles east of Malone station. | Multiple specimens. | |
| Plicatula | P. sportella | 1.5 miles east of Malone station. | 1 specimen. | A plicatulid. |
| Ptychomya | P. stantoni | 1.5 miles east of Malone station. | 23 specimens. | A crassatellid. |
| Tapes | T.? cuneovatus | 1.5 miles east of Malone station. | A right valve. | A venus clam. |
| Thracia | T.? maloniana | 1.5 miles east of Malone station. | 6 specimens. | A thraciid. |
| Trigonia | T. calderoni | 1.5 miles east of Malone station, & a mile east of Finlay station. | 11 specimens. | A trigoniid. |
| Trigonia | T. conferticostata | 1.5 miles east of Malone station. | A shell, 2 valves & fragments. | A trigoniid. |
| Trigonia | T. goodellii | 1.5 miles east of Malone station. | 18 specimens. | Reassigned to Craginella. |
| Trigonia | T. munita | West & east of Malone station. | 3 imperfect specimens & several fragments. | A trigoniid. |
| Trigonia | T. praestriata | East slope of Malone Mountain. | A mold. | A trigoniid. |
| Trigonia | T. proscabra | 1.5 miles east of Malone station. | About 35 specimens. | A trigoniid. |
| Trigonia | T. rudicostata | 1.5 miles east of Malone station. | 2 specimens. | A trigoniid. |
| Trigonia | T. vyschetzkii | 1.5 miles east of Malone station. | Numerous specimens. | A trigoniid. |
| Unicardium | U.? semirotundum | Various localities in & around Malone Mountain. | 12 specimens. | A lucinid. |
| Unicardium | U.? transversum | Various localities in & around Malone Mountain. | 16 specimens. | A lucinid. |

#### Bryozoans

Bryozoans reported from the Malone Formation :
| Genus | Species | Presence | Material | Notes | Images |
| Berenicea | B. maloniana | 1.5 miles east of Malone station. | Colonies. | A bereniceid. | |

#### Cephalopods

Cephalopods reported from the Malone Formation :
| Genus | Species | Presence | Material | Notes |
| Aspidoceras | A. alamitocensis | 1.5 miles east of Malone station. | Portion of a shell. | An ammonite. |
| Nautilus | N. burkarti | West side of the mountain southwest of Malone station. | An imperfect specimen. | A nautiloid. |
| Nautilus | N. naufragus | Northwest end of Malone Mountain. | 2 imperfect specimens. | A nautiloid. |
| Olcostephanus | O. malonianus | 1.5 miles east of Malone station. | A few parts of the whorls. | An ammonite. |
| Oppelia | O.? fallax | 1.5 miles east of Malone station. | Fragmentary specimens. | An ammonite. |
| Perisphinctes | P. aguilerai | Foothills west of Malone Mountain. | 7 fragments. | An ammonite. |
| Perisphinctes | P. clarki | Various localities in & around Malone Mountain. | Multiple specimens. | An ammonite. |
| Perisphinctes | P. felixi | 1.5 miles east of Malone station. | 2 specimens. | An ammonite. |
| Perisphinctes | P. potosinus | 1.5 miles east of Malone station. | Fragment. | An ammonite. |
| Perisphinctes | P. schucherti | Various localities in & around Malone Mountain. | Multiple specimens. | An ammonite. |

#### Corals

Corals reported from the Malone Formation :
| Genus | Species | Presence | Material | Notes | Images |
| Astrocoenia | A. maloniana | 1.5 miles east of Malone, Texas. | 9 specimens. | An astrocoeniid. | |

#### Echinoderms

Echinoderms reported from the Malone Formation :
| Genus | Species | Presence | Material | Notes | Images |
| Holectypus | H.? sp. | East slope of Malone Mountain. | A fragment. | A sea urchin. | |
| Pygurus | P. sp. | West side of Malone Mountain. | A fragment. | A sea urchin. | |

#### Gastropods

Gastropods reported from the Malone Formation :
| Genus | Species | Presence | Material | Notes |
| Acteonina | A.? maloniana | 1.5 miles east of Malone station. | Cast bearing 2 fragments. | An acteonid. |
| Cerithium | C. arcuiferum | 1.5 miles east of Malone station. | 1 specimen. | A cerith. |
| Delphinula | D. stantoni | 1.5 miles east of Malone station. | 5 specimens. | |
| Natica | N. bilabiata | 1.5 miles east of Malone station. | 1 specimen. | A moon snail. |
| Natica | N. finlayensis | Northwest end of Malone Mountain. | 1 specimen. | A moon snail. |
| Natica | N. inflecta | 1.5 miles east of Malone station. | 3 shells. | A moon snail. |
| Natica | N. williamsi | 1.5 miles east of Malone station. | Nearly 100 specimens. | A moon snail. |
| Nerinea | N. circumvoluta | 1.5 miles east of Malone station. | Several specimens. | A nerineid. |
| Nerinea | N. goodellii | 1.5 miles east of Malone station, & southern end of Malone Mountain. | Multiple specimens. | A nerineid. |
| Nerinella | N. stantoni | Various localities in & around Malone Mountain. | Several specimens. | A nerinellid. |
| Nerita | N. finlayensis | Northwest end of Malone Mountain. | 1 specimen. | A nerite. |
| Nerita | N. nodilirata | Lower strata. | 54 specimens. | A nerite. |
| Nerita | N. peroblata | 1.5 miles east of Malone station. | 1 specimen. | A nerite. |
| Pleurotomaria | P. circumtrunca | 1.5 miles east of Malone station. | 11 specimens. | A pleurotomariid. |
| Pseudomelania | P. goodellii | Various localities in & around Malone Mountain. | Multiple specimens. | A pseudomelaniid. |
| Turbo | T.? beneclathratus | 1.5 miles east of Malone station. | 1 specimen. | A turban snail. |
| Turritella | T. burkarti | East slope of Malone Mountain. | 1 specimen. | A turritellid. |
| Vermetus | V. cornejoi | 1.5 miles east of Malone station. | 8 specimens. | A worm shell. |

### Plants

Fossil remains of plants, including driftwood, are abundant in the Malone Formation, but not well preserved.