Uranium loss and aragoniteâ€“calcite age discordance in a calcitized aragonite stalagmite
- Permanent Link:
- Uranium loss and aragoniteâ€“calcite age discordance in a calcitized aragonite stalagmite
- Series Title:
- Quaternary International
- Lachniet, Matthew S.
Bernal, Juan Pablo
- Publication Date:
- Subjects / Keywords:
- Speleothem ( local )
Aragonite ( local )
Recrystallization ( local )
Uranium Series Dating ( local )
Laser Ablation ( local )
Mc-Icpms ( local )
- serial ( sobekcm )
- We analyzed uranium-series concentrations and isotopic ratios in a mixed aragonite and calcite stalagmite from Juxtlahuaca Cave, from the Sierra Madre del Sur of Mexico. The U-series data for the aragonite layers return highly precise and stratigraphically correct ages over the past ca. 4300 years. In contrast, age determinations from calcite layers are too old by several hundred years relative to the precise aragonite ages, have analytical uncertainties an order of magnitude larger than aragonite ages, and yield ages that do not overlap the aragonite ages within analytical uncertainties. Based on geochemical and petrographic observations, we interpret the calcite layers to have formed from recrystallization of aragonite soon after primary aragonite deposition. Calcite occurs as discontinuous lenses on and off the growth axis, and laminae can be traced between aragonite and calcite layers, demonstrating that visible growth banding is not effaced in the recrystallization process. Paired aragonite-calcite U-series data from coeval stratigraphic layers demonstrate that uranium concentrations decrease by two orders of magnitude during calcitization, and result in decreased (234U/238U). Uranium loss during diagenesis mimics a need for an age correction using an initial 230Th/232Th ratio one to two orders of magnitude larger than the bulk Earth ratio of 4.4 ± 2.2 × 10âˆ’6. A need for apparent high initial 230Th/232Th ratios results from ingrowth of 230Th during 234U decay.
- Original Version:
- Quaternary International, Vol. 14 (2012-08-12).
- Source Institution:
- University of South Florida Library
- Holding Location:
- University of South Florida
- Rights Management:
- This object is protected by copyright, and is made available here for research and educational purposes. Permission to reuse, publish, or reproduce the object beyond the bounds of Fair Use or other exemptions to copyright law must be obtained from the copyright holder.
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