USGS Open-File Report 95-673

Sediment Magnetic and Paleomagnetic Data from Buck Lake, Oregon

U.S. Geological Survey Open-File Report 95-673

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

Sediment magnetic and paleomagnetic studies were conducted on a core from Buck Lake, Klamath County, Oregon, that was collected as part of an investigation into the Quaternary climate history of the western United States. This report documents the methods used to obtain paleomagnetic directions, magnetic properties, and ancillary data, and presents these data in tabular form. Adam (1993) and Adam and others (1994) describe the site, the drilling methods, and lithology of the lacustrine sediments. Rosenbaum and others (1994) present preliminary interpretations of the sediment magnetic data and show that variations in magnetic properties closely reflect changes in climate as interpreted from the pollen record.

Methods

Sampling: Paleomagnetic specimens, 3.2 cm³ in volume, were taken in plastic boxes. Pedestals were cut in the core, boxes were placed over the pedestals, and the sediment in the boxes was then cut from the core and the boxes were sealed. Orientation was maintained with respect to the core axis but the specimens were not azimuthally oriented. Each paleomagnetic specimen was given a unique box number and the depth interval (with respect to the top of the core segment) covered by each box was recorded. Subsequently each specimen was assigned a second unique number, the sample number. These boxed samples were used for measurements of magnetic susceptibility, paleomagnetic directions and magnitudes, laboratory induced magnetizations, and hysteresis properties.

Core material removed from around each paleomagnetic specimen was placed in one or more numbered vials. The depth interval contained in each vial corresponds closely (but not exactly) to the interval sampled by a paleomagnetic specimen. These vials were later assigned sample numbers. Material in these vials was used to determine grain size, and elemental concentrations.

Paleomagnetic Directions: Directions and magnitudes of natural remanent magnetization and of magnetization after alternating-field demagnetization were determined with a cryogenic magnetometer (sensitivity better than 10^-5A/m), a low-speed (5 Hz) spinner magnetometer (sensitivity approximately equal to 10^-3A/m), or a high-speed (90 Hz) spinner magnetometer (sensitivity better than 10^-5 A/m). Each specimen was subjected to progressive alternating-field demagnetization to at least 60 mT. Progressive demagnetization occurred in at least five steps (peak inductions of 10, 20, 30, 40 and 60 mT) and many specimens were demagnetized at additional levels. Characteristic directions of magnetization were calculated by fitting lines to demagnetization data ( Kirschvink, 1980) which visually appeared to define coherent components when displayed on orthogonal vector diagrams.

Magnetic Susceptibility: A susceptometer (sensitivity better than 10^-5 volume SI), operating at about 600 Hz or 6000 Hz, was used to measure low frequency (MS_LF) and high-frequency (MS_HF) magnetic susceptibilities. The frequency dependence of magnetic susceptibility (FD) was calculated as

Laboratory Induced Magnetizations: A low speed-spinner magnetometer or a high-speed spinner magnetometer was used to measure anhysteretic remanent magnetization (ARM) and isothermal remanent magnetization (IRM). Following AF demagnetization, ARM was imparted to each specimen in a alternating induction of 100 mT and DC bias of 0.1 mT. Subsequently, an impulse magnetizer was used to impart IRMs. First specimens were given an IRM in an induction of 1.2 T (IRM_1.2), and then they were given an oppositely directed IRM in an induction of 0.3 T (IRM_-0.3). The "hard" isothermal remanent magnetization (HIRM) and the S parameter were calculated as

as suggested by King and Channel (1991).

Hysteresis Properties: Hysteresis loops were generated for a subset of the paleomagnetic specimens using a vibrating sample magnetometer at the Institute for Rock Magnetism at the University of Minnesota. The maximum induction used was about 1.4 T. For each loop, high field (or paramagnetic) magnetic susceptibility was determined by fitting lines to a portion of the data for inductions above about 0.9 T. The induced magnetization due to this paramagnetic susceptibility was subtracted from the observed magnetizations prior to calculation of hysteresis properties.

Curie Temperatures: Curie temperatures were determined for magnetic minerals separated from bulk sediment that had been placed in bags during sampling. The separations were done by dispersing the sediment in water ( with a small amount of surfactant) and pumping the resulting slurry past a magnet using a technique similar to that described by Petersen and others ( 1986). Magnetization, in an induction of 0.3 T or greater, was measured as a function of temperature using a sensitive balance similar to that described by Larson and others (1975).

Grain Size Analyses: Bulk sediment grain sizes (between 0.2 and 50 microns ) were obtained for sediment in 21 vials using an automated particle-size analyzer. These results are summarized here as the percentage of sediment greater than 3.2 microns in size.

Elemental Abundances: Sediment from vials was prepared for energy- dispersive X-ray fluorescence analysis by thorough drying and subsequent pulverization in a shatter box. Analyses were made at the Department of Geological Sciences, University of Colorado. Analyses were made for Ba, Cr, Cu, Fe, La, Mn, Ni, Rb, Ti, V, Zn and Zr. In addition, concentrations of total carbon and carbonate carbon were determined by coulometry ( Engleman and others, 1985). Organic carbon content was determined by taking the difference between total carbon and carbonate carbon.

Reference

Adam, D.P., 1993, Field core processing techniques used by U.S.G.S. 1991 drilling operations in the Upper Klamath basin, Oregon and California: U. S. Geological Survey Open-file Report No. 93-20, 16 p.

Adam, D.P., Rieck, H.J., McGann, M.L., Schiller, K., and Sarna-Wojcicki, A. M., 1994, Lithologic description of sediment cores from Buck Lake, Klamath County, Oregon: U.S. Geological Survey Open-file Report No. 94-12, 48 p.

Engleman, E.E., Jackson, L.L., Norton, D.R., and Fischer, A.G., 1985, Determination of carbonate carbon in geological materials by coulometric titration: Chemical Geology, v. 53, p. 125-128.

King, J.W., and Channel, J.E.T., 1991, Sedimentary magnetism, environmental magnetism, and magnetostratigraphy: Reviews of Geophysics, Supplement, p. 358-370.

Kirschvink, J.L., 1980, The least-squares line and plane and the analysis of palaeomagnetic data: Geophysical Journal of the Royal Astronomical Society, v. 62, 699-718.

Larson, E.E., Hoblitt, R.P., and Watson, D.E., 1975, Gas-mixing techniques in thermo magnetic analysis: Geophysical Journal of the Royal Astronomical Society, v. 43, p. 607-620.

Petersen, N., Von Dobonek, T., and Vali, H., 1986, Fossil bacterial magnetite in deep-sea sediments from the South Atlantic Ocean: Nature, v. 320, p. 611-615.

Rosenbaum, J.G., Reynolds, R.L., Fitzmaurice, P., Adam, D.P., Sarna- Wojcicki, A.M., and Kerwin, M.W., 1994, Covariance of magnetic and pollen records from Quaternary sediment, Buck Lake and Caledonia Marsh, southern Oregon: Proceedings of the VIIth International Symposium on the Observation of the Continental Crust Through Drilling, p. 199-202.

TABLE 1. Sample Numbers and Depths

download tab-delimited text file
Sample No: A unique sample number assigned regardless of sample type.
Sample Box No: A unique number assigned to paleomagnetic samples that are placed in plastic boxes.
Vial No: A unique number assigned to samples removed from the core and placed in vials.
Slug: Core segment identification. Core runs were numbered consecutively. Subdivisions of a core run were labeled A (upper) and B (lower).
Depth in hole: Depth computed by adding midpoint of depth interval and depth to top of slug.
Grain Size: For the fraction of a sample less than 50 microns in size, the percentage of a sample larger than 3.2 microns.
Table for ancillary data: Column identifies existence of hysteresis data (Table 4), elemental data obtained by X-ray fluorescence (Table 5), and carbon analyses (Table 6).

TABLE 2. Paleomagnetic Data

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Sample Box No: A unique number assigned to paleomagnetic samples that are placed in plastic boxes.
Depth: Depth in hole as in Table 1.
Magnetometer: Magnetometer used to measure remanent magnetization in the USGS Denver rock magnetism laboratory -- S is a 5 hertz spinner magnetometer, C is a cryogenic magnetometer, and J is a 90 hertz spinner magnetometer.
Declination: Declination of the characteristic magnetization. Characteristic directions of magnetization were determined by fitting lines to demagnetization data.
Inclination: Inclination of the characteristic magnetization.
NRM: The magnitude of natural remanent magnetization in Amperes/meter (A/m).
Magnetization removed in demagnetization interval: The difference in magnitude between the magnetizations for the lowest and highest demagnetization steps included in calculating the characteristic magnetization.
Demagnetization interval used for linear fit: The highest and lowest demagnetization steps in milliTesla (mT) used in calculating the characteristic direction.
No. of points used in linear fit: The number of demagnetization steps used in calculating the characteristic direction.
Error angle: The maximum angular deviation for the demagnetization steps used in calculating the characteristic direction.
Subjective quality of demagnetization path: A consensus ranking (A, B, or C) of the linearity of the demagnetization path, after visual inspection of a vector endpoint diagram.

TABLE 3. Sediment Magnetic Data

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Sample Box No: A unique number assigned to paleomagnetic samples that are placed in plastic boxes.
Depth: Depth in hole as in Table 1.
MS: Magnetic susceptibility (SI volume) measured at about 600 hertz.
FD of MS: Frequency dependence of magnetic susceptibility.
NRM: Magnitude of natural remanent magnetization.
ARM: Magnitude of anhysteretic remanent magnetization.
IRM _1.2T: Isothermal remanent magnetization acquired in an induction of 1.2 T.
IRM _-0.3T: Isothermal remanent magnetization after exposure to an induction of 1.2 T followed by exposure to an oppositely directed induction of 0.3 T.
HIRM: "Hard" isothermal remanent magnetization = (IRM_1.2T - IRM_-0.3T)/2.
S: The "S-parameter" = -IRM_1.2T/IRM_-0.3T.

TABLE 4. Hysteresis Parameters

download tab-delimited text file
Sample Box No: A unique number assigned to paleomagnetic samples that are placed in plastic boxes.
Depth: Depth in hole as in Table 1.
Paramagnetic MS: Paramagnetic magnetic susceptibility determined from the slope of the hysteresis curve above an induction of 0.9 T.
Msat: Saturation magnetization determined after removal of paramagnetic component.
Mrs: Saturation remanent magnetization.
Hc: Coercivity determined after removal of paramagnetic component.
Hcr: Coercivity of remanence.

TABLE 5. Elemental Abundances from X-ray Fluorescence

download tab-delimited text file
Vial No: A unique number assigned to samples removed from the core and placed in vials.
Paired Sample Box No: Box number of the closest magnetic specimen.
Depth: Depth in hole as in Table 1.

TABLE 6. Carbon Abundances

download tab-delimited text file
Vial No: A unique number assigned to samples removed from the core and placed in vials.
Paired Sample Box No: Box number of the closest magnetic specimen.
Depth: Depth in hole as in Table 1.

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