230 Th ∕ U isochron dating of cryogenic cave carbonates

• Published in: Geochronology
• Main Authors: P. Töchterle, S. D. Steidle, R. L. Edwards, Y. Dublyansky, C. Spötl, X. Li, J. Gunn, G. E. Moseley
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2022
• Subjects: Geology; QE1-996.5; Stratigraphy; QE640-699; permafrost
• Online Access: https://doi.org/10.5194/gchron-4-617-2022; https://doaj.org/article/92af2640c5a44eb8985ffcd1e2b586ba

Cryogenic cave carbonates (CCCs) are a type of speleothem, typically dated with <math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msup><mi/><mn mathvariant="normal">230</mn></msup><mi mathvariant="normal">Th</mi><mo>/</mo><mi mathvariant="normal">U</mi></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="43pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="9d0a396b451698ee2c327cdb6628050e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="gchron-4-617-2022-ie00004.svg" width="43pt" height="15pt" src="gchron-4-617-2022-ie00004.png"/></svg:svg> disequilibrium methods, that provide evidence of palaeo-permafrost conditions. In the field, CCCs occur as distinct patches of millimetre- to centimetre-sized loose crystals and crystal aggregates on the floors of cave chambers, so they lack a framework that would allow ages to be validated by stratigraphic order. Correction factors for the initial 230 Th ( 230 Th 0 ) are often based on the bulk-earth-derived initial <math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msup><mi/><mn mathvariant="normal">230</mn></msup><mi mathvariant="normal">Th</mi><msup><mo>/</mo><mn mathvariant="normal">232</mn></msup><mi mathvariant="normal">Th</mi></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="61pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="9cdbb0c7f20e3abf3a8f3624d7bcd32e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="gchron-4-617-2022-ie00005.svg" width="61pt" height="15pt" src="gchron-4-617-2022-ie00005.png"/></svg:svg> activity ratio ( <math xmlns="http://www.w3.org/1998/Math/MathML" ...