Electron spin resonance (ESR) signals, thermoluminescence (TL), and optically stimulated luminescence (OSL) have all been used to date material from the Quaternary (Ikeya
The E1’ center intensity of quartz can be used to investigate the provenance of aeolian dust (Naruse
As no E1’ center is observed in quartz crystals from young bedrock, the amount of the various impurities in quartz is a useful index for estimating the provenance of sediments of Quaternary volcanic origin (Shimada and Takada, 2008; Shimada
In this study, we investigate the relationships among ESR signals of quartz in modern river bed sediments and bedrocks of the Kizu River basin using the dose-saturated signal intensities of the Al and Ti-Li centers. In addition, we use these ESR signal intensities to estimate the mixing ratios of the source materials that make up the river bed sediments.
Bedrock is broken down by weathering into unconsolidated materials, which are then carried downstream by rivers. In this study, modern river bed sediments and bedrock samples were collected at sites S1–S7and R1– R5, respectively, from the Kizu River basin, western Japan (
Samples S1–S5 and R1–R3 were collected along the Nabari River, one of the large tributaries of the Kizu River in the southern part of the basin. Samples S6–S7 and R4–R5 were collected along the main course of the Kizu River. Muro pyroclastic flow deposits (sample R1) are widely distributed in the upper (southern) section of the Nabari River and along the main course of the Kizu River. Metamudstone with sandstone (sample R2) from the mid-Paleozoic Tamba Belt is distributed in the upper (southern) and middle reaches of the Nabari River, and along the main course of the Kizu River. Ao granite (sample R3) and Yagyu granite (sample R4) are widely distributed along the middle reaches of the Nabari River and along the main course of the Kizu River, and Shigaraki granite (sample R5) is found in the lower (northern) basin of the Kizu River (
Quartz particles in fluvial sediments are moved downstream by the tractive force of the river. Therefore, in this study we used sand-sized quartz grains from river bed sediments of the Kizu River to estimate the composition and sources of these deposits. The samples of crushed rocks and river sediments were sieved to separate out the 500 μm and 1 mm fractions. Magnetic minerals were removed using a magnetic separator. The sieved samples were treated with 6M hydrochloric acid (HCl) overnight, and then with a 1% HF and 1% HNO3 mixture for 12 h, prior to heavy liquid (sodium polytungstate solution) separation. The quartz grains were etched with 46% HF for 1 h to dissolve any contaminating feldspar and then treated with 6M HCl overnight. Finally, the samples were crushed and re-sieved into fractions containing 120 and 250 μm quartz grains.
The ESR dose response curves of quartz grains from impurity centers are known to grow with high radiation doses (Yokoyama
ESR measurements were conducted using a JES-X320 X-band spectrometer (JEOL RESONANCE Inc.) with the Liquid Helium Variable Temperature System (ES-CT470). The Al and Ti-Li center signals from the quartz samples were measured at 77 K (–196°C) using a microwave power of 5 mW, a sweep time of 2 min, a time constant of 0.03 s, an amplitude of field modulation of 0.1 mT, and a modulation frequency of 100 kHz.
The Al and Ti-Li center signal intensities obtained from the quartz of the metamudstone with sandstone sample R2 and the river sediment sample S4 increased with the gamma ray dose, becoming almost saturated above 2.5 kGy (
Each sample was divided into five aliquots and then each aliquot was measured five times to investigate variations in the Al and Ti-Li center signal intensity of the quartz in the same sample. Deviations of the Al and Ti-Li center signal intensity from the quartz from the present-day river bed sediments (S1–S7) and bedrock (R1–R5) samples were between 1% and 6% in a given sample (
Sample numbers and names, and ESR signal intensities.Sample Name Al center signal intensity (a.u.) Ti–Li center signal intensity (a.u.) R1 Muro pyroclastic flow deposits 384 ± 11.8 72 ± 0.3 R2 Metamudstone with sandstone 217 ± 3.2 24 ± 0.6 R3 Ao granite 210 ± 6.1 2 ± 0.1 R4 Yagyu granite 89 ± 1.3 17 ± 0.5 R5 Shigaraki granite 82 ± 2.1 6 ± 0.1 S1 Present river sediment-1 225 ± 10.1 36 ± 1.0 S2 Present river sediment-2 219 ± 7.5 28 ± 1.1 S3 Present river sediment-3 286 ± 3.9 42 ± 0.9 S4 Present river sediment-4 192 ± 6.1 21 ± 1.0 S5 Present river sediment-5 226 ± 5.3 28 ± 2.0 S6 Present river sediment-6 206 ± 5.8 22 ± 0.9 S7 Present river sediment-7 177 ± 7.5 24 ± 1.7
When two sources of quartz with ESR signal intensities a and b are combined with a mixing ratio of x: (1 – x), the ESR signal intensity,
To investigate variations in the Al and Ti-Li center signal intensity of the quartz in the volcanic (R1) and granitic (R5) samples, we tested five mixed samples based on the following x values (
ESR signal intensities of artificially mixed samples created by mixing samples R1 and R5 (n = 5).R1 mixting ratio (%) R5 mixting ratio (%) Al center signal intensity (a.u.) Ti–Li center signal intensity (a.u.) Estimated data 25 75 158 22 50 50 233 39 75 25 309 55 Experimental data 0 100 82 6 25 75 174 23 50 50 239 38 75 25 290 55 100 0 384 72
The dose-saturated ESR intensities of samples S1–S7 and R1–R5 are shown in
As shown in
As for samples S3, S4, and S5, there would be additional large contributions from the Ao granite (R3) that crops out in the upstream section of the river above these three sampling sites. When three sources with Al and Ti-Li center signal intensities a and a’, b and b’, and c and c’ mix in the ratio x:y:z, the resultant signal intensity of the Al (d) and Ti-Li (d’) center can be expressed as follows:
Mixing ratios of the present-day river bed sediments and ESR signal intensities of the samples.Sample Major possible source rocks and sediments Mixting ratio (%) estimated from Al center signal intensities Mixting ratio (%) estimated from Ti-Li center signal intensities S1 R1 5 23 R2 95 77 S2 R1 1 8 R2 99 92 S3 R1 42 R2 49 R3 9 S4 R1 –16 R2 137 R3 –21 S5 R1 5 R2 102 R3 –7 S5 S3 36 33 S4 64 67 S6 R2 86 R3 6 R4 8 S7 R2 68 R4 53 R5 –21
where
In
The mixing ratio R1:R2:R3 for S3 was calculated using
Sample site S5 is located downstream from the junction of two rivers, one of which flows through site S3 and the other through S4 (
As shown in
We made a tentative estimate of the mixing ratios using the ESR Al and Ti-Li center signal intensities from only the 0.5–1.0 mm fraction of the quartz grains in the present-day river sediments; however, to quantitatively estimate the precise provenance of sediments we should consider the composition, grain size distributions, and sorting during transportation of the minerals in the sediments. These tasks will be the subject of a future investigation.
The dose-saturated ESR signal intensities of quartz grains from samples of present-day river bed sediments in the Kizu River plot overlap with those of possible source bedrocks in a Al versus Ti-Li signal diagram (