Allenby Formation

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 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 dated the formation as Oligocene, an age followed by Arnold. 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

of samples from the Thomas ranch site by Dillhoff et al. 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	Images
Aquifoliaceae	Ilex	Unidentified	Pollen	A holly palynomorph
Arecaceae	Sabal	Cf. †Sabal granopollenites	Pollen	A palm palynomorph
Buxaceae	†Erdtmanipollis	†Erdtmanipollis pachysandroides	Pollen	A box family palynomorph
Betulaceae	Alnus	Unidentified	Pollen & macrofossils	An alder palynomorph
Betulaceae	Betula	Unidentified	Pollen & macrofossils	A birch palynomorph
Betulaceae	Carpinus	Unidentified	Pollen	A hornbeam palynomorph
Betulaceae	Corylus	unidentified	Pollen	A hazelnut palynomorph
Cupressaceae	Cunninghamia	unidentified	Pollen	A Cunninghamia like palynomorph
Cupressaceae	Sequoiapollenites	Unidentified	Pollen & macrofossils	A redwood palynomorph
Cupressaceae	Taxodiaceaepollenites	Unidentified	Pollen & macrofossils	A Taxodioideae subfamily palynomorph
Elaeagnaceae	Cf. ''Elaeagnus	Unidentified	Pollen	An elaeagnaceous palynomorph, similar to oleaster
Ericaceae	unidentified	Unidentified	Pollen	An ericaceous palynomorph of uncertain affinity
Fagaceae	Castanea	Unidentified	Pollen	A chestnut palynomorph
Fagaceae	†Eotrigonobalanus	Unidentified	Pollen	A fagaceous palynomorph
Fagaceae	Fagus	"Fagus Pollen type 3"	Pollen	A beech palynomorph
Fagaceae	Fagus	"Fagus Pollen type 2"	Pollen	A beech palynomorph
Fagaceae	†Paraquercus	†Paraquercus eocaena	Pollen	A fagaceous palynomorph
Fagaceae	Quercus	"Quercus Pollen type 1"	Pollen	An oak palynomorph, similar to Quercus Group Lobatae pollen
Fagaceae	Quercus	"Quercus Pollen type 2"	Pollen	An oak palynomorph, ancestral type with Quercus Group Ilex morphology
Fagaceae	†Trigonobalanopsis	Unidentified	Pollen	A fagaceous palynomorph
Fagaceae	Unidentified	Unidentified	Pollen	A Fagoideceous palynomorph
Fagaceae	Cf. Quercus	Unidentified	Pollen	A fagaceous palynomorph, similar to oak
Ginkgoaceae	†Cycadopites	†Cycadopites follicularis	Pollen & macrofossils	A Ginkgo palynomorph
Hamamelidaceae	Liquidambar	Unidentified	Pollen	A sweet gum palynomorph
Juglandaceae	Carya	Unidentified	Pollen	A hickory palynomorph
Juglandaceae	Pterocarya	Unidentified	Pollen	A hickory palynomorph
Lycopodiaceae	Lycopodium	Unidentified	Pollen	A lycopod palynomorph
Malvaceae	Tilia	Unidentified	Pollen	A linden palynomorph
Osmundaceae	Osmundasporites	Unidentified	Pollen	An osmundaceous fern palynomorph
Pinaceae	Abies	Unidentified	Pollen & macrofossils	A fir palynomorph
Pinaceae	†Alisporites	Unidentified	Pollen	A pine family palynomorph
Pinaceae	Picea	Unidentified	Pollen	A Picea palynomorph
Pinaceae	Pinus	Unidentified	Pollen & macrofossils	A Pinus palynomorph
Pinaceae	†Pityosporites	Unidentified	Pollen	A pine family palynomorph
Pinaceae	Pseudolarix	Unidentified	Pollen & macrofossils	A Pseudolarix palynomorph
Pinaceae	Tsuga	Unidentified	Pollen	A Tsuga palynomorph
Pinaceae	Cf. Larix	Unidentified	Pollen	A Laricoidae palynomorph, similar to larch
Pinaceae	Cf. Pseudotsuga	Unidentified	Pollen	A Laricoidae palynomorph, similar to pseudotsuga
Platanaceae	Platanus	Unidentified	Pollen	A Platanus palynomorph
Potamogetonaceae	Potamogeton	Unidentified	Pollen	A Potamogeton palynomorph
Rosaceae	Unidentified	Unidentified	Pollen & macrofossils	Rose famnily palynomorphs
Salicaceae	Salix	Unidentified	Pollen	A willow palynomorph
Salviniaceae	Azolla	Unidentified	Pollen & macrofossils	A duck weed palynomorph
Sapindaceae	Acer	Unidentified	Pollen & macrofossils	A maple palynomorph
Sapindaceae	Aesculus	Unidentified	Pollen & macrofossils	A horse chestnut palynomorph
Sapotaceae	Unidentified	Unidentified	Pollen	A sapotaceous palynomorph
Taxaceae	Taxus	Unidentified	Pollen	A yew palynomorph
Ulmaceae	Ulmus	Unidentified	Pollen & macrofossils	An elm palynomorph
incertae sedis	†Pistillipollenites	†Pistillipollenites macgregorii''	Pollen	A palynomorph of uncertain affinity, possibly a Gentianaceae or Euphorbiaceae species