A multi-proxy assessment of terrace formation in the lower Trinity River valley, Texas
A proposed null hypothesis for fluvial terrace formation is that internally generated or autogenic processes, such as lateral migration and river-bend cutoff, produce variabilities in channel incision that lead to the abandonment of floodplain segments as terraces. Alternatively, fluvial terraces ha...
Saved in:
| Published in: | Earth surface dynamics Vol. 10; no. 3; pp. 635 - 651 |
|---|---|
| Main Authors: | , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Gottingen
Copernicus GmbH
28-06-2022
Copernicus Publications |
| Subjects: | |
| Online Access: | Get full text |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | A proposed null hypothesis for fluvial terrace formation is that
internally generated or autogenic processes, such as lateral migration and
river-bend cutoff, produce variabilities in channel incision that lead to the
abandonment of floodplain segments as terraces. Alternatively, fluvial
terraces have the potential to record past environmental changes from
external forcings that include temporal changes in sea level and
hydroclimate. Terraces in the Trinity River valley have been previously
characterized as Deweyville groups and interpreted to record episodic cut
and fill during late Pleistocene sea level variations. Our study uses
high-resolution topography of a bare-earth digital elevation model derived
from airborne lidar surveys along ∼ 88 linear kilometers of the modern
river valley. We measure both differences in terrace elevations and widths
of paleo-channels preserved on these terraces in order to have two
independent constraints on terrace formation mechanisms. For 52 distinct
terraces, we quantify whether terrace elevations fit distinct planes –
expected for allogenic terrace formation tied to punctuated sea level and/or
hydroclimate change – by comparing variability in a grouped set of
Deweyville terrace elevations against variability associated with randomly
selected terrace sets. Results show Deweyville groups record an initial
valley floor abandoning driven by allogenic forcing, which transitions into
autogenic forcing for the formation of younger terraces. For these different
terrace sets, the slope amongst different terraces stays constant. For 79
paleo-channel segments preserved on these terraces, we connected observed
changes in paleo-channel widths to estimates for river paleo-hydrology over
time. Our measurements suggest the discharge of the Trinity River increased
systematically by a factor of ∼ 2 during the late Pleistocene.
Despite this evidence of increased discharge, the similar down-valley slopes
between terrace sets indicate that there were likely no increases in
sediment-to-water discharge ratios that could be linked to allogenic terrace
formation. This is consistent with our elevation clustering analysis that
suggests younger terraces are indistinguishable in their elevation variance
from autogenic terrace formation mechanisms, even if the changing
paleo-channel dimensions might, viewed in isolation, provide a mechanism for
allogenic terrace formation. Methods introduced here combine river-reach-scale observations of terrace sets and paleo-hydrology with local
observations of terraces and paleo-channels to show how interpretations of
allogenic versus autogenic terrace formation can be evaluated within a
single river system. |
|---|---|
| ISSN: | 2196-632X 2196-6311 2196-632X |
| DOI: | 10.5194/esurf-10-635-2022 |