Comment on "Formation of chenier plain of the Doñana marshland (SW Spain): Observations and geomorphic model" by A. Rodríguez-Ramírez and C.M. Yáñez-Camacho [Marine Geology 254 (2008) 187-196], Marine Geology, this Issue] and other researchers in their papers and comments about the marine radiocarbon reservoir effect in the Gulf of Cádiz are unreliable. The previous regional investigations (Soares's comment [A.M.M. Soares, 2010, Comment on "Formation of chenier plain of the Doñana marshland (SW Spain): Observations and geomorphic model" by A. Rodríguez-Ramírez and C.M. Yáñez-Camacho [Marine Geology 254 (2008) 187-196], Marine Geology, this Issue] and others papers) about the calibration of radiocarbon marine samples cannot be ignored or undervalued. At present, accurate and reliable ΔR values exist and must be used when building up chronological frameworks for the interpretation of Holocene marine environments. During the interval 2000-200 BP or circa 4500 BP ΔR values from the Andalusian coast of the Gulf of Cádiz are invariably lower than those from the Algarvian coast. Its calculated weighted mean is -135 ± 20 14 C yr. Between 4000 BP and 2000 BP ΔR data are still lacking but a conservative ΔR value of 100 ± 100 14 C yr can be adopted.