and Flooding History in the Southern San Joaquin Valley, California
of Research Project
in terminal lake basins in the Southern San Joaquin Valley including Buena Vista
Lake and Kern Lake preserve a record of the regional climate history and
flooding of the Kern River and other streams feeding the basin. We propose to
collect a series of cores from these lakes and use established geophysical,
geochemical, and lithologic techniques to unravel the regional paleoclimate and
the history of flooding in the area.
goals are important on a societal level. Paleoclimatological studies have made
great strides towards the understanding of natural climate change, a necessary
starting point toward the characterization and mitigation of anthropogenic
global warming. Despite these advances, there is a need for detailed regional
climate records to test a growing family of computer-generated global and
regional climate models.
is a common problem in Kern County as it is in most semi-arid environments. In
fact, many of the students and teachers involved in this research will have
friends or relatives who have been directly affected by such flooding within the
past decade, or have even been affected themselves. Knowledge of natural
flooding frequencies would better our understanding of the effect of
urbanization, agriculture, and the alteration of watercourses on the modern
flooding regime. Furthermore, a time-dependent look at flooding frequencies,
particularly in the context of a paleoclimate record, would aid in the
prediction of flood frequency in light of predicted global warming.
research on both regional paleoclimate and the temporal and spatial distribution
of flooding would provide essential information toward the understanding of
deposition on the Kern River Alluvial Fan. This geomorphologic feature is the
site of the world's most effective water banking projects.
project draws on our expertise in Paleoclimatology and Geochemistry and takes
advantage of CSUB’s already existing research facilities including
laboratories for trace-element analysis and environmental magnetism, and the
CSUB Geotechnology Center. The
project also offers numerous opportunities for student recruitment and learning
at multiple levels particularly due to the multidisciplinary approaches of our
We will achieve a
better understanding of regional paleoclimate and flooding histories through the
objectives listed below (Note: identified in this list are the corresponding
methods which are each discussed in more detail in a following section).
Acquisition and Sampling of Sediments.
(cores from terminal lake basins, upstream flood deposits)
Age Control and Correlation of Cores. (14C,
tephrochronology, paleomagnetism, environmental magnetism)
Acquisition of Climate Records (ostracode
paleontology, geochemistry, lithologic/petrographic description, environmental
Reconstruction of Flooding History (lithologic/petrographic
description, granulometry, environmental magnetism)
Provenance Determination (lithologic/petrographic
description, geochemistry of clastic fraction, environmental magnetism)
southern San Joaquin Basin is an active sedimentary basin located in
south-central California at the southern end of the Great Valley (Fig. 1). Its Quaternary sediments are dominated by the
Kern River Alluvial Fan and its terminal lakes, Kern Lake and Buena Vista Lake.
This is presently a closed system. However, in extremely wet years prior to the
construction of the modern irrigation system, Buena Vista Lake overflowed into
Tulare Lake and the San Joaquin River system.
Quaternary deposits in this system are reviewed in Hoots et
al. (1954), Wood et al. (1964),
Dale et al. (1966), Croft (1972), Page
(1986) and Bartow (1991). Briefly, the geological setting is as follows.
Although the dominant source of sediment are weathered crystalline basement and
batholithic rocks from the southern Sierra Nevada catchment areas of the Kern
River and Caliente Creek, the terminal lakes also receive input from the Coast
Ranges to the west and the San Emigdio Mountains to the south. Clasts from these
latter sources dominantly consist of weathered marine sediments. Thus the
sediments from these source area are, in principle, distinguishable using the
methods described below.
few exceptions (e.g., Atwater et al.,
1986; Davis, 1999) regional paleoclimate studies have been restricted to areas
outside of the southern San Joaquin Valley (e.g., Mehringer, 1986; Scuderi,
1993; Smith et al., 1997; Benson,
1999; Clark et al., 1999; Hendy and
Kennett, 1999; Rose and Wigand, 1999; Whitlock and Grigg, 1999; Negrini, in
press). Consistent with these studies, we expect to acquire paleoclimate records
from Kern and Buena Vista lakes which reflect the high amplitude changes
associated with Milankovitch-scale (>10,000 yr periods) global climate change
and millennial scale global climate change (1,00-10,000 yr periods) and
possibly, lower amplitude changes associated with
We also expect to recover a record of flooding events, perhaps reflecting a dynamic character in the frequency of flooding due to climate change. For example, higher temperatures observed in western Pacific waters in the middle Holocene (Gagan et al., 1998) suggests more powerful El Niño events during this time of generally warmer global climate. Furthermore, the northward advancement of summer monsoonal storms expected during the middle Holocene would have enhanced flooding in the southern San Joaquin Valley. Regardless of the mechanism, if increased flooding is observed during the middle Holocene interval of slightly elevated temperature, this would predict local effects of global warming of particular interest to local high school students and teachers involved in this project.
1. Sediment properties will be mainly governed by
climate change. We anticipate observing changes in these properties resulting
from the following:
a. Long-term Milankovitch-scale climate change (e.g., OIS stages 1-5 will
b. Higher frequency, millennial-scale climate change reflecting GISP2
archetypical record of global climate change. This may possibly
throughout entire record including Holocene though it should be more pronounced
in Pleistocene when amplitudes of change were higher.
Flooding history will be uncovered and will also be governed by climate change.
If flooding is more related to summer monsoonal storms, then expect higher
frequency during mid-Holocene. If not, then higher frequency flooding will
follow stadial conditions.
Acquisition of Cores and Flood Deposits.
Core sites will be selected primarily on scientific merit but also based on
availability of access. Over the course of this project we plan to acquire at
least six cores. One core will come from near the depocenter of each lake, one
from near the margin of the lake toward each provenance source (e.g., toward and
away from the Sierra Nevada). For coring we will use a Giddings 25-SCT (Model HD65RPST) coring rig purchased with
funds from this grant. One of the investigators (RN) has experience with one of
these rigs. They are capable of acquiring oriented 4-inch core in lacustrine
sediments to depths of 70 feet.
Transparent plastic liners will be used in all cases. Drillers notes will
be taken on site including top and bottom depths for each drive, percent
recovery, position of recovered core relative to enclosing plastic liner, and
visual description of lithology as possible through core sleeve. Core segments
will be sealed with plastic caps, labeled with name and depths, and shipped to
holding facility (refrigerated room at CSUB). A full suite of analyses will be
done on core samples as described in the subsequent segments of the method
will sample directly deposits from floods occurring in the last several years in
streambeds and floodplains from all catchments feeding Kern and Buena Vista
Lakes. These samples will be described petrographically and analyzed for
elemental abundances and environmental magnetism attributes as described in the
|Visual Description and Sampling of Cores.
Within one month of acquisition, cores will be sampled. First, magnetic
susceptibility will be measured using the pass through susceptibility meter.
Second, the plastic liners will be cut in half parallel to the core axes and the
cores will be exposed and split with a potter's wire. Third, the lithology of
the cores will be described in detail followed by photographs. Fourth, adjacent
2 x 2 x 2 cm samples will be extracted from one of the core splits and stored in
plastic boxes of the same shape. Half of each core will be archived whole.
Because the measurement of sediment magnetism is a non-destructive process, it
will be done first. One set of boxed samples will be measured a Spinner
magnetometer at the CSUB paleomagnetics laboratory after cleaning in that
facility's Molspin AF demagnetizer. This procedure will likely result in a
record of the earth's paleomagnetic field vector for this site. Because this
information is well constrained for western North America for the time interval
represented by our cores (Negrini and Davis, 1992; Lund, 1996; Bradley, 1999),
this record potentially constrains age control. The magnetism of this suite of
samples will be remeasured after being subjected to various anysteretic and
isothermal remnant magnetizations (e.g., ARM, SIRM, IRM, backfield IRM). This
latter set of procedures will constrain the concentration, mineralogy, and
grain-size of the magnetic carrier grains which have proven to be useful
parameters regarding the environment of sediment deposition and, hence, the
detection of paleoclimate change and flooding history (e.g., Oldfield and
Thompson, 1986; Peck et al., 1994;
Negrini et al., 2000). The
environmental magnetism parameters will also be useful in the correlation of
cores taken from nearby sites.
A split of one set of boxed samples will be used for ostracode paleontological
and paleoecological analyses as per the procedures outlined in Palacios-Fest et
al. (1993). First, ostracodes will be separated from the sediments and then
the relative percentages of taxa will be determined and the condition of the
shells will be described (e.g., degree of encrustation) for each sample. The
former set of data will be expressed in terms of a salinity index wherein a
ratio is calculated which compares weighted abundances of salinophile species
with weighted abundances of species which prefer fresh water. This parameter has
proven useful in determining lake salinity which, in turn, is often closely
related to lake depth (e.g., Cohen et al.,
|Granulometry and Petrographic Description. Another split of one set of boxed samples will
be analyzed for grain size. The coarse fraction will be removed in a sieve and
described under petrographic microscope in order to help constrain provenance.
The remaining fine fraction will be passed through a particle size analyzer
recently purchased by CSUB. The grain-size spectrum will help us to constrain
lake depth and "event" input (e.g., pulses of coarse sediment from
floods and/or turbidity flows).
Analysis. Another split of one set of boxed samples will
be analyzed for total organic (TOC) and total inorganic (TIC) carbon using the
loss-on-ignition method. The remaining fraction of sediment after this procedure
will be dissolved in a microwave digester and analyzed for major and
trace-element abundances in CSUB's Perkin-Elmer Elan 6100 ICP-MS instrument.
Finally, elemental abundances of ostracode will also be measured in the ICP-MS.
This set of geochemical data should allow us to constrain several environmental
conditions at the time of deposition including depth, salinity, and temperature
of water, and also, provenance and diagenetic history.
This material is based upon work supported by the National Science Foundation under Grant No. 0303324.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
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