DYNAMICS OF DEPOSITION AND FOSSIL PRESERVATION AT THE EARLY EOCENE OKANAGAN HIGHLANDS OF BRITISH COLUMBIA, CANADA: INSIGHTS FROM ORGANIC GEOCHEMISTRY
Author:
LOWE ALEXANDER J.1, DIEFENDORF AARON F.2, SCHLANSER KRISTEN M.2, SUPER JAMES3, WEST CHRISTOPHER K.4, GREENWOOD DAVID R.5
Affiliation:
1. 1 Department of Biology, University of Washington, 24 Kincaid Hall, Seattle, Washington 98195, USA 2. 2 Department of Geology, University of Cincinnati, Cincinnati, Ohio 45221, USA 3. 3 Department of Earth and Planetary Sciences, Yale University, New Haven, Connecticut 06511, USA 4. 4 Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, AB, Canada, T6G 2E3 5. 5 Department of Biology, Brandon University, 270 18th Street, Brandon, MB, Canada, R7A 6A9
Abstract
ABSTRACT
The early Eocene Okanagan Highland fossil sites of Washington (USA) and British Columbia (Canada) contain exquisitely preserved plant and insect fossils that showcase a critical time and place in the evolution of the Northern Hemisphere temperate deciduous biome. A comprehensive understanding of the dynamics of fossil deposition and preservation at these sites is not fully resolved but is critical for reliable reconstructions of these ancient forests. To expand on previous interpretations (e.g., deep, stratified, anoxic lake bottoms) and address uncertainties about the environment of deposition (e.g., distance to shore, influence of diatoms), we analyzed sediment samples from three Okanagan Highland fossil sites—McAbee, Falkland, and Driftwood Canyon—for organic biomarkers, their stable carbon isotopic compositions, and glycerol dialkyl glycerol tetraethers (GDGTs; at McAbee only). Terpenoids suggest relative trends in gymnosperm abundance between sites that agree with prior macrofossil evidence, though absolute values may overestimate local gymnosperm abundance. A combination of biomarker evidence indicates a predominantly autochthonous aquatic source (e.g., diatoms) for organic matter in shale and mudstone samples, even contributing to long chain n-alkanes and likely to branched GDGTs, which are often assumed to be terrestrially sourced. In combination with biomarker evidence for anoxia and stratification, fossiliferous shales are interpreted to have been deposited offshore in deep and mesotrophic lakes that were thermally stratified with an anoxic hypolimnion, away from in-flowing tributaries, while a coal horizon at Driftwood Canyon was deposited in a shallower, eutrophic, anoxic wetland. Anoxic conditions likely minimized some degradation-based biases and promoted high quality fossil preservation. Deposition of sediment and fossil remains offshore and away from inflowing tributaries suggest fossil plants were locally sourced but highlights the need for careful consideration of transport-induced biases.
Publisher
Society for Sedimentary Geology
Subject
Paleontology,Ecology, Evolution, Behavior and Systematics
Reference119 articles.
1. Albro,
P.W.,
1976,
Bacterial waxes,
inKolattukudyP.E.(ed.),Chemistry and Biochemistry of Natural Waxes:
Elsevier,
Amsterdam,
p.419–
445. 2. Andrae,
J.W.,
McInerney,
F.A.,
and
Sniderman,J.M.K,
2020,
Carbon isotope systematics of leaf wax n-alkanes in a temperate lacustrine depositional environment:
Organic Geochemistry,
v.150,
p.104121,
doi: 10.1016/j.orggeochem. 2020.104121. 3. Archibald,
S.B.,
Bossert,
W.H.,
Greenwood,
D.R.,
and
Farrell,B.D,
2010,
Seasonality, the latitudinal gradient of diversity, and Eocene insects:
Paleobiology,
v.36,
p.374–
398,
doi: 10.1666/09021.1. 4. Archibald,
S.B.,
Greenwood,
D.R.,
and
Mathewes,R.W.,
2013,
Seasonality, montane beta diversity, and Eocene insects: testing Janzen's dispersal hypothesis in an equable world:
Palaeogeography, Palaeoclimatology, Palaeoecology,
v.371,
p.1–
8,
doi: 10.1016/j.palaeo. 2012.10.043. 5. Archibald,
S.B.,
Greenwood,
D.R.,
Smith,
R.Y.,
Mathewes,
R.W.,
and
Basinger,J.F.,
2011,
Great Canadian Lagerstätten, 1, early Eocene Lagerstätten of the Okanagan Highlands (British Columbia and Washington State):
Geoscience Canada,
v.38,
p.155–
164.
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