Attribute_Accuracy_Report:
Sampling:
Samples used for paleomagnetic directions, magnetic
susceptibility, and laboratory induced magnetizations were taken
approximately every 5 cm. The majority of the core was soft, and
a cube with a volume of 3.2 cm3 oriented with respect to the top
of the core could be inserted directly into the sediment.
Approximately every 100 cm, a 10 to 20 cm interval of sediment was
collected and stored in bags for magnetic mineral separations.
Paleomagnetic directions:
Natural Remanent Magnetization (NRM) was measured on oriented
samples using a 90-Hz spinner magnetometer with a sensitivity
better than 10-5 A/m. Samples were demagnetized in steps through
alternating-field (AF) demagnetization with peak fields of 5, 10,
15, 20, 30, 40, 60 and 80 milliTeslas (mT).
Laboratory induced magnetization:
Magnetizations were measured with a high speed spinner
magnetometer. 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.
First IRM was imparted in a 1.2T induction (IRM1.2T). The samples
were then magnetized in the opposite direction using an induction
of 0.3T (IRM-0.3T).
Elemental Abundance:
Elemental abundances were determined on selected samples using
energy dispersive X-ray fluorescence analysis.
Organic carbon was determined on selected samples as the
difference between total and inorganic carbon. Sample splits were
combusted in oxygen for 5 minutes at 960oC. Total CO2 was
measured using Total CO2 was measured using a coulometer.
Inorganic carbon was then determined through acidification with
perchloric acid and measured with a coulometer.
Source_Information:
Source_Citation:
Citation_Information:
Originator: Adam, D.P.
Originator: Rieck, H.J.
Originator: McGann, M.L.
Originator: Schiller, K.
Originator: Sarna-Wojcicki, A.M.
Publication_Date: 1994
Title:
Lithologic description of sediment cores from Grass Lake,
Siskiyou County, California U.S. Geological Survey Open-file
Report No. 94-651, 36pp.
Edition: First
Series_Information:
Series_Name: U.S. Geological Survey Open-File Report
Issue_Identification: 94-651
Publication_Information:
Publication_Place: Menlo Park, California
Publisher: U.S. Geological Survey
Type_of_Source_Media: paper
Source_Time_Period_of_Content:
Time_Period_Information:
Single_Date/Time:
Calendar_Date: Quaternary
Source_Currentness_Reference: publication date
Source_Citation_Abbreviation: Adam and others (1994)
Source_Contribution: site description, drilling methods, lithology of sediments
Source_Information:
Source_Citation:
Citation_Information:
Originator: Best, P.J.
Publication_Date: 1996
Title:
Environmental controls on magnetic mineralogy and
geochemistry of late Quaternary lacustrine sediments from
Grass Lake and Tule Lake, northern California: M.S. Thesis,
139 p.
Edition: First
Series_Information:
Series_Name: Masters of Science Thesis
Issue_Identification: none
Publication_Information:
Publication_Place: Boulder Colorado
Publisher: University of Colorado, Boulder
Type_of_Source_Media: paper
Source_Time_Period_of_Content:
Time_Period_Information:
Single_Date/Time:
Calendar_Date: Quaternary
Source_Currentness_Reference: publication date
Source_Citation_Abbreviation: Best, 1996
Source_Contribution: background study
Process_Step:
Process_Description:
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.
Process_Date: Unknown
Process_Step:
Process_Description:
Paleomagnetic Directions
Natural Remanent Magnetization (NRM) was measured on oriented
samples using a 90-Hz spinner magnetometer with a sensitivity
better than 10-5 A/m. Samples were demagnetized in steps
through alternating-field (AF) demagnetization with peak fields
of 5, 10, 15, 20, 30, 40, 60 and 80 milliTeslas (mT).
Declination and inclination were calculated from a best fit line
of the demagnetization data displayed as orthogonal vector
diagrams.
Process_Date: Unknown
Process_Step:
Process_Description:
Magnetic Susceptibility
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.
Process_Date: Unknown
Process_Step:
Process_Description:
Laboratory induced magnetization
After the paleomagnetic analysis, anhysteretic remanent
magnetization (ARM) and isothermal remanent magnetization (IRM)
experiments, magnetizationswere measured with a high speed
spinner magnetometer. 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. First IRM was imparted in a 1.2T induction (
IRM1.2T). The samples 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:
HIRM=(IRM1.2T+IRM-0.3T)/2
S=IRM-0.3T/IRM1.2T
Process_Date: Unknown
Process_Step:
Process_Description:
Elemental Abundance
Elemental abundances were determined on selected samples using
energy dispersive X-ray fluorescence analysis at the University
of Colorado's Department of Geological Sciences. Contents of
Cr, Cu, Fe, Mn, Mo, Nb, Ni, Rb, Sr, Ti, V, Y, Zn and Zr were
measured.
Process_Date: Unknown
Process_Step:
Process_Description:
Determination of carbon content
Organic carbon was determined on selected samples as the
difference between total and inorganic carbon. Sample splits
were combusted in oxygen for 5 minutes at 960oC. Total CO2 was
measured using a coulometer. Inorganic carbon was then
determined through acidification with perchloric acid and
measured with a coulometer.
Process_Date: Unknown
Process_Step:
Process_Description: Creation of original metadata record
Process_Date: 19970822
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Kevin M. Foley
Contact_Organization: U.S. Geological Survey
Contact_Position: Physical Scientist
Contact_Address:
Address_Type: mailing address
Address: U.S. Geological Survey
Address: 12201 Sunrise Valley Drive Mail Stop 918
City: Reston
State_or_Province: Virginia
Postal_Code: 20192
Country: USA
Contact_Voice_Telephone: (703) 648-5285
Contact_Facsimile_Telephone: (703) 648-6560
Contact_Electronic_Mail_Address: kfoley@usgs.gov
