Universität zu Köln

Fenton, Cassandra R., Niedermann, Samuel, Dunai, Tibor and Binnie, Steven A. (2019). The SPICE project: Production rates of cosmogenic Ne-21, Be-10, and C-14 in quartz from the 72 ka SP basalt flow, Arizona, USAu. Quat. Geochronol., 54. OXFORD: ELSEVIER SCI LTD. ISSN 1878-0350

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Abstract

The SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt with an Ar-40/Ar-39 age of 72 +/- 4 ka (2 sigma). The flow is preserved in the desert climate of northern Arizona, USA. Its unweathered appearance and the lack of soil development indicate it has undergone negligible erosion and/or burial, making it an ideal site for direct calibration of cosmogenic nuclide production rates. Cross-calibrated production rates and production rate ratios for cosmogenic Ne-21, Be-10, and C-14 have been determined from SP flow quartz. Production rate ratios for Ne-21/Be-10, Ne-21/C-14, and C-14/Be-10 are based on the total, local production rates of each cosmogenic nuclide, independent of scaling models, and have error-weighted means (+/- 2 sigma uncertainty) of 4.44 +/- 0.32, 1.43 +/- 0.10, and 2.85 +/- 0.21, respectively. Error-weighted mean, sea-level, high latitude (SLHL) total reference production rates of Ne-21, Be-10, and C-14 are 17.0 +/- 1.1, 3.84 +/- 0.27, and 11.2 +/- 0.6 at/g/yr (2 sigma), respectively, using time-independent Lal (1991)/Stone (2000) (St) scaling factors. St scaled spallogenic Be-10 and C-14 rates are 3.73 +/- 0.26 and 9.2 +/- 0.6 at/g/yr, respectively. Ne-21 and Be-10 production rates are integrated over the past 72 ka, whereas C-14 production rates are integrated over 25 ka, the time at which SP flow quartz has reached saturation with respect to C-14. These rates overlap within 2 sigma uncertainty with other St-scaled production rates in the literature, including the total reference SLHL Ne-21 production rate of Niedermann (2000), which is revised in this paper to 16.8 +/- 3.3 at/g/yr (2 sigma; St scaling) to reflect a recent change in age control at the Sierra Nevada sites. All SLHL production rates are lower if time-dependent Sf, Sa, and Lm scaling factors are used. For example, error-weighted mean, sea-level, high latitude (SLHL) total reference production rates for Be-10 as calculated in the CREp online calculator range from 3.49 +/- 0.23 to 3.74 +/- 0.25 at/g/yr (2 sigma), using time-dependent Lm scaling factors. Commonly used SLHL Be-10 and C-14 production rates in the literature were calibrated on surfaces that have been exposed to cosmic rays for less than 20 ka. Between 20 and 50 ka, the geomagnetic field is proposed to have been weaker than it is today. Production rates of cosmogenic nuclides increase during periods of weaker geomagnetic field strength. However, our study finds no measureable difference between St-scaled production rates of cosmogenic Ne-21 and Be-10 over the past 20 ka and St-scaled Ne-21 and Be-10 production rates over the past 72 ka. As such, the study suggests that Ne-21 and Be-10 production rates in quartz were not significantly greater during the proposed period of decreased magnetic strength from 20 to 50 ka.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Fenton, Cassandra R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Niedermann, Samuel UNSPECIFIED UNSPECIFIED UNSPECIFIED Dunai, Tibor UNSPECIFIED UNSPECIFIED UNSPECIFIED Binnie, Steven A. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-132023
DOI:	10.1016/j.quageo.2019.101019
Journal or Publication Title:	Quat. Geochronol.
Volume:	54
Date:	2019
Publisher:	ELSEVIER SCI LTD
Place of Publication:	OXFORD
ISSN:	1878-0350
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language PRODUCTION-RATE CALIBRATION; IN-SITU C-14; ACCELERATOR MASS-SPECTROMETRY; FRANCISCO VOLCANIC FIELD; SURFACE EXPOSURE AGES; GEOMAGNETIC-FIELD; DRY VALLEYS; TRANSANTARCTIC MOUNTAINS; TERRESTRIAL ROCKS; DENUDATION RATES Multiple languages Geography, Physical; Geosciences, Multidisciplinary Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/13202