ORIGINAL PAPER Elemental and isotopic geochemistry of carbonate rocks from the Pila Spi Formation (Middle–Late Eocene), Kurdistan Region, Northern Iraq: implication for depositional environment Faraj Habeeb Tobia 1 & Hikmat Safi Al-Jaleel 1 & Awaz Kareem Rasul 1 Received: 9 April 2020 /Accepted: 20 August 2020 # Saudi Society for Geosciences 2020 Abstract Major, trace, rare earth elements (REE), and stable isotopic compositions in carbonate rocks of Pila Spi Formation were measured to constrain the source of rare earth elements and depositional environment. The low ΣREE content (average = 6.53 ppm, n = 14) indicates that the carbonates seawater-like REE patterns with (1) LREE depletion (average (Nd/Yb) n = 0.81), (2) HREE enrichment, (3) negative Ce anomaly (average = 0.91), and (4) superchondritic Y/Ho ratio (average = 30.07); slightly lower average value of Y/Ho ratio than the typical seawater value (~ 44–74) suggests modification of the seawater by input of fresh water. The (Nd/Yb) n and (Dy/Yb) n ratios of the Pila Spi carbonates have similarity with that of the Arabian sea carbonate. The low concentrations of U (0.35–1.0 ppm) suggest the deposition under oxygen-rich environment. This study indicates that the carbonates still preserve their original seawater-like REE pattern, provided that the contamination with terrigenous materials was small, and they serve as a seawater proxy. The Pila Spi carbonates have δ 13 C values ranged from - 6.17 to 0.76‰ PDB, and the δ 18 O values range between - 3.85 and 0.46‰ PDB. The positive correlation between δ 13 C and δ 18 O(r = 0.949, n = 14) values indicates the alteration of original isotopic compositions due to diagenesis. Finally, it is conceived that the Pila Spi carbonate was deposited in the lagoon environment with seawater invading and mixing of the continental (terrigenous) materials to the basin is viable. Keywords : Stable isotope . Carbonate rocks . Eocene . Northern Iraq . Provenance Introduction Depositional environment of the carbonate rocks can be depicted by chemical, physical, and biological parameters. The major and trace elements provide knowledge about the overall composition of the carbonate rocks and their deposi- tional conditions (Srivastava and Singh 2017). Furthermore, rare earth elements (REE) patterns are mainly influenced by depositional environment (Murray et al. 1992; Madhavaraju and Ramasamy 1999) and diagenetic processes (Schieber 1988; Armstrong-Altrin et al. 2003; Morad et al. 2010; Tobia 2018). Also, REEs are regarded as an indicator to de- positional environment such as marine anoxia (German and Elderfield 1990; Murray et al. 1991), palaeooceanic redox conditions (Elderfield and Pagett 1986; Liu et al. 1988; Jones and Manning 1994; Kato et al. 2002; Pattan et al. 2005; Deepulal et al. 2012; Tobia and Shangola 2016; Patra and Singh 2017), and variations in surface productivity (Toyoda et al. 1990). The distribution and employment of the REEs in carbonate rocks and marine waters have been discussed by several researchers (Piper 1974; Elderfield et al. 1990; Webb and Kamber 2000; Armstrong-Altrin et al. 2003 ; Nothdurft et al. 2004 ; Alexander et al. 2008 ; Madhavaraju et al. 2010; Nagarajan et al. 2011). Stable isotope (oxygen and carbon) signatures of carbon- ates have been used to provide information on climatic and environmental conditions (Tanner 2009). The nature of the depositional environment and diagenesis may influence the Responsible Editor: Domenico M. Doronzo * Faraj Habeeb Tobia farajabba58@gmail.com; faraj.tobia@su.edu.krd Hikmat Safi Al-Jaleel hikmatsafi@gmail.com Awaz Kareem Rasul awaz.rasul@su.edu.krd 1 Department of Geology, Salahaddin University, Erbil, Kurdistan Region, Iraq Arabian Journal of Geosciences (2020) 13:925 https://doi.org/10.1007/s12517-020-05884-9