Li,D., Shields-Zhou,G.A., Ling,H.-F. and Thirlwall,M.(2011): Dissolution methods for strontium isotope stratigraphy: Guideline for the use of bulk carbonate and phosphorite rocks. Chemical Geology, 290, 133-144.

『ストロンチウム同位体層序のための溶解法:炭酸塩とリン酸塩の全岩を用いるための指針』


Abstract
 Diverse carbonate dissolution methods have been applied to bulk carbonate rocks in order to target least altered components for strontium isotope stratigraphy (SIS). This is especially important for Precambrian and Cambrian studies for which no suitable skeletal material is available. On proven method for bulk limestones involves the removal of up to a third of the powdered sample using an acid pre-leach before partial dissolution of the rest of the sample using a weak acid or acid buffer solution. We applied a similar technique to dissolve a range of lithologies (limestone, dolostone and phosphorite) and compared the strontium isotopic composition of various leaches to contemporaneous seawater. Our results vindicate this approach and allow us to conclude that some dolomitic and phosphatic rock components may retain a near-primary seawater 87Sr/86Sr composition once contaminant strontium from secondary calcite and other phases has been removed. Commonly applied trace element (e.g. Mn/Sr, Mg/Ca) and isotopic (C,O) screening cut-offs were also examined in the light of these results, and proved unreliable particularly in the case of dolostones and partially dolomitized limestones. We recommend that rigid sample selection and sequential leaching procedures be applied to all SIS studies bulk materials and propose a general protocol for strontium isotope studies on marine authigenic rocks which may also be applicable to rare earth element and other geochemical studies of marine authigenic minerals in the future.

Keywords: Strontium isotope stratigraphy; Limestone; Dolostone; Phosphorite; Dissolution methods』

1. Introduction
2. Geological setting and stratigraphy
3. Methods
 3.1. Sample selection and extraction
 3.2. Dissolution of samples and mass spectrometric analysis
4. Results
 4.1. Elemental results
 4.2. Sr isotope results
5. Discussion
 5.1. Selection criteria
  5.1.1. Petrographic criteria
  5.1.2. Geochemical selection
 5.2. Physical extraction
 5.3. Chemical pre-treatment
 5.4. Sample dissolution
6. Discussions
Acknowledgments
References


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