| Title | Early-Middle Devonian paleosols and palustrine beds of NW Canada in the context of land plant evolution and global spreads of anoxia |
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| Author | Kabanov, P |
| Source | Global and Planetary Change vol. 204, 103573, 2021 p. 1-25, https://doi.org/10.1016/j.gloplacha.2021.103573  Open Access |
| Image |  |
| Year | 2021 |
| Alt Series | Natural Resources Canada, Contribution Series 20210113 |
| Publisher | Elsevier |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf; html |
| Province | Northwest Territories |
| NTS | 95; 96A; 96B; 96C; 96D; 96E; 96F; 96G; 96H; 96J; 96K; 96L; 96M; 96N; 105I; 105O; 105P; 106A; 106B; 106C; 106F; 106G; 106H; 106I; 106J; 106K; 106M; 106N; 106O; 106P; 107A; 107B; 117A |
| Area | Mackenzie River |
| Lat/Long WENS | -140.0000 -120.0000 69.0000 60.0000 |
| Subjects | environmental geology; geochemistry; paleontology; stratigraphy; Nature and Environment; Science and Technology; Lower Devonian; Middle Devonian; paleosols; wetlands; evolution; paleoenvironment;
depositional environment; isotopic studies; carbon isotopes; oxygen isotopes; diagenesis; bedrock geology; lithology; sedimentary rocks; carbonates; limestones; fossil plants; biostratigraphy; paleogeography; wells; Mackenzie-Peel Plateau; Canadian
Cordillera; Ancestral North America; Laurentia; Laramide Orogeny; outcrops; Phanerozoic; Paleozoic; Carboniferous; Devonian; Silurian; Ordovician; Cambrian |
| Illustrations | location maps; geoscientific sketch maps; cross-sections; profiles; lithologic logs; lithologic sections; photographs; photomicrographs; spectra; plots; tables; biostratigraphic charts |
| Program | GEM-GeoNorth: Geo-mapping for Energy and Minerals |
| Released | 2021 07 08 |
| Abstract | Dozens of subaerial exposure surfaces are assessed in cores from cyclic peritidal carbonates of the Emsian-Eifelian (~410-385 Ma) age. These surfaces range from incipient erosional surfaces to
paleokarst profiles and thick (>1 m) calcretic-clayey paleosols. Palustrine carbonates intervening at multiple levels in same strata are the earliest known occurrence of a typical palustrine facies in a coastal carbonate plain environment. None of
paleokarst and paleosol profiles contain traces of vascular-plant root penetration, and only palustrine facies exhibit swarms of thin rhizoliths. These findings are within the context of Devonian paleosols on marine carbonate substrates where root
traces and laminar calcretes are extremely rare (only 2 reports), and no instances of root penetrations are trackable from unconformities in pre-Givetian carbonate successions. The delta-13C and delta-18O signatures indicate variable diagenetic reset
of isotopic composition. Modest delta-13Cvpdb offset towards lighter values is preserved in two thicker paleosols (-3.4 to -8.0 permille in calcretic matrix vs. -1.35 to -6.5 permille in parent limestone). Such offsets are very rare in pre-Late
Devonian pedogenic carbonates, and their attribution to plant-derived CO2 is dubious. It is inferred that the land surface in calcimagnesian landscapes remained a regolith or primary desert (i.e., was never colonized by tracheophytes) long after the
spread of vascular plants in more favorable wetland settings. Furthermore, the advent of seed reproductive strategy in the latest Devonian and plant adaptations to aridic habitats manifesting in fossil floras only since Pennsylvanian indicate that
much of land surface remained within the realm of primary desert long after the afforestation of wetlands. The direct (plant roots, shoots and spores) and indirect (sedimentary features) fossil records of land greening during the Paleozoic are not
corroborating the hypothesis holding the primordial embryophytic cover on land accountable for the Late Ordovician atmospheric oxygenation-decarbonization event. It is further argued that the evolution of root systems and plant stature could hardly
trigger anoxic events and biotic crises in the Devonian marine realm. |
| Summary | (Plain Language Summary, not published)
Knowledge on the earliest evolutionary steps of vegetated landscapes mostly arrives from the floodplain sedimentary strata, but such deposits are too
scarce in the Early-Middle Paleozoic sedimentary archive. Surfaces of sedimentation breaks in shallow-marine carbonate stata avail much more representative archive of pioneer land ecosystems, and this study demonstrates how much can be learned from
this underused archive. Dozens of subaerial exposure surfaces are assessed in cores from cyclic peritidal carbonates of Devonian (~410-385 Myr) age, including ancient karst profiles and well developed ancient soils (paleosols). Marshland (palustrine)
carbonate deposits intervene at multiple levels in same strata and are the earliest known occurrence of a typical palustrine carbonate in a coastal carbonate-plain environment. None of paleokarst and paleosol profiles contain traces of vascular-plant
root penetration, and only palustrine facies exhibit swarms of thin rhizoliths. These findings are within the context of Devonian paleosols on marine carbonate substrates where root traces and laminar calcretes are extremely rare (only 2 reports),
and no instances are reported from strata older than ~385 Myr. It is inferred that the land surface of carbonate coastal plains remained a regolith or primary desert (i.e., was never colonized by higher plants) long after the spread of vascular
plants in more favorable wetland settings. Furthermore, fossil plant records indicate restriction of vascular plants to humid wetland settings with no tolerance to droughts until at least mid-Carboniferous (~323 Myr). As such, much of land surface
remained within the realm of primary desert long after the afforestation of wetlands which commenced some 394 Myr ago. The direct (plant roots, shoots and spores) and indirect (sedimentary features) fossil records of land greening during the
Paleozoic Era are not corroborating the hypothesis holding the primordial land plant cover accountable for the Late Ordovician atmospheric oxygenation-decarbonization event. It is further argued that the evolution of root systems and plant stature
cannot be a trigger of numerous anoxic events and biotic crises in the Devonian marine realm. |
| GEOSCAN ID | 328381 |
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