Eocene Okanagan Highlands

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Outcrop of the Klondike Mountain Formation

The Eocene Okanagan Highlands or Eocene Okanogan Highlands are a series of

Paleocene–Eocene thermal maximum, and before the increased cooling of the middle and late Eocene to Oligocene. The fossiliferous deposits of the region were noted as early as 1873, with small amounts of systematic work happening in the 1870–1920s on British Columbian sites, and 1920–1930s for Washington sites. Focus and more detailed descriptive work on the Okanagan Highland
sites started in the late 1960s.

Extent

Temporal correlation to select North American Formations

The majority of the paleolake deposits are

Boundary District along the Canada–United States border.[3]

There is debate as to the affiliation of the, now lost, Quesnel sites with the Greater Okanagan Highlands. Archibald et al (2018) in the monograph overview of the Highlands Hymenoptera included them as part of the series. However the certainty for the placement was later questioned by Archibald and Cannings (2022) who opted to tentatively exclude Quesnel from the highlands while discussing the history of field collecting in the region.[4]

History

George Mercer Dawson in 1885

The earliest geological work in south and central British Columbian sites was during exploratory expeditions under the leadership of

Edward Wilber Berry. The insects were first detailed by Samuel Hubbard Scudder, with follow-up papers by Anton Handlirsch.[8] 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.[9] The first brief work on fish from the Highlands occurred with the 1893 report by Edward Drinker Cope on several fish sent to him by George Dawson from the Tranquille and Princeton areas. While Cope deemed the Tranquille specimens too incomplete to identify, he did provide the description for "Amyzon" brevipinne from the Similkameen River fossils.[10][11]

Wesley Wehr in 1998

Columbia River Basalts.[15] This similarity was again noted by Chester A. Arnold during his review of the conifer flora associated with the Princeton basin. Arnold noted the Allenby sites shared over half of the taxa that had been previously reported from Republic.[16]

Starting in the early 1960s and extending through the 1980s were a series of papers on the British Columbian sites combining palynology and the newly devised process of

potassium–argon dating to better understand the geochronology of the sites.[8] The first report of K–Ar dating at a group of sites was by Glenn E. Rouse and William H. Mathews (1961) who tested biotite samples from four locations. They sampled volcanic ashes from Princeton and Rock Creek; a Trachyte flow from Savona Mountain and a diabase flow or sill from Tranquille, returning results of 49 to 45 million years ago, then classified as Early Middle Eocene. They noted the very distinct similarities with the Republic flora, as Arnold had, and posited that the Republic fossils were of the same age, and not Oligocene as then considered. Based on the estimated age, the sites were noted to be coeval with the Green River Formation but that the floras of the two regions were drastically different, and that more study was needed.[17]

The term "Okanagan Highlands" for Eocene formations of the region was coined by

Lagerstätten"[1] 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.[1]

Preservation types

Princeton Chert and "Ashnola shale" interbeds

The majority of formations in the Eocene Okanagan Highlands preserve compression fossils in sandstone to shale rock deposited from lake environments where seasonal mixing and anoxia were prevalent. Additionally, two important non-compression biotas are present in the Eocene Okanagan Highlands: A permineralized

subbituminous coal of the Hat Creek Coal Formation around Hat Creek hosts an amber fauna, the Hat Creek amber which preserves many small insects that would likely not be found in the compression biotas.[21]

Paleoclimate

Virunga Mountains over Lake Edward

Based on paleobotanical proxies and

geochemical data, the highlands are thought to have been between 500–1,500 m (1,600–4,900 ft) in elevation, placing them similar to or higher than the modern sites.[22] Estimates of the mean annual temperature have been derived from climate leaf analysis multivariate program (CLAMP) analysis and leaf margin analysis (LMA) of both the Princeton and Republic paleofloras. The CLAMP results, after multiple linear regressions for Republic, gave a mean annual temperature of approximately 8.0 °C (46.4 °F), while the LMA gave 9.2 ± 2.0 °C (48.6 ± 3.6 °F). Princeton's multiple linear regression CLAMP results gave a slightly lower 5.1 °C (41.2 °F), and the LMA returned a mean annual temperature of 5.1 ± 2.2 °C (41.2 ± 4.0 °F). This is lower than the mean annual temperature estimates given for the coastal Puget Group, which is estimated to have been between 15–18.6 °C (59.0–65.5 °F). The bioclimatic analysis for Republic and Princeton suggest mean annual precipitation amounts of 115 ± 39 cm (45 ± 15 in) and 114 ± 42 cm (45 ± 17 in) respectively.[23]

The warm temperate uplands floras of 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 highlands have been compared to the upland ecological islands in the Virunga Mountains within the Albertine Rift of the African rift valley.[24]

Paleobiota

Main articles: Paleofauna of the Eocene Okanagan Highlands and Paleoflora of the Eocene Okanagan Highlands

The Eocene Okanagan Highlands hosted a diverse mix of temperate and tropical paleobiotic elements,[22] with the forests having the first significant proportions of temperate plants in North America.[25]

The paleobotanical community was a mixture of plants found in subtropical evergreen and temperate deciduous forests.[22] Included in the forest were a number of important modern temperate flowering plant families such as Betulaceae, Rosaceae, and Sapindaceae, plus the conifer family Pinaceae. Study of the deciduous plants from the highlands has documented the occurrence of heteromorphic leaves derived from sun versus shade conditions and long shoot or short shoot buds.[25] The paleobotanical community of the Republic area has been noted as the most diverse floral community of the Okanagan Highlands, with some estimates ranging to over 68 families and 134 genera being present.[26]

References

  1. ^ a b c Archibald, S.; Greenwood, D.; Smith, R.; Mathewes, R.; Basinger, J. (2011). "Great Canadian Lagerstätten 1. Early Eocene Lagerstätten of the Okanagan Highlands (British Columbia and Washington State)". Geoscience Canada. 38 (4): 155–164.
  2. ^
    doi:10.1139/E04-095
    .
  3. ^ Höy, T.; Friedman, R.; Gabites, J. Paleogene Penticton Group, Boundary area, Southern British Columbia (Parts of NTS 082E): Geochronology and Implications for Precious Metal Mineralization (PDF) (Report). Geoscience BC Summary of Activities 2020: Minerals, Geoscience BC, Report 2021-01. Geoscience BC. pp. 55–66. Retrieved 5 November 2022.
  4. S2CID 250035713
    .
  5. ^ Selwyn, A. (1879). "Summary report of the operations of the Geological Corps, to 31st December, 1878". Geological Survey of Canada, Report of Progress for. 1877–1878: 4.
  6. ^ Scudder, S. (1877). "Appendix to Mr. George M. Dawson's report. The insects of the Tertiary beds at Quesnel". Geological Survey of Canada, Report of Progress for. 1875–1876: 266–280.
  7. ^ Scudder, S. H (1879). "Appendix A. The fossil insects collected in 1877, by Mr. G.M. Dawson, in the interior of British Columbia". Geological Survey of Canada, Report of Progress for. 1877–1878: 175–185.
  8. ^
    doi:10.1139/cjes-2015-0177
    .
  9. ^ Penhallow, D.P. (1908). "A report on Tertiary plants of British Columbia, collected by Lawrence M. Lambe in 1906 together with a discussion of previously recorded Tertiary floras". Report 1013. Canada Department of Mines, Geological Survey Branch. pp. 1–167.
  10. ^ Cope, E. (1893). "Fossil fishes from British Columbia". Proceedings of the Academy of Natural Sciences of Philadelphia. 45: 401–402.
  11. doi:10.1080/14772019.2021.1968966
    .
  12. ^ Umpleby, J. B. (1910). "Geology and ore deposits of Republic mining district". Washington Geological Survey. 1.
  13. doi:10.5479/si.00963801.52-2177.235
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  14. doi:10.3133/pp154H
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  15. doi:10.3133/pp186J
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  16. ^ Arnold, C. A. (1955). "Tertiary conifers from the Princeton coal field of British Columbia" (PDF). University of Michigan: Contributions from the Museum of Paleontology. 12: 245–258.
  17. S2CID 35856387
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  18. ^ Wehr, W.; Schorn, H. (1992). "Current research on Eocene conifers at Republic, Washington". Washington Geology. 20 (2): 22–23.
  19. doi:10.1139/e05-012
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  20. hdl:1807/73571
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  21. S2CID 90017208
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  22. ^
    S2CID 236890548
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  23. doi:10.1139/e04-100
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  24. S2CID 225050834
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  25. ^
    hdl:1807/71962
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  26. doi:10.1139/e04-072
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