We quantified the thickness of early Eocene calcareous nannofossils and linked it to different depositional environment parameters. Discoasters and placoliths do not respond in the same manner. Carbonate content affects discoasters and induces overgrowth, but palaeowater depth affects placoliths and can induce dissolution. We also find that the ratio of non-overgrown to overgrown Discoaster multiradiatus is a potential quantitative placolith preservation indicator.