La Quinta Formation, sometimes referred to as the Simojovel Formation, is a geological formation in Chiapas, Simojovel in Mexico, deposited during the Late Oligocene into the early Miocene. It is the oldest known formation where Mexican amber can be found.
Geology The La Quinta Formation is a part of the larger Simojovel Group, and can be found outcropping near Chiapas in Mexico. It is overlain by the Mazantic Shale, whilst it is underlain by the Rancho Berlin Sandstone.
Members The La Quinta Formation is composed of three fossiliferous members, which are as follows, in stratigraphic order (lowest to highest):
Camino Carretero Member: This member, known to get up to in thickness, is primarily composed of various sandstones. Some of the sandstone layers are noted to be cemented with calcium carbonate, whilst non-calcareous sandstones layers range from brown-ochre to grey weather limoitic fine-grained, alternating massive to thin-bedded fine to coarse-grained brown weathering, coarse-grained arkosic, blue-grey to buff-micaceous fine-grained buff to brown weathering, and buff medium-grained micaceous buff to ochre weathering tuffaceous medium-grained with inter-bedded calcareous rocks. Towards the upper of the member, the various sandstones give way to tuffaceous sandstones, ranging from buff to limonitic or red tuffaceous sandstone, which is inter-bedded with siltstone, to massive silty medium-grained micaceous tuffaceous limonitic weathering sandstone. Throughout this member, shales are also present, starting as a blue-grey calcareous shale in the lower sections of the member, giving way to sandy shale, buff to micaceous-green shale, buff-micaceous silty ochre weathering shale, fissule limonitic shale, and reddish-brown fissile shale towards the middle sections, although almost become completely absent in the upper sections, save for a layer of dark-grey to black shale. Siltstones are also common within the lower sections of the member, ranging from sandy siltstone, buff to ochre-micaceous siltstone, tan siltstone with inter-bedded marly, tan to dark green-grey weathering siltstone to fine-grained sandstone, blue-grey to brown calcareous siltstone to fine-grained sandstone, tuffaceous massive grey limonitic weathering siltstone to medium-grained sandstone, and minor tuffaceous limonitic weathering sandy siltstones. Limestones can also be found, although it is notably uncommon, only being found as thin layers in the lower and upper sections of member.
Florida Limestone Member: This member, known to get up to in thickness, is predominately composed of silty limestone, calcareous shale, sandy limestone. In other outcroppings, the member is also composed of algal limestone, lignitic limestone, and massive white limestone.
Finca Carmitto Member: This member, which is roughly thick, is primarily composed of sandy pebble conglomerate in its lower section, whilst in the upper section it is composed of dark-grey to black rubbly shale and thin light buff-whitish weathering medium-grained calcareous sandstone, which is laminated in nature.
Dating Using U–Pb dating on zircon samples collected from around the upper amber bearing sections, the Mexican amber biota of the La Quinta Formation was constrained to between and .
Paleobiota The biota of the La Quinta Formation is primarily composed of various arthropods, from wasps such as Hyptia deansi, to ostracods as Thalassocypria. It is also home to a wide variety of plants, such as the fabacid Simojoflorum mijangosii.
Insecta
GenusSpeciesNotesImagesHyptia H. deansiEnsign wasp.Schwenckfeldina S. archoicaFungus gnat.Mastotermes M. electromexicusTermite.Termitaradus T. proteraTermite bug.Aphaenogaster A. praerelictaAnt.Dicromantispa D. electromexicanaMantidfly.Leptopharsa L. tacanaeLace bug.Trichoribates T. roynortoniCeratozetid mite.Erpetogomphus E. shiiGomphid dragonfly.Argia Argia sp.Coenagrionid dragonfly.Eulaema E. (Apeulaema) zigrasiApid bee.
Ostracoda
GenusSpeciesNotesImagesThalassocypria T. cumangulus T. electri T. resinae T. nicokarasziCandonid ostracods.Paracypria P. inujimensisCandonid ostracod.Parapontoparta Parapontoparta sp. P. lagranjaeCandonid ostracods.Dolerocypria (?) D. (?) robinsmithiCandonid ostracod.Hemicypris Hemicypris sp.Cypridid ostracod.Edessa E. proteraPentatomid insect.
Copepoda
GenusSpeciesNotesImagesCletocamptus (?) Cletocamptus (?) sp.Harpacticoid copepod.Enhydrosoma Enhydrosoma sp.Harpacticoid copepod.Darcythompsonia Darcythompsonia sp.Harpacticoid copepod.Leptocaris Leptocaris sp.Harpacticoid copepod.
Nematoda
GenusSpeciesNotesImagesOligaphelenchoides O. atreboraAphelenchoidid nematode.Oligodiplogaster O. antiquaDiplogasterid nematode.Vetus V. robustusRhabditid nematode.
Cnidaria
GenusSpeciesNotesImagesColpophyllia C. willoughbiensisMussid coral.Goniopora G. hilliPoritid coral.Porites P. anguillensis P. portoricensis P. waylandiPoritid coral.Siderastrea S. confertaSiderastreid coral.Acropora A. panamensisAcroporid coral.Diploastrea D. crassolamellataDiploastraeid coral.Antiguastrea A. cellulosaMerulinid coral.Goniastrea G. canalisMerulinid coral.Montastraea M. canalis M. endothecataMontastraeid coral.
Flora
GenusSpeciesNotesImagesHymenaea H. mexicana H. allendisLegume fabacids.Simojoflorum S. mijangosiiMimosoid fabacid.Acacia Acacia sp.Mimosoid fabacid.Crudia Crudia sp.Detarioid fabacids.Cedrela Cedrela sp.Meliacid angiosperm.Guarea Guarea sp.Meliacid angiosperm.Pelliciera Pelliciera sp.Tetrameristacid angiosperm.Rhizophora Rhizophora sp.Rhizophoracid angiosperm.Tapiriraizophora T. durhamiiAnacardiacid angiosperm.Ilex Ilex sp.Aquifoliacid angiosperm.Staphylea S. ochoterenaeStaphyleacid angiosperm.Swietenia S. miocenicaMeliacid angiosperm.Picea Picea sp.Pinacid spruce tree pollen.Pinus (?) Pinus (?) sp.Pinacid spruce tree pollen.Podocarpus Podocarpus sp.Podocarpacid tree pollen.Selaginella Selaginella sp.Selaginellacid lycophyte pollen.Sphaeropteris Sphaeropteris sp.Cyatheacid tree fern pollen.Ceratopteris Ceratopteris sp.Pteridacid fern pollen.Pteris Pteris sp.Pteridacid fern pollen.Antrophyum Antrophyum sp.Vittarioid fern pollen.Cryosophila Cryosophila sp.Coryphoid palm tree pollen. Misspelled as Crysophila in Graham, 1999.
Undetermined
GenusSpeciesNotesImagesCletodidae copepod Cletodidae sp.Harpacticoid copepod of uncertain affinities, although is assignable to the family Cletodidae.Laophontidae copepod Laophontidae sp.Harpacticoid copepod of uncertain affinities, although is assignable to the family Laophontidae.Ectinosomatidae (?) copepod Ectinosomatidae (?) sp.Harpacticoid copepod of uncertain affinities, tentatively is assignable to the family Ectinosomatidae.Palmae type 1 ???Palm tree pollen of unknown affinity.Aguiaria type ???Bombacacid pollen of unknown affinity, bears similarities to Aguiaria.Ericaceae pollen ???Ericacid pollen of unknown affinity.Juglandaceae pollen ???Juglandacid pollen of uncertain affinity, either assignable to Alfaroa or Oreomunnea.Myrtaceae pollen ???Myrtacid pollen of uncertain affinity, either assignable to Eugenia or Myrcia.Unknown 1 - 5 ???Pollens of unknown affinity.
See also List of fossiliferous stratigraphic units in Mexico 2017 in arthropod paleontology
References