A comprehensive geochronological study of a pelagic sediment core altered by hydrothermal processes from the Mid Atlantic Ridge (14.5°N) was carried out using both the ²³⁰ Th _excess and the radiocarbon methods. Complementary foraminiferal tests and oxygen-isotope determinations were done. The main task was to check whether ²³⁰ Th _excess dating of such diagenetically changed sediments yields reliable absolute ages. For this purpose the vertical distribution of the ²³⁸ U, ²³⁴ U, ²³² Th and ²³⁰ Th activities along the core was measured. The results proved that it was not disturbed during the aging of the sediment. The long-term hydrothermal influence had been constant during at least the last 300 ka and did not change the natural ²³⁰ Th _excess distribution along the core. Hence, ²³⁰ Th _excess dating yields reliable ages and allows to calculate sedimentation rate. Between the uppermost and lowermost sublayers of the core we obtained 1.35±0.15 cm/ka which agrees with 1.47±0.03 cm/ka derived from conventional ¹⁴ C ages. These numerical dates, the results of the foraminiferal tests and the ¹⁸ O values place the studied sediments to the marine isotope stage 5 (MIS 5). These dates are well correlated with the corresponding sedimentary records from pelagic sediments of the North Atlantic Ocean.