Vol.:(0123456789) 1 3 Journal of Sedimentary Environments (2021) 6:1–12 https://doi.org/10.1007/s43217-020-00040-5 ORIGINAL ARTICLE Rare‑earth element (REE) geochemistry of late Paleocene–middle Eocene phosphate nodules in the Subathu Basin of Solan District, Himachal Pradesh, India M. Shuaib 1  · K. F. Khan 1  · A. Hussain 1  · M. Jawad 1  · Shamim A. Dar 2 Received: 27 August 2020 / Revised: 21 November 2020 / Accepted: 2 December 2020 / Published online: 4 January 2021 © The Author(s), under exclusive licence to Springer Nature Switzerland AG part of Springer Nature 2021 Abstract The phosphate nodules are solely confned to the Green facies of late Paleocene–middle Eocene Subathu Formation in the Subathu Basin of Solan District, Himachal Pradesh, India. The phosphate nodules are hard and compact, elliptical, rounded to well rounded, usually dull earthy to dark grayish in color and break with sharp and conchoidal surfaces. The present study deals with the rare-earth elements (REE) geochemical characteristics viz. hat-shaped, enrichment of middle REE relative to light REE and heavy REE, negative Eu and weak negative to weak positive Ce anomalies and values of ratios such as Er/Nd (0.07–0.19), Y/Ho (32–48), La/Nd (0.46–0.90), (La/Sm) N (0.18–0.47) and (La/Yb) N (0.26–0.51). It appears that the seawater conditions or growth mechanisms were diferent at the time of formation of cores and rims of the nodules as indicated by the contrast REE concentrations, respectively. Although in both cases very similar REE spectra are observed, rims are much more likely to show a diagenetic alteration front than cores. The Y/Ho ratio (32–48) suggests that the principal source of REE was the terrigenous sediments followed by seawater in the rims and cores of these nodules. The results of this study suggest a dominant role of diagenetic processes in the REE concentration and distribution as well as possible suboxic to anoxic conditions during the formation of cores and rims of phosphate nodules, as also evident by the presence of pyritic nodules in the Subathu Basin of Solan District. Keywords REE geochemistry · Phosphate nodules · Solan · Subathu formation · Middle REE · Diagenetic processes 1 Introduction Marine sediments are known to host phosphate nodules throughout the geological past (Stalder and Rozendaal 2004) and in recent sediments of phosphatic nature (Ras- mussen et al. 1998; Jiang et al. 2007). Phosphate sediments in diatomaceous organic-rich layers have been reported at the western margin of South Africa, continental margin of Peru–Chile and Baja California of Mexico (Veeh et al. 1973; Birch 1979; Schufert et al. 1994). These are areas of ocean high productivity zones of organic matter in the world. How- ever, according to O’Brien et al. (1981), low productivity zones of oceans also show the presence of phosphates where assimilation of phosphorus was probably attributed by the presence of organic matter and bacteria. It is well known that signifcant concentration of REE can be incorporated in phosphate nodules at the time of early diagenesis during their growth in marine sediments (Kidder et al. 2003). The REE geochemistry of phosphorites can be used as a tool to characterize a depositional environment because various REE profles are seen in diferent marine depositional conditions. For example, cerium depletions refect exposure to oxidized seawater, fat patterns are inter- preted to display detrital infuence, and light REE depletions suggest the infuence of weathering. In phosphatic sedi- ments, the original seawater REE pattern and its concentra- tions may be altered by various processes such as weather- ing, burial diagenesis, and metamorphism (McArthur and Walsh 1984; Fazio et al. 2007), so, the REE concentration and its distribution in phosphates can vary from one basin Communicated by M. V. Alves Martins * M. Shuaib shuaibamu16@gmail.com 1 Department of Geology, Aligarh Muslim University, Aligarh 202002, UP, India 2 Department of Geology, Centre of Advanced Study, Institute of Science, Banaras Hindu University, Varanasi 221005, India