Indiana University-Purdue University Indianapolis (IUPUI) / The evolution of land plant root systems occurred stepwise throughout the
Devonian, with the first evidence of complex root systems appearing in the mid-Givetian.
This biological innovation provided an enhanced pathway for the transfer of terrestrial
phosphorus (P) to the marine system via weathering and erosion. This enhancement is
consistent with paleosol records and has led to hypotheses about the causes of marine
eutrophication and mass extinctions during the Devonian. To gain insight into the
transport of P between terrestrial and marine domains, presented here are geochemical
records from a survey of Middle and Late Devonian lacustrine and near lacustrine
sequences that span some of these key marine extinction intervals. Root innovation is
hypothesized to have enhanced P delivery and results from multiple Devonian sequences
from Euramerica show evidence of a net loss of P from terrestrial sources coincident with
the appearance of early progymnosperms. Evidence from multiple Middle to Late
Devonian sites (from Greenland and northern Scotland/Orkney), reveal a near-identical
net loss of P. Nitrogen and Carbon isotopes from a subset of these lakes confirm elevated
input of terrestrial plant material concurrent with P perturbations. Terrestrial P input
appears to be episodic in nature, suggesting land plant expansion was driven by an
external catalyst in the study region. All sites analyzed are temporally proximal to significant marine extinctions,
including precise correlation with the Kačák extinction event and the two pulses
associated with the Frasnian-Famennian (F/F) mass extinction. The episodic expansion of
terrestrial plants appears to be tied to variations in regional and global climate, and in the
case of the F/F extinction, also to atmospheric changes associated with large scale
volcanism. Using P data presented here as an input into an Earth system model of the
coupled C-N-P-O2-S biogeochemical cycles shows that globally scaled riverine
phosphorus export during the Frasnian-Famennian mass extinction generates widespread
marine anoxia consistent with the geologic record. While timing precludes land plants as
an initiating mechanism in the F/F extinction, these results suggest they are implicated in
every marine extinction event in the Mid to Late Devonian.
| Identifer | oai:union.ndltd.org:IUPUI/oai:scholarworks.iupui.edu:1805/30877 |
| Date | 12 1900 |
| Creators | Smart, Matthew Stephen |
| Contributors | Filippelli, Gabriel, Gilhooly, William III, Barth, Andrew, Wilson, Jeffrey |
| Source Sets | Indiana University-Purdue University Indianapolis |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
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