The Allenby formation is a sedimentary rock formation in British Columbia which was deposited during the Ypresian stage of the Early Eocene. It consists of conglomerates, sandstones with interbedded shales and coal. The shales contain an abundance of insect, fish and plant fossils known from 1877 and onward, while the Princeton Chert was first indented in the 1950s and is known from anatomically preserved plants.
There are several notable fossil producing localities in the Princeton & Tulameen basins. Historical collection sites included Nine Mile Creek, Vermilian Bluffs, and Whipsaw Creek, while modern sites include One Mile Creek, Pleasant Valley, Thomas Ranch, and the Princeton Chert.
Extent and correlation The Allenby is estimated to have an overall extent of approximately , though actual outcroppings of the formation make up less than 1% of the formation, while other exploratory contact is via boreholes and mines. The half-graben which contains the formation is separated into two major depositional basins, the Princeton basin around Princeton, British Columbia and the Tulameen basin centered approximately west. The grabens extensional faults at the eastern side of the basin place the hanging wall Allenby strata in contact with much older foot wall strata of the Nicola Formation which dates to the Upper Triassic.
The Allenby Formation is the southern-most of the Eocene Okanagan Highlands lakes in British Columbia, and second most southern site after the Klondike Mountain Formation of Republic, Washington and northern Ferry County. In British Columbia, the formation is coeval to the Tranquille Formation, known from the McAbee Fossil Beds and Falkland site, the Coldwater Beds, known from the Quilchena site, and Driftwood Canyon Provincial Park. The highlands, including the Allenby Formation, have been described as one of the "Great Canadian Lagerstätten" based on the diversity, quality and unique nature of the biotas that are preserved. The highlands temperate biome preserved across a large transect of lakes recorded many of the earliest appearances of modern genera, while also documenting the last stands of ancient lines.
The warm temperate uplands floras of the Allenby Formation and the highlands, associated with downfaulted lacustrine basins and active volcanism are noted to have no exact modern equivalents, due to the more seasonally equitable conditions of the Early Eocene. However, the formation has been compared to the upland ecological islands in the Virunga Mountains within the Albertine Rift of the African rift valley.
The earliest work in the region was on exploratory expeditions in 1877 and 1878, with fossils collected in the areas of Nine-Mile Creek, Vermilian Bluffs on the Similkameen River, and Whipsaw Creek. While reporting on additional plant fossils collected from British Columbia, Penhallow (1906) noted the likely coeval status of the Princeton basins with many of the sites now considered the Okanagan Highlands. Modern collecting has centered on the areas around One Mile Creek, Pleasant Valley, and Thomas Ranch.
Age The age estimates for the Allenby Formation have varied a number of times since the first explorations happened in the 1870s. Shaw (1952) dated the formation as Oligocene, an age followed by Arnold (1955). Half a decade later, the older age of was first suggested, with a younger age being suggested at in 2000 and an older date of obtained from uranium–lead dating of zircons from Vermilion Bluffs shale in 2005.
Lithology The Allenby is composed of cyclical sedimentation events that were deposited along the course of a river-system in conjunction with depositional areas from nearby lakes and wetlands. Coeval volcanic eruptive events are recorded as interbeds of tephras and lavas, while the riverine course is marked with depositional areas of conglomerates and sandstones. The quieter environments are noted for finer layers of shales and coalified layers.
The coal seams throughout the formation are typically sub-bituminous.
Notable in conjunction with the coal seams are sections of chert which formed during silica rich periods. The rapid cyclical changes from coal to chert and back are not noted in any other fossil locality in the world. An estimated 49 coal-chert cycles are known, though the exact conditions for this process are not well understood. Silica rich volcanic episodes in the region during deposition would have been needed for formation of the cherts, while slowly moving waters and gently subsiding terrains would be needed for the peats and fens to accumulate. Rates of organic deposition in swamps have been estimated at in modern temperate climates, this suggests the time needed for each chert layer would be at least 100 years or more, with the full sequence of cycles taking place over no more than 15,000 years.
Palynoflora Palynological analysis of samples from the Thomas ranch site by Dillhoff et al. (2013) resulted in the identification of 32 pollen and spore types that were assignable to family or genus level, with a total number of distinct pollen and spore types, including unassignable morphotypes, number over 70. The predominant pollens of the site are conifers, which make up between 85%–97% of the total pollens, while the angiosperm pollens are dominated by members of Betulaceae.
Several pteridophyte families and genera are represented as spore fossils alone, without corresponding megafossil records, including Lycopodiaceae, Osmundaceae, and Schizaeaceae. Similarly, at least three additional conifer genera are only present as pollen fossils and up to 12 angiosperms are present in the pollen record. Sometimes considered a Biostratgraphic index fossil, the angiosperm palynospecies Pistillipollenites macgregorii has been recovered from several sites in the Allenby Formation, while the palynospecies Erdtmanipollis pachysandroides is rare, having only been reported from the formation twice.
Family Genus Species Pollen/Macrofossil Notes ImagesAquifoliaceaeIlex UnidentifiedPollenA holly palynomorphArecaceaeSabalCf. †Sabal granopollenitesPollenA palm palynomorphBuxaceae†Erdtmanipollis†Erdtmanipollis pachysandroidesPollenA box family palynomorphBetulaceaeAlnusUnidentifiedPollen & macrofossilsAn alder palynomorph BetulaceaeBetula UnidentifiedPollen & macrofossilsA birch palynomorph BetulaceaeCarpinusUnidentifiedPollenA hornbeam palynomorph BetulaceaeCorylus unidentifiedPollenA hazelnut palynomorph CupressaceaeCunninghamiaunidentifiedPollenA Cunninghamia like palynomorphCupressaceaeSequoiapollenitesUnidentifiedPollen & macrofossilsA redwood palynomorphCupressaceaeTaxodiaceaepollenitesUnidentifiedPollen & macrofossilsA Taxodioideae subfamily palynomorphElaeagnaceaeCf. ElaeagnusUnidentifiedPollenAn elaeagnaceous palynomorph, similar to oleasterEricaceaeunidentifiedUnidentifiedPollenAn ericaceous palynomorph of uncertain affinityFagaceaeCastanea UnidentifiedPollenA chestnut palynomorph Fagaceae†EotrigonobalanusUnidentifiedPollenA fagaceous palynomorph FagaceaeFagus"Fagus Pollen type 3"PollenA beech palynomorph FagaceaeFagus"Fagus Pollen type 2"PollenA beech palynomorph Fagaceae†Paraquercus†Paraquercus eocaenaPollenA fagaceous palynomorph FagaceaeQuercus"Quercus Pollen type 1"PollenAn oak palynomorph, similar to Quercus Group Lobatae pollen FagaceaeQuercus"Quercus Pollen type 2"PollenAn oak palynomorph, ancestral type with Quercus Group Ilex morphology Fagaceae†TrigonobalanopsisUnidentifiedPollenA fagaceous palynomorph FagaceaeUnidentified UnidentifiedPollenA Fagoideceous palynomorphFagaceaeCf. QuercusUnidentifiedPollenA fagaceous palynomorph, similar to oak Ginkgoaceae†Cycadopites†Cycadopites follicularisPollen & macrofossilsA Ginkgo palynomorphHamamelidaceaeLiquidambar UnidentifiedPollenA sweet gum palynomorphJuglandaceaeCaryaUnidentifiedPollenA hickory palynomorph JuglandaceaePterocaryaUnidentifiedPollenA hickory palynomorph LycopodiaceaeLycopodiumUnidentifiedPollenA lycopod palynomorphMalvaceaeTiliaUnidentifiedPollenA linden palynomorphOsmundaceaeOsmundasporitesUnidentifiedPollenAn osmundaceous fern palynomorphPinaceaeAbies UnidentifiedPollen & macrofossilsA fir palynomorph Pinaceae†AlisporitesUnidentifiedPollenA pine family palynomorphPinaceaePiceaUnidentifiedPollenA Picea palynomorphPinaceaePinusUnidentifiedPollen & macrofossilsA Pinus palynomorphPinaceae†PityosporitesUnidentifiedPollen A pine family palynomorphPinaceaePseudolarixUnidentifiedPollen & macrofossilsA Pseudolarix palynomorphPinaceaeTsugaUnidentifiedPollenA Tsuga palynomorphPinaceaeCf. LarixUnidentifiedPollenA Laricoidae palynomorph, similar to larchPinaceaeCf. Pseudotsuga UnidentifiedPollenA Laricoidae palynomorph, similar to pseudotsuga PlatanaceaePlatanusUnidentifiedPollenA Platanus palynomorphPotamogetonaceaePotamogetonUnidentifiedPollenA Potamogeton palynomorphRosaceaeUnidentifiedUnidentifiedPollen & macrofossilsRose famnily palynomorphsSalicaceaeSalixUnidentifiedPollenA willow palynomorphSalviniaceaeAzollaUnidentifiedPollen & macrofossilsAn aquatic fern palynomorphSapindaceaeAcerUnidentifiedPollen & macrofossilsA maple palynomorph SapindaceaeAesculusUnidentifiedPollen & macrofossilsA horse chestnut palynomorph SapotaceaeUnidentified UnidentifiedPollenA sapotaceous palynomorphTaxaceaeTaxusUnidentifiedPollenA yew palynomorphUlmaceaeUlmusUnidentifiedPollen & macrofossilsAn elm palynomorphincertae sedis†Pistillipollenites†Pistillipollenites macgregoriiPollenA palynomorph of uncertain affinity, possibly a Gentianaceae or Euphorbiaceae species
Compression paleobiota A group of six mosses were described from the Allenby Formation by Kuc (1972, 1974) representing the genera Ditrichites, Hypnites and Plagiopodopsis, with two species placed in the morphogenus Muscites. Dillhoff et al. (2013) identified twelve distinct gymnosperm taxa spanning the families Cupressaceae, Ginkgoaceae, and Pinaceae. While being the minority component of the Thomas Ranch flora by total fossil numbers, angiosperms have a higher diversity, with 45 distinct morphotypes represented as foliage, reproductive structures, or both. Seventeen of the morphotypes are identifiable to genus or species, with members of the family Betulaceae being most prominent. At least common one leaf type is suggested to possibly represent an extinct plant order, but has not been described. Only two pteridophyte species have been described from the compression flora, Azolla primaeva by Penhallow (1890) and Equisetum similkamense by Dawson (1878).
The following fossil conifers, pteridophytes, ginkgophytes and bryophytes have been described from the Allenby Formation:
Bryophytes Family Genus Species Authority Notes ImagesAmblystegiaceae†Hypnites†Hypnites jovet-astiae(Kuc) MillerAn amblystegiaceous mossFirst described as Palaeohypnum jovet-asti, moved to Hypnites jovet-astiae in 1980†Hypnites steerei(Kuc) MillerAn amblystegiaceous mossFirst described as Palaeohypnum steerei, moved to Hypnites steerei in 1980Bartramiaceae†Plagiopodopsis†Plagiopodopsis eocenicus(Kuc) MillerA bartramiaceous mossFirst described as Muscites eocenicus, moved to Plagiopodopsis eocenicus in 1980Incertae Sedis†Ditrichites†Ditrichites fylesiKucA ditrichalean moss of uncertain family placement†Muscites†Muscites maycockiKucA moss of uncertain placement†Muscites†Muscites ritchieiKucA moss of uncertain placement
Pteridophytes Family Genus Species Authority Notes ImagesEquisetaceaeEquisetum†Equisetum similkamenseDawsonA scouring rushSalviniaceaeAzolla†Azolla primaeva(Penhallow) ArnoldA mosquito fernFirst described as Azollophyllum primaevum
Gingkophytes Family Genus Species Authority Notes ImagesGinkgoaceaeGinkgoGinkgo bilobaLinnaeusA ginkgo†Ginkgo dissectaMustoe, 2002A ginkgo with highly dissected leaves
Pinophytes Family Genus Species Authority Notes ImagesCupressaceaeChamaecyparis†Chamaecyparis linguaefolia(Lesquereux) MacGinitieA false cypressMetasequoia†Metasequoia occidentalis(Newberry) ChaneyA dawn redwood