Geochemistry of Limestone from the Douala Sub-basin, Cameroon: Implications on Diagenesis, Depositional Environment and Paleotemperature

Abstract

The geochemistry of limestone from Nkapa and Logbajeck formations, Douala sub-basin, has been studied using major, trace elements and stable isotopes in order to decipher paleo-redox condition, depositional and post-depositional imprints and paleotemperature. Collectively, U/Th Ni/Co, V (V + N), V/Cr and Ce/Ce* ratios clearly indicate an oxic depositional condition for the samples. The ratios of Mn/Sr suggest less significant diagenetic alteration on limestone composition. The carbon isotopic signals δ¹³C ranged from − 0.26 to 0.86‰ PDB while oxygen isotope δ¹⁸O is from − 2.24 to − 7.94‰.‰ PDB. The isotopic composition of δ¹³C (− 1.9 to 0.79‰) shows a discrepancy from modern carbonate sediments. The poor correlation and scattered distribution of δ¹³C versus δ¹⁸O plot in calcareous sediments reflect different degrees of burial diagenesis and/or the potential impact of meteoric water. The average estimated temperature of formation for the limestone is 44.08 °C revealing a warm period during its deposition. The paleosalinity values (Z) for the studied area vary from 111.45 to 127.11‰ indicating a marine to fresh water depositional environment. The δ¹³O versus δ¹⁸O bivariate diagram indicates that the limestone is predominantly marine limestone, freshwater limestone, late cement and Pleistocene limestone.