Late Pleistocene Mono Basin Beach Berms, California: Preliminary OSL Ages

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1 Late Pleistocene Mono Basin Beach Berms, California: Preliminary OSL Ages Larry N. Smith: Geological Engineering, Montana Tech Guleed A.H. Ali, Sidney Hemming: Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory, Columbia University Mayank Jain, Reza Sohbati, Jan-Pieter Buylaert: Center for Nuclear Technologies, Technical University of Denmark, DTU Risø Campus Scott Stine: Department of Anthropology, Geography, and Environmental Studies, California State University-East Bay

2 California and western Nevada Mono Basin is currently internally drained Glaciated on SW side of basin in late Pleistocene

3 Mono Lake basin shoreline berms (about 35 berms recognized) High stand Younger Dryas Post-Younger Dryas NASA.gov

4 Mono Lake basin shoreline berms (about 35 berms recognized) High stand Younger Dryas Post-Younger Dryas NASA.gov

5 Development of Mono Beach Berms Suite of ~35 berms at different elevations Some more substantial, some less A few, distinctive double berms Current Lake Level Highest recognized

6 Development of Mono Beach Berms Build highest berm

7 Development of Mono Beach Berms Retreat from highest berm

8 Development of Mono Beach Berms Water fluctuations over decades few hundreds of years redistributes sediment to form next highest berm Sediment is redistributed and concentrated

9 Development of Mono Beach Berms Water fluctuations over decades few hundreds of years redistributes sediment to form next highest berm Sediment is redistributed and concentrated

10 Neogene andesite Quartz monzonite & metamorphic rocks Neogene basalt & trachybasalt Longshore drift Quaternary rhyolite

11 286 m (6844ft) beach berm 5 cm of fine-med sand, overlain by a meter of sandy gravel with calcrete Younger Dryas stand dated by Goat Ranch Tufa (U-Th) ka

overlain by planar parallel pebble gravel

12 266m (6777ft) berm Two samples 2m lower than Younger Dryas berm expected age ~ ka Fine-medium grained sand with sandy pebble gravel above and below, overlain by planar parallel pebble gravel with sand Upper flow regime foreshore environment

13 2162m (792ft) Ultimate high stand berm Well rounded finegrained sand; planar laminated, underlain by granule gravel with crude bedding and fine-grained sand Upper flow regime backshore environment

14 Purified Quartz & K-rich feldspar sample preparation Wet sieve for 18-25μ fraction Acid cleaning with 1% HCL & organic matter removal with H 2 O 2 Heavy liquid separation (2.58 g cm-1) Etching of quartz 4% HF & feldspar in 1% HF Quartz purity tested using infrared (IR) stimulation

15 OSL (cts per.16 s) Lx/Tx Prob. Density OSL (cts per.16 s) Lx/Tx Prob. Density Mono Basin Younger Dryas beach berm Two examples of Continuous Wave data Feldspar contamination leads to high background 8, 7, 6, 5, 4, 3, 2, 1, 5 Contribution of unbleached Feldspar to signal Time (s) 3 Natural 25ß Dose (s) Dose (s) , 11, 1, 9, 8, 7, 6, 5, 4, 3, 2, 1, Time (s) 25 3 Natural 25ß Dose (s) Dose (s) 5 6 7

16 Grays Beach berm correlated to Younger Dryas high stand Etched twice, but still noisy data and high background Used Pulsed OSL to decrease background levels due to Feldspar Continuous Wave Preheat Plateau (47/48 aliquots) Average De 53.6 ± 3.2 Gr Pulsed OSL Preheat Plateau (2/24 aliquots) Average De = ± 4.2 Gr Background subtraction in Continuous Wave data leads to lower estimated doses due to feldspar contamination of quartz signal

17 Pulsed OSL measurements TL/OSL Risø DA-15 Post-IR (IR 87 ± 4 nm) Pulsed OSL Blue (47 ± 3 nm) stimulation Pulse 5μs on 2μs off Detection of quartz signal through UV filters Large aliquot (5-8 mm stainless steel cups) appropriate for late Pleistocene samples* * Murray et al. (215) Radiation Measurements and Thomsen et al. (216) Quaternary Geochronology

18 Pulsed OSL (cts per.2 s) Lx/Tx Standardised Estimate Dose (s) Pulsed OSL results for YD berm 13/24 cups passed screening 6.92 ± 2.93 Gy (dose rate of 4.54±.3 Gy/ka) ± 1.13 ka 1,4 1,2 1, Time (s) Natural 4ß Dose (s) Precision (%) 5 6 9, 8, 7, 6, 5, 4, 3, 2, 1,

Feldspar age uncorrected for fading (ka) Mono Basin Quartz vs Feldspar estimated dose High Stand berm has high estimated dose (225 Gy) but no Feldspar data 2 Quartz bleaches in sunlight

19 Feldspar age uncorrected for fading (ka) Mono Basin Quartz vs Feldspar estimated dose High Stand berm has high estimated dose (225 Gy) but no Feldspar data 2 Quartz bleaches in sunlight much more readily Therefore lower uncorrected Feldspar ages show Quartz is likely well bleached (Murray et al., 212) Quartz age (ka) Conclusion: Beach berms likely well bleached

20 Post-Younger Dryas ±1. ka (14/18 aqts) ±1.2 ka (9/16 aqts) ± 1.7 ka (5 aqts) Pulsed OSL Quartz Ages (assuming 4% ± 4% w.c.) Younger Dryas ±1.1 (28/33 aqts) Ultimate High Stand Berm (likely tectonically deformed) ±25 ka (6 aqts)

22 Lake-Level Record: U-Th & stratigraphy

23 Conclusions First-cycle quartz and feldspar in the Mono Basin are appropriate for optical dating Beach berm sediments are well bleached Preliminary optical dates in the basin are consistent with U-Th series dates on high density carbonates Optical dating of suite of beach berms may clarify late Pleistocene to Holocene climatic transitions in eastern California desert region

Pleistocene Terrace Deposits of the Crystal Geyser Area e. r G. P5 5o. M1/Qal. M3 3y M4 M5 M5. 5o M6y P6. M1/Qal

Pleistocene Terrace Deposits of the Crystal Geyser Area e. r G. P5 5o. M1/Qal. M3 3y M4 M5 M5. 5o M6y P6. M1/Qal 0 M6 C O N T O UR IN T E R V A L 4 0 F E E T NO R T H A ME R IC A N V E R T IC A L D A T UM O F 1 9 8 8 500 METERS KILOMETERS 0.5 S C A L E 1 : 1 2,0 0 0 r M1/Qal USU-780 P6 1000 1 5o M6y P6 y M4 M5 M5