Taherpour Khalil Abad, Morteza, and Elham Mojtahedin. “Biostratigraphic Study on Calcareous Nannofossils in South Gorgan, North of Iran”. Iranian Journal of Earth Sciences, vol. 9, no. 1, Oct. 2017, pp. 146-53, https://oiccpress.com/ijes/article/view/5805.