Precise Dating of Flood-Plain Stratigraphy Using Changes in Tree-Ring Anatomy Following Burial
Abstract
Determination of sediment deposition rates from stratigraphy is typically limited by a scarcity of chronological information. We present a method for precise dating of sedimentary beds based on the change in anatomy of tree rings upon burial. When stems of tamarisk (Tamarix ramosissima)and sandbar willow (Salix exigua) are buried, subsequent annual rings in the buried portions become narrower and vessels within the rings become larger. Observation of these changes can be combined with tree ring counts to determine the year of deposition of sedimentary beds that are at least 10 cm thick. Using a backhoe we dug trenches across the flood plain at three locations along the arroyo of the Rio Puerco, New Mexico. At each cross section we prepared a detailed stratigraphic description and excavated several tamarisks to depths as great as 5 meters. From each excavated tree we cut and sanded 10-50 slabs for tree-ring analysis. We cross-dated slabs within and between plants and used the burial signature in the tree rings to date all sedimentary beds in the stratigraphic profile near each plant. We then used the trench stratigraphy to convert depths of sediment deposition around individual trees to areas of deposition in the cross section. In the lower Rio Puerco introduction of tamarisk in 1926 occurred just prior to the beginning of channel narrowing and arroyo filling. Thus the tamarisks record a process of channel change to which they may have contributed. Aggradation has not been synchronous along the lower arroyo. For example, near Highway 6 and Belen, the flood plain has aggraded more than 2 m since 1970, while there has been little aggradation downstream at Bernardo. Much of the sediment deposition in levies at Highway 6 occurred during a flood in 1988. Future work will document longitudinal variation in the arroyo so that we can convert areas of sediment deposition in cross sections to volumes in the arroyo.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.H31A0234F
- Keywords:
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- 1815 Erosion and sedimentation;
- 1824 Geomorphology (1625);
- 1851 Plant ecology