Sediment Transport and Depositional History from Nested Alluvial Fans to
Flood Plains Using Single-grain Luminescence
Abstract
Critical research questions such as how geomorphic and sedimentary
systems modulate sediment movements and what are the timing, controls,
and duration of significant sediment transport and deposition over
submillennial to millennial timescales are still poorly understood,
especially in the semi-arid Southern California. Although several
sediment tracing and chronometric methods are available to address these
questions, we still do not know well about the dominant controls and
durations of sediment transport from the upper catchment source to the
downstream sink. To examine this issue, here we used luminescence ages
from K-feldspar sand grains from the range-front nested alluvial fans to
the ~12-km-downstream in the flood plains of the Mission
Creek catchment, Southern California. From a total of 29 sediment
samples with >1,400 single grain (175–215 µm sizes)
luminescence ages, we identified at least six depositional periods both
in the upstream and downstream deposits in the catchment with no
significant lag during the Holocene. Additional six significant
depositional periods are also identified during the late Pleistocene
(since the last ~100 ka) in the upstream alluvial fan
deposits. These depositional periods correspond reasonably well with the
late Pleistocene and Holocene intervals of wetter-than-average climate
conditions based on hydroclimatic proxies from nearby locations. We,
therefore, reinforces the concept that climate, especially wetter
intervals, likely plays the first-order control on significant sediment
deposition on submillennial to millennial timescales in the Mission
Creek catchment. We also applied a detailed multi-elevated-temperature
post-IR IRSL (MET-pIRIR) dating and bleaching experiment to examine
whether sediment migration from the upstream to the downstream produces
any significant changes in luminescence measurement (equivalent dose)
signals. Any substantial changes in MET-pIRIR signals will be used to
quantify the sediment movement characteristics (i.e., repeated flooding
and burial events) within the catchment system.