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The geomorphic dynamics and environmental history of an upper deltaic floodplain tract in the Sacramento–San Joaquin Delta, California, USA
Author(s) -
Brown K. J.,
Pasternack G. B.
Publication year - 2004
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.1088
Subject(s) - overbank , geology , sedimentary depositional environment , delta , radiocarbon dating , floodplain , canyon , deposition (geology) , san joaquin , sediment , geomorphology , geochemistry , physical geography , hydrology (agriculture) , paleontology , soil science , geography , structural basin , cartography , geotechnical engineering , aerospace engineering , engineering
A multi‐proxy approach was used to examine the geomorphic dynamics and environmental history of an upper deltaic oodplain tract in the Sacramento–San Joaquin Delta, California. Three long cores were collected from the McCormack–Williamson Tract (MWT) and these cores were analyzed for bulk density, loss‐on‐ignition, ne (clay and silt) content, Al concentration, magnetic susceptibility, pollen, and charcoal. Radiocarbon dates obtained for the cores were converted into calendar years and an age–depth model was constructed. Long‐term vertical accretion and sedimentation rates were estimated from the age–depth model. Cross‐core relations show that coarse sediment generally accumulates more rapidly and has greater magnetic susceptibility compared to ne sediment. Percentage ne and LOI data show a strong linear relationship that indicates ooding is the primary mechanism for the deposition of particular organic matter on the oodplain and that landscape wash load has contributed a highly consistent fraction of persistent organic matter averaging 5·5 per cent to the site. Down‐core grain size proles show two hydrological domains in the cores, namely millennial ne–coarse uctuations superimposed on general up‐core ning. Coarse sediment is viewed as channel or near‐channel overbank deposits, whereas ne deposits are considered to be distal overbank ood deposits. The coarse–ne uctuations are indicative of changing depositional settings as channels migrated laterally across MWT, whereas the upward ning trend reects a combination of self‐limiting overbank deposition as oodplain elevation increased and decreasing competence as sea‐level rise reduced ood‐pulse energy slopes. MWT has been cross‐cut and incised numerous times in the past, only to have the channels abandoned and subsequently lled by ne sediment. The channels around MWT attained their modern conguration about 4000 years ago. MWT likely came under tidal inuence at about 2500 cal BP. Wetlands have recently developed on MWT, but they are inorganic sediment dominated. Copyright © 2004 John Wiley & Sons, Ltd.