USGS Open-File Report 96-293 USGS visual identity and link to main Web site

Sediment Magnetic, Paleomagnetic, and Geochemical Data from Quaternary Lacustrine Sediment in two Cores from Tule Lake, Siskiyou County, California

U.S. Geological Survey Open-File Report 96-293

by By Patti J. Best1, Richard L. Reynolds1, Joseph G. Rosenbaum1, Walter Dean1, Jeannine Honey1, John Drexler2, and David P. Adam3

1 U.S. Geological Survey, Denver, Colorado
2 University of Colorado, Boulder, Colorado
3 U.S. Geological Survey, Menlo Park, California

This report is preliminary and has not been reviewed for conformity with U. S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Introduction

As part of the U.S. Geological Survey's Global Change and Climate History Program, sediment magnetic and geochemical results have been obtained from the top 60 meters of lacustrine sediments recovered in two cores from Tule Lake in northern California. The sediment magnetic and geochemical data, presented here in tabular form, complement studies of diatoms and pollen in the cores that are the bases for published paleoclimatic interpretations (Adam and others, 1989; Bradbury, 1991). Comparisons of magnetic mineral and geochemical records to the existing climate records may provide insight into the response of lake-watershed system to climate change (e.g., Rosenbaum and others, 1996). This report also documents the methods used to obtain the magnetic properties and geochemical data. Adam and others (1989) describe the site, the drilling methods, and lithology of the lacustrine sediments.

Methods

Sampling (Table 1): Samples used for magnetic susceptibility and laboratory induced magnetizations were taken approximately every 5 cm. Samples, approximately 8 cm3 in volume and representing about 2 cm of depth in the core, were carved from the core and placed into plastic bags. Each such sample was assigned a unique number. Samples were transferred from bags into plastic cubes (3.2 cm3 in volume) for magnetic mineral measurements. Selected samples were used for geochemical and sedimentologic analysis.

Magnetic Susceptibility (Table 2): Volume susceptibility (MS) was measured using a susceptometer with a sensitivity better than 10-5 volume SI. Samples were measured in a 0.1 mT induction at a low frequency of 600 Hz (MSlf) and high frequency of 6000 Hz (MShf). For each sample, the MS value was determined as the mean of four measurements. Frequency dependent susceptibility was calculated as:

FDMS=(MSlf-MShf)/MSlf.

Laboratory Induced Magnetization (Table 2):A high-speed spinner magnetometer was used to measure anhysteretic remanent magnetization (ARM) and isothermal remanent magnetization (IRM). ARM was imparted in a decreasing AF from a peak induction of 100 mT and a DC bias of 0.1 mT. IRM magnetizations were generated at room temperature using an impulse magnetizer. Samples were first subjected to IRM in a 1.2T induction (IRM1.2T.) and were then were then magnetized in the opposite direction using an induction of 0.3T (IRM -0.3T). Hard isothermal remanent magnetization (HIRM) and the S-parameter were calculated as follows (King and Channel, 1991):

HIRM=(IRM1.2T+IRM-0.3T)/2

S=IRM-0.3T/IRM1.2T

Elemental Abundance (Tables 3 and 4): Elemental abundance were determined on selected samples using energy dispersive X-ray fluorescence analysis at the University of Colorado's Department of Geological Sciences. Abundance of Cr, Cu, Fe, Mn, Mo, Nb, Ni, Rb, Sr, Ti, V, Y, Zn and Zr were measured.

Total carbon and inorganic (carbonate) carbon were determined using a coulometer on splits of powdered 1-cm samples of sediment (see Engleman and others, 1985) (Table 4). The carbonate in the untreated whole sample was acidified with perchloric acid to liberate CO2, which was titrated in the coulometer cell to measure carbonate carbon. Total carbon was measured by titrating CO2 liberated during sample combustion at 1050°C in a stream of oxygen. The technique has a precision of better than 0.5% for both carbonate and total carbon. Organic carbon was calculated as the difference between total and carbonate carbon.

References

TABLE 1. Sample Numbers and Depths

Tule Lake Sample no.: A unique sample number used for all measurements.

Core no.: Identifies core. Five cores were recovered from Tule Lake. This document provides data from cores 1 and 2.

Drive no.: Identifies location in the core. Each core was divided into drives numbered sequentially starting with 1 at the top. Some drives have been further divided into slugs indicated by letters, starting with A at the top of the drive.

Drive depth: The depth in meters of the top of the drive from the top of the core. Taken from driller's reports.

Sample depth in drive (m): Midpoint of sample depth interval in meters.

Sample depth in core (m): Sample depth within drive (m) plus adjusted depth from top of core.

Adjusted depth in core (m): The depth in meters of the top of the drive from the top of the core. Depths for core 2 have been lowered by 1.17 meters based on the location of the Trego Hot Springs ash located in each core (see Bradbury, 1991).

Sample density (kg/m3): Density of sample calculated from the mass of the dried box samples used in magnetic mineral studies.

TABLE 2. Sediment Magnetic Data
Sample no.: A unique sample number used for all measurements.

Core no.: Core number from which sample was taken.

Depth: Depth of sample in meters from top of the core.

Adjusted depth: The adjusted depth in meters from the top of the core.

MSLF: Low-frequency magnetic susceptibility in m3/kg.

FDMS: Frequency-dependent magnetic susceptibility in percent.

IRM (1.2T): Isothermal remanent magnetization from induction in a 1.2 tesla field at room temperature. Expressed in Am2/kg.

IRM (-.3T): Isothermal remanent magnetization from induction in a -0.3 tesla field at room temperature. Expressed in Am2/kg.

S: (S Ratio) calculated as IRM (-0.3T)/IRM(1.2T).

HIRM: Hard isothermal remanent magnetization: HIRM is calculated as: [IRM(1.2T) + IRM(-0.3T)]/2 and expressed in Am2/kg.

ARM: Anhysteretic remanent magnetization in Am2/kg.

TABLE 3. Elemental Abundances from X-ray Fluorescence
Tule Lake Sample no.: A unique sample number used for all measurements. The first number in the sample number refers to the core from which the sample was taken.

Adjusted depth: Adjusted depth of sample in meters from top of core.

Elements: The elements analyzed are listed below. The units are either weight percent (Wt%) or parts per million (ppm).

Elements
symbol element unit
Cr Chromium ppm
Cu Copper ppm
Fe Iron Wt%
Mn Manganese ppm
Mo Molybdenum ppm
Nb Niobium ppm
Ni Nickel ppm
Rb Rubidium ppm
Sr Strontium ppm
Ti Titanium Wt%
V Vanadium ppm
Y Yttrium ppm
Zn Zinc ppm
Zr Zirconium ppm

TABLE 4. Carbon Abundances

Tule Lake Sample no.: A unique sample number used for all measurements. TL1-samples are from core 1; TL-2 samples from core 2.

Adjusted depth: Adjusted depth of sample in meters from top of core.

Total Carbon: Percent of carbon (both organic and inorganic) in sample.

Carbonate Carbon: Percent of inorganic carbon in sample. Blank entries indicate that samples were not analyzed for carbonate carbon. These samples came from intervals for which previous results (W. Dean, unpublished data) indicated lack of carbonate carbon. In the calculation of organic carbon for these samples, it is assumed that carbonate carbon is absent.

Organic Carbon: Percent of organic carbon in sample. Calculated as total carbon minus carbonate carbon.


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