A repository of Earth’s first U-mineralized phosphatic dolostone from Paleoproterozoic ~2.0 Ga Vempalle Formation, Cuddapah Basin
Description
All data used for the research described in the article "A repository of Earth’s first U-mineralized phosphatic dolostone from Paleoproterozoic ~2.0 Ga Vempalle Formation, Cuddapah Basin" authored by Deepak Agarwal and Bulusu Sreenivas are uploaded here. In this study, we carried out a geochemical analysis on drill core samples of cherty dolostone (CD), U-mineralized dolostone (UMD), and massive dolostone (MD). The Major and trace element concentration of the samples are presented in Table 1 and the REE concentration of the samples are presented in Table 2. Data representing Varimax rotated factor analysis of the massive dolostone, high-U dolostone > 100 ppm, and cherty dolostone are presented in Tables S1, S2, and S3, respectively. In our research, we carried out geochemical analysis on drill core samples of dolostone belonging to 2 billion year old Vempalle Formation of the Cuddapah Supergroup. The geochemical signatures record the transition of the depositional environment from anoxic during the deposition of the lower Vempalle Formation (MD and UMD) to oxic during the deposition of the upper Vempalle Formation (CD). The Lower Vempalle Formation records the first significant U-mineralized phosphatic dolostone of the Earth history post-dating the global-scale glaciation due to upwelling nutrient-rich water, marine transgression, and rising sea levels. We propose that the Lower Vempalle Formation records the global signatures of Paleoproterozoic oceanic overturn and anoxic to euxinic depositional environmental transition.
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For geochemical analysis, core samples were thoroughly washed in deionized water by ultra-sonicating for 30 minutes. Dried samples were then chipped (~ 5 to 10 mm) with a hammer. After removing the weathered part, sample chips were taken for preparing ~ 15-20 g of fine powder (~300 mesh size) using agate mortar and pestle to avoid trace metal contamination during sample preparation. Major element analyses were performed on pressed powder pellets using an X-Ray Fluorescence Spectrometer (XRF; Phillips MagiX PRO-PW 2440). The loss on ignition (LOI) was determined in fused silica crucibles at 900 °C in an electrical muffle furnace. For trace elements, including REE analysis, three acid HF-HNO3-HClO4 closed vial digestion method was adopted, and solutions were prepared under clean laboratory conditions using double distilled acids. 50 mg of the finely powdered sample was weighed for each and taken in Perfluoroalkoxy Vials (PFA Teflon Vials). Concentrated acid mixture (1ml HNO3 + 3 ml HF + 0.5 ml HClO4) was added. Samples were then kept for digestion at 70 °C for 48 hours. In between, samples were ultra-sonicated twice for 1 hour each to mix the sample properly with acid. Following these, digested samples were dried on hot plates at 100 °C, and HClO4 was dried at 180 °C in the fume hood. After complete drying, 1 ml of 1:1 HNO3 was added to check if the samples had been digested. After complete digestion of the samples, 1 ml of 1:1 HNO3 was added. Finally, a 100 ml solution was made, adding 4 ml Concentrated HNO3 + 1 ml of 1 ppm Rh in 2% HNO3 as internal standard + 95 ml of Milli-Q water. The samples were diluted to 500 ppm TDS (total dissolved solids) for trace element analysis. The trace elements, including REEs, were analyzed using Thermo XSeriesII ICP-MS (Inductively Coupled Plasma Mass Spectrometer) at LA-MC-ICPMS laboratory, CSRI-NGRI. An external calibration procedure has been adopted for the analysis, with Rh as an internal standard. Geological standards were used for external calibration. The certified reference materials were analyzed as an unknowns to check the accuracy and precision of the data. Also, a few samples were run in duplicate to check the precision of the data, with an accuracy of better than ±10 % and a precision of better than ±3 %.
Institutions
- National Geophysical Research Institute CSIRTelangana, Hyderabad