Major, trace and rare earth element (REE) geochemistry of carbonate rocks of the Neoproterozoic Shahabad Formation, southern India were studied in order to investigate the depositional environment and source for the REEs. The PAAS (Post Archaean Australian Shale) normalized REE + Y pattern of Shahabad limestones have consistent seawater-like pattern i.e., i) LREE depletion (average (Nd/Yb) SN = 0.64 ± 0.08), ii) negative Ce anomaly, iii) positive Gd anomaly (average Gd SN /Gd * = 1.05 ± 0.16), iv) superchondritic Y/Ho ratio (average Y/Ho = 38.13 ± 21.35). The depletion of LREE and enrichment of HREE are clearly indicated by the (La/ Yb) SN , (Dy/Yb) SN and (Nd/Yb) SN ratios, which suggest the retention of seawater characteristics in these limestones. The negative Ce anomaly reflects the incorporation of REE directly from seawater or from the pore water under oxic condition, and also reveals the mixing of two-component systems with terrigenous clay (detrital) in the marine sediments. The terrigenous input in these limestones is confirmed by positive correlation of ΣREE with Al 2 O 3 , negative correlation of ΣREE with CaO and differences in Y/Ho ratios. V, Cr, and Sc, are positively correlated with Ti, and strong positive correlation of ΣREE with Fe 2 O 3 , Ni, Cr, Sc, and Y also indicate the presence of terrigenous materials in the Shahabad limestones.

The weathering conditions, provenance, and tectonic setting of shales from the Pimienta (PF; upper Jurassic), Huayacocotla (HF; lower Jurassic), and Méndez Formations (MF; upper Cretaceous) of the Molango Region, Hidalgo, Mexico have been studied for the first time using mineralogy, major, and trace element data. The X-ray diffraction (XRD) data reveals that the shales consist mostly of illite and muscovite clay minerals. The SEM-EDS study indicates that the PF and HF shales are rich in phosphate minerals and MF shales are abundant in zircon mineral. The chemical index of alteration (CIA  59 to 93) and their position in the A-CN-K (Al 2 O 3-CaO + Na 2 O-K 2 O) ternary diagram point to moderate to intense weathering in the source region. The La/Sc, Th/Sc, and La/Co ratios are more enriched and the Cr/Th and Eu/Eu * ratios are more depleted in MF shales than in the PF and HF shales, indicating derivation from a more felsic source than the PF and HF shales. Similarly, the average Zr content in MF shales (475 ± 185) is higher than in PF (133.9 ± 9.3) and HF shales (139.6 ± 18.2), which suggests a more enriched concentration of zircon mineral among the MF than the other shales (F calc = 32.9820669 and (F crit) 99% = 6.48949, where F calc > (F crit) 99% indicates that data populations are significantly different at 99% confidence level). The LREE enrichment, flat HREE, and negative Eu anomalies in chondrite-normalized plots are attributed to felsic source rock characteristics for the three groups of shales. The trace element concentrations point to an extensional setting (passive margin) for the Jurassic shales (PF and HF) and an active margin setting for the Cretaceous shales (MF).

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